Science.gov

Sample records for magma

  1. Magma dynamics

    NASA Astrophysics Data System (ADS)

    Bergantz, George

    What are the processes that drive magmatic diversity? How is it that volcanic centers can exist for millions of years erupting a variety of chemical types? What are the means by which large batholithic complexes become assembled? Magmas (silicate melts)differ from other geophysical fluids, such as oceans and atmospheres, in that their physiochemical history is largely governed by the processes of solidification and melting. This yields a system with strongly varying physical properties where bouyancy can be generated in complex ways. Much of the recent progress has come from numerical and experimental work specifically directed at the complex interactions of multicomponent systems undergoing phase changes and transport. Geochemical studies also indicate that magmatism is the result of thermal and chemical perturbations on a crustal scale.

  2. Magma Mingling of Multiple Mush Magmas

    NASA Astrophysics Data System (ADS)

    Graham, B.; Leitch, A.; Dunning, G.

    2016-12-01

    This field, petrographic, and geochemical study catalogues complicated magma mingling at the field to thin section scale, and models the emplacement of multiple crystal-rich pulses into a growing magma chamber. Modern theories present magma chambers as short-lived reservoirs that are continuously fed by intermittent magma pulses and suggest processes that occur within them can be highly dynamic. Differences in the rheology of two mingling magmas, largely affected by crystallinity, can result in varied textural features that can be preserved in igneous rocks. Field evidence of complex magma mingling is observed at Wild Cove, located along the northeast shoreline of Fogo Island, Newfoundland, an area interpreted to represent the roof/wall region of the Devonian Fogo Batholith. Fine-grained intermediate enclaves are contained in host rocks of similar composition and occur in round to amoeboid shapes. Dykes of similar composition are also observed near enclaves suggesting they were broken up into globules in localized areas. These provide evidence for a possible mechanism by which enclaves were formed as dykes passed through a more liquid-rich region of the magma chamber. The irregular but sharp nature of the boundaries between units suggest that all co-existed as "mushy" magmas with variable crystallinities reflecting a wide range in temperature between their respective liquidus and solidus. Textural evidence of complex mingling between mush units includes the intrusion of tonalite dykes into quartz diorite and granite mushes. The dykes were later pulled apart and subsequently back-intruded by liquid from the host mush (Figure). Observed magmatic tubes of intermediate magma cross-cutting through magma of near identical composition likely reflect compaction of the underlying mush after intrusion of new pulses of magma into the system. Petrographic examination of contacts between units reveals that few are chilled and medium to coarse grained boundaries are the norm.

  3. Magma Energy Extraction

    SciTech Connect

    Dunn, J.C.; Ortega, A.; Hickox, C.E.; Chu, T.Y.; Wemple, R.P.; Boehm, R.F.

    1987-01-20

    The rate at which energy can be extracted from crustal magma bodies has an important influence on the economic viability of the magma energy concept. Open heat exchanger systems where fluid is circulated through solidified magma offer the promise of high energy extraction rates. This concept was successfully demonstrated during experiments in the molten zone of Kilauea Iki lava lake. Ongoing research is directed at developing a fundamental understanding of the establishment and long term operation of open systems in a crustal magma body. These studies show that magma solidifying around a cooled borehole will be extensively fractured and form a permeable medium through which fluid can be circulated. Numerical modeling of the complete magma energy extraction process predicts that high quality thermal energy can be delivered to the wellhead at rates that will produce from 25 to 30 MW electric. 10 figs., 10 refs.

  4. The Meaning of "Magma"

    NASA Astrophysics Data System (ADS)

    Bartley, J. M.; Glazner, A. F.; Coleman, D. S.

    2016-12-01

    Magma is a fundamental constituent of the Earth, and its properties, origin, evolution, and significance bear on issues ranging from volcanic hazards to planetary evolution. Unfortunately, published usages indicate that the term "magma" means distinctly different things to different people and this can lead to miscommunication among Earth scientists and between scientists and the public. Erupting lava clearly is magma; the question is whether partially molten rock imaged at depth and too crystal-rich to flow should also be called magma. At crystal fractions > 50%, flow can only occur via crystal deformation and solution-reprecipitation. As the solid fraction increases to 90% or more, the material becomes a welded crystal framework with melt in dispersed pores and/or along grain boundaries. Seismic images commonly describe such volumes of a few % melt as magma, yet the rheological differences between melt-rich and melt-poor materials make it vital not to confuse a large rock volume that contains a small melt fraction with melt-rich material. To ensure this, we suggest that "magma" be reserved for melt-rich materials that undergo bulk fluid flow on timescales consonant with volcanic eruptions. Other terms should be used for more crystal-rich and largely immobile partially molten rock (e.g., "crystal mush," "rigid sponge"). The distinction is imprecise but useful. For the press, the public, and even earth scientists who do not study magmatic systems, "magma" conjures up flowing lava; reports of a large "magma" body that contains a few percent melt can engender the mistaken perception of a vast amount of eruptible magma. For researchers, physical processes like crystal settling are commonly invoked to account for features in plutonic rocks, but many such processes are only possible in melt-rich materials.

  5. Meteoric water in magmas

    USGS Publications Warehouse

    Friedman, I.; Lipman, P.W.; Obradovich, J.D.; Gleason, J.D.; Christiansen, R.L.

    1974-01-01

    Oxygen isotope analyses of sanidine phenocrysts from rhyolitic sequences in Nevada, Colorado, and the Yellowstone Plateau volcanic field show that ??18O decreased in these magmas as a function of time. This decrease in ??18O may have been caused by isotopic exchange between the magma and groundwater low in 18O. For the Yellowstone Plateau rhyolites, 7000 cubic kilometers of magma could decrease in ??18O by 2 per mil in 600,000 years by reacting with water equivalent to 3 millimeters of precipitation per year, which is only 0.3 percent of the present annual precipitation in this region. The possibility of reaction between large magmatic bodies and meteoric water at liquidus temperatures has major implications in the possible differentiation history of the magma and in the generation of ore deposits.

  6. Meteoric water in magmas.

    PubMed

    Friedman, I; Lipman, P W; Obradovich, J D; Gleason, J D; Christiansen, R L

    1974-06-07

    Oxygen isotope analyses of sanidine phenocrysts from rhyolitic sequences in Nevada, Colorado, and the Yellowstone Plateau volcanic field show that delta(18)O decreased in these magmas as a function of time. This decrease in delta(18)O may have been caused by isotopic exchange between the magma and groundwater low in (18)O. For the Yellowstone Plateau rhyolites, 7000 cubic kilometers of magma could decrease in delta(18)O by 2 per mil in 600,000 years by reacting with water equivalent to 3 millimeters of precipitation per year, which is only 0.3 percent of the present annual precipitation in this region. The possibility of reaction between large magmatic bodies and meteoric water at liquidus temperatures has major implications in the possible differentiation history of the magma and in the generation of ore deposits.

