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.

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.

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

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.

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.

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)

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.

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.

Large reservoirs: Chapter 17

Science.gov (United States)

Miranda, Leandro E.; Bettoli, Phillip William

2010-01-01

Large impoundments, defined as those with surface area of 200 ha or greater, are relatively new aquatic ecosystems in the global landscape. They represent important economic and environmental resources that provide benefits such as flood control, hydropower generation, navigation, water supply, commercial and recreational fisheries, and various other recreational and esthetic values. Construction of large impoundments was initially driven by economic needs, and ecological consequences received little consideration. However, in recent decades environmental issues have come to the forefront. In the closing decades of the 20th century societal values began to shift, especially in the developed world. Society is no longer willing to accept environmental damage as an inevitable consequence of human development, and it is now recognized that continued environmental degradation is unsustainable. Consequently, construction of large reservoirs has virtually stopped in North America. Nevertheless, in other parts of the world construction of large reservoirs continues. The emergence of systematic reservoir management in the early 20th century was guided by concepts developed for natural lakes (Miranda 1996). However, we now recognize that reservoirs are different and that reservoirs are not independent aquatic systems inasmuch as they are connected to upstream rivers and streams, the downstream river, other reservoirs in the basin, and the watershed. Reservoir systems exhibit longitudinal patterns both within and among reservoirs. Reservoirs are typically arranged sequentially as elements of an interacting network, filter water collected throughout their watersheds, and form a mosaic of predictable patterns. Traditional approaches to fisheries management such as stocking, regulating harvest, and in-lake habitat management do not always produce desired effects in reservoirs. As a result, managers may expend resources with little benefit to either fish or fishing. Some locally

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

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

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

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.

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

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.

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.

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.

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.

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.

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

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.

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.

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

South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically

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.

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.

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

antecrystic zircons require a model where eruptible rhyolites are generated by extracting melt and zircons from a long-lived mush of immobile crystal-rich magma. In this process the larger sanidine crystals remain trapped in the locked crystal network. The extracted melts (plus antecrystic zircon) amalgamate into a liquid dominated (i.e., eruptible) magma body that is maintained as a physically distinct entity relative to the bulk of the long-lived crystal mush. Zircon surfaces and sanidines in each rhyolite crystallize after melt extraction/amalgamation and their ages constrain the residence time of eruptible magmas at Yellowstone. Residence times of the large volume rhyolites (~40 – 70 km3) are ≤ 1 kyr (conservatively < 6 kyr), which suggests that large volumes of rhyolite can be generated rapidly by extracting melt from a crystal mush. Because the lifespan of the crystal mush that sourced the Central Plateau Member rhyolites is two orders of magnitude longer than the residence time of eruptible magma bodies within the reservoir, it is apparent that the Yellowstone magma reservoir spends most of its time in a largely-crystalline (i.e., uneruptible) state, similar to the present-day magma reservoir, and that eruptible magma bodies are ephemeral features.

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.

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.

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

Oxygen isotope study of the Long Valley magma system, California: isotope thermometry and convection in large silicic magma bodies

Science.gov (United States)

Bindeman, Ilya; Valley, John

2002-07-01

Products of voluminous pyroclastic eruptions with eruptive draw-down of several kilometers provide a snap-shot view of batholith-scale magma chambers, and quench pre-eruptive isotopic fractionations (i.e., temperatures) between minerals. We report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite, pyroxene, and zircon from individual pumice clasts of ignimbrite and fall units of caldera-forming 0.76 Ma Bishop Tuff (BT), pre-caldera Glass Mountain (2.1-0.78 Ma), and post-caldera rhyolites (0.65-0.04 Ma) to characterize the long-lived, batholith-scale magma chamber beneath Long Valley Caldera in California. Values of δ18O show a subtle 1‰ decrease from the oldest Glass Mountain lavas to the youngest post-caldera rhyolites. Older Glass Mountain lavas exhibit larger ( 1‰) variability of δ18O(quartz). The youngest domes of Glass Mountain are similar to BT in δ18O(quartz) values and reflect convective homogenization during formation of BT magma chamber surrounded by extremely heterogeneous country rocks (ranging from 2 to +29‰). Oxygen isotope thermometry of BT confirms a temperature gradient between "Late" (815 °C) and "Early" (715 °C) BT. The δ18O(quartz) values of "Early" and "Late" BT are +8.33 and 8.21‰, consistent with a constant δ18O(melt)=7.8+/-0.1‰ and 100 °C temperature difference. Zircon-melt saturation equilibria gives a similar temperature range. Values of δ18O(quartz) for different stratigraphic units of BT, and in pumice clasts ranging in pre-eruptive depths from 6 to 11 km (based on melt inclusions), and document vertical and lateral homogeneity of δ18O(melt). Worldwide, five other large-volume rhyolites, Lava Creek, Lower Bandelier, Fish Canyon, Cerro Galan, and Toba, exhibit equal δ18O(melt) values of earlier and later erupted portions in each of the these climactic caldera-forming eruptions. We interpret the large-scale δ18O homogeneity of BT and other large magma chambers as evidence

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.

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.

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

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.

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

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.

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

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.

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

Magma viscosity estimation based on analysis of erupted products. Potential assessment for large-scale pyroclastic eruptions

International Nuclear Information System (INIS)

Takeuchi, Shingo

2010-01-01

After the formulation of guidelines for volcanic hazards in site evaluation for nuclear installations (e.g. JEAG4625-2009), it is required to establish appropriate methods to assess potential of large-scale pyroclastic eruptions at long-dormant volcanoes, which is one of the most hazardous volcanic phenomena on the safety of the installations. In considering the volcanic dormancy, magma eruptability is an important concept. The magma eruptability is dominantly controlled by magma viscosity, which can be estimated from petrological analysis of erupted materials. Therefore, viscosity estimation of magmas erupted in past eruptions should provide important information to assess future activities at hazardous volcanoes. In order to show the importance of magma viscosity in the concept of magma eruptability, this report overviews dike propagation processes from a magma chamber and nature of magma viscosity. Magma viscosity at pre-eruptive conditions of magma chambers were compiled based on previous petrological studies on past eruptions in Japan. There are only 16 examples of eruptions at 9 volcanoes satisfying data requirement for magma viscosity estimation. Estimated magma viscosities range from 10 2 to 10 7 Pa·s for basaltic to rhyolitic magmas. Most of examples fall below dike propagation limit of magma viscosity (ca. 10 6 Pa·s) estimated based on a dike propagation model. Highly viscous magmas (ca. 10 7 Pa·s) than the dike propagation limit are considered to lose eruptability which is the ability to form dikes and initiate eruptions. However, in some cases, small precursory eruptions of less viscous magmas commonly occurred just before climactic eruptions of the highly viscous magmas, suggesting that the precursory dike propagation by the less viscous magmas induced the following eruptions of highly viscous magmas (ca. 10 7 Pa·s). (author)

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.

The Role of Tectonic Stress in Triggering Large Silicic Caldera Eruptions

Science.gov (United States)

Cabaniss, Haley E.; Gregg, Patricia M.; Grosfils, Eric B.

2018-05-01

We utilize 3-D temperature-dependent viscoelastic finite element models to investigate the mechanical response of the host rock supporting large caldera-size magma reservoirs (volumes >102 km3) to local tectonic stresses. The mechanical stability of the host rock is used to determine the maximum predicted repose intervals and magma flux rates that systems may experience before successive eruption is triggered. Numerical results indicate that regional extension decreases the stability of the roof rock overlying a magma reservoir, thereby promoting early-onset caldera collapse. Alternatively, moderate amounts of compression (≤10 mm/year) on relatively short timescales (stresses on reservoir stability, our models indicate that the process of rejuvenation and mechanical failure is likely to take place over short time periods of hundreds to thousands of years. These findings support the short preeruption melt accumulation timescales indicated by U series disequilibrium studies.

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.

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

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.

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

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

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.

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

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

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.

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.

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

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

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)

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

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.

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.

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

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).

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.

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.

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

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

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.

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

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.

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.

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

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.

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.

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

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

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.

Sustainability of small reservoirs and large scale water availability under current conditions and climate change

NARCIS (Netherlands)

Krol, Martinus S.; de Vries, Marjella J.; van Oel, Pieter R.; Carlos de Araújo, José

2011-01-01

Semi-arid river basins often rely on reservoirs for water supply. Small reservoirs may impact on large-scale water availability both by enhancing availability in a distributed sense and by subtracting water for large downstream user communities, e.g. served by large reservoirs. Both of these impacts

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

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.

The Largs high-latitude oxygen isotope anomaly (New Zealand) and climatic controls of oxygen isotopes in magma

International Nuclear Information System (INIS)

Blattner, P.; Williams, J.G.

1991-01-01

In northern Fiordland the Brook Street terrane of New Zealand consists of two units - the predominantly basaltic Plato and the predominantly andesitic Largs terrane. The Permian Plato terrane has normal to slightly enriched δ 18 O values, whereas the Largs terrane, which is of similar pre-early Triassic age, has not yielded a single normal δ 18 O SMOW result, with all of 17 total rocks showing less than 3.2per mille, seven less than -4per mille, and two less than -9per mille. These strongly anomalous data confirm an earlier suggested terrestrial character of Largs deposition, and demand the presence of Permo-Triassic geothermal systems running on subAntarctic to Antarctic meteoric water. The skewed data spectrum suggests a relatively immature flow system and likely values for the recharge water are -20per mille δ 18 O or less. For a climate distribution similar to the present one, inlcuding polar ice caps, this would indicate over 70deg of southern latitude. Rafts and xenoliths of Largs rocks have been entrained within Mackay Intrusives in the early Triassic. On field evidence the Mackay magmas have also intruded an early Darran Complex, but this complex has been substantially reactivated in the Cretaceous. It has δ 18 O values near 5.0per mille, which is distinctly low for island arc magmas. Since the complex is isotopically homogenous, its δ 18 O is unlikely to be a direct effect of the relatively shallow Largs terrane. More probable is a climate related slight depression of the δ 18 O of magma sources, in which other high-latitude, low-δ 18 O sediments and geothermal systems have been involved. (orig.)

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.

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.

Sustainability of small reservoirs and large scale water availability under current conditions and climate change

OpenAIRE

Krol, Martinus S.; de Vries, Marjella J.; van Oel, P.R.; Carlos de Araújo, José

2011-01-01

Semi-arid river basins often rely on reservoirs for water supply. Small reservoirs may impact on large-scale water availability both by enhancing availability in a distributed sense and by subtracting water for large downstream user communities, e.g. served by large reservoirs. Both of these impacts of small reservoirs are subject to climate change. Using a case-study on North-East Brazil, this paper shows that climate change impacts on water availability may be severe, and impacts on distrib...

Designing adaptive operating rules for a large multi-purpose reservoir

Science.gov (United States)

Geressu, Robel; Rougé, Charles; Harou, Julien

2017-04-01

Reservoirs whose live storage capacity is large compared with annual inflow have "memory", i.e., their storage levels contain information about past inflows and reservoir operations. Such "long-memory" reservoirs can be found in basins in dry regions such as the Nile River Basin in Africa, the Colorado River Basin in the US, or river basins in Western and Central Asia. There the effects of a dry year have the potential to impact reservoir levels and downstream releases for several subsequent years, prompting tensions in transboundary basins. Yet, current reservoir operation rules in those reservoirs do not reflect this by integrating past climate history and release decisions among the factors that influence operating decisions. This work proposes and demonstrates an adaptive reservoir operating rule that explicitly accounts for the recent history of release decisions, and not only current storage level and near-term inflow forecasts. This implies adding long-term (e.g., multiyear) objectives to the existing short-term (e.g., annual) ones. We apply these operating rules to the Grand Ethiopian Renaissance Dam, a large reservoir under construction on the Blue Nile River. Energy generation has to be balanced with the imperative of releasing enough water in low flow years (e.g., the minimum 1, 2 or 3 year cumulative flow) to avoid tensions with downstream countries, Sudan and Egypt. Maximizing the minimum multi-year releases could be of interest for the Nile problem to minimize the impact on performance of the large High Aswan Dam in Egypt. Objectives include maximizing the average and minimum annual energy generation and maximizing the minimum annual, two year and three year cumulative releases. The system model is tested using 30 stochastically generated streamflow series. One can then derive adaptive release rules depending on the value of one- and two-year total releases with respect to thresholds. Then, there are 3 sets of release rules for the reservoir depending

Evidence for large compositional ranges in coeval melts erupted from Kīlauea's summit reservoir: Chapter 7

Science.gov (United States)

Helz, Rosalind T.; Clague, David A.; Mastin, Larry G.; Rose, Timothy R.; Carey, Rebecca; Cayol, Valérie; Poland, Michael P.; Weis, Dominique

2015-01-01

Petrologic observations on Kīlauea's lavas include abundant microprobe analyses of glasses, which show the range of melts available in Kīlauea's summit reservoir over time. During the past two centuries, compositions of melts erupted within the caldera have been limited to MgO = 6.3–7.5 wt%. Extracaldera lavas of the 1959, 1971, and 1974 eruptions contain melts with up to 10.2, 8.9, and 9.2 wt% MgO, respectively, and the 1924 tephra contains juvenile Pele's tears with up to 9.1 wt% MgO. Melt compositions from explosive deposits at Kīlauea, including the Keanakāko‘i (A.D. 1500–1800), Kulanaokuaiki (A.D. 400–1000), and Pāhala (10–25 ka) tephra units, show large ranges of MgO contents. The range of melt MgO is 6.5–11.0 wt% for the Keanakāko‘i; the Kulanaokuaiki extends to 12.5% MgO and the Pāhala Ash includes rare shards with 13–14.5% MgO. The frequency distributions for MgO in the Keanakāko‘i and Kulanaokuaiki glasses are bimodal, suggesting preferential magma storage at two different depths. Kīlauea's summit reservoir contains melts ranging from 6.5 to at least 11.0 wt% MgO, and such melts were available for sampling near instantaneously and repeatedly over centuries. More magnesian melts are inferred to have risen directly from greater depth.

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.

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.

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

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.

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.

Fishery management problems and possibilities on large southeastern reservoirs

Science.gov (United States)

Parsons, John W.

1958-01-01

Principal problems concerning the fisheries of large reservoirs in the Southeast are: inefficient and highly selective exploitation of fish stocks, and protection and reclamation of damaged or threatened fisheries in tailwaters and tributary streams. Seven mainstream reservoirs on which data are available support an average angling pressure of 4.9 trips per acre per year and an average catch of 16 pounds of sport fish and 6 pounds of food fish. Commercial take is 7 pounds per acre. The rate of catch of sport fish, based upon tag returns, is only 3 percent. Sixteen storage reservoirs support an average angling pressure of 5.0 trips per acre per year and an average catch of 13 pounds of sport fish and 1 pound of food fish. Commercial catch is of no significance. Average rate of catch of sport fish is 17 percent of the catchable population. Fish population studies indicate that there are twice as many sport fish and four times as many food fish in mainstream than there are in storage reservoirs.

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.

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.

Rapid Crystallization of the Bishop Magma

Science.gov (United States)

Gualda, G. A.; Anderson, A. T.; Sutton, S. R.

2007-12-01

is 2 orders of magnitude smaller than the shortest durations derived from geochronology. In the current paradigm, this implies that the Bishop magma existed virtually free of crystals for 100-200 ka. Occasional recharge of the system could cause resorption of crystals. The challenge, however, is to explain how a large- volume, liquid- and volatile-rich system, was prevented from erupting for over 100 ka. The trouble is such that it puts into question the whole concept of a long-lived, liquid-rich magma body. Evidence has accumulated to show that the Bishop magma was stratified and did not convect during crystallization, the stratification was established prior to phenocryst crystallization, and crystal migration did not significantly perturb the stratification. All these are simpler to explain if liquid-rich magma only existed for a short period of time, and we estimate the time as being on the order of 1 ka. The geospeedometric timescale inferred can be reconciled with the geochronological evidence if we interpret zircon crystallization ages as reflecting episodic growth in response to waxing and waning of a mushy body, rather than continuous crystallization from liquid-rich magma in a long-lived, large-volume magma body. We speculate that only after 100-200 ka did favorable conditions emerge and allowed for the generation of a large volume of liquid-rich magma. Once such a body of magma was established, it progressed rather quickly towards eruption.

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.

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

Volcán de Colima has a historical record with major explosive eruptions occurring every ~100 years (1606, 1690, 1818, and 1913) followed by intra-Plinian effusive activity. The 1818 and 1913 Plinian eruptions erupted andesitic magmas (Pl > Opx > Cpx >> Hbl + Fe-Ti oxides + Ap and rare resorbed Ol) with homogeneous bulk compositions (1913; 58.3 × 0.5 wt.% SiO2, 1818; 58.9 × 0.2 wt.% SiO2; Saucedo et al., 2010). Instead, intra-Plinian magmas are devoid of hornblende and have compositions of 59-61 wt. % in silica (Savov et al., 2008). Pre-eruptive temperatures of oxide Fe-Ti pairs in 1818 and 1913 products yielded temperatures of 830×20°C colder than intra-Plinian magmas usually >970°C (Luhr et al., 2002) depending on the mineral phase analyzed. Amphibole in 1818 and 1913 products consists of two populations: a) large xenocrysts, with plag-px-Fe-Ti oxide rims with equilibrium pressures and temperatures of 380 MPa and 950 °C (Ridolfi et al., 2010), and b) microphenocryst with equilibrium pressures and temperatures of 190-280 MPa and 870-910 °C, respectively. Some phenocrysts in the 1818 magma have a high pressure core overgrowth by a low pressure rim. In order to understand the storage conditions of Colima explosive magmas we carried out a set of hydrothermal experiments with a 1818 pumice sample. Experiments were water oversaturated and close to the oxygen fugacity of the NNO buffer. Experiments show that amphibole is stable at pressures greater than 75 MPa at 850°C, and greater than 100 MPa at 925°C. For the same range of temperature, plagioclase is stable at pressures below ~210 MPa and 100 MPa, respectively. Experimental plagioclase and experimental glass were analyzed and compared to those from the natural sample, yielding an approximate storage pressure of 210 MPa. This pressure is confirmed by the chemical equilibrium of microphenocrystic amphibole of the natural sample. Given the nearly equivalent composition of the most recent Plinain magmas is

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.

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.

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).

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.

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.

Magma paths at Piton de la Fournaise Volcano

OpenAIRE

Michon , Laurent; Ferrazzini , Valérie; Di Muro , Andrea

2016-01-01

International audience; Several patterns of magma paths have been proposed since the 1980s for Piton de la Fournaise volcano. Given the significant differences, which are presented here, we propose a reappraisal of the magma intrusion paths using a 17-years-long database of volcano-tectonic seismic events and a detailed mapping of the scoria cones. At the edifice scale, the magma propagates along two N120 trending rift zones. They are wide, linear, spotted by small to large scoria cones and r...

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

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

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

Magma storage constrains by compositional zoning of plagioclase from dacites of the caldera forming eruptions of Vetrovoy Isthmus and Lvinaya Past’ Bay (Iturup Island, Kurile Islands)

Science.gov (United States)

Maksimovich, I. A.; Smirnov, S. Z.; Kotov, A. A.; Timina, T. Yu; Shevko, A. V.

2017-12-01

The Vetrovoy Isthmus and the Lvinaya Past’ Bay on the Iturup island (Kuril island arc) are the results of large Plinian eruptions of compositionally similar dacitic magmas. This study is devoted to a comparative analysis of the storage and crystallization conditions for magma reservoirs, which were a source of large-scale explosive eruptions. The plagioclase is most informative mineral in studying of the melt evolution. The studied plagioclases possess a complex zoning patterns, which are not typical for silicic rocks in island-arc systems. It was shown that increase of Ca in the plagioclase up to unusually high An95 is related to increase of H2O pressure in both volcanic magma chambers. The study revealed that minerals of the Vetrovoy Isthmus and Lvinaya Past’ crystallized from compositionally similar melts. Despite the compositional similarity of the melts, the phenocryst assemblage of the Lvinaya Past’ differs from the Vetrovoy Isthmus by the presence of the amphibole, which indicates that the pressure in the magmatic chamber exceeded 1-2 kbar at a 4-6 wt. % of H2O in the melt. The rocks of the Vetrovoy Isthmus do not contain amphibole phenocrysts, but melt and fluid inclusions assemblages in plagioclase demonstrate that the magma degassed in the course of evolution. This is an indication that the pressure did not exceed significantly 1-2 kbar.

Assessment of disturbance at three spatial scales in two large tropical reservoirs

Directory of Open Access Journals (Sweden)

Letícia de Morais

2016-12-01

Full Text Available Large reservoirs are an increasingly common feature across tropical landscapes because of their importance for water supply, flood control and hydropower, but their ecological conditions are infrequently evaluated. Our objective was to assess the range of disturbances for two large tropical reservoirs and their influences on benthic macroinvertebrates. We tested three hypotheses: i a wide variation in the level of environmental disturbance can be observed among sites in the reservoirs; ii the two reservoirs would exhibit a different degree of disturbance level; and iii the magnitude of disturbance would influence the structure and composition of benthic assemblages. For each reservoir, we assessed land use (macroscale, physical habitat structure (mesoscale, and water quality (microscale. We sampled 40 sites in the littoral zones of both Três Marias and São Simão Reservoirs (Minas Gerais, Brazil. At the macroscale, we measured cover percentages of land use categories in buffer areas at each site, where each buffer was a circular arc of 250 m. At the mesoscale, we assessed the presence of human disturbances in the riparian and drawdown zones at the local (site scale. At the microscale, we assessed water quality at each macroinvertebrate sampling station using the Micro Disturbance Index (MDI. To evaluate anthropogenic disturbance of each site, we calculated an integrated disturbance index (IDI from a buffer disturbance index (BDI and a local disturbance index (LDI. For each site, we calculated richness and abundance of benthic macroinvertebrates, Chironomidae genera richness, abundance and percent Chironomidae individuals, abundance and percent EPT individuals, richness and percent EPT taxa, abundance and percent resistant individuals, and abundance and percent non-native individuals. We also evaluated the influence of disturbance on benthic macroinvertebrate assemblages at the entire-reservoir scale. The BDI, LDI and IDI had significantly

The influence of magma viscosity on convection within a magma chamber

Science.gov (United States)

Schubert, M.; Driesner, T.; Ulmer, P.

2012-12-01

magma chamber but the heat loss is limited by the conductive heat transport along the edges. The goal of the study is to consider magma degassing in terms of implementing solubility of water in dependence of temperature, pressure and composition and find a parameterization for the viscosity that considers the developing bubbles. References Ardia, P., Giordano, D., and Schmidt, M. W., 2008, A model for the viscosity of rhyolite as a function of H2O-content and pressure: A calibration based on centrifuge piston cylinder experiments: Geochimica Et Cosmochimica Acta, v. 72, no. 24, p. 6103-6123. Candela, P. A., 1991, Physics of Aqueous Phase Evolution in Plutonic Environments: American Mineralogist, v. 76, no. 7-8, p. 1081-1091. Cathles, L. M., and Shannon, R., 2007, How potassium silicate alteration suggests the formation of porphyry ore deposits begins with the nearly explosive but barren expulsion of large volumes of magmatic water: Earth and Planetary Science Letters, v. 262, no. 1-2, p. 92-108. Giordano, D., Russell, J. K., and Dingwell, D. B., 2008, Viscosity of magmatic liquids: A model: Earth and Planetary Science Letters, v. 271, no. 1-4, p. 123-134. Moore, G., Vennemann, T., and Carmichael, I. S. E., 1998, An empirical model for the solubility of H2O in magmas to 3 kilobars: American Mineralogist, v. 83, no. 1-2, p. 36-42.

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.

The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas

Science.gov (United States)

Su, Yanqing; Huber, Christian; Bachmann, Olivier; Zajacz, Zoltán; Wright, Heather M.; Vazquez, Jorge A.

2016-01-01

The release of large amounts of sulfur to the stratosphere during explosive eruptions affects the radiative balance in the atmosphere and consequentially impacts climate for up to several years after the event. Quantitative estimations of the processes that control the mass balance of sulfur between melt, crystals, and vapor bubbles is needed to better understand the potential sulfur yield of individual eruption events and the conditions that favor large sulfur outputs to the atmosphere. The processes that control sulfur partitioning in magmas are (1) exsolution of volatiles (dominantly H2O) during decompression (first boiling) and during isobaric crystallization (second boiling), (2) the crystallization and breakdown of sulfide or sulfate phases in the magma, and (3) the transport of sulfur-rich vapor (gas influx) from deeper unerupted regions of the magma reservoir. Vapor exsolution and the formation/breakdown of sulfur-rich phases can all be considered as closed-system processes where mass balance arguments are generally easier to constrain, whereas the contribution of sulfur by vapor transport (open system process) is more difficult to quantify. The ubiquitous “excess sulfur” problem, which refers to the much higher sulfur mass released during eruptions than what can be accounted for by amount of sulfur originally dissolved in erupted melt, as estimated from melt inclusion sulfur concentrations (the “petrologic estimate”), reflects the challenges in closing the sulfur mass balance between crystals, melt, and vapor before and during a volcanic eruption. In this work, we try to quantify the relative importance of closed- and open-system processes for silicic arc volcanoes using kinetic models of sulfur partitioning during exsolution. Our calculations show that crystallization-induced exsolution (second boiling) can generate a significant fraction of the excess sulfur observed in crystal-rich arc magmas. This result does not negate the important role of

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.

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

Assessment of nutrient loadings of a large multipurpose prairie reservoir

Science.gov (United States)

Morales-Marín, L. A.; Wheater, H. S.; Lindenschmidt, K. E.

2017-07-01

The relatively low water flow velocities in reservoirs cause them to have high capacities for retaining sediments and pollutants, which can lead to a reduction in downstream nutrient loading. Hence, nutrients can progressively accumulate in reservoirs, resulting in the deterioration of aquatic ecosystems and water quality. Lake Diefenbaker (LD) is a large multipurpose reservoir, located on the South Saskatchewan River (SSR), that serves as a major source of freshwater in Saskatchewan, Canada. Over the past several years, changes in land use (e.g. expansion of urban areas and industrial developments) in the reservoir's catchment have heightened concerns about future water quality in the catchment and in the reservoir. Intensification of agricultural activities has led to an increase in augmented the application of manure and fertilizer for crops and pasture. Although previous research has attempted to quantify nutrient retention in LD, there is a knowledge gap related to the identification of major nutrient sources and quantification of nutrient export from the catchment at different spatial scales. Using the SPAtially Referenced Regression On Watershed (SPARROW) model, this gap has been addressed by assessing water quality regionally, and identifying spatial patterns of factors and processes that affect water quality in the LD catchment. Model results indicate that LD retains about 70% of the inflowing total nitrogen (TN) and 90% of the inflowing total phosphorus (TP) loads, of which fertilizer and manure applied to agricultural fields contribute the greatest proportion. The SPARROW model will be useful as a tool to guide the optimal implementation of nutrient management plans to reduce nutrient inputs to LD.

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.

Magma Chamber Model of Batur Caldera, Bali, Indonesia: Compositional Variation of Two Facies, Large-Volume Dacitic Ignimbrites

Directory of Open Access Journals (Sweden)

Igan S. Sutawidjaja

2015-05-01

Full Text Available DOI:10.17014/ijog.2.2.111-124Batur is one of the finest known calderas on Earth, and is the source of at least two major ignimbrite eruptions with a combined volume of some 84 km3 and 19 km3. These ignimbrites have a similar compositions, raising the question of whether they are geneticaly related. The Batur Ignimbrite-1 (BI-1 is crystal poor, containing rhyodacitic (68 - 70wt % SiO2, white to grey pumices and partly welded and unwelded. The overlying Batur Ignimbrite-2 (BI-2 is a homogeneous grey to black dacitic pumices (64 - 66 wt % SiO2, unwelded and densely welded (40 - 60% vesicularity, crystal and lithic rich. Phase equilibria indicate that the Batur magma equilibrated at temperatures of 1100 - 1300oC with melt water contents of 3 - 6 wt%. The post-eruptive Batur magma was cooler (<1100oC and it is melt more water rich (> 6 wt % H2O. A pressure of 20 kbar is infered from mineral barometry for the Batur magma chamber. Magmatic chamber model is one in which crystals and melt separate from a convecting Batur magma by density differences, resulting in a stratified magma chamber with a homogeneous central zone, a crystal-rich accumulation zone near the walls or base, and a buoyant, melt-rich zone near the top. This is consistent with the estimated magma temperatures and densities: the pre-eruptive BI-1 magma was hoter (1300oC and more volatile rich (6 wt % H2O with density 2.25 g/cm3 than the BI-2 magma (1200oC; 4 wt % H2O in density was higher (2.50 g/cm3. Batur melt characteristics and intensive parameters are consistent with a volatile oversaturation-driven eruption. However, the higher H2O content, high viscosity and low crystal content of the BI-1 magma imply an external eruption trigger.

Hydrogen isotopic fractionation during crystallization of the terrestrial magma ocean

Science.gov (United States)

Pahlevan, K.; Karato, S. I.

2016-12-01

Models of the Moon-forming giant impact extensively melt and partially vaporize the silicate Earth and deliver a substantial mass of metal to the Earth's core. The subsequent evolution of the terrestrial magma ocean and overlying vapor atmosphere over the ensuing 105-6 years has been largely constrained by theoretical models with remnant signatures from this epoch proving somewhat elusive. We have calculated equilibrium hydrogen isotopic fractionation between the magma ocean and overlying steam atmosphere to determine the extent to which H isotopes trace the evolution during this epoch. By analogy with the modern silicate Earth, the magma ocean-steam atmosphere system is often assumed to be chemically oxidized (log fO2 QFM) with the dominant atmospheric vapor species taken to be water vapor. However, the terrestrial magma ocean - having held metallic droplets in suspension - may also exhibit a much more reducing character (log fO2 IW) such that equilibration with the overlying atmosphere renders molecular hydrogen the dominant H-bearing vapor species. This variable - the redox state of the magma ocean - has not been explicitly included in prior models of the coupled evolution of the magma ocean-steam atmosphere system. We find that the redox state of the magma ocean influences not only the vapor speciation and liquid-vapor partitioning of hydrogen but also the equilibrium isotopic fractionation during the crystallization epoch. The liquid-vapor isotopic fractionation of H is substantial under reducing conditions and can generate measurable D/H signatures in the crystallization products but is largely muted in an oxidizing magma ocean and steam atmosphere. We couple equilibrium isotopic fractionation with magma ocean crystallization calculations to forward model the behavior of hydrogen isotopes during this epoch and find that the distribution of H isotopes in the silicate Earth immediately following crystallization represents an oxybarometer for the terrestrial

Innovation-driven efficient development of the Longwangmiao Fm large-scale sulfur gas reservoir in Moxi block, Sichuan Basin

Directory of Open Access Journals (Sweden)

Xinhua Ma

2016-03-01

Full Text Available The Lower Cambrian Longwangmiao Fm gas reservoir in Moxi block of the Anyue Gas field, Sichuan Basin, is the largest single-sandbody integrated carbonate gas reservoir proved so far in China. Notwithstanding this reservoir's advantages like large-scale reserves and high single-well productivity, there are multiple complicated factors restricting its efficient development, such as a median content of hydrogen sulfide, low porosity and strong heterogeneity of fracture–cave formation, various modes of gas–water occurrences, and close relation between overpressure and stress sensitivity. Up till now, since only a few Cambrian large-scale carbonate gas reservoirs have ever been developed in the world, there still exists some blind spots especially about its exploration and production rules. Besides, as for large-scale sulfur gas reservoirs, the exploration and construction is costly, and production test in the early evaluation stage is severely limited, all of which will bring about great challenges in productivity construction and high potential risks. In this regard, combining with Chinese strategic demand of strengthening clean energy supply security, the PetroChina Southwest Oil & Gas Field Company has carried out researches and field tests for the purpose of providing high-production wells, optimizing development design, rapidly constructing high-quality productivity and upgrading HSE security in the Longwangmiao Fm gas reservoir in Moxi block. Through the innovations of technology and management mode within 3 years, this gas reservoir has been built into a modern large-scale gas field with high quality, high efficiency and high benefit, and its annual capacity is now up to over 100 × 108 m3, with a desirable production capacity and development indexes gained as originally anticipated. It has become a new model of large-scale gas reservoirs with efficient development, providing a reference for other types of gas reservoirs in China.

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

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.

238U-230Th-226Ra systematics applied to the active oceanic volcanism. Constraints on the duration and processes of magmas formation

International Nuclear Information System (INIS)

Claude-Ivana, Ch.

