WorldWideScience

Sample records for sub-crustal magma reservoir

  1. Rapid heterogeneous assembly of multiple magma reservoirs prior to Yellowstone supereruptions.

    Science.gov (United States)

    Wotzlaw, Jörn-Frederik; Bindeman, Ilya N; Stern, Richard A; D'Abzac, Francois-Xavier; Schaltegger, Urs

    2015-09-10

    Large-volume caldera-forming eruptions of silicic magmas are an important feature of continental volcanism. The timescales and mechanisms of assembly of the magma reservoirs that feed such eruptions as well as the durations and physical conditions of upper-crustal storage remain highly debated topics in volcanology. Here we explore a comprehensive data set of isotopic (O, Hf) and chemical proxies in precisely U-Pb dated zircon crystals from all caldera-forming eruptions of Yellowstone supervolcano. Analysed zircons record rapid assembly of multiple magma reservoirs by repeated injections of isotopically heterogeneous magma batches and short pre-eruption storage times of 10(3) to 10(4) years. Decoupled oxygen-hafnium isotope systematics suggest a complex source for these magmas involving variable amounts of differentiated mantle-derived melt, Archean crust and hydrothermally altered shallow-crustal rocks. These data demonstrate that complex magma reservoirs with multiple sub-chambers are a common feature of rift- and hotspot related supervolcanoes. The short duration of reservoir assembly documents rapid crustal remelting and two to three orders of magnitude higher magma production rates beneath Yellowstone compared to continental arc volcanoes. The short pre-eruption storage times further suggest that the detection of voluminous reservoirs of eruptible magma beneath active supervolcanoes may only be possible prior to an impending eruption.

  2. Implications of magma transfer between multiple reservoirs on eruption cycling.

    Science.gov (United States)

    Elsworth, Derek; Mattioli, Glen; Taron, Joshua; Voight, Barry; Herd, Richard

    2008-10-10

    Volcanic eruptions are episodic despite being supplied by melt at a nearly constant rate. We used histories of magma efflux and surface deformation to geodetically image magma transfer within the deep crustal plumbing of the Soufrière Hills volcano on Montserrat, West Indies. For three cycles of effusion followed by discrete pauses, supply of the system from the deep crust and mantle was continuous. During periods of reinitiated high surface efflux, magma rose quickly and synchronously from a deflating mid-crustal reservoir (at about 12 kilometers) augmented from depth. During repose, the lower reservoir refilled from the deep supply, with only minor discharge transiting the upper chamber to surface. These observations are consistent with a model involving the continuous supply of magma from the deep crust and mantle into a voluminous and compliant mid-crustal reservoir, episodically valved below a shallow reservoir (at about 6 kilometers).

  3. Making mushy magma chambers in the lower continental crust: Cold storage and compositional bimodality

    Science.gov (United States)

    Jackson, Matthew; Blundy, Jon; Sparks, Steve

    2017-04-01

    Increasing geological and geophysical evidence suggests that crustal magma reservoirs are normally low melt fraction 'mushes' rather than high melt fraction 'magma chambers'. Yet high melt fractions must form within these mush reservoirs to explain the observed flow and eruption of low crystallinity magmas. In many models, crystallinity is linked directly to temperature, with higher temperature corresponding to lower crystallinity (higher melt fraction). However, increasing temperature yields less evolved (silicic) melt composition for a given starting material. If mobile, low crystallinity magmas require high temperature, it is difficult to explain how they can have evolved composition. Here we use numerical modelling to show that reactive melt flow in a porous and permeable mush reservoir formed by the intrusion of numerous basaltic sills into the lower continental crust produces magma in high melt fraction (> 0.5) layers akin to conventional magma chambers. These magma-chamber-like layers contain evolved (silicic) melt compositions and form at low (close to solidus) temperatures near the top of the mush reservoir. Evolved magma is therefore kept in 'cold storage' at low temperature, but also at low crystallinity so the magma is mobile and can leave the mush reservoir. Buoyancy-driven reactive flow and accumulation of melt in the mush reservoir controls the temperature and composition of magma that can leave the reservoir. The modelling also shows that processes in lower crustal mush reservoirs produce mobile magmas that contain melt of either silicic or mafic composition. Intermediate melt compositions are present but are not within mobile magmas. Silicic melt compositions are found at high melt fraction within the magma-chamber like layers near the top of the mush reservoir. Mafic melt compositions are found at high melt fraction within the cooling sills. Melt elsewhere in the reservoir has intermediate composition, but remains trapped in the reservoir because

  4. Resonance oscillations of the Soufrière Hills Volcano (Montserrat, W.I.) magmatic system induced by forced magma flow from the reservoir into the upper plumbing dike

    Science.gov (United States)

    Chen, Chin-Wu; Huang, Hsin-Fu; Hautmann, Stefanie; Sacks, I. Selwyn; Linde, Alan T.; Taira, Taka'aki

    2018-01-01

    Short-period deformation cycles are a common phenomenon at active volcanoes and are often attributed to the instability of magma flow in the upper plumbing system caused by fluctuations in magma viscosity related to cooling, degassing, and crystallization. Here we present 20-min periodic oscillations in ground deformation based on high-precision continuous borehole strain data that were associated with the 2003 massive dome-collapse at the Soufrière Hills Volcano, Montserrat (West Indies). These high-frequency oscillations lasted 80 min and were preceded by a 4-hour episode of rapid expansion of the shallow magma reservoir. Strain amplitude ratios indicate that the deformational changes were generated by pressure variations in the shallow magma reservoir and - with reversed polarity - the adjacent plumbing dike. The unusually short period of the oscillations cannot be explained with thermally induced variations in magma properties. We investigate the underlying mechanism of the oscillations via a numerical model of forced magma flow through a reservoir-dike system accounting for time-dependent dilation/contraction of the dike due to a viscous response in the surrounding host rock. Our results suggest that the cyclic pressure variations are modulated by the dynamical interplay between rapid expansion of the magma chamber and the incapacity of the narrow dike to take up fast enough the magma volumes supplied by the reservoir. Our results allow us to place first order constraints on the viscosity of crustal host rocks and consequently its fractional melt content. Hence, we present for the first time crustal-scale in situ measurements of rheological properties of mush zones surrounding magmatic systems.

  5. Magma-sponge hypothesis and stratovolcanoes: Case for a compressible reservoir and quasi-steady deep influx at Soufrière Hills Volcano, Montserrat

    Science.gov (United States)

    Voight, Barry; Widiwijayanti, Christina; Mattioli, Glen; Elsworth, Derek; Hidayat, Dannie; Strutt, M.

    2010-02-01

    We use well-documented time histories of episodic GPS surface deformation and efflux of compressible magma to resolve apparent magma budget anomalies at Soufrière Hills volcano (SHV) on Montserrat, WI. We focus on data from 2003 to 2007, for an inflation succeeded by an episode of eruption-plus-deflation. We examine Mogi-type and vertical prolate ellipsoidal chamber geometries to accommodate both mineralogical constraints indicating a relatively shallow pre-eruption storage, and geodetic constraints inferring a deeper mean-pressure source. An exsolved phase involving several gas species greatly increases andesite magma compressibility to depths >10 km (i.e., for water content >4 wt%, crystallinity ˜40%), and this property supports the concept that much of the magma transferred into or out of the crustal reservoir could be accommodated by compression or decompression of stored reservoir magma (i.e., the “magma-sponge”). Our results suggest quasi-steady deep, mainly mafic magma influx of the order of 2 m3s-1, and we conclude that magma released in eruptive episodes is approximately balanced by cumulative deep influx during the eruptive episode and the preceding inflation. Our magma-sponge model predicts that between 2003 and 2007 there was no evident depletion of magma reservoir volume at SHV, which comprises tens of km3 with radial dimensions of order ˜1-2 km, in turn implying a long-lived eruption.

  6. Linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved Yellowstone-type supervolcanoes

    Science.gov (United States)

    Wotzlaw, J.F.; Bindeman, I.N.; Watts, Kathryn E.; Schmitt, A.K.; Caricchi, L.; Schaltegger, U.

    2014-01-01

    The geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations, the A.D. 1815 Tambora (Indonesia) eruption. Perhaps nowhere on Earth are deposits of such supereruptions more prominent than in the Snake River Plain–Yellowstone Plateau (SRP-YP) volcanic province (northwest United States). While magmatic activity at Yellowstone is still ongoing, the Heise volcanic field in eastern Idaho represents the youngest complete caldera cycle in the SRP-YP, and thus is particularly instructive for current and future volcanic activity at Yellowstone. The Heise caldera cycle culminated 4.5 Ma ago in the eruption of the ∼1800 km3 Kilgore Tuff. Accessory zircons in the Kilgore Tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity, and the vast majority are 18O depleted. This suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low-δ18O meteoric-hydrothermal fluids. Prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir. U-Pb geochronology of isotopically diverse zircons using chemical abrasion–isotope dilution–thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206Pb/238U date of 4.4876 ± 0.0023 Ma (MSWD = 1.5; n = 24). These zircon crystallization ages are also indistinguishable from the sanidine 40Ar/39Ar dates, and thus zircons crystallized close to eruption. This requires that shallow crustal melting, assembly of isolated batches into a supervolcanic magma reservoir, homogenization, and eruption occurred extremely rapidly, within the resolution of our geochronology (103–104 yr). The crystal-scale image of the reservoir configuration, with several isolated magma batches, is very similar to the

  7. Boron isotope fractionation in magma via crustal carbonate dissolution.

    Science.gov (United States)

    Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

    2016-08-04

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  8. Boron isotope fractionation in magma via crustal carbonate dissolution

    Science.gov (United States)

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-08-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to -41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  9. The PROTEUS Experiment: Active Source Seismic Imaging of the Crustal Magma Plumbing Structure of the Santorini Arc Volcano

    Science.gov (United States)

    Hooft, E. E. E.; Morgan, J. V.; Nomikou, P.; Toomey, D. R.; Papazachos, C. V.; Warner, M.; Heath, B.; Christopoulou, M. E.; Lampridou, D.; Kementzetzidou, D.

    2016-12-01

    The goal of the PROTEUS seismic experiment (Plumbing Reservoirs Of The Earth Under Santorini) is to examine the entire crustal magma plumbing system beneath a continental arc volcano and determine the magma geometry and connections throughout the crust. These physical parameters control magma migration, storage, and eruption and inform the question of how physical and chemical processing of magma at arc volcanoes forms the andesitic rock compositions that dominate the lower continental crust. These physical parameters are also important to understand volcanic-tectonic interactions and geohazards. Santorini is ideal for these goals because the continental crust has been thinned by extension and so the deep magmatic system is more accessible, also it is geologically well studied. Since the volcano is a semi-submerged, it was possible to collect a unique 3D marine-land active source seismic dataset. During the PROTEUS experiment in November-December of 2015, we recorded 14,300 marine sound sources from the US R/V Langseth on 89 OBSIP short period ocean bottom seismometers and 60 German and 5 Greek land seismometers. The experiment was designed for high-density spatial sampling of the seismic wavefield to allow us to apply two state-of-the-art 3D inversion methods: travel time tomography and full waveform inversion. A preliminary travel time tomography model of the upper crustal seismic velocity structure of the volcano and surrounding region is presented in an accompanying poster. We also made marine geophysical maps of the seafloor using multi-beam bathymetry and of the gravity and magnetic fields. The new seafloor map reveals the detailed structure of the major fault system between Santorini and Amorgos, of associated landslides, and of newly discovered volcanic features. The PROTEUS project will provide new insights into the structure of the whole crustal magmatic system of a continental arc volcano and its evolution within the surrounding tectonic setting.

  10. Evidence for crustal recycling during the Archean: the parental magmas of the stillwater complex

    International Nuclear Information System (INIS)

    McCallum, I.S.

    1988-01-01

    The petrology and geochemistry of the Stillwater Complex, an Archean (2.7 Ga) layered mafic intrusion in the Beartooth Mountains of Montana, is discussed. Efforts to reconstruct the compositions of possible parental magmas and thereby place some constraints on the composition and history of their mantle source regions was studied. A high-Mg andesite or boninite magma best matches the crystallization sequences and mineral compositions of Stillwater cumulates, and represents either a primary magma composition or a secondary magma formed, for example, by assimilation of crustal material by a very Mg-rich melt such as komatiite. Isotopic data do not support the extensive amounts of assimilation required by the komatiite parent hypothesis, and it is argued that the Stillwater magma was generated from a mantle source that had been enriched by recycling and homogenization of older crustal material over a large area

  11. The mechanics of shallow magma reservoir outgassing

    Science.gov (United States)

    Parmigiani, A.; Degruyter, W.; Leclaire, S.; Huber, C.; Bachmann, O.

    2017-08-01

    Magma degassing fundamentally controls the Earth's volatile cycles. The large amount of gas expelled into the atmosphere during volcanic eruptions (i.e., volcanic outgassing) is the most obvious display of magmatic volatile release. However, owing to the large intrusive:extrusive ratio, and considering the paucity of volatiles left in intrusive rocks after final solidification, volcanic outgassing likely constitutes only a small fraction of the overall mass of magmatic volatiles released to the Earth's surface. Therefore, as most magmas stall on their way to the surface, outgassing of uneruptible, crystal-rich magma storage regions will play a dominant role in closing the balance of volatile element cycling between the mantle and the surface. We use a numerical approach to study the migration of a magmatic volatile phase (MVP) in crystal-rich magma bodies ("mush zones") at the pore scale. Our results suggest that buoyancy-driven outgassing is efficient over crystal volume fractions between 0.4 and 0.7 (for mm-sized crystals). We parameterize our pore-scale results for MVP migration in a thermomechanical magma reservoir model to study outgassing under dynamical conditions where cooling controls the evolution of the proportion of crystal, gas, and melt phases and to investigate the role of the reservoir size and the temperature-dependent viscoelastic response of the crust on outgassing efficiency. We find that buoyancy-driven outgassing allows for a maximum of 40-50% volatiles to leave the reservoir over the 0.4-0.7 crystal volume fractions, implying that a significant amount of outgassing must occur at high crystal content (>0.7) through veining and/or capillary fracturing.

  12. On the conditions of magma mixing and its bearing on andesite production in the crust.

    Science.gov (United States)

    Laumonier, Mickael; Scaillet, Bruno; Pichavant, Michel; Champallier, Rémi; Andujar, Joan; Arbaret, Laurent

    2014-12-15

    Mixing between magmas is thought to affect a variety of processes, from the growth of continental crust to the triggering of volcanic eruptions, but its thermophysical viability remains unclear. Here, by using high-pressure mixing experiments and thermal calculations, we show that hybridization during single-intrusive events requires injection of high proportions of the replenishing magma during short periods, producing magmas with 55-58 wt% SiO2 when the mafic end-member is basaltic. High strain rates and gas-rich conditions may produce more felsic hybrids. The incremental growth of crustal reservoirs limits the production of hybrids to the waning stage of pluton assembly and to small portions of it. Large-scale mixing appears to be more efficient at lower crustal conditions, but requires higher proportions of mafic melt, producing more mafic hybrids than in shallow reservoirs. Altogether, our results show that hybrid arc magmas correspond to periods of enhanced magma production at depth.

  13. Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

    Science.gov (United States)

    Ebinger, C. J.; Keir, D.; Bastow, I. D.; Whaler, K.; Hammond, J. O. S.; Ayele, A.; Miller, M. S.; Tiberi, C.; Hautot, S.

    2017-12-01

    The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow-moving African continent, which last experienced orogeny during the Pan-African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas-rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises 20% new magmatic material ponded in the lower crust and intruded as sills and dikes at shallower depths. In the Main Ethiopian Rift, intrusions comprise 30% of the crust below axial zones of dike-dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow-spreading ridges. Our comparisons suggest that transitional crust, including seaward dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15-20 km thick crust. In the 30 Ma Recent CVL, which lacks a hot spot age progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hot spot toward the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology, and contributing significantly to global carbon and water fluxes.

  14. Lead and strontium isotopic evidence for crustal interaction and compositional zonation in the source regions of Pleistocene basaltic and rhyolitic magmas of the Coso volcanic field, California

    Science.gov (United States)

    Bacon, C.R.; Kurasawa, H.; Delevaux, M.H.; Kistler, R.W.; Doe, B.R.

    1984-01-01

    The isotopic compositions of Pb and Sr in Pleistocene basalt, high-silica rhyolite, and andesitic inclusions in rhyolite of the Coso volcanic field indicate that these rocks were derived from different levels of compositionally zoned magmatic systems. The 2 earliest rhyolites probably were tapped from short-lived silicic reservoirs, in contrast to the other 36 rhyolite domes and lava flows which the isotopic data suggest may have been leaked from the top of a single, long-lived magmatic system. Most Coso basalts show isotopic, geochemical, and mineralogic evidence of interaction with crustal rocks, but one analyzed flow has isotopic ratios that may represent mantle values (87Sr/86Sr=0.7036,206Pb/204Pb=19.05,207Pb/204Pb=15.62,208Pb/204Pb= 38.63). The (initial) isotopic composition of typical rhyolite (87Sr/86Sr=0.7053,206Pb/204Pb=19.29,207Pb/204Pb= 15.68,208Pb/204Pb=39.00) is representative of the middle or upper crust. Andesitic inclusions in the rhyolites are evidently samples of hybrid magmas from the silicic/mafic interface in vertically zoned magma reservoirs. Silicic end-member compositions inferred for these mixed magmas, however, are not those of erupted rhyolite but reflect the zonation within the silicic part of the magma reservoir. The compositional contrast at the interface between mafic and silicic parts of these systems apparently was greater for the earlier, smaller reservoirs. ?? 1984 Springer-Verlag.

  15. Magma Reservoirs Feeding Giant Radiating Dike Swarms: Insights from Venus

    Science.gov (United States)

    Grosfils, E. B.; Ernst, R. E.

    2003-01-01

    Evidence of lateral dike propagation from shallow magma reservoirs is quite common on the terrestrial planets, and examination of the giant radiating dike swarm population on Venus continues to provide new insight into the way these complex magmatic systems form and evolve. For example, it is becoming clear that many swarms are an amalgamation of multiple discrete phases of dike intrusion. This is not surprising in and of itself, as on Earth there is clear evidence that formation of both magma reservoirs and individual giant radiating dikes often involves periodic magma injection. Similarly, giant radiating swarms on Earth can contain temporally discrete subswarms defined on the basis of geometry, crosscutting relationships, and geochemical or paleomagnetic signatures. The Venus data are important, however, because erosion, sedimentation, plate tectonic disruption, etc. on Earth have destroyed most giant radiating dike swarm's source regions, and thus we remain uncertain about the geometry and temporal evolution of the magma sources from which the dikes are fed. Are the reservoirs which feed the dikes large or small, and what are the implications for how the dikes themselves form? Does each subswarm originate from a single, periodically reactivated reservoir, or do subswarms emerge from multiple discrete geographic foci? If the latter, are these discrete foci located at the margins of a single large magma body, or do multiple smaller reservoirs define the character of the magmatic center as a whole? Similarly, does the locus of magmatic activity change with time, or are all the foci active simultaneously? Careful study of giant radiating dike swarms on Venus is yielding the data necessary to address these questions and constrain future modeling efforts. Here, using giant radiating dike swarms from the Nemesis Tessera (V14) and Carson (V43) quadrangles as examples, we illustrate some of the dike swarm focal region diversity observed on Venus and briefly explore some

  16. Probing magma reservoirs to improve volcano forecasts

    Science.gov (United States)

    Lowenstern, Jacob B.; Sisson, Thomas W.; Hurwitz, Shaul

    2017-01-01

    When it comes to forecasting eruptions, volcano observatories rely mostly on real-time signals from earthquakes, ground deformation, and gas discharge, combined with probabilistic assessments based on past behavior [Sparks and Cashman, 2017]. There is comparatively less reliance on geophysical and petrological understanding of subsurface magma reservoirs.

  17. Pb isotopes during crustal melting and magma mingling - A cautionary tale from the Miki Fjord macrodike, central east Greenland

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Lesher, Charles

    2010-01-01

    Pb isotopic data are presented for hybrid rocks formed by mingling between mantle-derived tholeiitic magma of the Eocene Miki Fjord macrodike (East Greenland) and melt derived from the adjacent Precambrian basement. Bulk mixing and AFC processes between end-members readily identified in the field...... grain boundaries during disequilibrium melting of the host rock by the mafic magma. The crustal melt involved in magma interactions was therefore heterogeneous with respect to Pb isotopes on a metre-scale. These results illustrate the difficulties inherent in interpreting isotopic variations...... in contaminated mafic magmas even when the end-members are well constrained by field relations. We show that the Pb isotopic composition of the crustal contaminants and contamination trajectories for the Miki Fjord hybrid magmatic lithologies are markedly different from regional basement gneisses and contaminated...

  18. Magma Supply of Southwest Indian Ocean: Implication from Crustal Thickness Anomalies

    Science.gov (United States)

    Chiheng, L.; Jianghai, L.; Huatian, Z.; Qingkai, F.

    2017-12-01

    The Southwest Indian Ridge (SWIR) is one of the world's slowest spreading ridges with a full spreading rate of 14mm a-1, belonging to ultraslow spreading ridge, which are a novel class of spreading centers symbolized by non-uniform magma supply and crustal accretion. Therefore, the crustal thickness of Southwest Indian Ocean is a way to explore the magmatic and tectonic process of SWIR and the hotspots around it. Our paper uses Residual Mantle Bouguer Anomaly processed with the latest global public data to invert the relative crustal thickness and correct it according to seismic achievements. Gravity-derived crustal thickness model reveals a huge range of crustal thickness in Southwest Indian Ocean from 0.04km to 24km, 7.5km of average crustal thickness, and 3.5km of standard deviation. In addition, statistics data of crustal thickness reveal the frequency has a bimodal mixed skewed distribution, which indicates the crustal accretion by ridge and ridge-plume interaction. Base on the crustal thickness model, we divide three types of crustal thickness in Southwest Indian Ocean. About 20.31% of oceanic crust is 9.8km thick as thick crust. Furthermore, Prominent thin crust anomalies are associated with the trend of most transform faults, but thick crust anomalies presents to northeast of Andrew Bain transform fault. Cold and depleted mantle are also the key factors to form the thin crust. The thick crust anomalies are constrained by hotspots, which provide abundant heat to the mantle beneath mid-ocean ridge or ocean basin. Finally, we roughly delineate the range of ridge-plume interaction and transform fault effect.

  19. Lead Isotope Compositions of Acid Residues from Olivine-Phyric Shergottite Tissint: Implications for Heterogeneous Shergottite Source Reservoirs

    Science.gov (United States)

    Moriwaki, R.; Usui, T.; Yokoyama, T.; Simon, J. I.; Jones, J. H.

    2015-01-01

    Geochemical studies of shergottites suggest that their parental magmas reflect mixtures between at least two distinct geochemical source reservoirs, producing correlations between radiogenic isotope compositions and trace element abundances. These correlations have been interpreted as indicating the presence of a reduced, incompatible element- depleted reservoir and an oxidized, incompatible- element-enriched reservoir. The former is clearly a depleted mantle source, but there is ongoing debate regarding the origin of the enriched reservoir. Two contrasting models have been proposed regarding the location and mixing process of the two geochemical source reservoirs: (1) assimilation of oxidized crust by mantle derived, reduced magmas, or (2) mixing of two distinct mantle reservoirs during melting. The former requires the ancient Martian crust to be the enriched source (crustal assimilation), whereas the latter requires isolation of a long-lived enriched mantle domain that probably originated from residual melts formed during solidification of a magma ocean (heterogeneous mantle model). This study conducts Pb isotope and trace element concentration analyses of sequential acid-leaching fractions (leachates and the final residues) from the geochemically depleted olivine-phyric shergottite Tissint. The results suggest that the Tissint magma is not isotopically uniform and sampled at least two geochemical source reservoirs, implying that either crustal assimilation or magma mixing would have played a role in the Tissint petrogenesis.

  20. Sub-crustal seismic activity beneath Klyuchevskoy Volcano

    Science.gov (United States)

    Carr, M. J.; Droznina, S.; Levin, V. L.; Senyukov, S.

    2013-12-01

    events observed at a site closest to the epicenter to delay times of Ps phases in RFs that we associate with the crust-mantle transition. Both observations are essentially differences between travel times of S and P waves originating at the same place, and traversing the same velocity structure. Consequently, the uncertainty of the velocity structure beneath the KVG does not influence the comparison. For all events nominally located at 28-30 km beneath KVG the S-P time at the nearest site (CIR) significantly exceeds 4 seconds. Given that crust-mantle boundary Ps times at nearby sites are ~3 s, these earthquakes take place in the upper mantle. Both recent RFs and wide-angle reflection (Deep Seismic Sounding) studies in the late 1970s identified additional boundaries beneath KVG at depths in excess of 40 km. The nature of these boundaries is unclear, however their sharpness suggests chemical changes or the presence of fluids or melts. Chemistry of Klyuchevskoy lavas suggests sub-crustal origin with no clear magma chamber within the crust. Sub-crustal earthquakes we describe show that processes in the magma conduit at the base of the crust beneath KVG are vigorous enough to promote brittle failure in the surrounding mantle rock. The complex seismic structure of the uppermost mantle beneath KVG may reflect a history of magma injection that is accompanied by seismic energy release.

  1. Magnetotelluric Investigations of the Yellowstone Caldera: Understanding the Emplacement of Crustal Magma Bodies

    Science.gov (United States)

    Gurrola, R. M.; Neal, B. A.; Bennington, N. L.; Cronin, R.; Fry, B.; Hart, L.; Imamura, N.; Kelbert, A.; Bowles-martinez, E.; Miller, D. J.; Scholz, K. J.; Schultz, A.

    2017-12-01

    Wideband magnetotellurics (MT) presents an ideal method for imaging conductive shallow magma bodies associated with contemporary Yellowstone-Snake River Plain (YSRP) magmatism. Particularly, how do these magma bodies accumulate in the mid to upper crust underlying the Yellowstone Caldera, and furthermore, what role do hydrothermal fluids play in their ascent? During the summer 2017 field season, two field teams from Oregon State University and the University of Wisconsin-Madison installed forty-four wideband MT stations within and around the caldera, and using data slated for joint 3-D inversion with existing seismic data, two 2-D vertical conductivity sections of the crust and upper mantle were constructed. These models, in turn, provide preliminary insight into the emplacement of crustal magma bodies and hydrothermal processes in the YSRP region.

  2. Thermal evolution of magma reservoirs in the shallow crust and incidence on magma differentiation: the St-Jean-du-Doigt layered intrusion (Brittany, France)

    Science.gov (United States)

    Barboni, M.; Bussy, F.; Ovtcharova, M.; Schoene, B.

    2009-12-01

    Understanding the emplacement and growth of intrusive bodies in terms of mechanism, duration, thermal evolution and rates are fundamental aspects of crustal evolution. Recent studies show that many plutons grow in several Ma by in situ accretion of discrete magma pulses, which constitute small-scale magmatic reservoirs. The residence time of magmas, and hence their capacities to interact and differentiate, are controlled by the local thermal environment. The latter is highly dependant on 1) the emplacement depth, 2) the magmas and country rock composition, 3) the country rock thermal conductivity, 4) the rate of magma injection and 5) the geometry of the intrusion. In shallow level plutons, where magmas solidify quickly, evidence for magma mixing and/or differentiation processes is considered by many authors to be inherited from deeper levels. We show however that in-situ differentiation and magma interactions occurred within basaltic and felsic sills at shallow depth (0.3 GPa) in the St-Jean-du-Doigt bimodal intrusion, France. Field evidence coupled to high precision zircon U-Pb dating document progressive thermal maturation within the incrementally built laccolith. Early m-thick mafic sills are homogeneous and fine-grained with planar contacts with neighbouring felsic sills; within a minimal 0.5 Ma time span, the system gets warmer, adjacent sills interact and mingle, and mafic sills are differentiating in the top 40 cm of the layer. Rheological and thermal modelling show that observed in-situ differentiation-accumulation processes may be achieved in less than 10 years at shallow depth, provided that (1) the differentiating sills are injected beneath consolidated, yet still warm basalt sills, which act as low conductive insulating screens, (2) the early mafic sills accreted under the roof of the laccolith as a 100m thick top layer within 0.5 My, and (3) subsequent and sustained magmatic activity occurred on a short time scale (years) at an injection rate of ca. 0

  3. Magma reservoirs and neutral buoyancy zones on Venus - Implications for the formation and evolution of volcanic landforms

    Science.gov (United States)

    Head, James W.; Wilson, Lionel

    1992-01-01

    The production of magma reservoirs and neutral buoyancy zones (NBZs) on Venus and the implications of their development for the formation and evolution of volcanic landforms are examined. The high atmospheric pressure on Venus reduces volatile exsolution and generally serves to inhibit the formation of NBZs and shallow magma reservoirs. For a range of common terrestrial magma-volatile contents, magma ascending and erupting near or below mean planetary radius (MPR) should not stall at shallow magma reservoirs; such eruptions are characterized by relatively high total volumes and effusion rates. For the same range of volatile contents at 2 km above MPR, about half of the cases result in the direct ascent of magma to the surface and half in the production of neutral buoyancy zones. NBZs and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on Venus than on earth. For a fixed volatile content, NBZs become deeper with increasing elevation: over the range of elevations treated in this study (-1 km to +4.4 km) depths differ by a factor of 2-4. Factors that may account for the low height of volcanoes on Venus are discussed.

  4. Magnesium Isotopes as a Tracer of Crustal Materials in Volcanic Arc Magmas in the Northern Cascade Arc

    Directory of Open Access Journals (Sweden)

    Aaron W. Brewer

    2018-03-01

    Full Text Available Fifteen North Cascade Arc basalts and andesites were analyzed for Mg isotopes to investigate the extent and manner of crustal contributions to this magmatic system. The δ26Mg of these samples vary from within the range of ocean island basalts (the lightest being −0.33 ± 0.07‰ to heavier compositions (as heavy as −0.15 ± 0.06‰. The observed range in chemical and isotopic composition is similar to that of other volcanic arcs that have been assessed to date in the circum-pacific subduction zones and in the Caribbean. The heavy Mg isotope compositions are best explained by assimilation and fractional crystallization within the deep continental crust with a possible minor contribution from the addition of subducting slab-derived fluids to the primitive magma. The bulk mixing of sediment into the primitive magma or mantle source and the partial melting of garnet-rich peridotite are unlikely to have produced the observed range of Mg isotope compositions. The results show that Mg isotopes may be a useful tracer of crustal input into a magma, supplementing traditional methods such as radiogenic isotopic and trace element data, particularly in cases in which a high fraction of crustal material has been added.

  5. Magma fluxes and recurreance rate of eruptions at Nevado de Toluca volcano (Mexico)

    Science.gov (United States)

    Weber, Gregor; Probst, Line; Arce, José L.; Caricchi, Luca

    2017-04-01

    Forecasting the frequency and size of volcanic eruptions is a long-term goal for hazard mitigation. The frequency at which a given crustal magmatic system is driven towards a critical state and the magnitude of the resulting volcanic events are linked to the supply rate of fresh magma, crustal properties, and tectonic setting. Our ability to forecast the recurrence rate of eruptions is hampered by the lack of data on key variables such as the average magma flux locally and globally. The aim of this project is to identify the average magma supply rate and injection frequency for eruptions of different magnitude and eruptive style. We centred our study at Nevado de Toluca in Mexico, a subduction-related volcano with an eruptive history spanning about 1.5 million years of comparatively well documented effusive and explosive eruptions dominantly of dacitic composition. We carry out in-situ high precision zircon geochronology for a sequence of eruptions of different magnitude to obtain a distribution of crystal ages from which average crustal magma fluxes can be calculated. Eruptive fluxes will be constrained by extracting lava flow volumes from a digital elevation model. A combination of whole rock and mineral chemistry will provide quantitative insights on petrogenetic processes and on the frequency at which intensive parameters changed within the magma reservoir before the eruptions. Our results will be integrated in a global database including other volcanic systems and literature data to attempt to identify similarities and differences between magmatic reservoirs feeding volcanic eruptions of different magnitude. The final target of this project is to identify the physical factors controlling the recurrence rate of volcanic eruptions at regional and global scale.

  6. Incremental growth of an upper crustal, A-type pluton, Argentina: Evidence of a re-used magma pathway

    Science.gov (United States)

    Alasino, Pablo H.; Larrovere, Mariano A.; Rocher, Sebastián; Dahlquist, Juan A.; Basei, Miguel A. S.; Memeti, Valbone; Paterson, Scott; Galindo, Carmen; Macchioli Grande, Marcos; da Costa Campos Neto, Mario

    2017-07-01

    Carboniferous igneous activity in the Sierra de Velasco (NW Argentina) led to the emplacement of several magmas bodies at shallow levels (relationships) intrusive units are: (1) the Asha unit (340 ± 7 Ma): a tabular to funnel-shaped intrusion emplaced during a regional strain field dominated by WSW-ENE shortening with contacts discordant to regional host-rock structures; (2) the San Blas unit (344 ± 2 Ma): an approximate cylindrical-shaped intrusion formed by multiple batches of magmas, with a roughly concentric fabric pattern and displacement of the host rock by ductile flow of about 35% of shortening; and (3) the Hualco unit (346 ± 6 Ma): a small body with a possible mushroom geometry and contacts concordant to regional host-rock structures. The magma pulses making up these units define two groups of A-type granitoids. The first group includes the peraluminous granitic rocks of the Asha unit generated mostly by crustal sources (εNdt = - 5.8 and εHft in zircon = - 2.9 to - 4.5). The second group comprises the metaluminous to peraluminous granitic rocks of the youngest units (San Blas and Hualco), which were formed by a heterogeneous mixture between mantle and crustal sources (εNdt = + 0.6 to - 4.8 and εHft in zircon = + 3 to - 6). Our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non-consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials. As the plutonic system matures, the ascent of magmas is governed by the visco-elastic flow of host rock that for younger batches include older hot magma mush. The latter results in ductile downward flow of older, during rise of younger magma. Such complexes may reflect the plutonic portion of volcanic centers where chemically distinct magmas are erupted.

  7. Monitoring Vertical Crustal Deformation and Gravity Variations during Water Level Changes at the Three Gorges Reservoir

    Directory of Open Access Journals (Sweden)

    WANG Wei

    2017-06-01

    Full Text Available Monitoring vertical crustal deformation and gravity changes during water level changes at the Three Gorges reservoir is important for the safe operation of the Three Gorges Dam and for the monitoring and prevention of a regional geological disaster. In this study, we determined vertical crustal deformation and gravity changes during water level variations of the Three Gorges reservoir from direct calculations and actual measurements and a comprehensive solution. We used water areas extracted image data from the ZY-3 satellite and water level data to calculate gravity changes and vertical crustal deformation caused by every 5 m change in the water level due to storage and drainage of the Three Gorges reservoir from 145 m to 175 m. The vertical crustal deformation was up to 30 mm. The location of gravity change above 20 μ Gal(1 Gal=10-2 m/s2 was less than 2 km from the centerline of the Yangtze River. The CORS ES13 in Badong, near the reservoir, measured the vertical crustal deformation during water level changes. Because of the small number of CORS and gravity stations in the Three Gorges reservoir area, monitoring deformation and gravity related to changes in the Three Gorges reservoir water level cannot be closely followed. Using 26 CORS and some of the gravity stations in the Three Gorges area and based on loading deformation and the spherical harmonic analysis method, an integrated solution of vertical deformation and gravity variations during water level changes of the reservoir was determined, which is consistent with the actual CORS monitoring results. By comparison, we found that an integrated solution based on a CORS network can effectively enhance the capability of monitoring vertical crustal deformation and gravity changes during water level variations of the reservoir.

  8. The evolution of hydrous magmas in the Tongariro Volcanic Centre : the 10 ka Pahoka-Mangamate eruptions

    International Nuclear Information System (INIS)

    Auer, A.; Palin, J.M.; White, J.D.L.; Nakagawa, M.; Stirling, C.

    2015-01-01

    The majority of arc-type andesites in the Tongariro Volcanic Centre are highly porphyritic, hornblende-free, two-pyroxene andesites. An exception is tephras from the c. 10,000 ka Pahoka-Mangamate event. Magmas of these Plinian eruptions bypassed the extensive crustal mush columns under the central volcanoes and sequentially derived a series of almost aphyric rocks spanning a compositional range from dacite to basaltic andesite. Mineral composition, trace element and isotopic data suggest that this eruptive series tapped a mid-crustal magma reservoir, resulting in the initial eruption of an hydrous dacitic magma and several following eruptions characterised by less-evolved and less-hydrous compositions at progressively higher temperatures and substantially lower 87 Sr/ 86 Sr ratios. Systematic changes in magma chemistry are also reflected in a sequential change in phenocryst content starting with an early hornblende-plagioclase-dominated assemblage to a late olivine-plagioclase-dominated assemblage. (author).

  9. The timing of compositionally-zoned magma reservoirs and mafic 'priming' weeks before the 1912 Novarupta-Katmai rhyolite eruption

    Science.gov (United States)

    Singer, Brad S.; Costa, Fidel; Herrin, Jason S.; Hildreth, Wes; Fierstein, Judith

    2016-01-01

    The June 6, 1912 eruption of more than 13 km3 of dense rock equivalent (DRE) magma at Novarupta vent, Alaska was the largest of the 20th century. It ejected >7 km3 of rhyolite, ~1.3 km3 of andesite and ~4.6 km3 of dacite. Early ideas about the origin of pyroclastic flows and magmatic differentiation (e.g., compositional zonation of reservoirs) were shaped by this eruption. Despite being well studied, the timing of events that led to the chemically and mineralogically zoned magma reservoir remain poorly known. Here we provide new insights using the textures and chemical compositions of plagioclase and orthopyroxene crystals and by reevaluating previous U-Th isotope data. Compositional zoning of the magma reservoir likely developed a few thousand years before the eruption by several additions of mafic magma below an extant silicic reservoir. Melt compositions calculated from Sr contents in plagioclase fill the compositional gap between 68 and 76% SiO2 in whole pumice clasts, consistent with uninterrupted crystal growth from a continuum of liquids. Thus, our findings support a general model in which large volumes of crystal-poor rhyolite are related to intermediate magmas through gradual separation of melt from crystal-rich mush. The rhyolite is incubated by, but not mixed with, episodic recharge pulses of mafic magma that interact thermochemically with the mush and intermediate magmas. Hot, Mg-, Ca-, and Al-rich mafic magma intruded into, and mixed with, deeper parts of the reservoir (andesite and dacite) multiple times. Modeling the relaxation of the Fe-Mg concentrations in orthopyroxene and Mg in plagioclase rims indicates that the final recharge event occurred just weeks prior to the eruption. Rapid addition of mass, volatiles, and heat from the recharge magma, perhaps aided by partial melting of cumulate mush below the andesite and dacite, pressurized the reservoir and likely propelled a ~10 km lateral dike that allowed the overlying rhyolite to reach the surface.

  10. Contrasting estimates on the depth of magma storage zones in volcanic systems from mineral barometry and phase equilibrium experiments: a case study from Mount Merapi, Indonesia

    Science.gov (United States)

    Erdmann, Saskia; Martel, Caroline

    2015-04-01

    Mount Merapi, located in central Java, erupts on average every 5-10 years by discharging block-and-ash flows that pose local, but spatially restricted hazards. In 2010, however, the volcano erupted with a force that has been unprecedented in over 100 years. Its proximity to the metropolis of Yogyakarta with a population of >4 million makes short- and long-term eruption forecasting a task of vital importance. Critical to the appraisal of the volcano's hazard potential are tight constraints on its upper-crustal magma plumbing system and particularly on the location of its pre-eruptive reservoir. Previous petrological studies have estimated on the basis of amphibole and clinopyroxene barometry that the main magma storage zone below Merapi is located at depths of >10-15 km, while geophysical surveys have inferred significant magma storage zones at depths of ~5.5-9 km. We have carried out phase equilibrium experiments on basaltic andesite erupted in 2010, which indicate that the main pre-eruptive reservoir is located at a depth of ~7-8 km (~200 MPa). Our results thus corroborate the findings of earlier geophysical surveys and highlight the extreme uncertainty of mineral-based pressure estimates for volcanic magma systems. We point out that the commonly employed amphibole barometric calibrations of Ridolfi et al. (2010) and Ridolfi & Renzulli (2012) calculate low crystallization pressure for amphibole crystallized from felsic melt and high crystallization pressure for amphibole crystallized from mafic melt, and that the calculated pressure is thus largely unrelated to true values. Commonly employed clinopyroxene barometers (e.g., those of Nimis 1999; Putirka 2008) are also of limited use for estimating the location of crustal magma reservoirs, because the methods have large standard errors and are extremely temperature-sensitive. As a result, the calculated crystallization pressures inevitably indicate crystallization over a large range of depths, often from deep- to

  11. Extensive, water-rich magma reservoir beneath southern Montserrat

    Science.gov (United States)

    Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

    2016-05-01

    protracted crustal magma storage system.

  12. Lava lake level as a gauge of magma reservoir pressure and eruptive hazard

    Science.gov (United States)

    Patrick, Matthew R.; Anderson, Kyle R.; Poland, Michael P.; Orr, Tim R.; Swanson, Donald A.

    2015-01-01

    Forecasting volcanic activity relies fundamentally on tracking magma pressure through the use of proxies, such as ground surface deformation and earthquake rates. Lava lakes at open-vent basaltic volcanoes provide a window into the uppermost magma system for gauging reservoir pressure changes more directly. At Kīlauea Volcano (Hawaiʻi, USA) the surface height of the summit lava lake in Halemaʻumaʻu Crater fluctuates with surface deformation over short (hours to days) and long (weeks to months) time scales. This correlation implies that the lake behaves as a simple piezometer of the subsurface magma reservoir. Changes in lava level and summit deformation scale with (and shortly precede) changes in eruption rate from Kīlauea's East Rift Zone, indicating that summit lava level can be used for short-term forecasting of rift zone activity and associated hazards at Kīlauea.

  13. Evolution of deep crustal magma structures beneath Mount Baekdu volcano (MBV) intraplate volcano in northeast Asia

    Science.gov (United States)

    Rhie, J.; Kim, S.; Tkalcic, H.; Baag, S. Y.

    2017-12-01

    Heterogeneous features of magmatic structures beneath intraplate volcanoes are attributed to interactions between the ascending magma and lithospheric structures. Here, we investigate the evolution of crustal magmatic stuructures beneath Mount Baekdu volcano (MBV), which is one of the largest continental intraplate volcanoes in northeast Asia. The result of our seismic imaging shows that the deeper Moho depth ( 40 km) and relatively higher shear wave velocities (>3.8 km/s) at middle-to-lower crustal depths beneath the volcano. In addition, the pattern at the bottom of our model shows that the lithosphere beneath the MBV is shallower (interpret the observations as a compositional double layering of mafic underplating and a overlying cooled felsic structure due to fractional crystallization of asthenosphere origin magma. To achieve enhanced vertical and horizontal model coverage, we apply two approaches in this work, including (1) a grid-search based phase velocity measurement using real-coherency of ambient noise data and (2) a transdimensional Bayesian joint inversion using multiple ambient noise dispersion data.

  14. Rapid differentiation in a sill-like magma reservoir: a case study from the campi flegrei caldera.

    Science.gov (United States)

    Pappalardo, Lucia; Mastrolorenzo, Giuseppe

    2012-01-01

    In recent decades, geophysical investigations have detected wide magma reservoirs beneath quiescent calderas. However, the discovery of partially melted horizons inside the crust is not sufficient to put constraints on capability of reservoirs to supply cataclysmic eruptions, which strictly depends on the chemical-physical properties of magmas (composition, viscosity, gas content etc.), and thus on their differentiation histories. In this study, by using geochemical, isotopic and textural records of rocks erupted from the high-risk Campi Flegrei caldera, we show that the alkaline magmas have evolved toward a critical state of explosive behaviour over a time span shorter than the repose time of most volcanic systems and that these magmas have risen rapidly toward the surface. Moreover, similar results on the depth and timescale of magma storage were previously obtained for the neighbouring Somma-Vesuvius volcano. This consistency suggests that there might be a unique long-lived magma pool beneath the whole Neapolitan area.

  15. Lower crustal strength controls on melting and type of oceanization at magma-poor margins

    Science.gov (United States)

    Ros, E.; Perez-Gussinye, M.; Araujo, M. N.; Thoaldo Romeiro, M.; Andres-Martinez, M.; Morgan, J. P.

    2017-12-01

    Geodynamical models have been widely used to explain the variability in the architectonical style of conjugate rifted margins as a combination of lithospheric deformation modes, which are strongly influenced by lower crustal strength. We use 2D numerical models to show that the lower crustal strength also plays a key role on the onset and amount of melting and serpentinization during continental rifting. The relative timing between melting and serpentinization onsets controls whether the continent-ocean transition (COT) of margins will be predominantly magmatic or will mainly consist of exhumed and serpentinized mantle. Based on our results for magma-poor continental rifting, we propose a genetic link between margin architecture and COT styles that can be used as an additional tool to help interpret and understand the processes leading to margin formation. Our results show that strong lower crusts and very slow extension velocities (architecture of the magma-poor section of the South Atlantic, we suggest that the COT of the northern sector, Camamu-Gabon basins, is more likely to consist of exhumed mantle with intruded magmatism, while to the South, the Camamu-Kwanza and North Santos-South Kwanza conjugates, may be better characterized by a predominantly magmatic COT.

  16. Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow.

    Science.gov (United States)

    Gudmundsson, Magnús T; Jónsdóttir, Kristín; Hooper, Andrew; Holohan, Eoghan P; Halldórsson, Sæmundur A; Ófeigsson, Benedikt G; Cesca, Simone; Vogfjörd, Kristín S; Sigmundsson, Freysteinn; Högnadóttir, Thórdís; Einarsson, Páll; Sigmarsson, Olgeir; Jarosch, Alexander H; Jónasson, Kristján; Magnússon, Eyjólfur; Hreinsdóttir, Sigrún; Bagnardi, Marco; Parks, Michelle M; Hjörleifsdóttir, Vala; Pálsson, Finnur; Walter, Thomas R; Schöpfer, Martin P J; Heimann, Sebastian; Reynolds, Hannah I; Dumont, Stéphanie; Bali, Eniko; Gudfinnsson, Gudmundur H; Dahm, Torsten; Roberts, Matthew J; Hensch, Martin; Belart, Joaquín M C; Spaans, Karsten; Jakobsson, Sigurdur; Gudmundsson, Gunnar B; Fridriksdóttir, Hildur M; Drouin, Vincent; Dürig, Tobias; Aðalgeirsdóttir, Guðfinna; Riishuus, Morten S; Pedersen, Gro B M; van Boeckel, Tayo; Oddsson, Björn; Pfeffer, Melissa A; Barsotti, Sara; Bergsson, Baldur; Donovan, Amy; Burton, Mike R; Aiuppa, Alessandro

    2016-07-15

    Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption. We use multiparameter geophysical and geochemical data to show that the 110-square-kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, near-exponential decline of both collapse rate and the intensity of the 180-day-long eruption. Copyright © 2016, American Association for the Advancement of Science.

  17. Numerical modeling perspectives on zircon crystallization and magma reservoir growth at the Laguna del Maule volcanic field, central Chile

    Science.gov (United States)

    Andersen, N. L.; Dufek, J.; Singer, B. S.

    2017-12-01

    Magma reservoirs in the middle to upper crust are though to accumulate incrementally over 104 -105 years. Coupled crystallization ages and compositions of zircon are a potentially powerful tracer of reservoir growth and magma evolution. However, complex age distributions and disequilibrium trace element partitioning complicate the interpretation of the zircon record in terms of magmatic processes. In order to make quantitative predictions of the effects of magmatic processes that contribute reservoir growth and evolution—such as cooling and crystallization, magma recharge and mixing, and rejuvenation and remelting of cumulate-rich reservoir margins—we develop a model of zircon saturation and growth within a numerical framework of coupled thermal transfer, phase equilibrium, and magma dynamics. We apply this model to the Laguna del Maule volcanic field (LdM), located in central Chile. LdM has erupted at least 40 km3 of rhyolite from 36 vents distributed within a 250 km2 lake basin. Ongoing unrest demonstrates the large, silicic magma system beneath LdM remains active to this day. Zircon from rhyolite erupted between c. 23 and 1.8 ka produce a continuous distribution of 230Th-238U ages ranging from eruption to 40 ka, as well as less common crystal domains up to 165 ka and rare xenocrysts. Zircon trace element compositions fingerprint compositionally distinct reservoirs that grew within the larger magma system. Despite the dominantly continuous distributions of ages, many crystals are characterized by volumetrically substantial, trace element enriched domains consistent with rapid crystal growth. We utilize numerical simulations to assess the magmatic conditions required to catalyze these "blooms" of crystallization and the magma dynamics that contributed to the assembly of the LdM magma system.

  18. Crustal contamination and crystal entrapment during polybaric magma evolution at Mt. Somma-Vesuvius volcano, Italy: Geochemical and Sr isotope evidence

    Science.gov (United States)

    Piochi, M.; Ayuso, R.A.; de Vivo, B.; Somma, R.

    2006-01-01

    New major and trace element analyses and Sr-isotope determinations of rocks from Mt. Somma-Vesuvius volcano produced from 25 ky BP to 1944 AD are part of an extensive database documenting the geochemical evolution of this classic region. Volcanic rocks include silica undersaturated, potassic and ultrapotassic lavas and tephras characterized by variable mineralogy and different crystal abundance, as well as by wide ranges of trace element contents and a wide span of initial Sr-isotopic compositions. Both the degree of undersaturation in silica and the crystal content increase through time, being higher in rocks produced after the eruption at 472 AD (Pollena eruption). Compositional variations have been generally thought to reflect contributions from diverse types of mantle and crust. Magma mixing is commonly invoked as a fundamental process affecting the magmas, in addition to crystal fractionation. Our assessment of geochemical and Sr-isotopic data indicates that compositional variability also reflects the influence of crustal contamination during magma evolution during upward migration to shallow crustal levels and/or by entrapment of crystal mush generated during previous magma storage in the crust. Using a variant of the assimilation fractional crystallization model (Energy Conservation-Assimilation Fractional Crystallization; [Spera and Bohrson, 2001. Energy-constrained open-system magmatic processes I: General model and energy-constrained assimilation and fractional crystallization (EC-AFC) formulation. J. Petrol. 999-1018]; [Bohrson, W.A. and Spera, F.J., 2001. Energy-constrained open-system magmatic process II: application of energy-constrained assimilation-fractional crystallization (EC-AFC) model to magmatic systems. J. Petrol. 1019-1041]) we estimated the contributions from the crust and suggest that contamination by carbonate rocks that underlie the volcano (2 km down to 9-10 km) is a fundamental process controlling magma compositions at Mt. Somma

  19. Sombrero uplift above the Altiplano-Puna Magma Body: evidence of a ballooning mid-crustal diapir.

    Science.gov (United States)

    Fialko, Yuri; Pearse, Jill

    2012-10-12

    The Altiplano-Puna ultralow-velocity zone in the central Andes, South America, is the largest active magma body in Earth's continental crust. Space geodetic observations reported an uplift in the Altiplano-Puna proper at a rate of ~10 mm/year; however, the nature of the inferred inflation source has been uncertain. We present data showing that the uplift has persisted at a nearly constant rate over the past two decades, and is surrounded by a broad zone of subsidence. We show that the ongoing uplift and peripheral subsidence may result from a large mid-crustal diapir fed by partial melt from the Altiplano-Puna Magma Body.

  20. Volcano geodesy: The search for magma reservoirs and the formation of eruptive vents

    Science.gov (United States)

    Dvorak, J.J.; Dzurisin, D.

    1997-01-01

    Routine geodetic measurements are made at only a few dozen of the world's 600 or so active volcanoes, even though these measurements have proven to be a reliable precursor of eruptions. The pattern and rate of surface displacement reveal the depth and rate of pressure increase within shallow magma reservoirs. This process has been demonstrated clearly at Kilauea and Mauna Loa, Hawaii; Long Valley caldera, California; Campi Flegrei caldera, Italy; Rabaul caldera, Papua New Guinea; and Aira caldera and nearby Sakurajima, Japan. Slower and lesser amounts of surface displacement at Yellowstone caldera, Wyoming, are attributed to changes in a hydrothermal system that overlies a crustal magma body. The vertical and horizontal dimensions of eruptive fissures, as well as the amount of widening, have been determined at Kilauea, Hawaii; Etna, Italy; Tolbachik, Kamchatka; Krafla, Iceland; and Asal-Ghoubbet, Djibouti, the last a segment of the East Africa Rift Zone. Continuously recording instruments, such as tiltmeters, extensometers, and dilatometers, have recorded horizontal and upward growth of eruptive fissures, which grew at rates of hundreds of meters per hour, at Kilauea; Izu-Oshima, Japan; Teishi Knoll seamount, Japan; and Piton de la Fournaise, Re??union Island. In addition, such instruments have recorded the hour or less of slight ground movement that preceded small explosive eruptions at Sakurajima and presumed sudden gas emissions at Galeras, Colombia. The use of satellite geodesy, in particular the Global Positioning System, offers the possibility of revealing changes in surface strain both local to a volcano and over a broad region that includes the volcano.

  1. The 3550 year BP-1944 A.D.magma-plumbing system of Somma-Vesuvius: constraints on its behaviour and present state through a review of Sr-Nd isotope data

    Directory of Open Access Journals (Sweden)

    G. Mastrolorenzo

    2004-06-01

    Full Text Available Vesuvius, dominating the densely-populated Neapolitan area, is one of the most dangerous volcanoes in the World. Its destructive power derives from energetic subplinian and plinian eruptions, such as the one which occurred in 79 A.D. Generally such large-scale events follow a long period of quiescence; a behaviour interpreted as the gradual build-up of magma volumes between periods of major activity. After the 1631 subplinian eruption until the last 1944 A.D. eruption, it experienced an almost continuous and less energetic explosive/effusive activity. The erupted magmas are characterized by undersaturated potassic to ultrapotassic nature, and compositional and Sr-isotopic variability. Furthermore geobarometric studies indicate two different crystallization depths located at 4 and >11 km, respectively. According to most of the recent literature, the eruptions were triggered by the injection in a shallower magma chamber, of isotopically distinct magma batches derived from heterogeneous mantle source(s and/or contamination processes occurred within the deep reservoir. In our review of petrochemical data, we consider the period between the 3550 years BP plinian eruption and the 472 A.D. sub-plinian eruption, which includes 79 A.D. event, and the most recent period of activity which started in 1631 A.D. and lasted up to the 1944 A.D. eruption, characterized by a near continuous effusive/explosive activity. For both periods we identify a correlation between Sr-isotopical features of magmas and their crystallization depth. In particular, we show that pyroxenes have Sr-isotopic ratios lower than 0.7074 and an equilibrium crystallization depth of 22-11 km. Moreover feldspars have higher 87Sr/86Sr values (0.7075-7 and an equilibrium crystallization depth of about 4 km. Therefore the most radiogenic magmas did not derive from a deeper reservoir but their higher Sr-isotopic ratios have been acquired at a shallower depth likely by crustal contamination

  2. Decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano.

    Science.gov (United States)

    Druitt, T H; Costa, F; Deloule, E; Dungan, M; Scaillet, B

    2012-02-01

    Caldera-forming volcanic eruptions are low-frequency, high-impact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with devastating effects on local and global scales. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-forming eruption of Santorini volcano, Greece, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption. Despite the large volume of erupted magma (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicic magma batches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems.

  3. Evidence for a magma reservoir beneath the Taipei metropolis of Taiwan from both S-wave shadows and P-wave delays.

    Science.gov (United States)

    Lin, Cheng-Horng

    2016-12-23

    There are more than 7 million people living near the Tatun volcano group in northern Taiwan. For the safety of the Taipei metropolis, in particular, it has been debated for decades whether or not these volcanoes are active. Here I show evidence of a deep magma reservoir beneath the Taipei metropolis from both S-wave shadows and P-wave delays. The reservoir is probably composed of either a thin magma layer overlay or many molten sills within thick partially molten rocks. Assuming that 40% of the reservoir is partially molten, its total volume could be approximately 350 km 3 . The exact location and geometry of the magma reservoir will be obtained after dense seismic arrays are deployed in 2017-2020.

  4. Timescales of mixing and storage for Keanakāko`i Tephra magmas (1500-1820 C.E.), Kīlauea Volcano, Hawai`i

    Science.gov (United States)

    Lynn, Kendra J.; Garcia, Michael O.; Shea, Thomas; Costa, Fidel; Swanson, Donald A.

    2017-09-01

    The last 2500 years of activity at Kīlauea Volcano (Hawai`i) have been characterized by centuries-long periods dominated by either effusive or explosive eruptions. The most recent period of explosive activity produced the Keanakāko`i Tephra (KT; ca. 1500-1820 C.E.) and occurred after the collapse of the summit caldera (1470-1510 C.E.). Previous studies suggest that KT magmas may have ascended rapidly to the surface, bypassing storage in crustal reservoirs. The storage conditions and rapid ascent hypothesis are tested here using chemical zoning in olivine crystals and thermodynamic modeling. Forsterite contents (Fo; [Mg/(Mg + Fe) × 100]) of olivine core and rim populations are used to identify melt components in Kīlauea's prehistoric (i.e., pre-1823) plumbing system. Primitive (≥Fo88) cores occur throughout the 300+ years of the KT period; they originated from mantle-derived magmas that were first mixed and stored in a deep crustal reservoir. Bimodal olivine populations (≥Fo88 and Fo83-84) record repeated mixing of primitive magmas and more differentiated reservoir components shallower in the system, producing a hybrid composition (Fo85-87). Phase equilibria modeling using MELTS shows that liquidus olivine is not stable at depths >17 km. Thus, calculated timescales likely record mixing and storage within the crust. Modeling of Fe-Mg and Ni zoning patterns (normal, reverse, complex) reveal that KT magmas were mixed and stored for a few weeks to several years before eruption, illustrating a more complex storage history than direct and rapid ascent from the mantle as previously inferred for KT magmas. Complexly zoned crystals also have smoothed compositional reversals in the outer 5-20 µm rims that are out of Fe-Mg equilibrium with surrounding glasses. Diffusion models suggest that these rims formed within a few hours to a few days, indicating that at least one additional, late-stage mixing event may have occurred shortly prior to eruption. Our study

  5. Chemical Evidence for Vertical Transport from Magma Chambers to the Surface During Mid-Ocean Ridge Volcanic Eruptions

    Science.gov (United States)

    Sinton, J. M.; Rubin, K. H.

    2009-12-01

    Many mid-ocean ridge eruptions show significant internal chemical heterogeneity; in general, the amount of chemical heterogeneity within eruptions scales with erupted volume. These variations reflect magmatic processes occurring in magma reservoirs prior to or possibly during eruption. For example, systematic variations in Mg# with along-axis distance in the early 90’s Aldo-Kihi (S. EPR near 17.5°S), 1996 N. Gorda, 1993 Co-Axial (Juan de Fuca Ridge), and 1991-2 and 2005-6 9°50’N EPR eruptions is unlikely to be related to fractionation during emplacement, and rather reflects variations in sub-axial magma reservoirs prior to eruption. Such variations are inconsistent with well-mixed sub-axial reservoirs and, in some cases, require relatively long-lived, systematic variations in reservoir temperatures along axis. Chemical heterogeneity within the Aldo-Kihi eruption preserves spatial variations in mantle-derived isotopic and trace element ratios with implications for the temporal and spatial scales of magma injections to the crust and along-axis mixing within shallow reservoirs. These spatial variations are difficult to reconcile with significant (> ~1 km) along-axis magma transport, as are striking correlations of chemical compositions with surface geological discontinuities or seismically imaged sub-axial magma chamber reflectors in the S. Hump (S. EPR), 9°50’N EPR, N. Gorda and 1975-1984 Krafla (N. Iceland) eruptive units. Rather, spatial correlations between surface lava compositions and sub-axial magma chamber properties or long-lived axial morphology suggest that most of the erupted magma was transported nearly vertically from the underlying reservoirs to the surface during these eruptions. In the case of the Krafla eruption, coincident deformation suggests a component of lateral melt migration at depth, despite chemical evidence for vertical transport of erupted lava from more than one chemical reservoir. In addition, along-ridge movement of earthquake

  6. Estimates of volume and magma input in crustal magmatic systems from zircon geochronology: the effect of modelling assumptions and system variables

    Directory of Open Access Journals (Sweden)

    Luca eCaricchi

    2016-04-01

    Full Text Available Magma fluxes in the Earth’s crust play an important role in regulating the relationship between the frequency and magnitude of volcanic eruptions, the chemical evolution of magmatic systems and the distribution of geothermal energy and mineral resources on our planet. Therefore, quantifying magma productivity and the rate of magma transfer within the crust can provide valuable insights to characterise the long-term behaviour of volcanic systems and to unveil the link between the physical and chemical evolution of magmatic systems and their potential to generate resources. We performed thermal modelling to compute the temperature evolution of crustal magmatic intrusions with different final volumes assembled over a variety of timescales (i.e., at different magma fluxes. Using these results, we calculated synthetic populations of zircon ages assuming the number of zircons crystallising in a given time period is directly proportional to the volume of magma at temperature within the zircon crystallisation range. The statistical analysis of the calculated populations of zircon ages shows that the mode, median and standard deviation of the populations varies coherently as function of the rate of magma injection and final volume of the crustal intrusions. Therefore, the statistical properties of the population of zircon ages can add useful constraints to quantify the rate of magma injection and the final volume of magmatic intrusions.Here, we explore the effect of different ranges of zircon saturation temperature, intrusion geometry, and wall rock temperature on the calculated distributions of zircon ages. Additionally, we determine the effect of undersampling on the variability of mode, median and standards deviation of calculated populations of zircon ages to estimate the minimum number of zircon analyses necessary to obtain meaningful estimates of magma flux and final intrusion volume.

  7. Bubble accumulation and its role in the evolution of magma reservoirs in the upper crust.

    Science.gov (United States)

    Parmigiani, A; Faroughi, S; Huber, C; Bachmann, O; Su, Y

    2016-04-28

    Volcanic eruptions transfer huge amounts of gas to the atmosphere. In particular, the sulfur released during large silicic explosive eruptions can induce global cooling. A fundamental goal in volcanology, therefore, is to assess the potential for eruption of the large volumes of crystal-poor, silicic magma that are stored at shallow depths in the crust, and to obtain theoretical bounds for the amount of volatiles that can be released during these eruptions. It is puzzling that highly evolved, crystal-poor silicic magmas are more likely to generate volcanic rocks than plutonic rocks. This observation suggests that such magmas are more prone to erupting than are their crystal-rich counterparts. Moreover, well studied examples of largely crystal-poor eruptions (for example, Katmai, Taupo and Minoan) often exhibit a release of sulfur that is 10 to 20 times higher than the amount of sulfur estimated to be stored in the melt. Here we argue that these two observations rest on how the magmatic volatile phase (MVP) behaves as it rises buoyantly in zoned magma reservoirs. By investigating the fluid dynamics that controls the transport of the MVP in crystal-rich and crystal-poor magmas, we show how the interplay between capillary stresses and the viscosity contrast between the MVP and the host melt results in a counterintuitive dynamics, whereby the MVP tends to migrate efficiently in crystal-rich parts of a magma reservoir and accumulate in crystal-poor regions. The accumulation of low-density bubbles of MVP in crystal-poor magmas has implications for the eruptive potential of such magmas, and is the likely source of the excess sulfur released during explosive eruptions.

  8. A Physical Model for Three-Phase Compaction in Silicic Magma Reservoirs

    Science.gov (United States)

    Huber, Christian; Parmigiani, Andrea

    2018-04-01

    We develop a model for phase separation in magma reservoirs containing a mixture of silicate melt, crystals, and fluids (exsolved volatiles). The interplay between the three phases controls the dynamics of phase separation and consequently the chemical and physical evolution of magma reservoirs. The model we propose is based on the two-phase damage theory approach of Bercovici et al. (2001, https://doi.org/10.1029/2000JB900430) and Bercovici and Ricard (2003, https://doi.org/10.1046/j.1365-246X.2003.01854.x) because it offers the leverage of considering interface (in the macroscopic limit) between phases that can deform depending on the mechanical work and phase changes taking place locally in the magma. Damage models also offer the advantage that pressure is defined uniquely to each phase and does not need to be equal among phases, which will enable us to consider, in future studies, the large capillary pressure at which fluids are mobilized in mature, crystal-rich, magma bodies. In this first analysis of three-phase compaction, we solve the three-phase compaction equations numerically for a simple 1-D problem where we focus on the effect of fluids on the efficiency of melt-crystal separation considering the competition between viscous and buoyancy stresses only. We contrast three sets of simulations to explore the behavior of three-phase compaction, a melt-crystal reference compaction scenario (two-phase compaction), a three-phase scenario without phase changes, and finally a three-phase scenario with a parameterized second boiling (crystallization-induced exsolution). The simulations show a dramatic difference between two-phase (melt crystals) and three-phase (melt-crystals-exsolved volatiles) compaction-driven phase separation. We find that the presence of a lighter, significantly less viscous fluid hinders melt-crystal separation.

  9. An assessment of the Th-Hf-Ta diagram as a discriminant for tectomagnetic classifications and in the detection of crustal contamination of magmas

    International Nuclear Information System (INIS)

    Thompson, R.N.; Morrison, M.A.; Mattey, D.P.; Dickin, A.P.; Moorbath, S.

    1980-01-01

    The Th-Hf-Ta diagram, recently proposed as a means of discriminating basalts erupted in various tectonic environments and of detecting crustal contamination in such magmas, is shown to be unsatisfactory for both of its stated purposes. Data are presented for Th, Hf, Ta, Sr and Sr- and Pb-isotopes in basic lavas and a dolerite sill from the ensialic British Tertiary Volcanic Province (BTVP). Taken in conjunction with published results, the isotopic ratios show that some of the BTVP basic magmas are essentially uncontaminated by continental crust, except for the selective introduction of small variable amounts of unradiogenic Pb. Those BTVP magmas which show appreciable isotopic contamination have interacted with either upper or lower crust, or both. Th/(Hf + Ta) is insensitive to contamination with the Th-poor lower crust of cratons but rises during gross contamination with Th-rich upper crust. BTVP basic magmas containing negligible to moderate crustal isotopic components plot in the field of the Th-Hf-Ta diagram occupied by normal mid-ocean ridge basalts. Other volcanic provinces of known tectonic setting which plot wholly or partially outside their appropriate fields on the Th-Hf-Ta diagram are: the Hawaii-Emperor Seamount Chain, the Snake River Plain (Idaho, U.S.A.), the Azores and the Gregory Rift (Kenya). (orig.)

  10. Density of alkaline magmas at crustal and upper mantle conditions by X-ray absorption

    Science.gov (United States)

    Seifert, R.; Malfait, W.; Petitgirard, S.; Sanchez-Valle, C.

    2011-12-01

    Silicate melts are essential components of igneous processes and are directly involved in differentiation processes and heat transfer within the Earth. Studies of the physical properties of magmas (e.g., density, viscosity, conductivity, etc) are however challenging and experimental data at geologically relevant pressure and temperature conditions remain scarce. For example, there is virtually no data on the density at high pressure of alkaline magmas (e.g., phonolites) typically found in continental rift zone settings. We present in situ density measurements of alkaline magmas at crustal and upper mantle conditions using synchrotron X-ray absorption. Measurements were conducted on ID27 beamline at ESRF using a panoramic Paris-Edinburgh Press (PE Press). The starting material is a synthetic haplo-phonolite glass similar in composition to the Plateau flood phonolites from the Kenya rift [1]. The glass was synthesized at 1673 K and 2.0 GPa in a piston-cylinder apparatus at ETH Zurich and characterized using EPMA, FTIR and density measurements. The sample contains less than 200 ppm water and is free of CO2. Single-crystal diamond cylinders (Øin = 0.5 mm, height = 1 mm) were used as sample containers and placed in an assembly formed by hBN spacers, a graphite heater and a boron epoxy gasket [2]. The density was determined as a function of pressure (1.0 to 3.1 GPa) and temperature (1630-1860 K) from the X-ray absorption contrast at 20 keV between the sample and the diamond capsule. The molten state of the sample during the data collection was confirmed by X-ray diffraction measurements. Pressure and temperature were determined simultaneously from the equation of state of hBN and platinum using the the double isochor method [3].The results are combined with available density data at room conditions to derive the first experimental equation of state (EOS) of phonolitic liquids at crustal and upper mantle conditions. We will compare our results with recent reports of the

  11. Continental crustal formation and recycling: Evidence from oceanic basalts

    Science.gov (United States)

    Saunders, A. D.; Tarney, J.; Norry, M. J.

    1988-01-01

    Despite the wealth of geochemical data for subduction-related magma types, and the clear importance of such magmas in the creation of continental crust, there is still no concensus about the relative magnitudes of crustal creation versus crustal destruction (i.e., recycling of crust into the mantle). The role of subducted sediment in the formation of the arc magmas is now well documented; but what proportion of sediment is taken into the deeper mantle? Integrated isotopic and trace element studies of magmas erupted far from presently active subduction zones, in particular basaltic rocks erupted in the ocean basins, are providing important information about the role of crustal recycling. By identifying potential chemical tracers, it is impossible to monitor the effects of crustal recycling, and produce models predicting the mass of material recycled into the mantle throughout long periods of geological time.

  12. Dynamics of differentiation in magma reservoirs

    Science.gov (United States)

    Jaupart, Claude; Tait, Stephen

    1995-09-01

    In large magma chambers, gradients of temperature and composition develop due to cooling and to fractional crystallization. Unstable density differences lead to differential motions between melt and crystals, and a major goal is to explain how this might result in chemical differentiation of magma. Arriving at a full description of the physics of crystallizing magma chambers is a challenge because of the large number of processes potentially involved, the many coupled variables, and the different geometrical shapes. Furthermore, perturbations are caused by the reinjection of melt from a deep source, eruption to the Earth's surface, and the assimilation of country rock. Physical models of increasing complexity have been developed with emphasis on three fundamental approaches. One is, given that large gradients in temperature and composition may occur, to specify how to apply thermodynamic constraints so that coexisting liquid and solid compositions may be calculated. The second is to leave the differentiation trend as the solution to be found, i.e., to specify how cooling occurs and to predict the evolution of the composition of the residual liquid and of the solid forming. The third is to simplify the physics so that the effects of coupled heat and mass transfer may be studied with a reduced set of variables. The complex shapes of magma chambers imply that boundary layers develop with density gradients at various angles to gravity, leading to various convective flows and profiles qf liquid stratification. Early studies were mainly concerned with describing fluid flow in the liquid interior of large reservoirs, due to gradients developed at the margins. More recent work has focused on the internal structure and flow field of boundary layers and in particular on the gradients of solid fraction and interstitial melt composition which develop within them. Crystal settling may occur in a surprisingly diverse range of regimes and may lead to intermittent deposition

  13. Magma interaction in the root of an arc batholith

    Science.gov (United States)

    Chapman, T.; Robbins, V.; Clarke, G. L.; Daczko, N. R.; Piazolo, S.

    2016-12-01

    Fiordland, New Zealand, preserves extensive Cretaceous arc plutons, emplaced into parts of the Delamerian/Ross Orogen. Dioritic to gabbroic material emplaced at mid to lower crustal levels are exposed in the Malaspina Pluton (c. 1.2 GPa) and the Breaksea Orthogneiss (c. 1.8 GPa). Distinct magmatic pulses can be mapped in both of these plutons consistent with cycles of melt advection. Relationships are consistent with predictions from lower crustal processing zones (MASH and hot zones) considered important in the formation of Cordilleran margins. Metamorphic garnet growth is enhanced along magmatic contacts, such as where hornblende gabbronorite is cut by garnet-clinopyroxene-bearing diorite. Such features are consistent with cycles of incremental emplacement, younger magma having induced localised garnet granulite metamorphism in wall rock of older material. Temperature estimates and microstructures preserved in garnet granulite are consistent with sub-solidus, water-poor conditions in both the Malaspina and Breaksea Orthogneiss. The extent and conditions of the metamorphism implies conditions and duration was incapable of partially melting older wall rock material. The nature of interactions in intermediate to basic compositions are assessed in terms of magma genesis in the Cretaceous batholith. Most of the upper crustal felsic I-type magmatism along the margin being controlled by high-pressure garnet-clinopyroxene fractionation.

  14. Re-appraisal of the Magma-rich versus Magma-poor Paradigm at Rifted Margins: consequences for breakup processes

    Science.gov (United States)

    Tugend, J.; Gillard, M.; Manatschal, G.; Nirrengarten, M.; Harkin, C. J.; Epin, M. E.; Sauter, D.; Autin, J.; Kusznir, N. J.; McDermott, K.

    2017-12-01

    Rifted margins are often classified based on their magmatic budget only. Magma-rich margins are commonly considered to have excess decompression melting at lithospheric breakup compared with steady state seafloor spreading while magma-poor margins have suppressed melting. New observations derived from high quality geophysical data sets and drill-hole data have revealed the diversity of rifted margin architecture and variable distribution of magmatism. Recent studies suggest, however, that rifted margins have more complex and polyphase tectono-magmatic evolutions than previously assumed and cannot be characterized based on the observed volume of magma alone. We compare the magmatic budget related to lithospheric breakup along two high-resolution long-offset deep reflection seismic profiles across the SE-Indian (magma-poor) and Uruguayan (magma-rich) rifted margins. Resolving the volume of magmatic additions is difficult. Interpretations are non-unique and several of them appear plausible for each case involving variable magmatic volumes and mechanisms to achieve lithospheric breakup. A supposedly 'magma-poor' rifted margin (SE-India) may show a 'magma-rich' lithospheric breakup whereas a 'magma-rich' rifted margin (Uruguay) does not necessarily show excess magmatism at lithospheric breakup compared with steady-state seafloor spreading. This questions the paradigm that rifted margins can be subdivided in either magma-poor or magma-rich margins. The Uruguayan and other magma-rich rifted margins appear characterized by an early onset of decompression melting relative to crustal breakup. For the converse, where the onset of decompression melting is late compared with the timing of crustal breakup, mantle exhumation can occur (e.g. SE-India). Our work highlights the difficulty in determining a magmatic budget at rifted margins based on seismic reflection data alone, showing the limitations of margin classification based solely on magmatic volumes. The timing of

  15. Fine crustal and uppermost mantle S-wave velocity structure beneath the Tengchong volcanic area inferred from receiver function and surface-wave dispersion: constraints on magma chamber distribution

    Science.gov (United States)

    Li, Mengkui; Zhang, Shuangxi; Wu, Tengfei; Hua, Yujin; Zhang, Bo

    2018-03-01

    The Tengchong volcanic area is located in the southeastern margin of the collision zone between the Indian and Eurasian Plates. It is one of the youngest intraplate volcano groups in mainland China. Imaging the S-wave velocity structure of the crustal and uppermost mantle beneath the Tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity. In this study, we analyze teleseismic data from nine broadband seismic stations in the Tengchong Earthquake Monitoring Network. We then image the crustal and uppermost mantle S-wave velocity structure by joint analysis of receiver functions and surface-wave dispersion. The results reveal widely distributed low-velocity zones. We find four possible magma chambers in the upper-to-middle crust and one in the uppermost mantle. The chamber in the uppermost mantle locates in the depth range from 55 to 70 km. The four magma chambers in the crust occur at different depths, ranging from the depth of 7 to 25 km in general. They may be the heat sources for the high geothermal activity at the surface. Based on the fine crustal and uppermost mantle S-wave velocity structure, we propose a model for the distribution of the magma chambers.

  16. Shallow-level magma-sediment interaction and explosive behaviour at Anak Krakatau (Invited)

    Science.gov (United States)

    Troll, V. R.; Jolis, E. M.; Dahren, B.; Deegan, F. M.; Blythe, L. S.; Harris, C.; Berg, S. E.; Hilton, D. R.; Freda, C.

    2013-12-01

    Crustal contamination of ascending arc magmas is generally thought to be a significant process which occurs at lower- to mid-crustal magma storage levels where magmas inherit their chemical and isotopic character by blending, assimilation and differentiation [1]. Anak Krakatau, like many other volcanoes, erupts shallow-level crustal xenoliths [2], indicating a potential role for upper crustal modification and hence late-stage changes to magma rheology and thus potential eruptive behaviour. Distinguishing deep vs. shallow crustal contamination processes at Krakatau, and elsewhere, is therefore crucial to understand and assess pre-eruptive magmatic conditions and their associated hazard potential. Here we report on a multi-disciplinary approach to unravel the crustal plumbing system of the persistently-active and dominantly explosive Anak Krakatau volcano [2, 3], employing rock-, mineral- and gas-isotope geochemistry and link these results with seismic tomography [4]. We show that pyroxene crystals formed at mid- and lower-crustal levels (9-11 km) and carry almost mantle-like isotope signatures (O, Sr, Nd, He), while feldspar crystals formed dominantly at shallow levels (< 5km) and display unequivocal isotopic evidence for late stage contamination (O, Sr, Nd). This obeservation places a significant element of magma-crust interaction into the uppermost, sediment-rich crust beneath the volcano. Magma storage in the uppermost crust can thus offer a possible explanation for the compositional modifications of primitive Krakatau magmas, and likely provides extra impetus to increased explosivity at Anak Krakatau. [1] Annen, et al., 2006. J. Petrol. 47, 505-539. [2] Gardner, et al., 2013. J. Petrol. 54, 149-182. [3] Dahren, et al., 2012. Contrib. Mineral. Petrol. 163, 631-651. [4] Jaxybulatov, et al., 2011. J. Volcanol. Geoth. Res. 206, 96-105.

  17. The crustal magma storage system of Volcán Quizapu, Chile, and the effects of magma mixing on magma diversity

    Science.gov (United States)

    Bergantz, George W.; Cooper, Kari M.; Hildreth, Edward; Ruprecht, Phillipp

    2012-01-01

    Crystal zoning as well as temperature and pressure estimates from phenocryst phase equilibria are used to constrain the architecture of the intermediate-sized magmatic system (some tens of km3) of Volcán Quizapu, Chile, and to document the textural and compositional effects of magma mixing. In contrast to most arc magma systems, where multiple episodes of open-system behavior obscure the evidence of major magma chamber events (e.g. melt extraction, magma mixing), the Quizapu magma system shows limited petrographic complexity in two large historical eruptions (1846–1847 and 1932) that have contrasting eruptive styles. Quizapu magmas and peripheral mafic magmas exhibit a simple binary mixing relationship. At the mafic end, basaltic andesite to andesite recharge magmas complement the record from peripheral cones and show the same limited range of compositions. The silicic end-member composition is almost identical in both eruptions of Quizapu. The effusive 1846–1847 eruption records significant mixing between the mafic and silicic end-members, resulting in hybridized andesites and mingled dacites. These two compositionally simple eruptions at Volcán Quizapu present a rare opportunity to isolate particular aspects of magma evolution—formation of homogeneous dacite magma and late-stage magma mixing—from other magma chamber processes. Crystal zoning, trace element compositions, and crystal-size distributions provide evidence for spatial separation of the mafic and silicic magmas. Dacite-derived plagioclase phenocrysts (i.e. An25–40) show a narrow range in composition and limited zonation, suggesting growth from a compositionally restricted melt. Dacite-derived amphibole phenocrysts show similar restricted compositions and furthermore constrain, together with more mafic amphibole phenocrysts, the architecture of the magmatic system at Volcán Quizapu to be compositionally and thermally zoned, in which an andesitic mush is overlain by a homogeneous dacitic

  18. Sr- and Nd- isotope variations along the Pleistocene San Pedro - Linzor volcanic chain, N. Chile: Tracking the influence of the upper crustal Altiplano-Puna Magma Body

    Science.gov (United States)

    Godoy, Benigno; Wörner, Gerhard; Le Roux, Petrus; de Silva, Shanaka; Parada, Miguel Ángel; Kojima, Shoji; González-Maurel, Osvaldo; Morata, Diego; Polanco, Edmundo; Martínez, Paula

    2017-07-01

    Subduction-related magmas that erupted in the Central Andes during the past 10 Ma are strongly affected by crustal assimilation as revealed by an increase in 87Sr/86Sr isotope ratios with time that in turn are correlated with increased crustal thickening during the Andean orogeny. However, contamination is not uniform and can be strongly influenced locally by crustal composition, structure and thermal condition. This appears to be the case along the NW-SE San Pedro - Linzor volcanic chain (SPLVC) in northern Chile, which straddles the boundary of a major zone of partial melt, the Altiplano_Puna Magma Body (APMB). Herein we report 40Ar/39Ar ages, compositional and isotope data on lavas from the SPLVC that track the influence of this zone of partial melting on erupted lavas with geochronological and geochemical data. Ages reported here indicate that SPLVC has evolved in the last 2 M.y., similar to other volcanoes of the Western Cordillera (e.g. Lascar, Uturuncu, Putana). 87Sr/86Sr ratios increase systematically along the chain from a minimum value of 0.7057 in San Pedro dacites to a maximum of 0.7093-0.7095 for the Toconce and Cerro de Leon dacites in the SE. These changes are interpreted to reflect the increasing interaction of SPLVC parental magmas with partial melt within the APMB eastwards across the chain. The 87Sr/86Sr ratio and an antithetic trend in 143Nd/144Nd is therefore a proxy for the contribution of melt from the APMB beneath this volcanic chain. Similar 87Sr/86Sr increases and 143Nd/144Nd decreases are observed in other transects crossing the boundary of the APMB. Such trends can be recognized from NW to SE between Aucanquilcha, Ollagüe, and Uturuncu volcanoes, and from Lascar volcano to the N-S-trending Putana-Sairecabur-Licancabur volcanic chain to the north. We interpret these isotopic trends as reflecting different degrees of interaction of mafic parental melts with the APMB. High 87Sr/86Sr, and low 143Nd/144Nd reveal zones where the APMB is

  19. Sr and Nd isotope geochemistry of coexisting alkaline magma series, Cantal, Massif Central, France

    International Nuclear Information System (INIS)

    Downes, H.

    1984-01-01

    Sr and Nd isotope analyses are presented for Tertiary continental alkaline volcanics from Cantal, Massif Central, France. The volcanics belong to two main magma series, silica-saturated and silica-undersaturated (with rare nephelinites). Trace element and isotopic data indicate a common source for the basic parental magmas of both major series; the nephelinites in contrast must have been derived from a mantle source which is isotopically and chemically distinct from that which gave rise to the basalts and basanites. 87 Sr/ 86 Sr initial ratios range from 0.7034 to 0.7056 in the main magma series (excluding rhyolites) and 143 Nd/ 144 Nd ratios vary between 0.512927 and 0.512669; both are correlated with increasing SiO 2 in the lavas. The data can be explained by a model of crustal contamination linked with fractional crystallisation. This indicates that crustal magma chambers are the sites of differentiation since only rarely do evolved magmas not show a crustal isotopic signature and conversely basic magmas have primitive isotopic ratios unless they contain obviuos crustal-derived xenocrysts. Potential contaminants include lower crustal granulites or partial melts of upper crustal units. Equal amounts of contamination are required for both magma series, refuting hypotheses of selective contamination of the silica-saturated series. The isotopic characteristics of the apparently primary nephelinite lavas demonstrates widespread heterogeneity in the mantle beneath Cantal. Some rhyolites, previously thought to be extremely contaminated or to be crustally derived, are shown to have undergone post-emplacement hydrothermal alteration. (orig.)

  20. Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals.

    Science.gov (United States)

    Rubin, Allison E; Cooper, Kari M; Till, Christy B; Kent, Adam J R; Costa, Fidel; Bose, Maitrayee; Gravley, Darren; Deering, Chad; Cole, Jim

    2017-06-16

    Silicic volcanic eruptions pose considerable hazards, yet the processes leading to these eruptions remain poorly known. A missing link is knowledge of the thermal history of magma feeding such eruptions, which largely controls crystallinity and therefore eruptability. We have determined the thermal history of individual zircon crystals from an eruption of the Taupo Volcanic Zone, New Zealand. Results show that although zircons resided in the magmatic system for 10 3 to 10 5 years, they experienced temperatures >650° to 750°C for only years to centuries. This implies near-solidus long-term crystal storage, punctuated by rapid heating and cooling. Reconciling these data with existing models of magma storage requires considering multiple small intrusions and multiple spatial scales, and our approach can help to quantify heat input to and output from magma reservoirs. Copyright © 2017, American Association for the Advancement of Science.

  1. Crustal thermal state and origin of silicic magma in Iceland: the case of Torfajökull, Ljósufjöll and Snæfellsjökull volcanoes

    Science.gov (United States)

    Martin, E.; Sigmarsson, O.

    2007-05-01

    Pleistocene and Holocene peralkaline rhyolites from Torfajökull (South Iceland Volcanic Zone) and Ljósufjöll central volcanoes and trachytes from Snæfellsjökull (Snæfellsnes Volcanic Zone) allow the assessment of the mechanism for silicic magma genesis as a function of geographical location and crustal geothermal gradient. The low δ18O (2.4‰) and low Sr concentration (12.2 ppm) measured in Torfajökull rhyolites are best explained by partial melting of hydrated metabasaltic crust followed by major fractionation of feldspar. In contrast, very high 87Sr/86Sr (0.70473) and low Ba (8.7 ppm) and Sr (1.2 ppm) concentrations measured in Ljósufjöll silicic lavas are best explained by fractional crystallisation and subsequent 87Rb decay. Snæfellsjökull trachytes are also generated by fractional crystallisation, with less than 10% crustal assimilation, as inferred from their δ18O. The fact that silicic magmas within, or close to, the rift zone are principally generated by crustal melting whereas those from off-rift zones are better explained by fractional crystallisation clearly illustrates the controlling influence of the thermal state of the crust on silicic magma genesis in Iceland.

  2. Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

    Science.gov (United States)

    Danielson, Lisa R.; Metcalf, Rodney V.; Miller, Calvin F.; Rhodes Gregory T.; Wooden, J. L.

    2013-01-01

    The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the

  3. Short lived radionuclides in gases and magmas: contribution to the study of degassing and of the dynamics of magmatic reservoirs

    International Nuclear Information System (INIS)

    Gauthier, P.J.

    1998-01-01

    Crystallization and magma degassing at Stromboli (Italy) and Merapi (Indonesia) volcanoes are studied through 230 Th- 226 Ra- 210 Pb and 210 Pb- 210 Bi- 210 Po disequilibria in lavas and gases. An attempt to date crystallization by internal isochrones in ( 226 Ra)/Ba - ( 230 Th)/Ba and ( 210 Pb)/Pb - ( 226 Ra)/Pb diagrams reveals the complex evolution of these arc magmas. Several models (instantaneous but non simultaneous crystallization of the different mineral phases; continuous crystallization) are proposed to explain the lack of simple isochrones. The influence of other magmatic processes (assimilation, magma reinjection, degassing...) is discussed. The role played by radon loss from magmas (controlled by the ex solution of major gas species) on 210 Pb- 226 Ra disequilibria in lavas is examined through a model of dynamic degassing. At Stromboli, the magma reservoir has reached a steady-state and is rapidly renewed, thus explaining (Pb/Ra) ratios close to 1. At Merapi, the evolution of the reservoir is controlled by a succession of low dynamics degassing periods ( 2 analyses in the volcanic plume. The contribution of Etna as a source of atmospheric pollution is estimated during periods of contrasted volcanic activity and is compared to the volcanic emissions worldwide. (author)

  4. Buffered and unbuffered dike emplacement on Earth and Venus - Implications for magma reservoir size, depth, and rate of magma replenishment

    Science.gov (United States)

    Parfitt, E. A.; Head, J. W., III

    1993-01-01

    Models of the emplacement of lateral dikes from magma chambers under constant (buffered) driving pressure conditions and declining (unbuffered) driving pressure conditions indicate that the two pressure scenarios lead to distinctly different styles of dike emplacement. In the unbuffered case, the lengths and widths of laterally emplaced dikes will be severely limited and the dike lengths will be highly dependent on chamber size; this dependence suggests that average dike length can be used to infer the dimensions of the source magma reservoir. On Earth, the characteristics of many mafic-dike swarms suggest that they were emplaced in buffered conditions (e.g., the Mackenzie dike swarm in Canada and some dikes within the Scottish Tertiary). On Venus, the distinctive radial fractures and graben surrounding circular to oval features and edifices on many size scales and extending for hundreds to over a thousand km are candidates for dike emplacement in buffered conditions.

  5. Io's theothermal (sulfur) - Lithosphere cycle inferred from sulfur solubility modeling of Pele's magma supply

    Science.gov (United States)

    Battaglia, Steven M.; Stewart, Michael A.; Kieffer, Susan W.

    2014-06-01

    Surface deposits of volatile compounds such as water (Earth) or sulfur (Io) on volcanically active bodies suggest that a magmatic distillation process works to concentrate volatiles in surface reservoirs. On Earth, this is the combined hydrologic and tectonic cycle. On Io, sulfurous compounds are transferred from the interior to the surface reservoirs through a combination of a mantle-sourced magmatic system, vertical cycling of the lithosphere, and a sulfur-dominated crustal thermal system that we here call the "theothermal" system. We present a geochemical analysis of this process using previously inferred temperature and oxygen fugacity constraints of Pele's basaltic magma to determine the behavior of sulfur in the ionian magmas. Sulfate to sulfide ratios of Pele's magma are -4.084 ± 0.6 and -6.442 ± 0.7 log10 units, comparable to or lower than those of mid-ocean ridge basalts. This reflects the similarity of Io's oxidation state with Earth's depleted mantle as previously suggested by Zolotov and Fegley (Zolotov, M.Y., Fegley, B. [2000]. Geophys. Res. Lett. 27, 2789-2792). Our calculated limits of sulfur solubility in melts from Pele's patera (˜1100-1140 ppm) are also comparable to terrestrial mid-ocean ridge basalts, reflecting a compositional similarity of mantle sources. We propose that the excess sulfur obvious on Io's surface comes from two sources: (1) an insoluble sulfide liquid phase in the magma and (2) theothermal near-surface recycling.

  6. Magma-poor vs. magma-rich continental rifting and breakup in the Labrador Sea

    Science.gov (United States)

    Gouiza, M.; Paton, D.

    2017-12-01

    Magma-poor and magma-rich rifted margins show distinct structural and stratigraphic geometries during the rift to breakup period. In magma-poor margins, crustal stretching is accommodated mainly by brittle faulting and the formation of wide rift basins shaped by numerous graben and half-graben structures. Continental breakup and oceanic crust accretion are often preceded by a localised phase of (hyper-) extension where the upper mantle is embrittled, serpentinized, and exhumed to the surface. In magma-rich margins, the rift basin is narrow and extension is accompanied by a large magmatic supply. Continental breakup and oceanic crust accretion is preceded by the emplacement of a thick volcanic crust juxtaposing and underplating a moderately thinned continental crust. Both magma-poor and magma-rich rifting occur in response to lithospheric extension but the driving forces and processes are believed to be different. In the former extension is assumed to be driven by plate boundary forces, while in the latter extension is supposed to be controlled by sublithospheric mantle dynamics. However, this view fails in explaining observations from many Atlantic conjugate margins where magma-poor and magma-rich segments alternate in a relatively abrupt fashion. This is the case of the Labrador margin where the northern segment shows major magmatic supply during most of the syn-rift phase which culminate in the emplacement of a thick volcanic crust in the transitional domain along with high density bodies underplating the thinned continental crust; while the southern segment is characterized mainly by brittle extension, mantle seprentinization and exhumation prior to continental breakup. In this work, we use seismic and potential field data to describe the crustal and structural architectures of the Labrador margin, and investigate the tectonic and mechanical processes of rifting that may have controlled the magmatic supply in the different segments of the margin.