  7. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine V.; Giordano, Guido

    2014-11-01

    Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; petrologists have used the eruptive products to probe conditions of magma storage (and thus processes that drive magma evolution), while volcanologists have used them to study the conditions under which large volumes of magma are transported to, and emplaced on, the Earth's surface. Traditionally, both groups have worked on the assumption that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. Here we explore the implications of complex magma reservoir configurations for eruption dynamics and caldera formation. We first examine mafic systems, where stacked-sill models have long been invoked but which rarely produce explosive eruptions. An exception is the 2010 eruption of Eyjafjallajökull volcano, Iceland, where seismic and petrologic data show that multiple sills at different depths fed a multi-phase (explosive and effusive) eruption. Extension of this concept to larger mafic caldera-forming systems suggests a mechanism to explain many of their unusual features, including their protracted explosivity, spatially variable compositions and pronounced intra-eruptive pauses. We then review studies of more common intermediate and silicic caldera-forming systems to examine inferred conditions of magma storage, time scales of melt accumulation, eruption triggers, eruption dynamics and caldera collapse. By compiling data from large and small, and crystal-rich and crystal-poor, events, we compare eruptions that are well explained by simple evacuation of a zoned

  8. Kimberlites: Magmas or mixtures?

    NASA Astrophysics Data System (ADS)

    Patterson, Michael; Francis, Don; McCandless, Tom

    2009-11-01

    Although the presence of xenocrystic olivine is widely recognized in kimberlite, there is little consensus about its contribution to the existing estimates for the composition of kimberlite magma. Whole rock geochemistry is critical to the debate regarding the composition of kimberlite magma, however, it has received little attention as an indicator of diamond grade due to conventional thought that diamonds are xenocrysts unrelated to their host kimberlite. The Foxtrot kimberlite Field in Northern Québec is comprised of at least three distinct kimberlite intrusions exhibiting variation in both diamond grade and geochemistry making it an ideal suite with which to test a possible correlation between diamond grade and whole rock composition. Olivine is ubiquitous (30 to 70%) in the Foxtrot kimberlites and exhibits a restricted composition that overlaps that of olivine in harzburgite xenoliths suggesting that the majority of olivine is xenocrystic. Carbonate is also abundant (8 to 35%) in the Foxtrot kimberlites and exhibits magmatic textures requiring that carbon be considered in any petrogenetic model for the Foxtrot kimberlites. Pearce element ratio analysis assuming P as a conserved element indicates that much of the major element variation in the Foxtrot kimberlites can be explained by variable amounts of olivine and orthopyroxene in proportions (~ 80/20), similar to that of cratonic mantle xenoliths. The xenocrystic nature of olivine requires that the contribution of mantle harzburgite must be removed to constrain the composition of the magma. The calculated magma composition that results from the mathematical removal of olivine and orthopyroxene (80/20) from the whole rock compositions is significantly poorer in MgO (15 wt.%) and silica (~ 24 wt.%), but CO 2 rich (~ 17 wt.%) compared to previous estimates for kimberlite magma. The Foxtrot kimberlites are best modelled as mixtures of harzburgite mantle and a relatively carbonate-rich magma. According to this

  9. Watching magma from space

    USGS Publications Warehouse

    Lu, Zhong; Wicks, Charles W.; Dzurisin, Daniel; Thatcher, Wayne R.; Freymueller, Jeffrey T.; McNutt, Stephen R.; Mann, Dorte

    2000-01-01

    Westdahl is a broad shield volcano at the western end of Unimak Island in the Aleutian chain. It has apparently been dormant since a 1991-92 eruption and seismicity levels have been low. However, satellite radar imaging shows that in the years following 1992 the upper flanks of Westdahl have risen several centimeters, probably from the influx of new magma deep below its summit. Until now, deep magma reservoirs have been difficult to detect beneath most volcanoes. But using space geodetic technologies, specifically interferometric synthetic aperture radar (InSAR), we have discovered a deep magmatic source beneath Westdahl. 

  10. Self Sealing Magmas

    NASA Astrophysics Data System (ADS)

    von Aulock, Felix W.; Wadsworth, Fabian B.; Kennedy, Ben M.; Lavallee, Yan

    2015-04-01

    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.

  11. Magma energy for power generation

    SciTech Connect

    Dunn, J.C.

    1987-01-01

    Thermal energy contained in crustal magma bodies represents a large potential resource for the US and magma generated power could become a viable alternative in the future. Engineering feasibility of the magma energy concept is being investigated as part of the Department of Energy's Geothermal Program. This current project follows a seven-year Magma Energy Research Project where scientific feasibility of the concept was concluded.

  12. Crystals in magma chambers

    NASA Astrophysics Data System (ADS)

    Higgins, M.

    2011-12-01

    Differentiation processes in igneous systems are one way in which the diversity of igneous rocks is produced. Traditionally, magmatic diversity is considered as variations in the overall chemical composition, such as basalt and rhyolite, but I want to extend this definition to include textural diversity. Such textural variations can be manifested as differences in the amount of crystalline (and immiscible liquid) phases and in the origin and identity of such phases. One important differentiation process is crystal-liquid separation by floatation or decantation, which clearly necessitates crystals in the magma. Hence, it is important to determine if magmas in chambers (sensu lato) have crystals. The following discussion is framed in generalities - many exceptions occur. Diabase (dolerite) dykes are a common, widespread result of regional mafic magmatism. The rims of most diabase dykes have few or no phenocrysts and crystals in the cores are commonly thought to have crystallized in place. Hence, this major mafic magmatic source did not have crystals, although compositional diversity of these dykes is commonly explained by crystal-liquid separation. This can be resolved if crystallisation was on the walls on the magma chamber. Similarly, most flood basalts are low in crystals and separation of those that are present cannot always explain the observed compositional diversity. Crystal-rich flows do occur, for example the 'Giant Plagioclase Basalts' of the Deccan series, but the crystals are thought to form or accumulate in a crystal-rich zone beneath the roof of the chamber - the rest of the chamber probably has few crystals. Some magmas from Hawaii contain significant amounts of olivine crystals, but most of these are deformed and cannot have crystallised in the chamber. In this case the crystals are thought to grow as the magma passes through a decollement zone. They may have grown on the walls or been trapped by filters. Basaltic andesite ignimbrites generally have

  13. Magma energy: a feasible alternative

    SciTech Connect

    Colp, J.L.

    1980-03-01

    A short review of the work performed by Sandia Laboratories in connection with its Magma Energy Research Project is provided. Results to date suggest that boreholes will remain stable down to magma depths and engineering materials can survive the downhole environments. Energy extraction rates are encouraging. Geophysical sensing systems and interpretation methods require improvement, however, to clearly define a buried magma source.

  14. Mush Column Magma Chambers

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.

    2002-12-01

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

  15. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, John H.

    1999-01-01

    The question of whether the Earth ever passed through a magma ocean stop is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of mar (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of An contrast strongly to those of the Earth: (1) the extremely ancient ages of the martian core, mantle, and crust (approx. 4.55 b.y.); (2) the highly depleted nature of the martian mantle; and (3) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle.

  16. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine; Giordano, Guido

    2015-04-01

    Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; traditionally, both have assumed that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. We discuss the implications of syn-eruptive melt extraction from complex, rather than simple, reservoirs and its potential control over eruption size and style, and caldera collapse timing and style. Implications extend to monitoring of volcanic unrest and eruption progress under conditions where successive melt lenses may be tapped. We conclude that emerging views of complex magma reservoir configurations provide exciting opportunities for re-examining volcanological concepts of caldera-forming systems

  17. Lunar magma transport phenomena

    NASA Technical Reports Server (NTRS)

    Spera, Frank J.

    1992-01-01

    An outline of magma transport theory relevant to the evolution of a possible Lunar Magma Ocean and the origin and transport history of the later phase of mare basaltic volcanism is presented. A simple model is proposed to evaluate the extent of fractionation as magma traverses the cold lunar lithosphere. If Apollo green glasses are primitive and have not undergone significant fractionation en route to the surface, then mean ascent rates of 10 m/s and cracks of widths greater than 40 m are indicated. Lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics. The predominant vapor species appear to be CO CO2, and COS. Near the lunar surface, the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high-speed ejection of vapor and pyroclasts to form lunary fire fountain deposits such as the Apollo 17 orange and black glasses and Apollo 15 green glass.

  18. The Surtsey Magma Series

    PubMed Central

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

    2015-01-01

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50th anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption’s four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland’s Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume. PMID:26112644

  19. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, J. H.

    1999-01-01

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

  20. Magma energy: engineering feasibility of energy extraction from magma bodies

    SciTech Connect

    Traeger, R.K.