1997-02-01

The development of a new precise analytical technique for measuring radioactive disequilibria by TIMS has enabled to put constraints on both the extend and time scale of incompatible element fractionation during magma formation in oceanic islands. Three different settings have been studied: the Grande Comore volcanoes (Comores archipelago), Tenerife and Lanzarote volcanism (Canary islands) and four islands within the Azores: Sao Miguel, Terceira, Pico and Faial islands. The Comores and Canaries archipelagoes are both lying on an old thick oceanic lithosphere. The detailed case in Grande Comore shows evidence for a process of interaction of the Comore plume with the underlying lithosphere. In the Canaries, the lithosphere also contributes to lava formation either during the differentiation (in Tenerife) or during mantle melting (in Lanzarote). Within the Azores, U-series measurements reveal large geochemical and isotopic variations between the different islands that we interpret as reflecting heterogeneities in the Azore plume. In particular, the U-Th fractionation in Sao Miguel volcanics is though to result from melting of an hydrous sediment-bearing mantle. The magma transit times have been found to be very short (1000 yr) in all the basaltic series. This very rapid migration of the melts is an evidence for the absence of large magma chamber and for processes of fracturing during melt transports. However, this model does not apply in the case of the very evolved volcanic series in Tenerife island (Canaries) where transit times of c.a. 100000 yr indicate the presence of a large magmatic reservoir. (author)

{sup 238}U-{sup 230}Th-{sup 226}Ra systematics applied to the active oceanic volcanism. Constraints on the duration and processes of magmas formation; Systematique {sup 238}U-{sup 230}Th-{sup 226}Ra appliquee au volcanisme actif oceanique. Contraintes sur la duree et les processus de formation des magmas

Energy Technology Data Exchange (ETDEWEB)

Claude-Ivana, Ch

1997-02-01

The development of a new precise analytical technique for measuring radioactive disequilibria by TIMS has enabled to put constraints on both the extend and time scale of incompatible element fractionation during magma formation in oceanic islands. Three different settings have been studied: the Grande Comore volcanoes (Comores archipelago), Tenerife and Lanzarote volcanism (Canary islands) and four islands within the Azores: Sao Miguel, Terceira, Pico and Faial islands. The Comores and Canaries archipelagoes are both lying on an old thick oceanic lithosphere. The detailed case in Grande Comore shows evidence for a process of interaction of the Comore plume with the underlying lithosphere. In the Canaries, the lithosphere also contributes to lava formation either during the differentiation (in Tenerife) or during mantle melting (in Lanzarote). Within the Azores, U-series measurements reveal large geochemical and isotopic variations between the different islands that we interpret as reflecting heterogeneities in the Azore plume. In particular, the U-Th fractionation in Sao Miguel volcanics is though to result from melting of an hydrous sediment-bearing mantle. The magma transit times have been found to be very short (1000 yr) in all the basaltic series. This very rapid migration of the melts is an evidence for the absence of large magma chamber and for processes of fracturing during melt transports. However, this model does not apply in the case of the very evolved volcanic series in Tenerife island (Canaries) where transit times of c.a. 100000 yr indicate the presence of a large magmatic reservoir. (author)

Geophysical Investigations of Magma Plumbing Systems at Cerro Negro Volcano, Nicaragua

Science.gov (United States)

MacQueen, Patricia Grace

Cerro Negro near Leon, Nicaragua is a very young (163 years), relatively small basaltic cinder cone volcano that has been unusually active during its short lifespan (recurrence interval 6--7 years), presenting a significant hazard to nearby communities. Previous studies have raised several questions as to the proper classification of Cerro Negro and its relation to neighboring Las Pilas-El Hoyo volcano. Analysis of Bouguer gravity data collected at Cerro Negro has revealed connected positive density anomalies beneath Cerro Negro and Las Pilas-El Hoyo. These findings suggest that eruptions at Cerro Negro may be tapping a large magma reservoir beneath Las Pilas-El Hoyo, implying that Cerro Negro should be considered the newest vent on the Las Pilas-El Hoyo volcanic complex. As such, it is possible that the intensity of volcanic hazards at Cerro Negro may eventually increase in the future to resemble those pertaining to a stratovolcano. Keywords: Cerro Negro; Las Pilas-El Hoyo; Bouguer gravity; magmatic plumbing systems; potential fields; volcano.

a Stochastic Approach to Multiobjective Optimization of Large-Scale Water Reservoir Networks

Science.gov (United States)

Bottacin-Busolin, A.; Worman, A. L.

2013-12-01

A main challenge for the planning and management of water resources is the development of multiobjective strategies for operation of large-scale water reservoir networks. The optimal sequence of water releases from multiple reservoirs depends on the stochastic variability of correlated hydrologic inflows and on various processes that affect water demand and energy prices. Although several methods have been suggested, large-scale optimization problems arising in water resources management are still plagued by the high dimensional state space and by the stochastic nature of the hydrologic inflows. In this work, the optimization of reservoir operation is approached using approximate dynamic programming (ADP) with policy iteration and function approximators. The method is based on an off-line learning process in which operating policies are evaluated for a number of stochastic inflow scenarios, and the resulting value functions are used to design new, improved policies until convergence is attained. A case study is presented of a multi-reservoir system in the Dalälven River, Sweden, which includes 13 interconnected reservoirs and 36 power stations. Depending on the late spring and summer peak discharges, the lowlands adjacent to Dalälven can often be flooded during the summer period, and the presence of stagnating floodwater during the hottest months of the year is the cause of a large proliferation of mosquitos, which is a major problem for the people living in the surroundings. Chemical pesticides are currently being used as a preventive countermeasure, which do not provide an effective solution to the problem and have adverse environmental impacts. In this study, ADP was used to analyze the feasibility of alternative operating policies for reducing the flood risk at a reasonable economic cost for the hydropower companies. To this end, mid-term operating policies were derived by combining flood risk reduction with hydropower production objectives. The performance

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.

Chlorine as a geobarometer tool: Application to the large explosive eruptions of Vesuvius

Science.gov (United States)

Balcone-Boissard, Hélène; Boudon, Georges; Cioni, Raffaello; Zdanowicz, Géraldine; Orsi, Giovanni; Civetta, Lucia

2015-04-01

One of the current stakes in modern volcanology is the definition of magma storage conditions which has direct implications on the eruptive style and thus on the associated risks and the management of likely related crisis. In alkaline differentiated magmas, chlorine (Cl), contrary to H2O, occurs as a minor volatile species but may be used as a geobarometer. Numerous experimental studies on Cl solubility have highlighted its saturation conditions in alkaline silicate melts. The NaCl-H2O system is characterized by immiscibility under wide ranges of pressure, temperature and NaCl content (pre-eruptive H2O content for the different magma compositions, varying between 3.5 and 7 wt%. The results, in large agreement with literature, are very promising. The Cl geobarometer may help scientists to define the reservoir dynamics through time and provide strong constraints on pre-eruptive conditions, of outmost importance for the interpretation of the monitoring data and the identification of precursory signals.

Magma chamber processes in central volcanic systems of Iceland

DEFF Research Database (Denmark)

Þórarinsson, Sigurjón Böðvar; Tegner, Christian

2009-01-01

are composed of 2-10 m thick melanocratic layers rich in clinopyroxene and sometimes olivine, relative to the thicker overlying leucocratic oxide gabbros. While the overall compositional variation is limited (Mg# clinopyroxene 72-84; An% plagioclase 56-85), the melanocratic bases display spikes in Mg# and Cr2O......3 of clinopyroxene and magnetite indicative of magma replenishment. Some macrorhythmic units show mineral trends indicative of up-section fractional crystallisation over up to 100 m, whereas others show little variation. Two populations of plagioclase crystals (large, An-rich and small, less An......-rich) indicate that the recharge magma carried plagioclase xenocrysts (high An-type). The lack of evolved gabbros suggests formation in a dynamic magma chamber with frequent recharge, tapping and fractionation. Modelling of these compositional trends shows that the parent magma was similar to known transitional...

Influence of volatile degassing on the eruptibility of large igneous province magmatic systems

Science.gov (United States)

Mittal, T.; Richards, M. A.

2017-12-01

Magmatic volatiles, in particular their buoyancy, may play a critical role in determining whether a magma reservoir can build up enough overpressure leading to drive flood basalt eruptions (Black & Manga 2017). Thus, it is important to understand the extent to which volatiles can remain trapped in a magmatic system and how they influence the eruptibility. Although the high-temperature metamorphic aureloe around a magma chamber is typically considered to have low permeability due to ductile creep, recent theoretical, experimental, and field work (e.g. Noriaki et al. 2017) have highlighted the role of dynamic permeability in magmatic systems. Consequently, the effective permeability of the crust when magma is present in the system can be orders of magnitude larger than that of exhumed rock samples. We model dynamic permeability changes as a competition between hydro-fracturing (increased porosity) and fracture closure by ductile creep and hydrothermal mineral precipitation (reduced porosity) and find yearly-to-decadal time-scales for periodic fracturing and fluid loss events and an increase in average permeability. We then use a fully coupled poro-thermo-elastic framework to model to explore the macroscopic influence of volatile loss on the stress state of the crust in this higher time-averaged permeability setting. We derive new semi-analytical solutions and combine them with a magma chamber box model (modified from Degruyter & Huber 2014) to analyze system-scale dynamics for both basaltic and silicic magmatic systems. We find that passive degassing likely has a substantial temporal influence on the stress distribution in the crust and the highly crystalline mush zone immediately surrounding a magma reservoir, and find an additional scale : pore-pressure diffusion timescale that exerts a first-order control on the magnitude and frequency of volcanic eruptions. We also explore how disconnected magma batches interact indirectly with each other and its implications for

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

Timescales of Quartz Crystallization and the Longevity of the Bishop Giant Magma Body

Energy Technology Data Exchange (ETDEWEB)

Gualda, Guilherme A.R.; Pamukcu, Ayla S.; Ghiorso, Mark S.; Anderson, Jr. , Alfred T.; Sutton, Stephen R.; Rivers, Mark L. (OFM Res.); (Vanderbilt); (UC)

2013-04-08

Supereruptions violently transfer huge amounts (100 s-1000 s km{sup 3}) of magma to the surface in a matter of days and testify to the existence of giant pools of magma at depth. The longevity of these giant magma bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant magma body, which erupted {approx}760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop magma body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of <10,000 years, more typically within 500-3,000 years before eruption. We conclude that large-volume, crystal-poor magma bodies are ephemeral features that, once established, evolve on millennial timescales. We also suggest that zircon crystals, rather than recording the timescales of crystallization of a large pool of crystal-poor magma, record the extended periods of time necessary for maturation of the crust and establishment of these giant magma bodies.

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

Ensemble seasonal forecast of extreme water inflow into a large reservoir

Directory of Open Access Journals (Sweden)

A. N. Gelfan

2015-06-01

Full Text Available An approach to seasonal ensemble forecast of unregulated water inflow into a large reservoir was developed. The approach is founded on a physically-based semi-distributed hydrological model ECOMAG driven by Monte-Carlo generated ensembles of weather scenarios for a specified lead-time of the forecast (3 months ahead in this study. Case study was carried out for the Cheboksary reservoir (catchment area is 374 000 km2 located on the middle Volga River. Initial watershed conditions on the forecast date (1 March for spring freshet and 1 June for summer low-water period were simulated by the hydrological model forced by daily meteorological observations several months prior to the forecast date. A spatially distributed stochastic weather generator was used to produce time-series of daily weather scenarios for the forecast lead-time. Ensemble of daily water inflow into the reservoir was obtained by driving the ECOMAG model with the generated weather time-series. The proposed ensemble forecast technique was verified on the basis of the hindcast simulations for 29 spring and summer seasons beginning from 1982 (the year of the reservoir filling to capacity to 2010. The verification criteria were used in order to evaluate an ability of the proposed technique to forecast freshet/low-water events of the pre-assigned severity categories.

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.

Application of parallel computing techniques to a large-scale reservoir simulation

International Nuclear Information System (INIS)

Zhang, Keni; Wu, Yu-Shu; Ding, Chris; Pruess, Karsten

2001-01-01

Even with the continual advances made in both computational algorithms and computer hardware used in reservoir modeling studies, large-scale simulation of fluid and heat flow in heterogeneous reservoirs remains a challenge. The problem commonly arises from intensive computational requirement for detailed modeling investigations of real-world reservoirs. This paper presents the application of a massive parallel-computing version of the TOUGH2 code developed for performing large-scale field simulations. As an application example, the parallelized TOUGH2 code is applied to develop a three-dimensional unsaturated-zone numerical model simulating flow of moisture, gas, and heat in the unsaturated zone of Yucca Mountain, Nevada, a potential repository for high-level radioactive waste. The modeling approach employs refined spatial discretization to represent the heterogeneous fractured tuffs of the system, using more than a million 3-D gridblocks. The problem of two-phase flow and heat transfer within the model domain leads to a total of 3,226,566 linear equations to be solved per Newton iteration. The simulation is conducted on a Cray T3E-900, a distributed-memory massively parallel computer. Simulation results indicate that the parallel computing technique, as implemented in the TOUGH2 code, is very efficient. The reliability and accuracy of the model results have been demonstrated by comparing them to those of small-scale (coarse-grid) models. These comparisons show that simulation results obtained with the refined grid provide more detailed predictions of the future flow conditions at the site, aiding in the assessment of proposed repository performance

Mathematical modeling of large floating roof reservoir temperature arena

Directory of Open Access Journals (Sweden)

Liu Yang

2018-03-01

Full Text Available The current study is a simplification of related components of large floating roof tank and modeling for three dimensional temperature field of large floating roof tank. The heat transfer involves its transfer between the hot fluid in the oil tank, between the hot fluid and the tank wall and between the tank wall and the external environment. The mathematical model of heat transfer and flow of oil in the tank simulates the temperature field of oil in tank. Oil temperature field of large floating roof tank is obtained by numerical simulation, map the curve of central temperature dynamics with time and analyze axial and radial temperature of storage tank. It determines the distribution of low temperature storage tank location based on the thickness of the reservoir temperature. Finally, it compared the calculated results and the field test data; eventually validated the calculated results based on the experimental results.

Amphibole as an archivist of magmatic crystallization conditions: problems, potential, and implications for inferring magma storage prior to the paroxysmal 2010 eruption of Mount Merapi, Indonesia

Science.gov (United States)

Erdmann, Saskia; Martel, Caroline; Pichavant, Michel; Kushnir, Alexandra

2014-06-01

Amphibole is widely employed to calculate crystallization temperature and pressure, although its potential as a geobarometer has always been debated. Recently, Ridolfi et al. (Contrib Mineral Petrol 160:45-66, 2010) and Ridolfi and Renzulli (Contrib Mineral Petrol 163:877-895, 2012) have presented calibrations for calculating temperature, pressure, fO2, melt H2O, and melt major and minor oxide composition from amphibole with a large compositional range. Using their calibrations, we have (i) calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations; and (ii) calculated crystallization conditions for amphibole from basaltic-andesitic pyroclasts erupted during the paroxysmal 2010 eruption of Mount Merapi in Java, Indonesia, to infer pre-eruptive conditions. Our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates. Calculated fO2 and melt SiO2 content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions. However, calculated crystallization pressure and melt H2O content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters. Amphibole from Merapi's pyroclasts yields calculated conditions of ~200-800 MPa, ~900-1,050 °C, ~NNO + 0.3-NNO + 1.1, ~3.7-7.2 wt% melt H2O, and ~58-71 wt% melt SiO2. We interpret the variations in calculated temperature, fO2, and melt SiO2 content as reasonable estimates, but conclude that the large calculated pressure variation for amphibole from Merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range. In contrast, bimodal pressure estimates obtained for other arc magmas

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

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

Large Scale Landslide Database System Established for the Reservoirs in Southern Taiwan

Science.gov (United States)

Tsai, Tsai-Tsung; Tsai, Kuang-Jung; Shieh, Chjeng-Lun

2017-04-01

Typhoon Morakot seriously attack southern Taiwan awaken the public awareness of large scale landslide disasters. Large scale landslide disasters produce large quantity of sediment due to negative effects on the operating functions of reservoirs. In order to reduce the risk of these disasters within the study area, the establishment of a database for hazard mitigation / disaster prevention is necessary. Real time data and numerous archives of engineering data, environment information, photo, and video, will not only help people make appropriate decisions, but also bring the biggest concern for people to process and value added. The study tried to define some basic data formats / standards from collected various types of data about these reservoirs and then provide a management platform based on these formats / standards. Meanwhile, in order to satisfy the practicality and convenience, the large scale landslide disasters database system is built both provide and receive information abilities, which user can use this large scale landslide disasters database system on different type of devices. IT technology progressed extreme quick, the most modern system might be out of date anytime. In order to provide long term service, the system reserved the possibility of user define data format /standard and user define system structure. The system established by this study was based on HTML5 standard language, and use the responsive web design technology. This will make user can easily handle and develop this large scale landslide disasters database system.

Crystalline heterogeneities and instabilities in thermally convecting magma chamber

Science.gov (United States)

Culha, C.; Suckale, J.; Qin, Z.

2016-12-01

A volcanic vent can supply different densities of crystals over an eruption time period. This has been seen in Hawai'i's Kilauea Iki 1959 eruption; however it is not common for all Kilauea or basaltic eruptions. We ask the question: Under what conditions can homogenous magma chamber cultivate crystalline heterogeneities? In some laboratory experiments and numerical simulations, a horizontal variation is observed. The region where crystals reside is identified as a retention zone: convection velocity balances settling velocity. Simulations and experiments that observe retention zones assume crystals do not alter the convection in the fluid. However, a comparison of experiments and simulations of convecting magma with crystals suggest that large crystal volume densities and crystal sizes alter fluid flow considerably. We introduce a computational method that fully resolves the crystalline phase. To simulate basaltic magma chambers in thermal convection, we built a numerical solver of the Navier-Stoke's equation, continuity equation, and energy equation. The modeled magma is assumed to be a viscous, incompressible fluid with a liquid and solid phase. Crystals are spherical, rigid bodies. We create Rayleigh-Taylor instability through a cool top layer and hot bottom layer and update magma density while keeping crystal temperature and size constant. Our method provides a detailed picture of magma chambers, which we compare to other models and experiments to identify when and how crystals alter magma chamber convection. Alterations include stratification, differential settling and instabilities. These characteristics are dependent on viscosity, convection vigor, crystal volume density and crystal characteristics. We reveal that a volumetric crystal density variation may occur over an eruption time period, if right conditions are met to form stratifications and instabilities in magma chambers. These conditions are realistic for Kilauea Iki's 1959 eruption.

Effects of Rotation on the Differentiation of a terrestrial Magma Ocean

Science.gov (United States)

Maas, C.; Hansen, U.

2014-12-01

It is widely accepted that the Earth experienced several large impacts during its early evolution which led to the formation of one or more magma oceans. Differentiation processes in such a magma ocean are of great importance for the initial conditions of mantle convection and for the subsequent mantle structure. Convection in a magma ocean is most likely very vigorous. Further, rotation of the early Earth is supposed to be very fast. Therefore, and due to the small viscosity, it can be assumed that differentiation is strongly affected by rotation.To study the influence of rotation on the crystallization of a magma ocean, we employed a 3D Cartesian numerical model with low Prandtl number and used a discrete element method to describe silicate crystals.Our results show a crucial dependence on crystal density, rotation rate and latitude. Low rotation at the pole leads to a large fraction of suspended particles. With increasing rotation the particles settle at the bottom and form a stable stratified layer. In contrast to that at the equator at low rotation all particles settle at the bottom, at higher rotation they form a layer of significant thickness and at the highest rotation rate the particles accumulate in the middle of the magma ocean. In addition to that, we observe that due to the Coriolis force silicate crystals with different densities separate from each other. While lighter particles are at the bottom, denser particles accumulate at mid-depth at the same rotation rate. This could result in an unstable stratified mantle in the equatorial region after magma ocean solidification.All in all, rotation could lead to an asymmetrical crystallization of the magma ocean, with a contrary layering at the pole and the equator. This affects the composition of the early mantle and could explain the development of a localized magma ocean at the core-mantle boundary and the development of phase transitions observed in seismology, like the mantle transition zone.

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

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.

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.

The parent magma of the nakhlite meteorites - Clues from melt inclusions

Science.gov (United States)

Harvey, Ralph P.; Mcsween, Harry Y., Jr.

1992-01-01

Several forms of trapped liquid found within nakhlite meteorites have been examined, including interstitial melt and magmatic inclusions within the cores of large olivine grains. Differences in the mineralogy and texture between two types of trapped melt inclusions, and between these inclusions and the mesostasis, indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early-forming olivine and augite. Parent liquids were calculated from the mineralogy of large inclusions in Nakhla and Governador Valadares, using a system of mass-balance equations solved by linear regression methods. The chosen parental liquids were cosaturated in olivine and augite and had Mg/Fe values consistent with measured augite/liquid Kds. These parental magma compositions are similar to other published compositions for Nakhla, Chassigny, and Shergotty parental melts, and may correspond to a significant magma type on Mars.

Pressure waves in a supersaturated bubbly magma

Science.gov (United States)

Kurzon, I.; Lyakhovsky, V.; Navon, O.; Chouet, B.

2011-01-01

We study the interaction of acoustic pressure waves with an expanding bubbly magma. The expansion of magma is the result of bubble growth during or following magma decompression and leads to two competing processes that affect pressure waves. On the one hand, growth in vesicularity leads to increased damping and decreased wave amplitudes, and on the other hand, a decrease in the effective bulk modulus of the bubbly mixture reduces wave velocity, which in turn, reduces damping and may lead to wave amplification. The additional acoustic energy originates from the chemical energy released during bubble growth. We examine this phenomenon analytically to identify conditions under which amplification of pressure waves is possible. These conditions are further examined numerically to shed light on the frequency and phase dependencies in relation to the interaction of waves and growing bubbles. Amplification is possible at low frequencies and when the growth rate of bubbles reaches an optimum value for which the wave velocity decreases sufficiently to overcome the increased damping of the vesicular material. We examine two amplification phase-dependent effects: (1) a tensile-phase effect in which the inserted wave adds to the process of bubble growth, utilizing the energy associated with the gas overpressure in the bubble and therefore converting a large proportion of this energy into additional acoustic energy, and (2) a compressive-phase effect in which the pressure wave works against the growing bubbles and a large amount of its acoustic energy is dissipated during the first cycle, but later enough energy is gained to amplify the second cycle. These two effects provide additional new possible mechanisms for the amplification phase seen in Long-Period (LP) and Very-Long-Period (VLP) seismic signals originating in magma-filled cracks.

A combination of streamtube and geostatical simulation methodologies for the study of large oil reservoirs

Energy Technology Data Exchange (ETDEWEB)

Chakravarty, A.; Emanuel, A.S.; Bernath, J.A. [Chevron Petroleum Technology Company, LaHabra, CA (United States)

1997-08-01

The application of streamtube models for reservoir simulation has an extensive history in the oil industry. Although these models are strictly applicable only to fields under voidage balance, they have proved to be useful in a large number of fields provided that there is no solution gas evolution and production. These models combine the benefit of very fast computational time with the practical ability to model a large reservoir over the course of its history. These models do not, however, directly incorporate the detailed geological information that recent experience has taught is important. This paper presents a technique for mapping the saturation information contained in a history matched streamtube model onto a detailed geostatistically derived finite difference grid. With this technique, the saturation information in a streamtube model, data that is actually statistical in nature, can be identified with actual physical locations in a field and a picture of the remaining oil saturation can be determined. Alternatively, the streamtube model can be used to simulate the early development history of a field and the saturation data then used to initialize detailed late time finite difference models. The proposed method is presented through an example application to the Ninian reservoir. This reservoir, located in the North Sea (UK), is a heterogeneous sandstone characterized by a line drive waterflood, with about 160 wells, and a 16 year history. The reservoir was satisfactorily history matched and mapped for remaining oil saturation. A comparison to 3-D seismic survey and recently drilled wells have provided preliminary verification.

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

Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling

Energy Technology Data Exchange (ETDEWEB)

P. K. Pande

1998-10-29

Initial drilling of wells on a uniform spacing, without regard to reservoir performance and characterization, must become a process of the past. Such efforts do not optimize reservoir development as they fail to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. These reservoirs are typically characterized by: o Large, discontinuous pay intervals o Vertical and lateral changes in reservoir properties o Low reservoir energy o High residual oil saturation o Low recovery efficiency

Platinum-bearing chromite layers are caused by pressure reduction during magma ascent.

Science.gov (United States)

Latypov, Rais; Costin, Gelu; Chistyakova, Sofya; Hunt, Emma J; Mukherjee, Ria; Naldrett, Tony

2018-01-31

Platinum-bearing chromitites in mafic-ultramafic intrusions such as the Bushveld Complex are key repositories of strategically important metals for human society. Basaltic melts saturated in chromite alone are crucial to their generation, but the origin of such melts is controversial. One concept holds that they are produced by processes operating within the magma chamber, whereas another argues that melts entering the chamber were already saturated in chromite. Here we address the problem by examining the pressure-related changes in the topology of a Mg 2 SiO 4 -CaAl 2 Si 2 O 8 -SiO 2 -MgCr 2 O 4 quaternary system and by thermodynamic modelling of crystallisation sequences of basaltic melts at 1-10 kbar pressures. We show that basaltic melts located adjacent to a so-called chromite topological trough in deep-seated reservoirs become saturated in chromite alone upon their ascent towards the Earth's surface and subsequent cooling in shallow-level chambers. Large volumes of these chromite-only-saturated melts replenishing these chambers are responsible for monomineralic layers of massive chromitites with associated platinum-group elements.

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.

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

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

Aquatic macrophytes in the large, sub-tropical Itaipu Reservoir, Brazil.

Science.gov (United States)

Mormul, Roger Paulo; Ferreira, Fernando Alves; Michelan, Thaisa Sala; Carvalho, Priscilla; Silveira, Marcio José; Thomaz, Sidinei Magela

2010-12-01

In the last three decades, rapid assessment surveys have become an important approach for measuring aquatic ecosystem biodiversity. These methods can be used to detect anthropogenic impacts and recognize local or global species extinctions. We present a floristic survey of the aquatic macrophytes along the Brazilian margin of the Itaipu Reservoir conducted in 2008 and compare this with a floristic survey conducted ten years earlier. We used ordination analysis to determine whether assemblage composition differed among reservoir arms. Macrophyte species were sampled in each of the 235 sampling stations using a boat, which was positioned inside three places of each macrophyte stand to record species and search for small plants. We also collected submerged plants using a rake with the boat moving at constant velocity for ten minutes. We assigned individual macrophyte species to life form and identified representative species for each life form. A total of 87 macrophyte taxa were identified. The "emergent" life forms contained the highest number of species, followed by "rooted submerged" life forms. The extensive survey of macrophytes undertaken in September 2008 recorded more species than a survey conducted between 1995 and 1998. This could be due to changes in water physico-chemistry, disturbances due to water drawdown and the long period between surveys, which may have allowed natural colonization by other species. Additionally, differences in the classification systems and taxonomic resolution used in the surveys may account for differences in the number of species recorded. Assemblage composition varied among the arms and was affected by underwater radiation (as measured using a Secchi disk) and fetch. Five non-native species were found. Two of these non-native species (Urochloa subquadripara and Hydrilla verticillata) are of special concern because they have a high frequency of occurrence and occupy large marginal areas of the reservoir. Future surveys should be

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.

Timescales of quartz crystallization and the longevity of the Bishop giant magma body.

Science.gov (United States)

Gualda, Guilherme A R; Pamukcu, Ayla S; Ghiorso, Mark S; Anderson, Alfred T; Sutton, Stephen R; Rivers, Mark L

2012-01-01

Supereruptions violently transfer huge amounts (100 s-1000 s km(3)) of magma to the surface in a matter of days and testify to the existence of giant pools of magma at depth. The longevity of these giant magma bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant magma body, which erupted ~760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop magma body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of magma bodies are ephemeral features that, once established, evolve on millennial timescales. We also suggest that zircon crystals, rather than recording the timescales of crystallization of a large pool of crystal-poor magma, record the extended periods of time necessary for maturation of the crust and establishment of these giant magma bodies.

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.

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.

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

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

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

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.

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.

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.

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-Year change in water chemistry of large freshwater Reservoir Danjiangkou, China

Science.gov (United States)

Li, Siyue; Ye, Chen; Zhang, Quanfa

2017-08-01

Danjiangkou Reservoir, an important drinking water source, has become a hot spot internationally due to its draining catchment has been increasingly affected by anthropogenic activities. However, its natural water chemistry (major elements) received little attention though it is crucial for water quality and aquatic ecology. Major ions during 2004-2014 were determined using stoichiometry to explore their shifts and the driving factors in the Danjiangkou Reservoir. Results show significant differences in monthly, spatial and annual concentrations of major ions. Waters are controlled by carbonate weathering with the dominant ions of Ca2+ and HCO3- total contributing 74% to the solutes, which are consistent with regional geography. Carbonate dissolution was produced by sulfuric acid and carbonic acid in particular. The relative abundance of Ca2+ gradually decreases, Na+ + K+ abundance, however, has doubled in the recent 11 years. Population and human activities were the major drivers for several major ions, i.e., Cl- and Na+ concentrations were explained by population and GDP, and SO42- by GDP, industrial sewage and energy consumption. Estimation indicated that domestic salts and atmospheric deposition contributed 56% and 22% to Cl-, respectively. We conclude waters in the Reservoir are naturally controlled by rock weathering whilst some key elements largely contributed by anthropogenic activities.

Derivation of Optimal Operating Rules for Large-scale Reservoir Systems Considering Multiple Trade-off

Science.gov (United States)

Zhang, J.; Lei, X.; Liu, P.; Wang, H.; Li, Z.

2017-12-01

Flood control operation of multi-reservoir systems such as parallel reservoirs and hybrid reservoirs often suffer from complex interactions and trade-off among tributaries and the mainstream. The optimization of such systems is computationally intensive due to nonlinear storage curves, numerous constraints and complex hydraulic connections. This paper aims to derive the optimal flood control operating rules based on the trade-off among tributaries and the mainstream using a new algorithm known as weighted non-dominated sorting genetic algorithm II (WNSGA II). WNSGA II could locate the Pareto frontier in non-dominated region efficiently due to the directed searching by weighted crowding distance, and the results are compared with those of conventional operating rules (COR) and single objective genetic algorithm (GA). Xijiang river basin in China is selected as a case study, with eight reservoirs and five flood control sections within four tributaries and the mainstream. Furthermore, the effects of inflow uncertainty have been assessed. Results indicate that: (1) WNSGA II could locate the non-dominated solutions faster and provide better Pareto frontier than the traditional non-dominated sorting genetic algorithm II (NSGA II) due to the weighted crowding distance; (2) WNSGA II outperforms COR and GA on flood control in the whole basin; (3) The multi-objective operating rules from WNSGA II deal with the inflow uncertainties better than COR. Therefore, the WNSGA II can be used to derive stable operating rules for large-scale reservoir systems effectively and efficiently.

Lithium enrichment in intracontinental rhyolite magmas leads to Li deposits in caldera basins.

Science.gov (United States)

Benson, Thomas R; Coble, Matthew A; Rytuba, James J; Mahood, Gail A

2017-08-16

The omnipresence of lithium-ion batteries in mobile electronics, and hybrid and electric vehicles necessitates discovery of new lithium resources to meet rising demand and to diversify the global lithium supply chain. Here we demonstrate that lake sediments preserved within intracontinental rhyolitic calderas formed on eruption and weathering of lithium-enriched magmas have the potential to host large lithium clay deposits. We compare lithium concentrations of magmas formed in a variety of tectonic settings using in situ trace-element measurements of quartz-hosted melt inclusions to demonstrate that moderate to extreme lithium enrichment occurs in magmas that incorporate felsic continental crust. Cenozoic calderas in western North America and in other intracontinental settings that generated such magmas are promising new targets for lithium exploration because lithium leached from the eruptive products by meteoric and hydrothermal fluids becomes concentrated in clays within caldera lake sediments to potentially economically extractable levels.Lithium is increasingly being utilized for modern technology in the form of lithium-ion batteries. Here, using in situ measurements of quartz-hosted melt inclusions, the authors demonstrate that preserved lake sediments within rhyolitic calderas have the potential to host large lithium-rich clay deposits.

RAPID TIMESCALES FOR MAGMA OCEAN CRYSTALLIZATION ON THE HOWARDITE-EUCRITE-DIOGENITE PARENT BODY

International Nuclear Information System (INIS)

Schiller, Martin; Paton, Chad; Bizzarro, Martin; Baker, Joel; Creech, John; Millet, Marc-Alban; Irving, Anthony

2011-01-01

Asteroid 4 Vesta has long been postulated as the source for the howardite-eucrite-diogenite (HED) achondrite meteorites. Here we show that Al-free diogenite meteorites record variability in the mass-independent abundance of 26 Mg ( 26 Mg*) that is correlated with their mineral chemistry. This suggests that these meteorites captured the Mg-isotopic evolution of a large-scale differentiating magma body with increasing 27 Al/ 24 Mg during the lifespan of the short-lived 26 Al nuclide (t 1/2 ∼ 730,000 yr). Thus, diogenites and eucrites represent crystallization products of a large-scale magma ocean associated with the differentiation and magmatic evolution of the HED parent body. The 26 Mg* composition of the most primitive diogenites requires onset of the magma ocean crystallization within 0.6 -0.4 +0.5 Myr of solar system formation. Moreover, 26 Mg* variations among diogenites and eucrites imply that near complete solidification of the HED parent body occurred within the following 2-3 Myr. Thermal models predict that such rapid cooling and magma ocean crystallization could only occur on small asteroids (<100 km), implying that 4 Vesta is not the source of the HED meteorites.

Evidence for large reservoirs of water/mud in Utopia and Acidalia Planitiae on Mars

Science.gov (United States)

Ivanov, M. A.; Hiesinger, H.; Erkeling, G.; Reiss, D.

