Sample records for volcanic arc magmas

  1. Magma genesis of the acidic volcanism in the intra-arc rift zone of the Izu volcanic arc, Japan (United States)

    Haraguchi, S.; Tokuyama, H.; Ishii, T.


    The Izu volcanic arc extends over 550 km from the Izu Peninsula, Japan, to the Nishinoshima Trough or Sofugan tectonic line. It is the northernmost segment of the Izu-Bonin-Mariana arc system, which is located at the eastern side of the Philippine Sea Plate. The recent magmatism of the Izu arc is bimodal and characterized by basalt and rhyolite (e.g. Tamura and Tatsumi 2002). In the southern Izu arc, volcanic front from the Aogashima to the Torishima islands is characterized by submarine calderas and acidic volcanisms. The intra-arc rifting, characterized by back-arc depressions, small volcanic knolls and ridges, is active in this region. Volcanic rocks were obtained in 1995 during a research cruise of the R/V MOANA WAVE (Hawaii University, cruise MW9507). Geochemical variation of volcanic rocks and magma genesis was studied by Hochstaedter et al. (2000, 2001), Machida et al (2008), etc. These studies focused magma and mantle dynamics of basaltic volcanism in the wedge mantle. Acidic volcanic rocks were also dredged during the curies MW9507. However, studies of these acidic volcanics were rare. Herein, we present petrographical and chemical analyses of these acidic rocks, and compare these results with those of other acidic rocks in the Izu arc and lab experiments, and propose a model of magma genesis in a context of acidic volcanism. Dredge sites by the cruise MW9507 are 120, and about 50 sites are in the rift zone. Recovered rocks are dominated by the bimodal assemblage of basalt-basaltic andesite and dacite-rhyolite. The most abundant phase is olivine basalt, less than 50 wt% SiO2. Andesites are minor in volume and compositional gap from 56 to 65 wt% SiO2 exists. The across-arc variation of the HFSE contents and ratios, such as Zr/Y and Nb/Zr of rhyolites exhibit depleted in the volcanic front side and enriched in reararc side. This characteristic is similar to basaltic volcanism pointed out by Hochstaedter et al (2000). The petrographical features of rhyolites

  2. The record of magma chamber processes in plagioclase phenocrysts at Thera Volcano, Aegean Volcanic Arc, Greece (United States)

    Stamatelopoulou-Seymour, Karen; Vlassopoulos, Dimitrios; Pearce, Thomas H.; Rice, Craig


    Lavas and pyroclastic rocks throughout the volcanic stratigraphy of the Tertiary-Quaternary volcanic complex of Thera in the Aegean island arc display inhomogenous plagioclase populations and phenocryst resorption textures, interpreted as indicative of magma mixing. Plagioclase zoning characteristics studied by Nomarski and laser interferometry techniques establish three main categories of plagioclase: (i) inherited plagioclase (nucleated in endmember prior to initial mixing event) (ii) in situ plagioclase (nucleated in mixed or hybrid magma) and (iii) xenocrystic plagioclase. Nomarski contrast images and linearized compositional zoning profiles reveal striking differences between calcic and sodic plagioclases, depending on the composition of the lava in which they are hosted. These differences reflect the contrasting effects of changes in physical-chemical parameters in basic vis-a-vis more acidic melts during magma mixing and/or influx of new magma into the subvolcanic magma chamber, as well as the influence of magma chamber dynamics on plagioclase equilibration. Variations in bulk major and trace element abundances of Thera volcanic products reflect the dominant overprint of crystal fractionation, but decoupling between major and trace element fractionation models and variations in incompatible trace element distributions are all indicative of magma mixing processes, consistent with compositional and textural zoning in plagioclases.

  3. Primitive magmas at five Cascade volcanic fields: Melts from hot, heterogeneous sub-arc mantle (United States)

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


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

  4. The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas (United States)

    Su, Y.; Huber, Christian; Bachmann, Olivier; Zajacz, Zoltán.; Wright, Heather; Vazquez, Jorge


    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 vapor

  5. The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas (United States)

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


    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

  6. Warm storage for arc magmas. (United States)

    Barboni, Mélanie; Boehnke, Patrick; Schmitt, Axel K; Harrison, T Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas


    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the "cold storage" model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

  7. Transition of magma genesis estimated by change of chemical composition of Izu-bonin arc volcanism associated with spreading of Shikoku Basin (United States)

    Haraguchi, S.; Ishii, T.


    the Shikoku basin, and these rocks show about 26Ma, at the beginning of activity of Shikoku Basin, of Ar-Ar ages (Ishizuka, pers comm.). Therefore, it is considered that these volcanics are associated with rifting acrivity before spreading of back-arc basin. Based on these observations, it is considered that the chemical characteristics of Izu-Ogasawara arc volcanism were changed at spreading of Shikoku Basin. That is, low incompatible element content activity had continued from tholeiitic activity in the Haha-Jima during early arc volcanism to normal arc volcanism in the Izu forearc region recovered during ODP Leg126 operation. High incompatible element activity had begun at the beginning of back-arc basin activity, and incompatible element content of Izu arc magma was decreasing after spreading of Shikoku Basin to recent activity. We considered these characteristics are interpreted that mantle beneath island arc were change depleted composition to enrich composition at the back arc basin activity. And we assumed that this mantle movement is associated with back-arc basin activity.

  8. The temporal evolution of back-arc magmas from the Auca Mahuida shield volcano (Payenia Volcanic Province, Argentina) (United States)

    Pallares, Carlos; Quidelleur, Xavier; Gillot, Pierre-Yves; Kluska, Jean-Michel; Tchilinguirian, Paul; Sarda, Philippe


    In order to better constrain the temporal volcanic activity of the back-arc context in Payenia Volcanic Province (PVP, Argentina), we present new K-Ar dating, petrographic data, major and trace elements from 23 samples collected on the Auca Mahuida shield volcano. Our new data, coupled with published data, show that this volcano was built from about 1.8 to 1.0 Ma during five volcanic phases, and that Auca Mahuida magmas were extracted from, at least, two slightly different OIB-type mantle sources with a low partial melting rate. The first one, containing more garnet, was located deeper in the mantle, while the second contains more spinel and was thus shallower. The high-MgO basalts (or primitive basalts) and the low-MgO basalts (or evolved basalts), produced from the deeper and shallower lherzolite mantle sources, respectively, are found within each volcanic phase, suggesting that both magmatic reservoirs were sampled during the 1 Myr lifetime of the Auca Mahuida volcano. However, a slight increase of the proportion of low-MgO basalts, as well as of magmas sampled from the shallowest source, can be observed through time. Similar overall petrological characteristics found in the Pleistocene-Holocene basaltic rocks from Los Volcanes and Auca Mahuida volcano suggest that they originated from the same magmatic source. Consequently, it can be proposed that the thermal asthenospheric anomaly is probably still present beneath the PVP. Finally, our data further support the hypothesis that the injection of hot asthenosphere with an OIB mantle source signature, which was triggered by the steepening of the Nazca subducting plate, induced the production of a large volume of lavas within the PVP since 2 Ma.

  9. Late Cenozoic tephrostratigraphy offshore the southern Central American Volcanic Arc: 2. Implications for magma production rates and subduction erosion (United States)

    Schindlbeck, J. C.; Kutterolf, S.; Freundt, A.; Straub, S. M.; Vannucchi, P.; Alvarado, G. E.


    Pacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of tephra layers established by tephrochonostratigraphy in Part 1 indicates a nearly continuous highly explosive eruption record for the Costa Rican and the Nicaraguan volcanic arc within the last 8 Myr. The widely distributed marine tephra layers comprise the major fraction of the respective erupted tephra volumes and masses thus providing insights into regional and temporal variations of large-magnitude explosive eruptions along the southern Central American Volcanic Arc (CAVA). We observe three pulses of enhanced explosive volcanism between 0 and 1 Ma at the Cordillera Central, between 1 and 2 Ma at the Guanacaste and at >3 Ma at the Western Nicaragua segments. Averaged over the long-term the minimum erupted magma flux (per unit arc length) is ˜0.017 g/ms. Tephra ages, constrained by Ar-Ar dating and by correlation with dated terrestrial tephras, yield time-variable accumulation rates of the intercalated pelagic sediments with four prominent phases of peak sedimentation rates that relate to tectonic processes of subduction erosion. The peak rate at >2.3 Ma near Osa particularly relates to initial Cocos Ridge subduction which began at 2.91 ± 0.23 Ma as inferred by the 1.5 Myr delayed appearance of the OIB geochemical signal in tephras from Barva volcano at 1.42 Ma. Subsequent tectonic re-arrangements probably involved crustal extension on the Guanacaste segment that favored the 2-1 Ma period of unusually massive rhyolite production.

  10. Age, geochemical and isotopic variations in volcanic rocks from the Coastal Range of Taiwan: Implications for magma generation in the Northern Luzon Arc (United States)

    Lai, Yu-Ming; Song, Sheng-Rong; Lo, Ching-Hua; Lin, Te-Hsien; Chu, Mei-Fei; Chung, Sun-Lin


    This paper reports the first systematic analysis of age and geochemical variations in volcanic rocks from the Coastal Range of Taiwan, the Northern Luzon Arc. The rocks, recovered from four main volcanoes, vary from low-K tholeiitic to medium-K calc-alkaline basalts to dacites. The rocks are typical of arc magmatic products, exhibiting enrichment in the large ion lithophile elements and depletion in the high field strength elements. Our new 40Ar/39Ar age data constrain the youngest eruption time in each of the four volcanoes, i.e., from north to south, at 7.2 Ma (Yuemei), 4.2 Ma (Chimei), 6.2 Ma (Chengkuang'ao) and 8.5 Ma (Tuluanshan), respectively. These data indicate that volcanism in the Northern Luzon Arc did not cease progressively from north to south, as previously alleged. The high and broadly uniform Nd isotope ratios [εNd = + 10.1 to + 8.8] and trace element characteristics of the rocks suggest a principal magma source from the depleted mantle wedge. Their overall geochemical variations are ascribed to magma chamber processes. The effects of magmatic differentiation and crustal contamination differ among each volcano, most likely owing to the discrepancy of residence time in individual magma chambers. Consequently, we propose a binary mixing model for the magma generation that involves arc magmas sourced from the depleted mantle wedge and up to 5% crustal contamination with a continental fragment split off from the Eurasian margin.

  11. Fluid-melt partitioning of sulfur in differentiated arc magmas and the sulfur yield of explosive volcanic eruptions (United States)

    Masotta, M.; Keppler, H.; Chaudhari, A.


    The fluid-melt partitioning of sulfur (DSfluid/melt) in differentiated arc magmas has been experimentally investigated under oxidizing conditions (Re-ReO2 buffer) from 800 to 950 °C at 200 MPa. The starting glasses ranged in composition from trachyte to rhyolite and were synthesized targeting the composition of the residual melt formed after 10-60% crystallization of originally trachy-andesitic, dacitic and rhyodacitic magmas (Masotta and Keppler, 2015). Fluid compositions were determined both by mass balance and by Raman spectroscopy of fluid inclusions. DSfluid/melt increases exponentially with increasing melt differentiation, ranging from 2 to 15 in the trachytic melt, from 20 to 100 in the dacitic and rhyodacitic melts and from 100 to 120 in the rhyolitic melt. The variation of the DSfluid/melt is entirely controlled by the compositional variation of the silicate melt, with temperature having at most a minor effect within the range investigated. Experiments from this study were used together with data from the literature to calibrate the following model that allows predicting DSfluid/melt for oxidized arc magmas: where nbo/t is the non-bridging oxygen atoms per tetrahedron, ASI is the alumina saturation index, Al# and Ca# are two empirical compositional parameters calculated in molar units (Al # = XAl2O3/XSiO2 +XTiO2 +XAl2O3 and Ca # = XCaO/XNa2O +XK2O). The interplay between fluid-melt partitioning and anhydrite solubility determines the sulfur distribution among anhydrite, melt and fluid. At increasing melt polymerization, the exponential increase of the partition coefficient and the decrease of anhydrite solubility favor the accumulation of sulfur either in the fluid phase or as anhydrite. On the other hand, the higher anhydrite solubility and lower partition coefficient for less polymerized melts favor the retention of sulfur in the melt. At equilibrium conditions, these effects yield a maximum of the sulfur fraction in the fluid phase for slightly

  12. Constraints on the origin and evolution of magmas in the Payún Matrú Volcanic Field, Quaternary Andean Back-arc of Western Argentina

    NARCIS (Netherlands)

    Hernando, I.R.; Aragón, E.; Frei, R.; González, P.D.; Spakman, W.


    The Payún Matrú Volcanic Field (Pleistocene–Holocene) is located in the Andean back-arc of the Southern Volcanic Zone, western Argentina, and is contemporaneous with the Andean volcanic arc at the same latitude. It includes two polygenetic, mostly trachytic volcanoes: Payún Matrú (with a summit cald

  13. Deep-crustal magma reservoirs beneath the Nicaraguan volcanic arc, revealed by 2-D and semi 3-D inversion of magnetotelluric data (United States)

    Brasse, Heinrich; Schäfer, Anja; Díaz, Daniel; Alvarado, Guillermo E.; Muñoz, Angélica; Mütschard, Lutz


    A long-period magnetotelluric (MT) experiment was conducted in early 2009 in western Nicaragua to study the electrical resistivity and thus fluid/melt distribution at the Central American continental margin where the Cocos plate subducts beneath the Caribbean plate. Strike analysis yields a preference direction perpendicular to the profile, with moderate deviation from two-dimensionality, however. Two-dimensional modeling maps the sediments of the Nicaraguan Depression and a high-conductivity zone in the mid-crust, slightly offset from the arc. Further conductors are modeled in the backarc. However, these features are probably artifacts when a 2-D program is applied to data which show moderate 3-D characteristics. 3-D inversion clarifies the situation, and the major remaining conductive structure is now quasi directly beneath the volcanic chain and interpreted as a deep-seated magma deposit. Conductivity in the backarc is also relatively high and may either be caused by still existing partial melts beneath the Paleocene to Miocene volcanic arcs or by related metallic deposits in the aureoles of hydrothermal alteration.

  14. Constraints on the origin and evolution of magmas in the Payún Matrú Volcanic Field, Quaternary Andean back-arc of western Argentina

    DEFF Research Database (Denmark)

    Hernadno, I R; Aragón, E; Frei, Robert


    and Sr–Nd isotopic compositions of the basaltic lavas and Payún Matrú rocks indicate that the trachytes of Payún Matrú are the result of fractional crystallization of basaltic parent magmas without significant upper crustal contamination, and that the basalts have a geochemical similarity to ocean island...... basalt (La/Nb = 0·8–1·5, La/Ba = 0·05–0·08). The Sr–Nd isotopic compositions of the basaltic to trachytic rocks range between 0·703813 and 0·703841 (87Sr/86Sr) and 0·512743 and 0·512834 (143Nd/144Nd). Mass-balance and Rayleigh fractionation models support the proposed origin of the trachytes...... that the basaltic lavas originated in the asthenospheric mantle, probably within the spinel stability field and beneath an attenuated continental lithosphere in the back-arc area. The lack of a slab-fluid signature in the Payún Matrú Volcanic Field rocks, along with unpublished and published geophysical results...

  15. Recognizing subtle evidence for silicic magma derivation from petrochemically-similar arc crust: Isotopic and chemical evidence for the bimodal volcanic series of Gorely Volcanic Center, Kamchatka, Russia (United States)

    Seligman, A. N.; Bindeman, I. N.; Ellis, B. S.; Ponomareva, V.; Leonov, V.


    The Kamchatka Peninsula is home to some of the most prolific subduction related volcanic activity in the world. Gorely caldera and its central volcano are located in the rear of its currently active Eastern Volcanic Front. Recent work determined the presence of explosive ignimbrite eruptions sourced from Gorely volcano during the Pleistocene. We studied 32 eruptive units, including tephrochronologically-dated Holocene tephra, stratigraphically-arranged ignimbrites, as well as pre- and post-caldera lavas. We analyzed oxygen isotope ratios of pyroxene and plagioclase grains by laser fluorination, and major and trace element compositions of whole rocks. In addition, we determined 87Sr/86Sr and 143Nd/144Nd ratios of caldera-forming ignimbrite eruptions. Chemical compositions show that Gorely eruptive units range from basalt to basaltic andesite in the "Pra-Gorely" stages prior to caldera formation and the modern Gorely stages forming its current edifice. In contrast, eruptive material from earlier ignimbrites exposed at Opasny Ravine consists primarily of dacite. Whole rock analyses for Gorely indicate that silicic rocks and ignimbrites volumetrically dominate all other products, forming separate bimodal peaks in our SiO2-frequency diagram. In addition, trace element concentrations and ratios define two trends, one for more silicic and another for more mafic material. δ18Omelt values range from a low of 4.85 up to 6.22‰, where the lowest value was found in the last caldera forming eruption, suggesting incorporation of hydrothermally-altered material from earlier eruptions. 87Sr/86Sr and 143Nd/144Nd ratios range from 0.70328 to 0.70351 and from 0.51303 to 0.51309 respectively, with higher and more diverse values being characteristic of earlier ignimbrite units; again suggesting incorporation of surrounding crustal material. In contrast to these results, MELTS modeling using a variety of likely primitive basalts from Gorely shows it is possible to obtain silicic

  16. Anhydrite solubility in differentiated arc magmas (United States)

    Masotta, M.; Keppler, H.


    The solubility of anhydrite in differentiated arc magmas was experimentally studied at 200 MPa and 800-1000 °C over a range of oxygen fugacities, from 0.5 log units above the Ni-NiO buffer to the hematite-magnetite buffer. Anhydrite is stable only at oxidizing conditions (fO2 ⩾ Re-ReO2), whereas sulfides only form under reducing conditions. The solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption. At oxidizing conditions, the solubility product of anhydrite increases with temperature, nbo/t and melt water content. We provide a new calibration of the anhydrite solubility product (KSP = XCaO * XSO3), which reproduces all available experimental data with greatly improved accuracy: In this equation, the molar fractions XCaO and XSO3 in the melt as well as the number of non-bridging oxygen atoms per tetrahedron (nbo/t) are calculated on an anhydrous basis (H2O refers to the melt water content, T is temperature in Kelvin). We apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 Mt. Pinatubo dacite eruption was unusually large, because only a small fraction of the sulfur was locked up in anhydrite. In general, high sulfur yields are expected when anhydrite solubility in the melt is high, i.e. for somewhat depolymerized melts. For rhyolitic systems, most of the available sulfur will be locked up in anhydrite, so that even very large eruptions may only have a small effect on global surface temperatures. Our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions.

  17. The Fina Nagu volcanic complex: Unusual submarine arc volcanism in the rapidly deforming southern Mariana margin (United States)

    Brounce, Maryjo; Kelley, Katherine A.; Stern, Robert; Martinez, Fernando; Cottrell, Elizabeth


    In the Mariana convergent margin, large arc volcanoes disappear south of Guam even though the Pacific plate continues to subduct and instead, small cones scatter on the seafloor. These small cones could form either due to decompression melting accompanying back-arc extension or flux melting, as expected for arc volcanoes, or as a result of both processes. Here, we report the major, trace, and volatile element compositions, as well as the oxidation state of Fe, in recently dredged, fresh pillow lavas from the Fina Nagu volcanic chain, an unusual alignment of small, closely spaced submarine calderas and cones southwest of Guam. We show that Fina Nagu magmas are the consequence of mantle melting due to infiltrating aqueous fluids and sediment melts sourced from the subducting Pacific plate into a depleted mantle wedge, similar in extent of melting to accepted models for arc melts. Fina Nagu magmas are not as oxidized as magmas elsewhere along the Mariana arc, suggesting that the subduction component responsible for producing arc magmas is either different or not present in the zone of melt generation for Fina Nagu, and that amphibole or serpentine mineral destabilization reactions are key in producing oxidized arc magmas. Individual Fina Nagu volcanic structures are smaller in volume than Mariana arc volcanoes, although the estimated cumulative volume of the volcanic chain is similar to nearby submarine arc volcanoes. We conclude that melt generation under the Fina Nagu chain occurs by similar mechanisms as under Mariana arc volcanoes, but that complex lithospheric deformation in the region distributes the melts among several small edifices that get younger to the northeast.

  18. Slab melting and magma generation beneath the southern Cascade Arc (United States)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.


    Magma formation in subduction zones is interpreted to be caused by flux melting of the mantle wedge by fluids derived from dehydration of the downgoing oceanic lithosphere. In the Cascade Arc and other hot-slab subduction zones, however, most dehydration reactions occur beneath the forearc, necessitating a closer investigation of magma generation processes in this setting. Recent work combining 2-D steady state thermal models and the hydrogen isotope composition of olivine-hosted melt inclusions from the Lassen segment of the Cascades (Walowski et al., 2014; in review) has shown that partial melting of the subducted basaltic crust may be a key part of the subduction component in hot arcs. In this model, fluids from the slab interior (hydrated upper mantle) rise through the slab and cause flux-melting of the already dehydrated MORB volcanics in the upper oceanic crust. In the Shasta and Lassen segments of the southern Cascades, support for this interpretation comes from primitive magmas that have MORB-like Sr isotope compositions that correlate with subduction component tracers (H2O/Ce, Sr/P) (Grove et al. 2002, Borg et al. 2002). In addition, mass balance calculations of the composition of subduction components show ratios of trace elements to H2O that are at the high end of the global arc array (Ruscitto et al. 2012), consistent with the role of a slab-derived melt. Melting of the subducted basaltic crust should contribute a hydrous dacitic or rhyolitic melt (e.g. Jego and Dasgupta, 2013) to the mantle wedge rather than an H2O-rich aqueous fluid. We are using pHMELTS and pMELTS to model the reaction of hydrous slab melts with mantle peridotite as the melts rise through the inverted thermal gradient in the mantle wedge. The results of the modeling will be useful for understanding magma generation processes in arcs that are associated with subduction of relatively young oceanic lithosphere.

  19. Stress fields of the overriding plate at convergent margins and beneath active volcanic arcs. (United States)

    Apperson, K D


    Tectonic stress fields in the overriding plate at convergent plate margins are complex and vary on local to regional scales. Volcanic arcs are a common element of overriding plates. Stress fields in the volcanic arc region are related to deformation generated by subduction and to magma generation and ascent processes. Analysis of moment tensors of shallow and intermediate depth earthquakes in volcanic arcs indicates that the seismic strain field in the arc region of many convergent margins is subhorizontal extension oriented nearly perpendicular to the arc. A process capable of generating such a globally consistent strain field is induced asthenospheric corner flow below the arc region.

  20. Magma storage under Iceland's Eastern Volcanic Zone (United States)

    Maclennan, J.; Neave, D.; Hartley, M. E.; Edmonds, M.; Thordarson, T.; Morgan, D. J.


    The Eastern Volcanic Zone (EVZ) of Iceland is defined by a number of volcanic systems and large basaltic eruptions occur both through central volcanoes (e.g. Grímsvötn) and on associated fissure rows (e.g. Laki, Eldgjá). We have collected a large quantity of micro-analytical data from a number of EVZ eruptions, with the aim of identifying common processes that occur in the premonitory stages of significant volcanic events. Here, we focus on the AD 1783 Laki event, the early postglacial Saksunarvatn tephra and the sub-glacially erupted Skuggafjöll tindar and for each of these eruptions we have >100 olivine-hosted or plagioclase-hosted melt inclusion analyses for major, trace and volatile elements. These large datasets are vital for understanding the history of melt evolution in the plumbing system of basaltic volcanoes. Diverse trace element compositions in melt inclusions hosted in primitive macrocrysts (i.e. Fo>84, An>84) indicate that the mantle melts supplied to the plumbing system of EVZ eruptions are highly variable in composition. Concurrent mixing and crystallisation of these melts occurs in crustal magma bodies. The levels of the deepest of these magma bodies are not well constrained by EVZ petrology, with only a handful of high-CO2 melt inclusions from Laki providing evidence for magma supply from >5 kbar. In contrast, the volatile contents of melt inclusions in evolved macrocrysts, which are close to equilibrium with the carrier liquids, indicate that final depths of inclusion entrapment are 0.5-2 kbar. The major element composition of the matrix glasses shows that the final pressure of equilibration between the melt and its macrocryst phases also occurred at 0.5-2 kbar. The relationship between these pressures and seismic/geodetic estimates of chamber depths needs to be carefully evaluated. The melt inclusion and macrocryst compositional record indicates that injection of porphyritic, gas-rich primitive melt into evolved/enriched and degassed shallow

  1. Water content of primitive low-K tholeiitic basalt magma from Iwate Volcano, NE Japan arc: implications for differentiation mechanism of frontal-arc basalt magmas (United States)

    Kuritani, Takeshi; Yoshida, Takeyoshi; Kimura, Jun-Ichi; Hirahara, Yuka; Takahashi, Toshiro


    The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4-5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at ~200 MPa.

  2. Progressive enrichment of arc magmas caused by the subduction of seamounts under Nishinoshima volcano, Izu-Bonin Arc, Japan (United States)

    Sano, Takashi; Shirao, Motomaro; Tani, Kenichiro; Tsutsumi, Yukiyasu; Kiyokawa, Shoichi; Fujii, Toshitsugu


    The chemical composition of intraplate seamounts is distinct from normal seafloor material, meaning that the subduction of seamounts at a convergent margin can cause a change in the chemistry of the mantle wedge and associated arc magmas. Nishinoshima, a volcanic island in the Izu-Bonin Arc of Japan, has been erupting continuously over the past 2 years, providing an ideal opportunity to examine the effect of seamount subduction on the chemistry of arc magmas. Our research is based on the whole-rock geochemistry and the chemistry of minerals within lavas and air-fall scoria from Nishinoshima that were erupted before 1702, in 1973-1974, and in 2014. The mineral phases within the analyzed samples crystallized under hydrous conditions (H2O = 3-4 wt.%) at temperatures of 970 °C-990 °C in a shallow (3-6 km depth) magma chamber. Trace element data indicate that the recently erupted Nishinoshima volcanics are much less depleted in the high field strength elements (Nb, Ta, Zr, Hf) than other volcanics within the Izu-Bonin Arc. In addition, the level of enrichment in the Nishinoshima magmas has increased in recent years, probably due to the addition of material from HIMU-enriched (i.e., high Nb/Zr and Ta/Hf) seamounts on the Pacific Plate, which is being subducted westwards beneath the Philippine Sea Plate. This suggests that the chemistry of scoria from Nishinoshima volcano records the progressive addition of components derived from subducted seamounts.

  3. Temporal magma source changes at Gaua volcano, Vanuatu island arc (United States)

    Beaumais, Aurélien; Bertrand, Hervé; Chazot, Gilles; Dosso, Laure; Robin, Claude


    Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a large volcano marked by a caldera that hosts the active Mount Garet summit cone. In this paper, a geochemical study including Sr, Nd, Pb and Hf isotopic compositions of 25 lavas emitted since 1.8 Ma is presented, with a focus on the volcanic products that preceded (old volcanics, main cone and pyroclastic series) and followed (Mount Garet) the caldera forming event. All lavas show an island arc signature with enrichment in LILE and depletion in HFSE. Post-caldera lavas define a medium-K calc-alkaline trend, whereas lavas from the former main cone have high-K calc-alkaline compositions. Compared to the pre-caldera volcanic suite, the Mount Garet lavas have similar Th/Nb ( 1.5), 143Nd/144Nd ( 0.51295) and 176Hf/177Hf ( 0.28316) ratios, but higher Ba/La ( 42 vs. 27) and 87Sr/86Sr (0.70417 vs. 0.70405) ratios and lower Ce/Pb ( 2.7 vs. 4.6), La/Sm ( 2.5 vs. 4.0) and 206Pb/204Pb (18.105 vs. 18.176) ratios. High Th/Nb and low Nd and Hf isotopic ratios compared to N-MORB suggest the contribution of 2% of subducted sediment melt to the mantle source of Gaua magmas. Most of the observed differences between pre- and post-caldera lavas can be accounted for by the involvement of at least two portions of the mantle wedge, metasomatized by different slab-derived aqueous fluids. In addition, the lower La/Sm (at a given 143Nd/144Nd) ratios of Mount Garet lavas suggest a higher degree of partial melting ( 10-15%) compared to the pre-caldera lavas ( 5%). The Santa Maria Pyroclastic Series (SMPS) eruption probably triggered the caldera collapse, in response to emptying of the magmatic chamber. This event may have allowed new access to the surface for a geochemically distinct batch of magma issued from a separate magma chamber, resulting in the birth and construction of Mount Garet within the caldera. As both magmatic suites were emitted over a very short time, the storage of their parental

  4. H2O and CO2 in magmas from the Mariana arc and back arc systems (United States)

    Newman, Sally; Stolper, Edward; Stern, Robert


    We examined the H2O and CO2 contents of glasses from lavas and xenoliths from the Mariana arc system, an intraoceanic convergent margin in the western Pacific, which contains an active volcanic arc, an actively spreading back arc basin, and active behind-the-arc cross-chain volcanoes. Samples include (1) glass rims from Mariana arc, Mariana trough, and cross-chain submarine lavas; (2) glass inclusions in arc and trough phenocrysts; and (3) glass inclusions from a gabbro + anorthosite xenolith from Agrigan (Mariana arc). Glass rims of submarine arc lavas contain 0.3-1.9 wt % H2O, and CO2 is below detection limits. Where they could be compared, glass inclusions in arc phenocrysts contain more H2O than their host glasses; most arc glasses and phenocryst inclusions contain no detectable CO2, with the exception of those from a North Hiyoshi shoshonite, which contains 400-600 ppm. The glass inclusions from the Agrigan xenolith contain 4-6% H2O, and CO2 is below the detection limit. Glasses from the cross-chain lavas are similar to those from the arc: H2O contents are 1.4-1.7 wt %, and CO2 is below detection limits. Volatile contents in Mariana trough lava glass rims are variable: 0.2-2.8 wt % H2O and 0-300 ppm CO2. Glass inclusions from trough phenocrysts have water contents similar to the host glass, but they can contain up to 875 ppm CO2. Volatile contents of melt inclusions from trough and arc lavas and from the xenolith imply minimum depths of crystallization of ~1-8 km. H2O and CO2 contents of Mariana trough glasses are negatively correlated, indicating saturation of the erupting magma with a CO2-H2O vapor at the pressure of eruption (~400 bars for these samples), with the vapor ranging from nearly pure CO2 at the CO2-rich end of the glass array to nearly pure H2O at the H2O-rich end. Degassing of these magmas on ascent and eruption leads to significant loss of CO2 (thereby masking preeruptive CO2 contents) but minimal disturbance of preeruptive H2O contents. For

  5. Differentiation mechanism of frontal-arc basalt magmas (United States)

    Kuritani, T.; Yoshida, T.; Kimura, J.; Hirahara, Y.; Takahashi, T.


    In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from low-temperature mush zones (boundary layer fractionation) (Jaupart and Tait, 1995, and references therein). The geochemical path caused by boundary layer fractionation can be fairly different from a path resulting from homogeneous fractionation (e.g., Langmuir, 1989). Therefore, it is important to understand the relative contributions of these fractionation mechanisms in magma chambers. Kuritani (2009) examined the relative roles of the two fractionation mechanisms in cooling basaltic magma chambers using a thermodynamics-based mass balance model. However, the basaltic magmas examined in the work were alkali-rich (Na2O+K2O > 4 wt.%). In this study, to explore differentiation mechanisms of frontal-arc basalt magmas that are volumetrically much more important than rear-arc alkali basalt magmas, the relative roles of the two fractionation mechanisms are examined for low-K tholetiitic basalt magma from Iwate Volcano, NE Japan arc, using the same mass balance model. First, the water content and the temperature of the Iwate magma were estimated. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-81) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase. It is inferred from these observations that the phenocrysts with variable compositions were derived from a common magma with variable temperature in a magma chamber, and the plagioclase phenocrysts were all derived from mushy boundary layers along the walls of the magma chamber. By

  6. Submarine volcanoes along the Aegean volcanic arc (United States)

    Nomikou, Paraskevi; Papanikolaou, Dimitrios; Alexandri, Matina; Sakellariou, Dimitris; Rousakis, Grigoris


    The Aegean volcanic arc has been investigated along its offshore areas and several submarine volcanic outcrops have been discovered in the last 25 years of research. The basic data including swath bathymetric maps, air-gun profiles, underwater photos and samples analysis have been presented along the four main volcanic groups of the arc. The description concerns: (i) Paphsanias submarine volcano in the Methana group, (ii) three volcanic domes to the east of Antimilos Volcano and hydrothermal activity in southeast Milos in the Milos group, (iii) three volcanic domes east of Christiana and a chain of about twenty volcanic domes and craters in the Kolumbo zone northeast of Santorini in the Santorini group and (iv) several volcanic domes and a volcanic caldera together with very deep slopes of several volcanic islands in the Nisyros group. The tectonic structure of the volcanic centers is described and related to the geometry of the arc and the neotectonic graben structures that usually host them. The NE-SW direction is dominant in the Santorini and Nisyros volcanic groups, located at the eastern part of the arc, where strike-slip is also present, whereas NW-SE direction dominates in Milos and Methana at the western part, where co-existence of E-W disrupting normal faults is observed. The volcanic relief reaches 1100-1200 m in most cases. This is produced from the outcrops of the volcanic centers emerging usually at 400-600 m depth and ending either below sea level or at high altitudes of 600-700 m on the islands. Hydrothermal activity at relatively high temperatures observed in Kolumbo is remarkable whereas low temperature phenomena have been detected in the Santorini caldera around Kameni islands and in the area southeast of Milos. In Methana and Nisyros, hydrothermal activity seems to be limited in the coastal areas without other offshore manifestations.

  7. Formation of volcanic edifices in response to changes in magma budget at intermediate spreading rate ridges (United States)

    Howell, J.; White, S. M.; Bohnenstiehl, D. R.; Bizimis, M.


    The spatial and abundance distributions of volcanic edifices along mid-ocean ridges have a well known correlation with spreading rate. Along slow spreading centers, volcanic edifices are normally distributed about the segment center. Volcanic edifices along fast spreading centers have the opposing trend, i.e. edifices form primarily at the ends of segments. However, in ridges affected by plumes and at back arc basins, the spatial and abundance distributions of volcanic edifices differ from that observed at normal ridges of the same spreading rate. This suggests that magma supply rate may control the spatial and abundance distribution of volcanic edifices. Recent geophysical and geochemical studies along the Galapagos Spreading Centers (GSC), Juan de Fuca Ridge (JdFR), Southeast Indian Ridge (SEIR) and the Valu Fa (VF) and Eastern Lau Spreading Centers (ELSC) put tight constraints on crustal thickness, making it possible investigate the effect of magma budget and axial morphology on the formation of volcanic edifices. Volcanic edifices are described according to their volume, shape (their height to basal radius ratio) and their location relative to the end or center of a segment (abundance distribution). For the GSC, the shape and distribution of volcanic edifices correlate with changes in crustal thickness and axial morphology, consistent with a magma supply control on their formation in this region. This relationship is not apparent along the SEIR or JdFR, where edifices show little variation with changes in axial morphology at relatively constant spreading rates. Results for VF and ELSC are what we expect for changes in spreading rate, not axial morphology. Our study suggests that the formation of volcanic edifices at intermediate spreading rate ridges are influenced by magma budget but only when it is above a certain threshold.

  8. Volatile content of Hawaiian magmas and volcanic vigor (United States)

    Blaser, A. P.; Gonnermann, H. M.; Ferguson, D. J.; Plank, T. A.; Hauri, E. H.; Houghton, B. F.; Swanson, D. A.


    We test the hypothesis that magma supply to Kīlauea volcano, Hawai'i may be affected by magma volatile content. We find that volatile content and magma flow from deep source to Kīlauea's summit reservoirs are non-linearly related. For example, a 25-30% change in volatiles leads to a near two-fold increase in magma supply. Hawaiian volcanism provides an opportunity to develop and test hypotheses concerning dynamic and geochemical behavior of hot spot volcanism on different time scales. The Pu'u 'Ō'ō-Kupaianaha eruption (1983-present) is thought to be fed by essentially unfettered magma flow from the asthenosphere into a network of magma reservoirs at approximately 1-4 km below Kīlauea's summit, and from there into Kīlauea's east rift zone, where it erupts. Because Kīlauea's magma becomes saturated in CO2 at about 40 km depth, most CO2 is thought to escape buoyantly from the magma, before entering the east rift zone, and instead is emitted at the summit. Between 2003 and 2006 Kīlauea's summit inflated at unusually high rates and concurrently CO2emissions doubled. This may reflect a change in the balance between magma supply to the summit and outflow to the east rift zone. It remains unknown what caused this surge in magma supply or what controls magma supply to Hawaiian volcanoes in general. We have modeled two-phase magma flow, coupled with H2O-CO2 solubility, to investigate the effect of changes in volatile content on the flow of magma through Kīlauea's magmatic plumbing system. We assume an invariant magma transport capacity from source to vent over the time period of interest. Therefore, changes in magma flow rate are a consequence of changes in magma-static and dynamic pressure throughout Kīlauea's plumbing system. We use measured summit deformation and CO2 emissions as observational constraints, and find from a systematic parameter analysis that even modest increases in volatiles reduce magma-static pressures sufficiently to generate a 'surge' in

  9. Linking magma reservoir processes to the frequency and magnitude of volcanic eruptions (United States)

    Sheldrake, Tom; Caricchi, Luca


    The frequency of volcanic eruptions is fundamentally related to processes controlling the accumulation of eruptible magma at depth and the pressurisation of the magmatic reservoir. Here we present a combined statistical-empirical approach to link the frequency and magnitude of volcanic eruptions observed in different arcs to important parameters controlling the growth of subvolcanic reservoirs of eruptible magma. Such understanding is important for two reasons; firstly it presents an insight into how and why the frequency of eruptions varies between different groups of volcanoes; and secondly, it provides constraints for models that are used to interpret geochemical and geophysical data. To perform the analysis we further develop an analytical model that uses a Monte Carlo sampling approach to simulate the accumulation and eruption of magmatic reservoirs (Caricchi et al., 2014). By inverting the geological record of volcanic eruptions we can solve the Monte Carlo model to quantify parameters such as magma input and frequency of magma injection. Our results indicate systematic variation in the frequency of eruptions of various magnitudes between exchangeable groups of volcanoes, which can be related to variations of parameters such as average magma fluxes and thickness of the crust. Caricchi, L., C. Annen, J. Blundy, G. Simpson, and V. Pinel, 2014, Nature Geoscience, v. 7, no. 2, p. 126-130, doi:10.1038/ngeo2041.

  10. The Origin of ‘OIB-Type’ Magmas in the Central Mexican Volcanic Belt (United States)

    Straub, S. M.; Gomez-Tuena, A.; Zellmer, G. F.; Cai, Y.; Stuart, F. M.; Espinasa-Perena, R.; Langmuir, C. H.; Goldstein, S. L.


    Many models consider a primary mantle origin of high-Mg andesites, but the subarc mantle of arcs producing high-Mg andesites remains poorly defined. In the monogenetic volcanic field of Sierra Chichinautzin (central Mexican Volcanic Belt), high-Mg andesites are spatially and temporally intimately associated with mildly alkaline basalts and basaltic andesites, variously referred to as ‘OIB-type’, ‘intraplate’ or ‘high-Nb arc basalts’ (Wallace and Carmichael 1999, Contrib Mineral Petrol; Schaaf et al. 2005, J Petrol). ‘OIB-type’ magmas and high-Mg andesites have erupted within a few hundreds to thousands of years from vents only a few kilometers apart, or may even have erupted jointly from single vents. It has been suggested that these ‘OIB-type’ magmas were melts from subarc mantle yet unmodified by subduction fluxes while high-Mg andesites were produced from mantle sources residual to the ‘OIB-type’ magmas. In order to test this model, we investigated ‘OIB-type’ magmas erupting from three young and closely spaced monogenetic volcanoes in the Sierra Chichinautzin Volcanic Field (V. Chichinautzin, V. Suchiooc, Cuescomates vent). The primitive olivine-phyric alkaline basalts and basaltic andesites (SiO2 = 49.6-53.5 wt%; Mg#=62-68 and MgO= 6.5-8.3 wt%) have high Ni (97-179 ppm), Nb (18-34 ppm), Nb/La (0.9-1.2) and 3He/4He ratios (R/Ra = 7.3-8.0) typical of near-primary mantle magmas unaffected by the passage through the ~47 km thick continental crust. However, all ‘OIB-type’ magmas contain high-Ni olivines that are indicative of siliceous slab melts infiltrating and reacting with peridotite mantle (Straub et al., 2008, G-cubed; Wang & Gaetani 2008, Contrib Mineral Petrol). Significant slab additions to the mantle source of the ‘OIB-type’ magmas are further confirmed by Sr-Nd-Pb systematics. We suggest that ‘OIB-type’ arc magmas reflect fertilization of a pre-existing MORB-type subarc mantle by enriched, little fractionated slab

  11. Compositional variability in mafic arc magmas over short spatial and temporal scales: Evidence for the signature of mantle reactive melt channels (United States)

    Rawson, Harriet; Keller, Tobias; Fontijn, Karen; Pyle, David M.; Mather, Tamsin A.; Smith, Victoria C.; Naranjo, José A.


    Understanding arc magma genesis is critical to deciphering the construction of continental crust, understanding the relationship between plutonic and volcanic rocks, and for assessing volcanic hazards. Arc magma genesis is complex. Interpreting the underlying causes of major and trace element diversity in erupted magmas is challenging and often non-unique. To navigate this complexity mafic magma diversity is investigated using sample suites that span short temporal and spatial scales. These constraints allow us to evaluate models of arc magma genesis and their geochemical implications based on physical arguments and recent model results. Young volcanic deposits (≲18 kyr) are analysed from the Southern Volcanic Zone (SVZ), Chile, in particular suites of scoria cones on the flanks of arc stratovolcanoes that have erupted relatively primitive magmas of diverse compositions. Our study is centred on the high-resolution post-glacial tephrochronological record for Mocho-Choshuenco volcano where tight age constraints and a high density of scoria cones provide a spatially well-resolved mafic magma dataset. Two compositional trends emerge from the data. Firstly, magmas from cones on the flanks of the main edifice become more mafic with distance from the central vent. This is attributed to fractional crystallisation processes within the crust, with distal cones sampling less differentiated magmas. Secondly, there is a set of cones with distinct major and trace element compositions that are more primitive but enriched in incompatible elements relative to the central system and other 'normal SVZ' magmas. This distinct signature - termed the 'Kangechi' signature - is observed at three further clusters of cones within the SVZ. This is attributed to greater preservation of the enriched melt signature arising from reactive melt transport within the mantle wedge. Our model has important implications for arc magma genesis in general, and in particular for the spatial and temporal

  12. Magma chamber processes in central volcanic systems of Iceland

    DEFF Research Database (Denmark)

    Þórarinsson, Sigurjón Böðvar; Tegner, Christian


    New field work and petrological investigations of the largest gabbro outcrop in Iceland, the Hvalnesfjall gabbro of the 6-7 Ma Austurhorn intrusive complex, have established a stratigraphic sequence exceeding 800 m composed of at least 8 macrorhythmic units. The bases of the macrorhythmic units......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...... olivine basalts from Iceland that had undergone about 20% crystallisation of olivine, plagioclase and clinopyroxene and that the macrorhythmic units formed from thin magma layers not exceeding 200-300 m. Such a "mushy" magma chamber is akin to volcanic plumbing systems in settings of high magma supply...

  13. Silicic Arc Magmas And Silicic Slab Melts: The Melt-Rock Reaction Link (United States)

    Straub, S. M.; Gomez-Tuena, A.; Bolge, L. L.; Espinasa-Perena, R.; Bindeman, I. N.; Stuart, F. M.; Zellmer, G. F.


    While a genetic link between silicic arc magmas and silicic melts from the subducted slab has long been proposed, this hypothesis is commonly refuted because most arc magmas lack a 'garnet-signature' which such slab melts must have. A comprehensive geochemical study of high-Mg# arc magmas from the Quaternary central Mexican Volcanic Belt (MVB), however, shows that this conflict can be reconciled if melt-rock reaction processes in the mantle wedge were essential to arc magma formation. In the central MVB, monogenetic and composite volcanoes erupt high-Mg# basalts to andesites with highly variable trace element patterns. These magmas contain high-Ni olivines (olivine Ni higher than permissible for olivines in partial peridotite melts) with high 3He/4He = 7-8 Ra that provide strong evidence for silicic slab components that infiltrate the subarc mantle to produce olivine-free segregations of 'reaction pyroxenite' in the sources of individual volcanoes. Melting of silica-excess and silica-deficient reaction pyroxenites can then produce high-Mg# basaltic and dacitic primary melts that mix during ascent through mantle and crust to form high-Mg# andesites. Mass balance requires that reaction pyroxenites contain at least >15-18 wt%, and likely more, of slab component. However, because the HREE of the slab component are efficiently retained in the eclogitic slab, elements Ho to Lu in partial melts from reaction pyroxenites remain controlled by the mantle and maintain MORB-normalized Ho/Lun ˜1.15 close to unity. In contrast, the MREE to LREE and fluid mobile LILE of the arc magmas are either controlled, or strongly influenced, by slab-contributions. The origin from hybrid sources also shows in the major elements that are blends of mantle-derived elements (Mg, Ca, Mn, Fe, Ti) and elements augmented by slab contributions (Si, Na, K, P, and possibly Al). Moreover, strong correlations between bulk rock SiO2, 87Sr/86Sr and δ18O (olivines) can be interpreted as mixtures of subarc

  14. Gravitational removal of volcanic arc roots in Cordilleran orogens (United States)

    Currie, C. A.; Ducea, M. N.; DeCelles, P. G.; Beaumont, C.


    Cordilleran orogens, such as the central Andes, form above subduction zones and their evolution depends on processes associated with oceanic plate subduction and continental plate shortening. Such orogens are characterized by abundant arc volcanism and the formation of thick (>30 km) granitoid batholiths. The magma composition is consistent with a multi-stage model, in which parental mantle-derived basaltic magmas stagnate within the continental lithosphere and then undergo differentiation. Felsic partial melts rise through the crust, leaving a high-density garnet pyroxenite root in the deep lithosphere. Here, we study the dynamics of gravitational removal of this root using regional two-dimensional thermal-mechanical models of subduction below a continent. In the models, the volcanic arc location is determined dynamically based on subduction zone thermal structure, and formation of the batholith-root complex is simulated by changing the density of the volcanic arc lithosphere over time. For the lithosphere structure used in our models, arc roots that undergo even a small density increase are readily removed through gravitational foundering for a wide range of root strengths and subduction rates. The dynamics of removal depend on the relative rates of downward gravitational growth and horizontal shearing by subduction-induced mantle flow. Gravitational growth dominates for high root densification rates, high root viscosities and low subduction rates, leading to drip-like removal of the root as a single downwelling over 1-3 Myr. At lower growth rates, the root is removed over ~6 Myr through shear entrainment, as it is carried sideways by mantle flow and then subducted on top of the oceanic plate. In all models, >80% of the root is removed, making this an effective way to thin mantle lithosphere in the volcanic arc region. This can help resolve the mass problem in the central Andes, where observations indicate a thin mantle lithosphere, despite significant crustal

  15. Mantle temperature control on composition of arc magmas along the Central Kamchatka Depression (United States)

    Portnyagin, Maxim; Constantin Manea, Vlad


    Abundant volcanism in the Central Kamchatka Depression (CKD)adjacent to the Kamchatka-Aleutian Arc junction occurswhere the Pacific slab edge is subducting beneath Kamchatka.Here we summarize published data on CKD rocks and demonstratea systematic south-to-north change of their compositions frommoderately fractionated basalt-andesite tholeiitic series tohighly fractionated basalt-rhyolite calc-alkaline series includinghigh-magnesian andesites near the slab edge. Localized slabmelting at the slab edge cannot explain these regional geochemicalvariations. Instead, we propose that the thermal state of themantle wedge can be the key factor governing the compositionof CKD magmas. We integrate the results from petrology and numericmodeling to demonstrate the northward decrease of the mantlewedge temperatures beneath CKD volcanoes, which correlates withdecreasing slab dip, length of mantle columns, and magma flux.We envision two petrogenetic models, which relate the compositionof erupted magmas to the subduction parameters beneath the CKD.The first model suggests that mantle temperature governs melt-peridotiteequilibria and favors generation of andesitic primary meltsin cold mantle regions above the shallowly subducting Pacificslab edge. Alternatively, mantle temperature may control magmaticproductivity along the CKD, which decreases sharply toward theslab edge and thus allows more extensive magma fractionationdeeper in the crust and mixing of highly evolved and mantle-derivedmagmas to generate Si-rich "primitive" magmas. These resultspoint to a possible casual link between deep mantle and shallowcrustal magmatic processes. Similar effects of mantle temperatureon the composition and productivity of arc magmatism are expectedelsewhere, particularly in volcanic regions associated withsignificant slab dip variation along the arc.

  16. Seismic Tremors and Magma Wagging During Explosive Volcanism (United States)

    Jellinek, M.; Bercovici, D.


    Volcanic tremor is a ubiquitous feature of explosive eruptions. This ground oscillation persists for minutes to weeks and is characterized by a remarkably narrow band of frequencies (i.e., ~0.5 - 7 Hz). Prior to major eruptions, tremor can occur in concert with ground deformation probably related to a buildup of magmatic gas. 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, thereby predicting 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 observed.

  17. Rhyolite magma evolution recorded in isotope and trace element composition of zircon from Halle Volcanic Complex (United States)

    Słodczyk, E.; Pietranik, A.; Breitkreuz, C.; Fanning, C. M.; Anczkiewicz, R.; Ehling, B.-C.


    Voluminous felsic volcanic magmas were formed in Central Europe at the Carboniferous/Permian boundary in numerous pull-apart basins; one of which is the Saale Basin, which holds the Halle Volcanic Complex (HVC), the focus of this study. The rhyolites in the HVC formed laccoliths and scarce lavas, and occur in two different textural types: fine and coarse porphyritic. Zircon isotope and trace element composition was analysed in four units, two per each textural type. Zircon from the different units shows similar ranges in εHf (- 4.1 to - 8.1) and δ18O values (6.51-8.26), indicating similar sources and evolution processes for texturally diverse rhyolites from the HVC. Scarce inherited zircon ranges from ~ 315 Ma to ~ 2100 Ma with the major groupings around 315-550 Ma. These ages are typical for Devonian arc magmatic activity (350-400 Ma) and Cadomian igneous rocks (500-600 Ma), which occur in the basement presently underlying the HVC. Therefore, the source of the rhyolites was multicomponent and probably represented by a basement composed of various crystalline rocks. Trace elements in zircon show similar distributions in all analysed samples, which is broadly consistent with zircon cores crystallizing in a less evolved magma undergoing limited fractional crystallization, whilst the zircon rims crystallized from a magma undergoing extensive fractional crystallization of major and accessory minerals. Interestingly, comparison of the zircon composition in HVC rhyolites and other rhyolites worldwide shows that the observed trends are similar in such rhyolites despite the values being different. This may suggest that most of the zircon in rhyolites crystallizes at a similar stage in the rhyolite magma evolution, from magmas undergoing extensive crystallization of major phases and apatite. The implication is that most of the zircon represents late stage crystallization, but also that antecrystic component may be present and preserve information on the development of

  18. Distinctly different parental magmas for plutons and lavas in the central Aleutian arc (United States)

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


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

  19. H_2O and CO_2 in magmas from the Mariana arc and back arc systems


    Newman, Sally; Stolper, Edward; STERN, Robert


    We examined the H2O and CO2 contents of glasses from lavas and xenoliths from the Mariana arc system, an intraoceanic convergent margin in the western Pacific, which contains an active volcanic arc, an actively spreading back arc basin, and active behind-the-arc cross-chain volcanoes. Samples include (1) glass rims from Mariana arc, Mariana trough, and cross-chain submarine lavas; (2) glass inclusions in arc and trough phenocrysts; and (3) glass inclusions from a gabbro + anorthosite xenolith...

  20. Role of large flank-collapse events on magma evolution of volcanoes. Insights from the Lesser Antilles Arc (United States)

    Boudon, Georges; Villemant, Benoît; Friant, Anne Le; Paterne, Martine; Cortijo, Elsa


    Flank-collapse events are now recognized as common processes of destruction of volcanoes. They may occur several times on a volcanic edifice pulling out varying volumes of material from km3 to thousands of km3. In the Lesser Antilles Arc, a large number of flank-collapse events were identified. Here, we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles. On Montagne Pelée (Martinique), magma production rate has been sustained during several thousand years following a 32 ka old flank-collapse event. Basic and dense magmas were emitted through open-vent eruptions that generated abundant scoria flows while significantly more acidic magmas were produced before the flank collapse. The rapid building of a new cone increased the load on magma bodies at depth and the density threshold. Magma production rate decreased and composition of the erupted products changed to more acidic compared to the preceding period of activity. These low density magma generated plinian and dome-forming eruptions up to the Present. In contrast at Soufrière Volcanic Centre of St. Lucia and at Pitons du Carbet in Martinique, the flank-collapses have an opposite effect: in both cases, the acidic magmas erupted immediately after the flank-collapses. These magmas are highly porphyritic (up to 60% phenocrysts) and much more viscous than the magmas erupted before the flank-collapses. They have been generally emplaced as voluminous and uptight lava domes (called “the Pitons”). Such magmas could not ascent without a significant decrease of the threshold effect produced by the volcanic edifice loading before the flank-collapse.

  1. Magnesium isotope geochemistry in arc volcanism (United States)

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  2. Magnesium isotope geochemistry in arc volcanism. (United States)

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  3. Ages and geochemical comparison of coeval plutons and volcanics from the central and eastern Aleutian arc (United States)

    Cai, Y.; Kelemen, P. B.; Goldstein, S. L.; Yogodzinski, G. M.; Hemming, S. R.; Rioux, M. E.; Cooperdock, E. H. G.


    On average, arc volcanics are compositionally different from the bulk continental crust. The relatively little known plutonic part of intra-oceanic arcs is more similar to continental crust, and may play a significant role for understanding continental crust formation. Our pilot study [1] demonstrated that in the central and eastern Aleutian islands, predominantly tholeiitic Quaternary volcanic rocks have statistically different Pb-Nd-Sr-Hf isotopic signatures than predominantly calc-alkaline Miocene and older plutonic rocks, showing that these plutonics and volcanics were derived from compositionally different sources. However, studies of older volcanics are needed to determine whether (1) there was a change in magma chemistry in the central and eastern Aleutian arc between the Miocene and the present-day, or (2) coeval plutonics and volcanics are compositionally different, and formed by different processes. For example, silica- and water-rich calc-alkaline magmas may preferentially stall and form plutons after extensive degassing and rapid viscosity increase in the mid-crust, while silica- and water-poor tholeiitic magmas tend to erupt at the surface. Here we report new geochronological and geochemical results on samples collected during the 2015 GeoPRISMS shared logistics field campaign. We collected more than 500 volcanic and plutonic samples from Unalaska, Umnak and Atka islands, including pillow lavas, sills, and larger plutons. A subset of 50 samples has been analyzed for major and trace element chemistry, Pb-Nd-Sr-Hf isotopes, and Ar-Ar geochronology. So far,40Ar/39Ar cooling dates measured for the volcanics span a wide range, from zero to 35 Ma, which is comparable to the age distribution of the plutons ( 9 Ma to 39 Ma) from these islands. The forthcoming, combined geochronology and geochemistry of coeval plutonics and volcanics will contribute to our understanding of the connections between arc magmatism and continental crust formation. [1] Cai et al

  4. Tectonic shortening and coeval volcanism during the Quaternary, Northeast Japan arc

    Indian Academy of Sciences (India)

    Koji Umeda; Masao Ban; Shintaro Hayashi; Tomohiro Kusano


    The Northeast Japan arc, a mature volcanic arc with a back-arc marginal basin (Japan Sea), is located on a convergent plate boundary along the subducting Pacific plate and the overriding North American plate. From a compilation and analysis of stratigraphy, radiometric age and data on erupted magma volumes, 176 eruptive episodes identified from 69 volcanoes so far, indicate that notable changes in eruption style, magma discharge rates and distribution of eruptive centres occurred around 1.0 Ma. Before ca.1.0 Ma, large-volume felsic eruptions were dominant, forming large calderas in the frontal arc, a region of low crustal strain rate. After ca. 1.0 Ma to the present, the calc-alkaline andesite magma eruptions in the frontal and rear arcs, synchronous with crustal shortening characterized by reverse faulting, resulted in stratovolcano development along narrow uplifted zones. Although, it is widely assumed that magma cannot rise easily in a compressional setting, some of the magma stored within basal sills could be extruded where N–S-trending uplifted mountains bounded by reverse faults formed since about ca.1.0 Ma.

  5. The Galapagos-OIB signature of the central Costa Rican volcanic front: arc-hotspot interaction (United States)

    Gazel, E.; Carr, M. J.; Hoernle, K.; Feigenson, M. D.; Hauff, F.; Szymanski, D.; van den Bogaard, P.


    Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America have isotopic and trace element compositions with an OIB affinity, similar to the Galapagos hotspot lavas. Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene-Pliocene ca. 6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hotspot tracks (the Seamount Province and the Cocos/Coiba Ridges) at the Middle American Trench. The higher Pb isotopic ratios, relatively low Nd isotopic ratios and enriched geochemical signature of central Costa Rican magmas can be explained by arc-hotspot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridges (Central Galapagos Domain). Geological, geochemical, and isotopic evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hotspot tracks, which started to collide with the margin ~8 Ma ago. The Galapagos hotspot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

  6. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    KAUST Repository

    Ruch, Joel


    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic and structural field data along the strike-slip Central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion; consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activity steadily migrated eastward and currently focus on a 10 km long x 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter-term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the Central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  7. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy) (United States)

    Ruch, J.; Vezzoli, L.; De Rosa, R.; Di Lorenzo, R.; Acocella, V.


    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic, and structural field data along the strike-slip central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures, and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activities steadily migrated eastward and currently focus on a 10 km long × 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  8. Geodynamical evolution of Central Andes at 24°S as inferred by magma composition along the Calama-Olacapato-El Toro transversal volcanic belt (United States)

    Matteini, M.; Mazzuoli, R.; Omarini, R.; Cas, R.; Maas, R.


    Miocene to Recent volcanism on the Puna plateau (Central Andes) developed in three geological settings: (a) volcanic arc in the Western Cordillera (Miocene-Recent); (b) trans-arc along the main NW-SE transverse fault systems (Miocene); and (c) back-arc, mainly monogenic volcanic centres (Pliocene-Quaternary). We have studied the evolution of the arc-trans-arc volcanism along one of the most extensive transverse structures of Central Andes, the Calama-Olacapato-El Toro, at 24°S. Compositional variations from arc to trans-arc volcanism provide insights into petrogenesis and magma source regions. Puntas Negras and Rincon volcanic centres are arc-type and have typical calc-alkaline geochemical and Sr-Nd-Pb isotopic characteristics. East of the arc, lavas of the Tul-Tul, Del Medio and Pocitos complexes (TUMEPO) are heavy rare earth element-depleted and could be derived from 20-30% of partial melting of a lower crustal garnet-bearing metabasite. These liquids could be variably mixed with arc magmas at the base of the crust (MASH). This suggests important contributions from lower crustal sources to TUMEPO centres. Products at the Quevar and Aguas Calientes volcanic complexes to the east of TUMEPO show a prominent upper crustal signature (high 86Sr/ 87Sr, low 143Nd/ 144Nd) and could represent mixtures of 20-30% TUMEPO-type liquids with up to 70-80% of upper crustal melts. We propose a geodynamic model to explain geochemical variations for the arc-trans-arc transverse volcanism from the Upper Miocene to Recent. In our model, arc volcanism is linked to dehydration of the subducting Nazca plate, which produces typical calc-alkaline compositions. During the Upper Miocene (10-5 Ma), lithospheric evolution in the Puna plateau was dominated by thickening of ductile lower crust and thinning of the lithosphere. Lower crustal melting was promoted by concomitant asthenospheric upwelling and water release from the amphibolite-eclogite transformation, yielding TUMEPO magmas with lower

  9. Contrasting sediment melt and fluid signatures for magma components in the Aeolian Arc: Implications for numerical modeling of subduction systems (United States)

    Zamboni, Denis; Gazel, Esteban; Ryan, Jeffrey G.; Cannatelli, Claudia; Lucchi, Federico; Atlas, Zachary D.; Trela, Jarek; Mazza, Sarah E.; De Vivo, Benedetto


    The complex geodynamic evolution of Aeolian Arc in the southern Tyrrhenian Sea resulted in melts with some of the most pronounced along the arc geochemical variation in incompatible trace elements and radiogenic isotopes worldwide, likely reflecting variations in arc magma source components. Here we elucidate the effects of subducted components on magma sources along different sections of the Aeolian Arc by evaluating systematics of elements depleted in the upper mantle but enriched in the subducting slab, focusing on a new set of B, Be, As, and Li measurements. Based on our new results, we suggest that both hydrous fluids and silicate melts were involved in element transport from the subducting slab to the mantle wedge. Hydrous fluids strongly influence the chemical composition of lavas in the central arc (Salina) while a melt component from subducted sediments probably plays a key role in metasomatic reactions in the mantle wedge below the peripheral islands (Stromboli). We also noted similarities in subducting components between the Aeolian Archipelago, the Phlegrean Fields, and other volcanic arcs/arc segments around the world (e.g., Sunda, Cascades, Mexican Volcanic Belt). We suggest that the presence of melt components in all these locations resulted from an increase in the mantle wedge temperature by inflow of hot asthenospheric material from tears/windows in the slab or from around the edges of the sinking slab.

  10. Magnesium isotope geochemistry in arc volcanism (United States)

    Teng, Fang-Zhen; Hu, Yan


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration. PMID:27303032

  11. Volatile Evolution of Magma Associated with the Solchiaro Eruption in the Phlegrean Volcanic District (Italy) (United States)

    Esposito, R.; Bodnar, R. J.; de Vivo, B.; Lima, A.; Fedele, L.; Shimizu, N.; Hunter, J.


    The Phlegrean volcanic district (PVD) in southern Italy is one of the best known volcanic hazard areas in the world. More than 1.5 million people live in close proximity to the volcanic centers. The PVD comprises three volcanic fields: the Campi Flegrei caldera and the islands of Ischia and Procida. We studied volatiles plus major and trace elements in the magma associated with the Solchiaro eruption on the Island of Procida, Italy, to gain a better understanding of the relationship between pre-eruptive volatiles and magmatic evolution. The Solchiaro eruption is one of the more primitive products erupted in the PVD and provides information on the source of later more evolved magmas associated with this volcanic system. The composition of the magma before eruption was determined by analyzing 104 melt inclusions (MIs) in forsteritic olivine, glass embayment plus rim glasses, and high vesciculated glasses selected from 4 representative samples. The composition of MIs was recalculated and ranges from basaltic to trachy-basaltic. Among major elements potassium shows the highest variability, from 0.5 to 6 wt%. MI define a continuous trend based on major and minor element compositions. Embayments matrix glass and high vesciculated glasses define a field that suggests a discontinuous process. Compatible to incompatible trace element ratios in early melts are highly variable and represent the melt phase before or at the very beginning of assimilation-fractional crystallization (FCA) processes. Intermediate melt compositions reflect continuing FCA processes, late melt compositions suggest that the FCA process was aborted before eruption. Volatile contents of early melt are highly variable and reflect source heterogeneities, and the melts are interpreted to be undersaturated. Intermediate melts were volatile saturated and H2O-CO2 contents define a degassing path. Depths of trapping of MI range from 4.4 to 2.2 km, and are calculated based on Newman and Lowenstern (2002) and

  12. Lateral variation of H2O contents in Quaternary Magma of central Northeastern Japan arc (United States)

    Miyagi, I.; Matsu'ura, T.; Itoh, J.; Morishita, Y.


    Water plays a key role in the genesis and eruptive mechanisms of subduction zone volcanoes. We estimated bulk rock water content of both frontal and back arc volcanoes from Northeastern Japan arc in order to understand the lateral variation of magmatic H2O contents in the island arc magma. Our analytical targets are the Adachi volcano located near the volcanic front and the Hijiori volcano located on back arc side. In this study, the bulk magmatic H2O content is estimated by a simple mass balance calculation of the chemistry of bulk rock and melt inclusions in phenocrysts; the melt H2O contents of melt inclusions analyzed by SIMS or EPMA are corrected according to the difference in K2O content between melt inclusions and bulk rock. The bulk magmatic H2O we obtained is 8 wt. % or even more for Adachi and is 2-3 wt. % for Hijiori. Thus, the frontal volcano has higher H2O than the back arc volcano. Although our data are opposed to the previous estimation on the lateral variation of H2O contents in Quaternary volcanoes of Northeastern Japan arc (e.g., Sakuyama, 1979), thermodynamic computations using MELTS (Ghiorso and Sack, 1995) suggest that the amount of bulk magmatic H2O we estimated is consistent with petrographical observations. Our data imply a regional characteristics in the type of eruption that the H2O rich frontal volcanoes will erupt explosively and those H2O poor back arc ones will be effusive, which implication is consistent with actual geological observations that volcanoes located on back arc side of the Northeastern Japan arc generally comprise lava flow (e.g., Iwaki, Kanpu, Chokai, Gassan), in contrast to the frontal ones that produced voluminous tephra (e.g., Osorezan, Towada, Narugo, Adachi). This research project has been conducted under the research contract with Nuclear and Industrial Safety Agency (NISA).

  13. Slab melting and magma formation beneath the southern Cascade arc (United States)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.; Rasmussen, D. J.; Weis, D.


    The processes that drive magma formation beneath the Cascade arc and other warm-slab subduction zones have been debated because young oceanic crust is predicted to largely dehydrate beneath the forearc during subduction. In addition, geochemical variability along strike in the Cascades has led to contrasting interpretations about the role of volatiles in magma generation. Here, we focus on the Lassen segment of the Cascade arc, where previous work has demonstrated across-arc geochemical variations related to subduction enrichment, and H-isotope data suggest that H2O in basaltic magmas is derived from the final breakdown of chlorite in the mantle portion of the slab. We use naturally glassy, olivine-hosted melt inclusions (MI) from the tephra deposits of eight primitive (MgO > 7 wt%) basaltic cinder cones to quantify the pre-eruptive volatile contents of mantle-derived melts in this region. The melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), suggesting extensive dehydration of the downgoing plate prior to reaching sub-arc depths and little input of slab-derived B into the mantle wedge. However, correlations of volatile and trace element ratios (H2O/Ce, Cl/Nb, Sr/Nd) in the melt inclusions demonstrate that geochemical variability is the result of variable addition of a hydrous subduction component to the mantle wedge. Furthermore, correlations between subduction component tracers and radiogenic isotope ratios show that the subduction component has less radiogenic Sr and Pb than the Lassen sub-arc mantle, which can be explained by melting of subducted Gorda MORB beneath the arc. Agreement between pMELTS melting models and melt inclusion volatile, major, and trace element data suggests that hydrous slab melt addition to the mantle wedge can produce the range in primitive compositions erupted in the Lassen region. Our results provide further evidence that chlorite-derived fluids from the mantle portion of the

  14. Bulk arc strain, crustal thickening, magma emplacement, and mass balances in the Mesozoic Sierra Nevada arc (United States)

    Cao, Wenrong; Paterson, Scott; Saleeby, Jason; Zalunardo, Sean


    Quantifying crustal deformation is important for evaluating mass balance, material transfer, and the interplay between tectonism and magmatism in continental arcs. We present a dataset of >650 finite strain analyses compiled from published works and our own studies with associated structural, geochronologic, and geobarometric information in central and southern Sierra Nevada, California, to quantify the arc crust deformation. Our results show that Mesozoic tectonism results in 65% arc-perpendicular bulk crust shortening under a more or less plane strain condition. Mesozoic arc magmatism replaced ∼80% of this actively deforming arc crust with plutons requiring significantly greater crustal thickening. We suggest that by ∼85 Ma, the arc crust thickness was ∼80 km with a 30-km-thick arc root, resulting in a ∼5 km elevation. Most tectonic shortening and magma emplacement must be accommodated by downward displacements of crustal materials into growing crustal roots at the estimated downward transfer rate of 2-13 km/Myr. The downward transfer of crustal materials must occur in active magma channels, or in "escape channels" in between solidified plutons that decrease in size with time and depth resulting in an increase in the intensity of constrictional strain with depth. We argue that both tectonism and magmatism control the thickness of the crust and surface elevation with slight modification by surface erosion. The downward transported crustal materials initially fertilize the MASH zone thus enhancing to the generation of additional magmas. As the crustal root grows it may potentially pinch out and cool the mantle wedge and thus cause reduction of arc magmatism.

  15. Why do mafic arc magmas contain ˜4wt% water on average? (United States)

    Plank, Terry; Kelley, Katherine A.; Zimmer, Mindy M.; Hauri, Erik H.; Wallace, Paul J.