    1983-12-01

    A research program was carried out from 1975 to 1982 to evaluate the scientific feasibility of extracting energy from magma, i.e., to determine if there were any fundamental scientific roadblocks to tapping molten magma bodies at depth. The next stage of the program is to evaluate the engineering feasibility of extracting energy from magma bodies and to provide insight into system economics. This report summarizes the plans, schedules and estimated costs for the engineering feasibility study. Tentative tasks and schedules are presented for discussion and critique. A bibliography of past publications on magma energy is appended for further reference. 69 references.

  1. Crystallization of the magma ocean

    NASA Astrophysics Data System (ADS)

    Caracas, R.; Nomura, R.; Hirose, K.; Ballmer, M. D.

    2015-12-01

    We model the crystallization of the magma ocean using pyrolite as a proxy for its composition. We employ first-principles molecular-dynamics calculations to determine the density of the magmas. We use diamond-anvil cell experiments to trace the chemical evolution of the magmas during cooling and crystallization. We build a grid of pressure and temperature points, following the chemical evolution of the magma during the entire fractional crystallization of perovskite. Then we construct a geodynamical model of the evolving magma fully taking into account the density and chemistry of the melts and crystals. We show that the dynamics of the crystallization of the magma ocean is highly dependent (i) on extrinsic parameters, like pressure at the core-mantle boundary and temperature profile through the magma ocean, and (ii) on intrinsic parameters, like relative density relations between the melt and the crystals and vigor of the stirring. Formation of a solid layer in the middle of the magma ocean is possible, which can lead to the eventual formation of a basal magma ocean.

  2. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles…

  3. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles…

  4. Mercury's Magma Ocean

    NASA Astrophysics Data System (ADS)

    Parman, S. W.; Parmentier, E. M.; Wang, S.

    2016-12-01

    The crystallization of Mercury's magma ocean (MMO) would follow a significantly different path than the terrestrial or lunar magma ocean. Evidence from the MESSENGER mission [1] indicates that Mercury's interior has an oxygen fugacity (fO2) orders of magnitude lower any other terrestrial planet (3-8 log units below the iron-wustite buffer = IW-3 to IW-8; [2]). At these conditions, silicate melts and minerals have negligible Fe contents. All Fe is present in sulfides or metal. Thus, the build up of Fe in the last dregs of the lunar magma ocean, that is so important to its evolution, would not happen in the MMO. There would be no overturn or plagioclase flotation crust. Sulfur solubility in silicate melts increases dramatically at low fO2, from 1 wt% at IW-3 to 8wt% at IW-8 [3]. Thus it is possible, perhaps probable, that km-thick layers of sulfide formed during MMO crystallization. Some of the sulfides (e.g. CaS) have high partition coefficients for trace elements and so could control the spatial distribution of radioactive heat producing elements such as U, Th and K. This in turn would have first order effects on the thermal and chemical evolution of the planet. The distribution of the sulfide layers depend upon the density of the sulfides that form in the MMO. At such low fO2, S forms compounds with a range of elements not typical for other planets: Ca, Mg, Na, K. The densities of these sulfides vary widely, with Mg and Ca-rich sulfides being more dense than estimated MMO densities, and Na and K-rich sulfides being less dense than the MMO. Thus sulfide sinking and floating may produce substantial chemical layering on Mercury, potentially including an Mg-Ca rich deep layer and a Na-K rich shallow layer or possibly floatation crust. The total amount of S in the MMO depends on the fO2 and the bulk S content of Mercury, both of which are poorly constrained. In the most extreme case, if the MMO had an fO2of IW-8 and was sulfide saturated from the start, a total

  5. Volatile Changes in Magma Related to Magma Evolution: Influences From Magma Mixing, Crustal Assimilation, and Crystallization

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.; Gardner, J.

    2008-12-01

    The volatile budget of magma is the cumulative product of magma mixing, crustal assimilation, and crystallization, with the concentration of each volatile resulting from how much is added by each process and whether the magma is gas saturate. In order to clarify how volatile budgets fluctuate during magma evolution, we are measuring volatile concentrations in melt inclusions trapped within individual zones of plagioclase crystals from different dacitic Plinian eruptions and a recent small-scale explosion of Popocatépetl Volcano. The plagioclase zones were analyzed for their anorthite (An) composition and their Sr isotopic (87Sr/86Sr) composition in order to investigate the evolutionary processes responsible for crystal growth and their relation to volatile concentrations measured in the melt inclusions. In general, plagioclase from all eruptions display three different correlations between An content and Sr isotopes, with each recording different conditions under which crystals grew. Some crystals have nearly constant 87Sr/86Sr compositions from core to rim with either variable An compositions or a continuous decrease in An, suggesting these crystals were affected only by crystallization and, in some cases, thermal fluctuations. Other crystals display anti-correlations between An and Sr isotopes, which record mass inputs into the system from either magma mixing or crustal assimilation. Single crystals record a variety of processes during their growth, and single pumices contain an extremely heterogeneous population of such crystals, suggesting that the magma system is highly dynamic. Our preliminary results show that water can vary by several weight percent and carbon dioxide by hundreds of ppm between different zones of individual crystals. Interestingly, we find that inclusions related to recharge events by hotter, more primitive magma are more hydrous than those related to assimilation of more radiogenic wall rock. This suggests that the volatile budget of

  6. Magma-magma interaction in the mantle beneath eastern China

    NASA Astrophysics Data System (ADS)

    Zeng, Gang; Chen, Li-Hui; Yu, Xun; Liu, Jian-Qiang; Xu, Xi-Sheng; Erdmann, Saskia

    2017-04-01

    In addition to magma-rock and rock-rock reaction, magma-magma interaction at mantle depth has recently been proposed as an alternative mechanism to produce the compositional diversity of intraplate basalts. However, up to now no compelling geochemical evidence supports this novel hypothesis. Here we present geochemistry for the Longhai basalts from Fujian Province, southeastern China, which demonstrates the interaction between two types of magma at mantle depth. At Longhai, the basalts form two groups, low-Ti basalts (TiO2/MgO < 0.25) and high-Ti basalts (TiO2/MgO > 0.25). Calculated primary compositions of the low-Ti basalts have compositions close to L + Opx + Cpx + Grt cotectic, and they also have low CaO contents (7.1-8.1 wt %), suggesting a mainly pyroxenite source. Correlations of Ti/Gd and Zr/Hf with the Sm/Yb ratios, however, record binary mixing between the pyroxenite-derived melt and a second, subordinate source-derived melt. Melts from this second source component have low Ti/Gd and high Zr/Hf and Ca/Al ratios, thus likely representing a carbonated component. The Sr, Nd, Hf, and Pb isotopic compositions of the high-Ti basalts are close to the low-Ti basalts. The Sm/Yb ratio of the high-Ti basalts, however, is markedly elevated and characterized by crossing rare earth element patterns at Ho, suggesting that they have source components comparable to the low-Ti basalts, but that they have experienced garnet and clinopyroxene fractionation. We posit that mingling of SiO2-saturated tholeiitic magma with SiO2-undersaturated alkaline magma might trigger such fractionation. Therefore, the model of magma-magma interaction and associated deep evolution of magma in the mantle is proposed to explain the formation of Longhai basalts. It may, moreover, serve as a conceptual model for the formation of tholeiitic to alkaline intraplate basalts worldwide.

  7. Warm storage for arc magmas.

    PubMed

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

    2016-12-06

    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.

  8. Warm storage for arc magmas

    PubMed Central

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

    2016-01-01

    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. PMID:27799558

  9. Warm storage for arc magmas

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    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.

  10. Multiphase Dynamics of Magma Oceans

    NASA Astrophysics Data System (ADS)

    Boukaré, Charles-Edouard; Ricard, Yanick; Parmentier, Edgar M.