2015-03-01

Utopia and Acidalia Planitiae show a set of similar morphologic features indicative of the presence of large reservoirs of water/mud in these regional topographic lows. The most important of these features are: (1) impact crater ejecta morphology that progressively changes from ballistic/rampart at the basins periphery to strongly degraded pancake-like in the central portions of the basins, and (2) etched flows (interpreted as mudflows) that are concentrated in those regions of the central portions of both basins where the pancake-like ejecta prevail. The Vastitas Borealis Formation (VBF) in Utopia and Acidalia Planitiae represents the uppermost stratigraphic limit of possible reservoirs in both basins and has practically the same age in these regions; ∼3.57 (±0.02) Ga in Utopia Planitia and ∼3.61 (+0.05/-0.08) Ga in Acidalia Planitia. The southern contact of the VBF closely follows specific contour lines in Utopia Planitia (∼-3.6 km ± 54 m, over a distance of ∼1500 km) and Acidalia Planitia (∼-3.9 km ± 70 m, over the distance of ∼6000 km). The presence of the large water/mud reservoirs and the age and topographic configuration of the VBF in Utopia and Acidalia Planitiae are consistent with the existence of an extensive single body of water (an ocean) in the northern plains of Mars.

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.

Aquatic macrophytes in the large, sub-tropical Itaipu Reservoir, Brazil

Directory of Open Access Journals (Sweden)

Roger Paulo Mormul

2010-12-01

Full Text Available In the last three decades, rapid assessment surveys have become an important approach for measuring aquatic ecosystem biodiversity. These methods can be used to detect anthropogenic impacts and recognize local or global species extinctions. We present a floristic survey of the aquatic macrophytes along the Brazilian margin of the Itaipu Reservoir conducted in 2008 and compare this with a floristic survey conducted ten years earlier. We used ordination analysis to determine whether assemblage composition differed among reservoir arms. Macrophyte species were sampled in each of the 235 sampling stations using a boat, which was positioned inside three places of each macrophyte stand to record species and search for small plants. We also collected submerged plants using a rake with the boat moving at constant velocity for ten minutes. We assigned individual macrophyte species to life form and identified representative species for each life form. A total of 87 macrophyte taxa were identified. The "emergent" life forms contained the highest number of species, followed by "rooted submerged" life forms. The extensive survey of macrophytes undertaken in September 2008 recorded more species than a survey conducted between 1995 and 1998. This could be due to changes in water physico-chemistry, disturbances due to water drawdown and the long period between surveys, which may have allowed natural colonization by other species. Additionally, differences in the classification systems and taxonomic resolution used in the surveys may account for differences in the number of species recorded. Assemblage composition varied among the arms and was affected by underwater radiation (as measured using a Secchi disk and fetch. Five non-native species were found. Two of these non-native species (Urochloa subquadripara and Hydrilla verticillata are of special concern because they have a high frequency of occurrence and occupy large marginal areas of the reservoir. Future

The magma ocean as an impediment to lunar plate tectonics

Science.gov (United States)

Warren, Paul H.

1993-01-01

The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

The Krafla International Testbed (KMT): Ground Truth for the New Magma Geophysics

Science.gov (United States)

Brown, L. D.; Kim, D.; Malin, P. E.; Eichelberger, J. C.

2017-12-01

Recent developments in geophysics such as large N seismic arrays , 4D (time lapse) subsurface imaging and joint inversion algorithms represent fresh approaches to delineating and monitoring magma in the subsurface. Drilling at Krafla, both past and proposed, are unique opportunities to quantitatively corroborate and calibrate these new technologies. For example, dense seismic arrays are capable of passive imaging of magma systems with resolutions comparable to that achieved by more expensive (and often logistically impractical) controlled source surveys such as those used in oil exploration. Fine details of the geometry of magma lenses, feeders and associated fluid bearing fracture systems on the scale of meters to tens of meters are now realistic targets for surface seismic surveys using ambient energy sources, as are detection of their temporal variations. Joint inversions, for example of seismic and MT measurements, offer the promise of tighter quantitative constraints on the physical properties of the various components of magma and related geothermal systems imaged by geophysics. However, the accuracy of such techniques will remain captive to academic debate without testing against real world targets that have been directly sampled. Thus application of these new techniques to both guide future drilling at Krafla and to be calibrated against the resulting borehole observations of magma are an important step forward in validating geophysics for magma studies in general.

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.

APPLICATION OF INTEGRATED RESERVOIR MANAGEMENT AND RESERVOIR CHARACTERIZATION

Energy Technology Data Exchange (ETDEWEB)

Jack Bergeron; Tom Blasingame; Louis Doublet; Mohan Kelkar; George Freeman; Jeff Callard; David Moore; David Davies; Richard Vessell; Brian Pregger; Bill Dixon; Bryce Bezant

2000-03-01

Reservoir performance and characterization are vital parameters during the development phase of a project. Infill drilling of wells on a uniform spacing, without regard to characterization does not optimize development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, especially carbonate reservoirs. These reservoirs are typically characterized by: (1) large, discontinuous pay intervals; (2) vertical and lateral changes in reservoir properties; (3) low reservoir energy; (4) high residual oil saturation; and (5) low recovery efficiency. The operational problems they encounter in these types of reservoirs include: (1) poor or inadequate completions and stimulations; (2) early water breakthrough; (3) poor reservoir sweep efficiency in contacting oil throughout the reservoir as well as in the nearby well regions; (4) channeling of injected fluids due to preferential fracturing caused by excessive injection rates; and (5) limited data availability and poor data quality. Infill drilling operations only need target areas of the reservoir which will be economically successful. If the most productive areas of a reservoir can be accurately identified by combining the results of geological, petrophysical, reservoir performance, and pressure transient analyses, then this ''integrated'' approach can be used to optimize reservoir performance during secondary and tertiary recovery operations without resorting to ''blanket'' infill drilling methods. New and emerging technologies such as geostatistical modeling, rock typing, and rigorous decline type curve analysis can be used to quantify reservoir quality and the degree of interwell communication. These results can then be used to develop a 3-D simulation model for prediction of infill locations. The application of reservoir surveillance techniques to identify additional reservoir ''pay'' zones

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.

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.

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.

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.

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.

Evolution of the magma feeding system during a Plinian eruption: The case of Pomici di Avellino eruption of Somma-Vesuvius, Italy

Science.gov (United States)

Massaro, S.; Costa, A.; Sulpizio, R.

2018-01-01

The current paradigm for volcanic eruptions is that magma erupts from a deep magma reservoir through a volcanic conduit, typically modelled with fixed rigid geometries such as cylinders. This simplistic view of a volcanic eruption does not account for the complex dynamics that usually characterise a large explosive event. Numerical simulations of magma flow in a conduit combined with volcanological and geological data, allow for the first description of a physics-based model of the feeding system evolution during a sustained phase of an explosive eruption. The method was applied to the Plinian phase of the Pomici di Avellino eruption (PdA, 3945 ±10 cal yr BP) from Somma-Vesuvius (Italy). Information available from volcanology, petrology, and lithology studies was used as input data and as constraints for the model. In particular, Mass Discharge Rates (MDRs) assessed from volcanological methods were used as target values for numerical simulations. The model solutions, which are non-unique, were constrained using geological and volcanological data, such as volume estimates and types of lithic components in the fall deposits. Three stable geometric configurations of the feeding system (described assuming elliptical cross-section of variable dimensions) were assessed for the Eruptive Units 2 and 3 (EU2, EU3), which form the magmatic Plinian phase of PdA eruption. They describe the conduit system geometry at time of deposition of EU2 base, EU2 top, and EU3. A 7-km deep dyke (length 2 a = 200-4 00 m, width 2 b = 10- 12 m), connecting the magma chamber to the surface, characterised the feeding system at the onset of the Plinian phase (EU2 base). The feeding system rapidly evolved into hybrid geometric configuration, with a deeper dyke (length 2 a = 600- 800 m, width 2 b = 50 m) and a shallower cylindrical conduit (diameter D = 50 m, dyke-to-cylinder transition depth ∼2100 m), during the eruption of the EU2 top. The deeper dyke reached the dimensions of 2 a = 2000 m and

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

Depths of Magma Chambers in the Icelandic Crust

Science.gov (United States)

Kelley, D. F.; Kapostasy, D. D.; Barton, M.

2004-05-01

There is considerable interest in the structure and thermal state of the crust in Iceland, which lies across the Mid Atlantic Ridge. However, interpretations of seismic and gravity data yield conflicting views of the nature of the lower crust. Some interpretations prefer a model in which the lower crust (15-25 km) is relatively cool and solid, whereas other interpretations, based largely on gravity data, prefer a model in which the lower crust is relatively warm and possibly partially molten. Knowledge of the depth of magma chambers is critical to constrain the geothermal gradient in Icelandic crust and to resolve discrepancies in interpretation of geophysical data. Analyses of aphyric lavas and of glasses in Icelandic lavas erupted from 11 volcanic centers have been compiled. The compositions are picritic and basaltic with SiO2 - 47 to 50 wt%, MgO - 6 to 15wt%, FeO - 8 to 14wt%, to, Na2O - 1.3 to 3.3 wt%, and K2O - 0.03-46 wt%. The pressures of equilibration of these liquids with ol, high-Ca pyx and plag were estimated qualitatively from projections into the pseudoternary system Ol-Di-Silica using methods described by Walker and coworkers and Grove and coworkers. The results (ca. 0.5 GPa) indicate crystallization in magma chambers located at about 16 km depth. Equilibration pressures were also calculated using the method described by Yang and coworkers and by a modified version of this method. Calculated pressures (0.45±0.15 GPa) indicate magma chambers located at 15±4 km depth. Equilibration pressures for Rekjanes Ridge glasses determined using the same techniques are 0.2±0.1 GPa, corresponding to depths of 7.6±3 km. The results indicate the presence of magma chambers in the deep Icelandic crust and that the latter is relatively warm. Shallower chambers (3-7 km) have been identified from seismic studies suggesting a complex magma plumbing system. The results also confirm that magma chambers beneath Iceland are located at greater depths than those beneath the

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

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

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.

Crystallization sequence of the Upper Border Series of the Skaergaard Intrusion: Revised subdivision and implications for Chamber-Scale Magma Homogeneity

DEFF Research Database (Denmark)

Salmonsen, Lars Peter; Tegner, Christian

2013-01-01

from the roof of the magma chamber, differs from that in the Layered Series formed at the floor. The proposed deviation would require chemical stratification of the magma, and a reexamination of the crystallization sequence therefore has important implications for understanding the dynamics...... of the crystallization sequences and the anorthite contents of plagioclase cores in the three series imply that the Skaergaard magma chamber solidified by in situ crystallization along the floor, walls and roof from one, largely homogenous, convecting magma body....

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

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

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.

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.

Understanding the monotonous life of open vent mafic volcanoes

Science.gov (United States)

Costa Rodriguez, F.; Ruth, D. C. S.; Bornas, M.; Rivera, D. J. V. I.

2016-12-01

Mafic open vent volcanoes display prominent degassing plumes during quiescence but also erupt frequently, every few months or years. Their small and mildly explosive eruptions (volatile contents indicate that the magma reservoir system extends at least to 5 km depth. Mg/Fe pyroxene zoning and diffusion modeling suggests that mafic magma intrusion in a shallow, crystal-rich and more evolved reservoir has occurred repeatedly. The time scale for this process is the same for all 9 events, starting about 2 years prior and continuing up to eruption. We estimate the relative proportions of injecting to resident magma that vary from about 0.2 to 0.7, probably reflecting the local crystal-melt interaction during intrusion. The near constant magma composition is probably the result of buffering of new incoming magma by a crystal-rich upper reservoir, and erupted magmas are physical mixtures. However, we do not find evidence of large-scale crystal recycling from one eruption to another, implying the resetting of the system after each event. The recurrent eruptions and intrusions could be driven by the near continuous degassing of the volcano that induces a mass imbalance which leads to magma movement from depth to the shallow system [e.g., 1]. [1] Girona et al. (2016). Science Reports doi:10.1038/srep18212

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

A rapid mechanism to remobilize and homogenize highly crystalline magma bodies.

Science.gov (United States)

Burgisser, Alain; Bergantz, George W

2011-03-10

The largest products of magmatic activity on Earth, the great bodies of granite and their corresponding large eruptions, have a dual nature: homogeneity at the large scale and spatial and temporal heterogeneity at the small scale. This duality calls for a mechanism that selectively removes the large-scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal-rich, viscous conditions seemingly resistant to mixing. Here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization (unzipping) of highly viscous crystal-rich mushes. We demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning. What distinguishes our model is the recognition that the process has two stages. Initially, a stiff mushy magma is reheated from below, producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer. When the thickening mobile layer becomes sufficiently buoyant, it penetrates the overlying viscous mushy magma. This second stage rapidly exports homogenized material from the lower mobile layer to the top of the system, and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing. Model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption. The agreement between calculated and observed unzipping rates for historical eruptions at Pinatubo and at Montserrat demonstrates the general applicability of the model. This mechanism furthers our understanding of both the formation of periodically homogenized plutons (crust building) and of ignimbrites by large eruptions.

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.)

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.

Drilling into Rhyolitic Magma at Shallow depth at Krafla Volcanic Complex, NE-Iceland

Science.gov (United States)

Mortensen, A. K.; Markússon, S. H.; Gudmundsson, Á.; Pálsson, B.

2017-12-01

Krafla volcanic complex in NE-Iceland is an active volcano but the latest eruption was the Krafla Fires in 1975-1984. Though recent volcanic activity has consisted of basaltic fissure eruptions, then it is rhyolitic magma that has been intercepted on at least two occasions while drilling geothermal production wells in the geothermal field suggesting a layered magma plumbing system beneath the Krafla volcanic complex. In 2008 quenched rhyolitic glass was retrieved from the bottom of well KJ-39, which is 2865 m deep ( 2571 m true vertical depth). In 2009 magma was again encountered at an even shallower depth and in more than 2,5 km distance from the bottom of well KJ-39, but in 2009 well IDDP-1 was drilled into magma three times just below 2100 m depth. Only on the last occasion was quenched glass retrieved to confirm that magma had been encountered. In well KJ-39 the quenched glass was rhyolitic in composition. The glass contained resorbed minerals of plagioclase, clinopyroxene and titanomagnetite, but the composition of the glass resembles magma that has formed by partial melting of hydrated basalt. The melt was encountered among cuttings from impermeable, coarse basaltic intrusives at a depth, where the well was anticipated to penetrate the Hólseldar volcanic fissure. In IDDP-1 the quenched glass was also rhyolitic in composition. The glass contained less than 5% of phenocrysts, but the phenocryst assemblage included andesine plagioclase, augite, pigeonite, and titanomagnetite. At IDDP-1 the melt was encountered below a permeable zone composed of fine to coarse grained felsite and granophyre. The disclosure of magma in two wells at Krafla volcanic complex verify that rhyolitic magma can be encountered at shallow depth across a larger area within the caldera. The encounter of magma at shallow depth conforms with that superheated conditions have been found at >2000 m depth in large parts of Krafla geothermal field.

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.

Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies.

Science.gov (United States)

Falgarone, E; Zwaan, M A; Godard, B; Bergin, E; Ivison, R J; Andreani, P M; Bournaud, F; Bussmann, R S; Elbaz, D; Omont, A; Oteo, I; Walter, F

2017-08-24

Starburst galaxies at the peak of cosmic star formation are among the most extreme star-forming engines in the Universe, producing stars over about 100 million years (ref. 2). The star-formation rates of these galaxies, which exceed 100 solar masses per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Consequently, starburst galaxies are ideal for studying the interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH + , is a most useful molecule for such studies because it cannot form in cold gas without suprathermal energy input, so its presence indicates dissipation of mechanical energy or strong ultraviolet irradiation. Here we report the detection of CH + (J = 1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts near 2.5. This line has such a high critical density for excitation that it is emitted only in very dense gas, and is absorbed in low-density gas. We find that the CH + emission lines, which are broader than 1,000 kilometres per second, originate in dense shock waves powered by hot galactic winds. The CH + absorption lines reveal highly turbulent reservoirs of cool (about 100 kelvin), low-density gas, extending far (more than 10 kiloparsecs) outside the starburst galaxies (which have radii of less than 1 kiloparsec). We show that the galactic winds sustain turbulence in the 10-kiloparsec-scale environments of the galaxies, processing these environments into multiphase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star-formation rates. Another mass input is therefore required for these reservoirs, which could be provided by ongoing mergers or cold-stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase of a galaxy instead of quenching it.

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

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.

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

Temporal variations in volumetric magma eruption rates of Quaternary volcanoes in Japan

Science.gov (United States)

Yamamoto, Takahiro; Kudo, Takashi; Isizuka, Osamu

2018-04-01

Long-term evaluations of hazard and risk related to volcanoes rely on extrapolations from volcano histories, including the uniformity of their eruption rates. We calculated volumetric magma eruption rates, compiled from quantitative eruption histories of 29 Japanese Quaternary volcanoes, and analyzed them with respect to durations spanning 101-105 years. Calculated eruption rates vary greatly (101-10-4 km3 dense-rock equivalent/1000 years) between individual volcanoes. Although large basaltic stratovolcanoes tend to have high eruption rates and relatively constant repose intervals, these cases are not representative of the various types of volcanoes in Japan. At many Japanese volcanoes, eruption rates are not constant through time, but increase, decrease, or fluctuate. Therefore, it is important to predict whether eruption rates will increase or decrease for long-term risk assessment. Several temporal co-variations of eruption rate and magmatic evolution suggest that there are connections between them. In some cases, magma supply rates increased in response to changing magma-generation processes. On the other hand, stable plumbing systems without marked changes in magma composition show decreasing eruption rates through time.[Figure not available: see fulltext.

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.

Temperatures and isotopic evolution of silicic magmas, Taupo Volcanic Zone and Coromandel, New Zealand

International Nuclear Information System (INIS)

Blattner, P.; Rui-Zhong, Hu; Graham, I.J.; Houston-Eleftheriadis, C.

1996-01-01

A new set of oxygen and strontium isotope data on rhyolitic lavas and ignimbrites of the Taupo Volcanic Zone (TVZ) and the Coromandel Peninsula provides new limits for petrogenetic models. For oxygen isotopes, the rock matrix is frequently altered, so that values for magma need to be phenocryst based. Within TVZ a trend towards more negative delta 1 8 O values for more recent magmas appears likely (average before about 1 Ma and for Coromandel near 8.0 per thousand; after 1 Ma near 7.5 per thousand). This could indicate the gradual removal of supracrustal contaminants from the zones of magma accumulation and extrusion. Similar trends within Coromandel cannot yet be resolved. A generally positive correlation is found for oxygen and strontium isotopes of magmas. Most magmas have a limited range of isotopic values, which then becomes a useful fingerprint (e.g., the Mamaku, Matahina, and Waiotapu Ignimbrites). A narrow range of eruption temperatures of 880 plus or minus 60degC is derived from quartz-plagioclase fractionations of 0.98 plus or minus 0.25 per thousand delta 1 8 O for 15 magmas. Some delta 1 8 O values of quartz and feldspar phenocrysts are sufficiently low to suggest interaction between surface water and magma. However, large negative oxygen isotope anomalies (such as known from Yellowstone), could be no more than partially concealed by the isotopically less depleted meteoric water of New Zealand, and have not yet been found in New Zealand. (author). 45 refs., 3 tabs., 6 figs

Loki Patera as the Surface of a Magma Sea

Science.gov (United States)

Matson, D. L.; Davies, A. G.; Veeder, G. J.; Rathbun, J. A.; Johnson, T. V.

2004-01-01

Inspired by the finding of Schubert et al that Io's figure is consistent with a hydrostatic shape, we explore the consequences of modeling Loki Patera as the surface of a large magma sea. This model is attractive because of its sheer simplicity and its usefulness in interpreting and predicting observations. Here, we report on that work.

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.

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.

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.

Direct evidence for the origin of low-18O silicic magmas: Quenched samples of a magma chamber's partially-fused granitoid walls, Crater Lake, Oregon

International Nuclear Information System (INIS)

Bacon, C.R.; Adami, L.H.; Lanphere, M.A.

1989-01-01

Partially fused granitoid blocks were ejected in the climactic eruption of Mount Mazama, which was accompanied by collapse of Crater Lake caldera. Quartz, plagioclase, and glass in the granitoids have much lower δ 18 O values (-3.4 to +4.9per mille) than any fresh lavas of Mount Mazama and the surrounding region (+5.8 to +7.0per mille). Oxygen isotope fractionation between phases in granitoids is consistent with equilibrium at T≥900deg C following subsolidus exchange with hydrothermal fluids of meteoric origin. Assimilation of ≅ 10-20% of material similar to these granitoids can account for the O and Sr isotopic compositions of lavas and juvenile pyroclasts derived from the climactic magma chamber, many of which have δ 18 O values ≅ 0.5per mille or more lower than comparable lavas of Mount Mazama. The O isotope data provide the only clear evidence for such assimilation because the mineralogy and chemical and radiogenic isotopic compositions of the granitoids (dominantly granodiorite) are similar to those of erupted juvenile magmas. The granitoid blocks from Crater Lake serve as direct evidence for the origin of 18 O depletion in large, shallow silicic magma bodies. (orig.)

Carbon Sequestration in a Large Hydroelectric Reservoir: An Integrative Seismic Approach

NARCIS (Netherlands)

Mendonca, R.; Kosten, S.; Sobek, S.; Cole, J.J.; Bastos, A.C.; Albuquerque, A.L.; Cardoso, S.J.; Roland, F.

2014-01-01

Artificial reservoirs likely accumulate more carbon than natural lakes due to their unusually high sedimentation rates. Nevertheless, the actual magnitude of carbon accumulating in reservoirs is poorly known due to a lack of whole-system studies of carbon burial. We determined the organic carbon

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.

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

Hydrothermal processes above the Yellowstone magma chamber: Large hydrothermal systems and large hydrothermal explosions

Science.gov (United States)

Morgan, L.A.; Shanks, W.C. Pat; Pierce, K.L.

2009-01-01

Hydrothermal explosions are violent and dramatic events resulting in the rapid ejection of boiling water, steam, mud, and rock fragments from source craters that range from a few meters up to more than 2 km in diameter; associated breccia can be emplaced as much as 3 to 4 km from the largest craters. Hydrothermal explosions occur where shallow interconnected reservoirs of steam- and liquid-saturated fluids with temperatures at or near the boiling curve underlie thermal fields. Sudden reduction in confi ning pressure causes fluids to fl ash to steam, resulting in signifi cant expansion, rock fragmentation, and debris ejection. In Yellowstone, hydrothermal explosions are a potentially signifi cant hazard for visitors and facilities and can damage or even destroy thermal features. The breccia deposits and associated craters formed from hydrothermal explosions are mapped as mostly Holocene (the Mary Bay deposit is older) units throughout Yellowstone National Park (YNP) and are spatially related to within the 0.64-Ma Yellowstone caldera and along the active Norris-Mammoth tectonic corridor. In Yellowstone, at least 20 large (>100 m in diameter) hydrothermal explosion craters have been identifi ed; the scale of the individual associated events dwarfs similar features in geothermal areas elsewhere in the world. Large hydrothermal explosions in Yellowstone have occurred over the past 16 ka averaging ??1 every 700 yr; similar events are likely in the future. Our studies of large hydrothermal explosion events indicate: (1) none are directly associated with eruptive volcanic or shallow intrusive events; (2) several historical explosions have been triggered by seismic events; (3) lithic clasts and comingled matrix material that form hydrothermal explosion deposits are extensively altered, indicating that explosions occur in areas subjected to intense hydrothermal processes; (4) many lithic clasts contained in explosion breccia deposits preserve evidence of repeated fracturing

Adakitic magmas: modern analogues of Archaean granitoids

Science.gov (United States)

Martin, Hervé

1999-03-01

Both geochemical and experimental petrological research indicate that Archaean continental crust was generated by partial melting of an Archaean tholeiite transformed into a garnet-bearing amphibolite or eclogite. The geodynamic context of tholeiite melting is the subject of controversy. It is assumed to be either (1) subduction (melting of a hot subducting slab), or (2) hot spot (melting of underplated basalts). These hypotheses are considered in the light of modern adakite genesis. Adakites are intermediate to felsic volcanic rocks, andesitic to rhyolitic in composition (basaltic members are lacking). They have trondhjemitic affinities (high-Na 2O contents and K 2O/Na 2O˜0.5) and their Mg no. (0.5), Ni (20-40 ppm) and Cr (30-50 ppm) contents are higher than in typical calc-alkaline magmas. Sr contents are high (>300 ppm, until 2000 ppm) and REE show strongly fractionated patterns with very low heavy REE (HREE) contents (Yb≤1.8 ppm, Y≤18 ppm). Consequently, high Sr/Y and La/Yb ratios are typical and discriminating features of adakitic magmas, indicative of melting of a mafic source where garnet and/or hornblende are residual phases. Adakitic magmas are only found in subduction zone environments, exclusively where the subduction and/or the subducted slab are young (subducted and where the adakitic character of the lavas correlates well with the young age of the subducting oceanic lithosphere. In typical subduction zones, the subducted lithosphere is older than 20 Ma, it is cool and the geothermal gradient along the Benioff plane is low such that the oceanic crust dehydrates before it reaches the solidus temperature of hydrated tholeiite. Consequently, the basaltic slab cannot melt. The released large ion lithophile element (LILE)-rich fluids rise up into the mantle wedge, inducing both its metasomatism and partial melting. Afterwards, the residue is made up of olivine+clinopyroxene+orthopyroxene, such that the partial melts are HREE-rich (low La/Yb and Sr

Temperatures and isotopic evolution of silicic magmas, Taupo Volcanic Zone and Coromandel, New Zealand

International Nuclear Information System (INIS)

Blattner, P.; Rui-Zhong H.; Graham, I.J.; Houston-Eleftheriadis, C.

1996-01-01

A new set of oxygen and strontium isotope data on rhyolitic lavas and ignimbrites of the Taupo Volcanic Zone (TVZ) and the Coromandel Peninsula provides new limits for petrogenic models. For oxygen isotopes, the rock matrix is frequently altered, so that values for magma need to be phenocryst based. Within TVZ a trend towards more negative δ 1 8O values for more recent magmas appears likely (average before about 1 Ma and for Coromandel near 8.0 per mille; after 1 Ma near 7.5 per mille). This could indicate the gradual removal of supracrustal contaminants from the zones of magma accumulation and extrusion. Similar trends within Coromandel cannot yet be resolved. A generally positive correlation is found for oxygen and strontium isotopes of magmas. Most magmas have a limited range of isotopic values, which then becomes a fingerprint (e.g., the Mamaku, Matahina, and Waiotapu Ignimbrites). A narrow range of eruption temperatures of 880 ± 60 o C is derived from quartz-plagioclase fractionations of 0.98 ± 0.25 per mille δ 1 8O values of quartz and feldspar phenocrysts are sufficiently low to suggest interaction between surface water and magma. However, large negative oxygen isotope anomalies (such as known from Yellowstone), could be no more than partially concealed by the isotopically less depleted meteoric water of New Zealand, and have not yet been found in New Zealand. (authors). 45 refs., 6 figs., 3 tabs

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

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.

Depositional features and stratigraphic sections in granitic plutons: implications for the emplacement and crystallization of granitic magma

Science.gov (United States)

Wiebe, R. A.; Collins, W. J.

1998-09-01

Many granitic plutons contain sheet-like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature, more mafic magma during crystallization of the granitic plutons. Small-scale structures associated with these bodies (e.g. load-cast and compaction features, silicic pipes extending from granitic layers into adjacent gabbroic sheets) indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber (on granitic crystal mush and beneath crystal-poor magma) while the mafic magma was incompletely crystallized. These structures indicate 'way up', typically toward the interior of the intrusions, and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition. Hence, these plutons preserve a stratigraphic history of events involved in the construction (filling, replenishment) and crystallization of the magma chamber. The distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions, which usually preserve mutual intrusive contacts and 'dike-sill' relations of different magma types. The considerable thickness of material that can be interpreted as depositional, and the evidence for replenishment, suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton. Thus, magma chambers may be constructed much more slowly than presently envisaged. The present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber (along with the underlying solidified granite and country rock) sank during continuing episodes of magma chamber replenishment. These internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber.

Understanding the True Stimulated Reservoir Volume in Shale Reservoirs

KAUST Repository

Hussain, Maaruf; Saad, Bilal; Negara, Ardiansyah; Sun, Shuyu

2017-01-01

Successful exploitation of shale reservoirs largely depends on the effectiveness of hydraulic fracturing stimulation program. Favorable results have been attributed to intersection and reactivation of pre-existing fractures by hydraulically

Flood risk management for large reservoirs

International Nuclear Information System (INIS)

Poupart, M.

2006-01-01

Floods are a major risk for dams: uncontrolled reservoir water level may cause dam overtopping, and then its failure, particularly for fill dams. Poor control of spillway discharges must be taken into consideration too, as it can increase the flood consequences downstream. In both cases, consequences on the public or on properties may be significant. Spillway design to withstand extreme floods is one response to these risks, but must be complemented by strict operating rules: hydrological forecasting, surveillance and periodic equipment controls, operating guides and the training of operators are mandatory too, in order to guarantee safe operations. (author)

Heterogeneity in lunar anorthosite meteorites: implications for the lunar magma ocean model.

Science.gov (United States)

Russell, Sara S; Joy, Katherine H; Jeffries, Teresa E; Consolmagno, Guy J; Kearsley, Anton

2014-09-13

The lunar magma ocean model is a well-established theory of the early evolution of the Moon. By this model, the Moon was initially largely molten and the anorthositic crust that now covers much of the lunar surface directly crystallized from this enormous magma source. We are undertaking a study of the geochemical characteristics of anorthosites from lunar meteorites to test this model. Rare earth and other element abundances have been measured in situ in relict anorthosite clasts from two feldspathic lunar meteorites: Dhofar 908 and Dhofar 081. The rare earth elements were present in abundances of approximately 0.1 to approximately 10× chondritic (CI) abundance. Every plagioclase exhibited a positive Eu-anomaly, with Eu abundances of up to approximately 20×CI. Calculations of the melt in equilibrium with anorthite show that it apparently crystallized from a magma that was unfractionated with respect to rare earth elements and ranged in abundance from 8 to 80×CI. Comparisons of our data with other lunar meteorites and Apollo samples suggest that there is notable heterogeneity in the trace element abundances of lunar anorthosites, suggesting these samples did not all crystallize from a common magma source. Compositional and isotopic data from other authors also suggest that lunar anorthosites are chemically heterogeneous and have a wide range of ages. These observations may support other models of crust formation on the Moon or suggest that there are complexities in the lunar magma ocean scenario to allow for multiple generations of anorthosite formation. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

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.

Conditions of deep magma chamber beneath Fuji volcano estimated from high- P experiments

Science.gov (United States)

Asano, K.; Takahashi, E.; Hamada, M.; Ushioda, M.; Suzuki, T.

2012-12-01

boundary, shallow level magma chamber is difficult to maintain for long time due to the large stress and deformation. Accordingly, the magma composition of Fuji volcano is buffered by the large AFC magma chamber in the lower crust (Takahashi et al., this conference). Fig.1 SiO2-K2O diagram for Fuji volcano products (diamonds) and volcanoes in Izu-arc. Melt compositional trend obtained by 4 kbar and 7 kbar experiments are shown with arrows.

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

Reservoir floodplains support distinct fish assemblages

Science.gov (United States)

Miranda, Leandro E.; Wigen, S. L.; Dagel, Jonah D.

2014-01-01

Reservoirs constructed on floodplain rivers are unique because the upper reaches of the impoundment may include extensive floodplain environments. Moreover, reservoirs that experience large periodic water level fluctuations as part of their operational objectives seasonally inundate and dewater floodplains in their upper reaches, partly mimicking natural inundations of river floodplains. In four flood control reservoirs in Mississippi, USA, we explored the dynamics of connectivity between reservoirs and adjacent floodplains and the characteristics of fish assemblages that develop in reservoir floodplains relative to those that develop in reservoir bays. Although fish species richness in floodplains and bays were similar, species composition differed. Floodplains emphasized fish species largely associated with backwater shallow environments, often resistant to harsh environmental conditions. Conversely, dominant species in bays represented mainly generalists that benefit from the continuous connectivity between the bay and the main reservoir. Floodplains in the study reservoirs provided desirable vegetated habitats at lower water level elevations, earlier in the year, and more frequently than in bays. Inundating dense vegetation in bays requires raising reservoir water levels above the levels required to reach floodplains. Therefore, aside from promoting distinct fish assemblages within reservoirs and helping promote diversity in regulated rivers, reservoir floodplains are valued because they can provide suitable vegetated habitats for fish species at elevations below the normal pool, precluding the need to annually flood upland vegetation that would inevitably be impaired by regular flooding. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Special relativity derived from spacetime magma.

Science.gov (United States)

Greensite, Fred

2014-01-01

We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid) existing on the union of spacetime frame components [Formula: see text] and Euclidean [Formula: see text] which is consistent with an "inversion symmetry" constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of "inverse norms" which play major roles with respect to various unital [Formula: see text]-algebras more generally.

Special relativity derived from spacetime magma.

Directory of Open Access Journals (Sweden)

Fred Greensite

Full Text Available We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid existing on the union of spacetime frame components [Formula: see text] and Euclidean [Formula: see text] which is consistent with an "inversion symmetry" constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of "inverse norms" which play major roles with respect to various unital [Formula: see text]-algebras more generally.