    The last 15 yr have seen an explosion of data on the volatile contents of magmas parental to arc volcanoes. This has occurred due to the intense study of melt inclusions trapped in volcanic phenocrysts, aliquots of magma that have presumably escaped degassing during eruption. The surprising first-order result is the narrow range in H2O concentrations in the least degassed melt inclusions from each volcano. Nearly all arc volcanoes are sourced with mafic magmas that contain 2-6 wt% H2O. The average for each arc varies even less, from 3.2 (for the Cascades) to 4.5 (for the Marianas), with a global average of 3.9±0.4 wt% H2O. Significant variations occur from volcano to volcano within each arc, but the means are indistinguishable within one s.d. The narrow range and common average value for H2O are in stark contrast to the concentrations of most other subduction tracers, such as Nb or Ba, which vary by orders of magnitude. A modulating process, either in the crust or mantle, is likely responsible for the restricted range in the H2O contents of arc melt inclusions. One possibility is that melt inclusion H2O values reflect vapor saturation at the last storage depth in the crust prior to eruption. In this scenario, magmas rise from the mantle with variable H2O contents (>4 wt%), become vapor-saturated and start degassing, and continue to degas up until the depth at which they stall. If the stalling depths are ∼6 km, which is common for storage depths beneath volcanoes, magmas would be saturated at ∼4 wt% H2O, and melt inclusions, most of which become closed during further ascent, would thus record ≤4 wt% H2O. Another possibility is that the mantle melting process modulates water content in the melt such that magmas rise out of the mantle with ∼4 wt% H2O. A strong relationship between the water content of the source, H2O(o) and the degree of melting (F) maintains nearly constant water contents in the melt for a restricted range in mantle temperature. Magmas with

  16. Submarine Arc Volcanism in the Southern Mariana Arc: Results of Recent ROV studies (United States)

    Nichols, A. R.; Tamura, Y.; Stern, R. J.; Embley, R. W.; Hein, J. R.; Jordan, E.; Ribeiro, J. M.; Sica, N.; Kohut, E. J.; Whattam, S. A.; Hirahara, Y.; Senda, R.; Nunokawa, A.


    The submarine Diamante cross-arc volcanoes (~16°N) and the Sarigan-Zealandia Bank Multi-Volcano Complex (SZBMVC; ~16°45’N), north and south, respectively, of Anatahan Island in the southern Mariana Arc, were studied during several dives in June 2009 using the ROV Hyper-Dolphin, cruise NT09-08 (R/V Natsushima); neither has been studied in detail before. The data collected provide a new perspective on how the subduction factory operates to complement previous studies on other cross-arc volcanic chains in the Izu-Bonin-Mariana Arc. The Diamante complex consists of three major edifices, two cones (West and Central Diamante) and a more complex caldera-like edifice at the volcanic front (East Diamante). West and Central Diamante are basaltic volcanoes but East Diamante has a more complex history. Our studies indicate initial construction of a basaltic volcano. Magmatic evolution led to a violent caldera-forming and quieter dome-building events. Post-caldera quiescence allowed a carbonate platform to grow, now preserved on the eastern caldera wall. Felsic magma or hot rock provides a heat source for an active hydrothermal field associated with felsic domes in the caldera, which NOAA investigators discovered in 2004. A new type of hydrothermal deposit was discovered in the hydrothermal field, consisting of large sulfide-sulfate mounds topped by bulbous constructions of low-temperature Fe and Mn oxides. Vents on the mounds were observed to emit shimmering water. The SZBMVC consists of six closely spaced edifices whose loci are aligned along two parallel trends, one along the volcanic front (Zealandia Bank, Sarigan and South Sarigan), and one about 15 km west towards the rear-arc (Northwest Zealandia, West Zealandia and West Sarigan). Zealandia Bank dives revealed that, as with East Diamante, initial activity was basaltic and became more evolved with time. The western half of Zealandia Bank is dominated by felsic lavas centered on a small (~2 km diameter) caldera and

  17. Numerical modeling of volcanic arc development (United States)

    Gerya, T.; Gorczyk, W.; Nikolaeva, K.


    We have created a new coupled geochemical-petrological-thermomechanical numerical model of subduction associated with volcanic arc development. The model includes spontaneous slab bending, subducted crust dehydration, aqueous fluid transport, mantle wedge melting and melt extraction resulting in crustal growth. Two major volcanic arc settings are modeled so far: active continental margins, and intraoceanic subduction. In case of Pacific-type continental margin two fundamentally different regimes of melt productivity are observed in numerical experiments which are in line with natural observations: (1) During continuous convergence with coupled plates highest amounts of melts are formed immediately after the initiation of subduction and then decrease rapidly with time due to the steepening of the slab inclination angle precluding formation of partially molten mantle wedge plumes; (2) During subduction associated with slab delamination and trench retreat resulting in the formation of a pronounced back arc basin with a spreading center in the middle melt production increases with time due to shallowing/stabilization of slab inclination associated with upward asthenospheric mantle flow toward the extension region facilitating propagation of hydrous partially molten plumes from the slab. In case of spontaneous nucleation of retreating oceanic subduction two scenarios of tecono-magmatic evolution are distinguished: (1) decay and, ultimately, the cessation of subduction and related magmatic activity, (2) increase in subduction rate (to up to ~12 cm/yr) and stabilization of subduction and magmatic arc growth. In the first case the duration of subduction correlates positively with the intensity of melt extraction: the period of continued subduction increases from 15,4 Myrs to 47,6 Myrs with the increase of melt extraction threshold from 1% to 9%. In scenario (1) the magmatic arc crust includes large amounts of rocks formed by melting of subducted crust atop the thermally

  18. The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny (United States)

    Richards, Jeremy P.


    Global data for measured Fe2O3/FeO ratios and Cu contents in unaltered volcanic and intrusive arc rocks indicate that, on average, they are slightly more oxidized than other magmas derived from depleted upper mantle (such as MORB), but contain similar Cu contents across their compositional ranges. Although Cu scatters to elevated values in some intermediate composition samples, the bulk of the data show a steady but gentle trend to lower concentrations with differentiation, reaching modal values of 50-100 ppm in andesitic rocks. These data suggest that Cu is mildly compatible during partial melting and fractionation processes, likely reflecting minor degrees of sulfide saturation throughout the magmatic cycle. However, the volume of sulfides must be small such that significant proportions of the metal content remain in the magma during fractionation to intermediate compositions. Previous studies have shown that andesitic magmas containing 50 ppm Cu can readily form large porphyry-type Cu deposits upon emplacement in the upper crust. A review of the literature suggests that the elevated oxidation state in the asthenospheric mantle wedge source of arc magmas (ΔFMQ ≈ + 1 ± 1) derives from the subduction of seawater-altered and oxidized oceanic crust, and is transmitted into the mantle wedge via prograde metamorphic dehydration fluids carrying sulfate and other oxidizing components. Progressive hydration and oxidation of the mantle wedge may take up to 10 m.y. to reach a steady state from the onset of subduction, explaining the rarity of porphyry deposits in primitive island arcs, and the late formation of porphyries in continental arc magmatic cycles. Magmas generated from this metasomatized and moderately oxidized mantle source will be hydrous basalts containing high concentrations of sulfur, mainly dissolved as sulfate or sulfite. Some condensed sulfides (melt or minerals) may be present due to the high overall fS2, despite the moderately high oxidation state

  19. Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions (United States)

    Johnson, E. R.


    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.

  20. The role of amphibole in the evolution of arc magmas and crust: the case from the Jurassic Bonanza arc section, Vancouver Island, Canada (United States)

    Larocque, Jeff; Canil, Dante


    The Jurassic Bonanza arc, on Vancouver Island, British Columbia, represents an exhumed island arc crustal section of broadly diorite composition. We studied bodies of mafic and ultramafic cumulates within deeper levels of the arc to constrain the conditions and fractionation pathways leading from high-Mg basalt to andesite and dacite. Major element trends coupled with textural information show the intercumulus crystallization of amphibole, as large oikocrysts enclosing olivine in primitive cumulates controls the compositions of liquids until the onset of plagioclase crystallization. This process is cryptic, occurring only in the plutonic section, and explains the paucity of amphibole in mafic arc volcanics and the change in the Dy/Yb ratios in many arc suites with differentiation. The correlation of octahedral Al in hornblende with pressure in liquidus experiments on high-Mg basalts is applied as an empirical barometer to hornblendes from the Bonanza arc. It shows that crystallization took place at 470-880 MPa in H2O-saturated primitive basaltic magmas. There are no magmatic equivalents to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will shift the bulk arc composition to the high-Mg# andesite composition of bulk continental crust. Garnet removal from wet magmas appears to be the key factor in producing continental crust, requiring high pressures and thick crust. Because oceanic island arcs are built on thinner crust, the long-term process generating the bulk continental crust is the accretion of island arcs to continental margins with attendant tectonic thickening.

  1. Petrological mapping of Volcanic Plumbing Systems using amphiboles in mixed intermediate magmas (United States)

    Kiss, Balázs; Harangi, SzZabolcs; Hauzenberger, Christoph; Ntaflos, Theodoros; Mason, Paul R. D.


    Petrological mapping of volcanic plumbing systems (VPS) is essential to understand the magma evolution and to interpret geophysical signals of monitored volcanoes. The mapping includes the determination of the compositions of magmas feed the system and their storage depths. Intermediate magmas are usually formed by magma mixing a processes that mask the real compositional variation of magmas feed the VPS. However phenocrysts can preserve this information in their chemical stratigraphy. Amphibole can be a powerful tool in these studies because it can incorporate petrogenetically important trace elements primarily controlled by the coexisting melt composition, additionally the major element composition can be used to calculate pressure. We studied the zoning, texture and major and trace element composition of amphiboles from the Ciomadul, a late pleistocen dacite volcano. The erupted dacites contain abundant amphibole phenocrysts. Amphibole coexist with all of the rock forming minerals (e.g. with quartz or with olivine) indicating their diverse origin. The amphiboles show large major element compositional variation (e.g. Al2O3: 6-15 wt%) accompanied with large variation in trace element (e.g. Cr: 10-3000 ppm, Sr: 55-855 ppm, Eu/Eu*: 0.62-1.19) even in a single sample or single crystal and they represent antecryst (reworked) and phenocryst (in situ crystallized) populations. Such a large compositional variation of amphiboles is commonly observed at andesite-dacite arc volcanoes. Hornblendes (antecryst1) have low Al, Mg/Fe, and negative Eu-anomaly; they equilibrated with rhyolitic melt at near-solidus temperature. Antecryst2 is represented by Cr-, Mg-rich amphiboles; they can contain Cr-spinel inclusions suggesting near-liquidus crystallization from primitive mafic melts. Phenocrysts show large compositional variation sample by sample that is different from the antecrysts suggesting variable pre-eruptive conditions. The antecrysts are derived from a stratified (mafic

  2. Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry (United States)

    Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.


    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 <900°C are dominated by early crystallization of hornblende and apatite, and late crystallization (~<780°C) of titanite

  3. Halogen behaviours during andesitic magma degassing: from magma chamber to volcanic plume (United States)

    Balcone-Boissard, H.; Villemant, B.; Boudon, G.; Michel, A.


    Halogen (F, Cl, Br and I) behaviours during degassing of H2O-rich silicic magmas are investigated using volatile content analysis in glass (matrix glass and melt inclusions) of volcanic clasts (pumice and lava-dome fragments) in a series of plinian, vulcanian and lava dome-forming eruptions. Examples are taken from andesitic systems in subduction zones: Montagne Pelée and Soufrière Hills of Montserrat (Lesser Antilles) and Santa Maria-Santiaguito (Guatemala). Halogens behaviour during shallow degassing primarily depends on their incompatible character in melts and on H2O solubility. But variations in pre-eruptive conditions, degassing kinetics and syn-eruptive melt crystallisation, induce large variations in halogen extraction efficiency during H2O degassing, up to prevent halogen loss. In all studied systems, Cl, Br and I are not fractionated neither by differentiation nor by degassing processes: thus Cl/Br/I ratios remain well preserved in melts from reservoirs to eruption. These ratios measured in erupted clasts are characteristic of pre-eruptive magma compositions and may be used to trace deep magmatic processes. Moreover, during plinian eruptions, Cl, Br and I are extracted by H2O degassing but less efficiently than predicted by available experimental fluid-melt partition coefficients, by a factor as high as 5. F behaves as an incompatible element and, contrary to other halogens, is never significantly extracted by degassing. Degassing during lava dome-forming eruptions of andesitic magmas occurs mainly at equilibrium and is more efficient at extracting halogens and H2O than explosive degassing. The mobility of H2O and halogens depends on their speciation in both silicate melts and exsolved fluids which strongly varies with pressure. We suggest that the rapid pressure decrease during highly explosive eruptions prevents complete volatile speciation at equilibrium and consequently strongly limits halogen degassing.

  4. The volcanic response to deglaciation: Evidence from glaciated arcs and a reassessment of global eruption records (United States)

    Watt, Sebastian F. L.; Pyle, David M.; Mather, Tamsin A.

    Several lines of evidence have previously been used to suggest that ice retreat after the last glacial maximum (LGM) resulted in regionally-increased levels of volcanic activity. It has been proposed that this increase in volcanism was globally significant, forming a substantial component of the post-glacial rise in atmospheric CO2, and thereby contributing to climatic warming. However, as yet there has been no detailed investigation of activity in glaciated volcanic arcs following the LGM. Arc volcanism accounts for 90% of present-day subaerial volcanic eruptions. It is therefore important to constrain the impact of deglaciation on arc volcanoes, to understand fully the nature and magnitude of global-scale relationships between volcanism and glaciation. The first part of this paper examines the post-glacial explosive eruption history of the Andean southern volcanic zone (SVZ), a typical arc system, with additional data from the Kamchatka and Cascade arcs. In all cases, eruption rates in the early post-glacial period do not exceed those at later times at a statistically significant level. In part, the recognition and quantification of what may be small (i.e. less than a factor of two) increases in eruption rate is hindered by the size of our datasets. These datasets are limited to eruptions larger than 0.1 km3, because deviations from power-law magnitude-frequency relationships indicate strong relative under-sampling at smaller eruption volumes. In the southern SVZ, where ice unloading was greatest, eruption frequency in the early post-glacial period is approximately twice that of the mid post-glacial period (although frequency increases again in the late post-glacial). A comparable pattern occurs in Kamchatka, but is not observed in the Cascade arc. The early post-glacial period also coincides with a small number of very large explosive eruptions from the most active volcanoes in the southern and central SVZ, consistent with enhanced ponding of magma during

  5. Spatial distribution of helium isotopes in volcanic gases and thermal waters along the Vanuatu (New Hebrides) volcanic arc (United States)

    Jean-Baptiste, P.; Allard, P.; Fourré, E.; Bani, P.; Calabrese, S.; Aiuppa, A.; Gauthier, P. J.; Parello, F.; Pelletier, B.; Garaebiti, E.


    We report the first helium isotope survey of volcanic gases, hot springs and some olivine phenocrysts along the Vanuatu island arc, from Tanna in the south to Vanua Lava in the north. Low CO2 content and low 3He/4He ratios in thermal fluids of Epi (4.0 ± 0.1 Ra), Efate (4.5 ± 0.1 Ra) and Pentecost (5.3 ± 0.5 Ra) islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former (Pliocene) arc. Instead, presently active Vanuatu volcanoes display 3He/4He and C/3He ratios typical of subduction-related volcanic arcs: 3He/4He ratios range from 6.4 ± 0.5 Ra in southernmost Tanna and 7.23 ± 0.09 Ra in northernmost Vanua Lava to typical MORB values in the central islands of Gaua (7.68 ± 0.06 Ra), Ambrym (7.6 ± 0.8 Ra) and Ambae (7 ± 2 Ra in groundwaters, 7.9 ± 1.4 Ra in olivine phenocrysts, and 8.0 ± 0.1 Ra in summit fumaroles of Aoba volcano). On Ambrym, however, we discover that hydrothermal manifestations separated by only 10-15 km on both sides of a major E-W transverse fault zone crossing the island are fed by two distinct helium sources, with different 3He/4He signatures: while fluids in southwest Ambrym (Baiap and Sesivi areas) have typical arc ratios (7.6 ± 0.8 Ra), fluids on the northwest coast (Buama Bay area) display both higher 3He/4He ratios (9.8 ± 0.2 Ra in waters to 10.21 ± 0.08 Ra in bubbling gases) and lower C/3He ratios that evidence a hotspot influence. We thus infer that the influx of Indian MORB mantle beneath the central Vanuatu arc, from which Ambrym magmas originate, also involves a 3He-rich hotspot component, possibly linked to a westward influx of Samoan hotspot material or another yet unknown local source. This duality in magmatic He source at Ambrym fits with the bimodal composition and geochemistry of the erupted basalts, implying two distinct magma sources and feeding systems. More broadly, the wide He isotopic variations detected along the Vanuatu

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

    Energy Technology Data Exchange (ETDEWEB)

    Goldstein, N.E.; Flexser, S.


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

  7. Along-arc geochemical and isotopic variations in Javanese volcanic rocks: 'crustal' versus 'source' contamination at the Sunda arc, Indonesia (United States)

    Handley, H.; Blichert-Toft, J.; Turner, S.; Macpherson, C. G.


    Understanding the genesis of volcanic rocks in subduction zone settings is complicated by the multitude of differentiation processes and source components that exert control on lava geochemistry. Magma genesis and evolution at the Sunda arc is controlled and influenced by 1) along arc changes in the composition and thickness of the overriding Eurasian plate, 2) the variable age of the subducting oceanic crust and, 3) changes in the type and amount of sediment deposited on the subducting plate. Along-arc changes in geochemistry have long been recognised in the Sunda arc (Whitford, 1975), but debate still prevails over the cause of such variations and the relative importance of shallow (crustal) versus deep (subduction) contamination at the Sunda arc, Indonesia. Detailed study of individual Sunda arc volcanic centres is, therefore, a prerequisite in order to establish the relative importance and contributions of various potential source components and composition modifying differentiation processes at individual volcanoes, prior to an along arc comparative petrogenetic investigation. We present new radiogenic isotope data for Javanese volcanoes, which is combined with our recently published (Handley et al., 2007; Handley et al., 2008, Handley et al., 2010; Handley et al., 2011) geochemical and isotopic data of Javanese volcanic rocks along with data from other detailed geochemical studies to establish whether variable contributions from the subducting slab, or a change in crustal architecture of the overriding plate, best explain along-arc variations in isotope ratios and trace element characteristics. In West and Central Java Sr isotope ratios of the volcanic rocks broadly correlate with inferred lithospheric thickness implicating a shallow level control on isotopic composition. However, key trace element ratios combined with Hf isotope data indicate that the subducted slab and slab thermal regime also exert major control on the composition of the erupted Javanese

  8. Abundances of F,Cl S and P in Volcanic Magmas and Their Evolution,Wudalianchi

    Institute of Scientific and Technical Information of China (English)


    F,Cl,S and P were determined,using electron microprobe,in magmatic inclusions trapped within minerals and glass mesostasis from Wudalianchi volcanic rocks.The initial volcanic magma from Wudalianchi corresponds to the basanitic magma crystallized near the surface(pressure<91Mpa).The potential H2O content of this magma is in the range2-4wt.%.The initial composition of volcanic magmas varies regularly from early to late volcanic events.From the Middle Pleistocene to the recent eruptions(1719-1721yr.),the basicity of volcanic magma tends to increase,as reflected by an increase in MgO and CaO contents and by a progressive decrease in SiO2 and K2O contents.Meanwhile ,from early(Q2) to late(Q3) episodic eruptions of the Middle Pleistocene,the initial concentrations of chlorine in volcanic magmas range from 1430-1930 ppm to 1700 ppm and decrease to 700-970ppm for the first episodic eruption during the Holcene(Q41).The chlorine concentrations of vokanic magmas of recent eruption(Q42) are increased again to 2600-2870 ppm.A parallel evolution trend for phosphorus and chlorine concentrations in magmas has been certified:1500-5970ppm(Q2)→3500-4210ppm(Q3)→1100-3500ppm(Q41)→6800-7900ppm(Q42).The fluorine contents of volcanic magmas,from early to late volcanic events ,show the same trend:770-2470ppm→200-700ppm→700-800ppm.During the crystallization-evolution of volcanic magmas,fluorine and phosphorus tend to be enriched in residual magmas as a result of crystal-melt differentiation,for example,the fluorine contents reach 5000-6800ppm and the phosphorus contents,2.93wt.% in residual magmas.An appreciable amount of chlorine may be lost from water rich volcanic magmas prior to eruption as a result of degassing.Apparently,water serves as a gas carrier for the chlorine.The chlorine contents of residual magmas may decrease to 100-300ppm.The volcanic magmas from Wudalianchi are poor in sulfur,normally ranging from 200 to 400ppm .On account of the behavior of sulfur in magmas

  9. Geochemical Variation of Subducting Pacific Crust Along the Izu-Bonin Arc System and its Implications on the Generation of Arc Magmas (United States)

    Durkin, K.; Castillo, P.; Abe, N.; Kaneko, R.; Straub, S. M.; Garcia, E. S. M.; Yan, Q.; Tamura, Y.


    Subduction zone magmatism primarily occurs due to flux melting of the mantle wedge that has been metasomatized by the slab component. The latter is enriched in volatiles and fluid-mobile elements and derived mainly from subducted sediments and altered oceanic crust (AOC). Subduction input has been linked to arc output in many studies, but this relationship is especially well documented in sedimented arc-trench systems. However, the Izu-Bonin system is sediment-poor, therefore the compositional and latitudinal variations (especially in Pb isotopes) of its arc magmas must be sourced from the subduction component originating primarily from the AOC. Pb is a very good tracer of recycled AOC that may contribute 50% or more of arc magma Pb. Izu-Bonin arc chemistry suggests a subduction influx of Indian-type crust, but the subducting crust sampled at ODP Site 1149 is Pacific-type. The discrepancy between subduction input and arc output calls into question the importance of the AOC as a source of the subduction component, and raises major concerns with our understanding of slab input. During the R/V Revelle 1412 cruise in late 2014, we successfully dredged vertical fault scarps at several sites from 27.5 N to 34.5 N, spanning a range of crustal ages that include a suggested compositional change at ~125 Ma. Major element data show an alkali enrichment towards the north of the study transect. Preliminary incompatible trace element data (e.g. Ba, Zr and Sr) data support this enrichment trend. Detailed mass balance calculations supported by Sr, Nd, Hf and especially Pb isotope analyses will be performed to evaluate whether the AOC controls the Pb isotope chemistry of the Izu-Bonin volcanic arc.

  10. Modeling Central American Volcanic Front Primitive Lavas with the Arc Basalt Simulator (abs 4.0) (United States)

    Feigenson, M.; Carr, M. J.; Gazel, E.


    We have used the Arc Basalt Simulator (ABS), developed by J-I Kimura, to explore the conditions and components of melting beneath the Central American volcanic front. ABS is a comprehensive forward model that incorporates slab dehydration and melting and mantle wedge fluxing and melting using realistic P-T conditions and experimentally determined phase relations and partition coefficients. We have applied ABS version 4.00, which includes melting/dehydration relations in eight distinct subducting layers, to model representative magma types along the Central American volcanic front. These magmas are first projected to primary melt compositions by the addition of olivine until they reach Fo90. Then, using a wide range of input parameters including variations in slab components, extent of peridotite depletion, depth of slab dehydration and wedge fluxing and degree of peridotite melting, successful model fits are generated (based on trace element and isotope matching). The solution space is probed using a Monte Carlo technique to cover the enormous range of parameter values. Nicaragua and Costa Rica represent geochemical and geophysical end members of the volcanic front, differing greatly in volcano volume, slab dip beneath the volcano, isotopic composition and incompatible element enrichment. Using appropriate input compositions for ABS 4.0, we find through millions of simulations that the Cerro Negro primary magma (Nicaragua) requires high degrees of source melting (22-27%) and large amounts of slab-derived water (3-5%). In contrast, the Irazu primary magma (central Costa Rica) is generated from more enriched sources with only a small amount of water (less than 0.5%) and at low degrees of partial melting (less than 5%). Other Central American lavas with intermediate geochemical characteristics are produced from conditions within the Nicaragua-Costa Rica range. By reproducing the lava geochemistry with ABS 4.0, it becomes possible to extract constraints on source input

  11. Geochemistry and petrogenesis of extension-related magmas close to the volcanic front of the central part of the Trans-Mexican Volcanic Belt (United States)

    Verma, Surendra P.; Torres-Sánchez, Darío; Velasco-Tapia, Fernando; Subramanyam, K. S. V.; Manikyamba, C.; Bhutani, Rajneesh


    New geochemical data for 23 samples from the Sierra de Chichinautzin (SCN) and Sierra Santa Catarina (SSC) located at the volcanic front of the central part of the Trans-Mexican Volcanic Belt were combined with the published data on 580 samples from the SCN to explore the origin and evolution of the Quaternary trachybasalt and basalt to andesite and dacite. The rare-earth element concentrations for the evolved intermediate and acid rocks are lower than those for the more basic varieties, implying that the evolved magmas cannot be generated by a simple fractional crystallisation process without crustal assimilation. The size of the Nb and Ta negative anomalies increases from basic to acid, which is similar to the behaviour of most continental rifts and extension-related areas, but contrasts from all island and continental arcs. The multidimensional tectonomagmatic diagrams indicate a continental rift setting from basic and alkaline intermediate magmas. The SSC represents a new site of within-plate alkaline magmas discovered in this work, which complements the earlier interpretation of the adjacent SCN as a manifestation of continental rift or extension-related magmatism.

  12. Late Miocene volcanism and intra-arc tectonics during the early development of the Trans-Mexican Volcanic Belt (United States)

    Ferrari, Luca; Conticelli, Sandro; Vaggelli, Gloria; Petrone, Chiara M.; Manetti, Piero


    The early stage of the Trans-Mexican Volcanic Belt (hereafter TMVB) is marked by widespread, mafic to intermediate, volcanism emplaced between 11 and 7 Ma from the Pacific coast to the longitude of Mexico City, to the north of the modern volcanic arc. Petrological and geochronological data support the hypothesis that this volcanism made up a unique late Miocenic central Mexican comagmatic province. Mafic lavas at the mouth of the Gulf of California and along the northwestern sector of the TMVB made up the Nayarit district, which includes calc-alkaline to transitional varieties. The central sector of the TMVB is characterized by two basaltic districts: the Jalisco-Guanajuato and the Queretaro-Hidalgo, which are distinguished from the westernmost ones by their lower Nb/La and generally lower HFSE/LILE values, as well as by spider diagrams characterized by larger negative spikes at Th, Ta, Nb, and Ti. The surface occurrence of the late Miocene basalts appears to be controlled by pre-existing zones of crustal weakness that channeled the mafic magmas. Field observations suggest that these structures have been reactivated in a transtensional fashion induced by differential tectonic motion of crustal blocks to the south and to the north of the TMVB. Starting from ˜12 Ma the TMVB separates a northern tectonic domain, subject to the developing divergent Pacific-North America plate boundary, from a southern tectonic domain, characterized by oblique subduction of the Rivera and Cocos plates. Apparently, far field stresses related to these complex plate boundaries reactivated older suture zones, allowing rapid uprise of mantle-derived magmas. The subduction-related signature shown by Miocene mafic lavas of the Jalisco-Guanajuato district argues against the existence of mantle plumes beneath this sector of the North America plate. On the other hand, the occurrence in the western TMVB and in the Guadalajara region of a large volume of mafic magmas, which sometimes show

  13. Off-axis magmatism along a subaerial back-arc rift: Observations from the Taupo Volcanic Zone, New Zealand. (United States)

    Hamling, Ian J; Hreinsdóttir, Sigrun; Bannister, Stephen; Palmer, Neville


    Continental rifting and seafloor spreading play a fundamental role in the generation of new crust. However, the distribution of magma and its relationship with tectonics and volcanism remain poorly understood, particularly in back-arc settings. We show evidence for a large, long-lived, off-axis magmatic intrusion located on the margin of the Taupo Volcanic Zone, New Zealand. Geodetic data acquired since the 1950s show evidence for uplift outside of the region of active extension, consistent with the inflation of a magmatic body at a depth of ~9.5 km. Satellite radar interferometry and Global Positioning System data suggest that there was an increase in the inflation rate from 2003 to 2011, which correlates with intense earthquake activity in the region. Our results suggest that the continued growth of a large magmatic body may represent the birth of a new magma chamber on the margins of a back-arc rift system.

  14. Oxidation of shallow conduit magma: Insight from μ-XANES analysis on volcanic ash particle (United States)

    Miwa, T.; Ishibashi, H.; Iguchi, M.


    Redox state of magma is important to understand dynamics of volcanic eruptions because magma properties such as composition of degassed volatiles, stability field of minerals, and rheology of magma depend on redox state. To evaluate redox state of magma, Fe3+/ΣFe ratio [= Fe3+/( Fe3++ Fe2+)] of volcanic glass has been measured non-destructively by Fe-K edge μ-XANES (micro X-ray Absorption Near Edge Structure) spectroscopy (e.g., Cottrell and Kelly, 2011). We performed textural, compositional, and Fe-K edge μ-XANES analyses on volcanic ash to infer oxidation process of magma at shallow conduit during eruption at Bromo Volcano, Indonesia. The volcanic ash particles were collected in 24th March 2011 by real-time sampling from ongoing activity. The activity was characterized by strombolian eruption showing magma head ascended to near the ground surface. The ash sample contains two type of volcanic glasses named as Brown and Black glasses (BrG and BlG), based on their color. Textual analysis shows microlite crystallinities are same in the two type of glasses, ranging from 0 to 3 vol.%. EPMA analyses show that all of the glasses have almost identical andesitic composition with SiO2 = 60 wt.%. In contrast, Fe-K edge μ-XANES spectra with the analytical method by Ishibashi et al. (in prep) demonstrate that BrG (Fe3+/ΣFe = 0.20-0.26) is more oxidized than BlG (Fe3+/ΣFe = 0.32-0.60). From combination of the glass composition, the measured Fe3+/ΣFe ratio and 1060 degree C of temperature (Kress and Carmichael, 1991), the oxygen fugacities are estimated to be NNO and NNO+4 for BrG and BlG, respectively. The volcanic glasses preserve syn-eruptive physicochemical conditions by rapid quenching due to their small size ranging from 125 to 250 μm. Our results demonstrate that BrG and BlG magmas are textually and chemically identical but their redox conditions are different at the eruption. The oxidation of magma can be caused by following two processes; 1) diffusive transport

  15. The Chahnaly low sulfidation epithermal gold deposit, western Makran volcanic arc, southeastern Iran (United States)

    Sholeh, Ali; Rastad, Ebrahim; Huston, David L.; Gemmell, J. Bruce; Taylor, Ryan D.


    The Chahnaly low-sulfidation epithermal Au deposit and nearby Au prospects are located northwest of the intermittently active Bazman stratovolcano on the western end of the Makran volcanic arc, which formed as the result of subduction of the remnant Neo-Tethyan oceanic crust beneath the Lut block. The arc hosts the Siah Jangal epithermal and Kharestan porphyry prospects, near Taftan volcano, as well as the Saindak Cu-Au porphyry deposit and world-class Reko Diq Cu-Au porphyry deposit, near Koh-i-Sultan volcano to the east-northeast in Pakistan. The host rocks for the Chahnaly deposit include early Miocene andesite and andesitic volcaniclastic rocks that are intruded by younger dacitic domes. Unaltered late Miocene dacitic ignimbrites overlie these rocks. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology data yield ages between 21.8 and 9.9 Ma for the acidic-intermediate regional volcanism. The most recent volcanic activity of the Bazman stratovolcano involved extrusion of an olivine basalt during Pliocene to Quaternary times. Interpretation of geochemical data indicate that the volcanic rocks are synsubduction and calc-alkaline to subalkaline. The lack of a significant negative Eu anomaly, a listric-shaped rare earth element pattern, and moderate La/Yb ratios of host suites indicate a high water content of the source magma.

  16. Differences between boninite and tholeiite primary magmas in Izu-Bonin-Mariana arc: constraints from an Os isotope perspective (United States)

    Senda, R.; Shimizu, K.; Suzuki, K.


    Geochemical data of arc primary magmas provide information on how elements behave in the subduction system. In order to constrain Os behavior in a subduction system, Os isotope ratios of whole rock and chromium spinels (Cr-spinels) in boninites, a type of high-Mg andesite, and tholeiites from Izu-Bonin-Mariana (IBM) arc, have been determined. Cr-spinel crystallizes at an early stage of fractional crystallization and therefore can preserve primary information of its magma source. Furthermore Os is highly compatible in Cr-spinels, and thus Os isotope ratios determined from Cr-spinel in volcanic rocks provide information on the magmatic history and origin. We investigated the difference in Os isotopic compositions between the primary boninite and primary tholeiite in IBM arc to understand the behavior of Os during arc magma generation. The whole rock Os isotope ratios of both boninites (187Os/188Os = 0.1240-0.1828) and tholeiites (187Os/188Os = 0.1658-0.2832) are higher and more variable than those of Cr-spinels (from boninites: 187Os/188Os = 0.1229-0.1242, from tholeiites: 187Os/188Os = 0.1429-0.1512). In both cases, this is likely to be due to the rock assimilating crustal materials with more radiogenic Os isotope ratios than the mantle during magma ascent after Cr-spinel crystallization. The initial Os isotope ratios of Cr-spinel from boninites (187Os/188Os(i) = 0.1206-0.1242) are similar to those of abyssal peridotites from the forearc region of IBM [1]. This suggests that the Os in the boninite primary magma originates from unradiogenic depleted mantle, not from radiogenic fertile mantle or subducted materials. On the other hand, Os isotope ratios of Cr-spinels from tholeiites are higher than those from boninites. Crustal contamination possibly contributed to the more radiogenic Os isotopic composition of the tholeiite magma. The difference in Os isotope ratios between boninite and tholeiites indicate that they have a different origin and evolutionary history

  17. Current perspectives on energy and mass fluxes in volcanic arcs (United States)

    Leeman, William; Davidson, Jon; Fischer, Tobias; Grunder, Anita; Reagan, Mark; Streck, Martin

    Volcanoes of the Pacific Ring of Fire and other convergent margins worldwide are familiar manifestations of nature's energy, account for about 25% of global volcanic outputs, dominate volcanic gas emissions to the atmosphere, and pose significant physical threats to a large human population. Yet the processes behind this prolific activity remain poorly understood.An international “State of the Arc” (SOTA) conference was held in August on the slopes of Mt. Hood, Oregon, to address current views on the energy and mass fluxes in volcanic arcs. This meeting brought together some 90 leading experts and students of subduction zones and their related magmatism.

  18. A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc. (United States)

    Klaver, Martijn; Carey, Steven; Nomikou, Paraskevi; Smet, Ingrid; Godelitsas, Athanasios; Vroon, Pieter


    This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely-operated vehicle that were analyzed for major element, trace element and Sr-Nd-Hf-Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave-bearing pumices that are nearly identical in composition (73 wt.% SiO2, 4.2 wt.% K2O). Lava bodies exposed in the crater and enclaves are basalts to andesites (52-60 wt.% SiO2). Biotite and amphibole are common phenocryst phases, in contrast with the typically anhydrous mineral assemblages of Santorini. The strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the Kolumbo magmas indicates that Kolumbo and Santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated. Moreover, the Kolumbo samples are derived from a distinct, more enriched mantle source that is characterized by high Nb/Yb (>3) and low (206)Pb/(204)Pb (<18.82) that has not been recognized in the Santorini volcanic products. The strong dissimilarity in both petrogenesis and inferred mantle sources between Kolumbo and Santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field.

  19. Geochemistry of basalts from small eruptive centers near Villarrica stratovolcano, Chile: Evidence for lithospheric mantle components in continental arc magmas (United States)

    Hickey-Vargas, R.; Sun, M.; Holbik, S.


    In the Central Southern Volcanic Zone (CSVZ) of the Andes, the location of stratovolcanoes and monogenetic small eruptive centers (SEC) is controlled by the Liquiñe-Ofqui Fault Zone (LOFZ), a trench-parallel strike-slip feature of over 1000 km length. The geochemistry of basalts from SEC is different from those of stratovolcanoes, and are termed Type 2 and Type 1 basalts, respectively. In the region of Villarrica stratovolcano, contemporaneous SEC are more MgO-rich, and have greater light rare earth element (LREE) enrichment, lower 87Sr/86Sr and 143Nd/144Nd, and lower ratios of large ion lithophile elements (LILE) to LREE and high field strength elements (HFSE). A unique finding in this region is that basalts from one SEC, San Jorge, has Type 1 character, similar to basalts from Villarrica stratovolcano. Type 1 basalts from Villarrica and San Jorge SEC have strong signals from time-sensitive tracers of subduction input, such as high 10Be/9Be and high (238U/230Th), while Type 2 SEC have low 10Be/9Be and (238U/230Th) near secular equilibrium. Based on new trace element, radiogenic isotope and mineral analyses, we propose that Type 1 basaltic magma erupted at San Jorge SEC and Villarrica stratovolcano forms by melting of the ambient actively subduction-modified asthenosphere, while Type 2 SEC incorporate melts of pyroxenite residing in the supra-subduction zone mantle lithosphere. This scenario is consistent with the close proximity of the volcanic features and their inferred depths of magma separation. The pyroxenite forms from arc magma produced during earlier episodes of subduction modification and magmatism, which extend back >300 Ma along this segment of the western South American margin. Type 2 basaltic magmas may reach the surface during LOFZ-related decompression events, and they may also be a normal but episodic part of the magma supply to large stratovolcanoes, resulting in cryptic geochemical variations over time. The presence and mobilization of stored

  20. Stability of volcanic conduits: insights from magma ascent modelling and possible consequences on eruptive dynamics (United States)

    Aravena, Alvaro; de'Michieli Vitturi, Mattia; Cioni, Raffaello; Neri, Augusto


    Geological evidences of changes in volcanic conduit geometry (i.e. erosive processes) are common in the volcanic record, as revealed by the occurrence of lithic fragments in most pyroclastic deposits. However, the controlling factors of conduit enlargement mechanisms are still partially unclear, as well as the influence of conduit geometry in the eruptive dynamics. Despite physical models have been systematically used for studying volcanic conduits, their mechanical stability has been poorly addressed. In order to study the mechanical stability of volcanic conduits during explosive eruptions, we present a 1D steady-state model which considers the main processes experimented by ascending magmas, such as crystallization, drag forces, fragmentation, outgassing and degassing; and the application of the Mogi-Coulomb collapse criterion, using a set of constitutive equations for studying typical cases of rhyolitic and trachytic explosive volcanism. From our results emerge that conduit stability is mainly controlled by magma rheology and conduit dimensions. Indeed, in order to be stable, feeding conduits of rhyolitic eruptions need larger radii respect to their trachytic counterparts, which is manifested in the higher eruption rates usually observed in rhyolitic explosive eruptions, as confirmed by a small compilation of global data. Additionally, for both magma compositions, we estimated a minimum magma flux for developing stable conduits (˜3ṡ106 kg/s for trachytic magmas and ˜8ṡ107 kg/s for rhyolitic magmas), which is consistent with the unsteady character commonly observed in low-mass flux events (e.g. sub-Plinian eruptions), which would be produced by episodic collapse events of the volcanic conduit, opposite to the mainly stationary high-mass flux events (e.g. Plinian eruptions), characterized by stable conduits. For a given magma composition, a minimum radius for reaching stable conditions can be computed, as a function of inlet overpressure and water content

  1. Structure and petrology of newly discovered volcanic centers in the northern Kermadec-southern Tofua arc, South Pacific Ocean (United States)

    Graham, Ian J.; Reyes, Agnes G.; Wright, Ian C.; Peckett, Kimberley M.; Smith, Ian E. M.; Arculus, Richard J.


    . Exceptions are rocks from "U" volcanic center, which have low vesicularity and low glass contents across a wide compositional range, indicating effusive eruption. Disequilibrium mineral textures, the frequent occurrence of xenoliths and xenocrysts, and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids, having resided only a short time in upper crustal reservoirs prior to eruption. Silicic magmas are major components of NKST arc volcanism and caldera formation is the dominant eruptive style. The scale of silicic magmatism is in marked contrast to the dominant basaltic-andesitic magmatism in the southern Kermadec arc. With evidence from other arcs, silicic magmatism is now recognized as a major feature of intraoceanic arcs globally.

  2. The relationship between subduction zone redox budget and arc magma fertility (United States)

    Evans, K.-A.; Tomkins, A.-G.


    A number of lines of evidence point to a causal link between oxidised slab-derived fluids, oxidised sub-arc mantle, and the formation of economic concentrations of metals such as Cu and Au that require oxidised magmas. However, trace element evidence from some trace element and isotope data suggests that sub-arc mantle is no more oxidised than mantle elsewhere. A simple analytical model is applied to constrain the evolution of sub-arc mantle oxidation state as a function of redox-budget fluxes from the subducting slab. Influential variables include the solubility of Fe 3+ and SO 42 - in slab-derived fluids, the geometry of the infiltration of slab-derived fluids in sub-arc mantle, the coupling between slab-derived and arc-output redox budgets, and the concentration of redox-buffering elements such as Fe and S in the sub-arc mantle. Plausible Archean and Proterozoic redox budget fluxes would not have created oxidised sub-arc mantle without input from ferric iron or sulphate dissolved in non-aqueous fluids such as silicate melts. Aqueous-borne Phanerozoic redox budget fluxes, on the other hand, which are dominated by the sulphate component, could have increased sub-arc fO 2 by up to three log 10 units. The results are generally consistent with the proposed elevated fO 2 for sub-arc mantle, but no resolution was found for the apparent contradiction between high proposed fO 2 values derived from iron-based oxybarometry and the lower values inferred from trace element and isotope evidence. Increases in sub-arc mantle fO 2 are favoured by focussed fluid infiltration and magma generation, weak coupling between slab and arc-output redox budgets, and restricted redox-buffering in the sub-arc mantle. Fertile arc segments for ore deposits associated with oxidised magmas require fluid chemistry and pressure-temperature gradients that enhance Fe 3+ and SO 42 - solubility in aqueous and silica-rich fluids, tectonic stress regimes that favour focussed transfer of components into

  3. Silica-enriched mantle sources of subalkaline picrite-boninite-andesite island arc magmas (United States)

    Bénard, A.; Arculus, R. J.; Nebel, O.; Ionov, D. A.; McAlpine, S. R. B.


    Primary arc melts may form through fluxed or adiabatic decompression melting in the mantle wedge, or via a combination of both processes. Major limitations to our understanding of the formation of primary arc melts stem from the fact that most arc lavas are aggregated blends of individual magma batches, further modified by differentiation processes in the sub-arc mantle lithosphere and overlying crust. Primary melt generation is thus masked by these types of second-stage processes. Magma-hosted peridotites sampled as xenoliths in subduction zone magmas are possible remnants of sub-arc mantle and magma generation processes, but are rarely sampled in active arcs. Published studies have emphasised the predominantly harzburgitic lithologies with particularly high modal orthopyroxene in these xenoliths; the former characteristic reflects the refractory nature of these materials consequent to extensive melt depletion of a lherzolitic protolith whereas the latter feature requires additional explanation. Here we present major and minor element data for pristine, mantle-derived, lava-hosted spinel-bearing harzburgite and dunite xenoliths and associated primitive melts from the active Kamchatka and Bismarck arcs. We show that these peridotite suites, and other mantle xenoliths sampled in circum-Pacific arcs, are a distinctive peridotite type not found in other tectonic settings, and are melting residues from hydrous melting of silica-enriched mantle sources. We explore the ability of experimental studies allied with mantle melting parameterisations (pMELTS, Petrolog3) to reproduce the compositions of these arc peridotites, and present a protolith ('hybrid mantle wedge') composition that satisfies the available constraints. The composition of peridotite xenoliths recovered from erupted arc magmas plausibly requires their formation initially via interaction of slab-derived components with refractory mantle prior to or during the formation of primary arc melts. The liquid

  4. Preliminary geochemical characterization of volcanic and geothermal fluids discharged from the Ecuadorian volcanic arc.


    Inguaggiato, S.; Hidalgo, S.; Beate, B.; Bourquin, J.


    In Ecuador, magmatism results from the subduction of the Nazca Plate beneath the North Western part of South America (Pennington, 1981; Kellogg and Vega, 1995; Witt et al., 2006). North of 2.5°S, the Ecuadorian Quaternary volcanic arc is characterized by about 60 volcanoes distributed in three different parallel chains. Many of these volcanoes are potentially active or currently in activity and display associated geothermal fields. South of this latitude, no active arc is present in Ecuador. ...

  5. Linear volcanic segments in the Sunda Arc, Indonesia: Implications for arc lithosphere control upon volcano distribution (United States)

    Macpherson, C. G.; Pacey, A.; McCaffrey, K. J.


    The overall curvature of many subduction zones is immediately apparent and the term island arc betrays the common assumption that subduction zone magmatism occurs in curved zones. This assumption can be expressed by approximating island arcs as segments of small circles on the surface of a sphere. Such treatments predict that the location of arc volcanoes is related to their vertical separation from the slab (in fact, the depth to seismicity in the slab) and require that the primary control on the locus of magmatism lies either within the subducted slab or the mantle wedge that separates the subducted and overriding lithospheric plates. The concept of curved arcs ignores longstanding observations that magmatism in many subduction systems occurs as segments of linearly arranged volcanic centres. Further evidence for this distribution comes from the close relationship between magmatism and large scale, arc-parallel fabrics in some arcs. Similarly, exposures of deep arc crust or mantle often reveal elongation of magmatic intrusions sub-parallel to the inferred trend of the arc. The Sunda Arc forms the Indonesian islands from Sumatra to Alor and provides an important test for models of volcano distribution for several reasons. First, Sunda has hosted abundant historic volcanic activity. Second, with the notable exception of Krakatau, every volcano in the arc is subaerial from base to cone and, therefore, can be readily identified where there is a suitable extent of local mapping that can be used to ground-truth satellite imagery. Third, there are significant changes in the stress regime along the length of the arc, allowing the influence of the upper plate to be evaluated by comparison of different arc segments. Finally, much of the Sunda Arc has proved difficult to accommodate in models that try to relate volcano distribution to the depth to the subducted slab. We apply an objective line-fitting protocol; the Hough Transform, to explore the distribution of volcanoes

  6. Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan (United States)

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


    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.

  7. Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan (United States)

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


    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

  8. Shallow magma chamber under the Wudalianchi Volcanic Field unveiled by seismic imaging with dense array (United States)

    Li, Zhiwei; Ni, Sidao; Zhang, Baolong; Bao, Feng; Zhang, Senqi; Deng, Yang; Yuen, David A.


    The Wudalianchi Volcano Field (WDF) is a typical intraplate volcano in northeast China with generation mechanism not yet well understood. As its last eruption was around 300 years ago, the present risk for volcano eruption is of particular public interest. We have carried out a high-resolution ambient noise tomography to investigate the location of magma chambers beneath the volcanic cones with a dense seismic array of 43 seismometers and ~ 6 km spatial interval. Significant low-velocity anomalies up to 10% are found at 7-13 km depth under the Weishan volcano, consistent with the pronounced high electrical-conductivity anomalies from previous magnetotelluric survey. We propose these extremely low velocity anomalies can be interpreted as partial melting in a shallow magma chamber with volume at least 200 km3 which may be responsible for most of the recent volcanic eruptions in WDF. Therefore, this magma chamber may pose a serious hazard for northeast China.

  9. The arc arises: The links between volcanic output, arc evolution and melt composition (United States)

    Brandl, Philipp A.; Hamada, Morihisa; Arculus, Richard J.; Johnson, Kyle; Marsaglia, Kathleen M.; Savov, Ivan P.; Ishizuka, Osamu; Li, He


    Subduction initiation is a key process for global plate tectonics. Individual lithologies developed during subduction initiation and arc inception have been identified in the trench wall of the Izu-Bonin-Mariana (IBM) island arc but a continuous record of this process has not previously been described. Here, we present results from International Ocean Discovery Program Expedition 351 that drilled a single site west of the Kyushu-Palau Ridge (KPR), a chain of extinct stratovolcanoes that represents the proto-IBM island arc, active for ∼25 Ma following subduction initiation. Site U1438 recovered 150 m of oceanic igneous basement and ∼1450 m of overlying sediments. The lower 1300 m of these sediments comprise volcaniclastic gravity-flow deposits shed from the evolving KPR arc front. We separated fresh magmatic minerals from Site U1438 sediments, and analyzed 304 glass (formerly melt) inclusions, hosted by clinopyroxene and plagioclase. Compositions of glass inclusions preserve a temporal magmatic record of the juvenile island arc, complementary to the predominant mid-Miocene to recent activity determined from tephra layers recovered by drilling in the IBM forearc. The glass inclusions record the progressive transition of melt compositions dominated by an early 'calc-alkalic', high-Mg andesitic stage to a younger tholeiitic stage over a time period of 11 Ma. High-precision trace element analytical data record a simultaneously increasing influence of a deep subduction component (e.g., increase in Th vs. Nb, light rare earth element enrichment) and a more fertile mantle source (reflected in increased high field strength element abundances). This compositional change is accompanied by increased deposition rates of volcaniclastic sediments reflecting magmatic output and maturity of the arc. We conclude the 'calc-alkalic' stage of arc evolution may endure as long as mantle wedge sources are not mostly advected away from the zones of arc magma generation, or the rate of

  10. Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs (United States)

    Blundy, Jon; Mavrogenes, John; Tattitch, Brian; Sparks, Steve; Gilmer, Amy


    Porphyry copper deposits (PCDs) are characterised by a close spatial and temporal association with small, hypabyssal intrusions of silicic magmas in volcanic arcs. PCD formation requires elevated chlorine and water to concentrate copper in magmatic hypersaline liquids (or brines), and elevated sulphur to precipitate copper-rich sulphides. These twin requirements are hard to reconcile with experimental and petrological evidence that voluminous chlorine-rich, hydrous silicic magmas, of the variety favourable to copper enrichment, lack sufficient sulphur to precipitate directly the requisite quantities of sulphides. These features are, however, consistent with observations of active volcanic arcs whereby PCDs can be viewed as roots of dome volcanoes above shallow reservoirs where silicic magmas accumulate over long time spans. During protracted periods of dormancy metal-enriched dense brines accumulate in and above the silicic reservoir through slow, low-pressure degassing. Meanwhile cogenetic volatile-rich mafic magmas and their exsolved, sulphur and CO2-rich fluids accumulate in deeper reservoirs. Periodic destabilisation of these reservoirs leads to short-lived bursts of volcanism liberating sulphurous gases, which react with the shallow-stored brines to form copper-rich sulphides and acidic vapours. We test this hypothesis with a novel set of 'porphyry in a capsule' experiments designed to simulate low-pressure (1-2 kbar) interaction of basalt-derived, sulphur-rich gases with brine-saturated, copper-bearing, but sulphur-free, granite. Experiments were run at 720-850 ° C in cold-seal apparatus with basaltic andesite, loaded with H2O and S, situated below dacite, loaded with H2O, Cl and Cu. At run conditions both compositions are substantially degassed and crystallized. S-rich gas from the basaltic andesite ascends to react with Cu-rich brines exsolved from the dacite, Our experiments reveal the direct precipitation of copper-sulphide minerals, in vugs and veins

  11. An Early Cretaceous volcanic arc/marginal basin transition zone, Peninsula hardy, southernmost Chile (United States)

    Miller, Christopher A.; Barton, Michael; Hanson, Richard E.; Fleming, Thomas H.


    The Hardy Formation represents a latest Jurassic-Early Cretaceous volcanic arc that was located along the Pacific margin of southern South America. It was separated from the continent by a marginal basin floored by portions of an ophiolite sequence (the Rocas Verdes ophiolites). The transition between the arc and marginal basin occurs on Peninsula Hardy, southernmost Chile, where there is a lateral facies transition from arc deposits of the Hardy Formation into proximal marginal basin fill of the Yahgan Formation. Interfingering of arc and marginal basin sequences demonstrates that subduction-related arc magmatism was concurrent with marginal basin formation. The lateral facies transition is reflected in the geochemistry of volcanic rocks from the Hardy and Yahgan formations. Basalts, andesites and dacites of the arc sequence follow a calc-alkaline differentiation trend whereas basalts from the marginal basin follow a tholeiitic differentiation trend. Estimates of temperature and oxygen fugacity for crystallization of the arc andesites are similar to values reported for other calc-alkaline andesites. It is suggested that water activity influenced the early or late crystallization of Ti-magnetite and this controlled the style of differentiation of the magmas erupted on Peninsula Hardy. Magmas with high water contents evolved along the calc-alkaline differentiation trend whereas those with low water contents evolved along the tholeiitic differentiation trend. Some rhyolites are differentiated from the calc-alkaline andesites and dacites, but most appear to be the products of crustal anatexis on the basis of trace-element evidence. The arc basalts and some marginal basin basalts show relative enrichment in LILE, relative depletion in HFSE, and enrichment in LREE. Other marginal basin basalts are LREE depleted and show small relative depletions in HFSE. Basalts with both calc-alkaline and tholeiitic affinities can also be recognized in the Rocas Verdes ophiolites

  12. Volcanic tremors and magma wagging: gas flux interactions and forcing mechanism (United States)

    Bercovici, David; Jellinek, A. Mark; Michaut, Chloé; Roman, Diana C.; Morse, Robert


    Volcanic tremor is an important precursor to explosive eruptions and is ubiquitous across most silicic volcanic systems. Oscillations can persist for days and occur in a remarkably narrow frequency band (i.e. 0.5-7 Hz). The recently proposed magma-wagging model of Jellinek & Bercovici provides a basic explanation for the emergence and frequency evolution of tremor that is consistent with observations of many active silicic and andesitic volcanic systems. This model builds on work suggesting that the magma column rising in the volcanic conduit is surrounded by a permeable vesicular annulus of sheared bubbles. The magma-wagging model stipulates that the magma column rattles within the spring like foam of the annulus, and predicts oscillations at the range of observed tremor frequencies for a wide variety of volcanic environments. However, the viscous resistance of the magma column attenuates the oscillations and thus a forcing mechanism is required. Here we provide further development of the magma-wagging model and demonstrate that it implicitly has the requisite forcing to excite wagging behaviour. In particular, the extended model allows for gas flux through the annulus, which interacts with the wagging displacements and induces a Bernoulli effect that amplifies the oscillations. This effect leads to an instability involving growing oscillations at the lower end of the tremor frequency spectrum, and that drives the system against viscous damping of the wagging magma column. The fully non-linear model displays tremor oscillations associated with pulses in gas flux, analogous to observations of audible `chugging'. These oscillations also occur in clusters or envelopes that are consistent with observations of sporadic tremor envelopes. The wagging model further accurately predicts that seismic signals on opposite sides of a volcano are out of phase by approximately half a wagging or tremor period. Finally, peaks in gas flux occur at the end of the growing instability

  13. Internal triggering of volcanic eruptions: tracking overpressure regimes for giant magma bodies (United States)

    Tramontano, Samantha; Gualda, Guilherme A. R.; Ghiorso, Mark S.


    Understanding silicic eruption triggers is paramount for deciphering explosive volcanism and its potential societal hazards. Here, we use phase equilibria modeling to determine the potential role of internal triggering - wherein magmas naturally evolve to a state in which eruption is inevitable - in rhyolitic magma bodies. Whole-rock compositions from five large to super-sized rhyolitic deposits are modeled using rhyolite-MELTS. By running simulations with varying water contents, we can track crystallization and bubble exsolution during magma solidification. We use simulations with variable enthalpy and fixed pressure for the five compositions. The interplay between bubble exsolution and crystallization can lead to an increase in the system volume, which can lead to magma overpressurization. We find that internal triggering is possible for high-silica rhyolite magmas crystallizing at pressures below 300 MPa (50 wt.%, which makes magma immobile - high-silica rhyolite eruptions from such depths would require external triggering, but examples are scarce or entirely absent. Calculated crystallinities at which the critical overpressure threshold is reached compare favorably with observed crystal contents in natural samples for many systems, suggesting that internal evolution plays a critical role in triggering eruptions. Systems in which fluid saturation happens late relative to crystallization or in which degassing is effective can delay or avoid internal triggering. We argue that priming by crystallization and bubble exsolution is critical for magma eruption, and external triggering serves simply as the final blow - rather than being the driving force - of explosive rhyolitic eruptions.

  14. Investigating Compositional Links Between Arc Magmas And The Subducted Altered Oceanic Crust (United States)

    Straub, S. M.


    Arc magmatism is causally related to the recycling of materials from the subducting plate. Numerous studies showed that the recycled material flux is dominated by recycled continental crust (oceanic sediment, eroded crust) and altered oceanic igneous crust (AOC). The crustal component is highly enriched, and thus its signal in arc magmas can readily be distinguished from mantle wedge contributions. In contrast, the impact of the AOC flux is much more difficult to detect, since the AOC isotopically resembles the mantle. Mass balance studies of arc input and output suggest that the recycled flux from the thick (6000 meter on average) AOC may buffer the flux of the recycled continental crust to the point of concealment in arc settings where the latter is volumetrically minor. In particular, highly fluid- mobile elements Sr and Pb in arc magmas are strongly influenced by the AOC, implying that the arc chemistry may allow for inferring the Sr and Pb isotopic composition of the subducted AOC. This hypothesis is being tested by a compilation of published data of high-quality trace element and isotope compositions from global arcs. In agreement with previous studies, our results confirm that the Sr-rich fluids released from the AOC control the arc Sr isotopes, whereby the slightly elevated 87Sr/86Sr (up to 0.705) of many arcs may principally reflect the similarly elevated Sr isotope ratios of the AOC rather than a recycled crustal component. In contrast, the arc Pb isotope ratios are influenced by both the AOC and the recycled crustal component which create the typical binary mixing arrays. These arrays should then point to the Pb isotope composition of the AOC and the recycled crust, respectively. However, as the proportions of these end members may strongly vary in arc magmas, the exact 206Pb/204Pb of the subducted AOC in a given setting is challenging. Remarkably, the Pb isotope systematics from well-constrained western Aleutian (minimal sediment subduction) and central

  15. Modeling magma flow in volcanic conduit with non-equilibrium crystallization (United States)

    Yulia, Tsvetkova


    Modeling magma flow in volcanic conduit including with non -equilibrium crystallization There is a set of models of magma flow in volcanic conduits which predicts oscillations in magma discharge during extrusion of lava domes. These models neglect heating of surrounding rocks and use 1D approximation of the flow in the conduit. Here magma flow is investigated with an account of heat exchange between surrounding rocks and magma and different dependences viscosity on temperature and crystal concentration. Stick-slip conditions were applied at the wall. The flow is assumed to be quasi-static and quasi 1D. Only vertical component of velocity vector is present, thus, we do not consider horizontal momentum balance. At the top of the conduit the pressure is assumed to be fixed, chamber pressure changes according with magma influx and outflux. First set of simulation was made for the viscosity that depends on cross-section average crystal concentration and parabolic velocity profile. In earlier models that account for crystal growth kinetics the temperature was allowed to change only due to the release of latent heat of crystallization. Heat transfer leads to cooling of the outer parts of the conduit leading to high crystal contents and high magma viscosities. Changes in viscosity result in changes in discharge rate. For the non-isothermal case there is no motion during most part of the cycle and a portion of magma solidifies at the top of the conduit forming a plug. During repose period chamber pressure is growing due to influx of fresh magma, and magma discharge rate starts to increase. Influx of hot magma into the conduit leads to decrease in friction resulting in a jump in discharge rate that lead to depressurization of magma chamber. Discharge rate decreases and magma solidifies again. For isothermal model with the same parameters discharge rate monotonically tends to the value of Qin. Simulation reveal that crystal content changes significantly across the conduit

  16. Detailed Seismic Reflection Images of the Central American Volcanic Arc (United States)

    McIntosh, K. D.; Fulthorpe, C. S.


    New high-resolution seismic reflection profiles across the Central American volcanic arc (CAVA) reveal an asymmetric deformation pattern with large-scale folding and uplift of basinal strata in the forearc contrasted by intrusive bodies, normal faults, and possible strikes-slip faults in the backarc. Since Miocene times the CAVA has migrated seaward, apparently impinging on the Sandino forearc basin and creating or modifying the low-lying Nicaragua depression, which contains the backarc and much of the arc. However the structural nature of the depression and its possible relationship to forearc sliver movement is poorly known. In November-December 2004 we recorded a large, high-resolution, seismic reflection dataset largely on the Pacific shelf (forearc) area of Central America, extending from NW Costa Rica to the SE edge of El Salvador's territorial waters. We seized an opportunity to study the nature of the CAVA by recording data into the Gulf of Fonseca, a large embayment at the intersection of Nicaragua, Honduras, and El Salvador. With 3 GI airguns and a 2100 m streamer we recorded data with typical penetration of 2-3 seconds in the Sandino basin and frequency content of ~10-250 Hz (at shallow levels). Penetration was limited over the arc summit with high velocity volcanic rocks encountered at depths as shallow as a few hundred meters. To the NE the edge of the Nicaragua depression occurs abruptly; our data show a well-developed sedimentary basin 1.5-3 km thick separated by numerous steeply-dipping faults. The broadband signal and good penetration of this dataset will help us determine the chronology of arc development in this position and the styles of deformation in the forearc, arc, and backarc areas. In turn, this will help us understand the regional tectonic and stratigraphic development of this margin due to the profound affects of the arc.

  17. Seismotectonic pattern and the source region of volcanism in the central part of Sunda Arc (United States)

    Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří


    The seismotectonic pattern in the central part of the Sunda Arc (Java, Nusa Tenggara) was studied in relation to the distribution of active calc-alkaline volcanoes, using global seismological data. Hypocentral determinations of the International Seismological Centre from the period 1964-1999, as relocated by Engdahl, and Harvard Centroid Moment Tensor Solutions from the period 1976-2003 were used. The following phenomena, which could assist the location of the source region of primary magma for island arc calc-alkaline volcanism, were observed: (1) An aseismic gap without any strong teleseismically recorded earthquakes was found in the Wadati-Benioff zone of the subducting slab along the whole investigated region of the Sunda Arc, forming a continuous strip of laterally variable depth and shape, at depths between 100 and 200 km. The absence of strong earthquakes (with mb>4.0) indicates a significant change in the mechanical properties of the subducting slab at intermediate depths. All active calc-alkaline volcanoes in the Sunda Arc are located above this gap. (2) The majority of earthquakes occurring in the lithospheric wedge of the Eurasian Plate above the subducted slab could be attributed to several deep-rooted seismically active fracture zones of regional extent. All delineated active fracture zones display a thrust tectonic regime as shown by the available fault plane solutions. (3) Clusters of earthquakes were found beneath active volcanoes of western Java, Bali and Nusa Tenggara in the lithospheric wedge above the slab and identified as seismically active columns. These clusters occur only beneath the volcanoes that are located at the outcrops of seismically active fracture zones. We interpret the earthquakes in these clusters beneath volcanoes as events induced by magma transport through the medium of the lithospheric wedge that has been subcritically pre-stressed by the process of plate convergence. (4) Beneath the volcanoes of central Java no seismically

  18. Textural and chemical variation in phenocrysts from the early eruptions of Lutao volcanic island, the northern Luzon arc (United States)

    Liu, Y.; Iizuka, Y.; Huang, K.


    The Lutao volcanic island at the northern end of Luzon arc was formed by the subduction of South China Sea Plate beneath the Philippine Sea plate. Three edifices on the island were built up by pyroclastic deposits from different eruption stages. In this study, the textural and chemical zonings in phenocrysts are used to characterize the subvolcanic magma chamber for the earliest eruption stage (1.4-2.0 Ma). The high 143Nd/144Nd and 176Hf/177Hf ratios of six volcanic breccias collected from the lowermost layer indicate that they were derived from a common depleted mantle source. However, their compositional variations cannot be explained by simple fractional crystallization. The textures and compositions of the phenocrysts reveal the complication in the magma chamber processes. Compared to the average primitive arc basalts, two basaltic andesites have similar major element compositions with higher incompatible trace element abundances. The un-zoned or normally zoned olivine, plagioclase, and pyroxenes indicate the relatively undisturbed processes (961-1011°C and 2.8-5.5 kb) at the earlier crystallization stage. The peritectic olivine and abundance melt inclusions accompanied by abrupt XAn increase at the rims of plagioclase inferred recharge of H2O-rich mafic melt at later stage, which also triggered rapid eruption. The cryptic magma mixing had limited effect on isotopic signatures and major element variations, but had great chance to modify the bulk trace element abundances. In contrast, plagioclase phenocrysts in four low-mg# basaltic samples contain An-rich dissolved or resorbed cores with abundant melt inclusions, which were formed from rapid decompression of volatile-rich magma at H2O-undersaturated conditions. The calcic plagioclase and minor Mg-rich olivine formed at greater depth were rapidly brought to magma chamber to crystallized sodic plagioclase rim, clinopyroxene, and minor orthopyroxene (954-994°C and 2.1-4.1 kb). The normally zoned clinopyroxene

  19. Lateral variation of H2O/K2O ratios in Quaternary Magma of the Northeastern Japan arc (United States)

    Miyagi, I.


    Water plays a fundamental role in the magma genesis beneath subduction zones. In order to estimate a spatial distribution of the density of water flux in the wedge mantle of the Northeastern Japan arc, this study examines a lateral variation of pre-eruptive bulk rock H2O/K2O contents among volcanoes located both in the frontal and in back arc settings. The analytical targets are the frontal volcanoes Nigorikawa (N42.12 E140.45), Zenikame (N41.74 E140.85), Adachi (N38.22 E140.65), and Nanashigure (N40.07 E141.11), and the back arc ones Hijiori (N38.61 E140.17) and Kanpu (N39.93 E139.88). The bulk magmatic H2O content (TH2O) is calculated from a mass balance of hydrogen isotopic ratios among three phases in a batch of magma; dissolved water in melt, excess H2O vapor, and hydrous phenocrysts such as amphiboles (Miyagi and Matsubaya, 2003). Since the amount of H2O in hydrous phenocryst is negligible, the bulk magmatic H2O content can be written as TH2O = (30 XD CD) / (15 - dT + dMW), where dMW is the measured hydrogen isotopic ratio of hydrous phenocrysts, XD is a melt fraction of magma, CD is a water concentration of the melt, and dT is hydrogen isotopic ratios of a bulk magma (assumed to be -50 per-mil). Both XD and CD are estimated from bulk rock chemistry of the sample using the MELTS program (Ghiorso and Sack, 1995). Hydrogen isotopic fractionation factors are assumed to be -15 and -30 per-mil for vapor and hydrous mineral, and vapor and silicate melt, respectively. There observed a clear difference among the H2O/K2O ratios of bulk magmas from the frontal and back arc volcanoes. For instance higher H2O/K2O wt ratios was observed in the frontal volcanoes (Nigorikawa 5.3, Zenikame 11-12, Adachi 8-10, and Nanashigure 4-18), while lower H2O/K2O wt ratios was observed in the back arc ones (Kanpu 0-2.5 and Hijiori 1.4). The lateral variation of H2O/K2O ratios infer the higher water flux through the frontal side of wedge mantle, which can be a potential cause of the

  20. Deep seismic sounding investigation into the deep structure of the magma system in Changbaishan-Tianchi volcanic region

    Institute of Scientific and Technical Information of China (English)

    张先康; 张成科; 赵金仁; 杨卓欣; 李松林; 张建狮; 刘宝峰; 成双喜; 孙国伟; 潘素珍


    The magma system of Changbaishan-Tianchi Volcanic region is studied with three-dimensional deep seismic sounding (DSS) technique. The results show that the magma system of Changbaishan-Tianchi volcanic region, mainly characterized by low velocity of P wave, can be divided into three parts in terms of depth. At the depth range of 9(15 km, the distribution of the magma system is characterized by extensiveness, large scale and near-SN orientation. This layer is the major place for magma storage. From the depth of 15 km down to the lower crust, it is characterized by small lateral scale, which indicates the (trace( of magma intrusion from the upper mantle into the crust and also implies that the magma system most probably extends to the upper mantle, or even deeper.(less than 8(9 km deep), the range of magma distribution is even smaller, centering on an SN-oriented area just north of the Tianchi crater. If low velocity of P wave is related to the magma system, it then reflects that the magma here is still in a state of relatively high temperature. In this sense, the magma system of Changbaishan-Tianchi volcanic region is at least not (remains(, in other words, it is in an (active( state.

  1. Parental arc magma compositions dominantly controlled by mantle-wedge thermal structure (United States)

    Turner, Stephen J.; Langmuir, Charles H.; Katz, Richard F.; Dungan, Michael A.; Escrig, Stéphane


    The processes that lead to the fourfold variation in arc-averaged compositions of mafic arc lavas remain controversial. Control by the mantle-wedge thermal structure is supported by chemical correlations with the thickness of the underlying arc crust, which affects the thermal state of the wedge. Control by down-going slab temperature is supported by correlations with the slab thermal parameter. The Chilean Southern Volcanic Zone provides a test of these hypotheses. Here we use chemical data to demonstrate that the Southern Volcanic Zone and global arc averages define the same chemical trends, both among elements and between elements and crustal thickness. But in contrast to the global arc system, the Southern Volcanic Zone is built on crust of variable thickness with a constant slab thermal parameter. This natural experiment, along with a set of numerical simulations, shows that global arc compositional variability is dominated by different extents of melting that are controlled by the thermal structure of the mantle wedge. Slab temperatures play a subordinate role. Variations in the subducting slab's fluid flux and sediment compositions, as well as mantle-wedge heterogeneities, produce second-order effects that are manifested as distinctive trace element and isotopic signatures; these can be more clearly elucidated once the importance of wedge thermal structure is recognized.

  2. Stratigraphy, petrology, and geochemistry of the Spurr Volcanic Complex, eastern Aleutian Arc, Alaska. [(Appendix for geothermal fluid chemistry)

    Energy Technology Data Exchange (ETDEWEB)

    Nye, C.J.


    The Spurr Volcanic Complex (SVC) is a calcalkaline, medium-K, sequence of andesites erupted over the last quarter of a million years by the easternmost currently active volcanic center in the Aleutian Arc. The ancestral Mt. Spurr was built mostly of andesites of uniform composition (58 to 60% SiO/sub 2/), although andesite production was episodically interrupted by the introduction of new batches of more mafic magma. Near the end of the Pleistocene the ancestral Mt. Spurr underwent Bezyianny-type avalanche caldera formation, resulting in the production of a volcanic debris avalanche with overlying ashflows. Immediately afterward, a large dome (the present Mt. Spurr) was emplaced in the caldera. Both the ashflows and dome are made of acid andesite more silicic than any analyzed lavas from the ancestral Mt. Spurr (60 to 63% SiO/sub 2/), yet contain olivine and amphibole xenocrysts derived from more mafic magma. The mafic magma (53 to 57% SiO/sub 2/) erupted during and after dome emplacement, forming proto-Crater Peak and Crater Peak. Hybrid pyroclastic flows and lavas were also produced. Proto-Crater Peak underwent glacial dissection prior to the formation of Crater Peak in approximately the same location. Appendices II through VIII contain a summary of mineral compositions; Appendix I contains geochemical data. Appendix IX by R.J. Motyka and C.J. Nye describes the chemistry of geothermal fluids. 78 refs., 16 figs., 3 tabs.