    2017-04-01

    Since the earliest study of the Apollo lunar samples, the magma ocean hypothesis has received increasing consideration for explaining the early evolution of terrestrial planets. Giant impacts seem to be able to melt significantly large planets at the end of their accretion. The evolution of the resulting magma ocean would set the initial conditions (thermal and compositionnal structure) for subsequent long-term solid-state planet dynamics. However, magma ocean dynamics remains poorly understood. The major challenge relies on understanding interactions between the physical properties of materials (e.g., viscosity (at liquid or solid state), buoyancy) and the complex dynamics of an extremely vigorously convecting system. Such complexities might be neglected in cases where liquidus/adiabat interactions and density stratification leads to stable situations. However, interesting possibilities arise when exploring magma ocean dynamics in other regime. In the case of the Earth, recent studies have shown that the liquidus might intersect the adiabat at mid-mantle depth and/or that solids might be buoyant at deep mantle conditions. These results require the consideration of more sophisticated scenarios. For instance, how does bottom-up crystallization look with buoyant crystals? To understand this complex dynamics, we develop a multiphase phase numerical code that can handle simultaneously phase change, the convection in each phase and in the slurry, as well as the compaction or decompaction of the two phases. Although our code can only run in a limited parameter range (Rayleigh number, viscosity contrast between phases, Prandlt number), it provides a rich dynamics that illustrates what could have happened. For a given liquidus/adiabat configuration and density contrast between melt and solid, we explore magma ocean scenarios by varying the relative timescales of three first order processes: solid-liquid separation, thermo-chemical convective motions and magma ocean cooling.

  11. Mare basalt magma source region and mare basalt magma genesis

    SciTech Connect

    Binder, A.B.

    1982-11-15

    Given the available data, we find that the wide range of mare basaltic material characteristics can be explained by a model in which: (1) The mare basalt magma source region lies between the crust-mantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73--80% olivine, 11--14% pyroxene, 4--8% plagioclase, 0.2--9% ilmenite and 1--1.5% chromite. (2) The source region consists of two or more density-graded rhythmic bands, whose compositions grade from that of the very low TiO/sub 2/ magma source regions (0.2% ilmenite) to that of the very high TiO/sub 2/ magma source regions (9% ilmenite). These density-graded bands are proposed to have formed as co-crystallizing olivine, pyroxene, plagioclase, ilmenite, and chromite settled out of a convecting magma (which was also parental to the crust) in which these crystals were suspended. Since the settling rates of the different minerals were governed by Stoke's law, the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals. Thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase. The reverse being the case for those units deposited near the ascending sides of the convection cells.

  12. Parsing Aleutian Arc Magma Compositions

    NASA Astrophysics Data System (ADS)

    Nye, C. J.

    2011-12-01

    The first-order subdivision of Aleutian arc magma compositions is based on SiO2, and the second-order subdivision is usually based on the change of FeOt/MgO as a function of SiO2, resulting in the additional twofold subdivision into (TH) and calcalkaline (CA) magmas. However, additional robust compositional variations exist. The two most important of these are (1) variation of the calcium number [Ca#; Ca/(Na+Ca)] as a function of SiO2, and (2) the Rate of Incompatible Trace-element Enrichment (RITE) at individual volcanic centers. Additionally, the data show that the low FeOt/MgO of CA andesite and dacite is more controlled by MgO excess than FeOt depletion. The Ca# of andesites and dacites is strongly bimodal. The low-Ca# group is "calc-alkalic", while the high-Ca# group is "calcic", using Peacock (1931) criteria. A continuum of Ca#s exists, but lavas intermediate between high-Ca# and low-Ca# are much less abundant. Ca#s merge below about 55% SiO2, and have a simple normal distribution. RITE, with rare but important exceptions, is generally constant at the temporal and spatial scale of a single volcano. Among high-RITE magmas LILE, LREE, HFSE, and Th increase ~3.5-fold, and HREE increase ~2.5-fold from basalt or basaltic-andesite through andesite to dacite. There is no strong indication that RITE is silica-dependant. High-RITE magmas develop a strong negative Eu anomaly, and are qualitatively compatible with an origin primarily involving fractionation of plagioclase-dominated mineral assemblages. Low-RITE magmas, in contrast, have nearly invariant REE and HFSE, and LILE and Th increase merely 1.5-fold over the same silica range. Low-RITE magmas are not compatible with fractionation of a plagioclase-dominant mineral assemblage. Alternative qualitatively plausible explanations (needing rigorous evaluation) include fractionation of an ultramafic mineral assemblage (Alaskan-type mafic-ultramafic bodies may be a model; see USGS Prof Paper 1564); that low-RITE basaltic

  13. Volatile budget of Eyjafjallajokull magmas

    NASA Astrophysics Data System (ADS)

    Sigurdsson, H.; Mandeville, C. W.

    2010-12-01

    Volatile elments played a critical role in the style of activity during the 2010 eruptions of the glacier-covered Eyjafjallajokull volcano in Iceland. The alkali basalt flank eruption at Fimmvorduhals was dominated by vigorous fire fountaining that produced dominantly spatter-fed aa lava flows. Production of fine ash during the subsequent summit eruption has been variously attributed to magma fragmentation, either due to water-ice-magma interaction related to the 250 m thick glacier cover over the crater, or juvenile volatile content of the magma. Considering the great impact of the ash dispersal on trans-North Atlantic aviation, knowledge of the fragmentation mechanism and the relative roles of juvenile magmatic gases versus phreatomagmatic fragmentation is of prime significance. To evaluate the potential importance of juvenile components, the concentrations of volatiles in magmas erupted in 2010 from Eyjafjallajokull volcano in Iceland have been measured. Analysis of glass inclusions in olivine Fo 77-85 and plagioclase phenocrysts in the alkali basalt magma erupted at Fimmvorduhals flank eruption contain high total volatiles in the range 0.96 - 2.12 wt.%, and sulfur 0.10 - 0.16 wt.%. These glass inclusions are comparable to major element bulk composition of Fimmvörduháls alkali basalt lavas. In contrast, tephra from the explosive summit crater eruption are trachy-andesitic. This magma contains a rather wide range of olivine and plagioclase phenocrysts of Fo48-79 and An 69-81, with both basaltic and andesitic glass inclusions. This diversity is also reflected in a much wider range of total volatile content from 0.1 - 2.88 wt.% and sulfur 0.1 - 0.24 wt.%. At the basic end, the glass inclusions are comparable to the Fimmvorduhals alkali basalt lava, but some have andesitic composition. The highest volatile content is observed in the andesitic glass inclusions in plagioclase An78. Further analysis of glass inclusions and matrix glass by FTIR and ion probe is in

  14. Magma, Magma, Quite Contaminated, How Does Your Garnet Grow?

    NASA Astrophysics Data System (ADS)

    Lackey, J.; Romero, G. A.; Valley, J. W.

    2010-12-01

    Garnet in granitoid rocks has drawn considerable attention and discussion because of uncertainty surrounding its origins. For example, enrichment of Al, resulting in peraluminous magmas capable of crystallizing garnets, may be controlled by contamination or extreme differentiation; Mn enrichment in aplitic and pegmatitic phases suggests garnet may appear only at relatively low, near solidus temperatures. Peritectic garnet, grown by magma-wallrock reaction, may be confused with magmatic garnet, and xenocrysts of metamorphic garnet, entrained from wallrocks, further complicate interpretation. We address these uncertainties with the SIMS analysis of oxygen isotope variations in single garnet crystals and crystal populations in granitic rocks. Values of δ18O were measured on a CAMECA IMS 1280 using a 10 µm spot size and typical precision of ± 0.3 at 2 standard deviations. Analyses were corrected for instrumental mass fractionation according to the newly solved bias correction protocol for garnet (Page et al. 2010). Samples were collected from the Devonian Togus and Hallowell plutons in the south central Maine. These plutons are an ideal site for this study because they are peraluminous and contain pervasive garnet, they locally intrude pelitic, garnet-bearing wallrocks, and they have field evidence of xenolith entrainment and peritectic reaction of xenoliths and the host magmas. Garnet δ18O values of 7.5-10.5‰ show a large range of crustal input to host magmas. Crystal-to-crystal variation of δ18O in hand-samples varies up to 2‰, confirming that garnet populations have complex origins. Traverses (20-50 spots) of single crystals show that δ18O varies up to 1‰, with rims of crystals (outer 50-100µm) being up to 1‰ higher or lower than interiors. Increases of δ18O are interpreted as late-stage contamination, whereas lower δ18O rims, with correspondence to decreasing Fe/Mg ratio, suggest growth during falling magma temperature (50-100°C). Some garnet

  15. Partially molten magma ocean model

    SciTech Connect

    Shirley, D.N.