  7. Variations in magma supply rate at Kilauea Volcano, Hawaii

    Science.gov (United States)

    Dvorak, John J.; Dzurisin, Daniel

    1993-01-01

    When an eruption of Kilauea lasts more than 4 months, so that a well-defined conduit has time to develop, magma moves freely through the volcano from a deep source to the eruptive site at a constant rate of 0.09 km3/yr. At other times, the magma supply rate to Kilauea, estimated from geodetic measurements of surface displacements, may be different. For example, after a large withdrawal of magma from the summit reservoir, such as during a rift zone eruption, the magma supply rate is high initially but then lessens and exponentially decays as the reservoir refills. Different episodes of refilling may have different average rates of magma supply. During four year-long episodes in the 1960s, the annual rate of refilling varied from 0.02 to 0.18 km3/yr, bracketing the sustained eruptive rate of 0.09 km3/yr. For decade-long or longer periods, our estimate of magma supply rate is based on long-term changes in eruptive rate. We use eruptive rate because after a few dozen eruptions the volume of magma that passes through the summit reservoir is much larger than the net change of volume of magma stored within Kilauea. The low eruptive rate of 0.009 km3/yr between 1840 and 1950, compared to an average eruptive rate of 0.05 km3/yr since 1950, suggests that the magma supply rate was lower between 1840 and 1950 than it has been since 1950. An obvious difference in activity before and since 1950 was the frequency of rift zone eruptions: eight rift zone eruptions occurred between 1840 and 1950, but more than 20 rift zone eruptions have occurred since 1950. The frequency of rift zone eruptions influences magma supply rate by suddenly lowering pressure of the summit magma reservoir, which feeds magma to rift zone eruptions. A temporary drop of reservoir pressure means a larger-than-normal pressure difference between the reservoir and a deeper source, so magma is forced to move upward into Kilauea at a faster rate.

  8. Better constraints on the size and volatile content of the Mount St. Helens magma reservoir following the end of the 2004-2008 eruption

    Science.gov (United States)

    Mastin, L. G.; Lisowski, M.; Beeler, N.; Roeloffs, E.

    2008-12-01

    The October 2004-January 2008 eruption of Mount St. Helens produced about 93 million cubic meters dense-rock equivalent (DRE) lava at a continuous rate that decreased monotonically from ~6 m3 s-1 to zero over its duration. From late October 2004 through the end of the eruption, continuous GPS stations around the mountain recorded inward deflation at a rate that dropped monotonically below the noise level by early 2007. The geodetic signal is consistent with a volume change Δ Vc of ~16-25M m3 in an ellipsoidal reservoir of volume Vc centered at ~9-14 km depth beneath the crater. Throughout the eruption we used physically based models to extrapolate trends in lava-dome volume and deflation, and to forecast the duration and final erupted volume, Ve, using assumed or geologically constrained values of Vc, average recharge rate R into the reservoir, and compressibilities of magma (Km = ( 1/ρ m )( ∂ ρ m /∂ p )) and of the reservoir (Kc = ( 1/Vc )( ∂ Vc /∂ p )), where ρ m is magma density and p is pressure). Curves that neglected recharge consistently under-predicted both the final duration and volume, while those that assumed a constant recharge rate predicted indefinite duration and volume. The fact that the eruption ended several months after deflation stopped suggests that the long-term average recharge was close to zero, or at least much less than the average eruption rate. The discrepancy between Ve (93M m3) and Δ VC (16-25M m3) can be accounted for by the elastic relation Ve /Δ Vc = ( 1 + Km /Kc ), with Km = 3 - 4 × 10- 10 Pa-1 calculated for reservoir magma with 1- 1.5% bubbles (constrained from gas studies of the erupted lava), and Kc = 1.1 - 1.5 × 10 - 10 Pa-1. Assuming that the pressure drop dp in the reservoir was only slightly greater than the ~5 MPa increase in pressure at the 2004 vent elevation due to growth of the 220-m-high lava dome, the elastic relation Ve = VC dp( Kc + Km ) suggests that the eruption could have been fed by a reservoir

  9. Ground Tilt Time Delays between Kilauea Volcano's Summit and East Rift Zone Caused by Magma Reservoir Buffering

    Science.gov (United States)

    Haney, M. M.; Patrick, M. R.; Anderson, K. R.

    2016-12-01

    A cyclic pattern of ground deformation, called a deflation-inflation (DI) cycle, is commonly observed at Kilauea Volcano, Hawai`i. These cycles are an important part of Kilauea's eruptive activity because they directly influence the level of the summit lava lake as well as the effusion rate (and resulting lava flow hazard) at the East Rift Zone eruption site at Pu`u `O`o. DI events normally span several days, and are measured both at the summit and at Pu`u `O`o cone (20 km distance). Signals appear first at the summit and are then observed at Pu`u `O`o after an apparent delay of between 0.5 and 10 hours, which has been previously interpreted as reflecting magma transport time. We propose an alternate explanation, in which the apparent delay is an artifact of buffering by the small magma reservoir thought to exist at Pu`u `O`o. Simple Poiseuille flow modeling demonstrates that this apparent delay can be reproduced by the changing balance of inflow (from the summit) and outflow (to surface lava flows) at the Pu`u `O`o magma reservoir. The apparent delay is sensitive to the geometry of the conduit leaving Pu`u `O`o, feeding surface lava flows. We demonstrate how the reservoir buffering is quantitatively equivalent to a causal low-pass filter, which explains both the apparent delay as well as the smoothed, skewed nature of the signal at Pu`u `O`o relative to the summit. By comparing summit and Pu`u `O`o ground tilt signals over an extended time period, it may be possible to constrain the changing geometry of the shallow magmatic system through time.

  10. Locating the depth of magma supply for volcanic eruptions, insights from Mt. Cameroon.

    Science.gov (United States)

    Geiger, Harri; Barker, Abigail K; Troll, Valentin R

    2016-10-07

    Mt. Cameroon is one of the most active volcanoes in Africa and poses a possible threat to about half a million people in the area, yet knowledge of the volcano's underlying magma supply system is sparse. To characterize Mt. Cameroon's magma plumbing system, we employed mineral-melt equilibrium thermobarometry on the products of the volcano's two most recent eruptions of 1999 and 2000. Our results suggest pre-eruptive magma storage between 20 and 39 km beneath Mt. Cameroon, which corresponds to the Moho level and below. Additionally, the 1999 eruption products reveal several shallow magma pockets between 3 and 12 km depth, which are not detected in the 2000 lavas. This implies that small-volume magma batches actively migrate through the plumbing system during repose intervals. Evolving and migrating magma parcels potentially cause temporary unrest and short-lived explosive outbursts, and may be remobilized during major eruptions that are fed from sub-Moho magma reservoirs.

  11. Basalt generation at the Apollo 12 site. Part 2: Source heterogeneity, multiple melts, and crustal contamination

    Science.gov (United States)

    Neal, Clive R.; Hacker, Matthew D.; Snyder, Gregory A.; Taylor, Lawrence A.; Liu, Yun-Gang; Schmitt, Roman A.

    1994-01-01

    The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modeling, and proportions of fractionating phases were determined using the MAGFOX prograqm of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts-produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an 'r' value of 0.3). (2) Ilmenite basalts-produced by variable degrees of partial melting (4-8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts-produced by variable degrees of partial melting (5-10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and

  12. Caldera resurgence driven by magma viscosity contrasts.

    Science.gov (United States)

    Galetto, Federico; Acocella, Valerio; Caricchi, Luca

    2017-11-24

    Calderas are impressive volcanic depressions commonly produced by major eruptions. Equally impressive is the uplift of the caldera floor that may follow, dubbed caldera resurgence, resulting from magma accumulation and accompanied by minor eruptions. Why magma accumulates, driving resurgence instead of feeding large eruptions, is one of the least understood processes in volcanology. Here we use thermal and experimental models to define the conditions promoting resurgence. Thermal modelling suggests that a magma reservoir develops a growing transition zone with relatively low viscosity contrast with respect to any newly injected magma. Experiments show that this viscosity contrast provides a rheological barrier, impeding the propagation through dikes of the new injected magma, which stagnates and promotes resurgence. In explaining resurgence and its related features, we provide the theoretical background to account for the transition from magma eruption to accumulation, which is essential not only to develop resurgence, but also large magma reservoirs.

  13. A Thermodynamic Approach for Modeling H2O-CO2 Solubility in Alkali-rich Mafic Magmas at Mid-crustal Pressures

    Science.gov (United States)

    Allison, C. M.; Roggensack, K.; Clarke, A. B.

    2017-12-01

    Volatile solubility in magmas is dependent on several factors, including composition and pressure. Mafic (basaltic) magmas with high concentrations of alkali elements (Na and K) are capable of dissolving larger quantities of H2O and CO2 than low-alkali basalt. The exsolution of abundant gases dissolved in alkali-rich mafic magmas can contribute to large explosive eruptions. Existing volatile solubility models for alkali-rich mafic magmas are well calibrated below 200 MPa, but at greater pressures the experimental data is sparse. To allow for accurate interpretation of mafic magmatic systems at higher pressures, we conducted a set of mixed H2O-CO2 volatile solubility experiments between 400 and 600 MPa at 1200 °C in six mafic compositions with variable alkali contents. Compositions include magmas from volcanoes in Italy, Antarctica, and Arizona. Results from our experiments indicate that existing volatile solubility models for alkali-rich mafic magmas, if extrapolated beyond their calibrated range, over-predict CO2 solubility at mid-crustal pressures. Physically, these results suggest that volatile exsolution can occur at deeper levels than what can be resolved from the lower-pressure experimental data. Existing thermodynamic models used to calculate volatile solubility at different pressures require two experimentally derived parameters. These parameters represent the partial molar volume of the condensed volatile species in the melt and its equilibrium constant, both calculated at a standard temperature and pressure. We derived these parameters for each studied composition and the corresponding thermodynamic model shows good agreement with the CO2 solubility data of the experiments. A general alkali basalt solubility model was also constructed by establishing a relationship between magma composition and the thermodynamic parameters. We utilize cation fractions from our six compositions along with four compositions from the experimental literature in a linear

  14. Magma flow through elastic-walled dikes

    NARCIS (Netherlands)

    Bokhove, Onno; Woods, A.W.; de Boer, A

    2005-01-01

    A convection–diffusion model for the averaged flow of a viscous, incompressible magma through an elastic medium is considered. The magma flows through a dike from a magma reservoir to the Earth’s surface; only changes in dike width and velocity over large vertical length scales relative to the

  15. Coupled interactions between volatile activity and Fe oxidation state during arc crustal processes

    Science.gov (United States)

    Humphreys, Madeleine C.S.; Brooker, R; Fraser, D.C.; Burgisser, A; Mangan, Margaret T.; McCammon, C

    2015-01-01

    Arc magmas erupted at the Earth’s surface are commonly more oxidized than those produced at mid-ocean ridges. Possible explanations for this high oxidation state are that the transfer of fluids during the subduction process results in direct oxidation of the sub-arc mantle wedge, or that oxidation is caused by the effect of later crustal processes, including protracted fractionation and degassing of volatile-rich magmas. This study sets out to investigate the effect of disequilibrium crustal processes that may involve coupled changes in H2O content and Fe oxidation state, by examining the degassing and hydration of sulphur-free rhyolites. We show that experimentally hydrated melts record strong increases in Fe3+/∑Fe with increasing H2O concentration as a result of changes in water activity. This is relevant for the passage of H2O-undersaturated melts from the deep crust towards shallow crustal storage regions, and raises the possibility that vertical variations in fO2 might develop within arc crust. Conversely, degassing experiments produce an increase in Fe3+/∑Fe with decreasing H2O concentration. In this case the oxidation is explained by loss of H2 as well as H2O into bubbles during decompression, consistent with thermodynamic modelling, and is relevant for magmas undergoing shallow degassing en route to the surface. We discuss these results in the context of the possible controls on fO2 during the generation, storage and ascent of magmas in arc settings, in particular considering the timescales of equilibration relative to observation as this affects the quality of the petrological record of magmatic fO2.

  16. Petrological constraints on the recycling of mafic crystal mushes, magma ascent and intrusion of braided sills in the Torres del Paine mafic complex (Patagonia)

    Science.gov (United States)

    Leuthold, Julien; Müntener, Othmar; Baumgartner, Lukas; Putlitz, Benita

    2014-05-01

    Cumulate and crystal mush disruption and reactivation are difficult to recognise in coarse grained shallow plutonic rocks. Mafic minerals included in hornblende and zoned plagioclase provide snapshots of early crystallization and cumulate formation, but are difficult to interpret in terms of the dynamics of magma ascent and possible links between silicic and mafic rock emplacement. We will present the field relations, the microtextures and the mineral chemistry of the Miocene mafic sill complex of the Torres del Paine intrusive complex (Patagonia, Chile) and its sub-vertical feeder-zone. The mafic sill complex was built up by a succession of braided sills of shoshonitic and high-K calc-alkaline porphyritic hornblende-gabbro and fine grained monzodioritic sills. The mafic units were over-accreted over 41±11 ka, underplating the overlying granite. Local diapiric structures and felsic magma accumulation between sills indicate limited separation of intercumulus liquid from the mafic sills. Anhedral hornblende cores, with olivine + clinopyroxene ± plagioclase ± apatite inclusions, crystallized at temperatures >900°C and pressures of ~300 to ~500 MPa. The corresponding rims and monzodiorite matrix crystallized at 950°C) from the middle crust reservoir to the emplacement level. We show that hornblende-plagioclase thermobarometry is a useful monitor for the determination of segregation conditions of granitic magmas from gabbroic crystal mushes, and for monitoring the evolution of shallow crustal magmatic crystallization, decompression and cooling.

  17. In defense of Magnetite-Ilmenite Thermometry in the Bishop Tuff and its implication for gradients in silicic magma reservoirs

    Science.gov (United States)

    Evans, Bernard W; Hildreth, Edward; Bachmann, Olivier; Scaillet, Bruno

    2016-01-01

    Despite claims to the contrary, the compositions of magnetite and ilmenite in the Bishop Tuff correctly record the changing conditions of T and fO2 in the magma reservoir. In relatively reduced (∆NNO magmas (e.g., Bishop Tuff, Taupo units), Ti behaves compatibly (DTi ≈ 2-3.5), leading to a decrease in TiO2 activity in the melt with cooling and fractionation. In contrast, FeTi-oxides are poorer in TiO2 in more oxidized magmas (∆NNO > 1, e.g., Fish Canyon Tuff, Pinatubo), and the d(aTiO2)/dT slope can be negative. Biotite, FeTi-oxides, liquid, and possibly plagioclase largely maintained equilibrium in the Bishop Tuff magma (unlike the pyroxenes, and cores of quartz, sanidine, and zircon) prior ro and during a mixing event triggered by a deeper recharge, which, based on elemental diffusion profiles in minerals, took place at least several decades before eruption. Equilibrating phases and pumice compositions show evolving chemical variations that correlate well with mutually consistent temperatures based on the FeTi-oxides, sanidine-plagioclase, and ∆18O quartz-magnetite pairs. Early Bishop Tuff (EBT) temperatures are lower (700 to ~780‎°C) than temperatures (780 to >820°C) registered in Late Bishop Tuff (LBT), the latter defined here not strictly stratigraphically, but by the presence of orthopyroxene and reverse-zoned rims on quartz and sanidine. The claimed similarity in compositions, Zr-saturation temperatures and thermodynamically calculated temperatures (730-740°C) between EBT and less evolved LBT reflect the use of glass inclusions in quartz cores in LBT that were inherited from the low temperature rhyolitic part of the reservoir characteristic of the EBT. LBT temperatures as high as 820°C, the preservation of orthopyroxene, and the presence of reverse-zoned minerals (quartz, sanidine, zircons) are consistent with magma recharge at the base of the zoned reservoir, heating the cooler rhyolitic melt, partly remelting cumulate mush, and introducing

  18. The chemically zoned 1949 eruption on La Palma (Canary Islands): Petrologic evolution and magma supply dynamics of a rift zone eruption

    Science.gov (United States)

    Klügel, Andreas; Hoernle, Kaj A.; Schmincke, Hans-Ulrich; White, James D. L.

    2000-03-01

    The 1949 rift zone eruption along the Cumbre Vieja ridge on La Palma involved three eruptive centers, 3 km spaced apart, and was chemically and mineralogically zoned. Duraznero crater erupted tephrite for 14 days and shut down upon the opening of Llano del Banco, a fissure that issued first tephrite and, after 3 days, basanite. Hoyo Negro crater opened 4 days later and erupted basanite, tephrite, and phonotephrite, while Llano del Banco continued to issue basanite. The eruption ended with Duraznero erupting basanite with abundant crustal and mantle xenoliths. The tephrites and basanites from Duraznero and Llano del Banco show narrow compositional ranges and define a bimodal suite. Each batch ascended and evolved separately without significant intermixing, as did the Hoyo Negro basanite, which formed at lower degrees of melting. The magmas fractionated clinopyroxene +olivine±kaersutite±Ti-magnetite at 600-800 MPa and possibly 800-1100 MPa. Abundant reversely zoned phenocrysts reflect mixing with evolved melts at mantle depths. Probably as early as 1936, Hoyo Negro basanite entered the deep rift system at 200-350 MPa. Some shallower pockets of this basanite evolved to phonotephrite through differentiation and assimilation of wall rock. A few months prior to eruption, a mixing event in the mantle may have triggered the final ascent of the magmas. Most of the erupted tephrite and basanite ascended from mantle depths within hours to days without prolonged storage in crustal reservoirs. The Cumbre Vieja rift zone differs from the rift zones of Kilauea volcano (Hawaii) in lacking a summit caldera or a summit reservoir feeding the rift system and in being smaller and less active with most of the rift magma solidifying between eruptions.

  19. Tracing crustal contamination along the Java segment of the Sunda Arc, Indonesia

    Science.gov (United States)

    Jolis, E. M.; Troll, V.; Deegan, F.; Blythe, L.; Harris, C.; Freda, C.; Hilton, D.; Chadwick, J.; Van Helden, M.

    2012-04-01

    Arc magmas typically display chemical and petrographic characteristics indicative of crustal input. Crustal contamination can take place either in the mantle source region or as magma traverses the upper crust (e.g. [1]). While source contamination is generally considered the dominant process (e.g. [2]), late-stage crustal contamination has been recognised at volcanic arcs too (e.g. [3]). In light of this, we aim to test the extent of upper crustal versus source contamination along the Java segment of the Sunda arc, which, due its variable upper crustal structure, is an exemplary natural laboratory. We present a detailed geochemical study of 7 volcanoes along a traverse from Anak-Krakatau in the Sunda strait through Java and Bali, to characterise the impact of the overlying crust on arc magma composition. Using rock and mineral elemental geochemistry, radiogenic (Sr, Nd and Pb) and, stable (O) isotopes, we show a correlation between upper crustal composition and the degree of upper crustal contamination. We find an increase in 87Sr/86Sr and δ18O values, and a decrease in 143Nd/144Nd values from Krakatau towards Merapi, indicating substantial crustal input from the thick continental basement present. Volcanoes to the east of Merapi and the Progo-Muria fault transition zone, where the upper crust is thinner, in turn, show considerably less crustal input in their isotopic signatures, indicating a stronger influence of the mantle source. Our new data represent a systematic and high-resolution arc-wide sampling effort that allows us to distinguish the effects of the upper crust on the compositional spectrum of individual volcanic systems along the Sunda arc. [1] Davidson, J.P, Hora, J.M, Garrison, J.M & Dungan, M.A 2005. Crustal Forensics in Arc Magmas. J. Geotherm. Res. 140, 157-170; [2] Debaille, V., Doucelance, R., Weis, D., & Schiano, P. 2005. Geochim. Cosmochim. Acta, 70,723-741; [3] Gasparon, M., Hilton, D.R., & Varne, R. 1994. Earth Planet. Sci. Lett., 126, 15-22.

  20. Aleutian tholeiitic and calc-alkaline magma series I: The mafic phenocrysts

    Science.gov (United States)

    Kay, S. Mahlburg; Kay, Robert W.

    1985-07-01

    Diagnostic mafic silicate assemblages in a continuous spectrum of Aleutian volcanic rocks provide evidence for contrasts in magmatic processes in the Aleutian arc crust. Tectonic segmentation of the arc exerts a primary control on the variable mixing, fractional crystallization and possible assimilation undergone by the magmas. End members of the continuum are termed calc-alkaline (CA) and tholeiitic (TH). CA volcanic rocks (e.g., Buldir and Moffett volcanoes) have low FeO/MgO ratios and contain compositionally diverse phenocryst populations, indicating magma mixing. Their Ni and Cr-rich magnesian olivine and clinopyroxene come from mantle-derived mafic olivine basalts that have mixed with more fractionated magmas at mid-to lower-crustal levels immediately preceding eruption. High-Al amphibole is associated with the mafic end member. In contrast, TH lavas (e.g., Okmok and Westdahl volcanoes) have high FeO/MgO ratios and contain little evidence for mixing. Evolved lavas represent advanced stages of low pressure crystallization from a basaltic magma. These lavas contain groundmass olivine (FO 40 50) and lack Ca-poor pyroxene. Aleutian volcanic rocks with intermediate FeO/MgO ratios are termed transitional tholeiitic (TTH) and calc-alkaline (TCA). TCA magmas are common (e.g., Moffett, Adagdak, Great Sitkin, and Kasatochi volcanoes) and have resulted from mixing of high-Al basalt with more evolved magmas. They contain amphibole (high and low-Al) or orthopyroxene or both and are similar to the Japanese hypersthene-series. TTH magmas (e.g., Okmok and Westdahl) contain orthopyroxene or pigeonite or both, and show some indication of upper crustal mixing. They are mineralogically similar to the Japanese pigeonite-series. High-Al basalt lacks Mg-rich mafic phases and is a derivative magma produced by high pressure fractionation of an olivine tholeiite. The low pressure mineral assemblage of high-Al basalt results from crystallization at higher crustal levels.

  1. Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile

    Science.gov (United States)

    Singer, Brad S.; Andersen, Nathan L.; Le Mével, Hélène; Feigl, Kurt L.; DeMets, Charles; Tikoff, Basil; Thurber, Clifford H.; Jicha, Brian R.; Cardonna, Carlos; Córdova, Loreto; Gil, Fernando; Unsworth, Martyn J.; Williams-Jones, Glyn; Miller, Craig W.; Fierstein, Judith; Hildreth, Edward; Vazquez, Jorge A.

    2014-01-01

    Explosive eruptions of large-volume rhyolitic magma systems are common in the geologic record and pose a major potential threat to society. Unlike other natural hazards, such as earthquakes and tsunamis, a large rhyolitic volcano may provide warning signs long before a caldera-forming eruption occurs. Yet, these signs—and what they imply about magma-crust dynamics—are not well known. This is because we have learned how these systems form, grow, and erupt mainly from the study of ash flow tuffs deposited tens to hundreds of thousands of years ago or more, or from the geophysical imaging of the unerupted portions of the reservoirs beneath the associated calderas. The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007, the crust there has been inflating at an astonishing rate of at least 25 cm/yr. This unique opportunity to investigate the dynamics of a large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively under way is stimulating a new international collaboration. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ca. 20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. The next phase of this investigation seeks to enlarge the sets of geophysical and geochemical data and to use these observations in numerical models of system dynamics.

  2. Chapter 9 The magma feeding system of Somma-Vesuvius (Italy) strato-volcano: new inferences from a review of geochemical and Sr, Nd, Pb and O isotope data

    Science.gov (United States)

    Piochi, M.; de Vivo, B.; Ayuso, R.A.

    2006-01-01

    A large database of major, trace and isotope (Sr, Nd, Pb, O) data exists for rocks produced by the volcanic activity of Somma-Vesuvius volcano. Variation diagrams strongly suggest a major role for evolutionary processes such as fractional crystallization, contamination, crystal trapping and magma maxing, occurring after magma genesis in the mantle. Most mafic magmas are enriched in LILE (Light Ion Lithophile Elements; K. Rb, Ba), REE (Ce, Sm) and Y, show small Nb-Ta negative anomalies, and have values of Nb/Zr at about 0.15. Enrichments in LILE, REE, Nb and Ta do not correlate with Sr isotope values or degree of both K enrichment and silica undersaturation. The results indicate mantle source heterogeneity produced by slab-derived components beneath the volcano. However, the Sr isotope values of Somma-Vesuvius increase from 0.7071 up to 0.7081 with transport through the uppermost 11-12 km of the crust. The Sr isotope variation suggests that the crustal component affected the magmas during ascent through the lithosphere to the surface. Our new geochemical assessment based on chemical, isotopic and fluid inclusion data points to the existence of three main levels of magma storage. Two of the levels are deep and may represent long-lived reservoirs; the uppermost crustal level probably coincides with the volcanic conduit. The deeper level of magma storage is deeper than 12 km and fed the 1944 AD eruption. The intermediate level coincides with the seismic discontinuity detected by Zollo et al. (1996) at about 8 km. This intermediate level supplies magmas with 87Sr/86Sr values between 0.7071 and 0.7074, and ??O18system. ?? 2006 Elsevier B.V. All rights reserved.

  3. Crustal Thickness Beneath Libya and the Origin of Partial Melt Beneath AS Sawda Volcanic Province From Receiver Function Constraints

    Science.gov (United States)

    Lemnifi, Awad A.; Elshaafi, Abdelsalam; Browning, John; Aouad, Nassib S.; El Ebaidi, Saad K.; Liu, Kelly K.; Gudmundsson, Agust

    2017-12-01

    This study investigates crustal thickness and properties within the Libyan region. Results obtained from 15 seismic stations belonging to the Libyan Center for Remote Sensing and Space Science are reported, in addition to 3 seismic stations publically available, using receiver functions. The results show crustal thicknesses ranging from 24 km to 36 km (with uncertainties ranging between ±0.10 km and ±0.90 km). More specifically, crustal thickness ranges from 32 km to 36 km in the southern portion of the Libyan territory then becomes thinner, between 24 km and 30 km, in the coastal areas of Libya and thinnest, between 24 km and 28 km, in the Sirt Basin. The observed high Vp/Vs value of 1.91 at one station located at the AS Sawda Volcanic Province in central Libya indicates the presence of either partial melt or an abnormally warm area. This finding suggests that magma reservoirs beneath the Libyan territory may still be partially molten and active, thereby posing significant earthquake and volcanic risks. The hypothesis of an active magma source is further demonstrated though the presence of asthenospheric upwelling and extension of the Sirt Basin. This study provides a new calculation of unconsolidated sediment layers by using the arrival time of the P to S converted phases. The results show sediments thicknesses of 0.4 km to 3.7 km, with the Vp/Vs values ranging from 2.2 to 4.8. The variations in crustal thickness throughout the region are correlated with surface elevation and Bouguer gravity anomalies, which suggest that they are isostatically compensated.

  4. Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz.

    Science.gov (United States)

    Budd, David A; Troll, Valentin R; Deegan, Frances M; Jolis, Ester M; Smith, Victoria C; Whitehouse, Martin J; Harris, Chris; Freda, Carmela; Hilton, David R; Halldórsson, Sæmundur A; Bindeman, Ilya N

    2017-01-25

    Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic δ 18 O values. Overall, Toba quartz crystals exhibit comparatively high δ 18 O values, up to 10.2‰, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in δ 18 O values in outermost growth zones compared to their cores, with values as low as 6.7‰ (maximum ∆ core-rim  = 1.8‰). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-δ 18 O component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-δ 18 O component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.

  5. Optimizing and Quantifying CO<sub>2sub> Storage Resource in Saline Formations and Hydrocarbon Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Bosshart, Nicholas W. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Ayash, Scott C. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Azzolina, Nicholas A. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Peck, Wesley D. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Gorecki, Charles D. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Ge, Jun [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Jiang, Tao [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Burton-Kelly, Matthew E. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Anderson, Parker W. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Dotzenrod, Neil W. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center; Gorz, Andrew J. [Univ. of North Dakota, Grand Folks, ND (United States). Energy & Environmental Research Center

    2017-06-30

    In an effort to reduce carbon dioxide (CO<sub>2sub>) emissions from large stationary sources, carbon capture and storage (CCS) is being investigated as one approach. This work assesses CO<sub>2sub> storage resource estimation methods for deep saline formations (DSFs) and hydrocarbon reservoirs undergoing CO<sub>2sub> enhanced oil recovery (EOR). Project activities were conducted using geologic modeling and simulation to investigate CO<sub>2sub> storage efficiency. CO<sub>2sub> storage rates and efficiencies in DSFs classified by interpreted depositional environment were evaluated at the regional scale over a 100-year time frame. A focus was placed on developing results applicable to future widespread commercial-scale CO<sub>2sub> storage operations in which an array of injection wells may be used to optimize storage in saline formations. The results of this work suggest future investigations of prospective storage resource in closed or semiclosed formations need not have a detailed understanding of the depositional environment of the reservoir to generate meaningful estimates. However, the results of this work also illustrate the relative importance of depositional environment, formation depth, structural geometry, and boundary conditions on the rate of CO<sub>2sub> storage in these types of systems. CO<sub>2sub> EOR occupies an important place in the realm of geologic storage of CO<sub>2sub>, as it is likely to be the primary means of geologic CO<sub>2sub> storage during the early stages of commercial implementation, given the lack of a national policy and the viability of the current business case. This work estimates CO<sub>2sub> storage efficiency factors using a unique industry database of CO<sub>2sub> EOR sites and 18 different reservoir simulation models capturing fluvial clastic and shallow shelf carbonate depositional environments for reservoir depths of 1219 and 2438 meters (4000 and 8000 feet) and 7.6-, 20-, and 64-meter (25-, 66

  6. Evolution of silicic magmas in the Kos-Nisyros volcanic center, Greece: a petrological cycle associated with caldera collapse

    Science.gov (United States)

    Bachmann, Olivier; Deering, Chad D.; Ruprecht, Janina S.; Huber, Christian; Skopelitis, Alexandra; Schnyder, Cedric

    2012-01-01

    Multiple eruptions of silicic magma (dacite and rhyolites) occurred over the last ~3 My in the Kos-Nisyros volcanic center (eastern Aegean sea). During this period, magmas have changed from hornblende-biotite-rich units with low eruption temperatures (≤750-800°C; Kefalos and Kos dacites and rhyolites) to hotter, pyroxene-bearing units (>800-850°C; Nisyros rhyodacites) and are transitioning back to cooler magmas (Yali rhyolites). New whole-rock compositions, mineral chemistry, and zircon Hf isotopes show that these three types of silicic magmas followed the same differentiation trend: they all evolved by crystal fractionation and minor crustal assimilation (AFC) from parents with intermediate compositions characterized by high Sr/Y and low Nb content, following a wet, high oxygen fugacity liquid line of descent typical of subduction zones. As the transition between the Kos-Kefalos and Nisyros-type magmas occurred immediately and abruptly after the major caldera collapse in the area (the 161 ka Kos Plateau Tuff; KPT), we suggest that the efficient emptying of the magma chamber during the KPT drew out most of the eruptible, volatile-charged magma and partly solidified the unerupted mush zone in the upper crust due to rapid unloading, decompression, and coincident crystallization. Subsequently, the system reestablished a shallow silicic production zone from more mafic parents, recharged from the mid to lower crust. The first silicic eruptions evolving from these parents after the caldera collapse (Nisyros units) were hotter (up to >100°C) than the caldera-forming event and erupted from reservoirs characterized by different mineral proportions (more plagioclase and less amphibole). We interpret such a change as a reflection of slightly drier conditions in the magmatic column after the caldera collapse due to the decompression event. With time, the upper crustal intermediate mush progressively transitioned into the cold-wet state that prevailed during the Kefalos

  7. A Tale of Two Olivines: Magma Ascent in the Auckland Volcanic Field, New Zealand

    Science.gov (United States)

    Smid, E. R.; McGee, L. E.; Smith, I. E.; Lindsay, J. M.

    2013-12-01

    The Auckland Volcanic Field (AVF) is a nephelinitic to subalkali basaltic monogenetic field centered on the city of Auckland, New Zealand. Lavas are olivine-phyric, and the deposits of several volcanoes in the field contain olivine crystals with chrome spinel (Cr-spinel) inclusions. Microprobe analyses show at least two populations of olivine, categorised by their Mg# and their spinel inclusion compositions: the first has olivines that are euhedral, have compositions slightly less forsteritic than expected for whole rock Mg#, and have Cr-spinel inclusions with relatively low Cr2O3 contents of ~20%. These are interpreted as antecrysts inherited from the mantle source that yielded their host magma. The second population is characterised by olivines that are sub- to euhedral, are significantly more forsteritic than expected from their host whole rock Mg#, and have Cr-spinel inclusons with relatively high Cr2O3 contents of ~50%. These are interpreted as xenocrysts. The composition of these high Cr2O3 spinels very closely resembles the composition of spinels within olivines in dunite sampled from the Dun Mountain Ophiolite on the South Island of New Zealand. The northward extension of the Dun Mountain complex beneath the North Island is defined by the Junction Magnetic Anomaly, marking a crustal terrane boundary that underlies the Auckland Volcanic Field. These data indicate that the magmas that have risen to produce the volcanoes of the Auckland Volcanic Field have carried crystals from an underlying ultramafic crust as well as from their asthenospheric source. Euhedral olivine crystals which do not contain Cr-spinel are also present in AVF lavas and these are interpreted as true phenocrysts that crystallised directly from their host magmas. The lack of reaction textures at crystal margins suggests rapid ascent rates. A crustal origin for the xenocrysts not only has large implications for ascent rate modelling of olivines, but also for the crustal structure of the

  8. Melt inclusion: methods, applications and problem: Silica-rich melts in quartz xenoliths from Vulcano islands and their bearing on processes of crustal melting and crust-magma interaction in the Aeolian Arc, Italy

    NARCIS (Netherlands)

    Frezzotti, M.L.; Zavon, V.; Peccerillo, A.; Nikogosian, I.

    2002-01-01

    Silica-rich melts in quartz xenoliths from Vulcano islands and their bearing on processes of crustal melting and crust-magma interaction in the Aeolian Arc, Italy Proceedings of workshop Melt inclusion: methods, applications and problem. Napoli, Italy, September 2002, p. 71-73

  9. Geological Model of Supercritical Geothermal Reservoir on the Top of the Magma Chamber

    Science.gov (United States)

    Tsuchiya, N.

    2017-12-01

    model for "Beyond Brittle" and "Supercritical" geothermal reservoir, which is located at the top of magma chamber of granite-porphyry system, will be revealed.

  10. Artificial magma and applications of the blasting technique

    Energy Technology Data Exchange (ETDEWEB)

    Ichioka, K [Chugoku Kaki KK, Japan

    1974-01-01

    Artifical magma is discussed. Solid magma is a high temperature source and fluid magma is also a heat carrier. Iron ores are examples of solid magma, silica-borate is an example of a hydrophobic heat carrier magma assuming a liquid phase at 600/sup 0/C, and S, Ag, Pb, etc. are also examples of heat carrier magma. In addition to these examples, basic salts such as NaNO/sub 3/, KNO/sub 3/, NaCl, CaCl, KCl, BaCl, and Na/sub 4/B/sub 4/O/sub 7/ can be used as artifical magma. These are artifical magmas or heat mediums capable of capturing geothermal heat when circulated inside volcanoes. The blasting technique's applications in geothermal wells are also discussed. The technique can be used to expand a well's diameter, repair the well bottom, regenerate old wells, clean wells, or cut steel pipe. Two figures and one table are provided.

  11. Magma storage in a strike-slip caldera.

    Science.gov (United States)

    Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E

    2016-07-22

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

  12. Quaternary volcanism near the Valley of Mexico: implications for subduction zone magmatism and the effects of crustal thickness variations on primitive magma compositions

    Science.gov (United States)

    Wallace, Paul J.; Carmichael, Ian S. E.

    The Valley of Mexico and surrounding regions of Mexico and Morelos states in central Mexico contain more than 250 Quaternary eruptive vents in addition to the large, composite volcanoes of Popocatépetl, Iztaccíhuatl, and Nevado de Toluca. The eruptive vents include cinder and lava cones, shield volcanoes, and isolated andesitic and dacitic lava flows, and are most numerous in the Sierra Chichináutzin that forms the southern terminus of the Valley of Mexico. The Chichináutzin volcanic field (CVF) is part of the E-W-trending Mexican Volcanic Belt (MVB), a subduction-related volcanic arc that extends across Mexico. The crustal thickness beneath the CVF ( 50km) is the greatest of any region in the MVB and one of the greatest found in any arc worldwide. Lavas and scoriae erupted from vents in the CVF include alkaline basalts and calc-alkaline basaltic andesites, andesites, and dacites. Both alkaline and calc-alkaline groups contain primitive varieties that have whole rock Mg#, MgO, and Ni contents, and liquidus olivine compositions (<=Fo90) that are close to those expected of partial melts from mantle peridotite. Primitive varieties also show a wide range of incompatible trace element abundances (e.g. Ba 210-1080ppm Ce 25-100ppm Zr 130-280ppm). Data for primitive calc-alkaline rocks from both the CVF and other regions of the MVB to the west are consistent with magma generation in an underlying mantle wedge that is depleted in Ti, Zr, and Nb and enriched in large ion lithophile (K, Ba, Rb) and light rare earth (La, Ce) elements. Extents of partial melting estimated from Ti and Zr data are lower for primitive calc-alkaline magmas in the CVF than for those from the regions of the MVB to the west where the crust is thinner. The distinctive major element compositions (low CaO and Al2O3, high SiO2) of the primitive calc-alkaline magmas in the CVF indicate a more refractory mantle source beneath this region of thick crust. In contrast, primitive alkaline magmas from the

  13. Short-circuiting magma differentiation from basalt straight to rhyolite?

    Science.gov (United States)

    Ruprecht, P.; Winslow, H.

    2017-12-01

    Silicic magmas are the product of varying degrees of crystal fractionation and crustal assimilation/melting. Both processes lead to differentiation that is step-wise rather than continuous for example during melt separation from a crystal mush (Dufek and Bachmann, 2010). However, differentiation is rarely efficient enough to evolve directly from a basaltic to a rhyolitic magma. At Volcán Puyehue-Cordón Caulle, Chile, the magma series is dominated by crystal fractionation where mixing trends between primitive and felsic end members in the bulk rock compositions are almost absent (e.g. P, FeO, TiO2 vs. SiO2). How effective fraction is in this magmatic system is not well-known. The 2011-12 eruption at Cordón Caulle provides new constraints that rhyolitic melts may be derived directly from a basaltic mush. Minor, but ubiquitous mafic, crystal-rich enclaves co-erupted with the predominantly rhyolitic near-aphyric magma. These enclaves are among the most primitive compositions erupted at Puyehue-Cordón Caulle and geochemically resemble closely basaltic magmas that are >10 ka old (Singer et al. 2008) and that have been identified as a parental tholeiitic mantle-derived magma (Schmidt and Jagoutz, 2017) for the Southern Andean Volcanic Zone. The vesiculated nature, the presence of a microlite-rich groundmass, and a lack of a Eu anomaly in these encalves suggest that they represent recharge magma/mush rather than sub-solidus cumulates and therefore have potentially a direct petrogenetic link to the erupted rhyolites. Our results indicate that under some conditions crystal fractionation can be very effective and the presence of rhyolitic magmas does not require an extensive polybaric plumbing system. Instead, primitive mantle-derived magmas source directly evolved magmas. In the case, of the magma system beneath Puyehue-Cordón Caulle, which had three historic rhyolitic eruptions (1921-22, 1960, 2011-12) these results raise the question whether rhyolite magma extraction

  14. The evolution of magma during continental rifting: New constraints from the isotopic and trace element signatures of silicic magmas from Ethiopian volcanoes

    Science.gov (United States)

    Hutchison, William; Mather, Tamsin A.; Pyle, David M.; Boyce, Adrian J.; Gleeson, Matthew L. M.; Yirgu, Gezahegn; Blundy, Jon D.; Ferguson, David J.; Vye-Brown, Charlotte; Millar, Ian L.; Sims, Kenneth W. W.; Finch, Adrian A.

    2018-05-01

    Magma plays a vital role in the break-up of continental lithosphere. However, significant uncertainty remains about how magma-crust interactions and melt evolution vary during the development of a rift system. Ethiopia captures the transition from continental rifting to incipient sea-floor spreading and has witnessed the eruption of large volumes of silicic volcanic rocks across the region over ∼45 Ma. The petrogenesis of these silicic rocks sheds light on the role of magmatism in rift development, by providing information on crustal interactions, melt fluxes and magmatic differentiation. We report new trace element and Sr-Nd-O isotopic data for volcanic rocks, glasses and minerals along and across active segments of the Main Ethiopian (MER) and Afar Rifts. Most δ18 O data for mineral and glass separates from these active rift zones fall within the bounds of modelled fractional crystallization trajectories from basaltic parent magmas (i.e., 5.5-6.5‰) with scant evidence for assimilation of Pan-African Precambrian crustal material (δ18 O of 7-18‰). Radiogenic isotopes (εNd = 0.92- 6.52; 87Sr/86Sr = 0.7037-0.7072) and incompatible trace element ratios (Rb/Nb productivity or where crustal structure inhibits magma ascent). This has important implications for understanding the geotectonic settings that promote extreme melt evolution and, potentially, genesis of economically-valuable mineral deposits in ancient rift-settings. The limited isotopic evidence for assimilation of Pan-African crustal material in Ethiopia suggests that the pre-rift crust beneath the magmatic segments has been substantially modified by rift-related magmatism over the past ∼45 Ma; consistent with geophysical observations. We argue that considerable volumes of crystal cumulate are stored beneath silicic volcanic systems (>100 km3), and estimate that crystal cumulates fill at least 16-30% of the volume generated by crustal extension under the axial volcanoes of the MER and Manda Hararo

  15. Nature of the magma storage system beneath the Damavand volcano (N. Iran): An integrated study

    Science.gov (United States)

    Eskandari, Amir; Amini, Sadraddin; De Rosa, Rosanna; Donato, Paola

    2018-02-01

    by crystal fractionation from the reconstructed primary magma (13 wt% MgO) with the minor role of recharge and crustal assimilation. Phenocrysts in TT lavas recorded a wide range of temperature and pressure of crystallization; at least three main levels of magma storage can be recognized according to the statistical analysis of the models, at 6-8 kb (22-28 km), 4-6 kb (15-22 km), and 0.6-3 kb (2-11 km), respectively. The temperature of crystallization ranged from 1430 to 1180 °C for primary mafic magma to alkali olivine basalts and 1180-800 °C for TT suite. According to the current geophysical models, the present structure of the magma storage system in the crust beneath the Damavand volcano consists of three major accumulation zones located at 20 km, 6-8 km and 3-4.5 km depth. Our data enlarge this scenario, suggesting a more complex magma storage system strongly controlled by the transpressional tectonic regime. Multi-depth magma reservoirs may account for the local thickening of crust below the volcano. The polybaric fractionation model, using the MELTS algorithm, reproduces mineralogy and chemical variations of minerals and whole rock of the Damavand TT lavas. However, some discrepancies between major elements of models and trends of data can be ascribed to the recharge of more mafic magma, minor crustal assimilation, disaggregation of crystal-rich mushes and uptake of magmatic inclusions, as well as crystals from different crustal levels. The polybaric differentiation as the fractionation and/or accumulation of crystals was the probable mechanism for explaining the scarcity of mafic volcanic rocks at the Damavand volcano.

  16. Comparative Magma Oceanography

    Science.gov (United States)

    Jones, J. H.

    1999-01-01

    The question of whether the Earth ever passed through a magma ocean stage is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of martian (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of Mars contrast strongly to those of the Earth: (i) the extremely ancient ages of the martian core, mantle, and crust (about 4.55 b.y.); (ii) the highly depleted nature of the martian mantle; and (iii) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle. The easiest way to explain the ages and diverse isotopic compositions of martian basalts is to postulate that Mars had an early magma ocean. Cumulates of this magma ocean were later remelted to form the SNC meteorite suite and some of these melts assimilated crustal materials enriched in incompatible elements. The REE pattern of the crust assimilated by these SNC magmas was LREE enriched. If this pattern is typical of the crust as a whole, the martian crust is probably similar in composition to melts generated by small degrees of partial melting (about 5%) of a primitive source. Higher degrees of partial melting would cause the crustal LREE pattern to be essentially flat. In the context of a magma ocean model, where large degrees of partial melting presumably prevailed, the crust would have to be dominated by late-stage, LREE-enriched residual liquids. Regardless of the exact physical setting, Nd and W isotopic evidence indicates that martian geochemical reservoirs must have formed early and that they have not been efficiently remixed since. The important point is that in both the Moon and Mars we see evidence of a magma ocean phase and that we recognize it as such. Several lines of theoretical inference point to an early Earth that was also hot

  17. Evolution of the volcanic plumbing systemof Alicudi (Aeolian Islands - Italy: evidence from fluid and melt inclusionsin quartz xenoliths

    Directory of Open Access Journals (Sweden)

    A. Peccerillo

    2004-06-01

    Full Text Available Quartz-rich xenoliths in lavas (basalts to andesites; 90-30 ka from Alicudi contain abundant melt and fluid inclusions. Two generations of CO2-rich fluid inclusions are present in quartz-rich xenolith grains: early (Type I inclusions related to partial melting of the host xenoliths, and late Type II inclusions related to the fluid trapping during xenolith ascent. Homogenisation temperatures of fluid inclusions correspond to two density intervals: 0.93-0.68 g/cm3 (Type I and 0.47-0.26 g/cm3 (Type II. Early Type I fluid inclusions indicate trapping pressures around 6 kbar, which are representative for the levels of partial melting of crustal rocks and xenolith formation. Late Type II fluid inclusions show lower trapping pressures, between 1.7 kbar and 0.2 kbar, indicative for shallow magma rest and accumulation during ascent to the surface. Data suggest the presence of two magma reservoirs: the first is located at lower crustal depths (about 24 km, site of fractional crystallization, mixing with source derived magma, and various degrees of crustal assimilation. The second magma reservoir is located at shallow crustal depths (about 6 km, the site where magma rested for a short time before erupting.

  18. Early Neoarchaean A-type granitic magmatism by crustal reworking ...

    Indian Academy of Sciences (India)

    29

    understand their petrogenesis and tectonic setting. .... crystallize from magmas with temperatures significantly higher than those of other intracrustal ...... blanketing by greenstone belt volcanic rocks, crustal thickening and hot subduction or a. 1.

  19. Magma addition rates in continental arcs: New methods of calculation and global implications

    Science.gov (United States)

    Ratschbacher, B. C.; Paterson, S. R.

    2017-12-01

    The transport of mass, heat and geochemical constituents (elements and volatiles) from the mantle to the atmosphere occurs via magma addition to the lithosphere. Calculation of magma addition rates (MARs) in continental arcs based on exposed proportions of igneous arc rocks is complex and rarely consistently determined. Multiple factors influence MAR calculations such as crust versus mantle contributions to magmas, a change in MARs across the arc and with depths throughout the arc crustal column, `arc tempos' with periods of high and low magmatic activity, the loss of previous emplaced arc rocks by subsequent magmatism and return to the mantle, arc migration, variations in the intrusive versus extrusive additions and evolving arc widths and thicknesses during tectonism. All of these factors need to be considered when calculating MARs.This study makes a new attempt to calculate MARs in continental arcs by studying three arc sections: the Famatinian arc, Argentina, the Sierra Nevada batholith, California and the Coast Mountain batholith, Washington and British Columbia. Arcs are divided into fore-arc, main arc and back arc sections and `boxes' with a defined width, length and thickness spanning upper middle and lower crustal levels are assigned to each section. Representative exposed crustal slices for each depth are then used to calculate MARs based on outcrop proportions for each box. Geochemical data is used to infer crustal recycling percentages and total thickness of the arc. Preliminary results show a correlation between MARs, crustal thicknesses and magmatic flare-up durations. For instance, the Famatinian arc shows a strong decrease in MARs between the main arc section (9.4 km3/Ma/arc-km) and the fore-arc (0.61 km3/Ma/arc-km) and back-arc (1.52 km3/Ma/arc-km) regions and an increase in the amount of magmatism with depth.Global MARs over geologic timescales have the potential to investigate mantle melt generation rates and the volatile outgassing contribution

  20. Magma injection into a long-lived reservoir to explain geodetically measured uplift: Application to the 2007-2014 unrest episode at Laguna del Maule volcanic field, Chile.

    Science.gov (United States)

    Le Mével, Hélène; Gregg, Patricia M; Feigl, Kurt L

    2016-08-01

    Moving beyond the widely used kinematic models for the deformation sources, we present a new dynamic model to describe the process of injecting magma into an existing magma reservoir. To validate this model, we derive an analytical solution and compare its results to those calculated using the Finite Element Method. A Newtonian fluid characterized by its viscosity, density, and overpressure (relative to the lithostatic value) flows through a vertical conduit, intruding into a reservoir embedded in an elastic domain, leading to an increase in reservoir pressure and time-dependent surface deformation. We apply our injection model to Interferometric Synthetic Aperture Radar (InSAR) data from the ongoing unrest episode at Laguna del Maule (Chile) volcanic field that started in 2007. Using a grid search optimization, we minimize the misfit to the InSAR displacement data and vary the three parameters governing the analytical solution: the characteristic timescale τ P for magma propagation, the maximum injection pressure, and the inflection time when the acceleration switches from positive to negative. For a spheroid with semimajor axis a = 6200 m, semiminor axis c = 100 m, located at a depth of 4.5 km in a purely elastic half-space, the best fit to the InSAR displacement data occurs for τ P =9.5 years and an injection pressure rising up to 11.5 MPa for 2 years. The volume flow rate increased to 1.2 m 3 /s for 2 years and then decreased to 0.7 m 3 /s in 2014. In 7.3 years, at least 187 × 10 6 m 3 of magma was injected.

  1. Magma emplacement in 3D

    Science.gov (United States)

    Gorczyk, W.; Vogt, K.

    2017-12-01

    Magma intrusion is a major material transfer process in Earth's continental crust. Yet, the mechanical behavior of the intruding magma and its host are a matter of debate. In this study, we present a series of numerical thermo-mechanical experiments on mafic magma emplacement in 3D.In our model, we place the magmatic source region (40 km diameter) at the base of the mantle lithosphere and connect it to the crust by a 3 km wide channel, which may have evolved at early stages of magmatism during rapid ascent of hot magmatic fluids/melts. Our results demonstrate continental crustal response due to magma intrusion. We observe change in intrusion geometries between dikes, cone-sheets, sills, plutons, ponds, funnels, finger-shaped and stock-like intrusions as well as injection time. The rheology and temperature of the host-rock are the main controlling factors in the transition between these different modes of intrusion. Viscous deformation in the warm and deep crust favours host rock displacement and magma pools along the crust-mantle boundary forming deep-seated plutons or magma ponds in the lower to middle-crust. Brittle deformation in the cool and shallow crust induces cone-shaped fractures in the host rock and enables emplacement of finger- or stock-like intrusions at shallow or intermediate depth. A combination of viscous and brittle deformation forms funnel-shaped intrusions in the middle-crust. Low-density source magma results in T-shaped intrusions in cross-section with magma sheets at the surface.

  2. Magma oceanography. II - Chemical evolution and crustal formation. [lunar crustal rock fractional crystallization model

    Science.gov (United States)

    Longhi, J.

    1977-01-01

    A description is presented of an empirical model of fractional crystallization which predicts that slightly modified versions of certain of the proposed whole moon compositions can reproduce the major-element chemistry and mineralogy of most of the primitive highland rocks through equilibrium and fractional crystallization processes combined with accumulation of crystals and trapping of residual liquids. These compositions contain sufficient Al to form a plagioclase-rich crust 60 km thick on top of a magma ocean that was initially no deeper than about 300 km. Implicit in the model are the assumptions that all cooling and crystallization take place at low pressure and that there are no compositional or thermal gradients in the liquid. Discussions of the cooling and crystallization of the proposed magma ocean show these assumptions to be disturbingly naive when applied to the ocean as a whole. However, the model need not be applied to the whole ocean, but only to layers of cooling liquid near the surface.

  3. A dynamic balance between magma supply and eruption rate at Kilauea volcano, Hawaii

    Science.gov (United States)

    Denlinger, R.P.

    1997-01-01

    The dynamic balance between magma supply and vent output at Kilauea volcano is used to estimate both the volume of magma stored within Kilauea volcano and its magma supply rate. Throughout most of 1991 a linear decline in volume flux from the Kupaianaha vent on Kilauea's east rift zone was associated with a parabolic variation in the elevation of Kilauea's summit as vent output initially exceeded then lagged behind the magma supply to the volcano. The correspondence between summit elevation and tilt established with over 30 years of data provided daily estimates of summit elevation in terms of summit tilt. The minimum in the parabolic variation in summit tilt and elevation (or zero elevation change) occurs when the magma supply to the reservoir from below the volcano equals the magma output from the reservoir to the surface, so that the magma supply rate is given by vent flux on that day. The measurements of vent flux and tilt establish that the magma supply rate to Kilauea volcano on June 19, 1991, was 217,000 ?? 10,000 m3/d (or 0.079 ?? 0.004 km3/yr). This is close to the average eruptive rate of 0.08 km3/yr between 1958 and 1984. In addition, the predictable response of summit elevation and tilt to each east rift zone eruption near Puu Oo since 1983 shows that summit deformation is also a measure of magma reservoir pressure. Given this, the correlation between the elevation of the Puu Oo lava lake (4 km uprift of Kupaianaha and 18 km from the summit) and summit tilt provides an estimate for magma pressure changes corresponding to summit tilt changes. The ratio of the change in volume to the change in reservoir pressure (dV/dP) during vent activity may be determined by dividing the ratio of volume erupted to change in summit tilt (dV/dtilt) by the ratio of pressure change to change in summit tilt (dP/dtilt). This measure of dV/dP, when combined with laboratory measurements of the bulk modulus of tholeitic melt, provides an estimate of 240 ?? 50 km3 for the volume

  4. Magma genesis, storage and eruption processes at Aluto volcano, Ethiopia: lessons from remote sensing, gas emissions and geochemistry

    Science.gov (United States)

    Hutchison, William; Biggs, Juliet; Mather, Tamsin; Pyle, David; Gleeson, Matthew; Lewi, Elias; Yirgu, Gezahgen; Caliro, Stefano; Chiodini, Giovanni; Fischer, Tobias

    2016-04-01

    One of the most intriguing aspects of magmatism during the transition from continental rifting to sea-floor spreading is that large silicic magmatic systems develop within the rift zone. In the Main Ethiopian Rift (MER) these silicic volcanoes not only pose a significant hazard to local populations but they also sustain major geothermal resources. Understanding the journey magma takes from source to surface beneath these volcanoes is vital for determining its eruption style and for better evaluating the geothermal resources that these complexes host. We investigate Aluto, a restless silicic volcano in the MER, and combine a wide range of geochemical and geophysical techniques to constrain magma genesis, storage and eruption processes and shed light on magmatic-hydrothermal-tectonic interactions. Magma genesis and storage processes at Aluto were evaluated using new whole-rock geochemical data from recent eruptive products. Geochemical modelling confirms that Aluto's peralkaline rhyolites, that constitute the bulk of recent erupted products, are generated from protracted fractionation (>80 %) of basalt that is compositionally similar to rift-related basalts found on the margins of the complex. Crustal melting did not play a significant role in rhyolite genesis and melt storage depths of ~5 km can reproduce almost all aspects of their geochemistry. InSAR methods were then used to investigate magma storage and fluid movement at Aluto during an episode of ground deformation that took place between 2008 and 2010. Combining new SAR imagery from different viewing geometries we identified an accelerating uplift pulse and found that source models support depths of magmatic and/or fluid intrusion at ~5 km for the uplift and shallower depths of ~4 km for the subsidence. Finally, gas samples collected on Aluto in 2014 were used to evaluate magma and fluid transport processes. Our results show that gases are predominantly emanating from major fault zones on Aluto and that they

  5. Yellowstone-Snake River Plain seismic profilling experiment: Crustal structure of the eastern Snake River Plain

    International Nuclear Information System (INIS)

    Braile, L.W.; Smith, R.B.; Ansorge, J.; Baker, M.R.; Sparlin, M.A.; Prodehl, C.; Schilly, M.M.; Healy, J.H.; Mueller, S.; Olsen, K.H.

    1982-01-01

    Seismic refraction profiles recorded along the eastern Snake River Plain (ESRP) in southeastern Idaho during the 1978 Yellowstone-Snake River Plain cooperative seismic profiling experiment are interpreted to infer the crustal velocity and attenuation (Q-1) structure of the ESRP. Travel-time and synthetic seismogram modeling of a 250 km reversed refraction profile as well as a 100 km detailed profile indicate that the crust of the ESRP is highly anomalous. Approximately 3 to 6 km of volcanic rocks (with some interbedded sediments) overlie an upper-crustal layer (compressional velocity approx. =6.1 km/s) which thins southwestward along the ESRP from a thickness of 10 km near Island Park Caldera to 2 to 3 km beneath the central and southwestern portions of the ESRP. An intermediate-velocity (approx. =6.5 km/s) layer extends from approx. =10 to approx. =20 km depth. a thick (approx. =22 km) lower crust of compressional velocity 6.8 km/s, a total crustall thickness of approx. =42 km, and a P/sub n/ velocity of approx. =7.9 km/s is observed in the ESRP, similar to the western Snake River Plain and the Rocky Mountains Provinces. High attenuation is evident on the amplitude corrected seismic data due to low-Q values in the volcanic rocks (Q/sub p/ = 20 to 200) and throughout the crust (Q/sub p/ = 160 to 300). Based on these characteristics of the crustal structure and volcanic-age progression data, it is suggested that the ESRP has resulted from an intensitive period of intrusion of mantle-derived basaltic magma into the upper crust generating explosive silicic volcanism and associated regional uplift and caldera collapse. This activity began about 15 m.y. ago in southwestern Idaho and has migrated northeast to its present position at Yellowstone. Subsequent cooling of the intruded upper crust results in the 6.5 km/s velocity intermediate layer. Crustal subsidence and periodic basaltic volcanism as represented by the ESRP complete the sequence of crustal evolution

  6. Estimating the Crustal Power Spectrum From Vector Magsat Data: Crustal Power Spectrum

    Science.gov (United States)

    Lowe, David A. J.; Parker, Robert L.; Purucker, Michael E.; Constable, Catherine G.

    2000-01-01

    The Earth's magnetic field can be subdivided into core and crustal components and we seek to characterize the crustal part through its spatial power spectrum (R(sub l)). We process vector Magsat data to isolate the crustal field and then invert power spectral densities of flight-local components along-track for R(sub l) following O'Brien et al. [1999]. Our model (LPPC) is accurate up to approximately degree 45 (lambda=900 km) - this is the resolution limit of our data and suggests that global crustal anomaly maps constructed from vector Magsat data should not contain features with wavelengths less than 900 km. We find continental power spectra to be greater than oceanic ones and attribute this to the relative thicknesses of continental and oceanic crust.

  7. Upward migration of Vesuvius magma chamber over the past 20,000 years.

    Science.gov (United States)

    Scaillet, B; Pichavant, M; Cioni, R

    2008-09-11

    Forecasting future eruptions of Vesuvius is an important challenge for volcanologists, as its reawakening could threaten the lives of 700,000 people living near the volcano. Critical to the evaluation of hazards associated with the next eruption is the estimation of the depth of the magma reservoir, one of the main parameters controlling magma properties and eruptive style. Petrological studies have indicated that during past activity, magma chambers were at depths between 3 and 16 km (refs 3-7). Geophysical surveys have imaged some levels of seismic attenuation, the shallowest of which lies at 8-9 km depth, and these have been tentatively interpreted as levels of preferential magma accumulation. By using experimental phase equilibria, carried out on material from four main explosive events at Vesuvius, we show here that the reservoirs that fed the eruptive activity migrated from 7-8 km to 3-4 km depth between the ad 79 (Pompeii) and ad 472 (Pollena) events. If data from the Pomici di Base event 18.5 kyr ago and the 1944 Vesuvius eruption are included, the total upward migration of the reservoir amounts to 9-11 km. The change of preferential magma ponding levels in the upper crust can be attributed to differences in the volatile content and buoyancy of ascending magmas, as well as to changes in local stress field following either caldera formation or volcano spreading. Reservoir migration, and the possible influence on feeding rates, should be integrated into the parameters used for defining expected eruptive scenarios at Vesuvius.

  8. Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 2. Coeruptive deflation, July-August 2008

    Science.gov (United States)

    Lu, Zhong; Dzurisin, Daniel

    2010-01-01

    A hydrovolcanic eruption near Cone D on the floor of Okmok caldera, Alaska, began on 12 July 2008 and continued until late August 2008. The eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and ∼3 km below sea level (bsl), which began immediately after Okmok's previous eruption in 1997. In this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar (InSAR) techniques to produce a suite of 2008 coeruption deformation maps. Most of the surface deformation that occurred during the eruption is explained by deflation of a Mogi-type source located beneath the center of the caldera and 2–3 km bsl, i.e., essentially the same source that inflated prior to the eruption. During the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1/e time constant of ∼13 days. We envision a sponge-like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath Okmok caldera. The rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface. A similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring-fracture system.

  9. Are U-Series Disequilibria Transparent to Crustal Processing of Magma? A Case Study at Bezymianny and Klyuchevskoy Volcanoes, Kamchatka, Russia

    Science.gov (United States)

    Kayzar, T. M.; Nelson, B. K.; Bachmann, O.; Portnyagin, M.; Ponomareva, V.

    2010-12-01

    Disequilibria in the short-lived uranium-series isotopic system can provide timescales of magma production, modification and transport in all tectonic settings. In volcanic arcs, the field has converged on the concept that (238U/230Th) and (226Ra/230Th) activities greater than one are a result of fluid fluxing from the slab to mantle wedge, and that the preservation of (226Ra/230Th) disequilibria requires rapid transport of melts from the mantle wedge to the surface (226Ra returns to equilibrium with 230Th in ~8000 years). The need for rapid transport coupled with the incompatibility of U-series elements suggest that U-series fractionation is not measurably affected by crustal processes. However, some well-studied arc systems, including the very productive Central Kamchatka Depression (CKD) of the Kamchatkan volcanic arc, show U-series data that are in conflict with this commonly accepted model. Our study focuses on two neighboring volcanic systems, Bezymianny and Klyuchevskoy volcanoes in the CKD. Separated by ~10km, these two systems are thought to share the same mantle source. Klyuchevskoy has primitive compositions (51-56 wt%) while Bezymianny erupts more differentiated andesites (57-63 wt% SiO2); therefore, by examining the U-series signals in these two systems it is possible to decouple a primary signal from one having undergone crustal processing. We record whole rock (238U/230Th) values for Bezymianny ranging from 0.94 to 0.96 in modern eruptive products, while (226Ra/230Th) are >1. We also observe a similar signal in older (212-6791BP) tephra deposits from Klyuchevskoy, measuring (238U/230Th) of 0.92-0.99 (unpublished data, collaborative research with the KALMAR project). (238U/230Th) local bulk rock or partial melts to fractionate U, Th, and Ra from one another. In particular, we focus on minor mineral phases, such as apatite and magnetite, which are present during early stages of differentiation (andesites) and may fractionate U from Th. We measure U and

  10. The effect of pressurized magma chamber growth on melt migration and pre-caldera vent locations through time at Mount Mazama, Crater Lake, Oregon

    Science.gov (United States)

    Karlstrom, Leif; Wright, Heather M.; Bacon, Charles R.

    2015-01-01

    The pattern of eruptions at long-lived volcanic centers provides a window into the co-evolution of crustal magma transport, tectonic stresses, and unsteady magma generation at depth. Mount Mazama in the Oregon Cascades has seen variable activity over the last 400 ky, including the 50 km3 climactic eruption at ca. 7.7 ka that produced Crater Lake caldera. The physical mechanisms responsible for the assembly of silicic magma reservoirs that are the precursors to caldera-forming eruptions are poorly understood. Here we argue that the spatial and temporal distribution of geographically clustered volcanic vents near Mazama reflects the development of a centralized magma chamber that fed the climactic eruption. Time-averaged eruption rates at Mount Mazama imply an order of magnitude increase in deep magma influx prior to the caldera-forming event, suggesting that unsteady mantle melting triggered a chamber growth episode that culminated in caldera formation. We model magma chamber–dike interactions over ∼50 ky preceding the climactic eruption to fit the observed distribution of surface eruptive vents in space and time, as well as petrologically estimated deep influx rates. Best fitting models predict an expanding zone of dike capture caused by a growing, oblate spheroidal magma chamber with 10–30 MPa of overpressure. This growing zone of chamber influence causes closest approaching regional mafic vent locations as well as more compositionally evolved Mazama eruptions to migrate away from the climactic eruptive center, returning as observed to the center after the chamber drains during the caldera-forming eruption.

  11. Magmatism at different crustal levels in the ancient North Cascades magmatic arc

    Science.gov (United States)

    Shea, E. K.; Bowring, S. A.; Miller, R. B.; Miller, J. S.

    2013-12-01

    The mechanisms of magma ascent and emplacement inferred from study of intrusive complexes have long been the subject of intense debate. Current models favor incremental construction based on integration of field, geochemical, geochronologic, and modeling studies. Much of this work has been focused on a single crustal level. However, study of magmatism throughout the crust is critical for understanding how magma ascends through and intrudes surrounding crustal material. Here, we present new geochronologic and geochemical work from intrusive complexes emplaced at a range of crustal depths in the Cretaceous North Cascades magmatic arc. These complexes were intruded between 92 and 87 Ma at depths of at ≤5 -10 km, ~20 km, and ~25 km during this time. U-Pb CA-TIMS geochronology in zircon can resolve Jack-Entiat intrusive complex, a highly elongate amalgamation of intrusions recording two episodes of magmatism between~92-88 Ma and ~80-77 Ma. Each of these complexes provides a window into crustal processes that occur at different depths. Our data suggest assembly of the Black Peak intrusive complex occurred via a series of small (0.5-2 km2) magmatic increments from ~92 Ma to ~87 Ma. Field relations and zircon trace element geochemistry indicate each of these increments were emplaced and crystallized as closed systems-we find no evidence for mixing between magmas in the complex. However, zircon inheritance becomes more common in younger intrusions, indicating assimilation of older plutonic material, possibly during magma production or transport. The Seven-Fingered Jack intrusive complex, emplaced around 15-20 km, preserves a much more discontinuous record of intrusion than the Black Peak. Our data indicate major magmatism in the complex occurred between ~92.1-91.1 Ma. Inheritance in the Seven-Fingered Jack is common, particularly along contacts between intrusions. The Tenpeak intrusive complex, assembled between ~92 Ma and 89 Ma, represents one of the deepest exhumed

  12. A coupled petrological-geodynamical model to investigate the evolution of crustal magmatic systems

    Science.gov (United States)

    Kaus, B. J. P.; Rummel, L.; White, R. W.

    2017-12-01

    The evolution of crustal magmatic systems can be analyzed from different physical and chemical perspectives. Most previous work focus either on the petrological side (considering thermal effects and ignoring mechanics), or on the mechanical evolution (assuming a fixed melt chemistry). Here, we consider both by combining a 2D finite element code, MVEP2, with a thermodynamic modelling approach (Perple_X). Density, melt fraction and the chemical composition of the liquid and solid phase are computed for different starting rock compositions and the evolving chemistry is tracked on markers via 10 main oxides (SiO2-TiO2-Al2O3-Cr2O3-MgO-FeO-CaO-Na2O-K2O-H2O). As soon as the local chemistry changes due to melt extraction, new phase diagrams are computed based on the residual solid chemistry for the deflated magma chamber or on the liquid chemistry for newly generated magma filled fractures. To investigate the chemical evolution in magma chambers and magma filled fractures, we inject mafic sills periodically at varying depth levels into the continental crust. The initial sill injections are focused in either one or two main zones in the crust and may interact with each other. The formation of magma filled fractures from this partially molten zone is tracked with a semi analytical dike initiation algorithm that forms new dikes as a function of the local stress field above the partially molten region and subsequently depletes and compacts the magma source region. Dike generation is thus affected by the background strain rate, amount and depth of melt accumulations as well as parameters that control the plastic and viscous behaviour of the crust (e.g. cohesion, viscous creep flow low etc.). Results show that magma filled fractures triggered by sill injections preferentially form under extensional conditions, particularly within the middle crust (in ca. 25 km depth). Magma chambers in the lower continental crust, on the other hand, are stable over a longer period of time due a

  13. Toward an integrative spatiotemporal architecture of the magma plumbing system leading to systematic Plinian eruption at Montagne Pelée Martinique (Lesser Antilles)

    Science.gov (United States)

    Boudon, G.; Balcone-Boissard, H.; Lyonnet, E.; Morgan, D. J.

    2017-12-01

    The dynamic of crustal magma reservoir may be at the origin of pressure/temperature variations that may trigger magma ascent and eruption. These changes can be registered during crystal growth and can probably produce at the surface geophysical or/and geochemical signals that could be registered by monitoring network, constituting precursory signals. For volcanoes where the plumbing system is well established in terms of volume and depth for a given cycle, repetitive eruptions of the same order of magnitude and involving similar magma composition may occur. It was the case for Montagne Pelée (Martinique, Lesser Antilles), sadly known for the 1902 lava dome-forming eruption that killed 30 000 inhabitants, and that produce repetitive Plinian eruptions in the last 15 ky. Are the perturbations in the dynamic of the magma storage identical for all these eruptions and is the timescale between these perturbations and the eruptions in the same order of magnitude? In the last decade, intracristalline diffusion modelling has been increasingly used to constrain timescale of magmatic processes. Recently this kind of investigations has been coupled to a petrological model of the magma storage region to better wholly describe its behaviour through a Crystal System Analysis (CSA) approach. Here we aim at constraining the pre-eruptive dynamic of the reservoir giving birth to the Plinian eruptions at Montagne Pelée. Precisely we attempt to identify the processes at the origin of the eruptions and the timescale between this process and the eruption. By studying the last five Plinian eruptions of this volcano the question of the systematic occurrence of one process at the same time prior eruption will be discussed. To achieve this goal we performed a detailed petrological description of the eruptive products of the first Plinian phase of these eruptions to build a CSA tree through EPMA and SEM analyses, coupled to Fe-Mg diffusion modelling in orthopyroxenes to retrieve timescale

  14. Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan

    Science.gov (United States)

    Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

    2016-01-01

    Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide. PMID:27619897

  15. Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan.

    Science.gov (United States)

    Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

    2016-09-13

    Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.

  16. Zircons reveal magma fluxes in the Earth's crust.

    Science.gov (United States)

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2014-07-24

    Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet.

  17. Compressible magma flow in a two-dimensional elastic-walled dike

    NARCIS (Netherlands)

    Woods, A.W.; Bokhove, Onno; de Boer, A; Hill, B.E.

    2006-01-01

    The ascent of magma to the Earth's surface is commonly modeled by assuming a fixed dike or flow geometry from a deep subsurface reservoir to the surface. In practice, however, this flow geometry is produced by deformation of the crust by ascending overpressured magma. Here, we explore how this

  18. Coupling Thermal and Chemical Signatures of Crustal Magma Bodies: Energy-Constrained Eruption, Recharge, Assimilation, and Fractional Crystallization (E'RAχFC)

    Science.gov (United States)

    Bohrson, W. A.; Spera, F. J.

    2004-12-01

    Energy-Constrained Eruption, Recharge, Assimilation and Fractional Crystallization (E'RAχFC) tracks the evolution of an open-system magmatic system by coupling conservation equations governing energy, mass and species (isotopes and trace elements). By linking the compositional characteristics of a composite magmatic system (host magma, recharge magma, wallrock, eruptive reservoir) to its mass and energy fluxes, predictions can be made about the chemical evolution of systems characterized by distinct compositional and thermal characteristics. An interesting application of E'RAχFC involves documenting the influence distinct thermal regimes have on the chemical evolution of magmatic systems. Heat transfer between a magma-country rock system at epizonal depths can be viewed as a conjugate heat transfer problem in which the average country rock-magma boundary temperature, Tb, is governed by the relative vigor of hydrothermal convection in the country rock vs. magma convection. For cases where hydrothermal circulation is vigorous and magmatic heat is efficiently transported away from the boundary, contact aureole temperatures (~Tb) are low. In cases where magmatic heat can not be efficiently transported away from the boundary and hydrothermal cells are absent or poorly developed, Tb is relatively high. Simultaneous solution of the differential equations governing momentum and energy conservation and continuity for the coupled hydrothermal-magmatic conjugate heat transfer system enables calculation of the characteristic timescale for EC-RAFC evolution and development of hydrothermal deposits as a function of material and medium properties, sizes of systems and relative efficiency of hydrothermal vs. magmatic heat transfer. Characteristic timescales lie in the range 102-106 yr depending on system size, magma properties and permeability among other parameters. In E'RAχFC, Tb is approximated by the user-defined equilibration temperature, Teq, which is the temperature at

  19. Magma chamber interaction giving rise to asymmetric oscillations

    Science.gov (United States)

    Walwer, D.; Ghil, M.; Calais, E.

    2017-12-01

    Geodetic time series at four volcanoes (Okmok, Akutan, Shishaldin, and Réunion) are processed using Multi-channel Singular Spectrum Analysis (M-SSA) and reveal sawtooth-shaped oscillations ; the latter are characterized by short intervals of fast inflations followed by longer intervals of slower deflations. At Okmok and Akutan, the oscillations are first damped and then accentuated. At Okmok, the increase in amplitude of the oscillations is followed by an eruption. We first show that the dynamics of these four volcanoes bears similarities with that of a simple nonlinear, dissipative oscillator, indicating that the inflation-deflation episodes are relaxation oscillations. These observations imply that ab initio dynamical models of magma chambers should possess an asymmetric oscillatory regime. Next, based on the work of Whitehead and Helfrich [1991], we show that a model of two magma chambers — connected by a cylindrical conduit in which the magma viscosity depends on temperature — gives rise to asymmetric overpressure oscillations in the magma reservoirs. These oscillations lead to surface deformations that are consistent with those observed at the four volcanoes in this study. This relaxation oscillation regime occurs only when the vertical temperature gradient in the host rock between the two magma chambers is large enough and when the magma flux entering the volcanic system is sufficiently high. The magma being supplied by a deeper source region, the input flux depends on the pressure difference between the source and the deepest reservoir. When this difference is not sufficiently high, the magma flux exponentially decreases, leading to damped oscillations as observed at Akutan and Okmok. The combination of observational and modeling results clearly supports the role of relaxation oscillations in the dynamics of volcanic systems.

  20. Numerical modeling of magma-tectonic interactions at Pacaya Volcano, Guatemala

    Science.gov (United States)

    Wauthier, C.

    2017-12-01

    Pacaya Volcano is composed of several volcanic cones located along the southern rim of the Amatitlan caldera, approximately 25 km south of Guatemala City. It is a basaltic volcano located in the Central American Volcanic Arc. The shallow magma plumbing system at Pacaya likely includes at least three magma reservoirs: a very shallow ( 0.2-0.4 km depth) reservoir located below and possibly within the MacKenney cone, a 4 km deep reservoir located northwest of the summit, and a shallow dike-like conduit below the summit which fed the recent flank eruptions. Pacaya's western flank is slipping in a stick-slip fashion, and the instability seems associated with larger volume eruptions. Flank instability phases indeed occurred in 2010 and 2014 in coincidence with major intrusive and eruptive phases, suggesting a positive feedback between the flank motion and major intrusions. Simple analytical models are insufficient to fit the geodetic observations and model the flank processes and their mechanical interactions with the magmatic system. Here, numerical modeling approaches are used to characterize the 2014 flank deformation episode and magma-tectonic interactions.

  1. Fault-Magma Interactions during Early Continental Rifting: Seismicity of the Magadi-Natron-Manyara basins, Africa

    Science.gov (United States)

    Weinstein, A.; Oliva, S. J.; Ebinger, C.; Aman, M.; Lambert, C.; Roecker, S. W.; Tiberi, C.; Muirhead, J.

    2017-12-01

    Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2D studies. We analyze seismicity data from a 13-month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3D velocity model reveal lower crustal earthquakes along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 66 earthquakes, and a longer time period of relocated earthquakes from global arrays reveal an along-axis stress rotation of 50 o ( N150 oE) in the magmatically active zone. Using Kostrov summation of local and teleseismic mechanisms, we find opening directions of N122ºE and N92ºE north and south of the magmatically active zone. The stress rotation facilitates strain transfer from border fault systems, the locus of early stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Earthquakes are largely driven by stress state around inflating magma bodies, and more dike intrusions with surface faulting, eruptions, and earthquakes are expected.

  2. Modeling Magma Mixing: Evidence from U-series age dating and Numerical Simulations

    Science.gov (United States)

    Philipp, R.; Cooper, K. M.; Bergantz, G. W.

    2007-12-01

    Magma mixing and recharge is an ubiquitous process in the shallow crust, which can trigger eruption and cause magma hybridization. Phenocrysts in mixed magmas are recorders for magma mixing and can be studied by in- situ techniques and analyses of bulk mineral separates. To better understand if micro-textural and compositional information reflects local or reservoir-scale events, a physical model for gathering and dispersal of crystals is necessary. We present the results of a combined geochemical and fluid dynamical study of magma mixing processes at Volcan Quizapu, Chile; two large (1846/47 AD and 1932 AD) dacitic eruptions from the same vent area were triggered by andesitic recharge magma and show various degrees of magma mixing. Employing a multiphase numerical fluid dynamic model, we simulated a simple mixing process of vesiculated mafic magma intruded into a crystal-bearing silicic reservoir. This unstable condition leads to overturn and mixing. In a second step we use the velocity field obtained to calculate the flow path of 5000 crystals randomly distributed over the entire system. Those particles mimic the phenocryst response to the convective motion. There is little local relative motion between silicate liquid and crystals due to the high viscosity of the melts and the rapid overturn rate of the system. Of special interest is the crystal dispersal and gathering, which is quantified by comparing the distance at the beginning and end of the simulation for all particle pairs that are initially closer than a length scale chosen between 1 and 10 m. At the start of the simulation, both the resident and new intruding (mafic) magmas have a unique particle population. Depending on the Reynolds number (Re) and the chosen characteristic length scale of different phenocryst-pairs, we statistically describe the heterogeneity of crystal populations on the thin section scale. For large Re (approx. 25) and a short characteristic length scale of particle

  3. El Hierro's floating stones as messengers of crust-magma interaction at depth

    Science.gov (United States)

    Burchardt, S.; Troll, V. R.; Schmeling, H.; Koyi, H.; Blythe, L. S.; Longpré, M. A.; Deegan, F. M.

    2012-04-01

    During the early stages of the submarine eruption that started on October 10 2011 south of El Hierro, Canary Islands, Spain, peculiar eruption products were found floating on the sea surface. These centimetre- to decimetre-sized "bombs" have been termed "restingolites" after the nearby village La Restinga and consist of a basaltic rind and a white to light grey core that resembles pumice in texture. According to Troll et al. (2011; see also Troll et al. EGU 2012 Abstracts), this material consists of a glassy matrix hosting extensive vesicle networks, which results in extremely low densities allowing these rocks to float on sea water. Mineralogical and geochemical analyses reveal that the "restingolites" originate from the sedimentary rocks (sand-, silt-, and mudstones) that form layer 1 of the oceanic crust beneath El Hierro. During the onset and early stages of the eruption, magma ponded at the base of this sedimentary sequence, breaking its way through the sedimentary rocks to the ocean floor. The textures of the "restingolites" reveal that crust-magma interaction during fragmentation and transport of the xenoliths involved rapid partial melting and volatile exsolution. Xenoliths strikingly similar to those from El Hierro are known from eruptions on other Canary Islands (e.g. La Palma, Gran Canaria, and Lanzarote). In fact, they resemble in texture xenoliths of various protoliths from volcanic areas worldwide (e.g. Krakatao, Indonesia, Cerro Quemado, Guatemala, Laacher See, Germany). This indicates that the process of partial melting and volatile exsolution, which the "restingolites" bear witness of, is probably occurring frequently during shallow crustal magma emplacement. Thermomechanical numerical models of the effect of the density decrease associated with the formation of vesicle networks in partially molten xenoliths show that xenoliths of crustal rocks initially sink in a magma chamber, but may start to float to the chamber roof once they start to heat up

  4. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions.

    Science.gov (United States)

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-12-15

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes.

  5. Transport of metals and sulphur in magmas by flotation of sulphide melt on vapour bubbles

    Science.gov (United States)

    Mungall, J. E.; Brenan, J. M.; Godel, B.; Barnes, S. J.; Gaillard, F.

    2015-03-01

    Emissions of sulphur and metals from magmas in Earth’s shallow crust can have global impacts on human society. Sulphur-bearing gases emitted into the atmosphere during volcanic eruptions affect climate, and metals and sulphur can accumulate in the crust above a magma reservoir to form giant copper and gold ore deposits, as well as massive sulphur anomalies. The volumes of sulphur and metals that accumulate in the crust over time exceed the amounts that could have been derived from an isolated magma reservoir. They are instead thought to come from injections of multiple new batches of vapour- and sulphide-saturated magmas into the existing reservoirs. However, the mechanism for the selective upward transfer of sulphur and metals is poorly understood because their main carrier phase, sulphide melt, is dense and is assumed to settle to the bottoms of magma reservoirs. Here we use laboratory experiments as well as gas-speciation and mass-balance models to show that droplets of sulphide melt can attach to vapour bubbles to form compound drops that float. We demonstrate the feasibility of this mechanism for the upward mobility of sulphide liquids to the shallow crust. Our work provides a mechanism for the atmospheric release of large amounts of sulphur, and contradicts the widely held assumption that dense sulphide liquids rich in sulphur, copper and gold will remain sequestered in the deep crust.

  6. Fault-magma interactions during early continental rifting: Seismicity of the Magadi-Natron-Manyara basins, Africa

    Science.gov (United States)

    Weinstein, A.; Oliva, S. J.; Ebinger, C. J.; Roecker, S.; Tiberi, C.; Aman, M.; Lambert, C.; Witkin, E.; Albaric, J.; Gautier, S.; Peyrat, S.; Muirhead, J. D.; Muzuka, A. N. N.; Mulibo, G.; Kianji, G.; Ferdinand-Wambura, R.; Msabi, M.; Rodzianko, A.; Hadfield, R.; Illsley-Kemp, F.; Fischer, T. P.

    2017-10-01

    Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2-D studies. We analyze seismicity data from a 13 month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3-D velocity model reveal lower crustal earthquakes beneath the central basins and along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 65 earthquakes, and 13 from a catalogue prior to our array reveal an along-axis stress rotation of ˜60° in the magmatically active zone. New and prior mechanisms show predominantly normal slip along steep nodal planes, with extension directions ˜N90°E north and south of an active volcanic chain consistent with geodetic data, and ˜N150°E in the volcanic chain. The stress rotation facilitates strain transfer from border fault systems, the locus of early-stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Results indicate that earthquakes are largely driven by stress state around inflating magma bodies.

  7. Two magma bodies beneath the summit of Kilauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

    Science.gov (United States)

    Pietruszka, Aaron J.; Heaton, Daniel E.; Marske, Jared P.; Garcia, Michael O.

    2015-01-01

    The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas—from 1959 to the active Halema‘uma‘u lava lake—to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir ∼2–4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body 4 km3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969–1974 Mauna Ulu, 1983-present Pu‘u ‘Ō‘ō and 2008-present Halema‘uma‘u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

  8. Constraints on timescales and mechanics of magmatic underplating from InSAR observations of large active magma sills in the Earth's crust.

    Science.gov (United States)

    Fialko, Y.

    2002-12-01

    Theoretical models of the granitoid magma generation due to magmatic underplating predict that anatectic melts are produced on quite short timescales of the order of the crystallization time of typical mafic underplates (e.g., 102-10^3 years for sill intrusions that are a few tens to a few hundred meters thick). If so, the intrusion of mafic underplates, the volume changes associated with in situ melting, and the subsequent evacuation of the resulting granitoid magmas can each generate geodetically observable deformation. Geodetic measurements in areas of contemporaneous large active magma bodies may therefore provide critical constraints on the timescales and dynamics of crustal anatexis. We use Interferometric Synthetic Aperture Radar (InSAR) observations in regions of the ongoing crustal magmatism to constrain typical rates of the large-scale melt generation and/or migration, and to test the proposed models of the granitic melt production. Our primary targets include large mid-crustal magma bodies imaged by seismic studies, in particular, the Socorro (New Mexico, USA), the Altiplano-Puna (south America), and the south Tibet (Asia) magma bodies. All these magma bodies are located at depth of 19-20 km, suggesting a strong rheological or buoyancy control on the transition from a vertical to a horizontal magma flow. Stacked interferometric data from the Socorro magma body indicate a quasi-steady uplift with a maximum rate of 3-4 mm/yr over the last 10 years covered by the InSAR observations. The uplift morphology can be well described by an elastic inflation of the Socorro sill. We show that deformation models that allow for the viscous-like rheology of the mid-to-lower crust cannot be easily reconciled with the geodetic data. However, thermodynamic modeling, in conjunction with inferences of the nearly constant uplift rates, suggest that the deformations associated with the intrusion emplacement must involve a significant inelastic component. Such inelastic

  9. Petrological cycles and caldera-forming events

    Science.gov (United States)

    Bachmann, O.; Deering, C. D.

    2012-12-01

    Many caldera-forming events can be framed within broad petrological cycles; volcanic stratigraphy typically defines a trend from mafic to more silicic magmas with time, culminating in the catastrophic evacuation of an upper crustal reservoir filled with the silicic magma, followed by a return to the eruption of more mafic magmas shortly after caldera collapse. Understanding how such cycles develop has clear implications for characterizing the current state of an active system. Here, we focus on a detailed examination of the well-exposed Quaternary Kos-Nisyros eruptive sequence (eastern Aegean arc) to frame a potential model for such cycles. On the basis of zircon U/Th/Pb ages, building the upper crustal magma chamber large enough to induce caldera collapse required at least a few hundred thousand years. This timeframe is necessary not only for the accumulation of large amounts of viscous, gas-rich silicic magma, but also to heat the upper crust sufficiently to allow the developing reservoir to be maintained above the solidus. In the Kos-Nisyros volcanic center, small eruptions precede the caldera-forming event and mark this period of thermal maturation as the system transitions from intermediate to silicic magma, reaching the most-evolved state only shortly prior to the caldera-forming event, the Kos Plateau Tuff (> 60 km3 of volatile-rich, high-silica rhyolite). The Kos Plateau Tuff was then followed by small-volume eruptions of more mafic magma (basaltic andesite, andesite, and dacites) that are characterized by a drier mineral assemblage. With time, the system transitioned back to cold, wet, high-SiO2 rhyolite. We suggest that the changes in magma composition and mineralogy following the caldera-forming event are due to a near-complete crystallization of the non-erupted mush in the upper crustal reservoir as it is abruptly decompressed during eruption. This rapid crystallization (1) leads to the formation of a porphyritic texture in the crystalline residual - a

  10. The global chemical systematics of arc front stratovolcanoes: Evaluating the role of crustal processes

    Science.gov (United States)

    Turner, Stephen J.; Langmuir, Charles H.

    2015-07-01

    Petrogenetic models for convergent margins should be consistent with the global systematics of convergent margin volcanic compositions. A newly developed tool for compiling and screening data from the GEOROC database was used to generate a global dataset of whole rock chemical analyses from arc front stratovolcano samples. Data from 227 volcanoes within 31 volcanic arc segments were first averaged by volcano and then by arc to explore global systematics. Three different methods of data normalization produce consistent results that persist across a wide range of Mg# [Mg# =Mg / (Mg +Fe) ]. Remarkably coherent systematics are present among major and trace element concentrations and ratios, with the exception of three arcs influenced by mantle plumes and Peru/N. Chile, which is built on exceptionally thick crust. Chemical parameters also correlate with the thickness of the overlying arc crust. In addition to previously established correlations of Na6.0 with Ca6.0 and crustal thickness, correlations are observed among major elements, trace elements, and trace element ratios (e.g. La/Yb, Dy/Yb, Zr/Sm, Zr/Ti). Positive correlations include "fluid mobile," "high field strength," and "large ion lithophile" element groups, with concentrations that vary by a factor of five in all groups. Incompatible element enrichments also correlate well with crustal thickness, with the greatest enrichment found at arcs with the thickest crust. Intra-crustal processes, however, do not reproduce the global variations. High pressure fractionation produces intermediate magmas enriched in aluminum, but such magmas are rare. Furthermore, differences among magma compositions at various volcanic arcs persist from primitive to evolved compositions, which is inconsistent with the possibility that global variations are produced by crystal fractionation at any pressure. Linear relationships among elements appear to be consistent with mixing between depleted primary magma and an enriched contaminant

  11. Modeling and Crustal Structure in the Future Reservoir of Jequitaí, Brazil

    Science.gov (United States)

    Teixeira, C. D.; Von Huelsen, M. G.; Chemale, F., Jr.; Nascimento, A. V. D. S., Sr.; do Sacramento, V., Sr.; Garcia, V. B. P., Sr.

    2017-12-01

    Integrated geophysical and geological data analysis in the state of Minas Gerais, Brazil, allowed the modeling of the subsurface framework in a region where a reservoir - the Jequitaí reservoir - will be constructed. Studies of this nature during the previous stages of the construction of large hydroelectric projects are highly important, because the regional geology understanding associated with geophysical data interpretation can help to prevent damage in the physical structure of the dam, which will aid in its preservation. The use of gravity and magnetic data in a 2D crustal model provided information on a possible framework of the area and revealed features not mapped until now, which may be useful for further studies and can contribute to the understanding of this portion of the crust. The results show the presence of high gravity anomalies in the southern part of the study area, besides extensive lineaments that cross the whole area, interpreted as possible faults and dykes. Depth estimation techniques, such as Euler deconvolution and radially averaged power spectrum, allowed the identification of continuous structures up to 400 m depth, and showed differences in the basement depth in the northern and southern portions of the study area. Inversion of the gravity data along a profile crossing a gravity anomaly yielded to information about the depth, thickness and shape of a possible intrusive body. The geological-geophysical model was consistent with the interpretations based on surface geology and in the gravity and magnetic signal, because the section could be modeled respecting the geophysical data and the pre-existing structural proposals.

  12. Primitive magmas at five Cascade volcanic fields: Melts from hot, heterogeneous sub-arc mantle

    Science.gov (United States)

    Bacon, C.R.; Bruggman, P.E.; Christiansen, R.L.; Clynne, M.A.; Donnelly-Nolan, J. M.; Hildreth, W.