Reservoir Engineering Management Program

Energy Technology Data Exchange (ETDEWEB)

Howard, J.H.; Schwarz, W.J.

1977-12-14

The Reservoir Engineering Management Program being conducted at Lawrence Berkeley Laboratory includes two major tasks: 1) the continuation of support to geothermal reservoir engineering related work, started under the NSF-RANN program and transferred to ERDA at the time of its formation; 2) the development and subsequent implementation of a broad plan for support of research in topics related to the exploitation of geothermal reservoirs. This plan is now known as the GREMP plan. Both the NSF-RANN legacies and GREMP are in direct support of the DOE/DGE mission in general and the goals of the Resource and Technology/Resource Exploitation and Assessment Branch in particular. These goals are to determine the magnitude and distribution of geothermal resources and reduce risk in their exploitation through improved understanding of generically different reservoir types. These goals are to be accomplished by: 1) the creation of a large data base about geothermal reservoirs, 2) improved tools and methods for gathering data on geothermal reservoirs, and 3) modeling of reservoirs and utilization options. The NSF legacies are more research and training oriented, and the GREMP is geared primarily to the practical development of the geothermal reservoirs. 2 tabs., 3 figs.

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.

Aging Reservoirs in a Changing Climate: Examining Storage Loss of Large Reservoirs and Variability of Sedimentation Rate in a Dominant Cropland Region

Science.gov (United States)

Rahmani, V.; Kastens, J.; deNoyelles, F.; Huggins, D.; Martinko, E.

2015-12-01

Dam construction has multiple environmental and hydrological consequences including impacts on upstream and downstream ecosystems, water chemistry, and streamflow. Behind the dam the reservoir can trap sediment from the stream and fill over time. With increasing population and drinking and irrigation water demands, particularly in the areas that have highly variable weather and extended drought periods such as the United States Great Plains, reservoir sedimentation escalates water management concerns. Under nearly all projected climate change scenarios we expect that reservoir water storage and management will come under intense scrutiny because of the extensive use of interstate river compacts in the Great Plains. In the state of Kansas, located in the Great Plains, bathymetric surveys have been completed during the last decade for many major lakes by the Kansas Biological Survey, Kansas Water Office, and the U.S. Army Corps of Engineers. In this paper, we studied the spatial and temporal changes of reservoir characteristics including sedimentation yield, depletion rate, and storage capacity loss for 24 federally-operated reservoirs in Kansas. These reservoirs have an average age of about 50 years and collectively have lost approximately 15% of their original capacity, with the highest annual observed single-reservoir depletion rate of 0.84% and sedimentation yield of 1,685 m3 km-2 yr-1.

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.

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.

Oil Reservoir Production Optimization using Optimal Control

DEFF Research Database (Denmark)

Völcker, Carsten; Jørgensen, John Bagterp; Stenby, Erling Halfdan

2011-01-01

Practical oil reservoir management involves solution of large-scale constrained optimal control problems. In this paper we present a numerical method for solution of large-scale constrained optimal control problems. The method is a single-shooting method that computes the gradients using the adjo...... reservoir using water ooding and smart well technology. Compared to the uncontrolled case, the optimal operation increases the Net Present Value of the oil field by 10%.......Practical oil reservoir management involves solution of large-scale constrained optimal control problems. In this paper we present a numerical method for solution of large-scale constrained optimal control problems. The method is a single-shooting method that computes the gradients using...

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.

Evaluation of an Empirical Reservoir Shape Function to Define Sediment Distributions in Small Reservoirs

Directory of Open Access Journals (Sweden)

Bogusław Michalec

2015-08-01

Full Text Available Understanding and defining the spatial distribution of sediment deposited in reservoirs is essential not only at the design stage but also during the operation. The majority of research concerns the distribution of sediment deposition in medium and large water reservoirs. Most empirical methods do not provide satisfactory results when applied to the determination of sediment deposition in small reservoirs. Small reservoir’s volumes do not exceed 5 × 106 m3 and their capacity-inflow ratio is less than 10%. Long-term silting measurements of three small reservoirs were used to evaluate the method described by Rahmanian and Banihashemi for predicting sediment distributions in small reservoirs. Rahmanian and Banihashemi stated that their model of distribution of sediment deposition in water reservoir works well for a long duration operation. In the presented study, the silting rate was used in order to determine the long duration operation. Silting rate is a quotient of volume of the sediment deposited in the reservoir and its original volume. It was stated that when the silting rate had reached 50%, the sediment deposition in the reservoir may be described by an empirical reservoir depth shape function (RDSF.

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

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)

Large Dam Effects on Flow Regime and Hydraulic Parameters of river (Case study: Karkheh River, Downstream of Reservoir Dam

Directory of Open Access Journals (Sweden)

Farhang Azarang

2017-06-01

Full Text Available Introduction: The critical role of the rivers in supplying water for various needs of life has led to engineering identification of the hydraulic regime and flow condition of the rivers. Hydraulic structures such dams have inevitable effects on their downstream that should be well investigated. The reservoir dams are the most important hydraulic structures which are the cause of great changes in river flow conditions. Materials and Methods: In this research, an accurate assessment was performed to study the flow regime of Karkheh river at downstream of Karkheh Reservoir Dam as the largest dam in Middle East. Karkheh River is the third waterful river of Iran after Karun and Dez and the third longest river after the Karun and Sefidrud. The Karkheh Dam is a large reservoir dam built in Iran on the Karkheh River in 2000. The Karkheh Reservoir Dam is on the Karkheh River in the Northwestern Khouzestan Province, the closest city being Andimeshk to the east. The part of Karkheh River, which was studied in this research is located at downstream of Karkheh Reservoir Dam. This interval is approximately 94 km, which is located between PayePol and Abdolkhan hydrometric stations. In this research, 138 cross sections were used along Karkheh River. Distance of cross sections from each other was 680m in average. The efficient model of HEC-RAS has been utilized to simulate the Karkheh flow conditions before and after the reservoir dam construction using of hydrometric stations data included annually and monthly mean discharges, instantaneous maximum discharges, water surface profiles and etc. Three defined discharges had been chosen to simulate the Karkheh River flow; maximum defined discharge, mean defined discharge and minimum defined discharge. For each of these discharges values, HEC-RAS model was implemented as a steady flow of the Karkheh River at river reach of study. Water surface profiles of flow, hydraulic parameters and other results of flow regime in

Determination of residual oil saturation from time-lapse pulsed neutron capture logs in a large sandstone reservoir

International Nuclear Information System (INIS)

Syed, E.V.; Salaita, G.N.; McCaffery, F.G.

1991-01-01

Cased hole logging with pulsed neutron tools finds extensive use for identifying zones of water breakthrough and monitoring oil-water contacts in oil reservoirs being depleted by waterflooding or natural water drive. Results of such surveys then find direct use for planning recompletions and water shutoff treatments. Pulsed neutron capture (PNC) logs are useful for estimating water saturation changes behind casing in the presence of a constant, high-salinity environment. PNC log surveys run at different times, i.e., in a time-lapse mode, are particularly amenable to quantitative analysis. The combined use of the original open hole and PNC time-lapse log information can then provide information on remaining or residual oil saturations in a reservoir. This paper reports analyses of historical pulsed neutron capture log data to assess residual oil saturation in naturally water-swept zones for selected wells from a large sandstone reservoir in the Middle East. Quantitative determination of oil saturations was aided by PNC log information obtained from a series of tests conducted in a new well in the same field

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.

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.

Silicic magma differentiation in ascent conduits. Experimental constraints

Science.gov (United States)

Rodríguez, Carmen; Castro, Antonio

2017-02-01

Crystallization of water-bearing silicic magmas in a dynamic thermal boundary layer is reproduced experimentally by using the intrinsic thermal gradient of piston-cylinder assemblies. The standard AGV2 andesite under water-undersaturated conditions is set to crystallize in a dynamic thermal gradient of about 35 °C/mm in 10 mm length capsules. In the hotter area of the capsule, the temperature is initially set at 1200 °C and decreases by programmed cooling at two distinct rates of 0.6 and 9.6 °C/h. Experiments are conducted in horizontally arranged assemblies in a piston cylinder apparatus to avoid any effect of gravity settling and compaction of crystals in long duration runs. The results are conclusive about the effect of water-rich fluids that are expelled out the crystal-rich zone (mush), where water saturation is reached by second boiling in the interstitial liquid. Expelled fluids migrate to the magma ahead of the solidification front contributing to a progressive enrichment in the fluxed components SiO2, K2O and H2O. The composition of water-rich fluids is modelled by mass balance using the chemical composition of glasses (quenched melt). The results are the basis for a model of granite magma differentiation in thermally-zoned conduits with application of in-situ crystallization equations. The intriguing textural and compositional features of the typical autoliths, accompanying granodiorite-tonalite batholiths, can be explained following the results of this study, by critical phenomena leading to splitting of an initially homogeneous magma into two magma systems with sharp boundaries. Magma splitting in thermal boundary layers, formed at the margins of ascent conduits, may operate for several km distances during magma transport from deep sources at the lower crust or upper mantle. Accordingly, conduits may work as chromatographic columns contributing to increase the silica content of ascending magmas and, at the same time, leave behind residual mushes that

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.

Orientation of the eruption fissures controlled by a shallow magma chamber in Miyakejima

Directory of Open Access Journals (Sweden)

Nobuo Geshi

2016-11-01

Full Text Available Orientation of the eruption fissures and composition of the lavas of the Miyakejima volcano indicate tectonic influence of a shallow magma chamber on the distribution of eruption fissures. We examined the distributions and magmatic compositions of 23 fissures that formed within the last 2800 years, based on a field survey and a new dataset of 14C ages. The dominant orientation of the eruption fissures in the central portion of the volcano was found to be NE-SW, which is perpendicular to the direction of regional maximum horizontal compressive stress (σHmax. Magmas that show evidences of magma mixing between basaltic and andesitic magmas erupted mainly from the eruption fissures with a higher offset angle from the regional σHmax direction. The presence of a shallow dike-shaped magma chamber controls the distribution of the eruption fissures. The injection of basaltic magma into the shallow andesitic magma chamber caused the temporal rise of internal magmatic pressure in the shallow magma chamber. Dikes extending from the andesitic magma chamber intrude along the local compressive stress field which is generated by the internal excess pressure of the andesitic magma chamber. As the result, the eruption fissures trend parallel to the elongation direction of the shallow magma chamber. Injection of basaltic magma into the shallow andesitic magma chamber caused the magma mixing. Some basaltic dikes from the deep-seated magma chamber reach the ground surface without intersection with the andesitic magma chamber. The patterns of the eruption fissures can be modified in the future as was observed in the case of the destruction of the shallow magma chamber during the 2000 AD eruption.

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.

The Surtsey Magma Series.

Science.gov (United States)

Schipper, C Ian; Jakobsson, Sveinn P; White, James D L; Michael Palin, J; Bush-Marcinowski, Tim

2015-06-26

The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50(th) anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption's four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland's Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume.

Deep magma transport at Kilauea volcano, Hawaii

Science.gov (United States)

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

2006-01-01

The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5?? and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325??, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0

Partially molten magma ocean model

International Nuclear Information System (INIS)

Shirley, D.N.

1983-01-01

The properties of the lunar crust and upper mantle can be explained if the outer 300-400 km of the moon was initially only partially molten rather than fully molten. The top of the partially molten region contained about 20% melt and decreased to 0% at 300-400 km depth. Nuclei of anorthositic crust formed over localized bodies of magma segregated from the partial melt, then grew peripherally until they coverd the moon. Throughout most of its growth period the anorthosite crust floated on a layer of magma a few km thick. The thickness of this layer is regulated by the opposing forces of loss of material by fractional crystallization and addition of magma from the partial melt below. Concentrations of Sr, Eu, and Sm in pristine ferroan anorthosites are found to be consistent with this model, as are trends for the ferroan anorthosites and Mg-rich suites on a diagram of An in plagioclase vs. mg in mafics. Clustering of Eu, Sr, and mg values found among pristine ferroan anorthosites are predicted by this model

Seasonal Changes and Spatial Variation in Water Quality of a Large Young Tropical Reservoir and Its Downstream River

Directory of Open Access Journals (Sweden)

Teck-Yee Ling

2017-01-01

Full Text Available This study examined the water quality of the large young tropical Bakun hydroelectric reservoir in Sarawak, Malaysia, and the influence of the outflow on the downstream river during wet and dry seasons. Water quality was determined at five stations in the reservoir at three different depths and one downstream station. The results show that seasons impacted the water quality of the Bakun Reservoir, particularly in the deeper water column. Significantly lower turbidity, SRP, and TP were found during the wet season. At 3–6 m, the oxygen content fell below 5 mg/L and hypoxia was also recorded. Low NO2--N, NO3--N, and SRP and high BOD5, OKN, and TP were observed in the reservoir indicating organic pollution. Active logging activities and the dam construction upstream resulted in water quality deterioration. The outflow decreased the temperature, DO, and pH and increased the turbidity and TSS downstream. Elevated organic matter and nutrients downstream are attributable to domestic discharge along the river. This study shows that the downstream river was affected by the discharge through the turbines, the spillway operations, and domestic waste. Therefore, all these factors should be taken into consideration in the downstream river management for the health of the aquatic organisms.

Understanding the True Stimulated Reservoir Volume in Shale Reservoirs

KAUST Repository

Hussain, Maaruf

2017-06-06

Successful exploitation of shale reservoirs largely depends on the effectiveness of hydraulic fracturing stimulation program. Favorable results have been attributed to intersection and reactivation of pre-existing fractures by hydraulically-induced fractures that connect the wellbore to a larger fracture surface area within the reservoir rock volume. Thus, accurate estimation of the stimulated reservoir volume (SRV) becomes critical for the reservoir performance simulation and production analysis. Micro-seismic events (MS) have been commonly used as a proxy to map out the SRV geometry, which could be erroneous because not all MS events are related to hydraulic fracture propagation. The case studies discussed here utilized a fully 3-D simulation approach to estimate the SRV. The simulation approach presented in this paper takes into account the real-time changes in the reservoir\\'s geomechanics as a function of fluid pressures. It is consisted of four separate coupled modules: geomechanics, hydrodynamics, a geomechanical joint model for interfacial resolution, and an adaptive re-meshing. Reservoir stress condition, rock mechanical properties, and injected fluid pressure dictate how fracture elements could open or slide. Critical stress intensity factor was used as a fracture criterion governing the generation of new fractures or propagation of existing fractures and their directions. Our simulations were run on a Cray XC-40 HPC system. The studies outcomes proved the approach of using MS data as a proxy for SRV to be significantly flawed. Many of the observed stimulated natural fractures are stress related and very few that are closer to the injection field are connected. The situation is worsened in a highly laminated shale reservoir as the hydraulic fracture propagation is significantly hampered. High contrast in the in-situ stresses related strike-slip developed thereby shortens the extent of SRV. However, far field nature fractures that were not connected to

Thermally-assisted Magma Emplacement Explains Restless Calderas.

Science.gov (United States)

Amoruso, Antonella; Crescentini, Luca; D'Antonio, Massimo; Acocella, Valerio

2017-08-11

Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei caldera, Italy. Campi Flegrei experienced at least 4 major unrest episodes in the last decades. Our results indicate that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust. Our thermal models show that this repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth ~3 ka before the last eruption. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks. Our model of thermally-assisted unrest may have a wider applicability, possibly explaining also the dynamics of other restless calderas.

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.

«Magma»: as origens de Guimarães Rosa

Directory of Open Access Journals (Sweden)

Luiz Cláudio Vieira de Oliveira

2011-10-01

Full Text Available Resumo: Leitura de Magma, de Guimarães Rosa, com o objetivo de indicar a presença de temas, fragmentos, personagens, expressões e recursos estilísticos ali existentes, em outros textos do autor, cronologicamente posteriores.Palavras-chave: Literatura brasileira; Guimarães Rosa; Magma.Résumé: Lecture de Magma, de Guimarães Rosa, ayant l’objectif de montrer la présence de quelques sujets, fragments, personnages, expressions et traits stylistiques, que y sont présents, et aussi dans autres textes du même auteur, chronologiquement postérieurs.Mots-clés: Littérature brésilienne; Guimarães Rosa; Magma.Keywords: Brazilian literature; Guimarães Rosa; Magma.

Beyond peak reservoir storage? A global estimate of declining water storage capacity in large reservoirs

NARCIS (Netherlands)

Wisser, D.; Frolking, S.; Hagen, Stephen; Bierkens, M.F.P.|info:eu-repo/dai/nl/125022794

2013-01-01

Water storage is an important way to cope with temporal variation in water supply anddemand. The storage capacity and the lifetime of water storage reservoirs can besignificantly reduced by the inflow of sediments. A global, spatially explicit assessment ofreservoir storage loss in conjunction with

Field and Experimental Constraints on the Dynamics of Replenished Silicic Magma Chambers

Science.gov (United States)

Bain, A. A.; Jellinek, M.

2008-12-01

The underlying causes of catastrophic caldera-forming volcanic eruptions remain poorly understood. However, the occurrence of magma mixing within bimodal systems has become increasingly linked with such eruptions. In particular, buoyancy effects related to unstable density contrasts arising as a result of silicic- basaltic magma interactions may play an important role in the growth, differentiation and catastrophic eruption of silicic magma chambers. Evidence of such magmatic interactions can be found in layered intrusions from the Coastal Maine Magmatic Province (USA), where well-exposed cross-sections reveal hundreds of laterally-extensive basaltic sheets, apparently injected as intrusive lava flows onto the growing floors of silicic magma chambers. Interfaces between mafic and silicic layers are commonly sharply defined and exhibit deformation parallel to the inferred direction of palaeo-gravity. Our field observations suggest that the cooling, settling and buckling of gravitationally-unstable mafic replenishments may have driven large-scale (basalt layer depth) and small- scale (crystal diameter) upwelling and/or overturning of underlying buoyant silicic cumulate material. In order to characterize the full range of buoyancy effects, we carried out extensive spectral analysis of high- resolution digital field measurements from the Pleasant Bay and Mount Desert Island intrusions. In many cases, Rayleigh-Taylor theory and the longest measured wavelength of deformation indicate that a large and potentially-quantifiable fraction of the original, pre-replenishment silicic cumulate thickness may be missing, implying that vertical mass transfer has occurred. In addition, the shortest wavelengths of deformation are generally consistent with observed length-scales of crystals and clumps of crystals at these localities. With the aim of understanding the initial conditions that gave rise to these field observations, we conduct a series of laboratory experiments in which we

RECENT ADVANCES IN NATURALLY FRACTURED RESERVOIR MODELING

OpenAIRE

ORDOÑEZ, A; PEÑUELA, G; IDROBO, E. A; MEDINA, C. E

2001-01-01

Large amounts of oil reserves are contained in naturally fractured reservoirs. Most of these hydrocarbon volumes have been left behind because of the poor knowledge and/or description methodology of those reservoirs. This lack of knowledge has lead to the nonexistence of good quantitative models for this complicated type of reservoirs. The complexity of naturally fractured reservoirs causes the need for integration of all existing information at all scales (drilling, well logging, seismic, we...

The Application of a Multi-Beam Echo-Sounder in the Analysis of the Sedimentation Situation of a Large Reservoir after an Earthquake

Directory of Open Access Journals (Sweden)

Zhong-Luan Yan

2018-04-01

Full Text Available The Wenchuan Earthquake took place in the upper reach catchment of the Min River. It resulted in large amounts of loose materials gathering in the river channel, leading to changes in the sediment transport system in this area. The Zipingpu Reservoir is the last and the largest reservoir located in the upper reach of the Min River. It is near the epicenter and receives sediment from upstream. This paper puts forward a study on the reservoir sedimentation and storage capacity of the Zipingpu Reservoir, employing a multi-beam echo-sounder system in December 2012. Then, the data were merged with digital line graphics and shuttle radar topography mission data in ArcGIS to build a digital elevation model and triangulate the irregular network of Zipingpu Reservoir. Via the analysis of the bathymetric data, the results show the following: (1 The main channels of the reservoir gradually aggrade to a flat bottom from the deep-cutting valley. Sedimentation forms a reach with a W-shaped longitudinal thalweg profile and an almost zero slope reach in the upstream section of the reservoir due to the natural barrier induced by a landslide; (2 The loss ratios of the wetted cross-section surface are higher than 10% in the upstream section of the reservoir and higher than 40% in the natural barrier area; (3 Comparing the surveyed area storage capacity of December 2012 with March 2008, the Zipingpu Reservoir has lost 15.28% of its capacity at the dead storage water level and 10.49% of its capacity at the flood limit water level.

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.

Influence of conduit flow mechanics on magma rheology and the growth style of lava domes

Science.gov (United States)

Husain, Taha; Elsworth, Derek; Voight, Barry; Mattioli, Glen; Jansma, Pamela

2018-06-01

We develop a 2-D particle-mechanics model to explore different lava-dome growth styles. These range from endogenous lava dome growth comprising expansion of a ductile dome core to the exogenous extrusion of a degassed lava plug resulting in generation of a lava spine. We couple conduit flow dynamics with surface growth of the evolving lava dome, fuelled by an open-system magma chamber undergoing continuous replenishment. The conduit flow model accounts for the variation in rheology of ascending magma that results from degassing-induced crystallization. A period of reduced effusive flow rates promote enhanced degassing-induced crystallization. A degassed lava plug extrudes exogenously for magmas with crystal contents (ϕ) of 78 per cent, yield strength >1.62 MPa, and at flow rates of 3 m3 s-1) for magma with lower relative yield strengths (p = 3 MPa) at the conduit exit is forced out by the high discharge rate pulse (2 process, which has been observed at Mount St. Helens and other locations, largely reflects gravitational loading of dome with a viscous core, with retardation by yield strength and talus friction.

Petrology of the 1995/2000 Magma of Copahue, Argentina

Science.gov (United States)

Goss, A.; Varekamp, J. C.

2001-05-01

Phreatomagmatic eruptions of Copahue in July/August,1995 and July/August 2000 produced mixed juvenile clasts, silica-rich debris from the hydrothermal system, and magmatic scoria with 88 percent SiO2. These high-SiO2 clasts carry an as yet unidentified (crystobalite?), euhedral silica phase in great abundance, which is riddled with tan, primary melt inclusions. The mixed clasts have bands of mafic material with small euhedral olivine, clinopyroxene, and plagioclase that are mixed with an intermediate magma with coarser, resorbed phenocrysts of olivine, plagioclase, clino- and ortho- pyroxene, and rare occurrences of the silica phase. These ejecta are intimate mixtures of a relatively felsic magma similar to Pleistocene Copahue lavas and a mafic basaltic andesite, with minor contributions of a magma contaminated with silica-rich hydrothermal wallrock material. Two-pyroxene geothermometry indicates crystallization temperatures of 1020 deg - 1045 deg C. Glass inclusions (59-63 percent SiO2) in plagioclase and olivine crystals yield very low volatile contents in the melt (0.4-1.5 percent H2O). The 1995/2000 magmas resided at shallow level and degassed into the active volcano-hydrothermal system which discharges acid fluids into the Copahue crater lake and hot springs. More mafic magma intruded this shallow batch and the mixture rose into the hydrothermal system and assimilated siliceous wall rock. A Ti-diffusion profile in a magnetite crystal suggests that the period between magma mixing and eruption was on the order of 4-10 weeks, and the temperature difference between resident and intruding magma was about 50-60 oC.

Uranium and thorium concentration process during partial fusion and crystallization of granitic magma

International Nuclear Information System (INIS)

Cuney, M.

1982-01-01

Two major processes, frequently difficult to distinguish, lead to uranium and thorium enrichment in igneous rocks and more particularly in granitoids; these are partial melting and fractional crystallization. Mont-Laurier uranothoriferous pegmatoids, Bancroft and Roessing deposits are examples of radioelement concentrations resulting mostly of low grade of melting on essentially metasedimentary formations deposited on a continental margin or intracratonic. Fractional crystallization follows generally partial melting even in migmatitic areas. Conditions prevailing during magma crystallization and in particular oxygen fugacity led either to the formation of uranium preconcentrations in granitoids, or to its partition in the fluid phase expelled from the magma. No important economic uranium deposit appears to be mostly related to fractional crystallization of large plutonic bodies

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

Applicability of WRF-Lake System in Studying Reservoir-Induced Impacts on Local Climate: Case Study of Two Reservoirs with Contrasting Characteristics

Science.gov (United States)

Wang, F.; Zhu, D.; Ni, G.; Sun, T.

2017-12-01

Large reservoirs play a key role in regional hydrological cycles as well as in modulating the local climate. The emerging large reservoirs in concomitant with rapid hydropower exploitation in southwestern China warrant better understanding of their impacts on local and regional climates. One of the crucial pathways through which reservoirs impact the climate is lake-atmospheric interaction. Although such interactions have been widely studied with numeric weather prediction (NWP) models, an outstanding limitation across various NWPs resides on the poor thermodynamic representation of lakes. The recent version of Weather Research and Forecasting (WRF) system has been equipped with a one-dimensional lake model to better represent the thermodynamics of large water body and has been shown to enhance the its predication skill in the lake-atmospheric interaction. In this study, we further explore the applicability of the WRF-Lake system in two reservoirs with contrasting characteristics: Miyun Reservoir with an average depth of 30 meters in North China Plain, and Nuozhadu Reservoir with an average depth of 200 meters in the Tibetan Plateau Region. Driven by the high spatiotemporal resolution meteorological forcing data, the WRF-Lake system is used to simulate the water temperature and surface energy budgets of the two reservoirs after the evaluation against temperature observations. The simulated results show the WRF-Lake model can well predict the vertical profile of water temperature in Miyun Reservoir, but underestimates deep water temperature and overestimates surface temperature in the deeper Nuozhadu Reservoir. In addition, sensitivity analysis indicates the poor performance of the WRF-Lake system in Nuozhadu Reservoir could be attributed to the weak vertical mixing in the model, which can be improved by tuning the eddy diffusion coefficient ke . Keywords: reservoir-induced climatic impact; lake-atmospheric interaction; WRF-Lake system; hydropower exploitation

Volcanic systems of Iceland and their magma source

Science.gov (United States)

Sigmarsson, Olgeir

2017-04-01

-crust boundary or within the crust in magma reservoirs that are still feeding the volcanic systems. A second possible explanation for absence of temporal variations of isotope ratios for a given volcanic system during the last 10 thousand years is that the roots of these systems lie at further depths within the mantle. In that case, extensive fertile source rock of recycled origin with distinct isotope composition must feed the volcanic system and that the melt extraction mechanism from these source regions does not alter (or homogenize) the final melt products. The consequences of these two mechanisms and possible discrimination between them will be discussed.

Carbon dioxide in magmas and implications for hydrothermal systems

Science.gov (United States)

Lowenstern, J. B.

2001-01-01

This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems

Tube pumices as strain markers of the ductile-brittle transition during magma fragmentation

Science.gov (United States)

Martí, J.; Soriano, C.; Dingwell, D. B.

1999-12-01

Magma fragmentation-the process by which relatively slow-moving magma transforms into a violent gas flow carrying fragments of magma-is the defining feature of explosive volcanism. Yet of all the processes involved in explosively erupting systems, fragmentation is possibly the least understood. Several theoretical and laboratory studies on magma degassing and fragmentation have produced a general picture of the sequence of events leading to the fragmentation of silicic magma. But there remains a debate over whether magma fragmentation is a consequence of the textural evolution of magma to a foamed state where disintegration of walls separating bubbles becomes inevitable due to a foam-collapse criterion, or whether magma is fragmented purely by stresses that exceed its tensile strength. Here we show that tube pumice-where extreme bubble elongation is observed-is a well-preserved magmatic `strain marker' of the stress state immediately before and during fragmentation. Structural elements in the pumice record the evolution of the magma's mechanical response from viscous behaviour (foaming and foam elongation) through the plastic or viscoelastic stage, and finally to brittle behaviour. These observations directly support the hypothesis that fragmentation occurs when magma undergoes a ductile-brittle transition and stresses exceed the magma's tensile strength.

The 1998-2002 activity of Piton de la Fournaise, Réunion island: lessons in magma supply and transfers

Science.gov (United States)

Semet, M. P.; Joron, J.-L.; Staudacher, T.

2003-04-01

In March 1998, Piton de la Fournaise, one of the most frequently active aerial volcanoes on earth, awoke after an unusually long sleep of almost 6 years. This eruption, which was also preceded and accompanied by uncommon patterns of seismicity and deformation (Staudacher et al., 1998), lasted about six months and was followed to the end of 2002 by 9 eruptive episodes of about one week to a little more than a month duration. In these episodes, seismicity and deformations were those more customarily observed. The total amount of erupted magma over this 5 year period amounts to ca. 120 Mm3, which yields an average production rate close to 0.3 m3/s. Suites of lava samples were regularly obtained for each of these episodes, often as water-quenched molten lava, and examined in the laboratory for their petrography and geochemistry. Two subtly differing magmas were erupted in the 1998 episode from two locations. The voluminous lavas vented North of the central cone (Kapor and related vents) were of the ordinary Steady State Basalts (SSB) type modeled by Albarède et al. (1997) yet showed minor but significant evolution through the six months of eruption. Those vented to the South of the cone (Hudson crater) were apparently fed directly and rapidly from depths ca. 15 km, the crust-upper-mantle boundary under Réunion. Hudson samples are of a type observed mostly in peripheral vents but rarely in central eruptions. They are characterized by major and trace element signatures indicating enhanced clinopyroxene fractionation (a high pressure fractionating phase) relative to SSB. In the subsequent 9 eruptions, lavas were again of the SSB kindred, sometimes rich (50 modal %) in cumulative xenocrystic olivine (e.g. June 2001 and January, 2002). Significant chemical differences with the Kapor trend indicate that they were not fed from the same reservoir nor were they akin to Hudson samples. Glass analyses in the quenched post-1998 samples have an almost invariable composition

Magma transport and olivine crystallization depths in Kīlauea's east rift zone inferred from experimentally rehomogenized melt inclusions

Science.gov (United States)

Tuohy, Robin M.; Wallace, Paul J.; Loewen, Matthew W.; Swanson, Donald A.; Kent, Adam J. R.

2016-07-01

Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2 concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai'i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n = 10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n = 38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at <6 km depth, with the majority of olivine in the 1-3 km depth range. These depths are consistent with the interpretation that the Kīlauea Iki magma was supplied from Kīlauea's summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the summit

Shallow magma diversions during explosive diatreme-forming eruptions.

Science.gov (United States)

Le Corvec, Nicolas; Muirhead, James D; White, James D L

2018-04-13

The diversion of magma is an important mechanism that may lead to the relocation of a volcanic vent. Magma diversion is known to occur during explosive volcanic eruptions generating subterranean excavation and remobilization of country and volcanic rocks. However, feedbacks between explosive crater formation and intrusion processes have not been considered previously, despite their importance for understanding evolving hazards during volcanic eruptions. Here, we apply numerical modeling to test the impacts of excavation and subsequent infilling of diatreme structures on stress states and intrusion geometries during the formation of maar-diatreme complexes. Explosive excavation and infilling of diatremes affects local stress states which inhibits magma ascent and drives lateral diversion at various depths, which are expected to promote intra-diatreme explosions, host rock mixing, and vent migration. Our models demonstrate novel mechanisms explaining the generation of saucer-shaped sills, linked with magma diversion and enhanced intra-diatreme explosive fragmentation during maar-diatreme volcanism. Similar mechanisms will occur at other volcanic vents producing crater-forming eruptions.

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.

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

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.

An Isotopic Perspective into the Magmatic Evolution and Architecture of the Rift Zones of Kīlauea Volcano

Science.gov (United States)

Pietruszka, A. J.; Marske, J. P.; Garcia, M. O.; Heaton, D. E.; Rhodes, M. M.

2016-12-01

We present Pb, Sr, and Nd isotope ratios for Kīlauea's historical rift zone lavas (n=50) to examine the magmatic evolution and architecture of the volcano's East Rift Zone (ERZ) and Southwest Rift Zone (SWRZ). Our results show that Kīlauea's historical eruptive period was preceded by the delivery of a major batch of magma from the summit reservoir to the ERZ. The timing of this intrusion, most likely in the late 17th century, was probably related to the 300-yr period of explosive eruptions that followed the formation of the modern caldera (Swanson et al., 2012; JVGR). This rift-stored magma was a component in lavas from lower ERZ (LERZ) eruptions in 1790(?), 1840, 1955, and 1960. The only other components in these LERZ lavas are related to summit lavas erupted (1) after the 1924 collapse of Halemáumáu and (2) during episodes of high fountaining at Kīlauea Iki in 1959. Thus, the intrusion of magma from the summit reservoir into the LERZ is a rare occurrence that is tied to major volcanological events. Intrusions from the summit reservoir in the 1960s likely flushed most older, stored magma from the upper ERZ (UERZ) and middle ERZ (MERZ), leaving large pockets of 1960s-era magma to serve as a dominant component in many subsequent rift lavas. An increase in the duration of pre-eruptive magma storage from the UERZ ( 0-7 yr) to the MERZ ( 0-19 yr) to the LERZ (up to 335 yr) is likely controlled by a decrease in the rate of magma supply to the more distal portions of the ERZ. Lavas from several UERZ eruptions in the 1960s and 1970s have a component of mantle-derived magma that bypassed the summit reservoir. There is no evidence for a summit bypass into the MERZ, LERZ, or the volcanically active portion of the SWRZ. These results support a recent model for Kīlauea's plumbing system (Poland et al., 2014; USGS Prof. Pap. 1801): the ERZ is connected to the deeper "South Caldera" magma body and the volcanic SWRZ is connected to the shallower Halemáumáu magma body.