    1983-02-15

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

  16. Magma rheology variation in sheet intrusions (Invited)

    NASA Astrophysics Data System (ADS)

    Magee, C.; O'Driscoll, B.; Petronis, M. S.; Stevenson, C.

    2013-12-01

    The rheology of magma fundamentally controls igneous intrusion style as well as the explosivity and type of volcanic eruptions. Importantly, the dynamic interplay between the viscosity of magma and other processes active during intrusion (e.g., crystallisation, magma mixing, assimilation of crystal mushes and/or xenolith entrainment) will likely bear an influence on the temporal variation of magma rheology. Constraining the timing of rheological changes during magma transit therefore plays an important role in understanding the nuances of volcanic systems. However, the rheological evolution of actively emplacing igneous intrusions cannot be directly studied. While significant advances have been made via experimental modelling and analysis of lava flows, how these findings relate to intruding magma remains unclear. This has led to an increasing number of studies that analyse various characteristics of fully crystallised intrusions in an attempt to ';back-out' the rheological conditions governing emplacement. For example, it has long been known that crystallinity affects the rheology and, consequently, the velocity of intruding magma. This means that quantitative textural analysis of crystal populations (e.g., crystal size distribution; CSD) used to elucidate crystallinity at different stages of emplacement can provide insights into magma rheology. Similarly, methods that measure flow-related fabrics (e.g., anisotropy of magnetic susceptibility; AMS) can be used to discern velocity profiles, a potential proxy for the magma rheology. To illustrate these ideas, we present an integrated AMS and petrological study of several sheet intrusions located within the Ardnamurchan Central Complex, NW Scotland. We focus on the entrainment and transport dynamics of gabbroic inclusions that were infiltrated by the host magma upon entrainment. Importantly, groundmass magnetic fabrics within and external to these inclusions are coaxial. This implies that a deviatoric stress was

  17. Shallow magma targets in the western US

    SciTech Connect

    Hardee, H.C.

    1984-10-01

    Within the next few years a hole will be drilled into a shallow magma body in the western US for the purpose of evaluating the engineering feasibility of magma energy. This paper examines potential drilling sites for these engineering feasibility experiments. Target sites high on the list are ones that currently exhibit good geophysical and geological data for shallow magma and also have reasonable operational requirements. Top ranked sites for the first magma energy well are Long Valley, CA, and Coso/Indian Wells, CA. Kilauea, HI, also in the top group, is an attractive site for some limited field experiments. A number of additional sites offer promise as eventual magma energy sites, but sparsity of geophysical data presently prevents these sites from being considered for the first magma energy well.

  18. Differentiation of Historical Hekla Magmas

    NASA Astrophysics Data System (ADS)

    Oswald, P.; Geist, D.; Harpp, K.; Christensen, B.; Wallace, P.

    2007-12-01

    straightforward way to the rock compositions, lack significant zoning, and have little variation in each sample. Some lavas show thin reaction rims of pyroxene mantling olivine crystals. Our interpretation is that the phenocrysts grew from the host liquids after the SiO2 gradient was established in the magma reservoir. The data collected thus far are consistent with a persistent basaltic andesite magma chamber beneath Hekla volcano in which the top of the magma column evolves through fractional crystallization proportional to the length of time between eruption events. Melt inclusions in olivine from the 2000 basaltic andesite tephra and 1104 rhyolite tephra have H2O contents ranging from 2.5-2.7 wt.% and 4.6-6.0 wt.%, respectively, but CO2 contents for all melt inclusions are below detection. Calculated vapor saturation pressures at magmatic temperatures range from ~0.6 kbars for the basaltic andesite to 1.4-2.2 kbars for the rhyolite. These values are significantly less than the >3 kbar estimate for the present-day Hekla magma chamber indicating either: 1) crystallization under vapor-undersaturated conditions in the magma reservoir; or 2) formation of at least some crystals within the conduit system above the reservoir. The ubiquitous zoning in Hekla magmas suggests a stable thermal state and recharge rate through time extending at least since the last large rhyolite eruption.

  19. Strontium Isotopes and Magma Dynamics

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ellis, B. S.; Ramos, F. C.

    2010-12-01

    Over the past decade, it has become clear that volcanic rocks commonly exhibit internal heterogeneity in radiogenic isotopes. In particular, strontium isotopic disequilibrium between co-exisitng phenocrysts, between phenocrysts and matrix, and isotopic zoning within single crystals has been demonstrated in basalts, andesites, dacites, rhyolites and alkaline magmas; in some cases, the range in 87Sr/86Sr among different components in the same rock may equal or exceed the bulk-rock range seen in the entire formation, volcanic center, or province. High-temperature “Snake River type” rhyolites appear to be an exception. Despite the occurrence of Snake River Plain rhyolites in a region of isotopically highly variable crust and mantle, and significant differences from rhyolite unit to rhyolite unit, internally they are near-homogeneous in 87Sr/86Sr. Little or no zoning is found within feldspar phenocrysts, and feldspars within a single unit are tightly grouped. Some units show minor contrasts between phenocrysts and matrix. High temperature rhyolitic magmas possess a unique combination of temperature and melt viscosity. Although they are typically 200°C hotter than common rhyolites, the effect on visocity is offset by lower water contents (~2 wt%), hence their melt viscosities are in the same range as common, water-rich, cool rhyolites (105 - 106 Pa s). Yet magmatic temperatures are in the same range as basaltic andesites and andesites, consequently cation diffusion rates in feldspar are 2 - 3 orders of magnitude greater than in common rhyolites. We hypothesize that this combination of characteristics promotes Sr isotopic homogeneity: high melt viscosities tend to inhibit crystal transfer and mixing of isotopically distinct components on timescales shorter than those required for diffusive homogenization of Sr between phenocrysts and matrix (100 - 1000 years). This is not the case for most magmas, in which either crystal transfer is rapid (<< 100 years) due to low

  20. Magma mixing in a zoned alkalic intrusion

    SciTech Connect

    Price, J.G.; Henry, C.D.; Barker, D.S.; Rubin, J.N.

    1985-01-01

    The Marble Canyon stock is unique among the alkalic intrusions of the Trans-Pecos magmatic province in being zoned from a critically silica-undersaturated rim of alkali gabbro (AG) to a silica-oversaturated core of quartz syenite (QS). Hybrid rocks of intermediate chemical and mineralogical compositions occur between the rim and core. Nepheline-syenite dikes occur only within the AG. Silica-rich dikes of quartz trachyte, pegmatite, and aplite cut the AG, QS, and hybrid rocks. Thermodynamic calculations of silica activity in the magmas illustrate the presence of two trends with decreasing temperature: a silica-poor trend from AG to nepheline syenite and a silica-rich trend from hybrid rocks to QS. Least-square modeling of rock and mineral compositions suggests 1) the nepheline syenites were derived by crystal-liquid fractionation from nearly solidified AG at the rim of the stock, 2) AG magma farther from the rim mixed with a small proportion of granitic magma, and 3) the mixture then differentiated to produce the hybrid rocks and QS. Zirconium dioxide inclusions in plagioclase crystals of the hybrid rocks and QS indicate that the AG magma contained some crystals before it mixed with the granitic magma. Two origins for the granitic magma are possible: 1) a late-stage differentiate of a mantle-derived hypersthene-normative magma and 2) melting of crustal material by the AG magma. Recognition of magma mixing might not have been possible if the AG had been hypersthene-normative.