  3. Oxygen isotope geochemistry of the lassen volcanic center, California: Resolving crustal and mantle contributions to continental Arc magmatism (United States)

    Feeley, T.C.; Clynne, M.A.; Winer, G.S.; Grice, W.C.


    This study reports oxygen isotope ratios determined by laser fluorination of mineral separates (mainly plagioclase) from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the Lassen Volcanic Center (LVC), northern California. Plagioclase separates from nearly all rocks have ??18O values (6.1-8.4%) higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back-arc regions of the southernmost Cascades during the late Cenozoic. Most LVC magmas must therefore contain high 18O crustal material. In this regard, the ??18O values of the volcanic rocks show strong spatial patterns, particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust. Rhyodacitic magmas erupted from vents located within 3.5 km of the inferred center of the LVC have consistently lower ??18 O values (average 6.3% ?? 0.1%) at given SiO2 contents relative to rocks erupted from distal vents (>7.0 km; average 7.1% ?? 0.1%). Further, magmas erupted from vents situated at transitional distances have intermediate values and span a larger range (average 6.8% ?? 0.2%). Basaltic andesitic to andesitic composition rocks show similar spatial variations, although as a group the ??18O values of these rocks are more variable and extend to higher values than the rhyodacitic rocks. These features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas, followed by mixing or mingling with silicic magmas formed by partial melting of initially high 18O continental crust (??? 9.0%) increasingly hybridized by lower ??18O (???6.0%) mantle-derived basaltic magmas toward the center of the system. Mixing calculations using estimated endmember source ??18O values imply that LVC magmas contain on a molar oxygen basis approximately 42 to 4% isotopically heavy continental crust, with proportions declining in a broadly regular fashion toward the

  4. NOAA Deepwater Exploration of the Marianas 2016: Volcanic arc and Backarc Basin (United States)

    Stern, R. J.; Brounce, M. N.; Chadwick, B.; Fryer, P. B.; Glickson, D.; Merle, S. G.


    Legs 1 and 3 of NOAA Okeanos Explorer EX1605 devoted a total of 17 ROV dives to exploring the Mariana magmatic arc and backarc basin (BAB). Dives were carried out on 11 submarine arc volcanoes, the submerged slopes of two volcanic islands, and at 3 BAB sites along 1000 km of the Mariana arc system. Four of the studied arc volcanoes are extinct, three are dormant, and six are active. All BAB dives were on the spreading ridge between 15-17°N, which is volcanically active. Geologic highpoints of these dives include: 1) discovery of an extinct hydrothermal chimney ( 15m tall) in Fina Nagu A (Leg 1, Dive 7; L1D7); 2) observations of very fresh (<3 years old) BAB pillow basalts (L1D9); 3) discovery of a very active BAB hydrothermal field (T 340°C, active chimneys up to 30m tall; L1D11); 4) examination of Esmeralda Bank crater floor (active venting but too murky to find vents; L1D19); 5) discovery of hydrothermal vents with vent fauna on Chamorro volcano (L3D7; T 30°C, active chimneys 2m tall); and 6) examination of active venting and S degassing at 500-350 m depth on Daikoku volcano (L3D9). Video clips of some of the most exciting discoveries and examinations will be presented. We plan to compare previous bathymetry over the active volcanoes with what was collected during EX1605 to quantify how these edifices have changed since when these were previously mapped, over the past 13 years or less. These dives also provided visual evidence in support of the hypothesis that individual edifices of the Fina Nagu Volcanic Complex increase in age from NE to SW, interpreted as due to the motion of actively-extending lithosphere of the southern Mariana BAB to the SW over a relatively fixed source of arc magma above the subducting Pacific plate (Brounce et al. G3 2016). Continuous interaction between biologists and geologists on EX1605 allowed us to identify regions of high faunal density on hard substrates around some active volcanoes, for example Esmeralda Bank, presumably

  5. Arc-rift transition volcanism in the Volcanic Hills, Jacumba and Coyote Mountains, San Diego and Imperial Counties, california (United States)

    Fisch, Gregory Zane

    Neogene volcanism associated with the subduction of the Farallon-Pacific spreading center and the transition from a subduction zone to a rift zone has been studied extensively in Baja, California, Mexico. One of the main goals of these studies was to find a geochemical correlation with slab windows that may have formed during that complicated transition. While workers have been able to find distinct geochemical signatures in samples from Baja California, none have shown statistically significant correlation with samples from southern California that are thought to be related to the same arc-rift transition events. All of the basaltic samples from this study of southern California rocks have prominent Nb depletions typical of island-arc subduction-related volcanism, in contrast to the chemistry of Baja California volcanics that have trace element patterns typical of synrift related volcanism. The work done by previous investigators has been additionally complicated due to each investigator's choice of important ratios or patterns, which bears little, if any, correlation with work done by others working in the same area. For example, Martin-Barajas et al. (1995) use K/Rb ratios in their study of the Puertocitos Volcanic Province, while Castillo (2008) argues that Sr/Y vs. Y is a better indicator of petrogenetic processes. Little petrologic work has been done on Neogene volcanic rocks in the Imperial Valley and eastern San Diego County region of Southern California. This thesis combines new research with that of previous workers and attempts to establish a better understanding of the processes involved with the transition volcanism. Prior work documents significant differences in the geochemistry between some of these areas, especially those in close proximity to each other (e.g. the Volcanic Hills and Coyote Mountains). These differences were thought to be largely the result different magmatic sources. The potential of finding two differing magma types in close

  6. The Role of Philippine Sea Plate to the Genesis of Quaternary Magmas of Northern Kyushu Island, Japan, Inferred from Along-Arc Geochemical Variations (United States)

    Shibata, T.; Yoshikawa, M.; Itoh, J.; Ujike, O.; Miyoshi, M.; Takemura, K.


    Quaternary volcanoes on Kyushu Island comprise volcanoes Himeshima, Futagoyama, Yufu-Tsurumi, Kuju, Aso, Kirishima and Sakurajima from north to south alongstrike the volcanic front. Adakitic lavas are observed from Yufu-Tsurumi and Kuju volcanoes in northern Kyushu (Kita et al., 2001; Sugimoto et al., 2007), whereas no Quaternary adakites were observed at Aso (e.g., Hunter, 1998) and the volcanoes south of Aso along the entire Ryukyu arc. Sugimoto et al. (2007) suggested that the trace element and Sr, Nd, and Pb isotopic compositions of adakitic magmas from Yufu-Tsurumi volcano indicate derivation of the magmas by partial melting of the subducting PSP. In contrast, Zellmer et al. (2012) suggested that these adakites may have formed by fractional crystallization of mantle-derived mafic magmas within the garnet stability field in the crust. The Honshu-Kyushu arc transition is a particular favorable setting to address these controversial models for the origin of the adakitic lavas, because of the potential relationship between the PSP materials and the alongstrike variation of the lava chemistry. The Palau-Kyushu ridge divides the oceanic crust of the PSP into northeastern and southwestern segments with ages of 26-15 (Shikoku Basin) and 60-40 Ma (West Philippine Basin), respectively (Mahony et al., 2011). Although there are no clear plate images beneath northern Kyushu, the northern extension of the Palau-Kyushu ridge potentially corresponds to the boundary between the SW Japan and Ryukyu arcs. If adakite genesis was related to the subducted slab rather than the overlying crust, then the spatial distribution of Quaternary adakites should correlate with the age of the subducted PSP. In order to test such correlation and elucidate the petrogenesis of the northern Kyushu adakites, we compiled major and trace elements and Sr-Nd-Pb isotope ratios from volcanoes along the arc front that includes the transition from adakitic to non-adakitic arc volcanism. Comprehensive

  7. Deducing the magma chamber processes of middle Eocene volcanics, Sivas and Tokat regions; NE Turkey: Insights from clinopyroxene chemistry (United States)

    Göçmengil, Gönenç; Karacık, Zekiye; Genç, Ş. Can; Prelevic, Dejan


    Middle Eocene Tokat and Sivas volcanic successions occur within the İzmir-Ankara-Erzincan suture zone. Different models are suggested for the development of the middle Eocene volcanism such as post-collisional, delamination and slab-breakoff models as well as the arc magmatism. In both areas, volcanic units cover all the basement units with a regional disconformity and comprise lavas spanning a compositional range from mainly basalt-basaltic andesite to a lesser amount trachyte. Here, we report mineral chemistry of different basaltic lavas through transect from northern continent (Tokat region, Pontides) to southern continent (Sivas region, Kırşehir block) to deduce the characteristics of the magma chamber processes which are active during the middle Eocene. Basaltic lavas include olivine bearing basalts (Ol-basalt: ± olivine + clinopyroxene + plagioclase); amphibole bearing basaltic andesite (Amp-basaltic andesite: amphibole + clinopyroxene + plagioclase ± biotite) and pyroxene bearing basaltic andesite (Px-basaltic andesite: clinopyroxene + plagioclase). Microlitic, glomeroporphyric and pilotaxitic texture are common. Clinopyroxene phenocrystals (macro ≥ 750 μm and micro ≤300 μm) are common in all three lava series which are investigated by transecting core to rim compositional profiles. They are generally augite and diopside; euhedral to subhedral in shape with oscillatory, normal and reverse zoning patterns. Also, all clinopyroxene phenocrystals are marked by moderately high Mg# (for Ol-basalt: 67-91; avg. 80; Amp-basaltic andesite: 76-83, avg: 80; Px -basaltic andesite 68-95, avg: 81). In Ol-basalt, clinopyroxene phenocrystals show normal zonation (high Mg# cores and low Mg# rims). In Amp-basaltic andesite, clinopyroxenes are generally homogenous in composition with minor variation of Mg# towards the rims. On the contrary, in Px-basaltic andesite, clinopyroxene macro phenocrystals show reverse zonation with the core with low Mg# and the rims with

  8. Sr, Nd, Pb Isotope geochemistry and magma evolution of the potassic volcanic rocks, Wudalianchi, Northeast China (United States)

    Junwen, W.; Guanghong, X.; Tatsumoto, M.; Basu, A.R.


    Wudalianchi volcanic rocks are the most typical Cenozoic potassic volcanic rocks in eastern China. Compositional comparisons between whole rocks and glasses of various occurrences indicate that the magma tends to become rich in silica and alkalis as a result of crystal differentiation in the course of evolution. They are unique in isotopic composition with more radiogenic Sr but less radiogenic Pb.87Sr /86 Sr is higher and143Nd/144Nd is lower than the undifferentiated global values. In comparison to continental potash volcanic rocks, Pb isotopes are apparently lower. These various threads of evidence indicate that the rocks were derived from a primary enriched mantle which had not been subjected to reworking and shows no sign of incorporation of crustal material. The correlation between Pb and Sr suggests the regional heterogeneity in the upper mantle in terms of chemical composition. ?? 1989 Institute of Geochemistry, Chinese Academy of Sciences.

  9. Hydrogen isotope investigation of amphibole and biotite phenocrysts in silicic magmas erupted at Lassen Volcanic Center, California (United States)

    Underwood, S.J.; Feeley, T.C.; Clynne, M.A.


    Hydrogen isotope ratio, water content and Fe3 +/Fe2 + in coexisting amphibole and biotite phenocrysts in volcanic rocks can provide insight into shallow pre- and syn-eruptive magmatic processes such as vesiculation, and lava drainback with mixing into less devolatilized magma that erupts later in a volcanic sequence. We studied four ~ 35 ka and younger eruption sequences (i.e. Kings Creek, Lassen Peak, Chaos Crags, and 1915) at the Lassen Volcanic Center (LVC), California, where intrusion of crystal-rich silicic magma mushes by mafic magmas is inferred from the varying abundances of mafic magmatic inclusions (MMIs) in the silicic volcanic rocks. Types and relative proportions of reacted and unreacted hydrous phenocryst populations are evaluated with accompanying chemical and H isotope changes. Biotite phenocrysts were more susceptible to rehydration in older vesicular glassy volcanic rocks than coexisting amphibole phenocrysts. Biotite and magnesiohornblende phenocrysts toward the core of the Lassen Peak dome are extensively dehydroxylated and reacted from prolonged exposure to high temperature, low pressure, and higher fO2 conditions from post-emplacement cooling. In silicic volcanic rocks not affected by alteration, biotite phenocrysts are often relatively more dehydroxylated than are magnesiohornblende phenocrysts of similar size; this is likely due to the ca 10 times larger overall bulk H diffusion coefficient in biotite. A simplified model of dehydrogenation in hydrous phenocrysts above reaction closure temperature suggests that eruption and quench of magma ascended to the surface in a few hours is too short a time for substantial H loss from amphibole. In contrast, slowly ascended magma can have extremely dehydrogenated and possibly dehydrated biotite, relatively less dehydrogenated magnesiohornblende and reaction rims on both phases. Eruptive products containing the highest proportions of mottled dehydrogenated crystals could indicate that within a few days

  10. The influence of Ryukyu subduction on magma genesis in the Northern Taiwan Volcanic Zone and Middle Okinawa Trough - Evidence from boron isotopes (United States)

    Pi, Ju-Lien; You, Chen-Feng; Wang, Kuo-Lung


    Boron (B) is an excellent geochemical tracer for investigating crustal recycling processes at convergent margins, due to its high fluid mobility under high P-T conditions, distinct elemental abundances and isotopic compositions in the mantle wedge and subducting slabs. The Northern Taiwan Volcanic Zone (NTVZ), wherein the nature of magma genesis has long been a topic of debate, is located at the rear side of the Okinawa Trough (OT), an atypical back-arc rift in the Ryukyu subduction system. In this study, B and B isotopes (δ11B) were measured in 19 volcanic rocks collected from the NTVZ and the middle Okinawa Trough (MOT) to assess the influence of the Ryukyu subduction system on magma genesis. The B concentrations in the MOT and NTVZ volcanic rocks are 5.8 to 13.6 mg/L and 2.2 to 48.6 mg/L, respectively. The large B abundances variation in the NTVZ was caused mainly by variable degrees of partial melting. The Nb/B and δ11B in the MOT have small ranges of 0.5 to 0.6 and - 2.7‰ to 0.2‰, respectively, whereas they range widely from 0.4 to 2.5 and from - 8.6‰ to 2.4‰, respectively in the NTVZ. These Nb/B values suggest that the magma contains a smaller subduction component than that normally observed in arcs, although this component is still more substantial than in a typical back-arc setting. The δ11B results indicate insignificant influence of the subducting Philippine Sea Plate at 2.6 Ma, but it becomes more substantial later in the NTVZ. The mixing proportions of sediment derived fluids in onshore volcanoes in the NTVZ imply a rather heterogeneous mantle wedge near the plate boundary, most likely due to either a heterogeneous source of slab derived fluids or more complicated mantle flow. A substantial B flux from the subducting slab in the incipient back-arc rifting in the MOT and NTVZ may reflect characteristics of a cold, steep and fast subducting slab, which may be capable of carrying volatiles efficiently into greater depth in subduction zones. The

  11. Transient magmatic control in a tectonic domain: the central Aeolian volcanic arc (South Italy)

    KAUST Repository

    Ruch, Joel


    The background stress field in volcanic areas may be overprinted by that produced by transient magmatic intrusions, generating local faulting. These events are rarely monitored and thus not fully understood, generating debate about the role of magma and tectonics in any geodynamic setting. Here we carried out a field structural analysis on the NNW-SSE strike-slip system of the central Aeolian Arc, Italy (Lipari and Vulcano islands) with ages constrained by stratigraphy to better capture the tectonic and magmatic evolution at the local and regional scales. We consider both islands as a single magmatic system and define 5 principal stratigraphic units based on magmatic and tectonic activity. We collected >500 measurements of faults, extension fractures and dikes at 40 sites, mostly NNE-SSW to NNW-SSE oriented with a dominant NS orientation. These structures are governed quasi exclusively by pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral slip, the latter being mostly related to old deposits (>50 ka). We further reconstructed the evolution of the Vulcano-Lipari system during the last ~20 ka and find that it consists of an overall half-graben-like structure, with faults with predominant eastward dips. Field evidence suggests that faulting occurs often in temporal and spatial relation with magmatic events, suggesting that most of the observable deformation derived from transient magmatic activity, rather than from steady regional tectonics. To explain the dominant magmatic and episodic extension in a tectonic dominant domain, we propose a model where the regional N-S trending maximum horizontal stress, responsible for strike-slip activity, locally rotates to vertical in response to transient pressurization of the magmatic system and magma rise below Lipari and Vulcano. This has possibly generated the propagation of N-S trending dikes in the past 1 ka along a 10 km long by 1 km wide crustal corridor, with important

  12. Rhyolite thermobarometry and the shallowing of the magma reservoir, Coso volcanic field, California (United States)

    Manley, C.R.; Bacon, C.R.


    The compositionally bimodal Pleistocene Coso volcanic field is located at the western margin of the Basin and Range province ~ 60 km north of the Garlock fault. Thirty-nine nearly aphyric high-silica rhyolite domes were emplaced in the past million years: one at 1 Ma from a transient magma reservoir, one at ~ 0.6 Ma, and the rest since ~ 0.3 Ma. Over the past 0.6 My, the depth from which the rhyolites erupted has decreased and their temperatures have become slightly higher. Pre-eruptive conditions of the rhyolite magmas, calculated from phenocryst compositions using the two-oxide thermometer and the Al-in-hornblende barometer, ranged from 740??C and 270 MPa (2.7 kbar; ~ 10 km depth) for the ~ 0.6 Ma magma, to 770??C and 140 MPa (1.4 kbar; ~ 5.5 km) for the youngest (~ 0.04 Ma) magma. Results are consistent with either a single rhyolitic reservoir moving upward through the crust, or a series of successively shallower reservoirs. As the reservoir has become closer to the surface, eruptions have become both more frequent and more voluminous.

  13. Postcaldera volcanism and hydrothermal activity revealed by autonomous underwater vehicle surveys in Myojin Knoll caldera, Izu-Ogasawara arc (United States)

    Honsho, Chie; Ura, Tamaki; Kim, Kangsoo; Asada, Akira


    Myojin Knoll caldera, one of the submarine silicic calderas lying on the volcanic front of the northern Izu-Ogasawara arc, has attracted increasing attention since the discovery of a large hydrothermal field called the Sunrise deposit. Although numerous submersible surveys have been conducted in Myojin Knoll caldera, they have not sufficiently explored areas to produce a complete picture of the caldera and understand the origin of the Sunrise deposit. We conducted comprehensive deep-sea surveys using an autonomous underwater vehicle and obtained high-resolution bathymetric and magnetic data and sonar images from ~70% of the caldera. The detailed bathymetric map revealed that faulting and magma eruptions, possibly associated with an inflation-deflation cycle of the magma reservoir during postcaldera volcanism, had generally occurred in the caldera wall. The main dome of the central cone was covered with lava flows and exhibits exogenous growth, which is unusual for rhyolitic domes. The magnetization distribution in the central cone indicates preferential magma intrusion along a NW-SE direction. It is presumed that magma migrated along this direction and formed a rhyolite dome at the foot of the southeastern caldera wall, where the Sunrise deposit occurs. The Sunrise deposit is composed mainly of three ridges extending in slope directions and covers ~400 × ~400 m. Magnetization reduction in the deposit area is small, indicating that the alteration zone beneath the Sunrise deposit is slanting rather than vertical. It is presumed that several slanting and near-vertical volcanic vents serve as pathways of hydrothermal fluid in Myojin Knoll caldera.

  14. A multidisciplinary study on the crustal nature of volcanic conduits and magma reservoirs (United States)

    Flinders, Ashton F.

    Volcanic settings vary widely not only in their eruptive style and products, but in the manner magma travels from deep sources to individual eruptive centers. Imaging these pathways, and their associated crustal reservoirs, provides unique and unprecedented views into these environments. Imaging techniques are varied with the strength of the technique often based on data availability. As such, we focus on two methods---gravity and seismic---in two different settings, each with its own unique volcanic environments, crustal structures, and associated data resources. The first, the Hawaiian Islands, are the most geologically studied hot-spot islands in the world, yet the only large-scale compilation of marine and land gravity data is more than 45 years old. We present a new chain-wide gravity compilation allowing us to locate current and former volcanic centers, major rift zones, a previously suggested volcano, and show that volcanoes along the chain are composed of a small proportion of intrusive material (sourced melt to the surface. We image two zones of reduced velocity, one of which correlates with a proposed extensive zone of mid-crustal partial melt which likely supplies evolved magmas to the surrounding volcanoes and vents, including Mounts St. Helens and Adams.

  15. Segmentation of the Cascade Arc Based on Compositional and Sr and Nd Isotopic Variations in Primitive Volcanic Rocks (United States)

    Schmidt, M. E.; Grunder, A. L.


    defined by Guffanti and Weaver (1988) based on volcanic vent distributions. The tectonic framework of the Cascade Arc is reflected in the composition of erupted primitive magmas that in turn are evidence for variable mantle source domains and melting regimes beneath the arc. Where subduction is orthogonal, calcalkaline magmas dominate (North segment), but where subduction is oblique and the arc is extensional and LKTs dominate (Central segment). Enriched primitive compositions found in the Columbia segment may be due to accreted Columbia Embayment lithospheric mantle. The large degree of variability found at the South segment seems to be related to high water contents in primitive magmas that may be related to deformation of the Gorda Plate, subduction of the Mendocino Fracture Zone and(or) enhanced melting associated with the edge of the plate.

  16. Recurrence rate and magma effusion rate for the latest volcanism on Arsia Mons, Mars (United States)

    Richardson, Jacob A.; Wilson, James A.; Connor, Charles B.; Bleacher, Jacob E.; Kiyosugi, Koji


    Magmatism and volcanism have evolved the Martian lithosphere, surface, and climate throughout the history of Mars. Constraining the rates of magma generation and timing of volcanism on the surface clarifies the ways in which magma and volcanic activity have shaped these Martian systems. The ages of lava flows on other planets are often estimated using impact crater counts, assuming that the number and size-distribution of impact craters per unit area reflect the time the lava flow has been on the surface and exposed to potential impacts. Here we show that impact crater age model uncertainty is reduced by adding stratigraphic information observed at locations where neighboring lavas abut each other, and demonstrate the significance of this reduction in age uncertainty for understanding the history of a volcanic field comprising 29 vents in the 110-km-diameter caldera of Arsia Mons, Mars. Each vent within this caldera produced lava flows several to tens of kilometers in length; these vents are likely among the youngest on Mars, since no impact craters in their lava flows are larger than 1 km in diameter. First, we modeled the age of each vent with impact crater counts performed on their corresponding lava flows and found very large age uncertainties for the ages of individual vents, often spanning the estimated age for the entire volcanic field. The age model derived from impact crater counts alone is broad and unimodal, with estimated peak activity in the field around 130 Ma. Next we applied our volcano event age model (VEAM), which uses a directed graph of stratigraphic relationships and random sampling of the impact crater age determinations to create alternative age models. Monte Carlo simulation was used to create 10,000 possible vent age sets. The recurrence rate of volcanism is calculated for each possible age set, and these rates are combined to calculate the median recurrence rate of all simulations. Applying this approach to the 29 volcanic vents, volcanism

  17. Drilling of Submarine Shallow-water Hydrothermal Systems in Volcanic Arcs of the Tyrrhenian Sea, Italy (United States)

    Petersen, S.; Augustin, N.; de Benedetti, A.; Esposito, A.; Gaertner, A.; Gemmell, B.; Gibson, H.; He, G.; Huegler, M.; Kleeberg, R.; Kuever, J.; Kummer, N. A.; Lackschewitz, K.; Lappe, F.; Monecke, T.; Perrin, K.; Peters, M.; Sharpe, R.; Simpson, K.; Smith, D.; Wan, B.


    Seafloor hydrothermal systems related to volcanic arcs are known from several localities in the Tyrrhenian Sea in water depths ranging from 650 m (Palinuro Seamount) to less than 50 m (Panarea). At Palinuro Seamount 13 holes (Metal enrichment at the top of the deposit is evident in some cores with polymetallic (Zn, Pb, Ag) sulfides overlying more massive and dense pyritic ore. The massive sulfide mineralization at Palinuro Seamount contains a number of unusual minerals, including enargite, tennantite, luzonite, and Ag-sulfosalts, that are not commonly encountered in mid-ocean ridge massive sulfides. In analogy to epithermal deposits forming on land, the occurrence of these minerals suggests a high sulfidation state of the hydrothermal fluids during deposition implying that the mineralizing fluids were acidic and oxidizing rather than near-neutral and reducing as those forming typical base metal rich massive sulfides along mid-ocean ridges. Oxidizing conditions during sulfide deposition can probably be related to the presence of magmatic volatiles in the mineralizing fluids that may be derived from a degassing magma chamber. Elevated temperatures within sediment cores and TV-grab stations (up to 60°C) indicate present day hydrothermal fluid flow. This is also indicated by the presence of small tube-worm bushes present on top the sediment. A number of drill holes were placed around the known phreatic gas-rich vents of Panarea and recovered intense clay-alteration in some holes as well as abundant massive anhydrite/gypsum with only trace sulfides along a structural depression suggesting the presence of an anhydrite seal to a larger hydrothermal system at depth. The aim of this study is to understand the role that magmatic volatiles and phase separation play in the formation of these precious and trace element-rich shallow water (hydrothermal systems in the volcanic arcs of the Tyrrhenian Sea.

  18. From Magma Chamber to Tephra- what can volcanic titanite tell us about pre-eruptive processes? (United States)

    Iddon, Fiona; McLeod, Graham; Dempster, Tim; Walshaw, Richard; Everard, Lucie


    Large volume, apparently homogenous, crystal rich pyroclastic deposits, or so called 'monotonous intermediates' are often considered to represent erupted batholiths. Their formation and life-cycle can be preceded and eruptions triggered by highly complex magma chamber processes, with multiple periods of recharge, mixing and thermal oscillations [1]. This information is difficult to observe, even at the crystal scale due to fragmentation or re-equilibration with subsequent recharge events. Titanite is a geochemically robust mineral that acts as a reservoir for trace elements, in particular the HFSEs and REEs. This ability to act as a primary control on the trace element budget of a melt [2], coupled with its refractory nature, allows titanite to preserve compositional zoning, proven to act as a reliable record of magma chamber conditions even in long-lived plutons [3]. This study extends the use of titanite to volcanic rocks via a coupled micro-textural and geochemical study of titanites from the Fish Canyon Tuff, Colorado. Regarded as the largest ever recorded pyroclastic deposit, it is thought that the batholith-sized magma chamber cooled to a rigid crystalline mush prior to thermal rejuvenation via underplating mafic magma [1]. It is additionally suggested this may have acted as a trigger for the eruption [1]. Results have shown the titanites to possess trace element zoning reflecting changes in melt composition and chamber conditions. Dissolution horizons and inclusion suites additionally provide evidence for multiple changes in temperature and oxygen fugacity aiding the interpretation of pre-eruptive processes. The study is ongoing with investigation of titanite from the Cerro Galan Ignimbrite, Argentina. The deposit again is suggested to have undergone a complex magma chamber growth and recharge history, with further proposals of multiple magma storage locations at different crustal levels [4]. The crystal zoning may provide further evidence for this, however

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

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


    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).

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

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


    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.

  1. Magmatic relationships and ages between adakites, magnesian andesites and Nb-enriched basalt-andesites from Hispaniola: Record of a major change in the Caribbean island arc magma sources (United States)

    Escuder Viruete, J.; Contreras, F.; Stein, G.; Urien, P.; Joubert, M.; Pérez-Estaún, A.; Friedman, R.; Ullrich, T.


    Located in the Cordillera Central of the Dominican Republic, the Late Cretaceous Tireo Fm (TF) records a major change of the magma sources in the Caribbean island arc. It comprises a > 3 km thick sequence of arc-related volcanic and volcano-sedimentary rocks with variable geochemical characteristics. Combined detailed mapping, stratigraphy, geochemistry and U-Pb/Ar-Ar geochronology show that the volcanic rocks of the Tireo Fm include two main volcanic sequences. The lower volcanic sequence is dominated by monotonous submarine vitric-lithic tuffs and volcanic breccias of andesite to basaltic andesite, with minor interbedded flows of basalts and andesites. Fossil and (U-Pb and 40Ar- 39Ar) geochronological data show that arc magmatism in the lower sequence began to accumulate before ˜ 90 Ma, from the Aptian to Turonian. These rocks constitute an island arc tholeiitic suite, derived from melting by fluxing of a mantle wedge with subduction-related hydrous fluids. The upper volcanic sequence is characterized by a spatial and temporal association of adakites, high-Mg andesites, and Nb-enriched basalts, which collectivelly define a shift in the composition of the subduction-related erupted lavas. A dacitic to rhyolitic explosive volcanism with subaerial and episodic aerial eruptions, and sub-volcanic emplacements of domes, characterize mainly this stratigraphic interval. The onset of this volcanism took place at Turonian-Coniacian boundary and continued in the Santonian to Lower Campanian, with minor events in the Late Campanian. Adakites represent melts of the subducting slab, magnesian andesites the product of hybridization of adakite liquids with mantle peridotite, and Nb-enriched basalts melts of the residue from hybridization. We propose a model of oblique ridge subduction at ˜ 90 Ma and possibly subsequent slab window formation, as principal cause of magmatic variations recorded in the Caribbean island arc, above a southwestern-dipping subduction zone.

  2. Systematic Osmium Isotope Binary Mixing Arrays in Arc Volcanism (United States)

    Alves, S.; Alves, S.; Schiano, P.; Capmas, F.; Allegre, C. J.


    reflect a binary mixing process. All trends converge towards unradiogenic compositions similar to those of upper mantle peridotites. These mixing relationships might be ascribed to a general contamination process; however, a single shallow-level process of crustal assimilation is hardly reconciled with the diversity of basements (from oceanic crust to continental crust compositions) of the selected arc volcanoes, the occurrence of the mixing lines for both primary and differentiated samples, the temporal variations observed for a given volcano, and the absence of co-variations between Os contents, isotope ratios, and indices of differentiation. On the other hand, the radiogenic components may be simply explained by varying the amount of oceanic crust and sediments in the source of these arc lavas. Similar mixing relationships are also seen at the sample scale, which suggests that the Os distribution in the magma prevents the mantle unradiogenic Os to equilibrate with the radiogenic Os coming from the subducted materials transferred via fluids or melts.

  3. Andesite petrogenesis in a hybrid arc-rift setting: the Western Trans-Mexican Volcanic Belt (United States)

    Gómez-Tuena, A.; Vázquez-Duarte, A.; Díaz-Bravo, B.; Mori, L.


    The western sector of the Mexican subduction zone is characterized by the steep subduction of one of the youngest slabs on the planet (Rivera plate), and by the existence of a continental rift at ~230 km to the north from the trench (the so-called Tepic-Zacoalco rift, TZR), under which the subducted slab is either extremely deep or even absent (>250 km). The volcanic front is located at ~170 km from the trench and contains abundant potassic-alkaline lamprophyres with strong subduction (Ba/Ta= 1600-6000) and garnet signatures (Gd/Yb= 2-8), that have been recently interpreted as influenced by deep K2O-rich slab melts or supercritical fluids (Gómez-Tuena et al., 2011, GCA). In contrast, the most mafic rocks within the TZR are high-Nb, intraplate-like basalts that appear to derive from low extents of melting of a dryer (Ba/Ta= 800-60) and shallower (Gd/Yb= 2-2.5) mantle source. Even though a simple transition from an arc environment to an extensional tectonic regime is apparent when only the most primitive volcanic rocks are taken into account, the scenario becomes more complicated since at least five stratovolcanoes have been erupting typical arc andesites within the TZR over the last million years (San Juan, Sanganguey, Tepetiltic, Ceboruco and Tequila). Surprisingly, true calc-alkaline basalts that could be parental to andesites have not been found, indicating that andesites may have a direct mantle origin. Indeed, mayor and trace element compositions of volcanic rocks from western Mexico arrange in discrete suites with linear trends that are indicative of mixing, but they form sub-parallel arrays that do not converge to a common primitive basaltic melt, and often follow diverging trends in trace element-ratio plots. Melt-crust interactions likely occurred during magma ascent, since the volcanic rocks frequently include xenoliths and disequilibrium textures, but correlations among isotopic compositions and indexes of fractionation are not clearly observed in the

  4. Precaldera lavas of the southeast San Juan Volcanic Field: Parent magmas and crustal interactions (United States)

    Colucci, M. T.; Dungan, M. A.; Ferguson, K. M.; Lipman, P. W.; Moorbath, S.


    Early intermediate composition volcanic rocks of the Oligocene (circa 34-29 Ma) southeast San Juan volcanic field, southern Colorado, comprise the Conejos Formation. Conejos lavas include both high-K calc-alkaline and alkaline magma series (54-69% SiO2) ranging in composition from basaltic andesite (basaltic trachyandesite) to dacite (trachydacite). The subsequent Platoro caldera complex (29-27 Ma) was superimposed on a cluster of broadly precursory Conejos stratocones. Precaldera volcanism occurred in three pulses corresponding to three time-stratigraphic members: (1) the Horseshoe Mountain member, (2) the Rock Creek member, and (3) the Willow Mountain member. Each member exhibits distinctive phenocryst modes and incompatible trace element contents. Horseshoe Mountain lavas (hornblende-phyric) have relatively low alkali and incompatible element abundances, Rock Creek lavas (anhydrous phenocrysts) and ash-flow tuffs have the highest abundances, and Willow Mountain lavas (diverse mineralogy) are intermediate. All Conejos lavas exhibit low ratios of lead (206Pb/204Pb = 17.5 to 18.2) and neodymium (ɛNd = -8 to -4) isotopes and high 87Sr/86Sr (0.7045 to 0.7056) compared to depleted asthenospheric mantle. These values lie between those of likely mantle compositions and the isotopic composition of Proterozoic crust of the southern Rocky Mountains. Mafic lavas of the Horseshoe Mountain member have the lowest Pb and Nd isotope ratios among Conejos members but trend toward higher isotopic values with increasing degrees of differentiation. Compositions within the Rock Creek series trend toward higher Pb and lower Nd isotope ratios with increasing SiO2. Willow mountain volcanic sequences define diverse chemical-isotopic correlations. We interpret the chemical and isotopic differences observed between mafic lavas of each member to reflect derivation from compositionally distinct mantle derived parent magmas that have experienced extensive deep level crustal contamination

  5. Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption. (United States)

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


    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.

  6. Mixing and mingling in the evolution of andesite dacite magmas; evidence from co-magmatic plutonic enclaves, Taupo Volcanic Zone, New Zealand (United States)

    Cole, J. W.; Gamble, J. A.; Burt, R. M.; Carroll, L. D.; Shelley, D.


    within the magma chambers beneath a typical volcanic arc.

  7. Trans-lithospheric scheme of arc magma transfer and evolution (Invited) (United States)

    Bouilhol, P.; Schmidt, M. W.; Connolly, J. A.; Burg, J.


    Understanding the formation of magmatic arcs requires not only conceiving the formation of primitive arc melts, but also their evolution during migration from the mantle source to the arc. Indeed, the chemical characteristics of arc-melts are acquired during a complex process involving the slab input, the mantle wedge, and transfer of the melt at the base of and in the crust. Because the retrograde thermal regime in the upper portion of the mantle wedge is hostile to melt transport, the dominant mechanism by which melts ascend from their source through the mantle remains uncertain and mainly based on theoretical and exported models from MOR settings because of the scarcity of observations available. Within the lower crust, melts must be efficiently transferred toward higher structural levels to feed plutons and volcanoes but such melt highways are elusive and not always recognized as such. Petro-geochemical and structural analyses conducted on a mantle and lower crust section of the Kohistan Paleo-Island Arc (The Sapat Complex, Pakistan) unravel some aspects of the transfer and evolution of arc-magmas. The dominantly harzburgitic mantle shows a continuum of transport mechanisms ranging from pervasive to fully segregated melt flow, related to the formation of dunitic conduits associated with clinopyroxene-rich zones. Structural observations, linked to rock chemistry and numerical simulations show that primitive melts where transferred via porosity waves within the mantle. This efficient way of forming mantle conduit will drain the primitive mantle source region until melting cease. During this transfer, a competitive series of reaction-crystallization marks the staggering of melt evolution. The crustal section, fed with the same primitive melt, is predominantly composed of meta-plutonics that host kilometer-scale pyroxenite bodies. Within the bodies, sub-vertical magmatic and reactional structures indicate vertical magma percolation accompanied by massive cumulate

  8. Halogen content in Lesser Antilles arc volcanic rocks : exploring subduction recycling (United States)

    Thierry, Pauline; Villemant, Benoit; Caron, Benoit


    Halogens (F, Cl, Br and I) are strongly reactive volatile elements which can be used as tracers of igneous processes, through mantle melting, magma differentiation and degassing or crustal material recycling into mantle at subduction zones. Cl, Br and I are higly incompatible during partial melting or fractional cristallization and strongly depleted in melts by H2O degassing, which means that no Cl-Br-I fractionation is expected through magmatic differenciation [current thesis]. Thus, Cl/Br/I ratios in lavas reflect the halogen content of their mantle sources. Whereas these ratios seemed quite constant (e.g. Cl/Br =300 as seawater), recent works suggest significant variations in arc volcanism [1,2]. In this work we provide high-precision halogen measurements in volcanic rocks from the recent activity of the Lesser Antilles arc (Montserrat, Martinique, Guadeloupe, Dominique). Halogen contents of powdered samples were determined through extraction in solution by pyrohydrolysis and analysed by Ion Chromatography for F and Cl and high performance ICP-MS (Agilent 8800 Tripe Quad) for Cl, Br and I [3,4]. We show that lavas - and mantle sources - display significant vraiations in Cl/Br/I ratios along the Lesser Antilles arc. These variations are compared with Pb, Nd and Sr isotopes and fluid-mobile elements (Ba, U, Sr, Pb etc.) compositions which vary along the arc from a nothern ordinary arc compositions to a southern 'crustal-like' composition [5,6]. These characteristics are attributed to subducted sediments recycling into the mantle wedge, whose contribution vary along the arc from north to south [7,8]. The proportion of added sediments is also related to the distance to the trench as sediment melting and slab dehydration may occur depending on the slab depth [9]. Further Cl-Br-I in situ measurements by LA-ICP-MS in Lesser Antilles arc lavas melt inclusions will be performed, in order to provide better constraints on the deep halogen recycling cycle from crust to

  9. The influence of magmatic differentiation on the oxidation state of Fe in a basaltic arc magma

    Energy Technology Data Exchange (ETDEWEB)

    Kelley, Katherine A.; Cottrell, Elizabeth (Rhode Island); (Smithsonian)


    Subduction zone basalts are more oxidized than basalts from other tectonic settings (e.g., higher Fe{sup 3+}/{Sigma}Fe), and this contrast may play a central role in the unique geochemical processes that generate arc and continental crust. The processes generating oxidized arc magmas, however, are poorly constrained, although they appear inherently linked to subduction. Near-surface differentiation processes unique to arc settings might drive oxidation of magmas that originate in equilibrium with a relatively reduced mantle source. Alternatively, arc magmas could record the oxidation conditions of a relatively oxidized mantle source. Here, we present new measurements of olivine-hosted melt inclusions from a single eruption of Agrigan volcano, Marianas, in order to test the influence of differentiation processes vs. source conditions on the Fe{sup 3+}/{Sigma}Fe ratio, a proxy for system oxygen fugacity (fO{sub 2}). We determined Fe{sup 3+}/{Sigma}Fe ratios in glass inclusions using {mu}-XANES and couple these data with major elements, dissolved volatiles, and trace elements. After correcting for post-entrapment crystallization, Fe{sup 3+}/{Sigma}Fe ratios in the Agrigan melt inclusions (0.219 to 0.282), and their modeled fO{sub 2}s ({Delta}QFM + 1.0 to + 1.8), are uniformly more oxidized than MORB, and preserve a portion of the evolution of this magma from 5.7 to 3.2 wt.% MgO. Fractionation of olivine {+-} clinopyroxene {+-} plagioclase should increase Fe{sup 3+}/{Sigma}Fe as MgO decreases in the melt, but the data show Fe{sup 3+}/{Sigma}Fe ratios decreasing as MgO decreases below 5 wt.% MgO. The major element trajectories, taken in combination with this strong reduction trend, are inconsistent with crystallization of common ferromagnesian phases found in the bulk Agrigan sample, including magnetite. Rather, decreasing Fe{sup 3+}/{Sigma}Fe ratios correlate with decreasing S concentrations, suggesting that electronic exchanges associated with SO{sub 2} degassing may

  10. Geophysical imaging of buried volcanic structures within a continental back-arc basin

    DEFF Research Database (Denmark)

    Stratford, Wanda Rose; Stern, T.A.


    Hidden beneath the ~2 km thick low-velocity volcaniclastics on the western margin of the Central Volcanic Region, North Island, New Zealand, are two structures that represent the early history of volcanic activity in a continental back-arc. These ~20×20 km structures, at Tokoroa and Mangakino, fo...

  11. Geothermal systems in volcanic arcs: Volcanic characteristics and surface manifestations as indicators of geothermal potential and favorability worldwide (United States)

    Stelling, P.; Shevenell, L.; Hinz, N.; Coolbaugh, M.; Melosh, G.; Cumming, W.


    This paper brings a global perspective to volcanic arc geothermal assessments by evaluating trends and correlations of volcanic characteristic and surface manifestation data from world power production sites in subduction zone volcanic settings. The focus of the work was to evaluate volcanic centers individually and as a group in these arcs by correlating various geologic characteristics with known potential to host electricity grade geothermal systems at the volcanic centers. A database was developed that describes key geologic factors expected to be indicative of productive geothermal systems in a global training set, which includes all 74 subduction zone volcanic centers world-wide with current or proven power production capability. Importantly, this data set only contains data from subduction zone volcanoes and contains no negative cases, limiting the populations of any statistical groups. Regardless, this is the most robust geothermal benchmark training set for magmatic-heated systems to date that has been made public. The work reported here is part of a larger project that included data collection, evaluation, correlations and weightings, fairway and favorability modeling and mapping, prediction of blind systems, and uncertainty analysis to estimate errors associated with model predictions. This first paper describes volcano characteristics, compositions and eruption ages and trends along with surface manifestation observations and temperatures as they relate to known power producing systems. Our findings show a strong correlation between the presence and size of active flank fumarole areas and installed power production. Additionally, the majority of volcanic characteristics, including long-held anecdotal correlations related to magmatic composition or size, have limited to no correlation with power production potential. Notable exceptions are correlations between greater power yield from geothermal systems associated with older (Pleistocene) caldera systems

  12. Experimental analysis of bubble-driven magma motion in a volcanic conduit and how it affects lava lake sustainability (United States)

    Pansino, S. G.; Calder, E. S.; Menand, T.


    The effect of bubble ascent dynamics on magma motion within a conduit has not previously been well studied. Investigation of bubble dynamics is undertaken using an analogue model for magma convection in a volcanic conduit, representing the upper-most section where large bubbles or gas slugs can be present. In the experiments, bubbles rise through an initially stagnant medium in a cylindrical tube and the resulting liquid descent velocity (liquid flux) is measured. The effects of gas flux and liquid viscosity on liquid flux are determined. It is shown that liquid flux depends on gas flux and on the two-phase flow regime. The induced liquid flux is an order of magnitude higher when the two-phase flow regime is turbulent rather than laminar. For each flow regime, scaling analysis is used to describe how the liquid flux changes with gas flux (using experimentally-derived data). The liquid flux is roughly 15% of the gas flux in the turbulent regime and 1% of the gas flux in the laminar regime. These models are then applied to field and remote sensing data from selected volcanoes to determine how the magma flux estimation changes with consideration of bubble dynamics. Bubble-driven liquid motions can have a significant effect on magma convection in low-viscosity systems (less than 103 Pa*s), affecting the shallowest hundreds to tens of meters of magma in the conduit. In higher-viscosity magmas, these effects are more suppressed, causing laminar flow proportions of magma flux. Keywords: magma convection, lava lakes, bubble-driven convection, persistent volcanism, gas dynamics, two-phase flow, degassing

  13. Landscape evolution within a retreating volcanic arc, Costa Rica, Central America (United States)

    Marshall, Jeffrey S.; Idleman, Bruce D.; Gardner, Thomas W.; Fisher, Donald M.


    Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and landscape evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls landscape evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 40Ar/39Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tárcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character.

  14. The trace-element characteristics of Aegean and Aeolian volcanic arc marine tephra (United States)

    Clift, Peter; Blusztajn, Jerzy


    High-silica volcanic ashes are found within deep-sea sediments throughout the Eastern Mediterranean. Although coring by Ocean Drilling Program has penetrated Lower Pliocene (˜4 Ma) sediments, few ashes older than 400 k.y. have been recovered, suggesting a young initiation to subaerial Aegean Arc volcanism. Ashes derived from the Aegean volcanic front were cored south and east of the arc, and are typified by medium-K, calc-alkaline major-element compositions, contrasting with high-K ashes from the Aeolian Arc found in the Ionian Sea and as far east as Crete. Ion microprobe analysis of individual glass shards shows that all the ashes have a light rare earth element (LREE)-enriched pattern after normalizing against a chondrite standard. Aeolian Arc-derived ashes show greater enrichment than those from the Aegean area. Within the latter set, two groups are discernible, a mildly enriched set similar to the volcanoes of the arc volcanic front, and a more enriched group corresponding to lavas from the backarc region or possible from western Anatolia. Multi-element `spider diagrams' also show a bimodal division of enriched and depleted Aegean ashes, possibly caused by source depletion due to melt extraction in the Aegean backarc followed by remelting under the volcanic front. Relative Nb depletion, a characteristic of arc volcanism, is seen to be modest in Aegean and non-existent in Aeolian ashes. Using B/Be as a proxy for the flux of material from the subducting slab, this influence is seen to be low in the Aeolian Arc but higher than at Vesuvius. B/Be is higher again in the Aegean Arc. These differences may reflect the rate of subduction in each system. Data suggest caution is required when correlating ashes solely on the basis of major elements, as alkaline ashes from the central part of the study may be derived from Italy or from the Aegean backarc.

  15. Rifting, volcanism, and magma genesis at the northern end of the Danakil Depression: The Alid volcanic center of Eritrea (Invited) (United States)

    Lowenstern, J. B.; Clynne, M. A.; Duffield, W. A.; Smith, J. G.; Woldegiorgis, L.


    The Alid volcanic center, Eritrea, is a structural dome formed by subvolcanic intrusion of pyroxene-bearing rhyolite, subsequently erupted as pumice and lava, during the period 40,000 to 15,000 years ago. The northern Danakil Depression is thought to be the most recently developed part of the Afar, and represents an active continental rift subparallel to the Red Sea spreading center. The location of Alid may be controlled by the intersection of the structural grain of the NE trending Senafe-Alid lineament with the NW trending Danakil Depression. Our work began as a geothermal assessment (Duffield et al., 1997, USGS Open-file 97-291) that found evidence for 300 meters of vertical offset of early Pleistocene basalt flows over the past 1.1 million years. Structural uplift at Alid reveals Proterozoic metamorphic basement rocks overlain by Quaternary marine sediments including siltstone, and sandstones interbedded with pillow lavas and hyaloclastites. These units are overlain by subaerial amphibole-bearing rhyolites (dated at ~200 ka), basalts, and andesites that were deposited on a relatively flat surface and before significant growth of a large volcanic edifice. About 1 km of structural uplift of the marine sediments began 40 ka when pyroxene-bearing rhyolitic magma intruded close to the surface. Uplift was accompanied by contemporaneous eruptions of pumice falls and more common obsidian domes and lava flows over the next 20,000 years. Uplift apparently ceased after eruption of pyroclastic flows and vent-clogging lava about 15 ka. The pumice deposits contain cognate xenoliths of granophyric pyroxene-granite (Lowenstern et al., 1997, J. Petrol. 38:1707). Our geochronology of the uplift is consistent with the idea that growth of the Alid volcanic center played a role in isolating the southern Danakil Depression from the Red Sea, helping to initiate dessication of the rift and producing the young evaporites found today at Baddha and further south at Dallol. U

  16. The Relationship Between the Signature of Subducted Sediments in Volcanic Gases and Volatile Flux along the Central American Volcanic Arc (United States)

    Fischer, T. P.; Zimmer, M. M.; Hilton, D. R.; Shaw, A. M.; Cameron, B. I.; Walker, J. A.; Molina C., E.


    Volcanic arcs are locations where elements are recycled from the Earth's surface into the mantle. Fluxes of volcanic volatile emissions can vary significantly along a single arc and a fundamental aim of arc-related studies is to quantify these variations and compare them to subduction zone parameters. As part of the Central American arc study, we report N2, He and Ar abundance relationships and N-isotope ratios for 7 volcanic centers in Guatemala to complement on-going studies in Costa Rica. In Guatemala, the arc crust is thicker and older than in Costa Rica and the entire sediment sequence on the down-going plate is likely to contribute to the slab flux. Sulfur dioxide fluxes vary significantly along the arc (2001 measurements): in the Guatemala segment, Fuego and Pacaya emit a total of ~1500 t/day whereas in Costa Rica, Arenal and Poas are emitting only ~190 t/day. The Guatemalan volcanic centers of Amatitlan-Pacaya, Fuego, Moyuta, Tecuamburro, Amatitlan, Zunil and San Marcos have N2/He ratios ranging from 2200 - 8100, typical for arc-related fluids. N2/Ar ratios (40-500) and the high N2/He indicate addition of N2 from subducted sediments or arc crust to a mantle derived component (N2/He Guatemala are in contrast to typical mantle-derived N2/He ratios (160 - 600) measured at Poas and Turialba, Costa Rica. Nitrogen isotope ratios for the Guatemalan volcanic centers range from δ 15N = + 1.0‰ for San Marcos to + 5.8‰ for Fuego (δ 15N air = 0.0‰ ), indicating a sedimentary nitrogen component. The mantle-derived N2/He ratios for Poas (- 3.0‰ ) are consistent with a more mantle-like δ 15N. In Guatemala, the highest 3He/4He ratios (7.6 for Pacaya and 7.3 Ra for Fuego) correlate with the lowest N2/He ratios (1500 and 2100) and high δ 15N values (+3.8‰ and +5.8‰ ). Mixing relationships (3He/4He and δ 15N) suggest that at Fuego and Pacaya up to 20% of the nitrogen is of subducted sedimentary origin, contrary to Poas and Turialba where the slab derived

  17. Is gold solubility subject to pressure variations in ascending arc magmas? (United States)

    Jégo, Sébastien; Nakamura, Michihiko; Kimura, Jun-Ichi; Iizuka, Yoshiyuki; Chang, Qing; Zellmer, Georg F.


    Magmas play a key role in the genesis of epithermal and porphyry ore deposits, notably by providing the bulk of ore metals to the hydrothermal fluid phase. It has been long shown that the formation of major deposits requires a multi-stage process, including the concentration of metals in silicate melts at depth and their transfer into the exsolved ore fluid in more superficial environments. Both aspects have been intensively studied for most of noble metals in subsurface conditions, whereas the effect of pressure on the concentration (i.e., solubility) of those metals in magmas ascending from the sublithospheric mantle to the shallow arc crust has been quite neglected. Here, we present new experimental data aiming to constrain the processes of gold (Au) dissolution in subduction-linked magmas along a range of depth. We have conducted hydrous melting experiments on two dacitic/adakitic magmas at 0.9 and 1.4 GPa and ∼1000 °C in an end-loaded piston cylinder apparatus, under fO2 conditions close to NNO as measured by solid Co-Pd-O sensors. Experimental charges were carried out in pure Au containers, the latter serving as the source of gold, in presence of variable amounts of H2O and, for half of the charges, with elemental sulfur (S) so as to reach sulfide saturation. Au concentrations in melt quenched to glass were determined by LA-ICPMS. When compared to previous data obtained at lower pressures and variable redox conditions, our results show that in both S-free and sulfide-saturated systems pressure has no direct, detectable effect on melt Au solubility. Nevertheless, pressure has a strong, negative effect on sulfur solubility. Since gold dissolution is closely related to the behavior of sulfur in reducing and moderately oxidizing conditions, pressure has therefore a significant but indirect effect on Au solubility. The present study confirms that Au dissolution is mainly controlled by fO2 in S-free melts and by a complex interplay of fO2 and melt S2

  18. Magma types and mantle sources of the Bárðarbunga volcanic system, Iceland (United States)

    Halldórsson, Sæmundur; Rubin, Ken; Sverrisdóttir, Guðrún; Sigurðsson, Gylfi


    The Bárðarbunga volcanic system (BVS) represents one of the largest volcanic systems in Iceland, extending ~190 km from the northern boundary of Torfajökull in the south to Dyngjufjöll Ytri in the north, and intersecting the largely ice-covered Bárðarbunga volcano. The extensive length of the BVS thus allows sampling of an unusually large section of the mantle underlying Iceland's Eastern rift zone. Perhaps surprisingly, the degree of mantle source heterogeneity beneath the BVS remains poorly known. We have recently undertaken a detailed study of the BVS because such data are fundamental for understanding the magmatic history and magma delivery system beneath of the BVS, including those that led to recent volcanism north of Dyngjujökull. Here, we present major and trace element analyses, as well as high-precision Pb isotope analyses, of several Holocene lava flows from the Dyngjuháls area and from rocks representing the basement, flanks and nunataks of the ice-free part of the Bárðarbunga volcano. We compare these data to those on a suite of recently collected fissure basalts from the Veiðivötn fissure swarm in the south and the new lava north of Dyngjujökull in order to study the geochemical characteristics of the BVS as a whole. The BVS has generated fairly primitive tholeiites (MgO ~6-9 wt.%) throughout the Holocene. Evolved basaltic compositions (MgO ≤6 wt.%) that are often associated with large and mature caldera systems in Iceland (e.g., Krafla and Askja), appear to be notably absent in the BVS within our current sample set (although might still exist in the largely ice-covered Bárðarbunga volcano). Significantly, no highly evolved rocks (dacite, rhyolite) have been associated with the BVS. It is therefore unlikely that a long-lived and relatively shallow (18.40. In contrast, subglacial formations in the Dyngjuháls region, form a single trend with 206Pb/204Pb always melts to the BVS, in different proportions in space and time. However

  19. Open-system behaviour of magmatic fluid phase and transport of copper in arc magmas at Krakatau and Batur volcanoes, Indonesia (United States)

    Agangi, Andrea; Reddy, Steven M.


    The Sunda arc of Indonesia is an excellent example of how volcanic processes at convergent plate margins affect the distribution of metals and control the distribution of ore deposits. In this paper, we report microtextural observations and microanalytical data (SEM-EDS and LA-ICP-MS) of silicate and sulfide melt inclusions from fresh samples of volcanic rocks from the 2008 eruption of Mt. Krakatau and 1963 eruption of Mt. Batur, Sunda arc, Indonesia that bear implications on the concentration and transport of Cu and other chalcophile elements in mafic-intermediate magmas in arc settings. These multi-phase inclusions contain glass, amphibole and plagioclase, together with co-trapped apatite, magnetite, sulfides and lobed, drop-like Fe-oxide. We observed two stages of sulfide formation: 1) early-formed sulfide globules (pyrrhotite and intermediate solid solution), which derived from an immiscible sulfide melt and only occur as inclusions in phenocrysts; and 2) late-formed, irregular Cu-rich sulfides (intermediate solid solution to bornite), which were deposited in the presence of an aqueous fluid, and are contained as fluid phase precipitates in vapour bubbles of melt inclusions and in vesicles, as well as finely dispersed grains in the groundmass. Microtextural observations and X-ray elemental maps show that interaction between sulfide globules and aqueous fluid resulted in partial oxidation and transfer of Cu between the fluid and the sulfide phase. A compilation of whole-rock analyses from the Sunda arc indicates that Cu reaches 250-300 ppm in mafic samples (SiO2 ≤ 52 wt.%), and then suddenly drops with progressive fractionation to MS analyses of whole multi-phase melt inclusions hosted in olivine, pyroxene and plagioclase indicate variable Cu and S contents (Cu up to 6000 ppm), which do not correlate with fractionation indicators (e.g. SiO2, MgO, Rb), consistent with co-trapping of Cusbnd S phases with silicate melt. The highest Cu concentrations, Cu/S and

  20. Prodigious emission rates and magma degassing budget of major, trace and radioactive volatile species from Ambrym basaltic volcano, Vanuatu island Arc (United States)

    Allard, P.; Aiuppa, A.; Bani, P.; Métrich, N.; Bertagnini, A.; Gauthier, P.-J.; Shinohara, H.; Sawyer, G.; Parello, F.; Bagnato, E.; Pelletier, B.; Garaebiti, E.


    Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H2O, CO2, SO2 and H2S in crater rim emissions, coupled with filter-pack determination of SO2, halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by its two main active craters, Benbow and Marum. These share a high water content ( 93 mol%), similar S/Cl, Cl/F, Br/Cl molar ratios, similar (210Po/210Pb) and (210Bi/210Pb) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO2/SO2 ratio (1.0 and 5.6-3.0, respectively) is attributed to deeper gas-melt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO2 plume flux (90 kg s- 1 or 7800 tons d- 1) demonstrates a prevalent degassing contribution ( 65%) of Benbow crater in that period and allows us to quantify the total volatile fluxes during medium-level eruptive activity of the volcano. Results reveal that Ambrym ranks among the most powerful volcanic gas emitters on Earth, producing between 5% and 9% of current estimates for global subaerial volcanic emissions of H2O, CO2, HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO2, HF, HBr, Hg, 210Po and 210Pb, and over 30% of Ag, Se and Sn. Global flux estimates thus need to integrate its contribution and be revised accordingly. Prodigious gas emission from Ambrym does not result from an anomalous volatile enrichment nor a differential excess degassing of its feeding basalt: this latter contains relatively modest

  1. Behavior of volatiles in arc volcanism : geochemical and petrologic evidence from active volcanoes in Indonesia

    NARCIS (Netherlands)

    Hoog, J.C.M. de


    Large amounts of material are recycled along subduction zones by uprising magmas, of which volcanoes are the surface expression. This thesis focuses on the behavior of volatiles elements (S, Cl, H) during these recycling processes. The study area is the Indonesian arc system, which hosts

  2. Behavior of volatiles in arc volcanism : geochemical and petrologic evidence from active volcanoes in Indonesia

    NARCIS (Netherlands)

    Hoog, J.C.M. de


    Large amounts of material are recycled along subduction zones by uprising magmas, of which volcanoes are the surface expression. This thesis focuses on the behavior of volatiles elements (S, Cl, H) during these recycling processes. The study area is the Indonesian arc system, which hosts

  3. Continental arc volcanism as the principal driver of icehouse-greenhouse variability (United States)

    McKenzie, N. Ryan; Horton, Brian K.; Loomis, Shannon E.; Stockli, Daniel F.; Planavsky, Noah J.; Lee, Cin-Ty A.


    Variations in continental volcanic arc emissions have the potential to control atmospheric carbon dioxide (CO2) levels and climate change on multimillion-year time scales. Here we present a compilation of ~120,000 detrital zircon uranium-lead (U-Pb) ages from global sedimentary deposits as a proxy to track the spatial distribution of continental magmatic arc systems from the Cryogenian period to the present. These data demonstrate a direct relationship between global arc activity and major climate shifts: Widespread continental arcs correspond with prominent early Paleozoic and Mesozoic greenhouse climates, whereas reduced continental arc activity corresponds with icehouse climates of the Cryogenian, Late Ordovician, late Paleozoic, and Cenozoic. This persistent coupled behavior provides evidence that continental volcanic outgassing drove long-term shifts in atmospheric CO2 levels over the past ~720 million years.

  4. Geophysical Evidence for the Locations, Shapes and Sizes, and Internal Structures of Magma Chambers beneath Regions of Quaternary Volcanism (United States)

    Iyer, H. M.


    This paper is a review of seismic, gravity, magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume. A dramatic decrease in density and seismic velocity, and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks. The geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock. Although seismic refraction techniques, with sophisticated instrumentation and analytical procedures, are routinely used for detailed studies of crustal structure in volcanic regions, their application for magma detection has been quite limited. In one study, in Yellowstone National Park, U.S.A., fan-shooting and time-term techniques have been used to detect an upper-crustal magma chamber. Attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in Kamchatka. Strong attenuation of shear waves from regional earthquakes, interpreted as a diffraction effect, has been used to model magma chambers in Alaska, Kamchatka, Iceland, and New Zealand. One of the most powerful techniques in modern seismology, the seismic reflection technique with vibrators, was used to confirm the existence of a strong reflector in the crust near Socorro, New Mexico, in the Rio Grande Rift. This reflector, discovered earlier from data from local earthquakes, is interpreted as a sill-like magma body. In the Kilauea volcano, Hawaii, mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle. On the other hand, in the Usu volcano, Japan, the magma conduits are delineated by zones of seismic quiescence. Three-dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and

  5. The Dras arc: two successive volcanic events on eroded oceanic crust (United States)

    Reuber, Ingrid


    The Dras arc is recognized as a volcanic arc system in the western part of the Indus suture zone and it constitutes the link between the Ladakh batholith and the Kohistan arc. This study is based on detailed mapping of the area between Dras, Kargil and Sanku which revealed the following: (1) The ultramafics of Dras and Thasgam can be followed across the Suru Dras ridge and are not intrusive into the arc volcanics, but instead constitute the most probably oceanic substratum of these volcanics. (2) Successive volcanic events are distinguished: (a) Dras I is a variable volcaniclastic series rich in slates and carbonates, which can probably be assigned to the Albo-Cenomanian, as dated by orbitolines. This series is intruded by gabbro, diorite and granite and is deformed, essentially in the northern part. It is unconformably overlain by (b) the Dras II pyroclastics which grade southward into volcanic breccia and thus enable the location of the centres of volcanic activity during this younger period.

  6. Geology and geochemistry characteristics of the Chiapanecan Volcanic Arc (Central Area), Chiapas Mexico (United States)

    Mora, J. C.; Jaimes-Viera, M. C.; Garduño-Monroy, V. H.; Layer, P. W.; Pompa-Mera, V.; Godinez, M. L.


    The Chiapanecan Volcanic Arc (CVA), located in the central portion of the State of Chiapas, is a 150 km stretch of volcanoes irregularly aligned in the northwest direction between two great volcanic features: the Trans-Mexican Volcanic Belt to the northwest and the Central American Volcanic Arc to the southeast. The CVA is located in a complex zone marking the interaction of the North American, Caribbean and Cocos plates, near the Motagua-Polochic fault system, the boundary between North American and Caribbean plates. The central part of the CVA is composed of an irregular northwest alignment of at least 10 volcanic structures generally lying along NNW-SSE-trending faults splayed from the Motagua-Polochic system. Among the structures there are seven volcanic domes (Huitepec, Amahuitz, La Iglesia, Mispía, La Lanza, Venustiano Carranza and Santotón), one explosion crater (Navenchauc), one collapse structure (Apas), and one dome complex (Tzontehuitz). In the majority of the structures there is a clear resurgence with the formation of several domes in the same structure, with the destruction of previous domes (Navenchauc) or with the formation of new explosion craters or collapse structures (Apas). The volcanic activity in the CVA was mainly effusive accompanied by explosive and phreatomagmatic events and is characterized by volcanic domes accompanied by block-and-ash-flows, ash flows with accretionary lapilli, falls, and pumice flows. The volcanic structures and deposits are calcalkaline in composition with a medium to high content of potassium. CVA volcanic rocks vary from andesite to dacite with SiO 2 between 57 and 66 wt.%, show low concentrations of Ti, P, Nb and Ta, are enriched in Light Rare Earths, depleted in Heavy Rare Earths, and show a small Eu anomaly; all indicative of arc-related volcanism associated with subduction of the Cocos plate under the North American plate, but complicated by the geometry of the plate boundary fault system.

  7. Magma evolution and ascent at the Craters of the Moon and neighboring volcanic fields, southern Idaho, USA: implications for the evolution of polygenetic and monogenetic volcanic fields (United States)

    Putirka, Keith D.; Kuntz, Mel A.; Unruh, Daniel M.; Vaid, Nitin


    The evolution of polygenetic and monogenetic volcanic fields must reflect differences in magma processing during ascent. To assess their evolution we use thermobarometry and geochemistry to evaluate ascent paths for neighboring, nearly coeval volcanic fields in the Snake River Plain, in south-central Idaho, derived from (1) dominantly Holocene polygenetic evolved lavas from the Craters of the Moon lava field (COME) and (2) Quaternary non-evolved, olivine tholeiites (NEOT) from nearby monogenetic volcanic fields. These data show that NEOT have high magmatic temperatures (1205 + or - 27 degrees C) and a narrow temperature range (50 degrees C). Prolonged storage of COME magmas allows them to evolve to higher 87Sr/86Sr and SiO2, and lower MgO and 143Nd/144Nd. Most importantly, ascent paths control evolution: NEOT often erupt near the axis of the plain where high-flux (Yellowstone-related), pre-Holocene magmatic activity replaces granitic middle crust with basaltic sills, resulting in a net increase in NEOT magma buoyancy. COME flows erupt off-axis, where felsic crustal lithologies sometimes remain intact, providing a barrier to ascent and a source for crustal contamination. A three-stage ascent process explains the entire range of erupted compositions. Stage 1 (40-20 km): picrites are transported to the middle crust, undergoing partial crystallization of olivine + or - clinopyroxene. COME magmas pass through unarmored conduits and assimilate 1% or less of ancient gabbroic crust having high Sr and 87Sr/86Sr and low SiO2. Stage 2 (20-10 km): magmas are stored within the middle crust, and evolve to moderate MgO (10%). NEOT magmas, reaching 10% MgO, are positively buoyant and migrate through the middle crust. COME magmas remain negatively buoyant and so crystallize further and assimilate middle crust. Stage 3 (15-0 km): final ascent and eruption occurs when volatile contents, increased by differentiation, are sufficient (1-2 wt % H2O) to provide magma buoyancy through the

  8. Evaluation of the ongoing rifting and subduction processes in the geochemistry of magmas from the western part of the Mexican Volcanic Belt (United States)

    Verma, Surendra P.; Pandarinath, Kailasa; Rivera-Gómez, M. Abdelaly


    A compilation of new and published geochemical data for 1512 samples of volcanic rocks from the western part of the Mexican Volcanic Belt was first subdivided according to the age group (136 samples of Miocene and 1376 samples of Pliocene-Holocene). Rocks of the younger group were then subdivided as Rift (1014 samples from the triple-rift system) and No Rift (362 samples outside of the triple-rift system) or Near Trench (937 samples) and Far Trench (439 samples) magmas. These subdivisions were considered separately as basic, intermediate, and acid magmatic rocks. The application of the conventional and multidimensional techniques confirmed the great tectonic and geochemical complexity of this region. The presence of oceanic-type basalts suggested to result from a mantle plume was not confirmed from the tectonomagmatic multidimensional diagrams. The Miocene rocks, which are present at the surface far from the Middle-America Trench, showed a likely continental rift setting in most diagrams for basic rocks and a continental arc setting for intermediate rocks. These differences can be explained in terms of the petrogenetic origin of the magmas. Unlike the current thinking, the triple-rift system seems to have influenced the chemistry of Pliocene-Holocene basic rocks, which indicated a continental rift setting. The Pliocene-Holocene intermediate and acid rocks, however, did not show such an influence. The Pliocene-Holocene basic rocks indicated a continental rift setting, irrespective of the Near Trench and Far Trench subdivision because numerous Near Trench rocks also lie in the triple-rift and graben systems. However, the intermediate rocks having a crustal component in their genesis indicated a continental arc (Near Trench) or a transitional arc to within-plate setting (Far Trench). The acid rocks having a crustal component also suggested a continental arc (Near Trench) or a transitional setting (Far Trench). The application of the tectonomagmatic multidimensional

  9. Basalt-Limestone and Andesite-Limestone Interaction in the Arc Crust - Implications for Volcanic Degassing of CO2 (United States)

    Carter, L. B.; Dasgupta, R.