    1997-01-01

    Major and trace element concentrations, including REE by isotope dilution, and Sr, Nd, Pb, and O isotope ratios have been determined for 38 mafic lavas from the Mount Adams, Crater Lake, Mount Shasta, Medicine Lake, and Lassen volcanic fields, in the Cascade arc, northwestern part of the United States. Many of the samples have a high Mg# [100Mg/(Mg + FeT) > 60] and Ni content (>140 ppm) such that we consider them to be primitive. We recognize three end-member primitive magma groups in the Cascades, characterized mainly by their trace-element and alkali-metal abundances: (1) High-alumina olivine tholeiite (HAOT) has trace element abundances similar to N-MORB, except for slightly elevated LILE, and has Eu/Eu* > 1. (2) Arc basalt and basaltic andesite have notably higher LILE contents, generally have higher SiO2 contents, are more oxidized, and have higher Cr for a given Ni abundance than HAOT. These lavas show relative depletion in HFSE, have lower HREE and higher LREE than HAOT, and have smaller Eu/Eu* (0.94-1.06). (3) Alkali basalt from the Simcoe volcanic field east of Mount Adams represents the third end-member, which contributes an intraplate geochemical signature to magma compositions. Notable geochemical features among the volcanic fields are: (1) Mount Adams rocks are richest in Fe and most incompatible elements including HFSE; (2) the most incompatible-element depleted lavas occur at Medicine Lake; (3) all centers have relatively primitive lavas with high LILE/HFSE ratios but only the Mount Adams, Lassen, and Medicine Lake volcanic fields also have relatively primitive rocks with an intraplate geochemical signature; (4) there is a tendency for increasing 87Sr/86Sr, 207Pb/204Pb, and ??18O and decreasing 206Pb/204Pb and 143Nd/144Nd from north to south. The three end-member Cascade magma types reflect contributions from three mantle components: depleted sub-arc mantle modestly enriched in LILE during ancient subduction; a modern, hydrous subduction component

  13. Magma degassing triggered by static decompression at Kīlauea Volcano, Hawai‘i

    Science.gov (United States)

    Poland, Michael P.; Jeff, Sutton A.; Gerlach, Terrence M.

    2009-01-01

    During mid-June 2007, the summit of Kīlauea Volcano, Hawai‘i, deflated rapidly as magma drained from the subsurface to feed an east rift zone intrusion and eruption. Coincident with the deflation, summit SO2 emission rates rose by a factor of four before decaying to background levels over several weeks. We propose that SO2 release was triggered by static decompression caused by magma withdrawal from Kīlauea's shallow summit reservoir. Models of the deflation suggest a pressure drop of 0.5–3 MPa, which is sufficient to trigger exsolution of the observed excess SO2 from a relatively small volume of magma at the modeled source depth beneath Kīlauea's summit. Static decompression may also explain other episodes of deflation accompanied by heightened gas emission, including the precursory phases of Kīlauea's 2008 summit eruption. Hazards associated with unexpected volcanic gas emission argue for increased awareness of magma reservoir pressure fluctuations.

  14. Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.

    Science.gov (United States)

    Di Vito, Mauro A; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

    2016-08-25

    Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.

  15. Erupted frothy xenoliths may explain lack of country-rock fragments in plutons

    Science.gov (United States)

    Burchardt, Steffi; Troll, Valentin R.; Schmeling, Harro; Koyi, Hemin; Blythe, Lara

    2016-01-01

    Magmatic stoping is discussed to be a main mechanism of magma emplacement. As a consequence of stoping, abundant country-rock fragments should occur within, and at the bottom of, magma reservoirs as “xenolith graveyards”, or become assimilated. However, the common absence of sufficient amounts of both xenoliths and crustal contamination have led to intense controversy about the efficiency of stoping. Here, we present new evidence that may explain the absence of abundant country-rock fragments in plutons. We report on vesiculated crustal xenoliths in volcanic rocks that experienced devolatilisation during heating and partial melting when entrained in magma. We hypothesise that the consequential inflation and density decrease of the xenoliths allowed them to rise and become erupted instead of being preserved in the plutonic record. Our thermomechanical simulations of this process demonstrate that early-stage xenolith sinking can be followed by the rise of a heated, partially-molten xenolith towards the top of the reservoir. There, remnants may disintegrate and mix with resident magma or erupt. Shallow-crustal plutons emplaced into hydrous country rocks may therefore not necessarily contain evidence of the true amount of magmatic stoping during their emplacement. Further studies are needed to quantify the importance of frothy xenolith in removing stoped material. PMID:27804996

  16. The role of amphibole in Merapi arc magma petrogenesis: insights from petrology and geochemistry of lava hosted xenoliths and xenocrysts

    Science.gov (United States)

    Chadwick, J. P.; Troll, V. R.; Schulz, B.; Dallai, L.; Freda, C.; Schwarzkopf, L. M.; Annersten, H.; Skogby, H.

    2010-05-01

    Recently, increasing attention has been paid to the role of amphibole in the differentiation of arc magmas. The geochemical composition of these magmas suggests that deep to mid crustal fractionation of amphibole has occurred. However, this phase is typically an infrequent modal phenocryst phase in subduction zone eruptive deposits(1). Nevertheless, erupted material only represents a portion of the magmatism produced in subduction zone settings, with many opportunities for melts to stall on route to the surface. This discrepancy between whole rock geochemistry and petrological interpretation of arc magmas has lead many scientists to postulate that, at mid to deep crustal levels, there may be significant volumes of amphibole bearing lithologies. Amphibole instability at shallow levels can also contribute to its scarcity in eruptive deposits. This argument is strengthened by field and petrological evidence, including the widespread occurrence of amphibole-rich intrusive rocks in exhumed orogenicbelts formed during subduction zone activity, e.g. the Adamello batholith (2),as well as the presence of amphibole-rich xenoliths and xenocrysts preserved in arc lavas worldwide, e.g. in Indonesia, Antilles, and Central America. Thus, amphibole appears to play an integral role in subduction zone magmatism and identifying and constraining this role is central to understanding arc magma petrogenisis. Amphibole-rich melts or bodies in the deep to mid crust could be a significant hydrous reservoir for intra-crustal melts and fluids (1). In this preliminary study, we have carried out petrological and geochemical analyses of recent basaltic andesite and amphibole bearing crystalline igneous inclusions and xenocrysts from Merapi volcano in Java, Indonesia. The basaltic andesite geochemistry is consistent with amphibole fractionation and the crystalline inclusions are cogenetic to the Merapi magmatic system. These inclusions are likely to represent fractionation residues reflecting

  17. Temporal constraints on magma generation and differentiation in a continental volcano: Buckland, eastern Australia

    Science.gov (United States)

    Crossingham, Tracey J.; Ubide, Teresa; Vasconcelos, Paulo M.; Knesel, Kurt M.; Mallmann, Guilherme

    2018-03-01

    The eastern margin of the Australian continent hosts a large number of Cenozoic intraplate volcanoes along a 2000 km long track. Here, we study mafic lavas from the Buckland volcano, Queensland, located in the northern (older) segment of this track, to assess magma generation and differentiation through time. The rocks are aphanitic to microporphyritic basalts, trachy-basalts and basanites. Incompatible element geochemistry together with Sr-Nd-Pb isotope ratios indicate that magmas formed from an enriched mantle I (EMI)-like garnet-bearing source with variable degrees of crustal contamination. Whole rock elemental variations suggest fractionation of olivine, plagioclase, clinopyroxene and/or magnetite. There is no petrographic or geochemical evidence of magma mixing in the studied rocks (e.g., lack of recycled minerals), suggesting a relatively quick ascent from the source to the surface without major storage at shallow levels. 40Ar/39Ar geochronology reveals two stages of volcanism: 30.3 ± 0.1 Ma and 27.4 ± 0.2 Ma. The Old Buckland (30.3 ± 0.1 Ma) melts have negative K anomalies, and incompatible element ratios suggest the occurrence of residual hydrous minerals in a metasomatised mantle source. We therefore infer that at the onset of volcanism, deep-mantle-derived magmas interacted with metasomatised sub-continental lithospheric mantle (SCLM). Major and trace element data, clinopyroxene thermobarometry and thermodynamic modelling indicate magma evolution by assimilation and fractional crystallisation (AFC) during ascent through the crust. Following a hiatus in volcanic activity of 2.5 Ma, eruption of Young Buckland (27.4 ± 0.2 Ma) lavas marked a shift towards more alkaline compositions. Trace element compositions indicate lower degrees of partial melting and a lack of interaction with metasomatic components. Young Buckland lavas become progressively more SiO2-saturated up stratigraphy, suggesting an increase in the degree of partial melting with time. Young

  18. Geochemical evidences of magma dynamics at Campi Flegrei (Italy)

    Science.gov (United States)

    Caliro, S.; Chiodini, G.; Paonita, A.

    2014-05-01

    Campi Flegrei caldera, within the Neapolitan area of Italy, is potentially one of the most dangerous volcanoes in the world, and during the last decade it has shown clear signs of reactivation, marked by the onset of uplift and changes in the geochemistry of gas emissions. We describe a 30-year-long data set of the CO2-He-Ar-N2 compositions of fumarolic emissions from La Solfatara crater, which is located in the center of the caldera. The data display continuous decreases in both the N2/He and N2/CO2 ratios since 1985, paralleled by an increase in He/CO2. These variations cannot be explained by either processes of boiling/condensation in the local hydrothermal system or with changes in the mixing proportions between a magmatic vapor and hydrothermal fluids. We applied the magma degassing model of Nuccio and Paonita (2001, Earth Planet. Sci. Lett. 193, 467-481) using the most recent inert-gas solubilities in order to interpret these peculiar features in accordance with petrologic constraints derived from the ranges of the melt compositions and reservoir pressures at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a remarkably good agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-term geochemical changes. Recalling that (i) a sill-like reservoir of gases at a depth of 3-4 km seems to be the main source of ground inflation and (ii) there is petrologic and geophysical evidence for a reservoir of magma at about 8 km below Campi Flegrei, we suggest that the most-intense episodes of inflation occur when the gas supply to the sill-like reservoir comes from the 8 km-deep magma, although fluids exsolved by magma bodies at shallower depths also contribute to the gas budget. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature

  19. Disclosing Multiple Magma Degassing Sources Offers Unique Insights of What's Behind the Campi Flegrei Caldera Unrest

    Science.gov (United States)

    Moretti, R.; Civetta, L.; Orsi, G.; Arienzo, I.; D'Antonio, M.; Di Renzo, V.

    2013-12-01

    The definition of the structure and evolution of the magmatic system of Campi Flegrei caldera (CFc), Southern Italy, has been a fundamental tool for the assessment of the short-term volcanic hazard. The ensemble of geophysical and petrologic data show that the CFc magmatic system has been -and still is- characterized by two major reservoirs at different depths. From the deep one (around 8 km), less evolved magmas crystallize and degas, supplying fluids and magmas to the shallow (3-4 km) reservoirs. A thorough reconstruction of processes occurring in magma chamber/s prior and/or during the CFc eruptions has shown that magmas entering shallow reservoirs mixed with resident and crystallized batches. Also the 1982-85 unrest episode has been related to a magma intrusion of 2.1 x 10^7 m^3 at 3-4 km depth, on the basis of geophysical data (ground deformation, gravimetry, seismic imaging) and their interpretation. Thermodynamic evaluation of magma properties, at the time of emplacement, suggests for such an intrusion a bulk density of 2.000 kg/m^3 . Such a value testifies the high amount of exsolved volatiles within the system. The available record of geochemical and isotopic data on surface fumaroles, coupled with melt inclusion data, has already shown that dual (deep and shallow) magma degassing from such two reservoirs, as well as their interaction with the hydrothermal system, allows explaining the relevant fluctuations observed at crater fumaroles after the 1982-85 magma intrusion. An important role was played by the rapid crystallization (around 30 years) of the shallow magma, such that in the recent years gas discharges should be fuelled mostly by the deep magma. Such a process is well recorded in the fumarolic gas composition of the last ~10 years, but has to be reconciled with the unrest dynamics which took place after year 2000, characterized by a slow but continuous ground uplift. All geochemical indicators (major species and noble gases) point to three possible

  20. Magmatism and crustal extension: Constraining activation of the ductile shearing along the Gediz detachment, Menderes Massif (western Turkey)

    Science.gov (United States)

    Rossetti, Federico; Asti, Riccardo; Faccenna, Claudio; Gerdes, Axel; Lucci, Federico; Theye, Thomas

    2017-06-01

    The Menderes Massif of western Turkey is a key area to study feedback relationships between magma generation/emplacement and activation of extensional detachment tectonics. Here, we present new textural analysis and in situ U-(Th)-Pb titanite dating from selected samples collected in the transition from the undeformed to the mylonitized zones of the Salihli granodiorite at the footwall of the Neogene, ductile-to-brittle, top-to-the-NNE Gediz-Alaşheir (GDF) detachment fault. Ductile shearing was accompanied by the fluid-mediated sub-solidus transformation of the granodiorite to orthogneiss, which occurred at shallower crustal levels and temperatures compatible with the upper greenschist-to-amphibolite facies metamorphic conditions (530-580 °C and P system ages during fluid-assisted syn-tectonic re-crystallisation in the transition from magma crystallization and emplacement (at 16-17 Ma) to the syn-tectonic, solid-state shearing (at 14-15 Ma). A minimum time lapse of ca. 1-2 Ma is then inferred between the crustal emplacement of the Salihli granodiorite and nucleation of the ductile extensional shearing along the Gediz detachment. The reconstruction of the cooling history of the Salihli granodiorite documents a punctuated evolution dominated by two episodes of rapid cooling, between 14 Ma and 12 Ma ( 100 °C/Ma) and between 3 and 2 Ma ( 105 °C/Ma). We relate the first episode to nucleation and development of post-emplacement of ductile shearing along the GDF and the second to brittle high-angle faulting, respectively. Our dataset suggests that in the Menderes Massif the activation of ductile extension was a consequence, rather than the cause, of magma emplacement in the extending crust.

  1. Melt zones beneath five volcanic complexes in California: an assessment of shallow magma occurrences

    Energy Technology Data Exchange (ETDEWEB)

    Goldstein, N.E.; Flexser, S.

    1984-12-01

    Recent geological and geophysical data for five magma-hydrothermal systems were studied for the purpose of developing estimates for the depth, volume and location of magma beneath each area. The areas studied were: (1) Salton Trough, (2) The Geysers-Clear Lake, (3) Long Valley caldera, (4) Coso volcanic field, and (5) Medicine Lake volcano, all located in California and all selected on the basis of recent volcanic activity and published indications of crustal melt zones. 23 figs.

  2. Crustal growth of the Izu-Ogasawara arc estimated from structural characteristics of Oligocene arc

    Science.gov (United States)

    Takahashi, N.; Yamashita, M.; Kodaira, S.; Miura, S.; Sato, T.; No, T.; Tatsumi, Y.

    2011-12-01

    Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out seismic surveys using a multichannel reflection system and ocean bottom seismographs, and we have clarified crustal structures of whole Izu-Ogasawara (Bonin)-Marina (IBM) arc since 2002. These refection images and velocity structures suggest that the crustal evolution in the intra-oceanic island arc accompanies with much interaction of materials between crust and mantle. Slow mantle velocity identified beneath the thick arc crusts suggests that dense crustal materials transformed into the mantle. On the other hand, high velocity lower crust can be seen around the bottom of the crust beneath the rifted region, and it suggests that underplating of mafic materials occurs there. Average crustal production rate of the entire arc is larger than expected one and approximately 200 km3/km/Ma. The production rate of basaltic magmas corresponds to that of oceanic ridge. Repeated crustal differentiation is indispensable to produce much light materials like continental materials, however, the real process cannot still be resolved yet. We, therefore, submitted drilling proposals to obtain in-situ middle crust with P-wave velocity of 6 km/s. In the growth history of the IBM arc, it is known by many papers that boninitic volcanisms preceded current bimodal volcanisms based on basaltic magmas. The current volcanisms accompanied with basaltic magmas have been occurred since Oligocene age, however, the tectonic differences to develop crustal architecture between Oligocene and present are not understood yet. We obtained new refraction/reflection data along an arc strike of N-S in fore-arc region. Then, we estimate crustal structure with severe change of the crustal thickness from refraction data, which are similar to that along the volcanic front. Interval for location of the thick arc crust along N-S is very similar to that along the volcanic front. The refection image indicates that the basement of the fore

  3. Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption.

    Science.gov (United States)

    Ripepe, Maurizio; Donne, Dario Delle; Genco, Riccardo; Maggio, Giuseppe; Pistolesi, Marco; Marchetti, Emanuele; Lacanna, Giorgio; Ulivieri, Giacomo; Poggi, Pasquale

    2015-05-18

    Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.

  4. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

    Science.gov (United States)

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

    2016-09-01

    Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

  5. The Origin of Tholeiitic and Calc-Alkaline Trends in Arc Magmas

    Science.gov (United States)

    Luffi, P. I.; Lee, C.

    2012-12-01

    It has long been recognized that tholeiitic (TH, high-Fe/Mg) and calc-alkaline (CA, low-Fe/Mg) magmatic series define the two most important igneous differentiation trends shaping Earth's crust. While oceanic crust formation at mid-ocean ridges is typically confined to a TH trend, arc magmatism at convergent margins, considered to significantly contribute to continent formation, generates both TH and CA trends. Thus, the origin of these trends - a key issue to understanding how continental crust forms - is matter of ongoing debate. Prevalent factors thought to contribute to the TH-CA duality are: 1) redox conditions (oxygen fugacity, fO2) and H2O contents in magmas, which control the onset and abundance of high-Fe/Mg oxide mineral fractionation; 2) crystallization depths that regulate the fractionating solid assemblage and thereby the solid/liquid Kd(Fe-Mg). Relying on an extensive geochemical dataset of modern arc volcanics and thermodynamic phase equilibria modeling, here we examine the validity and relative importance of these factors in arc petrogenesis. First, to discriminate igneous rocks more efficiently, we formulate an improved CA/TH index solely based on FeO-MgO systematics. We then confirm on a quantitative basis that, on regional scales, arcs formed on thick crust tend to be more calk-alkaline than those emplaced on thinner crust are, and show that the effect of fO2 on the CA/TH index in arc magmas is more significant than that of H2O. Importantly, we demonstrate that CA trends typical for continental arcs only form when crystal fractionation is accompanied by the assimilation of oxidized crustal components; in the absence of buffering oxidized assimilants fractionating magmas follow a TH trend more common in island arcs, irrespective of their H2O content and initial fO2 level. We find that high-pressure fractionation of amphibole and garnet in arc magmas occurs too late to have a significant influence on the CA/TH index; in addition, garnet-melt and

  6. Geodynamic controls on the contamination of Cenozoic arc magmas in the southern Central Andes: Insights from the O and Hf isotopic composition of zircon

    Science.gov (United States)

    Jones, Rosemary E.; Kirstein, Linda A.; Kasemann, Simone A.; Dhuime, Bruno; Elliott, Tim; Litvak, Vanesa D.; Alonso, Ricardo; Hinton, Richard

    2015-09-01

    Subduction zones, such as the Andean convergent margin of South America, are sites of active continental growth and crustal recycling. The composition of arc magmas, and therefore new continental crust, reflects variable contributions from mantle, crustal and subducted reservoirs. Temporal (Ma) and spatial (km) variations in these contributions to southern Central Andean arc magmas are investigated in relation to the changing plate geometry and geodynamic setting of the southern Central Andes (28-32° S) during the Cenozoic. The in-situ analysis of O and Hf isotopes in zircon, from both intrusive (granitoids) and extrusive (basaltic andesites to rhyolites) Late Cretaceous - Late Miocene arc magmatic rocks, combined with high resolution U-Pb dating, demonstrates distinct across-arc variations. Mantle-like δ18O(zircon) values (+5.4‰ to +5.7‰ (±0.4 (2σ))) and juvenile initial εHf(zircon) values (+8.3 (±0.8 (2σ)) to +10.0 (±0.9 (2σ))), combined with a lack of zircon inheritance suggests that the Late Cretaceous (∼73 Ma) to Eocene (∼39 Ma) granitoids emplaced in the Principal Cordillera of Chile formed from mantle-derived melts with very limited interaction with continental crustal material, therefore representing a sustained period of upper crustal growth. Late Eocene (∼36 Ma) to Early Miocene (∼17 Ma) volcanic arc rocks present in the Frontal Cordillera have 'mantle-like' δ18O(zircon) values (+4.8‰ (±0.2 (2σ) to +5.8‰ (±0.5 (2σ))), but less radiogenic initial εHf(zircon) values (+1.0 (±1.1 (2σ)) to +4.0 (±0.6 (2σ))) providing evidence for mixing of mantle-derived melts with the Late Paleozoic - Early Mesozoic basement (up to ∼20%). The assimilation of both Late Paleozoic - Early Mesozoic Andean crust and a Grenville-aged basement is required to produce the higher than 'mantle-like' δ18O(zircon) values (+5.5‰ (±0.6 (2σ) to +7.2‰ (±0.4 (2σ))) and unradiogenic, initial εHf(zircon) values (-3.9 (±1.0 (2σ)) to +1.6 (±4.4 (2

  7. Complexities in Shallow Magma Transport at Kilauea (Invited)

    Science.gov (United States)

    Swanson, D. A.

    2013-12-01

    The standard model of Kilauea's shallow plumbing system includes magma storage under the caldera and conduits in the southwest rift zone (SWRZ) and the east rift zone (ERZ). As a field geologist, I find that seemingly aberrant locations and trends of some eruptive vents indicate complexities in shallow magma transport not addressed by the standard model. This model is not wrong but instead incomplete, because it does not account for the development of offshoots from the main plumbing. These offshoots supply magma to the surface at places that tell us much about the complicated stress system within the volcano. Perhaps most readily grasped are fissures peripheral to the north and south sides of the caldera. Somehow magma can apparently be injected into caldera-bounding faults from the summit reservoir complex, but the process and pathways are unclear. Of more importance is the presence of fissures with ENE trends on the east side of the caldera, including Kilauea Iki. Is this a rift zone that forms an acute angle with the ERZ? I think there is another explanation: the main part of the ERZ has migrated ~5 km SSE during the past few tens of thousands of years owing to seaward movement of the south flank, but older parts of the rift zone can be reactivated. The fissures east of the caldera have the ERZ trend and may record such reactivation; this interpretation includes the location of the largest eruption (15th century) known from Kilauea. Whether or not this interpretation has validity, the question remains: what changes in the plumbing system allow magma to erupt east of the caldera? The SWRZ can be divided into two sections, the SWRZ proper and the seismically active part (SASWRZ) southeast of the SWRZ. The total width of both sections is ~4 km. The SWRZ might be migrating SSE, as is the ERZ. Fissures in the SWRZ proper trend SW. Fissures in the SASWRZ, however, have ENE trends like that of the ERZ, although, because of en echelon offsets, the fissure zone itself

  8. The geophysical character of southern Alaska - Implications for crustal evolution

    Science.gov (United States)

    Saltus, R.W.; Hudson, T.L.; Wilson, Frederic H.

    2007-01-01

    The southern Alaska continental margin has undergone a long and complicated history of plate convergence, subduction, accretion, and margin-parallel displacements. The crustal character of this continental margin is discernible through combined analysis of aeromagnetic and gravity data with key constraints from previous seismic interpretation. Regional magnetic data are particularly useful in defining broad geophysical domains. One of these domains, the south Alaska magnetic high, is the focus of this study. It is an intense and continuous magnetic high up to 200 km wide and ∼1500 km long extending from the Canadian border in the Wrangell Mountains west and southwest through Cook Inlet to the Bering Sea shelf. Crustal thickness beneath the south Alaska magnetic high is commonly 40–50 km. Gravity analysis indicates that the south Alaska magnetic high crust is dense. The south Alaska magnetic high spatially coincides with the Peninsular and Wrangellia terranes. The thick, dense, and magnetic character of this domain requires significant amounts of mafic rocks at intermediate to deep crustal levels. In Wrangellia these mafic rocks are likely to have been emplaced during Middle and (or) Late Triassic Nikolai Greenstone volcanism. In the Peninsular terrane, the most extensive period of mafic magmatism now known was associated with the Early Jurassic Talkeetna Formation volcanic arc. Thus the thick, dense, and magnetic character of the south Alaska magnetic high crust apparently developed as the response to mafic magmatism in both extensional (Wrangellia) and subduction-related arc (Peninsular terrane) settings. The south Alaska magnetic high is therefore a composite crustal feature. At least in Wrangellia, the crust was probably of average thickness (30 km) or greater prior to Triassic mafic magmatism. Up to 20 km (40%) of its present thickness may be due to the addition of Triassic mafic magmas. Throughout the south Alaska magnetic high, significant crustal growth

  9. Low-pressure evolution of arc magmas in thickened crust: The San Pedro-Linzor volcanic chain, Central Andes, Northern Chile

    Science.gov (United States)

    Godoy, Benigno; Wörner, Gerhard; Kojima, Shoji; Aguilera, Felipe; Simon, Klaus; Hartmann, Gerald

    2014-07-01

    Magmatism at Andean Central Volcanic Zone (CVZ), or Central Andes, is strongly influenced by differentiation and assimilation at high pressures that occurred at lower levels of the thick continental crust. This is typically shown by high light to heavy rare earth element ratios (LREE/HREE) of the erupted lavas at this volcanic zone. Increase of these ratios with time is interpreted as a change to magma evolution in the presence of garnet during evolution of Central Andes. Such geochemical signals could be introduced into the magmas be high-pressure fractionation with garnet on the liquidus and/or assimilation from crustal rocks with a garnet-bearing residue. However, lavas erupted at San Pedro-Linzor volcanic chain show no evidence of garnet fractionation in their trace element patterns. This volcanic chain is located in the active volcanic arc, between 22°00‧S and 22°30‧S, over a continental crust ˜70 km thick. Sampled lavas show Sr/Y and Sm/Yb ratios Chile. We relate our geochemical observations to shallow crustal evolution of primitive magmas involving a high degree of assimilation of upper continental crust. We emphasize that low pressure AFC- (Assimilation Fractional Crystallization) type evolution of the San Pedro-Linzor volcanic chain reflects storage, fractionation, and contamination of mantle-derived magmas at the upper felsic crust (<40 km depth). The ascent of mantle-derived magmas to mid-crustal levels is related with the extensional regime that has existed in this zone of arc-front offset since Late-Miocene age, and the relatively thin portion of mafic lower crust observed below the volcanic chain.

  10. Magma Transport from Deep to Shallow Crust and Eruption

    Science.gov (United States)

    White, R. S.; Greenfield, T. S.; Green, R. G.; Brandsdottir, B.; Hudson, T.; Woods, J.; Donaldson, C.; Ágústsdóttir, T.

    2016-12-01

    We have mapped magma transport paths from the deep (20 km) to the shallow (6 km) crust and in two cases to eventual surface eruption under several Icelandic volcanoes (Askja, Bardarbunga, Eyjafjallajokull, Upptyppingar). We use microearthquakes caused by brittle fracture to map magma on the move and tomographic seismic studies of velocity perturbations beneath volcanoes to map the magma storage regions. High-frequency brittle failure earthquakes with magnitudes of typically 0-2 occur where melt is forcing its way through the country rock, or where previously frozen melt is repeatedly re-broken in conduits and dykes. The Icelandic crust on the rift zones where these earthquakes occur is ductile at depths greater than 7 km beneath the surface, so the occurrence of brittle failure seismicity at depths as great as 20 km is indicative of high strain rates, for which magma movement is the most likely explanation. We suggest that high volatile pressures caused by the exsolution of carbon dioxide in the deep crust is driving the magma movement and seismicity at depths of 15-20 km. Eruptions from shallow crustal storage areas are likewise driven by volatile exsolution, though additional volatiles, and in particular water are also involved in the shallow crust.

  11. Pressures of Partial Crystallization of Magmas Along Transforms: Implications for Crustal Accretion

    Science.gov (United States)

    Scott, J. L.; Zerda, C.; Brown, D.; Ciaramitaro, S. C.; Barton, M.

    2016-12-01

    Plate spreading at mid-ocean ridges is responsible for the creation of most of the crust on earth. The ridge system is very complex and many questions remain unresolved. Among these is the nature of magma plumbing systems beneath transform faults. Pervious workers have suggested that increased conductive cooling along transforms promotes higher pressures of partial crystallization, and that this explains the higher partial pressures of crystallization inferred for magmas erupted along slow spreading ridges compared to magmas erupted along faster spreading ridges. To test this hypothesis, we undertook a detailed analysis of pressures of partial crystallization for magmas erupted at 3 transforms along the fast to intermediate spreading East Pacific Rise(Blanco, Clipperton, and Siqueiros) and 3 transforms along the slow spreading Mid Atlantic Ridge(Famous Transform B, Kane, and 15°20'N). Pressures of partial crystallization were calculated from the compositions of glasses (quenched liquids) lying along the P (and T) dependent olivine, plagioclase, and augite cotectic using the method described by Kelley and Barton (2008). Published analyses of mid-ocean ridge basalt glasses sampled from these transforms and surrounding ridge segments were used as input data. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The pressures of partial crystallization for the remaining 916 samples ranged from 0 to 520 MPa with the great majority ( 95%) of sample returning pressures of less than 300 MPa. Pressures of 300 MPa) are associated with a small number of samples from the Pacific segments. Except for the Blanco, pressures of partial crystallization do not increase as transforms are approached. These observations contrast with those of previous workers, who reported anomalously high pressures (up to 1000 MPa) for a large number of samples erupted near both Atlantic

  12. Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

    Science.gov (United States)

    Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-Zhu

    2013-01-01

    The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

  13. Chronological evidence that the Moon is either young or did not have a global magma ocean.

    Science.gov (United States)

    Borg, Lars E; Connelly, James N; Boyet, Maud; Carlson, Richard W

    2011-08-17

    Chemical evolution of planetary bodies, ranging from asteroids to the large rocky planets, is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth. The Earth's Moon is the archetypical example of this type of differentiation. Evidence for a lunar magma ocean is derived largely from the widespread distribution, compositional and mineralogical characteristics, and ancient ages inferred for the ferroan anorthosite (FAN) suite of lunar crustal rocks. The FANs are considered to be primary lunar flotation-cumulate crust that crystallized in the latter stages of magma ocean solidification. According to this theory, FANs represent the oldest lunar crustal rock type. Attempts to date this rock suite have yielded ambiguous results, however, because individual isochron measurements are typically incompatible with the geochemical make-up of the samples, and have not been confirmed by additional isotopic systems. By making improvements to the standard isotopic techniques, we report here the age of crystallization of FAN 60025 using the (207)Pb-(206)Pb, (147)Sm-(143)Nd and (146)Sm-(142)Nd isotopic systems to be 4,360 ± 3 million years. This extraordinarily young age requires that either the Moon solidified significantly later than most previous estimates or the long-held assumption that FANs are flotation cumulates of a primordial magma ocean is incorrect. If the latter is correct, then much of the lunar crust may have been produced by non-magma-ocean processes, such as serial magmatism.

  14. Magma wagging and whirling in volcanic conduits

    Science.gov (United States)

    Liao, Yang; Bercovici, David; Jellinek, Mark

    2018-02-01

    Seismic tremor characterized by 0.5-7 Hz ground oscillations commonly occur before and during eruptions at silicic volcanoes with widely ranging vent geometries and edifice structures. The ubiquitous characteristics of this tremor imply that its causes are potentially common to silicic volcanoes. Here we revisit and extend to three dimensions the magma-wagging model for tremor (Jellinek and Bercovici, 2011; Bercovici et al., 2013), wherein a stiff magma column rising in a vertical conduit oscillates against a surrounding foamy annulus of bubbly magma, giving rise to tremor. While prior studies were restricted to two-dimensional lateral oscillations, here we explore three-dimensional motion and additional modes of oscillations. In the absence of viscous damping, the magma column undergoes 'whirling' motion: the center of each horizontal section of the column traces an elliptical trajectory. In the presence of viscous effect we identify new 'coiling' and 'uncoiling' column bending shapes with relatively higher and comparable rates of dissipation to the original two-dimensional magma wagging model. We also calculate the seismic P-wave response of the crustal material around the volcanic conduit to the new whirling motions and propose seismic diagnostics for different wagging patterns using the time-lag between seismic stations. We test our model by analyzing pre-eruptive seismic data from the 2009 eruption of Redoubt Volcano. In addition to suggesting that the occurrence of elliptical whirling motion more than 1 week before the eruption, our analysis of seismic time-lags also implies that the 2009 eruption was accompanied by qualitative changes in the magma wagging behavior including fluctuations in eccentricity and a reversal in the direction of elliptical whirling motion when the eruption was immediately impending.

  15. Origin of primitive ocean island basalts by crustal gabbro assimilation and multiple recharge of plume-derived melts

    Science.gov (United States)

    Borisova, Anastassia Y.; Bohrson, Wendy A.; Grégoire, Michel

    2017-07-01

    Chemical Geodynamics relies on a paradigm that the isotopic composition of ocean island basalt (OIB) represents equilibrium with its primary mantle sources. However, the discovery of huge isotopic heterogeneity within olivine-hosted melt inclusions in primitive basalts from Kerguelen, Iceland, Hawaii and South Pacific Polynesia islands implies open-system behavior of OIBs, where during magma residence and transport, basaltic melts are contaminated by surrounding lithosphere. To constrain the processes of crustal assimilation by OIBs, we employed the Magma Chamber Simulator (MCS), an energy-constrained thermodynamic model of recharge, assimilation and fractional crystallization. For a case study of the 21-19 Ma basaltic series, the most primitive series ever found among the Kerguelen OIBs, we performed sixty-seven simulations in the pressure range from 0.2 to 1.0 GPa using compositions of olivine-hosted melt inclusions as parental magmas, and metagabbro xenoliths from the Kerguelen Archipelago as wallrock. MCS modeling requires that the assimilant is anatectic crustal melts (P2O5 ≤ 0.4 wt.% contents) derived from the Kerguelen oceanic metagabbro wallrock. To best fit the phenocryst assemblage observed in the investigated basaltic series, recharge of relatively large masses of hydrous primitive basaltic melts (H2O = 2-3 wt%; MgO = 7-10 wt.%) into a middle crustal chamber at 0.2 to 0.3 GPa is required. Our results thus highlight the important impact that crustal gabbro assimilation and mantle recharge can have on the geochemistry of mantle-derived olivine-phyric OIBs. The importance of crustal assimilation affecting primitive plume-derived basaltic melts underscores that isotopic and chemical equilibrium between ocean island basalts and associated deep plume mantle source(s) may be the exception rather than the rule.

  16. Imaging irregular magma reservoirs with InSAR and GPS observations: Application to Kilauea and Copahue volcanoes

    Science.gov (United States)

    Lundgren, P.; Camacho, A.; Poland, M. P.; Miklius, A.; Samsonov, S. V.; Milillo, P.

    2013-12-01

    The availability of synthetic aperture radar (SAR) interferometry (InSAR) data has increased our awareness of the complexity of volcano deformation sources. InSAR's spatial completeness helps identify or clarify source process mechanisms at volcanoes (i.e. Mt. Etna east flank motion; Lazufre crustal magma body; Kilauea dike complexity) and also improves potential model realism. In recent years, Bayesian inference methods have gained widespread use because of their ability to constrain not only source model parameters, but also their uncertainties. They are computationally intensive, however, which tends to limit them to a few geometrically rather simple source representations (for example, spheres). An alternative approach involves solving for irregular pressure and/or density sources from a three-dimensional (3-D) grid of source/density cells. This method has the ability to solve for arbitrarily shaped bodies of constant absolute pressure/density difference. We compare results for both Bayesian (a Markov chain Monte Carlo algorithm) and the irregular source methods for two volcanoes: Kilauea, Hawaii, and Copahue, Argentina-Chile border. Kilauea has extensive InSAR and GPS databases from which to explore the results for the irregular method with respect to the Bayesian approach, prior models, and an extensive set of ancillary data. One caveat, however, is the current restriction in the irregular model inversion to volume-pressure sources (and at a single excess pressure change), which limits its application in cases where sources such as faults or dikes are present. Preliminary results for Kilauea summit deflation during the March 2011 Kamoamoa eruption suggests a northeast-elongated magma body lying roughly 1-1.5 km below the surface. Copahue is a southern Andes volcano that has been inflating since early 2012, with intermittent summit eruptive activity since late 2012. We have an extensive InSAR time series from RADARSAT-2 and COSMO-SkyMed data, although both are

  17. The effect of prior hydrothermal alteration on the melting behaviour during rhyolite formation in Yellowstone, and its importance in the generation of low-δ18O magmas

    Science.gov (United States)

    Troch, Juliana; Ellis, Ben S.; Harris, Chris; Ulmer, Peter; Bachmann, Olivier

    2018-01-01

    Constraining the contribution of crustal lithologies to silicic magmas has important implications for understanding the dynamics of these potentially highly explosive systems. Low-δ18O rhyolite lavas erupted after caldera-forming events in Yellowstone have been interpreted as the products of bulk crustal melting of previously deposited and hydrothermally altered rhyolitic material in the down-dropped caldera roof. For lack of compositional data, the "self-cannibalisation bulk melting"-theory relies on the assumption that hydrothermally altered materials are near-cotectic and hydrous (>3 wt% H2O) and will therefore readily melt at temperatures below 850 °C. In this study, we examine the drillcores Y2, Y9 and Y13 from a USGS drilling campaign in Yellowstone in order to characterise the hydrothermally altered material in terms of major and trace elements, oxygen isotopes and water contents. Rhyolite δ18O values can decrease from "normal" (+5.8 to +6.1‰) on the surface to as low as -5‰ at depths of 100-160 m and probably lower as a function of increasing temperature with depth. While material in the drillcores is variably altered and silicified, oxygen isotope exchange in these samples is not accompanied by systematic changes in major and trace element composition and is independent of uptake of water. More than 75% of the drillcore samples have 1100 °C. Therefore, large-scale bulk melting is unrealistic and low-δ18O rhyolite magmas more likely result from assimilation of <30% partially melted altered crust with low δ18O into a normal-δ18O rhyolite magma from the main reservoir. This mechanism is supported by isotopic mass-balance models as well as thermal and volumetric constraints, and may be similarly applicable to other low-δ18O settings worldwide.

  18. Io: Loki Patera as a Magma Sea

    Science.gov (United States)

    Matson, Dennis L.; Davies, Ashley Gerard; Veeder, Glenn J.; Rathbun, Julie A.; Johnson, Torrence V.; Castillo, Julie C.

    2006-01-01

    We develop a physical model for Loki Patera as a magma sea. We calculate the total volume of magma moving through the Loki Patera volcanic system every resurfacing cycle (approx.540 days) and the resulting variation in thermal emission. The rate of magma solidification at times reaches 3 x 10(exp 6) kg per second, with a total solidified volume averaging 100 cu km per year. A simulation of gas physical chemistry evolution yields the crust porosity profile and the timescale when it will become dense enough to founder in a manner consistent with observations. The Loki Patera surface temperature distribution shows that different areas are at different life cycle stages. On a regional scale, however, there can be coordinated activity, indicated by the wave of thermal change which progresses from Loki Patera's SW quadrant toward the NE at a rate of approx.1 km per day. Using the observed surface temperature distribution, we test several mechanisms for resurfacing Loki Patera, finding that resurfacing with lava flows is not realistic. Only the crustal foundering process is consistent with observations. These tests also discovered that sinking crust has a 'heat deficit' which promotes the solidification of additional magma onto the sinking plate ("bulking up"). In the limiting case, the mass of sinking material can increase to a mass of approx.3 times that of the foundering plate. With all this solid matter sinking, there is a compensating upward motion in the liquid magma. This can be in excess of 2 m per year. In this manner, solid-liquid convection is occurring in the sea.

  19. The 2006-2009 activity of the Ubinas volcano (Peru): Petrology of the 2006 eruptive products and insights into genesis of andesite magmas, magma recharge and plumbing system

    Science.gov (United States)

    Rivera, Marco; Thouret, Jean-Claude; Samaniego, Pablo; Le Pennec, Jean-Luc

    2014-01-01

    Following a fumarolic episode that started six months earlier, the most recent eruptive activity of the Ubinas volcano (south Peru) began on 27 March 2006, intensified between April and October 2006 and slowly declined until December 2009. The chronology of the explosive episode and the extent and composition of the erupted material are documented with an emphasis on ballistic ejecta. A petrological study of the juvenile products allows us to infer the magmatic processes related to the 2006-2009 eruptions of the andesitic Ubinas volcano. The juvenile magma erupted during the 2006 activity shows a homogeneous bulk-rock andesitic composition (56.7-57.6 wt.% SiO2), which belongs to a medium- to high-K calc-alkaline series. The mineral assemblage of the ballistic blocks and tephra consists of plagioclase > two-pyroxenes > Fe-Ti oxide and rare olivine and amphibole set in a groundmass of the same minerals with a dacitic composition (66-67 wt.% SiO2). Thermo-barometric data, based on two-pyroxene and amphibole stability, records a magma temperature of 998 ± 14 °C and a pressure of 476 ± 36 MPa. Widespread mineralogical and textural features point to a disequilibrium process in the erupted andesite magma. These features include inversely zoned "sieve textures" in plagioclase, inversely zoned clinopyroxene, and olivine crystals with reaction and thin overgrowth rims. They indicate that the pre-eruptive magmatic processes were dominated by recharge of a hotter mafic magma into a shallow reservoir, where magma mingling occurred and triggered the eruption. Prior to 2006, a probable recharge of a mafic magma produced strong convection and partial homogenization in the reservoir, as well as a pressure increase and higher magma ascent rate after four years of fumarolic activity. Mafic magmas do not prevail in the Ubinas pre-historical lavas and tephras. However, mafic andesites have been erupted during historical times (e.g. AD 1667 and 2006-2009 vulcanian eruptions). Hence

  20. Area of Interest 1, CO<sub>2sub> at the Interface. Nature and Dynamics of the Reservoir/Caprock Contact and Implications for Carbon Storage Performance

    Energy Technology Data Exchange (ETDEWEB)

    Mozley, Peter [New Mexico Institute Of Mining And Technology, Socorro, NM (United States); Evans, James [New Mexico Institute Of Mining And Technology, Socorro, NM (United States); Dewers, Thomas [New Mexico Institute Of Mining And Technology, Socorro, NM (United States)

    2014-10-31

    We examined the influence of geologic features present at the reservoir/caprock interface on the transmission of supercritical CO<sub>2sub> into and through caprock. We focused on the case of deformation-band faults in reservoir lithologies that intersect the interface and transition to opening-mode fractures in caprock lithologies. Deformation-band faults are exceeding common in potential CO<sub>2sub> injection units and our fieldwork in Utah indicates that this sort of transition is common. To quantify the impact of these interface features on flow and transport we first described the sedimentology and permeability characteristics of selected sites along the Navajo Sandstone (reservoir lithology) and Carmel Formation (caprock lithology) interface, and along the Slickrock Member (reservoir lithology) and Earthy Member (caprock lithology) of the Entrada Sandstone interface, and used this information to construct conceptual permeability models for numerical analysis. We then examined the impact of these structures on flow using single-phase and multiphase numerical flow models for these study sites. Key findings include: (1) Deformation-band faults strongly compartmentalize the reservoir and largely block cross-fault flow of supercritical CO<sub>2sub>. (2) Significant flow of CO<sub>2sub> through the fractures is possible, however, the magnitude is dependent on the small-scale geometry of the contact between the opening-mode fracture and the deformation band fault. (3) Due to the presence of permeable units in the caprock, caprock units are capable of storing significant volumes of CO<sub>2sub>, particularly when the fracture network does not extend all the way through the caprock. The large-scale distribution of these deformation-bandfault-to-opening-mode-fractures is related to the curvature of the beds, with greater densities of fractures in high curvature regions. We also examined core and outcrops from the Mount Simon Sandstone and Eau Claire

  1. Geochemistry and volatile content of magmas feeding explosive eruptions at Telica volcano (Nicaragua)

    Science.gov (United States)

    Robidoux, P.; Rotolo, S. G.; Aiuppa, A.; Lanzo, G.; Hauri, E. H.

    2017-07-01

    Telica volcano, in north-west Nicaragua, is a young stratovolcano of intermediate magma composition producing frequent Vulcanian to phreatic explosive eruptions. The Telica stratigraphic record also includes examples of (pre)historic sub-Plinian activity. To refine our knowledge of this very active volcano, we analyzed major element composition and volatile content of melt inclusions from some stratigraphically significant Telica tephra deposits. These include: (1) the Scoria Telica Superior (STS) deposit (2000 to 200 years Before Present; Volcanic Explosive Index, VEI, of 2-3) and (2) pyroclasts from the post-1970s eruptive cycle (1982; 2011). Based on measurements with nanoscale secondary ion mass spectrometry, olivine-hosted (forsterite [Fo] > 80) glass inclusions fall into 2 distinct clusters: a group of H2O-rich (1.8-5.2 wt%) inclusions, similar to those of nearby Cerro Negro volcano, and a second group of CO2-rich (360-1700 μg/g CO2) inclusions (Nejapa, Granada). Model calculations show that CO2 dominates the equilibrium magmatic vapor phase in the majority of the primitive inclusions (XCO2 > 0.62-0.95). CO2, sulfur (generally 400 MPa) and early crystallization of magmas. Chlorine exhibits a wide concentration range (400-2300 μg/g) in primitive olivine-entrapped melts (likely suggesting variable source heterogeneity) and is typically enriched in the most differentiated melts (1000-3000 μg/g). Primitive, volatile-rich olivine-hosted melt inclusions (entrapment pressures, 5-15 km depth) are exclusively found in the largest-scale Telica eruptions (exemplified by STS in our study). These eruptions are thus tentatively explained as due to injection of deep CO2-rich mafic magma into the shallow crustal plumbing system. More recent (post-1970), milder (VEI 1-2) eruptions, instead, do only exhibit evidence for low-pressure (P viscosity of resident magma in shallow plumbing system (< 2.4 km), due to crystallization and degassing.

  2. Contrasting sodic and mildly potassic magma differentiation lineages at The Pleaides volcanic complex, northern Victoria Land, Antarctica

    Science.gov (United States)

    Kim, J.; Park, J. W.; Lee, J.; Kyle, P. R.; Lee, M. J.

    2017-12-01

    The magma evolution of The Pleiades, a Quaternary alkaline volcanic complex in northern Victoria Land, Antarctica, is investigated using major and trace elements, and Sr, Nd and Pb isotopic data. The volcanic rocks can be subdivided into two distinct magmatic lineages based on petrography and whole-rock compositions: (1) a sodic silica-undersaturated alkaline lineage with abundant kaersutite phenocrysts, and (2) a mildly-potassic and mildly-alkaline, nearly silica-saturated lineage containing olivine but not kaersutite. The basanite and trachybasalt of both lineages exhibit similar degrees of negative K anomalies, moderately steep rare earth element patterns, and elevated trace element ratios such as Ce/Pb (> 20) and Nb/U (> 38), suggesting their primary magmas were generated by low degree (≤3%) of partial melting of amphibole and garnet-bearing mantle sources. The sodic lineage is characterized by elevated 206Pb/204Pb (>19.5) ratios and narrow ranges of 87Sr/86Sr (0.70313-0.70327) and 143Nd/144Nd (0.51289-0.51290) ratios consistent with a significant HIMU component typical of Neogene volcanic rocks in Antarctica. The mafic rocks of the potassic lineage have isotopic compositions similar to those of the sodic lineage, however the evolved lavas in the lineage have higher 87Sr/86Sr (> 0.7035) and lower 143Nd/144Nd (< 0.51285) and 206Pb/204Pb (< 19.3) ratios than the mafic rocks, suggesting significant amounts of crustal contamination. The pressure-temperature paths estimated by clinopyroxene-liquid thermobarometry are similar in each lineage. The mafic magmas were emplaced at Moho depths ( 1.2 GPa) and the evolved magmas pooled at middle-crustal depths ( 0.7 GPa). Mass-balance calculations based on whole-rock and mineral compositions show that kaersutite fractionation has played a major role in magma differentiation of the sodic lineage whereas the compositional variations of the potassic lineage can be ascribed to fractionation of a kaersutite-free mineral

  3. Ocean-Continent Transition Structure of the Pelotas Magma-Rich Continental Margin, South Atlantic

    Science.gov (United States)

    Harkin, Caroline; Kusznir, Nick; Roberts, Alan; Manatschal, Gianreto; McDermott, Ken

    2017-04-01

    Rifted continental margins in the southern South Atlantic are magma-rich showing well developed volcanic extrusives known as seaward dipping reflectors (SDRs). Here we examine the magma-rich continental rifted margin of the Pelotas Basin, offshore Brazil. Deep seismic reflection data displays a large package of seaward dipping reflectors with an approximate width of 200 km and a varying thickness of 10 km to 17 km that have previously been interpreted as volcanic SDRs. We examine these SDRs to explore if they are composed predominantly of basaltic or sedimentary-volcaniclastic material. We also study the thickness of the crustal basement beneath the SDRs. Additionally we investigate if these SDRs are underlain by thin 'hyper-extended' continental crust or if they have been deposited on new magmatic basement. The answers to these questions are important in understanding the structure and formation processes of magma-rich continental margins. We use gravity inversion to investigate SDR composition by varying the proportion of basalt to sediments-volcaniclastics (basalt fraction) which determines the SDR densities in the gravity inversion. By matching the Moho depth and two-way travel time from gravity inversion and deep seismic reflection data, we determine the lateral variation in basalt fraction of the SDRs. Our analysis suggests: 1) There is an overall pattern of SDR basalt fraction and bulk density decreasing oceanward. This could be due to increasing sediment content oceanward or it could result from the change in basalt flows to hyaloclastites as water depth increases. 2) The SDR package can be split into two distinct sub packages based on the basalt fraction results, where the proximal side of each package has a higher basalt fraction and density. 3) The inner SDR package contains reflectors that bear a resemblance to the SDRs described by Hinz (1981) corresponding to syn-tectonic volcanic eruptions into an extensional basin, while the outer SDR package has

  4. Primative components, crustal assimilation, and magmatic degassing of the 2008 Kilauea summit eruption

    Science.gov (United States)

    Rowe, Michael C.; Thornber, Carl R.; Orr, Tim R.

    2015-01-01

    Simultaneous summit and rift zone eruptions at Kīlauea starting in 2008 reflect a shallow eruptive plumbing system inundated by a bourgeoning supply of new magma from depth. Olivine-hosted melt inclusions, host glass, and bulk lava compositions of magma erupted at both the summit and east rift zone demonstrate chemical continuity at both ends of a well-worn summit-to-rift pipeline. Analysis of glass within dense-cored lapilli erupted from the summit in March – August 2008 show these are not samplings of compositionally distinct magmas stored in the shallow summit magma reservoir, but instead result from remelting and assimilation of fragments from conduit wall and vent blocks. Summit pyroclasts show the predominant and most primitive component erupted to be a homogenous, relatively trace-element-depleted melt that is a compositionally indistinguishable from east rift lava. Based on a “top-down” model for the geochemical variation in east rift zone lava over the past 30 years, we suggest that the apparent absence of a 1982 enriched component in melt inclusions, as well as the proposed summit-rift zone connectivity based on sulfur and mineral chemistry, indicate that the last of the pre-1983 magma has been flushed out of the summit reservoir during the surge of mantle-derived magma from 2003-2007.

  5. Rapid mixing and short storage timescale in the magma dynamics of a steady-state volcano

    Science.gov (United States)

    Petrone, Chiara Maria; Braschi, Eleonora; Francalanci, Lorella; Casalini, Martina; Tommasini, Simone

    2018-06-01

    Steady-state volcanic activity implies equilibrium between the rate of magma replenishment and eruption of compositionally homogeneous magmas, lasting for tens to thousands of years in an open conduit system. The Present-day activity of Stromboli volcano (Aeolian Islands, Southern Italy) has long been recognised as typical of a steady-state volcano, with a shallow magmatic reservoir (highly porphyritic or hp-magma) continuously refilled by more mafic magma (with low phenocryst content or lp-magma) at a constant rate and accompanied by mixing, crystallisation and eruption. Our aim is to clarify the timescale and dynamics of the plumbing system at the establishment of the Present-day steady-state activity (volcanoes.

  6. The Relation Between Plate Spreading Rate, Crustal Thickness and Axial Relief at Mid-Ocean Ridges

    Science.gov (United States)

    Liu, Z.; Buck, W. R.

    2017-12-01

    Variations in axial valley relief and in faulting at plate spreading centers are clearly related to magma supply and axial lithospheric structure. Previous models that consider the interaction of magmatic dikes with lithospheric stretching do not successfully reproduce both of these trends. We present the first model that reproduces these trends by making simple assumptions about the partitioning of magma between dikes, gabbros and extrusives. A key concept is that dikes open not only in the brittle axial lithosphere but also into the underlying ductile crust, where they cool to form gabbro. The amount of gabbro so intruded depends on magma pressure that is related to axial relief. The deeper the valley the less magma goes into gabbros and the more magma is available for dikes to accommodate plate separation. We define the fraction of plate separation rate accommodated by dikes as M. If Mreasonable. Finally, we describe themo-mechanical models that allow us to relate plate spreading rate and crustal thickness and to axial valley depth.

  7. Assessing reservoir performance risk in CO{sub 2} storage projects

    Energy Technology Data Exchange (ETDEWEB)

    Bowden, A.R. [URS Corp., San Francisco, CA (United States); Rigg, A. [CRC for Greenhouse Gas Technologies, Canberra (Australia)

    2005-07-01

    One of the main issues for researchers involved with geological storage of carbon dioxide (CO{sub 2}) has been the development of a proper methodology to assess and compare alternative CO{sub 2} injection projects on the basis of risk. Consideration needs to be given to technical aspects, such as the risk of leakage and the effectiveness of the intended reservoir, as well as less tangible aspects such as the value and safety of geological storage of CO{sub 2}, and potential impacts on the community and environment. The Geological Disposal of Carbon Dioxide (GEODISC), was a research program of the Australian Petroleum Cooperative Research Centre which identified 56 potential environmentally sustainable sites for CO{sub 2} injection (ESSCIs) within Australia. Several studies were carried out, involving detailed evaluation of the suitability of 4 selected sites, including Dongara, Petrel, Gippsland and Carnarvon. The GEODISC program included a risk assessment research module which required a complete and quantified risk assessment of CO{sub 2} injection as a storage option. Primary goals were to assess the risk of leakage, to assess the effectiveness of the intended reservoir, and to assess negative consequences to facilitate comparison of alternative sites. This paper discussed the background and risk assessment model. Key performance indicators (KPIs) were also developed to address the purpose of risk assessment. It was concluded that the RISQUE method is an appropriate approach and that potential injection projects can be measured against six KPIs including containment; effectiveness; self-funding potential; wider community benefits; community safety and community amenity. 6 refs., 3 tabs., 3 figs.

  8. Mush Column Magma Chambers

    Science.gov (United States)

    Marsh, B. D.

    2002-12-01

    Magma chambers are a necessary concept in understanding the chemical and physical evolution of magma. The concept may well be similar to a transfer function in circuit or time series analysis. It does what needs to be done to transform source magma into eruptible magma. In gravity and geodetic interpretations the causative body is (usually of necessity) geometrically simple and of limited vertical extent; it is clearly difficult to `see' through the uppermost manifestation of the concentrated magma. The presence of plutons in the upper crust has reinforced the view that magma chambers are large pots of magma, but as in the physical representation of a transfer function, actual magma chambers are clearly distinct from virtual magma chambers. Two key features to understanding magmatic systems are that they are vertically integrated over large distances (e.g., 30-100 km), and that all local magmatic processes are controlled by solidification fronts. Heat transfer considerations show that any viable volcanic system must be supported by a vertically extensive plumbing system. Field and geophysical studies point to a common theme of an interconnected stack of sill-like structures extending to great depth. This is a magmatic Mush Column. The large-scale (10s of km) structure resembles the vertical structure inferred at large volcanic centers like Hawaii (e.g., Ryan et al.), and the fine scale (10s to 100s of m) structure is exemplified by ophiolites and deeply eroded sill complexes like the Ferrar dolerites of the McMurdo Dry Valleys, Antarctica. The local length scales of the sill reservoirs and interconnecting conduits produce a rich spectrum of crystallization environments with distinct solidification time scales. Extensive horizontal and vertical mushy walls provide conditions conducive to specific processes of differentiation from solidification front instability to sidewall porous flow and wall rock slumping. The size, strength, and time series of eruptive behavior

  9. Crustal structure of the Gulf of Aden southern margin: Evidence from receiver functions on Socotra Island (Yemen)

    Science.gov (United States)

    Ahmed, Abdulhakim; Leroy, Sylvie; Keir, Derek; Korostelev, Félicie; Khanbari, Khaled; Rolandone, Frédérique; Stuart, Graham; Obrebski, Mathias

    2014-12-01

    Breakup of continents in magma-poor setting occurs primarily by faulting and plate thinning. Spatial and temporal variations in these processes can be influenced by the pre-rift basement structure as well as by early syn-rift segmentation of the rift. In order to better understand crustal deformation and influence of pre-rift architecture on breakup we use receiver functions from teleseismic recordings from Socotra which is part of the subaerial Oligo-Miocene age southern margin of the Gulf of Aden. We determine variations in crustal thickness and elastic properties, from which we interpret the degree of extension related thinning and crustal composition. Our computed receiver functions show an average crustal thickness of ~ 28 km for central Socotra, which decreases westward along the margin to an average of ~ 21 km. In addition, the crust thins with proximity to the continent-ocean transition to ~ 16 km in the northwest. Assuming an initial pre-rift crustal thickness of 35 km (undeformed Arabian plate), we estimate a stretching factor in the range of ~ 2.1-2.4 beneath Socotra. Our results show considerable differences between the crustal structure of Socotra's eastern and western sides on either side of the Hadibo transfer zone; the east displays a clear intracrustal conversion phase and thick crust when compared with the western part. The majority of measurements across Socotra show Vp/Vs ratios of between 1.70 and 1.77 and are broadly consistent with the Vp/Vs values expected from the granitic and carbonate rock type exposed at the surface. Our results strongly suggest that intrusion of mafic rock is absent or minimal, providing evidence that mechanical thinning accommodated the majority of crustal extension. From our observations we interpret that the western part of Socotra corresponds to the necking zone of a classic magma-poor continental margin, while the eastern part corresponds to the proximal domain.

  10. Evidence for on-going inflation of the Socorro Magma Body, New Mexico, from interferometric synthetic aperture radar imaging

    Science.gov (United States)

    Fialko, Yuri; Simons, Mark

    Interferometric synthetic aperture radar (InSAR) imaging of the central Rio Grande rift (New Mexico, USA) during 1992-1999 reveals a crustal uplift of several centimeters that spatially coincides with the seismologically determined outline of the Socorro magma body, one of the largest currently active magma intrusions in the Earth’s continental crust. Modeling of interferograms shows that the observed deformation may be due to elastic opening of a sill-like intrusion at a rate of a few millimeters per year. Despite an apparent constancy of the geodetically determined uplift rate, thermodynamic arguments suggest that it is unlikely that the Socorro magma body has formed via steady state elastic inflation.

  11. Zircon reveals protracted magma storage and recycling beneath Mount St. Helens

    Science.gov (United States)

    Claiborne, L.L.; Miller, C.F.; Flanagan, D.M.; Clynne, M.A.; Wooden, J.L.

    2010-01-01

    Current data and models for Mount St. Helens volcano (Washington, United States) suggest relatively rapid transport from magma genesis to eruption, with no evidence for protracted storage or recycling of magmas. However, we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust, cool and crystallize beneath the volcano, and are then rejuvenated and incorporated by hotter, young magmas on their way to the surface. Estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century. Zircon elemental compositions reflect the increasing influence of mafic input into the system through time, recording growth from hotter, less evolved magmas tens of thousands of years prior to the appearance of mafic magmas at the surface, or changes in whole-rock geochemistry and petrology, and providing a new, time-correlated record of this evolution independent of the eruption history. Zircon data thus reveal the history of the hidden, long-lived intrusive portion of the Mount St. Helens system, where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh influxes of magmas that traverse the intrusive reservoir before erupting. ?? 2010 Geological Society of America.

  12. Imaging the complex geometry of a magma reservoir using FEM-based linear inverse modeling of InSAR data: application to Rabaul Caldera, Papua New Guinea

    Science.gov (United States)

    Ronchin, Erika; Masterlark, Timothy; Dawson, John; Saunders, Steve; Martì Molist, Joan

    2017-06-01

    We test an innovative inversion scheme using Green's functions from an array of pressure sources embedded in finite-element method (FEM) models to image, without assuming an a-priori geometry, the composite and complex shape of a volcano deformation source. We invert interferometric synthetic aperture radar (InSAR) data to estimate the pressurization and shape of the magma reservoir of Rabaul caldera, Papua New Guinea. The results image the extended shallow magmatic system responsible for a broad and long-term subsidence of the caldera between 2007 February and 2010 December. Elastic FEM solutions are integrated into the regularized linear inversion of InSAR data of volcano surface displacements in order to obtain a 3-D image of the source of deformation. The Green's function matrix is constructed from a library of forward line-of-sight displacement solutions for a grid of cubic elementary deformation sources. Each source is sequentially generated by removing the corresponding cubic elements from a common meshed domain and simulating the injection of a fluid mass flux into the cavity, which results in a pressurization and volumetric change of the fluid-filled cavity. The use of a single mesh for the generation of all FEM models avoids the computationally expensive process of non-linear inversion and remeshing a variable geometry domain. Without assuming an a-priori source geometry other than the configuration of the 3-D grid that generates the library of Green's functions, the geodetic data dictate the geometry of the magma reservoir as a 3-D distribution of pressure (or flux of magma) within the source array. The inversion of InSAR data of Rabaul caldera shows a distribution of interconnected sources forming an amorphous, shallow magmatic system elongated under two opposite sides of the caldera. The marginal areas at the sides of the imaged magmatic system are the possible feeding reservoirs of the ongoing Tavurvur volcano eruption of andesitic products on the

  13. Crustal tomography of the 2016 Kumamoto earthquake area in West Japan using P and PmP data

    Science.gov (United States)

    Wang, Haibo; Zhao, Dapeng; Huang, Zhouchuan; Xu, Mingjie; Wang, Liangshu; Nishizono, Yukihisa; Inakura, Hirohito

    2018-05-01

    A high-resolution model of three-dimensional (3-D) P-wave velocity (Vp) tomography of the crust in the source area of the 2016 Kumamoto earthquake (M 7.3) in West Japan is determined using a large number of arrival times of first P-waves and reflected P-waves from the Moho discontinuity (PmP). The PmP data are collected from original seismograms of the Kumamoto aftershocks and other local crustal events in Kyushu. Detailed resolution tests show that the addition of the PmP data can significantly improve the resolution of the crustal tomography, especially that of the lower crust. Our results show that significant low-velocity (low-V) anomalies exist in the entire crust beneath the active arc volcanoes, which may reflect the pathway of arc magmas. The 2016 Kumamoto earthquake occurred at the edge of a small low-V zone in the upper crust. A significant low-V anomaly is revealed in the lower crust beneath the source zone, which may reflect the arc magma and fluids ascending from the mantle wedge. These results suggest that the rupture nucleation of the 2016 Kumamoto earthquake was affected by fluids and arc magma.

  14. Crustal movements due to Iceland's shrinking ice caps mimic magma inflow signal at Katla volcano.

    Science.gov (United States)

    Spaans, Karsten; Hreinsdóttir, Sigrún; Hooper, Andrew; Ófeigsson, Benedikt Gunnar

    2015-05-20

    Many volcanic systems around the world are located beneath, or in close proximity to, ice caps. Mass change of these ice caps causes surface movements, which are typically neglected when interpreting surface deformation measurements around these volcanoes. These movements can however be significant, and may closely resemble movements due to magma accumulation. Here we show such an example, from Katla volcano, Iceland. Horizontal movements observed by GPS on the flank of Katla have led to the inference of significant inflow of magma into a chamber beneath the caldera, starting in 2000, and continuing over several years. We use satellite radar interferometry and GPS data to show that between 2001 and 2010, the horizontal movements seen on the flank can be explained by the response to the long term shrinking of ice caps, and that erratic movements seen at stations within the caldera are also not likely to signify magma inflow. It is important that interpretations of geodetic measurements at volcanoes in glaciated areas consider the effect of ice mass change, and previous studies should be carefully reevaluated.

  15. Superheat in magma oceans

    Science.gov (United States)

    Jakes, Petr

    1992-01-01

    The existence of 'totally molten' planets implies the existence of a superheat (excess of heat) in the magma reservoirs since the heat buffer (i.e., presence of crystals having high latent heat of fusion) does not exist in a large, completely molten reservoir. Any addition of impacting material results in increase of the temperature of the melt and under favorable circumstances heat is stored. The behavior of superheat melts is little understood; therefore, we experimentally examined properties and behavior of excess heat melts at atmospheric pressures and inert gas atmosphere. Highly siliceous melts (70 percent SiO2) were chosen for the experiments because of the possibility of quenching such melts into glasses, the slow rate of reaction in highly siliceous composition, and the fact that such melts are present in terrestrial impact craters and impact-generated glasses. Results from the investigation are presented.

  16. Evaluating crustal contributions to enriched shergottites from the petrology, trace elements, and Rb-Sr and Sm-Nd isotope systematics of Northwest Africa 856

    Science.gov (United States)

    Ferdous, J.; Brandon, A. D.; Peslier, A. H.; Pirotte, Z.

    2017-08-01

    The origin of the incompatible trace element (ITE) characteristics of enriched shergottites has been critical for examining two contradicting scenarios to explain how these Martian meteorites form. The first scenario is that it reflects ITE enrichment in an early-formed mantle reservoir whereas the second scenario attributes it to assimilation of ancient Martian crust (∼4-4.5 Ga) by ITE-depleted magmas. Strongly differentiated shergottite magmas may yield added constraints for determining which scenario can best explain this signature in enriched shergottites. The meteorite Northwest Africa (NWA) 856 is a basaltic shergottite that, unlike many enriched shergottites, lacks olivine and has undergone extensive differentiation from more primitive parent magma. In similarity to other basaltic shergottites, NWA 856 is comprised primarily of compositionally zoned clinopyroxenes (45% pigeonite and 23% augite), maskelynite (23%) and accessory minerals such as ulvöspinel, merrillite, Cl-apatite, ilmenite, pyrrhotite, baddeleyite and silica polymorph. The CI-chondrite normalized rare earth element (REE) abundance patterns for its maskelynite, phosphates, and its whole rock are flat with corresponding light-REE depletions in clinopyroxenes. The 87Rb-87Sr and 147Sm-143Nd internal isochron ages are 162 ± 14 (all errors are ±2σ) Ma and 162.7 ± 5.5 Ma, respectively, with an initial εNdI = -6.6 ± 0.2. The Rb-Sr isotope systematics are affected by terrestrial alteration resulting in larger scatter and a less precise internal isochron age. The whole rock composition is used in MELTS simulations to model equilibrium and fractional crystallization sequences to compare with the crystallization sequence from textural observations and to the mineral compositions. These models constrain the depth of initial crystallization to a pressure range of 0.4-0.5 GPa (equivalent to 34-42 km) in anhydrous conditions at the Fayalite-Magnetite-Quartz buffer, and consistently reproduce the

  17. Water Partitioning in Planetary Embryos and Protoplanets with Magma Oceans

    Science.gov (United States)

    Ikoma, M.; Elkins-Tanton, L.; Hamano, K.; Suckale, J.

    2018-06-01

    The water content of magma oceans is widely accepted as a key factor that determines whether a terrestrial planet is habitable. Water ocean mass is determined as a result not only of water delivery and loss, but also of water partitioning among several reservoirs. Here we review our current understanding of water partitioning among the atmosphere, magma ocean, and solid mantle of accreting planetary embryos and protoplanets just after giant collisions. Magma oceans are readily formed in planetary embryos and protoplanets in their accretion phase. Significant amounts of water are partitioned into magma oceans, provided the planetary building blocks are water-rich enough. Particularly important but still quite uncertain issues are how much water the planetary building blocks contain initially and how water goes out of the solidifying mantle and is finally degassed to the atmosphere. Constraints from both solar-system explorations and exoplanet observations and also from laboratory experiments are needed to resolve these issues.

  18. INTERACTIONS BETWEEN GABBROID AND GRANITOID MAGMAS DURING FORMATION OF THE PREOBRAZHENSKY INTRUSION, EAST KAZAKHSTAN

    Directory of Open Access Journals (Sweden)

    S. V. Khromykh

    2017-01-01

    upper rock levels. Examples of the magma interaction causing the formation of mingling structures at the middle and upper crust levels can be viewed as indicative of ‘fast’, active processes of the mantle‐crust interaction, when the mantle magmas actively drain the lithosphere and melt the substance of the lower‐middle crust. An important role is played by the temperature gradient in the sublithospheric mantle. It directly affects the degree of its melting and the volumes of basite magmas. Nonetheless, the permeability of the lithosphere is also important – the above‐described scenario is possible if the lithosphere is either thin or easily permeable due to the development of strike‐slip and extension fractures. In the Late Paleozoic, the territory of East Kazakhstan was part of the Altai collision system of hercinides. The late stages of its evolution (300–280 Ma were accompanied by large‐scale mantle and crustal magma‐ tism corresponding to the formation of the Late Palaeozoic large igneous province related to the activity of the Tarim mantle plume. The influence of the mantle plume on the lithospheric mantle led to an increase in the temperature gradient, and the lithosphere weakened by shear movements of the collapsing orogenic structure was permeable to mantle magmas, which caused the processes of mantle‐crustal interaction.

  19. Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

    Science.gov (United States)

    Stelten, Mark; Cooper, Kari M.; Vazquez, Jorge A.; Calvert, Andrew T.; Glessner, Justin G

    2015-01-01

    We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to

  20. Hf isotope evidence for variable slab input and crustal addition in basalts and andesites of the Taupo Volcanic Zone, New Zealand

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Troll, Valentin R.; Gamble, J.A.

    2017-01-01

    -Nd isotopes. Here we present new Hf isotope data for a selection of volcanic rocks and crustal lithologies fromthe Taupo Volcanic Zone (TVZ), NewZealand and propose that the scatter in Hf-Nd isotopes indicates heterogeneity in the parental magmas prior to interactions with crustal lithologies. The observed......, whereas younger lavas have probably interacted more with mid- to shallow crustal meta-sedimentary greywacke-argillite lithologies of the Permian to Cretaceous composite Torlesse Terrane. Hf-Nd isotopic compositions of meta-igneous granulite xenoliths from Mt. Ruapehu are consistent with previous...

  1. Isotopic disequilibrium among commingled hybrid magmas: Evidence for a two-stage magma mixing-commingling process in the Mt. Perkins Pluton, Arizona

    International Nuclear Information System (INIS)

    Metcalf, R.V.; Smith, E.I.; Reed, R.C.

    1995-01-01

    The syn-extensional Miocene Mt. Perkins pluton, northwestern Arizona, cooled rapidly due to its small size (6 km 2 ) and shallow emplacement (7.5 km) and allows examination of commingled rocks that experienced little isotopic exchange. Within the pluton, quartz dioritic to granodioritic host rocks (58-68 wt% SiO 2 ) enclose dioritic enclaves (50-55 wt% SiO 2 ) and a portion contains enclave-free granodiorite (70-74 wt% SiO 2 ). Fine-grained, crenulate enclave margins and a lack of advanced mixing structures (e.g., schlieren, flow fabrics, etc.) indicate an incipient stage of commingling. Isotopic variation between enclaves and enclosing host rocks is large (6.8 to 10.6 ε Nd units; 0.0036 to 0.0046 87 Sr/ 86 Sr units), suggesting isotopic disequilibrium. Comparison of an enclave core and rim suggests that isotopic exchange with the host magma was limited to the enclave rim. Enclaves and hosts collectively form a calc-alkaline suite exhibiting a large range of ε Nd (+1.2 to -12.5) and initial 87 Sr/ 86 Sr (0.705 to 0.71267) with a correlation among ε Nd , initial 87 Sr/ 86 Sr, and major and trace element compositions. Modeling suggests that the suite formed by magma hybridization involving magma mixing accompanied by fractional crystallization. The magma mixing must have predated commingling at the present exposure level and indicates a larger mixing chamber at depth. Isotopic and trace element data suggests mixing end-members were asthenospheric mantle-derived mafic and crustal-derived felsic magmas. Fractional crystallization facilitated mixing by reducing the rheological contrasts between the mafic and felsic mixing end-members. 58 refs., 11 figs., 3 tabs

  2. CO{sub 2} interfacial properties: application to multiphase flow at reservoir conditions; Proprietes interfaciales du CO{sub 2}: application aux ecoulements en milieu poreux en pression et temperature

    Energy Technology Data Exchange (ETDEWEB)

    Chalbaud, C

    2007-07-15

    In this work we deal with the interfacial properties of CO{sub 2} at reservoir conditions with a special interest on deep saline aquifers. Each chapter of this dissertation represents a different physical scale studied with different experimental devices and simulation tools. The results obtained in the first part of this study represent a complete data set of brine-CO{sub 2} interfacial tension at reservoir conditions. A semi-analytical equation is proposed in order to facilitate the work of reservoir engineers. The second deals with the interfacial properties at the pore scale using glass micro-models at different wettability conditions. This part shows the wetting behavior of CO{sub 2} on hydrophobic or oil-wet solid surfaces. A pore network model was used for the interpretation and exploitation of these results. The third part corresponds to two different experimental approaches at the core scale at different wettability conditions associated to a modelling at flue Darcy scale. This part is a significant contribution to the validation of COORES compositional reservoir simulator developed by IFP. It has also allow us to estimate multiphase properties, Pc and kr, for brine-CO{sub 2} systems at reservoir conditions. This study presents the necessary scales to model CO{sub 2} storage in deep saline aquifers. (author)

  3. Modulation of magmatic processes by carbon dioxide

    Science.gov (United States)

    Caricchi, L.; Sheldrake, T. E.; Blundy, J. D.

    2017-12-01

    Volatile solubility in magmas increases with pressure, although the solubility of CO2 is much lower than that of H2O. Consequently, magmas rising from depth release CO2-rich fluids, which inevitably interact with H2O-poor magmas in the upper crust (CO2-flushing). CO2-flushing triggers the exsolution of H2O-rich fluids, leading to an increase of volume and magma crystallisation. While the analyses of eruptive products demonstrates that this process operates in virtually all magmatic system, its impact on magmatic and volcanic processes has not been quantified. Here we show that depending on the initial magma crystallinity, and the depth of magma storage, CO2-flushing can lead to volcanic eruptions or promote conditions that favour the impulsive release of mineralising fluids. Our calculations show that the interaction between a few hundred ppm of carbonic fluids, and crystal-poor magmas stored at shallow depths, produces rapid pressurisation that can potentially lead to an eruption. Further addition of CO2 increases magma compressibility and crystallinity, reducing the potential for volcanic activity, promoting the formation of ore deposits. Increasing the depth of fluid-magma interaction dampens the impact of CO2-flushing on the pressurisation of a magma reservoir. CO2-flushing may result in surface inflation and increases in surface CO2 fluxes, which are commonly considered signs of an impending eruption, but may not necessarily result in eruption depending on the initial crystallnity and depth of the magmatic reservoir. We propose that CO2-flushing is a powerful agent modulating the pressurisation of magma reservoirs and the release of mineralising fluids from upper crustal magma reservoirs.

  4. Satellite Geodesy Captures Offset Magma Supply Associated With Lava Lake Appearance at Masaya Volcano, Nicaragua

    Science.gov (United States)

    Stephens, K. J.; Wauthier, C.

    2018-03-01

    Ascending and descending Interferometric Synthetic Aperture Radar data sets from various satellites (CSK, RSAT-2, ALOS-2, and Sentinel-1) show a maximum of ˜8 cm ground inflation in Masaya caldera over a 15 month period (6 November 2015 to 1 September 2016). The center of inflation is located in the NW part of the caldera, north of the active Santiago vent which has hosted a new lava lake since 11 December 2015. Simultaneous inversions of those Interferometric Synthetic Aperture Radar data sets using a neighbourhood algorithm demonstrate that a spherical magma reservoir explains the geodetic data, with a horizontal location ˜3 km north of the active Santiago vent and a depth-to-center ˜3 km. The associated modeled volume increase (˜0.0042 km3) is lower than the "excess" magma volume inferred from gas measurements from November 2015 to February 2016. The magma reservoir offset from the current center of eruptive activity may be the result of preexisting caldera structures.

  5. The 1994-2001 eruptive period at Rabaul, Papua New Guinea: Petrological and geochemical evidence for basalt injections into a shallow dacite magma reservoir, and significant SO2 flux

    Science.gov (United States)

    Patia, H.; Eggins, S. M.; Arculus, R. J.; McKee, C. O.; Johnson, R. W.; Bradney, A.

    2017-10-01

    The eruptions that began at Rabaul Caldera on 19 September 1994 had two focal points, the vents Tavurvur and Vulcan, located 6 km apart on opposing sides of the caldera. Vulcan eruptives define a tight cluster of dacite compositions, whereas Tavurvur eruptives span an array from equivalent dacite compositions to mafic andesites. The eruption of geochemically and mineralogically identical dacites from both vents indicates sourcing from the same magma reservoir. This, together with previously reported H2O-CO2 volatile contents of dacite melt inclusions, a caldera-wide seismic low-velocity zone, and a seismically active caldera ring fault structure are consistent with the presence at 3-6 km depth of an extensive, tabular dacitic magma body having volume of about 15-150 km3. The Tavurvur andesites form a linear compositional array and have strongly bimodal phenocryst assemblages that reflect dacite hybridisation with a mafic basalt. The moderately large volume SO2 flux documented in the Tavurvur volcanic plume (and negligible SO2 flux in the Vulcan plume) combined with high dissolved S contents of basaltic melt inclusions trapped in olivine of Tavurvur eruptives, indicate that the amount of degassed basaltic magma was 0.1 km3 and suggest that the injection of this magma was confined to the Tavurvur-side (eastern to northeastern sector) of the caldera. Circumstantial evidence suggests that the eruption was triggered and evolved in response to a series of basaltic magma injections that may have commenced in 1971 and continued up until at least the start of the 1994 eruptions. The presence of zoned plagioclase phenocrysts reflecting older basalt-dacite interaction events (i.e. anorthite cores overgrown with thick andesine rims), evaluation of limited available data for the products of previous eruptions in 1878 and 1937-1943, and the episodic occurrence of major intra-caldera seismo-deformational events indicates that the shallow magma system at Rabaul Caldera is

  6. Geophysical Evidence for the Locations, Shapes and Sizes, and Internal Structures of Magma Chambers beneath Regions of Quaternary Volcanism

    Science.gov (United States)

    Iyer, H. M.

    1984-04-01

    at the onset of melting of rocks and to delineate in three dimensions the shape of the partly melted zone. Similarly, decreases in density and electrical resistivity in rocks during melting, can be detected. Seismic refraction and reflection are not yet used extensively in magma chamber studies. In a study, in the Yellowstone region, seismic delays occurring in a fan-shooting configuration and time-term modelling show the presence of an intense molten zone in the upper crust. Deep seismic sounding (a combination of seismic refraction and reflection) and modelling amplitude and velocity changes of diffracted seismic waves from explosions and earthquakes, have enabled mapping of small and large magma chambers beneath many volcanoes in Kamchatka, U.S.S.R. Teleseismic P-wave residuals have been used to model low-velocity bodies, interpreted as magma chambers, in several Quaternary volcanic centres in the U.S.A. The results show that magma chambers with volumes of a few hundred to a few thousand cubic kilometres volume seem to be confined to regions of silicic volcanism. Many of the magma bodies seem to have upper-mantle roots implying that they are not isolated pockets of partial melt, but may be deriving their magma supplies from deeper parental sources. Medium or large crustal magma chambers are absent in the andesitic volcanoes of western United States and the basaltic Kilauea volcano, Hawaii. However, regional velocity models of the Oregon Cascades and Hawaii show evidence for the presence of magma reservoirs in the upper mantle. The transport of magma to the upper crust in these regions probably occurs rapidly through narrow conduits, with transient storage occurring in small chambers of a few cubic kilometres volume. Very little use has been made of the gravity and magnetic maps to model magma chambers. The number of available case histories, though few, indicate that these data can be very useful to give constraints on the density and temperature in magma chambers

  7. Trace element modelling of magma evolution in the Fongen-Hyllingen Intrusion, Trondheim region, Norway

    International Nuclear Information System (INIS)

    Mohamed A Abu El-Rus

    2003-01-01

    The trace element evolution of the Fongen-Hyllingen Intrusion has been studied on the basis of ICPMS analyses of 21 whole rocks and 12 plagioclase separates. Emphasis has been placed on Stage IV of the intrusion that crystallized essentially after magma addition had ceased. Whereas the compositions of minerals and rocks in Stage IV exhibit strong normal fractionation trends, crustal contamination is evident in a wide range of incompatible element ratios that should be relatively constant if simple fractional crystallization prevailed. Crustal contamination in Stage IV is confirmed by isotopic studies. The distribution of incompatible elements in Stage IV can be successfully explained by AFC modelling. Olivine compositions and isotopic ratios in the most primitive cumulates together with the slight LREE-enrichment in their coexisting melts suggest that the FHI parental magma was subjected to at least olivine fractionation during ascent to the magma chamber. This resulted in a decrease in the Mg-number of the melt without changing its isotopic ratio and incompatible trace element ratios. The slight enrichment in LREE and relatively low Zr/Y ratios in the melt coexisting with the most primitive cumulates imply that the FHI primary melt was derived from garnet-free mantle. The relative abundance of incompatible elements in the most primitive calculated melts, geochemically similar to low-Ti continental flood basalts, suggest that a subcontinental mantle source was most probable for the parental melt for FHI. (author)

  8. Mid-Ocean Ridge Melt Supply and Glacial Cycles: A 3D EPR Study of Crustal Thickness, Layer 2A, and Bathymetry

    Science.gov (United States)

    Boulahanis, B.; Aghaei, O.; Carbotte, S. M.; Huybers, P. J.; Langmuir, C. H.; Nedimovic, M. R.; Carton, H. D.; Canales, J. P.

    2017-12-01

    Recent studies suggest that eustatic sea level fluctuations induced by glacial cycles in the Pleistocene may influence mantle-melting and volcanic eruptions at mid-ocean ridges (MOR), with models predicting variation in oceanic crustal thickness linked to sea level change. Previous analyses of seafloor bathymetry as a proxy for crustal thickness show significant spectral energy at frequencies linked to Milankovitch cycles of 1/23, 1/41, and 1/100 ky-1, however the effects of faulting in seafloor relief and its spectral characteristics are difficult to separate from climatic signals. Here we investigate the hypothesis of climate driven periodicity in MOR magmatism through spectral analysis, time series comparisons, and statistical characterization of bathymetry data, seismic layer 2A thickness (as a proxy for extrusive volcanism), and seafloor-to-Moho thickness (as a proxy for total magma production). We utilize information from a three-dimensional multichannel seismic study of the East Pacific Rise and its flanks from 9°36`N to 9°57`N. We compare these datasets to the paleoclimate "LR04" benthic δ18O stack. The seismic dataset covers 770 km2 and provides resolution of Moho for 92% of the imaged region. This is the only existing high-resolution 3-D image across oceanic crust, making it ideal for assessing the possibility that glacial cycles modulate magma supply at fast spreading MORs. The layer 2A grid extends 9 km (170 ky) from the ridge axis, while Moho imaging extends to a maximum of 16 km (310 ky). Initial results from the East Pacific Rise show a relationship between sea level and both crustal thickness and sea floor depth, consistent with the hypothesis that magma supply to MORs may be modulated by glacial cycles. Analysis of crustal thickness and bathymetry data reveals spectral peaks at Milankovitch frequencies of 1/100 ky-1 and 1/41 ky-1 where datasets extend sufficiently far from the ridge. The layer 2A grid does not extend sufficiently far from the

  9. Petrologic evolution of Miocene-Pliocene mafic volcanism in the Kangal and Gürün basins (Sivas-Malatya), central east Anatolia: Evidence for Miocene anorogenic magmas contaminated by continental crust

    Science.gov (United States)

    Kocaarslan, Ayça; Ersoy, E. Yalçın

    2018-06-01

    This study discusses the geochemical features of the Early-Middle Miocene and Pliocene basaltic (SiO2 = 46-52; MgO = 6-10 wt%) to andesitic (SiO2 = 59; MgO = 4 wt%) rocks exposed in the Gürün and Kangal basins (Sivas, eastern part of central Anatolia), respectively. The basaltic rocks are characterized by alkaline to tholeiitic affinities, while the more evolved andesitic samples show calc-alkaline affinity. Trace element variations reveal that they can be evaluated in three sub-groups, each represented by different contents of trace elements for given Nb contents. Primary magmas of each groups were likely produced by different degrees of partial melting ( 1-2, 2-3, 7-10% respectively) from a common mantle source, subsequently underwent different degrees of fractionation and crustal contamination. Derivation from a common mantle source of the primitive magmas of each group is supported by similar Sr, Nd and Pb isotopic ratios. Increasing degrees of partial melting seem to be responsible for the alkaline to tholeiitic variation among the basaltic samples, while higher degrees of crustal contamination (AFC) resulted in calc-alkaline affinity of the more evolved samples. Most primitive Pliocene samples show intra-plate (anorogenic) geochemical features, while the more evolved Miocene calc-alkaline samples resemble geochemically subduction-related (orogenic) magmatic rocks. However, on the basis of detailed geochemical models, we propose that the calc-alkaline affinity among the Miocene samples can also be gained by crustal contamination of their primary magmas which were also anorogenic in character. If this is true, overall, the Miocene and Pliocene basaltic to andesitic rocks in the Gürün and Kangal basins appear to may have formed by variable degrees of partial melting of a common anorogenic mantle that had not been subject to subduction-related metasomatism. This is an alternative approach to the general view assuming the Early-Middle Miocene magmatic activity

  10. Transient shallow reservoirs beneath small eruptive centres: Constraints from Mg-Fe interdiffusion in olivine

    Science.gov (United States)

    Morgado, E.; Parada, M. A.; Morgan, D. J.; Gutiérrez, F.; Castruccio, A.; Contreras, C.

    2017-11-01

    Small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes, an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes. The Caburgua cones of the Andean Southern Volcanic Zone from a basaltic small eruptive centre where this can be tested. Here, we use MELTS simulations, and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the Mg-Fe diffusion modelling to determine the magma residence times of those rims in the crust. Results yield timescales varying from a few days to dozens of days, and if freezing is to be avoided, can only be explained by some form of storage or slow transport through at least one shallow magma body. The longest durations of magma residence seen in the olivine rim zones are up to 471 days. These timescales are shorter than those estimated (decadal) from the nearby, more-differentiated, and well-established stratovolcano, Villarrica, which has a dominantly basaltic andesite composition. For Caburgua cones, we propose the existence of a transient reservoir, in contrast to a long-lived reservoir such as that inferred beneath the adjacent Villarrica stratovolcano.

  11. Magma Diversity in the Trans-Mexican Volcanic Belt: the role of Mantle Heterogeneities, Slab-derived Fluxes and Crustal Contamination.

    Science.gov (United States)

    Schaaf, P.; Valdez, G.; Siebe, C.; Carrasco, G.

    2005-12-01

    Popocatepetl gas plumes can be explained by the ingestion of limestone by the rising magma. Long-lived recycling of oceanic crust and sediments into the mantle, varying amounts of mantle and slab flux heterogeneities, and obvious crustal assimilation processes are responsible for the complex element and isotope distributions observed along the TMVB.

  12. Evidence of a global magma ocean in Io's interior.

    Science.gov (United States)

    Khurana, Krishan K; Jia, Xianzhe; Kivelson, Margaret G; Nimmo, Francis; Schubert, Gerald; Russell, Christopher T

    2011-06-03

    Extensive volcanism and high-temperature lavas hint at a global magma reservoir in Io, but no direct evidence has been available. We exploited Jupiter's rotating magnetic field as a sounding signal and show that the magnetometer data collected by the Galileo spacecraft near Io provide evidence of electromagnetic induction from a global conducting layer. We demonstrate that a completely solid mantle provides insufficient response to explain the magnetometer observations, but a global subsurface magma layer with a thickness of over 50 kilometers and a rock melt fraction of 20% or more is fully consistent with the observations. We also place a stronger upper limit of about 110 nanoteslas (surface equatorial field) on the dynamo dipolar field generated inside Io.

  13. Finite-element modeling of magma chamber-host rock interactions prior to caldera collapse

    Science.gov (United States)

    Kabele, Petr; Žák, Jiří; Somr, Michael

    2017-06-01

    Gravity-driven failure of shallow magma chamber roofs and formation of collapse calderas are commonly accompanied by ejection of large volumes of pyroclastic material to the Earth's atmosphere and thus represent severe volcanic hazards. In this respect, numerical analysis has proven as a key tool in understanding the mechanical conditions of caldera collapse. The main objective of this paper is to find a suitable approach to finite-element simulation of roof fracturing and caldera collapse during inflation and subsequent deflation of shallow magma chambers. Such a model should capture the dominant mechanical phenomena, for example, interaction of the host rock with magma and progressive deformation of the chamber roof. To this end, a comparative study, which involves various representations of magma (inviscid fluid, nearly incompressible elastic, or plastic solid) and constitutive models of the host rock (fracture and plasticity), was carried out. In particular, the quasi-brittle fracture model of host rock reproduced well the formation of tension-induced radial and circumferential fractures during magma injection into the chamber (inflation stage), especially at shallow crustal levels. Conversely, the Mohr-Coulomb shear criterion has shown to be more appropriate for greater depths. Subsequent magma withdrawal from the chamber (deflation stage) results in further damage or even collapse of the chamber roof. While most of the previous studies of caldera collapse rely on the elastic stress analysis, the proposed approach advances modeling of the process by incorporating non-linear failure phenomena and nearly incompressible behaviour of magma. This leads to a perhaps more realistic representation of the fracture processes preceding roof collapse and caldera formation.

  14. Assessing Reservoir Depositional Environments to Develop and Quantify Improvements in CO<sub>2sub> Storage Efficiency. A Reservoir Simulation Approach

    Energy Technology Data Exchange (ETDEWEB)

    Okwen, Roland [University of Illinois, Champaign, IL (United States); Frailey, Scott [University of Illinois, Champaign, IL (United States); Leetaru, Hannes [University of Illinois, Champaign, IL (United States); Moulton, Sandy [Illinois State Geological Survey, Champaign, IL (United States)

    2014-09-30

    The storage potential and fluid movement within formations are dependent on the unique hydraulic characteristics of their respective depositional environments. Storage efficiency (E) quantifies the potential for storage in a geologic depositional environment and is used to assess basinal or regional CO<sub>2sub> storage resources. Current estimates of storage resources are calculated using common E ranges by lithology and not by depositional environment. The objectives of this project are to quantify E ranges and identify E enhancement strategies for different depositional environments via reservoir simulation studies. The depositional environments considered include deltaic, shelf clastic, shelf carbonate, fluvial deltaic, strandplain, reef, fluvial and alluvial, and turbidite. Strategies considered for enhancing E include CO<sub>2sub> injection via vertical, horizontal, and deviated wells, selective completions, water production, and multi-well injection. Conceptual geologic and geocellular models of the depositional environments were developed based on data from Illinois Basin oil fields and gas storage sites. The geologic and geocellular models were generalized for use in other US sedimentary basins. An important aspect of this work is the development of conceptual geologic and geocellular models that reflect the uniqueness of each depositional environment. Different injection well completions methods were simulated to investigate methods of enhancing E in the presence of geologic heterogeneity specific to a depositional environment. Modeling scenarios included horizontal wells (length, orientation, and inclination), selective and dynamic completions, water production, and multiwell injection. A Geologic Storage Efficiency Calculator (GSECalc) was developed to calculate E from reservoir simulation output. Estimated E values were normalized to diminish their dependency on fluid relative permeability. Classifying depositional environments according to

  15. Late Neoproterozoic to Carboniferous genesis of A-type magmas in Avalonia of northern Nova Scotia: repeated partial melting of anhydrous lower crust in contrasting tectonic environments

    Science.gov (United States)

    Murphy, J. Brendan; Shellnutt, J. Gregory; Collins, William J.