  1. Electromagnetic imaging of crustal magma bodies

    NASA Astrophysics Data System (ADS)

    Unsworth, M. J.

    2016-12-01

    Magma bodies are the location of a number of important processes that have formed the crust. In a magma chamber, a parent magma differentiates to produce magmas with a range of compositions that may either be erupted, or crystallize to form intrusions. Geological studies of erupted lavas and crystallized magma bodies exposed at the surface have given valuable information about processes occurring in magma bodies. Numerical modelling has given important insights into the complex processes occurring in these bodies. Geophysical studies complement geological observations and give real time images of magma bodies. Seismic studies have delineated a number of magma bodies and can constrain the melt fraction through studies of velocity and attenuation, while geodetic data have detected time variations in size through the associated surface deformation. Electromagnetic (EM) methods offer an alternative view of crustal magmatism. Both magma bodies and associated hydrothermal systems are characterized by electrical resistivity values that are much lower than the surrounding crystalline rock. Magnetotellurics (MT) is one of the most widely used EM methods and can image the subsurface resistivity structure in 3-D using natural EM signals. The resistivity of the magma body depends on the amount, geometry and composition of the melt. Interpretation of the electrical resistivity of partially molten zones was previously quite non-unique. However, when resistivity models are combined with (1) other geophysical data, (2) petrological constrains of melt composition and (3) laboratory measurements of the resistivity of partial melts, the non-uniqueness can be greatly reduced. This presentation will review what can be determined about crustal magma bodies using EM methods. The MT method will be reviewed with an emphasis on which resistivity model features of magmatic and hydrothermal are well resolved by EM surveys. The approach outlined above to reduce the uncertainty in resistivity

  2. Exploring fractionation models for Martian magmas

    NASA Astrophysics Data System (ADS)

    Udry, Arya; Balta, J. Brian; McSween, Harry Y.

    2014-01-01

    primary compositions, i.e., magmas that did not experience fractionation and/or contamination after extraction from the mantle, occur as a subset of Martian meteorites and a few lavas analyzed on the planet's surface by rovers. Eruptions of primary magmas are rare on Earth and presumably on Mars. Previous studies of fractional crystallization of Martian primary magmas have been conducted under isobaric conditions, simulating idealized crystallization in magma chambers. Polybaric fractionation, which occurs during magma ascent, has not been investigated in detail for Martian magmas. Using the MELTS algorithm and the pMELTS revision, we present comprehensive isobaric and polybaric thermodynamic calculations of the fractional crystallization of four primary or parental Martian magmas (Humphrey, Fastball, Y-980459 shergottite, and nakhlite parental melts) using various pressure-temperature paths, oxygen fugacities, and water contents to constrain how these magmas might evolve. We then examine whether known Martian alkaline rock compositions could have formed through fractional crystallization of these magmas under the simulated conditions. We find that isobaric and polybaric crystallization paths produce similar residual melt compositions, but given sufficient details, we may be able to distinguish between them. We calculate that Backstay (Gusev Crater) likely formed by fractionation of a primary magma under polybaric conditions, while Jake_M (Gale Crater) may have formed through melting of a metasomatized mantle, crustal assimilation, or fractional crystallization of an unknown primary magma. The best fits for the Backstay composition indicate that consideration of polybaric crystallization paths can help improve the quality of fit when simulating liquid lines of descent.

  3. Why do Martian Magmas erupt?

    NASA Astrophysics Data System (ADS)

    Balta, J. B.; McSween, H. Y.

    2011-12-01

    Eruption of silicate lava, whether on Earth or another planet, requires that at some depth the melt has lower density than the surrounding rocks. As the densities of silicate liquids change during crystallization, whether a particular silicate liquid will erupt or be trapped at a level of neutral buoyancy is a complex yet fundamental issue for planetary dynamics. In general, 3 factors drive surface eruptions: inherent buoyancy relative to mantle phases, compositional evolution, and volatile contents. These factors manifest on Earth as terrestrial basalts commonly have compositions close to a density minimum [1]. Recent work has produced estimates of Martian parental magma compositions [2-5] based on shergottite meteorites and from Gusev crater. Using the MELTS algorithm [6] and other density calibrations, we simulated evolution of these liquids, focusing on density changes. For much of the crystallization path, density is controlled by FeO. All of the liquids begin with ρ ~ 2.8 g/cc at 1 bar, and the evolution of liquid density is controlled by the liquidus phases. At low pressures, olivine is the liquidus phase for each melt, and as FeO is not incompatible in olivine, olivine crystallization decreases liquid density, increasing buoyancy with crystallization. However, FeO is incompatible in pyroxene, and thus liquids crystallizing pyroxene become denser and less buoyant with crystallization, producing liquids with densities up to and above 3.0 g/cc. As the olivine-pyroxene saturation relationship is affected by pressure and chemistry, the identity of the liquidus phase and density evolution will vary between magmas. Without spreading centers, Mars has no location where the mantle approaches the surface, and it is likely that any magma which is denser than the crust will stall below or within that crust. The crystallization path of a liquid is a function of pressure, with pyroxene crystallizing first at P > 10 kbar (~80 km depth), close to the base of the Martian

  4. Convection and mixing in magma chambers

    NASA Astrophysics Data System (ADS)

    Turner, J. S.; Campbell, I. H.

    1986-08-01

    This paper reviews advances made during the last seven years in the application of fluid dynamics to problems of igneous petrology, with emphasis on the laboratory work with which the authors have been particularly involved. Attention is focused on processes in magma chambers which produce diversity in igneous rocks, such as fractional crystallization, assimilation and magma mixing. Chamber geometry, and variations in the density and viscosity of the magma within it, are shown to play a major role in determining the dynamical behaviour and the composition of the erupted or solidified products. Various convective processes are first reviewed, and in particular the phenomenon of double-diffusive convection. Two types of double-diffusive interfaces between layers of different composition and temperature are likely to occur in magma chambers. A diffusive interface forms when a layer of hot dense magma is overlain by cooler less dense magma. Heat is transported between the layers faster than composition, driving convection in both layers and maintaining a sharp interface between them. If a layer of hot slightly less dense magma overlies a layer of cooler, denser but compositionally lighter magma, a finger interface forms between them, and compositional differences are transported downwards faster than heat (when each is expressed in terms of the corresponding density changes). Processes leading to the establishment of density, compositional and thermal gradients or steps during the filling of a magma chamber are considered next. The stratification produced, and the extent of mixing between the inflowing and resident magmas, are shown to depend on the flow rate and on the relation between the densities and viscosities of the two components. Slow dense inputs of magma may mix very little with resident magma of comparable viscosity as they spread across the floor of the chamber. A similar pulse injected with high upward momentum forms a turbulent "fountain", which is a

  5. Magma Energy Research Project, FY80 annual progress report

    SciTech Connect

    Colp, J.L.

    1982-04-01

    The technical feasibility of extracting energy from magma bodies is explored. Five aspects of the project are studied: resource location and definition, source tapping, magma characterization, magma/material compatibility, and energy extraction.

  6. Taxonomy of Magma Mixing II: Thermochemistry of Mixed Crystal-Bearing Magmas Using the Magma Chamber Simulator

    NASA Astrophysics Data System (ADS)

    Bohrson, W. A.; Spera, F. J.; Neilson, R.; Ghiorso, M. S.