    Volcanically emitted CO2 is generally mantle-derived, but high degassing rates at some arcs (e.g. Merapi [1] and Colli Albani Volcanic District [2]) are thought to be affected by magma-carbonate interaction in the upper plate. However, the effects of depth, temperature, and composition on this process are poorly known. We experimentally simulated magma (50%)-limestone (50%) wallrock interactions at 0.5-1.0 GPa, 1100-1200 °C using pure calcite and a hydrous (~3-5 wt.% H2O) melt (basalt, andesite, or dacite). At 1.0 GPa, 1200 °C starting melts are superliquidus, whereas in the presence of calcite, Ca-rich cpx ± Ca-scapolite are produced. With increasing T, basalt-calcite interaction causes the melt, on a volatile-free basis, to become silica-poor and Ca-rich with alumina decreasing as cpx becomes more CaTs-rich. The same trend is seen with all starting melt compositions as P decreases at a constant T (1200 °C), producing melts similar to ultracalcic (CaO/Al2O3>>1) melt inclusions found in arc settings. Shifting from basalt to andesite has little effect on SiO2 and CaO of the reacted melt (e.g. 37 wt.% SiO2, 42 wt.% CaO at 0.5 GPa, 1200 °C), whereas Al2O3 of andesite-derived reacted melt is lower, likely a result of lower alumina in the starting andesite. Wall-rock calcite consumption is observed to increase with increasing T, decreasing P, and increasing melt XSiO2. At 0.5 GPa between 1100 and 1200 °C, our basalt experiments yield carbonate assimilation from 22 to 48 wt.%. This decreases to 20 wt.% at 1.0 GPa, 1200 °C, whereas an andesitic composition assimilates 59 to 52 wt.% from 0.5 to 1.0 GPa at 1200 °C. The higher assimilation in andesite-added runs at high-T is because of lower silicate liquidus as evidenced by lower modal proportion or absence of cpx ± scapolite. Using a magma flux rate estimated for Mt. Vesuvius [3], we obtain a CO2 outflux for a single such volcano experiencing arc magma-calcite reaction [4] of at least 2-4% of the present

  10. Application of Clinopyroxene Chemistry to Interpret the Physical Conditions of Ascending Magma, a Case Study of Eocene Volcanic Rocks in the Ghohrud Area (North of Isfahan

    Directory of Open Access Journals (Sweden)

    Mohammad Sayari


    Full Text Available Introduction Volcanic rocks with a porphyritic texture have experienced two crystallization stages. The first is slow, resulting in phenocrysts, and the second, which took place at, or near the surface, or during intrusion into a cooler body of rock, result in a groundmass of glass, or fine crystals. The pressure and temperature history of a magma during crystallization is recorded in the chemical composition of the phenocrysts during both stages. These phenocrysts provide valuable data about the physicochemical conditions of the parent magma during the process of crystallization. The composition of clinopyroxene (cpx reflects not only the chemical condition and therefore the magmatic series, but also the physical conditions, i.e., temperature and pressure of a magma at the time when clinopyroxene crystallized. The Ghohrud area lies in the middle part of the Urumieh-Dokhtar Magmatic Arc , which is part of a much larger magmatic province extending in a vast region of convergence between Arabia and Eurasia north of the Zagros-Bitlis suture zone (Dilek et al., 2010. In the Ghohrud area, north of Isfahan, exposed Eocene volcanic rocks belong to the first pulse of Cenozoic volcanism of Iran (Sayari, 2015, ranging in composition from andesitic basalt to basalt. The basaltic rocks of the Ghohrud area are composed mainly of plagioclase phenocrysts surrounded by smaller crystals of clinopyroxene in a groundmass of microlites, glass and opaques. In this study, the clinopyroxene and plagioclase of these rocks were analyzed in order to estimate the physicochemical conditions of the parent magmas. Results Clinopyroxene and plagioclase phenocrysts of nineteen samples were analyzed with the electron microprobe. The chemical compositions of the clinopyroxenes were used to estimate both the chemical evolution and temperature and pressure conditions of the magmas during crystallization, using SCG, a specialized software for clinopyroxene thermobarometry (Sayari

  11. Bromine release during Plinian eruptions along the Central American Volcanic Arc (United States)

    Hansteen, T. H.; Kutterolf, S.; Appel, K.; Freundt, A.; Perez-Fernandez, W.; Wehrmann, H.


    Volcanoes of the Central American Volcanic Arc (CAVA) have produced at least 72 highly explosive eruptions within the last 200 ka. The eruption columns of all these “Plinian” eruptions reached well into the stratosphere such that their released volatiles may have influenced atmospheric chemistry and climate. While previous research has focussed on the sulfur and chlorine emissions during such large eruptions, we here present measurements of the heavy halogen bromine by means of synchrotron radiation induced micro-XRF microanalysis (SR-XRF) with typical detection limits at 0.3 ppm (in Fe rich standard basalt ML3B glass). Spot analyses of pre-eruptive glass inclusions trapped in minerals formed in magma reservoirs were compared with those in matrix glasses of the tephras, which represent the post-eruptive, degassed concentrations. The concentration difference between inclusions and matrix glasses, multiplied by erupted magma mass determined by extensive field mapping, yields estimates of the degassed mass of bromine. Br is probably hundreds of times more effective in destroying ozone than Cl, and can accumulate in the stratosphere over significant time scales. Melt inclusions representing deposits of 22 large eruptions along the CAVA have Br contents between 0.5 and 13 ppm. Br concentrations in matrix glasses are nearly constant at 0.4 to 1.5 ppm. However, Br concentrations and Cl/Br ratios vary along the CAVA. The highest values of Br contents (>8 ppm) and lowest Cl/Br ratios (170 to 600) in melt inclusions occur across central Nicaragua and southern El Salvador, and correlate with bulk-rock compositions of high Ba/La > 85 as well as low La/Yb discharged 700 kilotons of Br. On average, each of the remaining 21 CAVA eruptions studied have discharged c.100 kilotons of bromine. During the past 200 ka, CAVA volcanoes have emitted a cumulative mass of 3.2 Mt of Br through highly explosive eruptions. There are six periods in the past (c. 2ka, 6ka, 25ka, 40ka, 60ka, 75

  12. Halogens behaviours in Magma Degassing: Insights into Eruptive Dynamics, Hydrothermal Systems and Atmospheric Impact of Andesitic Volcanism (United States)

    Villemant, B.; Balcone, H.; Mouatt, J.; Michel, A.; Komorowski, J.; Boudon, G.


    Shallow degassing of H2O in andesitic magmas determines the eruptive styles of volcanic eruptions and contributes to the hydrothermal systems developed around active volcanoes. Halogens behaviour during magma degassing primarily depends on their incompatible behaviour in the melts and on water solubility. Thus, residual contents of halogens in volcanic juvenile vitric clasts may be used as tracers of H2O degassing processes during explosive and effusive eruptions. Because of the large range of water-melt partition coefficients of halogens and their relatively low diffusion coefficients, a comparison of F, Cl, Br and I contents in volcanic clasts in function of their vesicularity and micro-cristallinity allows to precisely model the main degassing processes and to establish constraints on pre-eruptive conditions. Halogens acids (HCl, HBr and HI) extracted in the vapour phase have much more complex behaviours because of their high solubility in low temperature thermal waters, their variable condensation temperatures and their very high reactivity when mixed with low temperature and oxidizing atmospheric gases. A comparison of model compositions of high temperature gases with the composition of thermal waters, and gases from fumaroles or plumes of active volcanoes allows to characterise the shallow volcanic system and its evolutionary states. Variable halogen behaviours are discussed for a variety of eruption types (plinian, vulcanian and dome-forming) and active volcanic systems from the Lesser Antilles (Montagne Pelee, Soufrière of Guadeloupe, Soufriere Hills of Montserrat).

  13. Constraints on the timing of Quaternary volcanism and duration of magma residence at Ciomadul volcano, east-central Europe, from combined U-Th/He and U-Th zircon geochronology (United States)

    Harangi, S.; Lukács, R.; Schmitt, A. K.; Dunkl, I.; Molnár, K.; Kiss, B.; Seghedi, I.; Novothny, Á.; Molnár, M.


    trigger several eruptions in a comparatively short time window. This classifies Ciomadul as a volcano with 'Potentially Active Magma Storage' (PAMS) which we propose to be common among the seemingly inactive volcanoes in volcanic arc regions. The potential for reactivation of these systems should be included into volcanic hazard assessments.

  14. Sr, Nd, Pb and Li isotope geochemistry and Ar-Ar dating of alkaline lavas from northern James Ross Island (Antarctic Peninsula) - implications for back-arc magma formation (United States)

    Kosler, J.; Magna, T.; Mlcoch, B.; Mixa, P.; Hendriks, B. W. H.; Holub, F. V.; Nyvlt, D.


    The elemental and isotopic (Sr, Nd, Pb and Li) composition of Cenozoic back-arc alkaline basalts emplaced east of the Antarctic Peninsula in James Ross Island Volcanic Group (JRIVG) is different from the compositions of the fore-arc alkaline volcanic rocks in Southern Shetlands and nearby Bransfield Strait. The variability in elemental and isotopic composition is not consistent with the JRIVG derivation from a single mantle source but rather it suggests that the magma was mainly derived from a depleted mantle with subordinate OIB-like enriched mantle component (EM II). The isotopic data are consistent with mantle melting during extension and possible roll-back of the subducted lithosphere of the Antarctic plate in Miocene to Pliocene times, as indicated by the existing geochronological data and the new Ar-Ar age determinations. Magma contamination by Triassic - Early Tertiary clastic sediments deposited in the back-arc basin was only localized and affected Li isotopic composition in two of the samples, while most of the basalts show very little variation in delta 7Li values, as anticipated for "mantle-driven" Li isotopic composition. These variations are difficult to resolve with radiogenic isotope systematics but Li isotopes may prove sensitive in tracking complex geochemical processes acting through the oceanic crust pile, including hydrothermal leaching and seawater equilibration.

  15. Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture (United States)

    Miyakawa, Ayumu; Sumita, Tatsuya; Okubo, Yasukuni; Okuwaki, Ryo; Otsubo, Makoto; Uesawa, Shimpei; Yagi, Yuji


    We resolve the density structure of a possible magma reservoir beneath Aso, an active volcano on Kyushu Island, Japan, by inverting gravity data. In the context of the resolved structure, we discuss the relationship between the fault rupture of the 2016 Kumamoto earthquake and Aso volcano. Low-density bodies were resolved beneath central Aso volcano using a three-dimensional inversion with an assumed density contrast of ±0.3 g/cm3. The resultant location of the southern low-density body is consistent with a magma reservoir reported in previous studies. No Kumamoto aftershocks occur in the southern low-density body; this aseismic anomaly may indicate a ductile feature due to high temperatures and/or the presence of partial melt. Comparisons of the location of the southern low-density body with rupture models of the mainshock, obtained from teleseismic waveform and InSAR data, suggest that the rupture terminus overlaps the southern low-density body. The ductile features of a magma reservoir could have terminated rupture propagation. On the other hand, a northern low-density body is resolved in the Asodani area, where evidence of current volcanic activity is scarce and aftershock activity is high. The northern low-density body might, therefore, be derived from a thick caldera fill in the Asodani area, or correspond to mush magma or a high-crystallinity magma reservoir that could be the remnant of an ancient intrusion.[Figure not available: see fulltext.

  16. The role of polybaric crystallization in genesis of andesitic magmas: Phase equilibria simulations of the Bezymianny volcanic subseries (United States)

    Almeev, Renat R.; Ariskin, Alexei A.; Kimura, Jun-Ichi; Barmina, Galina S.


    Using the updated COMAGMAT model, the crystallization sequences of a Bezymianny Volcano basaltic andesite (Kamchatka, Russia) are simulated in a wide range of thermodynamic conditions (P-T-fO2) as a function of H2O concentration. Comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1.5-2 wt.% H2O stored under 490-520 MPa pressure in the magma plumbing system beneath Bezymianny Volcano. The initial magma originates as a result of the polybaric evolution of mantle-derived high-Mg basaltic magmas of the adjacent Kliuchevskoi Volcano. The subsequent evolution of derivative hydrous and alumina-rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of ~ 12 MPa per 1% of crystallization. In the course of polybaric crystallization, compositions of pyroxene-bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent. However, hornblende-bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene-bearing andesite formation. They require high water contents and high pressures of crystallization. In this case, liquid composition should deviate from the chemical trend defined by the whole rock compositions.

  17. Localised magmatic constraints on continental back-arc volcanism in southern Mendoza, Argentina: the Santa Maria Volcano (United States)

    Espanon, Venera R.; Chivas, Allan R.; Turner, Simon P.; Kinsley, Leslie P. J.; Dosseto, Anthony


    The Payún Matrú Volcanic Field constitutes part of the continental back-arc in Argentina. This volcanic field has been the focus of several regional investigations; however, geochemical analysis of recent volcanoes (<8 ka) at the scale of an individual volcano has not been conducted. We present a morphological description for the Santa Maria Volcano in addition to results from major and trace element analysis and 238U-230Th-226Ra disequilibria. The trace element evidence suggests that the Santa Maria magmatic source has a composition similar to that of the local intraplate end member (resembling an ocean island basalt-like source), with a slight contribution from subduction-related material. The U-series analyses suggest a high 226Ra excess over 230Th for this volcano, which is not derived from a shallow process such as hydrothermal alteration or upper crustal contamination. Furthermore, intermediate-depth processes such as fractional crystallisation have been inferred for the Santa Maria Volcano, but they are not capable of producing the 226Ra excess measured. The 226Ra excess is explained by deep processes like partial melting of mantle lithologies with some influence from subducted Chilean trench sediments. Due to the short half-life of 226Ra (1600 years), we infer that fast magma ascent rates are required to preserve the high 226Ra excess.

  18. Geochemical variations in the Quaternary Andean back-arc volcanism, southern Mendoza, Argentina (United States)

    Espanon, Venera R.; Chivas, Allan R.; Kinsley, Leslie P. J.; Dosseto, Anthony


    The Payenia Basaltic Province (PBP) is located 450 km east of the Chile-Peru trench in central west Argentina, behind the Andean arc front, constituting the back-arc. In order to evaluate the influence of the subducting slab as well as the magmatic source of this region, two volcanic fields located at comparable distance to the trench, having abundant basaltic products and similar eruptive timeframes were chosen. The Llancanelo (LLVF) and the Payún Matrú (PMVF) volcanic fields are part of the PBP and exhibit abundant basaltic activity during the Pleistocene. The geochemical data suggest that the LLVF has some arc signatures which have been described as weak as they are not as pronounced as in the Andean arc. The weak arc signature is not derived from slab dehydration as high Th enrichment relative to U cannot be explained by this process. We relate the Th enrichment as well as the lack of large residual garnet signatures, to slab sediments in the source. In the case of the PMVF, no arc signature has been inferred despite being only 30 km south of the LLVF. However the PMVF has a composition similar to that of the local intraplate end member, represented by the Rio Colorado volcanic field. The two volcanic fields, LLVF and PMVF, show indications of lower crustal assimilation as they trend towards the lower continental crust end member in Nb/U vs Ce/Pb and Nb/Yb vs Th/Yb diagrams. The geochemical differences between the LLVF and the PMVF as well as between several volcanic fields are illustrated using spatial distribution maps of geochemical ratios. Using this new approach, the decrease in arc signature can be traced in the back-arc and the higher enrichment in high field strength elements (HFSE) relative to large ion lithophile elements (LILE) in the PMVF compared to the LLVF is explicitly shown. These geospatial maps provide a graphical manner to illustrate the presence of two distinct types of volcanism (OIB-like and arc-like) occurring in the same Quaternary

  19. Volcanic flood simulation of magma effusion using FLO-2D for drainage of a caldera lake at the Mt. Baekdusan (United States)

    Lee, Khil-Ha; Kim, Sung-Wook; Kim, Sang-Hyun


    Many volcanic craters and calderas are filled with large amounts of water that can pose significant flood hazards to downstream communities due to their high elevation and the potential for catastrophic releases of water. Recent reports pointed out the Baekdusan volcano that is located between the border of China and North Korea as a potential active volcano. Since Millennium Eruption around 1000 AD, smaller eruptions have occurred at roughly 100-year intervals, with the last one in 1903. Sudden release of huge volume of water stored in temporarily elevated caldera lakes are a recurrent feature of volcanic environments, due to the case with which outlet channels are blocked by and re-cut through, unwelded pyroclastic deposits. The volcano is showing signs of waking from a century-long slumber recently. Volcanic floods, including breakouts from volcanic lakes, can affect communities beyond the areas immediately affected by a volcanic eruption and cause significant hydrological hazards because floods from lake-filled calderas may be particularly large and high. Although a number of case studies have been presented in the literature, investigation of the underlying physical processes is required as well as a method for interpreting the process of the rapid release of water stored in a caldera lake. The development of various forecasting techniques to prevent and minimize economic and social damage is in urgent need. This study focuses on constructing a flood hazard map triggered by the magma effusion in the Baekdusan volcano. A physically-based uplift model was developed to compute the amount of water and time to peak flow. The ordinary differential equation was numerically solved using the finite difference method and Newton-Raphson iteration method was used to solve nonlinear equation. The magma effusion rate into the caldera lake is followed by examples at other volcanic activities. As a result, the hydrograph serves as an upper boundary condition when hydrodynamic

  20. Characteristics of Mineralized Volcanic Centers in Javanese Sunda Island Arc, Indonesia (United States)

    Setijadji, L. D.; Imai, A.; Watanabe, K.


    The subduction-related arc magmatism in Java island, Sunda Arc, Indonesia might have started in earliest Tertiary period, but the distinctively recognizable volcanic belts related with Java trench subduction occurred since the Oligocene. We compiled geoinformation on volcanic centers of different epochs, distribution of metallic mineral deposits, petrochemistry of volcanic rocks, geologic structures, and regional gravity image in order to elucidate characteristics of the known mineralized volcanic centers. Metallic deposits are present in various styles from porphyry-related, high-sulfidation, and low-sulfidation epithermal systems; all related with subaerial volcanism and subvolcanic plutonism. Only few and small occurrences of volcanigenic massive sulfides deposits suggest that some mineralization also occurred in a submarine environment. Most locations of mineral deposits can be related with location of Tertiary volcanic centers along the volcanic arcs (i.e. volcanoes whose genetic link with subduction is clear). On the other side there is no mineralization has been identified to occur associated with backarc magmatism whose genetic link with subduction is under debate. There is strong evidence that major metallic deposit districts are located within compressive tectonic regime and bound by coupling major, deep, and old crustal structures (strike-slip faults) that are recognizable from regional gravity anomaly map. So far the most economical deposits and the only existing mines at major industry scale are high-grade epithermal gold deposits which are young (Upper Miocene to Upper Pliocene), concentrated in Bayah dome complex in west Java, and are associated with alkalic magmatism-volcanism. On the other hand, known porphyry Cu-Au deposits are associated with old (Oligocene to Upper Miocene) stocks, and except for one case, all deposits are located in east Java. Petrochemical data suggest a genetic relationship between porphyry mineralization with low- to

  1. The 2007 Nazko, British Columbia, earthquake sequence: Injection of magma deep in the crust beneath the Anahim volcanic belt (United States)

    Cassidy, J.F.; Balfour, N.; Hickson, C.; Kao, H.; White, Rickie; Caplan-Auerbach, J.; Mazzotti, S.; Rogers, Gary C.; Al-Khoubbi, I.; Bird, A.L.; Esteban, L.; Kelman, M.; Hutchinson, J.; McCormack, D.


    On 9 October 2007, an unusual sequence of earthquakes began in central British Columbia about 20 km west of the Nazko cone, the most recent (circa 7200 yr) volcanic center in the Anahim volcanic belt. Within 25 hr, eight earthquakes of magnitude 2.3-2.9 occurred in a region where no earthquakes had previously been recorded. During the next three weeks, more than 800 microearthquakes were located (and many more detected), most at a depth of 25-31 km and within a radius of about 5 km. After about two months, almost all activity ceased. The clear P- and S-wave arrivals indicated that these were high-frequency (volcanic-tectonic) earthquakes and the b value of 1.9 that we calculated is anomalous for crustal earthquakes but consistent with volcanic-related events. Analysis of receiver functions at a station immediately above the seismicity indicated a Moho near 30 km depth. Precise relocation of the seismicity using a double-difference method suggested a horizontal migration at the rate of about 0:5 km=d, with almost all events within the lowermost crust. Neither harmonic tremor nor long-period events were observed; however, some spasmodic bursts were recorded and determined to be colocated with the earthquake hypocenters. These observations are all very similar to a deep earthquake sequence recorded beneath Lake Tahoe, California, in 2003-2004. Based on these remarkable similarities, we interpret the Nazko sequence as an indication of an injection of magma into the lower crust beneath the Anahim volcanic belt. This magma injection fractures rock, producing high-frequency, volcanic-tectonic earthquakes and spasmodic bursts.

  2. The pre-Kos Plateau Tuff Volcanic Rocks on Kefalos Peninsula (Kos Island, Dodecanese, Greece): Crescendo to the Largest Eruption of the Modern Aegean Arc (United States)

    Bachmann, O.; Schnyder, C.


    Young volcanic rocks (K-Ar ages of 3 to 0.5 Ma) from the Kefalos Peninsula (Kos Island, Dodecanese, Greece) erupted prior to the voluminous (>60 km\\ 3) Kos Plateau Tuff (KPT; Ar-Ar age of 0.16 Ma) were studied in order to better define the conditions that led to the paroxysmal eruption of the modern Aegean Arc. Two different whole-rock compositions were sampled on Kefalos peninsula; dacites (63-65 wt% SiO2) and rhyolites (75-77 wt% SiO2). Kefalos dacites are crystal-rich (>40% crystals), show high Sr-Ba contents compared to other continental arcs, and have "adakitic" Sr/Y ratios (>40). Kefalos rhyolites are typical high- SiO2 arc magmas, similar in composition and mineralogy to the KPT, but displaying lower crystallinities (30% in most of the KPT). The high Sr/Y ratios of the dacites is surprising in an area where the subducting slab is not particularly hot and the continental crust relatively thin (~30 km). If the low Y and high Sr-Ba contents result from the fact that magma formed deep enough to supress plagioclase and have garnet present, dacite magma generation must have occurred in the mantle. There is geochemical and mineralogical evidence for the Kefalos and KPT rhyolites being generated by fractional crystallization from magmas similar to the Kefalos dacites. However, the few distinctions between KPT and Kefalos rhyolites (KPT is more voluminous, contains more crystals, has lower whole-rock U and Th contents, and lower MgO-SiO2, but higher Al2O3-FeOtot in biotite) suggest slightly different conditions in the magma chambers. These observations, together with increasing explosivity of the volcanic products from ~3 Ma to 0.16 Ma, may indicate that the build-up to the large KPT eruption could be the result of an increase in magmatic water input in the system through time.

  3. Geology and Geochronology of the Central Part of Chiapanecan Volcanic Arc, Mexico. (United States)

    Layer, P. W.


    The Chiapanecan Volcanic Arc (CVA) is a 150 km stretch of volcanoes irregularly aligned in a northwest direction, including El Chichón volcano located in the central portion of the State of Chiapas, southern Mexico. It lies between two great volcanic features: the Trans-Mexican Volcanic Arc to the northwest, and the Central American Volcanic Arc to the southeast, in a complex zone of the interaction of the North American, Caribbean and Cocos Plates. The central part of the CVA is composed of an irregular northwest alignment of at least 12 volcanic structures located 80 km to the southeast of El Chichón (the only currently active volcano in the CVA). These structures include one explosion crater (Navenchauc), one collapse structure (Apas), one dome complex (Tzontehuitz) and nine volcanic domes (Navenchauc, Huitepec, Amahuitz, La Iglesia, Mispía, La Lanza, Venustiano Carranza, Miguel Hidalgo and Santotón) with associated pyroclastic flow deposits. The juvenile lithics from these deposits have a porphyritic texture with phenocrysts of plagioclase (±), amphibole (±), clinopyroxene (±), orthopyroxene (±) and Fe-Ti oxides surrounded by a matrix composed by microlites of plagioclase and glass. The chemical results obtained from representative samples from the deposits and structures indicate that these belong to the series of subalkaline rocks, and fall into the calcalkaline field with medium to high contents of potassium. They vary in their composition from andesite to dacite with an interval of silica between a 56 to a 66% (wt.). The ages reported in the literature and obtained in this study by means of the K-Ar and the 40Ar/39Ar methods, respectively, indicated that volcanism was episodic and spanned a time from 2100 ky ago (Tzontehuitz) to 225 ky ago (Venustiano Carranza).

  4. Significance of an Active Volcanic Front in the Far Western Aleutian Arc (United States)

    Yogodzinski, G. M.; Kelemen, P. B.; Hoernle, K.


    Discovery of a volcanic front west of Buldir Volcano, the western-most emergent Aleutian volcano, demonstrates that the surface expression of Aleutian volcanism falls below sea level just west of 175.9° E longitude, but is otherwise continuous from mainland Alaska to Kamchatka. The newly discovered sites of western Aleutian seafloor volcanism are the Ingenstrem Depression, a 60 km-long structural depression just west of Buldir, and an unnamed area 300 km further west, referred to as the Western Cones. These locations fall along a volcanic front that stretches from Buldir to Piip Seamount near the Komandorsky Islands. Western Aleutian seafloor volcanic rocks include large quantities of high-silica andesite and dacite, which define a highly calc-alkaline igneous series and carry trace element signatures that are unmistakably subduction-related. This indicates that subducting oceanic lithosphere is present beneath the westernmost Aleutian arc. The rarity of earthquakes below depths of 200 km indicates that the subducting plate is unusually hot. Some seafloor volcanoes are 6-8 km wide at the base, and so are as large as many emergent Aleutian volcanoes. The seafloor volcanoes are submerged in water depths >3000 m because they sit on oceanic lithosphere of the Bering Sea. The volcanic front is thus displaced to the north of the ridge of arc crust that underlies the western Aleutian Islands. This displacement, which developed since approximately 6 Ma when volcanism was last active on the islands, must be a consequence of oblique convergence in a system where the subducting plate and large blocks of arc crust are both moving primarily in an arc-parallel sense. The result is a hot-slab system where low subduction rates probably limit advection of hot mantle to the subarc, and produce a relatively cool and perhaps stagnant mantle wedge. The oceanic setting and highly oblique subduction geometry also severely limit rates of sediment subduction, so the volcanic rocks, which

  5. Volatile constraints on the magma supply, dynamics and plumbing system of a top-ranking basaltic gas emitter: Ambrym volcano, Vanuatu Arc (United States)

    Allard, Patrick


    P. Allard1,2, A. Aiuppa3,4, P. Bani5, N. Métrich1,6, A. Bertagnini6, M. Burton7, P-J. Gauthier5, F. Parello3, H. Shinohara8, G. Sawyer9, E. Bagnato3, E. Garaebiti10 1IPGP, UMR7154 CNRS, Paris France; 2INGV, Sezione di Catania, Italy; 3DiSTEM, Palermo University, Italy; 4INGV, Sezione di Palermo, Italy; 5LMV-OPGC, Clermont-Ferrand, France; 6INGV, Sezione di Pisa, Italy; 7SEAES, University of Manchester, UK; 8Geological Survey of Japan, Tsukuba, Japan; 9Department of Geography, University of Cambridge, UK; 10GEOHAZARD, Port Vila, Vanuatu. Ambrym basaltic volcano (central Vanuatu arc) is one of the most active volcanic systems of the Southwest Pacific region, where recurrent lava lake activity sustains voluminous gas release from two main cones, Benbow and Marum, in a 12 km-wide summit caldera. In 2007-2008 we could perform the first detailed investigations of gas emissions from this very active but remote and hardly accessible intra-oceanic arc volcano, combining ground-based and airborne measurements and using both in situ and remote sensing tools. The degassing budget of major, minor, trace and radioactive volatile species reveals that Ambrym ranks amongst the three most powerful persistent emitters of magmatic volatiles at global scale [1]. Coupled with the analysis of dissolved volatiles in the feeding basalt (olivine-hosted melt inclusions), the gas emission rates imply a very high average magma supply/degassing rate of 25 m3/s - 6 times the rate at Mount Etna - from a reservoir emplaced at about 4 km depth beneath the caldera floor. The chemical composition of emitted volcanic gases is compatible with dominant closed-system ascent and degassing of the basalt, followed by open degassing at shallow depth as water exsolution becomes extensive. The modest time-averaged extrusion rate, estimated from caldera infilling over the past 2 ka, requires convective downward recycling of the denser degassed magma in conduits with diameter of order 10 m. High resolution OP

  6. U-Pb (zircon) and geochemical constraints on the age, origin, and evolution of Paleozoic arc magmas in the Oyu Tolgoi porphyry Cu-Au district, southern Mongolia (United States)

    Wainwright, A.J.; Tosdal, R.M.; Wooden, J.L.; Mazdab, F.K.; Friedman, R.M.


    Uranium-Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu-Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (??Nd(t) range from +3.1 to +7.5 and 206Pb/204Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu-Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium-Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu-Au deposits are ~372Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu-Au mineralization are ~366Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu-Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late Devonian rocks associated with giant Cu-Au deposits from younger magmatic suites in the district. ?? 2010 Elsevier B.V.

  7. Locating the depth of magma supply for volcanic eruptions, insights from Mt. Cameroon (United States)

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


    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. PMID:27713494

  8. Locating the depth of magma supply for volcanic eruptions, insights from Mt. Cameroon. (United States)

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


    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.

  9. Immiscibility of high salinity fluids in volcanic rocks and the mechanism of magma degassing in the Dongying sag, eastern China

    Institute of Scientific and Technical Information of China (English)

    CHEN Yong; ZHOU Yaoqi; XIAO Huanqin; REN Yongjun; SUN Xinian; WANG Qiang; YAN Shiyong; LIU Chaoying


    Fluid inclusions that bear halite daughter min- erals were discovered in volcanic rocks at Pingnan area in the Dongying sag. The samples of the fluid inclusions collected from the BGX-15 well drill cores are hosted in quartz of diorite-porphyrite. The daughter minerals are identified as NaCl crystals after being observed under a microscope and analyzed by in situ Raman spectroscopy at -185℃. The results of micro-thermal analysis show that the homogeniza- tion temperatures of primary fluid inclusions are between 359 and 496℃, and the salinities of fluid inclusions are from 43.26 to 54.51 wt-%. All fluid inclusions in the studied sam- ples can be divided into five types including primary fluid inclusions and secondary fluid inclusions. The fact that five types of fluid inclusions were symbiotic in the same quartz grain implies that immiscibility happened in magma. Due to the decrease in temperature and pressure during the ascent of magma, the fluids became intensively immiscible. This pro- cess accelerates the degassing of CO2 from magma, but the remnant fluids with high salinity are preserved in fluid inclu- sions. Thus, the primary fluid inclusions are mainly in NaCl- H2O fluids and poor in CO2. The results of our study indicate that the degassing of magma and accumulation of CO2 gas at the Pingnan area are relative to the immiscibility of high salinity fluids. This discovery is important because it can help us have a further understanding of the mechanism of magma degassing and accumulation of the inorganic CO2 in eastern China.

  10. Abrupt change in magma generation processes across the Central American arc in southeastern Guatemala: flux-dominated melting near the base of the wedge to decompression melting near the top of the wedge (United States)

    Walker, J. A.; Carr, M. J.; Patino, L. C.; Johnson, C. M.; Feigenson, M. D.; Ward, R. L.


    Lavas erupted behind the volcanic front in southeastern Guatemala have many important distinctions from lavas erupted on the volcanic front. These include: generally higher MgO, Nb, Sr, TiO2, and rare earth element concentrations; higher La/Yb and Nb/Y ratios; and lower Ba/La, La/Nb, Ba/Zr and Zr/Nb ratios. These major and trace element distinctions are caused by reduced fractionation during ascent and storage in the crust, lower degrees of melting in the source, and greatly reduced contributions from the subducted Cocos plate in the source. In addition, because all of these important distinctions are even borne in lavas erupted within 20 km of the front, there is little apparent petrogenetic continuity between front and behind-the-front magmas. What little geochemical continuity exists is in radiogenic isotopes: 143Nd/144Nd falls across the arc, Pb isotopic ratios (except 206Pb/204Pb) rise across the arc, and 87Sr/86Sr rise across the arc after an initial discontinuity within 20 km of the front. These continuous across-arc changes in radiogenic isotopes are caused by increased contamination with older, more isotopically disparate rocks, away from the front. Once the effects of crustal contamination are removed, the remaining isotopic variability behind the front is non-systematic and reflects the inherent isotopic heterogeneity of the source, the mantle wedge. Geochemical disconnection in southeastern Guatemala suggests that behind-the-front magmas are produced by decompression melting near the top of the wedge, not by flux-dominated melting near the base of the wedge.

  11. Magma transfer and degassing budget: Application to the 2009-2010 eruptive crisis of Mt Garet (Vanuatu arc) (United States)

    Métrich, N.; Bertagnini, A.; Garaebiti, E.; Vergniolle, S.; Bani, P.; Beaumais, A.; Neuville, D. R.


    Mt Garet, on Gaua Island, is one of the active volcanoes of the Vanuatu arc. We report here a new dataset on lapilli and lava erupted during Mt Garet unrest in 2009-2010 and on products of the older activity of Gaua composite volcano. The present-day magma of Mt Garet is a trachy-andesite (52 wt.% SiO2) with relatively high Rb/Th (14.6) and Ba/La (41) ratios compared to the Gaua pre- and syn-caldera series, but typical of the central part of Vanuatu arc. Its mineral assemblage is mainly composed of plagioclase (An86-56) and clinopyroxene (Fs5-16) which display significant chemical variations, patchy zones, surface dissolution, and oscillatory zoning that imply episodes of high undercooling and growth rates. The paragenesis is complemented by Fe-Ti oxides and scarce olivine (Fo72-73). The melt inclusions are ubiquitous and their compositions cover a chemical spectrum from basalt to trachy-andesite. Volatile-rich basaltic inclusions (H2O: 2.7 wt.%, S: 0.15 wt.%, and Cl: 0.22 wt.%) are preserved in Mg-rich clinopyroxene whereas the majority of the melt inclusions is volatile poorer with, ≤ 1.0 wt.% of H2O, ≤ 0.05 wt.% of S, and 0.25-0.27 wt.% of Cl. At 1100 °C the measured viscosity of anhydrous magma of Mt Garet is 103.5 Pa s. Adding 0.8 to 2.5 wt.% of H2O decreases the melt viscosity by 0.5 to two orders of magnitude. Combining data on bulk rocks, minerals, and their melt inclusions together with the very first published gas fluxes acquired during the same period of activity, we propose that the high sulfur outgassing in 2009-2010 was produced by the degassing of a basaltic magma batch ( 0.027 km3) emplaced in a shallow reservoir. This scenario would require temperature and H2O-loss driven resorption/crystallization, magma mixing, and exsolution of an early gas phase rich in H2O, and S. We suggest here the 2009-2010 activity to be sustained by the existence of thermal convection driven at the bottom of the magma reservoir by cooling, and in which the bubbles

  12. Gas venting rates from submarine hydrothermal areas around the island of Milos, Hellenic Volcanic Arc (United States)

    Dando, P. R.; Hughes, J. A.; Leahy, Y.; Niven, S. J.; Taylor, L. J.; Smith, C.


    Gas seeps were located, by echo sounding, SCUBA divers and ROV observations, at hydrothermal sites around the island of Milos, in the Hellenic Volcanic Arc. Samples were collected by SCUBA divers and by a ROV from water depths between 3 and 110 m. Fifty-six flow rates from 39 individual seeps were measured and these ranged from 0.2 to 18.51 h -1 at the depth of collection. The major component, 54.9-91.9% of the gas, was carbon dioxide. Hydrogen (≤3%), methane (≤9.7%) and hydrogen sulphide (≤8.1%) were also measured. Hydrothermal free gas fluxes from the submarine hydrothermal areas around Milos were estimated to be greater than 10 10 moles y -1. It was concluded that submarine gas seeps along volcanic island arcs may be an important carbon dioxide source.

  13. Chlorine Stable Isotopes to reveal contribution of magmatic chlorine in subduction zones: the case of the Kamchatka-Kuril and the Lesser Antilles Volcanic Arcs (United States)

    Agrinier, Pierre; Shilobreeva, Svetlana; Bardoux, Gerard; Michel, Agnes; Maximov, Alexandr; Kalatcheva, Elena; Ryabinin, Gennady; Bonifacie, Magali


    By using the stable isotopes of chlorine (δ 37Cl), we have shown that magmatic chlorine (δ 37Cl ≤ -0.6 ‰ [1]) is different from surface chlorine (δ 37Cl ≈ 0 ‰ [1]) in hydrothermal system of Soufrière and Montagne Pelé from the young arc volcanic system of Lesser Antilles. First measurements on condensed chlorides from volcanic gases (e.g. [2], [3]) did not permitted to get sensible δ 37Cl values on degassed chlorine likely because chlorine isotopes are fractionated during the HClgas - chloride equilibrium in the fumaroles or during sampling artifacts. Therefore we have developed an alternative strategy based on the analysis of chloride in thermal springs, streams, sout{f}lowing on the flanks of the volcanoes. Due to the highly hydrophilic behavior of Cl, we hypothesize that thermal springs incorporate chlorine without fractionation of chlorine isotopes and might reflect the chlorine isotopic composition degassed by magmas [1]. Indeed Thermal spring with low δ 37Cl chlorides (≤ -0.6 perthousand{}) are linked with magmatic volatiles characters (3He ratio at 5 Ra at and δ 13C CO2 quad ≈ -3 perthousand{}). To go further in the potentiality of using the Chlorine isotopes to reveal contribution of magmatic chlorine in volcanic systems, we have started the survey of thermal springs and wells waters in the Kamchatka-Kuril volcanic mature Arc (on sites Mutnovsky, Paratunka, Nalychevsky, Khodutkinsky, Paramushir Island, identified by Taran, 2009 [4] for concentrations of chloride). Preliminary results show δ 37Cl values ranging from 0.5 to -0.2 ‰ and generally higher chloride concentrations. The δ 37Cl values are higher than the value recorded for the young arc volcanic system of lesser Antilles. At present moment very few negative δ 37Cl have been measured in the Kamchatka-Kuril volcanic mature Arc. [1] Li et al., 2015 EPSL in press. [2] Sharp et al. 2010 GCA. [3] Rizzo et al., 2013, EPSL, 371, 134. [4] Taran, 2009, GCA, 73, 1067

  14. Forearc Deformation, Arc Volcanism, and Landscape Evolution near the Cocos-Nazca-Caribbean Triple Junction (United States)

    Morell, K. D.; Fisher, D.; Gardner, T.; Protti, M.


    New geologic mapping in SE Costa Rica and SW Panama reveals a system of structures and landscape features that are actively propagating with the Cocos-Nazca-Caribbean Triple Junction. The triple junction migrates to the SE at ~50 km/my, so the upper plate inboard of the Nazca plate experiences a rapid change from steep, slow subduction of the Nazca plate to shallow, rapid subduction of the Cocos plate. High plate boundary coupling for ~100 km NW of the triple junction has led to the development of the Fila Costena Thrust Belt. Balanced cross-sections indicate that shortening rates are highest near the center of the thrust belt, and decrease to the SE nearest the triple junction, where the thrust belt abruptly terminates. Right lateral tear faults cut the thrusts of the Fila Costena and allow for a sharp gradient in upper plate shortening above the subducted projection of the Panama Fracture Zone (PFZ), or the Cocos-Nazca boundary. East of the triple junction, a ridge exposes a fault-related anticline that may represent the incipient propagation of the Fila Costena into Panama. The volcanic arc is active just to the east of the onland projection of the subducting PFZ (e.g., Volcan Baru), with the extinct Talamanca arc lying to the west of this projection. Lahar fans on the slopes of the active Volcan Baru are analogous to the backtilted lahars now restricted to the rear of the Fila Costena. The spatial and temporal distribution of arc volcanism is consistent with a mantle wedge restricted to the east of the PFZ that migrates eastward with the triple junction. The Rio Chiriqui drainage system is currently the only river that carries arc volcanics to the eastern thrust front. The river skirts the southeast edge of the thrust belt and is inset into lahar fans on the slopes of Volcan Baru. Uplifted Quaternary fluvial terraces, located several kilometers west from the current drainage system, are offset at the thrust front by about 100-150 m. Andesite clasts in these

  15. Magma Diversity in the Trans-Mexican Volcanic Belt: the role of Mantle Heterogeneities, Slab-derived Fluxes and Crustal Contamination. (United States)

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


    The Plio-Quaternary Trans-Mexican Volcanic Belt (TMVB) is related to subduction of the Cocos and Rivera plates underneath the North American plate. Non-parallelism of the magmatic arc with respect to the trench can be explained by oblique subduction and changes of dip angle. In this contribution we compare geochemical and Sr-Nd-Pb isotope data of five TMVB stratovolcanoes (from east to west: Colima Volcano, Nevado de Toluca, Popocatepetl, La Malinche, and Pico de Orizaba) and associated cinder cones. Volcanic products range in stratovolcanoes from andesites (e.g. Colima, Popocatepetl) to rhyolites (e.g. Pico de Orizaba), and from basalts to andesites in the monogenetic cones. Concentrations of incompatible elements correlate positively with Sr-Nd-Pb isotope ratios from east to west along the arc. 87Sr/86Sr, eNd, and 206Pb/204Pb range from 0.7034-0.7050, +6.9 to minus 1.8, and 18.57-18.78, respectively, displaying considerable differences. In the central TMVB, REE patterns of closely spaced high-Mg basaltic andesites differ substantially. This cannot be explained by fractional crystallization processes or differential partial melting of a homogeneous mantle source. Instead, it points towards small-scale mantle heterogeneities. LILE (e.g. Cs, Rb, Ba, Pb) and HFSE (e.g. Ta, Nb, Zr) display variations of orders in magnitude at different segments along the arc. These variations might correlate with amounts of slab-derived aqueous fluids and intensity of metasomatic reactions between the subducting lithosphere and the overlying mantle wedge. Isotopic ratios of mid-lower crustal xenoliths found in nearly all stratovolcano products reflect the nature of the underlying crust beneath the TMVB. Tertiary-Cretaceous plagiogranites (Colima), Cretaceous limestones (Popocatepetl), and Grenvillian quartzites (Pico de Orizaba)and their increasing radiogenic isotope ratios match well with the observed isotopic signatures of the stratovolcanoes. Moreover, elevated CO2 amounts in

  16. Recording the transition from flare-up to steady-state arc magmatism at the Purico-Chascon volcanic complex, northern Chile (United States)

    Burns, Dale H.; de Silva, Shanaka L.; Tepley, Frank; Schmitt, Axel K.; Loewen, Matthew W.


    The long-term evolution of continental magmatic arcs is episodic, where a few transient events of high magmatic flux or flare-ups punctuate the low-flux magmatism or "steady state" that makes up most of the arc history. How this duality manifests in terms of differences in crustal architecture, magma dynamics and chemistry, and the time scale over which transitions occur is poorly known. Herein we use multiscale geochemical and isotopic characteristics coupled with geothermobarometry at the Purico-Chascon Volcanic Complex (PCVC) in the Central Andes to identify a transition from flare-up to steady state arc magmatism over ∼800 kyr during which significant changes in upper crustal magmatic dynamics are recorded. The PCVC is one of the youngest volcanic centers related to a 10-1 Ma ignimbrite flare-up in the Altiplano-Puna Volcanic Complex of the Central Andes. Activity at the PCVC initiated 0.98 ± 0.03 Ma with the eruption of a large 80-100 km3 crystal-rich dacite ignimbrite. High, restricted 87Sr/86Sr isotope ratios between 0.7085 and 0.7090 in the bulk rock and plagioclase crystals from the Purico ignimbrite, combined with mineral chemistry and phase relationships indicate the dacite magma accumulated and evolved at relatively low temperatures around 800-850 °C in the upper crust at 4-8 km depth. Minor andesite pumice erupted late in the ignimbrite sequence records a second higher temperature (965 °C), higher pressure environment (17-20 km), but with similar restricted radiogenic bulk rock 87Sr/86Sr = 0.7089-0.7091 to the dacites. The compositional and isotopic characteristics of the Purico ignimbrite implicate an extensive zone of upper crustal mixing, assimilation, storage and homogenization (MASH) between ∼30 and 4 km beneath the PCVC ∼1 Ma. The final eruptions at the PCVC environments; an upper crustal environment identical to that recorded in the Purico ignimbrite, and a second deeper, ∼15-20 km depth, higher temperature (∼922-1001

  17. Magma displacements under insular volcanic fields, applications to eruption forecasting: El Hierro, Canary Islands, 2011-2013 (United States)

    García, A.; Fernández-Ros, A.; Berrocoso, M.; Marrero, J. M.; Prates, G.; De la Cruz-Reyna, S.; Ortiz, R.


    Significant deformations, followed by increased seismicity detected since 2011 July at El Hierro, Canary Islands, Spain, prompted the deployment of additional monitoring equipment. The climax of this unrest was a submarine eruption first detected on 2011 October 10, and located at about 2 km SW of La Restinga, southernmost village of El Hierro Island. The eruption ceased on 2012 March 5, after the volcanic tremor signals persistently weakened through 2012 February. However, the seismic activity did not end with the eruption, as several other seismic crises followed. The seismic episodes presented a characteristic pattern: over a few days the number and magnitude of seismic event increased persistently, culminating in seismic events severe enough to be felt all over the island. Those crises occurred in 2011 November, 2012 June and September, 2012 December to 2013 January and in 2013 March-April. In all cases the seismic unrest was preceded by significant deformations measured on the island's surface that continued during the whole episode. Analysis of the available GPS and seismic data suggests that several magma displacement processes occurred at depth from the beginning of the unrest. The first main magma movement or `injection' culminated with the 2011 October submarine eruption. A model combining the geometry of the magma injection process and the variations in seismic energy release has allowed successful forecasting of the new-vent opening.

  18. Trace Element Mobility During Mixing of Magmas as a Proxy for Determination of Volcanic Eruption Time-Scales (United States)

    Perugini, Diego; de Campos, Cristina P.; Petrelli, Maurizio; Poli, Gampiero; Dingwell, Donald B.


    Understanding the timing of volcanic eruptions is a central issue in volcanological research. To date, no one method appears capable of providing unequivocal information on the imminence of a volcanic explosion. One volcanic area in which the knowledge of eruption timescales is crucial is the Phlegrean Fields region home to more than 1.5 million people (Orsi et al., 1996). Recent magmatism (ca. 60ka BP to 1538 AD) has generated mostly explosive events; in the last 15 kyrs ca. 70 eruptions have been recognized (e.g. Orsi et al., 1996). Understanding the mechanisms triggering such eruptions is crucial, since the Phlegrean Fields caldera is considered as an active volcanic system that is thus likely to erupt in the future. To this aim, the variation of chemical element compositions in two pyroclastic sequences (Astroni 6 and Averno 2, Phlegrean Fields, Italy) is studied. Both sequences are compositionally zoned indicating a variability of melt compositions in the magma chamber prior to eruption. A clear dichotomy between the behavior of major vs. trace elements is also observed in both sequences, with major elements displaying nearly linear inter-elemental trends and trace elements showing a variable scattered behavior. Together with previous petrological investigations (e.g. Civetta et al., 1997) these observations are consistent with the hypothesis that magma mixing processes played a key role in the evolution of these two magmatic systems. Recently it has been suggested that mixing processes in igneous systems may strongly influence the mobility of trace elements inducing a ‘diffusive fractionation' phenomenon, whose extent depends on the mixing time-scale (Perugini et al., 2006; 2008). Here we merge information from 1) detailed geochemical studies of natural samples from Phlegrean Fields, 2) numerical simulations of magma mixing, and 3) magma mixing experiments (using as end-members natural compositions from Phlegrean Fields; e.g. De Campos et al., 2004) to

  19. A Linearized Model for Wave Propagation through Coupled Volcanic Conduit-crack Systems Filled with Multiphase Magma (United States)

    Liang, C.; Dunham, E. M.; OReilly, O. J.; Karlstrom, L.


    Both the oscillation of magma in volcanic conduits and resonance of fluid-filled cracks (dikes and sills) are appealing explanations for very long period signals recorded at many active volcanoes. While these processes have been studied in isolation, real volcanic systems involve interconnected networks of conduits and cracks. The overall objective of our work is to develop a model of wave propagation and ultimately eruptive fluid dynamics through this coupled system. Here, we present a linearized model for wave propagation through a conduit with multiple cracks branching off of it. The fluid is compressible and viscous, and is comprised of a mixture of liquid melt and gas bubbles. Nonequilibrium bubble growth and resorption (BGR) is quantified by introducing a time scale for mass exchange between phases, following the treatment in Karlstrom and Dunham (2015). We start by deriving the dispersion relation for crack waves travelling along the multiphase-magma-filled crack embedded in an elastic solid. Dissipation arises from magma viscosity, nonequilibrium BGR, and radiation of seismic waves into the solid. We next introduce coupling conditions between the conduit and crack, expressing conservation of mass and the balance of forces across the junction. Waves in the conduit, like those in the crack, are influenced by nonequilibrium BGR, but the deformability of the surrounding solid is far less important than for cracks. Solution of the coupled system of equations provides the evolution of pressure and fluid velocity within the conduit-crack system. The system has various resonant modes that are sensitive to fluid properties and to the geometry of the conduit and cracks. Numerical modeling of seismic waves in the solid allows us to generate synthetic seismograms.

  20. Quaternary fault-controlled volcanic vents and crustal thinning: new insights from the magma-rich Tyrrhenian passive margin (Italy) (United States)

    Cardello, Giovanni Luca; Conti, Alessia; Consorti, Lorenzo; Do Couto, Damien


    The discover of monogenic Quaternary volcanic vents, that were recently mapped along major fault zones both inland and offshore the Tyrrhenian magma-rich passive margin, poses questions about: timing and role they had into Plio-Pleistocene crustal thinning with relevant consequences for the hazard assessment of an area inhabited by some 0.5 million people. The present-day margin is stretched over 100 km between the Volsci Range (VR) and the Pontian escarpment, being defined by moderate shallow seismicity (Mw≤4.6), relative high geothermal gradient and ongoing hydrothermal activity. Although major central volcanoes (e.g., Colli Albani), occurring at major fault intersections are well studied, smaller volcanic fields were so far unconstrained. Both field survey in the VR and offshore high-resolution geophysical data, allow us to: 1) better define the anatomy of the poorly known VR volcanic field; 2) furnish new insights on the regional Quaternary dynamics; 3) propose modes and reason of magma emplacement. The VR is composed of about 40 punctual and linear monogenic and mostly phreatomagmatic vents occurring at the edges of the Apennine carbonate fold-and-thrust belt and within the VR backbone. Volcanites are characterized by zeolitized to incoherent tuffs and surge deposits locally covered by lavas and slope deposits. Most explosive units host carbonate-rich lithics with different degrees of rounding and decarbonation, which frequently belong to Albian-Cenomanian aquifers. By comparing cross-section with lithic analyses we demonstrate that fragmentation, transport, progressive disintegration and decarbonation occur at multiple depths, depending on the fold-and-thrust belt setting. Thus, along the same vent zone, juvenile lithic composition proves repeated fragmentation within pressured-aquifers, testifying for fissural activity with implications for local seismic and volcanic assessment. Pyroclastic deposits occur as well in the Pontina and Fondi coastal plains at

  1. Temporal and geochemical evolution of Miocene volcanism in the Andean back-arc between 36°S and 38°S and U-series analyses of young volcanic centers in the arc and back-arc, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup

    New 40Ar/39Ar, major and trace element, and Sr, Nd and Pb isotopic data for the c. 24-7 Ma volcanic rocks from the Andean back-arc (35°S – 38°S) in the Mendoza and Neuquén (Argentina) regions shed light on the Miocene evolution of the back-arc of the Southern Volcanic Zone. Incipient shallowing...... lasting from ~17 to ~9 Ma. The reoccurrence of extensive magmatism in the Sierra de Palaoco provides evidence for a retreat of the shallow subduction zone towards the west during the Late Miocene. Evidence for the ending of the time of flat subduction comes from major- and trace element chemistry and Nd...

  2. The impact of rapid recharge events on the evolution of magma chambers: Case studies of Santorini Volcano (Greece) and Volcan Quizapu (Chile) (United States)

    Degruyter, Wim; Huber, Christian; Bachmann, Olivier; Cooper, Kari; Kent, Adam


    Magma reservoirs in the crust are thought to be dominantly formed by episodic recharge events at rates that are much larger than the long-term average magma inflow rates. Hence, a better understanding of the evolution of a magma reservoir requires elucidating the mass change, pressurization, heating, deformation and the potential for an eruption associated with different recharge scenarios. Most importantly, the bifurcation in behavior between a recharge event that leads to eruption and one that will grow the chamber requires quantification for better volcanic hazard assessment. We use a numerical model to determine the change in pressure, temperature and volume of a magma chamber as it is exposed to a recharge event. The model is applied to the well-studied volcanic systems of Santorini Volcano (Greece) and Volcan Quizapu (Chile). We establish the rates and the duration of magma recharge events that will lead to an eruption. In doing so, we demonstrate the importance of the state of the magma chamber prior to the recharge event, i.e. its size and exsolved volatile content, on the subsequent evolution of the reservoir. In the case of Santorini, the model successfully reproduces the main features of the Minoan eruption and Nea Kameni activity, providing volume estimates for the active part of the current subvolcanic reservoir as well as information regarding the presence of exsolved volatiles. For Quizapu, we suggest that the change in eruptive style, from an effusive outpouring of lava in 1846-1847 to an explosive Plinian eruption in 1932, was controlled by a shift in the state of the magma chamber induced by the first eruption. These case studies show that thermo-mechanical models offer a new framework to integrate the historic eruption record with geodetic measurements and provide a context to understand the past, present and future of active volcanic centers.

  3. Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs (United States)

    Blundy, J.; Mavrogenes, J.; Tattitch, B.; Sparks, S.; Gilmer, A.


    Porphyry copper deposits, that is, copper ore associated with hydrothermal fluids rising from a magma chamber, supply 75% of the world's copper. They are typically associated with intrusions of magma in the crust above subduction zones, indicating a primary role for magmatism in driving mineralization. However, it is not clear that a single, copper-rich magmatic fluid could trigger both copper enrichment and the subsequent precipitation of sulphide ore minerals within a zone of hydrothermally altered rock. Here we draw on observations of modern subduction zone volcanism to propose an alternative process for porphyry copper formation. We suggest that copper enrichment initially involves metalliferous, magmatic hyper-saline liquids, or brines, that exsolve from large, magmatic intrusions assembled in the shallow crust over tens to hundreds of thousands of years. In a subsequent step, sulphide ore precipitation is triggered by the interaction of the accumulated brines with sulphur-rich gases, liberated in short-lived bursts from the underlying mafic magmas. We use high-temperature and high-pressure laboratory experiments to simulate such gas-brine interactions. The experiments yield copper-iron sulphide minerals and hydrogen chloride gas at magmatic temperatures of 700-800 °C, with textural and chemical characteristics that resemble those in porphyry copper deposits. We therefore conclude that porphyry copper ore forms in a two-stage process of brine enrichment followed by gas-induced precipitation.

  4. Comprehensive study of the seismotectonics of the easter Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1978--February 28, 1979

    Energy Technology Data Exchange (ETDEWEB)

    Jacob, K.H.; Davies, J.N.; Beavan, J.; Johnson, D.; House, L.; Krause, J.; Hickman, S.; Winslow, M.; Hauptman, J.; Mori, J.; Sykes, L.R.


    Based on the historic seismic record and accurate hypocenter data obtained from the eastern Aleutian seismic network, a relationship between the subduction-zone seismicity, volcano-trench separation, and the occurrence of great thrust earthquakes has been established for the Aleutian arc. On the basis of strong-motion accelerometer data it was found that high stress drops (540 t 650 bars) were associated with two moderate-size earthquakes (m/sub b/ = 6.0 and 5.8) within the Shumagin Islands seismic gap. This indicates that near the down-dip end of the major thrust zone, at depths of about 40 km, high tectonic stresses have accumulated within the gap segment of the arc. That such accumulation of stress is presently an ongoing process is corroborated by results from geodetic precision leveling on Unga Island. The leveling data indicate tilt rates of about 1 microradian/year. The tilting is directed down towards the trench and up towards the volcanic arc. Whether the recent activity of Pavlof, Shishaldin and Westdahl volcanoes indicates transmission of high tectonic stresses from the major thrust zone to the volcanic arc is unresolved. The search for a shallow magma chamber beneath the seismically monitored Pavlof volcano is still inconclusive although large amounts of recently acquired data remain to be analyzed. A geologic reconnaissance of the Shumagin Islands and the Adjacent Alaska Peninsula revealed Quaternary uplifted marine terraces and evidence for Holocene faulting. Both findings have severe implications for long-term tectonic activity and seismic hazards in the region of this seismic gap, portions of which are presently considered for off-shore hydrocarbon exploration and development. A critical analysis of th presently operating seimic data acquisition system reveals that a major change in remote sensing and central recording equipment is urgently needed for the Pavlof, Cold Bay, and Shumagin sections of the seismic array.

  5. Mafic magmas from Mount Baker in the northern Cascade arc, Washington: probes into mantle and crustal processes (United States)

    Moore, Nicole E.; Debari, Susan M.


    Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt of Park Butte (49.3-50.3 wt% SiO2, Mg# 64-65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of Lake Shannon (50.7-52.6 wt% SiO2, Mg# 58-62) and Sulphur Creek (51.2-54.6 wt% SiO2, Mg# 56-57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8-54.0 wt% SiO2, Mg# 68-70) and the HMA of Glacier Creek (58.3-58.7 wt% SiO2, Mg# 63-64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO2 suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite unit, Cathedral Crag (52.2-52.6 wt% SiO2, Mg# 55-58), is an Mg-poor differentiate of the Type 3 endmember. The calc

  6. Remelting of Neoproterozoic relict volcanic arcs in the Middle Jurassic: Implication for the formation of the Dexing porphyry copper deposit, Southeastern China (United States)

    Liu, Xuan; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Li, Qiu-Li; Yang, Yue-Heng; Liu, Yongsheng


    The Dexing copper deposit in southeastern China is a typical non-arc porphyry deposit, the origin of which has been a topic of debate for several decades. Here we present new results from U-Pb geochronology, whole-rock chemistry and Sr-Nd-Hf-O isotopic investigations on the ore-forming granodioritic porphyry. LA-ICPMS zircon U-Pb data suggest that the granodioritic porphyry was formed in the Middle Jurassic (ca. 172.5 Ma) probably associated with lithospheric thinning driven by either sub-continental lithospheric mantle delamination or asthenospheric upwelling. The porphyry displays both arc-like and adakitic trace element signatures. The adakitic features suggest that HREE (heavy rare earth elements)-rich minerals such as garnet and hornblende, in the absence of plagioclase resided in the source region. The arc-like signatures are broadly comparable with those of the proximal Neoproterozoic island arc rocks including the keratophyre from Shuangxiwu Group and associated granitoids indicating a potential genetic relationship. The porphyry has chondritic ɛNd(t) of - 0.28 to 0.25 and radiogenic ɛHf(t) of 2 to 7, and correspondingly, uniform two stage depleted mantle Nd model ages of 940-980 Ma and Hf model ages of 800-1100 Ma (mean ~ 920 Ma). On Nd and Hf isotopic evolution diagrams, these values are markedly similar to those of the adjacent Neoproterozoic arc rocks when calculated forward to the Mid-Jurassic. Zircons of the porphyry show mantle-like oxygen isotope characters with δ18O values clustering in the range of 4.7-5.9‰, similar to the values for the Neoproterozoic arc rocks mentioned above. The geochemical and isotopic features recorded in our study suggest mantle-derived magmas with no significant supracrustal input for the source of the porphyry. With regard to the source of the Cu ore, we consider a model involving the remelting of sulfide-bearing arc-related lower crustal source. Furthermore, the occurrence of a Neoproterozoic VMS (volcanic massive

  7. Geochemical characteristics of island-arc volcanic rocks in the Nan-Nam Pat-Phetchabun zone, northern Thailand

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; YANG Wenqiang; ZHANG Zhibin; Chongpom Chonglakmani


    Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite series coming next. The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf. The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.

  8. Discovery of episodic volcanism at Prometheus on Io: implications for magma supply (United States)

    Davies, A. G.


    Galileo Near Infrared Mapping Spectrometer (NIMS) data show the ionian volcanoes Prometheus and Amirani have significant thermal emission in excess of non-volcanic background emission in every geometrically appropriate NIMS observation.

  9. Geodetic Constraints From The Volcanic Arc Of The Andaman - Nicobar Subduction Zone (United States)

    Earnest, A.; Krishnan, R.; Mayandi, S.; Sringeri, S. T.; Jade, S.


    We report first ever GPS derived surface deformation rates in the Barren and Narcondum volcanic islands east of Andaman-Nicobar archipelago which lies in the Bay of Bengal, a zone that generates frequent earthquakes, and coincides with the eastern plate boundary of India. The tectonics of this region is predominantly driven by the subduction of the Indian plate under the Burma plate. Andaman sea region hosts few volcanoes which lies on the inner arc extending between Sumatra and Myanmar with the sub-aerial expressions at Barren and Narcondum Islands. Barren Island, about 135 km ENE of Port Blair, is presently active with frequent eruptive histories whereas Narcondum is believed to be dormant. We initiated precise geodetic campaign mode measurements at Barren Island between 2007 to 2012 and one year (2011-2012) continuous measurements at Narcondum island. Preliminary results from this study forms a unique data set, being the first geodetic estimate from the volcanic arc of this subducting margin. Our analysis indicates horizontal convergence of the Barren benchmark to south-westward (SW) direction towards the Andaman accretionary fore-arc wedge where as the Narcondum benchmark recorded northeast (NE) motion. West of the Andaman fore-arc there is NE oriented subduction of the Indian plate which is moving at the rate of ~5 cm/yr. Convergence rates for the Indian plate from the Nuvel 1A model also show oblique convergence towards N23°E at 5.4 cm/yr. GPS derived inter seismic motion of Andaman islands prior to 2004 Sumatra earthquake is ~4.5 cm/yr NE. The marginal sea basin east of Barren Island at the Andaman spreading ridge has a NNW orienting opening of the sea-floor at 3.6 cm/yr. However the recent post seismic measurements of Andaman islands indicate rotation of displacement vectors from SW to NNE during 2005 to 2012. In this tectonic backdrop, the estimated rate of displacement of the volcanic islands probably represents a composite signal of tectonic as well as

  10. Effects of magma-induced stress within a cellular automaton model of volcanism (United States)

    Butters, Olivia J.; Sarson, Graeme R.; Bushby, Paul J.


    The cellular automaton model of Piegari, Di Maio, Scandone and Milano, J. Volc. Geoth. Res., 202, 22-28 (2011) is extended to include magma-induced stress (i.e. a local magma-related augmentation of the stress field). This constitutes a nonlinear coupling between the magma and stress fields considered by this model, which affects the statistical distributions of eruptions obtained. The extended model retains a power law relation between eruption size and frequency for most events, as expected from the self-organised criticality inspiring this model; but the power law now applies for a reduced range of size, and there are new peaks of relatively more frequent eruptions of intermediate and large size. The cumulative frequency of repose time between events remains well modelled by a stretched exponential function of repose time (approaching a pure exponential distribution only for the longest repose times), but the time scales of this behaviour are slightly longer, reflecting the increased preference for larger events. The eruptions are relatively more likely to have high volatile (water) content, so would generally be more explosive. The new model also naturally favours a central 'axial' transport conduit, as found in many volcano systems, but which otherwise must be artificially imposed within such models.

  11. Evolution of Eocene to Oligocene arc-related volcanism in the North Patagonian Andes (39-41°S), prior to the break-up of the Farallon plate (United States)

    Iannelli, Sofía B.; Litvak, Vanesa D.; Fernández Paz, Lucía; Folguera, Andrés; Ramos, Miguel E.; Ramos, Víctor A.


    Voluminous Paleogene magmatic rocks (44 to 29 Ma) are found in a retroarc position in the Northern Patagonian to Southern Central Andes ( 39-42°S), whose origin remains controversial. Geochemical data in these Eocene to Oligocene volcanic associations are herein used to unravel their origin and understand changes in subduction parameters. Geochemical signatures indicate arc-related associations and reflect changing geodynamic boundary conditions of the Andean margin through time. In particular, Eocene magmatism ( 44 Ma; Pilcaniyeu Belt) shows an alkaline-like signature and limited slab influence. Reported contemporaneous within-plate magmatism ( 47-43 Ma) in an easternmost position reflects a more typical enriched source. Oligocene arc-like volcanism ( 29 Ma; El Maitén Belt), which developed in an extensional retroarc setting, shows a higher contribution from slab-derived fluids and a calc-alkaline source. A comparison with younger arc-related magmas from the region ( 26-20 Ma), emplaced in an intra- to retroarc position (Cura Mallín and Abanico basins), indicates a progressive increase in slab-signature, associated with a tholeiitic magma source. We propose that these compositional variations could be directly related to changes in plate configuration before and after the Farallon plate break-up and the initiation of a more orthogonal convergence typical of the present Andean-type subduction zone.

  12. U-Series disequilibria, magma petrogenesis and flux rates along the depleted Tonga-Kermadec Island Arc.

    Energy Technology Data Exchange (ETDEWEB)

    Turner, S.; Hawkesworth, C.; Rogers, N.; Bartlett, J.; Smith, I.; Worthington, T. [The Open University, Milton Keynes, (United Kingdom). Department of Earth Sciences; Smith, I.; Worthington, T. [Auckland Univ. (New Zealand). Dept. of Geology


    The fluid contribution to the lava source has been calculated as -1 ppm Rb, 10 ppm Ba, 0.02 ppm U, 600 ppm K 0.2 ppm Pb and 30 ppm Sr. It has {sup 87}Sr/{sup 86}Sr = 0.7035 and {sup 206}Pb/{sup 204}Pb = 18.5 and thus is inferred to be derived from dehydration of the subducting altered oceanic crust. U-Th isotope disequilibria reflect the time since fluid release from the subducting slab and a pseudo-isochron through the lowest ({sup 230}Th/{sup 232}Th) lavas constrains this to be {approx} 50 000 yr. Significantly, U-Th isotope data record similar timescales in the Lesser Antilles ({approx}40 000 yr, Turner et al., 1996) and in the Marianas (30 000 yr, Elliott et al., 1996) which provides encouragement that these data reflect some general aspect of the flux rates beneath island arcs. Large {sup 226}Ra excesses have also been reported from Tonga-Kermadec (({sup 226}Ra/{sup 230}Th) = 1.5-3.0, Gill and Williams, 1990). Since {sup 226}Ra will return to secular equilibrium with {sup 230}Th (({sup 226}Ra/{sup 230}Th) = 1) within 7500 yr of Ra/Th fractionation the {sup 238}U/{sup 230}Th and {sup 226}Ra/{sup 230}Th disequilibria are clearly decoupled (see also Turner et al., 1996). This is an unexpected result and clearly the {sup 226}Ra/{sup 230}Th disequilibria must have developed after the process responsible for the major U/Th fractionation. It is suggested that Th-Ra isotope disequilibria record the time since partial melting and thus indicate rapid channelled magma ascent. Olivine gabbro xenoliths from Raoul are interpreted as cumulates to their host lavas with which they form zero age U-Th isochrons indicating that minimal time was spent in magma chambers. The subduction signature is not observed in lavas from the back arc island of Niuafo`ou and thus does not penetrate as far 200 km beyond the arc front volcanoes. These were derived from partial melting of fertile peridotite at 130-160 km depth with melt rates around 2 x 10{sup -4} kg m{sup -3} yr{sup -1}, possibly

  13. Geomorphic and exhumational response of the Central American Volcanic Arc to Cocos Ridge subduction (United States)

    Morell, Kristin D.; Kirby, Eric; Fisher, Donald M.; van Soest, Matthijs


    The timing of collision of the Cocos Ridge at the Middle America Trench remains one of the outstanding questions in the tectonic evolution of the Central American convergent margin. New analyses of the tectonic geomorphology of the Cordillera de Talamanca, the extinct volcanic arc inboard of the Cocos Ridge, coupled with low temperature thermochronometry data, provide insight into the cooling and erosional history of the arc from late Miocene to present. We identify a low-relief surface at high elevation along the northeastern flanks of the range, which represents a relict erosional landscape cut across shallow plutonic rocks of the arc edifice. Longitudinal profiles of rivers on this surface are isolated from steep downstream sections by prominent knickzones that are interpreted to reflect a migrating wave of transient incision generated during differential rock uplift of the range. Reconstruction of pre-incision profiles suggests that rock uplift during the growth of the Cordillera de Talamanca is no greater than ˜2 km. This inference is corroborated by results from our apatite (U-Th)/He and apatite fission track analyses along an elevation transect on Mt. Chirripó, the highest mountain in the Cordillera de Talamanca. Low-temperature cooling ages overlap significantly with published high-temperature40Ar/39Ar ages; the combined results imply that rapid cooling in the late Miocene was related to secular cooling of a shallow pluton, rather than exhumation. Our results imply that rapid incision along downstream channel segments, differential rock uplift, and growth of the Talamanca as a bivergent orogenic wedge associated with the onset of Cocos Ridge subduction are relatively young characteristics of the range. A review of previously published radiometric ages and revised plate reconstructions for the late Miocene further suggest that the cessation of arc volcanism in both the Cordillera de Talamanca and the Cordillera Central of western Panama was coeval with the

  14. A structural outline of the Yenkahe volcanic resurgent dome (Tanna Island, Vanuatu Arc, South Pacific) (United States)

    Merle, O.; Brothelande, E.; Lénat, J.-F.; Bachèlery, P.; Garaébiti, E.


    A structural study has been conducted on the resurgent Yenkahe dome (5 km long by 3 km wide) located in the heart of the Siwi caldera of Tanna Island (Vanuatu arc, south Pacific). This spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone - the Yasur volcano - in the west and exhibits an intriguing graben in its central part. Detailed mapping and structural observations make it possible to unravel the volcano-tectonic history of the dome. It is shown that, following the early formation of a resurgent dome in the west, a complex collapse (caldera plus graben) occurred and this was associated with the recent uplift of the eastern part of the present dome. Eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution.