    2018-03-01

    Avalonian rocks in northern mainland Nova Scotia are characterized by voluminous 640-600 Ma calc-alkalic to tholeiitic mafic to felsic magmas produced in a volcanic arc. However, after the cessation of arc activity, repeated episodes of felsic magmatism between ca. 580 Ma and 350 Ma are dominated by A-type geochemical characteristics. Sm-Nd isotopic data, combined with zircon saturation temperature estimates, indicate that these magmas were formed by high temperature (800-1050 °C) melting of the same anhydrous crustal source. Regional tectonic considerations indicate that A-type felsic magmatism was produced (1) at 580 Ma in a San Andreas-type strike slip setting, (2) at 495 Ma as Avalonia rifted off Gondwana, (3) at 465 and 455 in an ensialic island arc environment and (4) at 360-350 Ma during post-collisional, intra-continental strike-slip activity as Avalonia was translated dextrally along the Laurentian margin. These results attest to the importance of crustal source, rather than tectonic setting, in the generation of these A-type magmas and are an example of how additional insights are provided by comparing the geochemical and isotopic characteristics of igneous suites of different ages within the same terrane. They also suggest that the shallow crustal rocks in northern mainland Nova Scotia were not significantly detached from their lower crustal source between ca. 620 Ma and 350 Ma, a time interval that includes the separation of Avalonia from Gondwana, its drift and accretion to Laurentia as well as post-accretionary strike-slip displacement.

  16. Contrasting magmatic structures between small plutons and batholiths emplaced at shallow crustal level (Sierras de Córdoba, Argentina)

    Science.gov (United States)

    Pinotti, Lucio P.; D'Eramo, Fernando J.; Weinberg, Roberto F.; Demartis, Manuel; Tubía, José María; Coniglio, Jorge E.; Radice, Stefania; Maffini, M. Natalia; Aragón, Eugenio

    2016-11-01

    Processes like injection, magma flow and differentiation and influence of the regional strain field are here described and contrasted to shed light on their role in the formation of small plutons and large batholiths their magmatic structures. The final geometric and compositional arrangement of magma bodies are a complex record of their construction and internal flow history. Magma injection, flow and differentiation, as well as regional stresses, all control the internal nature of magma bodies. Large magma bodies emplaced at shallow crustal levels result from the intrusion of multiple magma batches that interact in a variety of ways, depending on internal and external dynamics, and where the early magmatic, growth-related structures are commonly overprinted by subsequent history. In contrast, small plutons emplaced in the brittle-ductile transition more likely preserve growth-related structures, having a relatively simple cooling history and limited internal magma flow. Outcrop-scale magmatic structures in both cases record a rich set of complementary information that can help elucidate their evolution. Large and small granitic bodies of the Sierra Pampeanas preserve excellent exposures of magmatic structures that formed as magmas stepped through different rheological states during pluton growth and solidification. These structures reveal not only the flow pattern inside magma chambers, but also the rheological evolution of magmas in response to temperature evolution.

  17. Magmatic architecture within a rift segment: Articulate axial magma storage at Erta Ale volcano, Ethiopia

    Science.gov (United States)

    Xu, Wenbin; Rivalta, Eleonora; Li, Xing

    2017-10-01

    Understanding the magmatic systems beneath rift volcanoes provides insights into the deeper processes associated with rift architecture and development. At the slow spreading Erta Ale segment (Afar, Ethiopia) transition from continental rifting to seafloor spreading is ongoing on land. A lava lake has been documented since the twentieth century at the summit of the Erta Ale volcano and acts as an indicator of the pressure of its magma reservoir. However, the structure of the plumbing system of the volcano feeding such persistent active lava lake and the mechanisms controlling the architecture of magma storage remain unclear. Here, we combine high-resolution satellite optical imagery and radar interferometry (InSAR) to infer the shape, location and orientation of the conduits feeding the 2017 Erta Ale eruption. We show that the lava lake was rooted in a vertical dike-shaped reservoir that had been inflating prior to the eruption. The magma was subsequently transferred into a shallower feeder dike. We also find a shallow, horizontal magma lens elongated along axis inflating beneath the volcano during the later period of the eruption. Edifice stress modeling suggests the hydraulically connected system of horizontal and vertical thin magmatic bodies able to open and close are arranged spatially according to stresses induced by loading and unloading due to topographic changes. Our combined approach may provide new constraints on the organization of magma plumbing systems beneath volcanoes in continental and marine settings.

  18. Columbia River volcanism - The question of mantle heterogeneity or crustal contamination

    Science.gov (United States)

    Carlson, R. W.; Lugmair, G. W.; Macdougall, J. D.

    1981-01-01

    It is found that, although crystal fractionation played an important role in producing the chemical characteristics of Columbia River Province basalts displaying a wide range of chemical and isotopic compositions, the isotopic variability calls for the involvement of at least two isotopically distinct components. The major and trace element characteristics of the main volume of the basalts are not consistent with a metasomatized mantle source region, and the presence of a primordial mantel component is not supported by the chemical data. Models of simple binary mixing between a primary magma and Precambrian sialic crustal materials, while satisfying the observed Nd and Sr isotopic variations, fail to account for major trace element abundances. The combination of crustal assimilation and fractional crystalization is found to give a superior fit to the compositional data.

  19. Crustal processes of the Mid-Ocean Ridge

    Science.gov (United States)

    Ballard, Richard D.; Craig, H.; Edmond, J.; Einaudi, M.; Holcomb, R.; Holland, H.D.; Hopson, C.A.; Luyendyk, B.P.; Macdonald, K.; Morton, J.; Orcutt, J.; Sleep, N.

    1981-01-01

    Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 ??N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

  20. Crustal processes of the mid-ocean ridge.

    Science.gov (United States)

    1981-07-03

    Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 degrees N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

  1. The Effect of Thermal Cycling on Crystal-Liquid Separation During Lunar Magma Ocean Differentiation

    Science.gov (United States)

    Mills, Ryan D.

    2013-01-01

    Differentiation of magma oceans likely involves a mixture of fractional and equilibrium crystallization [1]. The existence of: 1) large volumes of anorthosite in the lunar highlands and 2) the incompatible- rich (KREEP) reservoir suggests that fractional crystallization may have dominated during differentiation of the Moon. For this to have occurred, crystal fractionation must have been remarkably efficient. Several authors [e.g. 2, 3] have hypothesized that equilibrium crystallization would have dominated early in differentiation of magma oceans because of crystal entrainment during turbulent convection. However, recent numerical modeling [4] suggests that crystal settling could have occurred throughout the entire solidification history of the lunar magma ocean if crystals were large and crystal fraction was low. These results indicate that the crystal size distribution could have played an important role in differentiation of the lunar magma ocean. Here, I suggest that thermal cycling from tidal heating during lunar magma ocean crystallization caused crystals to coarsen, leading to efficient crystal-liquid separation.

  2. A conversion of CO{sub 2}-ECBM related lab observations to reservoir requirements

    Energy Technology Data Exchange (ETDEWEB)

    Gensterblum, Y.; Merkel, A.; Busch, A. [RWTH Aachen Univ. (Germany). Inst. of Geology and Geochemistry of Petroleum and Coal; Krooss, B.M. [Shell Global Solutions International, Rijswijk (Netherlands)

    2013-08-01

    To predict a CBM production profile either during primary or secondary production, aspects like coal permeability and porosity, density, ash and moisture content, initial gas-in-place (GIP) (from canister desorption tests), gas sorption capacity from laboratory isotherms (to obtain gas saturations and desorption pressure), gas diffusivities, coal volumetrics (thickness and areal extent) need to be understood as a minimum requirement. When dealing with CO{sub 2}-ECBM selective adsorption, counter diffusion in the coal matrix, or coal shrinkage and swelling (from CH{sub 4} desorption and CO{sub 2} adsorption, respectively) and the influence of moisture need to be investigated in addition to the parameters above. During CO{sub 2}-ECBM processes, the areal distribution of the CO{sub 2} injected is accomplished by flow through the cleat network. When CO{sub 2} is entering the coal matrix by a combined sorption/diffusion process it will adsorb to the coal inner surface and at the same time replace part of the CH{sub 4}. This replacement occurs either by a reduction in the CH{sub 4} partial pressure or by a higher selective sorption of CO{sub 2} over CH{sub 4}. Because of a concentration gradient between CH{sub 4} in the matrix compared to the cleat system, CH{sub 4} diffuses from the coal matrix into the cleat system where, by pressure drawdown towards a production well, it can be produced. In this context this presentation summarizes gas (CO{sub 2}, CH{sub 4}) and water sorption on coal and specifically addresses the following topics: - CH{sub 4} saturation development in CBM reservoir with depth (thermodynamic considerations); - CO{sub 2}-ECBM 'sweet spot' identification; - CH{sub 4} and CO{sub 2} sorption capacity as a function depth and rank; - CO{sub 2} and CH{sub 4} sorption on natural coals and its dependence on coal specific parameters like coal rank, maceral composition or ash content (Busch and Gensterblum, 2011); - Water sorption on coal, its

  3. Post waterflood CO{sub 2} miscible flood in light oil, fluvial-dominated deltaic reservoir. Annual report, October 1, 1993--September 30, 1994

    Energy Technology Data Exchange (ETDEWEB)

    Bou-Mikael, S.

    1995-07-01

    Texaco Exploration and Production Inc. (TEPI) and the U.S. Department of Energy (DOE) entered into a cost sharing cooperative agreement to conduct an Enhanced Oil Recovery demonstration project at Port Neches. The field is located in Orange County near Beaumont, Texas. The project will demonstrate the effectiveness of the CO{sub 2}, miscible process in Fluvial Dominated Deltaic reservoirs. It will also evaluate the use of horizontal CO{sub 2} injection wells to improve the overall sweep efficiency. A data base of FDD reservoirs for the gulf coast region will be developed by LSU, using a screening model developed by Texaco Research Center in Houston. Finally, the results and the information gained from this project will be disseminated throughout the oil industry via a series of SPE papers and industry open forums. Reservoir characterization efforts for the Marginulina sand, are in progress utilizing conventional and advanced technologies including 3-D seismic. Sidewall and conventional. cores were cut and analyzed, lab tests were conducted on reservoir fluids, reservoir BHP pressure and reservoir voidage were monitored as shown. Texaco is utilizing the above data to develop a Stratamodel to best describe and characterize the reservoir and to use it as an input for the compositional simulator. The current compositional model is being revised to integrate the new data from the 3-D seismic and field performance under CO{sub 2} injection, to ultimately develop an accurate economic model. All facilities work has been completed and placed in service including the CO{sub 2} pipeline and metering equipment, CO{sub 2} injection and production equipment, water injection equipment, well work and injection/production lines. The horizontal injection well was drilled and completed on January 15, 1994. CO{sub 2} purchases from Cardox continue at an average rate of 3600 MCFD. The CO{sub 2} is being injected at line pressure of 1350 psi.

  4. Volcanic systems of Iceland and their magma source

    Science.gov (United States)

    Sigmarsson, Olgeir

    2017-04-01

    Several active hot-spot volcanoes produce magma from mantle sources which composition varies on decadal time scale. This is probably best demonstrated by the recent work of Pietruszka and collaborators on Kilauea, Hawaii. In marked contrast, basalt lavas from volcanic system in Iceland located above the presumed centre of the Iceland mantle plume have uniform isotope composition over the last 10 thousand years. Volcanic systems are composed of a central volcano and a fissure swarm, or a combination of both and they represent a fundamental component of the neovolcanic zones in Iceland. Four such systems, those of Askja, Bárðarbunga, Kverkfjöll and Grímsvötn in central Iceland were chosen for investigation. The last three have central volcanoes covered by the Vatnajökull ice-sheet whereas part of their fissure swarms is ice-free. Tephra produced during subglacial eruptions together with lavas from the fissure swarms of Holocene age have been collected and analysed for Sr, Nd and Th isotope ratios. Those volcanic formations that can be univocally correlated to a given volcanic system display uniform isotope ratio but different from one volcanic system to another. An exception to this regularity is that Askja products have isotope ratios indistinguishable from those of Gímsvötn, but since these volcanic systems lies far apart their lava fields do not overlap. A practical aspect of these findings was demonstrated during the rifting event of Bárðarbunga and fissure eruption forming the Holuhraun lava field. Relatively low, O isotope ratios in these basalts and heterogeneous macrocrystal composition have been ascribed to important metabasaltic crustal contamination with or without crystal mush recycling. In that case a surprisingly efficient magma mixing and melt homogenization must have occurred in the past beneath the volcanic systems. One possibility is that during the rapid deglaciation much mantle melting occurred and melts accumulated at the mantle

  5. Crustal CO2 liberation during the 2006 eruption and earthquake events at Merapi volcano, Indonesia

    Science.gov (United States)

    Troll, Valentin R.; Hilton, David R.; Jolis, Ester M.; Chadwick, Jane P.; Blythe, Lara S.; Deegan, Frances M.; Schwarzkopf, Lothar M.; Zimmer, Martin

    2012-06-01

    High-temperature volcanic gas is widely considered to originate from ascending, mantle-derived magma. In volcanic arc systems, crustal inputs to magmatic gases mainly occur via subducted sediments in the mantle source region. Our data from Merapi volcano, Indonesia imply, however, that during the April-October 2006 eruption significant quantities of CO2 were added from shallow crustal sources. We show that prior to the 2006 events, summit fumarole gas δ13C(CO2) is virtually constant (δ13C1994-2005 = -4.1 ± 0.3‰), but during the 2006 eruption and after the shallow Yogyakarta earthquake of late May, 2006 (M6.4; hypocentres at 10-15 km depth), carbon isotope ratios increased to -2.4 ± 0.2‰. This rise in δ13C is consistent with considerable addition of crustal CO2 and coincided with an increase in eruptive intensity by a factor of ˜3 to 5. We postulate that this shallow crustal volatile input supplemented the mantle-derived volatile flux at Merapi, intensifying and sustaining the 2006 eruption. Late-stage volatile additions from crustal contamination may thus provide a trigger for explosive eruptions independently of conventional magmatic processes.

  6. Magma replenishment and volcanic unrest inferred from the analysis of VT micro-seismicity and seismic velocity changes at Piton de la Fournaise Volcano

    Science.gov (United States)

    Brenguier, F.; Rivemale, E.; Clarke, D. S.; Schmid, A.; Got, J.; Battaglia, J.; Taisne, B.; Staudacher, T.; Peltier, A.; Shapiro, N. M.; Tait, S.; Ferrazzini, V.; Di Muro, A.

    2011-12-01

    Piton de la Fournaise volcano (PdF) is among the most active basaltic volcanoes worldwide with more than one eruption per year on average. Also, PdF is densely instrumented with short-period and broad-band seismometers as well as with GPS receivers. Continuous seismic waveforms are available from 1999. Piton de la Fournaise volcano has a moderate inter-eruptive seismic activity with an average of five detected Volcano-Tectonic (VT) earthquakes per day with magnitudes ranging from 0.5 to 3.5. These earthquakes are shallow and located about 2.5 kilometers beneath the edifice surface. Volcanic unrest is captured on average a few weeks before eruptions by measurements of increased VT seismicity rate, inflation of the edifice summit, and decreased seismic velocities from correlations of seismic noise. Eruptions are usually preceded by seismic swarms of VT earthquakes. Recently, almost 50 % of seismic swarms were not followed by eruptions. Within this work, we aim to gather results from different groups of the UnderVolc research project in order to better understand the processes of deep magma transfer, volcanic unrest, and pre-eruptive magma transport initiation. Among our results, we show that the period 1999-2003 was characterized by a long-term increase of VT seismicity rate coupled with a long-term decrease of seismic velocities. These observations could indicate a long-term replenishment of the magma storage area. The relocation of ten years of inter-eruptive micro-seismicity shows a narrow (~300 m long) sub-vertical fault zone thus indicating a conduit rather than an extended magma reservoir as the shallow magma feeder system. Also, we focus on the processes of short-term volcanic unrest and prove that magma intrusions within the edifice leading to eruptions activate specific VT earthquakes that are distinct from magma intrusions that do not lead to eruptions. We thus propose that, among the different pathways of magma transport within the edifice, only one will

  7. Os and S isotope studies of ultramafic rocks in the Duke Island Complex, Alaska: variable degrees of crustal contamination of magmas in an arc setting and implications for Ni-Cu-PGE sulfide mineralization

    Science.gov (United States)

    Stifter, Eric C.; Ripley, Edward M.; Li, Chusi

    2016-10-01

    The Duke Island Complex is one of the several "Ural-Alaskan" intrusions of Cretaceous age that occur along the coast of SE Alaska. Significant quantities of magmatic Ni-Cu-PGE sulfide mineralization are locally found in the complex, primarily within olivine clinopyroxenites. Sulfide mineralization is Ni-poor, consistent with petrologic evidence which indicates that sulfide saturation was reached after extensive olivine crystallization. Olivine clinopyroxenites were intruded by magmas that produced sulfide-poor, adcumulate dunites. As part of a study to investigate the potential for Ni-rich sulfide mineralization in association with the dunites, a Re-Os and S isotope study of the dunites, as well as sulfide mineralization in the olivine clinopyroxenites, was initiated. Importantly, recent drilling in the complex identified the presence of sulfidic and carbonaceous country rocks that may have been involved in the contamination of magmas and generation of sulfide mineralization. γOs (110 Ma) values of two sulfidic country rocks are 1022 and 2011. δ34S values of the country rocks range from -2.6 to -16.1 ‰. 187Os/188Os ratios of sulfide minerals in the mineralization hosted by olivine clinopyroxenites are variable and high, with γOs (110 Ma) values between 151 and 2059. Extensive interaction with Re-rich sedimentary country rocks is indicated. In contrast, γOs (110 Ma) values of the dunites are significantly lower, ranging between 2 and 16. 187Os/188Os ratios increase with decreasing Os concentration. This inverse relation is similar to that shown by ultramafic rocks from several arc settings, as well as altered abyssal dunites and peridotites. The relation may be indicative of magma derivation from a sub-arc mantle that had experienced metasomatism via slab-derived fluids. Alternatively, the relation may be indicative of minor contamination of magma by crustal rocks with low Os concentrations but high 187Os/188Os ratios. A third alternative is that the low Os

  8. Crustal structure in Tengchong Volcano-Geothermal Area, western Yunnan, China

    Science.gov (United States)

    Wang, Chun-Yong; Huangfu, Gang

    2004-02-01

    Based upon the deep seismic sounding profiles carried out in the Tengchong Volcano-Geothermal Area (TVGA), western Yunnan Province of China, a 2-D crustal P velocity structure is obtained by use of finite-difference inversion and forward travel-time fitting method. The crustal model shows that a low-velocity anomaly zone exists in the upper crust, which is related to geothermal activity. Two faults, the Longling-Ruili Fault and Tengchong Fault, on the profile extend from surface to the lower crust and the Tengchong Fault likely penetrates the Moho. Moreover, based on teleseismic receiver functions on a temporary seismic network, S-wave velocity structures beneath the geothermal field show low S-wave velocity in the upper crust. From results of geophysical survey, the crust of TVGA is characterized by low P-wave and S-wave velocities, low resistivity, high heat-flow value and low Q. The upper mantle P-wave velocity is also low. This suggests presence of magma in the crust derived from the upper mantle. The low-velocity anomaly in upper crust may be related to the magma differentiation. The Tengchong volcanic area is located on the northeast edge of the Indian-Eurasian plate collision zone, away from the eastern boundary of the Indian plate by about 450 km. Based on the results of this paper and related studies, the Tengchong volcanoes can be classified as plate boundary volcanoes.

  9. Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden.

    Science.gov (United States)

    Andersson, Magnus; Almqvist, Bjarne S G; Burchardt, Steffi; Troll, Valentin R; Malehmir, Alireza; Snowball, Ian; Kübler, Lutz

    2016-06-10

    Magma transport through the Earth's crust occurs dominantly via sheet intrusions, such as dykes and cone-sheets, and is fundamental to crustal evolution, volcanic eruptions and geochemical element cycling. However, reliable methods to reconstruct flow direction in solidified sheet intrusions have proved elusive. Anisotropy of magnetic susceptibility (AMS) in magmatic sheets is often interpreted as primary magma flow, but magnetic fabrics can be modified by post-emplacement processes, making interpretation of AMS data ambiguous. Here we present AMS data from cone-sheets in the Alnö carbonatite complex, central Sweden. We discuss six scenarios of syn- and post-emplacement processes that can modify AMS fabrics and offer a conceptual framework for systematic interpretation of magma movements in sheet intrusions. The AMS fabrics in the Alnö cone-sheets are dominantly oblate with magnetic foliations parallel to sheet orientations. These fabrics may result from primary lateral flow or from sheet closure at the terminal stage of magma transport. As the cone-sheets are discontinuous along their strike direction, sheet closure is the most probable process to explain the observed AMS fabrics. We argue that these fabrics may be common to cone-sheets and an integrated geology, petrology and AMS approach can be used to distinguish them from primary flow fabrics.

  10. Controls on Magmatic and Hydrothermal Processes at Yellowstone Supervolcano: The Wideband Magnetotelluric Component of an Integrated MT/Seismic Investigation

    Science.gov (United States)

    Schultz, A.; Bennington, N. L.; Bowles-martinez, E.; Imamura, N.; Cronin, R. A.; Miller, D. J.; Hart, L.; Gurrola, R. M.; Neal, B. A.; Scholz, K.; Fry, B.; Carbonari, R.

    2017-12-01

    Previous seismic and magnetotelluric (MT) studies beneath Yellowstone (YS) have provided insight into the origin and migration of magmatic fluids within the volcanic system. However, important questions remain concerning the generation of magmatism at YS, the migration and storage of these magmatic fluids, as well as their relationships to hydrothermal expressions. Analysis of regional-scale EarthScope MT data collected previously suggests a relative absence of continuity in crustal partial melt accumulations directly beneath YS. This is in contrast to some seismic interpretations, although such long-period MT data have limited resolving power in the upper-to-mid crustal section. A wideband MT experiment was designed as a component of an integrated MT/seismic project to examine: the origin and location of magmatic fluids at upper mantle/lower crustal depths, the preferred path of migration for these magmatic fluids into the mid- to upper-crust, the resulting distribution of the magma reservoir, the composition of the magma reservoir, and implications for future volcanism at YS. A high-resolution wideband MT survey was carried out in the YS region in the summer of 2017, with more than forty-five wideband stations installed within and immediately surrounding the YS National Park boundary. These data provided nearly six decades of bandwidth ( 10-3 Hz -to- 103 Hz). Extraordinary permitting restrictions prevented us from using conventional installation methods at many of our sites, and an innovative "no-dig" subaerial method of wideband MT was developed and used successfully. Using these new data along with existing MT datasets, we are inverting for the 3D resistivity structure at upper crustal through upper mantle scales at YS. Complementary to this MT work, a joint inversion for the 3D crustal velocity structure is being carried out using both ambient noise and earthquake travel time data. Taken together, these data should better constrain the crustal velocity

  11. Effect of pressure on Fe3+/ΣFe ratio in a mafic magma and consequences for magma ocean redox gradients

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H. L.; Hirschmann, M. M.; Cottrell, E.; Withers, A. C.

    2017-05-01

    Experiments establishing the effect of pressure on the Fe3+/ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO<sub>2sub> were performed from 100 kPa to 7 GPa and 1400–1750 °C. Fe3+/ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe3+/ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O’Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe3+ ions of ~5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe2+ ions, from ~5 to ~6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe3+/ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al., 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe3+/ΣFe applicable to high pressure glasses. Consistent with interpretations of the Mössbauer hyperfine parameters, XANES pre-edge peak features in high pressure glasses are owing chiefly to the effects of pressure on the coordination of Fe2+ ions from ~5.5 to ~6, with negligible effects evident for Fe3+ ions. We use the new data to construct a thermodynamic model relating the effects of oxygen fugacity and pressure on Fe3+/ΣFe. We apply this model to calculate variations in oxygen fugacity in isochemical (constant Fe3+/ΣFe) columns of magma representative of magma oceans, in which fO2 is fixed at the base by equilibration with molten Fe. These calculations

  12. Modeling CO<sub>2sub> Sequestration in Saline Aquifer and Depleted Oil Reservoir To Evaluate Regional CO<sub>2sub> Sequestration Potential of Ozark Plateau Aquifer System, South-Central Kansas

    Energy Technology Data Exchange (ETDEWEB)

    Watney, W. Lynn [University Of Kansas Center For Research, Inc. Lawrence, KS (United States); Rush, Jason [University Of Kansas Center For Research, Inc. Lawrence, KS (United States); Raney, Jennifer [University Of Kansas Center For Research, Inc. Lawrence, KS (United States)

    2014-09-30

    1. Drilled, cored, and logged three wells to the basement and collecting more than 2,700 ft of conventional core; obtained 20 mi2 of multicomponent 3D seismic imaging and merged and reprocessed more than 125 mi2 of existing 3D seismic data for use in modeling CO<sub>2sub>- EOR oil recovery and CO<sub>2sub> storage in five oil fields in southern Kansas. 2. Determined the technical feasibility of injecting and sequestering CO<sub>2sub> in a set of four depleted oil reservoirs in the Cutter, Pleasant Prairie South, Eubank, and Shuck fields in southwest Kansas; of concurrently recovering oil from those fields; and of quantifying the volumes of CO2 sequestered and oil recovered during the process. 3. Formed a consortium of six oil operating companies, five of which own and operate the four fields. The consortium became part of the Southwest Kansas CO<sub>2sub>-EOR Initiative for the purpose of sharing data, knowledge, and interest in understanding the potential for CO<sub>2sub>-EOR in Kansas. 4. Built a regional well database covering 30,000 mi2 and containing stratigraphic tops from ~90,000 wells; correlated 30 major stratigraphic horizons; digitized key wells, including wireline logs and sample logs; and analyzed more than 3,000 drill stem tests to establish that fluid levels in deep aquifers below the Permian evaporites are not connected to the surface and therefore pressures are not hydrostatic. Connectivity with the surface aquifers is lacking because shale aquitards and impermeable evaporite layers consist of both halite and anhydrite. 5. Developed extensive web applications and an interactive mapping system that do the following: a. Facilitate access to a wide array of data obtained in the study, including core descriptions and analyses, sample logs, digital (LAS) well logs, seismic data, gravity and magnetics maps, structural and stratigraphic maps, inferred fault traces, earthquakes, Class I and II disposal wells, and

  13. Unusual Iron Redox Systematics of Martian Magmas

    Science.gov (United States)

    Danielson, L.; Righter, K.; Pando, K.; Morris, R. V.; Graff, T.; Agresti, D.; Martin, A.; Sutton, S.; Newville, M.; Lanzirotti, A.

    2012-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite. Morris et al. proposed that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks. Magnetite stability in terrestrial magmas is well understood, as are the stabilities of FeO and Fe2O3 in terrestrial magmas. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas, we have undertaken an experimental study with two emphases. First, we determine the FeO and Fe2O3 contents of super- and sub-liquidus glasses from a shergottite bulk composition at 1 bar to 4 GPa, and variable fO2. Second, we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition.

  14. Magma heating by decompression-driven crystallization beneath andesite volcanoes.

    Science.gov (United States)

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-07

    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

  15. Formation of continental crust in a temporally linked arc magma system from 5 to 30 km depth: ~ 90 Ma plutonism in the Cascades Crystalline Core composite arc section

    Science.gov (United States)

    Ratschbacher, B. C.; Miller, J. S.; Kent, A. J.; Miller, R. B.; Anderson, J. L.; Paterson, S. R.

    2015-12-01

    Continental crust has an andesitic bulk composition with a mafic lower crust and a granodioritic upper crust. The formation of stratified continental crust in general and the vertical extent of processes active in arc crustal columns leading to the differentiation of primitive, mantle-derived melts entering the lower crust are highly debated. To investigate where in the crustal column magma mixing, fractionation, assimilation and crystal growth occur and to what extent, we study the ~ 90 Ma magmatic flare-up event of the Cascades arc, a magma plumbing system from ~ 5 to 30 km depth. We focus on three intrusive complexes, emplaced at different depths during major regional shortening in an exceptionally thick crust (≥ 55 km1) but which are temporally related: the upper crustal Black Peak intrusion (1-3 kbar at 3.7 to 11 km; ~ 86.8 to 91.7 Ma2), the mid-crustal Mt. Stuart intrusion (3.5-4.0 kbar at 13 to 15 km; 90.8 and 96.3 Ma3) and the deep crustal Tenpeak intrusion (7 to 10 kbar at 25 to 37 km; 89.7 to 92.3 Ma4). These intrusive complexes are well characterized by geochronology showing that they have been constructed incrementally by multiple magma batches over their lifespans and thus allow the monitoring and comparison of geochemical parameters over time at different depths. We use a combination of whole rock major and trace element data and isotopes combined with detailed investigation of amphibole, which has been recognized to be important in the generation of calc-alkaline rocks in arcs to test the following hypotheses: (a) compositional bimodality is produced in the lower crust, whereas upper crustal levels are dominated by mixing to form intermediate compositions, or (b) differentiation occurs throughout the crustal column with different crystallizing phases and their compositions controlling the bulk chemistry. 1. Miller et al. 2009: GSA Special Paper 456, p. 125-149 2. Shea 2014: PhD thesis, Massachusetts Institute of Technology 3. Anderson et al. 2012

  16. Geochemical differentiation processes for arc magma of the Sengan volcanic cluster, Northeastern Japan, constrained from principal component analysis

    Science.gov (United States)

    Ueki, Kenta; Iwamori, Hikaru

    2017-10-01

    In this study, with a view of understanding the structure of high-dimensional geochemical data and discussing the chemical processes at work in the evolution of arc magmas, we employed principal component analysis (PCA) to evaluate the compositional variations of volcanic rocks from the Sengan volcanic cluster of the Northeastern Japan Arc. We analyzed the trace element compositions of various arc volcanic rocks, sampled from 17 different volcanoes in a volcanic cluster. The PCA results demonstrated that the first three principal components accounted for 86% of the geochemical variation in the magma of the Sengan region. Based on the relationships between the principal components and the major elements, the mass-balance relationships with respect to the contributions of minerals, the composition of plagioclase phenocrysts, geothermal gradient, and seismic velocity structure in the crust, the first, the second, and the third principal components appear to represent magma mixing, crystallizations of olivine/pyroxene, and crystallizations of plagioclase, respectively. These represented 59%, 20%, and 6%, respectively, of the variance in the entire compositional range, indicating that magma mixing accounted for the largest variance in the geochemical variation of the arc magma. Our result indicated that crustal processes dominate the geochemical variation of magma in the Sengan volcanic cluster.

  17. Geophysical Investigations of Crustal and Upper Mantle Structure of Oceanic Intraplate Volcanoes (OIVs)

    Science.gov (United States)

    Robinson, A. H.; Peirce, C.; Funnell, M.; Watts, A. B.; Grevemeyer, I.

    2016-12-01

    Oceanic intraplate volcanoes (OIVs) represent a record of the modification of the oceanic crust by volcanism related to a range of processes including hot-spots, small scale mantle convection, and localised lithospheric extension. Geophysical studies of OIVs show a diversity in crustal and upper mantle structures, proposed to exist on a spectrum between two end-members where the main control is the age of the lithosphere at the time of volcanism. This hypothesis states that where the lithosphere is older, colder, and thicker it is more resistant to vertical magmatism than younger, hotter, thinner lithosphere. It is suggested that the Moho acts as a density filter, permitting relatively buoyant magma to vertically intrude the crust, but preventing denser magma from ascending to shallow levels. A key control may therefore be the melting depth, known to affect magma composition, and itself related to lithosphere age. Combined geophysical approaches allow us to develop robust models for OIV crustal structures with quantifiable resolution and uncertainty. As a case study, we present results from a multi-approach geophysical experiment at the Louisville Ridge Seamount Chain, believed to have formed on young (travel-time modelling of picked arrivals, is tested against reflection and gravity data. We compare our observations with studies of other OIVs to test whether lithospheric age controls OIV structure. Comparisons are limited by the temporal and spatial distribution of lithosphere and volcano ages, but suggest the hypothesis does not hold for all OIV features. While age may be the main control on OIV structure, as it determines lithosphere thermal and mechanical properties, other factors such as thermal rejuvenation, mechanical weakening, and volcano load size and distribution, may also come into play.

  18. Influences of magma chamber ellipticity on ring fracturing and eruption at collapse calderas

    International Nuclear Information System (INIS)

    Holohan, Eoghan P; Walsh, John J; Vries, Benjamin van Wyk de; Troll, Valentin R; Walter, Thomas R

    2008-01-01

    Plan-view ellipticity of a pre-caldera magma reservoir, and its influence on the development of caldera ring fracturing and eruptive behaviour, have not previously been subjected to dedicated evaluation. We experimentally simulated caldera collapse into elliptical magma chambers and found that collapse into highly-elliptical chambers produced a characteristic pattern of ring-fault localization and lateral propagation. Although results are preliminary, the general deformation pattern for elliptical resurgence shows strong similarities to elliptical collapse. Ring faults accommodating uplift again initiate around the chamberos short axis and are reverse, but dip inward. Field and geophysical observations at several elliptical calderas of varying scale (e.g. Long Valley, Katmai, and Rabaul calderas) are consistent with a control from elliptical magma chamber geometry on ring fracturing and eruption, as predicted from our experiments.

  19. Influences of magma chamber ellipticity on ring fracturing and eruption at collapse calderas

    Energy Technology Data Exchange (ETDEWEB)

    Holohan, Eoghan P; Walsh, John J [Fault Analysis Group, School of Geological Sciences, University College Dublin, Belfield, Dublin 4 (Ireland); Vries, Benjamin van Wyk de [Laboratoire Magmas et Volcans, 5 rue Kessler, 63038 Clermont-Ferrand (France); Troll, Valentin R [Department of Earth Sciences, Uppsala University, SE-752 36, Uppsala (Sweden); Walter, Thomas R [GFZ Potsdam, Telegrafenberg, Potsdam, D-14473 (Germany)], E-mail: Eoghan.Holohan@ucd.ie

    2008-10-01

    Plan-view ellipticity of a pre-caldera magma reservoir, and its influence on the development of caldera ring fracturing and eruptive behaviour, have not previously been subjected to dedicated evaluation. We experimentally simulated caldera collapse into elliptical magma chambers and found that collapse into highly-elliptical chambers produced a characteristic pattern of ring-fault localization and lateral propagation. Although results are preliminary, the general deformation pattern for elliptical resurgence shows strong similarities to elliptical collapse. Ring faults accommodating uplift again initiate around the chamberos short axis and are reverse, but dip inward. Field and geophysical observations at several elliptical calderas of varying scale (e.g. Long Valley, Katmai, and Rabaul calderas) are consistent with a control from elliptical magma chamber geometry on ring fracturing and eruption, as predicted from our experiments.

  20. Modeling CO<sub>2sub> Sequestration in Saline Aquifer and Depleted Oil Reservoir To Evaluate Regional CO<sub>2sub> Sequestration Potential of Ozark Plateau Aquifer System, South-Central Kansas

    Energy Technology Data Exchange (ETDEWEB)

    Watney, W. Lynn [University Of Kansas Center For Research, Inc. Lawrence, KS (United States)

    2014-09-30

    1. Drilled, cored, and logged three wells to the basement and collecting more than 2,700 ft of conventional core; obtained 20 mi2 of multicomponent 3D seismic imaging and merged and reprocessed more than 125 mi2 of existing 3D seismic data for use in modeling CO<sub>2sub>- EOR oil recovery and CO<sub>2sub> storage in five oil fields in southern Kansas. 2. Determined the technical feasibility of injecting and sequestering CO<sub>2sub> in a set of four depleted oil reservoirs in the Cutter, Pleasant Prairie South, Eubank, and Shuck fields in southwest Kansas; of concurrently recovering oil from those fields; and of quantifying the volumes of CO2 sequestered and oil recovered during the process. 3. Formed a consortium of six oil operating companies, five of which own and operate the four fields. The consortium became part of the Southwest Kansas CO<sub>2sub>-EOR Initiative for the purpose of sharing data, knowledge, and interest in understanding the potential for CO<sub>2sub>-EOR in Kansas. 4. Built a regional well database covering 30,000 mi2 and containing stratigraphic tops from ~90,000 wells; correlated 30 major stratigraphic horizons; digitized key wells, including wireline logs and sample logs; and analyzed more than 3,000 drill stem tests to establish that fluid levels in deep aquifers below the Permian evaporites are not connected to the surface and therefore pressures are not hydrostatic. Connectivity with the surface aquifers is lacking because shale aquitards and impermeable evaporite layers consist of both halite and anhydrite. 5. Developed extensive web applications and an interactive mapping system that do the following: a. Facilitate access to a wide array of data obtained in the study, including core descriptions and analyses, sample logs, digital (LAS) well logs, seismic data, gravity and magnetics maps, structural and stratigraphic maps, inferred fault traces, earthquakes, Class I and II disposal wells, and

  1. The origin and evolution of silicic magmas during continental rifting: new constraints from trace elements and oxygen isotopes from Ethiopian volcanoes

    Science.gov (United States)

    Hutchison, W.; Boyce, A.; Mather, T. A.; Pyle, D. M.; Yirgu, G.; Gleeson, M. L.

    2017-12-01

    The petrologic diversity of rift magmas is generated by two key processes: interaction with the crust via partial melting or assimilation; and closed-system fractional crystallization of the parental magma. It is not yet known whether these two petrogenetic processes vary spatially between different rift settings, and whether there are any significant secular variations during rift evolution. The Ethiopian Rift is the ideal setting to test these hypotheses because it captures the transition from continental rifting to sea-floor spreading and has witnessed the eruption of large volumes of mafic and silicic volcanic rocks since 30 Ma. We use new oxygen isotope (δ18O) and trace element data to fingerprint fractional crystallisation and partial crustal melting processes in Ethiopia and evaluate spatial variations between three active rift segments. δ18O measurements are used to examine partial crustal melting processes. We find that most δ18O data from basalts to rhyolites fall within the bounds of modelled fractional crystallization trajectories (i.e., 5.5-6.5 ‰). Few samples deviate from this trend, emphasising that fractional crystallization is the dominant petrogenetic processes and that little fusible Precambrian crustal material (δ18O of 7-18 ‰) remain to be assimilated beneath the magmatic segments. Trace element systematics (e.g., Ba, Sr, Rb, Th and Zr) further underscore the dominant role of fractional crystallization but also reveal important variations in the degree of melt evolution between the volcanic systems. We find that the most evolved silicic magmas, i.e., those with greatest peralkalinity (molar Na2O+K2O>Al2O3), are promoted in regions of lowest magma flux off-axis and along rift. Our findings provide new information on the nature of the crust beneath Ethiopia's active magmatic segments and also have relevance for understanding ancient rift zones and the geotectonic settings that promote genesis of economically-valuable mineral deposits.

  2. History of CO/sub 2/

    Energy Technology Data Exchange (ETDEWEB)

    Degens, E T

    1979-01-01

    Upon arrival on earth, the reduced carbon pool split into a series of compartments: core, mantle, crust, hydrosphere, atmosphere, and biosphere. This distribution pattern is caused by the ability of carbon to adjust structurally to a wide range of pressure and temperature, and to form simple and complex molecules with oxygen, hydrogen and nitrogen. Transformation also involved oxidation of carbon to CO/sub 2/ which is mediated at depth by minerals, such as magnetite, and by water vapor above critical temperature. Guided by mineral-organic interactions, simple carbon compounds evolved in near surface environments towards physiologically interesting biochemicals. Life, as an autocatalytic system, is considered an outgrowth of such a development. This article discusses environmental parameters that control the CO/sub 2/ system, past and present. Mantle and crustal evolution is the dynamo recharging the CO/sub 2/ in sea and air; the present rate of CO/sub 2/ release from the magma is 0.05 x 10/sup 15/ g C per year. Due to the enormous buffer capacity of the chemical system ocean, such rates are too small to seriously effect the level of CO/sub 2/ in our atmosphere. In the light of geological field data and stable isotope work, it is concluded that the CO/sub 2/ content in the atmosphere has remained fairly uniform since early Precambrian time; CO/sub 2/ should thus have had little impact on paleoclimate. In contrast, the massive discharge of man-made CO/sub 2/ into our atmosphere may have serious consequences for climate, environment and society in the years to come.

  3. Using Earthquake Location and Coda Attenuation Analysis to Explore Shallow Structures Above the Socorro Magma Body, New Mexico

    Science.gov (United States)

    Schmidt, J. P.; Bilek, S. L.; Worthington, L. L.; Schmandt, B.; Aster, R. C.

    2017-12-01

    The Socorro Magma Body (SMB) is a thin, sill-like intrusion with a top at 19 km depth covering approximately 3400 km2 within the Rio Grande Rift. InSAR studies show crustal uplift patterns linked to SMB inflation with deformation rates of 2.5 mm/yr in the area of maximum uplift with some peripheral subsidence. Our understanding of the emplacement history and shallow structure above the SMB is limited. We use a large seismic deployment to explore seismicity and crustal attenuation in the SMB region, focusing on the area of highest observed uplift to investigate the possible existence of fluid/magma in the upper crust. We would expect to see shallower earthquakes and/or higher attenuation if high heat flow, fluid or magma is present in the upper crust. Over 800 short period vertical component geophones situated above the northern portion of the SMB were deployed for two weeks in 2015. This data is combined with other broadband and short period seismic stations to detect and locate earthquakes as well as to estimate seismic attenuation. We use phase arrivals from the full dataset to relocate a set of 33 local/regional earthquakes recorded during the deployment. We also measure amplitude decay after the S-wave arrival to estimate coda attenuation caused by scattering of seismic waves and anelastic processes. Coda attenuation is estimated using the single backscatter method described by Aki and Chouet (1975), filtering the seismograms at 6, 9 and 12 Hz center frequencies. Earthquakes occurred at 2-13 km depth during the deployment, but no spatial patterns linked with the high uplift region were observed over this short duration. Attenuation results for this deployment suggest Q ranging in values of 130 to 2000, averaging around Q of 290, comparable to Q estimates of other studies of the western US. With our dense station coverage, we explore attenuation over smaller scales, and find higher attenuation for stations in the area of maximum uplift relative to stations

  4. Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa

    Science.gov (United States)

    Günther, T.; Haase, K. M.; Klemd, R.; Teschner, C.

    2018-06-01

    We report a new whole-rock dataset of major and trace element abundances and 87Sr/86Sr-143Nd/144Nd isotope ratios for basaltic to rhyolitic lavas from the Rooiberg continental large igneous province (LIP). The formation of the Paleoproterozoic Rooiberg Group is contemporaneous with and spatially related to the layered intrusion of the Bushveld Complex, which stratigraphically separates the volcanic succession. Our new data confirm the presence of low- and high-Ti mafic and intermediate lavas (basaltic—andesitic compositions) with > 4 wt% MgO, as well as evolved rocks (andesitic—rhyolitic compositions), characterized by MgO contents of N, Nb/Y and Ti/Y), indicating a different petrogenesis. MELTS modelling shows that the evolved lavas are formed by fractional crystallization from the mafic low-Ti lavas at low-to-moderate pressures ( 4 kbar). Primitive mantle-normalized trace element patterns of the Rooiberg rocks show an enrichment of large ion lithophile elements (LILE), rare-earth elements (REE) and pronounced negative anomalies of Nb, Ta, P, Ti and a positive Pb anomaly. Unaltered Rooiberg lavas have negative ɛNdi (- 5.2 to - 9.4) and radiogenic ɛSri (6.6 to 105) ratios (at 2061 Ma). These data overlap with isotope and trace element compositions of purported parental melts to the Bushveld Complex, especially for the lower zone. We suggest that the Rooiberg suite originated from a source similar to the composition of the B1-magma suggested as parental to the Bushveld Lower Zone, or that the lavas represent eruptive successions of fractional crystallization products related to the ultramafic cumulates that were forming at depth. The Rooiberg magmas may have formed by 10-20% crustal assimilation by the fractionation of a very primitive mantle-derived melt within the upper crust of the Kaapvaal Craton. Alternatively, the magmas represent mixtures of melts from a primitive, sub-lithospheric mantle plume and an enriched sub-continental lithospheric mantle (SCLM

  5. Advanced Reservoir Characterization and Evaluation of CO{sub 2} Gravity Drainage in the Naturally Fractured Spraberry Trend Area, Class III

    Energy Technology Data Exchange (ETDEWEB)

    Knight, Bill; Schechter, David S.

    2001-11-19

    The goal of this project was to assess the economic feasibility of CO{sub 2} flooding the naturally fractured Spraberry Trend Area in west Texas. This objective was accomplished through research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interactions in the reservoirs, (3) reservoir performance analysis, and (4) experimental investigations on CO{sub 2} gravity drainage in Spraberry whole cores. The four areas have been completed and reported in the previous annual reports. This report provides the results of the final year of the project including two SPE papers (SPE 71605 and SPE 71635) presented in the 2001 SPE Annual Meeting in New Orleans, two simulation works, analysis of logging observation wells (LOW) and progress of CO{sub 2} injection.

  6. Crustal contributions to arc magmatism in the Andes of Central Chile

    Science.gov (United States)

    Hildreth, W.; Moorbath, S.

    1988-01-01

    Fifteen andesite-dacite stratovolcanoes on the volcanic front of a single segment of the Andean arc show along-arc changes in isotopic and elemental ratios that demonstrate large crustal contributions to magma genesis. All 15 centers lie 90 km above the Benioff zone and 280??20 km from the trench axis. Rate and geometry of subduction and composition and age of subducted sediments and seafloor are nearly constant along the segment. Nonetheless, from S to N along the volcanic front (at 57.5% SiO2) K2O rises from 1.1 to 2.4 wt %, Ba from 300 to 600 ppm, and Ce from 25 to 50 ppm, whereas FeO*/MgO declines from >2.5 to 1.4. Ce/Yb and Hf/Lu triple northward, in part reflecting suppression of HREE enrichment by deep-crustal garnet. Rb, Cs, Th, and U contents all rise markedly from S to N, but Rb/Cs values double northward - opposite to prediction were the regional alkali enrichment controlled by sediment subduction. K/Rb drops steeply and scatters greatly within many (biotite-free) andesitic suites. Wide diversity in Zr/Hf, Zr/Rb, Ba/Ta, and Ba/La within and among neighboring suites (which lack zircon and alkali feldspar) largely reflects local variability of intracrustal (not slab or mantle) contributions. Pb-isotope data define a limited range that straddles the Stacey-Kramers line, is bracketed by values of local basement rocks, in part plots above the field of Nazca plate sediment, and shows no indication of a steep (mantle+sedimentary) Pb mixing trend. 87Sr/86Sr values rise northward from 0.7036 to 0.7057, and 143Nd/144Nd values drop from 0.5129 to 0.5125. A northward climb in basal elevation of volcanic-front edifices from 1350 m to 4500 m elevation coincides with a Bougueranomaly gradient from -95 to -295 mgal, interpreted to indicate thickening of the crust from 30-35 km to 50-60 km. Complementary to the thickening crust, the mantle wedge beneath the front thins northward from about 60 km to 30-40 km (as slab depth is constant). The thick northern crust contains

  7. Isotopic tracers of sources, wells and of CO{sub 2} reactivity in geological reservoirs; Tracage isotopique des sources, puits et de la reactivite du CO{sub 2} dans les reservoirs geologiques

    Energy Technology Data Exchange (ETDEWEB)

    Assayag, N

    2006-12-15

    The aim of this research works consisted in studying the behaviour of the carbonate system (dissolved inorganic carbon: DIC) following a CO{sub 2} injection (artificial or natural), in geological reservoirs. One part of the study consisted in improving an analytical protocol for the measurement of {delta} {sup 13}C DIC and DIC, using a continuous flow mass spectrometer. As a first study, we have focused our attention on the Pavin Lake (Massif Central, France). Owing to its limnologic characteristics (meromictic lake) and a deep volcanic CO{sub 2} contribution, it can be viewed as a natural analogue of reservoir storing important quantities of CO{sub 2} in the bottom part. Isotopic measurements ({delta} {sup 18}O, {delta} {sup 13}C DIC) allowed to better constrain the dynamics of the lake (stratification, seasonal variations), the magnitudes of biological activities (photosynthesis, organic matter decay, methane oxidation, methano-genesis), carbon sources (magmatic, methano-genetic), and the hydrological budgets (sub-lacustrine inputs). The second study was conducted on the Lamont-Doherty test well site (NY, USA). It includes an instrumental borehole which cuts through most of the section of the Palisades sill and into the Newark Basin sediments. Single well push-pull tests were performed: a test solution containing conservative tracers and a reactive tracer (CO{sub 2}) was injected at a permeable depth interval located in basaltic and meta sedimentary rocks. After an incubation period, the test solution/groundwater mixture was extracted from the hydraulically isolated zone. Isotopic measurements ({delta} {sup 18}O, {delta} {sup 13}C DIC) confronted to chemical data (major elements) allowed to investigate the extent of in-situ CO{sub 2}-water-rock interactions: essentially calcite dissolution and at a lesser extend silicate dissolution...and for one of the test, CO{sub 2} degassing. (author)

  8. Crustal deformation and volcanism at active plate boundaries

    Science.gov (United States)

    Geirsson, Halldor

    Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and

  9. Onset of solid state mantle convection and mixing during magma ocean solidification

    Science.gov (United States)

    Maurice, Maxime; Tosi, Nicola; Samuel, Henri; Plesa, Ana-Catalina; Hüttig, Christian; Breuer, Doris

    2017-04-01

    The fractional crystallization of a magma ocean can cause the formation of a compositional layering that can play a fundamental role for the subsequent long-term dynamics of the interior, for the evolution of geochemical reservoirs, and for surface tectonics. In order to assess to what extent primordial compositional heterogeneities generated by magma ocean solidification can be preserved, we investigate the solidification of a whole-mantle Martian magma ocean, and in particular the conditions that allow solid state convection to start mixing the mantle before solidification is completed. To this end, we performed 2-D numerical simulations in a cylindrical geometry. We treat the liquid magma ocean in a parametrized way while we self-consistently solve the conservation equations of thermochemical convection in the growing solid cumulates accounting for pressure-, temperature- and, where it applies, melt-dependent viscosity as well as parametrized yield stress to account for plastic yielding. By testing the effects of different cooling rates and convective vigor, we show that for a lifetime of the liquid magma ocean of 1 Myr or longer, the onset of solid state convection prior to complete mantle crystallization is likely and that a significant part of the compositional heterogeneities generated by fractionation can be erased by efficient mantle mixing.

  10. The Jeffers Brook diorite-granodiorite pluton: style of emplacement and role of volatiles at various crustal levels in Avalonian appinites, Canadian Appalachians

    Science.gov (United States)

    Pe-Piper, Georgia; Piper, David J. W.

    2018-04-01

    Small appinite plutons ca. 610 Ma outcrop in the peri-Gondwanan Avalon terrane of northern Nova Scotia, with different structural levels exposed. Field mapping shows that the Jeffers Brook pluton is a laccolith emplaced along an upper crustal thrust zone, likely in a dilational jog in a regional dextral strike-slip system. The oldest rocks are probably mafic sills, which heated the area facilitating emplacement of intermediate magmas. Cross-cutting relationships show that both mafic and intermediate magmas were supplied throughout the history of pluton emplacement. The modal composition, mineral chemistry, and bulk chemistry of gabbro, diorite, tonalite, granodiorite, and granite have been studied in the main plutonic phases, dykes, and sills, and mafic microgranular enclaves. As with the type appinites in the Scottish Caledonides, the pluton shows evidence of high water content: the dominance of hornblende, locally within pegmatitic texture; vesicles and irregular felsic patches in enclaves; and late aplite dykes. Analyzed mafic microgranular enclaves are geochemically similar to larger diorite bodies in the pluton. Tonalite-granodiorite is distinct from the diorite in trace-element geochemistry and radiogenic isotopes. Elsewhere to the east, similar rocks of the same age form vertically sheeted complexes in major shear zones; hornblende chemistry shows that they were emplaced at a deeper upper crustal level. This implies that little of the observed geochemical variability in the Jeffers Brook pluton was developed within the pluton. The general requirements to form appinites are proposed to be small magma volumes of subduction-related magmas that reach the upper crust because of continual heating by mafic magmas moving through strike-slip fault pathways and trapping of aqueous fluids rather than venting through volcanic activity.

  11. Magmatic Longevity Constrained by ID-TIMS U-Pb Dating of Zircon and Titanite

    Science.gov (United States)

    Szymanowski, D.; Wotzlaw, J. F.; Ellis, B. S.; Bachmann, O.; Von Quadt, A.

    2016-12-01

    Clues about the timescales and thermal conditions associated with the growth and evacuation of large silicic magma reservoirs are frequently drawn from radiometric dating, diffusion modelling, or thermomechanical modelling. A growing amount of petrological and geochronological evidence, supported by thermal modelling, suggests that many silicic magma reservoirs may exist for some 104-106 years in the form of high-crystallinity mushes at relatively low temperatures ( 700-750°C; [1-3]). Geochronological studies addressing this issue typically utilise the U-Pb system in zircon capable of recording extended periods of crystallisation, particularly in evolved calc-alkaline systems that spend most of their lifetime zircon-saturated. In this study, we integrate U-Pb dating of zircon and titanite to investigate the longevity of the magma reservoir that produced the Kneeling Nun Tuff, a 35 Ma, >900 km3 crystal-rich rhyolitic super-eruption from the Mogollon-Datil volcanic field in New Mexico (USA). High-precision ID-TIMS U-Pb dates of single crystals of both zircon and titanite independently record a continuous crystallisation history over >400,000 years. We combine the dating of both accessory phases with textural, major, trace element and isotopic studies of single crystals, placing tight constraints on the thermal conditions of magma accumulation and storage while recording differentiation and rejuvenation processes within the magma reservoir. The results suggest a protracted `cool' upper-crustal storage of magma prior to the Kneeling Nun Tuff eruption followed by a melting event which reduced the magma crystallinity and conditioned it for eruption. [1] Bachmann & Bergantz (2004), J. Petrol. 45, 1565-1582. [2] Gelman et al. (2013), Geology 41, 759-762. [3] Cooper & Kent (2014), Nature 506, 480-483.

  12. Magma Expansion and Fragmentation in a Propagating Dike (Invited)

    Science.gov (United States)

    Jaupart, C. P.; Taisne, B.

    2010-12-01

    The influence of magma expansion due to volatile exsolution and gas dilation on dike propagation is studied using a new numerical code. Many natural magmas contain sufficient amounts of volatiles for fragmentation to occur well below Earth's surface. Magma fragmentation has been studied for volcanic flows through open conduits but it should also occur within dikes that rise towards Earth's surface. We consider the flow of a volatile-rich magma in a hydraulic fracture. The mixture of melt and gas is treated as a compressible viscous fluid below the fragmentation level and as a gas phase carrying melt droplets above it. A numerical code solves for elastic deformation of host rocks, the flow of the magmatic mixture and fracturing at the dike tip. With volatile-free magma, a dike fed at a constant rate in a uniform medium adopts a constant shape and width and rises at a constant velocity. With volatiles involved, magma expands and hence the volume flux of magma increases. With no fragmentation, this enhanced flux leads to acceleration of the dike. Simple scaling laws allow accurate predictions of dike width and ascent rate for a wide range of conditions. With fragmentation, dike behavior is markedly different. Due to the sharp drop of head loss that occurs in gas-rich fragmented material, large internal overpressures develop below the tip and induce swelling of the nose region, leading to deceleration of the dike. Thus, the paradoxical result is that, with no viscous impediment on magma flow and a large buoyancy force, the dike stalls. This process may account for some of the tuffisite veins and intrusions that are found in and around magma conduits, notably in the Unzen drillhole, Japan. We apply these results to the two-month long period of volcanic unrest that preceded the May 1980 eruption of Mount St Helens. An initial phase of rapid earthquake migration from the 7-8 km deep reservoir to shallow levels was followed by very slow progression of magma within the

  13. Hf and Nd Isotope Evidence for Production of an Incompatible Trace Element Enriched Crustal Reservoir in Early Earth (Invited)

    Science.gov (United States)

    Brandon, A. D.; Debaille, V.; Lapen, T. J.

    2010-12-01

    The final significant stage of accretion of the Earth was likely a collision between proto-Earth and a Mars sized impactor that formed the Moon. This event is thought to have produced enough thermal energy to melt all or most of the Earth, with a consequent magma ocean (MO). During subsequent cooling, the Earth would have formed its protocrust and corresponding mantle lithosphere, consisting of solidified basalt-komatiitic melt, in combination with buoyant cumulates and late stage residual melts from the MO. Relative to the convecting mantle, portions of this protolithosphere are likely to have been enriched in incompatible trace elements (ITE) in sufficient quantities to contain a significant amount of the bulk Earth’s budget for rare earth elements, U, Th, and Hf. If the protolithosphere was negatively buoyant, it may have overturned at or near the final stages of MO crystallization and a significant portion of that material may have been transported into the deep mantle where it resided and remixed into the convecting mantle over Earth history [1,2]. If the protolithosphere remained positively buoyant, its crust would have likely begun to erode from surface processes, and subsequently recycled back into the mantle over time as sediment and altered crust, once a subduction mechanism arose. The Nd and Hf isotopic compositions of Earth’s earliest rocks support the idea that an early-formed ITE-enriched reservoir was produced. The maxima in 142Nd/144Nd for 3.85 to 3.64 Ga rocks from Isua, Greenland decreases from +20 ppm to +12 ppm relative to the present day mantle value, respectively [3]. This indicates mixing of an early-formed ITE enriched reservoir back into the convecting mantle. In addition, zircons from the 3.1 Ga Jack Hills conglomerate indicate that material with an enriched 176Lu/177Hf of ~0.02 and an age of 4.4 Ga or greater was present at the Earth’s surface over the first 2 Ga of Earth history, supporting the scenario of a positively buoyant

  14. Magma Fertility is the First-Order Factor for the Formation of Porphyry Cu±Au Deposits

    Science.gov (United States)

    Park, J. W.; Campbell, I. H.; Malaviarachchi, S. P. K.; Cocker, H.; Nakamura, E.; Kay, S. M.

    2017-12-01

    Magma fertility, the metal abundance in magma, has been considered to be one of the key factors for the formation of porphyry Cu±Au deposits. In this study we provide clear evidence to support the hypothesis that the platinum group element (PGE) can be used to distinguish barren from ore-bearing Cu±Au felsic suites. We determined the PGE contents of three barren volcanic and subvolcanic suites from Argentina and Japan, and compare the results with two porphyry Cu-bearing subvolcanic suites from Chile and two porphyry Cu-Au-bearing suites from Australia. The barren suites are significantly depleted in PGE abundances by the time of fluid exsolution, which is attributed to early sulfide saturation at mid to lower crust depths or assimilation of chalcophile element-poor crustal materials. Barren magma, produced by melting continental crust, may have been initially deficient in chalcophile elements. In contrast, the Cu±Au ore-bearing suites contain at least an order of magnitude higher PGE contents than those of the barren suites by the time of fluid saturation. They are characterized by late sulfide saturation in a shallow magma chamber, which allows the chalcophile elements to concentrate in the fractionating magma from which they are sequestered by ore-forming fluids. We suggest the Pd/MgO and Pd/Pt ratios of igneous rocks can be used as magma fertility indicators, and to distinguish between barren, porphyry Cu and porphyry Cu-Au magmatic systems.

  15. Investigating the effect of steam, CO{sub 2}, and surfactant on the recovery of heavy oil reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Tian, S.; He, S. [China Univ. of Petroleum, Beijing (China). MOE Key Laboratory of Petroleum Engineering; Qu, L. [Shengli Oil Field Co. (China)]|[SINOPEC, Shengli (China)

    2008-10-15

    This paper presented the results of a laboratory study and numerical simulation in which the mechanisms of steam injection with carbon dioxide (CO{sub 2}) and surfactant were investigated. The incremental recoveries of 4 different scenarios were compared and analyzed in terms of phase behaviour. The study also investigated the effect of CO{sub 2} dissolution in oil and water; variation of properties of CO{sub 2}-oil phase equilibrium and CO{sub 2}-water phase equilibrium; variation of viscosity; and, oil volume and interfacial tension (IFT) during the recovery process. The expansion of a steam and CO{sub 2} front was also examined. A field application case of a horizontal well in a heavy oil reservoir in Shengli Oilfield in China was used to determine the actual dynamic performance of the horizontal well and to optimize the injection parameters of the CO{sub 2} and surfactant. The study revealed that oil recovery with the simultaneous injection of steam, CO{sub 2} and surfactant was higher than that of steam injection, steam with CO{sub 2} and steam with surfactant. The improved flow performance in super heavy oil reservoirs could be attributed to CO{sub 2} dissolution in oil which can swell the oil and reduce oil viscosity significantly. The proportion of CO{sub 2} in the free gas phase, oil phase and water phase varies with changes in reservoir pressure and temperature. CO{sub 2} decreases the temperature of the steam slightly, while the surfactant decreases the interfacial tension and helps to improve oil recovery. The study showed that the amount of injected CO{sub 2} and steam has a large effect on heavy oil recovery. Although oil production was found to increase with an increase in injected amounts, the ratio of oil to injected fluids must be considered to achieve optimum recovery. High steam quality and temperature can also improve super heavy oil recovery. The oil recovery was less influenced by the effect of the surfactant than by the effect of CO{sub 2

  16. The Transition from Volcanic to Rift Dominated Crustal Breakup - From the Vøring Plateau to the Lofoten Margin, Norway

    Science.gov (United States)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.; Flueh, E.; Murai, Y.

    2017-12-01

    The Vøring Plateau was part of the Northeast Atlantic igneous province (NAIP) during early Cenozoic crustal breakup. Crustal breakup at the Vøring Plateau occurred marginal to the deep Cretaceous basins on the shelf, with less extension of the crust. Intrusive magmatism and oceanic crust up to three times normal thickness caused a period of sub-aerial magmatism around breakup time. The transition to the Lofoten Margin is rapid to a deep-water plain. Still, there is some excess magmatism north of this transition, where early oceanic crustal thickness is reduced to half of that of the Vøring Plateau 150 km away. Our estimates of the earliest seafloor spreading rates using new ship-track magnetic profiles on different margin segments offer a clue to what caused this rapid transition. While crustal breakup occurred within the magnetic polarity C24r in other parts of the NAIP, there is a delayed breakup for the Lofoten/Vesterålen margin. Modeling of the earliest seafloor spreading with geomagnetic reversals, indicate a breakup within C24n.3n (anomaly 24b), approximately 1 m.y. later. Both old wide-angle seismic models (from Ocean Bottom Seismometers) off southern Lofoten and a newly published profile farther north show a strongly extended outer margin. Applying early seafloor half-spreading rates ( 30 mm/y) from other NAIP margin segments for 1 m.y. can account for 30 km extra extension, giving a factor of three crustal thinning, and gives a high strain rate of 3.2 ·10-14. Crustal breakup at the magma-poor Iberian Margin occurred at a low strain rate of 4.4·10-15, allowing the ascending mantle to cool, favoring tectonic extension over magmatism. Similar strain rates are found within the main Ethiopian Rift, but there is much magmatism and crustal separation is dominated by dike injection. Mantle tomography models show an exceptionally low seismic velocity below the area interpreted as an unusually hot upper mantle, which will favor magmatism. The transition from

  17. MAGNETAR FIELD EVOLUTION AND CRUSTAL PLASTICITY

    International Nuclear Information System (INIS)

    Lander, S. K.

    2016-01-01

    The activity of magnetars is believed to be powered by colossal magnetic energy reservoirs. We sketch an evolutionary picture in which internal field evolution in magnetars generates a twisted corona, from which energy may be released suddenly in a single giant flare, or more gradually through smaller outbursts and persistent emission. Given the ages of magnetars and the energy of their giant flares, we suggest that their evolution is driven by a novel mechanism: magnetic flux transport/decay due to persistent plastic flow in the crust, which would invalidate the common assumption that the crustal lattice is static and evolves only under Hall drift and Ohmic decay. We estimate the field strength required to induce plastic flow as a function of crustal depth, and the viscosity of the plastic phase. The star’s superconducting core may also play a role in magnetar field evolution, depending on the star’s spindown history and how rotational vortices and magnetic fluxtubes interact.

  18. AMS record of brittle dilation, viscous-stretching and gravity-driven magma ascent in area of magma-rich crustal extension (Vosges Mts., NE France)

    Czech Academy of Sciences Publication Activity Database

    Kratinová, Zuzana; Schulmann, K.; Edel, J.-B.; Tabaud, A.-S.

    2012-01-01

    Roč. 101, č. 3 (2012), s. 803-817 ISSN 1437-3254 R&D Projects: GA AV ČR KJB300120702 Institutional research plan: CEZ:AV0Z30120515 Keywords : anisotropy of magnetic susceptibility * crustal extension * magmatic fabrics * carboniferous Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.261, year: 2012

  19. Viscoelastic crustal deformation by magmatic intrusion: A case study in the Kutcharo caldera, eastern Hokkaido, Japan

    Science.gov (United States)

    Yamasaki, Tadashi; Kobayashi, Tomokazu; Wright, Tim J.; Fukahata, Yukitoshi

    2018-01-01

    Geodetic signals observed at volcanoes, particularly their temporal patterns, have required us to make the correlation between the surface displacement and magmatic process at depth in terms of viscoelastic crustal rheology. Here we use a parallelized 3-D finite element model to examine the response of the linear Maxwell viscoelastic crust and mantle to the inflation of a sill in order to show the characteristics of a long-term volcano deformation. In the model, an oblate-spheroidal sill is instantaneously or gradually inflated in a two-layered medium that consists of an elastic layer underlain by a viscoelastic layer. Our numerical experiments show that syn-inflation surface uplift is followed by post-inflation surface subsidence as the viscoelastic substrate relaxes. For gradual inflation events, the magnitude of inflation-induced uplift is reduced by the relaxation, through which the volume of a magma inferred by matching the prediction of an elastic model with observed surface uplift could be underestimated. For a given crustal viscosity, sill depth is the principal factor controlling subsidence caused by viscoelastic relaxation. The subsidence rate is highest when the inflation occurs at the boundary between the elastic and the viscoelastic layers. The mantle viscosity has an insignificant impact unless the depth of the inflation is greater than a half the crustal thickness. We apply the viscoelastic model to the interferometric synthetic aperture radar (InSAR) data in the Kutcharo caldera, eastern Hokkaido, Japan, where the surface has slowly subsided over a period of approximately three years following about a two-year period of inflation. The emplacement of a magmatic sill is constrained to occur at a depth of 4.5 km, which is significantly shallower than the geophysically imaged large-scale magma chamber. The geodetically detected deformation in the caldera reflects the small-scale emplacement of a magma that ascended from the deeper chamber, but not the

  20. Sedimentology and Reservoir Characteristics of Early Cretaceous Fluvio-Deltaic and Lacustrine Deposits, Upper Abu Gabra Formation, Sufyan Sub-basin, Muglad Rift Basin, Sudan

    Science.gov (United States)

    Yassin, Mohamed; Abdullatif, Osman; Hariri, Mustafa

    2017-04-01

    Sufyan Sub-basin is an East-West trending Sub-basin located in the northwestern part of the Muglad Basin (Sudan), in the eastern extension of the West and Central Africa Rift System (WCARS). The Early Cretaceous Abu Gabra Formation considered as the main source rock in the Muglad Basin. In Sufyan Sub-basin the Early Cretaceous Upper Abu Gabra Formation is the main oil-producing reservoir. It is dominated by sandstone and shales deposited in fluvio-deltaic and lacustrine environment during the first rift cycle in the basin. Depositional and post-depositional processes highly influenced the reservoir quality and architecture. This study investigates different scales of reservoir heterogeneities from macro to micro scale. Subsurface facies analysis was analyzed based on the description of six conventional cores from two wells. Approaches include well log analysis, thin sections and scanning electron microscope (SEM) investigations, grain-size, and X-ray diffraction (XRD) analysis of the Abu Gabra sandstone. The cores and well logs analyses revealed six lithofacies representing fluvio-deltaic and lacustrine depositional environment. The sandstone is medium to coarse-grained, poorly to moderately sorted and sub-angular to subrounded, Sub-feldspathic arenite to quartz arenite. On macro-scale, reservoir quality varies within Abu Gabra reservoir where it shows progressive coarsening upward tendencies with different degrees of connectivity. The upper part of the reservoir showed well connected and amalgamated sandstone bodies, the middle to lower parts, however, have moderate to low sandstone bodies' connectivity and amalgamation. On micro-scale, sandstone reservoir quality is directly affected by textures and diagenesis.The XRD and SEM analyses show that kaolinite and chlorite clay are the common clay minerals in the studied samples. Clay matrix and quartz overgrowth have significantly reduced the reservoir porosity and permeability, while the dissolution of feldspars

  1. A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites.

    Science.gov (United States)

    Reubi, Olivier; Blundy, Jon

    2009-10-29

    Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.

  2. Preliminary Report on U-Th-Pb Isotope Systematics of the Olivine-Phyric Shergottite Tissint

    Science.gov (United States)

    Moriwaki, R.; Usui, T.; Yokoyama, T.; Simon, J. I.; Jones, J. H.

    2014-01-01

    Geochemical studies of shergottites suggest that their parental magmas reflect mixtures between at least two distinct geochemical source reservoirs, producing correlations between radiogenic isotope compositions, and trace element abundances.. These correlations have been interpreted as indicating the presence of a reduced, incompatible-element- depleted reservoir and an oxidized, incompatible-element-rich reservoir. The former is clearly a depleted mantle source, but there has been a long debate regarding the origin of the enriched reservoir. Two contrasting models have been proposed regarding the location and mixing process of the two geochemical source reservoirs: (1) assimilation of oxidized crust by mantle derived, reduced magmas, or (2) mixing of two distinct mantle reservoirs during melting. The former clearly requires the ancient martian crust to be the enriched source (crustal assimilation), whereas the latter requires a long-lived enriched mantle domain that probably originated from residual melts formed during solidification of a magma ocean (heterogeneous mantle model). This study conducts Pb isotope and U-Th-Pb concentration analyses of the olivine-phyric shergottite Tissint because U-Th-Pb isotope systematics have been intensively used as a powerful radiogenic tracer to characterize old crust/sediment components in mantle- derived, terrestrial oceanic island basalts. The U-Th-Pb analyses are applied to sequential acid leaching fractions obtained from Tissint whole-rock powder in order to search for Pb isotopic source components in Tissint magma. Here we report preliminary results of the U-Th-Pb analyses of acid leachates and a residue, and propose the possibility that Tissint would have experienced minor assimilation of old martian crust.

  3. Crustal structure and inferred extension mode in the northern margin of the South China Sea

    Science.gov (United States)

    Gao, J.; Wu, S.; McIntosh, K. D.; Mi, L.; Spence, G.

    2016-12-01

    Combining multi-channel seismic reflection and satellite gravity data, this study has investigated the crustal structure and magmatic activities of the northern South China Sea (SCS) margin. Results show that a broad continent-ocean transition zone (COT) with more than 140 km wide is characterized by extensive igneous intrusion/extrusion and hyper-extended continental crust in the northeastern SCS margin, a broader COT with 220-265 km wide is characterized by crustal thinning, rift depression, structural highs with igneous rock and perhaps a volcanic zone or a zone of tilted fault blocks at the distal edge in the mid-northern SCS margin, and a narrow COT with 65 km wide bounded seawards by a volcanic buried seamount is characterized by extremely hyper-extended continental crust in the northwestern SCS margin, where the remnant crust with less than 3 km thick is bounded by basin-bounding faults corresponding to an aborted rift below the Xisha Trough with a sub-parallel fossil ridge in the adjacent Northwest Sub-basin. Results from gravity modeling and seismic refraction data show that a high velocity layer (HVL) is present in the outer shelf and slope below extended continental crust in the eastern portion of the northern SCS margin and is thickest (up to 10 km) in the Dongsha Uplift where the HVL gradually thins to east and west below the lower slope and finally terminates at the Manila Trench and Baiyun sag of the Pearl River Mouth Basin. The magmatic intrusions/extrusions and HVL may be related to partial melting caused by decompression of passive, upwelling asthenosphere which resulted primarily in post-rifting underplating and magmatic emplacement or modification of the crust. The northern SCS margin is closer to those of the magma-poor margins than those of volcanic margins, but the aborted rift near the northwestern continental margin shows that there may be no obvious detachment fault like that in the Iberia-Newfoundland type margin. The symmetric aborted

  4. Time-Lapse Seismic Monitoring and Performance Assessment of CO<sub>2sub> Sequestration in Hydrocarbon Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Datta-Gupta, Akhil [Texas Engineering Experiment Station, College Station, TX (United States)

    2017-06-15

    Carbon dioxide sequestration remains an important and challenging research topic as a potentially viable approach for mitigating the effects of greenhouse gases on global warming (e.g., Chu and Majumdar, 2012; Bryant, 2007; Orr, 2004; Hepple and Benson, 2005; Bachu, 2003; Grimston et al., 2001). While CO<sub>2sub> can be sequestered in oceanic or terrestrial biomass, the most mature and effective technology currently available is sequestration in geologic formations, especially in known hydrocarbon reservoirs (Barrufet et al., 2010; Hepple and Benson, 2005). However, challenges in the design and implementation of sequestration projects remain, especially over long time scales. One problem is that the tendency for gravity override caused by the low density and viscosity of CO<sub>2sub>. In the presence of subsurface heterogeneity, fractures and faults, there is a significant risk of CO<sub>2sub> leakage from the sequestration site into overlying rock compared to other liquid wastes (Hesse and Woods, 2010; Ennis-King and Patterson, 2002; Tsang et al., 2002). Furthermore, the CO<sub>2sub> will likely interact chemically with the rock in which it is stored, so that understanding and predicting its transport behavior during sequestration can be complex and difficult (Mandalaparty et al., 2011; Pruess et al., 2003). Leakage of CO<sub>2sub> can lead to such problems as acidification of ground water and killing of plant life, in addition to contamination of the atmosphere (Ha-Duong, 2003; Gasda et al., 2004). The development of adequate policies and regulatory systems to govern sequestration therefore requires improved characterization of the media in which CO<sub>2sub> is stored and the development of advanced methods for detecting and monitoring its flow and transport in the subsurface (Bachu, 2003).

  5. Crustally derived granites in Dali, SW China: new constraints on silicic magmatism of the Central Emeishan Large Igneous Province

    Science.gov (United States)

    Zhu, Bei; Peate, David W.; Guo, Zhaojie; Liu, Runchao; Du, Wei

    2017-10-01

    We have identified a new crustally derived granite pluton that is related to the Emeishan Large Igneous Province (ELIP). This pluton (the Wase pluton, near Dali) shows two distinct SHRIMP zircon U-Pb age groups ( 768 and 253 Ma). As it has an intrusive relationship with Devonian limestone, the younger age is interpreted as its formation, which is related to the ELIP event, whereas the 768 Ma Neoproterozoic-aged zircons were inherited from Precambrian crustal component of the Yangtze Block, implying the pluton has a crustally derived origin. This is consistent with its peraluminous nature, negative Nb-Ta anomaly, enrichment in light rare earth elements, high 87Sr/86Sr(i) ratio (0.7159-0.7183) and extremely negative ɛ(Nd)(i) values (-12.15 to -13.70), indicative of melts derived from upper crust materials. The Wase pluton-intruded Devonian strata lie stratigraphically below the Shangcang ELIP sequence, which is the thickest volcanic sequence ( 5400 m) in the whole ELIP. The uppermost level of the Shangcang sequence contains laterally restricted rhyolite. Although the rhyolite has the same age as the Wase pluton, its geochemical features demonstrate a different magma origin. The rhyolite displays moderate 87Sr/86Sr(i) (0.7053), slightly negative ɛ(Nd)(i) (-0.18) and depletions in Ba, Cs, Eu and Sr, implying derivation from differentiation of a mantle-derived mafic magma source. The coexistence of crustally and mantle-derived felsic systems, along with the robust development of dike swarms, vent proximal volcanics and thickest flood basalts piles in Dali, shows that the Dali area was probably where the most active Emeishan magmatism had once existed.

  6. Interactions between magma and the lithospheric mantle during Cenozoic rifting in Central Europe

    Science.gov (United States)

    Meyer, Romain; Elkins-Tanton, Linda T.

    2010-05-01

    During the Cenozoic, extensive intraplate volcanic activity occurred throughout Central Europe. Volcanic eruptions extend over France (the Massif Central), central Germany (Eifel, Vogelsberg, Rhön; Heldburg), the Czech Republic (the Eger graben) and SW Poland (Lower Silesia), a region ~1,200 km wide. The origin of this predominantly alkaline intraplate magmatism is often genetically linked to one or several mantle plumes, but there is no convincing evidence for this. We have measured Pb isotope ratios, together with major and trace elements, in a representative set of mafic to felsic igneous rocks from the intra-plate Cenozoic Rhön Mts. and the Heldburg dike swarm in order to gain insight into the melting source and petrogenetic history of these melts. Three different mafic rock types (tholeiitic basalt, alkali basalt, basanite) were distinguished based on petrography and geochemistry within the investigated areas. Except for the lherzolite-bearing phonolite from the Veste Heldburg all other evolved magmas are trachytes. REE geochemistry and calculated partial melting modeling experiments for the three mafic magma types point to different degrees of partial melting in a garnet-bearing mantle source. In addition a new version of the ternary Th-Hf-Ta diagram is presented in this study as a useful petrological tool. This diagram is not only able to define potentially involved melting source end-members (e.g. asthenosphere, sub-continental lithospheric mantle and continental crust) but also interactions between these members are illustrated. An advantage of this diagram compared to partial melting degree sensitive multi-element diagrams is that a ternary diagram is a closed system. An earlier version of this diagram has been recently used to establish the nature and extent of crust mantle melt interaction of volcanic rifted margins magmas (Meyer et al. 2009). The Th-Hf-Ta geochemistry of the investigated magmas is similar to spinel and garnet xenoliths from different

  7. Deformation patterns, magma supply, and magma storage at Karymsky Volcanic Center, Kamchatka, Russia, 2000-2010, revealed by InSAR

    Science.gov (United States)

    Ji, Lingyun; Izbekov, Pavel; Senyukov, Sergey; Lu, Zhong

    2018-02-01

    Under a complex geological region influenced by the subduction of the Pacific plate, Kamchatka Peninsula is one of the most active volcanic arcs in the Pacific Rim. Due to logistical difficulty in instrumentation, shallow magma plumbing systems beneath some of the Kamchatkan volcanoes are poorly understood. InSAR offers a safe and quick method for monitoring volcanic deformation with a high spatial resolution. In this study, a group of satellite radar interferograms that span the time interval from 2000 to 2010 shows eruptive and non-eruptive deformation at Karymsky Volcanic Center (KVC), Kamchatka, Russia. All the interferograms provide details of the activity around the KVC during 2000-2010, as follows: (1) from 2000 to 2004, the Karymsky-AN (Akademia Nauk) area deflated and the MS (Maly Semyachik) area inflated, (2) from 2004 to 2006, the Karymsky-AN area deflated with ongoing eruption, while the MS area subsided without eruption, (3) from 2006 to 2008, as with 2000-2004, the Karymsky-AN area deflated and the MS area inflated, (4) from 2008 to 2010, the Karymsky-AN area inflated up to 3 cm, and the MS area subsided. Point source models suggest that two magma reservoirs provide a good fit to the observed deformation. One source is located beneath the area between Karymsky and AN at a depth of approximately 7.0 km, and the other one is situated beneath MS at a depth of around 5.8 km. Synchronous deformation patterns suggest that two magma systems are fed from the same deep magma source and connected by a fracture zone. The InSAR results are consistent with GPS ground deformation measurements, seismic data, and petrological constraints.

  8. Evolution of silicic magmas in the Kos-Nisyros volcanic center: cycles associated with caldera collapse

    Science.gov (United States)

    Ruprecht, J. S.; Bachmann, O.; Deering, C. D.; Huber, C.; Skopelitis, A.; Schnyder, C.

    2010-12-01

    Multiple eruptions of silicic magma (dacite and rhyolites) occurred over the last ~ 3 My in the Kos-Nisyros volcanic center (eastern Aegean sea). Over the course of this period, magmas have changed from hornblende-biotite rich units with low eruption temperatures (≤750-800 °C; Kefalos and Kos units) to hotter (>800-850 °C), pyroxene-bearing units (Nisyros units) and are transitioning back to colder magmas (Yali units). Using bulk-rock compositions, mineral chemistry, and zircon Hf isotopes, we show that the two different types of silicic magmas followed the same differentiation trend; they all evolved by crystal fractionation (and minor assimilation) from parents with intermediate compositions characterized by high Sr/Y and low Nb content, following a wet, high oxygen fugacity liquid line of descent typical of subduction zones. As the transition between the Kos-Kefalos and Nisyros-type magmas occurred immediately and abruptly after the major caldera collapse in the area (the 161 ky Kos Plateau Tuff; KPT), we suggest that the efficient emptying of the magma chamber during the KPT drew most of the eruptible magma out and partly froze the silicic magma source zone in the upper crust due to rapid unloading, decompression and resulting crystallization. Therefore, the system had to reinstate a shallow silicic production zone from more mafic parents, recharged at temperatures typically around 850-900 °C from the mid to lower crust. The first silicic eruptions evolving from these parents after the caldera collapse (Nisyros units) were thus slightly hotter and less evolved than the Kefalos-Kos package. However, with time, the upper crustal intermediate mush grew and cooled, leading to interstitial melt compositions reaching again the highly-evolved, cold state that prevailed prior to the Kefalos-Kos. The recent (albeit not precisely dated) eruption of the high-SiO2 rhyolite of Yali suggests that another large, potentially explosive magma chamber is presently building

  9. The decompression of basaltic magma into a sub-surface repository

    NARCIS (Netherlands)

    Bokhove, Onno; Woods, A.W.

    2002-01-01

    We examine the ascent of volatile-rich basaltic magma through a vertical dike that intersects a horizontal tunnel of comparable cross-sectional area to the dike and located 300 $m$ below the surface and initially filled with air at atmospheric pressure. This process is a simplified representation of

  10. Crustal thinning and exhumation along a fossil magma-poor distal margin preserved in Corsica: A hot rift to drift transition?

    Science.gov (United States)

    Beltrando, Marco; Zibra, Ivan; Montanini, Alessandra; Tribuzio, Riccardo

    2013-05-01

    Rift-related thinning of continental basement along distal margins is likely achieved through the combined activity of ductile shear zones and brittle faults. While extensional detachments responsible for the latest stages of exhumation are being increasingly recognized, rift-related shear zones have never been sampled in ODP sites and have only rarely been identified in fossil distal margins preserved in orogenic belts. Here we report evidence of the Jurassic multi-stage crustal thinning preserved in the Santa Lucia nappe (Alpine Corsica), where amphibolite facies shearing persisted into the rift to drift transition. In this nappe, Lower Permian meta-gabbros to meta-gabbro-norites of the Mafic Complex are separated from Lower Permian granitoids of the Diorite-Granite Complex by a 100-250 m wide shear zone. Fine-grained syn-kinematic andesine + Mg-hornblende assemblages in meta-tonalites of the Diorite-Granite Complex indicate shearing at T = 710 ± 40 °C at P Lucia basement. These results imply that middle to lower crustal rocks can be cooled and exhumed rapidly in the last stages of rifting, when significant crustal thinning is accommodated in less than 5 Myr through the consecutive activity of extensional shear zones and detachment faults. High thermal gradients may delay the switch from ductile shear zone- to detachment-dominated crustal thinning, thus preventing the exhumation of middle and lower crustal rocks until the final stages of rifting.

  11. Preliminary crustal deformation model deduced from GPS and earthquakes’ data at Abu-Dabbab area, Eastern Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Abdel-Monem S. Mohamed

    2013-06-01

    From the seismic tomography study, the 3D Vp and Vp/Vs crustal models indicate high Vp/Vs values forms an elongated anomaly, in the central part of the study area, that extends from a depth of 12 km to about 1–2 km of depth is obtained. By using this crustal model in relocations all seismicity informed that most of the seismicity strongly tend to occur in a cluster manner exactly above the southern part of the study area. Based on the conducted source mechanism study, it is noticed that shallow earthquakes are associated by a high CLVD ratio (up to 40%. Furthermore, initiation of a high level seismic activity, without a large seismic main shock is observed in the Abu-Dabbab area. The distribution of micro-earthquakes tends to align in an ENE–WSW direction marking a zone of activity verse the Red Sea. The nucleation of the seismic activity beneath the southern part of the Abu-Dabbab crust is more consistent with the obtained crustal deformation result by increasing the crustal movement in the south part than the northern part. Then, based on the obtained results of the above mentioned studies; seismic tomography; source mechanisms, and crustal deformation we conclude that these seismic activities that are associated by crustal deformation are owing to some magma activity beneath the crust of the Abu-Dabbab area.

  12. Advanced reservoir characterization and evaluation of CO{sub 2} gravity drainage in the naturally fractured Spraberry Trend Area. Annual report, September 1, 1996--August 31, 1997

    Energy Technology Data Exchange (ETDEWEB)

    Schechter, D.S.

    1998-07-01

    The overall goal of this project is to assess the economic feasibility of CO{sub 2} flooding the naturally fractured Spraberry Trend Area in West Texas. This objective is being accomplished by conducting research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, (3) reservoir performance analysis, and (4) experimental investigations on CO{sub 2} gravity drainage in Spraberry whole cores. This report provides results of the second year of the five-year project for each of the four areas. In the first area, the author has completed the reservoir characterization, which includes matrix description and detection (from core-log integration) and fracture characterization. This information is found in Section 1. In the second area, the author has completed extensive inhibition experiments that strongly indicate that the weakly water-wet behavior of the reservoir rock may be responsible for poor waterflood response observed in many Spraberry fields. In the third area, the author has made significant progress in analytical and numerical simulation of performance in Spraberry reservoirs as seen in Section 3. In the fourth area, the author has completed several suites of CO{sub 2} gravity drainage in Spraberry and Berea whole cores at reservoir conditions and reported in Section 4. The results of these experiments have been useful in developing a model for free-fall gravity drainage and have validated the premise that CO{sub 2} will recover oil from tight, unconfined Spraberry matrix. The final three years of this project involves implementation of the CO{sub 2} pilot. Up to twelve new wells are planned in the pilot area; water injection wells to contain the CO{sub 2}, three production wells to monitor performance of CO{sub 2}, CO{sub 2} injection wells including one horizontal injection well and logging observation wells to monitor CO{sub 2} flood fronts. Results of drilling

  13. The evolution of the magmatic arc of Southern Peru (200-60 Ma), Arequipa area: insight from geochemical modeling

    Science.gov (United States)

    Demouy, S.; Benoit, M.; De Saint Blanquat, M.; Brunet, P.

    2012-12-01

    Cordilleran-type batholiths are built by prolonged arc activity along continental margins and may provide detailed magmatic records of the subduction system evolution. The magmas produced in subduction context involve both mantellic and crustal end members and are subject to various petrological processes. The MASH zones (Hildreth and Moorbath, 1988), at the basis of the continental crust, are the best places for the genesis of such hybrid magmas. The various geochemical signatures observed in the plutonic rocks, may also be attributed to source heterogeneities or generated by subsequent petrological processes. This study has focused in the Arequipa section of the Coastal Batholith of Southern Peru (200-60 Ma), in an area extending over 80x40 km. Major and trace elements as well as Sr and Nd isotopic analyses were performed in a set of 100 samples ranging from gabbro to granite. The obtained data highlight the wide heterogeneity of the geochemical signatures that is not related to the classification of the rocks. In first step, Rb/Sr systematic was used to isolate a set of samples plotting along a Paleocene isochron and defining a cogenetic suite. This suite appears to have evolved by simple fractional crystallization. By using reverse modeling, the parameters controlling the fractional crystallization process were defined, as partition coefficients, initial concentrations and amount of fractional crystallization. The other magmatic suites display a wide range of isotopic and geochemical signatures. To explain this heterogeneity, a model involving competition between fractional crystallization and magma mixing into MASH zones was proposed. A large range of hybrid magma types is potentially generated during the maturation of the system, but this range tends to disappear as fractionation and mixing occurs. Finally the model predicts the genesis of a homogeneous reservoir created at depth, from which magmas may evolve only by fractional crystallization. Therefore

  14. Amphibole Fractional Crystallization and Delamination in Arc Roots: Implications for the `Missing' Nb Reservoir in the Earth

    Science.gov (United States)

    Galster, F.; Chatterjee, R. N.; Stockli, D. F.

    2017-12-01

    Most geologic processes should not fractionate Nb from Ta but Earth's major silicate reservoirs have subchondritic Nb/Ta values. Nb/Ta of >10000 basalts and basaltic andesites from different tectonic settings (GEOROC) cluster around 16, indistinguishable from upper mantle values. In contrast, Nb/Ta in more evolved arc volcanics have progressively lower values, reaching continental crust estimates, and correlate negatively with SiO2 (see figure) and positively with TiO2 and MgO. This global trend suggests that differentiation processes in magmatic arcs could explain bulk crustal Nb/Ta estimates. Understanding processes that govern fractionation of Nb from Ta in arcs can provide key insights on continental crust formation and help identify Earth's `missing' Nb reservoir. Ti-rich phases (rutile, titanite and ilmenite) have DNb/DTa values in the evolved liquid. Lack of correlation between Nb/Ta and K2O in global volcanic rocks implies that biotite plays a minor role in fractionating Nb from Ta during differentiation. Experimental petrology and evidence from exposed arc sections indicate that amphibole fractionation and delamination of island arc roots can explain the andesitic composition of bulk continental crust. Experimental studies have shown that amphibole Mg# correlate with DNb/DTa and amphibole could effectively fractionate Nb from Ta. Preliminary data from lower to middle crustal amphiboles from preserved arcs show sub- to super-chondritic Nb/Ta up to >60. This suggests that delamination of amphibole-rich cumulates can be a viable mechanism for the preferential removal of Nb from the continental crust. Future examination of Nb/Ta ratios in lower crustal amphiboles from various preserved arcs will provide improved constraints on the Nb-Ta paradox of the silicate Earth.

  15. Using rocks to reveal the inner workings of magma chambers below volcanoes in Alaska’s National Parks

    Science.gov (United States)

    Coombs, Michelle L.; Bacon, Charles R.

    2012-01-01

    Alaska is one of the most vigorously volcanic regions on the planet, and Alaska’s national parks are home to many of the state’s most active volcanoes. These pose both local and more distant hazards in the form of lava and pyroclastic flows, lahars (mudflows), ash clouds, and ash fall. Alaska’s volcanoes lie along the arc of the Aleutian-Alaskan subduction zone, caused as the oceanic Pacific plate moves northward and dips below the North American plate. These volcanoes form as water-rich fluid from the down-going Pacific plate is released, lowering the melting temperature of rock in the overlying mantle and enabling it to partially melt. The melted rock (magma) migrates upward, collecting at the base of the approximately 25 mile (40 km) thick crust, occasionally ascending into the shallow crust, and sometimes erupting at the earth’s surface.During volcanic unrest, scientists use geophysical signals to remotely visualize volcanic processes, such as movement of magma in the upper crust. In addition, erupted volcanic rocks, which are quenched samples of magmas, can tell us about subsurface magma characteris-tics, history, and the processes that drive eruptions. The chemical compositions of and the minerals present in the erupted magmas can reveal conditions under which these magmas were stored in crustal “chambers”. Studies of the products of recent eruptions of Novarupta (1912), Aniakchak (1931), Trident (1953-74), and Redoubt (2009) volcanoes reveal the depths and temperatures of magma storage, and tell of complex interactions between magmas of different compositions. One goal of volcanology is to determine the processes that drive or trigger eruptions. Information recorded in the rocks tells us about these processes. Here, we demonstrate how geologists gain these insights through case studies from four recent eruptions of volcanoes in Alaska national parks.