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

Redox Evolution in Magma Oceans Due to Ferric/Ferrous Iron Partitioning

Science.gov (United States)

Schaefer, L.; Elkins-Tanton, L. T.; Pahlevan, K.

2017-12-01

A long-standing puzzle in the evolution of the Earth is that while the present day upper mantle has an oxygen fugacity close to the QFM buffer, core formation during accretion would have occurred at much lower oxygen fugacities close to IW. We present a new model based on experimental evidence that normal solidification and differentiation processes in the terrestrial magma ocean may explain both core formation and the current oxygen fugacity of the mantle without resorting to a change in source material or process. A commonly made assumption is that ferric iron (Fe3+) is negligible at such low oxygen fugacities [1]. However, recent work on Fe3+/Fe2+ ratios in molten silicates [2-4] suggests that the Fe3+ content should increase at high pressure for a given oxygen fugacity. While disproportionation was not observed in these experiments, it may nonetheless be occurring in the melt at high pressure [5]. Therefore, there may be non-negligible amounts of Fe3+ formed through metal-silicate equilibration at high pressures within the magma ocean. Homogenization of the mantle and further partitioning of Fe2+/Fe3+ as the magma ocean crystallizes may explain the oxygen fugacity of the Earth's mantle without requiring additional oxidation mechanisms. We present here models using different parameterizations for the Fe2+/Fe3+ thermodynamic relationships in silicate melts to constrain the evolution of the redox state of the magma ocean as it crystallizes. The model begins with metal-silicate partitioning at high pressure to form the core and set the initial Fe3+ abundance. Combined with previous work on oxygen absorption by magma oceans due to escape of H from H2O [6], we show that the upper layers of solidifying magma oceans should be more oxidized than the lower mantle. This model also suggests that large terrestrial planets should have more oxidized mantles than small planets. From a redox perspective, no change in the composition of the Earth's accreting material needs to be

The expected greenhouse benefits from developing magma power at Long Valley, California

International Nuclear Information System (INIS)

Haraden, John.

1995-01-01

Magma power is the production of electricity from shallow magma bodies. Before magma becomes a practical source of power, many engineering problems must still be solved. When they are solved, the most likely site for the first magma power plant is Long Valley, California, USA. In this paper, we examine the greenhouse benefits from developing Long Valley. By generating magma power and by curtailing an equal amount of fossil power, we estimate the expected mass and the expected discounted value of reduced CO 2 emissions. For both measures, the expected benefits seem to be substantial. (author)

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; Rico, Ciro; Scandone, Roberto; Terrasi, Filippo

2017-04-01

Defining and understanding the shallow transfer of magma at volcanoes is crucial to forecast eruptions, possibly the ultimate goal of volcanology. This is particularly challenging at felsic calderas experiencing unrest, which typically includes significant changes in seismicity, deformation and degassing rates. Caldera unrest is particularly frequent, affects wide areas and often does not culminate in an eruption. Moreover its evidence is usually complicated by the presence of a hydrothermal system. As a result, forecasting any eruption and vent-opening sites within a caldera is very difficult. The Campi Flegrei caldera (CFc), in the densely inhabited area of Naples (Italy), is commonly considered one of the most dangerous active volcanic systems. CFc is a 12 km wide depression hosting two nested calderas formed during the eruptions of the Campanian Ignimbrite ( 39 ka) and the Neapolitan Yellow Tuff ( 15 ka). In the last 5 ka, resurgence, with uplift >60 m close to the central part of the caldera, was accompanied by volcanism between 4.8 and 3.8 ka. After 3 ka of quiescence, increasing seismicity and uplift preceded the last eruption at Monte Nuovo in 1538 for several decades. The most recent activity culminated in four unrest episodes between 1950-1952, 1969-1972, 1982-1984 and 2005-Present, with a cumulative uplift at Pozzuoli of 4.5 m; the present unrest episode has been interpreted as being magma-driven. These unrest episodes are considered the most evident expression of a longer-term (centuries or more) restless activity. The post-1980 deformation largely results from a magmatic oblate or sill-like source at 4 km depth below Pozzuoli. Despite the restless activity of CFc, the recent unrest episodes did not culminate in eruption, so that any possibility to define the pre-eruptive shallow transfer of magma remains elusive. Indeed, this definition is a crucial step in order to identify and understand pre-eruptive processes, and thus to make any forecast. To fill

Climate variability and sedimentation of a hydropower reservoir

International Nuclear Information System (INIS)

Riedel, M.

2008-01-01

As part of the relicensing of a large Hydroelectric Project in the central Appalachians, large scale watershed and reservoir sedimentation models were developed to forecast potential sedimentation scenarios. The GIS based watershed model was spatially explicit and calibrated to long term observed data. Potential socio/economic development scenarios were used to construct future watershed land cover scenarios. Climatic variability and potential change analysis were used to identify future climate regimes and shifts in precipitation and temperature patterns. Permutations of these development and climate changes were forecasted over 50 years and used to develop sediment yield regimes to the project reservoir. Extensive field work and reservoir survey, including current and wave instrumentation, were used to characterize the project watershed, rivers and reservoir hydrodynamics. A fully 3 dimensional hydrodynamic reservoir sedimentation model was developed for the project and calibrated to observed data. Hydrologic and sedimentation results from watershed forecasting provided boundary conditions for reservoir inputs. The calibrated reservoir model was then used to forecast changes in reservoir sedimentation and storage capacity under different future climate scenarios. Results indicated unique zones of advancing sediment deltas and temporary storage areas. Forecasted changes in reservoir bathymetry and sedimentation patterns were also developed for the various climate change scenarios. The warmer and wetter scenario produced sedimentation impacts similar to extensive development under no climate change. The results of these analyses are being used to develop collaborative watershed and soil conservation partnerships to reduce future soil losses and reservoir sedimentation from projected development. (author)

Phenotypic plasticity in fish life-history traits in two neotropical reservoirs: Petit-Saut Reservoir in French Guiana and Brokopondo Reservoir in Suriname

Directory of Open Access Journals (Sweden)

Bernard de Mérona

Full Text Available Fish species are known for their large phenotypic plasticity in life-history traits in relation to environmental characteristics. Plasticity allows species to increase their fitness in a given environment. Here we examined the life-history response of fish species after an abrupt change in their environment caused by the damming of rivers. Two reservoirs of different age, both situated on the Guiana Shield, were investigated: the young Petit-Saut Reservoir in French Guiana (14 years and the much older Brokopondo Reservoir in Suriname (44 years. Six life-history traits in 14 fish species were studied and compared to their value in the Sinnamary River prior to the completion of Petit-Saut Reservoir. The traits analyzed were maximum length, absolute and relative length at first maturation, proportion of mature oocytes in ripe gonad, batch fecundity and mean size of mature oocytes. The results revealed a general increase of reproductive effort. All species showed a decrease in maximum length. Compared to the values observed before the dam constructions, eight species had larger oocytes and three species showed an increased batch fecundity. These observed changes suggest a trend towards a pioneer strategy. The changes observed in Petit-Saut Reservoir also seemed to apply to the 30 years older Brokopondo Reservoir suggesting that these reservoirs remain in a state of immaturity for a long time.

Nutrient budget for Saguling Reservoir, West Java, Indonesia.

Science.gov (United States)

Hart, Barry T; van Dok, Wendy; Djuangsih, Nani

2002-04-01

A preliminary nutrient budget for Saguling Reservoir is reported as a first attempt to quantify the behaviour of nutrients entering this reservoir. This work is part of a larger Indonesia-Australia collaborative research and training project, involving Padjadjaran University and Monash University, established to study nutrient dynamics in Saguling Reservoir. Saguling Reservoir, the first of a chain of three large reservoirs (Saguling, Cirata and Jatilahur), built on the Citarum River in central Java, was completed in 1985. It has already become highly polluted, particularly with domestic and industrial effluent (organic matter, nutrients, heavy metals) from the urban areas of Bandung (population 2 million). The reservoir experiences major water quality problems, including excessive growths of floating plants, toxic cyanobacterial blooms and regular fish-kills. The work reported in this paper shows that Saguling receives a very large nutrient load from the city of Bandung and because of this, is highly eutrophic. It is unlikely that the water quality of Saguling will improve until a substantial part of Bandung is sewered and adequate discharge controls are placed on the many industries in the region upstream of the reservoir.

Method of extracting heat from dry geothermal reservoirs

Science.gov (United States)

Potter, R.M.; Robinson, E.S.; Smith, M.C.

1974-01-22

Hydraulic fracturing is used to interconnect two or more holes that penetrate a previously dry geothermal reservoir, and to produce within the reservoir a sufficiently large heat-transfer surface so that heat can be extracted from the reservoir at a usefully high rate by a fluid entering it through one hole and leaving it through another. Introduction of a fluid into the reservoir to remove heat from it and establishment of natural (unpumped) convective circulation through the reservoir to accomplish continuous heat removal are important and novel features of the method. (auth)

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

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.

Geological model of supercritical geothermal reservoir related to subduction system

Science.gov (United States)

Tsuchiya, Noriyoshi

2017-04-01

Following the Great East Japan Earthquake and the accident at the Fukushima Daiichi Nuclear power station on 3.11 (11th March) 2011, geothermal energy came to be considered one of the most promising sources of renewable energy for the future in Japan. The temperatures of geothermal fields operating in Japan range from 200 to 300 °C (average 250 °C), and the depths range from 1000 to 2000 m (average 1500 m). In conventional geothermal reservoirs, the mechanical behavior of the rocks is presumed to be brittle, and convection of the hydrothermal fluid through existing network is the main method of circulation in the reservoir. In order to minimize induced seismicity, a rock mass that is "beyond brittle" is one possible candidate, because the rock mechanics of "beyond brittle" material is one of plastic deformation rather than brittle failure. Supercritical geothermal resources could be evaluated in terms of present volcanic activities, thermal structure, dimension of hydrothermal circulation, properties of fracture system, depth of heat source, depth of brittle factures zone, dimension of geothermal reservoir. On the basis of the GIS, potential of supercritical geothermal resources could be characterized into the following four categories. 1. Promising: surface manifestation d shallow high temperature, 2 Probability: high geothermal gradient, 3 Possibility: Aseismic zone which indicates an existence of melt, 4 Potential : low velocity zone which indicates magma input. Base on geophysical data for geothermal reservoirs, we have propose adequate tectonic model of development of the supercritical geothermal reservoirs. To understand the geological model of a supercritical geothermal reservoir, granite-porphyry system, which had been formed in subduction zone, was investigated as a natural analog of the supercritical geothermal energy system. Quartz veins, hydrothermal breccia veins, and glassy veins are observed in a granitic body. The glassy veins formed at 500-550 �

Phenotypic plasticity in fish life-history traits in two neotropical reservoirs : Petit-Saut Reservoir in French Guiana and Brokopondo Reservoir in Suriname

OpenAIRE

Merona de, Bernard; Mol, J.; Vigouroux, R.; Chaves, P. D.

2009-01-01

Fish species are known for their large phenotypic plasticity in life-history traits in relation to environmental characteristics. Plasticity allows species to increase their fitness in a given environment. Here we examined the life-history response of fish species after an abrupt change in their environment caused by the damming of rivers. Two reservoirs of different age, both situated on the Guiana Shield, were investigated: the young Petit-Saut Reservoir in French Guiana (14 years) and the ...

Magma mixing in granitic rocks of the central Sierra Nevada, California

Science.gov (United States)

Reid, John B.; Evans, Owen C.; Fates, Dailey G.

1983-12-01

The El Capitan alaskite exposed in the North American Wall, Yosemite National Park, was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite. Comparisons of petrographic and compositional data for these dikes and alaskite with published data for Sierra Nevada plutons lead us to suggest that mafic magmas were important in the generation of the Sierra Nevada batholith. Specifically, we conclude that: (1) intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite (rhyolitic) magmas; (2) interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements; (3) most mafic inclusions in Sierra Nevada plutons represent chilled pillows of mafic magmas, related by fractional crystallization and granitoid assimilation, that dissolve into their felsic host and contaminate it to intermediate (granodioritic) compositions; (4) vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton's domed ceiling causing the zoning (mafic margins-to-felsic core) that these plutons exhibit.

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)

Juvenile pumice and pyroclastic obsidian reveal the eruptive conditions necessary for the stability of Plinian eruption of rhyolitic magma

Science.gov (United States)

Giachetti, T.; Shea, T.; Gonnermann, H. M.; McCann, K. A.; Hoxsie, E. C.

2016-12-01

Significant explosive activity generally precedes or coexists with the large effusion of rhyolitic lava (e.g., Mono Craters; Medicine Lake Volcano; Newberry; Chaitén; Cordón Caulle). Such explosive-to-effusive transitions and, ultimately, cessation of activity are commonly explained by the overall waning magma chamber pressure accompanying magma withdrawal, albeit modulated by magma outgassing. The tephra deposits of such explosive-to-effusive eruptions record the character of the transition - abrupt or gradual - as well as potential changes in eruptive conditions, such as magma composition, volatiles content, mass discharge rate, conduit size, magma outgassing. Results will be presented from a detailed study of both the gas-rich (pumice) and gas-poor (obsidian) juvenile pyroclasts produced during the Plinian phase of the 1060 CE Glass Mountain eruption of Medicine Lake Volcano, California. In the proximal deposits, a multitude of pumice-rich sections separated by layers rich in dense clasts suggests a pulsatory behavior of the explosive phase. Density measurements on 2,600 pumices show that the intermediate, most voluminous deposits have a near constant median porosity of 65%. However, rapid increase in porosity to 75-80% is observed at both the bottom and the top of the fallout deposits, suggestive of rapid variations in magma degassing. In contrast, a water content of pyroclastic obsidians of approximately 0.6 wt% does remain constant throughout the eruption, suggesting that the pyroclastic obsidians degassed up to a constant pressure of a few megapascals. Numerical modeling of eruptive magma ascent and degassing is used to provide constraints on eruption conditions.

Molybdenite saturation in silicic magmas: Occurrence and petrological implications

Science.gov (United States)

Audetat, A.; Dolejs, D.; Lowenstern, J. B.

2011-01-01

We identified molybdenite (MoS2) as an accessory magmatic phase in 13 out of 27 felsic magma systems examined worldwide. The molybdenite occurs as small (molybdenite-saturated samples reveal 1-13 ppm Mo in the melt and geochemical signatures that imply a strong link to continental rift basalt-rhyolite associations. In contrast, arc-associated rhyolites are rarely molybdenite-saturated, despite similar Mo concentrations. This systematic dependence on tectonic setting seems to reflect the higher oxidation state of arc magmas compared with within-plate magmas. A thermodynamic model devised to investigate the effects of T, f O2 and f S2 on molybdenite solubility reliably predicts measured Mo concentrations in molybdenite-saturated samples if the magmas are assumed to have been saturated also in pyrrhotite. Whereas pyrrhotite microphenocrysts have been observed in some of these samples, they have not been observed from other molybdenite-bearing magmas. Based on the strong influence of f S2 on molybdenite solubility we calculate that also these latter magmas must have been at (or very close to) pyrrhotite saturation. In this case the Mo concentration of molybdenite-saturated melts can be used to constrain both magmatic f O2 and f S2 if temperature is known independently (e.g. by zircon saturation thermometry). Our model thus permits evaluation of magmatic f S2, which is an important variable but is difficult to estimate otherwise, particularly in slowly cooled rocks. ?? The Author 2011. Published by Oxford University Press. All rights reserved.

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.

Genesis of felsic plutonic magmas and their igneous enclaves

DEFF Research Database (Denmark)

Clemens, John D.; Maas, Roland; Waight, Tod Earle

2016-01-01

-type Pyalong pluton was emplaced, apparently along an east-west-orientated fracture zone. Around 367 Ma, the main I-type Baynton pluton intruded as numerous shallow-dipping sheets. The last plutonic event was the intrusion of the broad, thin, flat-lying, and crosscutting sheet of the I-type Beauvallet pluton...... the relatively high abundance of igneous-textured microgranular enclaves (MEs). The MEs show neither chemical nor isotope mixing trends with each other or with the host magmas. Variations in the Baynton magmas were derived from the heterogeneity of the source terrane, with individual magma batches formed from...

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.

MULTIDISCIPLINARY IMAGING OF ROCK PROPERTIES IN CARBONATE RESERVOIRS FOR FLOW-UNIT TARGETING

Energy Technology Data Exchange (ETDEWEB)

Stephen C. Ruppel

2005-02-01

Despite declining production rates, existing reservoirs in the US contain large quantities of remaining oil and gas that constitute a huge target for improved diagnosis and imaging of reservoir properties. The resource target is especially large in carbonate reservoirs, where conventional data and methodologies are normally insufficient to resolve critical scales of reservoir heterogeneity. The objectives of the research described in this report were to develop and test such methodologies for improved imaging, measurement, modeling, and prediction of reservoir properties in carbonate hydrocarbon reservoirs. The focus of the study is the Permian-age Fullerton Clear Fork reservoir of the Permian Basin of West Texas. This reservoir is an especially appropriate choice considering (a) the Permian Basin is the largest oil-bearing basin in the US, and (b) as a play, Clear Fork reservoirs have exhibited the lowest recovery efficiencies of all carbonate reservoirs in the Permian Basin.

AUTOMATED TECHNIQUE FOR FLOW MEASUREMENTS FROM MARIOTTE RESERVOIRS.

Science.gov (United States)

Constantz, Jim; Murphy, Fred

1987-01-01

The mariotte reservoir supplies water at a constant hydraulic pressure by self-regulation of its internal gas pressure. Automated outflow measurements from mariotte reservoirs are generally difficult because of the reservoir's self-regulation mechanism. This paper describes an automated flow meter specifically designed for use with mariotte reservoirs. The flow meter monitors changes in the mariotte reservoir's gas pressure during outflow to determine changes in the reservoir's water level. The flow measurement is performed by attaching a pressure transducer to the top of a mariotte reservoir and monitoring gas pressure changes during outflow with a programmable data logger. The advantages of the new automated flow measurement techniques include: (i) the ability to rapidly record a large range of fluxes without restricting outflow, and (ii) the ability to accurately average the pulsing flow, which commonly occurs during outflow from the mariotte reservoir.

Characteristics and Significance of Magma Emplacement Horizons, Black Sturgeon Sill, Nipigon, Ontario

Science.gov (United States)

Zieg, M. J.; Hone, S. V.

2017-12-01

Spatial scales strongly control the timescales of processes in igneous intrusions, particularly through the thermal evolution of the magma, which in turn governs the evolution of crystallinity, viscosity, and other important physical and chemical properties of the system. In this study, we have collected a highly detailed data set comprising geochemical (bulk rock composition), textural (size and alignment of plagioclase crystals), and mineralogical (modal abundance) profiles through the central portion of the 250 m thick Black Sturgeon diabase sill. In this data, we have identified characteristic signals in texture (soft and somewhat diffuse chills), composition (reversals in differentiation trends), and mineralogy (olivine accumulations), all coinciding and recurring at roughly 10 meter intervals. Based on these signatures, we are able to map out multiple zones representing discrete pulses of magma that were emplaced sequentially as the intrusion was inflated. Simple thermal calculations suggest that each 10 meters of new crystallization would require repose times on the order of 10-100 years. To build up 250 meters of magma at this rate would only require approximately 250-2500 years, significantly less than the thermal lifetime of the entire sill. The soft chills we observe in the Black Sturgeon sill are therefore consistent with a system that remained warm throughout the emplacement process. Successive pulses were injected into partially crystalline mush, rather than pure liquid (which would result in hybridization) or solid (which would produce sharp hard chills). Episodic emplacement is by now widely recognized as a fundamental process in the formation of large felsic magma chambers; our results suggest that this also may be an important consideration in understanding the evolution of smaller mafic intrusions.

Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions

Science.gov (United States)

Johnson, E. R.

2015-12-01

Island arc volcanoes can become submarine during cataclysmal caldera collapse. The passage of a volcanic vent from atmospheric to under water environment involves complex modifications of the eruption style and subsequent transport of the pyroclasts. Here, we use FTIR measurements of the volatile contents of glass and melt inclusions in the juvenile pumice clasts in the Sumisu basin and its surroundings (Izu-Bonin arc) to investigate changes in eruption depths, magma storage and degassing over time. This study is based on legacy cores from ODP 126, where numerous unconsolidated (250 m), massive to normally graded pumice lapilli-tuffs were recovered over four cores (788C, 790A, 790B and 791A). Glass and clast geochemistry indicate the submarine Sumisu caldera as the source of several of these pumice lapilli-tuffs. Glass chips and melt inclusions from these samples were analyzed using FTIR for H2O and CO2 contents. Glass chips record variable H2O contents; most chips contain 0.6-1.6 wt% H2O, corresponding to eruption depths of 320-2100 mbsl. Variations in glass H2O and pressure estimates suggest that edifice collapse occurred prior-to or during eruption of the oldest of these samples, and that the edifice may have subsequently grown over time. Sanidine-hosted melt inclusions from two units record variably degassed but H2O-rich melts (1.1-5.6 wt% H2O). The lowest H2O contents overlap with glass chips, consistent with degassing and crystallization of melts until eruption, and the highest H2O contents suggest that large amounts of degassing accompanied likely explosive eruptions. Most inclusions, from both units, contain 2-4 wt% H2O, which further indicates that the magmas crystallized at pressures of ~50-100 MPa, or depths ~400-2800 m below the seafloor. Further glass and melt inclusion analyses, including major element compositions, will elucidate changes in magma storage, degassing and evolution over time.

Understanding the rheology of two and three-phase magmas

Science.gov (United States)

Coats, R.; Cai, B.; Kendrick, J. E.; Wallace, P. A.; Hornby, A. J.; Miwa, T.; von Aulock, F. W.; Ashworth, J. D.; Godinho, J.; Atwood, R. C.; Lee, P. D.; Lavallée, Y.

2017-12-01

The rheology of magma plays a fundamental role in determining the style of a volcanic eruption, be it explosive or effusive. Understanding how magmas respond to changes in stress/ strain conditions may help to enhance eruption forecast models. The presence of crystals and bubbles in magmas alter the viscosity of suspensions and favor a non-Newtonian response. Thus, with the aim of grasping the rheological behavior of volcanic materials, uniaxial compressive tests were performed on natural and synthetic samples. A suite of variably porous (10-32 vol.%), highly crystalline ( 50 vol.%) dacite from the 1991-95 eruption of Mt Unzen, Japan, was selected as the natural material, while synthetic samples were sintered with desired porosities (Diamond Light Source. Unexpectedly, these observations suggest that fractures nucleate in crystals due to crystal interactions, before propagating through the interstitial melt. This ongoing study promises to uncover the way crystal-bearing magmas flow or fail, necessary to constrain magmatic processes and volcanic hazards.

Magma buoyancy and volatile ascent driving autocyclic eruptivity at Hekla Volcano (Iceland)

Science.gov (United States)

Hautmann, Stefanie; Sacks, I. Selwyn; Linde, Alan T.; Roberts, Matthew J.

2017-09-01

Volcanic eruptions are typically accompanied by ground deflation due to the withdrawal of magma from depth and its effusion at the surface. Here, based on continuous high-resolution borehole strain data, we show that ground deformation was absent during the major effusion phases of the 1991 and 2000 eruptions of Hekla Volcano, Iceland. This lack of surface deformation challenges the classic model of magma intrusion/withdrawal as source for volcanic ground uplift/subsidence. We incorporate geodetic and geochemical observables into theoretical models of magma chamber dynamics in order to constrain quantitatively alternative co- and intereruptive physical mechanisms that govern magma propagation and system pressurization. We find the lack of surface deformation during lava effusion to be linked to chamber replenishment from below whilst magma migrates as a buoyancy-driven flow from the magma chamber towards the surface. We further demonstrate that intereruptive pressure build-up is likely to be generated by volatile ascent within the chamber rather than magma injection. Our model explains the persistent periodic eruptivity at Hekla throughout historic times with self-initiating cycles and is conceptually relevant to other volcanic systems.

Integrated Water Basin Management Including a Large Pit Lake and a Water Supply Reservoir: The Mero-Barcés Basin

Science.gov (United States)

Delgado, Jordi; Juncosa-Rivera, Ricardo; Hernández-Anguiano, Horacio; Muñoz-Ibáñez, Andrea

2016-04-01

Water resource managers attempt to minimize conflicts among users, preserve the environment as much as possible, and satisfy user necessities at a minimum cost. Several European directives indirectly address mine restoration policies, with a goal of minimizing negative impacts and adding social and environmental value where possible. Water management must consider water sources, ecological flows, flood control, and variability in the demands for urban, industrial, and agricultural uses. In the context of the present study, the city of A Coruña is located in Galicia (NW Spain). The water supply system for this city and surrounding municipalities (~400.000 inhabitants) is based on the Abegondo-Cecebre reservoir. In cases when precipitation is scarce (e.g. no rain for more than seven consecutive months) and there is a seasonal increase in demand significantly stress the supply system so that, as occurred in 2010, shortages and water supply restrictions need to be considered. This is a clear indication of that, at present, the Abegondo-Cecebre reservoir has not enough capacity to cope with a scenario of increasing water demand (due to the vegetative and seasonal increase of population) and hydric stress likely connected with the widely acknowledged climate change. In the present context of monetary resources scarcity and society concern with respect large new public work projects, the construction of a new dam is challenging. However the opportunity provided by the recent flooding of the Meirama open pit (a large mine void that has been forced-flooded for its reclamation and it is located in the headwaters of one of the rivers draining towards the Abegondo-Cecebre reservoir) proves to be a significant new asset that will help to improve the future water management scenarios under the acknowledged uncertain conditions. In this study we have studied in detail the hydrochemistry of the affected systems (lake, river and reservoir) in order to make clear whether or not the

Mapping the Fluid Pathways and Permeability Barriers of a Large Gas Hydrate Reservoir

Science.gov (United States)

Campbell, A.; Zhang, Y. L.; Sun, L. F.; Saleh, R.; Pun, W.; Bellefleur, G.; Milkereit, B.

2012-12-01

An understanding of the relationship between the physical properties of gas hydrate saturated sedimentary basins aids in the detection, exploration and monitoring one of the world's upcoming energy resources. A large gas hydrate reservoir is located in the MacKenzie Delta of the Canadian Arctic and geophysical logs from the Mallik test site are available for the gas hydrate stability zone (GHSZ) between depths of approximately 850 m to 1100 m. The geophysical data sets from two neighboring boreholes at the Mallik test site are analyzed. Commonly used porosity logs, as well as nuclear magnetic resonance, compressional and Stoneley wave velocity dispersion logs are used to map zones of elevated and severely reduced porosity and permeability respectively. The lateral continuity of horizontal permeability barriers can be further understood with the aid of surface seismic modeling studies. In this integrated study, the behavior of compressional and Stoneley wave velocity dispersion and surface seismic modeling studies are used to identify the fluid pathways and permeability barriers of the gas hydrate reservoir. The results are compared with known nuclear magnetic resonance-derived permeability values. The aim of investigating this heterogeneous medium is to map the fluid pathways and the associated permeability barriers throughout the gas hydrate stability zone. This provides a framework for an understanding of the long-term dissociation of gas hydrates along vertical and horizontal pathways, and will improve the knowledge pertaining to the production of such a promising energy source.

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.

Seismic tremors and magma wagging during explosive volcanism.

Science.gov (United States)

Jellinek, A Mark; Bercovici, David

2011-02-24

Volcanic tremor is a ubiquitous feature of explosive eruptions. This oscillation persists for minutes to weeks and is characterized by a remarkably narrow band of frequencies from about 0.5 Hz to 7 Hz (refs 1-4). Before major eruptions, tremor can occur in concert with increased gas flux and related ground deformation. Volcanic tremor is thus of particular value for eruption forecasting. Most models for volcanic tremor rely on specific properties of the geometry, structure and constitution of volcanic conduits as well as the gas content of the erupting magma. Because neither the initial structure nor the evolution of the magma-conduit system will be the same from one volcano to the next, it is surprising that tremor characteristics are so consistent among different volcanoes. Indeed, this universality of tremor properties remains a major enigma. Here we employ the contemporary view that silicic magma rises in the conduit as a columnar plug surrounded by a highly vesicular annulus of sheared bubbles. We demonstrate that, for most geologically relevant conditions, the magma column will oscillate or 'wag' against the restoring 'gas-spring' force of the annulus at observed tremor frequencies. In contrast to previous models, the magma-wagging oscillation is relatively insensitive to the conduit structure and geometry, which explains the narrow band of tremor frequencies observed around the world. Moreover, the model predicts that as an eruption proceeds there will be an upward drift in both the maximum frequency and the total signal frequency bandwidth, the nature of which depends on the explosivity of the eruption, as is often observed.

Failed magmatic eruptions: Late-stage cessation of magma ascent

Science.gov (United States)

Moran, S.C.; Newhall, C.; Roman, D.C.

2011-01-01

When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: "deep intrusion", "shallow intrusion", "sluggish/viscous magmatic eruption", and "rapid, often explosive magmatic eruption". We define "failed eruptions" as instances in which magma reaches but does not pass the "shallow intrusion" stage, i. e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.

Effects of rotation on crystal settling in a terrestrial magma ocean: Spherical shell model

Science.gov (United States)

Maas, C.; Hansen, U.

2015-12-01

Like Moon or Mars, Earth experienced one or several deep magma ocean periods of globalextent in a later stage of its accretion. The crystallization of these magma oceans is of keyimportance for the chemical structure of Earth, the mantle evolution and the onset of platetectonics. Due to the fast rotation of early Earth and the small magma viscosity, rotationprobably had a profound effect on differentiation processes. For example, Matyska et al.[1994] propose that the distribution of heterogeneities like the two large low shear velocityprovinces (LLSVP) at the core mantle boundary is influenced by rotational dynamicsof early Earth. Further Garnero and McNamara [2008] suggest that the LLSVPs arevery long-living anomalies, probably reaching back to the time of differentiation andsolidification of Earth. However, nearly all previous studies neglect the effects of rotation.In our previous work using a Cartesian model, a strong influence of rotation as well asof latitude on the differentiation processes in an early magma ocean was revealed. Weshowed that crystal settling in an early stage of magma ocean crystallization cruciallydepends on latitude as well as on rotational strength and crystal density.In order to overcome the restrictions as to the geometry of the Cartesian model, we arecurrently developing a spherical model to simulate crystal settling in a rotating sphericalshell. This model will allow us not only to investigate crystal settling at the poles andthe equator, but also at latitudes in-between these regions, as well as the migration ofcrystals between poles and equator. ReferencesE. J. Garnero and A. K. McNamara. Structure and dynamics of earth's lower mantle.Science, 320(5876):626-628, 2008.C. Matyska, J. Moser, and D. A. Yuen. The potential influence of radiative heat transferon the formation of megaplumes in the lower mantle. Earth and Planetary ScienceLetters, 125(1):255-266, 1994.

Iron Redox Systematics of Shergottites and Martian Magmas

Science.gov (United States)

Righter, Kevin; Danielson, L. R.; Martin, A. M.; Newville, M.; Choi, Y.

2010-01-01

Martian meteorites record a range of oxygen fugacities from near the IW buffer to above FMQ buffer [1]. In terrestrial magmas, Fe(3+)/ SigmaFe for this fO2 range are between 0 and 0.25 [2]. Such variation will affect the stability of oxides, pyroxenes, and how the melt equilibrates with volatile species. An understanding of the variation of Fe(3+)/SigmaFe for martian magmas is lacking, and previous work has been on FeO-poor and Al2O3-rich terrestrial basalts. We have initiated a study of the iron redox systematics of martian magmas to better understand FeO and Fe2O3 stability, the stability of magnetite, and the low Ca/high Ca pyroxene [3] ratios observed at the surface.

Improved characterization of reservoir behavior by integration of reservoir performances data and rock type distributions

Energy Technology Data Exchange (ETDEWEB)

Davies, D.K.; Vessell, R.K. [David K. Davies & Associates, Kingwood, TX (United States); Doublet, L.E. [Texas A& M Univ., College Station, TX (United States)] [and others

1997-08-01

An integrated geological/petrophysical and reservoir engineering study was performed for a large, mature waterflood project (>250 wells, {approximately}80% water cut) at the North Robertson (Clear Fork) Unit, Gaines County, Texas. The primary goal of the study was to develop an integrated reservoir description for {open_quotes}targeted{close_quotes} (economic) 10-acre (4-hectare) infill drilling and future recovery operations in a low permeability, carbonate (dolomite) reservoir. Integration of the results from geological/petrophysical studies and reservoir performance analyses provide a rapid and effective method for developing a comprehensive reservoir description. This reservoir description can be used for reservoir flow simulation, performance prediction, infill targeting, waterflood management, and for optimizing well developments (patterns, completions, and stimulations). The following analyses were performed as part of this study: (1) Geological/petrophysical analyses: (core and well log data) - {open_quotes}Rock typing{close_quotes} based on qualitative and quantitative visualization of pore-scale features. Reservoir layering based on {open_quotes}rock typing {close_quotes} and hydraulic flow units. Development of a {open_quotes}core-log{close_quotes} model to estimate permeability using porosity and other properties derived from well logs. The core-log model is based on {open_quotes}rock types.{close_quotes} (2) Engineering analyses: (production and injection history, well tests) Material balance decline type curve analyses to estimate total reservoir volume, formation flow characteristics (flow capacity, skin factor, and fracture half-length), and indications of well/boundary interference. Estimated ultimate recovery analyses to yield movable oil (or injectable water) volumes, as well as indications of well and boundary interference.