  15. Application of a new multiphase multicomponent volcanic conduit model with magma degassing and crystallization to Stromboli volcano. (United States)

    La Spina, Giuseppe; Burton, Mike; de'Michieli Vitturi, Mattia


    Volcanoes exhibit a wide range of eruption styles, from relatively slow effusive eruptions, generating lava flows and lava domes, to explosive eruptions, in which very large volumes of fragmented magma and volcanic gas are ejected high into the atmosphere. During an eruption, much information regarding the magma ascent dynamics can be gathered: melt and exsolved gas composition, crystal content, mass flow rate and ballistic velocities, to name just a few. Due to the lack of direct observations of the conduit itself, mathematical models for magma ascent provide invaluable tools for a better comprehension of the system. The complexity of the multiphase multicomponent gas-magma-solid system is reflected in the corresponding mathematical model; a set of non-linear hyperbolic partial differential and constitutive equations, which describe the physical system, has to be formulated and solved. The standard approach to derive governing equations for two-phase flow is based on averaging procedures, which leads to a system of governing equations in the form of mass, momentum and energy balance laws for each phase coupled with algebraic and differential source terms which represent phase interactions. For this work, we used the model presented by de' Michieli Vitturi et al. (EGU General Assembly Conference Abstracts, 2013), where a different approach based on the theory of thermodynamically compatible systems has been adopted to write the governing multiphase equations for two-phase compressible flow (with two velocities and two pressures) in the form of a conservative hyperbolic system of partial differential equations, coupled with non-differential source terms. Here, in order to better describe the multicomponent nature of the system, we extended the model adding several transport equations to the system for different crystal components and different gas species, and implementing appropriate equations of state. The constitutive equations of the model are chosen to

  16. Million-year melt-presence in monotonous intermediate magma for a volcanic-plutonic assemblage in the Central Andes: Contrasting histories of crystal-rich and crystal-poor super-sized silicic magmas (United States)

    Kaiser, Jason F.; de Silva, Shanaka; Schmitt, Axel K.; Economos, Rita; Sunagua, Mayel


    The melt-present lifetime of super-sized monotonous intermediate magmas that feed supereruptions and end life as granodioritic plutons is investigated using zircon chronochemistry. These data add to the ongoing discussion on magma assembly rates and have implications for how continental batholiths are built. Herein, we estimate ∼1.1 Ma of continuous melt presence before and after the climactic caldera-forming 2.89 ± 0.01 Ma (2σ error) Pastos Grandes Ignimbrite (PGI) supereruption (∼1500 km3 of magma) in the Andes of southwest Bolivia. Zircon crystallization in PGI pumice and lava from the faulted Southern Postcaldera Dome span ∼0.7 Ma prior to the climactic eruption and formation of the eponymous caldera, whereas younger, unfaulted Postcaldera Dome lavas (termed Northern and Middle) and a granodioritic plutonic clast within the products of a Pleistocene eruption indicate a further ∼0.4 Ma of post-climactic zircon crystallization. Bulk-rock compositions as well as zircon thermometry and geochemistry indicate the presence of homogeneous dacitic magma before and after the climactic eruption, but a trend to zircon crystallization at higher temperatures and from less evolved melts is seen for post-climactic zircon. We propose a model in which a large volume of crystal-rich dacite magma was maintained above solidus temperatures by periodic andesitic recharge that is chemically invisible in the erupted components. The climactic caldera-forming eruption vented the upper portions of the magma system zircon was saturated. Zircon in postcaldera lavas indicate that residual magma from this system remained locally viable for eruption at least for some time after the caldera-forming event. Subsequently, deeper "remnant" dacite magma previously outside the zone of zircon saturation rose to shallower levels to re-establish hydraulic and isostatic equilibrium where zircon crystallization commenced anew, and drove more resurgent volcanism and uplift. The same magma

  17. Geochemistry and Petrogenesis of Volcanic Rocks in the Yeba Formation on the Gangdise Magmatic Arc, Tibet

    Institute of Scientific and Technical Information of China (English)

    Geng Quanru; Pan Guitang; Jin Zhenmin; Wang Liquan; Liao Zhongli


    The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagzê and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4 % and 64 %-69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66 %-1.01 %, much lower than those of continental tholeiite. The ΣREE contents of basalt and dacite are 60.3-135 μg/g and 126.4-167.9 μg/g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb*=0.54-1.17 averaging 0.84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb*=0.74-1.06 averaging 0.86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal lherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.

  18. The 3D Distribution of Magma Bodies that Fed the Paraná Silicic Volcanics, Brazil: A Combination of Field Evidence, Textural Analysis, and Geothermobarometry (United States)

    Harmon, L.; Gualda, G. A. R.; Gravley, D. M.


    The Paraná Silicic Volcanics include some of the largest eruptive deposits known in the geological record. However, we know very little about the magma bodies that fed these eruptions. Combining physical volcanology, geochemistry, and geothermobarometry techniques, we aim to find the sources of extinct magma bodies to build a 3D view of the magma structure at the time by discovering storage conditions, eruption styles, and post-eruption alteration. The approach elucidates temporal and spatial eruption styles and sequences of the silicic units that make up the Palmas unit of the Serra Geral formation, Brazil. We use field investigations to determine the history of volcanic deposits, domes, and changes in eruptive style; we map and characterize volcanic deposits based on thickness (thicker is proximal to source) and distribution of effusive (proximal to source) and explosive deposits. We focus on several exposed canyons that exhibit either exclusively explosive or effusive, or a clear progression from explosive to effusive deposits. The progression from explosive to effusive indicates a system change from explosively energetic to effusively waning. Additionally, observation of pervasive flow banding in both effusive and explosive deposits indicates rheomorphic flow through many portions of the field area, an indicator of hot emplacement. Geochemical work focuses on the pre-eruptive magma conditions to determine the depth of magma bodies. We utilize glass bearing samples of both the explosively deposited juvenile blob-like structures and obsidian samples to determine crystallization depth. The glass is variably altered, via silicification and devitrification processes, with the blobs more greatly silicified than the obsidian. We use rhyolite-MELTS geothermobarometry when pristine glass can be found. Initial results indicate shallow ( 80 MPa) storage conditions for the explosively erupted blobs. The combination of techniques builds a 3D understanding of extinct super

  19. Petrogenesis of meta-volcanic rocks from the Maimón Formation (Dominican Republic): Geochemical record of the nascent Greater Antilles paleo-arc (United States)

    Torró, Lisard; Proenza, Joaquín A.; Marchesi, Claudio; Garcia-Casco, Antonio; Lewis, John F.


    Metamorphosed basalts, basaltic andesites, andesites and plagiorhyolites of the Early Cretaceous, probably pre-Albian, Maimón Formation, located in the Cordillera Central of the Dominican Republic, are some of the earliest products of the Greater Antilles arc magmatism. In this article, new whole-rock element and Nd-Pb radiogenic isotope data are used to give new insights into the petrogenesis of the Maimón meta-volcanic rocks and constrain the early evolution of the Greater Antilles paleo-arc system. Three different groups of mafic volcanic rocks are recognized on the basis of their immobile element contents. Group 1 comprises basalts with compositions similar to low-Ti island arc tholeiites (IAT), which are depleted in light rare earth elements (LREE) and resemble the forearc basalts (FAB) and transitional FAB-boninitic basalts of the Izu-Bonin-Mariana forearc. Group 2 rocks have boninite-like compositions relatively rich in Cr and poor in TiO2. Group 3 comprises low-Ti island arc tholeiitic basalts with near-flat chondrite-normalized REE patterns. Plagiorhyolites and rare andesites present near-flat to subtly LREE-depleted chondrite normalized patterns typical of tholeiitic affinity. Nd and Pb isotopic ratios of plagiorhyolites, which are similar to those of Groups 1 and 3 basalts, support that these felsic lavas formed by anatexis of the arc lower crust. Geochemical modelling points that the parental basic magmas of the Maimón meta-volcanic rocks formed by hydrous melting of a heterogeneous spinel-facies mantle source, similar to depleted MORB mantle (DMM) or depleted DMM (D-DMM), fluxed by fluids from subducted oceanic crust and Atlantic Cretaceous pelagic sediments. Variations of subduction-sensitive element concentrations and ratios from Group 1 to the younger rocks of Groups 2 and 3 generally match the geochemical progression from FAB-like to boninite and IAT lavas described in subduction-initiation ophiolites. Group 1 basalts likely formed at magmatic

  20. Exponential decay of concentration variance during magma mixing: Robustness of a volcanic chronometer and implications for the homogenization of chemical heterogeneities in magmatic systems (United States)

    Rossi, Stefano; Petrelli, Maurizio; Morgavi, Daniele; González-García, Diego; Fischer, Lennart A.; Vetere, Francesco; Perugini, Diego


    The mixing of magmas is a fundamental process in the Earth system causing extreme compositional variations in igneous rocks. This process can develop with different intensities both in space and time, making the interpretation of compositional patterns in igneous rocks a petrological challenge. As a time-dependent process, magma mixing has been suggested to preserve information about the time elapsed between the injection of a new magma into sub-volcanic magma chambers and eruptions. This allowed the use of magma mixing as an additional volcanological tool to infer the mixing-to-eruption timescales. In spite of the potential of magma mixing processes to provide information about the timing of volcanic eruptions its statistical robustness is not yet established. This represents a prerequisite to apply reliably this conceptual model. Here, new chaotic magma mixing experiments were performed at different times using natural melts. The degree of reproducibility of experimental results was tested repeating one experiment at the same starting conditions and comparing the compositional variability. We further tested the robustness of the statistical analysis by randomly removing from the analysed dataset a progressively increasing number of samples. Results highlight the robustness of the method to derive empirical relationships linking the efficiency of chemical exchanges and mixing time. These empirical relationships remain valid by removing up to 80% of the analytical determinations. Experimental results were applied to constrain the homogenization time of chemical heterogeneities in natural magmatic system during mixing. The calculations show that, when the mixing dynamics generate millimetre thick filaments, homogenization timescales of the order of a few minutes are to be expected.

  1. Metagenomic investigation of the geologically unique Hellenic Volcanic Arc reveals a distinctive ecosystem with unexpected physiology. (United States)

    Oulas, Anastasis; Polymenakou, Paraskevi N; Seshadri, Rekha; Tripp, H James; Mandalakis, Manolis; Paez-Espino, A David; Pati, Amrita; Chain, Patrick; Nomikou, Paraskevi; Carey, Steven; Kilias, Stephanos; Christakis, Christos; Kotoulas, Georgios; Magoulas, Antonios; Ivanova, Natalia N; Kyrpides, Nikos C


    Hydrothermal vents represent a deep, hot, aphotic biosphere where chemosynthetic primary producers, fuelled by chemicals from Earth's subsurface, form the basis of life. In this study, we examined microbial mats from two distinct volcanic sites within the Hellenic Volcanic Arc (HVA). The HVA is geologically and ecologically unique, with reported emissions of CO2 -saturated fluids at temperatures up to 220°C and a notable absence of macrofauna. Metagenomic data reveals highly complex prokaryotic communities composed of chemolithoautotrophs, some methanotrophs, and to our surprise, heterotrophs capable of anaerobic degradation of aromatic hydrocarbons. Our data suggest that aromatic hydrocarbons may indeed be a significant source of carbon in these sites, and instigate additional research into the nature and origin of these compounds in the HVA. Novel physiology was assigned to several uncultured prokaryotic lineages; most notably, a SAR406 representative is attributed with a role in anaerobic hydrocarbon degradation. This dataset, the largest to date from submarine volcanic ecosystems, constitutes a significant resource of novel genes and pathways with potential biotechnological applications.

  2. Recent Rift Volcanism in the Northern Gulf of California and the Salton Through: Why a Preponderance of Evolved Magmas? (United States)

    Martín, A.; Weber, B.; Schmitt, A. K.; Lonsdale, P.


    Quaternary volcanoes and shallow intrusions throughout the northern Gulf Extensional Province provide a unique opportunity to characterize active crustal accretion associated with extreme continental rifting. In the Lower Delfin basin and Isla San Luis volcanic rocks have compositional continuity from basaltic andesite (>54 % SiO2) to sub-alkaline rhyolite, whereas Roca Consag in the Wagner basin, and Cerro Prieto are homogeneous, low-K, lithoidal, microlithic dacites. Salton Buttes surface lavas and a seamount in the Upper Delfin basin are dominantly rhyolitic. Basaltic xenoliths, intrusive basaltic sills and altered subsurface rhyolites are known from the Salton Trough and Cerro Prieto. All Quaternary volcanic rocks in the region have depleted (relative to CHUR) Nd isotopic compositions with ɛNd of +8.5 and +6.3 in the Salton Buttes and marginally lower values (+6.5 to +4.1) for Roca Consag, Lower Delfin basin and Isla San Luis. Rhyolite from the Upper Delfin basin yielded ɛNd of +2.2. These values are consistent with overall depleted 87Sr/86/Sr ratios (0.70353-0.70382). Only rhyolites from Lower and Upper Delfin basin have higher 87Sr/86Sr (0.70492 -0.70661) compared to coexisting andesites, which implies hydrothermal alteration and/or minor contamination by continental crust and/or sediments. Volcanic rocks within individual basins thus represent variably differentiated and, to a smaller degree, contaminated, co- genetic suites, as indicated by negative Eu anomalies that reflect plagioclase fractionation in rhyolites. Ion microprobe ages of zircons from Roca Consag are heterogeneous. The youngest ages are ~120 ka and several pre-Quaternary xenocrysts were observed, but the data define a dominant peak at ~1 Ma. The isotope data suggest recent differentiation of dominantly mantle-derived young crust. The preponderance of intermediate to felsic volcanism in the northern Gulf of California suggests that only low- density magmas can reach shallow levels where they

  3. Seismic tomography model reveals mantle magma sources of recent volcanic activity at El Hierro Island (Canary Islands, Spain) (United States)

    García-Yeguas, Araceli; Ibáñez, Jesús M.; Koulakov, Ivan; Jakovlev, Andrey; Romero-Ruiz, M. Carmen; Prudencio, Janire


    We present a 3-D model of P and S velocities beneath El Hierro Island, constructed using the traveltime data of more than 13 000 local earthquakes recorded by the Instituto Geográfico Nacional (IGN, Spain) in the period from 2011 July to 2012 September. The velocity models were performed using the LOTOS code for iterative passive source tomography. The results of inversion were thoroughly verified using different resolution and robustness tests. The results reveal that the majority of the onshore area of El Hierro is associated with a high-velocity anomaly observed down to 10-12-km depth. This anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 Myr and intrusive magmatic bodies. Below this high-velocity pattern, we observe a low-velocity anomaly, interpreted as a batch of magma coming from the mantle located beneath El Hierro. The boundary between the low- and high-velocity anomalies is marked by a prominent seismicity cluster, thought to represent anomalous stresses due to the interaction of the batch of magma with crust material. The areas of recent eruptions, Orchilla and La Restinga, are associated with low-velocity anomalies surrounding the main high-velocity block. These eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate. These results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands, such as in the Canaries, which is not yet clearly understood.

  4. High resolution seismic data coupled to Multibeam bathymetry of Stromboli island collected in the frame of the Stromboli geophysical experiment: implications with the marine geophysics and volcanology of the Aeolian Arc volcanic complex (Sicily, Southern Tyrrhenian sea, Italy). (United States)

    Aiello, Gemma; Di Fiore, Vincenzo; Marsella, Ennio; Passaro, Salvatore


    New high resolution seismic data (Subbottom Chirp) coupled to high resolution Multibeam bathymetry collected in the frame of the Stromboli geophysical experiment aimed at recording active seismic data and tomography of the Stromboli Island are here presented. The Stromboli geophysical experiment has been already carried out based on onshore and offshore data acquisition in order to investigate the deep structure and the location of the magma chambers of the Stromboli volcano. A new detailed swath bathymetry of Stromboli Island is here shown and discussed to reconstruct an up-to-date morpho-bathymetry and marine geology of the area compared to the volcanologic setting of the Aeolian Arc volcanic complex. Due to its high resolution the new Digital Terrain Model of the Stromboli Island gives interesting information about the submerged structure of the volcano, particularly about the volcano-tectonic and gravitational processes involving the submarine flanks of the edifice. Several seismic units have been identified based on the geologic interpretation of Subbottom Chirp profiles recorded around the volcanic edifice and interpreted as volcanic acoustic basement pertaining to the volcano and overlying slide chaotic bodies emplaced during its complex volcano-tectonic evolution. They are related to the eruptive activity of Stromboli, mainly poliphasic and to regional geological processes involving the intriguing geology of the Aeolian Arc, a volcanic area still in activity and needing improved research interest.

  5. Phenocryst complexity in andesites and dacites from the Tequila volcanic field, Mexico: resolving the effects of degassing vs. magma mixing (United States)

    Frey, Holli M.; Lange, Rebecca A.


    The petrology of five phenocryst-poor (2-5%) andesites and dacites, all of which were erupted from different short-lived, monogenetic vents, is compared to that of phenocryst-rich (10-25%) andesites erupted from the adjacent stratovolcano, Volcán Tequila, in the Mexican arc. Despite differences in phenocryst abundances, these magmas have comparable phase assemblages (plagioclase + orthopyroxene + titanomagnetite + ilmenite + apatite ± augite ± hornblende), and similarly wide variations in phenocryst compositions, coupled to complex zoning patterns. For the phenocryst-poor lavas, equilibrium pairs of two Fe-Ti oxides lead to a narrow range of calculated temperatures for each sample that range from 934 (±24) to 1,073 (±6)°C and oxygen fugacities that range from +0.1 to +0.7 log units relative to the Ni-NiO buffer. Application of the plagioclase-liquid hygrometer to each sample at these calculated temperatures leads to maximum melt water concentrations of 4.6-3.1 wt% during plagioclase crystallization, indicating that the magmas were fluid saturated at depths ≥6.4-4.5 km. There is a wide, continuous range in the composition of plagioclase (≤44 mol% An) and orthopyroxene (≤16% Mg#) phenocrysts in each sample, which is consistent with a loss of dissolved water (≤2.8 wt%) from the melt phase during degassing as the magmas ascended rapidly to the surface. Evidence is presented that shows the effect of dissolved water is to reduce the activity of MgO relative to FeO in the melt phase, which indicates that degassing will also affect the Mg# of pyroxene phenocrysts, with higher melt water concentrations favoring Fe-rich pyroxene. Both plagioclase and orthopyroxene commonly display diffusion-limited growth textures (e.g., skeletal and hopper crystals, large interior melt hollows, and swallow tails), which are consistent with large undercoolings produced by degassing-induced crystallization. Therefore, degassing is proposed as a possible cause for the phenocryst

  6. Late cenozoic vertical movements of non-volcanic islands in the Banda Arc area (United States)

    De Smet, M. E. M.; Fortuin, A. R.; Tjokrosapoetro, S.; Van Hinte, J. E.

    During onshore campaigns of the Snellius-II Expedition late Cenozoic sections were recorded and systematically sampled on the non-volcanic outer Banda Arc Islands of Timor, Buton, Buru, Seram and Kai. Microfaunal studies provided age and palaeobathymetric data to construct geohistory diagrams. Geohistory analysis of field and laboratory data allows to calculate rates of vertical movements of the island basements. The vertical movements were intermittent and differed widely from place to place in the arc; short periods of uplift alternated with longer periods of tectonic rest or subsidence and lateral variations in timing and magnitude seem to be more the rule than the exception. Movements affected larger segments of the arc at about the same time, especially since the late Pliocene, when widespread vertical movements started, which led to the present configuration of the arc. Rates of uplift or subsidence differed within each segment. On an intermediate scale, deformation has the character of tilting or doming of whole islands or parts of islands. On a local scale, various types of deformation occur. Calculated duration of uplift pulses is in the order of a million years where less than 50 cm·ka -1 of vertical movements are involved. Sections, however, with a high time stratigraphic resolutions show pulses of uplift with a duration of only some hundreds of thousands of years and rates of more than 500 cm·ka -1. The duration of such pulses therefore is comparable to that of eustatic third order sea level changes. But because their amplitude is an order of magnitude larger, this implies that in tectonically active areas eustatic signals, preserved in the sedimentary record, will be overprinted by tectonics, i.e. will be difficult to disentangle from the tectonic signal.

  7. Intermediate composition magma production in an intracontinental setting: Unusual andesites and dacites of the mid-Miocene Santa Rosa-Calico volcanic field, Northern Nevada (United States)

    Brueseke, Matthew E.; Hart, William K.


    The mid-Miocene Santa Rosa-Calico volcanic field (SC) of northern Nevada provides an outstanding example of the role open-system magmatic processes play in producing calc-alkaline and tholeiitic andesite-dacite magmas in an intracontinental setting. SC volcanism commenced at ˜ 16.7 Ma and is associated with the initial manifestations of the Yellowstone hotspot, the Columbia River-Steens flood basalt event(s), and the formation of the Northern Nevada rift. Locally a diverse package of magmatic products ranging from tholeiitic basalt to high-Si rhyolite was produced during an ˜ 2 myr duration. Within this package are the products of at least four distinct intermediate composition magmatic systems that may represent as much as 40% of the SC volcanic pile. These help differentiate the SC from contemporaneous Oregon Plateau volcanic fields (e.g. McDermitt, Lake Owyhee, Northwest Nevada) that are dominated by bimodal basalt-rhyolite assemblages. All SC intermediate units are characterized by textural and mineralogic complexities including xenoliths and xenocrysts of local crust and crystal clots of plagioclase ± clinopyroxene ± orthopyroxene ± oxide. SC intermediate units are dominantly tholeiitic, but include lava flows with transitional to calc-alkaline affinities. Relative to locally erupted Steens Basalt, SC intermediate lava flows have similar elemental enrichments and depletions, but dissimilar Sr and Nd isotopic compositions. These isotopic differences, coupled with the abundant disequilibrium features and variable incompatible element ratios, indicate that open system magmatic processes played a major role in the genesis of the intermediate units. SC silicic magmas were produced primarily via upper crustal melting of chemically and isotopically heterogeneous Cretaceous granitoid. Interaction between fractionating mafic Steens flood basalt magmas and the more evolved crustal melts ± assimilation of local upper crust provides a general template for the

  8. Volcanic stratigraphy and evidence of magma mixing in the Quaternary Payún Matrú volcano, andean backarc in western Argentina Estratigrafía volcánica y evidencia de mezcla de magmas en el volcán Payún Matrú del Cuaternario, en el retroarco andino de Argentina occidental

    Directory of Open Access Journals (Sweden)

    Irene R Hernando


    Full Text Available The Payún Matrú Volcanic Field is located in the Payenia Basaltic Province of the recent back-arc of western Argentina (35°S-38°S. This province is younger than 5 Ma, and most of its volcanic activity took place since 2 Ma. The Payún Matrú Volcanic Field contains two composite volcanoes, Payún Matrú and Payún Liso, and two basaltic fields in an E-W oriented zone, located east and west of the Payún Matrú volcano. Payún Matrú is the largest volcano of this volcanic field, and consists of a shield-shaped edifice with a circular summit caldera of 8 km in diameter. The composition of both composite volcanoes is alkaline and predominantly trachytic, having also minor intermediate lavas. The basaltic fields consist of basalts and trachybasalts, with clinopyroxene and abundant olivine as phenocrysts and also in the groundmass. Textures indicating mixing and mingling processes, such as dusty plagioclases along with clear ones, biotite replaced by anhydrous minerals and two groundmasses with a fluid-fluid relationship, are common in the early pre-caldera stage of Payún Matrú and some post-caldera lavas. The latest post-caldera lavas are trachytic, with clean sanidine phenocrysts without disequilibrium textures. A remarkable characteristic of the Payún Matrú Volcanic Field is the fact that the Payún Matrú caldera is surrounded by basaltic fields at its base, while no basalts were erupted in the caldera region. We propose that the absence of basaltic lavas in the Payún Matrú volcano is due to the presence of a magmatic chamber below it, and that the mafic magmas rising from deeper levels were unable to erupt without interaction with more evolved melts. Intermediate hybrid magmas produced as a consequence of magma mixing and mingling between basaltic and trachytic magmas, are present in the early and mid-history of Payún Matrú volcano. We present here new information about the Quaternary Payún Matrú Volcanic Field derived from field

  9. Late Cretaceous volcanic arc system in Southwest Korea: Occurrence, lithological characteristics, SHRIMP zircon U-Pb age, and tectonic implications (United States)

    Koh, Hee Jae; Kwon, Chang Woo


    In the southwest region of the Korean Peninsula, four large volcanoes, the Buan, Seonunsan, Wido, and Beopseongpo, with a maximum diameter of ca 20 km, form a distinct topographic undulation along the NE-SW-trending Hamyeol Fault. These volcanics comprise various types of pyroclastic, sedimentary, and lava/intrusive rocks, and are interpreted as remnants of calderas resulting from various volcanic eruptions, indicating that Hamyeol Fault, together with crustal extension, played an important role in volcano formation in this region. SHRIMP U-Pb ages of zircon isolated from each volcanics are as follows. For Buan Volcanics, Cheonmasan Tuff 87.23 ±0.92 Ma, Udongje Tuff 86.79 ±0.71 Ma, Seokpo Tuff 87.30 ±0.99 Ma and Yujeongje Tuff 86.66 ±0.93 Ma. For Seonunsan Volcanics, Gyeongsusan Tuff 84.9 ±1.1 Ma and Yeongije Tuff 86.61 ±0.67 Ma. These ages indicate that the four volcanics were formed in the Late Cretaceous. The ages are comparable to those of the volcanic rocks of the Aioi and Arima groups in Southwestern Japan, suggesting that the Late Cretaceous volcanic arc systems developed in a NE-SW direction from the Japanese Islands to the southwestern part of the Korean Peninsula caused by regional magmatism together with crustal deformation as reflected by occurrence of the volcanic rocks along the Hamyeol Fault.

  10. Magma intrusion near Volcan Tancítaro: Evidence from seismic analysis (United States)

    Pinzón, Juan I.; Núñez-Cornú, Francisco J.; Rowe, Charlotte A.


    Between May and June 2006, an earthquake swarm occurred near Volcan Tancítaro in Mexico, which was recorded by a temporary seismic deployment known as the MARS network. We located ∼1000 events from this seismic swarm. Previous earthquake swarms in the area were reported in the years 1997, 1999 and 2000. We relocate and analyze the evolution and properties of the 2006 earthquake swarm, employing a waveform cross-correlation-based phase repicking technique. Hypocenters from 911 events were located and divided into eighteen families having a correlation coefficient at or above 0.75. 90% of the earthquakes provide at least sixteen phase picks. We used the single-event location code Hypo71 and the P-wave velocity model used by the Jalisco Seismic and Accelerometer Network to improve hypocenters based on the correlation-adjusted phase arrival times. We relocated 121 earthquakes, which show clearly two clusters, between 9-10 km and 3-4 km depth respectively. The average location error estimates are <1 km epicentrally, and <2 km in depth, for the largest event in each cluster. Depths of seismicity migrate upward from 16 to 3.5 km and exhibit a NE-SW trend. The swarm first migrated toward Paricutin Volcano but by mid-June began propagating back toward Volcán Tancítaro. In addition to its persistence, noteworthy aspects of this swarm include a quasi-exponential increase in the rate of activity within the first 15 days; a b-value of 1.47; a jug-shaped hypocenter distribution; a shoaling rate of ∼5 km/month within the deeper cluster, and a composite focal mechanism solution indicating largely reverse faulting. These features of the swarm suggest a magmatic source elevating the crustal strain beneath Volcan Tancítaro.

  11. Multidisciplinary exploratory study of a geothermal resource in the active volcanic arc of Basse-Terre (Guadeloupe, Lesser Antilles) (United States)

    Navelot, Vivien; Favier, Alexiane; Géraud, Yves; Diraison, Marc; Corsini, Michel; Verati, Chrystèle; Lardeaux, Jean-Marc; Mercier de Lépinay, Jeanne; Munschy, Marc


    The GEOTREF project (high enthalpy geothermal energy in fractured reservoirs), supported by the French government program, "Investissements d'avenir" develops a sustainable geothermal resource in the Vieux Habitants area, 8-km south of the currently exploited Bouillante geothermal field. The Basse Terre Island is a recent volcanic arc (geothermal gradient of 70 ˚ C/km.

  12. Accessory mineral U-Th-Pb ages and 40Ar/39Ar eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California (United States)

    Simon, J.I.; Vazquez, J.A.; Renne, P.R.; Schmitt, A.K.; Bacon, C.R.; Reid, M.R.


    We determined Ar/Ar eruption ages of eight extrusions from the Pleistocene Coso volcanic field, a long-lived series of small volume rhyolitic domes in eastern California. Combined with ion-microprobe dating of crystal ages of zircon and allanite from these lavas and from granophyre geothermal well cuttings, we were able to track the range of magma-production rates over the past 650 ka at Coso. In ??? 230 ka rhyolites we find no evidence of protracted magma residence or recycled zircon (or allanite) from Pleistocene predecessors. A significant subset of zircon in the ???85 ka rhyolites yielded ages between ???100 and 200 Ma, requiring that generation of at least some rhyolites involves material from Mesozoic basement. Similar zircon xenocrysts are found in an ???200 ka granophyre. The new age constraints imply that magma evolution at Coso can occur rapidly as demonstrated by significant changes in rhyolite composition over short time intervals (???10's to 100's ka). In conjunction with radioisotopic age constraints from other young silicic volcanic fields, dating of Coso rhyolites highlights the fact that at least some (and often the more voluminous) rhyolites are produced relatively rapidly, but that many small-volume rhyolites likely represent separation from long-lived mushy magma bodies. ?? The Author(s) 2009.

  13. Deep long-period earthquakes west of the volcanic arc in Oregon: evidence of serpentine dehydration in the fore-arc mantle wedge (United States)

    Vidale, John E.; Schmidt, David A.; Malone, Stephen D.; Hotovec-Ellis, Alicia J.; Moran, Seth C.; Creager, Kenneth C.; Houston, Heidi


    Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction fore arc: 40–80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likely to be serpentinized and cold. The lack of fore-arc DLPs elsewhere along the arc suggests that localized heating may be dehydrating the serpentinized mantle wedge at these latitudes and causing DLPs by dehydration embrittlement. Higher heat flow in this region could be introduced by anomalously hot mantle, associated with the western migration of volcanism across the High Lava Plains of eastern Oregon, entrained in the corner flow proximal to the mantle wedge. Alternatively, fluids rising from the subducting slab through the mantle wedge may be the source of offset DLPs. As far as we know, these are among the first DLPs to be observed in the fore arc of a subduction-zone system.

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


    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

  15. The tectonic emplacement of Sumba in the Sunda-Banda Arc: paleomagnetic and geochemical evidence from the early Miocene Jawila volcanics

    NARCIS (Netherlands)

    Wensink, H.; Bergen, M.J. van


    The island of Sumba is a continental fragment in the fore-arc region near the transition between the Sunda Arc and Banda Arc in southeastern Indonesia. Paleomagnetic and geochemical evidence from the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final drift stage

  16. Oligocene and Miocene arc volcanism in northeastern California: evidence for post-Eocene segmentation of the subducting Farallon plate (United States)

    Colgan, J.P.; Egger, A.E.; John, D.A.; Cousens, B.; Fleck, R.J.; Henry, C.D.


    The Warner Range in northeastern California exposes a section of Tertiary rocks over 3 km thick, offering a unique opportunity to study the long-term history of Cascade arc volcanism in an area otherwise covered by younger volcanic rocks. The oldest locally sourced volcanic rocks in the Warner Range are Oligocene (28–24 Ma) and include a sequence of basalt and basaltic andesite lava flows overlain by hornblende and pyroxene andesite pyroclastic flows and minor lava flows. Both sequences vary in thickness (0–2 km) along strike and are inferred to be the erosional remnants of one or more large, partly overlapping composite volcanoes. No volcanic rocks were erupted in the Warner Range between ca. 24 and 16 Ma, although minor distally sourced silicic tuffs were deposited during this time. Arc volcanism resumed ca. 16 Ma with eruption of basalt and basaltic andesite lavas sourced from eruptive centers 5–10 km south of the relict Oligocene centers. Post–16 Ma arc volcanism continued until ca. 8 Ma, forming numerous eroded but well-preserved shield volcanoes to the south of the Warner Range. Oligocene to Late Miocene volcanic rocks in and around the Warner Range are calc-alkaline basalts to andesites (48%–61% SiO2) that display negative Ti, Nb, and Ta anomalies in trace element spider diagrams, consistent with an arc setting. Middle Miocene lavas in the Warner Range are distinctly different in age, composition, and eruptive style from the nearby Steens Basalt, with which they were previously correlated. Middle to Late Miocene shield volcanoes south of the Warner Range consist of homogeneous basaltic andesites (53%–57% SiO2) that are compositionally similar to Oligocene rocks in the Warner Range. They are distinctly different from younger (Late Miocene to Pliocene) high-Al, low-K olivine tholeiites, which are more mafic (46%–49% SiO2), did not build large edifices, and are thought to be related to backarc extension. The Warner Range is ∼100 km east of the

  17. Magma-derived gas influx and water-rock interactions in the volcanic aquifer of Mt. Vesuvius, Italy (United States)

    Federico, C.; Aiuppa, A.; Allard, P.; Bellomo, S.; Jean-Baptiste, P.; Parello, F.; Valenza, M.


    , two areas of high CO 2 release and enhanced rock leaching are recognized on the western (Torre del Greco) and southwestern (Torre Annunziata-Pompeii) flanks of Vesuvius, where important NE-SW and NW-SE tectonic structures are recognized. In contrast, waters flowing through the northern sector of the volcano are generally colder, less saline, and CO 2 depleted, despite in some cases containing significant concentrations of magma-derived helium. The remarkable differences among the various sectors of the volcano are reconciled in a geochemical interpretative model, which is consistent with recent structural and geophysical evidences on the structure of Somma-Vesuvius volcanic complex.

  18. The Implications of Petit-Spot Volcanism for the Origin of Alkaline Intraplate Magmas (United States)

    Pilet, S.; Rochat, L.; Abe, N.


    The compositions of alkaline lavas are mostly similar even though they are observed in various tectonic contexts. This similarity has been used to suggest that these rocks are all produced by deep processes. Nevertheless, the formation of petit-spot seamounts, which are interpreted as low-degree melts extracted from the base of the lithosphere in response to plate flexure, demonstrates that alkaline lavas could also be produced by shallow tectonic processes. In this presentation, petit-spot lavas will be compared to intraplate basalts to reveal the processes that control the petrogenesis of intraplate lavas. Petit-spot lavas are characterized by an alkaline basaltic composition rich in potassium (K2O/Na2O>0.7). This distinguishes them from oceanic island basalts, which are characterized by a lower alkali ratio. The K-rich nature of petit-spot melts is explained either by the melting of an asthenospheric mantle domain enriched in K2O, TiO2 and trace elements, or by the interaction of low-degree melts extracted from the low velocity zone (LVZ) with phlogopite-rich metasomatic lithologies present in the lower part of the lithospheric mantle; metasomatic cumulates formed during an early stage of LVZ melt migration. The latter model is supported by the recent discovery of metasomatized peridotite xenoliths in petit-spot lavas which demonstrates that low degree melts, similar in composition to the melts responsible for the formation of phlogopite-rich cumulates in continental lithospheric mantle, percolate through the oceanic lithospheric mantle producing a metasomatic enrichment. The involvement of metasomatic processes in the formation of petit-spot lavas provides a link to the metasomatic lithospheric model for the origin of alkaline magmas, a model that suggests that these rocks are not produced directly from the asthenosphere, but by the melting of hydrous veins produced by the percolation and differentiation of low degree asthonospheric melts across the

  19. Bimodal magmatism during the Diego Hernández Formation, Tenerife, Canary Islands: genesis and eruption-triggering of phonolitic magmas during ongoing mafic volcanism (United States)

    Olin, P. H.; Wolff, J. A.; Edgar, C. J.; Cas, R.; Martí, J.


    The Diego Hernández Formation (DHF) represents the explosive eruption of nearly 70 cubic km of phonolite over approximately 200 k.y. from the Las Cañadas caldera on Tenerife. Four chemostratigraphic units are distinguished on the basis of trace element contents: DHF bs (represented by the 370 ka Fortaleza and 347 ka Roque Members), DHF I (319 ka Aldea, 309 ka Fasnia, and 268 ka Poris Members), DHF II (Arafo and 223 ka Caleta Members), and DHF III (Cruz Sequence and the 196 ka Abrigo Member); all named units involve plinian and/or ignimbrite components that devastated a significant fraction of the island [1]. These chemostratigraphic units demarcate two dominant compositional trends distinct in incompatible element contents, and in Nb/Ta and REE ratios. DHF bs and DHF III plot along a high-Nb trend, and DHF I and DHF II plot along a low-Nb trend, a feature consistent with divergent fractionation histories involving titanite. Mafic magma was an important component of the DHF magmatic system and flanking mafic volcanism was ongoing during DHF time. Major phonolitic eruptions are conformably bounded by basanitic lavas and scoria deposits. Mafic magmatic components are identifiable in many of the phonolitic pyroclastic deposits as mafic, mingled and banded pumices, or as quenched mafic enclaves. Mafic components in the Abrigo, Caleta, and Poris Members are nearly geochemically identical to the underlying scoria or lava, suggesting that flanking mafic volcanism may in some cases be associated with subcaldera intrusive events that remobilize phonolitic magma to trigger major explosive eruptions. We envisage that the DHF represents a time when the intrusion of mantle-derived mafic magma in the lower crust supplied heat sufficient for the generation of intermediate tephriphonolite and phonotephrite magmas via melting of gabbroic/basaltic crust. Some of these intermediate magmas evolved to phonolite by crystal fractionation, a scenario consistent with DHF III

  20. 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. Volcanism in the Campania Plain: Vesuvius, Campi Flegrei and Ignimbrites


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


    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 mixing, occurring after magma genesis in the mantle. Most mafic magmas are enriched in LILE (K, Rb, Ba), REE (Ce, Sm) and Y, show small Nb–Ta negative anomalies, and have values of Nb/Zr ...

  1. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing (United States)

    Chang, J.M.; Feeley, T.C.; Deraps, M.R.


    The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

  2. Subduction of continental material in the Banda Arc, Eastern Indonesia : Sr-Nd-Pb isotope and trace-element evidence from volcanics and sediments

    NARCIS (Netherlands)

    Vroon, Pieter Z.


    This thesis presents the results of a geochemical study of the Banda Arc (East Indonesia) where magma genesis is influenced by subducted source components that are controlled by an active arc-continent collision. The main objective of this study is to investigate the role of subducted continental

  3. Age and chemical constraints of Volcán Tunupa: Implications for behind arc volcanism in the Bolivian central Andes (United States)

    salisbury, M. J.; Kent, A. J.; Jiménez, N.; Jicha, B. R.


    New 40Ar/39Ar age determinations of groundmass separates and whole-rock geochemical data constrain the Pleistocene eruptive history of Volcán Tunupa, a glacially-dissected composite volcano (~50 km3) situated between the Salar de Uyuni and Salar de Coipasa. Tunupa erupted ~110 km east of the arc front of the Western Cordillera of the central Andes near the eastern edge of the Intersalar Volcanic Field, an arc-perpendicular expression of volcanism that extends to the central Altiplano basin of Bolivia. 40Ar/39Ar age determinations indicate that the edifice was constructed between ~1.40 and 1.55 Ma, whereas nearby Cerro Huayrana lavas erupted ~ 11 Ma. Published ages from the Western Cordillera that are concordant with both Tunupa and Huayrana lavas demonstrate that the central Altiplano lavas are a long-lived expression of behind arc volcanism. The Tunupa lavas define a calc-alkaline trend from trachyandesite to trachydacite (wt.% SiO2 = 60.6 - 63.6; wt.% K2O + Na2O = 7.5 - 8.3) and are overlain by younger, more silicic (wt.% SiO2 = 66) trachydacitic domes. Major element compositions of Tunupa and Huayrana are enriched in FeO and TiO2 compared to the arc front. These lavas are also enriched in high field strength elements, notably Nb and Ta, and are characterized by considerably lower Ba/Nb and La/Ta ratios than arc front lavas in northern Chile. The geochemical and spatiotemporal patterns of the behind arc Tunupa and Huayrana lavas suggest different petrogenetic histories from typical central Andean arc lavas.

  4. Backarc tectonism, volcanism, and mass wasting shape seafloor morphology in the Santorini-Christiana-Amorgos region of the Hellenic Volcanic Arc (United States)

    Hooft, Emilie E. E.; Nomikou, Paraskevi; Toomey, Douglas R.; Lampridou, Danai; Getz, Claire; Christopoulou, Maria-Eleni; O'Hara, Daniel; Arnoux, Gillean M.; Bodmer, Miles; Gray, Melissa; Heath, Benjamin A.; VanderBeek, Brandon P.


    In subduction zone backarcs, extensional deformation and arc volcanism interact and these processes, together with mass wasting, shape the seafloor morphology. We present a new bathymetric map of the Santorini-Christiana-Amorgos backarc region of the Hellenic subduction zone by merging high-resolution multibeam swath data from the R/V Langseth PROTEUS seismic experiment with existing maps. The map together with Knudsen subbottom echosounding profiles reveal that recent tectonism, volcanism, and mass wasting are more prevalent in the Santorini-Amorgos region on the east side of Santorini than in the Christiana Basin on the west side. In the Santorini-Amorgos region, large normal faults form the Anydros and Anafi Basins. Where normal fault segments overlap, two nearby accommodation zones generate a relay ramp and the adjoining Anydros synclinal horst with associated complex faulting and elevated seismicity. The ongoing normal faulting in the Santorini-Amorgos region is accompanied by potentially tsunamigenic submarine landsliding; we identified a large submarine landslide along the Santorini-Amorgos Fault and a smaller landslide with an overlying debris chute along the Amorgos Fault. Volcanic activity is also focused in this eastern region along the Kolumbo lineament within the Anydros Basin. Within the Christiana Basin we discovered the Proteus Knoll and adjacent buried edifice. We suggest that this is an older volcanic edifice formed along the Hellenic Volcanic Arc between Santorini and Milos. Around Santorini itself, features formed during, and immediately after, the Late Bronze Age eruption dominate the seafloor morphology such as the northern strait and wrinkled seafloor pyroclastic flow deposits. This topography is continually reshaped at a smaller scale by ongoing mass wasting. We infer that the earthquake, volcanic, and tsunami activity of the Santorini-Amorgos region is a consequence of focused northwest-southeast extension as the southeastern Aegean moves

  5. First determination of dissolved volatiles in magmas of Mt Garet (Vanuatu arc). Origin of sulfur emissions (United States)

    Floury, P.; Metrich, N.; Bertagnini, A.; Garaebiti, E.; Hidalgo, S.; Beaumais, A.; Neuville, D.


    Mt Garet, on Gaua island, is one of the active volcanoes of the Vanuatu arc in the Southwest Pacific. This 360 m high cone emerges from the lake Letas in the summit caldera of a composite volcano. Since 1962, Mt Garet produced ash and gas plumes recurrently, the last explosive events being documented in 2009 - 2010. Airborne measurements of SO2 emission rates, the only data set presently available for this volcano, were realized in 2009 and revealed a high SO2 flux of, on average, 2955 tons per day [1]. We report here the very first data on the geochemistry of the scoriae emitted in January 2010, together with analyses of major elements and volatiles (H2O, Cl, S) in crystal-hosted melt inclusions and a detailed mineralogy of the samples. The 2010 scoriae are basaltic-andesites and are more evolved that the pre-1962 basaltic lava flows of Mt Garet. Their major and trace element evolution cannot be reconciled with a single process of fractional crystallization, but suggest mixing between a pre-1962 like basalt and an evolved trachydacitic end-member. This observation strongly suggests the recent development of a small reservoir beneath Mt Garet. The plagioclases (An89-73) and clinopyroxenes (Fs5-16) display a significant chemical range but do not clearly evidence reverse zoning. The paragenesis is complemented by Fe-Ti oxides (USP39-40) and scarce olivines (Fo72.7). Some crystals are obviously inherited (e.g., An-poor plagioclase). The melt inclusions are ubiquitous but of small size in each mineral phase. Their H2O content was specifically determined using micro-Raman spectroscopy (IPGP), with a series of basaltic glass standards previously developed for Raman calibration [2]. Data and spectrum are treated following [3]. As a whole melt inclusion compositions cover the whole chemical spectrum from basalt to trachydacite. Their contents in H2O (2.7-0.8 wt%), S (1570 - Journal of Volcanology and Geothermal Research, 211-212, 36-46 [2] Mercier et al., (2009) and (2010

  6. Post-collisional volcanism in a sinking slab setting—crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alborán volcanic province, southeastern Spain (United States)

    Zeck, H. P.; Kristensen, A. B.; Williams, I. S.


    Caldear Volcanic Group (CVG), a stratigraphically well defined, calc-alkaline rock complex within S a de Gata in the eastern part of the Alpine Betic mountain chain, S Spain, consists of three distinct formations: Hernández pyroxene andesites, Bujo hornblende-bearing pyroxene andesites and Viuda hornblende-bearing pyroxene dacites-rhyolites. The letter rock formation may have developed through crystal fractionation of mainly plagioclase and pyroxenes, however there is no direct relation between two formations. CVG has a domainal structure with a northeastern domain where Hernández formation is overlain by Bujo formation while Viuda formation is absent, and a southwestern domain where Viuda formation forms the only fractionate after Hernández formation. Hernández parent magma is thought generated through crustal anatexis by dehydration melting of a predominantly amphibolitic source rock complex which was formed by metamorphism from c. 500 Ma volcano-sedimentary parent material. The domainal structure of CVG is explained by compositional variation within this protogenetic complex. Single crystal U-Pb ages of c. 500 Ma to 1800 Ma for inherited zircon support the presence of clastic material of Proterozoic derivation within the original volcano-sedimentary complex. Regional study of syn-collisional rock formations (Alpine nappe complexes) indicate that the collisional tectonic stage in the Betic-Rif orogenic belt took place rather early (25-30 Ma?) and was followed by a stage of rapid regional rock uplift, fast cooling (c. 500°C/my) and extensional tectonics in the period 22-17 Ma. This later tectonic stage was set into motion by slab break-off which set the stage for a high temperature regime in the overlying lithosphere, providing the framework for the crustal melting and magma production responsible for the calc-alkaline rocks of Alborán volcanic province. Miocene zircon with ages ranging from c. 17 to 11 Ma indicate a rather protracted magmatic development

  7. From northern Gondwana passive margin to arc dismantling: a geochemical discrimination of Ordovician volcanisms (Sardinia, Italy) (United States)

    Gaggero, L.; Oggiano, G.; Buzzi, L.; Funedda, A.


    In Sardinia, one of the southernmost remain of the European Variscan belt, a crustal section through northern Gondwanan paleodomains is largely preserved. It bears significant evidence of igneous activity, recently detailed in field relationships and radiometric dating (Oggiano et al., submitted). A Cambro - Ordovician (491.7 ± 3.5 Ma ÷ 479.9 ± 2.1 Ma, LA-ICP-MS U-Pb zircon age) bimodal volcanic suite occurs with continuity in external and inner Variscan nappes of Sardinia below the so-called Sardic unconformity. The igneous suite represents an intraplate volcanic activity developed through subsequent episodes: i) an intermediate explosive and effusive volcanism, i.e. pyroclastic fall deposits and lava flows, embedded into epicontinental clastic sediments, culminating in silicic ignimbrite eruptions, and ii) mafic effusives. Geochemical data document a transitional, within-plate signature, e.g. the average Th/Ta (4.5) and La/Nb (2.7) overlap the upper continental crust values. The volcanites are characterized by slight fractionation of LREEs, nearly flat HREE abundance. The negative Eu anomaly increases towards evolved compositions. Some prominent HREE depletion (GdCN/YbCN = 13.8), and the high Nb/Y suggest a garnet-bearing source. The high 87Sr radiogenic content (87Sr/86Sr 490 Ma = 0.71169) and the epsilon Nd 490 Ma value of -6.54 for one dacite sample, imply a time integrated LREE-enriched source with a high Rb/Sr, such as a metasedimentary source. The stratigraphy of the succession and the geochemical composition of igneous members suggest a volcanic passive margin along the northern Gondwana at the early Ordovician. The bimodal Mid-Ordovician arc volcanism (465.4 ± 1.4 Ma, U-Pb zircon age; Oggiano et al., submitted) is developed in the external nappes (e.g. in Sarrabus and Sarcidano) and in the foreland occurs as clasts at the base of the Hirnantian succession (Leone et al. 1991). The Mid Ordovician sub-alkalic volcanic suite has reliable stratigraphic and

  8. The geochemistry and petrogenesis of volcanics and sheeted dikes from the Hatay (Kizildag) Ophiolite, southern Turkey: Possible formation with the Troodos Ophiolite, Cyprus, along fore-arc spreading centers (United States)

    Lytwyn, J. N.; Casey, J. F.


    Geochemical and petrological investigations of the Hatay (Kizildag) Ophiolite, southern Turkey, indicate that the volcanics and sheeted dikes compositionally range from island-arc tholeiites and basaltic andesites to transitional boninitictype lavas formed within a supra-subduction zone environment. Geochemical modeling indicates that the compositional trends within both the sheeted dike and pillow basalt sections of Hatay cannot be related through fractional crystallization alone but require multiple parental magmas of differing compositions within each unit. The more refractory liquids (higher MgO, Ni and Cr coupled with lower concentrations of Ti, Zr, Y and REE) formed at lower pressures (shallower depths) through greater degrees of partial melting of a more depleted mantle source relative to less-refractory magmas which formed at higher pressures and possibly lower degrees of melting. The Hatay volcanics and dikes span the compositional range of Lower Pillow Lavas (LPLs) and Upper Pillow Lavas (UPLs) from the Troodos Complex, Cyprus, suggesting, along with other evidence, that the two ophiolites may be petrogenetically and tectonically related. Formation of the Hatay and Troodos ophiolites was possibly associated with extension within a fore-arc environment following compression and detachment along an intra-oceanic ridge system and development of a subduction zone. The range of parental liquid compositions for volcanics and dikes may reflect variable mixing of geochemically diverse melt increments generated within a polybaric melting column in the mantle wedge. The melting column may have additionally received contributions of LREE-enriched melts from deeper, more juvenile (fertile) sources. Formation of parental liquids through variable mixing of melt increments appears to be common to both the Hatay and Troodos ophiolites.

  9. 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 (United States)

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


    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.

  10. The memory of volcanic waters: Shallow magma degassing revealed by halogen monitoring in thermal springs of La Soufrière volcano (Guadeloupe, Lesser Antilles) (United States)

    Villemant, Benoît; Hammouya, Gilbert; Michel, Agnès; Semet, Michel P.; Komorowski, Jean-Christophe; Boudon, Georges; Cheminée, Jean-Louis


    The halogen contents of thermal waters collected since 1979 at La Soufrière volcano (Guadeloupe, Lesser Antilles) are interpreted as a retarded record of magma degassing pulses dispersed into the hydrothermal system. The further the spring is located from the source, the larger the time delay and the older the event recorded in water chemistry. Using advection-dispersion transport models in porous media, we reconstruct the time-series of degassing pulses for the period 1971-1992 and show that it correlates with the seismic records. The 1975-1977 sismo-volcanic crisis at La Soufrière is thereby interpreted as the result of a magma intrusion at shallow depth (˜3 km) which likely began in approximately 1973 and degassed in a pulsatory regime during ˜15 yr. The recent recrudescence of fumarolic and seismic activity could represent the initial stage of new magma injection. Measurement of halogen contents in hydrothermal waters collected around active volcanoes may provide a powerful tool for detection of the initial stages of magma intrusions.

  11. Insights from Pb and O isotopes into along-arc variations in subduction inputs and crustal assimilation for volcanic rocks in Java, Sunda arc, Indonesia (United States)

    Handley, Heather K.; Blichert-Toft, Janne; Gertisser, Ralf; Macpherson, Colin G.; Turner, Simon P.; Zaennudin, Akhmad; Abdurrachman, Mirzam


    New Pb isotope data are presented for Gede Volcanic Complex, Salak and Galunggung volcanoes in West Java, Merbabu and Merapi volcanoes in Central Java and Ijen Volcanic Complex in East Java of the Sunda arc, Indonesia. New O isotope data for Merbabu and new geochemical and radiogenic isotope data (Sr-Nd-Hf-Pb) for three West Javanese, upper crustal, Tertiary sedimentary rocks are also presented. The data are combined with published geochemical and isotopic data to constrain the relative importance of crustal assimilation and subducted input of crustal material in petrogenesis in Java. Also discussed are the significance of limestone assimilation in controlling the geochemical and isotopic characteristics of erupted Javanese rocks and the geochemical impact upon central and eastern Javanese arc rocks due to the subduction of Roo Rise between 105 and 109°E. The negative correlation between Pb isotopes and SiO2, combined with mantle-like δ18O values in Gede Volcanic Complex rocks, West Java, are most likely explained by assimilation of more isotopically-primitive arc rocks and/or ophiolitic crust known to outcrop in West Java. The negative Pb isotope-SiO2 trend cannot be explained by assimilation of the known compositions of the upper crustal rocks. A peak in δ18O whole-rock and mineral values in Central Javanese volcanic rocks (Merbabu and Merapi) combined with along-arc trends in Sr isotope ratios suggest that a different or additional crustal assimilant exerts control on the isotopic composition of Central Javanese volcanic rocks. This assimilant (likely carbonate material) is characterised by high δ18O and high Sr isotope ratio but is not particularly elevated in its Pb isotopic ratio. Once the effects of crustal assimilation are accounted for, strong East to West Java regional variations in Ba concentration, Ba/Hf ratio and Pb isotopic composition are evident. These differences are attributed to heterogeneity in the subducted source input component along the

  12. CO2 contents of basaltic arc magmas from the southern Cascades: Corrections for shrinkage bubble effects and implications for crustal storage (United States)

    Walowski, K. J.; Wallace, P. J.; Aster, E. M.; Clynne, M. A.


    Volatiles such as H2O and CO2 play an important role in a variety of magmatic processes from magma generation to eruption, and melt inclusions (MI) - small volumes of melt trapped inside phenocrysts - have been used to measure their pre-eruptive concentrations. In particular, the volatile contents of MI from basaltic arc magmas have been used to track the role of dehydrating subducted oceanic lithosphere in magma formation in subduction zones. However, recent studies have shown that MI are imperfect storage containers and can lose H by diffusion through the mineral host and CO2 due to formation of a vapor bubble in the inclusion. Such results suggest that even the least degassed melt inclusions from a volcano may have volatile concentrations that underestimate the initial volatile contents of the magma. Thus, recognizing pre- and post-entrapment processes that influence MIs is important for interpreting magmatic processes at depth. Recent studies have developed methods that can be used to distinguish and correct for H diffusive loss (Bucholz et al., 2013) and CO2 loss to vapor bubbles (Wallace et al., 2015). Here, we focus on MI from eight cinder cones that erupted primitive basaltic magmas in the Lassen region of the Cascade arc, where H2O and Cl concentrations have been shown to relate to the amount of a subduction component added to the mantle wedge (Walowski et al., 2015). Using methods of Aster (2015), we correct for the loss of CO2 to a vapor bubble formed within a melt inclusion as the result of post-entrapment crystallization and thermal contraction. The results of the CO2 restoration calculations suggest that ~25-75% of the initial dissolved CO2 in the melt inclusions at the time of trapping was lost to a vapor bubble after entrapment. Trapping pressures for the restored CO2 and maximum H2O contents calculated using methods of Iacono-Marziano et al. (2012) range from ~2-5 kbar, equivalent to entrapment depths of ~7-18 km below the surface. The results

  13. Investigations of the geochemical controls on anomalous arsenic enrichment in the Santiago Peak Volcanics of Southern California: implications for arsenic distribution in volcanic arc systems (United States)

    Johnston, E. C.; Pollock, M.; Cathcart, E. M.; AlBashaireh, A.; O'shea, B. M.


    The Santiago Peak Volcanics (SPV) of Southern CA and Northern Baja CA, Mexico are remnants of a Cretaceous subaerial volcanic arc system that underwent greenschist facies metamorphism contemporaneous with volcanism. Observed SPV exposed at the surface of Black Mountain Open Space Park (San Diego, CA) exhibit anomalous arsenic (As) enrichment (100 - 480,000 ppm) up to five orders of magnitude greater than average for igneous rocks (1.5 ppm). We hypothesize that these rocks underwent localized syn-volcanic hydrothermal alteration along a highly fractured zone that today trends between N10°W and N20°W, leading to anomalous As enrichment on the spatial scale of tens of meters. We suspect that such As has been further mobilized by modern water-rock interactions. Using standard geochemical techniques (e.g. XRD, XRF, EDX) and mass balance analyses, we aim to (1) summarize the extent of As enrichment in altered SPV, and (2) present an integrated view of the interactions between ancient hydrothermal volcanic arc processes, surficial weathering, and observed As anomalies. Alteration textures of samples range from partially altered phenocrysts (i.e. minimally altered) to massive hydrothermal replacement, in which virtually all primary phases are altered to new hydrothermal minerals such as epidote, Fe-rich chlorite, and sericite (i.e. highly altered). Highly altered rocks contain average As concentrations (mean = 37,680 +/- 15,396 ppm, n = 23) >10,000 times that of minimally altered SPV (mean = 26 +/- 6 ppm As, n = 19). In some rocks, As-rich iron oxide and gypsum containing up to 900 ppm As are present as surficial rinds, suggesting modern day remobilization of As from hydrothermal host minerals, like arsenopyrite. These findings indicate that such As is highly soluble and, therefore, may be further mobilized by physical and chemical weathering. No other trace metals (e.g. Pb, Cu, Ag, Au) are consistently enriched above upper-crustal averages, and As does not always occur

  14. New Insights Into Volcanic Hazards in Western Mexico: Multiple Cone-Building Episodes at Arc Stratovolcanoes Revealed by 40Ar/39Ar Geochronology (United States)

    Frey, H. M.; Lewis-Kenedi, K.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.


    The detailed eruptive histories of two andesitic stratocones, Volcáns Ceboruco and Tequila, in the western Mexican arc have been documented using 40Ar/39Ar geochronology. The volumes of these volcanoes were obtained with mapping, airphotos, and digital elevation models. The age and volume data constrain the rate and duration of major cone-building events, which bears on the longevity of the underlying upper-crustal magma chambers that fed the eruptions. The results indicate that at each stratovolcano there were two discrete cone-building events, separated by a hiatus. At V. Tequila, six samples from the edifice yielded dates (196 +/- 8, 196 +/- 19, 178 +/- 8, 191 +/- 13, 216 +/- 11, and 198 +/- 11 ka; errors are 1 sigma) with a mean eruption age of 196 +/- 12 ka. Thus the bulk of the main edifice ( ˜31 km3) erupted within 24 kyrs (at the 2 sigma level), leading to a cone-building rate of > 1.3 km3/kyr. After a hiatus of ˜110 kyrs, ˜14 km3 of andesite erupted along the NW and SE flanks of V. Tequila at 90 +/- 19 ka. The last activity at V. Tequila produced a ˜2 km3 parasitic cone at ˜60 ka. Since an eruption has not occurred in the last 60 kyrs, V. Tequila is often considered an extinct volcano. This may be the view held by the > 75,000 inhabitants of the town of Tequila located on the northern flanks. A similar history of two discrete cone-building events is found at V. Ceboruco, ˜75 km to the NW. Seven samples taken from various parts of the edifice, including the inner caldera wall, indicate an initial cone-building event at ˜45 ka in which ˜37 km3 of andesite erupted. After a hiatus of nearly 44 kyrs, a second eruptive period began ˜1000 years ago. The first eruption to occur after the hiatus was Plinian and released 3-4 km3 of dacite. In the last 1 kyr, 9.5 km3 of andesite and dacite erupted effusively, culminating in the historic 1870 flow. The sobering conclusion, in terms of volcanic hazards assessment, is that the only Plinian eruption to occur

  15. Stratigraphic and geochemical evolution of an oceanic arc upper crustal section: The Jurassic Talkeetna Volcanic Formation, south-central Alaska (United States)

    Clift, P.D.; Draut, A.E.; Kelemen, P.B.; Blusztajn, J.; Greene, A.


    The Early Jurassic Talkeetna Volcanic Formation forms the upper stratigraphic level of an oceanic volcanic arc complex within the Peninsular Terrane of south-central Alaska. The section comprises a series of lavas, tuffs, and volcaniclastic debris-How and flow turbidite deposits, showing significant lateral facies variability. There is a general trend toward more volcaniclastic sediment at the top of the section and more lavas and tuff breccias toward the base. Evidence for dominant submarine, mostly mid-bathyal or deeper (>500 m) emplacement is seen throughout the section, which totals ???7 km in thickness, similar to modern western Pacific arcs, and far more than any other known exposed section. Subaerial sedimentation was rare but occurred over short intervals in the middle of the section. The Talkeetna Volcanic Formation is dominantly calc-alkatine and shows no clear trend to increasing SiO2 up-section. An oceanic subduction petrogenesis is shown by trace element and Nd isotope data. Rocks at the base of the section show no relative enrichment of light rare earth elements (LREEs) versus heavy rare earth elements (REES) or in melt-incompatible versus compatible high field strength elements (HFSEs). Relative enrichment of LREEs and HFSEs increases slightly up-section. The Talkeetna Volcanic Formation is typically more REE depleted than average continental crust, although small volumes of light REE-enriched and heavy REE-depleted mafic lavas are recognized low in the stratigraphy. The Talkeetna Volcanic Formation was formed in an intraoceanic arc above a north-dipping subduction zone and contains no preserved record of its subsequent collisions with Wrangellia or North America. ?? 2005 Geological Society of America.

  16. Zircon U-Pb Age Determination of Volcanic Eruptions in Lutao and Lanyu in the Northern Luzon Magmatic Arc

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    Wen-Yu Shao


    Full Text Available This paper reports for the first time zircon U-Pb ages of volcanic rocks and sands from Lutao and Lanyu, two islets off SE Taiwan in the north Luzon arc. The samples include (1 seven andesites from four volcanic units and three river/beach sands from Lutao and (2 five basaltic andesites from four volcanic units and two river/beach sands from Lanyu. The Lutao andesites contain abundant magmatic zircons, aging from ~1.54 to ~1.24 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 1.31 ±± 0.03 Ma (n = 190, MSWD = 2.6. This is slightly older than, or broadly coincident with, a mean 206Pb/238U age of 1.23 ±± 0.03 Ma (n = 103, MSWD = 1.9 given by detrital zircons from the three sands. The Lanyu volcanics appear to have less abundant magmatic zircons, aging from ~2.72 to ~2.35 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 2.61 ±± 0.13 Ma (n = 11, MSWD = 1.8. This accords with a mean 206Pb/238U age of 2.69 ±± 0.11 Ma (n = 34, MSWD = 4.7 obtained by detrital zircons from the two sands. The age data suggest that in Lutao and Lanyu the major volcanic eruptions occurred at ~1.3 and ~2.6 Ma, respectively. Moreover, volcanic samples from both islets contain various amounts of older inherited zircons, ~11% in Lutao and up to ~82% in Lanyu, which together with detrital zircons from the sands show main age peaks at ~150 Ma and ~1.9 and ~2.5 Ga, consistent with the notion for a _ continental crust involved in the genesis of the northern Luzon magmatic arc.

  17. Age and duration of intra-oceanic arc volcanism built on a suprasubduction zone type oceanic crust in southern Neotethys, SE Anatolia

    Directory of Open Access Journals (Sweden)

    Fatih Karaoğlan


    Full Text Available The southeastern Anatolia comprises numbers of tectono-magmatic/stratigraphic units such as the metamorphic massifs, the ophiolites, the volcanic arc units and the granitoid rocks. All of them play important role for the late Cretaceous evolution of the southern Neotethys. The spatial and temporal relations of these units suggest the progressive development of coeval magmatism and thrusting during the late Cretaceous northward subduction/accretion. Our new U-Pb zircon data from the rhyolitic rocks of the wide-spread volcanic arc unit show ages of (83.1 ± 2.2–(74.6 ± 4.4 Ma. Comparison of the ophiolites, the volcanic arc units and the granitoids suggest following late Cretaceous geological evolution. The ophiolites formed in a suprasubduction zone (SSZ setting as a result of northward intra-oceanic subduction. A wide-spread island-arc tholeiitic volcanic unit developed on the top of the SSZ-type crust during 83–75 Ma. Related to regional plate convergence, northward under-thrusting of SSZ-type ophiolites and volcanic arc units was initiated beneath the Tauride platform (Malatya-Keban and followed by the intrusion of I-type calc-alkaline volcanic arc granitoids during 84–82 Ma. New U-Pb ages from the arc-related volcanic-sedimentary unit and granitoids indicate that under-thrusting of ophiolites together with the arc-related units beneath the Malatya-Keban platform took place soon after the initiation of the volcanic arc on the top of the SSZ-type crust. Then the arc-related volcanic-sedimentary unit continued its development and lasted at ∼75 Ma until the deposition of the late Campanian–Maastrichtian shallow marine limestone. The subduction trench eventually collided with the Bitlis-Pütürge massif giving rise to HP-LT metamorphism of the Bitlis massif. Although the development of the volcanic arc units and the granitoids were coeval at the initial stage of the subduction/accretion both tectono-magmatic units were

  18. Magma injection beneath the urban area of Naples: a new mechanism for the 2012–2013 volcanic unrest at Campi Flegrei caldera (United States)

    D’Auria, Luca; Pepe, Susi; Castaldo, Raffaele; Giudicepietro, Flora; Macedonio, Giovanni; Ricciolino, Patrizia; Tizzani, Pietro; Casu, Francesco; Lanari, Riccardo; Manzo, Mariarosaria; Martini, Marcello; Sansosti, Eugenio; Zinno, Ivana


    We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km3 of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area. PMID:26279090

  19. P, T, X magma storage conditions of the dominantly silicic explosive eruptions from Santorini volcano (Aegean Arc, Greece) (United States)

    Cadoux, A.; Druitt, T. H.; Deloule, E.; Scaillet, B.


    It has been increasingly recognized that dramatic changes in magma storage conditions can occur over very short periods of time at a single volcano and might be in close relationships with stress variations imposed on the crustal plumbing by the overlying volcano as it changes shape and volume over time. The Santorini volcano (South Aegean Arc) is an ideal target to unravel these potential relationships as its history is marked by alternating episodes of edifice construction and caldera collapses and the chronostratigraphy is well constrained. We focused our study on the products of the four major, dominantly silicic, explosive eruptions of Santorini: the Lower Pumice 1 and 2 (200 to 180 ka; 1st explosive cycle) and, the Cape Riva and the Minoan (~ 21 to 3 ka, 2nd explosive cycle). In order to precisely define the P, T, fO2, X (X for volatiles) storage conditions of the silicic magmas prior to these eruptions, we carried out a detailed micro-petrological and geochemical study on natural samples combined with an experimental work. The selected silicic components of the four eruptions are dacite to rhyodacite (SiO2 = 67-70 wt.%) with similar mineral paragenesis (plagioclase, orthopyroxene, clinopyroxene, ilmenite, magnetite, apatite ± pyrrhotite) and crystallinity < 20%. High resolution BSE images of plagioclase and pyroxene phenocrysts and EMPA profiles reveal a complex crystallization history. Plagioclases display fine-scale oscillatory normal zoning, resorbtion zones where melt inclusions (MI) of rhyolitic compositions were trapped, and An-rich sieved cores. Clinopyroxenes also show zoning patterns and include rhyolitic MI. Both interstitial glass and MI are Cl-rich (~3000 ppm) while F and S are less abundant (F ≤ 700 ppm, S ≤ 100 ppm). Determination of H2O contents by SIMS is in progress at the CRPG-Nancy (previous measurements from the literature gave ~ 5 wt.% H2O in the Minoan rhyodacite and ~4 wt.% in the Lower Pumice 2). Ilmenite-magnetite geothermometry

  20. Water content, δD and δ11B tracking in the Vanuatu arc magmas (Aoba Island): Insights from olivine-hosted melt inclusions (United States)

    Métrich, Nicole; Deloule, Etienne


    Ion microprobe measurements of H and B isotopic ratios and H2O, B and trace element contents are reported here for a series of melt inclusions typical of alkaline basalts of Aoba Island in the central part of Vanuatu arc (Southwestern Pacific). The melt inclusions, hosted in olivine Fo86-90, display large ranges in trace element concentrations and hydrogen (δD from - 48.2 to + 61.7‰) and boron (δ11B from - 11.9 to + 6.4‰) isotopic compositions. The high deuterium enrichment (δD ≥ 0‰) observed in a small subset of melt inclusions requires a proton diffusion loss through the olivine network, in addition to late-stage magma interactions with aqueous saline fluids. These melt inclusions are therefore not considered as representative of the magma from which the olivine grew. In most melt inclusions, positive correlations between H2O, K2O, Ba and Sr lead us to determine the K2O/H2O (1.5 ± 0.2), H2O/Ba (46 ± 3 × 10- 4) and H2O/Sr (29 ± 2 × 10- 4) ratios of Aoba basalts. Overall correlations between δ11B, B/Nb, and B/Nd testify to the mixing between slab-derived fluids, preferentially enriched in δ11B and fluid mobile elements and a relatively depleted MORB-type mantle wedge beneath Aoba Island. Heavy δ11B (on average 5.4 ± 0.7‰) indicate slab-derived fluids, possibly involving serpentine, which would have a mean δD value of - 28.4 ± 7‰. The chemical and isotopic variability recorded by Aoba magmas (melt inclusions) is consistent with the geodynamic context of ridge-arc collision in the central segment of Vanuatu arc.