  16. Characteristics of volcanic reservoirs and distribution rules of effective reservoirs in the Changling fault depression, Songliao Basin

    Directory of Open Access Journals (Sweden)

    Pujun Wang

    2015-11-01

    Full Text Available In the Songliao Basin, volcanic oil and gas reservoirs are important exploration domains. Based on drilling, logging, and 3D seismic (1495 km2 data, 546 sets of measured physical properties and gas testing productivity of 66 wells in the Changling fault depression, Songliao Basin, eruptive cycles and sub-lithofacies were distinguished after lithologic correction of the 19,384 m volcanic well intervals, so that a quantitative analysis was conducted on the relation between the eruptive cycles, lithologies and lithofacies and the distribution of effective reservoirs. After the relationship was established between lithologies, lithofacies & cycles and reservoir physical properties & oil and gas bearing situations, an analysis was conducted on the characteristics of volcanic reservoirs and the distribution rules of effective reservoirs. It is indicated that 10 eruptive cycles of 3 sections are totally developed in this area, and the effective reservoirs are mainly distributed at the top cycles of eruptive sequences, with those of the 1st and 3rd Members of Yingcheng Formation presenting the best reservoir properties. In this area, there are mainly 11 types of volcanic rocks, among which rhyolite, rhyolitic tuff, rhyolitic tuffo lava and rhyolitic volcanic breccia are the dominant lithologies of effective reservoirs. In the target area are mainly developed 4 volcanic lithofacies (11 sub-lithofacies, among which upper sub-lithofacies of effusive facies and thermal clastic sub-lithofacies of explosion lithofacies are predominant in effective reservoirs. There is an obvious corresponding relationship between the physical properties of volcanic reservoirs and the development degree of effective reservoirs. The distribution of effective reservoirs is controlled by reservoir physical properties, and the formation of effective reservoirs is influenced more by porosity than by permeability. It is concluded that deep volcanic gas exploration presents a good

  17. The Acoculco caldera magmas: genesis, evolution and relation with the Acoculco geothermal system

    Science.gov (United States)

    Sosa-Ceballos, G.; Macías, J. L.; Avellán, D.

    2017-12-01

    The Acoculco Caldera Complex (ACC) is located at the eastern part of the Trans Mexican Volcanic Belt; México. This caldera complex have been active since 2.7 Ma through reactivations of the system or associated magmatism. Therefore the ACC is an excellent case scenario to investigate the relation between the magmatic heat supply and the evolution processes that modified magmatic reservoirs in a potential geothermal field. We investigated the origin and the magmatic processes (magma mixing, assimilation and crystallization) that modified the ACC rocks by petrography, major oxides-trace element geochemistry, and isotopic analysis. Magma mixing is considered as the heat supply that maintain active the magmatic system, whereas assimilation yielded insights about the depth at which processes occurred. In addition, we performed a series of hydrothermal experiments in order to constrain the storage depth for the magma tapped during the caldera collapse. Rocks from the ACC were catalogued as pre, syn and post caldera. The post caldera rocks are peralkaline rhyolites, in contrast to all other rocks that are subalkaline. Our investigation is focus to investigate if the collapse modified the plumbing system and the depth at which magmas stagnate and recorded the magmatic processes.

  18. Crystal reaming during the assembly, maturation, and waning of an eleven-million-year crustal magma cycle: thermobarometry of the Aucanquilcha Volcanic Cluster

    Science.gov (United States)

    Walker, Barry A.; Klemetti, Erik W.; Grunder, Anita L.; Dilles, John H.; Tepley, Frank J.; Giles, Denise

    2013-04-01

    Phenocryst assemblages of lavas from the long-lived Aucanquilcha Volcanic Cluster (AVC) have been probed to assess pressure and temperature conditions of pre-eruptive arc magmas. Andesite to dacite lavas of the AVC erupted throughout an 11-million-year, arc magmatic cycle in the central Andes in northern Chile. Phases targeted for thermobarometry include amphibole, plagioclase, pyroxenes, and Fe-Ti oxides. Overall, crystallization is documented over 1-7.5 kbar (~25 km) of pressure and ~680-1,110 °C of temperature. Pressure estimates range from ~1 to 5 kbar for amphiboles and from ~3 to 7.5 kbar for pyroxenes. Pyroxene temperatures are tightly clustered from ~1,000-1,100 °C, Fe-Ti oxide temperatures range from ~750-1,000 °C, and amphibole temperatures range from ~780-1,050 °C. Although slightly higher, these temperatures correspond well with previously published zircon temperatures ranging from ~670-900 °C. Two different Fe-Ti oxide thermometers (Andersen and Lindsley 1985; Ghiorso and Evans 2008) are compared and agree well. We also compare amphibole and amphibole-plagioclase thermobarometers (Ridolfi et al. 2010; Holland and Blundy 1994; Anderson and Smith 1995), the solutions from which do not agree well. In samples where we employ multiple thermometers, pyroxene temperature estimates are always highest, zircon temperature estimates are lowest, and Fe-Ti oxide and amphibole temperature estimates fall in between. Maximum Fe-Ti oxide and zircon temperatures are observed during the middle stage of AVC activity (~5-3 Ma), a time associated with increased eruption rates. Amphibole temperatures during this time are relatively restricted (~850-1,000 °C). The crystal record presented here offers a time-transgressive view of an evolving, multi-tiered subvolcanic reservoir. Some crystals in AVC lavas are likely to be true phenocrysts, but the diversity of crystallization temperatures and pressures recorded by phases in individual AVC lavas suggests erupting magma

  19. Prototyping and Testing a New Volumetric Curvature Tool for Modeling Reservoir Compartments and Leakage Pathways in the Arbuckle Saline Aquifer: Reducing Uncertainty in CO<sub>2sub> Storage and Permanence

    Energy Technology Data Exchange (ETDEWEB)

    Rush, Jason [Univ. of Kansas and Kansas Geological Survey, Lawrence, KS (United States); Holubnyak, Yevhen [Univ. of Kansas and Kansas Geological Survey, Lawrence, KS (United States); Watney, Willard [Univ. of Kansas and Kansas Geological Survey, Lawrence, KS (United States)

    2016-12-09

    petrophysical models to separate-vug rock fabrics along solution-enlarged fault and fracture systems. Simulation-based studies demonstrate a potential alternative field development model for developing CO<sub>2sub> storage sites that target carbonate reservoirs overprinted by paleokarst. Simulation results for this complex reservoir indicate that individual fault blocks could function as discrete containers for CO<sub>2sub> storage thereby reducing the risk of plume migration outside the legally defined extent of the permitted storage site. Vertically extensive, anastomosing, solution-enlarged fault/fracture systems — infilled by clay-rich sediments — would operate as non-to-low permeability vertical "curtains" that restrict CO<sub>2sub> movement beyond the confines of the CO<sub>2sub> storage site. Such a location could be developed in a checker-board fashion with CO<sub>2sub> injection operations occurring in one block and surveillance operations occurring in the adjacent block. Such naturally partitioned reservoirs may be ideal candidates for reducing risks associated with CO<sub>2sub> plume breakthrough.

  20. Sub-seasonal-to-seasonal Reservoir Inflow Forecast using Bayesian Hierarchical Hidden Markov Model

    Science.gov (United States)

    Mukhopadhyay, S.; Arumugam, S.

    2017-12-01

    Sub-seasonal-to-seasonal (S2S) (15-90 days) streamflow forecasting is an emerging area of research that provides seamless information for reservoir operation from weather time scales to seasonal time scales. From an operational perspective, sub-seasonal inflow forecasts are highly valuable as these enable water managers to decide short-term releases (15-30 days), while holding water for seasonal needs (e.g., irrigation and municipal supply) and to meet end-of-the-season target storage at a desired level. We propose a Bayesian Hierarchical Hidden Markov Model (BHHMM) to develop S2S inflow forecasts for the Tennessee Valley Area (TVA) reservoir system. Here, the hidden states are predicted by relevant indices that influence the inflows at S2S time scale. The hidden Markov model also captures the both spatial and temporal hierarchy in predictors that operate at S2S time scale with model parameters being estimated as a posterior distribution using a Bayesian framework. We present our work in two steps, namely single site model and multi-site model. For proof of concept, we consider inflows to Douglas Dam, Tennessee, in the single site model. For multisite model we consider reservoirs in the upper Tennessee valley. Streamflow forecasts are issued and updated continuously every day at S2S time scale. We considered precipitation forecasts obtained from NOAA Climate Forecast System (CFSv2) GCM as predictors for developing S2S streamflow forecasts along with relevant indices for predicting hidden states. Spatial dependence of the inflow series of reservoirs are also preserved in the multi-site model. To circumvent the non-normality of the data, we consider the HMM in a Generalized Linear Model setting. Skill of the proposed approach is tested using split sample validation against a traditional multi-site canonical correlation model developed using the same set of predictors. From the posterior distribution of the inflow forecasts, we also highlight different system behavior

  1. U-series isotopes in arc magma

    Energy Technology Data Exchange (ETDEWEB)

    Hawkesworth, C.; Turner, S.; McDermott, F.; Peate, D.; Van Calsteren, P.

    1997-12-31

    Thorium is not readily mobilized in the fluid component along destructive plate margins. Uranium is mobilized, and the resultant fractionation in U/Th can be used to estimate the rates of transfer slab derived components through the mantle wedge. The variations in Th/Yb, and by implication in the fractionation-corrected Th abundances of arc magmas largely depend on the contributions from subducted sediments. It is inferred that the distinctive high Th/Ta ratios of subduction related magmas primarily reflect the Th/Ta ratios of the subducted sediments, and that such high Th/Ta ratios are generated by processes other than those associated with recent subduction-related magmatism. Uranium and thorium isotopes have also been used to evaluate magma residence times within the crust. Thus, separated minerals and groundmass from six rocks erupted in the last 4,000 years from Soufriere on St. Vincent in the Lesser Antilles, scatter about a 50,000 year errorchron on the U-Th equiline diagram (Heath et al., 1977). Models are currently being developed to investigate how such apparent ages may relate to calculated replenishment times in steady state systems. Bulk continental crust has a lower U/Th ratio (0.25) than at least some estimates for the bulk Earth (0.26) and the depleted upper mantle (0.39). However, the island arc rocks with low U/Th ratios appear to have inherited those from subducted sediments, and arc rocks with a low sediment contribution have significantly higher U/Th. Consequently, the U/Th ratios of new crustal material generated along destructive plate margins are significantly higher than those of bulk continental crust. The low average U/Th of bulk crust may be primarily due to different crust generation processes in the Archaean, when U would be less mobile because conditions were less oxidising, and when residual garnet may have had more of a role in crust generation processes. Extended abstract. 4 figs., 23 refs.

  2. Orphan Basin crustal structure from a dense wide-angle seismic profile - Tomographic inversion

    Science.gov (United States)

    Watremez, Louise; Lau, K. W. Helen; Nedimović, Mladen R.; Louden, Keith E.; Karner, Garry D.

    2014-05-01

    Orphan Basin is located on the eastern margin of Canada, offshore of Newfoundland and East of Flemish Cap. It is an aborted continental rift formed by multiple episodes of rifting. The crustal structure across the basin has been determined by an earlier refraction study using 15 instruments on a 550 km long line. It shows that the continental crust was extended over an unusually wide region but did not break apart. The crustal structure of the basin thus documents stages in the formation of a magma-poor rifted margin up to crustal breakup. The OBWAVE (Orphan Basin Wide-Angle Velocity Experiment) survey was carried out to image crustal structures across the basin and better understand the processes of formation of this margin. The spacing of the 89 recording stations varies from 3 to 5 km along this 500-km-long line, which was acquired along a pre-existing reflection line. The highest resolution section corresponds to the part of the profile where the crust was expected to be the thinnest. We present the results from a joint tomography inversion of first and Moho reflected arrival times. The high data density allows us to define crustal structures with greater detail than for typical studies and to improve the understanding of the processes leading to the extreme stretching of continental crust. The final model was computed following a detailed parametric study to determine the optimal parameters controlling the ray-tracing and the inversion processes. The final model shows very good resolution. In particular, Monte Carlo standard deviations of crustal velocities and Moho depths are generally Orphan Basin is the result of rifting of a non-homogeneous Avalon terrane where the lower crust is primarily ductile.

  3. Rapid ascent of rhyolitic magma at Chaitén volcano, Chile.

    Science.gov (United States)

    Castro, Jonathan M; Dingwell, Donald B

    2009-10-08

    Rhyolite magma has fuelled some of the Earth's largest explosive volcanic eruptions. Our understanding of these events is incomplete, however, owing to the previous lack of directly observed eruptions. Chaitén volcano, in Chile's northern Patagonia, erupted rhyolite magma unexpectedly and explosively on 1 May 2008 (ref. 2). Chaitén residents felt earthquakes about 24 hours before ash fell in their town and the eruption escalated into a Plinian column. Although such brief seismic forewarning of a major explosive basaltic eruption has been documented, it is unprecedented for silicic magmas. As precursory volcanic unrest relates to magma migration from the storage region to the surface, the very short pre-eruptive warning at Chaitén probably reflects very rapid magma ascent through the sub-volcanic system. Here we present petrological and experimental data that indicate that the hydrous rhyolite magma at Chaitén ascended very rapidly, with velocities of the order of one metre per second. Such rapid ascent implies a transit time from storage depths greater than five kilometres to the near surface in about four hours. This result has implications for hazard mitigation because the rapidity of ascending rhyolite means that future eruptions may provide little warning.

  4. Magma evolution in the Pliocene Pleistocene succession of Kos, South Aegean arc (Greece)

    Science.gov (United States)

    Pe-Piper, Georgia; Moulton, Ben

    2008-11-01

    This study investigates the petrogenesis of Pliocene-Quaternary andesites, dacites and rhyolites of the island of Kos. These volcanic rocks differ from other volcanic centres in the South Aegean arc in the narrow range of Pliocene volcanic products, the abundance of high-silica rhyolite, the lower ɛNd for a given Sr isotope composition, and greater depth to the subducting slab. Pliocene and early Pleistocene dacite stocks and rhyolite domes are succeeded by younger tuffs, notably the 0.16 Ma Kos Plateau Tuff derived from a super-eruption of an andesite stratocone now subsided beneath the sea south of Kos. Volcanic products in tuffs have been sampled from lithic clasts. Andesite, dacite and rhyolite all have ɛNd ˜+ 1.5 to -1.5 and 86Sr/ 87Sr ˜ 0.7042; this unusual composition is argued to be the result of subduction of sediments derived from the River Nile. All rock types show structures indicative of widespread magma mixing, including complexly zoned plagioclase, clinopyroxene and amphibole containing glass inclusions of trachyte and rhyolite compositions. The observed rocks result from fractionation and mixing of three principal magma types: (a) calc-alkaline high-Al basalt that fractionated to andesite at the base of crust; (b) partially melted metabasaltic amphibolite underplated at the base of crust, that fractionated to produce high-SiO 2 rhyolite; and (c) a minor component of trachytic magma from partial melting of enriched subcontinental lithospheric mantle. The complexly zoned phenocrysts with glass inclusions provide specific evidence for mixing of these three components. Specifically, it was the emplacement of the andesite into a voluminous rhyolite magma in a mid-crustal magma chamber that led to the explosive Kos Plateau Tuff super-eruption.

  5. Isotopic characterisation of the sub-continental lithospheric mantle beneath Zealandia, a rifted fragment of Gondwana

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Scott, James M.; van der Meer, Quinten Har Adriaan

    2013-01-01

    The greater New Zealand region, known as Zealandia, represents an amalgamation of crustal fragments accreted to the paleo-Pacific Gondwana margin and which underwent significant thinning during the subsequent split from Australia and Antarctica in the mid-Cretaceous following opening of the Tasma...... Sea and the Southern Ocean. We present Sr, Nd and Pb isotopes and laser ablation trace element data for a comprehensive suite of clinopyroxene separates from spinel peridotite xenoliths (lherzolite to harzburgite) from the sub-continental lithospheric mantle across southern New Zealand...... composition, age or geographical separation. These isotopic compositions indicate that the sub-continental lithospheric mantle under southern New Zealand has a regionally distinct and pervasive FOZO to HIMU – like signature. The isotopic signatures are also similar to those of the alkaline magmas...... that transported the xenoliths and suggest that most of the HIMU signature observed in the volcanics could be derived from a major source component in the sub-continental lithospheric mantle. Trace element abundances in clinopyroxene are highly heterogeneous and vary from LREE-enriched, relatively flat and MORB...

  6. The Magmatic Plumbing System of the Campi Flegrei Caldera.

    Science.gov (United States)

    Lucia, C.; Ilenia, A.; Massimo, D.; Valeria, D.; Mauro, D.; Giovanni, O.

    2006-12-01

    The Campi Flegrei caldera is a nested and resurgent structure generated by at least two major collapses. Large sectors of the structural boundary of both calderas resulted from partial reactivation of pre-existing faults generated by regional tectonism. Its magmatic system is still active with the last eruption occurring in 1538 A.D. (Monte Nuovo), widespread fumaroles and hot springs activity, and the unrest episodes in the last 35 years, with a maximum net uplift of about 3.5 m in the Pozzuoli area. The definition of the history of the magmatic feeding system of this caldera, in terms of composition, time- scale and depth of crystallization, relation between composition of the erupted magma and structural position of the vent, and magma chamber processes, is of extreme importance for a better understanding of the dynamic conditions of the present day magma chamber and for evaluating of the extent to which the behavior of the magmatic system can be predicted. The Campi Flegrei caldera magmatic plumbing system is characterized by deep and shallow reservoirs. Campi Flegrei magmas originated in a subduction modified mantle source, stagnate at mid crustal level (20- 10 km depth), where they differentiated and are contaminated with the continental crust. From the "deep reservoir" shoshonitic to latitic magmas rise towards the surface along the NE aligned regional fault reactivated during the caldera collapse, whereas trachytic magmas rise mostly along faults and fractures bordering the resurgent block and the southern part of the Campi Flegrei caldera. Repeated arrival of trachytic to phonolitic magmas form shallow reservoirs at 4-3 km depth, in which differentiation and mixing processes occur before and during the eruption.

  7. Post waterflood CO{sub 2} miscible flood in light oil, fluvial: Dominated deltaic reservoirs. Second quarterly technical progress report, Fiscal year 1994, January 1, 1994--March 31, 1994

    Energy Technology Data Exchange (ETDEWEB)

    1994-04-29

    Production resumed from the Port Neches CO{sub 2} project on December 6, 1993, after a 75 days shut in period. Since that date production is continuing to improve on various wells that responded to CO{sub 2} injection. Current production is averaging 325 BOPD from 3 wells. This represents 4 folds increase from the production level prior to commencing CO{sub 2} injection. Texaco continue to purchase an average of 4.3 MMCF/D of CO{sub 2} from Cardox. The reservoir pressure increased with CO{sub 2} injection from 2460 psi in September 1993 to 3328 psi in January 1994. However, the reservoir pressure declined slightly since then to 2730 psi in March of this year because of reservoir imbalance due to downtime at the CO{sub 2} source. Currently, CO{sub 2} is being injected in 3 wells in the reservoir including the horizontal well drilled specifically for this purpose. The well, through its 250 ft horizontal section, is capable of taking all the available CO{sub 2} volume. However, injection rate in the well is restricted in order to distribute the CO{sub 2} evenly in the reservoir. Texaco is continuing its efforts to transfer this technology to other operators by presenting two papers at the SPE/DOE symposium that was hold on April 17--20, 1994, in Tulsa, Oklahoma. One paper will discuss reservoir characterization and project design, while the other paper will discuss the development of the screening model. This model is scheduled for release to the public in 1994, it will be a very useful screening and design tool for the industry. A topical report covering the environmental regulations and constrains related to the implementation of similar projects, will be released later this year.

  8. Magma Chambers, Thermal Energy, and the Unsuccessful Search for a Magma Chamber Thermostat

    Science.gov (United States)

    Glazner, A. F.

    2015-12-01

    Although the traditional concept that plutons are the frozen corpses of huge, highly liquid magma chambers ("big red blobs") is losing favor, the related notion that magma bodies can spend long periods of time (~106years) in a mushy, highly crystalline state is widely accepted. However, analysis of the thermal balance of magmatic systems indicates that it is difficult to maintain a significant portion in a simmering, mushy state, whether or not the system is eutectic-like. Magma bodies cool primarily by loss of heat to the Earth's surface. The balance between cooling via energy loss to the surface and heating via magma accretion can be denoted as M = ρLa/q, where ρ is magma density, L is latent heat of crystallization, a is the vertical rate of magma accretion, and q is surface heat flux. If M>1, then magma accretion outpaces cooling and a magma chamber forms. For reasonable values of ρ, L, and q, the rate of accretion amust be > ~15 mm/yr to form a persistent volume above the solidus. This rate is extremely high, an order of magnitude faster than estimated pluton-filling rates, and would produce a body 10 km thick in 700 ka, an order of magnitude faster than geochronology indicates. Regardless of the rate of magma supply, the proportion of crystals in the system must vary dramatically with depth at any given time owing to transfer of heat. Mechanical stirring (e.g., by convection) could serve to homogenize crystal content in a magma body, but this is unachievable in crystal-rich, locked-up magma. Without convection the lower part of the magma body becomes much hotter than the top—a process familiar to anyone who has scorched a pot of oatmeal. Thermal models that succeed in producing persistent, large bodies of magma rely on scenarios that are unrealistic (e.g., omitting heat loss to the planet's surface), self-fulfilling prophecies (e.g., setting unnaturally high temperatures as fixed boundary conditions), or physically unreasonable (e.g., magma is intruded

  9. CO<sub>2sub> Saline Storage Demonstration in Colorado Sedimentary Basins. Applied Studies in Reservoir Assessment and Dynamic Processes Affecting Industrial Operations

    Energy Technology Data Exchange (ETDEWEB)

    Nummedal, Dag [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Doran, Kevin [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Sitchler, Alexis [Trustees Of The Colorado School Of Mines, Golden, CO (United States); McCray, John [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Mouzakis, Katherine [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Glossner, Andy [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Mandernack, Kevin [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Gutierrez, Marte [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Pranter, Matthew [Trustees Of The Colorado School Of Mines, Golden, CO (United States); Rybowiak, Chris [Trustees Of The Colorado School Of Mines, Golden, CO (United States)

    2012-09-30

    This multitask research project was conducted in anticipation of a possible future increase in industrial efforts at CO<sub>2sub> storage in Colorado sedimentary basins. Colorado is already the home to the oldest Rocky Mountain CO<sub>2sub> storage site, the Rangely Oil Field, where CO<sub>2sub>-EOR has been underway since the 1980s. The Colorado Geological Survey has evaluated storage options statewide, and as part of the SW Carbon Sequestration Partnership the Survey, is deeply engaged in and committed to suitable underground CO<sub>2sub> storage. As a more sustainable energy industry is becoming a global priority, it is imperative to explore the range of technical options available to reduce emissions from fossil fuels. One such option is to store at least some emitted CO<sub>2sub> underground. In this NETL-sponsored CO<sub>2sub> sequestration project, the Colorado School of Mines and our partners at the University of Colorado have focused on a set of the major fundamental science and engineering issues surrounding geomechanics, mineralogy, geochemistry and reservoir architecture of possible CO<sub>2sub> storage sites (not limited to Colorado). Those are the central themes of this final report and reported below in Tasks 2, 3, 4, and 6. Closely related to these reservoir geoscience issues are also legal, environmental and public acceptance concerns about pore space accessibility—as a precondition for CO<sub>2sub> storage. These are addressed in Tasks 1, 5 and 7. Some debates about the future course of the energy industry can become acrimonius. It is true that the physics of combustion of hydrocarbons makes it impossible for fossil energy to attain a carbon footprint anywhere nearly as low as that of renewables. However, there are many offsetting benefits, not the least that fossil energy is still plentiful, it has a global and highly advanced distribution system in place, and the footprint that the fossil energy infrastructure occupies is

  10. Advanced Reservoir Characterization and Evaluation of CO{sub 2} Gravity Drainage in the Naturally Fractured Spraberry Trend Area

    Energy Technology Data Exchange (ETDEWEB)

    Schechter, D.S.

    1999-02-03

    The overall goal of this project is to assess the economic feasibility of CO{sub 2} flooding the naturally fractured Spraberry Trend Area in West Texas. This objective is being accomplished by conducting research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interactions in the reservoirs, (3) reservoir performance analysis, and, (4) experimental investigations on CO2 gravity drainage in Spraberry whole cores. This report provides results of the third year of the five-year project for each of the four areas including a status report of field activities leading up to injection of CO2.

  11. Magma reservoir at Mt. Vesuvius: Deeper than 10 km

    International Nuclear Information System (INIS)

    Natale, M.; Luongo, G.; Nunziata, C.; Panza, G.F.

    2005-07-01

    One- and two-dimensional Vp models were obtained by TomoVes experiment, all characterized by low Vp in the uppermost 500 m and a sharp discontinuity at about 2-3 km beneath the volcano. Large amplitude late arrivals were identified as P- to S-phases converted at the top, between 8 and 10 km deep, of a low velocity layer with a dramatic drop of Vs, from approximately 3.6 km/s to less than 1.0 km/s. Here we synthesize the interpretation of Rayleigh wave dispersion measurements, made by several authors, to delineate the extent of such anomalous layer of hot, partially molten, crust material. Our non-linear inversion of broad-band dispersion measurements, gives a thickness not greater than 0.35 km, if we assume Vs equal to 1.0 km/s. The volume occupied by this very low velocity layer, sill shaped, is compatible with the size of Mt. Vesuvius cone, but it develops above a much larger hot mass which could be the parental source as the erupted products are only few percent of magma chamber. (author)

  12. Natural CO{sub 2} migrations in the South-Eastern Basin of France: implications for the CO{sub 2} storage in sedimentary formations; Contribution a la connaissance des migrations de CO{sub 2} naturel dans le Bassin du Sud-Est de la France: enseignements pour le stockage geologique du CO{sub 2} dans les reservoirs sedimentaires

    Energy Technology Data Exchange (ETDEWEB)

    Rubert, Y.

    2009-03-15

    Study of natural CO{sub 2} analogues brings key informations on the factors governing the long term stability/instability of future anthropogenic CO{sub 2} storages. The main objective of this work, through the study of cores from V.Mo.2 well crosscutting the Montmiral natural reservoir (Valence Basin, France), is to trace the deep CO{sub 2} migrations in fractures. Petrographic, geochemical and micro-thermometric studies of the V.Mo.2 cores were thus performed in order: 1) to describe the reservoir filling conditions and 2) to detect possible CO{sub 2}-leakage through the sediments overlying the reservoir. Fluid inclusions from the Paleozoic crystalline basement record the progressive unmixing of a hot homogeneous aquo-carbonic fluid. The Montmiral reservoir was therefore probably fed by a CO{sub 2}-enriched gas component at the Late Cretaceous-Paleogene. The study of the sedimentary column in V.Mo.2 well, demonstrates that the CO{sub 2} did not migrate towards the surface through the thick marly unit (Domerian-Middle Oxfordian). These marls have acted as an impermeable barrier that prevented the upward migration of fluids. Two main stages of fluid circulation have been recognized: 1) an ante- Callovian one related to the Tethysian extension 2) a tertiary stage during which the upper units underwent a karstification, with CO{sub 2} leakage related but which remained confined into the deeper parts of the Valence Basin. Since the Paleogene, the Montmiral reservoir has apparently remained stable, despite the Pyrenean and alpine orogeneses. This is mainly due to the efficient seal formed by the thick marly levels and also to the local structuration in faulted blocks which apparently acted as efficient lateral barriers. (author)

  13. Magma-assisted strain localization in an orogen-parallel transcurrent shear zone of southern Brazil

    Science.gov (United States)

    Tommasi, AndréA.; Vauchez, Alain; Femandes, Luis A. D.; Porcher, Carla C.

    1994-04-01

    In a lithospheric-scale, orogen-parallel transcurrent shear zone of the Pan-African Dom Feliciano belt of southern Brazil, two successive generations of magmas, an early calc-alkaline and a late peraluminous, have been emplaced during deformation. Microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions. Magmatic deformation is indicated by the coexistence of aligned K-feldspar, plagioclase, micas, and/or tourmaline with undeformed quartz. Submagmatic deformation is characterized by strain features, such as fractures, lattice bending, or replacement reactions affecting only the early crystallized phases. High-temperature solid-state deformation is characterized by extensive grain boundary migration in quartz, myrmekitic K-feldspar replacement, and dynamic recrystallization of both K-feldspar and plagioclase. Decreasing temperature during solid-state deformation is inferred from changes in quartz crystallographic fabrics, decrease in grain size of recrystallized feldspars, and lower Ti amount in recrystallized biotites. Final low-temperature deformation is characterized by feldspar replacement by micas. The geochemical evolution of the synkinematic magmatism, from calc-alkaline metaluminous granodiorites with intermediate 87Sr/86Sr initial ratio to peraluminous granites with very high 87Sr/86Sr initial ratio, suggests an early lower crustal source or a mixed mantle/crustal source, followed by a middle to upper crustal source for the melts. Shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle, but, whatever the process initiating partial melting, lithospheric transcurrent shear zones may collect melt at different depths. Because they enhance the vertical permeability of the crust, these zones may then act as heat conductors (by advection), promoting an upward propagation of partial melting in the crust

  14. Geomechanical Framework for Secure CO<sub>2sub> Storage in Fractured Reservoirs and Caprocks for Sedimentary Basins in theMidwest United States

    Energy Technology Data Exchange (ETDEWEB)

    Sminchak, Joel [Battelle, Columbus, OH (United States)

    2017-09-29

    This report presents final technical results for the project Geomechanical Framework for Secure CO<sub>2sub> Storage in Fractured Reservoirs and Caprocks for Sedimentary Basins in the Midwest United States (DE-FE0023330). The project was a three-year effort consisting of seven technical tasks focused on defining geomechanical factors for CO<sub>2sub> storage applications in deep saline rock formations in Ohio and the Midwest United States, because geomechancial issues have been identified as a significant risk factor for large-scale CO<sub>2sub> storage applications. A basin-scale stress-strain analysis was completed to describe the geomechanical setting for rock formations of Ordovician-Cambrian age in Ohio and adjacent areas of the Midwest United States in relation to geologic CO<sub>2sub> storage applications. The tectonic setting, stress orientation-magnitude, and geomechanical and petrophysical parameters for CO<sub>2sub> storage zones and caprocks in the region were cataloged. Ten geophysical image logs were analyzed for natural fractures, borehole breakouts, and drilling-induced fractures. The logs indicated mostly less than 10 fractures per 100 vertical feet in the borehole, with mostly N65E principal stress orientation through the section. Geophysical image logs and other logs were obtained for three wells located near the sites where specific models were developed for geomechanical simulations: Arches site in Boone County, Kentucky; Northern Appalachian Basin site in Chautauqua County, New York; and E-Central Appalachian Basin site in Tuscarawas County, Ohio. For these three wells, 9,700 feet of image logs were processed and interpreted to provide a systematic review of the distribution within each well of natural fractures, wellbore breakouts, faults, and drilling induced fractures. There were many borehole breakouts and drilling-induced tensile fractures but few natural fractures. Concentrated fractures were present at the Rome-basal sandstone

  15. Geochemical and Sr-Nd-Pb-Li isotopic characteristics of volcanic rocks from the Okinawa Trough: Implications for the influence of subduction components and the contamination of crustal materials

    Science.gov (United States)

    Guo, Kun; Zhai, Shikui; Yu, Zenghui; Wang, Shujie; Zhang, Xia; Wang, Xiaoyuan

    2018-04-01

    The Okinawa Trough is an infant back-arc basin developed along the Ryukyu arc. This paper provides new major and trace element and Sr-Nd-Pb-Li isotope data of volcanic rocks in the Okinawa Trough and combines the published geochemical data to discuss the composition of magma source, the influence of subduction component, and the contamination of crustal materials, and calculate the contribution between subduction sediment and altered oceanic crust in the subduction component. The results showed that there are 97% DM and 3% EMI component in the mantle source in middle trough (MS), which have been influenced by subduction sediment. The Li-Nd isotopes indicate that the contribution of subduction sediment and altered oceanic crust in subduction component are 4 and 96%, respectively. The intermediate-acidic rocks suffer from contamination of continental crust material in shallow magma chamber during fractional crystallization. The acidic rocks in south trough have experienced more contamination of crustal material than those from the middle and north trough segments.

  16. Detailed crustal structure of the North China and its implication for seismicity

    Science.gov (United States)

    Jiang, Wenliang; Wang, Xin; Tian, Tian; Zhang, Jingfa; Wang, Donglei

    2014-02-01

    Since the Mesozoic-Cenozoic era the North China Craton has experienced an important tectonic transition and it has given rise to complicated crustal structure and strong earthquake activity. Based on the large-scale surface gravity data, we studied the detailed crustal structure and seismogenic mechanism of the North China. The results indicate that the North China presents typical characteristics of adjoining depression and uplift, alternating basins and hills, inhomogeneous density and also great differences in crustal structure and Moho topography. The upper and middle crustal structures are dominated by the NNE-striking tectonic units, with many faults cut down to the middle crust. The lower crust is characterized by the folding-structure, with high and low-density placed alternately from west to east, presenting lateral heterogeneous feature. Adjusted by the gravity isostasy, Moho topography of the North China fluctuates greatly. Compared with the North China Basin, crustal thickness in the Western Taihang, northern Yanshan and Luzhong areas are much thicker while those densities are lower than the North China Basin. The dominating tectonic direction of the Moho topography strikes NE to NNE and undulates alternately from west to east. The epicenters are mostly concentrated in the upper and middle crust, especially the transitional areas between the high and low-gravity anomalies. The Tancheng earthquake in 1668, Sanhe earthquake in 1673, Tangshan earthquake in 1976, and all other seismic tectonic zones of the North China are all distributed in area where magma moves strongly beneath the crust, which is considered to be related to the movement of the high density, unstable and heat flows along the deep passage from the uppermost and asthenosphere due to the subduction of the Pacific slab towards the Eurasian plate.

  17. Zircon evidence for incorporation of terrigenous sediments into the magma source of continental basalts.

    Science.gov (United States)

    Xu, Zheng; Zheng, Yong-Fei; Zhao, Zi-Fu

    2018-01-09

    Crustal components may be incorporated into continental basalts by either shallow contamination or deep mixing. While the former proceeds at crustal depths with common preservation of refractory minerals, the latter occurs at mantle depths with rare survival of relict minerals. Discrimination between the two mechanisms has great bearing to subcontinental mantle geochemistry. Here we report the occurrence of relict zircons in Cenozoic continental basalts from eastern China. A combined study of zircon U-Pb ages and geochemistry indicates that detrital zircons were carried by terrigenous sediments into a subcontinental subduction zone, where the zircon were transferred by fluids into the magma sources of continental basalts. The basalts were sampled from three petrotectonic units with distinct differences in their magmatic and metamorphic ages, making the crustal contamination discernible. The terrigenous sediments were carried by the subducting oceanic crust into the asthenospheric mantle, producing both soluble and insoluble materials at the slab-mantle interface. These materials were served as metasomatic agents to react with the overlying mantle wedge peridotite, generating a kind of ultramafic metasomatites that contain the relict zircons. Therefore, the occurrence of relict zircons in continental basalts indicates that this refractory mineral can survive extreme temperature-pressure conditions in the asthenospheric mantle.

  18. Episodic deflation-inflation events at Kīlauea Volcano and implications for the shallow magma system: Chapter 11

    Science.gov (United States)

    Anderson, Kyle R.; Poland, Michael; Johnson, Jessica H.; Miklius, Asta; Carey, Rebecca; Cayol, Valérie; Poland, Michael P.; Weis, Dominique

    2015-01-01

    Episodic variations in magma pressures and flow rates at Kīlauea Volcano, defined by a characteristic temporal evolution and termed deflation-inflation (DI) events, have been observed since at least the 1990s. DI events consist of transient, days-long deflations and subsequent reinflations of the summit region, accompanied since 2008 by fluctuations in the surface height of Kīlauea's summit lava lake. After a delay of minutes to hours, these events also often appear along the volcano's East Rift Zone in ground deformation data and as temporary reductions in eruption rate (sometimes followed by brief surges). Notable pauses in DI activity have preceded many eruptive events at Kīlauea. We analyzed more than 500 DI events recorded by borehole tiltmeters at the summit during 2000–2013. Inverse modeling suggests that DI-related ground deformation at the summit is generated by pressure transients in a shallow magma reservoir located beneath the east margin of Halema‘uma‘u Crater and that this reservoir has remained remarkably stable for more than a decade. Utilizing tilt data and variation in the level of the summit lava lake during a large DI event, we estimate a reservoir volume of approximately 1 km3 (0.2–5.5 km3 at 95% confidence).

  19. Temporal Evolution of Surface Deformation and Magma Sources at Pacaya Volcano, Guatemala Revealed by InSAR

    Science.gov (United States)

    Wnuk, K.; Wauthier, C.

    2016-12-01

    Pacaya Volcano, Guatemala is a persistently active volcano whose western flank is unstable. Despite continuous activity since 1961, a lack of high temporal resolution geodetic surveying has prevented detailed modeling of Pacaya's underlying magmatic plumbing system. A new, temporally dense dataset of Interferometric Synthetic Aperture Radar (InSAR) RADARSAT-2 images, spanning December 2012 to March 2014, shows magmatic deformation before and during major eruptions in January and March 2014. Inverse modeling of InSAR surface displacements suggest that three magma bodies are responsible for observed deformation: (1) a 3.7 km deep spherical reservoir located northwest of the summit, (2) a 0.4 km deep spherical source located directly west of the summit, and (3) a shallow dike below the summit that provides the primary transport pathway for erupted materials. Periods of heightened activity are brought on by magma pulses at depth, which result in rapid inflation of the edifice. We observe an intrusion cycle at Pacaya that consists of deflation of one or both magma reservoirs followed by dike intrusion. Intrusion volumes are proportional to reservoir volume loss, and do not always result in an eruption. Periods of increased activity culminate with larger dike fed eruptions. Large eruptions are followed by inter eruptive periods marked by a decrease in crater explosions and a lack of deformation. A full understanding of magmatic processes at Pacaya is required to assess potential impacts on other aspects of the volcano such as the unstable western flank. Co-eruptive flank motion appears to have initiated a new stage of volcanic rifting at Pacaya defined by repeated NW-SE dike intrusions. This creates a positive feedback relationship whereby magmatic forcing from eruptive dike intrusions induces flank motion

  20. Analysis of crustal thickness and off-axis low-velocity zones at the Endeavour segment of the Juan de Fuca Ridge

    Science.gov (United States)

    Wells, A. E.; Hooft, E. E.; Toomey, D. R.; Wilcock, W. S.; Weekly, R. T.

    2010-12-01

    Construction of the oceanic crust is often thought to occur by delivery of melt from the mantle to the ridge axis that is both segment-centered and rise-centered. However, recent seismic studies at the fast-spreading East Pacific Rise show that mantle melt delivery can be skewed relative to the rise leading to off-axis delivery of melt. Furthermore foci of mantle melt delivery occur on a length-scale shorter than that of a ridge segment and the region of greater melt supply, as measured by crustal thickness, does not correspond to the segment center. We use seismic data from the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge to investigate the spatial and temporal pattern of melt supply in this setting and whether off-axis delivery and transport of melt is a common occurrence. The Juan de Fuca Ridge has a transitional morphology characterized by fault-bounded ridges that parallel the spreading center. Previous models of the Endeavour segment inferred that the off-axis ridges are constructed during periods of enhanced magmatism and that these are separated by the remains of rift valleys generated during periods of reduced magmatism. This model may imply that crustal thickness should vary rapidly, with thicker crust beneath the off-axis ridges and thinner crust in between. Alternatively, on the basis of recent seismic reflection images of crustal magma bodies along the Juan de Fuca ridge this topography is thought to reflect magma-induced deformation resulting from feedbacks between the rheology of the crust above the magma sill and dike intrusion. In this case, short wavelength crustal thickness variations may not be present. The melting anomalies associated with various nearby seamount chains also influence processes along the Juan de Fuca Ridge. The seismic reflection work indicates that there is a ~40-km-wide plateau of greater crustal thickness (~0.5-1.0 km) at the center of the Endeavour segment that began forming about 0.7 Ma. The plateau

  1. The fluid dynamics of a basaltic magma chamber replenished by influx of hot, dense ultrabasic magma

    Science.gov (United States)

    Huppert, Herbert E.; Sparks, R. Stephen J.

    1981-09-01

    This paper describes a fluid dynamical investigation of the influx of hot, dense ultrabasic magma into a reservoir containing lighter, fractionated basaltic magma. This situation is compared with that which develops when hot salty water is introduced under cold fresh water. Theoretical and empirical models for salt/water systems are adapted to develop a model for magmatic systems. A feature of the model is that the ultrabasic melt does not immediately mix with the basalt, but spreads out over the floor of the chamber, forming an independent layer. A non-turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion. Both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock. The convection continues until the two layers have almost the same temperature. The compositions of the layers remain distinct due to the low diffusivity of mass compared to heat. The temperatures of the layers as functions of time and their cooling rate depend on their viscosities, their thermal properties, the density difference between the layers and their thicknesses. For a layer of ultrabasic melt (18% MgO) a few tens of metres thick at the base of a basaltic (10% MgO) magma chamber a few kilometres thick, the temperature of the layers will become nearly identical over a period of between a few months and a few years. During this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling. Olivines only settle after the two layers have nearly reached thermal equilibrium. At this stage residual basaltic melt segregates as the olivines sediment in the lower layer. Depending on its density, the released basalt can either mix convectively with the overlying basalt layer, or can continue as a separate

  2. Crustal structure, evolution, and volcanic unrest of the Alban Hills, Central Italy

    Science.gov (United States)

    Chiarabba, C.; Amato, A.; Delaney, P.T.

    1997-01-01

    The Alban Hills, a Quaternary volcanic center lying west of the central Apennines, 15-25 km southeast of Rome, last erupted 19ka and has produced approximately 290 km3 of eruptive deposits since the inception of volcanism at 580 ka. Earthquakes of moderate intensity have been generated there at least since the Roman age. Modern observations show that intermittent periods of swarm activity originate primarily beneath the youngest features, the phreatomagmatic craters on the west side of the volcano. Results from seismic tomography allow identification of a low-velocity region, perhaps still hot or partially molten, more than 6 km beneath the youngest craters and a high-velocity region, probably a solidified magma body, beneath the older central volcanic construct. Thirty centimeters of uplift measured by releveling supports the contention that high levels of seismicity during the 1980s and 1990s resulted from accumulation of magma beneath these craters. The volume of magma accumulation and the amount of maximum uplift was probably at least 40 ?? 106 m3 and 40 cm, respectively. Comparison of newer levelings with those completed in 1891 and 1927 suggests earlier episodes of uplift. The magma chamber beneath the western Alban Hills is probably responsible for much of the past 200 ka of eruptive activity, is still receiving intermittent batches of magma, and is, therefore, continuing to generate modest levels of volcanic unrest. Bending of overburden is the most likely cause of the persistent earthquakes, which generally have hypocenters above the 6-km-deep top of the magma reservoir. In this view, the most recent uplift and seismicity are probably characteristic and not precursors of more intense activity.

  3. Thermal and petrologic constraints on lower crustal melt accumulation under the Salton Sea Geothermal Field

    Science.gov (United States)

    Karakas, Ozge; Dufek, Josef; Mangan, Margaret T.; Wright, Heather M.; Bachmann, Olivier

    2017-06-01

    In the Salton Sea region of southern California (USA), concurrent magmatism, extension, subsidence, and sedimentation over the past 0.5 to 1.0 Ma have led to the creation of the Salton Sea Geothermal Field (SSGF)-the second largest and hottest geothermal system in the continental United States-and the small-volume rhyolite eruptions that created the Salton Buttes. In this study, we determine the flux of mantle-derived basaltic magma that would be required to produce the elevated average heat flow and sustain the magmatic roots of rhyolite volcanism observed at the surface of the Salton Sea region. We use a 2D thermal model to show that a lower-crustal, partially molten mush containing Salton Trough, and are consistent with seismic observations. Our results indicate limited melting and assimilation of pre-existing rocks in the lower crust. Instead, we find that basalt fractionation in the lower crust produces derivative melts of andesitic to dacitic composition. Such melts are then expected to ascend and accumulate in the upper crust, where they further evolve to give rise to small-volume rhyolite eruptions (Salton Buttes) and fuel local spikes in surface heat flux as currently seen in the SSGF. Such upper crustal magma evolution, with limited assimilation of hydrothermally altered material, is required to explain the slight decrease in δ18 O values of zircons (and melts) that have been measured in these rhyolites.

  4. APPLICATION OF RESERVOIR CHARACTERIZATION AND ADVANCED TECHNOLOGY TO IMPROVE RECOVERY AND ECONOMICS IN A LOWER QUALITY SHALLOW SHELF SAN ANDRES RESERVOIR

    Energy Technology Data Exchange (ETDEWEB)

    Tom Beebe

    2003-05-05

    The OXY-operated Class 2 Project at West Welch is designed to demonstrate how the use of advanced technology can improve the economics of miscible CO{sub 2} injection projects in lower quality Shallow Shelf Carbonate reservoirs. The research and design phase (Budget Period 1) primarily involved advanced reservoir characterization. The current demonstration phase (Budget Period 2) is the implementation of the reservoir management plan for an optimum miscible CO{sub 2} flood design based on the reservoir characterization. Although Budget Period 1 for the Project officially ended 12/31/96, reservoir characterization and simulation work continued during the Budget Period 2. During the seventh annual reporting period (8/3/00-8/2/01) covered by this report, work continued on interpretation of the interwell seismic data to create porosity and permeability profiles which were distributed into the reservoir geostatistically. The initial interwell seismic CO{sub 2} monitor survey was conducted and the acquired data processed and interpretation started. Only limited well work and facility construction were conducted in the project area. The CO{sub 2} injection initiated in October 1997 was continued, although the operator had to modify the operating plan in response to low injection rates, well performance and changes in CO{sub 2} supply. CO{sub 2} injection was focused in a smaller area to increase the reservoir processing rate. By the end of the reporting period three producers had shown sustained oil rate increases and six wells had experienced gas (CO{sub 2}) breakthrough.

  5. Volatile Contents in Mafic Magmas from two Aleutian volcanoes: Augustine and Makushin

    Science.gov (United States)

    Zimmer, M. M.; Plank, T.; Hauri, E. H.; Nye, C.; Faust Larsen, J.; Kelemen, P. B.

    2004-12-01

    contents at Pakushin reflect a difference in the primary magma, or in crustal stresses that favor low pressure fractionation and degassing. These questions will be addressed with further work on the trace element contents of the melt inclusions and on phenocryst-melt geobarometers.

  6. Shallow Miocene basaltic magma reservoirs in the Bahia de Los Angeles basin, Baja California, Mexico

    Science.gov (United States)

    Delgado-Argote, Luis A.; García-Abdeslem, Juan

    1999-01-01

    The basement in the Bahía de Los Angeles basin consists of Paleozoic metamorphic rocks and Cretaceous granitoids. The Neogene stratigraphy overlying the basement is formed, from the base to the top, by andesitic lava flows and plugs, sandstone and conglomeratic horizons, and Miocene pyroclastic flow units and basaltic flows. Basaltic dikes also intrude the whole section. To further define its structure, a detailed gravimetric survey was conducted across the basin about 1 km north of the Sierra Las Flores. In spite of the rough and lineal topography along the foothills of the Sierra La Libertad, we found no evidence for large-scale faulting. Gravity data indicates that the basin has a maximum depth of 120 m in the Valle Las Tinajas and averages 75 m along the gravimetric profile. High density bodies below the northern part of the Sierra Las Flores and Valle Las Tinajas are interpreted to be part of basaltic dikes. The intrusive body located north of the Sierra Las Flores is 2.5 km wide and its top is about 500 m deep. The lava flows of the top of the Sierra Las Flores, together with the distribution of basaltic activity north of this sierra, suggests that this intrusive body continues for 20 km along a NNW-trending strike. Between the sierras Las Flores and Las Animas, a 0.5-km-wide, 300-m-thick intrusive body is interpreted at a depth of about 100 m. This dike could be part of the basaltic activity of the Cerro Las Tinajas and the small mounds along the foothills of western Sierra Las Animas. The observed local normal faulting in the basin is inferred to be mostly associated with the emplacement of the shallow magma reservoirs below Las Flores and Las Tinajas.

  7. Experimental simulation of magma-carbonate interaction beneath Mt. Vesuvius, Italy

    Science.gov (United States)

    Jolis, E. M.; Freda, C.; Troll, V. R.; Deegan, F. M.; Blythe, L. S.; McLeod, C. L.; Davidson, J. P.

    2013-11-01

    We simulated the process of magma-carbonate interaction beneath Mt. Vesuvius in short duration piston-cylinder experiments under controlled magmatic conditions (from 0 to 300 s at 0.5 GPa and 1,200 °C), using a Vesuvius shoshonite composition and upper crustal limestone and dolostone as starting materials. Backscattered electron images and chemical analysis (major and trace elements and Sr isotopes) of sequential experimental products allow us to identify the textural and chemical evolution of carbonated products during the assimilation process. We demonstrate that melt-carbonate interaction can be extremely fast (minutes), and results in dynamic contamination of the host melt with respect to Ca, Mg and 87Sr/86Sr, coupled with intense CO2 vesiculation at the melt-carbonate interface. Binary mixing between carbonate and uncontaminated melt cannot explain the geochemical variations of the experimental charges in full and convection and diffusion likely also operated in the charges. Physical mixing and mingling driven by exsolving volatiles seems to be a key process to promote melt homogenisation. Our results reinforce hypotheses that magma-carbonate interaction is a relevant and ongoing process at Mt. Vesuvius and one that may operate not only on a geological, but on a human timescale.

  8. The Ladbroke Grove-Katnook carbon dioxide natural laboratory: a recent CO{sub 2} accumulation in a lithic sandstone reservoir

    Energy Technology Data Exchange (ETDEWEB)

    Watson, M.N. [Adelaide Univ., SA (Australia). Australian School of Petroleum; Zwingmann, N. [CSIRO Petroleum, Bentley, WA (Australia); Lemon, N.M. [Santos Ltd., Adelaide, SA (Australia)

    2004-08-01

    The Ladbroke Grove and Katnook Gas Fields, within the western Otway Basin, southeastern South Australia, provide a natural laboratory to study the effects of CO{sub 2} on siliciclastic reservoirs. CO{sub 2} degassing from nearby volcanics has migrated into the methane accumulation of the Ladbroke Grove Field within the Pretty Hill Formation. CO{sub 2} levels in the Ladbroke Grove Field range from 26 to 57 mol% while Katnook has less than 1 mol%. In Ladbroke Grove, the CO{sub 2} has altered or dissolved most of the reactive minerals, somewhat constrained by the Pleistocene to Recent age of the CO{sub 2} influx. The developed late-stage kaolinite, quartz and less soluble carbonate are products of the reactions involving CO{sub 2} and reactive minerals. The major formation water types were identified using the geochemical code EQ3NR. Ladbroke Grove waters above the gas-water contact (GWC) have bicarbonate levels an order of magnitude higher than the other waters analysed. Below the GWC, Ladbroke Grove and Katnook formation waters have similar ionic compositions, however, pH levels in Ladbroke Grove are low relative to Katnook. The Ladbroke Grove Field has efficiently stored CO{sub 2} in a gaseous and aqueous phase since the influx began in the Pleistocene. In addition, due to the high amount of reactive minerals within the reservoir, mineralisation of ferroan carbonates has also occurred as a more permanent form of mineral storage of some of the CO{sub 2}. (author)

  9. Crustal Magnetic Field Anomalies and Global Tectonics

    Science.gov (United States)

    Storetvedt, Karsten

    2014-05-01

    A wide variety of evidence suggests that the ruling isochron (geomagnetic polarity versus age) hypothesis of marine magnetic lineations has no merit - undermining therefore one of the central tenets of plate tectonics. Instead, variable induction by the ambient geomagnetic field is likely to be the principal agent for mega-scale crustal magnetic features - in both oceanic and continental settings. This revitalizes the fault-controlled susceptibility-contrast model of marine magnetic lineations, originally proposed in the late 1960s. Thus, the marine magnetic 'striping' may be ascribed to tectonic shearing and related, but variable, disintegration of the original iron-oxide mineralogy, having developed primarily along one of the two pan-global sets of orthogonal fractures and faults. In this way, fault zones (having the more advanced mineral alteration) would be characterized by relatively low susceptibility, while more moderately affected crustal sections (located between principal fault zones) would be likely to have less altered oxide mineralogy and therefore higher magnetic susceptibility. On this basis, induction by the present geomagnetic field is likely to produce oscillating magnetic field anomalies with axis along the principal shear grain. The modus operandi of the alternative magneto-tectonic interpretation is inertia-driven wrenching of the global Alpine age palaeo-lithosphere - triggered by changes in Earth's rotation. Increasing sub-crustal loss to the upper mantle during the Upper Mesozoic had left the ensuing Alpine Earth in a tectonically unstable state. Thus, sub-crustal eclogitization and associated gravity-driven delamination to the upper mantle led to a certain degree of planetary acceleration which in turn gave rise to latitude-dependent, westward inertial wrenching of the global palaeo-lithosphere. During this process, 1) the thin and mechanically fragile oceanic crust were deformed into a new type of broad fold belts, and 2) the continents

  10. Distinctly different parental magmas for plutons and lavas in the central Aleutian arc

    Science.gov (United States)

    Cai, Y.; Rioux, M. E.; Kelemen, P. B.; Goldstein, S. L.; Bolge, L.; Kylander-Clark, A. R.

    2014-12-01

    While it is generally agreed that continental crust is generated by arc magmatism, average arc lavas are basaltic while the bulk continental crust is andesitic, and this has led to many models for secondary reprocessing of the arc crust in order to form continental crust. We report new data on calc-alkaline plutons in the central Aleutians showing that they have distinctly different sources compared to Holocene tholeiitic lavas. Therefore the lavas are not representative of the net magmatic transfer from the mantle into the arc crust. Eocene to Miocene (9-39 Ma) intermediate to felsic plutonic rocks from the central Aleutian arc show higher SiO2 at a given Mg#, higher ɛNd- and ɛHf-values, and lower Pb isotope ratios than Holocene volcanic rocks from the same region. Instead, the plutonic rocks resemble volcanics from the western Aleutians isotopically, and have chemical compositions similar to bulk continental crust. These data could reflect temporal variation of Aleutian magma source compositions, from Eocene-Miocene "isotopically depleted" and predominantly calc-alkaline to Holocene "isotopically enriched" and predominantly tholeiitic. Alternatively, they may reflect different transport and emplacement processes for the magmas that form plutons and lavas: calc-alkaline magmas with higher Si content and high viscosity may preferentially form plutons, perhaps after extensive mid-crustal degassing of initially high water contents. The latter case implies that the upper and middle arc crust is more like the calc-alkaline bulk composition of the continental crust than the lavas alone. Crustal reprocessing mechanisms that preserve upper and middle arc crust, while removing lower arc crust, can account for the genesis and evolution of continental crust. Since gabbroic lower arc crust extends from ca 20-40 km depth, and is density stable over most of this depth range, "delamination" of dense lithologies [1] may not be sufficient to accomplish this. Alternatively

  11. Osmium isotope variations accompanying the eruption of a single lava flow field in the Columbia River Flood Basalt Province

    Science.gov (United States)

    Vye-Brown, C.; Gannoun, A.; Barry, T. L.; Self, S.; Burton, K. W.

    2013-04-01

    Geochemical interpretations of continental flood basalts usually assume that individual lava flows represent compositionally homogenous and rapidly erupted products of large well-mixed magma reservoirs. However, inflated pāhoehoe lavas may develop over considerable periods of time and preserve chemical variations that can be temporally linked through flow formation to eruption sequence thus providing an understanding of magma evolution over the timescale of a single eruption. This study presents comprehensive major, trace element and Re-Os isotope data for a single eruption that formed the 2660 km3 Sand Hollow flow field in the Columbia River Basalt Province, USA. Major and trace element variations accompanying flow emplacement (e.g. MgO 3.09-4.55 wt%, Ni 17.5-25.6 ppm) are consistent with fractional crystallisation, but other petrogenetic processes or variable sources cannot be distinguished. However, there is a systematic shift in the initial 187Os/188Os isotope composition of the magma (age corrected to 15.27 Ma), from 0.174 (lava core) to 1.444 (lava crust) within a single 35 m thick sheet lobe. Lava crust values are more radiogenic than any known mantle source, consistent with previous data indicating that neither an enriched reservoir nor the sub-continental lithospheric mantle are likely to have sourced these basalts. Rather, these data indicate that lavas emplaced during the earliest stages of eruption have higher degrees of crustal contamination. These results highlight the limitations of applying chemostratigraphic correlation across continental flood basalt provinces, the use of single data points to define melt sources and magmatic processes, and the dangers of using conventional isochron techniques in such basalt sequences for absolute chronology.

  12. The T-Reflection and the deep crustal structure of the Vøring Margin offshore Mid-Norway

    Science.gov (United States)

    Abdelmalak, M. M.; Faleide, J. I.; Planke, S.; Gernigon, L.; Zastrozhnov, D.; Shephard, G. E.; Myklebust, R.

    2017-12-01

    Volcanic passive margins are characterized by massive occurrence of mafic extrusive and intrusive rocks, before and during plate breakup, playing major role in determining the evolution pattern and the deep structure of magma-rich margins. Deep seismic reflection data frequently provide imaging of strong continuous reflections in the middle/lower crust. In this context, we have completed a detailed 2D seismic interpretation of the deep crustal structure of the Vøring volcanic margin, offshore mid-Norway, where high-quality seismic data allow the identification of high-amplitude reflections, locally referred to as the T-Reflection (TR). Using the dense seismic grid we have mapped the top of the TR in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The TR is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitude and contact relationships. The TR seems to be connected to deep sill networks and locally located at the continuation of basement high structures or terminates over fractures and faults. The spatial correlation between the filtered positive Bouguer gravity anomalies and the TR indicates that the latter represents a high impedance boundary contrast associated with a high-density/velocity body. Within an uncertainty of ± 2.5 km, the depth of the mapped TR is found to correspond to the depth of the top of the Lower Crustal Body (LCB), characterized by high P-wave velocities (>7 km/s), in 50% of the outer Vøring Margin areas, whereas different depths between the TR and the top LCB are estimated for the remaining areas. We present a tectonic scenario, where a large part of the deep structure could be composed of preserved upper continental basement and middle to lower crustal lenses of inherited and intruded high-grade metamorphic rocks. Deep

  13. Incremental assembly and prolonged consolidation of Cordilleran magma chambers--Evidence from the Southern Rocky Mountain volcanic field

    Science.gov (United States)

    Lipman, Peter W.

    2007-01-01

    Recent inference that Mesozoic Cordilleran plutons grew incrementally during >106 yr intervals, without the presence of voluminous eruptible magma at any stage, minimizes close associations with large ignimbrite calderas. Alternatively, Tertiary ignimbrites in the Rocky Mountains and elsewhere, with volumes of 1–5 × 103 km3, record multistage histories of magma accumulation, fractionation, and solidification in upper parts of large subvolcanic plutons that were sufficiently liquid to erupt. Individual calderas, up to 75 km across with 2–5 km subsidence, are direct evidence for shallow magma bodies comparable to the largest granitic plutons. As exemplified by the composite Southern Rocky Mountain volcanic field (here summarized comprehensively for the first time), which is comparable in areal extent, magma composition, eruptive volume, and duration to continental-margin volcanism of the central Andes, nested calderas that erupted compositionally diverse tuffs document deep composite subsidence and rapid evolution in subvolcanic magma bodies. Spacing of Tertiary calderas at distances of tens to hundreds of kilometers is comparable to Mesozoic Cordilleran pluton spacing. Downwind ash in eastern Cordilleran sediments records large-scale explosive volcanism concurrent with Mesozoic batholith growth. Mineral fabrics and gradients indicate unified flow-age of many pluton interiors before complete solidification, and some plutons contain ring dikes or other textural evidence for roof subsidence. Geophysical data show that low-density upper-crustal rocks, inferred to be plutons, are 10 km or more thick beneath many calderas. Most ignimbrites are more evolved than associated plutons; evidence that the subcaldera chambers retained voluminous residua from fractionation. Initial incremental pluton growth in the upper crust was likely recorded by modest eruptions from central volcanoes; preparation for caldera-scale ignimbrite eruption involved recurrent magma input and

  14. Magmatic and Crustal Differentiation History of Granitic Rocks from Hf-O Isotopes in Zircon

    Science.gov (United States)

    Kemp, , A. I. S.; Hawkesworth, , C. J.; Foster, , G. L.; Paterson, , B. A.; Woodhead, , J. D.; Hergt, , J. M.; Gray, , C. M.; Whitehouse, M. J.

    2007-02-01

    Granitic plutonism is the principal agent of crustal differentiation, but linking granite emplacement to crust formation requires knowledge of the magmatic evolution, which is notoriously difficult to reconstruct from bulk rock compositions. We unlocked the plutonic archive through hafnium (Hf) and oxygen (O) isotope analysis of zoned zircon crystals from the classic hornblende-bearing (I-type) granites of eastern Australia. This granite type forms by the reworking of sedimentary materials by mantle-like magmas instead of by remelting ancient metamorphosed igneous rocks as widely believed. I-type magmatism thus drives the coupled growth and differentiation of continental crust.

  15. Phreatic eruptions and deformation of Ioto Island (Iwo-jima), Japan, triggered by deep magma injection

    Science.gov (United States)

    Ueda, Hideki; Nagai, Masashi; Tanada, Toshikazu

    2018-03-01

    On Ioto Island (Iwo-jima), 44 phreatic eruptions have been recorded since 1889, when people began to settle there. Four of these eruptions, after the beginning of continuous observation by seismometers in 1976, were accompanied by intense seismic activity and rapid crustal deformation beforehand. Other eruptions on Ioto were without obvious crustal activities. In this paper, we discuss the mechanisms of phreatic eruptions on Ioto. Regular geodetic surveys and continuous GNSS observations show that Ioto intermittently uplifts at an abnormally high rate. All of the four eruptions accompanied by the precursors took place during intermittent uplifts. The crustal deformation before and after one of these eruptions revealed that a sill-like deformation source in the shallow part of Motoyama rapidly inflated before and deflated after the beginning of the eruption. From the results of a seismic array and a borehole survey, it is estimated that there is a layer of lava at a depth of about 100-200 m, and there is a tuff layer about 200-500 m beneath it. The eruptions accompanied by the precursors probably occurred due to abrupt boiling of hot water in hydrothermal reservoirs in the tuff layer, sealed by the lava layer and triggered by intermittent uplift. For the eruptions without precursors, the hydrothermal systems are weakly sealed by clay or probably occurred on the same principle as a geyser because phreatic eruptions had occurred beforehand and hydrostatic pressure is applied to the hydrothermal reservoirs.

  16. Deep magma transport at Kilauea volcano, Hawaii

    Science.gov (United States)

    Wright, T.L.; Klein, F.W.

    2006-01-01

    .4 my for Kilauea and 0.8 my for Mauna Loa are consistent with this model. Younger ages would apply if Kilauea began its growth south of the locus of maximum melting, as is true for Loihi seamount. We conclude that Kilauea is fed from below the eastern end of the zone of deep long-period earthquakes. Magma transport is vertical below 30 km, then sub-horizontal, following the oceanic mantle boundary separating plagioclase- and spinel-peridotite, then near-vertical beneath Kilauea's summit. The migration of the melting region within the hotspot and Kilauea's sampling of different sources within the melting region can explain (1) the long-term geochemical separation of Kilauea from neighboring volcanoes Mauna Loa and Loihi, and (2) the short-term changes in trace-element and isotope signatures within Kilauea. ?? 2005 Elsevier B.V. All rigths reserved.

  17. Advanced reservoir characterization and evaluation of CO{sub 2} gravity drainage in the naturally fractured Spraberry Trend Area. Annual report, September 1, 1995--August 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Schechter, D.S.

    1997-12-01

    The overall goal of this project is to assess the economic feasibility of CO{sub 2} flooding in the naturally fractured Spraberry Trend Area in West Texas. This objective is being accomplished by conducting research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, (3) analytical and numerical simulation of Spraberry reservoirs, and, (4) experimental investigations on CO{sub 2} gravity drainage in Spraberry whole cores. This report provides results of the first year of the five-year project for each of the four areas.

  18. The isotopic and chemical evolution of Mount St. Helens

    International Nuclear Information System (INIS)

    Halliday, A.N.; Fallick, A.E.; Dickin, A.P.; Mackenzie, A.B.; Stephens, W.E.

    1983-01-01

    Isotopic and major and trace element analysis of nine samples of eruptive products spanning the history of the Mt. St. Helens volcano suggest three different episodes; (1) 40,000-2500 years ago: eruptions of dacite with epsilonsub(Nd) = +5, epsilonsub(Sr) = -10, variable delta 18 O, 206 Pb/ 204 Pb approx.= 18.76, Ca/Sr approx.= 60, Rb/Ba- approx.= 0.1, La/Yb approx.= 18, (2) 2500-1000 years ago: eruptions of basalt, andesite and dacite with epsilonsub(Nd) = +4 to + 8, epsilonsub(Sr) = -7 to -22, variable delta 18 O (thought to represent melting of differing mantle-crust reservoirs), 206 Pb/ 204 Pb = 18.81-18.87, variable Ca/Sr, Rb/Ba, La/Yb and high Zr, (3) 1000 years ago to present day: eruptions of andesite and dacite with epsilonsub(Nd) = + 6, epsilonsub(Sr) = -13, delta 18 O approx.= 6per mille, variable 206 Pb/ 204 Pb, Ca/Sr approx.= 77, Rb/Ba = 0.1, La/Yb approx.= 11. None of the products exhibit Eu anomalies and all are LREE enriched. There is a strong correlation between 87 Sr/ 86 Sr and differentiation indices. These data are interpreted in terms of a mantle heat source melting young crust bearing zircon and garnet, but not feldspar, followed by intrusion of this crustal reservoir by mantle-derived magma which caused further crustal melting and contaminated the crustal magma system with mafic components. Since 1000 years ago all the eruptions have been from the same reservoir which has displayed a much more gradual re-equilibration of Pb isotopic compositions than other components suggesting that Pb is being transported via a fluid phase. The Nd and Sr isotopic compositions lie along the mantle array and suggest that the mantle underneath Mt. St. Helens is not as depleted as MORB sources. There is no indication of seawater involvement in the source region. (orig.)

  19. The isotopic and chemical evolution of Mount St. Helens

    Science.gov (United States)

    Halliday, A.N.; Fallick, A.E.; Dickin, A.P.; Mackenzie, A.B.; Stephens, W.E.; Hildreth, W.

    1983-01-01

    Isotopic and major and trace element analysis of nine samples of eruptive products spanning the history of the Mt. St. Helens volcano suggest three different episodes; (1) 40,000-2500 years ago: eruptions of dacite with ??{lunate}Nd = +5, ??{lunate}Sr = -10, variable ??18O, 206Pb/204Pb ??? 18.76, Ca/Sr ??? 60, Rb/Ba ??? 0.1, La/Yb ??? 18, (2) 2500-1000 years ago: eruptions of basalt, andesite and dacite with ??{lunate}Nd = +4 to +8, ??{lunate}Sr = -7 to -22, variable ??18O (thought to represent melting of differing mantle-crust reservoirs), 206Pb/204Pb = 18.81-18.87, variable Ca/Sr, Rb/Ba, La/Yb and high Zr, (3) 1000 years ago to present day: eruptions of andesite and dacite with ??{lunate}Nd = +6, ??{lunate}Sr = -13, ??18O ???6???, variable 206Pb/204Pb, Ca/Sr ??? 77, Rb/Ba = 0.1, La/Yb ??? 11. None of the products exhibit Eu anomalies and all are LREE enriched. There is a strong correlation between 87Sr/86Sr and differentiation indices. These data are interpreted in terms of a mantle heat source melting young crust bearing zircon and garnet, but not feldspar, followed by intrusion of this crustal reservoir by mantle-derived magma which caused further crustal melting and contaminated the crustal magma system with mafic components. Since 1000 years ago all the eruptions have been from the same reservoir which has displayed a much more gradual re-equilibration of Pb isotopic compositions than other components suggesting that Pb is being transported via a fluid phase. The Nd and Sr isotopic compositions lie along the mantle array and suggest that the mantle underneath Mt. St. Helens is not as depleted as MORB sources. There is no indication of seawater involvement in the source region. ?? 1983.

  20. Parallel Fast Multipole Boundary Element Method for crustal dynamics

    International Nuclear Information System (INIS)

    Quevedo, Leonardo; Morra, Gabriele; Mueller, R Dietmar

    2010-01-01

    Crustal faults and sharp material transitions in the crust are usually represented as triangulated surfaces in structural geological models. The complex range of volumes separating such surfaces is typically three-dimensionally meshed in order to solve equations that describe crustal deformation with the finite-difference (FD) or finite-element (FEM) methods. We show here how the Boundary Element Method, combined with the Multipole approach, can revolutionise the calculation of stress and strain, solving the problem of computational scalability from reservoir to basin scales. The Fast Multipole Boundary Element Method (Fast BEM) tackles the difficulty of handling the intricate volume meshes and high resolution of crustal data that has put classical Finite 3D approaches in a performance crisis. The two main performance enhancements of this method: the reduction of required mesh elements from cubic to quadratic with linear size and linear-logarithmic runtime; achieve a reduction of memory and runtime requirements allowing the treatment of a new scale of geodynamic models. This approach was recently tested and applied in a series of papers by [1, 2, 3] for regional and global geodynamics, using KD trees for fast identification of near and far-field interacting elements, and MPI parallelised code on distributed memory architectures, and is now in active development for crustal dynamics. As the method is based on a free-surface, it allows easy data transfer to geological visualisation tools where only changes in boundaries and material properties are required as input parameters. In addition, easy volume mesh sampling of physical quantities enables direct integration with existing FD/FEM code.

  1. Magma Mixing: Why Picrites are Not So Hot

    Science.gov (United States)

    Natland, J. H.

    2010-12-01

    porosity in regions where crustal-level magma chambers and flanking rift zones do not have a chance to form. Low-magma supply is favored. In the ocean basins, such upper mantle mainlining occurs only at certain fracture zones, deep propagating rifts at microplates, or ultra-slow spreading ridges, but no liquids (glasses) with >10% MgO occur at any of these places. On continents, rift structures through cratons might allow this, but so far no picrite, ferropicrite, or meimichite that has been adequately described from these places lacks evidence for end-member mixing. Low-temperature iron-rich magmas can accumulate in the deep lower crust and later rise to form substantial intrusions (e.g. Skaergaard) or erupt as flood basalts (Columbia River). Some komatiites might represent high-temperature liquids, but many are so altered that original liquid compositions cannot be deduced (e.g., Gorgona). The hottest intraplate volcano is Kilauea, Hawaii, where rare picrite glass with 15% MgO has an estimated eruptive temperature (1) of ~1350C and a potential temperature at 1 GPa of ~1420C. Lavas at all other linear island chains, Iceland and even west Greenland where picrites are abundant, are cooler than this. (1) Beattie, P., 1993. CMP 115: 103-111.

  2. Trace element and isotopic effects arising from magma migration beneath mid-ocean ridges

    International Nuclear Information System (INIS)

    Kenyon, P.M.

    1990-01-01

    The trace element concentrations and isotopic ratios in the magma erupted on mid-ocean ridges may differ from those in the source material due to physical effects such as porous flow dispersion, exchange of trace elements between the fluid and solid phases during magma migration, and convective mixing in magma chambers. These differences are in addition to those produced by better known processes such as fractional crystallization and partial melting. The effects of the three former processes are described. It is predicted that magma typically reaches the sub-ridge magma chambers with a spatial heterogeneity only slightly reduced from that of the source material, but with a subdued variation in time. Convective mixing then further reduces the spatial heterogeneity. Application of the results for convective mixing to a recent Fourier analysis of 87 Sr/ 86 Sr variations along the Mid-Atlantic Ridge suggests that the falloff in amplitude of variation observed with decreasing wavelength in the Mid-Atlantic Ridge data cannot be explained by convective mixing in magma chambers. Instead, it is postulated that this falloff is due to the mechanics of the production and/or the solid-state convective mixing of chemical and isotopic heterogeneities in the solid mantle. (orig.)

  3. Storage conditions of the mafic and silicic magmas at Cotopaxi, Ecuador

    Science.gov (United States)

    Martel, Caroline; Andújar, Joan; Mothes, Patricia; Scaillet, Bruno; Pichavant, Michel; Molina, Indira

    2018-04-01

    The 2015 reactivation of the Cotopaxi volcano urges us to understand the complex eruptive dynamics of Cotopaxi for better management of a potential major crisis in the near future. Cotopaxi has commonly transitioned from andesitic eruptions of strombolian style (lava flows and scoria ballistics) or nuées ardentes (pyroclastic flows and ash falls) to highly explosive rhyolitic ignimbrites (pumiceous pyroclastic flows), which entail drastically different risks. To better interpret geophysical and geochemical signals, Cotopaxi magma storage conditions were determined via existing phase-equilibrium experiments that used starting materials chemically close to the Cotopaxi andesites and rhyolites. The results suggest that Cotopaxi's most mafic andesites (last erupted products) can be stored over a large range of depth from 7 km to ≥16 km below the summit (pressure from 200 to ≥400 MPa), 1000 °C, NNO +2, and contain 4.5-6.0±0.7 wt% H2O dissolved in the melt in equilibrium with 30-40% phenocrysts of plagioclase, two pyroxenes, and Fe-Ti oxides. These mafic andesites sometimes evolve towards more silicic andesites by cooling to 950 °C. Rhyolitic magmas are stored at 200-300 MPa (i.e. 7-11 km below the summit), 750 °C, NNO +2, and contain 6-8 wt% H2O dissolved in a nearly aphyric melt (<5% phenocrysts of plagioclase, biotite, and Fe-Ti oxides). Although the andesites produce the rhyolitic magmas by fractional crystallization, the Cotopaxi eruptive history suggests reactivation of either reservoirs at distinct times, likely reflecting flux or time fluctuations during deep magma recharge.

  4. Effects of host rock stratigraphy on the formation of ring-faults and the initiation of collapse calderas

    International Nuclear Information System (INIS)

    Kinvig, H S; Geyer, A; Gottsmann, J

    2008-01-01

    Most collapse calderas can be attributed to subsidence of the magma chamber roof along bounding sub-vertical normal faults (ring-faults) after a decompression of the magma chamber, following eruption. Here, we present new numerical models that use a Finite Element Method to investigate the effects of variable crustal stratigraphy (lithology/thickness/order of strata) above a magma chamber, on local stress field distribution and how these in turn compare with existing criteria for ring-fault initiation. Results indicate that the occurrence and relative distribution of mechanically different lithologies may be influential in generating or inhibiting caldera collapse.

  5. Effects of host rock stratigraphy on the formation of ring-faults and the initiation of collapse calderas

    Energy Technology Data Exchange (ETDEWEB)

    Kinvig, H S; Geyer, A; Gottsmann, J [Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen' s Road, BS8 1RJ, Bristol (United Kingdom)

    2008-10-01

    Most collapse calderas can be attributed to subsidence of the magma chamber roof along bounding sub-vertical normal faults (ring-faults) after a decompression of the magma chamber, following eruption. Here, we present new numerical models that use a Finite Element Method to investigate the effects of variable crustal stratigraphy (lithology/thickness/order of strata) above a magma chamber, on local stress field distribution and how these in turn compare with existing criteria for ring-fault initiation. Results indicate that the occurrence and relative distribution of mechanically different lithologies may be influential in generating or inhibiting caldera collapse.

  6. CO{sub 2} huff-n-puff process in a light oil shallow carbonate reservoir. Annual report, January 1, 1996--December 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Prieditis, J.; Wehner, S.

    1998-01-01

    The application of cyclic CO{sub 2}, often referred to as the CO{sub 2} Huff-n-Puff process, may find its niche in the maturing waterfloods of the Permian Basin. Coupling the CO{sub 2} H-n-P process to miscible flooding applications could provide the needed revenue to sufficiently mitigate near-term negative cash flow concerns in the capital intensive miscible projects. Texaco Exploration & Production Inc. and the U.S. Department of Energy have teamed up in an attempt to develop the CO{sub 2} Huff-n-Puff process in the Grayburg and San Andres formations; a light oil, shallow shelf carbonate reservoir that exists throughout the Permian Basin. A significant amount of oil reserves are located in carbonate reservoirs. Specifically, the carbonates deposited in shallow shelf (SSC) environments make up the largest percentage of known reservoirs within the Permian Basin of North America. Many of these known resources have been under waterflooding operations for decades and are at risk of abandonment if crude oil recoveries cannot be economically enhanced. The selected site for this demonstration project is the Central Vacuum Unit waterflood in Lea County, New Mexico. Miscible CO{sub 2} flooding is the process of choice for enhancing recovery of light oils and already accounts for over 12% of the Permian Basin`s daily production. There are significant probable reserves associated with future miscible CO{sub 2} projects. However, many are marginally economic at current market conditions due to large up-front capital commitments for a peak response which may be several years in the future. The resulting negative cash-flow is sometimes too much for an operator to absorb. The CO{sub 2} H-n-P process is being investigated as a near-term option to mitigate the negative cash-flow situation--allowing acceleration of inventoried miscible CO{sub 2} projects when coupled together.

  7. The Cretaceous Duimiangou adakite-like intrusion from the Chifeng region, northern North China Craton: Crustal contamination of basaltic magma in an intracontinental extensional environment

    Science.gov (United States)

    Fu, Lebing; Wei, Junhao; Kusky, Timothy M.; Chen, Huayong; Tan, Jun; Li, Yanjun; Shi, Wenjie; Chen, Chong; Zhao, Shaoqing

    2012-03-01

    Zircon U-Pb ages, major and trace element and Sr, Nd and Pb isotope compositions of the Duimiangou (DMG) quartz monzonite from the Chifeng region on the northern North China Craton (NCC) were studied to investigate its derivation, evolution and geodynamic significance. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields an emplacement age of 128 ± 1 Ma for this intrusion, with numerous Mesozoic inherited zircons clustering at 219 ± 12 Ma and 161 ± 3 Ma, along with some ancient zircons with ages of 2.5 Ga, 1.77 Ga and 324 Ma. Bulk-rock analyses show that this intrusion is characterized by variable SiO2 (63.4-69.4 wt.%), Al2O3 (14.5-16.3 wt.%), Na2O + K2O (8.01-8.95 wt.%), and Mg# (41.3-48.0). They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies (mostly between 0.89-1.10), and depleted in heavy rare earth elements and high field strength elements, with high Sr/Y (63.7-101.7) and (La/Yb)N (20.5-31.0) ratios. The DMG intrusion formed in an intracontinental extensional setting contemporaneous with the formation of pull-apart basins, metamorphic core complexes and intense magmatism, rather than in a convergent margin. It has homogeneous Sr ((87Sr/86Sr)i = 0.7059-0.7066), Nd (εNd(t) = - 6.2 to - 7.2) and Pb ((206Pb/204Pb)i = 17.289-17.375, (207Pb/204Pb)i = 15.359-15.463, (208Pb/204Pb)i = 37.130-37.472) isotope compositions. Sr-Nd isotope modeling results, plus relatively young Nd model ages (1522-1618 Ma) and the presence of relict zircons, suggest that this intrusion could have originated from crustal contamination of newly formed basaltic melts derived from asthenospheric mantle, accompanied by fractional crystallization of K-feldspar, biotite, apatite, Fe-Ti oxides and minor hornblende and plagioclase. Thus, the DMG adakite-like intrusion may record the magmatic event associated with underplating of asthenospheric magma in an intracontinental extensional

  8. Crustal inheritance and arc magmatism: Magnetotelluric constraints from the Washington Cascades on top-down control

    Science.gov (United States)

    Bedrosian, P.; Peacock, J.; Bowles-martinez, E.; Schultz, A.; Hill, G.

    2017-12-01

    Worldwide, arc volcanism occurs along relatively narrow magmatic arcs, the locations of which are considered to mark the onset of dehydration reactions within the subducting slab. This `bottom-up' approach, in which the location of arc volcanism reflects where fluids and melt are generated, explains first-order differences in trench-to-arc distance and is consistent with known variations in the thermal structure and geometry of subducting slabs. At a finer scale, arc segmentation, magmatic gaps, and anomalous forearc and backarc magmatism are also frequently interpreted in terms of variations in slab geometry, composition, or thermal structure.The role of inherited crustal structure in controlling faulting and deformation is well documented; less well examined is the role of crustal structure in controlling magmatism. While the source distribution of melt and subduction fluids is critical to determining the location of arc magmatism, we argue that crustal structure provides `top-down' control on patterns or seismicity and deformation as well as the channeling and ascent of arc magmas. We present evidence within the Washington Cascades based upon correlation between a new three-dimensional resistivity model, potential-field data, seismicity, and Quaternary volcanism. We image a mid-Tertiary batholith, intruded within an Eocene crustal suture zone, and extending throughout much of the crustal column. This and neighboring plutons are interpreted to channel crustal fluids and melt along their margins within steeply dipping zones of marine to transitional metasedimentary rock. Mount St. Helens is interpreted to be fed by fluids and melt generated further east at greater slab depths, migrating laterally (underplating?) beneath the Spirit Lake batholith, and ascending through metasedimentary rocks within the brittle crust. At a regional scale, we argue that this concealed suture zone controls present-day deformation and seismicity as well as the distribution of forearc

  9. Recycling and recharge processes at the Hasandağ Stratovolcano, Central Anatolia: Insights on magma chamber systematics from plagioclase textures and zoning patterns

    Science.gov (United States)

    Gall, H. D.; Cipar, J. H.; Crispin, K. L.; Kürkçüoğlu, B.; Furman, T.

    2017-12-01

    We elucidate crystal recycling and magma recharge processes at Hasandağ by investigating compositional zoning patterns and textural variation in plagioclase crystals from Quaternary basaltic andesite through dacite lavas. Previous work on Hasandağ intermediate compositions identified thermochemical disequilibrium features and showed abundant evidence for magma mixing1,2. We expand on this work through detailed micro-texture and mineral diffusion analysis to explore the mechanisms and timescales of crystal transport and mixing processes. Thermobarometric calculations constrain the plumbing system to 1.2-2 kbar and 850-950°C, corresponding to a felsic magma chamber at 4.5 km. Electron microprobe results reveal plagioclase phenocrysts from all lava types have common core (An33-46) and rim (An36-64) compositions, with groundmass laths (An57-67) resembling the phenocryst rims. Low An cores are ubiquitous, regardless of bulk rock chemistry, and suggest a consistent composition within the magma reservoir prior to high An rim growth. High An rims are regularly enriched in Mg, Fe, Ti and Sr, which we attribute to mafic recharge and magma mixing. We assess mixing timescales by inverse diffusion modeling of Mg profiles across the core-rim boundaries. Initial results suggest mixing to eruption processes occur on the order of days to months. Heterogeneous calculated timescales within thin sections indicate crystal populations with different growth histories. Crystals often display prominent sieve-textured zones just inside the rim, as well as other disequilibrium features such as oscillatory zoning or resorbed and patchy-zoned cores. We interpret these textures to indicate mobilization of a homogeneous dacitic reservoir with abundant An35 plagioclase crystals by frequent injection of mafic magma. Variability in observed textures and calculated timescales manifests during defrosting of a highly crystalline felsic mush, through different degrees of magma mixing. This process

  10. Oxidation State of Iron in the Izu-Bonin Arc Initial Magma and Its Influence Factors

    Science.gov (United States)

    Li, H.; Arculus, R. J.; Brandl, P. A.; Hamada, M.; Savov, I. P.; Zhu, S.; Hickey-Vargas, R.; Tepley, F. J., III; Meffre, S.; Yogodzinski, G. M.; McCarthy, A.; Barth, A. P.; Kanayama, K.; Kusano, Y.; Sun, W.

    2014-12-01

    The redox state of mantle-derived magmas is a controversial issue, especially whether island arc basalts are more oxidized than those from mid-ocean ridges. Usually, arc magmas have higher Fe3+/Fe2+ and calculated oxygen fugacity (fO2) than mid-ocean ridge basalts (MORB). It is the high fO2 of arc magma that apparently delays onset of sulfide fractionation and sequestration of precious/base metals thereby facilitating the formation of many giant gold-copper deposits typically associated with subduction zones. But due to a paucity of Fe3+/Fe2+ data for primary mantle-derived arc magmas, the cause for high fO2 of these magma types is still controversial; causes may include inter alia subduction-released oxidized material addition to the mantle wedge source of arc magma, partial melting of subducted slab, and redox changes occurring during ascent of the magma. Fortunately, IODP expedition 351 drilling at IODP Site U1438 in the Amami-Sankaku Basin of the northwestern Philipine Sea, adjacent to the proto-Izu-Bonin Arc at the Kyushu-Palau Ridge (KPR), recovered not only volcaniclastics derived from the inception of Izu-Bonin Mariana (IBM) arc in the Eocene, but also similar materials for the Arc's subsequent evolution through to the Late Oligocene and abandonment of the KPR as a remnant arc. Samples of the pre-Arc oceanic crustal basement were also recovered enabling us to determine the fO2of the mantle preceding arc inception. As the oxidation state of iron in basaltic glass directly relates to the fO2 , the Fe3+/∑Fe ratio [Fe3+/(Fe3++ Fe2+)] of basaltic glass are quantified by synchrotron-facilitated micro X-ray Absorption Near Edge Structure (XANES) spectroscopy to reflect its fO2. Fe K-edge µ-XANES spectra were recorded in fluorescence mode at Beamline 15U1, Shanghai Synchrotron Radiation Facility (SSRF). Synthetic silicate glass with known Fe3+/∑Fe ratio was used in data handling. The experimental results as well as preliminary data from IODP Expedition 351

  11. Crustal moment of inertia of glitching pulsars with the KDE0v1 Skyrme interaction

    Energy Technology Data Exchange (ETDEWEB)

    Madhuri, K.; Routray, T.R.; Pattnaik, S.P. [Sambalpur University, School of Physics, Jyotivihar (India); Basu, D.N. [Variable Energy Cyclotron Center, Kolkata (India)

    2017-07-15

    The mass, radius and crustal fraction of moment of inertia in neutron stars are calculated using β-equilibrated nuclear matter obtained from the Skyrme effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars are determined from the thermodynamic stability conditions using the KDE0v1 set. The neutron star masses obtained by solving the Tolman-Oppenheimer-Volkoff equations using neutron star matter obtained from this set are able to describe highly massive compact stars ∝ 2M {sub CircleDot}. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches. This fraction is highly dependent on the core-crust transition pressure and corresponding density. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a limit for the radius of the Vela pulsar, R ≥ 3.69 + 3.44M/M {sub CircleDot}. Present calculations suggest that the crustal fraction of the total moment of inertia can be ∝ 6.3% due to crustal entrainment caused by the Bragg reflection of unbound neutrons by lattice ions. (orig.)

  12. Magnetic fabrics in characterization of magma emplacement and tectonic evolution of the Moyar Shear Zone, South India

    Directory of Open Access Journals (Sweden)

    P. Pratheesh

    2013-01-01

    Full Text Available The Moyar Shear Zone (MSZ of the South Indian granulite terrain hosts a prominent syenite pluton (∼560 Ma and associated NW-SE to NE-SW trending mafic dyke swarm (∼65 Ma and 95 Ma. Preliminary magnetic fabric studies in the mafic dykes, using Anisotropy of Magnetic Susceptibly (AMS studies at low-field, indicate successive emplacement and variable magma flow direction. Magnetic lineation and foliation in these dykes are identical to the mesoscopic fabrics in MSZ mylonites, indicating shear zone guided emplacement. Spatial distribution of magnetic lineation in the dykes suggests a common conduit from which the source magma has been migrated. The magnetic foliation trajectories have a sigmoidal shape to the north of the pluton and curve into the MSZ suggesting dextral sense of shear. Identical fabric conditions for magnetic fabrics in the syenite pluton and measured field fabrics in mylonite indicate syntectonic emplacement along the Proterozoic crustal scale dextral shear zone with repeated reactivation history.

  13. Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada.

    Science.gov (United States)

    Dodge, F.C.W.; Calk, L.C.; Kistler, R.W.

    1986-01-01

    This assemblage of pyroxenite, peridotite and mafic granulite xenoliths in the toe of a 10 m.y. trachybasalt flow remnant overlying late Cretaceous granitic rocks, indicates the presence of a mafic-ultramafic complex beneath this part of central California; orthopyroxenites, websterites and clinopyroxenites are dominant. A few of the xenoliths contain ovoid opaque patches that are apparently pseudomorphs after garnet and have pyralspite garnet compositions; using a garnet-orthopyroxene geobarometer, they indicate a lower crustal depth of approx 40 km. Abundant mafic granulites can be subdivided into those with Al2O3 = or 15% and showing considerable scatter on oxide variation diagrams. The high-alumina granulite xenoliths have relatively low 87Rb/86Sr but high 87Sr/86Sr, whereas the low-alumina and ultramafic xenoliths have a wide range of 87Rb/86Sr, but lower 87Sr/86Sr; the isotopic data indicate roughly the same age as that of overlying granitic plutons (approx 100 m.y.). However, the granitic rocks have initial 87Sr/86Sr ratios intermediate between those of the high-alumina and ultramafic xenoliths, suggesting that they result from the mixing of basaltic magma (represented by the ultramafic rocks) and crustal materials, with subsequent crystal fractionation.-R.A.H.

  14. Exploration and reservoir characterization; Technology Target Areas; TTA2 - Exploration and reservoir characterisation

    Energy Technology Data Exchange (ETDEWEB)

    2008-07-01

    In future, research within exploration and reservoir characterization will play an even more important role for Norway since resources are decreasing and new challenges like deep sea, harsh environment and last but not least environmental issues have to be considered. There are two major fields which have to be addressed within exploration and reservoir characterization: First, replacement of reserves by new discoveries and ultimate field recoveries in mature basins at the Norwegian Continental shelf, e.g. at the Halten Terrace has to be addressed. A wealth of data exists in the more mature areas. Interdisciplinary integration is a key feature of reservoir characterization, where available data and specialist knowledge need to be combined into a consistent reservoir description. A systematic approach for handling both uncertainties in data sources and uncertainties in basic models is needed. Fast simulation techniques are necessary to generate models spanning the event space, covering both underground based and model-based uncertainties. Second, exploration in frontier areas like the Barents Sea region and the deeper Voering Basin has to be addressed. The scarcity of wells in these frontier areas leads to uncertainties in the geological understanding. Basin- and depositional modelling are essential for predicting where source rocks and reservoir rocks are deposited, and if, when and which hydrocarbons are generated and trapped. Predictive models and improved process understanding is therefore crucial to meet these issues. Especially the challenges related to the salt deposits e.g. sub-salt/sub-basalt reservoir definitions in the Nordkapp Basin demands up-front research and technology developments. TTA2 stresses the need to focus on the development of new talents. We also see a strong need to push cooperation as far as possible in the present competitive environment. Projects that may require a substantial financial commitment have been identified. The following

  15. On the relation between Moho and sub-crustal stress induced by mantle convection

    International Nuclear Information System (INIS)

    Eshagh, Mehdi

    2015-01-01

    The sub-crustal stress components due to mantle convection have a direct relation with the spherical harmonic coefficients of the Earth’s disturbing potential like those of the Moho model, developed by the Vening–Meinesz–Moritz theory. In this paper, the relation between the stress components and the global and local models of Moho is mathematically developed in three different ways. Here, we present the S function (S) with a numerical differentiation approach to generate the stress components and we show that its spherical harmonic series is convergent to a degree of about 600 based on a mean global Moho depth of 23 km. An integral approach is developed for integration of a local Moho model for the stress recovery, but the kernels of this integral are not likely to be convergent and should be generated by their spectral forms to a limited degree. Another method is developed based on integral inversion, which is free of any mathematical problem and suitable for recovering S from an existing model of Moho. Our numerical presentation shows that the stress has a good agreement with the tectonic boundaries and the places at which the curvature of the Moho surface changes. (paper)

  16. The Meaning of "Magma"

    Science.gov (United States)

    Bartley, J. M.; Glazner, A. F.; Coleman, D. S.