The elusive Hadean enriched reservoir revealed by 142Nd deficits in Isua Archaean rocks.

Science.gov (United States)

Rizo, Hanika; Boyet, Maud; Blichert-Toft, Janne; O'Neil, Jonathan; Rosing, Minik T; Paquette, Jean-Louis

2012-11-01

The first indisputable evidence for very early differentiation of the silicate Earth came from the extinct (146)Sm-(142)Nd chronometer. (142)Nd excesses measured in 3.7-billion-year (Gyr)-old rocks from Isua (southwest Greenland) relative to modern terrestrial samples imply their derivation from a depleted mantle formed in the Hadean eon (about 4,570-4,000 Gyr ago). As dictated by mass balance, the differentiation event responsible for the formation of the Isua early-depleted reservoir must also have formed a complementary enriched component. However, considerable efforts to find early-enriched mantle components in Isua have so far been unsuccessful. Here we show that the signature of the Hadean enriched reservoir, complementary to the depleted reservoir in Isua, is recorded in 3.4-Gyr-old mafic dykes intruding into the Early Archaean rocks. Five out of seven dykes carry (142)Nd deficits compared to the terrestrial Nd standard, with three samples yielding resolvable deficits down to -10.6 parts per million. The enriched component that we report here could have been a mantle reservoir that differentiated owing to the crystallization of a magma ocean, or could represent a mafic proto-crust that separated from the mantle more than 4.47 Gyr ago. Our results testify to the existence of an enriched component in the Hadean, and may suggest that the southwest Greenland mantle preserved early-formed heterogeneities until at least 3.4 Gyr ago.

Hybrid Stochastic Forecasting Model for Management of Large Open Water Reservoir with Storage Function

Science.gov (United States)

Kozel, Tomas; Stary, Milos

2017-12-01

The main advantage of stochastic forecasting is fan of possible value whose deterministic method of forecasting could not give us. Future development of random process is described better by stochastic then deterministic forecasting. Discharge in measurement profile could be categorized as random process. Content of article is construction and application of forecasting model for managed large open water reservoir with supply function. Model is based on neural networks (NS) and zone models, which forecasting values of average monthly flow from inputs values of average monthly flow, learned neural network and random numbers. Part of data was sorted to one moving zone. The zone is created around last measurement average monthly flow. Matrix of correlation was assembled only from data belonging to zone. The model was compiled for forecast of 1 to 12 month with using backward month flows (NS inputs) from 2 to 11 months for model construction. Data was got ridded of asymmetry with help of Box-Cox rule (Box, Cox, 1964), value r was found by optimization. In next step were data transform to standard normal distribution. The data were with monthly step and forecast is not recurring. 90 years long real flow series was used for compile of the model. First 75 years were used for calibration of model (matrix input-output relationship), last 15 years were used only for validation. Outputs of model were compared with real flow series. For comparison between real flow series (100% successfully of forecast) and forecasts, was used application to management of artificially made reservoir. Course of water reservoir management using Genetic algorithm (GE) + real flow series was compared with Fuzzy model (Fuzzy) + forecast made by Moving zone model. During evaluation process was founding the best size of zone. Results show that the highest number of input did not give the best results and ideal size of zone is in interval from 25 to 35, when course of management was almost same for

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.

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.

Fragmentation, nucleation and migration of crystals and bubbles in the Bishop Tuff rhyolitic magma

Energy Technology Data Exchange (ETDEWEB)

Gualda, G.; Cook, D.L.; Chopra, R.; Qin, L.; Anderson, A.T.; Rivers, M. (UC)

2010-12-07

The Bishop Tuff (USA) is a large-volume, high-silica pyroclastic rhyolite. Five pumice clasts from three early stratigraphic units were studied. Size distributions were obtained using three approaches: (1) crushing, sieving and winnowing (reliable for crystals >100 {micro}m); (2) microscopy of 1 mm{sup 3} fragments (preferable for crystals <100 {micro}m); and (3) computerised X-ray microtomography of {approx}1 cm{sup 3} pumice pieces. Phenocryst fragments coated with glass are common, and the size distributions for all crystals are concave-upward, indicating that crystal fragmentation is an important magmatic process. Three groups are recognised, characterised by: (1) high-density (0.759-0.902 g cm{sup -3}), high-crystal content (14.4-15.3 wt.%) and abundant large crystals (>800 {micro}m); concave-downward size distributions for whole crystals indicate late-stage growth with limited nucleation, compatible with the slow cooling of a large, gas-saturated, stably stratified magma body; (2) low-density (0.499 g cm{sup -3}), low-crystal content (6.63 wt.%) and few large crystals; the approximately linear size distribution reveals that nucleation was locally important, perhaps close to the walls; and (3) intermediate characteristics in all respects. The volumetric fraction of bubbles inversely correlates with the number of large crystals. This is incompatible with isobaric closed-system crystallisation, but can be explained by sinking of large crystals and rise of bubbles in the magma.

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

Data Compression of Hydrocarbon Reservoir Simulation Grids

KAUST Repository

Chavez, Gustavo Ivan

2015-05-28

A dense volumetric grid coming from an oil/gas reservoir simulation output is translated into a compact representation that supports desired features such as interactive visualization, geometric continuity, color mapping and quad representation. A set of four control curves per layer results from processing the grid data, and a complete set of these 3-dimensional surfaces represents the complete volume data and can map reservoir properties of interest to analysts. The processing results yield a representation of reservoir simulation results which has reduced data storage requirements and permits quick performance interaction between reservoir analysts and the simulation data. The degree of reservoir grid compression can be selected according to the quality required, by adjusting for different thresholds, such as approximation error and level of detail. The processions results are of potential benefit in applications such as interactive rendering, data compression, and in-situ visualization of large-scale oil/gas reservoir simulations.

Assimilation of carbonate country rock by the parent magma of the Panzhihua Fe-Ti-V deposit (SW China: Evidence from stable isotopes

Directory of Open Access Journals (Sweden)

Clément Ganino

2013-09-01

Full Text Available The Panzhihua intrusion in southwest China is part of the Emeishan Large Igneous Province and host of a large Fe-Ti-V ore deposit. During emplacement of the main intrusion, multiple generations of mafic dykes invaded carbonate wall rocks, producing a large contact aureole. We measured the oxygen-isotope composition of the intrusions, their constituent minerals, and samples of the country rock. Magnetite and plagioclase from Panzhihua intrusion have δ18O values that are consistent with magmatic equilibrium, and formed from magmas with δ18O values that were 1–2‰ higher than expected in a mantle-derived magma. The unmetamorphosed country rock has high δ18O values, ranging from 13.2‰ (sandstone to 24.6–28.6‰ (dolomite. The skarns and marbles from the aureole have lower δ18O and δ13C values than their protolith suggesting interaction with fluids that were in exchange equilibrium with the adjacent mafic magmas and especially the numerous mafic dykes that intruded the aureole. This would explain the alteration of δ18O of the dykes which have significantly higher values than expected for a mantle-derived magma. Depending on the exact δ18O values assumed for the magma and contaminant, the amount of assimilation required to produce the elevated δ18O value of the Panzhihua intrusion was between 8 and 13.7 wt.%, assuming simple mixing. The exact mechanism of contamination is unclear but may involve a combination of assimilation of bulk country rock, mixing with a melt of the country rock and exchange with CO2-rich fluid derived from decarbonation of the marls and dolomites. These mechanisms, particularly the latter, were probably involved in the formation of the Fe-Ti-V ores.

Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

Science.gov (United States)

Rapp, J. F.; Draper, D. S.

2015-01-01

The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale magma ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar magma ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep magma ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow magma ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper magma ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after magma ocean crystallization and the nature of KREEP

Magma transport and storage at Kilauea volcano, Hawaii I: 1790-1952

Science.gov (United States)

Wright, T. L.; Klein, F.

2011-12-01

We trace the evolution of Kilauea from the time of the first oral records of an explosive eruption in 1790 to the long eruption in Halemaumau crater in 1952. The establishment of modern seismic and geodetic networks in the early 1960s showed that eruptions and intrusions were fed from two magma sources beneath the summit at depths of 2-6 and ~1 km respectively (sources 1 and 2), and that seaward spreading of the south flank took place on a decollement at 10-12 km depth at the base of the Kilauea edifice. A third diffuse, pressure-transmitting magma system (source 3) between the shallow East rift zone and the decollement was also identified. We test the null hypothesis that the volcano has behaved similarly throughout its lifetime, and conclude that the null hypothesis is not met for the period preceding the 1952 summit eruption because of changes in magma supply rate and differences in ground deformation patterns. The western missionaries arriving at Kilauea in 1823 were confronted with a caldera-wide lava lake. Filling rates determined by visual observation correspond to magma supply rates that averaged more than 0.3 km3/yr prior to 1840 and declined to 1894, when lava disappeared altogether at Halemaumau crater. The Hawaiian Volcano Observatory (HVO) was established by Thomas A. Jaggar in 1912 adjacent to the Volcano House Hotel on the rim of Kilauea. Instrumental observation at HVO began using a seismometer that doubled as a tiltmeter. A 1912-1924 magma supply rate of 0.024 km3/yr agreed with the rate of filling of Kilauea caldera from 1840-1894. 1924 was a critical year. An intrusion that moved down Kilauea's East rift zone beginning in February culminated beneath the lower East rift zone in April. In May, explosive eruptions accompanied a dramatic draining of Halemaumau. Triangulation results between 1912 and 1921 showed uplift extending far beyond Kilauea caldera and an equally large regional subsidence occurred between 1921 and 1927. HVO tilt narrows the

Mezcla de magmas en Vulcanello (Isla Vulcano, Italia

Directory of Open Access Journals (Sweden)

Aparicio, A.

2008-06-01

Full Text Available Volcanic activity in Vulcano starts about 350 ka ago and continues up to present day with the development of thre main episodes corresponding to the calderas of Piano and La Fossa, and Vulcanello. These cover a compositional range from rhyolitic to trachybasaltic rocks. This lithological diversity is produced by different petrogenetic processes such as fractional crystallization, assimilation coupled to fractional crystallization (AFC, mixing, etc.The eruption of Vulcanello area emitted trachyandesitic materials, including shoshonites and latites. A magma-mixing process is established between trachytes and shoshonites to origine latites. Trachytes and rhyolites are produced by fractional crystallization and by ACF processes (assimilation of sedimentary rocks from trachyandesitic magmas.La actividad volcánica de Isla Vulcano comienzó aproximadamente hace 350.000 años y continúa hasta la actualidad con el desarrollo de tres grandes episodios correspondientes a las caldera de Piano, caldera de Fossa y a Vulcanello, que han emitido piroclastos y coladas de composiciones muy variadas, desde riolitas a traquibasaltos. Esta variedad litológica ha sido relacionada con procesos petrogenéticos tan diversos como cristalización fraccionada, asimilación simultánea con cristalización (ACF, mezcla de magmas, etc.El episodio de Vulcanello emite rocas traquiandesíticas, con composiciones shoshoníticas y latíticas. Un proceso de mezcla de magmas es reconocido entre traquitas y shoshonitas para generar latitas. Traquitas y riolitas son producidas por procesos de cristalización fraccionada simple y por ACF con asimilación de rocas sedimentarias a partir de magmas traquiandesíticos.

Growing magma chambers control the distribution of small-scale flood basalts.

Science.gov (United States)

Yu, Xun; Chen, Li-Hui; Zeng, Gang

2015-11-19

Small-scale continental flood basalts are a global phenomenon characterized by regular spatio-temporal distributions. However, no genetic mechanism has been proposed to explain the visible but overlooked distribution patterns of these continental basaltic volcanism. Here we present a case study from eastern China, combining major and trace element analyses with Ar-Ar and K-Ar dating to show that the spatio-temporal distribution of small-scale flood basalts is controlled by the growth of long-lived magma chambers. Evolved basalts (SiO2 > 47.5 wt.%) from Xinchang-Shengzhou, a small-scale Cenozoic flood basalt field in Zhejiang province, eastern China, show a northward younging trend over the period 9.4-3.0 Ma. With northward migration, the magmas evolved only slightly ((Na2O + K2O)/MgO = 0.40-0.66; TiO2/MgO = 0.23-0.35) during about 6 Myr (9.4-3.3 Ma). When the flood basalts reached the northern end of the province, the magmas evolved rapidly (3.3-3.0 Ma) through a broad range of compositions ((Na2O + K2O)/MgO = 0.60-1.28; TiO2/MgO = 0.30-0.57). The distribution and two-stage compositional evolution of the migrating flood basalts record continuous magma replenishment that buffered against magmatic evolution and induced magma chamber growth. Our results demonstrate that the magma replenishment-magma chamber growth model explains the spatio-temporal distribution of small-scale flood basalts.

Experimental Fractional Crystallization of the Lunar Magma Ocean

Science.gov (United States)

Rapp, J. F.; Draper, D. S.

2012-01-01

The current paradigm for lunar evolution is of crystallization of a global scale magma ocean, giving rise to the anorthositic crust and mafic cumulate interior. It is thought that all other lunar rocks have arisen from this differentiated interior. However, until recently this paradigm has remained untested experimentally. Presented here are the first experimental results of fractional crystallization of a Lunar Magma Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].

Modeling of reservoir operation in UNH global hydrological model

Science.gov (United States)

Shiklomanov, Alexander; Prusevich, Alexander; Frolking, Steve; Glidden, Stanley; Lammers, Richard; Wisser, Dominik

2015-04-01

Climate is changing and river flow is an integrated characteristic reflecting numerous environmental processes and their changes aggregated over large areas. Anthropogenic impacts on the river flow, however, can significantly exceed the changes associated with climate variability. Besides of irrigation, reservoirs and dams are one of major anthropogenic factor affecting streamflow. They distort hydrological regime of many rivers by trapping of freshwater runoff, modifying timing of river discharge and increasing the evaporation rate. Thus, reservoirs is an integral part of the global hydrological system and their impacts on rivers have to be taken into account for better quantification and understanding of hydrological changes. We developed a new technique, which was incorporated into WBM-TrANS model (Water Balance Model-Transport from Anthropogenic and Natural Systems) to simulate river routing through large reservoirs and natural lakes based on information available from freely accessible databases such as GRanD (the Global Reservoir and Dam database) or NID (National Inventory of Dams for US). Different formulations were applied for unregulated spillway dams and lakes, and for 4 types of regulated reservoirs, which were subdivided based on main purpose including generic (multipurpose), hydropower generation, irrigation and water supply, and flood control. We also incorporated rules for reservoir fill up and draining at the times of construction and decommission based on available data. The model were tested for many reservoirs of different size and types located in various climatic conditions using several gridded meteorological data sets as model input and observed daily and monthly discharge data from GRDC (Global Runoff Data Center), USGS Water Data (US Geological Survey), and UNH archives. The best results with Nash-Sutcliffe model efficiency coefficient in the range of 0.5-0.9 were obtained for temperate zone of Northern Hemisphere where most of large

A complex magma reservoir system for a large volume intra- to extra-caldera ignimbrite: Mineralogical and chemical architecture of the VEI8, Permian Ora ignimbrite (Italy)

Science.gov (United States)

Willcock, M. A. W.; Bargossi, G. M.; Weinberg, R. F.; Gasparotto, G.; Cas, R. A. F.; Giordano, G.; Marocchi, M.

2015-11-01

Intra-caldera settings record a wealth of information on caldera-forming processes, yet field study is rarely possible due to lack of access and exposure. The Permian Ora Formation, Italy, preserves > 1000 m of vertical section through its intra-caldera succession. This provides an excellent opportunity to detail its mineralogical and geochemical architecture and gain understanding of the eruption evolution and insight into the pre-eruptive magma system. Detailed juvenile clast phenocryst and matrix crystal fragment point count and image analysis data, coupled with bulk-rock chemistry and single mineral compositional data, show that the Ora ignimbrite succession is rhyolitic (72.5-77.7% SiO2), crystal-rich (~ 25-57%; average 43%) and has a constant main mineral population (volcanic quartz + sanidine + plagioclase + biotite). Although a seemingly homogeneous ignimbrite succession, important subtle but detectable lateral and vertical variations in modal mineralogy and bulk-rock major and trace elements are identified here. The Ora Formation is comprised of multiple lithofacies, dominated by four densely welded ignimbrite lithofacies. They are crystal-rich, typically lithic-poor (pene-contemporaneous caldera depressions. Moreover, this data illustrates heterogeneity and local zonation from base-to-top of the main intra-caldera and extra-caldera successions. These variations together with crystal fragment size variations between ignimbrite lithofacies support the hypothesis of a multi-vent eruption process, incremental caldera in-filling by subtly compositionally different pyroclastic flow pulses, and a lower intensity eruption style (Willcock et al., 2013, 2014).

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

Reservoir characterization of Pennsylvanian sandstone reservoirs. Final report

Energy Technology Data Exchange (ETDEWEB)

Kelkar, M.

1995-02-01

This final report summarizes the progress during the three years of a project on Reservoir Characterization of Pennsylvanian Sandstone Reservoirs. The report is divided into three sections: (i) reservoir description; (ii) scale-up procedures; (iii) outcrop investigation. The first section describes the methods by which a reservoir can be described in three dimensions. The next step in reservoir description is to scale up reservoir properties for flow simulation. The second section addresses the issue of scale-up of reservoir properties once the spatial descriptions of properties are created. The last section describes the investigation of an outcrop.

Pressure effect on Fe3+/FeT in silicate melts and applications to magma redox, particularly in magma oceans

Science.gov (United States)

Zhang, H.; Hirschmann, M. M.

2014-12-01

The proportions of Fe3+ and Fe2+ in magmas reflect the redox conditions of their origin and influence the chemical and physical properties of natural silicate liquids, but the relationship between Fe3+/FeT and oxygen fugacity depends on pressure owing to different molar volumes and compressibilities of Fe3+ and Fe2+ in silicates. An important case where the effect of pressure effect may be important is in magma oceans, where well mixed (and therefore potentially uniform Fe3+/FeT) experiencses a wide range of pressures, and therefore can impart different ƒO2 at different depths, influencing magma ocean degassing and early atmospheres, as well as chemical gradients within magma oceans. To investigate the effect of pressure on magmatic Fe3+/FeT we conducted high pressure expeirments on ƒO2-buffered andestic liquids. Quenched glasses were analyzed by Mössbauer spectroscopy. To verify the accuracy of Mössbauer determinations of Fe3+/FeT in glasses, we also conducted low temperature Mössbauer studies to determine differences in the recoilless fraction (ƒ) of Fe2+ and Fe3. These indicate that room temperature Mössbauer determinations of on Fe3+/FeT glasses are systematically high by 4% compared to recoilless-fraction corrected ratios. Up to 7 GPa, pressure decreases Fe3+/FeT, at fixed ƒO2 relative to metal-oxide buffers, meaning that an isochemical magma will become more reduced with decreasing pressure. Consequently, for small planetary bodies such as the Moon or Mercury, atmospheres overlying their MO will be highly reducing, consisting chiefly of H2 and CO. The same may also be true for Mars. The trend may reverse at higher pressure, as is the case for solid peridotite, and so for Earth, Venus, and possibly Mars, more oxidized atmospheres above MO are possible. Diamond anvil experiments are underway to examine this hypothesis.

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.

Magma transport and olivine crystallization depths in Kīlauea’s East Rift Zone inferred from experimentally rehomogenized melt inclusions

Science.gov (United States)

Tuohy, Robin M; Wallace, Paul J.; Loewen, Matthew W; Swanson, Don; Kent, Adam J R

2016-01-01

Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai‘i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n=10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n=38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at <6 km depth, with the majority of olivine in the 1-3 km depth range. These depths are consistent with the interpretation that the Kīlauea Iki magma was supplied from Kīlauea’s summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the

Phenomena associated with magma expansion into a drift

International Nuclear Information System (INIS)

Gaffney, E.S.

2002-01-01

One of the significant threats to the proposed Yucca Mountain nuclear waste repository has been identified as the possibility of intersection of the underground structure by a basaltic intrusion. Based on the geology of the region, it is assumed that such an intrusion would consist of an alkali basalt similar to the nearby Lathrop Wells cone, which has been dated at about 78 ka. The threat of radioactive release may be either from eruption through the surface above the repository of basalt that had been contaminated or from migration through ground water of radionucleides released as a result of damage to waste packages that interact with the magma. As part of our study of these threats, we are analyzing the phenomena associated with magma expansion into drifts in tuff. The early phenomena of the encounter of volatile-rich basaltic magma with a drift are discussed here.

Bayesian estimation of magma supply, storage, and eruption rates using a multiphysical volcano model: Kīlauea Volcano, 2000-2012

Science.gov (United States)

Anderson, Kyle R.; Poland, Michael P.

2016-08-01

Estimating rates of magma supply to the world's volcanoes remains one of the most fundamental aims of volcanology. Yet, supply rates can be difficult to estimate even at well-monitored volcanoes, in part because observations are noisy and are usually considered independently rather than as part of a holistic system. In this work we demonstrate a technique for probabilistically estimating time-variable rates of magma supply to a volcano through probabilistic constraint on storage and eruption rates. This approach utilizes Bayesian joint inversion of diverse datasets using predictions from a multiphysical volcano model, and independent prior information derived from previous geophysical, geochemical, and geological studies. The solution to the inverse problem takes the form of a probability density function which takes into account uncertainties in observations and prior information, and which we sample using a Markov chain Monte Carlo algorithm. Applying the technique to Kīlauea Volcano, we develop a model which relates magma flow rates with deformation of the volcano's surface, sulfur dioxide emission rates, lava flow field volumes, and composition of the volcano's basaltic magma. This model accounts for effects and processes mostly neglected in previous supply rate estimates at Kīlauea, including magma compressibility, loss of sulfur to the hydrothermal system, and potential magma storage in the volcano's deep rift zones. We jointly invert data and prior information to estimate rates of supply, storage, and eruption during three recent quasi-steady-state periods at the volcano. Results shed new light on the time-variability of magma supply to Kīlauea, which we find to have increased by 35-100% between 2001 and 2006 (from 0.11-0.17 to 0.18-0.28 km3/yr), before subsequently decreasing to 0.08-0.12 km3/yr by 2012. Changes in supply rate directly impact hazard at the volcano, and were largely responsible for an increase in eruption rate of 60-150% between 2001 and

Reservoir management

International Nuclear Information System (INIS)

Satter, A.; Varnon, J.E.; Hoang, M.T.

1992-01-01

A reservoir's life begins with exploration leading to discovery followed by delineation of the reservoir, development of the field, production by primary, secondary and tertiary means, and finally to abandonment. Sound reservoir management is the key to maximizing economic operation of the reservoir throughout its entire life. Technological advances and rapidly increasing computer power are providing tools to better manage reservoirs and are increasing the gap between good and neural reservoir management. The modern reservoir management process involves goal setting, planning, implementing, monitoring, evaluating, and revising plans. Setting a reservoir management strategy requires knowledge of the reservoir, availability of technology, and knowledge of the business, political, and environmental climate. Formulating a comprehensive management plan involves depletion and development strategies, data acquisition and analyses, geological and numerical model studies, production and reserves forecasts, facilities requirements, economic optimization, and management approval. This paper provides management, engineers, geologists, geophysicists, and field operations staff with a better understanding of the practical approach to reservoir management using a multidisciplinary, integrated team approach

Reservoir management

International Nuclear Information System (INIS)

Satter, A.; Varnon, J.E.; Hoang, M.T.

1992-01-01

A reservoir's life begins with exploration leading to discovery followed by delineation of the reservoir, development of the field, production by primary, secondary and tertiary means, and finally to abandonment. Sound reservoir management is the key to maximizing economic operation of the reservoir throughout its entire life. Technological advances and rapidly increasing computer power are providing tools to better manage reservoirs and are increasing the gap between good and neutral reservoir management. The modern reservoir management process involves goal setting, planning, implementing, monitoring, evaluating, and revising plans. Setting a reservoir management strategy requires knowledge of the reservoir, availability of technology, and knowledge of the business, political, and environmental climate. Formulating a comprehensive management plan involves depletion and development strategies, data acquisition and analyses, geological and numerical model studies, production and reserves forecasts, facilities requirements, economic optimization, and management approval. This paper provides management, engineers geologists, geophysicists, and field operations staff with a better understanding of the practical approach to reservoir management using a multidisciplinary, integrated team approach

A cascade of magmatic events during the assembly and eruption of a super-sized magma body

Science.gov (United States)

Allan, Aidan. S. R.; Barker, Simon J.; Millet, Marc-Alban; Morgan, Daniel J.; Rooyakkers, Shane M.; Schipper, C. Ian; Wilson, Colin J. N.

2017-07-01

We use comprehensive geochemical and petrological records from whole-rock samples, crystals, matrix glasses and melt inclusions to derive an integrated picture of the generation, accumulation and evacuation of 530 km3 of crystal-poor rhyolite in the 25.4 ka Oruanui supereruption (New Zealand). New data from plagioclase, orthopyroxene, amphibole, quartz, Fe-Ti oxides, matrix glasses, and plagioclase- and quartz-hosted melt inclusions, in samples spanning different phases of the eruption, are integrated with existing data to build a history of the magma system prior to and during eruption. A thermally and compositionally zoned, parental crystal-rich (mush) body was developed during two periods of intensive crystallisation, 70 and 10-15 kyr before the eruption. The mush top was quartz-bearing and as shallow as 3.5 km deep, and the roots quartz-free and extending to >10 km depth. Less than 600 year prior to the eruption, extraction of large volumes of 840 °C low-silica rhyolite melt with some crystal cargo (between 1 and 10%), began from this mush to form a melt-dominant (eruptible) body that eventually extended from 3.5 to 6 km depth. Crystals from all levels of the mush were entrained into the eruptible magma, as seen in mineral zonation and amphibole model pressures. Rapid translation of crystals from the mush to the eruptible magma is reflected in textural and compositional diversity in crystal cores and melt inclusion compositions, versus uniformity in the outermost rims. Prior to eruption the assembled eruptible magma body was not thermally or compositionally zoned and at temperatures of 790 °C, reflecting rapid cooling from the 840 °C low-silica rhyolite feedstock magma. A subordinate but significant volume (3-5 km3) of contrasting tholeiitic and calc-alkaline mafic material was co-erupted with the dominant rhyolite. These mafic clasts host crystals with compositions which demonstrate that there was some limited pre-eruptive physical interaction of mafic

Sediment problems in reservoirs. Control of sediment deposits

Energy Technology Data Exchange (ETDEWEB)

Jacobsen, Tom

1997-12-31

When a reservoir is formed on a river, sediment will deposit in the reservoir. Such processes are unfortunate, for instance, for the implementation of hydroelectric energy. This thesis studies the problem of reservoir sedimentation and discusses methods of removing the sediments. Various aspects of reservoir sedimentation are discussed. Anthropogenic impacts seem to greatly affect the erosion processes. Temporal distribution is uneven, mainly because of the very large flood events. A world map showing the Reservoir Capacity: Annual Sediment Inflow ratio for reservoirs with volume equal to 10% of annual inflow has been prepared. The map shows that sedimentation is severe in the western parts of North and South America, eastern, southern and northern Africa, parts of Australia and most of Asia. The development of medium-sized reservoirs is difficult, as they are too large for conventional flushing technique and too small to store the sediment that accumulates during their economic lifetime. A computer model, SSIIM, was used with good results in a case study of two flood drawdown trials in Lake Roxburg, New Zealand. Two techniques have been developed that permits controlled suction of sediment and water into a pipe: the Slotted Pipe Sediment Sluicer (SPSS) and the Saxophone Sediment Sluicer (SSS). The techniques exploit the inflow pattern in through a slot in a pipe. An equation describing this inflow pattern was derived and verified experimentally. The SPSS is fixed near the reservoir bed, and sediment that deposits on top of it is removed in the sluicing process. The SSS sluices sediment from the surface of the sediment deposits. Some technical and economic conditions affecting the economics of sediment removal from reservoirs have been identified and studied. 79 refs., 112 figs., 14 tabs.

Assessing the role of large wood entrained in the 2013 Colorado Front Range flood in ongoing channel response and reservoir management

Science.gov (United States)

Bennett, Georgina; Rathburn, Sara; Ryan, Sandra; Wohl, Ellen; Blair, Aaron

2016-04-01

Considerable quantities of large wood (LW) may be entrained during floods with long lasting impacts on channel morphology, sediment and LW export, and downstream reservoir management. Here we present an analysis of LW entrained by an extensive flood in Colorado, USA. Over a 5 day period commencing 9th September 2013, up to 450 mm of rain, or ~1000% of the monthly average, fell in catchments spanning a 100-km-wide swath of the Colorado Front Range resulting in major flooding. Catchment response was dramatic, with reports of 100s - 1000s of years of erosion, destruction of infrastructure and homes, and sediment and LW loading within reservoirs. One heavily impacted catchment is the North St Vrain, draining 250km2 of the South Platte drainage basin. In addition to widespread channel enlargement, remote imagery reveals hundreds of landslides that delivered sediment and LW to the channel and ultimately to Ralph Price Reservoir, which provides municipal water to Longmont. The City of Longmont facilitated the removal of ~1050 m3 of wood deposited at the reservoir inlet by the flood but the potential for continued movement of large wood in the catchment presents an on-going concern for reservoir management. In collaboration with the City of Longmont, our objectives are (1) to quantify the volume of wood entrained by the flood and still stored along the channel, (2) characterize the size and distribution of LW deposits and (3) determine their role in ongoing catchment flood response and recovery. We utilize freely available pre and post flood NAIP 4-band imagery to calculate a normalized differential vegetation index (NDVI) difference map with which we calculate the area of vegetation entrained by the flood. We combine this with field assessments and a map of vegetation type automatically classified from optical satellite imagery to estimate the total flood-entrained volume of wood. Preliminary testing of 'stream selfies' - structure from motion imaging of LW deposits using

Experimental and petrological constraints on long-term magma dynamics and post-climactic eruptions at the Cerro Galán caldera system, NW Argentina

Science.gov (United States)

Grocke, Stephanie B.; Andrews, Benjamin J.; de Silva, Shanaka L.

2017-11-01

dome-forming magmas that decompressed more slowly (histories with results from new phase equilibria experiments suggests that during post-climactic volcanic activity at Cerro Galán, remnant CGI dome-forming magmas ascended from the shallow magma reservoir (< 4 km) to motivate resurgent uplift and erupt as lava domes either explosively as vesiculated clasts or effusively as dense clasts that make up the outer structure of lava domes.

Mechanisms of differentiation in the Skaergaard magma chamber

Science.gov (United States)

Tegner, C.; Lesher, C. E.; Holness, M. B.; Jakobsen, J. K.; Salmonsen, L. P.; Humphreys, M. C. S.; Thy, P.

2012-04-01

The Skaergaard intrusion is a superb natural laboratory for studying mechanisms of magma chamber differentiation. The magnificent exposures and new systematic sample sets of rocks that solidified inwards from the roof, walls and floor of the chamber provide means to test the relative roles of crystal settling, diffusion, convection, liquid immiscibility and compaction in different regions of the chamber and in opposite positions relative to gravity. Examination of the melt inclusions and interstitial pockets has demonstrated that a large portion of intrusion crystallized from an emulsified magma chamber composed of immiscible silica- and iron-rich melts. The similarity of ratios of elements with opposite partitioning between the immiscible melts (e.g. P and Rb) in wall, floor and roof rocks, however, indicate that large-scale separation did not occur. Yet, on a smaller scale of metres to hundred of metres and close to the interface between the roof and floor rocks (the Sandwich Horizon), irregular layers and pods of granophyre hosted by extremely iron-rich cumulates point to some separation of the two liquid phases. Similar proportions of the primocryst (cumulus) minerals in roof, wall and floor rocks indicate that crystal settling was not an important mechanism. Likewise, the lack of fractionation of elements with different behavior indicate that diffusion and fluid-driven metasomatism played relatively minor roles. Compositional convection and/or compaction within the solidifying crystal mush boundary layer are likely the most important mechanisms. A correlation of low trapped liquid fractions (calculated from strongly incompatible elements) in floor rocks with high fractionation density (the density difference between the crystal framework and the liquid) indicate that compaction is the dominating process in expelling evolved liquid from the crystal mush layer. This is supported by high and variable trapped liquid contents in the roof rocks, where gravity

Discovering Mathematics with Magma Reducing the Abstract to the Concrete

CERN Document Server

Bosma, Wieb

2006-01-01

With a design based on the ontology and semantics of algebra, Magma enables users to rapidly formulate and perform calculations in the more abstract parts of mathematics. This book introduces the role Magma plays in advanced mathematical research through 14 case studies which, in most cases, describe computations underpinning theoretical results.