  1. 210Pb- 226Ra and 228Ra- 232Th systematics in young arc lavas: implications for magma degassing and ascent rates (United States)

    Turner, Simon; Black, Stuart; Berlo, Kim


    New data show that island arc rocks have ( 210Pb/ 226Ra) o ratios which range from as low as 0.24 up to 2.88. In contrast, ( 228Ra/ 232Th) appears always within error of 1 suggesting that the large 226Ra-excesses observed in arc rocks were generated more than 30 years ago. This places a maximum estimate on melt ascent velocities of around 4000 m/year and provides further confidence that the 226Ra excesses reflect deep (source) processes rather than shallow level alteration or seawater contamination. Conversely, partial melting must have occurred more than 30 years prior to eruption. The 210Pb deficits are most readily explained by protracted magma degassing. Using published numerical models, the data suggest that degassing occurred continuously for periods up to several decades just prior to eruption but no link with eruption periodicity was found. Longer periods are required if degassing is discontinuous, less than 100% efficient or if magma is recharged or stored after degassing. The long durations suggest much of this degassing occurs at depth with implications for the formation of hydrothermal and copper-porphyry systems. A suite of lavas erupted in 1985-1986 from Sangeang Api volcano in the Sunda arc are characterised by deficits of 210Pb relative to 226Ra from which 6-8 years of continuous 222Rn degassing would be inferred from recent numerical models. These data also form a linear ( 210Pb)/Pb-( 226Ra)/Pb array which might be interpreted as a 71-year isochron. However, the array passes through the origin suggesting displacement downwards from the equiline in response to degassing and so the slope of the array is inferred not to have any age significance. Simple modelling shows that the range of ( 226Ra)/Pb ratios requires thousands of years to develop consistent with differentiation occurring in response to cooling at the base of the crust. Thus, degassing post-dated, and was not responsible for magma differentiation. The formation, migration and extraction

  2. Geochemical variability of hydrothermal emissions between three Pacific volcanic arc systems: Alaskan-Aleutian and Cascadian, North America and Taupo Volcanic Zone, New Zealand (United States)

    Blackstock, J. M.; Horton, T. W.; Gravley, D. M.; Deering, C. D.


    Knowledge of the source, transport, and fate of hydrothermal fluids in the upper crust informs our understanding and interpretation of ore-forming processes, volcanogenic hazards, geothermal resources, and volatile cycling. Co-variation between fluid inclusion CO2/CH4 and N2/Ar ratios is an established tracer of magmatic, meteoric, and crustal fluid end-members. Yet, this tracer has had limited application to macroscopic fluid reservoirs accessible via geothermal wells and hydrothermal features (e.g. pools). In this study, we compared the covariance CO2/CH4 and N2/Ar ratios of gases collected throughout the Taupo Volcanic Zone, New Zealand (TVZ), the Alaska-Aleutian Volcanic Arc, USA (AAVA), and the Cascadian Volcanic Arc, USA (CVA) with corresponding δ13C and 3He/4He values. Our findings show that there is good agreement between these proxies for different end-member contributions at coarse scales. However, some samples classified as meteoric water according to the CO2/CH4 and N2/Ar ratios also show more positive δ13C values (~ -7.0 per mil) and relatively higher 3He/4He ratios indicative of magmatic input from primarily mantle sources. This unexpected result may be related to magmatic fluids, CO2 in particular, mixing with predominantly meteoric derived waters. The potential to identify magmatic CO2 in groundwater samples overlying geothermal systems in differing volcanic arc settings using simple and cost-effective gas ratios is a promising step forward in the search for ';surface blind' but developable geothermal systems and volcanic monitoring. 3He/4He anomalies also support this inference and underscore the potential decoupling of thermal anomalies and magmatic-derived fluids in the Earth's crust. The general agreement between the co-variation of CO2/CH4 and N2/Ar ratios with other isotope and geochemical proxies for magmatic, meteoric, and crustal end-members is encouraging to employ expanded use of these ratios for both the exploration and monitoring of

  3. The link between volcanism and plutonism in epizonal magma systems; high-precision U-Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico (United States)

    Rioux, Matthew; Farmer, G. Lang; Bowring, Samuel A.; Wooton, Kathleen M.; Amato, Jeffrey M.; Coleman, Drew S.; Verplanck, Philip L.


    The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U-Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from ~44 to 34 Ma. The three largest caldera-related tuff units yielded weighted mean 206Pb/238U dates of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206Pb/238U date of 36.259 ± 0.021 Ma. Weighted mean 206Pb/238U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a high-silica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the final eruption. Calculated magmatic

  4. Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340 (United States)

    Le Friant, A.; Ishizuka, O.; Boudon, G.; Palmer, M. R.; Talling, P. J.; Villemant, B.; Adachi, T.; Aljahdali, M.; Breitkreuz, C.; Brunet, M.; Caron, B.; Coussens, M.; Deplus, C.; Endo, D.; Feuillet, N.; Fraas, A. J.; Fujinawa, A.; Hart, M. B.; Hatfield, R. G.; Hornbach, M.; Jutzeler, M.; Kataoka, K. S.; Komorowski, J.-C.; Lebas, E.; Lafuerza, S.; Maeno, F.; Manga, M.; Martínez-Colón, M.; McCanta, M.; Morgan, S.; Saito, T.; Slagle, A.; Sparks, S.; Stinton, A.; Stroncik, N.; Subramanyam, K. S. V.; Tamura, Y.; Trofimovs, J.; Voight, B.; Wall-Palmer, D.; Wang, F.; Watt, S. F. L.


    IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of preexisting low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or microfaulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits composed of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution data set to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation

  5. Oxygen isotope evolution of the Lake Owyhee volcanic field, Oregon, and implications for low-δ18O magmas of the Snake River Plain - Yellowstone hotspot (United States)

    Blum, T.; Kitajima, K.; Nakashima, D.; Valley, J. W.


    The Snake River Plain - Yellowstone (SRP-Y) hotspot trend is one of the largest known low-δ18O magmatic provinces, yet the timing and distribution of hydrothermal alteration relative to hotspot magmatism remains incompletely understood. Existing models for SRP-Y low-δ18O magma genesis differ regarding the timing of protolith alteration (e.g. Eocene vs. present), depth at which alteration occurs (e.g. 15 km vs. Owyhee volcanic field (LOVF) of east central Oregon to further identify magmatic oxygen isotope trends within the field. These data offer insight into the timing of alteration and the extent of the greater SRP-Y low-δ18O province, as well as the conditions that generate large low-δ18O provinces. 16-14 Ma silicic volcanism in the LOVF is linked to the pre-14 Ma SRP-Y hotspot, with volcanism partially overlapping extension in the north-south trending Oregon-Idaho Graben (OIG). Ion microprobe analyses of zircons from 16 LOVF silicic lavas and tuffs reveal homogeneous zircons on both the single grain and hand sample scales: individual samples have 2 S.D. for δ18O ranging from 0.27 to 0.96‰ (SMOW), and sample averages ranging from 1.8 to 6.0‰, excluding texturally chaotic and/or porous zircons which have δ18O values as low as 0.0‰. All low-δ18O LOVF magmas, including the caldera-forming Tuff of Leslie Gulch and Tuff of Spring Creek, are confined to the OIG, although not all zircons from within the OIG have low δ18O values. The presence and sequence of low-δ18O magmas in the LOVF and adjacent central Snake River Plain (CSRP) cannot be explained by existing caldera subsidence or pre-hotspot source models. These data, however, combined with volumetrically limited low-δ18O material in the adjacent Idaho Batholith and Basin and Range, are consistent with low-δ18O magmas generated by the superposition of high hotspot-derived thermal fluxes on active extensional structures (OIG extension in the LOVF, and Basin and Range rifting in the CSRP) thereby

  6. Two crustal flowing channels and volcanic magma migration underneath the SE margin of the Tibetan Plateau as revealed by surface wave tomography (United States)

    Wu, Tengfei; Zhang, Shuangxi; Li, Mengkui; Qin, Weibing; Zhang, Chaoyu


    The SE margin of the Tibetan Plateau is an important area to develop a better understanding of the plateau uplift and the Indian-Eurasian continental collision dynamics. Previous studies have reported widespread low-velocity anomalies beneath this region, particularly in the Tengchong volcanic field (TCVF). However, the spatial distribution and dynamic processes of these low-velocity anomalies are not well constrained. In this study, a 3-D S-wave velocity structure model of the crust and upper mantle (10-120 km) in the region is constructed by the inversion of surface wave dispersion data. A two-step inversion procedure is adopted to generate the S-wave velocity structure images. The measured phase velocities and inverted S-wave velocities jointly show a large-scale low-velocity anomaly distributed in the crust, consistent with the view that the region is the passageway of the eastward migration of Tibetan Plateau material. Two crustal flowing channels are clearly observed at depths of ∼20 km and ∼30 km, which connect and rotate clockwise around the Eastern Himalaya Syntaxis. Beneath the TCVF, there are two prominent low-velocity anomaly zones at depths of ∼15-25 km and ∼50-80 km, which indicate the existence of magma chambers. One of the crustal flowing channels is connected with the magma chamber of the TCVF, and the other has a short branch north of Kunming toward the Mile-Shizong fault at a depth of 20 km. Based on the distribution of the S-wave velocities under the TCVF, a dynamic model of the Tengchong volcano magma system is proposed to explain the migration patterns of the volcanic material.

  7. Evidence for Slab Melt Contributions to the Mexican Volcanic Belt and Other Young Hot Slab Arcs from Lu-Hf Isotopes (United States)

    Goldstein, S. L.; Cai, Y. M.; Langmuir, C. H.; Lagatta, A.; Straub, S. M.; Gomez-Tuena, A.; Martin Del Pozzo, A.


    Despite major advances in delineating the processes that govern magma generation at convergent margins, the problem persists of distinguishing slab, mantle wedge, and crustal contributions. A corrollary question is whether there is significant melting of subducted ocean crust. Especially in thick crust regions, the importance of crustal versus mantle contributions to lavas represents a long-standing fundamental issue in arc magma geochemistry. We show that frontal arc magmas from the Central Mexican Volcanic Belt (CMVB), including the large andesitic stratovolcanoes Popocatepetl and Nevado de Toluca, display negligible crustal contamination, and contain substantial contributions from melting of subducted Pacific ocean crust. Despite ca. 50 km thick continental crust, the CMVB erupts near primitive lavas including "high-Nb" alkaline basalts that show negligible "subduction signatures" in their trace element patterns. These "high-Nb" basalts define the regional mantle wedge composition in isotope-trace element space. The "normal" calcalkaline lavas form a negative correlation between Hf isotopes and Lu/Hf. One endmember is like the high Nb basalts representing the regional mantle wedge. The other endmember has higher Hf isotopes (approaching values of Pacific MORB) and very low Lu/Hf of less than 0.04 (e.g. compared to typical values of ca. 0.2 in Pacific MORB). The low Lu/Hf values require low degree partial melting of a source rich in garnet. The high Hf isotopes require a depleted mantle source with isotopes like Pacific MORB. Together the Lu-Hf data indicate a substantial component derived from melting of eclogitic Pacific ocean crust. A key feature of the data is that the stratovolcano lavas showing the largest slab melt signature also show the highest Hf isotope ratios and thus are more "depleted mantle-like" than the regional mantle wedge. Thus, the integrated data allow us to clearly distinguish between mantle and crustal sources in the CMVB and point to

  8. A new view into the Cascadia subduction zone and volcanic arc: Implications for earthquake hazards along the Washington margin (United States)

    Parsons, T.; Trehu, A.M.; Luetgert, J.H.; Miller, K.; Kilbride, F.; Wells, R.E.; Fisher, M.A.; Flueh, E.; ten Brink, U.S.; Christensen, N.I.


    In light of suggestions that the Cascadia subduction margin may pose a significant seismic hazard for the highly populated Pacific Northwest region of the United States, the U.S. Geological Survey (USGS), the Research Center for Marine Geosciences (GEOMAR), and university collaborators collected and interpreted a 530-km-long wide-angle onshore-offshore seismic transect across the subduction zone and volcanic arc to study the major structures that contribute to seismogenic deformation. We observed (1) an increase in the dip of the Juan de Fuca slab from 2??-7?? to 12?? where it encounters a 20-km-thick block of the Siletz terrane or other accreted oceanic crust, (2) a distinct transition from Siletz crust into Cascade arc crust that coincides with the Mount St. Helens seismic zone, supporting the idea that the mafic Siletz block focuses seismic deformation at its edges, and (3) a crustal root (35-45 km deep) beneath the Cascade Range, with thinner crust (30-35 km) east of the volcanic arc beneath the Columbia Plateau flood basalt province. From the measured crustal structure and subduction geometry, we identify two zones that may concentrate future seismic activity: (1) a broad (because of the shallow dip), possibly locked part of the interplate contact that extends from ???25 km depth beneath the coastline to perhaps as far west as the deformation front ???120 km offshore and (2) a crustal zone at the eastern boundary between the Siletz terrane and the Cascade Range.

  9. 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 (United States)

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


    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 τP 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 τP=9.5 years and an injection pressure rising up to 11.5 MPa for 2 years. The volume flow rate increased to 1.2 m3/s for 2 years and then decreased to 0.7 m3/s in 2014. In 7.3 years, at least 187 × 106 m3 of magma was injected.

  10. The role of viscous magma mush spreading in volcanic flank motion at Kīlauea Volcano, Hawai‘i (United States)

    Plattner, C.; Amelung, F.; Baker, S.; Govers, R.; Poland, M.


    Multiple mechanisms have been suggested to explain seaward motion of the south flank of Kīlauea Volcano, Hawai‘i. The consistency of flank motion during both waxing and waning magmatic activity at Kīlauea suggests that a continuously acting force, like gravity body force, plays a substantial role. Using finite element models, we test whether gravity is the principal driver of long-term motion of Kīlauea's flank. We compare our model results to geodetic data from Global Positioning System and interferometric synthetic aperture radar during a time period with few magmatic and tectonic events (2000-2003), when deformation of Kīlauea was dominated by summit subsidence and seaward motion of the south flank. We find that gravity-only models can reproduce the horizontal surface velocities if we incorporate a regional décollement fault and a deep, low-viscosity magma mush zone. To obtain quasi steady state horizontal surface velocities that explain the long-term seaward motion of the flank, we find that an additional weak zone is needed, which is an extensional rift zone above the magma mush. The spreading rate in our model is mainly controlled by the magma mush viscosity, while its density plays a less significant role. We find that a viscosity of 2.5 × 1017–2.5 × 1019 Pa s for the magma mush provides an acceptable fit to the observed horizontal surface deformation. Using high magma mush viscosities, such as 2.5 × 1019 Pa s, the deformation rates remain more steady state over longer time scales. These models explain a significant amount of the observed subsidence at Kīlauea's summit. Some of the remaining subsidence is probably a result of magma withdrawal from subsurface reservoirs

  11. The role of viscous magma mush spreading in volcanic flank motion at Kīlauea Volcano, Hawai`i (United States)

    Plattner, C.; Amelung, F.; Baker, S.; Govers, R.; Poland, M.


    Multiple mechanisms have been suggested to explain seaward motion of the south flank of Kīlauea Volcano, Hawai`i. The consistency of flank motion during both waxing and waning magmatic activity at Kīlauea suggests that a continuously acting force, like gravity body force, plays a substantial role. Using finite element models, we test whether gravity is the principal driver of long-term motion of Kīlauea's flank. We compare our model results to geodetic data from Global Positioning System and interferometric synthetic aperture radar during a time period with few magmatic and tectonic events (2000-2003), when deformation of Kīlauea was dominated by summit subsidence and seaward motion of the south flank. We find that gravity-only models can reproduce the horizontal surface velocities if we incorporate a regional décollement fault and a deep, low-viscosity magma mush zone. To obtain quasi steady state horizontal surface velocities that explain the long-term seaward motion of the flank, we find that an additional weak zone is needed, which is an extensional rift zone above the magma mush. The spreading rate in our model is mainly controlled by the magma mush viscosity, while its density plays a less significant role. We find that a viscosity of 2.5 × 1017-2.5 × 1019 Pa s for the magma mush provides an acceptable fit to the observed horizontal surface deformation. Using high magma mush viscosities, such as 2.5 × 1019 Pa s, the deformation rates remain more steady state over longer time scales. These models explain a significant amount of the observed subsidence at Kīlauea's summit. Some of the remaining subsidence is probably a result of magma withdrawal from subsurface reservoirs.

  12. The role of viscous magma mush spreading in volcanic flank motion at Kilauea Volcano, Hawai'i (United States)

    Plattner, Christina; Amelung, Falk; Baker, Scott; Govers, Rob; Poland, Mike


    Multiple mechanisms have been suggested to explain seaward motion of the south flank of Kīlauea Volcano, Hawai'i. The consistency of flank motion during both waxing and waning magmatic activity at Kīlauea suggests that a continuously acting force, like gravity body force, plays a substantial role. Using finite element models, we test whether gravity is the principal driver of long-term motion of Kīlauea's flank. We compare our model results to geodetic data from Global Positioning System and interferometric synthetic aperture radar during a time period with few magmatic and tectonic events (2000-2003), when deformation of Kīlauea was dominated by summit subsidence and seaward motion of the south flank. We find that gravity-only models can reproduce the horizontal surface velocities if we incorporate a regional décollement fault and a deep, low-viscosity magma mush zone. To obtain quasi steady state horizontal surface velocities that explain the long-term seaward motion of the flank, we find that an additional weak zone is needed, which is an extensional rift zone above the magma mush. The spreading rate in our model is mainly controlled by the magma mush viscosity, while its density plays a less significant role.We find that a viscosity of 2.5 x 10^17 - 2.5 x 10^19 Pa s for the magma mush provides an acceptable fit to the observed horizontal surface deformation. Using high magma mush viscosities, such as 2.5 x 10^19 Pa s, the deformation rates remain more steady state over longer time scales. These models explain a significant amount of the observed subsidence at Kīlauea's summit. Some of the remaining subsidence is probably a result of magma withdrawal from subsurface reservoirs.

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

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


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

  14. Hydrous basalt-limestone interaction at crustal conditions: Implications for generation of ultracalcic melts and outflux of CO2 at volcanic arcs (United States)

    Carter, Laura B.; Dasgupta, Rajdeep


    High degassing rates for some volcanoes, typically in continental arcs, (e.g., Colli Albani Volcanic District, Etna, Vesuvius, Italy; Merapi, Indonesia; Popocatepetl, Mexico) are thought to be influenced by magma-carbonate interaction in the crust. In order to constrain the nature of reaction and extent of carbonate breakdown, we simulated basalt-limestone wall-rock interactions at 0.5-1.0 GPa, 1100-1200 °C using a piston cylinder and equal mass fractions of calcite (CaCO3) and a hydrous (∼4 wt.% H2O) basalt in a layered geometry contained in AuPd capsules. All experiments produce melt + fluid + calcite ± clinopyroxene ± plagioclase ± calcic-scapolite ± spinel. With increasing T, plagioclase is progressively replaced by scapolite, clinopyroxene becomes CaTs-rich, and fluid proportion, as inferred from vesicle population, increases. At 1.0 GPa, 1200 °C our hydrous basalt is superliquidus, whereas in the presence of calcite, the experiment produces calcite + clinopyroxene + scapolite + melt. With the consumption of calcite with increasing T and decreasing P, melt, on a volatile-free basis, becomes silica-poor (58.1 wt.% at 1.0 GPa, 1100 °C to 34.9 wt.% at 0.5 GPa, 1200 °C) and CaO-rich (6.7 wt.% at 1.0 GPa, 1100 °C to 43.7 wt.% at 0.5 GPa, 1200 °C), whereas Al2O3 drops (e.g., 19.7 at 1100 °C to 12.8 wt.% at 1200 °C at 1.0 GPa) as clinopyroxene becomes more CaTs-rich. High T or low P melt compositions are 'ultracalcic,' potentially presenting a new hypothesis for the origin of ultracalcic melt inclusions in arc lava olivines. Wall-rock calcite consumption is observed to increase with increasing T and decreasing P. At 0.5 GPa, our experiments yield carbonate assimilation from 21.6 to 47.6% between 1100 and 1200 °C. Using measured CO2 outflux rates for Mts. Vesuvius, Merapi, Etna and Popocatepetl over a T variation of 1100 to 1200 °C at 0.5 GPa, we calculate 6-92% of magmatic input estimates undergo this extent of assimilation, suggesting that up to ∼3

  15. Magma Generation and Transport in Subduction Zones: Numerical Simulations of Chemical, Thermal and Mechanical Coupling During Magma Ascent by Porous Flow (United States)

    Arcay, D.; Gerya, T.; Tackley, P.


    Most subduction zones are characterized by significant magmatic activity responsible for building trench-parallel volcanic arcs above descending slabs. High magma production rates observed within the arcs result from infiltration of water-rich fluids released by slab dehydration. The released water triggers hydrous melting of hot mantle wedges located above the cold slabs. However, the process of magma transport from the melt generation region located above the hydrated slab surface at 100-300 km depth to the magma extraction zone at the volcanic arc surface, and its influence on mantle wedge deformation, are not well known. In particular, during basaltic liquid ascent through the mantle wedge, decreasing pressure and temperature changes are likely to induce significant compositional variations, especially in terms of dissolved water content. Relationships between melt transport and mantle wedge deformation are also not clearly understood. We present a numerical model of magma generation and transport in subduction zones, that simulates chemical, thermal, and mechanical interactions between fluids and solid rocks along the magma ascent pathway. Magma migration is modelled by a porous flow across a constant permeability matrix, while the solid downward current associated with subduction in the mantle wedge, is included. The heat advected by the percolating liquid phase as well as latent heat effect associated with melting will be included. Water exchanges between the molten rock and the solid matrix are computed as a function of pressure, temperature, and solubilities laws in melt. We will first present benchmark results to validate the porous flow modelling as well as the ernery equation resolution for a two- phase flow. The aqueous and magmatic fluid repartition within the mantle wedge will then be presented. Magma productivity rates, varying along the magma ascent path way, will be discussed as a function of magma viscosity.

  16. Evolving volcanism at the tip of a propagating arc: The earliest high-Mg andesites in northern New Zealand (United States)

    Booden, Mathijs A.; Smith, Ian E. M.; Mauk, Jeffrey L.; Black, Philippa M.


    A NNW-striking string of isolated volcanic centers, the Kiwitahi chain, erupted between 15 and 5.5 Ma in northern New Zealand. Prior to 6.2 Ma, the erupted rocks were plagioclase- and hornblende-dominated andesites, which are geochemically comparable to coeval andesites erupted in the nearby, much larger Coromandel Volcanic Zone (CVZ). Compared to CVZ andesites, however, the Kiwitahi andesites show more subdued incompatible element enrichments, and they generally have relatively unradiogenic Sr isotope compositions. These features, and the small eruption volumes involved, suggest that the Kiwitahi centers formed over the edge of a magmatic system that was centered on the CVZ. The Kiwitahi centers progressively become younger towards the SSE representing the migration over the time of the edge of this magmatic system. Between 6.2 and 5.5 Ma, four centers at the southern end of the chain erupted pyroxene-dominated, high-magnesium andesites that are geochemically unlike coeval andesites in the CVZ, but similar to Quaternary high-Mg andesites erupted along the western edge of the Taupo Volcanic Zone. These are the earliest known high-Mg andesites in northern New Zealand; their appearance may mark the inception of the current configuration where high-Mg andesite eruptions precede regular andesitic volcanism at the leading edge of the arc.

  17. Intraplate volcanism controlled by back-arc and continental structures in NE Asia inferred from transdimensional Bayesian ambient noise tomography (United States)

    Kim, Seongryong; Tkalčić, Hrvoje; Rhie, Junkee; Chen, Youlin


    Intraplate volcanism adjacent to active continental margins is not simply explained by plate tectonics or plume interaction. Recent volcanoes in northeast (NE) Asia, including NE China and the Korean Peninsula, are characterized by heterogeneous tectonic structures and geochemical compositions. Here we apply a transdimensional Bayesian tomography to estimate high-resolution images of group and phase velocity variations (with periods between 8 and 70 s). The method provides robust estimations of velocity maps, and the reliability of results is tested through carefully designed synthetic recovery experiments. Our maps reveal two sublithospheric low-velocity anomalies that connect back-arc regions (in Japan and Ryukyu Trench) with current margins of continental lithosphere where the volcanoes are distributed. Combined with evidences from previous geochemical and geophysical studies, we argue that the volcanoes are related to the low-velocity structures associated with back-arc processes and preexisting continental lithosphere.

  18. GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua (United States)

    Correa-Mora, F.; DeMets, C.; Alvarado, D.; Turner, H. L.; Mattioli, G.; Hernandez, D.; Pullinger, C.; Rodriguez, M.; Tenorio, C.


    We invert GPS velocities from 32 sites in El Salvador, Honduras and Nicaragua to estimate the rate of long-term forearc motion and distributions of interseismic coupling across the Middle America subduction zone offshore from these countries and faults in the Salvadoran and Nicaraguan volcanic arcs. A 3-D finite element model is used to approximate the geometries of the subduction interface and strike-slip faults in the volcanic arc and determine the elastic response to coupling across these faults. The GPS velocities are best fit by a model in which the forearc moves 14-16 mmyr-1 and has coupling of 85-100 per cent across faults in the volcanic arc, in agreement with the high level of historic and recent earthquake activity in the volcanic arc. Our velocity inversion indicates that coupling across the potentially seismogenic areas of the subduction interface is remarkably weak, averaging no more than 3 per cent of the plate convergence rate and with only two poorly resolved patches where coupling might be higher along the 550-km-long segment we modelled. Our geodetic evidence for weak subduction coupling disagrees with a seismically derived coupling estimate of 60 +/- 10 per cent from a published analysis of earthquake damage back to 1690, but agrees with three other seismologic studies that infer weak subduction coupling from 20th century earthquakes. Most large historical earthquakes offshore from El Salvador and western Nicaragua may therefore have been intraslab normal faulting events similar to the Mw 7.3 1982 and Mw 7.7 2001 earthquakes offshore from El Salvador. Alternatively, the degree of coupling might vary with time. The evidence for weak coupling indirectly supports a recently published hypothesis that much of the Middle American forearc is escaping to the west or northwest away from the Cocos Ridge collision zone in Costa Rica. Such a hypothesis is particularly attractive for El Salvador, where there is little or no convergence obliquity to drive the

  19. Petrologic imaging of silicic magma chambers: new calibration of Al-in-hornblende barometry and applications to the Long Valley - Mono - Inyo active volcanic system. (United States)

    Medard, E.; Martin, A. M.


    Traditional Al-in-hornblende barometry relies on the hypothesis that the Al content in amphibole only depends on pressure, through the Tschermack substitution. However, Al content in amphibole also varies with temperature through the edenite substitution, resulting in large errors in amphibole barometry. Using literature data, we have recalibrated a temperature-independent barometer based on octahedral Al for amphiboles in rhyolitic and dacitic compositions (Médard et al., Goldschmidt 2013). Experimental pressures are reproduced with an average error of 36 MPa in the 100-400 MPa range. Our new amphibole barometer has been used to investigate the depth of magma storage underneath the recent eruptions of the Mono-Inyo volcanic chain. Preliminary investigation of samples from the Glass Creek and Obsidian flows, associated with the youngest eruptive activity to the South of the chain (the 1350 AD Inyo eruption), contain Al-rich amphiboles ( 10 wt% Al2O3) crystallized at pressures of 260 ± 20 MPa (9.8 ± 0.7 km) and a temperature of 835 °C. Similar amphibole crystals have been analyzed from products of the 1700 AD eruption on Pahoa island to the north of the chain by Bray (2014). Identical crystallization pressures of 260 ± 40 MPa are derived from their compositions, suggesting a constant pressure of magma storage under the entire Mono-Inyo volcanic chain. Highly crystalline mush samples from the Glass Creek dome have been interpreted as remobilized magma from the older Long Valley magma chamber. Low-Al amphiboles ( 7 wt% Al2O3) from a mush sample also crystallized at 260 ± 20 MPa and a temperature of 705 °C. The storage depth has thus been constant in the entire Long Valley - Mono - Inyo system over time. A storage depth of 9.8 ± 0.7 km is in excellent agreement with recent seismic work by Seccia et al. (2011) who used Vs to infer the presence of a highly molten (30-60 % melt) magmatic reservoir 7-11 km beneath the Long Valley caldera. Traditional Al

  20. The Fish Canyon magma body, San Juan volcanic field, Colorado: Rejuvenation and eruption of an upper-crustal batholith (United States)

    Bachmann, Olivier; Dungan, M.A.; Lipman, P.W.


    More than 5000 km3 of nearly compositionally homogeneous crystalrich dacite (~68 wt % SiO2: ~45% Pl + Kfs + Qtz + Hbl + Bt + Spn + Mag + Ilm + Ap + Zrn + Po) erupted from the Fish Canyon magma body during three phases: (1) the pre-caldera Pagosa Peak Dacite (an unusual poorly fragmented pyroclastic deposit, ~ 200 km3); (2) the syn-collapse Fish Canyon Tuff (one of the largest known ignimbrites, ~ 5000 km3); (3) the post-collapse Nutras Creek Dacite (a volumetrically minor lava). The late evolution of the Fish Canyon magma is characterized by rejuvenation of a near-solidus upper-crustal intrusive body (mainly crystal mush) of batholithic dimensions. The necessary thermal input was supplied by a shallow intrusion of more mafic magma represented at the surface by sparse andesitic enclaves in late-erupted Fish Canyon Tuff and by the post-caldera Huerto Andesite. The solidified margins of this intrusion are represented by holocrystalline xenoliths with Fish Canyon mineralogy and mineral chemistry and widely dispersed partially remelted polymineralic aggregates, but dehydration melting was not an important mechanism in the rejuvenation of the Fish Canyon magma. Underlying mafic magma may have evolved H2O-F-S-Cl-rich fluids that fluxed melting in the overlying crystal mush. Manifestations of the late up-temperature magma evolution are: (1) resorbed quartz, as well as feldspars displaying a wide spectrum of textures indicative of both resorption and growth, including Rapakivi textures and reverse growth zoning (An27-28 to An32-33) at the margins of many plagioclase phenocrysts; (2) high Sr, Ba, and Eu contents in the high-SiO2 rhyolite matrix glass, which are inconsistent with extreme fractional crystallization of feldspar; (3) oscillatory and reverse growth zoning toward the margins of many euhedral hornblende phenocrysts (rimward increases from ~5??5-6 to 7??7-8??5 wt % Al2O3). Homogeneity in magma composition at the chamber-wide scale, contrasting with extreme textural

  1. The role of changing geodynamics in the progressive contamination of Late Cretaceous to Late Miocene arc magmas in the southern Central Andes (United States)

    Jones, Rosemary E.; Kirstein, Linda A.; Kasemann, Simone A.; Litvak, Vanesa D.; Poma, Stella; Alonso, Ricardo N.; Hinton, Richard


    The tectonic and geodynamic setting of the southern Central Andean convergent margin changed significantly between the Late Cretaceous and the Late Miocene, influencing magmatic activity and its geochemical composition. Here we investigate how these changes, which include changing slab-dip angle and convergence angles and rates, have influenced the contamination of the arc magmas with crustal material. Whole rock geochemical data for a suite of Late Cretaceous to Late Miocene arc rocks from the Pampean flat-slab segment (29-31 °S) of the southern Central Andes is presented alongside petrographic observations and high resolution age dating. In-situ U-Pb dating of magmatic zircon, combined with Ar-Ar dating of plagioclase, has led to an improved regional stratigraphy and provides an accurate temporal constraint for the geochemical data. A generally higher content of incompatible trace elements (e.g. Nb/Zr ratios from 0.019 to 0.083 and Nb/Yb from 1.5 to 16.4) is observed between the Late Cretaceous (~ 72 Ma), when the southern Central Andean margin is suggested to have been in extension, and the Miocene when the thickness of the continental crust increased and the angle of the subducting Nazca plate shallowed. Trace and rare earth element compositions obtained for the Late Cretaceous to Late Eocene arc magmatic rocks from the Principal Cordillera of Chile, combined with a lack of zircon inheritance, suggest limited assimilation of the overlying continental crust by arc magmas derived from the mantle wedge. A general increase in incompatible, fluid-mobile/immobile (e.g., Ba/Nb) and fluid-immobile/immobile (e.g., Nb/Zr) trace element ratios is attributed to the influence of the subducting slab on the melt source region and/or the influx of asthenospheric mantle. The Late Oligocene (~ 26 Ma) to Early Miocene (~ 17 Ma), and Late Miocene (~ 6 Ma) arc magmatic rocks present in the Frontal Cordillera show evidence for the bulk assimilation of the Permian-Triassic (P

  2. The Dras arc Complex: lithofacies and reconstruction of a Late Cretaceous oceanic volcanic arc in the Indus Suture Zone, Ladakh Himalaya (United States)

    Robertson, Alastair; Degnan, Paul


    The purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the Ladakh Himalayas. The mainly Late Cretaceous (Aptian—Paleocene?) Dras arc Complex in the Indus Suture Zone (N. India) is reconstructed as an oceanic arc, passing southwards into a proximal to distal forearc apron. The arc complex comprises three structural units. From west to east these are the Suru unit, the Naktul unit and the Nindam Formation. The Suru unit and the Naktul unit are unconformably underlain by dissected Late Jurassic? oceanic crust and mantle. The Suru unit preserves the interior of the arc and is divided into Dras 1 and Dras 2 sub-units. The Dras 1 Sub-unit, of mid-Late Cretaceous age, was intruded by arc plutonics, deformed, then unconformably overlain by the poorly dated Dras 2 Sub-unit (Lower Tertiary). The Dras 1 Sub-unit comprises arc extrusives, volcaniclastic and tuffaceous sedimentary rocks, and mainly redeposited shallow-water limestones. The Dras 2 Sub-unit is dominated by coarse volcaniclastics and lava flows, passing up into rhythmically layered acidic extrusives, with interbedded turbiditic siltstones and siliceous pelagic limestones. Further east, the Naktul unit is mainly clastic, with large volumes of massive volcaniclastic talus, thick-bedded debris flows, volcaniclastic turbidites and reworked shallow-water carbonates. Pillowed extrusives and ribbon radiolarites are present, mainly low in the succession in some areas, while pelagic carbonates are abundant near the top. The Naktul unit is interpreted as a proximal forearc apron. The Nindam Formation in the east is dominated by deep-water volcaniclastic turbidites, tuffaceous sediments and pelagic carbonates, with subordinate debris flows and is interpreted as a distal deep-water forearc succession. Cyclical alternations of mainly volcaniclastics and pelagic carbonates in the Nindam Formation

  3. Fracture development within a stratovolcano: The Karaha-Telaga Bodas geothermal field, Java volcanic arc (United States)

    Nemcok, M.; Moore, J.N.; Allis, R.; McCulloch, J.


    Karaha-Telaga Bodas, a vapour-dominated geothermal system located in an active volcano in western Java, is penetrated by more than two dozen deep geothermal wells reaching depths of 3 km. Detailed paragenetic and fluid-inclusion studies from over 1000 natural fractures define the liquid-dominated, transitional and vapour-dominated stages in the evolution of this system. The liquid-dominated stage was initiated by ashallow magma intrusion into the base of the volcanic cone. Lava and pyroclastic flows capped a geothermal system. The uppermost andesite flows were only weakly fractured due to the insulating effect of the intervening altered pyroclastics, which absorbed the deformation. Shear and tensile fractures that developed were filled with carbonates at shallow depths, and by quartz, epidote and actinolite at depths and temperatures over 1 km and 300??C. The system underwent numerous cycles of overpressuring, documented by subhorizontal tensile fractures, anastomosing tensile fracture patterns and implosion breccias. The development of the liquidsystem was interrupted by a catastrophic drop in fluid pressures. As the fluids boiled in response to this pressure drop, chalcedony and quartz were selectively deposited in fractures that had the largest apertures and steep dips. The orientations of these fractures indicate that the escaping overpressured fluids used the shortest possible paths to the surface. Vapour-dominated conditions were initiated at this time within a vertical chimney overlying the still hot intrusion. As pressures declined, these conditions spread outward to form the marginal vapour-dominated region encountered in the drill holes. Downward migration of the chimney, accompanied by growth of the marginal vapour-dominated regime, occurred as the intrusion cooled and the brittle-ductile transition migrated to greater depths. As the liquids boiled off, condensate that formed at the top of the vapour-dominated zone percolated downward and low

  4. A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; WEI Qirong; ZHANG Zhibin; ZHANG Hu


    Geochemical characteristics of the Upper Permian ( P2 ) continental marginal arc volcanic rocks are described, which have been found recently around the areas of Xiaodingxi and Zangli on the eastern side of the Yunxian-Lincang granite, in terms of rock assemblage, petrochemistry, REE, trace elements, Pb isotopes, geotectonic environment and so on. The volcanic rock assemblage is dominated by basalt-andesite-dacite, with minor trachyte andecite-trachyte; the volcanic rock series is predominated by the calc-alkaline series, with minor tholleiite series and alkaline series rocks; the volcanic rocks are characterized by high Al2O3 and low TiO2 , with K2O contents showing extremely strong polarity; the REE distribution patterns are characterized by LREE enrichment and right-inclined type; trace elements and large cation elements are highly enriched, Ti and Cr are depleted, and P and Nb are partially depleted; the Pb composition is of the Gondwana type; the petrochemical points mostly fall within the field of island-arc volcanic rocks, in consistency with the projection of data points of continental marginal volcanic rocks in the southern segment of the South Lancangjiang Belt and the North Lancangjiang Belt. This continental marginal arc volcanic rock belt, together with the ocean-ridge and ocean-island volcanic rocks and ophiolites in the Changning-Menglian Belt, constitute the ocean-ridge volcanic rock, ophiolite-arc rock-magmatic rock belts which are distributed in pairs, indicating that the Lancangjiang oceanic crust subducted eastwards. This result is of great importance in constraining the evolution of the paleo-Tethys in the Lancangjiang Belt.

  5. Geothermal Potential of the Cascade and Aleutian Arcs, with Ranking of Individual Volcanic Centers for their Potential to Host Electricity-Grade Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Shevenell, Lisa [ATLAS Geosciences, Inc., Reno, NV (United States); Coolbaugh, Mark [ATLAS Geosciences, Inc., Reno, NV (United States); Hinz, Nick [Univ. of Nevada, Reno, NV (United States); Stelling, Pete [Western Washington Univ., Bellingham, WA (United States); Melosh, Glenn [GEODE, Santa Rosa, CA (United States); Cumming, William [Cumming Geoscience, Santa Rosa, CA (United States)


    This project brings a global perspective to volcanic arc geothermal play fairway analysis by developing statistics for the occurrence of geothermal reservoirs and their geoscience context worldwide in order to rank U.S. prospects. The focus of the work was to develop play fairways for the Cascade and Aleutian arcs to rank the individual volcanic centers in these arcs by their potential to host electricity grade geothermal systems. The Fairway models were developed by describing key geologic factors expected to be indicative of productive geothermal systems in a global training set, which includes 74 volcanic centers world-wide with current power production. To our knowledge, this is the most robust geothermal benchmark training set for magmatic systems to date that will be made public.

  6. Rapid pre-eruptive thermal rejuvenation in a large silicic magma body: the case of the Masonic Park Tuff, Southern Rocky Mountain volcanic field, CO, USA (United States)

    Sliwinski, J. T.; Bachmann, O.; Dungan, M. A.; Huber, C.; Deering, C. D.; Lipman, P. W.; Martin, L. H. J.; Liebske, C.


    Determining the mechanisms involved in generating large-volume eruptions (>100 km3) of silicic magma with crystallinities approaching rheological lock-up ( 50 vol% crystals) remains a challenge for volcanologists. The Cenozoic Southern Rocky Mountain volcanic field, in Colorado and northernmost New Mexico, USA, produced ten such crystal-rich ignimbrites within 3 m.y. This work focuses on the 28.7 Ma Masonic Park Tuff, a dacitic ( 62-65 wt% SiO2) ignimbrite with an estimated erupted volume of 500 km3 and an average of 45 vol% crystals. Near-absence of quartz, titanite, and sanidine, pronounced An-rich spikes near the rims of plagioclase, and reverse zoning in clinopyroxene record the reheating (from 750 to >800 °C) of an upper crustal mush in response to hotter recharge from below. Zircon U-Pb ages suggest prolonged magmatic residence, while Yb/Dy vs temperature trends indicate co-crystallization with titanite which was later resorbed. High Sr, Ba, and Ti concentrations in plagioclase microlites and phenocryst rims require in-situ feldspar melting and concurrent, but limited, mass addition provided by the recharge, likely in the form of a melt-gas mixture. The larger Fish Canyon Tuff, which erupted from the same location 0.7 m.y. later, also underwent pre-eruptive reheating and partial melting of quartz, titanite, and feldspars in a long-lived upper crustal mush following the underplating of hotter magma. The Fish Canyon Tuff, however, records cooler pre-eruptive temperatures ( 710-760 °C) and a mineral assemblage indicative of higher magmatic water contents (abundant resorbed sanidine and quartz, euhedral amphibole and titanite, and absence of pyroxene). These similar pre-eruptive mush-reactivation histories, despite differing mineral assemblages and pre-eruptive temperatures, indicate that thermal rejuvenation is a key step in the eruption of crystal-rich silicic volcanics over a wide range of conditions.

  7. Oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 Merapi eruption (Central Java, Indonesia) (United States)

    Borisova, Anastassia Y.; Gurenko, Andrey A.; Martel, Caroline; Kouzmanov, Kalin; Cathala, Annick; Bohrson, Wendy A.; Pratomo, Indyo; Sumarti, Sri


    Chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions. In this work, high-resolution multicollector secondary ion mass spectrometry data reveal strong variations of δ18O values in three plagioclase crystals (800-1700 μm) from two representative basaltic andesite samples of the 2010 Merapi eruption (Central Java, Indonesia). The δ18O values (from 4.6‰ to 7.9‰) are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth. The lowest δ18O values (4.6-6.6‰) are found in anorthite-rich cores (An82-97), whereas higher δ18O values (5.7-7.9‰) are found in anorthite-poorer zones (An33-86), typically in crystal rims. Combining these new plagioclase δ18O data with δ18O of calc-silicate crustal xenoliths erupted between 1994 and 1998, the composition of glass inclusions hosted by the anorthite-rich plagioclase (An82-92), available experimental data, and the results of thermodynamic modeling using the Magma Chamber Simulator code, we conclude that the abundant anorthite-rich cores crystallized from a mantle-derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper (200-600 MPa) magma storage zone, whereas lower anorthite zones crystallized at shallower levels (100-200 MPa). The oxygen isotope variations in the plagioclase are explained by a two-stage model of interaction of the hydrous, mafic mantle-derived magma (1) with old crustal rocks depleted in 18O due to high temperature alteration that yielded the low δ18O values in the anorthite-rich cores at deep levels (13-20 km), and later (2) with 18O-enriched carbonate material that yielded the high δ18O values in anorthite-poorer zones at shallow levels (∼4.5-9 km). Thermodynamic modeling is consistent with ∼18 wt.% assimilation of crustal calc-silicate material at 925-950 °C and 100-200 MPa by the 2010 Merapi basaltic andesite magma prior to

  8. The link between volcanism and plutonism in epizonal magma systems; high-precision U–Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico (United States)

    Rioux, Matthew; Farmer, Lang; Bowring, Samuel; Wooton, Kathleen M.; Amato, Jeffrey M.; Coleman, Drew S.; Verplanck, Philip L.


    The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U–Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from ~44 to 34 Ma. The three largest caldera-related tuff units yielded weighted mean 206Pb/238U dates of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206Pb/238U date of 36.259 ± 0.021 Ma. Weighted mean 206Pb/238U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a high-silica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the

  9. On the conditions of magma mixing and its bearing on andesite production in the crust. (United States)

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


    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.

  10. Evidence for voluminous bimodal pyroclastic volcanism during rifting of a Paleoproterozoic arc at Snow Lake, Manitoba

    National Research Council Canada - National Science Library

    Lafrance, Bruno; Rubingh, Kate E; Gibson, Harold L


    ...) assemblage of the Flin Flon belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust-bounded Chisel sequence indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits...

  11. Sphene and zircon in the Highland Range volcanic sequence (Miocene, southern Nevada, USA): Elemental partitioning, phase relations, and influence on evolution of silicic magma (United States)

    Colombini, L.L.; Miller, C.F.; Gualda, G.A.R.; Wooden, J.L.; Miller, J.S.


    Sphene is prominent in Miocene plutonic rocks ranging from diorite to granite in southern Nevada, USA, but it is restricted to rhyolites in coeval volcanic sequences. In the Highland Range volcanic sequence, sphene appears as a phenocryst only in the most evolved rocks (72-77 mass% SiO2; matrix glass 77-78 mass% SiO2). Zr-in-sphene temperatures of crystallization are mostly restricted to 715 and 755??C, in contrast to zircon (710-920??C, Ti-in-zircon thermometry). Sphene rim/glass Kds for rare earth elements are extremely high (La 120, Sm 1200, Gd 1300, Lu 240). Rare earth elements, especially the middle REE (MREE), decrease from centers to rims of sphene phenocrysts along with Zr, demonstrating the effect of progressive sphene fractionation. Whole rocks and glasses have MREE-depleted, U-shaped REE patterns as a consequence of sphene fractionation. Within the co-genetic, sphene-rich Searchlight pluton, only evolved leucogranites show comparable MREE depletion. These results indicate that sphene saturation in intruded and extruded magmas occurred only in highly evolved melts: abundant sphene in less silicic plutonic rocks represents a late-stage 'bloom' in fractionated interstitial melt. ?? 2011 Springer-Verlag.

  12. Pre-eruptive conditions of the ~31 ka rhyolitic magma of Tlaloc volcano, Sierra Nevada Volcanic Range, Central Mexico (United States)

    Macias, J.; Arce, J.; Rueda, H.; Gardner, J.


    Tlaloc volcano is located at the northern tip of the Sierra Nevada Volcanic Range in Central Mexico. This Pleistocene to Recent volcanic range consists from north to south of Tlaloc-Telapón-Teyotl-Iztaccíhuatl-and- Popocatépetl volcanoes. While andesitic to barely dacitic volcanism dominates the southern part of the range (i.e. Popocatépetl and Iztaccíhuatl); dacitic and rare rhyolithic volcanism (i.e. Telapón, Tlaloc) dominates the northern end. The known locus of rhyolitic magmatism took place at Tlaloc volcano with a Plinian-Subplinian eruption that occurred 31 ka ago. The eruption emplaced the so-called multilayered fallout and pumiceous pyroclastic flows (~2 km3 DRE). The deposit consists of 95% vol. of juvenile particles (pumice + crystals) and minor altered lithics 5% vol. The mineral association of the pumice fragments (74-76 % wt. SiO2) consists of quartz + plagioclase + sanidine + biotite and rare oxides set in a glassy groundmass with voids. Melt inclusions in quartz phenocrysts suggest that prior to the eruption the rhyolitic contain ~7% of H2O and Toluca volcano (~6 km) some 50 km to the southwest.

  13. Felsic Magmatism through Intracrustal Melting of Previously Formed Volcanic-Arc Crust: Implications for Differentiation and Secular Evolution of the Continental Crust (United States)

    G R, R. K.; C, S.


    The fundamental challenge in understanding the origin and evolution of the continental crust is to recognize how primary mantle source, and oceanic crust, which are essentially mafic to ultramafic in composition, could differentiate into a more or less felsic compositions. It is possible to understand growth and differentiation of the continental crust by constraining the interplay of magmatism, deformation, and high-grade metamorphism in the lower crust. Here, we apply this knowledge on the lower crustal granitoids of southern India and speculate on the variations in geochemistry as a consequence of differentiation and secular evolution of the continental crust.The major groups of granitoids of southern India are classified as metatonalites, comparable to typical Archaean TTGs with pronounced calc-alkaline affinity, and metagranites which are magmatic fractionation produced by reworking of early crust. Metatonalites are sodic-trondhjemites with slightly magnesian, moderate LREE (average LaN = 103) and low HREE (average YbN = 2) characerestics, where as metagranites are calc-alkaline ferroan types with enriched LREE (average LaN = 427) and HREE (average YbN = 23). Petrogenetic characteristics of granitoids illustrate continuous evolution of a primary crust into diverse magmatic units by multiple stages of intracrustal differentiation processes attributed to following tectonic scenarios: (1) formation of tonalitic magma by low- to moderate-degree partial melting of hydrated basaltic crust at pressures high enough to stabilize garnet-amphibole residue and (2) genesis of granite in a continental arc-accretion setting by an episode of crustal remelting of the tonalitic crust, within plagioclase stability field. The first-stage formed in a flat-subduction setting of an volcanic-arc, leading to the formation of tonalites. The heat budget required is ascribed to the upwelling of the mantle and/or basaltic underplating. Progressive decline in mantle potential temperature

  14. Structure of magma reservoirs beneath Merapi and surrounding volcanic centers of Central Java modeled from ambient noise tomography (United States)

    Koulakov, Ivan; Maksotova, Gulzhamal; Jaxybulatov, Kayrly; Kasatkina, Ekaterina; Shapiro, Nikolai M.; Luehr, Birger-G.; El Khrepy, Sami; Al-Arifi, Nassir


    We present a three-dimensional model of the distribution of S-wave velocity in the upper crust to a depth of 20 km beneath Central Java based on the analysis of seismic ambient noise data recorded by more than 100 seismic stations in 2004 associated with the MERAMEX project. To invert the Rayleigh wave dispersion curves to construct 2-D group-velocity maps and 3-D distributions of S-wave velocity, we have used a new tomographic algorithm based on iterative linearized inversion. We have performed a series of synthetic tests that demonstrate significantly higher resolution in the upper crust with this model compared to the local earthquake travel-time tomography (LET) model previously applied for the same station network. Beneath the southern flank of Merapi, we identify a large low-velocity anomaly that can be split into two layers. The upper layer reflects the ˜1 km thick sedimentary cover of volcanoclastic deposits. The deeper anomaly at depths of ˜4-8 km may represent a magma reservoir with partially molten rock that feeds several volcanoes in Central Java. Beneath the Merapi summit, we observe another low-velocity anomaly as deep as 8 km that may be associated with the active magma reservoir that feeds the eruptive activity of Merapi. In the southern portion of the study area, in the lower crust, we identify a low-velocity anomaly that may represent the top of the pathways of volatiles and melts ascending from the slab that was previously inferred from the LET model results. We observe that this anomaly is clearly separate from the felsic magma reservoirs in the upper crust.

  15. The 10 April 2014 Nicaraguan Crustal Earthquake: Evidence of Complex Deformation of the Central American Volcanic Arc (United States)

    Suárez, Gerardo; Muñoz, Angélica; Farraz, Isaac A.; Talavera, Emilio; Tenorio, Virginia; Novelo-Casanova, David A.; Sánchez, Antonio


    On 10 April 2014, an M w 6.1 earthquake struck central Nicaragua. The main event and the aftershocks were clearly recorded by the Nicaraguan national seismic network and other regional seismic stations. These crustal earthquakes were strongly felt in central Nicaragua but caused relatively little damage. This is in sharp contrast to the destructive effects of the 1972 earthquake in the capital city of Managua. The differences in damage stem from the fact that the 1972 earthquake occurred on a fault beneath the city; in contrast, the 2014 event lies offshore, under Lake Managua. The distribution of aftershocks of the 2014 event shows two clusters of seismic activity. In the northwestern part of Lake Managua, an alignment of aftershocks suggests a northwest to southeast striking fault, parallel to the volcanic arc. The source mechanism agrees with this right-lateral, strike-slip motion on a plane with the same orientation as the aftershock sequence. For an earthquake of this magnitude, seismic scaling relations between fault length and magnitude predict a sub-surface fault length of approximately 16 km. This length is in good agreement with the extent of the fault defined by the aftershock sequence. A second cluster of aftershocks beneath Apoyeque volcano occurred simultaneously, but spatially separated from the first. There is no clear alignment of the epicenters in this cluster. Nevertheless, the decay of the number of earthquakes beneath Apoyeque as a function of time shows the typical behavior of an aftershock sequence and not of a volcanic swarm. The northeast-southwest striking Tiscapa/Ciudad Jardín and Estadio faults that broke during the 1972 and 1931 Managua earthquakes are orthogonal to the fault where the 10 April earthquake occurred. These orthogonal faults in close geographic proximity show that Central Nicaragua is being deformed in a complex tectonic setting. The Nicaraguan forearc sliver, between the trench and the volcanic arc, moves to the

  16. The 10 April 2014 Nicaraguan Crustal Earthquake: Evidence of Complex Deformation of the Central American Volcanic Arc (United States)

    Suárez, Gerardo; Muñoz, Angélica; Farraz, Isaac A.; Talavera, Emilio; Tenorio, Virginia; Novelo-Casanova, David A.; Sánchez, Antonio


    On 10 April 2014, an M w 6.1 earthquake struck central Nicaragua. The main event and the aftershocks were clearly recorded by the Nicaraguan national seismic network and other regional seismic stations. These crustal earthquakes were strongly felt in central Nicaragua but caused relatively little damage. This is in sharp contrast to the destructive effects of the 1972 earthquake in the capital city of Managua. The differences in damage stem from the fact that the 1972 earthquake occurred on a fault beneath the city; in contrast, the 2014 event lies offshore, under Lake Managua. The distribution of aftershocks of the 2014 event shows two clusters of seismic activity. In the northwestern part of Lake Managua, an alignment of aftershocks suggests a northwest to southeast striking fault, parallel to the volcanic arc. The source mechanism agrees with this right-lateral, strike-slip motion on a plane with the same orientation as the aftershock sequence. For an earthquake of this magnitude, seismic scaling relations between fault length and magnitude predict a sub-surface fault length of approximately 16 km. This length is in good agreement with the extent of the fault defined by the aftershock sequence. A second cluster of aftershocks beneath Apoyeque volcano occurred simultaneously, but spatially separated from the first. There is no clear alignment of the epicenters in this cluster. Nevertheless, the decay of the number of earthquakes beneath Apoyeque as a function of time shows the typical behavior of an aftershock sequence and not of a volcanic swarm. The northeast-southwest striking Tiscapa/Ciudad Jardín and Estadio faults that broke during the 1972 and 1931 Managua earthquakes are orthogonal to the fault where the 10 April earthquake occurred. These orthogonal faults in close geographic proximity show that Central Nicaragua is being deformed in a complex tectonic setting. The Nicaraguan forearc sliver, between the trench and the volcanic arc, moves to the

  17. Newly developed evidence for the original Tethysan island-arc volcanic rocks in the southern segment of the South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)


    This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.

  18. Effects of crustal thickness on magmatic differentiation in subduction zone volcanism: A global study (United States)

    Farner, Michael J.; Lee, Cin-Ty A.


    The majority of arc magmas are highly evolved due to differentiation within the lithosphere or crust. Some studies have suggested a relationship between crustal thickness and magmatic differentiation, but the exact nature of this relationship is unclear. Here, we examine the interplay of crustal thickness and magmatic differentiation using a global geochemical dataset compiled from active volcanic arcs and elevation as a proxy for crustal thickness. With increasing crustal thickness, average arc magma compositions become more silicic (andesitic) and enriched in incompatible elements, indicating that on average, arc magmas in thick crust are more evolved, which can be easily explained by the longer transit and cooling times of magmas traversing thick arc lithosphere and crust. As crustal thickness increases, arc magmas show higher degrees of iron depletion at a given MgO content, indicating that arc magmas saturate earlier in magnetite when traversing thick crust. This suggests that differentiation within thick crust occurs under more oxidizing conditions and that the origin of oxidation is due to intracrustal processes (contamination or recharge) or the role of thick crust in modulating melting degree in the mantle wedge. We also show that although arc magmas are on average more silicic in thick crust, the most silicic magmas (>70 wt.% SiO2) are paradoxically found in thin crust settings, where average compositions are low in silica (basaltic). We suggest that extreme residual magmas, such as those exceeding 70 wt.% SiO2, are preferentially extracted from shallow crustal magma bodies than from deep-seated magma bodies, the latter more commonly found in regions of thick crust. We suggest that this may be because the convective lifespan of crustal magma bodies is limited by conductive cooling through the overlying crustal lid and that magma bodies in thick crust cool more slowly than in thin crust. When the crust is thin, cooling is rapid, preventing residual magmas

  19. Late-Pleistocene to precolumbian behind-the-arc mafic volcanism in the eastern Mexican Volcanic Belt; implications for future hazards (United States)

    Siebert, Lee; Carrasco-Núñez, Gerardo


    An area of widespread alkaline-to-subalkaline volcanism lies at the northern end of the Cofre de Perote-Citlaltépetl (Pico de Orizaba) volcanic chain in the eastern Mexican Volcanic Belt (MVB). Two principal areas were active. About a dozen latest-Pleistocene to precolumbian vents form the 11-km-wide, E-W-trending Cofre de Perote vent cluster (CPVC) at 2300-2800 m elevation on the flank of the largely Pleistocene Cofre de Perote shield volcano and produced an extensive lava field that covers >100 km 2. More widely dispersed vents form the Naolinco volcanic field (NVF) in the Sierra de Chiconquiaco north of the city of Jalapa (Xalapa). Three generations of flows are delineated by cone and lava-flow morphology, degree of vegetation and cultivation, and radiocarbon dating. The flows lie in the behind-the-arc portion of the northeastern part of the MVB and show major- and trace-element chemical patterns transitional between intraplate and subduction zone environments. Flows of the oldest group originated from La Joya cinder cone (radiocarbon ages ˜42 000 yr BP) at the eastern end of the CPVC. This cone fed an olivine-basaltic flow field of ˜20 km 2 that extends about 14 km southeast to underlie the heavily populated northern outskirts of Jalapa, the capital city of the state of Veracruz. The Central Cone Group (CCG), of intermediate age, consists of four morphologically youthful cinder cones and associated vents that were the source of a lava field>27 km 2 of late-Pleistocene or Holocene age. The youngest group includes the westernmost flow, from Cerro Colorado, and a lava flow ˜2980 BP from the Rincón de Chapultepec scoria cone of the NVF. The latest eruption, from the compound El Volcancillo scoria cone, occurred about 870 radiocarbon years ago and produced two chemically and rheologically diverse lava flows that are among the youngest precolumbian flows in México and resemble paired aa-pahoehoe flows from Mauna Loa volcano. The El Volcancillo eruption

  20. Palaeoproterozoic Volcanic Massive Sulphides (VMS) in the Lithuanian crystalline basement: evidences for a back-arc tectonic setting (United States)

    Skridlaite, Grazina; Siliauskas, Laurynas


    In the southwestern part of the East European Craton (EEC), several events of Palaeoproterozoic volcanic arc magmatic activity were recognized in the concealed crystalline basement. In Lithuania, the TTG suites of 1.89 Ga and 1.86-1.84 Ga were later metamorphosed in amphibolite and granulite facies conditions. Remnants of a volcano-sedimentary sequence metamorphosed in green schist and amphibolite facies conditions were discovered in central and southern Lithuania. In southern Lithuania, the upper part of the Lazdijai 13 (Lz13) drilling (at c. 493 m depth) consists of exhalitic quartz chlorite cherts mixed with andesitic rocks. The rocks are impregnated with magnetite in some places replacing calcite. Most of the magnetite grains are overgrown by a dendritic kovelite, which may have formed while magnetite was still in aqueous surrounding. Other accessory minerals are xenotime, zircon, apatite, Sr-Ba sulphates etc. The cherts are underlain by a metaandesite which volcanic structures were obscured by hydrothermal alteration, i.e. the idiomorphic magnetite crystals and porphyritic plagioclase grains were replaced by clay minerals and quartz or muscovite in many places. Thin metamorphosed mudstone layers turned into garnet, biotite (+/-staurolite) and chlorite schists. The rocks were affected by silicification, chloritization, argilitization and carbonatization. Taking into account the rock composition, micro and macro scale alteration zones and absence of breccia, the whole package resembles an outer part of the VMS stockwork. The lower boundary at 526 m is sharp, marked by a quartz vein, below which lies quartz, biotite (+/- chlorite) bearing schist with minor tremolite (former sandstone). It was intensely affected by silicification, and was enriched in Na, K and Ca. Accessory minerals are monazite, xenotime, apatite and detrital zircon. The schist exhibits fine mineral foliation, and is fine-grained. A 4 m thick granitic vein cuts the rock at 654 m depth, below

  1. Complexity of In-situ zircon U-Pb-Hf isotope systematics during arc magma genesis at the roots of a Cretaceous arc, Fiordland, New Zealand (United States)

    Milan, L. A.; Daczko, N. R.; Clarke, G. L.; Allibone, A. H.


    Zircons from seventeen samples of Western Fiordland Orthogneiss (WFO) diorites and three samples of country rock (two schists and one Darran Suite diorite) from the lowermost exposed sections of the Median Batholith, Fiordland, New Zealand, were analysed for in-situ U-Pb and Hf-isotopes. The WFO represents the deeper levels of Early Cretaceous continental arc magmatism on the Pacific margin of Gondwana, marking the final stage of long-lived arc magmatism on the margin spanning the Palaeozoic. The WFO plutons were emplaced at high-P (mid to deep crust at c. 8-12 kbar) between 124 and 114 Ma. Minor very high-P (c. 18 kbar) WFO eclogite and omphacite granulite facies orthogneiss (Breaksea Orthogneiss) are inferred to have crystallised in the base of thickened crust at c. 124 Ma. Zircons from the Breaksea Orthogneiss are considered to be variably affected by Pb-loss due to emplacement of the adjacent (Malaspina) Pluton at c. 114 Ma. By identifying Pb-loss, magmatic ages were able to be inferred in respect to apparent Pb-loss ages. Hf isotope data for the WFO define an excursion to less radiogenic Hf isotope ratios with time, reflecting increased recycling of an old source component. Peaks at c. 555, 770 and 2480 Ma, determine the age spectra of inherited populations of zircons within the WFO. This contrasts with detrital zircon patterns in country rocks of the Takaka terrane, which include peaks at c. 465 Ma, and 1250-900 Ma that are absent in the WFO inheritance pattern. These results indicate a previously unrecognised Precambrian lower crustal component of New Zealand. Recycling of this lower crust became increasingly important as a source for the final stage or Mesozoic arc magmatism along this segment of the palaeo-Pacific margin of Gondwana.

  2. Magma-derived CO2 emissions in the Tengchong volcanic field, SE Tibet: Implications for deep carbon cycle at intra-continent subduction zone (United States)

    Zhang, Maoliang; Guo, Zhengfu; Sano, Yuji; Zhang, Lihong; Sun, Yutao; Cheng, Zhihui; Yang, Tsanyao Frank


    Active volcanoes at oceanic subduction zone have long been regard as important pathways for deep carbon degassed from Earth's interior, whereas those at continental subduction zone remain poorly constrained. Large-scale active volcanoes, together with significant modern hydrothermal activities, are widely distributed in the Tengchong volcanic field (TVF) on convergent boundary between the Indian and Eurasian plates. They provide an important opportunity for studying deep carbon cycle at the ongoing intra-continent subduction zone. Soil microseepage survey based on accumulation chamber method reveals an average soil CO2 flux of ca. 280 g m-2 d-1 in wet season for the Rehai geothermal park (RGP). Combined with average soil CO2 flux in dry season (ca. 875 g m-2 d-1), total soil CO2 output of the RGP and adjacent region (ca. 3 km2) would be about 6.30 × 105 t a-1. Additionally, we conclude that total flux of outgassing CO2 from the TVF would range in (4.48-7.05) × 106 t a-1, if CO2 fluxes from hot springs and soil in literature are taken into account. Both hot spring and soil gases from the TVF exhibit enrichment in CO2 (>85%) and remarkable contribution from mantle components, as indicated by their elevated 3He/4He ratios (1.85-5.30 RA) and δ13C-CO2 values (-9.00‰ to -2.07‰). He-C isotope coupling model suggests involvement of recycled organic metasediments and limestones from subducted Indian continental lithosphere in formation of the enriched mantle wedge (EMW), which has been recognized as source region of the TVF parental magmas. Contamination by crustal limestone is the first-order control on variations in He-CO2 systematics of volatiles released by the EMW-derived melts. Depleted mantle and recycled crustal materials from subducted Indian continental lithosphere contribute about 45-85% of the total carbon inventory, while the rest carbon (about 15-55%) is accounted by limestones in continental crust. As indicated by origin and evolution of the TVF

  3. Revealing the magmas degassing below closed-conduit active volcanoes: noble gases in volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy) (United States)

    Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.


    With the aim to constrain the nature of magma currently feeding the fumarolic field of Vulcano, we measured the elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions in high-K calcalcaline-shoshonitic and shoshonitic-potassic series so as to cover the entire volcanological history of Vulcano Island (Italy). The major and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic record of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-emitted Vulcanello latites (Punta del Roveto), which have high He- and Sr-isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs. Indeed, an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He isotope ratios between fluid inclusions and fumarolic gases showed that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that that the most probable magma which actually feeds the fumarolic emissions is a latitic body ponding at about 3-3.5 km of depth and flushed by fluids coming from a deeper and basic magma.

  4. The tectonic emplacement of Sumba in the Sunda-Banda Arc: paleomagnetic and geochemical evidence from the early Miocene Jawila volcanics (United States)

    Wensink, Hans; van Bergen, Manfred J.


    The island of Sumba is a continental fragment in the fore-arc region near the transition between the Sunda Arc and Banda Arc in southeastern Indonesia. Paleomagnetic and geochemical evidence from the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final drift stage and tectonic emplacement of the island. The lavas range from predominantly andesites to dacites, and display textural evidence for a weak metamorphism. Rock magnetic and mineral chemical data point to pseudo-single- to multi-domain (titano)magnetite (Fe 2.5-3Ti 0.5-0O 3), with grain sizes up to 10 μm, as the main carrier of remanence. The Jawila Formation reveals a ChRM direction with declination = 4.6°, inclination = - 19.2°, α95 = 9.9° and a paleolatitude of 9.9°S, which corroborates earlier results (Chamalaun and Sunata, 1982). Taking paleomagnetic evidence from other formations on the island into account, we conclude that the Sumba fragment has occupied approximately its present position since the Miocene. The calc-alkaline affinity and trace-element signatures of the lavas point to an origin in an arc environment. This occurrence of subduction-related volcanic activity in the early Miocene on Sumba implies that a volcanic arc existed south of the present-day East Sunda Arc, or that the island was located within the latter arc between Sumbawa and eastern Flores, and still had a minor southward drift to cover.

  5. Geochemistry of the Bonin Fore-arc Volcanic Sequence: Results from IODP Expedition 352 (United States)

    Godard, M.; Ryan, J. G.; Shervais, J. W.; Whattam, S. A.; Sakuyama, T.; Kirchenbaur, M.; Li, H.; Nelson, W. R.; Prytulak, J.; Pearce, J. A.; Reagan, M. K.


    The Izu-Bonin-Mariana intraoceanic arc system, in the western Pacific, results from ~52 My of subduction of the Pacific plate beneath the eastern margin of the Philippine Sea plate. Four sites were drilled south of the Bonin Islands during IODP Expedition 352 and 1.22 km of igneous basement was cored upslope to the west of the trough. These stratigraphically controlled igneous suites allow study of the earliest stages of arc development from seafloor spreading to convergence. We present the preliminary results of a detailed major and trace element (ICPMS) study on 128 igneous rocks drilled during Expedition 352. Mainly basalts and basaltic andesites were recovered at the two deeper water sites (U1440 and U1441) and boninites at the two westernmost sites (U1439 and U1442). Sites U1440 and U1441 basaltic suites are trace element depleted (e.g. Yb 4-6 x PM); they have fractionated REE patterns (LREE/HREE = 0.2-0.4 x C1-chondrites) compared to mid-ocean ridge basalts. They have compositions overlapping that of previously sampled Fore-Arc Basalts (FAB) series. They are characterized also by an increase in LILE contents relative to neighboring elements up-section (e.g. Rb/La ranging from FAB generation into their mantle source.

  6. Temporal and geochemical evolution of Miocene volcanism in the Andean back-arc between 36°S and 38°S and U-series analyses of young volcanic centers in the arc and back-arc, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup

    of the subducting slab at ca. 20 Ma is inferred. The eruption of 24-20 Ma alkali olivine basalt up to 500 km east of the trench marks the beginning of a long-lasting magmatic episode with widespread volcanism north of the Cortaderas lineament following a regional magmatic hiatus lasting from 39 Ma to 26 Ma...

  7. Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau: Constraints on mantle source of the underplated basic magma

    Institute of Scientific and Technical Information of China (English)

    LAI ShaoCong; QIN JiangFeng; LI YongFei; LONG Ping


    The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt, both characterized by the lower SiO2 (51%-54%), high refractory elements (i.e. Mg, Cr, Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE, i.e. Nb, Ta, Ti). Besides, the fairly low Sm/Yb value (3.07-4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383), and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = +0.02 to-0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 , △7/4Pb = 9.88 to 11.42, △Sr>50, implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area, this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block, and induced its partial melting, and then the melt underplated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.

  8. Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau:Constraints on mantle source of the underplated basic magma

    Institute of Scientific and Technical Information of China (English)


    The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt,both characterized by the lower SiO2 (51%―54%),high refractory elements (i.e. Mg,Cr,Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE,i.e. Nb,Ta,Ti). Be-sides,the fairly low Sm/Yb value (3.07―4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383),and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = +0.02 to -0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 ,△7/4Pb = 9.88 to 11.42,△Sr>50,implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area,this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block,and induced its partial melting,and then the melt under-plated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.

  9. Crustal and tectonic controls on large-explosive volcanic eruptions (United States)

    Sheldrake, Tom; Caricchi, Luca


    Quantifying the frequency-Magnitude (f-M) relationship for volcanic eruptions is important to estimate volcanic hazard. Furthermore, understanding how this relationship varies between different groups of volcanoes can provide insights into the processes that control the size and rate of volcanic events. Using a Bayesian framework, which allows us to conceptualise the volcanic record as a series of individual and unique time series, associated by a common group behaviour, we identify variations in the size and rate of volcanism in different volcanic arcs. These variations in behaviour are linked to key parameters that include the motion of subduction, rate of subduction, age of the slab and thickness of the crust. The effects of these parameters on volcanism are interpreted in terms of variations in mantle productivity and the thermal efficiency of magma transfer in arc crustal systems. Understanding the link between subduction architecture, heat content of magmatic systems, and volcanic activity will serve to improve our capacity to quantify volcanic hazard in regions with limited geological and historical records of volcanic activity.