    2016-12-01

    Magma is a fundamental constituent of the Earth, and its properties, origin, evolution, and significance bear on issues ranging from volcanic hazards to planetary evolution. Unfortunately, published usages indicate that the term "magma" means distinctly different things to different people and this can lead to miscommunication among Earth scientists and between scientists and the public. Erupting lava clearly is magma; the question is whether partially molten rock imaged at depth and too crystal-rich to flow should also be called magma. At crystal fractions > 50%, flow can only occur via crystal deformation and solution-reprecipitation. As the solid fraction increases to 90% or more, the material becomes a welded crystal framework with melt in dispersed pores and/or along grain boundaries. Seismic images commonly describe such volumes of a few % melt as magma, yet the rheological differences between melt-rich and melt-poor materials make it vital not to confuse a large rock volume that contains a small melt fraction with melt-rich material. To ensure this, we suggest that "magma" be reserved for melt-rich materials that undergo bulk fluid flow on timescales consonant with volcanic eruptions. Other terms should be used for more crystal-rich and largely immobile partially molten rock (e.g., "crystal mush," "rigid sponge"). The distinction is imprecise but useful. For the press, the public, and even earth scientists who do not study magmatic systems, "magma" conjures up flowing lava; reports of a large "magma" body that contains a few percent melt can engender the mistaken perception of a vast amount of eruptible magma. For researchers, physical processes like crystal settling are commonly invoked to account for features in plutonic rocks, but many such processes are only possible in melt-rich materials.

  17. Timing magma migration through the Icelandic Crust: from the Moho to the surface

    Science.gov (United States)

    Mutch, E. J. F.; Maclennan, J.; Edmonds, M.

    2017-12-01

    The rate of magma transfer throughout the crust, particularly the amount of time it takes for melt to travel from the upper mantle to the surface, is largely unknown. Only one previous study has investigated the timescales of transport of crystals that were in equilibrium with mantle melts [1]. Despite estimating timescales on the order of months to years, the depths from which these crystals were entrained is poorly constrained. Borgarhraun is an exceptionally well-characterised picrite lava flow in the Theistareykir Volcanic System of Northern Iceland. The crystal-cargo of this lava includes macrocrysts of olivine (Fo86-90), plagioclase (An84-90), clinopyroxene and spinel with much rarer wehrlitic nodules. Crystallisation has been estimated to have taken place in deep sub-Moho magma chambers ( 24 km). Melt inclusions in primitive olivine macrocrysts (Fo88-90) are the result of mixing a suite of geochemically distinct mantle melts that were CO2 undersaturated [2-3]. Zoning in the macrocrysts holds a record of concurrent crystallisation and mixing of these variable mantle melts, as well as ascent through the crust prior to eruption [4]. We have conducted a multi-phase, multi-element approach by applying finite-element diffusion models to wehrlite olivines and plagioclase macrocrysts to constrain the timescales of crystal residence and magma ascent prior to eruption. Model results suggest that at 1250 °C the timescale of final ascent was on the order of 20-50 days, whilst longer-term crystal residence times can exceed 700 years. This analysis shows that magma can ascend from the base of the crust to the surface in under a couple of months, suggesting picrites such as Borgarhraun are the result of high speed conduits to sub-Moho magma chambers. These rapid ascent timescales have important implications for the physical modelling of primitive magmas as well as for understanding the architecture of magma-plumbing systems in the temporal domain. References [1] Ruprecht

  18. Recent crustal movements

    Science.gov (United States)

    Maelzer, H.

    Calculation of temporal height changes for the determination of recent vertical crustal movements in northern, western, and southern Germany is described. Precise geodetic measurements and their analysis for the determination of recent crustal movements in north-eastern Iceland, western Venezuela, and central Peru are described. Determination of recent vertical crustal movements by leveling and gravity data; geodetic modeling of deformations and recent crustal movements; geodetic modeling of plate motions; and instrumental developments in geodetic measuring are discussed.

  19. Regional and temporal variability of melts during a Cordilleran magma pulse: Age and chemical evolution of the jurassic arc, eastern mojave desert, California

    Science.gov (United States)

    Barth, A.P.; Wooden, J.L.; Miller, David; Howard, Keith A.; Fox, Lydia; Schermer, Elizabeth R.; Jacobson, C.E.

    2017-01-01

    Intrusive rock sequences in the central and eastern Mojave Desert segment of the Jurassic Cordilleran arc of the western United States record regional and temporal variations in magmas generated during the second prominent pulse of Mesozoic continental arc magmatism. U/Pb zircon ages provide temporal control for describing variations in rock and zircon geochemistry that reflect differences in magma source components. These source signatures are discernible through mixing and fractionation processes associated with magma ascent and emplacement. The oldest well-dated Jurassic rocks defining initiation of the Jurassic pulse are a 183 Ma monzodiorite and a 181 Ma ignimbrite. Early to Middle Jurassic intrusive rocks comprising the main stage of magmatism include two high-K calc-alkalic groups: to the north, the deformed 183–172 Ma Fort Irwin sequence and contemporaneous rocks in the Granite and Clipper Mountains, and to the south, the 167–164 Ma Bullion sequence. A Late Jurassic suite of shoshonitic, alkali-calcic intrusive rocks, the Bristol Mountains sequence, ranges in age from 164 to 161 Ma and was emplaced as the pulse began to wane. Whole-rock and zircon trace-element geochemistry defines a compositionally coherent Jurassic arc with regional and secular variations in melt compositions. The arc evolved through the magma pulse by progressively greater input of old cratonic crust and lithospheric mantle into the arc magma system, synchronous with progressive regional crustal thickening.

  20. Oblique reactivation of lithosphere-scale lineaments controls rift physiography - the upper-crustal expression of the Sorgenfrei-Tornquist Zone, offshore southern Norway

    Science.gov (United States)

    Phillips, Thomas B.; Jackson, Christopher A.-L.; Bell, Rebecca E.; Duffy, Oliver B.

    2018-04-01

    Pre-existing structures within sub-crustal lithosphere may localise stresses during subsequent tectonic events, resulting in complex fault systems at upper-crustal levels. As these sub-crustal structures are difficult to resolve at great depths, the evolution of kinematically and perhaps geometrically linked upper-crustal fault populations can offer insights into their deformation history, including when and how they reactivate and accommodate stresses during later tectonic events. In this study, we use borehole-constrained 2-D and 3-D seismic reflection data to investigate the structural development of the Farsund Basin, offshore southern Norway. We use throw-length (T-x) analysis and fault displacement backstripping techniques to determine the geometric and kinematic evolution of N-S- and E-W-striking upper-crustal fault populations during the multiphase evolution of the Farsund Basin. N-S-striking faults were active during the Triassic, prior to a period of sinistral strike-slip activity along E-W-striking faults during the Early Jurassic, which represented a hitherto undocumented phase of activity in this area. These E-W-striking upper-crustal faults are later obliquely reactivated under a dextral stress regime during the Early Cretaceous, with new faults also propagating away from pre-existing ones, representing a switch to a predominantly dextral sense of motion. The E-W faults within the Farsund Basin are interpreted to extend through the crust to the Moho and link with the Sorgenfrei-Tornquist Zone, a lithosphere-scale lineament, identified within the sub-crustal lithosphere, that extends > 1000 km across central Europe. Based on this geometric linkage, we infer that the E-W-striking faults represent the upper-crustal component of the Sorgenfrei-Tornquist Zone and that the Sorgenfrei-Tornquist Zone represents a long-lived lithosphere-scale lineament that is periodically reactivated throughout its protracted geological history. The upper-crustal component of

  1. Crustal balance and crustal flux from shortening estimates in the Central Andes

    Science.gov (United States)

    Hindle, David; Kley, Jonas; Oncken, Onno; Sobolev, Stephan

    2005-01-01

    The Central Andes of South America form the second largest high elevation plateau on earth. Extreme elevations have formed on a noncollisional margin with abundant associated arc magmatism. It has long been thought that the crustal thickness necessary to support Andean topography was not accounted for by known crustal shortening alone. We show that this may in part be due to a two-dimensional treatment of the problem. A three-dimensional analysis of crustal shortening and crustal thickness shows that displacement of material towards the axis of the bend in the Central Andes has added a significant volume of crust not accounted for in previous comparisons. We find that present-day crustal thickness between 12°S and 25°S is accounted for (∼-10% to ∼+3%)with the same shortening estimates, and the same assumed initial crustal thickness as had previously led to the conclusion of a ∼25-35% deficit in shortening relative to volume of crustal material. We suggest that the present-day measured crustal thickness distribution may not match that predicted due to shortening, and substantial redistribution of crust may have occurred by both erosion and deposition at the surface and lower crustal flow in regions of the thermally weakened middle and lower crust.

  2. Magma storage conditions of historic Plinian eruptions of Volcán de Colima, México

    Science.gov (United States)

    Macias, J.; Arce, J.; Sosa, G.; Gardner, J. E.; Saucedo, R.

    2013-12-01

    possible to assume the storage pressure of the 1913 Plinian magma. Previous studies found ~6 wt. % of water dissolved in orthopyroxene melt inclusions in the 1913 magma (Luhr, 2006). That water concentration would be dissolved in a melt with the 1913 composition at ~200 MPa (Papale et al., 2006). Equilibrium pressure of 1913 amphiboles, microphenocrysts, and xenocrysts (280-380 MPa), overall, are deeper than those of the 1818 suggesting a deeper 1913 reservoir. Therefore, the 1818 amphiboles with lower pressure rims found in the natural sample could have been inherited from a previous magma (>280 MPa) seated at similar depths than the 1913 reservoir from which were taped. Luhr, J.F., 2002 JVGR 117, 169-194. Ridolfi, F., Renzulli, A., Puerini, M., 2010. Cont Min Petrol 160, 45-66. R. Saucedo, J.L. Macías, J.C. Gavilanes, J.L. Arce, J.C. Komorowski, J.E. Gardner, G. Valdez-Moreno JVGR 191, 149-166 Savov, I.P., Luhr, J.F., Navarro-Ochoa, C., 2008. JVGR 174: 241-256.

  3. Post waterflood CO{sub 2} miscible flood in light oil fluvial dominated deltaic reservoirs. Second quarterly technical progress report, [January 1, 1995--March 31, 1995

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-07-01

    Production from the Marg Area 1 at Port Neches is averaging 392 barrels of oil per day (BOPD) for this quarter. The production drop is due to fluctuation in both GOR and BS&W on various producing well, coupled with low water injectivity in the reservoir. We were unable to inject any tangible amount of water in the reservoir since late January. Both production and injection problems are currently being evaluated to improve reservoir performance. Well Kuhn (No. 6) was stimulated with 120 MMCF of CO{sub 2}, and was placed on production in February 1, 1995. The well was shut in for an additional month after producing dry CO{sub 2} initially. The well was opened again in early April and is currently producing about 40 BOPD. CO{sub 2} injection averaged 11.3 MMCFD including 4100 MMCFD purchased from Cardox, while water injection averaged 1000 BWPD with most of the injection occurring in the month of January.

  4. Volcanism on differentiated asteroids (Invited)

    Science.gov (United States)

    Wilson, L.

    2013-12-01

    The Dawn spacecraft's investigation of 4 Vesta, best-preserved of the early-forming differentiated asteroids, prompts a reappraisal of factors controlling igneous activity on such bodies. Analogy with melt transfer in zones of partial melting on Earth implies that silicate melts moved efficiently within asteroid mantles in complex networks of veins and dikes, so that only a few percent of the mantle consisted of melt at any one time. Thus even in cases where large amounts of mantle melting occurred, the melts did not remain in the mantle to form "magma oceans", but instead migrated to shallow depths. The link between magma flow rate and the stresses needed to keep fractures open and allow flow fast enough to avoid excessive cooling implies that only within asteroids with radii more than ~190-250 km would continuous magma flow from mantle to surface be possible. In all smaller asteroids (including Vesta) magma must have accumulated in sills at the base of the lithosphere (the conductively controlled ~10 km thick thermal boundary layer) or in crustal magma reservoirs near its base. Magma would then have erupted intermittently to the surface from these steadily replenished reservoirs. The average rates of eruption to the surface (or shallow intrusion) should balance the magma production rate, but since magma could accumulate and erupt intermittently from these reservoirs, the instantaneous eruption rates could be hundreds to thousands of cubic m/s, comparable to historic basaltic eruption rates on Earth and very much greater than the average mantle melting rate. The absence of asteroid atmospheres makes explosive eruptions likely even if magmas are volatile-poor. On asteroids with radii less than ~100 km, gases and sub-mm pyroclastic melt droplets would have had speeds exceeding the escape speed assuming a few hundred ppm volatiles, and only cm sized or larger clasts would have been retained. On larger bodies almost all pyroclasts will have returned to the surface

  5. 226Ra-230Th Disequilibria in Magmas from Llaima and Lonquimay Volcanoes, Chile: On the Roles and Rates of Subvolcanic Magmatic Processes.

    Science.gov (United States)

    Reubi, O.; Cooper, L. B.; Dungan, M. A.; Bourdon, B.

    2014-12-01

    226Ra excesses in mafic arc magmas are generally attributed to recent (contamination had a secondary influence on 226Ra-230Th disequilibria. Magmas with the highest AFC contribution have 226Ra-230Th close to equilibrium, implying that (226Ra-230Th) are mostly affected by either differentiation on time scales of ~8 kyr, or more likely, mixing with mush bodies several kyr old. Lonquimay magmas (52 to 64 wt% SiO2) are almost aphyric. Their evolution was controlled by fractional crystallization with limited crustal contamination. (226Ra-230Th) range from moderate 226Ra excesses to small deficits, and are negatively correlated with Ba/Th and MgO. These observations are difficult to reconcile with only slab-fluid addition and mantle melting. We posit that this (226Ra-230Th) range results from diffusive Ra-exchange between young recharge melts and an old crystal mush. A similar process may also explain 226Ra deficits at some other SVZ volcanoes. Thus (226Ra-230Th) in erupted magmas reflect modification of mantle-derived signatures by open-system magmatic processes in the crust. 1Sigmarsson et al., 2002, Earth and Planet. Sc. Lett. 196, 189-196. 2 Reubi et al., 2011, Earth and Planet. Sc. Lett. 303, 37-47.

  6. A hybrid composite dike suite from the northern Arabian Nubian Shield, southwest Jordan: Implications for magma mixing and partial melting of granite by mafic magma

    Science.gov (United States)

    Jarrar, Ghaleb H.; Yaseen, Najel; Theye, Thomas

    2013-03-01

    The Arabian Nubian Shield is an exemplary juvenile continental crust of Neoproterozoic age (1000-542 Ma). The post-collisional rift-related stage (~ 610 to 542 Ma) of its formation is characterized among others by the intrusion of several generations of simple and composite dikes. This study documents a suite of hybrid composite dikes and a natural example of partial melting of granite by a mafic magma from the northernmost extremity of Arabian Nubian Shield in southwest Jordan. The petrogenesis of this suite is discussed on the basis of field, petrographic, geochemical, and Rb/Sr isotopic data. These dikes give spectacular examples of the interaction between basaltic magma and the granitic basement. This interaction ranges from brecciation, partial melting of the host alkali feldspar granite to complete assimilation of the granitic material. Field structures range from intrusive breccia (angular partially melted granitic fragments in a mafic groundmass) to the formation of hybrid composite dikes that are up to 14 m in thickness. The rims of these dikes are trachyandesite (latite) with alkali feldspar ovoids (up to 1 cm in diameter); while the central cores are trachydacite to dacite and again with alkali feldspar ovoids and xenoliths from the dike rims. The granitic xenoliths in the intrusive breccia have been subjected to at least 33% partial melting. A seven-point Rb/Sr isochron from one of these composite dikes yields an age of 561 ± 33 Ma and an initial 87Sr/86Sr ratio of 0.70326 ± 0.0003 (2σ) and MSWD of 0.62. Geochemical modeling using major, trace, rare earth elements and isotopes suggests the generation of the hybrid composite dike suite through the assimilation of 30% to 60% granitic crustal material by a basaltic magma, while the latter was undergoing fractional crystallization at different levels in the continental crust.

  7. The Mineralogy, Geochemistry, and Redox State of Multivalent Cations During the Crystallization of Primitive Shergottitic Liquids at Various (f)O2. Insights into the (f)O2 Fugacity of the Martian Mantle and Crustal Influences on Redox Conditions of Martian Magmas.

    Science.gov (United States)

    Shearer, C. K.; Bell, A. S.; Burger, P. V.; Papike, J. J.; Jones, J.; Le, L.; Muttik, N.

    2016-01-01

    The (f)O2 [oxygen fugacity] of crystallization for martian basalts has been estimated in various studies to range from IW-1 to QFM+4 [1-3]. A striking geochemical feature of the shergottites is the large range in initial Sr isotopic ratios and initial epsilon(sup Nd) values. Studies by observed that within the shergottite group the (f)O2 [oxygen fugacity] of crystallization is highly correlated with these chemical and isotopic characteristics with depleted shergottites generally crystallizing at reduced conditions and enriched shergottites crystallizing under more oxidizing conditions. More recent work has shown that (f)O2 [oxygen fugacity] changed during the crystallization of these magmas from one order of magnitude in Y980459 (Y98) to several orders of magnitude in Larkman Nunatak 06319. These real or apparent variations within single shergottitic magmas have been attributed to mixing of a xenocrystic olivine component, volatile loss-water disassociation, auto-oxidation during crystallization of mafic phases, and assimilation of an oxidizing crustal component (e.g. sulfate). In contrast to the shergottites, augite basalts such as NWA 8159 are highly depleted yet appear to be highly oxidized (e.g. QFM+4). As a first step in attempting to unravel petrologic complexities that influence (f)O2 [oxygen fugacity] in martian magmas, this study explores the effect of (f)O2 [oxygen fugacity] on the liquid line of descent (LLD) for a primitive shergottite liquid composition (Y98). The results of this study will provide a fundamental basis for reconstructing the record of (f)O2 [oxygen fugacity] in shergottites and other martian basalts, its effect on both mineral chemistries and valence state partitioning, and a means for examining the role of crystallization (and other more complex processes) on the petrologic linkages between olivine-phyric and pyroxene-plagioclase shergottites.

  8. Exsolution lamellae in volcanic pyroxene; Single phenocryst thermometry for long-lived magmatic reservoir

    Science.gov (United States)

    I Made, R.; Herrin, J. S.; Tay, Y. Y.; Costa Rodriguez, F.

    2017-12-01

    Comprehensive understanding of the relevant timescales of thermal and chemical evolution of magma below the active volcanoes can help us to better anticipate volcanic eruptions and their likely precursor signals. In recent years, several lines of thermochronological inquiry have converged on a realization that, within many volcanic systems, magmas experience prolonged periods of relatively low-temperature storage prior to eruption during short duration transient events. This prolonged storage at low magmatic temperatures can result in series of solid state phase transformations within minerals, producing a petrologic record of their thermal history. In this example, we observed pigeonite exsolution lamellae in augite phenocrysts from the 2011 eruption of Cordon Caulle volcano, Chile. The small size of these features ( 70nm width and bear exsolution textures and apply this knowledge to understanding the thermal conditions of magma storage in long-lived volcanic reservoirs.

  9. The Relationship Between Carbonatitic, Melilititic and Potassic Trachytic Magma Types at the Saltpeterkop Carbonatite Complex, Sutherland, South Africa

    Science.gov (United States)

    Janney, P. E.; Marageni, M.

    2016-12-01

    The 74 Ma Saltpeterkop Carbonatite Complex near Sutherland, South Africa, is unusual in that it is one of the few southern African carbonatites with preserved volcanic features, including a 1 km-diameter tuff ring composed of silicified volcaniclastic breccia. Around the complex, the regionally flat-lying Karoo strata have been dramatically upwarped, with dips away from the Complex as high as 45°. Further, within about a 10 km radius of the center of the complex are hundreds of dikes, sills and diatremes composed mainly of carbonatite, potassic trachyte and olivine melilitite, with the spatial density of these intrusions decreasing with increasing distance. We have recently completed an in-depth geochemical reconnaissance of the Saltpeterkop complex, involving field sampling and whole-rock major and trace element analysis, with radiogenic and stable isotope measurements in progress. While the association with potassic trachytes is relatively common in southern African carbonatites, the presence of significant amounts of primitive olivine melilitite (30-40 wt.% SiO2, Mg# = 61-74) is unusual. Our preliminary model for the origin of the complex involves (1) ascent and intrusion of a mantle-derived carbonated and potassic magma into the mid-to upper crust, (2a) separation of an alkali carbonatite phase from this magma, resulting in intensive local fenitization and partial melting of mid-crustal rocks (thereby forming potassic trachytes), and possibly triggering the initial eruption, (2b) small amounts of primitive, but now less potassic, mantle-derived magma are emplaced as olivine melilitite dikes and diatremes, and (3) differentiation of the mantle-derived magma to generate significant quantities of mainly calcio- and ferro-carbonatite magmas emplaced as dykes and sills.

  10. The Effects of Varying Crustal Carbonate Composition on Assimilation and CO2 Degassing at Arc Volcanoes

    Science.gov (United States)

    Carter, L. B.; Holmes, A. K.; Dasgupta, R.; Tumiati, S.

    2015-12-01

    Magma-crustal carbonate interaction and subsequent decarbonation can provide an additional source of CO2 release to the exogenic system superimposed on mantle-derived CO2. Carbonate assimilation at present day volcanoes is often modeled by limestone consumption experiments [1-4]. Eruptive products, however, do not clearly display the characteristic ultracalcic melt compositions produced during limestone-magma interaction [4]. Yet estimated CO2outflux [5] and composition of volcanics in many volcanic systems may allow ~3-17% limestone- or dolostone-assimilated melt contribution. Crystallization may retain ultracalcic melts in pyroxenite cumulates. To extend our completed study on limestone assimilation, here we explore the effect of varying composition from calcite to dolomite on chemical and thermal decarbonation efficiency of crustal carbonates. Piston cylinder experiments at 0.5 GPa and 900-1200 °C demonstrate that residual mineralogy during interaction with magma shifts from CaTs cpx and anorthite/scapolite in the presence of calcite to Di cpx and Fo-rich olivine with dolomite. Silica-undersaturated melts double in magnesium content, while maintaining high (>30 wt.%) CaO values. At high-T, partial thermal breakdown of dolomite into periclase and CO2 is minimal (<5%) suggesting that in the presence of magma, CO2 is primarily released due to assimilation. Assimilated melts at identical P-T conditions depict similarly high volatile contents (10-20 wt.% by EMPA deficit at 0.5 GPa, 1150 °C with hydrous basalt) with calcite or dolomite. Analysis of the coexisting fluid phase indicates the majority of water is dissolved in the melt, while CO2 released from the carbonate is preferentially partitioned into the vapor. This suggests that although assimilated melts have a higher CO2 solubility, most of the CO2can easily degas from the vapor phase at arc volcanoes, possibly more so at volcanic plumbing systems traversing dolomite [8]. [1]Conte et al 2009 EuJMin (21) 763

  11. Magma Mixing: Magmatic Enclaves in Morne Micotrin, Dominica

    Science.gov (United States)

    Hickernell, S.; Frey, H. M.; Manon, M. R. F.; Waters, L. E.

    2017-12-01

    Magmatic enclaves in volcanic rocks provide direct evidence of magma mingling/mixing within a magma reservoir and may reinvigorate the system and trigger eruption, as documented at the Soufriere Hills in Montserrat. Lava domes on the neighboring island of Dominica also contain multiple enclave populations and may be evidence for similar magma chamber processes. The central dome of Micotrin is at the head of the Roseau Valley, which was filled with 3 km3 of pyroclastic deposits from eruptions spanning 65 - 25 ka. There appear to be two distinct types of enclaves in the crystal-rich Micotrin andesites (60 wt% SiO2), fine-grained and coarse-grained. Fine-grained mafic enclaves (52 wt% SiO2) vary in size from 1 to 15 cm in diameter, whereas the coarse-grained enclaves are generally larger and range from 3-20 cm. Fine-grained enclaves are saturated in plag (35%) + opx (35%) + cpx (20%) + oxides (10%). Average pyroxenes are 0.01 to 0.02 cm in size, whereas plagioclase averages 0.05 cm and up to 0.1 cm. The texture of the fine-grained enclaves is cumulate-like, devoid of microlites and matrix glass. Coarse-grained enclaves lack cpx and have different modal abundances and textures: plag (75%) + opx (10%) + oxides (5%) + plag microlites (10%). Plagioclase are 0.1 cm in size and orthopyroxenes average 0.05 cm. The coarse-grained enclaves are highly vesicular, a notable difference from the host as well as the fine-grained enclaves. The boundaries of both the fine- and coarse-grained enclaves are quite sharp and distinct and there do not appear to be enclave minerals disaggregated in the host rock. Temperatures were determined by two oxides. The fine-grained enclaves had two populations of magnetite, yielding 847 + 21° and 920 + 17°C. The coarse-grained enclave was 890 + 42 °C, but the oxides were extensively exsolved. Plagioclase composition in both coarse and fine-grained samples was comparable, ranging from An50 to An80. Despite compositional similarity the textures of

  12. Numerical modeling of magma-repository interactions

    NARCIS (Netherlands)

    Bokhove, Onno

    2001-01-01

    This report explains the numerical programs behind a comprehensive modeling effort of magma-repository interactions. Magma-repository interactions occur when a magma dike with high-volatile content magma ascends through surrounding rock and encounters a tunnel or drift filled with either a magmatic

  13. Crystallization conditions and petrogenesis of the lava dome from the ˜900 years BP eruption of Cerro Machín Volcano, Colombia

    Science.gov (United States)

    Laeger, Kathrin; Halama, Ralf; Hansteen, Thor; Savov, Ivan P.; Murcia, Hugo F.; Cortés, Gloria P.; Garbe-Schönberg, Dieter

    2013-12-01

    The last known eruption at Cerro Machín Volcano (CMV) in the Central Cordillera of Colombia occurred ˜900 years BP and ended with the formation of a dacitic lava dome. The dome rocks contain both normally and reversely zoned plagioclase (An24-54), unzoned and reversely zoned amphiboles of dominantly tschermakite and pargasite/magnesio-hastingsite composition and olivine xenocrysts (Fo = 85-88) with amphibole/clinopyroxene overgrowth, all suggesting interaction with mafic magma at depth. Plagioclase additionally exhibits complex oscillatory zoning patterns reflecting repeated replenishment, fractionation and changes in intrinsic conditions in the magma reservoir. Unzoned amphiboles and cores of the reversely zoned amphiboles give identical crystallization conditions of 910 ± 30 °C and 360 ± 70 MPa, corresponding to a depth of about 13 ± 2 km, at moderately oxidized conditions (f = +0.5 ± 0.2 ΔNNO). The water content in the melt, calculated based on amphibole chemistry, is 7.1 ± 0.4 wt.%. Rims of the reversely zoned amphiboles are relatively enriched in MgO and yield higher crystallization temperatures (T = 970 ± 25 °C), slightly lower melt H2O contents (6.1 ± 0.7 wt.%) and overlapping pressures (410 ± 100 MPa). We suggest that these rims crystallized following an influx of mafic melt into a resident magma reservoir at mid-crustal depths, further supported by the occurrence of xenocrystic olivine. Crystallization of biotite, albite-rich plagioclase and quartz occurred at comparatively low temperatures (probably during early stages of ascent or storage at shallower levels. Based on amphibole mineral chemistry, the felsic resident melt had a rhyolitic composition (71 ± 2 wt.% SiO2), whereas the hybrid magma, from which the amphibole rims crystallized, was dacitic (64 ± 3 wt.% SiO2). The bulk rock chemistry of the CMV lava dome dacites is homogenous. They have elevated (La/Nb)N ratios of 3.8-4.5, typical for convergent margin magmas, and display several

  14. How does continental lithosphere break-apart? A 3D seismic view on the transition from magma-poor rifted margin to magmatic oceanic lithosphere

    Science.gov (United States)

    Emmanuel, M.; Lescanne, M.; Picazo, S.; Tomasi, S.

    2017-12-01

    In the last decade, high-quality seismic data and drilling results drastically challenged our ideas about how continents break apart. New models address their observed variability and are presently redefining basics of rifting as well as exploration potential along deepwater rifted margins. Seafloor spreading is even more constrained by decades of scientific exploration along Mid Oceanic Ridges. By contrast, the transition between rifting and drifting remains a debated subject. This lithospheric breakup "event" is geologically recorded along Ocean-Continent Transitions (OCT) at the most distal part of margins before indubitable oceanic crust. Often lying along ultra-deepwater margin domains and buried beneath a thick sedimentary pile, high-quality images of these domains are rare but mandatory to get strong insights on the processes responsible for lithospheric break up and what are the consequences for the overlying basins. We intend to answer these questions by studying a world-class 3D seismic survey in a segment of a rifted margin exposed in the Atlantic. Through these data, we can show in details the OCT architecture between a magma-poor hyper-extended margin (with exhumed mantle) and a classical layered oceanic crust. It is characterized by 1- the development of out-of-sequence detachment systems with a landward-dipping geometry and 2- the increasing magmatic additions oceanwards (intrusives and extrusives). Geometry of these faults suggests that they may be decoupled at a mantle brittle-ductile interface what may be an indicator on thermicity. Furthermore, magmatism increases as deformation migrates to the future first indubitable oceanic crust what controls a progressive magmatic crustal thickening below, above and across a tapering rest of margin. As the magmatic budget increases oceanwards, full-rate divergence is less and less accommodated by faulting. Magmatic-sedimentary architectures of OCT is therefore changing from supra-detachment to magmatic

  15. Lower Crustal Strength Controls on Melting and Serpentinization at Magma-Poor Margins: Potential Implications for the South Atlantic

    Science.gov (United States)

    Ros, Elena; Pérez-Gussinyé, Marta; Araújo, Mario; Thoaldo Romeiro, Marco; Andrés-Martínez, Miguel; Morgan, Jason P.

    2017-12-01

    Rifted continental margins may present a predominantly magmatic continent-ocean transition (COT), or one characterized by large exposures of serpentinized mantle. In this study we use numerical modeling to show the importance of the lower crustal strength in controlling the amount and onset of melting and serpentinization during rifting. We propose that the relative timing between both events controls the nature of the COT. Numerical experiments for half-extension velocities serpentinized mantle underlain by some magmatic products. In contrast, a weak lower crust promotes margins with a gentle crustal tapering, small faults dipping both ocean- and landward and small syn-rift subsidence. Their COT is predominantly magmatic at any ultra-slow extension velocity and perhaps underlain by some serpentinized mantle. These margins can also be either symmetric or asymmetric. Our models predict that magmatic underplating mostly underlies the wide margin at weak asymmetric conjugates, whereas the wide margin is mainly underlain by serpentinized mantle at strong asymmetric margins. Based on this conceptual template, we propose different natures for the COTs in the South Atlantic.

  16. Intrusion of basaltic magma into a crystallizing granitic magma chamber: The Cordillera del Paine pluton in southern Chile

    Science.gov (United States)

    Michael, Peter J.

    1991-10-01

    The Cordillera del Paine pluton in the southernmost Andes of Chile represents a deeply dissected magma chamber where mafic magma intruded into crystallizing granitic magma. Throughout much of the 10x15 km pluton, there is a sharp and continuous boundary at a remarkably constant elevation of 1,100 m that separates granitic rocks (Cordillera del Paine or CP granite: 69 77% SiO2) which make up the upper levels of the pluton from mafic and comingled rocks (Paine Mafic Complex or PMC: 45 60% SiO2) which dominate the lower exposures of the pluton. Chilled, crenulate, disrupted contacts of mafic rock against granite demonstrate that partly crystallized granite was intruded by mafic magma which solidified prior to complete crystallization of the granitic magma. The boundary at 1,100 m was a large and stable density contrast between the denser, hotter mafic magma and cooler granitic magma. The granitic magma was more solidified near the margins of the chamber when mafic intrusion occurred, and the PMC is less disrupted by granites there. Near the pluton margins, the PMC grades upward irregularly from cumulate gabbros to monzodiorites. Mafic magma differentiated largely by fractional crystallization as indicated by the presence of cumulate rocks and by the low levels of compatible elements in most PMC rocks. The compositional gap between the PMC and CP granite indicates that mixing (blending) of granitic magma into the mafic magma was less important, although it is apparent from mineral assemblages in mafic rocks. Granitic magma may have incorporated small amounts of mafic liquid that had evolved to >60% SiO2 by crystallization. Mixing was inhibited by the extent of crystallization of the granite, and by the thermal contrast and the stable density contrast between the magmas. PMC gabbros display disequilibrium mineral assemblages including early formed zoned olivine (with orthopyroxene coronas), clinopyroxene, calcic plagioclase and paragasite and later-formed amphibole

  17. Cratonic roots and lower crustal seismicity: Investigating the role of deep intrusion in the Western rift, Africa

    Science.gov (United States)

    Drooff, C.; Ebinger, C. J.; Lavayssiere, A.; Keir, D.; Oliva, S. J.; Tepp, G.; Gallacher, R. J.

    2017-12-01

    Improved seismic imaging beneath the African continent reveals lateral variations in lithospheric thickness, and crustal structure, complementing a growing crust and mantle xenolith data base. Border fault systems in the active cratonic rifts of East Africa are characterized by lower crustal seismicity, both in magmatic sectors and weakly magmatic sectors, providing constraints on crustal rheology and, in some areas, magmatic fluid migration. We report new seismicity data from magmatic and weakly magmatic sectors of the East African rift zone, and place the work in the context of independent geophysical and geochemical studies to models for strain localization during early rifting stages. Specifically, multidisciplinary studies in the Magadi Natron rift sectors reveal volumetrically large magmatic CO2 degassing along border faults with seismicity along projections of surface dips to the lower crust. The magmatic CO2 degassing and high Vp/Vs ratios and reflectivity of the lower crust implies that the border fault serves a conduit between the lower crustal underplating and the atmospheric. Crustal xenoliths in the Eastern rift sector indicate a granulitic lower crust, which is relatively weak in the presence of fluids, arguing against a strong lower crust. Within magmatic sectors, seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Within some weakly magmatic sectors, lower crustal earthquakes also occur along projections of border faults to the lower crust (>30 km), and they are prevalent in areas with high Vp/Vs in the lower crust. Within the southern Tanganyika rift, focal mechanisms are predominantly normal with steep nodal planes. Our comparative studies suggest that pervasive metasomatism above a mantle plume, and melt extraction in thin zones between cratonic roots, lead to

  18. Pre-eruptive conditions of the phonolitic magma from the El Abrigo caldera-forming eruption (Las Canadas caldera, Tenerife, Canary Islands)

    International Nuclear Information System (INIS)

    Marti, J; Andujar, J; Costa, F; Wolff, J A; Carroll, M R

    2008-01-01

    We have performed phase equilibrium experiments to determine the pre-eruptive conditions of the largest phonolitic caldera-forming eruption (∼20 km3 of DRE) that occurred on Tenerife (Canary Islands). The Abrigo ignimbrite was erupted during the last caldera-forming episode (ca. 190 ka), from the Canadas caldera. Comparison of the natural and experimental phase proportions and compositions indicates that the phonolite at the roof of the Abrigo magma reservoir was at 130 ± 50 MPa (corresponding to ca. 4 - 5 km below the surface), 825 ± 25 oC, with 3 ± 1 wt% dissolved H2O and fO2 at the Ni-NiO buffer ? 1 log unit. This shows that the magma that produced the largest ignimbrite on Tenerife was stored at relatively shallow depths but was water-undersaturated, and its eruption was probably triggered by input of fresh mafic magma.

  19. Pre-eruptive conditions of the phonolitic magma from the El Abrigo caldera-forming eruption (Las Canadas caldera, Tenerife, Canary Islands)

    Energy Technology Data Exchange (ETDEWEB)

    Marti, J; Andujar, J; Costa, F [Institute of Earth Sciences ' Jaume Almera' , CSIC, C/ Lluis Sole I Sabaris, s/n Barcelona, 08028 Spain (Spain); Wolff, J A [School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99164-2812 (United States); Carroll, M R [Dipartimento di Scienze della Terra, Via Gentile III da Varano, Universita di Camerino, 62032 MC (Italy)], E-mail: jawolff@mail.wsu.edu, E-mail: Michael.carroll@unicam.it

    2008-10-01

    We have performed phase equilibrium experiments to determine the pre-eruptive conditions of the largest phonolitic caldera-forming eruption ({approx}20 km3 of DRE) that occurred on Tenerife (Canary Islands). The Abrigo ignimbrite was erupted during the last caldera-forming episode (ca. 190 ka), from the Canadas caldera. Comparison of the natural and experimental phase proportions and compositions indicates that the phonolite at the roof of the Abrigo magma reservoir was at 130 {+-} 50 MPa (corresponding to ca. 4 - 5 km below the surface), 825 {+-} 25 oC, with 3 {+-} 1 wt% dissolved H2O and fO2 at the Ni-NiO buffer ? 1 log unit. This shows that the magma that produced the largest ignimbrite on Tenerife was stored at relatively shallow depths but was water-undersaturated, and its eruption was probably triggered by input of fresh mafic magma.

  20. Advanced reservoir characterization and evaluation of CO{sub 2} gravity drainage in the naturally fractured Spraberry Trend Area. First annual technical progress report, September 1, 1995--August 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Schechter, D.S.

    1996-12-17

    The overall goal of this project is to assess the economic feasibility of CO{sub 2} flooding the naturally fractured Spraberry Trend Area in West Texas. This objective is being accomplished by conducting research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, (3) analytical and numerical simulation of Spraberry reservoirs, and, (4) experimental investigations on CO{sub 2} gravity drainage in Spraberry whole cores. This report provides results of the first year of the five-year project for each of the four areas.

  1. The influence of magma viscosity on convection within a magma chamber

    Science.gov (United States)

    Schubert, M.; Driesner, T.; Ulmer, P.

    2012-12-01

    Magmatic-hydrothermal ore deposits are the most important sources of metals like Cu, Mo, W and Sn and a major resource for Au. It is well accepted that they are formed by the release of magmatic fluids from a batholith-sized magma body. Traditionally, it has been assumed that crystallization-induced volatile saturation (called "second boiling") is the main mechanism for fluid release, typically operating over thousands to tens of thousands of years (Candela, 1991). From an analysis of alteration halo geometries caused by magmatic fluids, Cathles and Shannon (2007) suggested much shorter timescales in the order of hundreds of years. Such rapid release of fluids cannot be explained by second boiling as the rate of solidification scales with the slow conduction of heat away from the system. However, rapid fluid release is possible if convection is assumed within the magma chamber. The magma would degas in the upper part of the magma chamber and volatile poor magma would sink down again. Such, the rates of degassing can be much higher than due to cooling only. We developed a convection model using Navier-Stokes equations provided by the computational fluid dynamics platform OpenFOAM that gives the possibility to use externally derived meshes with complex (natural) geometries. We implemented a temperature, pressure, composition and crystal fraction dependent viscosity (Ardia et al., 2008; Giordano et al., 2008; Moore et al., 1998) and a temperature, pressure, composition dependent density (Lange1994). We found that the new viscosity and density models strongly affect convection within the magma chamber. The dependence of viscosity on crystal fraction has a particularly strong effect as the steep viscosity increase at the critical crystal fraction leads to steep decrease of convection velocity. As the magma chamber is cooling from outside to inside a purely conductive layer is developing along the edges of the magma chamber. Convection continues in the inner part of the

  2. Stress field control during large caldera-forming eruptions

    Directory of Open Access Journals (Sweden)

    Antonio Costa

    2016-10-01

    Full Text Available Crustal stress field can have a significant influence on the way magma is channelled through the crust and erupted explosively at the surface. Large Caldera Forming Eruptions (LCFEs can erupt hundreds to thousands of cubic kilometres of magma in a relatively short time along fissures under the control of a far-field extensional stress. The associated eruption intensities are estimated in the range 109 - 1011 kg/s. We analyse syn-eruptive dynamics of LCFEs, by simulating numerically explosive flow of magma through a shallow dyke conduit connected to a magma chamber that in turn is fed by a deeper magma reservoir, both under the action of an extensional far-field stress. Results indicate that huge amounts of high viscosity silicic magma can be erupted over timescales of a few to several hours. Our study provides answers to outstanding questions relating to the intensity and duration of catastrophic volcanic eruptions in the past. In addition, it presents far-reaching implications for the understanding of dynamics and intensity of large-magnitude volcanic eruptions on Earth and to highlight the necessity of a future research to advance our knowledge of these rare catastrophic events.

  3. A large hydrothermal reservoir beneath Taal Volcano (Philippines) revealed by magnetotelluric observations and its implications to the volcanic activity.

    Science.gov (United States)

    Alanis, Paul K B; Yamaya, Yusuke; Takeuchi, Akihiro; Sasai, Yoichi; Okada, Yoshihiro; Nagao, Toshiyasu

    2013-01-01

    Taal Volcano is one of the most active volcanoes in the Philippines. The magnetotelluric 3D forward analyses indicate the existence of a large high resistivity anomaly (∼100 Ω·m) with a volume of at least 3 km×3 km×3 km, which is capped by a conductive layer (∼10 Ω·m), beneath the Main Crater. This high resistivity anomaly is hypothesized to be a large hydrothermal reservoir, consisting of the aggregate of interconnected cracks in rigid and dense host rocks, which are filled with hydrothermal fluids coming from a magma batch below the reservoir. The hydrothermal fluids are considered partly in gas phase and liquid phase. The presence of such a large hydrothermal reservoir and the stagnant magma below may have influences on the volcano's activity. Two possibilities are presented. First, the 30 January 1911 explosion event was a magmatic hydrothermal eruption rather than a base-surge associated with a phreato-magmatic eruption. Second, the earlier proposed four eruption series may be better interpreted by two cycles, each consisting of series of summit and flank eruptions.

  4. Shallow velocity structure above the Socorro Magma Body from ambient noise tomography using the large-N Sevilleta array, central Rio Grande Rift, New Mexico

    Science.gov (United States)

    Worthington, L. L.; Ranasinghe, N. R.; Schmandt, B.; Jiang, C.; Finlay, T. S.; Bilek, S. L.; Aster, R. C.

    2017-12-01

    The Socorro Magma Body (SMB) is one of the largest recognized active mid-crustal magma intrusions globally. Inflation of the SMB drives sporadically seismogenic uplift at rates of up to of few millimeters per year. We examine the upper crustal structure of the northern section of the SMB region using ambient noise seismic data collected from the Sevilleta Array and New Mexico Tech (NMT) seismic network to constrain basin structure and identify possible upper crustal heterogeneities caused by heat flow and/or fluid or magma migration to shallower depths. The Sevilleta Array comprised 801 vertical-component Nodal seismic stations with 10-Hz seismometers deployed within the Sevilleta National Wildlife Refuge in the central Rio Grande rift north of Socorro, New Mexico, for a period of 12 days during February 2015. Five short period seismic stations from the NMT network located south of the Sevilleta array are also used to improve the raypath coverage outside the Sevilleta array. Inter-station ambient noise cross-correlations were computed from all available 20-minute time windows and stacked to obtain estimates of the vertical component Green's function. Clear fundamental mode Rayleigh wave energy is observed from 3 to 6 s period. Beamforming indicates prominent noise sources from the southwest, near Baja California, and the southeast, in the Gulf of Mexico. The frequency-time analysis method was implemented to measure fundamental mode Rayleigh wave phase velocities and the resulting inter-station travel times were inverted to obtain 2-D phase velocity maps. One-dimensional sensitivity kernels indicate that the Rayleigh wave phase velocity maps are sensitive to a depth interval of 1 to 8 km, depending on wave period. The maps show (up to 40%) variations in phase velocity within the Sevilleta Array, with the largest variations found for periods of 5-6 seconds. Holocene to upper Pleistocene, alluvial sediments found in the Socorro Basin consistently show lower phase

  5. Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 2: Predicted emplacement processes and observations)

    Science.gov (United States)

    Head, James W.; Wilson, Lionel

    2017-02-01

    We utilize a theoretical analysis of the generation, ascent, intrusion and eruption of basaltic magma on the Moon to develop new insights into magma source depths, supply processes, transport and emplacement mechanisms via dike intrusions, and effusive and explosive eruptions. We make predictions about the intrusion and eruption processes and compare these with the range of observed styles of mare volcanism, and related features and deposits. Density contrasts between the bulk mantle and regions with a greater abundance of heat sources will cause larger heated regions to rise as buoyant melt-rich diapirs that generate partial melts that can undergo collection into magma source regions; diapirs rise to the base of the anorthositic crustal density trap (when the crust is thicker than the elastic lithosphere) or, later in history, to the base of the lithospheric rheological trap (when the thickening lithosphere exceeds the thickness of the crust). Residual diapiric buoyancy, and continued production and arrival of diapiric material, enhances melt volume and overpressurizes the source regions, producing sufficient stress to cause brittle deformation of the elastic part of the overlying lithosphere; a magma-filled crack initiates and propagates toward the surface as a convex upward, blade-shaped dike. The volume of magma released in a single event is likely to lie in the range 102 km3 to 103 km3, corresponding to dikes with widths of 40-100 m and both vertical and horizontal extents of 60-100 km, favoring eruption on the lunar nearside. Shallower magma sources produce dikes that are continuous from the source region to the surface, but deeper sources will propagate dikes that detach from the source region and ascend as discrete penny-shaped structures. As the Moon cools with time, the lithosphere thickens, source regions become less abundant, and rheological traps become increasingly deep; the state of stress in the lithosphere becomes increasingly contractional

  6. How does the architecture of a fault system controls magma upward migration through the crust?

    Science.gov (United States)

    Iturrieta, P. C.; Cembrano, J. M.; Stanton-Yonge, A.; Hurtado, D.

    2017-12-01

    The orientation and relative disposition of adjacent faults locally disrupt the regional stress field, thus enhancing magma flow through previous or newly created favorable conduits. Moreover, the brittle-plastic transition (BPT), due to its stronger rheology, governs the average state of stress of shallower portions of the fault system. Furthermore, the BPT may coincide with the location of transient magma reservoirs, from which dikes can propagate upwards into the upper crust, shaping the inner structure of the volcanic arc. In this work, we examine the stress distribution in strike-slip duplexes with variable geometry, along with the critical fluid overpressure ratio (CFOP), which is the minimum value required for individual faults to fracture in tension. We also determine the stress state disruption of the fault system when a dike is emplaced, to answer open questions such as: what is the nature of favorable pathways for magma to migrate? what is the architecture influence on the feedback between fault system kinematics and magma injection? To this end, we present a 3D coupled hydro-mechanical finite element model of the continental lithosphere, where faults are represented as continuum volumes with an elastic-plastic rheology. Magma flow upon fracturing is modeled through non-linear Stoke's flow, coupling solid and fluid equilibrium. A non-linear sensitivity analysis is performed in function of tectonic, rheology and geometry inputs, to assess which are the first-order factors that governs the nature of dike emplacement. Results show that the CFOP is heterogeneously distributed in the fault system, and within individual fault segments. Minimum values are displayed near fault intersections, where local kinematics superimpose on regional tectonic loading. Furthermore, when magma is transported through a fault segment, the CFOP is now minimized in faults with non-favorable orientations. This suggests that these faults act as transient pathways for magma to

  7. Magmatic activity beneath the quiescent Three Sisters volcanic center, central Oregon Cascade Range, USA

    Science.gov (United States)

    Wicks, Charles W.; Dzurisin, Daniel; Ingebritsen, Steven; Thatcher, Wayne; Lu, Zhong; Iverson, Justin

    2002-04-01

    Images from satellite interferometric synthetic aperture radar (InSAR) reveal uplift of a broad ~10 km by 20 km area in the Three Sisters volcanic center of the central Oregon Cascade Range, ~130 km south of Mt. St. Helens. The last eruption in the volcanic center occurred ~1500 years ago. Multiple satellite images from 1992 through 2000 indicate that most if not all of ~100 mm of observed uplift occurred between September 1998 and October 2000. Geochemical (water chemistry) anomalies, first noted during 1990, coincide with the area of uplift and suggest the existence of a crustal magma reservoir prior to the uplift. We interpret the uplift as inflation caused by an ongoing episode of magma intrusion at a depth of ~6.5 km.

  8. Contamination of mantle magmas by crustal contributions: evidence from the brasiliano mobile belt in the State of Espirito Santo, Brazil

    International Nuclear Information System (INIS)

    Wiedemann, Cristina M.; mendes, Julio C.; Ludka, Isabel P.

    1995-01-01

    In the beginning of the late orogenic phase of the Pan african/Brasiliano Mobile Belt, in Espirito Santo and Rio de Janeiro States, along the Brazilian coast, tholeiitic gabbros intruded the coast Small bodies of clinopyroxene -gabbro-norites, hornblendi-gabbros and clinoorthopyroxenes -pyroxenites/hornblendites typical tholeiitic AFM-trends. The series of rocks reveal evidence of crustal contamination, but no signs of in situ mixing with granitic melts. The geochemical characteristics of the tholeiitic series and suites of magmatites,- present in the different evolutionary stages of the post-collisional magmatic arc, in the Brasiliano Coastal Mobile belt, in the States of Espirito Santo and Rio de Janeiro-, are regarded as an important tool for the recognition of a further contamination process of an already enriched mantle, at crustal levels, during Late Proterozoic/Early Paleozoic times. 33 refs., 11 figs., 2 tabs

  9. Upscaling verticle permeability within a fluvio-aeolian reservoir

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, S.D.; Corbett, P.W.M.; Jensen, J.L. [Heriot-Watt Univ., Edinburgh (United Kingdom)

    1997-08-01

    Vertical permeability (k{sub v}) is a crucial factor in many reservoir engineering issues. To date there has been little work undertaken to understand the wide variation of k{sub v} values measured at different scales in the reservoir. This paper presents the results of a study in which we have modelled the results of a downhole well tester using a statistical model and high resolution permeability data. The work has demonstrates and quantifies a wide variation in k{sub v} at smaller, near wellbore scales and has implications for k{sub v} modelling at larger scales.

  10. Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block

    Science.gov (United States)

    Xu, Wenjing; Xu, Xisheng; Zeng, Gang

    2017-08-01

    Several recent studies have documented that the silicic rocks (SiO2 > 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of "hidden" large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of 22,000 km2. In contrast, exposures of mafic rocks total only 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial 87Sr/86Sr = 0.7041-0.7102; εNd(t) = - 8.4 to + 1.8; weighted mean zircon εHf(t) = - 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59-13.1 and 3.5-20.9, respectively), and variable Th/La ratios (0.11-0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (- 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial 87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.

  11. Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry

    Science.gov (United States)

    Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.

    2015-12-01

    Porphyry Cu (Mo-Au) and epithermal Au-Ag ores are globally associated with shallow hydrous, strongly oxidized, and sulfur-rich arc intrusions. In many localities, long-lived magmatism includes evolution from early andesitic volcanic (v) and plutonic (p) rocks to later dacitic or rhyolitic compositions dominated by plutons. We compare zircon compositions from three igneous suites with different time spans: Yerington, USA (1 m.y., p>v), El Salvador, Chile (4 m.y., p>v), and Yanacocha, Peru (6 m.y., v>p). At Yerington granite dikes and ores formed in one event, at ES in 2 to 3 events spanning 3 m.y., and at Yanacocha in 6 events spanning 5 m.y. At both ES and Yanacocha, high-Al amphiboles likely crystallized at high temperature in the mid-crust and attest to deep magmas that periodically recharged the shallow chambers. At Yanacocha, these amphiboles contain anhydrite inclusions that require magmas were sulfur-rich and strongly oxidized (~NNO+2). The Ti-in-zircon geothermometer provides estimates of 920º to 620º C for zircon crystallization, and records both core to rim cooling and locally high temperature rim overgrowths. Ore-related silicic porphyries yield near-solidus crystallization temperatures of 750-650°C consistent with low zircon saturation temperatures. The latter zircons have large positive Ce/Ce* and small negative Eu/Eu*≥0.4 anomalies attesting to strongly oxidized conditions (Ballard et al., 2001), which we propose result from crystallization and SO2 loss to the magmatic-hydrothermal ore fluid (Dilles et al., 2015). The Hf, REE, Y, U, and Th contents of zircons are diverse in the magma suites, and Th/U vs Yb/Gd plots suggest a dominant role of crystal fractionation with lesser roles for both crustal contamination and mixing with high temperature deep-sourced mafic magma. Ce/Sm vs Yb/Gd plots suggest that magma REE contents at contamination are most evident in pre-ore magmas, whereas ore-forming intrusions at low temperatures are dominated by crystal

  12. Constraints on the formation of the Martian crustal dichotomy from remnant crustal magnetism

    Science.gov (United States)

    Citron, Robert I.; Zhong, Shijie

    2012-12-01

    The Martian crustal dichotomy characterizing the topographic difference between the northern and southern hemispheres is one of the most important features on Mars. However, the formation mechanism for the dichotomy remains controversial with two competing proposals: exogenic (e.g., a giant impact) and endogenic (e.g., degree-1 mantle convection) mechanisms. Another important observation is the Martian crustal remnant magnetism, which shows a much stronger field in the southern hemisphere than in the northern hemisphere and also magnetic lineations. In this study, we examine how exogenic and endogenic mechanisms for the crustal dichotomy are constrained by the crustal remnant magnetism. Assuming that the dichotomy is caused by a giant impact in the northern hemisphere, we estimate that the average thickness of ejecta in the southern hemisphere is 20-25 km. While such a giant impact may cause crustal demagnetization in the northern hemisphere, we suggest that the impact could also demagnetize the southern hemisphere via ejecta thermal blanketing, impact demagnetization, and heat transfer from the hot layer of ejecta, thus posing a challenge for the giant impact model. We explore how the pattern of magnetic lineations relates to endogenic theories of dichotomy formation, specifically crustal production via degree-1 mantle convection. We observe that the pattern of lineations roughly corresponds to concentric circles about a single pole, and determine the pole for the concentric circles at 76.5° E and 84.5° S, which nearly overlaps with the centroid of the thickened crust in the southern hemisphere. We suggest that the crustal magnetization pattern, magnetic lineations, and crustal dichotomy (i.e., thickened crust in the highlands) can be explained by a simple endogenic process; one-plume convection causes melting and crustal production above the plume in the southern hemisphere, and strong crustal magnetization and magnetic lineations are formed in the southern

  13. Petrology and geochemistry of charnockites (felsic ortho-granulites) from the Kerala Khondalite Belt, Southern India: Evidence for intra-crustal melting, magmatic differentiation and episodic crustal growth

    Science.gov (United States)

    Ravindra Kumar, G. R.; Sreejith, C.

    2016-10-01

    contents of Y (71-99 ppm; average 87), and low Sr/Y (average 2) ratios with significant negative Eu anomalies (Eu/Eu* = 0.03-0.31; average 0.23) and low Sr (average 160 ppm) contents. The protoliths of the TC are interpreted as being derived from partial melting of thickened oceanic-arc crust composed of Archaean mafic composite source rocks (i.e., eclogite and/or garnet amphibolite) with a garnet amphibolite residue. Geochemical features of the GC, such as high Rb/Sr (average 1.80) and Ba/Sr ratios (average values > 6), are considered as evidence for crustal reworking in their genesis, suggesting remelting of a quartzo-feldspathic (TTG) source, within the plagioclase stability fields. The geochemical features of the felsic ortho-granulite suite, substantiated with published geochronological data on members of the TC, GC, and AC suites, suggest a four-stage crustal evolution of the KKB. The first stage is marked by the formation of an over-thickened oceanic-arc. Zircon Hfc model ages of the TC and GC suites constrain the time of this juvenile magmatic crust-forming event as Meso- to Neoarchaean (2.8 to 2.6 Ga). The second stage corresponds to the production of TTG magmas by melting of the over-thickened oceanic-arc crust, subsequent to basaltic underplating during Palaeoproterozoic (ca. 2.1 Ga). The third stage was initiated by a transition in subduction style from shallow to steep due to continent-arc accretion. This stage is marked by the formation of granitic magmas through partial melting of the TTG crust and their differentiation into GC and TC. The zircon crystallization ages (1.89 and 1.85 Ga) of the GC indicate arc accretion occurred during the Palaeoproterozoic. The fourth stage of crustal evolution is correlated with the Mesoproterozoic ( 1.5 Ga) emplacement of megacrystic K-feldspar granites (protoliths to the AC and augen gneisses). The distinct petrography, geochemistry and crystallization ages of the AC suggests recurrence of megacrystic, high-K calc

  14. Crustal structure of the Murray Ridge, northwest Indian Ocean, from wide-angle seismic data

    Science.gov (United States)

    Minshull, T. A.; Edwards, R. A.; Flueh, E. R.

    2015-07-01

    The Murray Ridge/Dalrymple Trough system forms the boundary between the Indian and Arabian plates in the northern Arabian Sea. Geodetic constraints from the surrounding continents suggest that this plate boundary is undergoing oblique extension at a rate of a few millimetres per year. We present wide-angle seismic data that constrains the composition of the Ridge and of adjacent lithosphere beneath the Indus Fan. We infer that Murray Ridge, like the adjacent Dalrymple Trough, is underlain by continental crust, while a thin crustal section beneath the Indus Fan represents thinned continental crust or exhumed serpentinized mantle that forms part of a magma-poor rifted margin. Changes in crustal structure across the Murray Ridge and Dalrymple Trough can explain short-wavelength gravity anomalies, but a long-wavelength anomaly must be attributed to deeper density contrasts that may result from a large age contrast across the plate boundary. The origin of this fragment of continental crust remains enigmatic, but the presence of basement fabrics to the south that are roughly parallel to Murray Ridge suggests that it separated from the India/Seychelles/Madagascar block by extension during early breakup of Gondwana.

  15. The roles of fractional crystallization, magma mixing, crystal mush remobilization and volatile-melt interactions in the genesis of a young basalt-peralkaline rhyolite suite, the greater Olkaria volcanic complex, Kenya Rift valley

    Science.gov (United States)

    Macdonald, R.; Belkin, H.E.; Fitton, J.G.; Rogers, N.W.; Nejbert, K.; Tindle, A.G.; Marshall, A.S.

    2008-01-01

    The Greater Olkaria Volcanic Complex is a young (???20 ka) multi-centred lava and dome field dominated by the eruption of peralkaline rhyolites. Basaltic and trachytic magmas have been erupted peripherally to the complex and also form, with mugearites and benmoreites, an extensive suite of magmatic inclusions in the rhyolites. The eruptive rocks commonly represent mixed magmas and the magmatic inclusions are themselves two-, three- or four-component mixes. All rock types may carry xenocrysts of alkali feldspar, and less commonly plagioclase, derived from magma mixing and by remobilization of crystal mushes and/or plutonic rocks. Xenoliths in the range gabbro-syenite are common in the lavas and magmatic inclusions, the more salic varieties sometimes containing silicic glass representing partial melts and ranging in composition from anorthite ?? corundum- to acmite-normative. The peralkaline varieties are broadly similar, in major element terms, to the eruptive peralkaline rhyolites. The basalt-trachyte suite formed by a combination of fractional crystallization, magma mixing and resorption of earlier-formed crystals. Matrix glass in metaluminous trachytes has a peralkaline rhyolitic composition, indicating that the eruptive rhyolites may have formed by fractional crystallization of trachyte. Anomalous trace element enrichments (e.g. ??? 2000 ppm Y in a benmoreite) and negative Ce anomalies may have resulted from various Na- and K-enriched fluids evolving from melts of intermediate composition and either being lost from the system or enriched in other parts of the reservoirs. A small group of nepheline-normative, usually peralkaline, magmatic inclusions was formed by fluid transfer between peralkaline rhyolitic and benmoreitic magmas. The plumbing system of the complex consists of several independent reservoirs and conduits, repeatedly recharged by batches of mafic magma, with ubiquitous magma mixing. ?? The Author 2008. Published by Oxford University Press. All

  16. Geochemical and geological control on filling history of Eocene reservoirs, Maracaibo Basin, Venezuela

    Energy Technology Data Exchange (ETDEWEB)

    Alberdi, M.; Maguregui, J.; Toro, C.; Marquina, M. [Intevep S.A., Caracas (Venezuela)

    1996-08-01

    Crude oils of Eocene fluvio-deltaic reservoirs in {open_quotes}Bloque V{close_quotes} and {open_quotes}Centro Lago{close_quotes} fields in the center of the Maracaibo Lake show many differences in composition, which are due to stratigraphically and structurally controlled reservoir geometry and a low rate of in-reservoir mixing of at least two successive petroleum charges. Oils produced from the top of structural highs contain 18(H) oleanane, higher Pr/Ph and C{sub 23-3}/C{sub 24-4} ratios, a lower proportion of DBT/P compounds, and clearly different fingerprint patterns in the C{sub 6}-C{sub 15} range, than those observed in oils produced from the lower parts of the structures. These compositional differences suggest that two source rocks, or two distinctive organic facies within the same Cretaceous La Luna Formation, generated and filled vertically poorly connected Eocene reservoirs. On the other hand, saturate-biomarkers ratios, triaromatics (C{sub 21}/C{sub 21}+C{sub 28}), n-paraffins (n-C{sub 20}/n-C{sub 29}) and n-heptane index suggest that oils in upper reservoirs are slightly less mature than oils in lower reservoirs and, consequently filled the structure first. Additional evidence from formation water analysis and tectonic basin evolution allow us to interpret at least two petroleum pulses from Cretaceous source rocks during Upper Miocene to present day kitchens located in the Andes foredeep at the southeast of the study area.

  17. Lithospheric magma dynamics beneath the El Hierro Volcano, Canary Islands: insights from fluid inclusions

    Science.gov (United States)

    Oglialoro, E.; Frezzotti, M. L.; Ferrando, S.; Tiraboschi, C.; Principe, C.; Groppelli, G.; Villa, I. M.

    2017-10-01

    At active volcanoes, petrological studies have been proven to be a reliable approach in defining the depth conditions of magma transport and storage in both the mantle and the crust. Based on fluid inclusion and mineral geothermobarometry in mantle xenoliths, we propose a model for the magma plumbing system of the Island of El Hierro (Canary Islands). The peridotites studied here were entrained in a lava flow exposed in the El Yulan Valley. These lavas are part of the rift volcanism that occurred on El Hierro at approximately 40-30 ka. The peridotites are spinel lherzolites, harzburgites, and dunites which equilibrated in the shallow mantle at pressures between 1.5 and 2 GPa and at temperatures between 800 and 950 °C (low-temperature peridotites; LT), as well as at higher equilibration temperatures of 900 to 1100 °C (high-temperature peridotites; HT). Microthermometry and Raman analyses of fluid inclusions reveal trapping of two distinct fluid phases: early type I metasomatic CO2-N2 fluids ( X N2 = 0.01-0.18; fluid density (d) = 1.19 g/cm3), coexisting with silicate-carbonate melts in LT peridotites, and late type II pure CO2 fluids in both LT (d = 1.11-1.00 and 0.75-0.65 g/cm3) and HT ( d = 1.04-1.11 and 0.75-0.65 g/cm3) peridotites. While type I fluids represent metasomatic phases in the deep oceanic lithosphere (at depths of 60-65 km) before the onset of magmatic activity, type II CO2 fluids testify to two fluid trapping episodes during the ascent of xenoliths in their host mafic magmas. Identification of magma accumulation zones through interpretation of type II CO2 fluid inclusions and mineral geothermobarometry indicate the presence of a vertically stacked system of interconnected small magma reservoirs in the shallow lithospheric mantle between a depth of 22 and 36 km (or 0.67 to 1 GPa). This magma accumulation region fed a short-lived magma storage region located in the lower oceanic crust at a depth of 10-12 km (or 0.26-0.34 GPa). Following our model

  18. Fitful and protracted magma assembly leading to a giant eruption, Youngest Toba Tuff, Indonesia

    Science.gov (United States)

    Reid, Mary R; Vazquez, Jorge A.

    2017-01-01

    The paroxysmal eruption of the 74 ka Youngest Toba Tuff (YTT) of northern Sumatra produced an extraordinary 2800 km3 of non-welded to densely welded ignimbrite and co-ignimbrite ash-fall. We report insights into the duration of YTT magma assembly obtained from ion microprobe U-Th and U-Pb dates, including continuous age spectra over >50% of final zircon growth, for pumices and a welded tuff spanning the compositional range of the YTT. A relatively large subpopulation of zircon crystals nucleated before the penultimate caldera-related eruption at 501 ka, but most zircons yielded interior dates 100-300 ka thereafter. Zircon nucleation and growth was likely episodic and from diverse conditions over protracted time intervals of >100 to >500 ka. Final zircon growth is evident as thin rim plateaus that are in Th/U chemical equilibrium with hosts, and that give crystallization ages within tens of ka of eruption. The longevity and chemical characteristics of the YTT zircons, as well as evidence for intermittent zircon isolation and remobilization associated with magma recharge, is especially favored at the cool and wet eutectoid conditions that characterize at least half of the YTT, wherein heat fluxes could dissolve major phases but have only a minor effect on larger zircon crystals. Repeated magma recharge may have contributed to the development of compositional zoning in the YTT but, considered together with limited allanite, quartz, and other mineral dating and geospeedometry, regular perturbations to the magma reservoir over >400 ka did not lead to eruption until 74 ka ago.

  19. Volcanic-plutonic connections and metal fertility of highly evolved magma systems: A case study from the Herberton Sn-W-Mo Mineral Field, Queensland, Australia

    Science.gov (United States)

    Cheng, Yanbo; Spandler, Carl; Chang, Zhaoshan; Clarke, Gavin

    2018-03-01

    Understanding the connection between the highly evolved intrusive and extrusive systems is essential to explore the evolution of high silicic magma systems, which plays an important role in discussions of planetary differentiation, the growth of continents, crustal evolution, and the formation of highly evolved magma associated Sn-W-Mo mineral systems. To discern differences between "fertile" and "non-fertile" igneous rocks associated with Sn-W-Mo mineralization and reveal the genetic links between coeval intrusive and extrusive rocks, we integrate whole rock geochemistry, geochronology and Hf isotope signatures of igneous zircons from contemporaneous plutonic and volcanic rocks from the world-class Herberton Mineral Field of Queensland, Australia. The 310-300 Ma intrusive rocks and associated intra-plutonic W-Mo mineralization formed from relatively oxidized magmas after moderate degrees of crystal fractionation. The geochemical and isotopic features of the coeval volcanic succession are best reconciled utilizing the widely-accepted volcanic-plutonic connection model, whereby the volcanic rocks represent fractionated derivatives of the intrusive rocks. Older intrusions emplaced at 335-315 Ma formed from relatively low fO2 magmas that fractionated extensively to produce highly evolved granites that host Sn mineralization. Coeval volcanic rocks of this suite are compositionally less evolved than the intrusive rocks, thereby requiring a different model to link these plutonic-volcanic sequences. In this case, we propose that the most fractionated magmas were not lost to volcanism, but instead were effectively retained at the plutonic level, which allowed further localized build-up of volatiles and lithophile metals in the plutonic environment. This disconnection to the volcanism and degassing may be a crucial step for forming granite-hosted Sn mineralization. The transition between these two igneous regimes in Herberton region over a ∼30 m.y. period is attributed to

  20. Interferometric synthetic aperture radar study of Okmok volcano, Alaska, 1992-2003: Magma supply dynamics and postemplacement lava flow deformation

    Science.gov (United States)

    Lu, Z.; Masterlark, Timothy; Dzurisin, Daniel

    2005-01-01

    Okmok volcano, located in the central Aleutian arc, Alaska, is a dominantly basaltic complex topped with a 10-km-wide caldera that formed circa 2.05 ka. Okmok erupted several times during the 20th century, most recently in 1997; eruptions in 1945, 1958, and 1997 produced lava flows within the caldera. We used 80 interferometric synthetic aperture radar (InSAR) images (interferograms) to study transient deformation of the volcano before, during, and after the 1997 eruption. Point source models suggest that a magma reservoir at a depth of 3.2 km below sea level, located beneath the center of the caldera and about 5 km northeast of the 1997 vent, is responsible for observed volcano-wide deformation. The preeruption uplift rate decreased from about 10 cm yr−1 during 1992–1993 to 2 ∼ 3 cm yr−1 during 1993–1995 and then to about −1 ∼ −2 cm yr−1 during 1995–1996. The posteruption inflation rate generally decreased with time during 1997–2001, but increased significantly during 2001–2003. By the summer of 2003, 30 ∼ 60% of the magma volume lost from the reservoir in the 1997 eruption had been replenished. Interferograms for periods before the 1997 eruption indicate consistent subsidence of the surface of the 1958 lava flows, most likely due to thermal contraction. Interferograms for periods after the eruption suggest at least four distinct deformation processes: (1) volcano-wide inflation due to replenishment of the shallow magma reservoir, (2) subsidence of the 1997 lava flows, most likely due to thermal contraction, (3) deformation of the 1958 lava flows due to loading by the 1997 flows, and (4) continuing subsidence of 1958 lava flows buried beneath 1997 flows. Our results provide insights into the postemplacement behavior of lava flows and have cautionary implications for the interpretation of inflation patterns at active volcanoes.

  1. Magma evolution inside the 1631 Vesuvius magma chamber and eruption triggering

    Directory of Open Access Journals (Sweden)

    Stoppa Francesco

    2017-03-01

    Full Text Available Vesuvius is a high-risk volcano and the 1631 Plinian eruption is a reference event for the next episode of explosive unrest. A complete stratigraphic and petrographic description of 1631 pyroclastics is given in this study. During the 1631 eruption a phonolite was firstly erupted followed by a tephritic phonolite and finally a phonolitic tephrite, indicating a layered magma chamber. We suggest that phonolitic basanite is a good candidate to be the primitive parental-melt of the 1631 eruption. Composition of apatite from the 1631 pyroclastics is different from those of CO2-rich melts indicating negligible CO2 content during magma evolution. Cross checking calculations, using PETROGRAPH and PELE software, accounts for multistage evolution up to phonolite starting from a phonolitic basanite melt similar to the Vesuvius medieval lavas. The model implies crystal settling of clinopyroxene and olivine at 6 kbar and 1220°C, clinopyroxene plus leucite at a pressure ranging from 2.5 to 0.5 kbar and temperature ranging from 1140 to 940°C. Inside the phonolitic magma chamber K-feldspar and leucite would coexist at a temperature ranging from from 940 to 840°C and at a pressure ranging from 2.5 to0.5 kbar. Thus crystal fractionation is certainly a necessary and probably a sufficient condition to evolve the melt from phono tephritic to phonolitic in the 1631 magma chamber. We speculate that phonolitic tephrite magma refilling from deeper levels destabilised the chamber and triggered the eruption, as testified by the seismic precursor phenomena before 1631 unrest.

  2. Magma evolution inside the 1631 Vesuvius magma chamber and eruption triggering

    Science.gov (United States)

    Stoppa, Francesco; Principe, Claudia; Schiazza, Mariangela; Liu, Yu; Giosa, Paola; Crocetti, Sergio

    2017-03-01

    Vesuvius is a high-risk volcano and the 1631 Plinian eruption is a reference event for the next episode of explosive unrest. A complete stratigraphic and petrographic description of 1631 pyroclastics is given in this study. During the 1631 eruption a phonolite was firstly erupted followed by a tephritic phonolite and finally a phonolitic tephrite, indicating a layered magma chamber. We suggest that phonolitic basanite is a good candidate to be the primitive parental-melt of the 1631 eruption. Composition of apatite from the 1631 pyroclastics is different from those of CO2-rich melts indicating negligible CO2 content during magma evolution. Cross checking calculations, using PETROGRAPH and PELE software, accounts for multistage evolution up to phonolite starting from a phonolitic basanite melt similar to the Vesuvius medieval lavas. The model implies crystal settling of clinopyroxene and olivine at 6 kbar and 1220°C, clinopyroxene plus leucite at a pressure ranging from 2.5 to 0.5 kbar and temperature ranging from 1140 to 940°C. Inside the phonolitic magma chamber K-feldspar and leucite would coexist at a temperature ranging from from 940 to 840°C and at a pressure ranging from 2.5 to0.5 kbar. Thus crystal fractionation is certainly a necessary and probably a sufficient condition to evolve the melt from phono tephritic to phonolitic in the 1631 magma chamber. We speculate that phonolitic tephrite magma refilling from deeper levels destabilised the chamber and triggered the eruption, as testified by the seismic precursor phenomena before 1631 unrest.

  3. Juvenile crust formation in the Zimbabwe Craton deduced from the O-Hf isotopic record of 3.8-3.1 Ga detrital zircons

    Science.gov (United States)

    Bolhar, Robert; Hofmann, Axel; Kemp, Anthony I. S.; Whitehouse, Martin J.; Wind, Sandra; Kamber, Balz S.

    2017-10-01

    Hafnium and oxygen isotopic compositions measured in-situ on U-Pb dated zircon from Archaean sedimentary successions belonging to the 2.9-2.8 Ga Belingwean/Bulawayan groups and previously undated Sebakwian Group are used to characterize the crustal evolution of the Zimbabwe Craton prior to 3.0 Ga. Microstructural and compositional criteria were used to minimize effects arising from Pb loss due to metamorphic overprinting and interaction with low-temperature fluids. 207Pb/206Pb age spectra (concordance >90%) reveal prominent peaks at 3.8, 3.6, 3.5, and 3.35 Ga, corresponding to documented geological events, both globally and within the Zimbabwe Craton. Zircon δ18O values from +4 to +10‰ point to both derivation from magmas in equilibrium with mantle oxygen and the incorporation of material that had previously interacted with water in near-surface environments. In εHf-time space, 3.8-3.6 Ga grains define an array consistent with reworking of a mafic reservoir (176Lu/177Hf ∼0.015) that separated from chondritic mantle at ∼3.9 Ga. Crustal domains formed after 3.6 Ga depict a more complex evolution, involving contribution from chondritic mantle sources and, to a lesser extent, reworking of pre-existing crust. Protracted remelting was not accompanied by significant mantle depletion prior to 3.35 Ga. This implies that early crust production in the Zimbabwe Craton did not cause complementary enriched and depleted reservoirs that were tapped by later magmas, possibly because the volume of crust extracted and stabilised was too small to influence (asthenospheric) mantle isotopic evolution. Growth of continental crust through pulsed emplacement of juvenile (chondritic mantle-derived) melts, into and onto the existing cratonic nucleus, however, involved formation of complementary depleted subcontinental lithospheric mantle since the early Archaean, indicative of strongly coupled evolutionary histories of both reservoirs, with limited evidence for recycling and lateral

  4. Shallow system rejuvenation and magma discharge trends at Piton de la Fournaise volcano (La Réunion Island)

    Science.gov (United States)

    Coppola, D.; Di Muro, A.; Peltier, A.; Villeneuve, N.; Ferrazzini, V.; Favalli, M.; Bachèlery, P.; Gurioli, L.; Harris, A. J. L.; Moune, S.; Vlastélic, I.; Galle, B.; Arellano, S.; Aiuppa, A.

    2017-04-01

    Basaltic magma chambers are often characterized by emptying and refilling cycles that influence their evolution in space and time, and the associated eruptive activity. During April 2007, the largest historical eruption of Piton de la Fournaise (Île de La Réunion, France) drained the shallow plumbing system (> 240 ×106 m3) and resulted in collapse of the 1-km-wide summit crater. Following these major events, Piton de la Fournaise entered a seven-year long period of near-continuous deflation interrupted, in June 2014, by a new phase of significant inflation. By integrating multiple datasets (lava discharge rates, deformation, seismicity, gas flux, gas composition, and lava chemistry), we here show that the progressive migration of magma from a deeper (below sea level) storage zone gradually rejuvenated and pressurized the above-sea-level portion of the magmatic system consisting of a vertically-zoned network of relatively small-volume magma pockets. Continuous inflation provoked four small (CO2 enrichment of summit fumaroles, and involving emission of less differentiated lavas, to end with, (iii) three short-lived (∼2 day-long) pulses in lava and gas flux, coupled with arrival of cumulative olivine at the surface and deflation. The activity observed at Piton de la Fournaise in 2014 and 2015 points to a new model of shallow system rejuvenation and discharge, whereby continuous magma supply causes eruptions from increasingly deeper and larger magma storage zones. Downward depressurization continues until unloading of the deepest, least differentiated magma triggers pulses in lava and gas flux, accompanied by rapid contraction of the volcano edifice, that empties the main shallow reservoir and terminates the cycle. Such an unloading process may characterize the evolution of shallow magmatic systems at other persistently active effusive centers.

  5. Why Is There an Abrupt Transition from Solid Rock to Low Crystallinity Magma in Drilled Magma Bodies?

    Science.gov (United States)

    Eichelberger, J. C.; Carrigan, C. R.; Sun, Y.; Lavallée, Y.

    2017-12-01

    We report on a preliminary evaluation, from basic principles of heat and mass transfer, on the unexpectedly abrupt transition from cuttings of solid rock to fragments of crystal poor glass during drilling into magma bodies. Our analysis is based on conditions determined and inferred for the 2009 IDDP-1 well in Krafla Caldera, which entered apparently liquidus rhyolite magma at about 900oC at a depth of 2104 m. Simple conduction would predict some 30 m of crystallization and partial crystallization since the latest time the magma could have been intruded, approximately 30 years prior to discovery by drilling. Option 1: The expected crystallization of magma has occurred but interstitial melt remains. The pressure difference between lithostatic load of about 50 MPa on the mush and 20 MPa hydrostatic pressure in the well causes pore melt to flow from the permeable mush into the borehole, where it becomes the source of the quenched melt chips. To be viable, this mechanism must work over the time frame of a day. Option 2: The expected crystallization is occurring, but high Rayleigh number thermal convection in the magma chamber continuously displaces crystallizing roof magma by liquidus magma from the interior of the body. To be viable, this mechanism must result in overturning magma in the chamber on a time scale that is much shorter than that of crystallization. Option 3: Flow-induced crystal migration away from zones of high shear created during drilling into magma may preferentially produce low-crystal-content melt at the boundary of the borehole, which is then sampled.

  6. A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units: Lunar Magma Ocean Viscosity

    Energy Technology Data Exchange (ETDEWEB)

    Dygert, Nick [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Knoxville TN USA; Lin, Jung-Fu [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Marshall, Edward W. [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA; Kono, Yoshio [HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne IL USA; Gardner, James E. [Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin TX USA

    2017-11-21

    Much of the lunar crust is monomineralic, comprising >98% plagioclase. The prevailing model argues the crust accumulated as plagioclase floated to the surface of a solidifying lunar magma ocean (LMO). Whether >98% pure anorthosites can form in a flotation scenario is debated. An important determinant of the efficiency of plagioclase fractionation is the viscosity of the LMO liquid, which was unconstrained. Here we present results from new experiments conducted on a late LMO-relevant ferrobasaltic melt. The liquid has an exceptionally low viscosity of 0.22 $+0.11\\atop{-0.19}$to 1.45 $+0.46\\atop{-0.82}$ Pa s at experimental conditions (1,300–1,600°C; 0.1–4.4 GPa) and can be modeled by an Arrhenius relation. Extrapolating to LMO-relevant temperatures, our analysis suggests a low viscosity LMO would form a stratified flotation crust, with the oldest units containing a mafic component and with very pure younger units. Old, impure crust may have been buried by lower crustal diapirs of pure anorthosite in a serial magmatism scenario.

  7. Re-Os Isotopic Constraints on the Chemical Evolution and Differentiation of the Martian Mantle

    Science.gov (United States)

    Brandon, Alan D.; Walker, Richard J.

    2002-01-01

    The (187)Re-187Os isotopic systematics of SNC meteorites, thought to be from Mars, provide valuable information regarding the chemical processes that affected the Martian mantle, particularly with regard to the relative abundances of highly siderophile elements (HSE). Previously published data (Birck and Allegre 1994, Brandon et al. 2000), and new data obtained since these studies, indicate that the HSE and Os isotopic composition of the Martian mantle was primarily set in its earliest differentiation history. If so, then these meteorites provide key constraints on the processes that lead to variation in HSE observed in not only Mars, but also Earth, the Moon and other rocky bodies in the Solar System. Processes that likely have an effect on the HSE budgets of terrestrial mantles include core formation, magma ocean crystallization, development of juvenile crust, and the addition of a late veneer. Each of these processes will result in different HSE variation and the isotopic composition of mantle materials and mantle derived lavas. Two observations on the SNC data to present provide a framework for which to test the importance of each of these processes. First, the concentrations of Re and Os in SNC meteorites indicate that they are derived from a mantle that has similar concentrations to the Earth's mantle. Such an observation is consistent with a model where a chondritic late veneer replenished the Earth and Martian mantles subsequent to core formation on each planet. Alternative models to explain this observation do exist, but will require additional data to test the limitations of each. Second, Re-Os isotopic results from Brandon et al. (2000) and new data presented here, show that initial yos correlates with variations in the short-lived systems of (182)Hf- (182)W and (142)Sm-142Nd in the SNC meteorites (epsilon(sub W) and epsilon(sub 142Nd)). These systematics require an isolation of mantle reservoirs during the earliest differentiation history of Mars, and

  8. Potential Magma Chambers beneath the Tatun Volcanic Area, Taiwan: Results from Magnetotelluric Survey and Monitoring

    Science.gov (United States)

    Chen, C.

    2013-12-01

    Previous earthquakes analysis indicated existing seismicity anomaly beneath Tatun volcano, Taiwan, possibly caused by the fluid activity of the volcano. Helium isotope studies also indicated that over 60% of the fumarolic gases and vapors originated from deep mantle in the Tatun volcano area. The chemistry of the fumarolic gases and vapors and seismicity anomaly are important issues in view of possible magma chamber in the Tatun volcano, where is in the vicinity of metropolitan Taipei, only 15 km north of the capital city. In this study magnetotelluric (MT) soundings and monitoring were deployed to understand the geoelectric structures in the Tatun volcano as Electromagnetic methods are sensitive to conductivity contrasts and can be used as a supplementary tool to delineate reservoir boundaries. An anticline extending more than 10 km beneath the Chih-Shin-Shan and Da-You-Kan areas was recognized. Low resistivity at a shallow and highly porous layer 500m thick might indicate circulation of heated water. However, a high resistivity layer at depth between 2 and 6 km was detected. This layer could be associated with high micro-earthquakes zone. The characteristics of this layer produced by either the magma chamber or other geothermal activity were similar to that of some other active volcanic areas in the world. At 6 km underground was a dome structure of medium resistivity. This structure could be interpreted as a magma chamber in which the magma is possibly cooling down, as judged by its relatively high resistivity. The exact attributes of the magma chamber were not precisely determined from the limited MT soundings. At present, a joint monitors including seismic activity, ground deformation, volcanic gases, and changes in water levels and chemistry are conducted by universities and government agencies. When unusual activity is detected, a response team may do more ground surveys to better determine if an eruption is likely.

  9. Chemical consequences of compaction within the freezing front of a crystallizing magma ocean

    Science.gov (United States)

    Hier-Majumder, S.; Hirschmann, M. M.

    2013-12-01

    The thermal and compositional evolution of planetary magma oceans have profound influences on the early development and differentiation of terrestrial planets. During crystallization, rejection of elements incompatible in precipitating solids leads to petrologic and geochemical planetary differentiation, including potentially development of a compositionally stratified early mantle and evolution of thick overlying atmospheres. In cases of extremely efficient segregation of melt and crystals, solidified early mantles can be nearly devoid of key incompatible species including heat-producing (U, Th, K) and volatile (H,C,N,& noble gas) elements. A key structural component of a crystallizing magma ocean is the partially molten freezing front. The dynamics of this region influences the distribution of incompatible elements between the earliest mantle and the initial surficial reservoirs. It also can be the locus of heating owing to the dissipation of large amounts of tidal energy potentially available from the early Moon. The dynamics are influenced by the solidification rate, which is coupled to the liberation of volatiles owing to the modulating greenhouse effects in the overlying thick atmosphere. Compaction and melt retention in the freezing front of a magma ocean has received little previous attention. While the front advances during the course of crystallization, coupled conservation of mass, momentum, and energy within the front controls distribution and retention of melt within this layer. Due to compaction within this layer, melt distribution is far from uniform, and the fraction of melt trapped within this front depends on the rate of freezing of the magma ocean. During phases of rapid freezing, high amount of trapped melt within the freezing front retains a larger quantity of dissolved volatiles and the reverse is true during slow periods of crystallization. Similar effects are known from inferred trapped liquid fractions in layered mafic intrusions. Here we

  10. Surface uplift in the Central Andes driven by growth of the Altiplano Puna Magma Body.

    Science.gov (United States)

    Perkins, Jonathan P; Ward, Kevin M; de Silva, Shanaka L; Zandt, George; Beck, Susan L; Finnegan, Noah J

    2016-10-25

    The Altiplano-Puna Magma Body (APMB) in the Central Andes is the largest imaged magma reservoir on Earth, and is located within the second highest orogenic plateau on Earth, the Altiplano-Puna. Although the APMB is a first-order geologic feature similar to the Sierra Nevada batholith, its role in the surface uplift history of the Central Andes remains uncertain. Here we show that a long-wavelength topographic dome overlies the seismically measured extent of the APMB, and gravity data suggest that the uplift is isostatically compensated. Isostatic modelling of the magmatic contribution to dome growth yields melt volumes comparable to those estimated from tomography, and suggests that the APMB growth rate exceeds the peak Cretaceous magmatic flare-up in the Sierran batholith. Our analysis reveals that magmatic addition may provide a contribution to surface uplift on par with lithospheric removal, and illustrates that surface topography may help constrain the magnitude of pluton-scale melt production.

  11. Stress evolution during caldera collapse

    Science.gov (United States)

    Holohan, E. P.; Schöpfer, M. P. J.; Walsh, J. J.

    2015-07-01

    The mechanics of caldera collapse are subject of long-running debate. Particular uncertainties concern how stresses around a magma reservoir relate to fracturing as the reservoir roof collapses, and how roof collapse in turn impacts upon the reservoir. We used two-dimensional Distinct Element Method models to characterise the evolution of stress around a depleting sub-surface magma body during gravity-driven collapse of its roof. These models illustrate how principal stress orientations rotate during progressive deformation so that roof fracturing transitions from initial reverse faulting to later normal faulting. They also reveal four end-member stress paths to fracture, each corresponding to a particular location within the roof. Analysis of these paths indicates that fractures associated with ultimate roof failure initiate in compression (i.e. as shear fractures). We also report on how mechanical and geometric conditions in the roof affect pre-failure unloading and post-failure reloading of the reservoir. In particular, the models show how residual friction within a failed roof could, without friction reduction mechanisms or fluid-derived counter-effects, inhibit a return to a lithostatically equilibrated pressure in the magma reservoir. Many of these findings should be transferable to other gravity-driven collapse processes, such as sinkhole formation, mine collapse and subsidence above hydrocarbon reservoirs.

  12. Crustal thickness controlled by plate tectonics

    DEFF Research Database (Denmark)

    Artemieva, Irina M.; Meissner, Rolf

    2012-01-01

    /gabbro–eclogite phase transition in crustal evolution and the links between lithosphere recycling, mafic magmatism, and crustal underplating. We advocate that plate tectonics processes, togetherwith basalt/gabbro–eclogite transition, limit crustal thickness worldwide by providing effective mechanisms of crustal...

  13. Thermal modeling of the Clear Lake magmatic system, California: Implications for conventional and hot dry rock geothermal development

    Energy Technology Data Exchange (ETDEWEB)

    Stimac, J.; Goff, F.; Wohletz, K.

    1997-06-01

    The combination of recent volcanism, high heat flow ({ge} HFU or 167 mW/m{sup 2}), and high conductive geothermal gradient (up to 120{degree} C/km) makes the Clear Lake region of northern California one of the best prospects for hot dry rock (HDR) geothermal development in the US. The lack of permeability in exploration wells and lack of evidence for widespread geothermal reservoirs north of the Collayomi fault zone are not reassuring indications for conventional geothermal development. This report summarizes results of thermal modeling of the Clear Lake magmatic system, and discusses implications for HDR site selection in the region. The thermal models incorporate a wide range of constraints including the distribution and nature of volcanism in time and space, water and gas geochemistry, well data, and geophysical surveys. The nature of upper crustal magma bodies at Clear Lake is inferred from studying sequences of related silicic lavas, which tell a story of multistage mixing of silicic and mafic magma in clusters of small upper crustal chambers. Thermobarometry on metamorphic xenoliths yield temperature and pressure estimates of {approximately}780--900 C and 4--6 kb respectively, indicating that at least a portion of the deep magma system resided at depths from 14 to 21 km (9 to 12 mi). The results of thermal modeling support previous assessments of the high HDR potential of the area, and suggest the possibility that granitic bodies similar to The Geysers felsite may underlie much of the Clear Lake region at depths as little as 3--6 km. This is significant because future HDR reservoirs could potentially be sited in relatively shallow granitoid plutons rather than in structurally complex Franciscan basement rocks.

  14. Greenhouse Gas Emissions from U.S. Hydropower Reservoirs: FY2011 Annual Progress Report

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Arthur J [ORNL; Mosher, Jennifer J [ORNL; Mulholland, Patrick J [ORNL; Fortner, Allison M [ORNL; Phillips, Jana Randolph [ORNL; Bevelhimer, Mark S [ORNL

    2012-05-01

    The primary objective of this study is to quantify the net emissions of key greenhouse gases (GHG) - notably, CO{sub 2} and CH{sub 4} - from hydropower reservoirs in moist temperate areas within the U.S. The rationale for this objective is straightforward: if net emissions of GHG can be determined, it would be possible to directly compare hydropower to other power-producing methods on a carbon-emissions basis. Studies of GHG emissions from hydropower reservoirs elsewhere suggest that net emissions can be moderately high in tropical areas. In such areas, warm temperatures and relatively high supply rates of labile organic matter can encourage high rates of decomposition, which (depending upon local conditions) can result in elevated releases of CO{sub 2} and CH{sub 4}. CO{sub 2} and CH{sub 4} emissions also tend to be higher for younger reservoirs than for older reservoirs, because vegetation and labile soil organic matter that is inundated when a reservoir is created can continue to decompose for several years (Galy-Lacaux et al. 1997, Barros et al. 2011). Water bodies located in climatically cooler areas, such as in boreal forests, could be expected to have lower net emissions of CO{sub 2} and CH{sub 4} because their organic carbon supplies tend to be relatively recalcitrant to microbial action and because cooler water temperatures are less conducive to decomposition.

  15. From Mush to Eruption in 1000 Years: Rapid Assembly of the Super-Sized Oruanui Magma Body

    Science.gov (United States)

    Allan, A. S.; Morgan, D. J.; Wilson, C. J.; Millet, M.