THE VISCOUS TO BRITTLE TRANSITION IN CRYSTAL- AND BUBBLE-BEARING MAGMAS

Directory of Open Access Journals (Sweden)

Mattia ePistone

2015-11-01

Full Text Available The transition from viscous to brittle behaviour in magmas plays a decisive role in determining the style of volcanic eruptions. While this transition has been determined for one- or two-phase systems, it remains poorly constrained for natural magmas containing silicic melt, crystals, and gas bubbles. Here we present new experimental results on shear-induced fracturing of three-phase magmas obtained at high-temperature (673-1023 K and high-pressure (200 MPa conditions over a wide range of strain-rates (5·10-6 s-1 to 4·10-3 s-1. During the experiments bubbles are deformed (i.e. capillary number are in excess of 1 enough to coalesce and generate a porous network that potentially leads to outgassing. A physical relationship is proposed that quantifies the critical stress required for magmas to fail as a function of both crystal (0.24 to 0.65 and bubble volume fractions (0.09 to 0.12. The presented results demonstrate efficient outgassing for low crystal fraction ( 0.44 promote gas bubble entrapment and inhibit outgassing. The failure of bubble-free, crystal-bearing systems is enhanced by the presence of bubbles that lower the critical failure stress in a regime of efficient outgassing, while the failure stress is increased if bubbles remain trapped within the crystal framework. These contrasting behaviours have direct impact on the style of volcanic eruptions. During magma ascent, efficient outgassing reduces the potential for an explosive eruption and favours brittle behaviour, contributing to maintain low overpressures in an active volcanic system resulting in effusion or rheological flow blockage of magma at depth. Conversely, magmas with high crystallinity experience limited loss of exsolved gas, permitting the achievement of larger overpressures prior to a potential sudden transition to brittle behaviour, which could result in an explosive volcanic eruption.

What can Fe stable isotopes tell us about magmas?

DEFF Research Database (Denmark)

Stausberg, Niklas

the differentiation of magmas from the perspective of Fe stable isotopes, integrated with petrology, by studying igneous rocks and their constituent phases (minerals and glasses) from the Bushveld Complex, South Africa, Thingmuli, Iceland, Pantelleria, Italy, and the Bishop Tuff, USA. The findings are interpreted......The majority of the Earth’s crust is formed by magmas, and understanding their production and differentiation is important to interpret the geologic rock record. A powerful tool to investigate magmatic processes is the distribution of the stable isotopes of the major redox-sensitive element...... in magmas, Fe. Fe isotope compositions of magmatic rocks exhibit systematic differences, where the heaviest compositions are found in rhyolites and granites. Understanding of these systematics is complicated by a lack of constraints on Fe isotope fractionation among minerals and liquids under magmatic...

Constraint on the magma sources in Luzon Island Philippines by using P and S wave local seismic tomography

Science.gov (United States)

Nghia, N. C.; Huang, B. S.; Chen, P. F.

2017-12-01

The subduction of South China Sea beneath the Luzon Island has caused a complex setting of seismicity and magmatism because of the proposed ridge subduction and slab tearing. To constrain the validity of slab tearing induced by ridge subduction and their effect, we performed a P and S wave seismic tomography travel time inversion using LOTOS code. The dataset has been retrieved from International Seismological Centre from 1960 to 2008. A 1D velocity inverted by using VELEST with a Vp/Vs ratio of 1.74 is used as the starting input velocity for tomographic inversion. Total of 20905 P readings and 8126 S readings from 2355 earthquakes events were used to invert for velocity structure beneath Luzon Island. The horizontal tomographic results show low-velocity, high Vp/Vs regions at the shallow depth less than 50 km which are interpreted as the magmatic chambers of the volcanic system in Luzon. At the suspected region of slab tearing at 16oN to 18oN, two sources of magma have been indentified: slab window magma at shallow depth (< 50 km) and magma induced by mantle wedge partial melting from higher depth. This slab melting may have changed the composition of magmatic to become more silicic with high viscosity, which explains the volcanic gap in this region. At the region of 14oN to 15oN, large magma chambers under active volcanos are identified which explain the active volcanism in this region. Contrast to the region of slab tearing, in this region, the magma chambers are fed by only magma from partial melting of mantle wedge from the depth higher than 100 km. These observations are consistent with previous work on the slab tearing of South China Sea and the activities of volcanism in the Luzon Island.

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

Eruptive dynamics during magma decompression: a laboratory approach

Science.gov (United States)

Spina, L.; Cimarelli, C.; Scheu, B.; Wadsworth, F.; Dingwell, D. B.

2013-12-01

A variety of eruptive styles characterizes the activity of a given volcano. Indeed, eruptive styles can range from effusive phenomena to explosive eruptions, with related implications for hazard management. Rapid changes in eruptive style can occur during an ongoing eruption. These changes are, amongst other, related to variations in the magma ascent rate, a key parameter affecting the eruptive style. Ascent rate is in turn dependent on several factors such as the pressure in the magma chamber, the physical properties of the magma and the rate at which these properties change. According to the high number of involved parameters, laboratory decompression experiments are the best way to achieve quantitative information on the interplay of each of those factors and the related impact on the eruption style, i.e. by analyzing the flow and deformation behavior of the transparent volatile-bearing analogue fluid. We carried out decompression experiments following different decompression paths and using silicone oil as an analogue for the melt, with which we can simulate a range of melt viscosity values. For a set of experiments we added rigid particles to simulate the presence of crystals in the magma. The pure liquid or suspension was mounted into a transparent autoclave and pressurized to different final pressures. Then the sample was saturated with argon for a fixed amount of time. The decompression path consists of a slow decompression from the initial pressure to the atmospheric condition. Alternatively, samples were decompressed almost instantaneously, after established steps of slow decompression. The decompression path was monitored with pressure transducers and a high-speed video camera. Image analysis of the videos gives quantitative information on the bubble distribution with respect to depth in the liquid, pressure and time of nucleation and on their characteristics and behavior during the ongoing magma ascent. Furthermore, we also monitored the evolution of

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode.

Science.gov (United States)

Wright, Tim J; Ebinger, Cindy; Biggs, Juliet; Ayele, Atalay; Yirgu, Gezahegn; Keir, Derek; Stork, Anna

2006-07-20

Seafloor spreading centres show a regular along-axis segmentation thought to be produced by a segmented magma supply in the passively upwelling mantle. On the other hand, continental rifts are segmented by large offset normal faults, and many lack magmatism. It is unclear how, when and where the ubiquitous segmented melt zones are emplaced during the continental rupture process. Between 14 September and 4 October 2005, 163 earthquakes (magnitudes greater than 3.9) and a volcanic eruption occurred within the approximately 60-km-long Dabbahu magmatic segment of the Afar rift, a nascent seafloor spreading centre in stretched continental lithosphere. Here we present a three-dimensional deformation field for the Dabbahu rifting episode derived from satellite radar data, which shows that the entire segment ruptured, making it the largest to have occurred on land in the era of satellite geodesy. Simple elastic modelling shows that the magmatic segment opened by up to 8 m, yet seismic rupture can account for only 8 per cent of the observed deformation. Magma was injected along a dyke between depths of 2 and 9 km, corresponding to a total intrusion volume of approximately 2.5 km3. Much of the magma appears to have originated from shallow chambers beneath Dabbahu and Gabho volcanoes at the northern end of the segment, where an explosive fissural eruption occurred on 26 September 2005. Although comparable in magnitude to the ten year (1975-84) Krafla events in Iceland, seismic data suggest that most of the Dabbahu dyke intrusion occurred in less than a week. Thus, magma intrusion via dyking, rather than segmented normal faulting, maintains and probably initiated the along-axis segmentation along this sector of the Nubia-Arabia plate boundary.

Reconstructing modalities of magma storage in the crust by thermo-rheological modelling

Science.gov (United States)

Caricchi, L.; Annen, C.; Rust, A.; Blundy, J.

2012-04-01

During my PhD I worked under the supervision of Luigi Burlini studying the rheological behaviour of magma. Luigi was not only a great teacher and friend but he was also able to project the science he was performing beyond the obvious applications. This aspect of Luigi's approach shaped my approach to research and brought me to think to ways of applying the studies we performed together to unravel the complexity of nature that impassioned and inspired him. This contribution comes from the motivation and interest that Luigi created in me during the short, but truly memorable journey we shared together. This study combines petrology, thermal modelling and magma rheology to characterise timescales and modalities of magma emplacement in the Earth's crust. Thermal modelling was performed to determine the influence of magma injection rates in the crust on the temperature evolution of a magmatic body. The injected tonalitic magma was considered to contain dioritic enclaves, common in plutons. The contrast in chemical composition between host and enclaves leads to different crystallinities of these magmas during cooling and produce a rheological contrast that permits reciprocal deformation only in restricted temperature ranges. Characterising the thermal and rheological evolution of host magma and enclaves, we traced the evolution of strain recorded by these inclusions during the construction of an intrusion, showing that the strain recorded by enclaves distributed in different portions of a pluton can be used to constrain thermal evolution in time, magmatic fluxes and timescale of assemblage of magmatic bodies in the crust.

Deriving Area-storage Curves of Global Reservoirs

Science.gov (United States)

Mu, M.; Tang, Q.

2017-12-01

Basic information including capacity, dam height, and largest water area on global reservoirs and dams is well documented in databases such as GRanD (Global Reservoirs and Dams), ICOLD (International Commission on Large Dams). However, though playing a critical role in estimating reservoir storage variations from remote sensing or hydrological models, area-storage (or elevation-storage) curves of reservoirs are not publicly shared. In this paper, we combine Landsat surface water extent, 1 arc-minute global relief model (ETOPO1) and GRanD database to derive area-storage curves of global reservoirs whose area is larger than 1 km2 (6,000 more reservoirs are included). First, the coverage polygon of each reservoir in GRanD is extended to where water was detected by Landsat during 1985-2015. Second, elevation of each pixel in the reservoir is extracted from resampled 30-meter ETOPO1, and then relative depth and frequency of each depth value is calculated. Third, cumulative storage is calculated with increasing water area by every one percent of reservoir coverage area and then the uncalibrated area-storage curve is obtained. Finally, the area-storage curve is linearly calibrated by the ratio of calculated capacity over reported capacity in GRanD. The derived curves are compared with in-situ reservoir data collected in Great Plains Region in US, and the results show that in-situ records are well captured by the derived curves even in relative small reservoirs (several square kilometers). The new derived area-storage curves have the potential to be employed in global monitoring or modelling of reservoirs storage and area variations.

75 FR 28778 - Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, AZ

Science.gov (United States)

2010-05-24

... DEPARTMENT OF AGRICULTURE Natural Resources Conservation Service Magma Flood Retarding Structure... statement is not being prepared for the Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan... rehabilitate the Magma FRS to provide for continued flood protection for a portion of the Town of Florence and...

Evaluation of Gaussian approximations for data assimilation in reservoir models

KAUST Repository

Iglesias, Marco A.; Law, Kody J H; Stuart, Andrew M.

2013-01-01

is fundamental for the optimal management of reservoirs. Unfortunately, due to the large-scale highly nonlinear properties of standard reservoir models, characterizing the posterior is computationally prohibitive. Instead, more affordable ad hoc techniques, based

Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics.

Science.gov (United States)

La Spina, G; Burton, M; De' Michieli Vitturi, M; Arzilli, F

2016-12-12

Timescales of magma ascent in conduit models are typically assumed to be much longer than crystallization and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallization and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Here we use observations from Mount Etna's 2001 eruption and a magma ascent model to constrain timescales for crystallization and exsolution processes. Our results show that plagioclase reaches equilibrium in 1-2 h, whereas ascent times were magma ascent rate and disequilibrium crystallization and exsolution plays a key role in controlling eruption dynamics in basaltic volcanism.

Bayesian estimation of magma supply, storage, and eruption rates using a multiphysical volcano model: Kīlauea Volcano, 2000–2012

Science.gov (United States)

Anderson, Kyle R.; Poland, Michael

2016-01-01

Estimating rates of magma supply to the world's volcanoes remains one of the most fundamental aims of volcanology. Yet, supply rates can be difficult to estimate even at well-monitored volcanoes, in part because observations are noisy and are usually considered independently rather than as part of a holistic system. In this work we demonstrate a technique for probabilistically estimating time-variable rates of magma supply to a volcano through probabilistic constraint on storage and eruption rates. This approach utilizes Bayesian joint inversion of diverse datasets using predictions from a multiphysical volcano model, and independent prior information derived from previous geophysical, geochemical, and geological studies. The solution to the inverse problem takes the form of a probability density function which takes into account uncertainties in observations and prior information, and which we sample using a Markov chain Monte Carlo algorithm. Applying the technique to Kīlauea Volcano, we develop a model which relates magma flow rates with deformation of the volcano's surface, sulfur dioxide emission rates, lava flow field volumes, and composition of the volcano's basaltic magma. This model accounts for effects and processes mostly neglected in previous supply rate estimates at Kīlauea, including magma compressibility, loss of sulfur to the hydrothermal system, and potential magma storage in the volcano's deep rift zones. We jointly invert data and prior information to estimate rates of supply, storage, and eruption during three recent quasi-steady-state periods at the volcano. Results shed new light on the time-variability of magma supply to Kīlauea, which we find to have increased by 35–100% between 2001 and 2006 (from 0.11–0.17 to 0.18–0.28 km3/yr), before subsequently decreasing to 0.08–0.12 km3/yr by 2012. Changes in supply rate directly impact hazard at the volcano, and were largely responsible for an increase in eruption rate of 60–150% between

Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011-2013 seismic series associated to the volcanic activity of El Hierro Island

Science.gov (United States)

Díaz-Moreno, A.; Ibáñez, J. M.; De Angelis, S.; García-Yeguas, A.; Prudencio, J.; Morales, J.; Tuvè, T.; García, L.

2015-11-01

In this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of El Hierro, Canary Islands, during 2011-2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the Moho. We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement.

How Pore-Fluid Pressure due to Heavy Rainfall Influences Volcanic Eruptions, Example of 1998 and 2008 Eruptions of Cerro Azul (Galapagos)

Science.gov (United States)

Albino, F.; Amelung, F.; Gregg, P. M.

2016-12-01

About 30 worldwide seismic studies have shown a strong correlation between rainfall and earthquakes in the past 22 years (e.g. Costain and Bollinger, 2010). Such correlation has been explained by the phenomenon of hydro-seismicity via pore pressure diffusion: an increase of pore-fluid in the upper crust reduces the normal stress on faults, which can trigger shear failure. Although this pore pressure effect is widely known for earthquakes, this phenomenon and more broadly poro-elasticity process are not widely studied on volcanoes. However, we know from our previous works that tensile failures that open to propagate magma through the surface are also pore pressure dependent. We have demonstrated that an increase of pore pressure largely reduces the overpressure required to rupture the magma reservoir. We have shown that the pore pressure has more influence on reservoir stability than other parameters such as the reservoir depth or the edifice loading. Here, we investigate how small pore-fluid changes due to hydrothermal or aquifer refill during heavy rainfall may perturb the conditions of failure around magma reservoirs and, what is more, if these perturbations are enough to trigger magma intrusions. We quantify the pore pressure effect on magmatic system by combining 1) 1D pore pressure diffusion model to quantify how pore pressure changes from surface to depth after heavy rainfall events and 2) 2D poro-elastic numerical model to provide the evolution of failure conditions of the reservoir as a consequence of these pore pressure changes. Sensitivity analysis is also performed to characterize the influence on our results of the poro-elastic parameters (hydraulic diffusivity, permeability and porosity) and the geometry of the magma reservoir and the aquifer (depth, size, shape). Finally, we apply our methodology to Cerro Azul volcano (Galapagos) where both last eruptions (1998 and 2008) occurred just after heavy rainfall events, without any pre-eruptive inflation. In

Impact assessment of the introduction of Cichla kelberi in a large Neotropical reservoir and its lateral lagoons (Upper Paraná River Basin, Brazil

Directory of Open Access Journals (Sweden)

M. Ferrareze

Full Text Available Abstract This study aimed to understand how the introduction of Cichla kelberi in Rosana Reservoir (Paranapanema River affected the native ichthyofauna. Data on the structure of the small fish fauna assemblage were obtained before and after the introduction of this carnivorous species. Samplings were carried out in February and September of 2004, previously to the register of Cichla kelberi in the reservoir, and after its introduction, November of 2004, January, March, May and August of 2005, February and June of 2006, February and July of 2007, February and October of 2008 and February of 2009. A total of 4,693 fish, belonging to 43 different species was sampled between 2004 and 2009. The order Characiformes was the most abundant, followed by Perciformes and Siluriformes. Comparative analyses, before and after the introduction, could not demonstrate significant changes in composition, richness, abundance, biomass, mean length and diversity of fish. Aquatic insects were the main feeding item of C. kelberi, followed by tetragonopterinae fish. Cannibalism was recorded during the whole study period. The results showed that Cichla cannot deeply affect the ichthyofauna assemblages of a large Neotropical reservoir, at least in a short or medium term period after its introduction. The results also allowed concluding that the introduction of C. kelberi in the reservoir is in the phase 3. In this phase, the specie can survive and reproduce in the new environment; however it is not totally established and disseminated. The reasons for the fact that Cichla is still not dominant in Rosana Reservoir could be related to feeding competition, high rate of cannibalism and the presence of large amount of aquatic macrophytes (refuge zones. In spite of the results, the continuous monitoring of the role of non-native species on the local fish fauna is absolutely necessary because the impacts caused by colonization of this undesirable species can be magnified by

Sensitivity analysis and economic optimization studies of inverted five-spot gas cycling in gas condensate reservoir

OpenAIRE

Shams Bilal; Yao Jun; Zhang Kai; Zhang Lei

2017-01-01

Gas condensate reservoirs usually exhibit complex flow behaviors because of propagation response of pressure drop from the wellbore into the reservoir. When reservoir pressure drops below the dew point in two phase flow of gas and condensate, the accumulation of large condensate amount occurs in the gas condensate reservoirs. Usually, the saturation of condensate accumulation in volumetric gas condensate reservoirs is lower than the critical condensate saturation that causes trapping of large...

Economic valuation of the downstream hydrological effects of land use change: Large hydroelectric reservoirs

Science.gov (United States)

Aylward, Bruce Allan

1998-12-01

Land use change that accompanies economic development and population growth is intended to raise the economic productivity of land. An inevitable by product of this process is the alteration of natural vegetation and downstream hydrological function. This dissertation explores hydrological externalities of land use change in detail, particularly with regard to their economic impact on large hydroelectric reservoirs (LHRs). A review of the linkages between land use, hydrological function and downstream economic activity suggests that on theoretical grounds the net welfare effect of land use change on hydrological function will be indeterminate. Review of the literature suggests that, though the effects of downstream sedimentation will typically be negative, they may often be of little practical significance. The literature on water quantity impacts is sparse at best. This is most surprising in the case of the literature on LHRs where the potentially important and positive effects of increased water yield are typically ignored in favor of simplistic efforts to document the negative effects of reservoir sedimentation. In order to improve the methodological basis for the economic valuation of hydrological externalities, the dissertation considers existing techniques for the evaluation of non-marketed goods and services, clarifying the manner in which they have been and, in the future, may be applied to the topic at hand. A deterministic simulation model is then constructed for the case of LHRs. The model incorporates the effect of changes in water yield, the seasonal pattern of water yield and sedimentation of live and dead storage volumes as they affect reservoir operation and the production of hydroelectricity. The welfare effects of changes in the productivity of the LHR in the short run and changes to the power system expansion plan in the long run are evaluated using the marginal opportunity costs of alternative power sources and power plants, respectively. A case

The role of reservoir storage in large-scale surface water availability analysis for Europe

Science.gov (United States)

Garrote, L. M.; Granados, A.; Martin-Carrasco, F.; Iglesias, A.

2017-12-01

A regional assessment of current and future water availability in Europe is presented in this study. The assessment was made using the Water Availability and Adaptation Policy Analysis (WAAPA) model. The model was built on the river network derived from the Hydro1K digital elevation maps, including all major river basins of Europe. Reservoir storage volume was taken from the World Register of Dams of ICOLD, including all dams with storage capacity over 5 hm3. Potential Water Availability is defined as the maximum amount of water that could be supplied at a certain point of the river network to satisfy a regular demand under pre-specified reliability requirements. Water availability is the combined result of hydrological processes, which determine streamflow in natural conditions, and human intervention, which determines the available hydraulic infrastructure to manage water and establishes water supply conditions through operating rules. The WAAPA algorithm estimates the maximum demand that can be supplied at every node of the river network accounting for the regulation capacity of reservoirs under different management scenarios. The model was run for a set of hydrologic scenarios taken from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), where the PCRGLOBWB hydrological model was forced with results from five global climate models. Model results allow the estimation of potential water stress by comparing water availability to projections of water abstractions along the river network under different management alternatives. The set of sensitivity analyses performed showed the effect of policy alternatives on water availability and highlighted the large uncertainties linked to hydrological and anthropological processes.

Modelling of Reservoir Operations using Fuzzy Logic and ANNs

Science.gov (United States)

Van De Giesen, N.; Coerver, B.; Rutten, M.

2015-12-01

Today, almost 40.000 large reservoirs, containing approximately 6.000 km3 of water and inundating an area of almost 400.000 km2, can be found on earth. Since these reservoirs have a storage capacity of almost one-sixth of the global annual river discharge they have a large impact on the timing, volume and peaks of river discharges. Global Hydrological Models (GHM) are thus significantly influenced by these anthropogenic changes in river flows. We developed a parametrically parsimonious method to extract operational rules based on historical reservoir storage and inflow time-series. Managing a reservoir is an imprecise and vague undertaking. Operators always face uncertainties about inflows, evaporation, seepage losses and various water demands to be met. They often base their decisions on experience and on available information, like reservoir storage and the previous periods inflow. We modeled this decision-making process through a combination of fuzzy logic and artificial neural networks in an Adaptive-Network-based Fuzzy Inference System (ANFIS). In a sensitivity analysis, we compared results for reservoirs in Vietnam, Central Asia and the USA. ANFIS can indeed capture reservoirs operations adequately when fed with a historical monthly time-series of inflows and storage. It was shown that using ANFIS, operational rules of existing reservoirs can be derived without much prior knowledge about the reservoirs. Their validity was tested by comparing actual and simulated releases with each other. For the eleven reservoirs modelled, the normalised outflow, , was predicted with a MSE of 0.002 to 0.044. The rules can be incorporated into GHMs. After a network for a specific reservoir has been trained, the inflow calculated by the hydrological model can be combined with the release and initial storage to calculate the storage for the next time-step using a mass balance. Subsequently, the release can be predicted one time-step ahead using the inflow and storage.

FEASIBILITY STUDY OF SEDIMENT FLUSHING FROM MOSUL RESERVOIR, IRAQ

Directory of Open Access Journals (Sweden)

Thair Mahmood Al-Taiee

2015-02-01

Full Text Available The Feasibility of sediment flushing  from Mosul reservoir located northern iraq was conducted. Many up to date world criteria and indices for checking the efficiency of sediment flushing from reservoir which have been got through analyzing large amount of  data from many flushed reservoirs  in the world which were depended tested and applied in the present case study (Mosul Reservoir. These criteria and indices depend mainly on the hydrological , hydraulic and  topographical properties of the reservoirs in-addition to the operation plan of the reservoirs. They gave a good indication for checking the efficiency of the sediment flushing  process in the reservoirs. It was concluded that approximately the main criteria for the successful flushing sediment was  verified  in  Mosul  reservoir  such as  Sediment Balance Ratio   (SBR and the Long Term Capacity Ratio (LTCR,the shape factor  of reservoir (W/L and the hydraulic condition such as the percentage of (Qf/Qin and (Vf/Vin. This gave an indication that the processes of flushing sediment in Mosul reservoir is probably feasible and may be applied  in the future to maintain the water storage in the reservoir.

Limno-reservoirs as a new landscape, environmental and touristic resource: Pareja Limno-reservoir as a case of study (Guadalajara, Spain)

Science.gov (United States)

Díaz-Carrión, I.; Sastre-Merlín, A.; Martínez-Pérez, S.; Molina-Navarro, E.; Bienes-Allas, R.

2012-04-01

A limno-reservoir is a hydrologic infrastructure with the main goal of generating a body of water with a constant level in the riverine zone of a reservoir, building a dam that makes de limno-reservoir independent from the main body of water. This dam can be built in the main river supplying the reservoir or any tributary as well flowing into it. Despite its novel conception and design, around a dozen are already operative in some Spanish reservoirs. This infrastructure allows the new water body to be independent of the main reservoir management, so the water level stability is its main distinctive characteristic. It leads to the development of environmental, sports and cultural initiatives; which may be included in a touristic exploitation in a wide sense. An opinion poll was designed in 2009 to be carried out the Pareja Limno-reservoir (Entrepeñas reservoir area, Tajo River Basin, central Spain). The results showed that for both, Pareja inhabitants and occasional visitors, the limno-reservoir has become an important touristic resource, mainly demanded during summer season. The performance of leisure activities (especially swimming) are being the main brand of this novel hydraulic and environmental infrastructure, playing a role as corrective and/or compensatory action which is needed to apply in order to mitigate the environmental impacts of the large hydraulic constructions.

Terrestrial magma ocean and core segregation in the earth

Science.gov (United States)

Ohtani, Eiji; Yurimoto, Naoyoshi

1992-01-01

According to the recent theories of formation of the earth, the outer layer of the proto-earth was molten and the terrestrial magma ocean was formed when its radius exceeded 3000 km. Core formation should have started in this magma ocean stage, since segregation of metallic iron occurs effectively by melting of the proto-earth. Therefore, interactions between magma, mantle minerals, and metallic iron in the magma ocean stage controlled the geochemistry of the mantle and core. We have studied the partitioning behaviors of elements into the silicate melt, high pressure minerals, and metallic iron under the deep upper mantle and lower mantle conditions. We employed the multi-anvil apparatus for preparing the equilibrating samples in the ranges from 16 to 27 GPa and 1700-2400 C. Both the electron probe microanalyzer (EPMA) and the Secondary Ion Mass spectrometer (SIMS) were used for analyzing the run products. We obtained the partition coefficients of various trace elements between majorite, Mg-perovskite, and liquid, and magnesiowustite, Mg-perovskite, and metallic iron. The examples of the partition coefficients of some key elements are summarized in figures, together with the previous data. We may be able to assess the origin of the mantle abundances of the elements such as transition metals by using the partitioning data obtained above. The mantle abundances of some transition metals expected by the core-mantle equilibrium under the lower mantle conditions cannot explain the observed abundance of some elements such as Mn and Ge in the mantle. Estimations of the densities of the ultrabasic magma Mg-perovskite at high pressure suggest existence of a density crossover in the deep lower mantle; flotation of Mg-perovskite occurs in the deep magma ocean under the lower mantle conditions. The observed depletion of some transition metals such as V, Cr, Mn, Fe, Co, and Ni in the mantle may be explained by the two stage process, the core-mantle equilibrium under the lower

Illuminating magma shearing processes via synchrotron imaging

Science.gov (United States)

Lavallée, Yan; Cai, Biao; Coats, Rebecca; Kendrick, Jackie E.; von Aulock, Felix W.; Wallace, Paul A.; Le Gall, Nolwenn; Godinho, Jose; Dobson, Katherine; Atwood, Robert; Holness, Marian; Lee, Peter D.

2017-04-01

Our understanding of geomaterial behaviour and processes has long fallen short due to inaccessibility into material as "something" happens. In volcanology, research strategies have increasingly sought to illuminate the subsurface of materials at all scales, from the use of muon tomography to image the inside of volcanoes to the use of seismic tomography to image magmatic bodies in the crust, and most recently, we have added synchrotron-based x-ray tomography to image the inside of material as we test it under controlled conditions. Here, we will explore some of the novel findings made on the evolution of magma during shearing. These will include observations and discussions of magma flow and failure as well as petrological reaction kinetics.

Flood moderation by large reservoirs in the humid tropics of Western ghat region of Kerala, India

Energy Technology Data Exchange (ETDEWEB)

Abe, George [Centre for Water Resources Development and Management, Sub Centre, Kottayam South P.O, Kottayam-686 039, Kerala (India); James, E.J. [Water Institute and Dean (Research), Karunya University, Coimbatore-641 114, Tamil Nadu (India)

2013-07-01

Kerala State located in the humid tropics receives an average rainfall of 2810 mm. On an average 85% of this rainfall is received during the two monsoons spread from June to November. Midland and lowland regions of several of the river basins of Kerala experience severe flood events during the monsoons. Idamalayar hydro-electric project (1987) in Periyar River basin envisages flood control apart from power generation. This paper analyzes the flood moderation by Idamalayar reservoir considering the storage regime (inflow and outflow) which is subjected to a strong inter annual variability. The role of Idamalayar reservoir in controlling the monsoon floods is analyzed using daily data (1987-2010). The results of analysis show that the flood moderation by the reservoir is 92% when water storage is less than 50%. The reduction is 87% when reservoir storage is between 50 to 90% and moderation reduces to 62% when the reservoir storage is above 90%. Non-parametric trend analysis of fifty years of hydrologic data shows a reducing trend in inflow and storage during south-west monsoon which reduced spill and subsequent flood events during north-east monsoon.

Reservoir Sedimentation: Impact, Extent, and Mitigation

Science.gov (United States)

Hadley, Richard F.

Storage reservoirs play an important role in water resources development throughout the world. The one problem with reservoirs that is universal is the continual reduction in usable capacity caused by siltation. This book reviews the world picture of erosion and sediment yield, the large variations that exist, and the physical phenomena related to reservoir siltation. The book is in the Technical Paper series of The World Bank (Technical Paper 71) and is not a formal publication. Rather, it is intended to be circulated to encourage discussion and comment and to communicate results quickly. The book is reproduced from typescript, but this does not detract from the value of the contents as a useful text for hydrologrsts, engineers, and soil conservationists in developing countries.

Pareja limno-reservoir (Guadalajara, Spain): environmental and hydrologic aspects

International Nuclear Information System (INIS)

Molina Navarro, E.; Martinez Perez, S.; Sastre Merlin, A.

2010-01-01

The construction of small reservoir on the edge of large ones is an innovative idea designed to counteract some of the negative impacts caused by the construction and use of reservoirs. The denomination Limno-reservoirs is proposed here, as these water bodies are created to maintain a natural lake dynamics. Pareja's limno-reservoir is among the first limno-reservoirs in Spain, and its construction raises some questions about hydrological viability and siltation risk. The proposition of the methodologies to solve them and the evaluation of the first results is the aim of this study. A detailed water balance makes possible to affirm that, in a firs approach, the limno-reservoir is viable from the hydrological point of view, because the Ompolveda basin -Tajo's tributary at Entrepenas reservoir- has enough water resources to guarantee the permanence of the water body, even during dry years. To assess the siltation risk, a soil loss observation network will be monitoring the Ompolveda basin for the next three years to evaluate the net erosion in the watershed and the sediment delivery to the reservoir. (Author)

MAGMA: generalized gene-set analysis of GWAS data.

Science.gov (United States)

de Leeuw, Christiaan A; Mooij, Joris M; Heskes, Tom; Posthuma, Danielle

2015-04-01

By aggregating data for complex traits in a biologically meaningful way, gene and gene-set analysis constitute a valuable addition to single-marker analysis. However, although various methods for gene and gene-set analysis currently exist, they generally suffer from a number of issues. Statistical power for most methods is strongly affected by linkage disequilibrium between markers, multi-marker associations are often hard to detect, and the reliance on permutation to compute p-values tends to make the analysis computationally very expensive. To address these issues we have developed MAGMA, a novel tool for gene and gene-set analysis. The gene analysis is based on a multiple regression model, to provide better statistical performance. The gene-set analysis is built as a separate layer around the gene analysis for additional flexibility. This gene-set analysis also uses a regression structure to allow generalization to analysis of continuous properties of genes and simultaneous analysis of multiple gene sets and other gene properties. Simulations and an analysis of Crohn's Disease data are used to evaluate the performance of MAGMA and to compare it to a number of other gene and gene-set analysis tools. The results show that MAGMA has significantly more power than other tools for both the gene and the gene-set analysis, identifying more genes and gene sets associated with Crohn's Disease while maintaining a correct type 1 error rate. Moreover, the MAGMA analysis of the Crohn's Disease data was found to be considerably faster as well.

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

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.

History of the magmatic feeding system of the Campi Flegrei caldera (Italy)

Science.gov (United States)

Civetta, L.; Arienzo, I.; D'Antonio, M.; di Renzo, V.; di Vito, M. A.; Orsi, G.

2007-05-01

The definition of the magmatic feeding system of active volcanoes in terms of architecture, composition, crystallization time-scale, relationships between composition of the erupted magmas and structural position of the vents, and magma processes, is of paramount importance for volcanic hazards evaluation. Investigations aimed at defining the Campi Flegeri magmatic system, include detailed mineralogical, geochemical and isotopic analyses (Sr, Nd, Pb, Th,U). The magmatic feeding system of the Campi Flegrei caldera is characterized by deep and shallow magma reservoirs. In the deep reservoirs (20-10 km depth) mantle- derived magmas differentiated and were contaminated by continental crust. In the shallow reservoirs isotopically distinct magmas, further differentiated, contaminated, and mixed and mingled before eruptions. These processes generated isotopically distinct components, variably interacting with the different structural elements of the Campi Flegrei caldera through time. The relationships between the structural position of the eruption vents, during the last 15 ka of activity, and the isotopic composition of the magmas erupted at the Campi Flegrei caldera allow us to reconstruct the architecture of the magmatic feeding system and to infer the chemical and isotopic composition of the magma feeding a future eruption, according to vent position.