    2013-12-01

    Magma recharge and magma mixing contribute to the diversity of melt and crystal populations, the abundance and phase state of volatiles, and thermal and mass characteristics of crustal magma systems. The literature is replete with studies documenting mixing end-members and associated products, from mingled to hybridized, and a catalytic link between recharge/mixing and eruption is likely. Given its importance and the investment represented by thousands of detailed magma mixing studies, a multicomponent, multiphase magma mixing taxonomy is necessary to systematize the array of governing parameters (e.g., pressure (P), temperature (T), composition (X)) and attendant outcomes. While documenting the blending of two melts to form a third melt is straightforward, quantification of the mixing of two magmas and the subsequent evolution of hybrid magma requires application of an open-system thermodynamic model. The Magma Chamber Simulator (MCS) is a thermodynamic, energy, and mass constrained code that defines thermal, mass and compositional (major, trace element and isotope) characteristics of melt×minerals×fluid phase in a composite magma body-recharge magma-crustal wallrock system undergoing recharge (magma mixing), assimilation, and crystallization. In order to explore fully hybridized products, in MCS, energy and mass of recharge magma (R) are instantaneously delivered to resident magma (M), and M and R are chemically homogenized and thermally equilibrated. The hybrid product achieves a new equilibrium state, which may include crystal resorption or precipitation and/or evolution of a fluid phase. Hundreds of simulations systematize the roles that PTX (and hence mineral identity and abundance) and the mixing ratio (mass of M/mass of R) have in producing mixed products. Combinations of these parameters define regime diagrams that illustrate possible outcomes, including: (1) Mixed melt composition is not necessarily a mass weighted mixture of M and R magmas because

  7. More Evidence for Multiple Meteorite Magmas

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-02-01

    Cosmochemists have identified six main compositional types of magma that formed inside asteroids during the first 100 million years of Solar System history. These magmas vary in their chemical and mineralogical make up, but all have in common low concentrations of sodium and other volatile elements. Our low-sodium-magma diet has now changed. Two groups of researchers have identified a new type of asteroidal magma that is rich in sodium and appears to have formed by partial melting of previously unmelted, volatile-rich chondritic rock. The teams, one led by James Day (University of Maryland) and the other by Chip Shearer (University of New Mexico), studied two meteorites found in Antarctica, named Graves Nunatak 06128 and 06129, using a battery of cosmochemical techniques. These studies show that an even wider variety of magmas was produced inside asteroids than we had thought, shedding light on the melting histories and formation of asteroids.

  8. Depth of origin of magma in eruptions.

    PubMed

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-09-26

    Many volcanic hazard factors--such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses--relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide.

  9. Depth of origin of magma in eruptions

    PubMed Central

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-01-01

    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. PMID:24067336

  10. Gas-driven filter pressing in magmas

    USGS Publications Warehouse

    Sisson, T.W.; Bacon, C.R.

    1999-01-01

    Most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less. The buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization, and this process of gas-driven filter pressing assists the crystallization differentiation of magmas. For gas-driven filter pressing to be effective, the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt These conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs. Gas-driven filter pressing thereby adds fractionated melt to magma bodies. Gas-driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons; this process could also account for the production of voluminous, crystal-poor rhyolites.

  11. Forecasting the failure of heterogeneous magmas

    NASA Astrophysics Data System (ADS)

    Vasseur, J.; Wadsworth, F. B.; Lavallée, Y.; Bell, A. F.; Main, I. G.; Dingwell, D. B.

    2015-12-01

    Eruption prediction is a long-sought-after goal of volcanology. Yet applying existing techniques retrospectively (hindcasting), we fail to predict events more often than we success. As much of the seismicity associated with intermediate to silicic volcanic eruptions comes from the brittle response of the ascending magma itself, we clearly require a good understanding of the parameters that control the ability to forecast magma failure itself. Here, we present suites of controlled experiments at magmatic temperatures using a range of synthetic magmas to investigate the control of microstructures on the efficacy of forecast models for material failure. We find that the failure of magmas with very little microstructural heterogeneity - such as melts - is very challenging to predict; whereas, the failure of very heterogeneous magmas is always well-predicted. To shed further light on this issue, we provide a scaling law based on the relationship between the microstructural heterogeneity in a magma and the error in the prediction of its failure time. We propose this method be used to elucidate the variable success rate of predicting volcanic predictions. We discuss this scaling in the context of the birth, life and death of structural heterogeneity during magma ascent with specific emphasis on obsidian-forming eruptions such as Chaitèn, 2008. During such eruptions, the repetitive creation and destruction of fractures filled with granular magma, which are thought to be the in situ remnants of seismogenic fracturing itself, are expressions of the life-cycle of heterogeneity in an otherwise coherent, melt-rich magma. We conclude that the next generation of failure forecast tools available to monitoring teams should incorporate some acknowledgment of the magma microstructure and not be solely based on the geophysical signals prior to eruption.

  12. Magma chamber dynamics and Vesuvius eruption forecasting

    NASA Astrophysics Data System (ADS)

    Dobran, F.

    2003-04-01

    Magma is continuously or periodically refilling an active volcano and its eruption depends on the mechanical, fluid, thermal, and chemical aspects of the magma storage region and its surroundings. A cyclically loaded and unloaded system can fail from a weakness in the system or its surroundings, and the fluctuating stresses can produce system failures at stress levels that are considerably below the yield strength of the material. Magma in a fractured rock system within a volcano is unstable and propagates toward the surface with the rate depending on the state of the system defined by the inertia, gravity, friction, and permeability parameters of magma and its source region. Cyclic loading and unloading of magma from a reservoir caused by small- or medium-scale eruptions of Vesuvius can produce catastrophic plinian eruptions because of the structural failure of the system and the quiescent periods between these eruptions increase with time until the next eruption cycle which will be plinian or subplinian and will occur with a very high probability this century. Such a system behavior is predicted by a Global Volcanic Simulator of Vesuvius developed for simulating different eruption scenarios for the purpose of urban planning the territory, reducing the number of people residing too close to the cone of the volcano, and providing safety to those beyond about 5 km radius of the crater. The magma chamber model of the simulator employs a thermomechanical model that includes magma inflow and outflow from the chamber, heat and mass transfer between the chamber and its surroundings, and thermoelastoplastic deformation of the shell surrounding the magma source region. These magma chamber, magma ascent, and pyroclastic dispersion models and Vesuvius eruption forecasting are described in Dobran, F., VOLCANIC PROCESSES, Kluwer Academic/Plenum Publishers, 2001, 590 pp.

  13. The Effects of Preeruptive Magma Viscosity on Eruption Styles and Magma Eruption Rates

    NASA Astrophysics Data System (ADS)

    Tomiya, A.; Koyaguchi, T.; Kozono, T.; Takeuchi, S.

    2014-12-01

    We have collected data on magma eruption rate, which is one of the most fundamental parameters for a volcanic eruption. There are several compilations on eruption rates, for example, for Plinian eruptions (Carey and Sigurdsson, 1989), basaltic eruptions (Wadge, 1981), lava dome eruptions (Newhall and Melson, 1983), and all combined (Tomiya and Koyaguchi, 1998; Pyle, 2000). However, they did not quantitatively discuss the effects of magma viscosity, which must control eruption rates. Here, we discuss the effects of magma viscosity on eruption rates, by using 'preeruptive magma viscosities', which are important measures of magma eruptibility (Takeuchi, 2011). Preeruptive magma viscosity is the viscosity of magma (melt, dissolved water, and crystals) in the magma chamber at the preeruptive conditions, and can be approximately obtained only by the bulk rock SiO2 and phenocryst content, using an empirical formula (Takeuchi, 2010). We have found some interesting relationships, such as (1) eruption styles and rates are correlated to preeruptive magma viscosity but not correlated to bulk rock composition, and (2) the gap (ratio) in eruption rates between explosive and effusive phases in a series of eruptions is proportional to preeruptive magma viscosity. We also propose, by combining (1) and (2), that (3) the radius (or width) of volcanic conduit is positively correlated with preeruptive magma viscosity. Our data also show that the eruptive magmas are divided into two types. One is the low-viscosity type (basalt ~ phenocryst-poor andesite), characterized by lava flow and sub-Plinian eruptions. The other is the high-viscosity type (phenocryst-rich andesite ~ rhyolite), characterized by lava dome and Plinian eruptions. The boundary is at about 104 Pa s. These two types may be closely linked to the magma generation processes (fractional/batch crystallization vs. extraction from a mushy magma chamber).