    2012-12-01

    The mush model is useful in explaining how large volumes of evolved silicic melt can be generated in and extracted from a crystal-rich source to form crystal-poor rhyolite magma bodies at shallow crustal levels. It is unclear, however, how processes of melt extraction and/or formation of the melt-dominant magma body might be reflected in the crystal record, and what physical and temporal constraints can be applied. Textural observations and in situ geochemical fingerprints in crystals from pumices of the ~25.4 ka Oruanui eruption (Taupo, New Zealand), offer new perspectives on the processes, physical conditions and timing of the melt extraction and accumulation. Almost all orthopyroxene (opx) and plagioclase (plag) cores have textures showing a period of disequilibrium (partial dissolution and/or resorption) followed by stable conditions (infilling of raddled cores; euhedral rim overgrowths). Trace element contents in amphibole (amph), which was stable and actively crystallizing in all but the most evolved parcels of Oruanui magma, complement textural evidence showing that Mn and Zn liberated by opx dissolution were preferentially sequestered in amph. Concentrations of these opx-loving elements show a prominent inflection when plotted against indices of melt evolution (e.g. Eu/Eu* in amph) marking a return to opx stability and subsequent crystallization. Plagioclase, the most abundant crystal phase, records a more complex history with significant inheritance, but textural and chemical evidence suggests that at least some of Oruanui plag crystals experienced the same departure from and return to stability as the opx. Amphibole trace element data are linked to in situ estimates of P-T-fO2 and melt H2O determined via the Ridolfi et al. (2010: Contrib Mineral Petrol 160, 45) thermobarometer. Textural and geochemical evidence combined with P-T-H2O model values indicate that three major Oruanui crystal phases (opx, amph, plag) record a significant decompression event

  16. On the water saturation calculation in hydrocarbon sandstone reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Stalheim, Stein Ottar

    2002-07-01

    The main goal of this work was to identify the most important uncertainty sources in water saturation calculation and examine the possibility for developing new S{sub w} - equations or possibility to develop methods to remove weaknesses and uncertainties in existing S{sub w} - equations. Due to the need for industrial applicability of the equations we aimed for results with the following properties: The accuracy in S{sub w} should increase compared with existing S{sub w} - equations. The equations should be simple to use in petrophysical evaluations. The equations should be based on conventional logs and use as few as possible input parameters. The equations should be numerical stable. This thesis includes an uncertainty and sensitivity analysis of the most common S{sub w} equations. The results are addressed in chapter 3 and were intended to find the most important uncertainty sources in water saturation calculation. To increase the knowledge of the relationship between R{sub t} and S{sub w} in hydrocarbon sandstone reservoirs and to understand how the pore geometry affects the conductivity (n and m) of the rock a theoretical study was done. It was also an aim to examine the possibility for developing new S{sub w} - equations (or investigation an effective medium model) valid inhydrocarbon sandstone reservoirs. The results are presented in paper 1. A new equation for water saturation calculation in clean sandstone oil reservoirs is addressed in paper 2. A recommendation for best practice of water saturation calculation in non water wet formation is addressed in paper 3. Finally a new equation for water saturation calculation in thinly interbedded sandstone/mudstone reservoirs is presented in paper 4. The papers are titled: 1) Is the saturation exponent n a constant. 2) A New Model for Calculating Water Saturation In 3) Influence of wettability on water saturation modeling. 4) Water Saturation Calculations in Thinly Interbedded Sandstone/mudstone Reservoirs. A

  17. Reassessment of the origin of the Dun Mountain Ophiolite, New Zealand : Nd-isotopic and geochemical evolution of magma suites

    International Nuclear Information System (INIS)

    Sivell, W.J.; McCulloch, M.T.

    2000-01-01

    Magmatic suites with contrasting isotopic and geochemical compositions, sequentially emplaced in different tectonic regimes, comprise the Dun Mountain Ophiolite Belt (DMOB), New Zealand. At D'Urville Island, the northernmost exposure of the DMOB, earliest erupted (stage 1) pillow basalts ε Nd (T) = +6.3 to +7.5, and are incompatible element enriched, like basalts from geochemically anomalous ridge segments. Overlying stage 2 basalts (sheeted flows) show a narrow range of ε Nd (T) = +8.3 + or -0.2, with chemical characteristics of depleted backarc basin basalts. These rocks are intruded by mafic to silicic stage 3 magmas, which have high uniform initial 143 Nd/ 144 Nd ratios (ε Nd (T) = +9.3 + or -0.2) over a wide range of 147 Sm/ 144 Nd values (yielding a precise Early Permian Nd-isotope age of 278 ± 4 Ma (MSWD = 0.48)). Stage 3 magmas show pronounced subduction-related geochemical signatures similar to island arc tholeiites (IAT) from immature arcs. They are closely analogous to some (boninite)-IAT magmas which characterise 'infant arc' eruptive activity in forearc basins of present-day Western Pacific island arc systems. A wide variety of stage 3 magma compositions, ranging from near-primary basaltic dikes (Mg = 74) to extremely fractionated silicic plagiogranites with uniformly very depleted isotopic ratios, is consistent with slow spreading rates which gave rise to polybaric, closed-system fractionation of magmas and periodic chamber abandonment. Some stage 3 rocks with SiO 2 levels in the andesite range have low-TiO 2 contents and high Mg, and may be fractionated equivalents of boninites. High ε Nd (T) values of stage 3 magmas indicate a lack of subducted sediment with inherited crustal residence signatures, and reflect the extent of supra-subduction zone (SSZ) mantle wedge depletion. DMOB stage 3 magmas may represent foreac magmatism that was the precursor to normal subduction-related volcanism established by c. 265 Ma in the Brook Street Arc and derived

  18. Oxygen isotope geochemistry of the lassen volcanic center, California: Resolving crustal and mantle contributions to continental Arc magmatism

    Science.gov (United States)

    Feeley, T.C.; Clynne, M.A.; Winer, G.S.; Grice, W.C.

    2008-01-01

    This study reports oxygen isotope ratios determined by laser fluorination of mineral separates (mainly plagioclase) from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the Lassen Volcanic Center (LVC), northern California. Plagioclase separates from nearly all rocks have ??18O values (6.1-8.4%) higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back-arc regions of the southernmost Cascades during the late Cenozoic. Most LVC magmas must therefore contain high 18O crustal material. In this regard, the ??18O values of the volcanic rocks show strong spatial patterns, particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust. Rhyodacitic magmas erupted from vents located within 3.5 km of the inferred center of the LVC have consistently lower ??18 O values (average 6.3% ?? 0.1%) at given SiO2 contents relative to rocks erupted from distal vents (>7.0 km; average 7.1% ?? 0.1%). Further, magmas erupted from vents situated at transitional distances have intermediate values and span a larger range (average 6.8% ?? 0.2%). Basaltic andesitic to andesitic composition rocks show similar spatial variations, although as a group the ??18O values of these rocks are more variable and extend to higher values than the rhyodacitic rocks. These features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas, followed by mixing or mingling with silicic magmas formed by partial melting of initially high 18O continental crust (??? 9.0%) increasingly hybridized by lower ??18O (???6.0%) mantle-derived basaltic magmas toward the center of the system. Mixing calculations using estimated endmember source ??18O values imply that LVC magmas contain on a molar oxygen basis approximately 42 to 4% isotopically heavy continental crust, with proportions declining in a broadly regular fashion toward the

  19. Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil

    Directory of Open Access Journals (Sweden)

    SILVIA R. MEDEIROS

    2001-03-01

    Full Text Available At the end of the geotectonic cycle that shaped the northern segment of the Ribeira Mobile Belt (Upper Proterozoic to Paleozoic age, a late to post-collisional set of plutonic complexes, consisting of a wide range of lithotypes, intruded all metamorphic units. The Várzea Alegre Intrusive Complex is a post-collisional complex. The younger intrusion consists of an inversely zoned multistage structure envolved by a large early emplaced ring of megaporphyritic charnoenderbitic rocks. The combination of field, petrographic and geochemical data reveals the presence of at least two different series of igneous rocks. The first originated from the partial melting of the mantle. This was previously enriched in incompatible elements, low and intermediate REE and some HFS-elements. A second enrichment in LREE and incompatible elements in this series was due to the mingling with a crustal granitic magma. This mingling process changed the composition of the original tholeiitic magma towards a medium-K calc-alkalic magma to produce a suite of basic to intermediate rock types. The granitic magma from the second high-K, calc-alkalic suite originated from the partial melting of the continental crust, but with strong influence of mantle-derived melts.No final do ciclo tectônico que originou o segmento norte do Cinturão Móvel Ribeira (de idade Proterozóica Superior a Paleozóica, uma série de complexos plutônicos tardi- a pós-colisionais, consistindo de larga gama de litotipos, intrudiu todas as unidades metamórficas. O Complexo Intrusivo de Várzea Alegre é um desses complexos pós-colisionais. A intrusão mais jovem consiste de uma estrutura de multiplos estágios, envolvida por um largo anel de rochas charnoenderbíiticas megaporfirícas de posicionmento anterior. A combinação de dados de campo, petrográficos e geoquímicos revela a presença de pelo menos duas séries distintas de rochas ígneas. A primeira foi originada por fusão parcial do manto

  20. Non-Markovian reservoir-dependent squeezing

    International Nuclear Information System (INIS)

    Paavola, J

    2010-01-01

    The squeezing dynamics of a damped harmonic oscillator are studied for different types of environment without making the Markovian approximation. The squeezing dynamics of a coherent state depend on the reservoir spectrum in a unique way that can, in the weak coupling approximation, be analysed analytically. Comparison of squeezing dynamics for ohmic, sub-ohmic and super-ohmic environments is done, showing a clear connection between the squeezing-non-squeezing oscillations and reservoir structure. Understanding the effects occurring due to structured reservoirs is important both from a purely theoretical point of view and in connection with evolving experimental techniques and future quantum computing applications.

  1. Use of natural geochemical tracers to improve reservoir simulation models

    Energy Technology Data Exchange (ETDEWEB)

    Huseby, O.; Chatzichristos, C.; Sagen, J.; Muller, J.; Kleven, R.; Bennett, B.; Larter, S.; Stubos, A.K.; Adler, P.M.

    2005-01-01

    This article introduces a methodology for integrating geochemical data in reservoir simulations to improve hydrocarbon reservoir models. The method exploits routine measurements of naturally existing inorganic ion concentration in hydrocarbon reservoir production wells, and uses the ions as non-partitioning water tracers. The methodology is demonstrated on a North Sea field case, using the field's reservoir model, together with geochemical information (SO{sub 4}{sup 2}, Mg{sup 2+} K{sup +}, Ba{sup 2+}, Sr{sup 2+}, Ca{sup 2+}, Cl{sup -} concentrations) from the field's producers. From the data-set we show that some of the ions behave almost as ideal sea-water tracers, i.e. without sorption to the matrix, ion-exchange with the matrix or scale-formation with other ions in the formation water. Moreover, the dataset shows that ion concentrations in pure formation-water vary according to formation. This information can be used to allocate produced water to specific water-producing zones in commingled production. Based on an evaluation of the applicability of the available data, one inorganic component, SO{sub 4}{sup 2}, is used as a natural seawater tracer. Introducing SO{sub 4}{sup 2} as a natural tracer in a tracer simulation has revealed a potential for improvements of the reservoir model. By tracking the injected seawater it was possible to identify underestimated fault lengths in the reservoir model. The demonstration confirms that geochemical data are valuable additional information for reservoir characterization, and shows that integration of geochemical data into reservoir simulation procedures can improve reservoir simulation models. (author)

  2. Final report of a scalable, automated, semipermanent seismic array (SASSA) method for detecting CO<sub>2sub> extent during geologic CO<sub>2sub> injection

    Energy Technology Data Exchange (ETDEWEB)

    Burnison, Shaughn [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States); Livers-Douglas, Amanda [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States); Barajas-Olalde, Cesar [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States); Jin, Lu [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States); Vettleson, Heidi [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States); Hamiling, John [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States); Gorecki, Charles [University of North Dakota Energy & Environmental Research Center, Grand Forks, ND (United States)

    2017-12-15

    The scalable, automated, semipermanent seismic array (SASSA) project led and managed by the Energy & Environmental Research Center (EERC) was designed as a 3-year proof-of-concept study to evaluate and demonstrate an innovative application of the seismic method. The concept was to use a sparse surface array of 96 nodal seismic sensors paired with a single, remotely operated active seismic source at a fixed location to monitor for CO<sub>2sub> saturation changes in a subsurface reservoir by processing the data for time-lapse changes at individual, strategically chosen reservoir reflection points. The combination of autonomous equipment and modern processing algorithms was used to apply the seismic method in a manner different from the normal paradigm of collecting a spatially dense data set to produce an image. It was used instead to monitor individual, strategically chosen reservoir reflection points for detectable signal character changes that could be attributed to the passing of a CO<sub>2sub> saturation front or, possibly, changes in reservoir pressure. Data collection occurred over the course of 1 year at an oil field undergoing CO<sub>2sub> injection for enhanced oil recovery (EOR) and focused on four overlapping “five-spot” EOR injector–producer patterns. Selection, procurement, configuration, installation, and testing of project equipment and collection of five baseline data sets were completed in advance of CO<sub>2sub> injection within the study area. Weekly remote data collection produced 41 incremental time-lapse records for each of the 96 nodes. Validation was provided by two methods: 1) a conventional 2-D seismic line acquired through the center of the study area before injection started and again after the project ended and processed in a time-lapse manner and 2) by CO<sub>2sub> saturation maps created from reservoir simulations based on injection and production history matching. Interpreted results were encouraging but mixed, with

  3. Ground Deformation Related to Caldera Collapse and Ring-Fault Activity

    KAUST Repository

    Liu, Yuan-Kai

    2018-05-01

    Volcanic subsidence, caused by partial emptying of magma in the subsurface reservoir has long been observed by spaceborne radar interferometry. Monitoring long-term crustal deformation at the most notable type of volcanic subsidence, caldera, gives us insights of the spatial and hazard-related information of subsurface reservoir. Several subsiding calderas, such as volcanoes on the Galapagos islands have shown a complex ground deformation pattern, which is often composed of a broad deflation signal affecting the entire edifice and a localized subsidence signal focused within the caldera floor. Although numerical or analytical models with multiple reservoirs are proposed as the interpretation, geologically and geophysically evidenced ring structures in the subsurface are often ignored. Therefore, it is still debatable how deep mechanisms relate to the observed deformation patterns near the surface. We aim to understand what kind of activities can lead to the complex deformation. Using two complementary approaches, we study the three-dimensional geometry and kinematics of deflation processes evolving from initial subsidence to later collapse of calderas. Firstly, the analog experiments analyzed by structure-from-motion photogrammetry (SfM) and particle image velocimetry (PIV) helps us to relate the surface deformation to the in-depth structures. Secondly, the numerical modeling using boundary element method (BEM) simulates the characteristic deformation patterns caused by a sill-like source and a ring-fault. Our results show that the volcano-wide broad deflation is primarily caused by the emptying of the deep magma reservoir, whereas the localized deformation on the caldera floor is related to ring-faulting at a shallower depth. The architecture of the ring-fault to a large extent determines the deformation localization on the surface. Since series evidence for ring-faulting at several volcanoes are provided, we highlight that it is vital to include ring

  4. Ground Deformation Related to Caldera Collapse and Ring-Fault Activity

    KAUST Repository

    Liu, Yuan-Kai

    2018-01-01

    Volcanic subsidence, caused by partial emptying of magma in the subsurface reservoir has long been observed by spaceborne radar interferometry. Monitoring long-term crustal deformation at the most notable type of volcanic subsidence, caldera, gives us insights of the spatial and hazard-related information of subsurface reservoir. Several subsiding calderas, such as volcanoes on the Galapagos islands have shown a complex ground deformation pattern, which is often composed of a broad deflation signal affecting the entire edifice and a localized subsidence signal focused within the caldera floor. Although numerical or analytical models with multiple reservoirs are proposed as the interpretation, geologically and geophysically evidenced ring structures in the subsurface are often ignored. Therefore, it is still debatable how deep mechanisms relate to the observed deformation patterns near the surface. We aim to understand what kind of activities can lead to the complex deformation. Using two complementary approaches, we study the three-dimensional geometry and kinematics of deflation processes evolving from initial subsidence to later collapse of calderas. Firstly, the analog experiments analyzed by structure-from-motion photogrammetry (SfM) and particle image velocimetry (PIV) helps us to relate the surface deformation to the in-depth structures. Secondly, the numerical modeling using boundary element method (BEM) simulates the characteristic deformation patterns caused by a sill-like source and a ring-fault. Our results show that the volcano-wide broad deflation is primarily caused by the emptying of the deep magma reservoir, whereas the localized deformation on the caldera floor is related to ring-faulting at a shallower depth. The architecture of the ring-fault to a large extent determines the deformation localization on the surface. Since series evidence for ring-faulting at several volcanoes are provided, we highlight that it is vital to include ring

  5. Imaging the Laguna del Maule Volcanic Field, central Chile using magnetotellurics: Evidence for crustal melt regions laterally-offset from surface vents and lava flows

    Science.gov (United States)

    Cordell, Darcy; Unsworth, Martyn J.; Díaz, Daniel

    2018-04-01

    Magnetotelluric (MT) data were collected at the Laguna del Maule volcanic field (LdMVF), located in central Chile (36°S, 70.5°W), which has been experiencing unprecedented upward ground deformation since 2007. These data were used to create the first detailed three-dimensional electrical resistivity model of the LdMVF and surrounding area. The resulting model was spatially complex with several major conductive features imaged at different depths and locations around Laguna del Maule (LdM). A near-surface conductor (C1; 0.5 Ωm) approximately 100 m beneath the lake is interpreted as a conductive smectite clay cap related to a shallow hydrothermal reservoir. At 4 km depth, a strong conductor (C3; 0.3 Ωm) is located beneath the western edge of LdM. The proximity of C3 to the recent Pleistocene-to-Holocene vents in the northwest LdMVF and nearby hot springs suggests that C3 is a hydrous (>5 wt% H2O), rhyolitic partial melt with melt fraction >35% and a free-water hydrothermal component. C3 dips towards, and is connected to, a deeper conductor (C4; 1 Ωm). C4 is located to the north of LdM at >8 km depth below surface and is interpreted as a long-lived, rhyolitic-to-andesitic magma reservoir with melt fractions less than 35%. It is hypothesized that the deeper magma reservoir (C4) is providing melt and hydrothermal fluids to the shallower magma reservoir (C3). A large conductor directly beneath the LdMVF is not imaged with MT suggesting that any mush volume beneath LdM must be anhydrous (10 km) as it moves from the deep magma reservoir (C4) to create small, ephemeral volumes of eruptible melt (C3). It is hypothesized that there may be a north-south contrast in physical processes affecting the growth of melt-rich zones since major conductors are imaged in the northern LdMVF while no major conductors are detected beneath the southern vents. The analysis and interpretation of features directly beneath the lake is complicated by the surface conductor C1 which attenuates

  6. Crustal Deformation In the Northwestern Margin of the South China Sea: Results From Wide-angle Seismic Modeling

    Science.gov (United States)

    Huang, H.; Klingelhoefer, F.

    2017-12-01

    The South China Sea (SCS) has undergone episodic spreading during the Cenozoic Era. The long-term extension has shaped the continental margins of the SCS, leading to a progressive breakup of the lithosphere. Separated blocks and rift troughs, as controlled by tectonic stretching, contains key information about the deforming mechanism of the crust. In this work, we present a P-wave velocity model of a wide-angle seismic profile OBS2013-1 which passes through the NW margin of the SCS. Modeling of 25 ocean bottom seismometers (OBS) data revealed a detailed crustal structure and shallow complexities along the profile (Figure 1). The crust thins symmetrically across the Xisha Trough, from more than 20 km on flanks to 10 km in the central valley where the sediments thickens over 5 km; A volcano is situated on top of the centre basement high where the Moho drops slightly. At the distal margin around the Zhongsha Trough, the upper crust was detached and accordingly made the middle crust exhumed in a narrow area ( 20 km wide). Meanwhile, materials from the lower crust rises asymmetrically, increasing the crustal velocity by 0.3 km/s and may also giving rise to volcanisms along the hanging side. A 40 km wide hyper-stretched crust (with thickness of 5 km) was identified next to the Zhongsha Trough and covered by overflowing magma and post-rift sediments on the top. These observations argue for a depth-related and asymmetrically extension of the crust, including (1) detachment fault controls the deformation of the upper crust, leading to exhumation of the middle crust and asymmetrically rising of the lower crust, (2) The region adjacent to the exhumation region and with highly thinned crust can be considered as extinct OCT due to magma-starved supplying.

  7. Packing, Scheduling and Covering Problems in a Game-Theoretic Perspective

    Science.gov (United States)

    Karlstrom, Leif

    Magma transport pathways through Earth's crust span 12--15 orders of magnitude in time and space, with unsteadiness at all scales. However emergent organization of this system is widespread, recorded by spatial loci of volcanism at the surface and large-scale, rapid outpourings of magma throughout the geologic record. This thesis explores several mechanisms for the organization and time evolution of magma transport, from the deep crust to the surface. A primary focus (Chapters 2--5) is the filling, stability and drainage of magma chambers, structures which function both as reservoirs feeding individual volcanic eruptions and as stalling points in the crust where magma accumulates and differentiation occurs. We show that magma chambers may dictate the spatio-temporal organization of magma rising through crust (Chapters 2--3), control the surface eruptive progression of extreme mantle melting events (Chapter 4), and actively set the size of calderas that form during shallow, crystal rich eruptions (Chapter 5). Each of these chapters explores variations on a hypothesis: interactions between magma chamber stresses and the rheology of surrounding crustal materials evolve during magma transport and this unsteady process helps determine the magnitude, location, and timing of surface eruptions. The last part of this thesis (Chapters 6--7) focuses on surface transport processes, the meandering of melt channels on the surface of glaciers and lava flows. We show that the meandering instability is a generic feature of flow over an erodable substrate, despite significantly different fluid characteristics and erosion mechanics.

  8. Examining shear processes during magma ascent

    Science.gov (United States)

    Kendrick, J. E.; Wallace, P. A.; Coats, R.; Lamur, A.; Lavallée, Y.

    2017-12-01

    Lava dome eruptions are prone to rapid shifts from effusive to explosive behaviour which reflects the rheology of magma. Magma rheology is governed by composition, porosity and crystal content, which during ascent evolves to yield a rock-like, viscous suspension in the upper conduit. Geophysical monitoring, laboratory experiments and detailed field studies offer the opportunity to explore the complexities associated with the ascent and eruption of such magmas, which rest at a pivotal position with regard to the glass transition, allowing them to either flow or fracture. Crystal interaction during flow results in strain-partitioning and shear-thinning behaviour of the suspension. In a conduit, such characteristics favour the formation of localised shear zones as strain is concentrated along conduit margins, where magma can rupture and heal in repetitive cycles. Sheared magmas often record a history of deformation in the form of: grain size reduction; anisotropic permeable fluid pathways; mineral reactions; injection features; recrystallisation; and magnetic anomalies, providing a signature of the repetitive earthquakes often observed during lava dome eruptions. The repetitive fracture of magma at ( fixed) depth in the conduit and the fault-like products exhumed at spine surfaces indicate that the last hundreds of meters of ascent may be controlled by frictional slip. Experiments on a low-to-high velocity rotary shear apparatus indicate that shear stress on a slip plane is highly velocity dependent, and here we examine how this influences magma ascent and its characteristic geophysical signals.

  9. Chlorine as a geobarometer for alkaline magmas: Evidence from a systematic study of the eruptions of Mount Somma-Vesuvius

    Science.gov (United States)

    Balcone-Boissard, H.; Boudon, G.; Cioni, R.; Webster, J. D.; Zdanowicz, G.; Orsi, G.; Civetta, L.

    2016-02-01

    Defining the magma storage conditions of a volcanic system is a major goal in modern volcanology due to its direct implications for the style of a possible eruption, and thus on the associated risk of any crisis and the necessary management and mitigation strategies. Below 200 MPa and at equivalent depths, the strongly non-ideal behaviour of the H-C-O-S-Cl-F system in the silicate melt causes unmixing of the fluid phase to form an H2O-rich vapour and a hydrosaline phase in equilibrium with the silicate melt, both responsible for buffering the chlorine (Cl) concentration. Following this equilibrium, the Cl concentration in melts may be used as a geobarometer for alkaline magmas. Systematic application of this method to the main explosive eruptions of Mount Somma-Vesuvius highlights two main magma ponding zones, at ~180-200 and ~100 MPa. At these pressures, the maximum pre-eruptive H2O contents for the different magma compositions can be estimated; the results obtained, largely in agreement with the current literature, therefore confirm the validity of the method. The Cl geobarometer may help scientists to define the variation of the magmatic reservoir location through time and thus provide strong constraints on pre-eruptive conditions, which are of utmost importance for volcanic crisis management.

  10. Radiographic visualization of magma dynamics in an erupting volcano.

    Science.gov (United States)

    Tanaka, Hiroyuki K M; Kusagaya, Taro; Shinohara, Hiroshi

    2014-03-10

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures.

  11. Silica-enriched mantle sources of subalkaline picrite-boninite-andesite island arc magmas

    Science.gov (United States)

    Bénard, A.; Arculus, R. J.; Nebel, O.; Ionov, D. A.; McAlpine, S. R. B.

    2017-02-01

    Primary arc melts may form through fluxed or adiabatic decompression melting in the mantle wedge, or via a combination of both processes. Major limitations to our understanding of the formation of primary arc melts stem from the fact that most arc lavas are aggregated blends of individual magma batches, further modified by differentiation processes in the sub-arc mantle lithosphere and overlying crust. Primary melt generation is thus masked by these types of second-stage processes. Magma-hosted peridotites sampled as xenoliths in subduction zone magmas are possible remnants of sub-arc mantle and magma generation processes, but are rarely sampled in active arcs. Published studies have emphasised the predominantly harzburgitic lithologies with particularly high modal orthopyroxene in these xenoliths; the former characteristic reflects the refractory nature of these materials consequent to extensive melt depletion of a lherzolitic protolith whereas the latter feature requires additional explanation. Here we present major and minor element data for pristine, mantle-derived, lava-hosted spinel-bearing harzburgite and dunite xenoliths and associated primitive melts from the active Kamchatka and Bismarck arcs. We show that these peridotite suites, and other mantle xenoliths sampled in circum-Pacific arcs, are a distinctive peridotite type not found in other tectonic settings, and are melting residues from hydrous melting of silica-enriched mantle sources. We explore the ability of experimental studies allied with mantle melting parameterisations (pMELTS, Petrolog3) to reproduce the compositions of these arc peridotites, and present a protolith ('hybrid mantle wedge') composition that satisfies the available constraints. The composition of peridotite xenoliths recovered from erupted arc magmas plausibly requires their formation initially via interaction of slab-derived components with refractory mantle prior to or during the formation of primary arc melts. The liquid

  12. Relationships among cyanobacteria, zooplankton and fish in sub-bloom conditions in the Sulejow Reservoir

    Directory of Open Access Journals (Sweden)

    Zbigniew Kaczkowski

    2017-01-01

    Full Text Available The occurrence of cyanobacteria is particularly characteristic of shallow eutrophic waters, and they often form massive ‘blooms’ that can affect aquatic invertebrates and fish. However, even a low abundance of cyanobacteria can be hazardous to aquatic organisms, due to the production of toxic metabolites. The aim of this study was to investigate the relationship between cyanobacteria and their toxicity (biological activity towards zooplankton and fish communities, when only low concentrations of cyanobacterial chlorophyll a (less than 20 μg L-1 are detected, i.e. in sub-bloom conditions. Measurements were performed in Sulejow Reservoir (Central Poland, a shallow, lowland, eutrophic reservoir, in which cyanobacterial blooms occur regularly. Fish were assessed using echo-sounding (distribution and by gillnetting (species composition. Simultaneously, zooplankton, cyanobacteria and physico-chemical characteristics were studied at 14 stations situated along hydroacoustic transects. Parameters that characterized the cyanobacteria (cyanobacterial chlorophyll a concentration, the number of 16S rRNA and the mcyA gene copies and microcystin (MC concentration were consistently correlated (based on a principal component analysis, and the highest values were found in the downstream region of the study area. This ‘cyano-complex’ was also positively correlated with oxygen concentration, pH and phosphate levels, but was negatively correlated with temperature and the concentrations of nitrates and nitrites. In Sulejow Reservoir in 2013 the biomass of large zooplankton filter feeders decreased along with increasing MC concentration and fish densities, while small filter feeders did not present such relationships with regards to fish densities. Fish abundance tended to decrease at stations with a lower abundance of cyanobacteria and with growing toxic genotype copies and MC concentration.

  13. Sm-Nd and Ar-Ar Studies of DHO 908 and 489: Implications for Lunar Crustal History

    Science.gov (United States)

    Nyquist, L. E.; Shih, C. Y.; Reese, Y. D.; Park, J.; Bogard, D. D.; Garrison, D. H.; Yamaguchi, A.

    2011-01-01

    It is widely assumed that ferroan anorthosites (FANs) formed as flotation cumulates on a global lunar magma ocean (LMO). A corollary is that all FANs are approximately contemporaneous and formed with the same initial Nd-143/Nd-144 ratio. Indeed, a whole rock isochron for selected FANs (and An93 anorthosite) yields an isochron age of 4.42 +/- 0.13 Ga and initial Nd-143/Nd-144, expressed in epsilon-units, of epsilon(sub Nd,CHUR) = 0.3+/-0.3 relative to the CHondritic Uniform Reservoir , or epsilon(sub Nd,HEDPB)=-0.6+/-0.3 relative to the HED Parent Body. These values are in good agreement with the age (T) = 4.47+/-0.07 Ga, and epsilon(sub Nd,HEDPB) =-0.6 +/- 0.5 for FAN 67075. We also have studied anorthositic clasts in the Dhofar 908 and 489 lunar highland meteorites containing clasts of magnesian anorthosites (MAN) with Mg# approximately 75. Because of their relatively high Mg#, magnesian anorthosites should have preceded most FANs in crystallization from the LMO if both are LMO products. Thus, it is important to determine whether the Nd-isotopic data of MAN and FAN are consistent with a co-magmatic origin. We previously reported Sm-Nd data for white clast Dho 908 WC. Mafic minerals in this clast were too small to be physically separated for an isochron. However, we estimated initial Nd-143/Nd-144 for the clast by combining its bulk ("whole rock") Sm-Nd data with an Ar-39-Ar-40 age of 4.42+/-.04 Ga. Here we report additional Sm-Nd data for bulk samples of Dho 908 and its pair Dho 489.

  14. A Critical Review of the Impacts of Leaking CO<sub>2sub> Gas and Brine on Groundwater Quality

    Energy Technology Data Exchange (ETDEWEB)

    Qafoku, Nikolla [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Zheng, Liange [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Bacon, Diana H. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lawter, Amanda R. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Brown, Christopher F. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2015-09-30

    Geological carbon sequestration (GCS) is a global carbon emission reduction strategy involving the capture of CO<sub>2sub> emitted from fossil fuel burning power plants, as well as the subsequent injection of the captured CO<sub>2sub> gas into deep saline aquifers or depleted oil and gas reservoirs. A critical question that arises from the proposed GCS is the potential impacts of CO<sub>2sub> injection on the quality of drinking-water systems overlying CO<sub>2sub> sequestration storage sites. Although storage reservoirs are evaluated and selected based on their ability to safely and securely store emplaced fluids, leakage of CO<sub>2sub> from storage reservoirs is a primary risk factor and potential barrier to the widespread acceptance of geologic CO<sub>2sub> sequestration (OR Harvey et al. 2013; Y-S Jun et al. 2013; DOE 2007). Therefore, a systematic understanding of how CO<sub>2sub> leakage would affect the geochemistry of potable aquifers, and subsequently control or affect elemental and contaminant release via sequential and/or simultaneous abiotic and biotic processes and reactions is vital.

  15. Transient deformation in the Asal-Ghoubbet Rift (Djibouti) since the 1978 diking event: Is deformation controlled by magma supply rates?

    Science.gov (United States)

    Smittarello, D.; Grandin, R.; de Chabalier, J. B.; Doubre, C.; Deprez, A.; Masson, F.; Socquet, A.; Ibrahim Ahmed, S.

    2016-12-01

    Within the Afar Depression, the Asal-Ghoubbet Rift (AG Rift)in Djibouti lies in the subaerial continuation of the Aden ridge system. This segment constitutes a natural laboratory to study rifting processes and mechanisms involved in continental breakup and oceanic spreading. In November 1978, an exceptional rifting event occurred in the AG Rift. Regularly upgraded and improved geodetic technology has been used to monitor this event and the postdiking deformation. In light of recent results obtained for the Manda Hararo-Dabbahu rifting event (2005-2010), we propose that the horizontal and vertical geodetic data can be modeled with a double source, involving a dike-like inflation component aligned along the rift axis and a spherical pressure source located at midsegment below the Fieale caldera. By revisiting the codiking data, we propose that the reservoir below Fieale could have fed, at least partially, the 1978 injection and the contemporaneous Ardoukoba eruption and potentially induced local subsidence due to magma draining out of the central reservoir. As an alternative to previously proposed viscoelastic relaxation models, we reinterpret postdiking observations using a purely elastic rheology. We determine the relative contribution of a midsegment reservoir inflation and a dike-like opening component, together with their respective time evolutions. Our results suggest that interactions between steadily accumulating tectonic strain and temporal variations in melt supply to the shallow magma plumbing system below the AG Rift may entirely explain the geodetic observations and that viscoelastic deformation processes played a minor role in the 30 years following the 1978 rifting event.

  16. Evidence for seismogenic fracture of silicic magma.

    Science.gov (United States)

    Tuffen, Hugh; Smith, Rosanna; Sammonds, Peter R

    2008-05-22

    It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of approximately 600 degrees C (ref. 1). This thinking underpins our understanding of volcanic earthquakes, which are assumed to occur in cold rocks surrounding moving magma. However, the recent discovery of abundant brittle-ductile fault textures in silicic lavas has led to the counter-intuitive hypothesis that seismic events may be triggered by fracture and faulting within the erupting magma itself. This hypothesis is supported by recent observations of growing lava domes, where microearthquake swarms have coincided with the emplacement of gouge-covered lava spines, leading to models of seismogenic stick-slip along shallow shear zones in the magma. But can fracturing or faulting in high-temperature, eruptible magma really generate measurable seismic events? Here we deform high-temperature silica-rich magmas under simulated volcanic conditions in order to test the hypothesis that high-temperature magma fracture is seismogenic. The acoustic emissions recorded during experiments show that seismogenic rupture may occur in both crystal-rich and crystal-free silicic magmas at eruptive temperatures, extending the range of known conditions for seismogenic faulting.

  17. Degassing during magma ascent in the Mule Creek vent (USA)

    Science.gov (United States)

    Stasiuk, M.V.; Barclay, J.; Carroll, M.R.; Jaupart, Claude; Ratte, J.C.; Sparks, R.S.J.; Tait, S.R.

    1996-01-01

    , collapsing foams, implying the former existence of channels for gas migration. Local channelling of gas into the country rocks is suggested by the presence of sub-horizontal syn-eruptive rhyolitic tuffisite veins which depart from the vent margin and invade the adjacent country rock. In the central part of the vent, similar local channelling of gas is indicated by steep syn-eruption tuffisite veins which cut the rhyolite itself. We conclude that the suppression of explosive eruption resulted from gas separation from the ascending magma and vent structure by shear-related porous flow and channelling of gas through tuffisite veins. These mechanisms of gas loss may be responsible for the commonly observed transition from explosive to effusive behaviour during the eruption of silicic magma.

  18. Petrologic testament to changes in shallow magma storage and transport during 30+ years of recharge and eruption at Kīlauea Volcano, Hawai‘i: Chapter 8

    Science.gov (United States)

    Thornber, Carl R.; Orr, Tim R.; Heliker, Christina; Hoblitt, Richard P.; Carey, Rebecca; Cayol, Valérie; Poland, Michael P.; Weis, Dominique

    2015-01-01

    Petrologic monitoring of Kīlauea Volcano from January 1983 to October 2013 has yielded an extensive record of glass, phenocryst, melt inclusion, and bulk-lava chemistry from well-quenched lava. When correlated with 30+ years of geophysical and geologic monitoring, petrologic details testify to physical maturation of summit-to-rift magma plumbing associated with sporadic intrusion and prolonged magmatic overpressurization. Changes through time in bulk-lava major- and trace-element compositions, along with glass thermometry, record shifts in the dynamic balance of fractionation, mixing, and assimilation processes inherent to magma storage and transport during near-continuous recharge and eruption. Phenocryst composition, morphology, and texture, along with the sulfur content of melt inclusions, constrain coupled changes in eruption behavior and geochemistry to processes occurring in the shallow magmatic system. For the first 17 years of eruption, magma was steadily tapped from a summit reservoir at 1–4 km depth and circulating between 1180 and 1200°C. Furthermore, magma cooled another 30°C while flowing through the 18 km long rift conduit, before erupting olivine-spinel-phyric lava at temperatures of 1150–1170°C in a pattern linked with edifice deformation, vent formation, eruptive vigor, and presumably the flux of magma into and out of the summit reservoir. During 2000–2001, a fundamental change in steady state eruption petrology to that of relatively low-temperature, low-MgO, olivine(-spinel)-clinopyroxene-plagioclase-phryic lava points to a physical transformation of the shallow volcano plumbing uprift of the vent. Preeruptive comagmatic mixing between hotter and cooler magma is documented by resorption, overgrowth, and compositional zonation in a mixed population of phenocrysts grown at higher and lower temperatures. Large variations of sulfur (50 to >1000 ppm) in melt inclusions within individual phenocrysts and among phenocrysts in most samples

  19. The Boycott effect in magma chambers

    Science.gov (United States)

    Blanchette, F.; Peacock, T.; Bush, J. W. M.

    2004-03-01

    We investigate the plausibility of the stratified Boycott effect as a source of layering in magma chambers. Crystal settling within the magma chamber will generate buoyant fluid near the sloping sidewalls whose vertical ascent may be limited by the ambient stratification associated with vertical gradients in SiO2. The resulting flow may be marked by a layered structure, each layer taking the form of a convection cell spanning the lateral extent of the magma chamber. Using parameters relevant to magma chambers, we estimate that such convection cells would be established over a timescale of a month and have a depth on the order of 4m, which is roughly consistent with field observations of strata within solidified chambers.

  20. Magma-derived CO2 emissions in the Tengchong volcanic field, SE Tibet: Implications for deep carbon cycle at intra-continent subduction zone

    Science.gov (United States)

    Zhang, Maoliang; Guo, Zhengfu; Sano, Yuji; Zhang, Lihong; Sun, Yutao; Cheng, Zhihui; Yang, Tsanyao Frank

    2016-09-01

    Active volcanoes at oceanic subduction zone have long been regard as important pathways for deep carbon degassed from Earth's interior, whereas those at continental subduction zone remain poorly constrained. Large-scale active volcanoes, together with significant modern hydrothermal activities, are widely distributed in the Tengchong volcanic field (TVF) on convergent boundary between the Indian and Eurasian plates. They provide an important opportunity for studying deep carbon cycle at the ongoing intra-continent subduction zone. Soil microseepage survey based on accumulation chamber method reveals an average soil CO2 flux of ca. 280 g m-2 d-1 in wet season for the Rehai geothermal park (RGP). Combined with average soil CO2 flux in dry season (ca. 875 g m-2 d-1), total soil CO2 output of the RGP and adjacent region (ca. 3 km2) would be about 6.30 × 105 t a-1. Additionally, we conclude that total flux of outgassing CO2 from the TVF would range in (4.48-7.05) × 106 t a-1, if CO2 fluxes from hot springs and soil in literature are taken into account. Both hot spring and soil gases from the TVF exhibit enrichment in CO2 (>85%) and remarkable contribution from mantle components, as indicated by their elevated 3He/4He ratios (1.85-5.30 RA) and δ13C-CO2 values (-9.00‰ to -2.07‰). He-C isotope coupling model suggests involvement of recycled organic metasediments and limestones from subducted Indian continental lithosphere in formation of the enriched mantle wedge (EMW), which has been recognized as source region of the TVF parental magmas. Contamination by crustal limestone is the first-order control on variations in He-CO2 systematics of volatiles released by the EMW-derived melts. Depleted mantle and recycled crustal materials from subducted Indian continental lithosphere contribute about 45-85% of the total carbon inventory, while the rest carbon (about 15-55%) is accounted by limestones in continental crust. As indicated by origin and evolution of the TVF

  1. Crustal Seismic Anisotropy: Implications for Understanding Crustal Dynamics

    Science.gov (United States)

    Meltzer, A.; Christensen, N.; Okaya, D.

    2003-12-01

    The Nanga Parbat - Haramosh massif, in the core of the western syntaxis of the Himalaya, represents a unique exposure of mid-lower continental crust from beneath a collisional orogen. The exhumed core of the massif forms a large scale antiformal structure with axial orientation of N10E and associated lineation directed north-south with near-vertical dips. Laboratory measurements of seismic velocity on a suite of quartzofeldspathic gneisses from the massif show a relatively strong degree of anisotropy, up to 12.5% for compressional waves and up to 21% for shear waves. The degree of velocity anisotropy is primarily a function of mica content and rock fabric strength. The strong anisotropy measured in these rocks should be observable in recorded seismic field data and provides a means of mapping rock fabric at depth provided the rock fabric is coherent over appropriate length scales. An IRIS/PASSCAL deployment of 50 short period instruments recorded local and regional earthquakes to characterize seismicity and determine crustal structure beneath the massif as part of a multidisciplinary NSF Continental Dynamics study investigating the active tectonic processes responsible for exhumation and crustal reworking at Nanga Parbat. Microseismicity at Nanga Parbat is distributed along strike beneath the massif but exhibits a sharp drop-off laterally into adjacent terranes and with depth. This data set is ideal for studying crustal seismic anisotropy because the raypaths are restricted to the crust, sharp onsets in P and S allow for clear identification of arrivals, and source-receiver geometries sample a range of azimuths with respect to structure. Preliminary analysis indicates that the majority of local events exhibit some degree of splitting and that splitting patterns, while complicated, are coherent. While splitting delay normally increases with distance traveled through anisotropic material, the range of delay times can be due to heterogeneity in composition, lateral

  2. Adakitic magmas: modern analogues of Archaean granitoids

    Science.gov (United States)

    Martin, Hervé

    1999-03-01

    /Y). Contrarily, when a young (subducted, the geothermal gradient along the Benioff plane is high, so the temperature of hydrated tholeiite solidus is reached before dehydration occurs. Under these conditions, garnet and/or hornblende are the main residual phases giving rise to HREE-depleted magmas (high La/Yb). The lack of residual plagioclase accounts for the Sr enrichment (high Sr/Y) of the magma. Experimental petrologic data show that the liquids produced by melting of tholeiite in subduction-like P- T conditions are adakitic in composition. However, natural adakites systematically have higher Mg no., Ni and Cr contents, which are interpreted as reflecting interactions between the ascending adakitic magma generated in the subducted slab and the overlying mantle wedge. This interpretation has been recently corroborated by studies on ultramafic enclaves in Batan lavas where olivine crystals contain glass inclusions with adakitic compositions [Schiano, P., Clochiatti, R., Shimizu, N., Maury, R., Jochum, K.P., Hofmann, A.W., 1995. Hydrous, silica-rich melts in the sub-arc mantle and their relationships with erupted arc lavas. Nature 377 595-600.]. This is interpreted as demonstrating that adakitic magmas passed through the mantle wedge and interacted with it. Sajona [Sajona, F.G., 1995. Fusion de la croûte océanique en contexte de subduction collision: géochimie, géochronologie et pétrologie du magmatisme plioquaternaire de Mindanao (Philippines). Unpublished thesis, Brest University, France, 223 pp.] also considers that the high-Nb basalts, which are associated with adakites, reflect mantle-adakite interactions. Recent structural studies have demonstrated that plate tectonics operated during the first half of Earth history. The very strong similarities that exist between modern adakites and Archaean tonalite, trondhjemite and granodiorite (TTG) attest that both have the same source and petrogenesis. Consequently, when Archaean-like P- T conditions are exceptionally realised

  3. Seismic Tremors and Three-Dimensional Magma Wagging

    Science.gov (United States)

    Liao, Y.; Bercovici, D.

    2015-12-01

    Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the magma-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici et.al. 2013) that the magma column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the magma inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the magma column is restricted to one vertical plane, the three-dimensional model we employ allows the magma column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the magma column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the magma column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the magma column leading to a coiled wagging motion. For the viscous-magma model, we predict a similar damping rate for the uncoiled magma column as in the two-dimensional model, and faster damping for the coiled magma column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3

  4. The Magma Chamber Simulator: Modeling the Impact of Wall Rock Composition on Mafic Magmas during Assimilation-Fractional Crystallization

    Science.gov (United States)

    Creamer, J. B.; Spera, F. J.; Bohrson, W. A.; Ghiorso, M. S.

    2012-12-01

    Although stoichiometric titration is often used to model the process of concurrent Assimilation and Fractional Crystallization (AFC) within a compositionally evolving magma body, a more complete treatment of the problem involves simultaneous and self-consistent determination of stable phase relationships and separately evolving temperatures of both Magma (M) and Wall Rock (WR) that interact as a composite M-WR system. Here we present results of M-WR systems undergoing AFC forward modeled with the Magma Chamber Simulator (MCS), which uses the phase modeling capabilities of MELTS (Ghiorso & Sack 1995) as the thermodynamic basis. Simulations begin with one of a variety of mafic magmas (e.g. HAB, MORB, AOB) intruding a set mass of Wall Rock (e.g. lherzolite, gabbro, diorite, granite, metapelite), and heat is exchanged as the M-WR system proceeds towards thermal equilibrium. Depending on initial conditions, the early part of the evolution can involve closed system FC while the WR heats up. The WR behaves as a closed system until it is heated beyond the solidus to critical limit for melt fraction extraction (fc), ranging between 0.08 and 0.12 depending on WR characteristics including composition and, rheology and stress field. Once fc is exceeded, a portion of the anatectic liquid is assimilated into the Magma. The MCS simultaneously calculates mass and composition of the mineral assemblage (Magma cumulates and WR residue) and melt (anatectic and Magma) at each T along the equilibration trajectory. Sensible and latent heat lost or gained plus mass gained by the Magma are accounted for by the MCS via governing Energy Constrained- Recharge Assimilation Fractional Crystallization (EC-RAFC) equations. In a comparison of two representative MCS results, consider a granitic WR intruded by HAB melt (51 wt. % SiO2) at liquidus T in shallow crust (0.1 GPa) with a WR/M ratio of 1.25, fc of 0.1 and a QFM oxygen buffer. In the first example, the WR begins at a temperature of 100o

  5. Numerical modeling of bubble dynamics in magmas

    Science.gov (United States)

    Huber, Christian; Su, Yanqing; Parmigiani, Andrea

    2014-05-01

    Understanding the complex non-linear physics that governs volcanic eruptions is contingent on our ability to characterize the dynamics of bubbles and its effect on the ascending magma. The exsolution and migration of bubbles has also a great impact on the heat and mass transport in and out of magma bodies stored at shallow depths in the crust. Multiphase systems like magmas are by definition heterogeneous at small scales. Although mixture theory or homogenization methods are convenient to represent multiphase systems as a homogeneous equivalent media, these approaches do not inform us on possible feedbacks at the pore-scale and can be significantly misleading. In this presentation, we discuss the development and application of bubble-scale multiphase flow modeling to address the following questions : How do bubbles impact heat and mass transport in magma chambers ? How efficient are chemical exchanges between the melt and bubbles during magma decompression? What is the role of hydrodynamic interactions on the deformation of bubbles while the magma is sheared? Addressing these questions requires powerful numerical methods that accurately model the balance between viscous, capillary and pressure stresses. We discuss how these bubble-scale models can provide important constraints on the dynamics of magmas stored at shallow depth or ascending to the surface during an eruption.

  6. Crust-mantle contribution to Andean magmatism

    International Nuclear Information System (INIS)

    Ruiz, J; Hildreth, W; Chesley, J

    2001-01-01

    There has long been great interest in quantifying the contributions of the continental crust to continental arc magmas, such as those of the Andes using osmium isotopes (Alves et al., 1999; Borg et al., 2000; Brandon et al., 1996; McInnes et al., 1999). In general, Andean volcanic rocks of all compositions show relatively low Sr-isotope ratios and positive to mildly negative epsilon Nd values. Nonetheless, in the Southern Volcanic Zone of central Chile, basalt-andesite-dacite volcanoes along the Quaternary volcanic front were shown (by Hildreth and Moorbath, 1988) to have latitudinally systematic chemical variations, as well as a monotonic increase in 87Sr/Sr86 from ca. 0.7035 to 0.7055 and a decrease in epsilon Nd values from ca. +3 to -1. The isotopic variations correlate with basement elevation of the volcanic edifices and with Bouguer gravity anomalies, both of which are thought to reflect along-arc variations in thickness and average age of the underlying crust. Volcanoes with the most evolved isotopic signatures were fed through the thickest crust. Correlation of chemical and isotopic variations with crustal thickness was interpreted to be caused by Melting (of deep-crustal host rocks), Assimilation, Storage, and Homogenization (MASH) of mantle-derived magmas in long-lived lower-crustal reservoirs beneath each center prior to eruption. We have now determined Os-isotope ratios for a sample suite from these volcanoes (33-36 S lat.), representing a range of crustal thickness from ca. 60-35 km. The samples range in MgO from ca. 8-4% and in SiO2 from 51-57%. The most evolved eruptive products occur above the thickest crust and have 87Sr/86Sr ratios of 0.7054 and epsilon Nd values of -1.5. The 187Os/188Os ratios correlate with the other isotopic systems and with crustal thickness. Volcanoes on the thinnest crust have 187Os/188Os ratios of 0.18-0.21. Those on the thickest crust have 187Os/188Os ratios as high as 0.64. All the Os values are much too radiogenic to

  7. Drilling Magma for Science, Volcano Monitoring, and Energy

    Science.gov (United States)

    Eichelberger, J. C.; Lavallée, Y.; Blankenship, D.

    2017-12-01

    Magma chambers are central to understanding magma evolution, formation of continental crust, volcanism, and renewal of hydrothermal systems. Information from geology, petrology, laboratory experiments, and geophysical imagery has led to little consensus except a trend to see magma systems as being crystal-dominant (mush) rather than melt dominant. At high melt viscosities, crystal-liquid fractionation may be achieved by separation of melt from mush rather than crystals from liquid suspension. That the dominant volume has properties more akin to solid than liquid might explain the difficulty in detecting magma geophysically. Recently, geothermal drilling has intersected silicic magma at the following depths and SiO2 contents are: Puna, Hawaii, 2.5 km, 67 wt%; Menengai, Kenya 2.1 km, 67 wt%; Krafla, Iceland, 2.1 km, 75 wt%. Some similarities are: 1) Drillers encountered a "soft", sticky formation; 2) Cuttings or chips of clear quenched glass were recovered; 3) The source of the glass flowed up the well; 4) Transition from solid rock to recovering crystal-poor glass occurred in tens of meters, apparently without an intervening mush zone. Near-liquidus magma at the roof despite rapid heat loss there presents a paradox that may be explained by very recent intrusion of magma, rise of liquidus magma to the roof replacing partially crystallized magma, or extremely skewed representation of melt over mush in cuttings (Carrigan et al, this session). The latter is known to occur by filter pressing of ooze into lava lake coreholes (Helz, this session), but cannot be verified in actual magma without coring. Coring to reveal gradients in phase composition and proportions is required for testing any magma chamber model. Success in drilling into and controlling magma at all three locations, in coring lava lakes to over 1100 C, and in numerical modeling of coring at Krafla conditions (Su, this session) show this to be feasible. Other unprecedented experiments are using the known

  8. Reservoir storage and containment of greenhouse gases

    Energy Technology Data Exchange (ETDEWEB)

    Weir, G.J.; White, S.P.; Kissling, W.M. [Industrial Research Ltd., Lower Hutt (New Zealand)

    1995-03-01

    This paper considers the injection of CO{sub 2} into underground reservoirs. Computer models are used to investigate the disposal of CO{sub 2} generated by an 800 MW power station. A number of scenarios are considered, some of which result in containment of the CO{sub 2} over very long time scales and others result in the escape of the CO{sub 2} after a few hundred years.

  9. Using Cross-Correlation Methods to Characterize Earthquakes Associated with the Socorro Magma Body

    Science.gov (United States)

    Vieceli, R.; Bilek, S. L.; Worthington, L. L.; Schmandt, B.; Aster, R. C.; Dodge, D. A.; Pyle, M. L.; Walter, W. R.

    2017-12-01

    The Socorro Magma Body (SMB), a thin, sill-like body with a top surface-depth of 19 km situated within the Rio Grande Rift in central New Mexico, is one of the largest recognized continental mid-crustal magma bodies in the world by area. SMB-associated inflation leads to slow regional uplift of a few mm/yr and has been linked to longstanding concentrated shallow seismicity (history. In February 2015 seismic data were collected above the northern and most rapidly uplifting region of the SMB with a densely spaced temporary array, consisting of seven broadband and 804 short period Fairfield nodal vertical component seismographs. The total array area was 50 x 25 km with typical node spacing of 300 m along a road network. In this study, we exploit all available seismic network data in a cross-correlation framework developed at Lawrence Livermore National Laboratory to detect events and characterize earthquake swarms, clusters, and patterns occurring over the last 15 years. We use a power detector to build an initial catalog of small magnitude earthquakes, including 33 events (M <= 2.5) recorded during the February 2015 deployment, as templates to detect additional events. We also develop an updated shallow velocity model for the region and refine event hypocenters using Bayesloc, a bayesian, multiple-event location algorithm. This enhanced seismicity catalog will be utilized in interpreting the recent seismicity of the SMB. LLNL-ABS-735529

  10. Rapid Crystallization of the Bishop Magma

    Science.gov (United States)

    Gualda, G. A.; Anderson, A. T.; Sutton, S. R.

    2007-12-01

    Substantial effort has been made to understand the longevity of rhyolitic magmas, and particular attention has been paid to the systems in the Long Valley area (California). Recent geochronological data suggest discrete magma bodies that existed for hundreds of thousands of years. Zircon crystallization ages for the Bishop Tuff span 100-200 ka, and were interpreted to reflect slow crystallization of a liquid-rich magma. Here we use the diffusional relaxation of Ti zoning in quartz to investigate the longevity of the Bishop magma. We have used such an approach to show the short timescales of crystallization of Ti-rich rims on quartz from early- erupted Bishop Tuff. We have now recognized Ti-rich cores in quartz that can be used to derive the timescales of their crystallization. We studied four samples of the early-erupted Bishop. Hand-picked crystals were mounted on glass slides and polished. Cathodoluminescence (CL) images were obtained using the electron microprobe at the University of Chicago. Ti zoning was documented using the GeoSoilEnviroCARS x-ray microprobe at the Advanced Photon Source (Argonne National Lab). Quartz crystals in all 4 samples include up to 3 Ti-bearing zones: a central core (50-100 μm in diameter, ca. 50 ppm Ti), a volumetrically predominant interior (~40 ppm Ti), and in some crystals a 50-100 μm thick rim (50 ppm Ti). Maximum estimates of core residence times were calculated using a 1D diffusion model, as the time needed to smooth an infinitely steep profile to fit the observed profile. Surprisingly, even for the largest crystals studied - ca. 2 mm in diameter - core residence times are less than 1 ka. Calculated growth rates imply that even cm-sized crystals crystallized in less than 10 ka. Crystal size distribution data show that crystals larger than 3 mm are exceedingly rare, such that the important inference is that the bulk of the crystallization of the early-erupted Bishop magma occurred in only a few thousand years. This timescale

  11. Grain to outcrop-scale frozen moments of dynamic magma mixing in the syenite magma chamber, Yelagiri Alkaline Complex, South India

    Directory of Open Access Journals (Sweden)

    M.L. Renjith

    2014-11-01

    Full Text Available Magma mixing process is unusual in the petrogenesis of felsic rocks associated with alkaline complex worldwide. Here we present a rare example of magma mixing in syenite from the Yelagiri Alkaline Complex, South India. Yelagiri syenite is a reversely zoned massif with shoshonitic (Na2O + K2O=5–10 wt.%, Na2O/K2O = 0.5–2, TiO2 <0.7 wt.% and metaluminous character. Systematic modal variation of plagioclase (An11–16 Ab82–88, K-feldspar (Or27–95 Ab5–61, diopside (En34–40Fs11–18Wo46–49, biotite, and Ca-amphibole (edenite build up three syenite facies within it and imply the role of in-situ fractional crystallization (FC. Evidences such as (1 disequilibrium micro-textures in feldspars, (2 microgranular mafic enclaves (MME and (3 synplutonic dykes signify mixing of shoshonitic mafic magma (MgO = 4–5 wt.%, SiO2 = 54–59 wt.%, K2O/Na2O = 0.4–0.9 with syenite. Molecular-scale mixing of mafic magma resulted disequilibrium growth of feldspars in syenite. Physical entity of mafic magma preserved as MME due to high thermal-rheological contrast with syenite magma show various hybridization through chemical exchange, mechanical dilution enhanced by chaotic advection and phenocryst migration. In synplutonic dykes, disaggregation and mixing of mafic magma was confined within the conduit of injection. Major-oxides mass balance test quantified that approximately 0.6 portions of mafic magma had interacted with most evolved syenite magma and generated most hybridized MME and dyke samples. It is unique that all the rock types (syenite, MME and synplutonic dykes share similar shoshonitic and metaluminous character; mineral chemistry, REE content, coherent geochemical variation in Harker diagram suggest that mixing of magma between similar composition. Outcrop-scale features of crystal accumulation and flow fabrics also significant along with MME and synplutonic dykes in syenite suggesting that Yelagiri syenite magma chamber had evolved

  12. Anatexis, hybridization and the modification of ancient crust: Mesozoic plutonism in the Old Woman Mountains area, California

    Science.gov (United States)

    Miller, C.F.; Wooden, J.L.

    1994-01-01

    A compositionally expanded array of granitic (s.l.) magmas intruded the > 2 Ga crust of the Old Woman Mountains area between 160 and 70 Ma. These magmas were emplaced near the eastern (inland) edge of the Jurassic/Cretaceous arcs of western North America, in an area where magma flux, especially during the Jurassic, was considerably lower than to the west. The Jurassic intrusives and over half of the Cretaceous intrusives are predominantly metaluminous and variable in composition; a major Cretaceous suite comprises only peraluminous monzogranite. Only the Jurassic intrusions show clear evidence for the presence of mafic liquids. All units, including the most mafic rocks, reveal isotopic evidence for a significant crustal component. However, none of the Mesozoic intrusives matches in isotopic composition either average pre-intrusion crust or any major unit of the exposed crust. Elemental inconsistencies also preclude closed system derivation from exposed crust. Emplacement of these magmas, which doubled the volume of the mid- to upper crust, did not dramatically change its elemental composition. It did, however, affect its Nd and especially Sr isotopic composition and modify some of the distinctive aspects of the elemental chemistry. We propose that Jurassic magmatism was open-system, with a major influx of mantle-derived mafic magma interacting strongly with the ancient crust. Mesozoic crustal thickening may have led to closed-system crustal melting by the Late Cretaceous, but the deep crust had been profoundly modified by earlier Mesozoic hybridization so that crustal melts did not simply reflect the original crustal composition. The clear evidence for a crustal component in magmas of the Old Woman Mountains area may not indicate any fundamental differences from the processes at work elsewhere in this or other magmatic arcs where the role of pre-existing crust is less certain. Rather, a compositionally distinctive, very old crust may simply have yielded a more

  13. Development of large-volume rhyolitic ignibrites (LRI'S): The Chalupas Caldera, an example from Ecuador

    International Nuclear Information System (INIS)

    Hammersley, L.; DePaolo, D.J; Beate, B

    2001-01-01

    The mechanisms responsible for the generation of large volumes of silicic magma and the eruption of large-volume rhyolitic ignimbrites (LRI's) remain poorly understood. Of particular interest are the relative roles of crustal assimilation, fractional crystallization and magma supply and the processes by which large volumes of magma accumulate in crustal chambers rather than erupt in smaller batches. Isotope geochemistry, combined with study of major and trace element variations of lavas, can be used to infer the relative contribution of crustal material and continued magmatic supply. Timescales for the accumulation of magma can be estimated using detailed geochronology. Magma supply rates can be estimated from eruption rates of nearby volcanoes. In this study we investigate the evolution of the Chalupas LRI, a caldera system in the Ecuadorian Andes where LRI's are rare in comparison to the Southern Volcanic Zone (SVZ) of South America (au)

  14. Investigation of origin, subsurface processes and reservoir temperature of geothermal springs around Koh-i-Sultan volcano, Chagai, Pakistan

    International Nuclear Information System (INIS)

    Ahmad, M.; Rafique, M.; Iqbal, N.; Fazil, M.

    2009-07-01

    In Chagai area, seven springs with maximum surface temperature of 32.2 deg. C located in the vicinity of Miri Crater of Koh-i-Sultan Volcano were investigated using isotope and chemical techniques. Two springs of Padagi Kaur are MgSO/sub 4/ type, while all the other springs at Batal Kaur, Miri Kaur and Chigin Dik are Na-Cl type. Alteration of water to SO/sub 4/ type takes place by absorption of magmatic H/sub 2/S and the acidic solution is further responsible to dissolve rock salt and carbonate minerals. EC increases from Padagi springs (4940 and 8170 S/cm) to Chigin Dik springs (45600 S/cm). Chagai thermal manifestations receive recharge from meteoric waters in the vicinity of Padagi Kaur (east side of Miri Crater), which is heated by the hot magma chamber of Koh-i-Sultan most probably through deep circulation. Movement of the thermal water is from Miri Crater towards Chigin Dik area. Residence time is more than 60 years. The thermal waters do not have any contribution of shallow young groundwater and they have high 1/sup 8/O-shift (6 to 8%) due to rock-water interaction. Reservoir temperatures estimated by different chemical geo thermometers like Na-K, Na-K-Ca, Na-K-Mg 1/2 (triangular plot) are quite high (200-300 deg. C), while the silica and (SO/sub 4/-H/sub 2/O) geo thermometers give relatively low temperature ranges (107-144 deg. C and 112-206 deg. C respectively). (author)

  15. Viscosity controlled magma-carbonate interaction: a comparison of Mt. Vesuvius (Italy) and Mt. Merapi (Indonesia).

    Science.gov (United States)

    Blythe, L. S.; Misiti, V.; Masotta, M.; Taddeucci, J.; Freda, C.; Troll, V. R.; Deegan, F. M.; Jolis, E. M.

    2012-04-01

    Magma-carbonate interaction is increasingly seen as a viable and extremely important cause of magma contamination, and the generation of a crustally sourced CO2 phase (Goff et al., 2001; Freda et al., 2010). Even though the process is well recognized at certain volcanoes e.g. Popocatépetl, (Mexico); Merapi, (Indonesia); and Colli Albani, (Italy) (Goff et al., 2001; Deegan et al., 2010; Freda et al., 2010), neither the kinetics of carbonate assimilation nor its consequences for controlling the explosivity of eruptions have been constrained. Here we show the results of magma-carbonate interaction experiments conducted at 1200 °C and 0.5 GPa for varying durations (0 s, 60 s, 90 s and 300 s) for the Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) volcanic systems. We performed experiments using glassy starting materials specific to each volcano (shoshonite for Mt. Vesuvius, basaltic-andesite for Mt. Merapi) with different degrees of hydration (anhydrous vs hydration with ~ 2 wt % water) and using carbonate fragments of local origin; see Deegan et al., (2010) and Jolis et al., (2011). Experimental products include a gas phase (CO2-rich) and two melt phases, one pristine (Ca-normal) and one contaminated (Ca-rich) separated by a 'contamination front' which propagates outwards from the carbonate clast. Vesicles appear to nucleate in the contaminated glass and then migrate into the pristine one. Both contamination front propagation and bubble migration away from the carbonate are slower in anhydrous basaltic-andesite (Merapi anhydrous series) than in hydrated basaltic-andesite and shoshonite (Merapi and Vesuvius hydrated series), suggesting that assimilation speed is strongly controlled by the degree of hydration and the SiO2 content, both of which influence melt viscosity and hence diffusivity. As the carbonate dissolution proceeds in our experiments, initially dissolved and eventually exsolved CO2 builds up in the contaminated Ca-rich melt phase. Once melt volatile

  16. Experimental study of radium partitioning between anorthite and melt at 1 atm

    Energy Technology Data Exchange (ETDEWEB)

    Miller, S; Burnett, D; Asimow, P; Phinney, D; Hutcheon, I

    2007-03-08

    We present the first experimental radium mineral/melt partitioning data, specifically between anorthite and a CMAS melt at atmospheric pressure. Ion microprobe measurement of coexisting anorthite and glass phases produces a molar D{sub Ra} = 0.040 {+-} 0.006 and D{sub Ra}/D{sub Ba} = 0.23 {+-} 0.05 at 1400 C. Our results indicate that lattice strain partitioning models fit the divalent (Ca, Sr, Ba, Ra) partition coefficient data of this study well, supporting previous work on crustal melting and magma chamber dynamics that has relied on such models to approximate radium partitioning behavior in the absence of experimentally determined values.

  17. Precursory deformation and depths of magma storage revealed by regional InSAR time series surveys: example of the Indonesian and Mexican volcanic arcs

    Science.gov (United States)

    Chaussard, E.; Amelung, F.; Aoki, Y.

    2012-12-01

    Despite the threat posed to millions of people living in the vicinity of volcanoes, only a fraction of the worldwide ~800 potentially active arc volcanoes have geodetic monitoring. Indonesian and Mexican volcanoes are sparsely monitored with ground-based methods but especially dangerous, emphasizing the need for remote sensing monitoring. In this study we take advantage of over 1200 ALOS InSAR images to survey the entire west Sunda and Mexican volcanic arcs, covering a total of 500 000 km2. We use 2 years of data to monitor the background activity of the Indonesian arc, and 4 years of data at four volcanic edifices (Sinabung, Kerinci, Merapi, and Agung), as well as 4 years of data to survey the Mexican arc. We derive time-dependent ground deformation data using the Small Baseline technique with DEM error correction. We detect seven volcanoes with significant deformation in the west-Sunda arc: six inflating volcanoes (Sinabung, Kerinci, Slamet, Lawu, Lamongan, and Agung) and one deflating volcano (Anak Krakatau). Three of the six inflating centers erupted during or after the observation period. We detect inflation prior to Sinabung's first Holocene eruption in September 2010, followed by a small deflation of the summit area. A similar signal is observed at Kerinci before and after its April 2009 eruption. We also detect uplift prior to Slamet's eruption in April 2009. Agung, in Bali, whose last eruption was in 1964, has been inflating steadily between mid 2007 and early 2009, followed by a period with little deformation until mid-2011. Inflation not followed by eruption is also observed at Lamongan and Lawu, both historically active centers. The close relation between periods of activity and observed deformation suggests that edifice inflation is of magmatic origin and represents the pressurization of reservoirs caused by ascent of new magma. We model the observed deformation and show that the seven deforming Indonesian volcanoes have shallow magma reservoirs at ~1

  18. Volcanic emission of radionuclides and magma dynamics

    International Nuclear Information System (INIS)

    Lambert, G.; Le Cloarec, M.F.; Ardouin, B.; Le Roulley, J.C.

    1985-01-01

    210 Pb, 210 Bi and 210 Po, the last decay products of the 238 U series, are highly enriched in volcanic plumes, relative to the magma composition. Moreover this enrichment varies over time and from volcano to volcano. A model is proposed to describe 8 years of measurements of Mt. Etna gaseous emissions. The lead and bismuth coefficients of partition between gaseous and condensated phases in the magma are determined by comparing their concentrations in lava flows and condensated volatiles. In the case of volatile radionuclides, an escaping time is calculated which appears to be related to the volcanic activity. Finally, it is shown that that magma which is degassing can already be partly degassed; it should be considered as a mixture of a few to 50% of deep non-degassed magma with a well degassed superficial magma cell. (orig.)

  19. Multiple intersecting cohesive discontinuities in 3D reservoir geomechanics

    OpenAIRE

    Das, K. C.; Sandha, S.S.; Carol, Ignacio; Vargas, P.E.; Gonzalez, Nubia Aurora; Rodrigues, E.; Segura Segarra, José María; Lakshmikantha, Ramasesha Mookanahallipatna; Mello,, U.

    2013-01-01

    Reservoir Geomechanics is playing an increasingly important role in developing and producing hydrocarbon reserves. One of the main challenges in reservoir modeling is accurate and efficient simulation of arbitrary intersecting faults. In this paper, we propose a new formulation to model multiple intersecting cohesive discontinuities (faults) in reservoirs using the XFEM framework. This formulation involves construction of enrichment functions and computation of stiffness sub-matrices for bulk...

  20. Sub-surface structures and collapse mechanisms of summit pit craters

    Science.gov (United States)

    Roche, O.; van Wyk de Vries, B.; Druitt, T. H.

    2001-01-01

    Summit pit craters are found in many types of volcanoes and are generally thought to be the product of collapse into an underpressured reservoir caused by magma withdrawal. We investigate the mechanisms and structures associated with summit pit crater formation by scaled analogue experiments and make comparisons with natural examples. Models use a sand plaster mixture as analogue rock over a cylinder of silicone simulating an underpressured magma reservoir. Experiments are carried out using different roof aspect ratios (roof thickness/roof width) of 0.2-2. They reveal two basic collapse mechanisms, dependant on the roof aspect ratio. One occurs at low aspect ratios (≤1), as illustrated by aspect ratios of 0.2 and 1. Outward dipping reverse faults initiated at the silicone margins propagates through the entire roof thickness and cause subsidence of a coherent block. Collapse along the reverse faults is accommodated by marginal flexure of the block and tension fractures at the surface (aspect ratio of 0.2) or by the creation of inward dipping normal faults delimiting a terrace (aspect ratio of 1). At an aspect ratio of 1, overhanging pit walls are the surface expressions of the reverse faults. Experiments at high aspect ratio (>1.2) reveal a second mechanism. In this case, collapse occurs by stopping, which propagates upwards by a complex pattern of both reverse faults and tension fractures. The initial underground collapse is restricted to a zone above the reservoir and creates a cavity with a stable roof above it. An intermediate mechanism occurs at aspect ratios of 1.1-1.2. In this case, stopping leads to the formation of a cavity with a thin and unstable roof, which collapses suddenly. The newly formed depression then exhibits overhanging walls. Surface morphology and structure of natural examples, such as the summit pit craters at Masaya Volcano, Nicaragua, have many of the features created in the models, indicating that the internal structural geometry of

  1. APPLICATION OF RESERVOIR CHARACTERIZATION AND ADVANCED TECHNOLOGY TO IMPROVE RECOVERY AND ECONOMICS IN A LOWER QUALITY SHALLOW SHELF SAN ANDRES RESERVOIR

    Energy Technology Data Exchange (ETDEWEB)

    T. Scott Hickman; James J. Justice

    2001-06-16

    The Class 2 Project at West Welch was designed to demonstrate the use of advanced technologies to enhance the economics of improved oil recovery (IOR) projects in lower quality Shallow Shelf Carbonate (SSC) reservoirs, resulting in recovery of additional oil that would otherwise be left in the reservoir at project abandonment. Accurate reservoir description is critical to the effective evaluation and efficient design of IOR projects in the heterogeneous SSC reservoirs. Therefore, the majority of Budget Period 1 was devoted to reservoir characterization. Technologies being demonstrated include: (1) Advanced petrophysics; (2) Three-dimensional (3-D) seismic; (3) Crosswell bore tomography; (4) Advanced reservoir simulation; (5) Carbon dioxide (CO{sub 2}) stimulation treatments; (6) Hydraulic fracturing design and monitoring; and (7) Mobility control agents.

  2. Interaction of coeval felsic and mafic magmas from the Kanker ...

    Indian Academy of Sciences (India)

    66

    20 crystallization of the latter, results in hybrid magmas under the influence of thermal and. 21 chemical exchange. The mechanical exchange occurs between the coexisting magmas due to. 22 viscosity contrast, if the mafic magma enters slightly later into the magma chamber, when the. 23 felsic magma started to crystallize.

  3. Depth of origin of magma in eruptions.

    Science.gov (United States)

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-09-26

    Many volcanic hazard factors--such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses--relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide.

  4. Post waterflood CO{sub 2} miscible flood in light oil, fluvial - dominated deltaic reservoirs. Technical progress report, 4th quarter, fiscal year 1994, July 1, 1994--September 30, 1994

    Energy Technology Data Exchange (ETDEWEB)

    1994-10-15

    Production from the Port Neches project has reached a new high of 500 BOPD, as shown. Production from several wells has improved after changing WAGer and CO{sub 2} injection patterns. The WAG process appears to be effective in FDD reservoirs. The WAT process has improved the oil production rates and simultaneously decreased the CO{sub 2} production rates from wells with high GOR. Material balance calculations indicate that the reservoir pressure remained relatively flat, and a new BHP will be taken this month to verify the calculations. Total CO{sub 2} injection is averaging about 9.5 MMCFD, including 3.9 MMCFD purchased from Cardox, as shown, and the balance is recycled from the producing wells. Over 50% of the gas was produced from one well, Khun No. 33. A CO{sub 2} injection line was installed to huff-puff well Khun No. 6 that did not respond yet to CO{sub 2} injection in well Khun No. 17. After injecting a limited CO{sub 2} volume in well Khun No. 6, this will be followed by a short shut-in period, then the well will be placed on production.

  5. Muon Tomography of Deep Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Bonneville, Alain H.; Kouzes, Richard T.

    2016-12-31

    Imaging subsurface geological formations, oil and gas reservoirs, mineral deposits, cavities or magma chambers under active volcanoes has been for many years a major quest of geophysicists and geologists. Since these objects cannot be observed directly, different indirect geophysical methods have been developed. They are all based on variations of certain physical properties of the subsurface that can be detected from the ground surface or from boreholes. Electrical resistivity, seismic wave’s velocities and density are certainly the most used properties. If we look at density, indirect estimates of density distributions are performed currently by seismic reflection methods - since the velocity of seismic waves depend also on density - but they are expensive and discontinuous in time. Direct estimates of density are performed using gravimetric data looking at variations of the gravity field induced by the density variations at depth but this is not sufficiently accurate. A new imaging technique using cosmic-ray muon detectors has emerged during the last decade and muon tomography - or muography - promises to provide, for the first time, a complete and precise image of the density distribution in the subsurface. Further, this novel approach has the potential to become a direct, real-time, and low-cost method for monitoring fluid displacement in subsurface reservoirs.

  6. Constraining magma physical properties and its temporal evolution from InSAR and topographic data only: a physics-based eruption model for the effusive phase of the Cordon Caulle 2011-2012 rhyodacitic eruption

    Science.gov (United States)

    Delgado, F.; Kubanek, J.; Anderson, K. R.; Lundgren, P.; Pritchard, M. E.

    2017-12-01

    The 2011-2012 eruption of Cordón Caulle volcano in Chile is the best scientifically observed rhyodacitic eruption and is thus a key place to understand the dynamics of these rare but powerful explosive rhyodacitic eruptions. Because the volatile phase controls both the eruption temporal evolution and the eruptive style, either explosive or effusive, it is important to constrain the physical parameters that drive these eruptions. The eruption began explosively and after two weeks evolved into a hybrid explosive - lava flow effusion whose volume-time evolution we constrain with a series of TanDEM-X Digital Elevation Models. Our data shows the intrusion of a large volume laccolith or cryptodome during the first 2.5 months of the eruption and lava flow effusion only afterwards, with a total volume of 1.4 km3. InSAR data from the ENVISAT and TerraSAR-X missions shows more than 2 m of subsidence during the effusive eruption phase produced by deflation of a finite spheroidal source at a depth of 5 km. In order to constrain the magma total H2O content, crystal cargo, and reservoir pressure drop we numerically solve the coupled set of equations of a pressurized magma reservoir, magma conduit flow and time dependent density, volatile exsolution and viscosity that we use to invert the InSAR and topographic data time series. We compare the best-fit model parameters with independent estimates of magma viscosity and total gas content measured from lava samples. Preliminary modeling shows that although it is not possible to model both the InSAR and the topographic data during the onset of the laccolith emplacement, it is possible to constrain the magma H2O and crystal content, to 4% wt and 30% which agree well with published literature values.

  7. The competition between H<sub>2sub>O and CO<sub>2sub> adhesion at reservoir conditions

    DEFF Research Database (Denmark)

    Sølling, Theis Ivan; Budi, Akin; Mogensen, K.

    2015-01-01

    Density functional theory was applied (B3LYP) to answer whether conditions exist where CO2 adhesion to three different lithologies becomes stronger than H2O adhesion. The answer is that it does not seem to be the case. This is taken to indicate that the reservoirs that we have represented by simple...

  8. Integrated Reflection Seismic Monitoring and Reservoir Modeling for Geologic CO2 Sequestration

    Energy Technology Data Exchange (ETDEWEB)

    John Rogers

    2011-12-31

    The US DOE/NETL CCS MVA program funded a project with Fusion Petroleum Technologies Inc. (now SIGMA) to model the proof of concept of using sparse seismic data in the monitoring of CO{sub 2} injected into saline aquifers. The goal of the project was to develop and demonstrate an active source reflection seismic imaging strategy based on deployment of spatially sparse surface seismic arrays. The primary objective was to test the feasibility of sparse seismic array systems to monitor the CO{sub 2} plume migration injected into deep saline aquifers. The USDOE/RMOTC Teapot Dome (Wyoming) 3D seismic and reservoir data targeting the Crow Mountain formation was used as a realistic proxy to evaluate the feasibility of the proposed methodology. Though the RMOTC field has been well studied, the Crow Mountain as a saline aquifer has not been studied previously as a CO{sub 2} sequestration (storage) candidate reservoir. A full reprocessing of the seismic data from field tapes that included prestack time migration (PSTM) followed by prestack depth migration (PSDM) was performed. A baseline reservoir model was generated from the new imaging results that characterized the faults and horizon surfaces of the Crow Mountain reservoir. The 3D interpretation was integrated with the petrophysical data from available wells and incorporated into a geocellular model. The reservoir structure used in the geocellular model was developed using advanced inversion technologies including Fusion's ThinMAN{trademark} broadband spectral inversion. Seal failure risk was assessed using Fusion's proprietary GEOPRESS{trademark} pore pressure and fracture pressure prediction technology. CO{sub 2} injection was simulated into the Crow Mountain with a commercial reservoir simulator. Approximately 1.2MM tons of CO{sub 2} was simulated to be injected into the Crow Mountain reservoir over 30 years and subsequently let 'soak' in the reservoir for 970 years. The relatively small plume

  9. The role of magma mixing/mingling and cumulate melting in the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei, Southern Italy)

    Science.gov (United States)

    Forni, Francesca; Petricca, Eleonora; Bachmann, Olivier; Mollo, Silvio; De Astis, Gianfilippo; Piochi, Monica

    2018-06-01

    Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, 39 ka and Neapolitan Yellow Tuff, NYT, 15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a "mature" (i.e., sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge.

  10. Validating predictions made by a thermo-mechanical model of melt segregation in sub-volcanic systems

    Science.gov (United States)

    Roele, Katarina; Jackson, Matthew; Morgan, Joanna

    2014-05-01

    A quantitative understanding of the spatial and temporal evolution of melt distribution in the crust is crucial in providing insights into the development of sub-volcanic crustal stratigraphy and composition. This work aims to relate numerical models that describe the base of volcanic systems with geophysical observations. Recent modelling has shown that the repetitive emplacement of mantle-derived basaltic sills, at the base of the lower crust, acts as a heat source for anatectic melt generation, buoyancy-driven melt segregation and mobilisation. These processes form the lowermost architecture of complex sub-volcanic networks as upward migrating melt produces high melt fraction layers. These 'porosity waves' are separated by zones with high compaction rates and have distinctive polybaric chemical signatures that suggest mixed crust and mantle origins. A thermo-mechanical model produced by Solano et al in 2012 has been used to predict the temperatures and melt fractions of successive high porosity layers within the crust. This model was used as it accounts for the dynamic evolution of melt during segregation and migration through the crust; a significant process that has been neglected in previous models. The results were used to input starting compositions for each of the layers into the rhyolite-MELTS thermodynamic simulation. MELTS then determined the approximate bulk composition of the layers once they had cooled and solidified. The mean seismic wave velocities of the polymineralic layers were then calculated using the relevant Voight-Reuss-Hill mixture rules, whilst accounting for the pressure and temperature dependence of seismic wave velocity. The predicted results were then compared with real examples of reflectivity for areas including the UK, where lower crustal layering is observed. A comparison between the impedance contrasts at compositional boundaries is presented as it confirms the extent to which modelling is able to make predictions that are

  11. Using fumarolic inert gas composition to investigate magma dynamics at Campi Flegrei (Italy)

    Science.gov (United States)

    Chiodini, G.; Caliro, S.; Paonita, A.; Cardellini, C.

    2013-12-01

    Since 2000 the Campi Flegrei caldera sited in Neapolitan area (Italy), has showed signs of reactivation, marked by ground uplift, seismic activity, compositional variations of fumarolic effluents from La Solfatara, an increase of the fumarolic activity as well as of soil CO2 fluxes. Comparing long time series of geochemical signals with ground deformation and seismicity, we show that these changes are at least partially caused by repeated injections of magmatic fluid into the hydrothermal system. The frequency of these degassing episodes has increased in the last years, causing pulsed uplift episodes and swarms of low magnitude earthquakes. We focus here in the inert gas species (CO2-He-Ar-N2) of Solfatara fumaroles which displayed in the time spectacular and persistent variation trends affecting all the monitored vents. The observed variations, which include a continuous decrease of both N2/He and N2/CO2 ratios since 1985, paralleled by an increase of He/CO2, can not be explained neither with changes in processes of boiling-condensation in the local hydrothermal system nor with changes in the mixing proportions between a magmatic vapour and hydrothermal fluids. Consequently we investigated the possibility that the trends of inert gas species are governed by changes in the conditions controlling magma degassing at depth. We applied a magma degassing model, with the most recent updates for inert gas solubilities, after to have included petrologic constraints from the ranges of melt composition and reservoir pressure at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a surprising agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-time geochemical changes. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature of reactive

  12. Lunar magma transport phenomena

    Science.gov (United States)

    Spera, Frank J.

    1992-01-01

    An outline of magma transport theory relevant to the evolution of a possible Lunar Magma Ocean and the origin and transport history of the later phase of mare basaltic volcanism is presented. A simple model is proposed to evaluate the extent of fractionation as magma traverses the cold lunar lithosphere. If Apollo green glasses are primitive and have not undergone significant fractionation en route to the surface, then mean ascent rates of 10 m/s and cracks of widths greater than 40 m are indicated. Lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics. The predominant vapor species appear to be CO CO2, and COS. Near the lunar surface, the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high-speed ejection of vapor and pyroclasts to form lunary fire fountain deposits such as the Apollo 17 orange and black glasses and Apollo 15 green glass.

  13. Forecasting Effusive Dynamics and Decompression Rates by Magmastatic Model at Open-vent Volcanoes.

    Science.gov (United States)

    Ripepe, Maurizio; Pistolesi, Marco; Coppola, Diego; Delle Donne, Dario; Genco, Riccardo; Lacanna, Giorgio; Laiolo, Marco; Marchetti, Emanuele; Ulivieri, Giacomo; Valade, Sébastien

    2017-06-20

    Effusive eruptions at open-conduit volcanoes are interpreted as reactions to a disequilibrium induced by the increase in magma supply. By comparing four of the most recent effusive eruptions at Stromboli volcano (Italy), we show how the volumes of lava discharged during each eruption are linearly correlated to the topographic positions of the effusive vents. This correlation cannot be explained by an excess of pressure within a deep magma chamber and raises questions about the actual contributions of deep magma dynamics. We derive a general model based on the discharge of a shallow reservoir and the magmastatic crustal load above the vent, to explain the linear link. In addition, we show how the drastic transition from effusive to violent explosions can be related to different decompression rates. We suggest that a gravity-driven model can shed light on similar cases of lateral effusive eruptions in other volcanic systems and can provide evidence of the roles of slow decompression rates in triggering violent paroxysmal explosive eruptions, which occasionally punctuate the effusive phases at basaltic volcanoes.

  14. Global variations in gravity-derived oceanic crustal thickness: Implications on oceanic crustal accretion and hotspot-lithosphere interactions

    Science.gov (United States)

    Lin, J.; Zhu, J.

    2012-12-01

    We present a new global model of oceanic crustal thickness based on inversion of global oceanic gravity anomaly with constrains from seismic crustal thickness profiles. We first removed from the observed marine free-air gravity anomaly all gravitational effects that can be estimated and removed using independent constraints, including the effects of seafloor topography, marine sediment thickness, and the age-dependent thermal structure of the oceanic lithosphere. We then calculated models of gravity-derived crustal thickness through inversion of the residual mantle Bouguer anomaly using best-fitting gravity-modeling parameters obtained from comparison with seismically determined crustal thickness profiles. Modeling results show that about 5% of the global crustal volume (or 9% of the global oceanic surface area) is associated with model crustal thickness 8.6 km and is interpreted to have been affected by excess magmatism. The percentage of oceanic crustal volume that is associated with thick crustal thickness (>8.6 km) varies greatly among tectonic plates: Pacific (33%), Africa (50%), Antarctic (33%), Australia (30%), South America (34%), Nazca (23%), North America (47%), India (74%), Eurasia (68%), Cocos (20%), Philippine (26%), Scotia (41%), Caribbean (89%), Arabian (82%), and Juan de Fuca (21%). We also found that distribution of thickened oceanic crust (>8.6 km) seems to depend on spreading rate and lithospheric age: (1) On ocean basins younger than 5 Ma, regions of thickened crust are predominantly associated with slow and ultraslow spreading ridges. The relatively strong lithospheric plate at slow and ultraslow ridges might facilitate the loading of large magmatic emplacements on the plate. (2) In contrast, crustal thickness near fast and intermediately fast spreading ridges typically does not exceed 7-8 km. The relatively weak lithosphere at fast and intermediately fast ridges might make it harder for excess magmatism to accrete. We further speculate that

  15. U-series disequilibrium constraints on magma generation at the Jan Mayen hotspot

    Science.gov (United States)

    Rivers, E. R.; Chernow, R.; Elkins, L. J.; Sims, K. W.; Blichert-Toft, J.; Devey, C. W.

    2013-12-01

    The incompatible element-enriched magma source beneath the Jan Mayen Island hotspot influences melt generation on the adjacent northern Mid-Atlantic Ridge system and likely derives from either a small, local mantle plume, ancient Icelandic plume material emplaced in the mantle source, and/or sub-continental lithospheric mantle remnants emplaced locally by rifting of Greenland. The slow spreading Northern Kolbeinsey and Southern Mohns Ridges are immediately adjacent to Jan Mayen Island. Both have relatively shallow ridge axes, particularly the extremely shallow Eggvin Bank region of the Northern Kolbeinsey Ridge, which host anomalously large central volcanic edifices. We are currently collecting U-series disequilibrium and long-lived radiogenic isotope data for fresh, glassy mid-ocean ridge basalts from the Northern Kolbeinsey and Southern Mohns Ridge segments to better constrain source composition, depth of melting in the garnet peridotite stability field, solid mantle upwelling rates, and the nature of melt extraction beneath those segments. In particular, we are measuring isotopic data for geographically well-located samples collected from hummocky pillow basalt flows within the axial valley of the Northern Kolbeinsey Ridge segment as well as from the large volcanoes on both ridge segments, to further determine the role of the Jan Mayen hotspot in crustal construction on the Mid-Atlantic Ridge. Recently collected data show particularly high strontium isotope ratios consistent with trace element patterns that suggest a distinct local plume located beneath the Jan Mayen hotspot. A plume model for Jan Mayen is supported by new bathymetric imaging of adjacent ridge segments that reveals excess volcanism beneath the large axial volcanoes and a radial distribution of enrichment surrounding Jan Mayen Island. We predict that age-constrained U-series disequilibrium measurements will support active mantle upwelling focused beneath both Jan Mayen Island and the large axial

  16. Primordial crustal growth in northern Nigeria: preliminary Rb-Sr and Sm-Nd constraints from Kaduna migmatite-gneiss complex

    International Nuclear Information System (INIS)

    Dada, S. S.; Briqueu, L.; Birck, J. L.

    1998-01-01

    The Kaduna Migmatite-Gneiss Complex in the central area of the Northern shield includes variably migmatised granitotrondhjemitic gneisses and amphibolite of hitherto unknown age. The amphibolite enclaves and dykes are metatholeiites with comparatively unfractionated rare-earth patterns. The two main rock units (TTG and amphibolite) exhibit complementary geochemical signatures in the normalised abundance patterns of relatively incompatible elements and suggest possible derivation of the gneisses from subduction related mafic material. Sm-Nd and Rb-Sr isotopic data document early Archaean crustal formation of new crust and its subsequent late Archaean differentiation. These preliminary results form an evidence for a more extended crustal history in the heart of the Pan-African domain (ca. 600 Ma.). They suggest the differentiation of juvenile crustal protolith from a chondritic reservoir about 3.5 Ga. for the gneiss-amphibolite bimodal suite. A tectonothermal event about 3.1-3.0 Ga led to the emplacement of an early gneiss as indicated from Rb-Sr and U-Ph zircon analyses. Subsequent differentiation and/or reworking around 2.8-2.7 Ga is coherent with the Liberian orogeny within the West African- Latino American subregion

  17. In-Situ MVA of CO<sub>2 sub>Sequestration Using Smart Field Technology

    Energy Technology Data Exchange (ETDEWEB)

    Mohaghegh, Shahab D. [West Virginia Univ. Research Corporation, Morgantown, WV (United States)

    2014-09-01

    Capability of underground carbon dioxide storage to confine and sustain injected CO<sub>2 sub> for a long period of time is the main concern for geologic CO<sub>2 sub> sequestration. If a leakage from a geological CO<sub>2 sub> sequestration site occurs, it is crucial to find the approximate amount and the location of the leak, in a timely manner, in order to implement proper remediation activities. An overwhelming majority of research and development for storage site monitoring has been concentrated on atmospheric, surface or near surface monitoring of the sequestered CO<sub>2 sub>. This study aims to monitor the integrity of CO<sub>2 sub>storage at the reservoir level. This work proposes developing in-situ CO<sub>2 sub> Monitoring and Verification technology based on the implementation of Permanent Down-hole Gauges (PDG) or “Smart Wells” along with Artificial Intelligence and Data Mining (AI&DM). The technology attempts to identify the characteristics of the CO<sub>2 sub> leakage by de-convolving the pressure signals collected from Permanent Down-hole Gauges (PDG). Citronelle field, a saline aquifer reservoir, located in the U.S. was considered as the basis for this study. A reservoir simulation model for CO<sub>2 sub> sequestration in the Citronelle field was developed and history matched. PDGs were installed, and therefore were considered in the numerical model, at the injection well and an observation well. Upon completion of the history matching process, high frequency pressure data from PDGs were generated using the history matched numerical model using different CO<sub>2 sub>leakage scenarios. Since pressure signal behaviors were too complicated to de-convolute using any existing mathematical formulations, a Machine Learning-based technology was introduced for this purpose. An Intelligent Leakage Detection System (ILDS) was developed as the result of this effort using the machine learning and pattern recognition technologies. The ILDS

  18. Images of the East Africa Rift System from the Joint Inversion of Body Waves, Surface Waves, and Gravity: Investigating the Role of Magma in Early-Stage Continental Rifting

    Science.gov (United States)

    Roecker, S. W.; Ebinger, C. J.; Tiberi, C.; Mulibo, G. D.; Ferdinand-Wambura, R.; Muzuka, A.; Khalfan, M.; Kianji, G.; Gautier, S.; Albaric, J.; Peyrat, S.