  10. Neotectonic development of the El Salvador Fault Zone and implications for deformation in the Central America Volcanic Arc: Insights from 4-D analog modeling experiments (United States)

    Alonso-Henar, Jorge; Schreurs, Guido; Martinez-Díaz, José Jesús; Álvarez-Gómez, José Antonio; Villamor, Pilar


    The El Salvador Fault Zone (ESFZ) is an active, approximately 150 km long and 20 km wide, segmented, dextral strike-slip fault zone within the Central American Volcanic Arc striking N100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Structural field data and mapping suggest a phase of extension, at some stage during the evolution of the ESFZ. This phase would explain dip-slip movements on structures that are currently associated with the active, dominantly strike slip and that do not fit with the current tectonic regime. Field observations suggest trenchward migration of the arc. Such an extension and trenchward migration of the volcanic arc could be related to slab rollback of the Cocos plate beneath the Chortis Block during the Miocene/Pliocene. We carried out 4-D analog model experiments to test whether an early phase of extension is required to form the present-day fault pattern in the ESFZ. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures. This extensional phase is followed by a strike-slip dominated regime, which results in intersegment areas with local transtension and segments with almost pure strike-slip motion. The results of our experiments combined with field data along the Central American Volcanic Arc indicate that the slab rollback intensity beneath the Chortis Block is greater in Nicaragua and decreases westward to Guatemala.

  11. Sphene (Titanite) as Both Monitor and Driver of Evolution of Felsic Magma: Miocene Volcanic Plutonic and Rocks of the Colorado River Region, NV-AZ, USA (United States)

    Miller, C. F.; Colombini, L. L.; Wooden, J. L.; Mazdab, F. K.; Gualda, G. A.; Claiborne, L. E.; Ayers, J. C.


    Sphene is commonly the most abundant accessory mineral in metaluminous to weakly peraluminous igneous rocks. Its relatively large crystals preserve a wide array of zoning patterns and inclusions - notably, abundant other accessories and melt inclusions - and it is a major host for REE, U, Th, and HFSE. Thus it is a valuable repository of information about the history of the magmas from which it forms. Recent development of a Zr-in- sphene thermometer (Hayden et al CMP 155:529 2008) and of sensitive and precise in situ trace element analysis by SHRIMP-RG (Mazdab et al GSA abst 39:6:406 2007) permit more powerful exploitation of this repository. We have initiated a study of sphene in Miocene intrusive and extrusive rocks of the Colorado River extensional corridor for which extensive field, geochemical, and geochronological data provide context. Sphene is present as a late interstitial phase in some gabbros and diorites and common in quartz monzonites and granites. Among extrusive rocks, it occurs as phenocrysts in rhyolite lavas and tuffs that are products of small to giant eruptions (Peach Spring Tuff, >600 km3). Glasses that host sphene in the rhyolites are highly evolved (>76 wt% SiO2). Applying the Zr-in-sphene thermometer (TZr), SHRIMP-RG analyses indicate crystallization T between 730 and 810 C in both plutonic and volcanic rocks. This range is narrower than T estimates for zircon growth (Ti thermometry) for the same suite, which extend to somewhat lower and considerably higher values; zircons also tend to record more events and, evidently, longer histories. Ranges of REE patterns are variable and to some extent sample-specific, but all reveal common characteristics: (1) extremely high concentrations, especially for middle REE (maximum Sm in interiors 10-40x103 x chondrite); (2) deep negative Eu anomalies (Eu/Eu* ca. 0.1-0.2); (3) TZr and REE dropping toward rims - especially pronounced for MREE. Estimated Kds for REE from sphene rims and rhyolite glass or

  12. Early Permian arc-related volcanism and sedimentation at the western margin of Gondwana:Insight from the Choiyoi Group lower section

    Institute of Scientific and Technical Information of China (English)

    Leonardo Strazzere; Daniel A. Gregori; Leonardo Benedini


    Permian sedimentary and basic to intermediate volcanic rocks assigned to the Conglomerado del Río Blanco and Portezuelo del Cenizo Formation, lower part of the Choiyoi Group, crop out between the Cordon del Plata, Cordillera Frontal and Precordillera of Mendoza Province, Argentina. The sedimentary rocks are represented by six lithofacies grouped in three facies associations. They were deposited by mantled and gravitational flows modified by high-energy fluvial currents that evolved to low-energy fluvial and lacustrine environments. They constitute the Conglomerado del Río Blanco, which cover unconformably marine Carboniferous sequences. Five volcanic and volcaniclastic facies make up the beginning of volcanic activity. The first volcanic event in the Portezuelo del Cenizo is basaltic to andesitic lava-flows emplaced in the flanks of volcanoes. Lava collapse produced thick block and ash flows. Interbedding in the intermediate volcanic rocks, there are dacites of different geochemical signature, which indicate that the development of acidic volcanism was coetaneous with the first volcanic activity. The geochemistry of these rocks induces to consider that the Choiyoi Group Lower section belongs to a magmatic arc on continental crust. The age of this section is assigned to the lower Permian (277 ? 3.0 Ma, Kungurian age).

  13. Sandstone provenance and U-Pb ages of detrital zircons from Permian-Triassic forearc sediments within the Sukhothai Arc, northern Thailand: Record of volcanic-arc evolution in response to Paleo-Tethys subduction (United States)

    Hara, Hidetoshi; Kunii, Miyuki; Miyake, Yoshihiro; Hisada, Ken-ichiro; Kamata, Yoshihito; Ueno, Katsumi; Kon, Yoshiaki; Kurihara, Toshiyuki; Ueda, Hayato; Assavapatchara, San; Treerotchananon, Anuwat; Charoentitirat, Thasinee; Charusiri, Punya


    Provenance analysis and U-Pb dating of detrital zircons in Permian-Triassic forearc sediments from the Sukhothai Arc in northern Thailand clarify the evolution of a missing arc system associated with Paleo-Tethys subduction. The turbidite-dominant formations within the forearc sediments include the Permian Ngao Group (Kiu Lom, Pha Huat, and Huai Thak formations), the Early to earliest Late Triassic Lampang Group (Phra That and Hong Hoi formations), and the Late Triassic Song Group (Pha Daeng and Wang Chin formations). The sandstones are quartzose in the Pha Huat, Huai Thak, and Wang Chin formations, and lithic wacke in the Kiu Lom, Phra That, Hong Hoi and Pha Daeng formations. The quartzose sandstones contain abundant quartz, felsic volcanic and plutonic fragments, whereas the lithic sandstones contain mainly basaltic to felsic volcanic fragments. The youngest single-grain (YSG) zircon U-Pb age generally approximates the depositional age in the study area, but in the case of the limestone-dominant Pha Huat Formation the YSG age is clearly older. On the other hand, the youngest cluster U-Pb age (YC1σ) represents the peak of igneous activity in the source area. Geological evidence, geochemical signatures, and the YC1σ ages of the sandstones have allowed us to reconstruct the Sukhothai arc evolution. The initial Sukhothai Arc (Late Carboniferous-Early Permian) developed as a continental island arc. Subsequently, there was general magmatic quiescence with minor I-type granitic activity during the Middle to early Late Permian. In the latest Permian to early Late Triassic, the Sukhothai Arc developed in tandem with Early to Middle Triassic I-type granitic activity, Middle to Late Triassic volcanism, evolution of an accretionary complex, and an abundant supply of sediments from the volcanic rocks to the trench through a forearc basin. Subsequently, the Sukhothai Arc became quiescent as the Paleo-Tethys closed after the Late Triassic. In addition, parts of sediments of

  14. Submarine Hydrothermal Sites in Arc Volcanic-Back Arc Environment: Insight from Recent Marine Geophysical Investigations in the Southern Tyrrhenian Sea. (United States)

    Cocchi, L.; Ligi, M.; Bortoluzzi, G.; Petersen, S.; Plunkett, S.; Muccini, F.; Canese, S.; Caratori Tontini, F.; Carmisciano, C.


    Hydrothermal alteration processes involve mineralogical and chemical changes, which are reflected in a major modification of potential field patterns observed over hydrothermal areas. Basalt-hosted hydrothermal sites exhibit characteristic responses with magnetic lows and minima of the gravity field. Near bottom AUV (Autonomous Underwater Vehicle) based potential field surveys have become a very effective technique in deep sea exploration. Here we present results of recent ship-borne and near seafloor magnetic and gravity investigations at deep (Marsili and Palinuro seamounts) and shallow (Panarea, Basiluzzo and Secca del Capo) hydrothermal sites in the Southern Tyrrhenian Sea including multibeam bathymetry, seafloor reflectivity and seismic profiles. At Marsili seamount, a large Fe-Mn-oxyhydroxides-rich chimney field is located at the summit (500 m depth). This site is correlated with pronounced magnetic and gravity lows (0 A/m and 2.0 g/cm3). Deep tow magnetic survey (Cruise MAVA11) revealed strong association between the complicated magnetization pattern and the main volcano-tectonic features of the ridge. Hydrothermal manifestations at Palinuro seamount occur mainly on the western sector within the rim of a caldera structure at depth of 600m. Recent AUV based magnetic surveys (Cruise POS442, 2012 using AUV "Abyss") detailed a magnetization low interpreted to represent the local distribution of subseafloor hydrothermal alteration (potentially massive sulfide deposits), and also mapped previously undiscovered inactive chimney fields. Hydrothermal sites observed at the arc-related volcanic islands (Panarea, Basiluzzo, Eolo and Secca del Capo) are confined to shallow depths (less then 300m) and associated with large ochreaceous mounds, vents and chimney fields such as those observed E of Basiluzzo Island. At this site a recent magnetic survey (Cruise PANA13_ASTREA) combined with Remote Operated Vehicle (ROV) investigations revealed that the submarine geothermal

  15. The roles of fractional crystallization, magma mixing, crystal mush remobilization and volatile-melt interactions in the genesis of a young basalt-peralkaline rhyolite suite, the greater Olkaria volcanic complex, Kenya Rift valley (United States)

    Macdonald, R.; Belkin, H.E.; Fitton, J.G.; Rogers, N.W.; Nejbert, K.; Tindle, A.G.; Marshall, A.S.


    The Greater Olkaria Volcanic Complex is a young (???20 ka) multi-centred lava and dome field dominated by the eruption of peralkaline rhyolites. Basaltic and trachytic magmas have been erupted peripherally to the complex and also form, with mugearites and benmoreites, an extensive suite of magmatic inclusions in the rhyolites. The eruptive rocks commonly represent mixed magmas and the magmatic inclusions are themselves two-, three- or four-component mixes. All rock types may carry xenocrysts of alkali feldspar, and less commonly plagioclase, derived from magma mixing and by remobilization of crystal mushes and/or plutonic rocks. Xenoliths in the range gabbro-syenite are common in the lavas and magmatic inclusions, the more salic varieties sometimes containing silicic glass representing partial melts and ranging in composition from anorthite ?? corundum- to acmite-normative. The peralkaline varieties are broadly similar, in major element terms, to the eruptive peralkaline rhyolites. The basalt-trachyte suite formed by a combination of fractional crystallization, magma mixing and resorption of earlier-formed crystals. Matrix glass in metaluminous trachytes has a peralkaline rhyolitic composition, indicating that the eruptive rhyolites may have formed by fractional crystallization of trachyte. Anomalous trace element enrichments (e.g. ??? 2000 ppm Y in a benmoreite) and negative Ce anomalies may have resulted from various Na- and K-enriched fluids evolving from melts of intermediate composition and either being lost from the system or enriched in other parts of the reservoirs. A small group of nepheline-normative, usually peralkaline, magmatic inclusions was formed by fluid transfer between peralkaline rhyolitic and benmoreitic magmas. The plumbing system of the complex consists of several independent reservoirs and conduits, repeatedly recharged by batches of mafic magma, with ubiquitous magma mixing. ?? The Author 2008. Published by Oxford University Press. All

  16. Evidence of Arc Magma Genesis in a Paleo-Mantle Wedge, the Higashi-Akaishi Peridotite, Japan (United States)

    Till, C. B.; Guild, M. R.; Grove, T. L.; Carlson, R. W.


    Located in the Sanbagawa subduction-related high-pressure metamorphic belt in SW Japan on the island of Shikoku, the Higashi-akaishi peridotite body is composed of dunite, lherzolite and garnet clinopyroxenite, interfingered in one locality with quartz-rich eclogite. Previous work indicates the P-T history of the peridotite includes rapid prograde metamorphism with peak temperatures of 700-810°C and pressures of 2.9-3.8 GPa [1] at ~88-89 Ma followed by rapid exhumation at >2.5 cm/yr [2,3]. Major and trace element and isotopic data from samples within the Higashi-akaishi peridotite presented here and in another recent study [4] provide a record of subduction zone melting processes in a paleo-mantle wedge. Ultramafic samples range from 40-52 wt.% SiO2, 1-11 wt.% Al2O3 and 21-45 wt.% MgO with olivine and clinopyroxene Mg#'s as high as 0.93. The quartz-rich eclogite contains 62 wt.% SiO2, 6 wt.% MgO and 13 wt.% Al2O3 with trace element concentrations that are enriched relative to the ultramafic samples. 87Sr/86Sr (.703237-.704288), 143Nd/144Nd (ɛNd=+2 to +6) and Pb isotopic compositions are within the range of previously studied Japanese arc rocks. We interpret the pyroxenites as shallowly crystallized cumulates with varying amounts of trapped hydrous melt and the harzburgites as residues of melting. The peak P-T conditions of these rocks are similar to the solidus conditions of H2O-saturated fertile mantle near the base of the mantle wedge [5,6]. The presence of garnet porphyroblasts that enclose primary euhedral chlorite together with the chemical evidence, suggest these samples are associated with mantle melting in the presence of H2O. Major element modeling suggests the quartz-rich eclogite composition can be reproduced through mixing melts of subducted sediment with wet peridotite melts in the mantle wedge. Thus the Higashi-aikashi rock suite provides an in-situ record of the beginnings of hydrous melting and the mechanisms of metasomatism in the mantle wedge

  17. Boron isotope fractionation in magma via crustal carbonate dissolution. (United States)

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


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

  18. Revealing magma degassing below closed-conduit active volcanoes: Geochemical features of volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy) (United States)

    Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.


    The elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions have been measured for rocks at various degrees of evolution and belonging to high-K calcalkaline-shoshonitic and shoshonitic-potassic series in order to cover the entire volcanological history of Vulcano Island (Italy). The major- and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the theoretical value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic history of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-erupted Vulcanello latites (Punta del Roveto), which have anomalously high He isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs, since an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He-isotope ratios between fluid inclusions and fumarolic gases shows that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that the most probable magma which actually feeds the fumarolic emissions is a latitic body that ponded at about 3-3.5 km of depth and is flushed by fluids coming from a deeper and basic magma.

  19. On-and offshore tephrostratigraphy and -chronology of the southern Central American Volcanic Arc (CAVA) (United States)

    Schindlbeck, J. C.; Kutterolf, S.; Hemming, S. R.; Wang, K. L.


    Including the recently drilled CRISP sites (IODP Exp. 334&344) the deep sea drilling programs have produced 69 drill holes at 29 Sites during 9 Legs at the Central American convergent margin, where the Cocos plate subducts beneath the Caribbean plate. The CAVA produced numerous plinian eruptions in the past. Although abundant in the marine sediments, information and data regarding large late Cenozoic explosive eruptions from Costa Rica, Nicaragua, Honduras, El Salvador, and Guatemala remain very sparse and discontinuous on land. We have established a tephrostratigraphy from recent through Miocene times from the unique archive of ODP/IODP sites offshore Central America in which we identify tephra source regions by geochemical fingerprinting using major and trace element glass shard compositions. Here we present first order correlations of ­~500 tephra layers between multiple holes at a single site as well as between multiple sites. We identified ashes supporting Costa Rican (~130), Nicaraguan (17) and Guatemalan (27) sources as well as ~150 tephra layers from the Galápagos hotspot. Within our marine record we also identified well-known marker beds such as the Los Chocoyos tephra from Atitlán Caldera in Guatemala and the Tiribi Tuff from Costa Rica but also correlations to 15 distinct deposits from known Costa Rican and Nicaraguan eruptions within the last 4.1 Ma. These correlations, together with new radiometric age dates, provide the base for an improved tephrochronostratigraphy in this region. Finally, the new marine record of explosive volcanism offshore southern CAVA provides insights into the eruptive history of long-living volcanic complexes (e.g., Barva, Costa Rica) and into the distribution and frequency of large explosive eruptions from the Galápagos hotspot. The integrated approach of Ar/Ar age dating, correlations with on land deposits from CAVA, biostratigraphic ages and sediment accumulation rates improved the age models for the drilling sites.

  20. Investigation of the thermal regime and geologic history of the Cascade volcanic arc: First phase of a program for scientific drilling in the Cascade Range

    Energy Technology Data Exchange (ETDEWEB)

    Priest, G.R.


    A phased, multihole drilling program with associated science is proposed as a means of furthering our understanding of the thermal regime and geologic history of the Cascade Range of Washington, Oregon, and northern California. The information obtained from drilling and ancillary geological and geophysical investigations will contribute to our knowledge in the following general areas: (1) the magnitude of the regional background heat flow of parts of the Quaternary volcanic belt dominated by the most abundant volcanic rock types, basalt and basaltic andesite; (2) the nature of the heat source responsible for the regional heat-flow anomaly; (3) the characteristics of the regional hydrothermal and cold-water circulation; the rates of volcanism for comparison with models for the rate and direction of plate convergence of the Cascades; (5) the history of deformation and volcanism in the volcanic arc that can be related to subduction; (6) the present-day stress regime of the volcanic arc and the relation of these stresses to plate interactions and possible large earthquakes; and the current geometry of the subducted oceanic plate below the Cascade Range and the relationship of the plate to the distribution of heat flow, Quaternary volcanism, and Quaternary deformation. Phase I research will be directed toward a detailed investigation of the Santiam Pass segment. In concert with the Santiam Pass research, a detailed study of the nearby Breitenbush Hot Springs area is also recommended as a component of Phase I. The object of the Breitenbush research is to study one of the hottest known Cascade hydrothermal systems, which coincidentally also has a good geological and geophysical data base. A coordinated program of drilling, sampling, subsurface measurements, and surface surveys will be associated with the drilling of several holes.

  1. Middle Jurassic Topawa group, Baboquivari Mountains, south-central Arizona: Volcanic and sedimentary record of deep basins within the Jurassic magmatic arc (United States)

    Haxel, G.B.; Wright, J.E.; Riggs, N.R.; Tosdal, R.M.; May, D.J.


    Among supracrustal sequences of the Jurassic magmatic arc of the southwestern Cordillera, the Middle Jurassic Topawa Group, Baboquivari Mountains, south-central Arizona, is remarkable for its lithologic diversity and substantial stratigraphic thickness, ???8 km. The Topawa Group comprises four units (in order of decreasing age): (1) Ali Molina Formation-largely pyroclastic rhyolite with interlayered eolian and fluvial arenite, and overlying conglomerate and sandstone; (2) Pitoikam Formation-conglomerate, sedimentary breccia, and sandstone overlain by interbedded silt- stone and sandstone; (3) Mulberry Wash Formation-rhyolite lava flows, flow breccias, and mass-flow breccias, with intercalated intraformational conglomerate, sedimentary breccia, and sandstone, plus sparse within-plate alkali basalt and comendite in the upper part; and (4) Tinaja Spring Porphyry-intrusive rhyolite. The Mulberry Wash alkali basalt and comendite are genetically unrelated to the dominant calcalkaline rhyolite. U-Pb isotopic analyses of zircon from volcanic and intrusive rocks indicate the Topawa Group, despite its considerable thickness, represents only several million years of Middle Jurassic time, between approximately 170 and 165 Ma. Sedimentary rocks of the Topawa Group record mixing of detritus from a minimum of three sources: a dominant local source of porphyritic silicic volcanic and subvolcanic rocks, identical or similar to those of the Topawa Group itself; Meso- proterozoic or Cambrian conglomerates in central or southeast Arizona, which contributed well-rounded, highly durable, polycyclic quartzite pebbles; and eolian sand fields, related to Middle Jurassic ergs that lay to the north of the magmatic arc and are now preserved on the Colorado Plateau. As the Topawa Group evidently represents only a relatively short interval of time, it does not record long-term evolution of the Jurassic magmatic arc, but rather represents a Middle Jurassic "stratigraphic snapshot" of the arc

  2. Origin of Miocene andesite and dacite in the Goldfield-Superstition volcanic province, central Arizona: Hybrids of mafic and silicic magma mixing (United States)

    Fodor, R. V.; Johnson, Kelly G.


    The Miocene Goldfield-Superstition volcanic province (G-SVP), ∼8000 km2 in central Arizona, is composed largely of silicic pyroclastic rocks and lavas, and smaller volumes of alkalic basalt and intermediate-composition lavas. Volcanism began ∼20.5 Ma as sparse rhyolitic and mainly basaltic lavas followed by intermediate lavas, lasting until ∼19 Ma. At that time, ∼1 m.y. of silicic eruptions began, creating most of the G-SVP. Petrologic studies are available for basalts and some for silicic rocks, but petrologic/geochemical information is sparse for intermediate-composition lavas. These latter, andesites and dacites, are the focus of this study, in which we present the processes and sources responsible for their origins. Goldfield-Superstition andesites and dacites have SiO2 ∼56-70 wt.% and Na2O + K2O that qualifies some as trachy-andesite and -dacite. A prominent petrographic feature is plagioclase-phyric texture (∼11-30 vol% plagioclase), where oligoclase-andesine phenocrysts have cores surrounded by corroded, or reacted, zones, mantled by higher An% plagioclase. Where corroded zones are absent, margins are etched, curved, or embayed. Groundmass plagioclase is labradorite, also more calcic than the phenocrysts. Other minerals are quartz (subrounded; embayed), clinopyroxene, amphibole, biotite, and rare titanite and zircon. A salient compositional characteristic that provides insight to andesite-dacite origins with respect to other G-SVP rocks is revealed when using SiO2 as an index. Namely, abundances of many incompatible elements, mainly HFSE and REE, decrease over the low to high SiO2 range (i.e., abundances are lower in dacites than in co-eruptive andesites and underlying alkalic basalts). As examples: G-SVP basalts have ∼50-70 ppm La, and andesites-dacites have ∼59-22 ppm La; for Zr, basalts have ∼225-170 ppm, but most andesites-dacites have ∼180-50; for Y, basalts >20 ppm, andesites-dacites ∼18-9 ppm. To understand these trends of lower

  3. Discovery of an active shallow submarine silicic volcano in the northern Izu-Bonin Arc: volcanic structure and potential hazards of Oomurodashi Volcano (Invited) (United States)

    Tani, K.; Ishizuka, O.; Nichols, A. R.; Hirahara, Y.; Carey, R.; McIntosh, I. M.; Masaki, Y.; Kondo, R.; Miyairi, Y.


    Oomurodashi is a bathymetric high located ~20 km south of Izu-Oshima, an active volcanic island of the northern Izu-Bonin Arc. Using the 200 m bathymetric contour to define its summit dimensions, the diameter of Oomurodashi is ~20 km. Oomurodashi has been regarded as inactive, largely because it has a vast flat-topped summit at 100 - 150 meters below sea level (mbsl). During cruise NT07-15 of R/V Natsushima in 2007, we conducted a dive survey in a small crater, Oomuro Hole, located in the center of the flat-topped summit, using the remotely-operated vehicle (ROV) Hyper-Dolphin. The only heat flow measurement conducted on the floor of Oomuro Hole during the dive recorded an extremely high value of 4,200 mW/m2. Furthermore, ROV observations revealed that the southwestern wall of Oomuro Hole consists of fresh rhyolitic lavas. These findings suggest that Oomurodashi is in fact an active silicic submarine volcano. To confirm this hypothesis, we conducted detailed geological and geophysical ROV Hyper-Dolphin (cruise NT12-19). In addition to further ROV surveys, we carried out single-channel seismic (SCS) surveys across Oomurodashi in order to examine the shallow structures beneath the current edifice. The ROV surveys revealed numerous active hydrothermal vents on the floor of Oomuro Hole, at ~200 mbsl, with maximum water temperature measured at the hydrothermal vents reaching 194°C. We also conducted a much more detailed set of heat flow measurements across the floor of Oomuro Hole, detecting very high heat flows of up to 29,000 mW/m2. ROV observations revealed that the area surrounding Oomuro Hole on the flat-topped summit of Oomurodashi is covered by extensive fresh rhyolitic lava and pumice clasts with minimum biogenetic or manganese cover, suggesting recent eruption(s). These findings strongly indicate that Oomurodashi is an active silicic submarine volcano, with recent eruption(s) occurring from Oomuro Hole. Since the summit of Oomurodashi is in shallow water, it

  4. A 36,000-Year-Old Volcanic Eruption Depicted in the Chauvet-Pont d'Arc Cave (Ardèche, France)? (United States)

    Nomade, Sébastien; Genty, Dominique; Sasco, Romain; Scao, Vincent; Féruglio, Valérie; Baffier, Dominique; Guillou, Hervé; Bourdier, Camille; Valladas, Hélène; Reigner, Edouard; Debard, Evelyne; Pastre, Jean-François; Geneste, Jean-Michel


    Among the paintings and engravings found in the Chauvet-Pont d'Arc cave (Ardèche, France), several peculiar spray-shape signs have been previously described in the Megaloceros Gallery. Here we document the occurrence of strombolian volcanic activity located 35 km northwest of the cave, and visible from the hills above the cave entrance. The volcanic eruptions were dated, using 40Ar/39Ar, between 29 ± 10 ka and 35 ± 8 ka (2σ), which overlaps with the 14C AMS and thermoluminescence ages of the first Aurignacian occupations of the cave in the Megaloceros Gallery. Our work provides the first evidence of an intense volcanic activity between 40 and 30 ka in the Bas-Vivarais region, and it is very likely that Humans living in the Ardèche river area witnessed one or several eruptions. We propose that the spray-shape signs found in the Chauvet-Pont d'Arc cave could be the oldest known depiction of a volcanic eruption, predating by more than 34 ka the description by Pliny the Younger of the Vesuvius eruption (AD 79) and by 28 ka the Çatalhöyük mural discovered in central Turkey.

  5. Underplating of basaltic magmas and crustal growth in a continental arc: Evidence from Late Mesozoic intermediate-felsic intrusive rocks in southern Qiangtang, central Tibet (United States)

    Hao, Lu-Lu; Wang, Qiang; Wyman, Derek A.; Ou, Quan; Dan, Wei; Jiang, Zi-Qi; Wu, Fu-Yuan; Yang, Jin-Hui; Long, Xiao-Ping; Li, Jie


    account ophiolites in the Bangong-Nujiang Suture and Late Mesozoic magmatic rocks in the southern Qiangtang sub-block, we suggest that this area was located in a continental arc setting. Moreover, from the Late Jurassic to Early Cretaceous, the ancient lower crust in the southern Qiangtang sub-block was gradually replaced by mantle-derived juvenile materials. The crustal evolution indicates that, in a continental arc, basaltic magma underplating plays a key role in vertical crustal growth.

  6. Back arc extension, tectonic inheritance, and volcanism in the Ligurian Sea, Western Mediterranean (United States)

    Rollet, Nadège; Déverchère, Jacques; Beslier, Marie-Odile; Guennoc, Pol; Réhault, Jean-Pierre; Sosson, Marc; Truffert, Catherine


    The Ligurian basin, western Mediterranean Sea, has opened from late Oligocene to early Miocene times, behind the Apulian subduction zone and partly within the western Alpine belt. We analyze the deep structures of the basin and its conjugate margins in order to describe the tectonic styles of opening and to investigate the possible contributions of forces responsible for the basin formation, especially the pulling force induced by the retreating subduction hinge and the gravitational body force from the Alpine wedge. To undertake this analysis, we combine new multichannel seismic reflection data (Malis cruise, 1995) with other geophysical data (previous multichannel and monochannel seismic sections, magnetic anomalies) and constrain them by geological sampling from two recent cruises (dredges from Marco cruise, 1995, and submersible dives from Cylice cruise, 1997). From an analysis of basement morphology and seismic facies, we refine the extent of the different domains in the Ligurian Sea: (1) the continental thinned margins, with strong changes in width and structure along strike and on both sides of the ocean; (2) the transitional domain to the basin; and (3) a narrow, atypical oceanic domain. Margin structures are characterized by few tilted blocks along the narrow margins, where inherited structures seem to control synrift sedimentation and margin segmentation. On the NW Corsican margin, extension is distributed over more than 120 km, including offshore Alpine Corsica, and several oceanward faults sole on a relatively flat reflector. We interpret them as previous Alpine thrusts reactivated during rifting as normal faults soling on a normal ductile shear zone. Using correlations between magnetic data, seismic facies, and sampling, we propose a new map of the distribution of magmatism. The oceanic domain depicts narrow, isolated magnetic anomalies and is interpreted as tholeitic volcanics settled within an unroofed upper mantle, whereas calcalkaline volcanism

  7. The interplay between tectonics and volcanism: a key to unravel the nature of Andean geothermal systems (United States)

    Cembrano, J. M.


    Field mapping combined with seismic data document the interplay between tectonics and volcanism in the Andes. In the Central Volcanic Zone (CVZ) of northern Chile (22-24°S), Pleistocene east-west shortening and a thick crust (50-70 km) are associated with major composite dacitic-andesitic volcanoes and a few monogenetic basaltic eruptive centers. CVZ stratovolcanoes are devoided of flank vents; clusters of minor eruptive centers are uncommon. Composite volcanoes and minor eruptive centers are coeval with a NS-striking system of reverse faults and fault-propagation folds. Although dextral strike-slip crustal seismicity is recorded between 18 and 21°S, evidence for long-term, margin-parallel strike-slip deformation is absent. In contrast, volcanoes of the Southern Volcanic Zone (SVZ), between 38 and 46°S are built on a much thinner crust (30-40 km) during intra-arc dextral transpression. Crustal seismicity shows dextral strike-slip focal mechanisms. There, a wide variety of volcanic forms and compositions coexist along the same volcanic arc. Volcanoes range from single monogenetic cones lying on master faults to major composite volcanoes organized into either NE- or NW-trending chains, oblique to the continental margin. Flank vents and elongated clusters of minor eruptive centers are common. Compositions range from primitive basalts at minor eruptive centers, to highly evolved magmas at mature stratovolcanoes. I hypothesize that the kinematics of fault-fracture networks under which magma is transported through the crust is one fundamental factor controlling the wide variety of volcanic forms, volcanic alignment patterns and rock compositions along a single volcanic arc. As a first approximation, a thicker crust favors magma differentiation processes whereas a thinner crust prevents it. Likewise, whereas bulk intra-arc compression (vertical σ3) enhances longer residence times of magmas in the CVZ, strike-slip deformation (horizontal σ3) in SVZ provides

  8. Petrogenesis of Late Cretaceous lava flows from a Ceno-Tethyan island arc: The Raskoh arc, Balochistan, Pakistan (United States)

    Siddiqui, Rehanul Haq; Qasim Jan, M.; Asif Khan, M.


    The Raskoh arc is about 250 km long, 40 km wide and trends in an ENE direction. The oldest rock unit in the Raskoh arc is an accretionary complex (Early to Late Jurassic), which is followed in age by Kuchakki Volcanic Group, the most wide spread unit of the Raskoh arc. The Volcanic Group is mainly composed of basaltic to andesitic lava flows and volcaniclastics, including agglomerate, volcanic conglomerate, breccia and tuff, with subordinate shale, sandstone, limestone and chert. The flows generally form 3-15 m thick lenticular bodies but rarely reach up to 300 m. They are mainly basaltic-andesites with minor basalts and andesites. The main textures exhibited by these rocks are hypocrystalline porphyritic, subcumulophyric and intergranular. The phenocrysts comprise mainly plagioclase (An30-54 in Nok Chah and An56-64 in Bunap). They are embedded in a micro-cryptocrystalline groundmass having the same minerals. Apatite, magnetite, titanomagnetite and hematite occur as accessory minerals. Major, trace and rare earth elements suggest that the volcanics are oceanic island arc tholeiites. Their low Mg # (42-56) and higher FeO (total)/MgO (1.24-2.67) ratios indicate that the parent magma of these rocks was not directly derived from a mantle source but fractionated in an upper level magma chamber. The trace element patterns show enrichment in LILE and depletion in HFSE relative to N-MORB. Their primordial mantle-normalized trace element patterns show marked negative Nb anomalies with positive spikes on K, Ba and Sr which confirm their island arc signatures. Slightly depleted LREE to flat chondrite normalized REE patterns further support this interpretation. The Zr versus Zr/Y and Cr versus Y studies show that their parent magma was generated by 20-30% melting of a depleted mantle source. The trace elements ratios including Zr/Y (1.73-3.10), Ti/Zr (81.59-101.83), Ti/V (12.39-30.34), La/YbN (0.74-2.69), Ta/Yb (0.02-0.05) and Th/Yb (0.11-0.75) of the volcanics are more

  9. Volcanism and associated hazards: the Andean perspective (United States)

    Tilling, R. I.


    Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant improvements in reducing volcano risk in the Andean region. But much remains to be done.

  10. Volcanism and associated hazards: The Andean perspective (United States)

    Tilling, R.I.


    Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant improvements in reducing volcano risk in the Andean region. But much remains to be done.

  11. Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane (United States)

    Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan


    Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

  12. Origin of High-Alumina Basalt, Andesite, and Dacite Magmas. (United States)

    Hamilton, W


    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it.

  13. Petrology and geochemistry of volcanic rocks from the island of Panarea: implications for mantle evolution beneath the Aeolian island arc (southern Tyrrhenian sea) (United States)

    Calanchi, N.; Peccerillo, A.; Tranne, C. A.; Lucchini, F.; Rossi, P. L.; Kempton, P.; Barbieri, M.; Wu, T. W.


    island of Stromboli has a more radiogenic Sr-isotope signature, and shows trace element abundances and ratios that are intermediate between arc and intraplate compositions. Panarea mafic rocks have geochemical and isotopic signatures that are intermediate between those observed in the two sectors of the arc. The late-erupted CA scoriae of Panarea have trace element and isotopic compositions similar to those of the mafic rocks from the western islands of Filicudi and Alicudi, whereas the HKCA and shoshonitic mafic rocks have isotopic and trace element signatures that are closer to those of Stromboli. This reflects the particular position of Panarea, which is sited midway between the western-central arc and Stromboli. According to some recent views, subduction of the Ionian sea plate is actively occurring beneath the eastern Aeolian arc, with rollback of the subduction zone toward the southeast. The Tindari-Letoianni-Malta Escarpment fault zone is considered to be the boundary between the active subducting plate in the east and the African plate and western Aeolian arc in the west. It is suggested that the rollback of the Ionian plate generated inflow of mantle material from below the western arc into the mantle wedge above the subducting Ionian slab. This situation generated a hybrid mantle beneath Panarea, which resulted in a mixture of western-type and resident eastern-arc mantle materials; the latter had a composition akin to the source of Stromboli magmas. Early HKCA and shoshonitic magmatism tapped such a hybrid source, whereas the younger CA activity has been derived from melting of unmodified western-type mantle material. The late eruption of CA rocks with a composition similar to western arc can be explained by assuming that a continuing inflow process had increased the amount of western-type mantle with time, thus favouring the late appearance of CA magmas. This hypothesis accounts for the overall decrease of potassium with time, which is the opposite of the

  14. Time Evolution of Thermo-Mechanically and Chemically Coupled Magma Chambers (United States)

    Ozimek, C.; Karlstrom, L.; Erickson, B. A.


    Complexity in the volcanic eruption cycle reflects time variation both of magma inputs to the crustal plumbing system and of crustal melt storage zones (magma chambers). These data include timing and volumes of eruptions, as well as erupted compositions. Thus models must take into account the coupled nature of physical attributes. Here we combine a thermo-mechanical model for magma chamber growth and pressurization with a chemical model for evolving chamber compositions, in the limit of rapid mixing, to study controls on eruption cycles and compositions through time. We solve for the mechanical evolution of a 1D magma chamber containing melt, crystals and bubbles, in a thermally evolving and viscoelastic crust. This pressure and temperature evolution constrains the input values of a chemical box model (Lee et al., 2013) that accounts for recharge, eruption, assimilation and fractional crystallization (REAFC) within the chamber. We plan to study the influence of melt supply, input composition, and chamber depth eruptive fluxes and compositions. Ultimately we will explore multiple chambers coupled by elastic-walled dikes. We expect that this framework will facilitate self-consistent inversion of long-term eruptive histories in terms of magma transport physics. Lee, C.-T. A., Lee, T.-C., Wu, C.-T., 2013. Modeling the compositional evolution of recharging, evacuating, and fractionating (REFC) magma chambers: Implications for differentiationof arc magmas. Geochemica Cosmochimica Acta,

  15. Paleoproterozoic arc basalt-boninite-high magnesian andesite-Nb enriched basalt association from the Malangtoli volcanic suite, Singhbhum Craton, eastern India: Geochemical record for subduction initiation to arc maturation continuum (United States)

    Rajanikanta Singh, M.; Manikyamba, C.; Ganguly, Sohini; Ray, Jyotisankar; Santosh, M.; Dhanakumar Singh, Th.; Chandan Kumar, B.


    The Singhbhum Craton of eastern India preserves distinct signatures of ultramafic-mafic-intermediate-felsic magmatism of diverse geodynamic affiliations spanning from Paleo-Mesoarchean to Proterozoic. Here we investigate the 2.25 Ga Malangtoli volcanic rocks that are predominantly clinopyroxene- and plagioclase-phyric, calc-alkaline in nature, display basalt-basaltic andesite compositions, and preserve geochemical signatures of subduction zone magmatism. Major, trace and rare earth element characteristics classify the Malangtoli volcanic rocks as arc basalts, boninites, high magnesian andesites (HMA) and Nb enriched basalts (NEB). The typical LILE enriched-HFSE depleted geochemical attributes of the arc basalts corroborate a subduction-related origin. The boninitic rocks have high Mg# (0.8), MgO (>25 wt.%), Ni and Cr contents, high Al2O3/TiO2 (>20), Zr/Hf and (La/Sm)N (>1) ratios with low (Gd/Yb)N (54 wt.%), MgO (>6 wt.%), Mg# (0.47) with elevated Cr, Co, Ni and Th contents, depleted (Nb/Th)N, (Nb/La)N, high (Th/La)N and La/Yb (<9) ratio, moderate depletion in HREE and Y with low Sr/Y. The NEBs have higher Nb contents (6.3-24 ppm), lower magnitude of negative Nb anomalies with high (Nb/Th)pm = 0.28-0.59 and (Nb/La)pm = 0.40-0.69 and Nb/U = 2.8-34.4 compared to normal arc basalts [Nb = <2 ppm; (Nb/Th)pm = 0.10-1.19; (Nb/La)pm 0.17-0.99 and Nb/U = 2.2-44 respectively] and HMA. Arc basalts and boninites are interpreted to be the products of juvenile subduction processes involving shallow level partial melting of mantle wedge under hydrous conditions triggered by slab-dehydrated fluid flux. The HMA resulted through partial melting of mantle wedge metasomatized by slab-dehydrated fluids and sediments during the intermediate stage of subduction. Slab-melting and mantle wedge hybridization processes at matured stages of subduction account for the generation of NEB. Thus, the arc basalt-boninite-HMA-NEB association from Malangtoli volcanic suite in Singhbhum Craton

  16. Evaluating Complex Magma Mixing via Polytopic Vector Analysis (PVA in the Papagayo Tuff, Northern Costa Rica: Processes that Form Continental Crust

    Directory of Open Access Journals (Sweden)

    Guillermo E. Alvarado


    Full Text Available Over the last forty years, research has revealed the importance of magma mixing as a trigger for volcanic eruptions, as well as its role in creating the diversity of magma compositions in arcs. Sensitive isotopic and microchemical techniques can reveal subtle evidence of magma mixing in igneous rocks, but more robust statistical techniques for bulk chemical data can help evaluate complex mixing relationships. Polytopic vector analysis (PVA is a multivariate technique that can be used to evaluate suites of samples that are produced by mixing of two or more magma batches. The Papagayo Tuff of the Miocene-Pleistocene Bagaces Formation in northern Costa Rica is associated with a segment of the Central American Volcanic Arc. While this segment of the arc is located on oceanic plateau, recent (<8 Ma ignimbrites bear the chemical signatures of upper continental crust, marking the transition from oceanic to continental crust. The Papagayo Tuff contains banded pumice fragments consistent with one or more episodes of mixing/mingling to produce a single volcanic deposit. The PVA solution for the sample set is consistent with observations from bulk chemistry, microchemistry and petrographic data from the rocks. However, without PVA, the unequivocal identification of the three end-member solution would not have been possible.

  17. Post-Eocene volcanics of the Abazar district, Qazvin, Iran: Mineralogical and geochemical evidence for a complex magmatic evolution (United States)

    Asiabanha, A.; Bardintzeff, J. M.; Kananian, A.; Rahimi, G.


    The style of volcanism of post-Eocene volcanism in the Alborz zone of northern Iran is different to that of Eocene volcanism (Karaj Formation). Indeed, the volcanic succession of the Abazar district, located in a narrow volcanic strip within the Alborz magmatic assemblage, is characterized by distinct mineralogical and chemical compositions linked to a complex magmatic evolution. The succession was produced by explosive eruptions followed by effusive eruptions. Two main volcanic events are recognized: (1) a thin rhyolitic ignimbritic sheet underlain by a thicker lithic breccia, and (2) lava flows including shoshonite, latite, and andesite that overlie the first event across a reddish soil horizon. Plagioclase in shoshonite (An 48-92) shows normal zoning, whereas plagioclase in latite and andesite (An 48-75) has a similar composition but shows reverse and oscillatory zoning. QUILF temperature calculations for shoshonites and andesites yield temperatures of 1035 °C and 1029 °C, respectively. The geothermometers proposed by Ridolfi et al. (2010) and Holland and Blundy (1994) yield temperatures of 960 °C and 944 °C for latitic lava, respectively. The samples of volcanic rock show a typical geochemical signature of the continental arc regime, but the andesites clearly differ from the shoshonites, the latites and the rhyolites. The mineralogical and chemical characteristics of these rocks are explained by the following petrogenesis: (1) intrusion of a hot, mantle-depth mafic (shoshonitic) magma, which differentiated in the magma chamber to produce a latitic and then a rhyolitic liquid; (2) rhyolitic ignimbritic eruptions from the top of the magma chamber, following by shoshonitic and then latitic extrusions; (3) magma mingling between the latitic and andesitic magmas, as indicated by the occurrence of andesite clasts within the latite; and (4) andesitic effusions. The youngest volcanic events in the Alborz zone show a close chemical relationship with continental arc

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

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


    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.

  19. Chemical and isotopic relationship of mafic and felsic magmas in a sub-volcanic reservoir: The Guadalupe Igneous Complex (GIC), Sierra Nevada, California (United States)

    Ratschbacher, B. C.; Paterson, S. R.; Putirka, K. D.


    It is commonly believed that the interaction of mafic and felsic melts in the form of mixing/mingling as well as their genetic link in the form of fractionation play an important role in the formation of continental crust. The combination of whole rock major element content and isotopic signature, as presented in this study, is a powerful tool to identify the origin and genetic relation of mafic and felsic melts in magmatic arc settings where new material is added to the crust. The GIC is part of the Jurassic Sierran magmatic arc exposed in the Western Metamorphic Belt and contains two main units consisting of mafic (up to 9 wt. % MgO and 49 to 56 wt. % SiO2) and felsic (around 75 wt. % SiO2) rocks, which locally mingled and mixed to different proportions at a shallow emplacement level. In the lower parts of the GIC, fine-grained gabbros gradually evolve into the overlying diorite to meladiorite unit. A mingling zone separates these mafic rocks from granites, granophyres and overlying rhyolites in the upper part of the complex. Major element whole rock analyses show that the GIC is bimodal with gabbros and granitoids acting as endmembers in SiO2, MgO and CaO contents. For Al2O3, Na2O and other element oxides, the different units strongly overlap in compositions. Recent work using single grain zircon U-Pb dating found ages for both the gabbros and the felsic part of the complex of 151 Ma within uncertainty (Saleeby et al., 1989; Ernst et al., 2009, and unpublished data from this study). These ages are in agreement with Rb-Sr data from each unit, which fall on a 152×7 Ma isochron and therefore imply closed-system evolution. Major oxide data show that assimilation of the exposed surrounding host rocks is unlikely and cannot serve as an assimilant to reproduce the observed felsic compositions from the gabbroic rocks. Sri, Nd and Pb systematics show that all units except for capping granophyres and rhyolites plot close together implying a shared parental melt, which is

  20. The geochemistry of lithium-bearing geothermal water, Taupo Volcanic Zone, and shallow fluid processes in a very active silicic volcanic arc (United States)

    Dean, A. S.; Hoskin, P. W.; Rudnick, R. L.; Liu, X.; Boseley, C.


    The Li abundances and isotopic systematics of Taupo Volcanic Zone (TVZ) geothermal fluids preserves a record of processes occurring within shallow portions of geothermal reservoirs as well as deeper portions of the arc crust. Understanding Li cycling and isotopic fractionation in TVZ geothermal systems contributes to a more refined understanding of physicochemical processes affecting New Zealand's geothermal resources. A comprehensive dataset of 73 samples was compiled, with samples collected from geothermal surface features (springs, spouters, geysers, etc.) and electric-power industry production wells, collectively representing18 geothermal fields across the breadth and width the TVZ. No comparable dataset of fluid analyses exists. Ion chromatography, AAS, and quadrupole ICP-MS analyses were done for Li, Cl-, SiO2, SO42- K, Na, Ca, Mg, B, Sr and Pb concentrations. Lithium abundance in geothermal fluids from the TVZ have a dataset-wide average of 5.9 mg/L and range 4 μg/L to 29 mg/L. The Li abundance and Li/Cl ratios for geothermal water and steam condensates vary systematically as a result of boiling, mixing, and water/rock reaction. Lithium abundance and Li/Cl ratios are, therefore, indicators of shallow (above 2.5 km) and locally variable reservoir processes. δ7Li analysis of 63 samples was performed at the University of Maryland, College Park. Data quality was controlled by measurement of L-SVEC as a calibration standard and by multiple analysis of selected samples. The average δ7Li value for TVZ geothermal fluids is -0.8%. Most δ7Li values for geothermal water fall within a small range of about -3% to+2% indicating similar processes are causing similar isotopic fractionation throughout the region. Considered together, Li aundances and δ7Li values, in combination with numerical models, indicate possible evolution pathways and water/rock reactions in TVZ geothermal systems. Models based on rocks and surface water analysis indicate that Li cycles and

  1. The magmatic and eruptive response of arc volcanoes to deglaciation: insights from southern Chile (United States)

    Rawson, Harriet; Mather, Tamsin A.; Pyle, David M.; Smith, Victoria C.; Fontijn, Karen; Lachowycz, Stefan; Naranjo, José A.; Watt, Sebastian F. L.


    Volcanism exerts a major influence on Earth's atmosphere and surface environments. Understanding feedbacks between climate and long-term changes in rates or styles of volcanism is important, but unresolved. For example, it has been proposed that a pulse of activity at once-glaciated volcanoes contributed to increasing atmospheric carbon dioxide accelerating early Holocene climate change. In plate-tectonic settings where magmatism is driven by decompression melting there is convincing evidence that activity is modulated by changes in ice- or water-loading across glacial/interglacial cycles. The response of subduction-related volcanoes, where the crust is typically thicker and mantle melting is dominated by flux melting, remains unclear. Since arc volcanoes account for 90% of subaerial eruptions, they are the most significant sources of volcanic gases and tephra directly to the atmosphere. Testing the response of arc volcanoes to deglaciation requires careful work to piece together eruption archives. Records of effusive eruptions from long-lived, arc stratovolcanoes are challenging to obtain and date; while deposits from the explosive eruptions, which dominate arc records, are prone to erosion and reworking. Our new high-resolution post-glacial (Phase 3), eruptive fluxes have been elevated, and dominated by explosive eruptions of intermediate magmas. We propose that this time-varying behaviour reflects changes in crustal plumbing systems, and magma storage timescales. During glaciations, magmas stall in the crust and differentiate to form large, evolved melt reservoirs. After the ice load is removed, much of this stored magma erupts (Phase 1). Subsequently, less-differentiated melts infiltrate the shallow crust (Phase 2). Then, as storage timescales increase, volcanism returns towards more evolved compositions (Phase 3). We suggest that on these short timescales, these observed variations are unlikely to reflect changes in mantle melt flux. Instead, the phenomena are

  2. A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites. (United States)

    Reubi, Olivier; Blundy, Jon


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

  3. Geochemistry of Volcanic Rocks from International Ocean Discovery Program (IODP) Site 1438, Amami Sankaku Basin: Implications for Izu-Bonin-Mariana (IBM) Arc Initiation (United States)

    Hickey-Vargas, R.; Ishizuka, O.; Yogodzinski, G. M.; Bizimis, M.; Savov, I. P.; McCarthy, A. J.; Arculus, R. J.; Bogus, K.


    IODP Expedition 351 drilled 150 m of volcanic basement overlain by 1461 m of sedimentary material at Site 1438 in the Amami Sankaku basin, just west of the Kyushu Palau Ridge, the locus of IBM arc initiation. Age interpretations based on biostratigraphy (Arculus et al., Nat. Geosci., in-press) determined that the age of the basement section is between 64 and 51 Ma, encompassing the age of the earliest volcanic products of the IBM arc. The Site 1438 volcanic basement consists of multiple flows of aphyric microcrystalline to finely crystalline basalts containing plagioclase and clinopyroxene with rare olivine pseudomorphs. New XRF major and ICPMS trace element data confirm findings of shipboard analysis that the basalts are moderately differentiated (6-14 % MgO; Mg# = 51-83; 73-490 ppm Cr and 58-350 ppm Ni) with downcore variations related to flow units. Ti/V and Ti/Sc ratios are 16-27 and 75-152, respectively, with lowest values at the base of the core. One prominent characteristic of the basalts is their depletion of immobile highly incompatible elements compared with MORB. Basalts have MORB-normalized La/Nd of 0.5 to 0.9, and most have Th/La andesites from three sills in the lowermost sedimentary unit have arc-like trace element patterns with La/Nb > 3 and primitive mantle normalized La/Yb > 1. Our results suggest that mantle melting at the onset of subduction involved exceptionally depleted sources. Enrichment over time may be related to increasing subduction inputs and/or other processes, such as entrainment of fertile asthenosphere during extension of the overriding plate.

  4. Probabilities of future VEI ≥ 2 eruptions at the Central American Volcanic Arc: a statistical perspective based on the past centuries' eruption record (United States)

    Dzierma, Yvonne; Wehrmann, Heidi


    A probabilistic eruption forecast is provided for seven historically active volcanoes along the Central American Volcanic Arc (CAVA), as a pivotal empirical contribution to multi-disciplinary volcanic hazards assessment. The eruption probabilities are determined with a Kaplan-Meier estimator of survival functions, and parametric time series models are applied to describe the historical eruption records. Aside from the volcanoes that are currently in a state of eruptive activity (Santa María, Fuego, and Arenal), the highest probabilities for eruptions of VEI ≥ 2 occur at Concepción and Cerro Negro in Nicaragua, which are likely to erupt to 70-85 % within the next 10 years. Poás and Irazú in Costa Rica show a medium to high eruption probability, followed by San Miguel (El Salvador), Rincón de la Vieja (Costa Rica), and Izalco (El Salvador; 24 % within the next 10 years).

  5. The Boring Volcanic Field of the Portland-Vancouver area, Oregon and Washington: tectonically anomalous forearc volcanism in an urban setting (United States)

    Evarts, Russell C.; Conrey, Richard M.; Fleck, Robert J.; Hagstrum, Jonathan T.; O'Connor, Jim; Dorsey, Rebecca; Madin, Ian P.


    More than 80 small volcanoes are scattered throughout the Portland-Vancouver metropolitan area of northwestern Oregon and southwestern Washington. These volcanoes constitute the Boring Volcanic Field, which is centered in the Neogene Portland Basin and merges to the east with coeval volcanic centers of the High Cascade volcanic arc. Although the character of volcanic activity is typical of many monogenetic volcanic fields, its tectonic setting is not, being located in the forearc of the Cascadia subduction system well trenchward of the volcanic-arc axis. The history and petrology of this anomalous volcanic field have been elucidated by a comprehensive program of geologic mapping, geochemistry, 40Ar/39Ar geochronology, and paleomag-netic studies. Volcanism began at 2.6 Ma with eruption of low-K tholeiite and related lavas in the southern part of the Portland Basin. At 1.6 Ma, following a hiatus of ~0.8 m.y., similar lavas erupted a few kilometers to the north, after which volcanism became widely dispersed, compositionally variable, and more or less continuous, with an average recurrence interval of 15,000 yr. The youngest centers, 50–130 ka, are found in the northern part of the field. Boring centers are generally monogenetic and mafic but a few larger edifices, ranging from basalt to low-SiO2 andesite, were also constructed. Low-K to high-K calc-alkaline compositions similar to those of the nearby volcanic arc dominate the field, but many centers erupted magmas that exhibit little influence of fluids derived from the subducting slab. The timing and compositional characteristics of Boring volcanism suggest a genetic relationship with late Neogene intra-arc rifting.

  6. Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur (United States)

    Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.


    Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges betweenCampanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment

  7. Subterranean fragmentation of magma during conduit initiation and evolution in the shallow plumbing system of the small-volume Jagged Rocks volcanoes (Hopi Buttes Volcanic Field, Arizona, USA) (United States)

    Re, Giuseppe; White, James D. L.; Muirhead, James D.; Ort, Michael H.


    Monogenetic volcanoes have limited magma supply and lack long-lived sustained magma plumbing systems. They erupt once, often from multiple vents and sometimes over several years, and are rarely or never re-activated. Eruptive behavior is very sensitive to physical processes (e.g., volatile exsolution, magma-water interaction) occurring in the later stages of magma ascent at shallow crustal depths (flowing through dikes fragmented and conduits were formed. We have identified three main types of fragmental deposits, (1) buds (which emerge from dikes), (2) pyroclastic massifs, and (3) diatremes; these represent three different styles and intensities of shallow-depth magma fragmentation. They may develop successively and at different sites during the evolution of a monogenetic volcano. The deposits consist of a mixture of pyroclasts with varying degrees of welding and country-rock debris in various proportions. Pyroclasts are commonly welded together, but also reveal in places features consistent with phreatomagmatism, such as blocky shapes, dense groundmasses, and composite clasts (loaded and cored). The extent of fragmentation and the formation of subterranean open space controlled the nature of the particles and the architecture and geometry of these conduit structures and their deposits.

  8. Magma Fragmentation (United States)

    Gonnermann, Helge M.


    Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.

  9. Early Devonian back-arc extension in the eastern Central Asian Orogenic Belt: Evidence from a bimodal volcanic sequence from Xilinhot, central Inner Mongolia (North China) (United States)

    Liao, Wen; Xu, Bei; Wang, Yanyang; Zhao, Pan; Li, Qunsheng


    The Early Devonian bimodal volcanic sequence is firstly recognized in the Xilinhot area, central Inner Mongolia (North China). Zircon U-Pb dating of rhyolitic sample gives crystallization age of 407 ± 2 Ma, which is interpreted as the extrusive age of this bimodal volcanic sequence. Basaltic samples belong to tholeiite series whereas rhyolitic samples are peraluminous. Basaltic rocks show typical N-MORB-like REE and trace elemental patterns, with depletion of LREEs and negligible anomalies of Eu (δEu = 0.83-1.00). They have initial 87Sr/86Sr ratios ranging from 0.7077 to 0.7086, and positive εNd(t) values from +7.5to +9.0. By contrast, rhyolitic rocks show enrichment in LREEs and LILEs but depletion in HFSEs, with negative Eu anomalies (δEu = 0.58-0.68). They have negative εNd(t) values from -6.7 to -7.7 and TDM2 (Nd) values from 1695 to 1771 Ma. These elemental and isotopic data indicate that basaltic rocks were derived from a depleted mantle source with input of slab-derived fluids, whereas rhyolitic rocks might have been derived from remelting of Paleoproterozoic crustal materials. From our data and previous geological studies in this region, a back-arc setting was proposed for the Early Devonian bimodal volcanic rocks in the Xilinhot region. Subduction of the Paleo-Asian oceanic lithosphere caused opening of this back-arc basin and upwelling of mantle caused the formation of basalts and provided heat for remelting of crustal materials and formation of rhyolite.the

  10. Arc dacite genesis pathways: Evidence from mafic enclaves and their hosts in Aegean lavas (United States)

    Zellmer, G. F.; Turner, S. P.


    Mafic enclaves are commonly found in intermediate arc magmas, and their occurrence has been linked to eruption triggering by pre-eruptive magma mixing processes. New major, trace, Sr-Nd and U-Th isotope data of rocks from Nisyros in the Aegean volcanic arc are presented here. Pre-caldera samples display major and trace element trends that are consistent with fractionation of magnetite and apatite within intermediate compositions, and zircon within felsic compositions, and preclude extensive hybridization between mafic and felsic magmas. In contrast, post-caldera dacites form a mixing trend towards their mafic enclaves. In terms of U-series isotopes, most samples show small 238U excesses of up to ˜ 10%. Mafic enclaves have significantly higher U/Th ratios than their dacitic host lavas, precluding simple models that relate the mafic and felsic magmas by fractionation or aging alone. A more complicated petrogenetic scenario is required. The post-caldera dacites are interpreted to represent material remobilized from a young igneous protolith following influx of fresh mafic magma, consistent with the U-Th data and with Sr-Nd isotope constraints that point to very limited (Santorini in the same arc, there are many geochemical similarities between the two volcanic centers during the petrogenesis of the pre-caldera samples. However, striking differences are apparent for the post-caldera lavas: in Nisyros, dacites show geochemical and textural evidence for magma mixing and remobilization by influx of mafic melts, and they erupt as viscous lava domes; in Santorini, evidence for geochemical hybridization of dacites and mafic enclaves is weak, dacite petrogenesis does not involve protolith remobilization, and lavas erupt as less viscous flows. Despite these differences, it appears that mafic enclaves in intermediate Aegean arc magmas consistently yield timescales of at least 100 kyrs between U enrichment of the mantle wedge and eruption, on the upper end of those estimated

  11. The lateral extent of volcanic interactions during unrest and eruption (United States)

    Biggs, Juliet; Robertson, Elspeth; Cashman, Katharine


    Volcanic eruptions often occur simultaneously or tap multiple magma reservoirs. Such lateral interactions between magmatic systems are attributed to stress changes or hydraulic connections but the precise conditions under which coupled eruptions occur have yet to be quantified. Here we use interferometric synthetic aperture radar satellite data to analyse the surface deformation generated by volcanic unrest in the Kenyan Rift. We identify several magma sources located at depths of 2-5 km importantly, sources that are spaced less than about 10 km apart interact, whereas those spaced more than about 25 km apart do not. However, volcanoes up to 25 km apart have interacted in the geologic past. Thus, volcanic coupling is not simply controlled by the distance between the magma reservoirs. We then consider different tectonic settings globally, including intraplate volcanoes such as Hawaii and Yellowstone, arc volcanism in Alaska and Chile, and other rift settings, such as New Zealand, Iceland and Afar. We find that the most closely spaced magmatic interactions are controlled by the extent of a shallow crystal mush layer, stress changes can couple large eruptions over distances of about 20-40 km, and only large dyke intrusions or subduction earthquakes could generate coupled eruptions over distances of about 50-100 km.

  12. Role of the Alboran Sea volcanic arc choking the Mediterranean to the Messinian salinity crisis and foundering biota diversification in North Africa and Southeast Iberia (United States)

    Booth-Rea, Guillermo; Ranero, Cesar R.; Grevemer, Ingo


    The Mediterranean Sea desiccated ~5.96 million years ago when it became isolated from the world oceans during the Messinian salinity crisis. This event permitted the exchange of terrestrial biota between Africa and Iberia contributing to the present rich biodiversity of the Mediterranean region. The cause chocking the Mediterranean has been proposed to be tectonic uplift and dynamic topography but the driving mechanism still remains debated. We present a new wide-angle seismic profile that provides a detailed image of the thickness and seismic velocity distribution of the crust in the eastern Alboran basin. The velocity model shows a characteristic structure of a subduction-related volcanic arc with a high-velocity lower crust and a 16-18 km total-thickness igneous crust that magmatic accreted mostly between ~10-6 Ma across the eastern Alboran basin. Estimation of the isostatically corrected depth of the arc crust taking into account the original thermal structure and sediment-loading subsidence since 6 Ma places a large area of the eastern Alboran basin above sea level at the time. This estimation is supported by geophysical data showing subaereal erosional unconformities for that time. This model may explain several up-to-now-disputed features of the Messinian salinity crisis, including: the progressive isolation of the Mediterranean since 7.1 Ma with the disappearance of open marine taxa, the existence of evaporites mostly to the east of the volcanic arc, the evidence that the Gibraltar straits were not a land bridge offered by continuous Messinian open marine sediments at ODP site 976 in the western Alboran basin, the importance of southeastern Iberia and North Africa as centres of biota diversification since before the salinity crisis, and patterns of speciation irradiating from SE Iberia and the eastern Rif in some taxons.

  13. Geochemistry of the Ophiolite and Island-Arc Volcanic Rocks in the Mianxian-Lueyang Suture Zone,Southern Qinling and Their Tectonic Significance

    Institute of Scientific and Technical Information of China (English)


    Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly.The diabase dike swarm shows LREE enrichment but slightly negative Eu anomaly.Metamorphosed volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace element ratios of Ti/V,Th/Ta,Th/Yb and Ta/Yb.One is ths MORB-type basalt with LREE depletion,representing the fragments of oceanic crust and implying an association of the MORB-type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates during the Middle Paleozoic-Early Mesozoic era.The oter comprises the island-arc volcanic rocks including tholeiitic basalt and a large amount of calc-alkaline intermediate-acic volcanic rock,which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin.This indicates that the Mianxian-Lueyang limited ocean basin had undergone a whole process of development,evolution and vanishing from Devonian-Cretaceous to Permian.And the Qinling area had becone an independent lithospheric microplate,on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic-Early Mesozoic.That is to say.the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.

  14. Geology and geochemistry of Late Quaternary volcanism in northern Harrat Rahat, Kingdom of Saudi Arabia: implications for eruption dynamics, regional stratigraphy and magma evolution


    H. Murcia; J. M. Lindsay; K. Németh; I. E. M. Smith; S. J. Cronin; M. R. H. Moufti; N. N. El-Masry; Samuel Niedermann


    Harrat Rahat (,10 Ma) is one of the largest volcanic fields on western Arabia. In the north of the field, some of the youngest volcanic centres evolved through either point-like, complex or multiple aligned vents (i.e. along fissures), and have pyroclastic cones, lapilli fall deposits and/ or lava flows associated with them. The products reflect dominantly Hawaiian eruptions, and only one centre experienced phreatomagmatism. Results from new 3He surface-exposure dating provide ...

  15. The Alboran volcanic arc archipelago isolated the Mediterranean during the Messinian salinity crisis forming the land bridge for biota dispersal across the western Mediterranean (United States)

    Booth-Rea, Guillermo; Ranero, Cesar R.; Grevemeyer, Ingo


    The Mediterranean Sea desiccation during isolation from the world oceans created the well-known Messinian salinity crisis but also landbridges that permitted the exchange of terrestrial biota between Africa and Iberia contributing to the present biodiversity of the Mediterranean region. The hypotheses for the cause chocking the Mediterranean have typically sought to explain geological features, particularly the giant salt deposits, but the implications of the faunal changes occurring around that time remain inadequately integrated by current geological models. We present wide-angle seismic data that constrain for the first time the 16-18 km thick crust structure of a volcanic arc formed mostly between 10 to 6 Ma across the eastern region of the Alboran basin. The crustal structure supports that the arc created an archipelago forming a land bridge across the basin that largely isolated the Mediterranean. After the cessation of volcanic activity, the archipelago progressively submerged by thermal subsidence and accompanying sediment loading, having emerged islands that persisted into the Pleistocene time and shallow straits forming sills during the early Pliocene. The presence of an archipelago in the eastern region of the basin may explain a number of puzzling observations previously inexplicable by the proposed barriers closing the Gibraltar arc west of Alboran. The progressive volcanic build up of the archipelago together with the closure of the Betic and Rifean marine corridors would explain the initial isolation of the Mediterranean since 7.1 Ma and the exchange of terrestrial biota since 6.2 Ma, i.e. before desiccation, which diversified radiating from SE Iberia and the opposite segment of the eastern Rif. In addition, an eastern barrier agrees with the continuous Messinian-age open marine sediments drilled at ODP site 976 in the western Alboran basin, which may have been the refuge of typical Mediterranean taxa that rapidly repopulated the Mediterranean in the

  16. Characterization of geothermal paleosystem in the Lesser Antilles volcanic arc: structural, petrographic, thermodynamic and petrophysics analysis of Terre-de-Haut (Les Saintes archipelago, Lesser Antilles) (United States)

    Favier, Alexiane; Navelot, Vivien; Verati, Chrystèle; Lardeaux, Jean-Marc; Corsini, Michel; Diraison, Marc; Géraud, Yves; Mercier de Lépinay, Jeanne; Munschy, Marc


    This survey takes part in the GEOTREF project (high enthalpy geothermal energy in fractured reservoirs), supported by the French government program "Investments for the future". The program focuses on the exploration of geothermal resource in the Lesser Antilles volcanic arc. An exclusive license has been issued in the Vieux-Habitants area (Basse-Terre, Guadeloupe) to carry on the development of high-temperature geothermal energy in this active volcanic region. The deep geothermal reservoir on the Basse-Terre island could be characterized in exhumed paleosystems. The reference paleosystem in the Guadeloupe archipelago is located in Terre-de-Haut. Four major fault directions have been highlighted N000-N020, N050-N070, N090-N110 and N130-N140. Field observations emphasize three major cleavage directions overlaying the fault systems: N035-N060, N080-N110, N145-N165. Volcanic rocks affected by cleavage display several metamorphic transformation grades. The more transformed calc-alkaline rocks are located at the intersection of several cleavage directions. Mineralogical transformations due to metamorphism and surimposed fractures are also responsible for strong changes of petrophysical properties. In comparison with the reference protolith of andesitic lava flows outcropping in Vieux-Habitants, which have porosity and permeability lower than 5 % and 10-15 m2, andesites of Terre-de-Haut have better reservoir properties with connected porosity and permeability higher than 15 % and 10-14-10-15 m2 respectively. Thermodynamic modelling based on petrography and chemical composition of the most transformed rocks highlights a steady state mineral assemblage between 0.25 - 1.5 kbar and 350 - 450 ˚ C. It corresponds to a geothermal gradient higher than 120 to 150˚ C/km. This is consistent with temperatures measured in Bouillante wells. However, this geothermal gradient is notably higher to a usual volcanic arc conductive gradient estimated to 70-100˚ C/km. It can be explained

  17. Electromagnetic-wave radiation due to diastrophism of magma dike growth in Izu-Miyake volcanic eruptions in Japan in 2000

    Directory of Open Access Journals (Sweden)

    M. Hata


    Full Text Available A large 10 cm per day diastrophism of the crust was experienced between Kozu and Niijima Islands during the Izu-Miyake volcanic eruptions in Japan on 3–4 August 2000. The diastrophism was detected through GPS observation. The seismometer also complied a swarm of earth-quakes at this time. Our electromagnetic wave data, observed at 223 Hz at the Omaezaki site, about 110 km and 150 km northwest of the Kozu and Miyake Islands, respectively, detected a clear, anomalous magnetic flux radiation that corresponded well with the seismographic and GPS data. Similar radiation was received for about one week preceding the big volcanic eruption that occurred on 18 August 2000. These observations indicate that the electromagnetic wave monitoring system has the potential to monitor and/or warn of volcanic activity, and the facts disclose one of the mysterious radiation mechanisms of electromagnetic waves emitted from the Earth.

  18. Self Sealing Magmas (United States)

    von Aulock, Felix W.; Wadsworth, Fabian B.; Kennedy, Ben M.; Lavallee, Yan


    During ascent of magma, pressure decreases and bubbles form. If the volume increases more rapidly than the relaxation timescale, the magma fragments catastrophically. If a permeable network forms, the magma degasses non-violently. This process is generally assumed to be unidirectional, however, recent studies have shown how shear and compaction can drive self sealing. Here, we additionally constrain skin formation during degassing and sintering. We heated natural samples of obsidian in a dry atmosphere and monitored foaming and impermeable skin formation. We suggest a model for skin formation that is controlled by diffusional loss of water and bubble collapse at free surfaces. We heated synthetic glass beads in a hydrous atmosphere to measure the timescale of viscous sintering. The beads sinter at drastically shorter timescales as water vapour rehydrates an otherwise degassed melt, reducing viscosity and glass transition temperatures. Both processes can produce dense inhomogeneities within the timescales of magma ascent and effectively disturb permeabilities and form barriers, particularly at the margins of the conduit, where strain localisation takes place. Localised ash in failure zones (i.e. Tuffisite) then becomes associated with water vapour fluxes and alow rapid rehydration and sintering. When measuring permeabilities in laboratory and field, and when discussing shallow degassing in volcanoes, local barriers for degassing should be taken into account. Highlighting the processes that lead to the formation of such dense skins and sintered infills of cavities can help understanding the bulk permeabilities of volcanic systems.