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.)

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

Nonlinear Multigrid for Reservoir Simulation

DEFF Research Database (Denmark)

Christensen, Max la Cour; Eskildsen, Klaus Langgren; Engsig-Karup, Allan Peter

2016-01-01

efficiency for a black-oil model. Furthermore, the use of the FAS method enables a significant reduction in memory usage compared with conventional techniques, which suggests new possibilities for improved large-scale reservoir simulation and numerical efficiency. Last, nonlinear multilevel preconditioning...

Aquatic macrophytes in the large, sub-tropical Itaipu Reservoir, Brazil

OpenAIRE

Roger Paulo Mormul; Fernando Alves Ferreira; Thaisa Sala Michelan; Priscilla Carvalho; Marcio José Silveira; Sidinei Magela Thomaz

2010-01-01

In the last three decades, rapid assessment surveys have become an important approach for measuring aquatic ecosystem biodiversity. These methods can be used to detect anthropogenic impacts and recognize local or global species extinctions. We present a floristic survey of the aquatic macrophytes along the Brazilian margin of the Itaipu Reservoir conducted in 2008 and compare this with a floristic survey conducted ten years earlier. We used ordination analysis to determine whether assemblage ...

Constraints on dike propagation from continuous GPS measurements

Science.gov (United States)

Segall, P.; Cervelli, Peter; Owen, S.; Lisowski, M.; Miklius, Asta

2001-01-01

The January 1997 East Rift Zone eruption on Kilauea volcano, Hawaii, occurred within a network of continuous Global Positioning System (GPS) receivers. The GPS measurements reveal the temporal history of deformation during dike intrusion, beginning ??? 8 hours prior to the onset of the eruption. The dike volume as a function of time, estimated from the GPS data using elastic Green's functions for a homogeneous half-space, shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time. These observations are inconsistent with simple models of dike propagation, which predict accelerating dike volume up to the time of the eruption and little or no change thereafter. Deflationary tilt changes at Kilauea summit mirror the inferred dike volume history, suggesting that the rate of dike propagation is limited by flow of magma into the dike. A simple, lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption (rather than intrusion) is favored by high initial dike pressures, compressional stress states, large, compressible magma reservoirs, and highly conductive conduits linking the dike and source reservoirs. Comparison of model predictions to the observed dike volume history, the ratio of erupted to intruded magma, and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits. Interpretation is complicated by the presence of multiple source reservoirs, magma vesiculation and cooling, as well as spatial variations in dike-normal stress. Reinflation of the summit magma chamber following the eruption was measured by GPS and accompanied a rise in the level of the Pu'u O'o lava lake. For a spheroidal chamber these data imply a summit magma chamber volume of ??? 20 km3, consistent with recent estimates from seismic

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

Unscrambling the Omlette: a New Bubble and Crystal Clustering Mechanism in Chaotically Mixed Magma Flows

Science.gov (United States)

Robertson, J.; Metcalfe, G.; Wang, S.; Barnes, S. J.

2014-12-01

The concentration of bubbles, crystals or droplets into small volumes of magma is a key trigger for many interesting magmatic processes. For example, gas slugs driving Strombolian eruptions form from the coalesence of exsolved bubbles within a volcanic conduit, while Ni-Cu-PGE magmatic sulfide deposits require a concentration of dense sulfide droplets from a large volume of magma to form a massive ore body. However the physical mechanism for this clustering remains unresolved - especially since small particles in active magma flows are expected to mostly track flow streamlines rather than clustering. We have uncovered a previously unreported clustering mechanism which is applicable to magmatic flows. This mechanism involves the interaction of particles with two kinds of chaotic flow structure: (a) high-strain regions within the well-mixed chaotic zones of the flow, and (b) unmixed islands of stability within the chaotic flow, known as Kolmogorov-Arnold-Moser (KAM) regions. The first figure shows the difference between chaotic and KAM regions in a chaotic laminar pipe flow. Trapping occurs when particles are scattered from high-strain regions in the chaotic zones and become trapped in the KAM regions, leading to a rapid concentration of particles relative to their original distribution (shown in the second series of figures). Using a combination of these analogue experiments and theoretical analysis we outline the conditions under which this clustering process can occur. We examine the onset of secondary density-related instabilities and the effects of increased particle-particle interaction within the clustered particles, and highlight the impact of particle clustering on the dynamics of magma ascent and emplacement.

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

-Vesuvius in the last 8 ky BP. Contamination in the mid- to upper crust occurred repeatedly, after the magma chamber waxed with influx of new mantle- and crustal-derived magmas and fluids, and waned as a result of magma withdrawal and production of large and energetic plinian and subplinian eruptions. ?? 2005 Elsevier B.V. All rights reserved.

Zircon crytallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

Science.gov (United States)

Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.

2007-01-01

In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Miff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ??? 60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction). ?? 2007 Geological Society of America.

Zircon crystallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

Science.gov (United States)

Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.

2007-01-01

In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Tuff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ~60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction).

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

The structures and textures of the rhyolite in the Mule Creek vent (New Mexico, USA) indicate mechanisms by which volatiles escape from silicic magma during eruption. The vent outcrop is a 300-m-high canyon wall comprising a section through the top of a feeder conduit, vent and the base of an extrusive lava dome. Field relations show that eruption began with an explosive phase and ended with lava extrusion. Analyses of glass inclusions in quartz phenocrysts from the lava indicate that the magma had a pre-eruptive dissolved water content of 2.5-3.0 wt% and, during eruption, the magma would have been water-saturated over the vertical extent of the present outcrop. However, the vesicularity of the rhyolite is substantially lower than that predicted from closed-system models of vesiculation under equilibrium conditions. At a given elevation in the vent, the volume fraction of primary vesicles in the rhyolite increases from zero close to the vent margin to values of 20-40 vol.% in the central part. In the centre the vesicularity increases upward from approximately 20 vol.% at 300 m below the canyon rim to approximately 40 vol.% at 200 m, above which it shows little increase. To account for the discrepancy between observed vesicularity and measured water content, we conclude that gas escaped during ascent, probably beginning at depths greater than exposed, by flow through the vesicular magma. Gas escape was most efficient near the vent margin, and we postulate that this is due both to the slow ascent of magma there, giving the most time for gas to escape, and to shear, favouring bubble coalescence. Such shear-related permeability in erupting magma is supported by the preserved distribution of textures and vesicularity in the rhyolite: Vesicles are flattened and overlapping near the dense margins and become progressively more isolated and less deformed toward the porous centre. Local zones have textures which suggest the coalescence of bubbles to form permeable

The magma plumbing system in the Mariana Trough back-arc basin at 18° N

Science.gov (United States)

Lai, Zhiqing; Zhao, Guangtao; Han, Zongzhu; Huang, Bo; Li, Min; Tian, Liyan; Liu, Bo; Bu, Xuejiao

2018-04-01

Mafic magmas are common in back-arc basin, once stalled in the crust, these magmas may undergo different evolution. In this paper, compositional and textural variations of plagioclase as well as mineral-melt geothermobarometry are presented for basalts erupted from the central Mariana Trough (CMT). These data reveal crystallization conditions and we attempt a reconstruction of the magma plumbing system of the CMT. Plagioclase megacrysts, phenocrysts, microphenocrysts, microlites, olivine, spinel, and clinopyroxene have been recognized in basalt samples, using BSE images and compositional features. The last three minerals are homogeneous as microphenocrysts. Mineral-melt barometry indicates that plagioclase crystals crystallized and eventually grew into phenocrysts and megacrysts in mush zone with depth of 5-9 km, in which the normal zoning plagioclases crystallized in the interval of various batches of basic magma recharging. Plagioclase megacrysts and phenocrysts were dissolved and/or resorbed, when new basic magmas injected into the mush zone near Moho depth. It is inferred that magma extracted from the mush zone, and adiabatically ascended via different pathways. Some basaltic magmas underwent plagioclase and clinopyroxene microphenocrysts crystallization in low-pressure before eruption. Plagioclase microlites and outermost rims probably crystallized after eruption.

Formation of thick stratiform Fe-Ti oxide layers in layered intrusion and frequent replenishment of fractionated mafic magma: Evidence from the Panzhihua intrusion, SW China

Science.gov (United States)

Song, Xie-Yan; Qi, Hua-Wen; Hu, Rui-Zhong; Chen, Lie-Meng; Yu, Song-Yue; Zhang, Jia-Fei

2013-03-01

Panzhihua intrusion is one of the largest layered intrusions that hosts huge stratiform Fe-Ti oxide layers in the central part of the Emeishan large igneous province, SW China. Up to 60 m thick stratiform massive Fe-Ti oxide layers containing 85 modal% of magnetite and ilmenite and overlying magnetite gabbro compose cyclic units of the Lower Zone of the intrusion. The cyclic units of the Middle Zone consist of magnetite gabbro and overlying gabbro. In these cyclic units, contents of Fe2O3(t), TiO2 and Cr and Fe3+/Ti4+ ratio of the rocks decrease upward, Cr content of magnetite and forsterite percentage of olivine decrease as well. The Upper Zone consists of apatite gabbro characterized by enrichment of incompatible elements (e.g., 12-18 ppm La, 20-28 ppm Y) and increasing of Fe3+/Ti4+ ratio (from 1.3 to 2.3) upward. These features indicate that the Panzhihua intrusion was repeatedly recharged by more primitive magma and evolved magmas had been extracted. Calculations using MELTS indicate that extensive fractionation of olivine and clinopyroxene in deep level resulted in increasing Fe and Ti contents in the magma. When these Fe-Ti-enriched magmas were emplaced along the base of the Panzhihua intrusion, Fe-Ti oxides became an early crystallization phase, leading to a residual magma of lower density. We propose that the unusually thick stratiform Fe-Ti oxide layers resulted from coupling of gravity settling and sorting of the crystallized Fe-Ti oxides from Fe-Ti-enriched magmas and frequent magma replenishment along the floor of the magma chamber.

Parental magmas of Mare Fecunditatis - Evidence from pristine glasses

International Nuclear Information System (INIS)

Jin, Y.; Taylor, L.A.

1990-01-01

Results are presented on the petrography and electron microprobe analyses of 14 discrete glass beads from the Luna 16 core sample (21036,15) from Mare Fecunditatis regolith, that were previously characterized as representing pristine glasses. Compared to Apollo pristine glasses analyzed by Delano (1986), the Luna 16 pristine glasses have higher CaO and Al2O3 contents but lower MgO and Ni. On the basis of their contents of MgO, FeO, Al2O3, and CaO, these pristine glasses could be divided into two groups, A and B. It is suggested that at least two parental magmas are needed to explain the chemical variations among these glasses. The Group B glasses appear to represent primitive parental magma that evolved by olivine fractionation to the compositions of the Luna 16 aluminous mare basalts, whereas the Group A volcanic glasses may represent an unusual new basalt magma type that contains a high plagioclase component. 14 refs

Continuous magma recharge at Mt. Etna during the 2011-2013 period controls the style of volcanic activity and compositions of erupted lavas

Science.gov (United States)

Viccaro, Marco; Calcagno, Rosario; Garozzo, Ileana; Giuffrida, Marisa; Nicotra, Eugenio

2015-02-01

Volcanic rocks erupted during the January 2011 - April 2013 paroxysmal sequence at Mt. Etna volcano have been investigated through in situ microanalysis of mineral phases and whole rock geochemistry. These products have been also considered within the framework of the post-2001 record, evidencing that magmas feeding the 2011-2013 paroxysmal activity inherited deep signature comparable to that of the 2007-2009 volcanic rocks for what concerns their trace element concentration. Analysis performed on plagioclase, clinopyroxene and olivine, which are sensitive to differentiation processes, show respectively fluctuations of the An, Mg# and Fo contents during the considered period. Also major and trace elements measured on the whole rock provide evidence of the evolutionary degree variations through time. Simulations by MELTS at fixed chemical-physical parameters allowed the definition of feeding system dynamics controlling the geochemical variability of magmas during the 2011-2013 period. Specifically, compositional changes have been interpreted as due to superimposition of fractional crystallization and mixing in variable proportions with more basic magma ascending from intermediate to shallower levels of the plumbing system. Composition of the recharging end-member is compatible with that of the most basic magmas emitted during the 2007 and the early paroxysmal eruptions of 2012. Analysis of the erupted volumes of magma combined with its petrologic evolution through time support the idea that large volumes of magma are continuously intruded and stored in the intermediate plumbing system after major recharging phases in the deepest levels of it. Transient recharge from the intermediate to the shallow levels is then responsible for the paroxysmal eruptions.

Magma Mixing: Why Picrites are Not So Hot

Science.gov (United States)

Natland, J. H.

2010-12-01

Oxide gabbros or ferrogabbros are the late, low-temperature differentiates of tholeiitic magma and usually form as cumulates that can have 2-30% of the magmatic oxides, ilmenite and magnetite. They are common in the ocean crust and are likely ubiquitous wherever extensive tholeiitic magmatism has occurred, especially beneath thick lava piles such as at Hawaii, Iceland, oceanic plateaus, island arcs and ancient continental crust. When intruded by hot primitive magma including picrite, the oxide-bearing portions of these rocks are readily partially melted or assimilated into the magma and contribute to it a degree of iron and titanium enrichment that is not reflective of the mantle source of the primitive magma. The most extreme examples of such mixing are meimechites and ferropicrites, but this type of end-member mixing is even common in MORB. To the extent this process occurs, the eruptive picrite cannot be used to estimate compositions of partial melts of mantle rocks, nor their eruptive or potential temperatures, using olivine-liquid FeO-MgO backtrack procedures. Most picrites have glasses with compositions approximating those expected from low-pressure multiphase cotectic crystallization, and olivine that on average crystallized from liquids of nearly those compositions. The hallmark of such rocks is the presence of minerals other than olivine among phenocrysts (plagioclase at Iceland, clinopyroxene at many oceanic islands), Fe- and Ti-rich chromian spinel (ankaramites, ferropicrites and meimichites), and in some cases the presence of iron-rich olivine (hortonolite ~Fo65 in ferropicrites), Ti-rich kaersutitic amphibole and even apatite (meimechites); the latter two derive from late-stage, hydrous and geochemically enriched metamorphic or alkalic assimilants. This type of mixing, however, does not necessarily involve depleted and enriched mixing components. To avoid such mixing, primitive melts have to rise primarily through upper mantle rocks of near-zero melt

The role of liquid-liquid immiscibility and crystal fractionation in the genesis of carbonatite magmas: insights from Kerimasi melt inclusions

Science.gov (United States)

Guzmics, Tibor; Zajacz, Zoltán; Mitchell, Roger H.; Szabó, Csaba; Wälle, Markus

2015-02-01

We have reconstructed the compositional evolution of the silicate and carbonate melt, and various crystalline phases in the subvolcanic reservoir of Kerimasi Volcano in the East African Rift. Trace element concentrations of silicate and carbonate melt inclusions trapped in nepheline, apatite and magnetite from plutonic afrikandite (clinopyroxene-nepheline-perovskite-magnetite-melilite rock) and calciocarbonatite (calcite-apatite-magnetite-perovskite-monticellite-phlogopite rock) show that liquid immiscibility occurred during the generation of carbonatite magmas from a CO2-rich melilite-nephelinite magma formed at relatively high temperatures (1,100 °C). This carbonatite magma is notably more calcic and less alkaline than that occurring at Oldoinyo Lengai. The CaO-rich (32-41 wt%) nature and alkali-"poor" (at least 7-10 wt% Na2O + K2O) nature of these high-temperature (>1,000 °C) carbonate melts result from strong partitioning of Ca (relative to Mg, Fe and Mn) in the immiscible carbonate and the CaO-rich nature (12-17 wt%) of its silicate parent (e.g., melilite-nephelinite). Evolution of the Kerimasi carbonate magma can result in the formation of natrocarbonatite melts with similar composition to those of Oldoinyo Lengai, but with pronounced depletion in REE and HFSE elements. We suggest that this compositional difference results from the different initial parental magmas, e.g., melilite-nephelinite at Kerimasi and a nephelinite at Oldoinyo Lengai. The difference in parental magma composition led to a significant difference in the fractionating mineral phase assemblage and the element partitioning systematics upon silicate-carbonate melt immiscibility. LA-ICP-MS analysis of coeval silicate and carbonate melt inclusions provides an opportunity to infer carbonate melt/silicate melt partition coefficients for a wide range of elements. These data show that Li, Na, Pb, Ca, Sr, Ba, B, all REE (except Sc), U, V, Nb, Ta, P, Mo, W and S are partitioned into the carbonate

Structure, tectonic and petrology of mid-oceanic ridges and the Indian scenario

Digital Repository Service at National Institute of Oceanography (India)

Iyer, S.D.; Ray, Dwijesh

floor and the lower magma supply, thicker crust a nd deeper extent of hydrothermal cooling lead to episodic volcanism. Under these conditions, tectonic events rather than volcanic activities are more frequent than at faster spreading ridges, because... centres than at faster - spreading centres depending on whether or not a steady - state magma reservoir can be sustained at a given spreading rate 20 . The critical spreading rate, above which a steady - state magma reservoir can form and below which...

Prediction of reservoir compaction and surface subsidence

Energy Technology Data Exchange (ETDEWEB)

De Waal, J.A.; Smits, R.M.M.

1988-06-01

A new loading-rate-dependent compaction model for unconsolidated clastic reservoirs is presented that considerably improves the accuracy of predicting reservoir rock compaction and surface subsidence resulting from pressure depletion in oil and gas fields. The model has been developed on the basis of extensive laboratory studies and can be derived from a theory relating compaction to time-dependent intergranular friction. The procedure for calculating reservoir compaction from laboratory measurements with the new model is outlined. Both field and laboratory compaction behaviors appear to be described by one single normalized, nonlinear compaction curve. With the new model, the large discrepancies usually observed between predictions based on linear compaction models and actual (nonlinear) field behavior can be explained.

Empirical constraints on partitioning of platinum group elements between Cr-spinel and primitive terrestrial magmas

Science.gov (United States)

Park, Jung-Woo; Kamenetsky, Vadim; Campbell, Ian; Park, Gyuseung; Hanski, Eero; Pushkarev, Evgeny

2017-11-01

Recent experimental studies and in situ LA-ICP-MS analysis on natural Cr-spinel have shown that Rh and IPGEs (Ir-group platinum group elements: Ru, Ir, Os) are enriched in the lattice of Cr-spinel. However, the factors controlling the partitioning behaviour of these elements are not well constrained. In this study, we report the Rh, IPGE, and trace element contents in primitive Cr-spinel, measured by LA-ICP-MS, from nine volcanic suites covering various tectonic settings including island arc picrites, boninites, large igneous province picrites and mid-ocean ridge basalts. The aim is to understand the factors controlling the enrichment of Rh and IPGEs in Cr-spinels, to estimate empirical partition coefficients between Cr-spinel and silicate melts, and to investigate the role of Cr-spinel fractional crystallization on the PGE geochemistry of primitive magmas during the early stages of fractional crystallization. There are systematic differences in trace elements, Rh and IPGEs in Cr-spinels from arc-related magmas (Arc Group Cr-spinel), intraplate magmas (Intraplate Group Cr-spinel), and mid-ocean ridge magmas (MORB Group Cr-spinel). Arc Group Cr-spinels are systematically enriched in Sc, Co and Mn and depleted in Ni compared to the MORB Group Cr-spinels. Intraplate Group Cr-spinels are distinguished from the Arc Group Cr-spinels by their high Ni contents. Both the Arc and Intraplate Group Cr-spinels have total Rh and IPGE contents of 22-689 ppb whereas the MORB Group Cr-spinels are depleted in Rh and IPGE (total time-resolved spectra of LA-ICP-MS data for Cr-spinels mostly show constant count rates for trace element and Rh and IPGEs, suggesting homogeneous distribution of these elements in Cr-spinels. The PGE spikes observed in several Cr-spinels were interpreted to be PGE-bearing mineral inclusions and excluded from calculating the PGE contents of the Cr-spinels. On primitive mantle normalized diagrams the Arc Group Cr-spinels are characterized by a fractionated

Fortescue reservoir development and reservoir studies

Energy Technology Data Exchange (ETDEWEB)

Henzell, S.T.; Hicks, G.J.; Horden, M.J.; Irrgang, H.R.; Janssen, E.J.; Kable, C.W.; Mitchell, R.A.H.; Morrell, N.W.; Palmer, I.D.; Seage, N.W.

1985-03-01

The Fortescue field in the Gippsland Basin, offshore southeastern Australia is being developed from two platforms (Fortescue A and Cobia A) by Esso Australia Ltd. (operator) and BHP Petroleum. The Fortescue reservoir is a stratigraphic trap at the top of the Latrobe Group of sediments. It overlies the western flank of the Halibut and Cobia fields and is separated from them by a non-net sequence of shales and coals which form a hydraulic barrier between the two systems. Development drilling into the Fortescue reservoir commenced in April 1983 with production coming onstream in May 1983. Fortescue, with booked reserves of 44 stock tank gigalitres (280 million stock tank barrels) of 43/sup 0/ API oil, is the seventh major oil reservoir to be developed in the offshore Gippsland Basin by Esso/BHP. In mid-1984, after drilling a total of 20 exploration and development wells, and after approximately one year of production, a detailed three-dimensional, two-phase reservoir simulation study was performed to examine the recovery efficiency, drainage patterns, pressure performance and production rate potential of the reservoir. The model was validated by history matching an extensive suite of Repeat Formation Test (RFT) pressure data. The results confirmed the reserves basis, and demonstrated that the ultimate oil recovery from the reservoir is not sensitive to production rate. This result is consistent with studies on other high quality Latrobe Group reservoirs in the Gippsland Basin which contain undersaturated crudes and receive very strong water drive from the Basin-wide aquifer system. With the development of the simulation model during the development phase, it has been possible to more accurately define the optimal well pattern for the remainder of the development.

Mafic microgranular enclave swarms in the Chenar granitoid stock, NW of Kerman, Iran: evidence for magma mingling

Science.gov (United States)

Arvin, M.; Dargahi, S.; Babaei, A. A.

2004-10-01

Mafic microgranular enclaves (MME) are common in the Early to Middle Miocene Chenar granitoid stock, northwest of Kerman, which is a part of Central Iranian Eocene volcanic belt. They occur individually and in homogeneous or heterogeneous swarms. The MME form a number of two-dimensional structural arrangements, such as dykes, small rafts, vortices, folded lens-shapes and late swarms. The enclaves are elongated, rounded to non-elongated and subrounded in shape and often show some size-sorting parallel to direction of flow. Variation in the elongation of enclaves could reflect variations in the viscosity of the enclave, the time available for enclave deformation and differential strain during flow of the host granitoid magma. The most effective mechanism in the formation of enclave swarms in the Chenar granitoid stock was velocity gradient-related convection currents in the granitoid magma chamber. Gravitational sorting and the break-up of heterogeneous dykes also form MME swarms. The MME (mainly diorite to diorite gabbro) have igneous mineralogy and texture, and are marked by sharp contacts next to their host granitoid rocks. The contact is often marked by a chilled margin with no sign of solid state deformation. Evidence of disequilibrium is manifested in feldspars by oscillatory zoning, resorbed rims, mantling and punctuated growth, together with overgrowth of clinopyroxene/amphibole on quartz crystals, the acicular habit of apatites and the development of Fe-Ti oxides along clinopyroxene cleavages. These observations suggest that the MMEs are derived from a hybrid-magma formed as a result of the intrusion of a mafic magma into the base of a felsic magma chamber. The density contrast between hybrid-magma and the overlying felsic magma was reduced by the release of dissolved fluids and the ascent of exsolved gas bubbles from the mafic magma into the hybrid zone. Further convection in the magma chamber dispersed the hybridized magma as globules in the upper parts of

The detection of leakages in open reservoirs by the radioisotope sorption method

International Nuclear Information System (INIS)

Owczarczyk, A.; Wierzchnicki, R.; Urbanski, T.; Chmielewski, A.G.; Szpilowski, S.

1992-01-01

Location of leakages in large hydro-engineering plants and industrial water reservoirs is of great importance from view-point of both safety and economy of their exploitation. Large variety of water reservoirs encountered in hydro-engineering and industry calls for adaptation of investigation methods to their specific features. In the paper a number of methodological variants of known radiotracer technique developed at the INCT is presented. They are intended to detect and locate leakages in hydro-engineering reservoirs and dams as well as large open industrial tanks. The radioisotopes Au-198 and In-133 m being used for that purpose show excellent sorption characteristic on typical construction materials users to build such objects. (author). 8 refs, 8 figs

Mechanism study on a plague outbreak driven by the construction of a large reservoir in southwest china (surveillance from 2000-2015.

Directory of Open Access Journals (Sweden)

Xin Wang

2017-03-01

Full Text Available Plague, a Yersinia pestis infection, is a fatal disease with tremendous transmission capacity. However, the mechanism of how the pathogen stays in a reservoir, circulates and then re-emerges is an enigma.We studied a plague outbreak caused by the construction of a large reservoir in southwest China followed 16-years' surveillance.The results show the prevalence of plague within the natural plague focus is closely related to the stability of local ecology. Before and during the decade of construction the reservoir on the Nanpan River, no confirmed plague has ever emerged. With the impoundment of reservoir and destruction of drowned farmland and vegetation, the infected rodent population previously dispersed was concentrated together in a flood-free area and turned a rest focus alive. Human plague broke out after the enzootic plague via the flea bite. With the construction completed and ecology gradually of human residential environment, animal population and type of vegetation settling down to a new balance, the natural plague foci returned to a rest period. With the rodent density decreased as some of them died, the flea density increased as the rodents lived near or in local farm houses where had more domestic animals, and human has a more concentrated population. In contrast, in the Himalayan marmot foci of the Qinghai-Tibet Plateau in the Qilian Mountains. There are few human inhabitants and the local ecology is relatively stable; plague is prevalence, showing no rest period. Thus the plague can be significantly affected by ecological shifts.

Mechanism study on a plague outbreak driven by the construction of a large reservoir in southwest china (surveillance from 2000-2015).

Science.gov (United States)

Wang, Xin; Wei, Xiaoyu; Song, Zhizhong; Wang, Mingliu; Xi, Jinxiao; Liang, Junrong; Liang, Yun; Duan, Ran; Tian, Kecheng; Zhao, Yong; Tang, Guangpeng; You, Lv; Yang, Guirong; Liu, Xuebin; Chen, Yuhuang; Zeng, Jun; Wu, Shengrong; Luo, Shoujun; Qin, Gang; Hao, Huijing; Jing, Huaiqi

2017-03-01

Plague, a Yersinia pestis infection, is a fatal disease with tremendous transmission capacity. However, the mechanism of how the pathogen stays in a reservoir, circulates and then re-emerges is an enigma. We studied a plague outbreak caused by the construction of a large reservoir in southwest China followed 16-years' surveillance. The results show the prevalence of plague within the natural plague focus is closely related to the stability of local ecology. Before and during the decade of construction the reservoir on the Nanpan River, no confirmed plague has ever emerged. With the impoundment of reservoir and destruction of drowned farmland and vegetation, the infected rodent population previously dispersed was concentrated together in a flood-free area and turned a rest focus alive. Human plague broke out after the enzootic plague via the flea bite. With the construction completed and ecology gradually of human residential environment, animal population and type of vegetation settling down to a new balance, the natural plague foci returned to a rest period. With the rodent density decreased as some of them died, the flea density increased as the rodents lived near or in local farm houses where had more domestic animals, and human has a more concentrated population. In contrast, in the Himalayan marmot foci of the Qinghai-Tibet Plateau in the Qilian Mountains. There are few human inhabitants and the local ecology is relatively stable; plague is prevalence, showing no rest period. Thus the plague can be significantly affected by ecological shifts.

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

Magma explains low estimates of lithospheric strength based on flexure of ocean island loads

Science.gov (United States)

Buck, W. Roger; Lavier, Luc L.; Choi, Eunseo

2015-04-01

One of the best ways to constrain the strength of the Earth's lithosphere is to measure the deformation caused by large, well-defined loads. The largest, simple vertical load is that of the Hawaiian volcanic island chain. An impressively detailed recent analysis of the 3D response to that load by Zhong and Watts (2013) considers the depth range of seismicity below Hawaii and the seismically determined geometry of lithospheric deflection. These authors find that the friction coefficient for the lithosphere must be in the normal range measured for rocks, but conclude that the ductile flow strength has to be far weaker than laboratory measurements suggest. Specifically, Zhong and Watts (2013) find that stress differences in the mantle lithosphere below the island chain are less than about 200 MPa. Standard rheologic models suggest that for the ~50 km thick lithosphere inferred to exist below Hawaii yielding will occur at stress differences of about 1 GPa. Here we suggest that magmatic accommodation of flexural extension may explain Hawaiian lithospheric deflection even with standard mantle flow laws. Flexural stresses are extensional in the deeper part of the lithosphere below a linear island load (i.e. horizontal stresses orthogonal to the line load are lower than vertical stresses). Magma can accommodate lithospheric extension at smaller stress differences than brittle and ductile rock yielding. Dikes opening parallel to an island chain would allow easier downflexing than a continuous plate, but wound not produce a freely broken plate. The extensional stress needed to open dikes at depth depends on the density contrast between magma and lithosphere, assuming magma has an open pathway to the surface. For a uniform lithospheric density ρL and magma density ρM the stress difference to allow dikes to accommodate extension is: Δσxx (z) = g z (ρM - gρL), where g is the acceleration of gravity and z is depth below the surface. For reasonable density values (i.e. �

When Magma Meets Carbonate: Explosive Criminals of Climate Change?

Science.gov (United States)

Carter, L. B.

2017-12-01

The natural carbon cycle is a key component of global climate change. Identifying and quantifying all processes in the cycle is essential to determine the effects of human greenhouse gas contributions and make future predictions. Volcanoes are the main natural source of carbon dioxide to the atmosphere [1]. In settings where carbonate rocks underlie the edifice, they can be consumed by magma passing through, which can release extra CO2, potentially explaining the extremely high emissions at Mount Etna in Italy [2-4]. We conduct laboratory experiments, mimicking conditions in the crust, to study how different carbonate rocks interact with hot magmas at pressure, and determine the amount of CO2 generated. We find that some types of magma can raise volcanic gas output and cause more explosive and dangerous eruptions [5-6]. Others are more likely to release hot fluids to the surrounding rocks, releasing CO2 by skarnification, which leaves economically important ores like in the western US [3,7] but can weaken the subsurface, potentially leading to landslides. Gas can also be released on the flanks of a volcano or in regions lacking an active volcano, due to the breakdown of certain carbonate rocks by heat [7], seen as bubbling springs in Yellowstone [8]. Our experiments indicate that if dolostone, not limestone, surrounds a magma chamber, over half the CO2 that was locked in the crust can escape even at lower temperatures a distance away. These processes are perhaps pertinent to why the Earth's climate was warm >50 million years ago, when more magma-carbonate interaction likely occurred than today [3] and thus contributed several times the current volcanic output [4] to the atmosphere. As significant parts of the long-term carbon cycle, it is necessary to include magma-carbonate reactions when considering climate changes before taking into account human input. [1] Aiuppa et al 2017 ESciRev (168) 24-47; [2] Ganino and Arndt 2009 Geol (37) 323-326; [3] Lee et al. 2013

Halogen degassing during ascent and eruption of water-poor basaltic magma

Science.gov (United States)

Edmonds, M.; Gerlach, T.M.; Herd, Richard A.

2009-01-01

A study of volcanic gas composition and matrix glass volatile concentrations has allowed a model for halogen degassing to be formulated for K??lauea Volcano, Hawai'i. Volcanic gases emitted during 2004-2005 were characterised by a molar SO2/HCl of 10-64, with a mean of 33; and a molar HF/HCl of 0-5, with a mean of 1.0 (from approximately 2500 measurements). The HF/HCl ratio was more variable than the SO2/HCl ratio, and the two correlate weakly. Variations in ratio took place over rapid timescales (seconds). Matrix glasses of Pele's tears erupted in 2006 have a mean S, Cl and F content of 67, 85 and 173??ppm respectively, but are associated with a large range in S/F. A model is developed that describes the open system degassing of halogens from parental magmas, using the glass data from this study, previously published results and parameterisation of sulphur degassing from previous work. The results illustrate that halogen degassing takes place at pressures of < 1??MPa, equivalent to < ~ 35??m in the conduit. Fluid-melt partition coefficients for Cl and F are low (< 1.5); F only degasses appreciably at < 0.1??MPa above atmospheric pressure, virtually at the top of the magma column. This model reproduces the volcanic gas data and other observations of volcanic activity well and is consistent with other studies of halogen degassing from basaltic magmas. The model suggests that variation in volcanic gas halogen ratios is caused by exsolution and gas-melt separation at low pressures in the conduit. There is no evidence that either diffusive fractionation or near-vent chemical reactions involving halogens is important in the system, although these processes cannot be ruled out. The fluxes of HCl and HF from K??lauea during 2004-5 were ~ 25 and 12??t/d respectively. ?? 2008 Elsevier B.V.

Radioactive equilibria and disequilibria of U-series nuclides in erupting magmas from Izu arc volcanoes

International Nuclear Information System (INIS)

Sato, Jun; Kurihara, Yuichi; Takahashi, Masaomi

2009-01-01