    2015-12-01

    With several rift segments at different stages of the rifting cycle, and the last orogenic episode more than 500 Mya, the young (Ngorongoro caldera appears to be physically cut off from the magma beneath the main part of the rift zone by a relatively thin (< 10 km) wide zone of higher shear wave speeds that lies along the western edge of the fault-bounded rift. The narrow ridge of higher velocity lower crustal material may be a consequence of flexural uplift of the rift flank in response to stretching of strong, cratonic lithosphere.

  19. MAGMA: analysis of two-channel microarrays made easy.

    Science.gov (United States)

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph

    2007-07-01

    The web application MAGMA provides a simple and intuitive interface to identify differentially expressed genes from two-channel microarray data. While the underlying algorithms are not superior to those of similar web applications, MAGMA is particularly user friendly and can be used without prior training. The user interface guides the novice user through the most typical microarray analysis workflow consisting of data upload, annotation, normalization and statistical analysis. It automatically generates R-scripts that document MAGMA's entire data processing steps, thereby allowing the user to regenerate all results in his local R installation. The implementation of MAGMA follows the model-view-controller design pattern that strictly separates the R-based statistical data processing, the web-representation and the application logic. This modular design makes the application flexible and easily extendible by experts in one of the fields: statistical microarray analysis, web design or software development. State-of-the-art Java Server Faces technology was used to generate the web interface and to perform user input processing. MAGMA's object-oriented modular framework makes it easily extendible and applicable to other fields and demonstrates that modern Java technology is also suitable for rather small and concise academic projects. MAGMA is freely available at www.magma-fgcz.uzh.ch.

  20. Forecasting magma-chamber rupture at Santorini volcano, Greece.

    Science.gov (United States)

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-28

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

  1. CO{sub 2} Huff-n-Puff process in a light oil shallow shelf carbonate reservoir. 1994 Annual report

    Energy Technology Data Exchange (ETDEWEB)

    Wehner, S.C.

    1995-05-01

    It is anticipated that this project will show that the application of the CO{sub 2} Huff-n-Puff process in shallow shelf carbonates can be economically implemented to recover appreciable volumes of light oil. The goals of the project are the development of guidelines for cost-effective selection of candidate reservoirs and wells, along with estimating recovery potential. The selected site for the demonstration project is the Central Vacuum Unit waterflood in Lea County, New Mexico. Work is nearing completion on the reservoir characterization components of the project. The near-term emphasis is to, (1) provide an accurate distribution of original oil-in-place on a waterflood pattern entity level, (2) evaluate past recovery efficiencies, (3) perform parametric simulations, and (4) forecast performance for a site specific field demonstration of the proposed technology. Macro zonation now exists throughout the study area and cross-sections are available. The Oil-Water Contact has been defined. Laboratory capillary pressure data was used to define the initial water saturations within the pay horizon. The reservoir`s porosity distribution has been enhanced with the assistance of geostatistical software. Three-Dimensional kriging created the spatial distributions of porosity at interwell locations. Artificial intelligence software was utilized to relate core permeability to core porosity, which in turn was applied to the 3-D geostatistical porosity gridding. An Equation-of-State has been developed and refined for upcoming compositional simulation exercises. Options for local grid-refinement in the model are under consideration. These tasks will be completed by mid-1995, prior to initiating the field demonstrations in the second budget period.

  2. Rocks Whose Compositions are Determined by Flow Differentiation of Olivine- and Sulfide Droplet-Laden Magma: the Jinchuan Story

    Science.gov (United States)

    Li, C.; Ripley, E. M.; de Waal, S. A.; Xu, Z.

    2002-12-01

    The Jinchuan intrusion in western China is an elongated, deeply-dipping dyke-like body of dominantly olivine-rich ultramafic rocks of high magnesium basaltic magma. It hosts the second largest Ni-Cu sulfide deposit in the world. More than 500 million tones of sulfide ore grading 1.2 percent Ni and 0.7 percent Cu occur mostly as next-textured and disseminated sulfide (pyrrhotite, pentlendite and chalcopyrite) with cumulus olivine in about half of the rocks of the intrusion. Based on different petrological zonations, the Jinchuan intrusion is further divided into three segments: eastern, central and western segments. The central segment is characterized by concentric enrichments of cumulus olivine and sulfide, whereas the eastern and western segments are characterized by the increase of both cumulus olivine and sulfide toward the footwall. The forsterite contents of fresh olivine from different segments are similar and vary between 82 and 86 mole percent. The small range of olivine compositional variation corresponds to less than 6 percent of fractional crystallization. Mass balance calculations based on sulfide solubility in basaltic magma indicate that the volume of the parental magma of the sulfide is many times larger than that which is currently represented in the intrusion. Large amounts of cumulus olivine (more than 40 weight percent) in the marginal samples and high concentrations of sulfide in the intrusion are consistent with an interpretation that the Jinchuan intrusion was formed by olivine- and sulfide droplet-laden magma ascending through a subvertical conduit to a higher level. Differentiation processes of the olivine- and sulfide droplet-laden magma varied in different parts of the conduit. Sub-vertical flow differentiation controlled the central segment of the conduit, resulting in further enrichment of olivine crystals and sulfide droplets in the conduit center. In contrast, sub-lateral flow and gravitational differentiation dominated in the eastern

  3. Crustal Poisson’s ratio anomalies in the eastern part of North China and their origins

    Directory of Open Access Journals (Sweden)

    Wencai Yang

    2011-07-01

    Full Text Available Seismic tomography can provide both fine P-wave and S-wave velocity structures of the crust and upper mantle. In addition, with proper computation, Poisson’s ratio images from the seismic velocities can be determined. However, it is unknown whether Poisson’s ratio images have any advantages when compared with the P-wave and S-wave velocity images. For the purposes of this study, high-resolution seismic tomography under the eastern part of North China region was used to determine detailed 3-D crustal P- and S-wave seismic velocities structure, as well as Poisson’s ratio images. Results of Poisson’s ratio imaging show high Poisson’s ratio (high-PR anomalies located in the Hengshan-North Taihang-Zhangjiakou (H-NT-Z region, demonstrating that Poisson’s ratio imaging can provide new geophysical constraints for regional tectonic evolution. The H-NT-Z region shows a prominent and continuous high-PR anomaly in the upper crust. Based on Poisson’s ratio images at different depths, we find that this high-PR anomaly is extending down to the middle crust with thickness up to about 26 km. According to rock physical property measurements and other geological data, this crustal Poisson’s ratio anomaly can be explained by Mesozoic partial melting of the upper mantle and basaltic magma underplating related to the lithospheric thinning of the North China craton.

  4. Temporal evolution of granitic magmas in the Luanchuan metallogenic belt, east Qinling Orogen, central China: Implications for Mo metallogenesis

    Science.gov (United States)

    Li, Dong; Han, Jiangwei; Zhang, Shouting; Yan, Changhai; Cao, Huawen; Song, Yaowu

    2015-11-01

    -forming fluids were exsolved from the granitic melts in shallow-crustal magma chambers, resulting in the formation of the Mo deposits of the Luanchuan metallogenic belt. This model may account for the widespread late Mesozoic Mo deposits of eastern China.

  5. Crustal Deformation During the 2011 Volanic Crisis of El Hierro, Canary Islands, Revealed by Continuous GPS Observation

    Science.gov (United States)

    Sagiya, T.; Barrancos Martinez, J.; Calvo, D.; Padron, E.; Hernandez, G. H.; Hernández, P. A.; Perez Rodriguez, N.; Suárez, J. M. P.

    2012-04-01

    Seismo-volcnic activity of El Hierro started in the middle of July of 2011 and resulted in the active submarine eruption after October 12 south off La Restinga, the southern tip of the island. We have been operating one continuous GPS site on the island since 2004. Responding to the activity, we quickly installed 5 more GPS sites. Including another site operated by the Canary Islands Cartograhical Service (GRAFCAN) for a cartographic purpose, we have been monitoring 7 GPS sites equipped with dual-frequency receivers. We present the result of our crustal deformation monitoring and the magmatic activity inferred from the deformation data. In accordance with the deformation pattern, we divide the volcanic activity in 2011 into 4 stages. The first stage is from the middle of July to middle of September, during which steady magmatic inflation is estimated at the center of the island. The inflated volume of the first stage is estimated to be about 1.3 X 107 m3 at the depth of about 5km. The second stage, which continued until the first submarine eruption on October 12, is characterized by the accelerated deformation due to the upward as well as southward migration of magma. Additional inflation of about 2.1 X 107 m3 occurred in the depth range of 1-2km. The third stage continued for about 3 weeks after the first submarine eruption. During this stage, submarine eruption continues while no significant surface deformation is observed. It is considered magma supply from a deeper magma chamber continued during this 3 weeks period. Therefore, the total inflation volume during the first two stages gives the minimum estimate for the total magma volume. Since the beginning of November 2011, many GPS sites started subsiding. However, this deflation pattern is quite different from those in the shallow inflation stages. Horizontal deformation during this 4th stage is not significant, implying that deflation is occurring below the moho.

  6. Volatile-induced magma differentiation in the plumbing system of Mt. Etna volcano (Italy): evidence from glass in tephra of the 2001 eruption

    Science.gov (United States)

    Ferlito, Carmelo; Viccaro, Marco; Cristofolini, Renato

    2008-02-01

    Mount Etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries. For about 3 weeks, several eruptive fractures developed, emitting lava flows and tephra that significantly modified the landscape of the southern flank of the volcano. This event stimulated the attention of the scientific community especially for the simultaneous emission of petrologically distinct magmas, recognized as coming from different segments of the plumbing system. A stratigraphically controlled sampling of tephra layers was performed at the most active vents of the eruption, in particular at the 2,100 m (CAL) and at the 2,550 m (LAG) scoria cones. Detailed scanning electron microscope and energy dispersive x-ray spectrometer (SEM-EDS) analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous increase in Ti, Fe, P, and particularly of K and Cl in the upper layers of the LAG sequence. Mass balance and thermodynamic calculations have shown that this enrichment cannot be accounted for by “classical” differentiation processes, such as crystal fractionation and magma mixing. The analysis of petrological features of the magmas involved in the event, integrated with the volcanological evolution, has evidenced the role played by volatiles in controlling the magmatic evolution within the crustal portion of the plumbing system. Volatiles, constituted of H2O, CO2, and Cl-complexes, originated from a deeply seated magma body (DBM). Their upward migration occurred through a fracture network possibly developed by the seismic swarms during the period preceding the event. In the upper portion of the plumbing system, a shallower residing magma body (ABT) had chemical and physical conditions to receive migrating volatiles, which hence dissolved the mobilized elements producing the observed selective enrichment. This volatile-induced differentiation involved exclusively the lowest erupted

  7. Silicic magma generation at Askja volcano, Iceland

    Science.gov (United States)

    Sigmarsson, O.

    2009-04-01

    Rate of magma differentiation is an important parameter for hazard assessment at active volcanoes. However, estimates of these rates depend on proper understanding of the underlying magmatic processes and magma generation. Differences in isotope ratios of O, Th and B between silicic and in contemporaneous basaltic magmas have been used to emphasize their origin by partial melting of hydrothermally altered metabasaltic crust in the rift-zones favoured by a strong geothermal gradient. An alternative model for the origin of silicic magmas in the Iceland has been proposed based on U-series results. Young mantle-derived mafic protolith is thought to be metasomatized and partially melted to form the silicic end-member. However, this model underestimates the compositional variations of the hydrothermally-altered basaltic crust. New data on U-Th disequilibria and O-isotopes in basalts and dacites from Askja volcano reveal a strong correlation between (230Th/232Th) and delta 18O. The 1875 AD dacite has the lowest Th- and O isotope ratios (0.94 and -0.24 per mille, respectively) whereas tephra of evolved basaltic composition, erupted 2 months earlier, has significantly higher values (1.03 and 2.8 per mille, respectively). Highest values are observed in the most recent basalts (erupted in 1920 and 1961) inside the Askja caldera complex and out on the associated fissure swarm (Sveinagja basalt). This correlation also holds for older magma such as an early Holocene dacites, which eruption may have been provoked by rapid glacier thinning. Silicic magmas at Askja volcano thus bear geochemical signatures that are best explained by partial melting of extensively hydrothermally altered crust and that the silicic magma source has remained constant during the Holocene at least. Once these silicic magmas are formed they appear to erupt rapidly rather than mixing and mingling with the incoming basalt heat-source that explains lack of icelandites and the bi-modal volcanism at Askja

  8. Observations of coupled seismicity and ground deformation at El Hierro Island (2011-2014)

    Science.gov (United States)

    Gonzalez, P. J.

    2015-12-01

    New insights into the magma storage and evolution at oceanic island volcanoes are now being achieved using remotely sensed space geodetic techniques, namely satellite radar interferometry. Differential radar interferometry is a technique tracking, at high spatial resolution, changes in the travel-time (distance) from the satellites to the ground surface, having wide applications in Earth sciences. Volcanic activity usually is accompanied by surface ground deformation. In many instances, modelling of surface deformation has the great advantage to estimate the magma volume change, a particularly interesting parameter prior to eruptions. Jointly interpreted with petrology, degassing and seismicity, it helps to understand the crustal magmatic systems as a whole. Current (and near-future) radar satellite missions will reduce the revisit time over global sub-aerial volcanoes to a sub-weekly basis, which will increase the potential for its operational use. Time series and filtering processing techniques of such streaming data would allow to track subsurface magma migration with high precision, and frequently update over vast areas (volcanic arcs, large caldera systems, etc.). As an example for the future potential monitoring scenario, we analyze multiple satellite radar data over El Hierro Island (Canary Islands, Spain) to measure and model surface ground deformation. El Hierro has been active for more than 3 years (2011 to 2014). Initial phases of the unrest culminated in a submarine eruption (late 2011 - early 2012). However, after the submarine eruption ended, its magmatic system still active and affected by pseudo-regular energetic seismic swarms, accompanied by surface deformation without resumed eruptions. Such example is a great opportunity to understand the crustal magmatic systems in low magma supply-rate oceanic island volcanoes. This new approach to measure surface deformation processes is yielding an ever richer level of information from volcanology to

  9. Radiocarbon as a Reactive Tracer for Tracking Permanent CO<sub>2sub> Storage in Basaltic Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Matter, Juerg [Columbia Univ., New York, NY (United States); Stute, Martin [Columbia Univ., New York, NY (United States); Schlosser, Peter [Columbia Univ., New York, NY (United States); Broecker, Wallace [Columbia Univ., New York, NY (United States)

    2015-09-30

    In view of concerns about the long-term integrity and containment of CO<sub>2sub> storage in geologic reservoirs, many efforts have been made to improve the monitoring, verification and accounting methods for geologically stored CO<sub>2sub>. Our project aimed to demonstrate that carbon-14 (14C) could be used as a reactive tracer to monitor geochemical reactions and evaluate the extent of mineral trapping of CO<sub>2sub> in basaltic rocks. The capacity of a storage reservoir for mineral trapping of CO<sub>2sub> is largely a function of host rock composition. Mineral carbonation involves combining CO<sub>2sub> with divalent cations including Ca2+, Mg2+ and Fe2+. The most abundant geological sources for these cations are basaltic rocks. Based on initial storage capacity estimates, we know that basalts have the necessary capacity to store million to billion tons of CO<sub>2sub> via in situ mineral carbonation. However, little is known about CO2-fluid-rock reactions occurring in a basaltic storage reservoir during and post-CO<sub>2sub> injection. None of the common monitoring and verification techniques have been able to provide a surveying tool for mineral trapping. The most direct method for quantitative monitoring and accounting involves the tagging of the injected CO<sub>2sub> with 14C because 14C is not present in deep geologic reservoirs prior to injection. Accordingly, we conducted two CO<sub>2sub> injection tests at the CarbFix pilot injection site in Iceland to study the feasibility of 14C as a reactive tracer for monitoring CO<sub>2sub>-fluid-rock reactions and CO<sub>2sub> mineralization. Our newly developed monitoring techniques, using 14C as a reactive tracer, have been successfully demonstrated. For the first time, permanent and safe disposal of CO<sub>2sub> as environmentally benign carbonate minerals in basaltic rocks could be shown. Over 95% of the injected CO<sub>2sub> at the Carb

  10. Dacite petrogenesis on mid-ocean ridges: Evidence for oceanic crustal melting and assimilation

    Science.gov (United States)

    Wanless, V.D.; Perfit, M.R.; Ridley, W.I.; Klein, E.

    2010-01-01

    Whereas the majority of eruptions at oceanic spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, the formation of tholeiitic andesites and dacites at mid-ocean ridges (MORs) is a petrological enigma. Eruptions of MOR high-silica lavas are typically associated with ridge discontinuities and have produced regionally significant volumes of lava. Andesites and dacites have been observed and sampled at several locations along the global MOR system; these include propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Gal??pagos spreading center, and at the 9??N overlapping spreading center on the East Pacific Rise. Despite the formation of these lavas at various ridges, MOR dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes are controlling their chemistry. Although most geochemical variability in MOR basalts is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical data for MOR dacitic glasses suggest that contamination from a seawater-altered component is important in their petrogenesis. MOR dacites are characterized by elevated U, Th, Zr, and Hf, low Nb and Ta concentrations relative to rare earth elements (REE), and Al2O3, K2O, and Cl concentrations that are higher than expected from low-pressure fractional crystallization alone. Petrological modeling of MOR dacites suggests that partial melting and assimilation are both integral to their petrogenesis. Extensive fractional crystallization of a MORB parent combined with partial melting and assimilation of amphibole-bearing altered crust produces a magma with a geochemical signature similar to a MOR dacite. This supports the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas and may be significant in the generation of evolved MORB in

  11. Cumulate xenoliths from St. Vincent, Lesser Antilles Island Arc: a window into upper crustal differentiation of mantle-derived basalts

    Science.gov (United States)

    Tollan, P. M. E.; Bindeman, I.; Blundy, J. D.

    2012-02-01

    In order to shed light on upper crustal differentiation of mantle-derived basaltic magmas in a subduction zone setting, we have determined the mineral chemistry and oxygen and hydrogen isotope composition of individual cumulus minerals in plutonic blocks from St. Vincent, Lesser Antilles. Plutonic rock types display great variation in mineralogy, from olivine-gabbros to troctolites and hornblendites, with a corresponding variety of cumulate textures. Mineral compositions differ from those in erupted basaltic lavas from St. Vincent and in published high-pressure (4-10 kb) experimental run products of a St. Vincent high-Mg basalt in having higher An plagioclase coexisting with lower Fo olivine. The oxygen isotope compositions (δ18O) of cumulus olivine (4.89-5.18‰), plagioclase (5.84-6.28‰), clinopyroxene (5.17-5.47‰) and hornblende (5.48-5.61‰) and hydrogen isotope composition of hornblende (δD = -35.5 to -49.9‰) are all consistent with closed system magmatic differentiation of a mantle-derived basaltic melt. We employed a number of modelling exercises to constrain the origin of the chemical and isotopic compositions reported. δ18OOlivine is up to 0.2‰ higher than modelled values for closed system fractional crystallisation of a primary melt. We attribute this to isotopic disequilibria between cumulus minerals crystallising at different temperatures, with equilibration retarded by slow oxygen diffusion in olivine during prolonged crustal storage. We used melt inclusion and plagioclase compositions to determine parental magmatic water contents (water saturated, 4.6 ± 0.5 wt% H2O) and crystallisation pressures (173 ± 50 MPa). Applying these values to previously reported basaltic and basaltic andesite lava compositions, we can reproduce the cumulus plagioclase and olivine compositions and their associated trend. We conclude that differentiation of primitive hydrous basalts on St. Vincent involves crystallisation of olivine and Cr-rich spinel at depth

  12. Experimental Simulations of Lunar Magma Ocean Crystallization: The Plot (But Not the Crust) Thickens

    Science.gov (United States)

    Draper, D. S.; Rapp, J. F.; Elardo, S. M.; Shearer, C. K., Jr.; Neal, C. R.

    2016-01-01

    Numerical models of differentiation of a global-scale lunar magma ocean (LMO) have raised as many questions as they have answered. Recent orbital missions and sample studies have provided new context for a large range of lithologies, from the comparatively magnesian "purest anorthosite" reported by to Si-rich domes and spinel-rich clasts with widespread areal distributions. In addition, the GRAIL mission provided strong constraints on lunar crustal density and average thickness. Can this increasingly complex geology be accounted for via the formation and evolution of the LMO? We have in recent years been conducting extensive sets of petrologic experiments designed to fully simulate LMO crystallization, which had not been attempted previously. Here we review the key results from these experiments, which show that LMO differentiation is more complex than initial models suggested. Several important features expected from LMO crystallization models have yet to be reproduced experimentally; combined modelling and experimental work by our group is ongoing.

  13. Isotopic data bearing on the origin of Mesozoic and Tertiary granitic rocks in the western United States

    International Nuclear Information System (INIS)

    DePaolo, D.J.; Farmer, G.L.

    1984-01-01

    A regional survey of initial Nd and Sr isotopic compositions has been done on Mesozoic and Tertiary granitic rocks from a 500 000 km 2 area in California, Nevada, Utah, Arizona, and Colorado. The plutons, which range in composition from quartz diorite to monzogranite, are intruded into accreted oceanic geosynclinal terrains in the west and north and into Precambrian basement in the east. Broad geographic coverage allows the data to be interpreted in the context of the regional pre-Mesozoic crustal structure. Initial Nd isotopic compositions exhibit a huge range, encompassing values typical of oceanic magmatic arcs and Archean basement. The sources of the magmas can be inferred from the systematic geographic variability of Nd isotopic compositions. The plutons in the accreted terrains represent mantle-derived magma that assimilated crust while differentiating at deep levels. Those emplaced into Precambrian basement are mainly derived from the crust. The regional patterns can be understood in terms of: (1) the flux of mantle magma entering the crust; (2) crustal thickness; and (3) crustal age. The mantle magma flux apparently decreased inland; in the main batholith belts purely crustal granitic rocks are not observed because the flux was too large. Inland, crustal granite is common because mantle magma was scarce and the crust was thick, and hot enough to melt. The epsilonsub(Nd) values of peraluminous granite formed by melting of the Precambrian basement depend on the age of the local basement source. (author)

  14. Geochemical evolution of Cenozoic-Cretaceous magmatism and its relation to tectonic setting, southwestern Idaho, U.S.A

    International Nuclear Information System (INIS)

    Norman, M.D.; Leeman, W.P.

    1989-01-01

    Magmatism in the western United States spanned a change in tectonic setting from Mesozoic and early Tertiary plate convergence to middle and late Tertiary crustal extension. This paper presents new major element, trace element, and isotopic (Sr, Nd, Pb) data on a diverse suite of Cretaceous to Neogene igneous rocks from the Owyhee area of southwestern Idaho to evaluate possible relationships between the evolving tectonic regime and temporal changes in igneous activity. The oldest studied rocks are Cretaceous granitic intrusives that probably formed by large-scale mixing of Precambrian crust with subduction-related magmas. Silicic Eocene tuffs are also rich in crustal components, but have isotopic compositions unlike the Cretaceous intrusives. These data require at least two crustal sources that may correspond to domains of significantly different age (Archean vs. Proterozoic). The oldest mafic lavas in the study area are Oligocene andesites and basalts compositionally similar to subduction-related magmas derived from asthenospheric mantle and erupted through thick continental crust. Direct crustal involvement during oligocene time was limited to minor interaction with the mafic magmas. Miocene activity produced bimodal basalt-rhyolite suites and minor volumes of hybrid lavas. Compositions of Miocene basalts demonstrate the decline of subduction-related processes, and increased involvement of subcontinental lithospheric mantle as a magma source. Crustally-derived Miocene rhyolites have isotopic compositions similar to those of the Cretaceous granitic rocks but trace element abundances more typical of within-plate magmas. (orig./WB)

  15. Numerical modeling to assess the sensitivity and resolution of long-electrode electrical resistance tomography (LEERT) surveys to monitor CO<sub>2sub> migration, Phase 1B area

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez, Abelardo L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2010-05-18

    This document describes the results of a numerical modeling study that evaluated whether LEERT could be used successfully to monitor CO<sub>2sub> distribution in the Weyburn- Midale reservoir, Phase 1B area. The magnitude of electrical resistivity changes and the technique’s resolution depend on many site-specific factors including well separation distances, casing lengths, reservoir depth, thickness, and composition, and the effect of CO<sub>2sub> on the electrical properties of the reservoir. Phase 1B-specific numerical modeling of the electrical response to CO<sub>2sub> injection has been performed to assess sensitivity and resolution of the electrical surveys.

  16. High-Resolution Imaging of Axial Volcano, Juan de Fuca ridge.

    Science.gov (United States)

    Arnulf, A. F.; Harding, A. J.; Kent, G. M.

    2014-12-01

    To date, seismic experiments have been key in our understanding of the internal structure of volcanic systems. However, most experiments, especially subaerial-based, are often restricted to refraction geometries with limited numbers of sources and receivers, and employ smoothing constraints required by tomographic inversions that produce smoothed and blurry images with spatial resolutions well below the length scale of important features that define these magmatic systems. Taking advantage of the high density of sources and receivers from multichannel seismic (MCS) data should, in principle, allow detailed images of velocity and reflectivity to be recovered. Unfortunately, the depth of mid-ocean ridges has the detrimental effect of concealing critical velocity information behind the seafloor reflection, preventing first arrival travel-time tomographic approaches from imaging the shallowest and most heterogeneous part of the crust. To overcome the limitations of the acquisition geometry, here we are using an innovative multistep approach. We combine a synthetic ocean bottom experiment (SOBE), 3-D traveltime tomography, 2D elastic full waveform and a reverse time migration (RTM) formalism, and present one of the most detailed imagery to date of a massive and complex magmatic system beneath Axial seamount, an active submarine volcano that lies at the intersection of the Juan de Fuca ridge and the Cobb-Eickelberg seamount chain. We present high-resolution images along 12 seismic lines that span the volcano. We refine the extent/volume of the main crustal magma reservoir that lies beneath the central caldera. We investigate the extent, volume and physical state of a secondary magma body present to the southwest and study its connections with the main magma reservoir. Additionally, we present a 3D tomographic model of the entire volcano that reveals a subsiding caldera floor that provides a near perfect trap for the ponding of lava flows, supporting a "trapdoor

  17. Slab melting and magma formation beneath the southern Cascade arc

    Science.gov (United States)

    Walowski, Kristina J.; Wallace, Paul J.; Clynne, Michael A.; Rasmussen, D.J.; Weis, D.

    2016-01-01

    The processes that drive magma formation beneath the Cascade arc and other warm-slab subduction zones have been debated because young oceanic crust is predicted to largely dehydrate beneath the forearc during subduction. In addition, geochemical variability along strike in the Cascades has led to contrasting interpretations about the role of volatiles in magma generation. Here, we focus on the Lassen segment of the Cascade arc, where previous work has demonstrated across-arc geochemical variations related to subduction enrichment, and H-isotope data suggest that H2O in basaltic magmas is derived from the final breakdown of chlorite in the mantle portion of the slab. We use naturally glassy, olivine-hosted melt inclusions (MI) from the tephra deposits of eight primitive (MgO>7 wt%) basaltic cinder cones to quantify the pre-eruptive volatile contents of mantle-derived melts in this region. The melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), suggesting extensive dehydration of the downgoing plate prior to reaching sub-arc depths and little input of slab-derived B into the mantle wedge. However, correlations of volatile and trace element ratios (H2O/Ce, Cl/Nb, Sr/Nd) in the melt inclusions demonstrate that geochemical variability is the result of variable addition of a hydrous subduction component to the mantle wedge. Furthermore, correlations between subduction component tracers and radiogenic isotope ratios show that the subduction component has less radiogenic Sr and Pb than the Lassen sub-arc mantle, which can be explained by melting of subducted Gorda MORB beneath the arc. Agreement between pMELTS melting models and melt inclusion volatile, major, and trace element data suggests that hydrous slab melt addition to the mantle wedge can produce the range in primitive compositions erupted in the Lassen region. Our results provide further evidence that chlorite-derived fluids from the mantle portion of the

  18. Continental Delamination of the Romanian Eastern Carpathians: A Lower Crustal Origin of the Vrancea Seismogenic Zone?

    Science.gov (United States)

    Fillerup, M. A.; Knapp, J. H.; Knapp, C. C.

    2006-12-01

    Two lithosphere-scale, explosive-source seismic reflection profiles (DRACULA I and DACIA PLAN), inclusive of the hinterland and foreland of the Romanian Eastern Carpathians, provide new evidence for the geodynamic origin of the Vrancea Seismogenic Zone (VSZ) of Romania. These data, collected to evaluate existing subduction-related and delamination geodynamic models proposed to explain the intermediate depth seismicity associated with the Vrancea zone, show evidence of continental crust extending continuously above the VSZ from the Carpathian foreland well into the Transylvanian hinterland. Crustal thicknesses inferred from these data based on reflectivity show a 40-45 km crust below the Transylvanian basin abruptly shallowing to 32 km for ~120 km beneath the fold and thrust belt of the main Carpathian orogen and thickening again to 38-42 km crust in the foreland. This thinned crust outlines an apparent lower crustal sub-orogenic cavity that is overlain by a relatively subhorizontal reflective fabric absent of dipping reflectivity. The northwest dipping Vrancea seismogenic body, a 30x70x200 km volume of intermediate depth earthquakes, is located on the eastern flank of the apparently thin crust beneath the Carpathian orogen. Amplitude decay curves show penetration of seismic energy to a depth of ~60 km in the vicinity of the sub-orogenic cavity, implying this non- reflective zone is a geologic signature. Rotation of the VSZ about a hinge beneath the foreland basin at a depth of ~50 km restores to fill the lower-crustal cavity under the orogen, suggesting the VSZ represents a portion of brittle lower crust delaminated during continental lithospheric delamination which may have caused regional uplift of the Transylvanian basin. The lack of through-going, dipping crustal-scale boundaries along this composite lithospheric transect would appear to preclude subduction as an explanation for seismicity in the VSZ, consistent with abundant surface geologic data. These

  19. Origin of metaluminous and alkaline volcanic rocks of the Latir volcanic field, northern Rio Grande rift, New Mexico

    Science.gov (United States)

    Johnson, C.M.; Lipman, P.W.

    1988-01-01

    Volcanic rocks of the Latir volcanic field evolved in an open system by crystal fractionation, magma mixing, and crustal assimilation. Early high-SiO2 rhyolites (28.5 Ma) fractionated from intermediate compositionmagmas that did not reach the surface. Most precaldera lavas have intermediate-compositions, from olivine basaltic-andesite (53% SiO2) to quartz latite (67% SiO2). The precaldera intermediate-composition lavas have anomalously high Ni and MgO contents and reversely zoned hornblende and augite phenocrysts, indicating mixing between primitive basalts and fractionated magmas. Isotopic data indicate that all of the intermediate-composition rocks studied contain large crustal components, although xenocrysts are found only in one unit. Inception of alkaline magmatism (alkalic dacite to high-SiO2 peralkaline rhyolite) correlates with, initiation of regional extension approximately 26 Ma ago. The Questa caldera formed 26.5 Ma ago upon eruption of the >500 km3 high-SiO2 peralkaline Amalia Tuff. Phenocryst compositions preserved in the cogenetic peralkaline granite suggest that the Amalia Tuff magma initially formed from a trace element-enriched, high-alkali metaluminous magma; isotopic data suggest that the parental magmas contain a large crustal component. Degassing of water- and halogen-rich alkali basalts may have provided sufficient volatile transport of alkalis and other elements into the overlying silicic magma chamber to drive the Amalia Tuff magma to peralkaline compositions. Trace element variations within the Amalia Tuff itself may be explained solely by 75% crystal fractionation of the observed phenocrysts. Crystal settling, however, is inconsistent with mineralogical variations in the tuff, and crystallization is thought to have occurred at a level below that tapped by the eruption. Spatially associated Miocene (15-11 Ma) lavas did not assimilate large amounts of crust or mix with primitive basaltic magmas. Both mixing and crustal assimilation processes

  20. Role of crustal assimilation and basement compositions in the petrogenesis of differentiated intraplate volcanic rocks: a case study from the Siebengebirge Volcanic Field, Germany

    Science.gov (United States)

    Schneider, K. P.; Kirchenbaur, M.; Fonseca, R. O. C.; Kasper, H. U.; Münker, C.; Froitzheim, N.

    2016-06-01

    The Siebengebirge Volcanic Field (SVF) in western Germany is part of the Cenozoic Central European Volcanic Province. Amongst these volcanic fields, the relatively small SVF comprises the entire range from silica-undersaturated mafic lavas to both silica-undersaturated and silica-saturated differentiated lavas. Owing to this circumstance, the SVF represents a valuable study area representative of intraplate volcanism in Europe. Compositions of the felsic lavas can shed some new light on differentiation of intraplate magmas and on the extent and composition of potential crustal assimilation processes. In this study, we provide detailed petrographic and geochemical data for various differentiated SVF lavas, including major and trace element concentrations as well as Sr-Nd-Hf-Pb isotope compositions. Samples include tephriphonolites, latites, and trachytes with SiO2 contents ranging between 53 and 66 wt%. If compared to previously published compositions of mafic SVF lavas, relatively unradiogenic 143Nd/144Nd and 176Hf/177Hf coupled with radiogenic 87Sr/86Sr and 207Pb/204Pb lead to the interpretation that the differentiated volcanic rocks have assimilated significant amounts of lower crustal mafic granulites like the ones found as xenoliths in the nearby Eifel volcanic field. These crustal contaminants should possess unradiogenic 143Nd/144Nd and 176Hf/177Hf, radiogenic 87Sr/86Sr, and highly radiogenic 207Pb/204Pb compositions requiring the presence of ancient components in the central European lower crust that are not sampled on the surface. Using energy-constrained assimilation-fractional crystallisation (EC-AFC) model calculations, differentiation of the SVF lithologies can be modelled by approximately 39-47 % fractional crystallisation and 6-15 % crustal assimilation. Notably, the transition from silica-undersaturated to silica-saturated compositions of many felsic lavas in the SVF that is difficult to account for in closed-system models is also well explained by

  1. Loki Patera: A Magma Sea Story

    Science.gov (United States)

    Veeder, G. J.; Matson, D. L.; Rathbun, A. G.

    2005-01-01

    We consider Loki Patera on Io as the surface expression of a large uniform body of magma. Our model of the Loki magma sea is some 200 km across; larger than a lake but smaller than an ocean. The depth of the magma sea is unknown, but assumed to be deep enough that bottom effects can be ignored. Edge effects at the shore line can be ignored to first order for most of the interior area. In particular, we take the dark material within Loki Patera as a thin solidified lava crust whose hydrostatic shape follows Io's isostatic surface (approx. 1815 km radius of curvature). The dark surface of Loki appears to be very smooth on both regional and local (subresolution) scales. The thermal contrast between the low and high albedo areas within Loki is consistent with the observed global correlation. The composition of the model magma sea is basaltic and saturated with dissolved SO2 at depth. Its average, almost isothermal, temperature is at the liquidus for basalt. Additional information is included in the original extended abstract.

  2. Modes of continental extension in a crustal wedge

    KAUST Repository

    Wu, Guangliang

    2015-07-01

    © 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.

  3. Modes of continental extension in a crustal wedge

    KAUST Repository

    Wu, Guangliang; Lavier, Luc L.; Choi, Eunseo

    2015-01-01

    © 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.

  4. Petrogenesis of early cretaceous silicic volcanism in SE Uruguay. The role of mantle and crustal sources

    International Nuclear Information System (INIS)

    Lustrino, Michele; Morbidelli, Lucio; Marrazzo, Marianna; Melluso, Leone; Brotzu, Pietro; Tassinari, Colombo C.G.; Gomes, Celso B.; Ruberti, Excelso

    2010-01-01

    Early Cretaceous (∼129 Ma) silicic rocks crop out in SE Uruguay between the Laguna Merin and Santa Lucia basins in the Lascano, Sierra Sao Miguel, Salamanca and Minas areas. They are mostly rhyolites with minor quartz-trachytes and are nearly contemporaneous with the Parana-Etendeka igneous province and with the first stages of South Atlantic Ocean opening. A strong geochemical variability (particularly evident from Rb/Nb, Nb/Y trace element ratios) and a wide range of Sr-Nd isotopic ratios ( 143 Nd/ 144 Nd (129) =0.51178-0.51209; 87 Sr/ 86 Sr (129) =0.70840-0.72417) characterize these rocks. Geochemistry allows to distinguish two compositional groups, corresponding to the north-eastern (Lascano and Sierra Sao Miguel, emplaced on the Neo-Proterozoic southern sector of the Dom Feliciano mobile belt) and south-eastern localities (Salamanca, Minas, emplaced on the much older (Archean) Nico Perez terrane or on the boundary between the Dom Feliciano and Nico Perez terranes). These compositional differences between the two groups are explained by variable mantle source and crust contributions. The origin of the silicic magmas is best explained by complex processes involving assimilation and fractional crystallization and mixing of a basaltic magma with upper crustal lithologies, for Lascano and Sierra Sao Miguel rhyolites. In the Salamanca and Minas rocks genesis, a stronger contribution from lower crust is indicated. (author)

  5. Economics of Developing Hot Stratigraphic Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Greg Mines; Hillary Hanson; Rick Allis; Joseph Moore

    2014-09-01

    Stratigraphic geothermal reservoirs at 3 – 4 km depth in high heat-flow basins are capable of sustaining 100 MW-scale power plants at about 10 c/kWh. This paper examines the impacts on the levelized cost of electricity (LCOE) of reservoir depth and temperature, reservoir productivity, and drillhole/casing options. For a reservoir at 3 km depth with a moderate productivity index by hydrothermal reservoir standards (about 50 L/s/MPa, 5.6 gpm/psi), an LCOE of 10c/kWh requires the reservoir to be at about 200°C. This is the upper temperature limit for pumps. The calculations assume standard hydrothermal drilling costs, with the production interval completed with a 7 inch liner in an 8.5 inch hole. If a reservoir at 4 km depth has excellent permeability characteristics with a productivity index of 100 L/s/MPa (11.3 gpm/psi), then the LCOE is about 11 c/kWh assuming the temperature decline rate with development is not excessive (< 1%/y, with first thermal breakthrough delayed by about 10 years). Completing wells with modest horizontal legs (e.g. several hundred meters) may be important for improving well productivity because of the naturally high, sub-horizontal permeability in this type of reservoir. Reducing the injector/producer well ratio may also be cost-effective if the injectors are drilled as larger holes.

  6. Kinetics of the Formation and Dissociation of Gas Hydrates from CO<sub>2sub>-CH>4sub> Mixtures

    Directory of Open Access Journals (Sweden)

    Devinder Mahajan

    2012-07-01

    Full Text Available Sequestration of carbon dioxide (CO<sub>2sub> in the form of its hydrates in natural methane (CH<sub>4sub> hydrate reservoirs, via CO<sub>2sub>/CH>4sub> exchange, is an attractive pathway that also yields valuable CH<sub>4sub> gas as product. In this paper, we describe a macroscale experiment to form CO<sub>2sub> and CH<sub>4sub>-CO>2sub> hydrates, under seafloor-mimic conditions, in a vessel fitted with glass windows that provides visualization of hydrates throughout formation and dissociation processes. Time resolved pressure and temperature data as well as images of hydrates are presented. Quantitative gas conversions with pure CO<sub>2sub>, calculated from gas chromatographic measurements yielded values that range from 23 – 59% that correspond to the extent of formed hydrates. In CH<sub>4sub>-rich CH<sub>4sub>-CO>2sub> mixed gas systems, CH<sub>4sub> hydrates were found to form preferentially.

  7. Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997–2008

    Science.gov (United States)

    Lu, Zhong; Dzurisin, Daniel; Biggs, Juliet; Wicks, Charles; McNutt, Steve

    2010-01-01

    Starting soon after the 1997 eruption at Okmok volcano and continuing until the start of the 2008 eruption, magma accumulated in a storage zone centered ~3.5 km beneath the caldera floor at a rate that varied with time. A Mogi-type point pressure source or finite sphere with a radius of 1 km provides an adequate fit to the deformation field portrayed in time-sequential interferometric synthetic aperture radar images. From the end of the 1997 eruption through summer 2004, magma storage increased by 3.2–4.5 × 107 m3, which corresponds to 75–85% of the magma volume erupted in 1997. Thereafter, the average magma supply rate decreased such that by 10 July 2008, 2 days before the start of the 2008 eruption, magma storage had increased by 3.7–5.2 × 107 m3 or 85–100% of the 1997 eruption volume. We propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region. Eventually the effects of continuing magma supply and vesiculation of stored magma caused a critical pressure threshold to be exceeded, triggering the 2008 eruption. A similar pattern of initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption. In both cases, withdrawal of magma during the eruptions depressurized the shallow storage zone, causing significant volcano-wide subsidence and initiating a new intereruption deformation cycle.

  8. Spatial Relationship Between Crustal Structure and Mantle Seismicity in the Vrancea Seismogenic Zone of Romania

    Science.gov (United States)

    Knapp, C. C.; Enciu, D. M.; Knapp, J. H.

    2007-12-01

    Active crustal deformation and subsidence in the Southeast Carpathian foreland has previously been attributed to active foundering of thickened continental lithosphere beneath the Carpathian bend region (Knapp et al, 2005). The present study involves integration of active and passive-source seismic data in order to place constraints on the duration, timing, and scale of crustal deformation in the Carpathian foreland, and in particular to assess the genetic relationship with the Vrancea intermediate-depth seismogenic zone (VSZ). Relocated crustal earthquakes and focal mechanisms were correlated with four deep industry seismic profiles, the reprocessed DACIA PLAN deep seismic profile, and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles. Projection of foreland crustal hypocenters onto the deep seismic lines correlates well with previously identified crustal faults such as the Trotus and Sinaia, as well as the newly identified Ialomita Fault. Specifically, results of this study (1) image the full crustal and uppermost mantle structure of the Focsani Basin in the close proximity of the VSZ, (2) show evidence for a sub-horizontal, slightly east-dipping Moho in the vicinity of the VSZ and thinning of the crust towards the Carpathian orogen, (3) illustrate the conspicuous absence of west-dipping fabrics or structures in the crust and across the Moho, (4) present evidence that the Trotus Fault is a crustal-scale active fault with a dextral sense of motion, (5) suggest that the Paleozoic age Peceneaga-Camena and Capidava-Ovidiu Faults have not been active in post-Paleozoic time, and (6) show evidence for a new active crustal scale sinistral fault, named the Ialomita fault. Both the seismogenic Vrancea body and deformation in the Focsani Basin appear to be concentrically bound by the Trotus Fault in the north and east and the Sinaia-Ialomita Fault in the south, suggesting a coupled deformation between the VSZ and the

  9. On the detectability of Teide volcano magma chambers (Tenerife, Canary Islands) with magnetotelluric data

    Science.gov (United States)

    Piña-Varas, Perla; Ledo, Juanjo; Queralt, Pilar; Marcuello, Alex; Perez, Nemesio

    2018-01-01

    Tenerife has been the subject of numerous studies covering a wide range of fields. Many studies have been focused on characterising the magmatic plumbing system. Even so, a controversy still exists regarding the location and size of the current magma chambers. Several magnetotelluric (MT) surveys have been carried out in the island, but no conductivity anomalies associated with the chambers have been detected. We report the results of a set of tests conducted against the 3-D resistivity model of the island, to determine the characteristics of the detectable chambers with the MT data. The most remarkable results indicate that the MT dataset is incompatible with a large-scale mafic reservoir located at shallower depths than 8 km b.s.l. However, shallower phonolitic chambers smaller than 3 × 3 × 1 km3 could be undetected by the existing MT sites and new data should be acquired to confirm or not their existence. This new information is essential in volcanic islands like Tenerife, since many volcanic hazards are related to the size and depth of the sources of magma. Additionally, a joint interpretation of the obtained results together with other information is summarised in a hypothetical model, allowing us to better understand the internal structure of the island.[Figure not available: see fulltext.

  10. Characteristics of Young Rhyolites at Taupo, New Zealand: Implications for the Sub-Surface Plutonic System

    Science.gov (United States)

    Wilson, C. J.; Charlier, B. L.

    2007-12-01

    The young history of Taupo volcano captures the growth and destruction in the 26.5 ka ca. 530 km3 Oruanui eruption of a large rhyolitic magma body, together with the subsequent rejuvenation of magma sources below the volcano. Integration of field information with petrological and isotopic studies at the whole-pumice and single- crystal scales provide a picture of this history. Several important contrasts are inferred to exist between Taupo and comparably-sized, long-lived silicic foci such at Long Valley and in the Bishop Tuff. At Taupo the following are demonstrable. 1. Even in crystal-poor rhyolites like the Oruanui, many grains are inherited antecrysts or xenocrysts. The Oruanui crystal-poor rhyolite body was an open system, with influxes of crystals (plus melt) from remobilised older crystal mush, melted metasedimentary country rocks and plutonics, and crystal-poor basaltic to andesitic magmas. 2. All the Taupo rhyolites were well mixed prior to eruption, and there are no gradients in the eruption products to suggest that the holding chamber(s) were stratified to any extent. 3. Mafic magmas rose into, interacted with, and ponded on the floors of crystal-poor rhyolite in the Oruanui and Waimihia (3.5 ka) examples, again implying that the chamber floor was sharply defined, not a gradual progression down into a more crystal- rich root zone. 4. Pre-Oruanui activity involved contrasting magma types being generated simultaneously, but erupting from geographically separated vents. Post-Oruanui activity has seen (subtly) contrasting magma groups being erupted from vents in the same geographic area, but separated in time. The Oruanui and post-Oruanui magmas are different and do not appear to be related by consanguinity or by mixing - the Oruanui eruption effectively destroyed its magma body. These features are consistent with rhyolite magma generation at Taupo that is exceptionally fast, driven by high fluxes of mafic magmas into a highly heterogeneous crustal melange

  11. Case Studies of the ROZ CO<sub>2sub> Flood and the Combined ROZ/MPZ CO<sub>2sub> Flood at the Goldsmith Landreth Unit, Ector County, Texas. Using ''Next Generation'' CO<sub>2sub> EOR Technologies to Optimize the Residual Oil Zone CO<sub>2sub> Flood

    Energy Technology Data Exchange (ETDEWEB)

    Trentham, Robert C. [Univ. of Texas, Midland, TX (United States); Melzer, L. Stephen [Univ. of Texas, Midland, TX (United States); Kuuskraa, Vello [Advanced Resources International, Inc., Arlington, VA (United States); Koperna, George [Advanced Resources International, Inc., Arlington, VA (United States)

    2015-06-30

    The technology for CO<sub>2sub> Enhanced Oil Recovery (CO<sub>2sub> EOR) has significantly advanced since the earliest floods were implemented in the 1970s. At least for the Permian Basin region of the U.S., the oil recovery has been now been extended into residual oil zones (ROZs) where the mobile fluid phase is water and immobile phase is oil. But the nature of the formation and fluids within the ROZs has brought some challenges that were not present when flooding the MPZs. The Goldsmith-Landreth project in the Permian Basin was intended to first identify the most pressing issues of the ROZs floods and, secondly, begin to address them with new techniques designed to optimize a flood that commingled the MPZ and the ROZ. The early phase of the research conducted considerable reservoir and fluid characterization work and identified both technical and commercial challenges of producing the enormous quantities of water when flooding the ROZs. It also noted the differing water compositions in the ROZ as compared to the overlying MPZs. A new CO<sub>2sub> gas lift system using a capillary string was successfully applied during the project which conveyed the CO<sub>2sub> to the deeper and differing ROZ reservoir conditions at Goldsmith and added a second capillary string that facilitated applying scale inhibitors to mitigate the scaling tendencies of the mixing ROZ and MPZ formation waters. The project also undertook a reservoir modeling effort, using the acquired reservoir characterization data, to history match both the primary and water flood phases of the MPZ and to establish the initial conditions for a modeling effort to forecast response of the ROZ to CO<sub>2sub> EOR. With the advantage of many profile logs acquired from the operator, some concentration on the original pattern area for the ROZ pilot was accomplished to attempt to perfect the history match for that area. Several optional scenarios for producing the ROZ were simulated seeking to find the

  12. Geology, geochemistry and {sup 40}K-{sup 40}Ar geochronometry of Miocene magmatism in Algiers area, Northern Algeria; La magmatisme miocene de l`Est Algerois, geologie, geochimie et geochronologie {sup 40}K-{sup 40}Ar

    Energy Technology Data Exchange (ETDEWEB)

    Belanteur, O; Ouabadi, A; Semroud, B; Megartsi, M H [Algiers Univ. (Algeria). Faculte des Sciences; Bellon, H; Maury, R C; Coutelle, A [Brest Univ., 29 (France); Fourcade, S [Rennes-1 Univ., 35 (France)

    1996-12-31

    Miocene magmatic rocks outcrop within a narrow coastal strip east of Algiers. They include basaltic and andesitic lava flows and intrusions (Dellys, Cap Djinet), the Thenia granodioritic plug and the dacitic to rhyolitic lavas and pyroclastic flows from Zemmouri El Bahri and El Kerma. Despite the effects of hydrothermal alteration, {sup 40}K-{sup 40}Ar ages coupled with micropalaeontological data lead to recognition of two emplacement events at 16-15 and 14-12 Ma, respectively. All the studied calc-alkaline to potassic calc-alkaline rocks are enriched in highly incompatible elements and display negative Nb anomalies. Acid magmas have a pronounced crustal imprint ({sup 87}Sr{sup 86}Sr{sub i} =3D 0.7082 to 0.7155; {delta}{sup 18}O =3D +9 to +13 per mill) which together with La/Nb ratios argues for the occurrence of upper crustal contamination processes. However, the Nb-depletion of the associated basalts suggest that the studied magmas derive from a mantle source which underwent subduction-related metasomatic enrichments prior to their Miocene emplacement. (authors). 13 refs., 3 figs., 2 tabs.

  13. Energy R and D. Geothermal energy and underground reservoirs; R et D energie. Geothermie et reservoirs souterrains

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-07-01

    Geothermal energy appears as a viable economic alternative among the different renewable energy sources. The French bureau of geological and mining researches (BRGM) is involved in several research and development programs in the domain of geothermal energy and underground reservoirs. This document presents the content of 5 programs: the deep hot dry rock system of Soultz-sous-Forets (construction and testing of the scientific pilot, modeling of the reservoir structure), the development of low and high enthalpy geothermal energy in the French West Indies, the comparison of the geothermal development success of Bouillante (Guadeloupe, French West Indies) with the check of the geothermal development of Nyssiros (Greece) and Pantelleria (Italy), the development of the high enthalpy geothermal potentialities of Reunion Island, and the underground storage of CO{sub 2} emissions in geologic formations (deep aquifers, geothermal reservoirs, abandoned mines or oil reservoirs). (J.S.)

  14. Impact of CO<sub>2sub> on the Evolution of Microbial Communities Exposed to Carbon Storage Conditions, Enhanced Oil Recovery, and CO<sub>2sub> Leakage

    Energy Technology Data Exchange (ETDEWEB)

    Gulliver, Djuna M. [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Gregory, Kelvin B. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Civil and Environmental Engineering; Lowry, Gregory V. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Civil and Environmental Engineering

    2016-06-20

    Geologic carbon storage (GCS) is a crucial part of a proposed mitigation strategy to reduce the anthropogenic carbon dioxide (CO<sub>2sub>) emissions to the atmosphere. During this process, CO<sub>2sub> is injected as super critical carbon dioxide (SC-CO<sub>2sub>) in confined deep subsurface storage units, such as saline aquifers and depleted oil reservoirs. The deposition of vast amounts of CO<sub>2sub> in subsurface geologic formations could unintentionally lead to CO<sub>2sub> leakage into overlying freshwater aquifers. Introduction of CO<sub>2sub> into these subsurface environments will greatly increase the CO<sub>2sub> concentration and will create CO<sub>2sub> concentration gradients that drive changes in the microbial communities present. While it is expected that altered microbial communities will impact the biogeochemistry of the subsurface, there is no information available on how CO<sub>2sub> gradients will impact these communities. The overarching goal of this project is to understand how CO<sub>2sub> exposure will impact subsurface microbial communities at temperatures and pressures that are relevant to GCS and CO<sub>2sub> leakage scenarios. To meet this goal, unfiltered, aqueous samples from a deep saline aquifer, a depleted oil reservoir, and a fresh water aquifer were exposed to varied concentrations of CO<sub>2sub> at reservoir pressure and temperature. The microbial ecology of the samples was examined using molecular, DNA-based techniques. The results from these studies were also compared across the sites to determine any existing trends. Results reveal that increasing CO<sub>2sub> leads to decreased DNA concentrations regardless of the site, suggesting that microbial processes will be significantly hindered or absent nearest the CO<sub>2sub> injection/leakage plume where CO<sub>2sub> concentrations are highest. At CO<sub>2sub> exposures expected downgradient from the CO<sub>2sub> plume, selected microorganisms

  15. Impact of CO<sub>2sub> on the Evolution of Microbial Communities Exposed to Carbon Storage Conditions, Enhanced Oil Recovery, and CO<sub>2sub> Leakage

    Energy Technology Data Exchange (ETDEWEB)

    Gulliver, Djuna [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Gregory, Kelvin B. [Carnegie Mellon Univ., Pittsburgh, PA (United States); Lowry, Gregorgy V. [Carnegie Mellon Univ., Pittsburgh, PA (United States)

    2016-06-20

    Geologic carbon storage (GCS) is a crucial part of a proposed mitigation strategy to reduce the anthropogenic carbon dioxide (CO<sub>2sub>) emissions to the atmosphere. During this process, CO<sub>2sub> is injected as super critical carbon dioxide (SC-CO<sub>2sub>) in confined deep subsurface storage units, such as saline aquifers and depleted oil reservoirs. The deposition of vast amounts of CO<sub>2sub> in subsurface geologic formations could unintentionally lead to CO<sub>2sub> leakage into overlying freshwater aquifers. Introduction of CO<sub>2sub> into these subsurface environments will greatly increase the CO<sub>2sub>2 concentration and will create CO<sub>2sub> concentration gradients that drive changes in the microbial communities present. While it is expected that altered microbial communities will impact the biogeochemistry of the subsurface, there is no information available on how CO<sub>2sub> gradients will impact these communities. The overarching goal of this project is to understand how CO<sub>2sub> exposure will impact subsurface microbial communities at temperatures and pressures that are relevant to GCS and CO<sub>2sub> leakage scenarios. To meet this goal, unfiltered, aqueous samples from a deep saline aquifer, a depleted oil reservoir, and a fresh water aquifer were exposed to varied concentrations of CO<sub>2sub> at reservoir pressure and temperature. The microbial ecology of the samples was examined using molecular, DNA-based techniques. The results from these studies were also compared across the sites to determine any existing trends. Results reveal that increasing CO<sub>2sub> leads to decreased DNA concentrations regardless of the site, suggesting that microbial processes will be significantly hindered or absent nearest the CO<sub>2sub> injection/leakage plume where CO<sub>2sub> concentrations are highest. At CO<sub>2sub> exposures expected downgradient from the CO<sub>2sub> plume, selected microorganisms

  16. Effect of stratification on segregation in carbon dioxide miscible flooding in a water-flooded oil reservoir

    International Nuclear Information System (INIS)

    Bhatti, A.A.; Mahmood, S.M.; Amjad, B.

    2013-01-01

    Oil reservoirs are subjected to tertiary recovery by deploying any enhanced oil recovery (EOR) technique for the recovery of left over oil. Amongst many EOR methods one of the widely applied worldwide is CO/sub 2/ flooding through miscible, near miscible or immiscible displacement processes. CO/sub 2/ flooding process responds to a number of reservoir and fluid characteristics. These characteristics have strong effect on overall efficiency of the displacement process. Better understanding of the effect of different characteristics on displacement process is important to plan an efficient displacement process. In this work, the effect of stratification resulting in gravity segregation of the injected fluid is studied in an oil reservoir which is water-flooded during secondary phase of recovery. Sensitivity analysis is performed through successive simulation on Eclipse 300 (compositional) reservoir simulator. Process involves the continuous CO/sub 2/ injection in an oil reservoir with more than 1/3rd of original oil in place left after water flooding. Reservoir model with four different permeability layers is studied. Four patterns by changing the arrangement of the permeabilities of the layers are analysed. The effect of different arrangement or stratification on segregation of CO/sub 2/ and ultimately on the incremental oil recovery, is investigated. It has been observed that out of four arrangements, upward fining pattern relatively overcame the issue of the segregation of CO/sub 2/ and consequently 33% more oil with half injection volume is recovered when compared with the downward fining pattern. (author)

  17. Crystallization of oxidized, moderately hydrous arc basalt at mid-to-lower crustal pressures

    Science.gov (United States)

    Blatter, D. L.; Sisson, T. W.; Hankins, W. B.

    2012-12-01

    basalts to rhyolites or granites (ASI/wt% SiO2: 0.012-0.014), and do not commonly become peraluminous until SiO2 exceeds 69 wt%. These relations are consistent with plagioclase accompanying mafic silicates during nearly all evolution of arc magmas, with little or no early crystallization interval dominated by augite, unlike these and other high-pressure crystallization results. Possible implications are: (1) Parental basaltic arc magmas generally have <3 wt% H2O, and so saturate with plagioclase earlier than in these and other investigators' experiments, (2) These and other investigators' basaltic starting compositions have appropriate H2O but insufficient normative plagioclase, and so crystallize excessive augite before saturating with plagioclase, (3) Common parental arc magmas are basaltic andesites, not basalts, and undergo early crystallization dominated by orthopyroxene that does not modify melt ASI, and/or (4) The spectrum of common arc magma compositions is dominantly due to mixing of mafic magmas with evolved crustal melts or residual liquids that are saturated with plagioclase, thereby causing the coupled and consistent increase in SiO2 with ASI. What can be stated with confidence is that the simple case of deep crystallization-differentiation of hydrous basalt produces daughter liquids that differ in important aspects from common arc magmas.

  18. Violet Grove CO{sub 2} injection project : monitoring with timelapse VSP surveys

    Energy Technology Data Exchange (ETDEWEB)

    Coueslan, M.; Lawton, D. [Calgary Univ., Calgary, AB (Canada); Jones, M. [Schlumberger Canada Ltd., Calgary, AB (Canada)

    2006-07-01

    Several oil and gas fields in western Canada have been depleted through primary production and secondary recovery methods. Injecting carbon dioxide (CO{sub 2}) into a reservoir can enhance oil recovery (EOR) and has the potential benefit of CO{sub 2} sequestration, which reduces greenhouse gas emissions into the atmosphere. It has been estimated that western Canada has a practical CO{sub 2} storage capacity of about 3.3 Gt in its oil and gas reservoirs. In order to claim a reduction in CO{sub 2} emissions, however, the injected CO{sub 2} must be monitored to prove that it is being trapped in these reservoirs. For that reason, the Violet Grove site, near Drayton Valley, Alberta was chosen as a pilot site to study CO{sub 2} injection into a reservoir for enhanced recovery and carbon sequestration purposes. The reservoir is located in the Cardium Formation in the Pembina Field. It was expected that the CO{sub 2} would flow preferentially in the reservoir's dominant fracture orientation, which is northeast-southwest. Simultaneously acquired time-lapse multicomponent surface and borehole seismic surveys were used to monitor changes in the reservoir. Prior to CO{sub 2} injection, a baseline survey was acquired in March 2005. A second survey was acquired 8 months after CO{sub 2} injection. The borehole seismic data displayed higher bandwidth and increased resolution compared to the surface seismic data. The PS-wave borehole seismic data in particular showed much better results. Together, these seismic surveys provide lateral coverage of the area as well as high resolution images near the observation well. Preliminary results from the time-lapse analysis show an increase of 30 to 60 per cent in the reservoir reflectivity amplitudes in the 8 months between the baseline and monitor surveys, suggesting that the CO{sub 2} flood has progressed southwest of the injector, most likely along the dominant fracture trend. 7 refs., 5 figs.

  19. A glassy lava flow from Toconce volcano and its relation with the Altiplano-Puna Magma Body in Central Andes

    Science.gov (United States)

    Godoy, B.; Rodriguez, I.; Aguilera, F.

    2012-12-01

    Toconce is a composite stratovolcano located at the San Pedro - Linzor volcanic chain (SPLVC). This volcanic chain distributes within the Altiplano-Puna region (Central Andes) which is characterized by extensive rhyodacitic-to-rhyolitic ignimbritic fields, and voluminous domes of dacitic-to-rhyolitic composition (de Silva, 1989). The felsic melts that gave origin to ignimbrites and domes at this area were generated by mixing of mantle-derived magmas and anatectic melts assimilated during their ascent through the thick crust. Thus, partially molten layers exist in the upper crust below the APVC (de Silva et al., 2006). Evidence of large volumes of such melts has been also proposed by geophysical methods (i.e. the Altiplano-Puna Magma Body; Chmielowsky et al., 1999) In this work, petrography and whole rock, mineralogical and melt inclusions geochemistry of a glassy lava flow of Toconce volcano are presented. Petrographically, this lava flow shows a porphyric texture, with euhdral to subhedral plagioclase, ortho- and clino-pyroxene phenocrysts immersed in a glassy groundmass. Geochemically, the lava flow has 64.7% wt. SiO2. The glassy groundmass (~70% wt. SiO2) is more felsic than all the lavas in the volcanic chain (47-68% wt., Godoy et al., 2011). Analyzed orthopyroxene-hosted melt inclusions show an even higher SiO2 content (72-75% wt.), and a decreasing on Al2O3, Na2O, and CaO content with differentiation. Crystallization pressures of this lava flow, obtained using Putirka's two-pyroxene and clinopyroxene-liquid models (Putirka, 2008), range between 6 and 9 kbar. According to crystallization pressures, and major element composition, a felsic source located at shallow crustal pressures - where plagioclase is a stable mineralogical phase - originated the inclusions. This could be related to the presence of the Altiplano-Puna Magma Body (APMB) located below SPLVC. On the other hand, glassy groundmass, and disequilibrium textures in minerals of this lava flow could

  20. Crustal response to lithosphere evolution

    DEFF Research Database (Denmark)

    Artemieva, Irina; Thybo, Hans; Cherepanova, Yulia

    2012-01-01

    We present a new model for the structure of the crust in an area which stretches from the North Atlantic region in the west to the Verkhoyansk Ridge in the east and encompasses Greenland, Iceland, most of Europe, West Siberian basin, and the Siberian cratons. The model is based on critically asse......, thicknesses of different crustal layers, and Pn seismic velocities....... assessed results from various seismic studies, including reflection and refraction profiles and receiver function studies. The region includes a nearly continuous age record for crustal evolution over ca. 3.6-3.8 billion years. We present an analysis of the crustal structure heterogeneity in relation...

  1. Reduced-Order Model for Leakage Through an Open Wellbore from the Reservoir due to Carbon Dioxide Injection

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Lehua [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Oldenburg, Curtis M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2017-07-26

    Potential CO<sub>2sub> leakage through existing open wellbores is one of the most significant hazards that need to be addressed in geologic carbon sequestration (GCS) projects. In the framework of the National Risk Assessment Partnership (NRAP) which requires fast computations for uncertainty analysis, rigorous simulation of the coupled wellbore-reservoir system is not practical. We have developed a 7,200-point look-up table reduced-order model (ROM) for estimating the potential leakage rate up open wellbores in response to CO<sub>2sub> injection nearby. The ROM is based on coupled simulations using T2Well/ECO2H which was run repeatedly for representative conditions relevant to NRAP to create a look-up table response-surface ROM. The ROM applies to a wellbore that fully penetrates a 20-m thick reservoir that is used for CO<sub>2sub> storage. The radially symmetric reservoir is assumed to have initially uniform pressure, temperature, gas saturation, and brine salinity, and it is assumed these conditions are held constant at the far-field boundary (100 m away from the wellbore). In such a system, the leakage can quickly reach quasi-steady state. The ROM table can be used to estimate both the free-phase CO<sub>2sub> and brine leakage rates through an open well as a function of wellbore and reservoir conditions. Results show that injection-induced pressure and reservoir gas saturation play important roles in controlling leakage. Caution must be used in the application of this ROM because well leakage is formally transient and the ROM lookup table was populated using quasi-steady simulation output after 1000 time steps which may correspond to different physical times for the various parameter combinations of the coupled wellbore-reservoir system.

  2. Zircon Hf-O isotopic constraints on the origin of Late Mesozoic felsic volcanic rocks from the Great Xing'an Range, NE China

    Science.gov (United States)

    Gong, Mingyue; Tian, Wei; Fu, Bin; Wang, Shuangyue; Dong, Jinlong

    2018-05-01

    The voluminous Late Mesozoic magmatism was related to extensive re-melting of juvenile materials that were added to the Central East Asia continent in Phanerozoic time. The most favoured magma generation mechanism of Late Mesozoic magmas is partial melting of underplated lower crust that had radiogenic Hf-Nd isotopic characteristics, but this mechanism faces difficulties when interpreting other isotopic data. The tectonic environment controlling the generation of the Late Mesozoic felsic magmas is also in dispute. In this study, we obtained new U-Pb ages, and geochemical and isotopic data of representative Jurassic (154.4 ± 1.5 Ma) and Cretaceous (140.2 ± 1.5 Ma) felsic volcanic samples. The Jurassic sample has inherited zircon cores of Permian age, with depleted mantle-like εHf(t) of +7.4 - +8.5, which is in contrast with those of the magmatic zircons (εHf(t) = +2.4 ± 0.7). Whereas the inherited cores and the magmatic zircons have identical mantle-like δ18O composition ranges (4.25-5.29‰ and 4.69-5.54‰, respectively). These Hf-O isotopic characteristics suggest a mixed source of enriched mantle materials rather than ancient crustal components and a depleted mantle source represented by the inherited Permian zircon core. This mechanism is manifested by the eruption of Jurassic alkaline basalts originated from an enriched mantle source. The Cretaceous sample has high εHf(t) of +7.0 - +10.5, suggesting re-melting of a mafic magma derived from a depleted mantle-source. However, the sub-mantle zircon δ18O values (3.70-4.58‰) suggest the depleted mantle-derived mafic source rocks had experienced high temperature hydrothermal alteration at upper crustal level. Therefore, the Cretaceous felsic magma, if not all, could be generated by re-melting of down-dropped supracrustal volcanic rocks that experienced high temperature oxygen isotope alteration. The two processes, enriched mantle-contribution and supracrustal juvenile material re-melting, are new

  3. Fault-related CO<sub>2sub> degassing, geothermics, and fluid flow in southern California basins---Physiochemical evidence and modeling

    Energy Technology Data Exchange (ETDEWEB)

    Boles, James R. [Univ. of California, Santa Barbara, CA (United States); Garven, Grant [Tufts Univ., Medford, MA (United States)

    2015-08-04

    Our studies have had an important impact on societal issues. Experimental and field observations show that CO<sub>2sub> degassing, such as might occur from stored CO<sub>2sub> reservoir gas, can result in significant stable isotopic disequilibrium. In the offshore South Ellwood field of the Santa Barbara channel, we show how oil production has reduced natural seep rates in the area, thereby reducing greenhouse gases. Permeability is calculated to be ~20-30 millidarcys for km-scale fault-focused fluid flow, using changes in natural gas seepage rates from well production, and poroelastic changes in formation pore-water pressure. In the Los Angeles (LA) basin, our characterization of formation water chemistry, including stable isotopic studies, allows the distinction between deep and shallow formations waters. Our multiphase computational-based modeling of petroleum migration demonstrates the important role of major faults on geological-scale fluid migration in the LA basin, and show how petroleum was dammed up against the Newport-Inglewood fault zone in a “geologically fast” interval of time (less than 0.5 million years). Furthermore, these fluid studies also will allow evaluation of potential cross-formational mixing of formation fluids. Lastly, our new study of helium isotopes in the LA basin shows a significant leakage of mantle helium along the Newport Inglewood fault zone (NIFZ), at flow rates up to 2 cm/yr. Crustal-scale fault permeability (~60 microdarcys) and advective versus conductive heat transport rates have been estimated using the observed helium isotopic data. The NIFZ is an important deep-seated fault that may crosscut a proposed basin decollement fault in this heavily populated area, and appears to allow seepage of helium from the mantle sources about 30 km beneath Los Angeles. The helium study has been widely cited in recent weeks by the news media, both in radio and on numerous web sites.

  4. Fault-Related CO<sub>2sub> Degassing, Geothermics, and Fluid Flow in Southern California Basins--Physiochemical Evidence and Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Garven, Grant [Tufts Univ., Medford, MA (United States)

    2015-08-11

    Our studies have had an important impact on societal issues. Experimental and field observations show that CO<sub>2sub> degassing, such as might occur from stored CO<sub>2sub> reservoir gas, can result in significant stable isotopic disequilibrium. In the offshore South Ellwood field of the Santa Barbara channel, we show how oil production has reduced natural seep rates in the area, thereby reducing greenhouse gases. Permeability is calculated to be ~20-30 millidarcys for km-scale fault-focused fluid flow, using changes in natural gas seepage rates from well production, and poroelastic changes in formation pore-water pressure. In the Los Angeles (LA) basin, our characterization of formation water chemistry, including stable isotopic studies, allows the distinction between deep and shallow formations waters. Our multiphase computational-based modeling of petroleum migration demonstrates the important role of major faults on geological-scale fluid migration in the LA basin, and show how petroleum was dammed up against the Newport-Inglewood fault zone in a “geologically fast” interval of time (less than 0.5 million years). Furthermore, these fluid studies also will allow evaluation of potential cross-formational mixing of formation fluids. Lastly, our new study of helium isotopes in the LA basin shows a significant leakage of mantle helium along the Newport Inglewood fault zone (NIFZ), at flow rates up to 2 cm/yr. Crustal-scale fault permeability (~60 microdarcys) and advective versus conductive heat transport rates have been estimated using the observed helium isotopic data. The NIFZ is an important deep-seated fault that may crosscut a proposed basin decollement fault in this heavily populated area, and appears to allow seepage of helium from the mantle sources about 30 km beneath Los Angeles. The helium study has been widely cited in recent weeks by the news media, both in radio and on numerous web sites.

  5. A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production

    Science.gov (United States)

    Burton-Johnson, A.; Halpin, J.; Whittaker, J. M.; Graham, F. S.; Watson, S. J.

    2017-12-01

    We present recently published findings (Burton-Johnson et al., 2017) on the variability of Antarctic sub-glacial heat flux and the impact from upper crustal geology. Our new method reveals that the upper crust contributes up to 70% of the Antarctic Peninsula's subglacial heat flux, and that heat flux values are more variable at smaller spatial resolutions than geophysical methods can resolve. Results indicate a higher heat flux on the east and south of the Peninsula (mean 81 mWm-2) where silicic rocks predominate, than on the west and north (mean 67 mWm-2) where volcanic arc and quartzose sediments are dominant. Whilst the data supports the contribution of HPE-enriched granitic rocks to high heat flux values, sedimentary rocks can be of comparative importance dependent on their provenance and petrography. Models of subglacial heat flux must utilize a heterogeneous upper crust with variable radioactive heat production if they are to accurately predict basal conditions of the ice sheet. Our new methodology and dataset facilitate improved numerical model simulations of ice sheet dynamics. The most significant challenge faced remains accurate determination of crustal structure, particularly the depths of the HPE-enriched sedimentary basins and the sub-glacial geology away from exposed outcrops. Continuing research (particularly detailed geophysical interpretation) will better constrain these unknowns and the effect of upper crustal geology on the Antarctic ice sheet. Burton-Johnson, A., Halpin, J.A., Whittaker, J.M., Graham, F.S., and Watson, S.J., 2017, A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production: Geophysical Research Letters, v. 44, doi: 10.1002/2017GL073596.

  6. Spatial and temporal patterns of greenhouse gas emissions from Three Gorges Reservoir of China

    Directory of Open Access Journals (Sweden)

    Y. Zhao

    2013-02-01

    Full Text Available Anthropogenic activity has led to significant emissions of greenhouse gas (GHG, which is thought to play important roles in global climate changes. It remains unclear about the kinetics of GHG emissions, including carbon dioxide (CO<sub>2sub>, methane (CH<sub>4sub> and nitrous Oxide (N<sub>2sub>O from the Three Gorges Reservoir (TGR of China, which was formed after the construction of the famous Three Gorges Dam. Here we report monthly measurements for one year of the fluxes of these gases at multiple sites within the TGR region, including three major tributaries, six mainstream sites, two downstream sites and one upstream site. The tributary areas have lower CO<sub>2sub> fluxes than the main storage; CH<sub>4sub> fluxes in the tributaries and upper reach mainstream sites are relative higher. Overall, TGR showed significantly lower CH<sub>4sub> emission rates than most new reservoirs in temperate and tropical regions. We attribute this to the well-oxygenated deep water and high water velocities that may facilitate the consumption of CH<sub>4sub>. TGR's CO<sub>2sub> fluxes were lower than most tropical reservoirs and higher than most temperate systems. This could be explained by the high load of labile soil carbon delivered through erosion to the Yangtze River. Compared to fossil-fuelled power plants of equivalent power output, TGR is a very small GHG emitter – annual CO<sub>2sub>-equivalent emissions are approximately 1.7% of that of a coal-fired generating plant of comparable power output.

  7. Along-axis crustal structure of the Porcupine Basin from seismic refraction data modelling

    Science.gov (United States)

    Prada, Manel; Watremez, Louise; Chen, Chen; O'Reilly, Brian; Minshull, Tim; Reston, Tim; Wagner, Gerlind; Gaws, Viola; Klaschen, Dirk; Shannon, Patrick

    2016-04-01

    The Porcupine Basin is a tongue-shaped offshore basin SW of Ireland that formed during the opening of the North Atlantic Ocean. Its history of development involved several rifting and subsidence phases during the Late Paleozoic and Cenozoic, with a particular major rift phase occurring in Late Jurassic-Early Cretaceous times. Previous work, focused on subsidence analysis, showed that stretching factors (β) in the northern part of the basin are 6. However, recent studies based on seismic reflection and refraction profiles concluded that β in places along the basin axis were significantly higher, and suggested the presence of major crustal faulting and uppermost mantle serpentinization in the basin. Constraining β and the processes related to the formation of the basin will provide insights into aspects such as the tectonic response to lithospheric extension and the thermal evolution of the basin. Here we present the tomography results of five wide-angle seismic (WAS) profiles acquired across and along the basin axis. We used a travel time inversion method to model the WAS data and obtain P-wave velocity (Vp) models of the crust and uppermost mantle, together with the geometry of the main geological interfaces along each of these lines. Coincident seismic reflection profiles to each WAS line were also used to integrate the tectonic structure with the Vp model. These results improved constrains on the location of the base of the crust and allow to estimate maximum β (βmax) along each profile. The analysis shows that βmax values in the northern part of the basin are 5-6 times larger than estimates based on subsidence analysis. Towards the south, βmax increases up to 10, but then rapidly decreases to 3.3 southwards. These values are well within the range of crustal extension at which the crust becomes entirely brittle at magma-poor margins allowing the formation of major crustal faulting and serpentinization of the mantle. In agreement with this observation, Vp

  8. Unraveling the diversity in arc volcanic eruption styles: Examples from the Aleutian volcanic arc, Alaska

    Science.gov (United States)

    Larsen, Jessica F.

    2016-11-01

    The magmatic systems feeding arc volcanoes are complex, leading to a rich diversity in eruptive products and eruption styles. This review focuses on examples from the Aleutian subduction zone, encompassed within the state of Alaska, USA because it exhibits a rich diversity in arc structure and tectonics, sediment and volatile influx feeding primary magma generation, crustal magma differentiation processes, with the resulting outcome the production of a complete range in eruption styles from its diverse volcanic centers. Recent and ongoing investigations along the arc reveal controls on magma production that result in diversity of eruptive products, from crystal-rich intermediate andesites to phenocryst-poor, melt-rich silicic and mafic magmas and a spectrum in between. Thus, deep to shallow crustal "processing" of arc magmas likely greatly influences the physical and chemical character of the magmas as they accumulate in the shallow crust, the flow physics of the magmas as they rise in the conduit, and eruption style through differences in degassing kinetics of the bubbly magmas. The broad spectrum of resulting eruption styles thus depends on the bulk magma composition, melt phase composition, and the bubble and crystal content (phenocrysts and/or microlites) of the magma. Those fundamental magma characteristics are in turn largely determined by the crustal differentiation pathway traversed by the magma as a function of tectonic location in the arc, and/or the water content and composition of the primary magmas. The physical and chemical character of the magma, set by the arc differentiation pathway, as it ascends towards eruption determines the kinetic efficiency of degassing versus the increasing internal gas bubble overpressure. The balance between degassing rate and the rate at which gas bubble overpressure builds then determines the conditions of fragmentation, and ultimately eruption intensity.

  9. INVESTIGATION OF EFFICIENCY IMPROVEMENTS DURING CO2 INJECTION IN HYDRAULICALLY AND NATURALLY FRACTURED RESERVOIRS

    Energy Technology Data Exchange (ETDEWEB)

    David S. Schechter

    2005-04-27

    This report describes the work performed during the fourth year of the project, ''Investigating of Efficiency Improvements during CO{sub 2} Injection in Hydraulically and Naturally Fractured Reservoirs.'' The objective of this project is to perform unique laboratory experiments with artificially fractured cores (AFCs) and X-ray CT scanner to examine the physical mechanisms of bypassing in hydraulically fractured reservoirs (HFR) and naturally fractured reservoirs (NFR) that eventually result in more efficient CO{sub 2} flooding in heterogeneous or fracture-dominated reservoirs. In Chapter 1, we worked with DOE-RMOTC to investigate fracture properties in the Tensleep Formation at Teapot Dome Naval Reserve as part of their CO{sub 2} sequestration project. In Chapter 2, we continue our investigation to determine the primary oil recovery mechanism in a short vertically fractured core. Finally in Chapter 3, we report our numerical modeling efforts to develop compositional simulator with irregular grid blocks.

  10. Crustal contamination processes traced by helium isotopes: Examples from the Sunda arc, Indonesia

    Science.gov (United States)

    Gasparon, M.; Hilton, D. R.; Varne, R.

    1994-08-01

    Helium isotope data have been obtained on well-characterised olivine and clinopyroxene phenocrysts and xenocrysts from thirteen volcanic centres located between central Sumatra and Sumbawa in the Sunda arc of Indonesia. Olivine crystals in mantle xenoliths (Iherzolite) from Bukit Telor basalts are primitive (Mg# = 90), and their He-3/He-4 value (R/R(sub A) = 8.8) indicates that the Sumatran mantle wedge is MORB-like in helium isotope composition. All other samples have lower He-3/He-4 ratios ranging from 8.5R(sub A) to 4.5R(sub A), with most (thirteen out of eighteen) following a trend of more radiogenic He-3/He-4 values with decreasing Mg#. The only exceptions to this trend are phenocrysts from Batur, Agung and Kerinci, which have MORB-like He-3/He-4 values but relatively low Mg# (Mg# = 70-71), and two highly inclusion-rich clinopyroxenes which have He-3/He-4 values lower than other samples of similar Mg#. The results indicate that crustal contamination unrelated to subduction in the Sunda arc is clearly recorded in the He-3/He-4 characteristics of mafic phenocrysts of subaerial volcanics, and that addition of radiogenic helium is related to low-pressure differentiation processes affecting the melts prior to eruption. These conclusions may have widespread applicability and indicate that helium isotope variations can act as an extremely sensitive tracer of upper crustal contamination.

  11. Iron Redox Systematics of Martian Magmas

    Science.gov (United States)

    Righter, K.; Danielson, L.; Martin, A.; Pando, K.; Sutton, S.; Newville, M.

    2011-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite [1]. Morris et al. [1] propose that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks [2,3]. Magnetite stability in terrestrial magmas is well understood, as are the stability of FeO and Fe2O3 in terrestrial magmas [4,5]. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas we have undertaken an experimental study with two emphases. First we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition. Second, we determine the FeO and Fe2O3 contents of the same shergottite bulk composition at 1 bar and variable fO2 at 1250 C, and at variable pressure. These two goals will help define not only magnetite stability, but pyroxene-melt equilibria that are also dependent upon fO2.

  12. Experimental Study of the Partitioning of Siderophile Elements in a Crystallizing Lunar Magma Ocean

    Science.gov (United States)

    Galenas, M.; Righter, K.; Danielson, L.; Pando, K.; Walker, R. J.

    2012-01-01

    The distributions of trace elements between the lunar interior and pristine crustal rocks were controlled by the composition of starting materials, lunar core formation, and crystallization of the lunar magma ocean (LMO) [1]. This study focuses on the partitioning of highly siderophile elements (HSE) including Re, Os, Ir, Ru, Pt, Rh, Pd and Au as well as the moderately siderophile elements Mo and W, and the lithophile elements of Hf and Sr. Our experiments also include Ga, which can be slightly siderophile, but is mostly considered to be chalcophile. Partitioning of these elements is not well known at the conditions of a crystallizing LMO. Previous studies of HSE partitioning in silicate systems have yielded highly variable results for differing oxygen fugacity (fO2) and pressure [2-4]. For example, under certain conditions Pt is compatible in clinopy-roxene [2] and Rh and Ru are compatible in olivine [3]. The silicate compositions used for these experiments were nominally basaltic. Ruthenium, Rh, and Pd are incompatible in plagioclase under these conditions[4]. However, this latter study was done at extremely oxidizing conditions and at atmospheric pressure, possibly limiting the applicability for consideration of conditions of a crystallizing LMO. In this study we address the effects of pressure and oxygen fugacity on the crystal/liquid partition coefficients of these trace elements. We are especially interested in the plagioclase/melt partition coefficients so that it may be possible to use reverse modeling to constrain the concentrations of these elements in the lunar mantle through their abundances in pristine crustal rocks.

  13. The 2nd to 4th century explosive activity of Vesuvius: new data on the timing of the upward migration of the post-A.D. 79 magma chamber

    Directory of Open Access Journals (Sweden)

    Raffaello Cioni

    2013-11-01

    Full Text Available We present volcanological data on the deposits of the Santa Maria Member (SMM, the eruption cycle occurred at Vesuvius (Italy in the period between the A.D. 79 plinian and the A.D. 472 subplinan eruptions. Historical accounts report only sporadic, poorly reliable descriptions of the volcanic activity in this period, during which a stratified sequence of ash and lapilli beds, up to 150 cm thick, with a total volume estimated around 0.15 km3, was widely dispersed on the outer slopes of the volcano. Stratigraphic studies and component analyses suggest that activity was characterized by mixed hydromagmatic and magmatic processes. The eruption style has been interpreted as repeated alternations of continuous and prolonged ash emission activity intercalated with short-lived, violent strombolian phases. Analyses of the bulk rock composition reveal that during the entire eruption cycle, magma maintained an homogeneous phonotephritic composition. In addition, the general trends of major and trace elements depicted by the products of the A.D. 79 and A.D. 472 eruptions converge to the SMM composition, suggesting a common mafic end-member for these eruptions. The volatile content measured in pyroxene-hosted melt inclusions indicates two main values of crystallization pressures, around 220 and 70 MPa, roughly corresponding to the previously estimated depth of the magma reservoirs of the A.D. 79 and A.D. 472 eruptions, respectively. The study of SMM eruption cycle may thus contribute to understand the processes governing the volcano reawakening immediately after a plinian event, and the timing and modalities which govern the migration of the magma reservoir.

  14. Response to Comment on "Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals".

    Science.gov (United States)

    Cooper, Kari M; Till, Christy B; Kent, Adam J R; Costa, Fidel; Rubin, Allison E; Gravley, Darren; Deering, Chad; Cole, Jim; Bose, Maitrayee

    2017-12-22

    In a recent paper, we used Li concentration profiles and U-Th ages to constrain the thermal conditions of magma storage. Wilson and co-authors argue that the data instead reflect control of Li behavior by charge balance during partitioning and not by experimentally determined diffusion rates. Their arguments are based on (i) a coupled diffusion mechanism for Li, which has been postulated but has not been documented to occur, and (ii) poorly constrained zircon growth rates combined with the assumption of continuous zircon crystallization. Copyright © 2017, American Association for the Advancement of Science.

  15. Preliminary crustal deformation model deduced from GPS and earthquakes’ data at Abu-Dabbab area, Eastern Desert, Egypt

    Science.gov (United States)

    Mohamed, Abdel-Monem S.; Hosny, A.; Abou-Aly, N.; Saleh, M.; Rayan, A.

    2013-06-01

    align in an ENE-WSW direction marking a zone of activity verse the Red Sea. The nucleation of the seismic activity beneath the southern part of the Abu-Dabbab crust is more consistent with the obtained crustal deformation result by increasing the crustal movement in the south part than the northern part. Then, based on the obtained results of the above mentioned studies; seismic tomography; source mechanisms, and crustal deformation we conclude that these seismic activities that are associated by crustal deformation are owing to some magma activity beneath the crust of the Abu-Dabbab area.

  16. Novel CO<sub>2sub> Foam Concepts and Injection Schemes for Improving CO<sub>2sub> Sweep Efficiency in Sandstone and Carbonate Hydrocarbon Formations

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Quoc [Univ. of Texas, Austin, TX (United States). Department of Petroleum & Geosystems Engineering; Hirasaki, George [Rice Univ., Houston, TX (United States). Department of Chemical Engineering; Johnston, Keith [Univ. of Texas, Austin, TX (United States). Department of Chemical Engineering

    2015-02-05

    We explored cationic, nonionic and zwitterionic surfactants to identify candidates that have the potential to satisfy all the key requirements for CO<sub>2sub> foams in EOR. We have examined the formation, texture, rheology and stability of CO<sub>2sub> foams as a function of the surfactant structure and formulation variables including temperature, pressure, water/CO<sub>2 sub>ratio, surfactant concentration, salinity and concentration of oil. Furthermore, the partitioning of surfactants between oil and water as well as CO<sub>2sub> and water was examined in conjunction with adsorption measurements on limestone by the Hirasaki lab to develop strategies to optimize the transport of surfactants in reservoirs.

  17. Site characterization of the highest-priority geologic formations for CO<sub>2sub> storage in Wyoming

    Energy Technology Data Exchange (ETDEWEB)

    Surdam, Ronald C. [Univ. of Wyoming, Laramie, WY (United States); Bentley, Ramsey [Univ. of Wyoming, Laramie, WY (United States); Campbell-Stone, Erin [Univ. of Wyoming, Laramie, WY (United States); Dahl, Shanna [Univ. of Wyoming, Laramie, WY (United States); Deiss, Allory [Univ. of Wyoming, Laramie, WY (United States); Ganshin, Yuri [Univ. of Wyoming, Laramie, WY (United States); Jiao, Zunsheng [Univ. of Wyoming, Laramie, WY (United States); Kaszuba, John [Univ. of Wyoming, Laramie, WY (United States); Mallick, Subhashis [Univ. of Wyoming, Laramie, WY (United States); McLaughlin, Fred [Univ. of Wyoming, Laramie, WY (United States); Myers, James [Univ. of Wyoming, Laramie, WY (United States); Quillinan, Scott [Univ. of Wyoming, Laramie, WY (United States)

    2013-12-07

    This study, funded by U.S. Department of Energy National Energy Technology Laboratory award DE-FE0002142 along with the state of Wyoming, uses outcrop and core observations, a diverse electric log suite, a VSP survey, in-bore testing (DST, injection tests, and fluid sampling), a variety of rock/fluid analyses, and a wide range of seismic attributes derived from a 3-D seismic survey to thoroughly characterize the highest-potential storage reservoirs and confining layers at the premier CO<sub>2sub> geological storage site in Wyoming. An accurate site characterization was essential to assessing the following critical aspects of the storage site: (1) more accurately estimate the CO<sub>2sub> reservoir storage capacity (Madison Limestone and Weber Sandstone at the Rock Springs Uplift (RSU)), (2) evaluate the distribution, long-term integrity, and permanence of the confining layers, (3) manage CO<sub>2sub> injection pressures by removing formation fluids (brine production/treatment), and (4) evaluate potential utilization of the stored CO<sub>2sub>

  18. Magma Dynamics in Dome-Building Volcanoes

    Science.gov (United States)

    Kendrick, J. E.; Lavallée, Y.; Hornby, A. J.; Schaefer, L. N.; Oommen, T.; Di Toro, G.; Hirose, T.

    2014-12-01

    The frequent and, as yet, unpredictable transition from effusive to explosive volcanic behaviour is common to active composite volcanoes, yet our understanding of the processes which control this evolution is poor. The rheology of magma, dictated by its composition, porosity and crystal content, is integral to eruption behaviour and during ascent magma behaves in an increasingly rock-like manner. This behaviour, on short timescales in the upper conduit, provides exceptionally dynamic conditions that favour strain localisation and failure. Seismicity released by this process can be mimicked by damage accumulation that releases acoustic signals on the laboratory scale, showing that the failure of magma is intrinsically strain-rate dependent. This character aids the development of shear zones in the conduit, which commonly fracture seismogenically, producing fault surfaces that control the last hundreds of meters of ascent by frictional slip. High-velocity rotary shear (HVR) experiments demonstrate that at ambient temperatures, gouge behaves according to Byerlee's rule at low slip velocities. At rock-rock interfaces, mechanical work induces comminution of asperities and heating which, if sufficient, may induce melting and formation of pseudotachylyte. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The bulk composition, mineralogy and glass content of the magma all influence frictional behaviour, which supersedes buoyancy as the controlling factor in magma ascent. In the conduit of dome-building volcanoes, the fracture and slip processes are further complicated: slip-rate along the conduit margin fluctuates. The shear-thinning frictional melt yields a tendency for extremely unstable slip thanks to its pivotal position with regard to the glass transition. This thermo-kinetic transition bestows the viscoelastic melt with the ability to either flow or

  19. The onset of the volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians): Eruption chronology and magma type variation

    Science.gov (United States)

    Molnár, Kata; Harangi, Szabolcs; Lukács, Réka; Dunkl, István; Schmitt, Axel K.; Kiss, Balázs; Garamhegyi, Tamás; Seghedi, Ioan

    2018-04-01

    volcanic eruptions were often separated by prolonged (ca. 100 to 200 kyr) quiescence periods. Demonstration of recurrence of volcanism even after such long dormancy has to be considered in assessing volcanic hazards, particularly in seemingly inactive volcanic areas, where no Holocene eruptions occurred. The term of 'volcanoes with Potentially Active Magma Storage' illustrates the potential of volcanic rejuvenation for such long-dormant volcanoes with the existence of melt-bearing crustal magma body.

  20. Cost-benefit analyses for the development of magma power

    International Nuclear Information System (INIS)

    Haraden, John

    1992-01-01

    Magma power is the potential generation of electricity from shallow magma bodies in the crust of the Earth. Considerable uncertainty still surrounds the development of magma power, but most of that uncertainty may be eliminated by drilling the first deep magma well. The uncertainty presents no serious impediments to the private drilling of the well. For reasons unrelated to the uncertainty, there may be no private drilling and there may be justification for public drilling. In this paper, we present cost-benefit analyses for private and public drilling of the well. Both analyses indicate there is incentive for drilling. (Author)