  19. Geochemistry of anorthositic differentiated sills in the Archean (~ 2970 Ma) Fiskenæsset Complex, SW Greenland: Implications for parental magma compositions, geodynamic setting, and secular heat flow in arcs (United States)

    Polat, Ali; Fryer, Brian J.; Appel, Peter W. U.; Kalvig, Per; Kerrich, Robert; Dilek, Yildirim; Yang, Zhaoping


    and recycled back into the mantle as a residual cumulate, or was destroyed during thrusting and TTG intrusion. Both the Fiskenæsset Complex and associated tholeiitic basalts display similar Th-Nb-LREE patterns and plot along the same differentiation trend on Zr versus incompatible trace element diagrams, suggesting a possible petrogenetic link between the two suites of rocks. However, basalts do not display the same differentiation trend as the complex on several major and trace element diagrams. In addition, basalts and parental magma to the complex do not plot along the same fractionation line on Al 2O 3/TiO 2 versus incompatible trace element diagrams, implying that the Fiskenæsset layered intrusive rocks were not derived from tholeiitic basalts through fractional crystallization, as previously thought. Accordingly, we infer that the Fiskenæsset Complex and spatially associated basalts were derived from different mantle sources. Parental magmas to the Fiskenæsset Complex originated from a mantle source that was metasomatized by highly aluminous slab-derived melts. Layered anorthosite complexes are mostly restricted to the Archean and typically associated with tonalite-trondhjemite-granodiorite (TTG) gneisses. The petrogenesis of both suites appears to have been controlled mainly by slab melting, endorsing independent evidence for a secular change from slab-dominated melting to wedge-dominated melting in arc magmatism at the end of the Archean, reflecting higher geothermal gradients in Archean arcs than post-Archean counterparts.

  20. Tectonic focusing of voluminous basaltic eruptions in magma-deficient backarc rifts (United States)

    Anderson, Melissa O.; Hannington, Mark D.; Haase, Karsten; Schwarz-Schampera, Ulrich; Augustin, Nico; McConachy, Timothy F.; Allen, Katie


    The Coriolis Troughs of the New Hebrides subduction zone are among the youngest backarc rifts in the world. They reach depths of >3 km, despite their small size (Pacific, occur on the youngest lava flows. Comparison with similar axial volcanoes on the mid-ocean ridges suggests that the 46 ×106 m3 of sheet flows in the caldera could have been erupted in ridge. This study shows that the upper plate stresses can result in dramatic variability in magma supply and hydrothermal activity at the earliest stages of arc rifting and could explain the wide range of melt compositions, volcanic styles and mineral deposit types found in nascent backarc rifts.

  1. Mush Column Magma Chambers (United States)

    Marsh, B. D.


    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

  2. Contrasting records from mantle to surface of Holocene lavas of two nearby arc volcanic complexes: Caburgua-Huelemolle Small Eruptive Centers and Villarrica Volcano, Southern Chile (United States)

    Morgado, E.; Parada, M. A.; Contreras, C.; Castruccio, A.; Gutiérrez, F.; McGee, L. E.


    Most of the small eruptive centers of the Andean Southern Volcanic Zone are built over the Liquiñe-Ofqui Fault Zone (LOFZ), a NS strike-slip (> 1000 km length) major structure, and close to large stratovolcanoes. This contribution compares textural features, compositional parameters, and pre- and syn-eruptive P,T conditions, between basaltic lavas of the Caburgua-Huelemolle Small Eruptive Centers (CHSEC) and the 1971 basaltic andesite lava of the Villarrica Volcano located 10 km south of the CHSEC. Olivines and clinopyroxenes occur as phenocrysts and forming crystal clots of the studied lavas. They do not markedly show compositional differences, except for the more scattered composition of the CHSEC clinopyroxenes. Plagioclase in CHSEC lavas mainly occur as phenocrysts or as microlites in a glass-free matrix. Two groups of plagioclase phenocrysts were identified in the 1971 Villarrica lava based on crystal size, disequilibrium features and zonation patterns. Most of the CHSEC samples exhibit higher LaN/YbN and more scattered Sr-Nd values than 1971 Villarrica lava samples, which are clustered at higher 143Nd/144Nd values. Pre-eruptive temperatures of the CHSEC-type reservoir between 1162 and 1165 ± 6 °C and pressures between 10.8 and 11.4 ± 1.7 kb consistent with a deep-seated reservoir were obtained from olivine-augite phenocrysts. Conversely, olivine-augite phenocrysts of 1971 Villarrica lava samples record pre-eruptive conditions of two stages or pauses in the magma ascent to the surface: 1208 ± 6 °C and 6.3-8.1 kb ± 1.7 kb (deep-seated reservoir) and 1164-1175 ± 6 °C and ≤ 1.4 kb (shallow reservoir). At shallow reservoir conditions a magma heating prior to the 1971 Villarrica eruption is recorded in plagioclase phenocrysts. Syn-eruptive temperatures of 1081-1133 ± 6 °C and 1123-1148 ± 6 °C were obtained in CHSEC and 1971 Villarrica lava, respectively using equilibrium olivine-augite microlite pairs. The LOFZ could facilitate a direct transport to

  3. S-wave attenuation structure beneath the northern Izu-Bonin arc (United States)

    Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi


    To understand temperature structure or magma distribution in the crust and uppermost mantle, it is essential to know their attenuation structure. This study estimated the 3-D S-wave attenuation structure in the crust and uppermost mantle at the northern Izu-Bonin arc, taking into account the apparent attenuation due to multiple forward scattering. In the uppermost mantle, two areas of high seismic attenuation (high Q -1) imaged beneath the volcanic front were mostly colocated with low-velocity anomalies. This coincidence suggests that these high- Q -1 areas in low-velocity zones are the most likely candidates for high-temperature regions beneath volcanoes. The distribution of random inhomogeneities indicated the presence of three anomalies beneath the volcanic front: Two were in high- Q -1 areas but the third was in a moderate- Q -1 area, indicating a low correlation between random inhomogeneities and Q -1. All three anomalies of random inhomogeneities were rich in short-wavelength spectra. The most probable interpretation of such spectra is the presence of volcanic rock, which would be related to accumulated magma intrusion during episodes of volcanic activity. Therefore, the different distributions of Q -1 and random inhomogeneities imply that the positions of hot regions in the uppermost mantle beneath this arc have changed temporally; therefore, they may provide important constraints on the evolutionary processes of arc crust and volcanoes.

  4. Volcanism and associated hazards: the Andean perspective

    Directory of Open Access Journals (Sweden)

    R. I. Tilling


    Full Text Available Andean volcanism occurs within the Andean Volcanic Arc (AVA, which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions" recognized worldwide that have occurred from the Ordovician to the Pleistocene.

    The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru. The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (<0.05 km3 in 1985 of Nevado del Ruiz (Colombia killed about 25 000 people – the worst volcanic disaster in the Andean region as well as the second worst in the world in the 20th century. The Ruiz tragedy has been attributed largely to ineffective communications of hazards information and indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent

  5. Geochemistry and zircon U-Pb-Hf isotopes of Early Paleozoic arc-related volcanic rocks in Sonid Zuoqi, Inner Mongolia: Implications for the tectonic evolution of the southeastern Central Asian Orogenic Belt (United States)

    Chen, Yan; Zhang, Zhicheng; Li, Ke; Yu, Haifei; Wu, Tairan


    An Early Paleozoic acid volcanic sequence has been recently detected southeast of Sonid Zuoqi in central Inner Mongolia to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. First, the volcanic rocks have zircon U-Pb ages of 439-445 Ma. They are characterized by (a) a high silica content, moderate alkali content and low iron content; (b) enrichment in light rare earth elements, depletion of heavy rare earth elements, and negative Eu anomalies; and (c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic samples yield εHf(t) values of - 4.7 to + 9.2 with TDM2 ages of 835-1724 Ma. For petrogenesis, they were possibly arc derived, from predominant juvenile materials with subordinate ancient continental crust. Combined with previous studies, the Early Paleozoic Sonid Zuoqi arc magmatism can be divided into three stages: a primitive arc stage represented by 464-490 Ma low-K, calcic granitoids; a normal continental arc stage represented by 439-445 Ma medium-K, calcic to calcic-alkalic plutons and volcanic rocks and a syn-collisional stage represented by 423-424 Ma high-K granites. Furthermore, the timing and tectonic settings of the above magmatic rocks show similarities to those in Xilinhot and other areas of the northern Early to Mid-Paleozoic orogenic belt (NOB), although the rock assemblies and their proportions vary more or less in different areas. Accordingly, the NOB that formed on this arc was probably attributed to the northward subduction of the Paleo-Asian Ocean beginning at 500 Ma, which experienced this type of arc development and was terminated by a soft collision before the Late Devonian.

  6. Volcanic rock-hosted gold and base-metal mineralization associated with neoproterozoic-early Paleozoic back-arc extension in the Carolina terrane, southern Appalachian Piedmont

    Energy Technology Data Exchange (ETDEWEB)

    Feiss, P.G. (Univ. of North Carolina, Chapel Hill (United States)); Vance, R.K. (Georgia Southern Univ., Statesboro (United States)); Wesolowski, D.J. (Oak Ridge National Lab., TN (United States))


    Volcanogenic mineral deposits in the Carolina terrane, southern Appalachian Piedmont, include Kuroko-type polymetallic massive sulfide deposits and disseminated gold-pyrite deposits associated with propylitic, silicic, argillic, and advanced argillic alteration. Host rocks are metavolcaniclastic and metaepiclastic rocks of a Neoproterozoic-Early Cambrian magmatic arc. The favorable gold horizon is the transition from a lower succession of andesitic and rhyolitic pyroelastic rocks with basal mafic lavas to an upper sequence of epiclastic sedimentary units and minor lava and ash flows. Kuroko-type deposits are associated with mafic to bimodal volcanic rocks in the upper sequence. Whole-rock oxygen isotope analyses indicate that gold mineralization is associated with a transition from hydrothermal systems dominated by isotopically relatively light ([delta][sup 18]O = -6% to -10%) waters, typical of high-latitude subaerial systems, to seawater ([delta][sup 18]O = 0%). Plots of [delta][sup 18]O vs. SiO[sub 2] of the host rocks show a compositional gap associated with mineralization at the subaerial to submarine transition. Values of [delta][sup 18]O for the hydrothermal waters, lithostratigraphic analyses, and tectonic models of the Carolina terrane demonstrate that mineralization coincided with extension in a rifted arc. 34 refs., 3 figs.

  7. Depth of origin of magma in eruptions. (United States)

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria


    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.

  8. Generation of continental crust in intra-oceanic arcs (United States)

    Gazel, E.; Hayes, J. L.; Kelemen, P. B.; Everson, E. D.; Holbrook, W. S.; Vance, E.


    The origin of continental crust is still an unsolved mystery in the evolution of our planet. Although the best candidates to produce juvenile continental crust are intra-oceanic arcs these systems are dominated by basaltic lavas, and when silicic magmas are produced, the incompatible-element compositions are generally too depleted to be a good match for continental crust estimates. Others, such as the W. Aleutians, are dominated by andesitic melts with trace element compositions similar to average continental crust. In order to evaluate which intra-oceanic arcs produced modern continental crust, we developed a geochemical continental index (CI) through a statistical analysis that compared all available data from modern intra-oceanic arcs with global estimates of continental crust. Our results suggest that magmas from Costa Rica (100 have the least continent-like geochemical signatures. In these arcs the subducting plate is old (>100 Ma), not overprinted by enriched intraplate volcanism and the geochemistry may be dominated by slab-derived, aqueous fluids. We also found a strong correlation between the CI and average crustal P-wave velocity, validating the geochemical index with the available seismic data for intra-oceanic arcs. In conclusion, the production of young continental crust with compositions similar to Archean continental crust is an unusual process, limited to locations where there are especially voluminous partial melts of oceanic crust.

  9. Anomalous increase of diffuse CO_{2} emission from Brava (Cape Verde): evidence of volcanic unrest or increase gas release from a stationary magma body? (United States)

    García-Merino, Marta; García-Hernández, Rubén; Montrond, Eurico; Dionis, Samara; Fernandes, Paulo; Silva, Sonia V.; Alfama, Vera; Cabral, Jeremías; Pereira, Jose M.; Padrón, Eleazar; Pérez, Nemesio M.


    Brava (67 km2) is the southwestern most and the smallest inhabited island of the Cape Verde archipelago. It is located 18 km west of Fogo Island and rises 976 m from the sea level. Brava has not any documented historical eruptions, but its Holocene volcanism and relatively high seismic activity clearly indicate that it is an active volcanic island. Since there have been no historic eruptions in Brava, volcanic hazard awareness among the population and the authorities is very low; therefore, its volcano monitoring program is scarce. With the aim of helping to provide a multidisciplinary monitoring program for the volcanic surveillance of the island, diffuse CO2 emission surveys have been carried out since 2010; approximately every 2 years. Soil CO2 efflux measurements are periodically performed at ˜ 275 observation sites all over the island and after taking into consideration their accessibility and the island volcano-structural characteristics. At each sampling site, soil CO2 efflux measurement was performed by means of a portable NDIR sensor according to the accumulation chamber method. To quantify the total diffuse CO2 emission from Brava volcanic system, soil CO2 efflux maps were constructed using sequential Gaussian simulations (sGs). An increase trend of diffuse CO2 emission rate from 42 to 681 t d-1at Brava was observed; just one year prior the 2014-2015 Fogo eruption and almost three years before the anomalous seismic activity recorded on August 2016 with more than 1000 seismic events registered by the INMG on August 1st, 2016 (Bruno Faria, personal communication). Due to this anomalous seismic activity, a diffuse CO2 emission survey at Brava was performed from August 2 to 10, 2016, and the estimated degassing rate yield a value about 72 t d-1; typical background values. An additional survey was carried out from October 22 to November 6, 2016. For this last survey, the estimated diffuse CO2 emission from Brava showed the highest observed value with a

  10. Formation of lower continental crust by relamination of buoyant arc lavas and plutons (United States)

    Kelemen, Peter B.; Behn, Mark D.


    The formation of the Earth's continents is enigmatic. Volcanic arc magmas generated above subduction zones have geochemical compositions that are similar to continental crust, implying that arc magmatic processes played a central role in generating continental crust. Yet the deep crust within volcanic arcs has a very different composition from crust at similar depths beneath the continents. It is therefore unclear how arc crust is transformed into continental crust. The densest parts of arc lower crust may delaminate and become recycled into the underlying mantle. Here we show, however, that even after delamination, arc lower crust still has significantly different trace element contents from continental lower crust. We suggest that it is not delamination that determines the composition of continental crust, but relamination. In our conceptual model, buoyant magmatic rocks generated at arcs are subducted. Then, upon heating at depth, they ascend and are relaminated at the base of the overlying crust. A review of the average compositions of buoyant magmatic rocks -- lavas and plutons -- sampled from the Aleutians, Izu-Bonin-Marianas, Kohistan and Talkeetna arcs reveals that they fall within the range of estimated major and trace elements in lower continental crust. Relamination may thus provide an efficient process for generating lower continental crust.

  11. Crustal recycling by subduction erosion in the central Mexican Volcanic Belt (United States)

    Straub, Susanne M.; Gómez-Tuena, Arturo; Bindeman, Ilya N.; Bolge, Louise L.; Brandl, Philipp A.; Espinasa-Perena, Ramón; Solari, Luigi; Stuart, Finlay M.; Vannucchi, Paola; Zellmer, Georg F.


    Recycling of upper plate crust in subduction zones, or 'subduction erosion', is a major mechanism of crustal destruction at convergent margins. However, assessing the impact of eroded crust on arc magmas is difficult owing to the compositional similarity between the eroded crust, trench sediment and arc crustal basement that may all contribute to arc magma formation. Here we compare Sr-Nd-Pb-Hf and trace element data of crustal input material to Sr-Nd-Pb-Hf-He-O isotope chemistry of a well-characterized series of olivine-phyric, high-Mg# basalts to dacites in the central Mexican Volcanic Belt (MVB). Basaltic to andesitic magmas crystallize high-Ni olivines that have high mantle-like 3He/4He = 7-8 Ra and high crustal δ18Omelt = +6.3-8.5‰ implying their host magmas to be near-primary melts from a mantle infiltrated by slab-derived crustal components. Remarkably, their Hf-Nd isotope and Nd/Hf trace element systematics rule out the trench sediment as the recycled crust end member, and imply that the coastal and offshore granodiorites are the dominant recycled crust component. Sr-Nd-Pb-Hf isotope modeling shows that the granodiorites control the highly to moderately incompatible elements in the calc-alkaline arc magmas, together with lesser additions of Pb- and Sr-rich fluids from subducted mid-oceanic ridge basalt (MORB)-type altered oceanic crust (AOC). Nd-Hf mass balance suggests that the granodiorite exceeds the flux of the trench sediment by at least 9-10 times, corresponding to a flux of ⩾79-88 km3/km/Myr into the subduction zone. At an estimated thickness of 1500-1700 m, the granodiorite may buoyantly rise as bulk 'slab diapirs' into the mantle melt region and impose its trace element signature (e.g., Th/La, Nb/Ta) on the prevalent calc-alkaline arc magmas. Deep slab melting and local recycling of other slab components such as oceanic seamounts further diversify the MVB magmas by producing rare, strongly fractionated high-La magmas and a minor population of

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

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


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

  13. Kinematic variables and water transport control the formation and location of arc volcanoes. (United States)

    Grove, T L; Till, C B; Lev, E; Chatterjee, N; Médard, E


    The processes that give rise to arc magmas at convergent plate margins have long been a subject of scientific research and debate. A consensus has developed that the mantle wedge overlying the subducting slab and fluids and/or melts from the subducting slab itself are involved in the melting process. However, the role of kinematic variables such as slab dip and convergence rate in the formation of arc magmas is still unclear. The depth to the top of the subducting slab beneath volcanic arcs, usually approximately 110 +/- 20 km, was previously thought to be constant among arcs. Recent studies revealed that the depth of intermediate-depth earthquakes underneath volcanic arcs, presumably marking the slab-wedge interface, varies systematically between approximately 60 and 173 km and correlates with slab dip and convergence rate. Water-rich magmas (over 4-6 wt% H(2)O) are found in subduction zones with very different subduction parameters, including those with a shallow-dipping slab (north Japan), or steeply dipping slab (Marianas). Here we propose a simple model to address how kinematic parameters of plate subduction relate to the location of mantle melting at subduction zones. We demonstrate that the location of arc volcanoes is controlled by a combination of conditions: melting in the wedge is induced at the overlap of regions in the wedge that are hotter than the melting curve (solidus) of vapour-saturated peridotite and regions where hydrous minerals both in the wedge and in the subducting slab break down. These two limits for melt generation, when combined with the kinematic parameters of slab dip and convergence rate, provide independent constraints on the thermal structure of the wedge and accurately predict the location of mantle wedge melting and the position of arc volcanoes.

  14. LA-ICP-MS Pb-U Dating of Young Zircons from the Kos-Nisyros Volcanic Centre, SE Aegean Arc (Greece) (United States)

    Guillong, M.; Von Quadt, A.; Peytcheva, I.; Bachmann, O.


    Zircon Pb-U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos-Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay. Guillong, M. et al., 2014, JAAS, 29, p. 963-967; doi: 10.1039/c4ja00009a.

  15. Experimental Constraints on Mantle Heterogeneity and Mantle-Melt Equilibration Depths along the Volcanic Front of the Trans-Mexican Volcanic Belt (United States)

    Weaver, S.; Wallace, P. J.; Johnston, A.


    Primitive magmas erupted along the volcanic front in the Trans-Mexican Volcanic Belt (TMVB) span a wide geochemical range, with variations in silica, alkalies, and volatiles, indicating that the subarc mantle wedge is chemically heterogeneous. In this work we present the results of hydrous, near-liquidus piston-cylinder experiments for three chemically distinct primitive magmas that have erupted at the volcanic front along the TMVB. The experiments were aimed to constrain the mineralogy of equilibrium residues and final equilibration pressures and temperatures for these primitive melts over a range of H2O contents (1.5-7 wt%). The results provide an along-arc view of primitive magma equilibration conditions beneath the volcanic front of the TMVB. The experimental starting materials included a medium-K basaltic andesite (JR-28, Jorullo, Central Mexico; Weaver et al., 2011), potassic trachybasalt (JOR-46, La Pilita, central Mexico), and an alkali basalt (AY-509, Ayutla, western Mexico). The residual mineralogy for these three compositions at upper mantle pressures was harzburgite (JR-28) and wehrlite (JOR-46 and AY-509). Experimentally constrained equilibration pressures varied from 1.4 GPa-1.8 GPa, with the lowest pressure observed in the central Mexico lavas (Jorullo and La Pilita) and the highest pressures observed for the Ayutla basalt from western Mexico. Other experimental studies on primitive Mexican lavas have produced similar mantle residues and equilibration pressures; high-Mg basaltic andesite (Pelagatos, Mexico City region; Weber et al., 2011) and primitive absarokite (Mascota, Jalisco, western Mexico; Hesse and Grove, 2003) both equilibrated with harzburgite at 1.3 GPa and 1.6 GPa, respectively. We combine all of the available experimental data with recent geodynamic models of the mantle wedge beneath the TMVB to provide a comprehensive, along-arc perspective of mantle-melt equilibrium beneath the volcanic front. There is significant experimental and

  16. Electrical conductivity of water-bearing magmas (United States)

    Gaillard, F.


    Phase diagrams and chemical analyzes of crystals and glass inclusions of erupted lavas tell us that most explosive volcanic eruptions were caused by extremely water-rich pre-eruptive conditions. Volcanologists estimate volcanic hazards by the pre-eruptive water content of lavas erupted in the past and they hypothesize that future eruptions should show similar features. Alternatively, the development of methods allowing direct estimation of water content of magmas stored in the Earth’s interior would have the advantage of providing direct constraints about upcoming rather than past eruptions. Geoelectrical sounding, being the most sensitive probe to the chemical state of the Earth’s interior, seems a promising tool providing that its interpretation is based on relevant laboratory constraints. However, the current database of electrical conductivity of silicate melt merely constrains anhydrous composition. We have therefore undertaken an experimental program aiming at elucidating the effect of water on the electrical conductivity of natural magmas. Measurements (impedance spectroscopy) are performed using a two electrodes set-up in an internally heated pressure vessel. The explored temperature and pressure range is 25-1350°C and 0.1-400MPa. The material used is a natural rhyolitic obsidian. Hydration of this rhyolite is first performed in Pt capsules with 0.5, 1, 2 and 6wt% of water. In a second step, the conductivity measurements are performed at pressure and temperature in a modified Pt capsule. One end of the capsule is arc-welded whereas the other end is closed with the help of a BN cone and cement through which an inner electrode is introduced in the form a Pt wire. The capsule is used as outer electrode. The electrical cell has therefore a radial geometry. The rhyolite is introduced in the cell in the form of a cylinder drilled in the previously hydrated glass. At dwell condition, the melt is sandwiched between two slices of quartz avoiding any deformation

  17. Phlogopite and K-amphibole in the upper mantle: Implication for magma genesis in subduction zones

    Energy Technology Data Exchange (ETDEWEB)

    Sudo, Akira; Tatsumi, Yoshiyuki (Kyoto Univ. (Japan))


    High-pressure phase relations have been examined for phlogopite + diopside with and without enstatite under vapor absent conditions in the pressure range of 5 to 13 GPa and in the temperature range of 1,000 to 1,300C. Phlogopite in these systems can be stable up to 6-7 GPa and decomposes through pressure-dependent reactions to crystallize phases including potassic amphibole. The experimental results suggest that phlogopite, which is one of main hydrous phases in the downdragged hydrated peridotite at the base of mantle wedge, plays an important role in the formation of magmas at the backarc side of a volcanic arc. The existence of potassic amphibole at higher pressure regions may imply the involvement of subduction component in magma generation in the region far away from the trench axis.

  18. Formation of hybrid arc andesites beneath thick continental crust (United States)

    Straub, Susanne M.; Gomez-Tuena, Arturo; Stuart, Finlay M.; Zellmer, Georg F.; Espinasa-Perena, Ramon; Cai, Yue; Iizuka, Yoshiyuki


    Andesite magmatism at convergent margins is essential for the differentiation of silicate Earth, but no consensus exists as to andesite petrogenesis. Models proposing origin of primary andesite melts from mantle and/or slab materials remain in deadlock with the seemingly irrefutable petrographic and chemical evidence for andesite formation through mixing of basaltic mantle melts with silicic components from the overlying crust. Here we use 3He/4He ratios of high-Ni olivines to demonstrate the mantle origin of basaltic to andesitic arc magmas in the central Mexican Volcanic Belt (MVB) that is constructed on ~ 50 km thick continental crust. We propose that the central MVB arc magmas are hybrids of high-Mg# > 70 basaltic and dacitic initial mantle melts which were produced by melting of a peridotite subarc mantle interspersed with silica-deficient and silica-excess pyroxenite veins. These veins formed by infiltration of reactive silicic components from the subducting slab. Partial melts from pyroxenites, and minor component melts from peridotite, mix in variable proportions to produce high-Mg# basaltic, andesitic and dacitic magmas. Moderate fractional crystallization and recharge melt mixing in the overlying crust produces then the lower-Mg# magmas erupted. Our model accounts for the contrast between the arc-typical SiO2 variability at a given Mg# and the strong correlation between major element oxides SiO2, MgO and FeO which is not reproduced by mantle-crust mixing models. Our data further indicate that viscous high-silica mantle magmas may preferentially be emplaced as intrusive silicic plutonic rocks in the crust rather than erupt. Ultimately, our results imply a stronger turnover of slab and mantle materials in subduction zones with a negligible, or lesser dilution, by materials from the overlying crust.

  19. Lunar magma transport phenomena (United States)

    Spera, Frank J.


    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.

  20. Magma reservoirs from the upper crust to the Moho inferred from high-resolution Vp and Vs models beneath Mount St. Helens, Cascades, USA (United States)

    Kiser, Eric; Levander, Alan; Zelt, Colin; Palomeras, Imma; Schmandt, Brandon; Hansen, Steven; Creager, Kenneth; Ulberg, Carl


    Mount St. Helens is currently the most active volcano along the Cascadia arc. Though several studies investigated the magmatic system beneath Mount St. Helens following the May 18, 1980 eruption, tomographic imaging of the system has been limited to ~10 km depth due to the distribution of earthquakes in the region. This has made it difficult to estimate the volume of the shallow magma reservoir beneath the volcano, the regions of magma entry into the lower crust, and the connectivity of this magma system throughout the crust. The latter is particularly interesting as one interpretation of the Southern Washington Cascades Conductor (SWCC) suggests that the Mount St Helens and Mount Adams volcanic systems are connected in the middle crust (Hill et al., 2009). The multi-disciplinary iMUSH (imaging Magma Under St. Helens) project is designed to investigate these and other fundamental questions associated with Mount St. Helens. Here we present the first high-resolution 2D Vp and Vs models derived from travel-time data from the iMUSH 3D active-source seismic experiment. The experiment consisted of ~6000 seismograph stations which recorded 23 explosions and hundreds of local earthquakes. Directly beneath Mount St. Helens, we observe a high Vp/Vs body, inferred to be the upper/middle crustal magma reservoir, between 4 and 13 km depth. We observe a second high Vp/Vs body, likely of magmatic origin, at roughly the same depth beneath Indian Heaven Volcanic Field, which last erupted 9 ka. Southeast of Mount St. Helens is a low Vp column extending from the middle crust, ~15 km depth, to the Moho at ~40 km depth. A cluster of deep long-period events, typically associated with injection of magma, occurs at the northwestern boundary of this low Vp column. We interpret this as the middle-lower crust magma reservoir. In the lower crust, high Vp features bound the magma reservoir directly beneath Mount St. Helens and the Indian Heaven Volcanic Field. One explanation for these high Vp

  1. Structural control on volcanoes and magma paths from local- to orogen-scale: The central Andes case (United States)

    Tibaldi, A.; Bonali, F. L.; Corazzato, C.


    Assessing the parameters that control the location and geometry of magma paths is of paramount importance for the comprehension of volcanic plumbing systems and geo-hazards. We analyse the distribution of 1518 monogenic and polygenic volcanoes of Miocene-Quaternary age of the Central Volcanic Zone of the Andes (Chile-Bolivia-Argentina), and reconstruct the magma paths at 315 edifices by analysing the morphostructural characteristics of craters and cones. Then we compare these data with outcropping dykes, tectonic structures and state of stress. Most magma paths trend N-S, NW-SE, and NE-SW, in decreasing order of frequency. The N-S and NW-SE paths coexist in the northern and southern part of the study area, whereas N-S paths dominate east of the Salar de Atacama. Outcropping dykes show the same trends. The regional Holocene stress state is given by an E-W greatest horizontal principal stress. N-S and NNE-SSW reverse faults and folds affect deposits of 4.8, 3.2 and 1.3 Ma BP, especially in the central and southern study areas. A few NW-SE left-lateral strike-slip faults are present in the interior of the volcanic arc, part of which belong to the Calama-Olacapato-El Toro fault. The volcanic chain is also affected by several N-S- and NW-SE-striking normal faults that offset Pliocene and Quaternary deposits. The results indicate different scenarios of magma-tectonic interaction, given by N-S normal and reverse faults and N-S fold hinges that guide volcano emplacement and magma paths. Magma paths are also guided by strike-slip and normal NW-SE faults, especially in the northern part of the study area. Zones with verticalized strata, with bedding striking NE-SW, also acted as preferential magma paths. These data suggest that at convergence zones with continental crust, shallow magma paths can be more sensitive to the presence and geometry of upper crustal weakness zones than to the regional state of stress.

  2. About the Mechanism of Volcanic Eruptions

    CERN Document Server

    Nechayev, Andrei


    A new approach to the volcanic eruption theory is proposed. It is based on a simple physical mechanism of the imbalance in the system "magma-crust-fluid". This mechanism helps to explain from unified positions the different types of volcanic eruptions. A criterion of imbalance and magma eruption is derived. Stratovolcano and caldera formation is analyzed. High explosive eruptions of the silicic magma is discussed

  3. 天山石炭纪火山岩系中含有富Nb岛弧玄武岩吗?%Do the Tianshan Carboniferous volcanic successions contain Nb-enriched arc basalts?

    Institute of Scientific and Technical Information of China (English)

    夏林圻; 夏祖春; 徐学义; 李向民; 马中平


    中国西北部天山石炭纪-早二叠世裂谷火山作用代表了一个新近被认可的大火成岩省.有人认为,在天山石炭纪火山岩系中发育有富Nb岛弧玄武岩、埃达克岩和高镁安山岩组合.然而,该岩石组合具有与典型富Nb岛弧玄武岩、埃达克岩和高镁安山岩不同的化学和同位素特点,表明其并非是岛弧岩石组合.这一推断的岛弧岩石组合实际上是大陆板内火山岩组合,由未遭受地壳混染、受到地壳轻微混染和遭受地壳强烈混染的大陆火山岩组成.%The Tianshan Carboniferous-Early Permian rift-related volcanism in northwestern China represents a newly recognized large igneous province. It has been deemed that an assemblage of Nb-enriched arc basalt, adakite and high-Mg andesite occurred in the Tianshan Carboniferous volcanic successions. Divergent chemical and isotopic characteristics between this rock assemblage and the typical Nb-enriched arc basalts, adakites and high-Mg andesites reveal that the former is not arc related. This postulated arc-related assemblage is indeed an intracontinental volcanic assemblage that consists of crustally uncontaminated, less-contaminated and strongly contaminated continental volcanic rocks.

  4. Galapagos-OIB signature in southern Central America: Mantle refertilization by arc-hot spot interaction (United States)

    Gazel, Esteban; Carr, Michael J.; Hoernle, Kaj; Feigenson, Mark D.; Szymanski, David; Hauff, Folkmar; van den Bogaard, Paul


    Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America (central Costa Rica and Panama) have isotopic and trace element compositions with an ocean island basalt (OIB) affinity, similar to the Galapagos-OIB lavas (e.g., Ba/La 10, 206Pb/204Pb > 18.8). Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene ˜6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas similar to the Galapagos hot spot. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hot spot tracks (the Seamount Province and the Cocos/Coiba Ridge) at the Middle American Trench. The higher Pb isotopic ratios, relatively lower Sr and Nd isotopic ratios, and enriched incompatible-element signature of central Costa Rican magmas can be explained by arc-hot spot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridge (Central Galapagos Domain). Geological and geochemical evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hot spot tracks, which started to collide with the margin ˜8 Ma ago. The Galapagos hot spot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

  5. Periodicities in sediment temperature time-series at a marine shallow water hydrothermal vent in Milos Island (Aegean Volcanic arc, Eastern Mediterranean) (United States)

    Aliani, Stefano; Meloni, Roberto; Dando, Paul R.


    Time-series data sets of total bottom pressure (tidal plus atmospheric), seawater temperature and sediment temperature from a marine shallow hydrothermal vent (Milos, Hellenic Volcanic Arc, Aegean Sea) were studied to determine factors influencing periodicity at the vents. Bottom pressure and vent temperature were mainly opposite in phase, with the main fluctuations of vent temperature occurring at tidal frequencies. Although the fluctuations in atmospheric pressure were of the same order as those due to tidal pressure, the contribution of atmospheric pressure was considerably weaker at diurnal frequencies. Some sudden discontinuities in sediment temperature were recorded, at least one of these may have been caused by seismic events. Seawater temperature changes were not reflected in the sediment temperature record. Transient loadings, such as tidal loadings, barometric pressure and earth tides, may affect the pore pressure in sediments, influencing fluid expulsion and sediment temperature as a consequence. Most of the contribution to the fluctuations in sediment temperature depends on tidal loadings. Gravitational forces, in the form of earth tides, can also be involved and barometric pressure is probably responsible for long period temperature oscillations.

  6. Elastic flexure controls magma trajectories and explains the offset of primary volcanic activity upstream of mantle plume axis at la Réunion and Hawaii hotspot islands (United States)

    Gerbault, Muriel; Fontaine, Fabrice J.; Rabinowicz, Michel; Bystricky, Misha


    Surface volcanism at la Réunion and Hawaii occurs with an offset of 150-180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis: (i) it is 20 km thick, (ii) it has a 150 km radius, (iii) it lays at the base of the elastic part of the lithosphere, i.e., around ∼50-70 km depth where the temperature varies from ∼600 °C to ∼750 °C, (iv) it lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, and (vi) it is controlled by the visco-elastic relaxation time at ∼50-70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively. This indicates that this basal compression is actually a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., ∼150 km away from the plume head. There, melts propagate through dikes upwards to ∼35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30-35 km depth may thus host a magmatic reservoir where melts transported by dykes pond. Only after further magmatic differentiation can dykes resume their ascension up to the surface and begin forming a volcanic edifice. As the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards

  7. Isotopic Constraints (U, Th, Pb, Sr, Ar) on the Timing of Magma Generation, Storage and Eruption of a Late-Pleistocene Subvolcanic Granite, Alid Volcanic Center, Eritrea (United States)

    Lowenstern, J. B.; Charlier, B. L.; Wooden, J. L.; Lanphere, M. A.; Clynne, M. A.; Bullen, T. D.


    Isotopic analyses demonstrate that a shallow granophyric intrusion from the Alid volcanic center (AVC) was generated, intruded and crystallized over a 20,000-year period in the latest Pleistocene. The granophyre is not exposed, but was ejected as unmelted blocks within a ~1 km3 pyroclastic flow deposit around 15 ka and is a subvolcanic equivalent of the erupted rhyolitic pumice (Lowenstern et al., 1997: J Petrol 12, p. 1707-1721). The rock contains 2.59) is 15.2+/- 5.8 ka (all errors are 2 σ ). Two other splits with lower density (thus higher in Na) yielded ages older than 24 ka, and may retain some excess Ar. Thus, the time between intrusion and complete crystallization for the granophyre was Danakil Depression and are found as unmelted lithic xenoliths in lavas and tuffs of the AVC. Pb isotopes also rule out significant assimilation of Precambrian basement during genesis of the young granophyre. Similarly zircon grains, analyzed with the Stanford-USGS SHRIMP-RG, show little evidence for inheritance, with only a single 760 Ma zircon (U-Pb age) that was also petrographically different from the 130 other zircons in the mount. The other zircons yielded SHRIMP 238U230Th disequilibrium ages of Alidpage.html

  8. Cross-arc Variations in Lava Chemistry in the Tonga Arc-Lau Back Arc System, 19- 23°S (United States)

    Michael, P. J.; Bezos, A.; Langmuir, C. H.; Escrig, S.; Matzen, A. K.; Asimow, P.; Arculus, R.


    The Tonga arc system from 19°-23°S consists of the active Tofua arc, the Eastern Lau Spreading Center (ELSC; a back arc spreading center), and numerous seamounts between them. We use the excellent sampling of ELSC and 34 nearby seamounts, along with sparser published analyses of Tofua arc, to examine the spatial relations of chemistry and melting in this subduction system. The spatial constraints can be used to better understand the nature and mechanism of enrichment that is caused by subduction. Geochemistry along the axis of ELSC is related to its distance to the Tofua arc, which decreases continuously from 100 km in the north to 40 km in the south. The subduction influence (e.g., fluid mobile elements) along ELSC increases in several sharp gradients towards the south as ELSC gets closer to the arc. The six different tectonic segments of ELSC display mixing relationships in trace element ratio-ratio diagrams (e.g., Ba/La vs Th/La) in which one end member is a subduction component that is distinctive for each segment (Escrig et al., this meeting). We explore whether the distinctive subduction components of each ELSC segment are reflected by the Tofua arc that is adjacent to that segment, and by the intervening seamounts. Relationships between the arc, back arc and seamounts are different in the north and the south. In the south where the arc-back arc distance is smaller, the Tofua arc volcanic rocks share the distinctive trace element characteristics of their corresponding ELSC segment, and extend the mixing trajectories to higher, more arc-like values. Seamounts that are located between Tofua arc and ELSC also share the distinctive trace element characteristics of the local arc + back-arc, and are intermediate in their trace element ratios. These observations are consistent with the model of Langmuir et al., (2006) in which magmas of back arc spreading centers form from two components: a dry side similar to mid-ocean ridges and a wet (trenchward) side that

  9. Intensive hydration of the wedge mantle at the Kuril arc - NE Japan arc junction: implications from mafic lavas from Usu Volcano, northern Japan (United States)

    Kuritani, T.; Tanaka, M.; Yokoyama, T.; Nakagawa, M.; Matsumoto, A.


    The southwestern part of Hokkaido, northern Japan, is located at the junction of the NE Japan arc and the Kuril arc. The subducting Pacific plate under this region shows a hinge-like shape due to the dip change of the subducting plate along the trench. Because of the interest in this unique tectonic setting, this arc-arc junction has been the focus of extensive geophysical studies (e.g. Kita et al., 2010, Morishige and van Keken, 2014; Wada et al., 2015). This region is also known as an area in which magmatism has been intense; there are many active volcanoes such as Usu, Tarumae, and Komagatake, and large calderas including Toya, Shikotsu, and Kuttara. In this region, the temporal and spatial evolution of the volcanism and the chemical compositions of the volcanic rocks are well characterized (e.g. Nakagawa, 1992). However, the generation conditions of magmas have not been estimated for these volcanoes, probably because of the scarcity of basaltic products. Therefore, a possible link between the tectonic setting and the intense magmatism is still unclear. In this study, we carried out a petrological and geochemical study on mafic lavas (49.6-51.3 wt.% SiO2) from Usu Volcano, and estimated the conditions under which the magmas were generated. By application of a plagioclase-melt hygrometer to the plagioclase and the host magma, the water content of ~6.5 wt.% was obtained for the basaltic magma. Using this information, as well as the olivine maximum fractionation model (Tatsumi et al., 1983), the composition of the primary magma is estimated to be 47.9 wt.% SiO2, 15.1 wt.% MgO, and 4.1 wt.% H2O. Analyses using the multi-component thermodynamics suggest that the primary magma was generated in the source mantle with 0.9 wt.% H2O at 1310ºC and at 1.6 GPa. The water content of 0.9 wt.% of the source mantle is significantly higher than the estimates for the source mantle in the main NE Japan arc (hinge-like shape, and many fractures might have been developed in the slab

  10. First data on magma ascent and residence times retrieved from Fe-Mg and trace element zonation in olivine phenocrysts from Kamchatka basalts (United States)

    Gordeychik, Boris; Churikova, Tatiana; Kronz, Andreas; Simakin, Alexander; Wörner, Gerhard


    Compositional zonation in olivine phenocrysts and diffusion modelling have been used in the last ten years to estimate magma residence times and the duration of magma ascent. The fundamental assumption is that mixing with newly injected magma into a reservoir triggers diffusional exchange between mafic olivine crystals and more evolved magma and that this magma mixing eventually triggers eruption. If depth of mixing is known, this translates to ascent rates of magmas to the surface. We applied this approach to a series of different arc basalt lavas from Kamchatka to constrain the rates of magma ascent and magma resident in what is one of the most active subduction zones in the world that is also dominated by an abundance of unusually mafic magmas. Our sample collection cover the principal modes of arc magmatism in Kamchatka: from different volcanic complexes (stratovolcano, dikes, summit eruptions, monogenetic cones), of different age (from Late-Pleistocene to Holocene and recent eruptions), from different magmatic regimes (long-lived volcanoes vs. monogenetic eruptions) and different major element composition (from basalt to basaltic andesite of different geochemical character including LILE enrichments). We analyzed and modelled zonation profiles for a range of elements with different diffusivities (e.g. Mg-Fe, Ca, Ni, Mn, Cr) to assess the role of variable diffusivities as a function of major and trace elements in the olivines from different P-T conditions. First data were obtained on samples from the Klyuchevskoy, Shiveluch and Tolbachik, including recent most eruption in 2012/2013. These data show that for some samples the zonation patterns are much more complex than is usually observed: high-Mg olivines at different volcanoes have very different zonation patterns, including normally, reversely zoned grains or even show highly complex repetitive zonation that indicate large compositional changes in the surrounding magma at very short time scales (years). Thus

  11. Thermal vesiculation during volcanic eruptions (United States)

    Lavallée, Yan; Dingwell, Donald B.; Johnson, Jeffrey B.; Cimarelli, Corrado; Hornby, Adrian J.; Kendrick, Jackie E.; von Aulock, Felix W.; Kennedy, Ben M.; Andrews, Benjamin J.; Wadsworth, Fabian B.; Rhodes, Emma; Chigna, Gustavo


    Terrestrial volcanic eruptions are the consequence of magmas ascending to the surface of the Earth. This ascent is driven by buoyancy forces, which are enhanced by bubble nucleation and growth (vesiculation) that reduce the density of magma. The development of vesicularity also greatly reduces the ‘strength’ of magma, a material parameter controlling fragmentation and thus the explosive potential of the liquid rock. The development of vesicularity in magmas has until now been viewed (both thermodynamically and kinetically) in terms of the pressure dependence of the solubility of water in the magma, and its role in driving gas saturation, exsolution and expansion during decompression. In contrast, the possible effects of the well documented negative temperature dependence of solubility of water in magma has largely been ignored. Recently, petrological constraints have demonstrated that considerable heating of magma may indeed be a common result of the latent heat of crystallization as well as viscous and frictional heating in areas of strain localization. Here we present field and experimental observations of magma vesiculation and fragmentation resulting from heating (rather than decompression). Textural analysis of volcanic ash from Santiaguito volcano in Guatemala reveals the presence of chemically heterogeneous filaments hosting micrometre-scale vesicles. The textures mirror those developed by disequilibrium melting induced via rapid heating during fault friction experiments, demonstrating that friction can generate sufficient heat to induce melting and vesiculation of hydrated silicic magma. Consideration of the experimentally determined temperature and pressure dependence of water solubility in magma reveals that, for many ascent paths, exsolution may be more efficiently achieved by heating than by decompression. We conclude that the thermal path experienced by magma during ascent strongly controls degassing, vesiculation, magma strength and the effusive

  12. Volcano geodesy in the Cascade arc, USA (United States)

    Poland, Michael P.; Lisowski, Michael; Dzurisin, Daniel; Kramer, Rebecca; McLay, Megan; Pauk, Ben


    Experience during historical time throughout the Cascade arc and the lack of deep-seated deformation prior to the two most recent eruptions of Mount St. Helens might lead one to infer that Cascade volcanoes are generally quiescent and, specifically, show no signs of geodetic change until they are about to erupt. Several decades of geodetic data, however, tell a different story. Ground- and space-based deformation studies have identified surface displacements at five of the 13 major Cascade arc volcanoes that lie in the USA (Mount Baker, Mount St. Helens, South Sister, Medicine Lake, and Lassen volcanic center). No deformation has been detected at five volcanoes (Mount Rainier, Mount Hood, Newberry Volcano, Crater Lake, and Mount Shasta), and there are not sufficient data at the remaining three (Glacier Peak, Mount Adams, and Mount Jefferson) for a rigorous assessment. In addition, gravity change has been measured at two of the three locations where surveys have been repeated (Mount St. Helens and Mount Baker show changes, while South Sister does not). Broad deformation patterns associated with heavily forested and ice-clad Cascade volcanoes are generally characterized by low displacement rates, in the range of millimeters to a few centimeters per year, and are overprinted by larger tectonic motions of several centimeters per year. Continuous GPS is therefore the best means of tracking temporal changes in deformation of Cascade volcanoes and also for characterizing tectonic signals so that they may be distinguished from volcanic sources. Better spatial resolution of volcano deformation can be obtained through the use of campaign GPS, semipermanent GPS, and interferometric synthetic aperture radar observations, which leverage the accumulation of displacements over time to improve signal to noise. Deformation source mechanisms in the Cascades are diverse and include magma accumulation and withdrawal, post-emplacement cooling of recent volcanic deposits, magmatic

  13. Volcano geodesy in the Cascade arc, USA (United States)

    Poland, Michael; Lisowski, Michael; Dzurisin, Daniel; Kramer, Rebecca; McLay, Megan; Pauk, Benjamin


    Experience during historical time throughout the Cascade arc and the lack of deep-seated deformation prior to the two most recent eruptions of Mount St. Helens might lead one to infer that Cascade volcanoes are generally quiescent and, specifically, show no signs of geodetic change until they are about to erupt. Several decades of geodetic data, however, tell a different story. Ground- and space-based deformation studies have identified surface displacements at five of the 13 major Cascade arc volcanoes that lie in the USA (Mount Baker, Mount St. Helens, South Sister, Medicine Lake, and Lassen volcanic center). No deformation has been detected at five volcanoes (Mount Rainier, Mount Hood, Newberry Volcano, Crater Lake, and Mount Shasta), and there are not sufficient data at the remaining three (Glacier Peak, Mount Adams, and Mount Jefferson) for a rigorous assessment. In addition, gravity change has been measured at two of the three locations where surveys have been repeated (Mount St. Helens and Mount Baker show changes, while South Sister does not). Broad deformation patterns associated with heavily forested and ice-clad Cascade volcanoes are generally characterized by low displacement rates, in the range of millimeters to a few centimeters per year, and are overprinted by larger tectonic motions of several centimeters per year. Continuous GPS is therefore the best means of tracking temporal changes in deformation of Cascade volcanoes and also for characterizing tectonic signals so that they may be distinguished from volcanic sources. Better spatial resolution of volcano deformation can be obtained through the use of campaign GPS, semipermanent GPS, and interferometric synthetic aperture radar observations, which leverage the accumulation of displacements over time to improve signal to noise. Deformation source mechanisms in the Cascades are diverse and include magma accumulation and withdrawal, post-emplacement cooling of recent volcanic deposits, magmatic

  14. Geochemical study for volcanic surveillance

    Energy Technology Data Exchange (ETDEWEB)

    Panichi, C.; La Ruffa, G. [Consiglio Nazionale delle Ricerche, International Institute for Geothermal Research Ghezzano, PI (Italy)


    For years, geologists have been striving to reconstruct volcanic eruptions from the analysis of pyroclastic deposits and lava flows on the surface of the earth and in the oceans. This effort has produced valuable information on volcanic petrology and magma generation, separation, mixing, crystallisation, and interaction with water in phreatomagmatic and submarine eruptions. The volcanological process are tied to the dynamics of the earth's crust and lithosphere. The mantle, subducted oceanic crust, and continental crust contain different rock types and are sources of different magmas. Magmas consist primarily of completely or partially molten silicates containing volatile materials either dissolved in the melt or as bubbles of gas. The silicate and volatile portions affect the physical properties of magma and, therefore, the nature of a volcanic eruption.

  15. Recent crustal foundering in the Northern Volcanic Zone of the Andean arc: Petrological insights from the roots of a modern subduction zone (United States)

    Bloch, Elias; Ibañez-Mejia, Mauricio; Murray, Kendra; Vervoort, Jeffrey; Müntener, Othmar


    Periodic loss of the lower lithosphere into the convecting mantle due to gravitational instability is postulated to be a major mechanism for lithosphere recycling in orogenic zones, but unequivocal petrologic evidence of this process is elusive. The Granatifera Tuff, located in the Mercaderes-Rio Mayo area of the southern Colombian Andes, contains a wide variety of crustal and mantle xenoliths. Here we focus on the thermobarometry and Lu-Hf isotope systematics of crustal garnet clinopyroxenite xenoliths, the results of which offer the first evidence of recent, and likely active, crustal foundering in the Northern Volcanic Zone of the Andean arc. We find that most of these xenoliths equilibrated between 60-80 km depths, ∼7-27 km below the seismically determined Moho in this region, and that at least one crustal garnet clinopyroxenite re-equilibrated at depths exceeding 95 km. A second garnet clinopyroxenite equilibrated at ∼150 km depths, and is either foundered lithospheric material or the product of reaction between peridotite and a mobile component (either silicic melt or fluids) at >4 GPa. All of the investigated garnet clinopyroxenites are negatively buoyant relative to the upper mantle asthenosphere. The presence of minor amounts of secondary amphibole and orthopyroxene, coupled with the lack of major-element retrograde zonation in primary phases within these xenoliths, indicates that these rocks were rapidly transported to, and briefly resided at, shallow depths before eruption. Lu-Hf ages from two garnet clinopyroxenites and one garnet-clinopyroxene hornblendite are material, which the Mercaderes xenoliths document, without catastrophic removal of the crustal root.

  16. Pleistocene volcaniclastic units from North-Eastern Sicily (Italy): new evidence for calc-alkaline explosive volcanism in the Southern Tyrrhenian Sea (United States)

    Di Bella, Marcella; Italiano, Francesco; Sabatino, Giuseppe; Tripodo, Alessandro; Baldanza, Angela; Casella, Sergio; Pino, Paolo; Rasa', Riccardo; Russo, Selma


    A well-preserved volcaniclastic sequence crops out in Pleistocene marine sediments along the Tyrrhenian coastline of the Calabrian-Peloritani arc (Sicily, Italy), testifying the occurrence of Lower-Middle Pleistocene volcanic activity in Southern Tyrrhenian Sea. The presence of dominant highly vesicular and minor blocky glassy particles indicates that the volcanic clasts were originated by explosive events related to the ascent and violent emission of volatile-rich magmas accompanied by and/or alternated with hydromagmatic fragmentation due to magma-sea water interaction. Field investigations and sedimentological features of the studied volcaniclastic units suggest a deposition from sediment-water density flows. The chemical classification of the pumice clasts indicates prevalent rhyolitic and dacitic compositions with calc-alkaline to high-K calc-alkaline affinity. The geochemical features of immobile trace elements together with the presence of orthopyroxene are indicative of a provenance from an arc-type environment. The age (from 980-910 to 589 ka), the chemical composition and the evidence of subaerial explosive volcanic activity constrain the origin nature and temporal evolution of the arc-type volcanism in the Southern Tyrrhenian domain. Finally, the new information here provided contribute to a better understanding of the temporal geodynamic evolution of this sector of the Mediterranean domain.

  17. Sulfate Saturated Hydrous Magmas Associated with Hydrothermal Gold Ores (United States)

    Chambefort, I.; Dilles, J. H.; Kent, A. J.


    Hydrothermal ore deposits associated with arc magmatism represent important sulfur anomalies. During degassing of magmatic systems the volatile may transport metals and sulfur and produce deposits. The ultimate origin of the magma-derived sulfur is still uncertain. The Yanacocha high-sulfidation epithermal Au deposit, Peru, is hosted by a Miocene volcanic succession (ca. 16 to 8 Ma). Magmatic rocks are highly oxidized >NNO+2 and show a range of composition from andesite to dacite. Two populations of amphibole occur in the Yanacocha dacitic ignimbrite deposits (~7 and 12 wt% Al2O3). Low Al amphiboles crystallized at ~ 1.5-2 kbar and 800°C (Plag-Hb thermobarometry) in equilibrium with plagioclase and pyroxene. High Al amphiboles only contain inclusions of anhydrite associated with apatite (up to 1.2 wt% SO3), and have a higher Cr2O3 content (up to 1000 ppm). We estimate these amphiboles form near the magma's liquidus at P(H2O)> 3kbar and 950 to 1000°C of a basaltic, basaltic andesite ascending magma. Low Al amphibole presents an REE pattern with negative anomalies in Sr, Ti and Eu, characteristic of plagioclase and titanite fractionation in the magma. High Al amphiboles are less enriched in REE and have no Sr, Ti, or Eu anomaly. Rare crystals of high Al amphibole display a low Al rim marked by higher REE contents compared to the core and a negative Eu anomaly. Magmatic sulfate occurrences have been discovered through the 8 m.y. volcanic sequence. Rounded anhydrite crystals are found included within clinopyroxene and both high and low Al amphibole. The rare high Al amphiboles (from the sample RC6) contain up to ~10 vol.%, ~5-80 micrometer-long anhydrite as irregularly shaped (amoeboid) blebs that do not show crystallographic forms and do not follow host cleavages. Extremely rare sulfide inclusions are found in plagioclase (Brennecka, 2006). The major and trace element contents of Yanacocha magmatic anhydrite have been analyzed by electron microprobe and LA

  18. Eruptive Productivity of the Ceboruco-San Pedro Volcanic Field, Nayarit, Mexico (United States)

    Frey, H. M.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.


    High-precision 40Ar/39Ar geochronology coupled with GIS spatial analysis provides constraints on magma eruption rates over the past 1 Myr of the Ceboruco-San Pedro volcanic field (1870 km2), located in the Tepic-Zacoalco rift in western Mexico. The volcanic field is part of the Trans Mexican Volcanic arc and is dominated by the andesitic-dacitic stratocone of Volcan Ceboruco and includes peripheral fissure-fed flows, domes, and monogenetic cinder cones. The ages of these volcanic features were determined using 40Ar/39Ar laser step-heating techniques on groundmass or mineral separates, with 78% of the 52 analyses yielding plateau ages with a 2 sigma error < 50 kyrs. The volumes were determined using high resolution (1:50,000) digital elevation models, orthophotos, and GIS software, which allowed for the delineation of individual volcanic features, reconstruction of the pre-eruptive topography, and volume calculations by linear interpolation. The relative proportions of the 80 km3 erupted over the past 1 Myr are 14.5% basaltic andesite, 64.5% andesite, 20% dacite, and 1% rhyolite, demonstrating the dominance of intermediate magma types (in terms of silica content). Overall, there appears to be no systematic progression in the eruption of different magma types (e.g., basalt, andesite, dacite, etc.) with time. However, more than 75% of the total volume of lava within the Ceboruco-San Pedro volcanic field erupted in the last 100 kyrs. This reflects the youthfulness of Volcan Ceboruco, which was constructed during the last 50 kyrs and has a present day volume of 50 +/- 2.5 km3, accounting for 81% of the andesite and 50% of the dacite within the volcanic field. Eleven cinder cones, ranging from the Holocene to 0.37 Ma, display a narrow compositional range, with 52-58 wt% SiO2, 3-5.5 wt% MgO, and relatively high TiO2 concentrations (0.9-1.8 wt%). The total volume of the cinder cones is 0.83 km3. No lavas with < 51 wt% SiO2 have erupted in the past 1 Myr. Peripheral

  19. The South Tibetan Tadpole Zone: Ongoing density sorting at the Moho beneath the Indus-Tsangpo suture zone (and beneath volcanic arcs?) (United States)

    Kelemen, Peter; Hacker, Bradley


    at less than 700°C (e.g. Jackson 02). We build on earlier studies (LePichon et al 92, 97; Schulte-Pelkum et al 05; Monsalve et al 08) to develop the hypothesis that there is rapid growth of garnet at 80 km and 1000°C within subducting Indian crust, causing increased rock densities. Dense eclogites founder into the mantle, while relatively buoyant lithologies accumulate in thickening lower crust. Mantle return flow plus radioactive heating in thick, felsic crust maintains high temperature, facilitating formation of hybrid magmas and pyroxenites. The crustal volume grows at 760 cubic m/yr/m of strike length. Moho-depth earthquakes may be due to localized deformation and thermal runaway in weak layers and along the margins of dense, foundering diapirs (e.g., Larsen & Yuen 97; Braeck & Podladchikov 07; Kelemen & Hirth 07; Lister et al 08; Kufner et al 16). A similar process may take place at some convergent margins, where forearc crust is thrust beneath hot, magmatic arc crust, leading to extensive, Moho-depth density sorting and hybrid crust-mantle magmatism in Arc Tadpole Zones.

  20. Experimental Study of Lunar and SNC Magmas (United States)

    Rutherford, Malcolm J.


    The research described in this progress report involved the study of petrological, geochemical, and volcanic processes that occur on the Moon and the SNC meteorite parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the types of magmas (magma compositions) present, the role of volatiles in magmatic processes, and on processes of magma evolution on these planets. We are also interested in how these processes and magma types varied over time.In earlier work on the A15 green and A17 orange lunar glasses, we discovered a variety of metal blebs. Some of these Fe-Ni metal blebs occur in the glass; others (in A17) were found in olivine phenocrysts that we find make up about 2 vol 96 of the orange glass magma. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption . They also yield important information about the composition of the gas phase present, the gas that drove the lunar fire-fountaining. During the tenure of this grant, we have continued to work on the remaining questions regarding the origin and evolution of the gas phase in lunar basaltic magmas, what they indicate about the lunar interior, and how the gas affects volcanic eruptions. Work on Martian magmas petrogenesis questions during the tenure of this grant has resulted in advances in our methods of evaluating magmatic oxidation state variations in Mars and some new insights into the compositional variations that existed in the SNC magmas over time . Additionally, Minitti has continued to work on the problem of possible shock effects on the abundance and distribution of water in Mars minerals.

  1. Volcanic gas (United States)

    McGee, Kenneth A.; Gerlach, Terrance M.


    In Roman mythology, Vulcan, the god of fire, was said to have made tools and weapons for the other gods in his workshop at Olympus. Throughout history, volcanoes have frequently been identified with Vulcan and other mythological figures. Scientists now know that the “smoke" from volcanoes, once attributed by poets to be from Vulcan’s forge, is actually volcanic gas naturally released from both active and many inactive volcanoes. The molten rock, or magma, that lies beneath volcanoes and fuels eruptions, contains abundant gases that are released to the surface before, during, and after eruptions. These gases range from relatively benign low-temperature steam to thick hot clouds of choking sulfurous fume jetting from the earth. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other volcanic gases are hydrogen sulfide, hydrochloric acid, hydrogen, carbon monoxide, hydrofluoric acid, and other trace gases and volatile metals. The concentrations of these gas species can vary considerably from one volcano to the next.

  2. The Origin of Voluminous Dacite (vs. Andesite) at Mature, Thick Continental Arcs: A Reflection of Processes in the Deep Crust (United States)

    Lange, R. A.


    An outstanding question is why some continental arc segments are characterized by voluminous eruptions of dacite (65-70 wt% SiO2), whereas others erupt more andesite (58-64 wt% SiO2) than any other magma type. An example of the former is the Altiplano-Puna region of the central Andean arc, which has erupted a predominance of dacite over all magma types 10-1 Ma (de Silva, 1989). In contrast, a 200-km arc segment of the Mexican volcanic arc (Michoacán-Guanajuato arc segment) has erupted ~75% andesite, ~26% basaltic andesite and 20%) of hornblende-rich (~40%) gabbronorite in the deep crust, driven by mantle-derived basalt intrusions at depths of 30-40 km. The absence of any dacite or rhyolite along this arc segment indicates that interstitial liquid from crystal-rich andesites never segregated to form eruptible magma. Thus, little upper-crust differentiation occurred along this arc segment. On the basis of phase-equilibrium experiments in the literature (e.g., Sisson et al., 2005), it is proposed that rhyolite and dacite did form during partial melting of the lower arc crust, but at melt fractions too low (≤15%) to permit efficient transport to the upper crust (Vigneresse and Tikoff, 1999). It is further proposed that the reason why dacite is so abundant at mature thick continental arcs (e.g., Altiplano-Puno complex) may be because mantle-derived basalts are primarily emplaced at similar depths (~30-40 km) in continental arc crustal columns. If so, in the central Andean arc, a depth of 30-40 km is within the middle dioritic crust (Graeber and Asch, 1999). Partial melts of hornblende diorite (vs. hornblende gabbro) are predicted to be dacitic (vs. andesitic) at melt fractions of 20-25%, which permits transport to the upper crust. It is therefore proposed that it is deep crustal processes that determine whether andesite or dacite is the most voluminous magma type emplaced into the upper crust and erupted at arcs.

  3. Toward Forecasting Volcanic Eruptions using Seismic Noise

    CERN Document Server

    Brenguier, Florent; Campillo, Michel; Ferrazzini, Valerie; Duputel, Zacharie; Coutant, Olivier; Nercessian, Alexandre


    During inter-eruption periods, magma pressurization yields subtle changes of the elastic properties of volcanic edifices. We use the reproducibility properties of the ambient seismic noise recorded on the Piton de la Fournaise volcano to measure relative seismic velocity variations of less than 0.1 % with a temporal resolution of one day. Our results show that five studied volcanic eruptions were preceded by clearly detectable seismic velocity decreases within the zone of magma injection. These precursors reflect the edifice dilatation induced by magma pressurization and can be useful indicators to improve the forecasting of volcanic eruptions.

  4. Petrological and two-phase flow modelling of deep arc crust: insights on continental crust formation (United States)

    Riel, Nicolas; Bouilhol, Pierre; van Hunen, Jeroen; Cornet, Julien


    The genesis of felsic crust is generally attributed to two main processes: the differentiation of primary magmas by crystallization within the crust or uppermost mantle and the partial melting of older crustal rocks. The Mixing/Assimilation/Hybridization of these magmas in the deep crust (MASH zone) and their subsequent segregation constitutes the principal process by which continents have become differentiated into a more mafic, residual lower crust and a more felsic and hydrated upper crust. Although this model describes qualitatively how continental crust forms, little is known on the physical and chemical mechanisms occurring at the root of volcanic arcs. To assess the dynamics of partial melting, melt injection and hybridization in the deep crust, a new 2-D two-phase flow code using finite volume method has been developed. The formulation takes into account: (i) melt flow through porosity waves/channels, (ii) heat transfer, assuming local thermal equilibrium between solid and liquid, (iii) thermodynamic modelling of stable phases and (iv) injection of mantle-derived melt at the Moho. Our parametric study shows that pressure, heat influx and melt:rock ratio are the main parameters controlling the volume and composition of differentiated magma. Overall the composition of segregated products scatters in two groups: felsic (80-68% SiO2) and intermediate (60-52% SiO2), with an average andesitic composition. The bimodal distribution is controlled by amphibole which buffer the composition of segregated products to high SiO2-content when stable. As the amphibole-out melting reaction is crossed segregated products become intermediate. When compared to available geological evidence, the liquid line of descent of mantle-derived magma do not fit the Mg# versus silica trends of exposed volcanic arcs. Instead our modelling results show that reactive flow of those same magma through a mafic crust is able to reproduce such trends.

  5. Petrogenesis of volcanic rocks that host the world-class Agsbnd Pb Navidad District, North Patagonian Massif: Comparison with the Jurassic Chon Aike Volcanic Province of Patagonia, Argentina (United States)

    Bouhier, Verónica E.; Franchini, Marta B.; Caffe, Pablo J.; Maydagán, Laura; Rapela, Carlos W.; Paolini, Marcelo


    We present the first study of the volcanic rocks of the Cañadón Asfalto Formation that host the Navidad world-class Ag + Pb epithermal district located in the North Patagonian Massif, Patagonia, Argentina. These volcanic and sedimentary rocks were deposited in a lacustrine environment during an extensional tectonic regime associated with the breakup of Gondwana and represent the mafic to intermediate counterparts of the mainly silicic Jurassic Chon Aike Volcanic Province. Lava flows surrounded by autobrecciated carapace were extruded in subaerial conditions, whereas hyaloclastite and peperite facies suggest contemporaneous subaqueous volcanism and sedimentation. LA-ICPMS Usbnd Pb ages of zircon crystals from the volcanic units yielded Middle Jurassic ages of 173.9 ± 1.9 Ma and 170.8 ± 3 Ma. In the Navidad district, volcanic rocks of the Cañadón Asfalto Formation show arc-like signatures including high-K basaltic-andesite to high-K dacite compositions, Rb, Ba and Th enrichment relative to the less mobile HFS elements (Nb, Ta), enrichment in light rare earth elements (LREE), Ysbnd Ti depletion, and high Zr contents. These characteristics could be explained by assimilation of crustal rocks in the Jurassic magmas, which is also supported by the presence of zircon xenocrysts with Permian and Middle-Upper Triassic ages (281.3 Ma, 246.5, 218.1, and 201.3 Ma) and quartz xenocrysts recognized in these volcanic units. Furthermore, Sr and Nd isotope compositions suggest a contribution of crustal components in these Middle Jurassic magmas. High-K basaltic andesite has initial 87Sr/86Sr ratios of 0.70416-0.70658 and ξNd(t) values of -5.3 and -4. High-K dacite and andesite have initial 87Sr/86Sr compositions of 0.70584-0.70601 and ξNd(t) values of -4,1 and -3,2. The range of Pb isotope values (206Pb/204Pb = 18.28-18.37, 207Pb/204Pb = 15.61-15.62, and 208Pb/204Pb = 38.26-38.43) of Navidad volcanic rocks and ore minerals suggest mixing Pb sources with contributions of

  6. Triple oxygen isotope composition of the Campi Flegrei magma systems (United States)

    Iovine, Raffaella Silvia; Wörner, Gerhard; Pack, Andreas; Sengupta, Sukanya; Carmine Mazzeo, Fabio; Arienzo, Ilenia; D'Antonio, Massimo


    Sr-O isotope relationships in igneous rocks are a powerful tool to distinguish magma sources and quantify assimilation processes in magmatic rocks. Isotopic (87Sr/86Sr and 18O/16O-17O/16O) data have been acquired on whole rocks and separated minerals (feldspar, Fe-cpx, Mg-cpx, olivine phenocrysts) from pyroclastic products of the Campi Flegrei volcanic complex (Gulf of Naples, Southern Italy). Oxygen isotope ratios were measured by infrared laser fluorination using a Thermo MAT253 gas source isotope ratio mass spectrometer in dual inlet mode, on ˜2 mg of hand-picked phenocrysts. Variations in triple oxygen isotope ratios (17O/16O, 18O/16O) are expressed as the δ notation relative to VSMOW. Sr isotopic compositions were determined by thermal ionization mass spectrometry after standard cation-exchange methods on separated hand-picked phenocrysts (˜300 mg), and on whole rocks, in case of insufficient sample size to separate crystals. Sr-isotopes in Campi Flegrei minerals range from 0.707305 to 0.707605 and δ18O varies from 6.5 to 8.3‰ . Recalculated δ18Omelt values accordingly show a large range between 7.2 and 8.6‰ . Our data, compared with published δ18O-isotope data from other Italian volcanic centers (Alban Hills, Mts. Ernici, Ischia, Mt. Vesuvius, Aeolian Islands, Tuscany and Sardinia) and from subduction zones worldwide (Kamchatka, Lesser Antilles, Indonesia and Central Andean ignimbrites), show compositions that are very different from typical mantle values. Distinct trends and sources are recognized in our compilation from global data: (1) serpentinized mantle (Kamchatka), (2) sediment-enrichment in the mantle source (Indonesia, Lesser Antilles, Eolian arc), (3) assimilation of old radiogenic continental crust affecting magmas derived from sediment-modified mantle sources (Tuscany, Sardinia), (4) assimilation of lower crustal lithologies (Central Andes, Alban Hills, Mts. Ernici, Ischia). Sr-O-isotope values of Campi Flegrei and Vesuvius magmas

  7. The Upper- to Middle-Crustal Section of the Alisitos Oceanic Arc, (Baja, Mexico): an Analog of the Izu-Bonin-Marianas (IBM) Arc (United States)

    Medynski, S.; Busby, C.; DeBari, S. M.; Morris, R.; Andrews, G. D.; Brown, S. R.; Schmitt, A. K.


    The Rosario segment of the Cretaceous Alisitos arc in Baja California is an outstanding field analog for the Izu-Bonin-Mariana (IBM) arc, because it is structurally intact, unmetamorphosed, and has superior three-dimensional exposures of an upper- to middle-crustal section through an extensional oceanic arc. Previous work1, done in the pre-digital era, used geologic mapping to define two phases of arc evolution, with normal faulting in both phases: (1) extensional oceanic arc, with silicic calderas, and (2) oceanic arc rifting, with widespread diking and dominantly mafic effusions. Our new geochemical data match the extensional zone immediately behind the Izu arc front, and is different from the arc front and rear arc, consistent with geologic relations. Our study is developing a 3D oceanic arc crustal model, with geologic maps draped on Google Earth images, and GPS-located outcrop information linked to new geochemical, geochronological and petrographic data, with the goal of detailing the relationships between plutonic, hypabyssal, and volcanic rocks. This model will be used by scientists as a reference model for past (IBM-1, 2, 3) and proposed IBM (IBM-4) drilling activities. New single-crystal zircon analysis by TIMS supports the interpretation, based on batch SIMS analysis of chemically-abraded zircon1, that the entire upper-middle crustal section accumulated in about 1.5 Myr. Like the IBM, volcanic zircons are very sparse, but zircon chemistry on the plutonic rocks shows trace element compositions that overlap to those measured in IBM volcanic zircons by A. Schmitt (unpublished data). Zircons have U-Pb ages up to 20 Myr older than the eruptive age, suggesting remelting of older parts of the arc, simi