  14. Evidence for seismogenic fracture of silicic magma.

    PubMed

    Tuffen, Hugh; Smith, Rosanna; Sammonds, Peter R

    2008-05-22

    It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of approximately 600 degrees C (ref. 1). This thinking underpins our understanding of volcanic earthquakes, which are assumed to occur in cold rocks surrounding moving magma. However, the recent discovery of abundant brittle-ductile fault textures in silicic lavas has led to the counter-intuitive hypothesis that seismic events may be triggered by fracture and faulting within the erupting magma itself. This hypothesis is supported by recent observations of growing lava domes, where microearthquake swarms have coincided with the emplacement of gouge-covered lava spines, leading to models of seismogenic stick-slip along shallow shear zones in the magma. But can fracturing or faulting in high-temperature, eruptible magma really generate measurable seismic events? Here we deform high-temperature silica-rich magmas under simulated volcanic conditions in order to test the hypothesis that high-temperature magma fracture is seismogenic. The acoustic emissions recorded during experiments show that seismogenic rupture may occur in both crystal-rich and crystal-free silicic magmas at eruptive temperatures, extending the range of known conditions for seismogenic faulting.

  15. Time to Solidify an Ocean of Magma

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-03-01

    Cosmochemists are reasonably sure that a global ocean of magma surrounded the Moon when it formed. This was a monumentally important event in lunar history, forming the primary feldspar-rich crust of the lunar highlands and setting the stage for subsequent melting inside the Moon to make additional crustal rocks. Numerous questions remain about the complex array of processes that could have operated in such a huge amount of magma, and about how long it took to solidify the magma ocean. Alex Nemchin and colleagues at Curtin University of Technology (Australia), Westfailische Wilhelms-Universitat (Munster, Germany), and the Johnson Space Center (Houston, Texas, USA) dated a half-millimeter grain of the mineral zircon (ZrSiO4) in an impact melt breccia from the Apollo 17 landing site. They used an ion microprobe to measure the concentrations of lead and uranium isotopes in the crystal, finding that one portion of the grain recorded an age of 4.417 ± 0.006 billion years. Because zircon does not crystallize until more than 95% of the magma ocean has crystallized, this age effectively marks the end of magma ocean crystallization. Magma ocean cooling and crystallization began soon after the Moon-forming giant impact. Other isotopic studies show that this monumental event occurred 4.517 billion years ago. Thus, the difference between the two ages means that the magma ocean took 100 million years to solidify.

  16. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2004-01-01

    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.

  17. Magma Beneath Yellowstone National park.

    PubMed

    Eaton, G P; Christiansen, R L; Iyer, H M; Pitt, A D; Mabey, D R; Blank, H R; Zietz, I; Gettings, M E

    1975-05-23

    The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a

  18. Magma beneath Yellowstone National Park

    USGS Publications Warehouse

    Eaton, G.P.; Christiansen, R.L.; Iyer, H.M.; Pitt, A.M.; Mabey, D.R.; Blank, H.R.; Zietz, I.; Gettings, M.E.

    1975-01-01

    The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a

  19. Volatiles Which Increase Magma Viscosity

    NASA Astrophysics Data System (ADS)

    Webb, S.

    2015-12-01

    The standard model of an erupting volcano is one in which the viscosity of a decompressing magma increases as the volatiles leave the melt structure to form bubbles. It has now been observed that the addition of the "volatiles" P, Cl and F result in an increase in silicate melt viscosity. This observation would mean that the viscosity of selected degassing magmas would decrease rather than increase. Here we look at P, Cl and F as three volatiles which increase viscosity through different structural mechanisms. In all three cases the volatiles increase the viscosity of peralkaline composition melts, but appear to always decrease the viscosity of peraluminous melts. Phosphorus causes the melt to unmix into a Na-P rich phase and a Na-poor silicate phase. Thus as the network modifying Na (or Ca) are removed to the phosphorus-rich melt, the matrix melt viscosity increases. With increasing amounts of added phosphorus (at network modifying Na ~ P) the addition of further phosphorus causes a decrease in viscosity. The addition of chlorine to Fe-free aluminosilicate melts results in an increase in viscosity. NMR data on these glass indicates that the chlorine sits in salt-like structures surrounded by Na and/or Ca. Such structures would remove network-modifying atoms from the melt structure and thus result in an increase in viscosity. The NMR spectra of fluorine-bearing glasses shows that F takes up at least 5 different structural positions in peralkaline composition melts. Three of these positions should result in a decrease in viscosity due to the removal of bridging oxygens. Two of the structural positons of F, however, should result in an increase in viscosity as they require the removal of network-modifying atoms from the melt structure (with one of the structures being that observed for Cl). This would imply that increasing amounts of F might result in an increase in viscosity. This proposed increase in viscosity with increasing F has now been experimentally confirmed.

  20. Thermal stress fracturing of magma simulant materials

    SciTech Connect

    Wemple, R.P.; Longcope, D.B.

    1986-10-01

    Direct contact heat exchanger concepts for the extraction of energy from magma chambers are being studied as part of the DOE-funded Magma Energy Research Program at Sandia National Laboratories. These concepts require the solidification of molten material by a coolant circulated through a borehole drilled into the magma and subsequent fracture of the solid either as a natural consequence of thermal stress or by deliberate design (intentional flaws, high pressure, etc.). This report summarizes the results of several thermal stress fracturing experiments performed in the laboratory and compares the results with an analysis developed for use as a predictive tool. Information gained from this test series has been the basis for additional work now under way to simulate magma melt solidification processes.

  1. Magma Energy Overview and Status Report

    SciTech Connect

    Dunn, James C.

    1989-03-21

    Up to 500,000 Quads of thermal energy are believed to be contained in crustal magma bodies within the U.S. at temperatures in excess of 600 C and at depths less than 10 km. Scientific feasibility of utilizing this energy resource was concluded after a seven-year study that culminated in successful energy extraction experiments in molten rock at Kilauea Iki lava lake. The current DOE program is developing technology to experimentally extract energy from a silicic magma body so that engineering feasibility of the magma energy concept can be evaluated. At this point, significant progress has been achieved in three areas: Geophysics and site selection. Energy Extraction Processes, and Geochemistry/Materials. Future activities will be focused by drilling and evaluating a deep exploratory well in Long Valley caldera where active magma is expected.

  2. Energy extraction from crustal magma bodies

    SciTech Connect

    Dunn, J.C.

    1982-01-01

    An open heat exchanger system for extracting thermal energy directly from shallow crustal magma bodies is described. The concept relies on natural properties of magma to create a permeable, solidified region surrounding a borehole drilled into the magma chamber. The region is fractured, possessing large surface area, and is sealed from the overburden. Energy is extracted by circulating a fluid through the system. Thermal stress analysis shows that such a fractured region can be developed at depths up to 10 km. An open heat exchanger experiment conducted in the partial melt zone of Kilauea Iki lava lake demonstrated the validity of this concept. Effective heat transfer surface area an order of magnitude greater than the borehole area was established during a two-day test period. The open heat exchanger concept greatly extends the number of magma systems that can be economically developed to produce energy.

  3. Rheology of Halogen-Rich Magmas

    NASA Astrophysics Data System (ADS)

    Webb, S. L.

    2010-12-01

    The degassing of magma as it rises through the volcanic conduit to the surface affects the viscosity and rate of movement of the magma. While the production of bubbles in the magma decreases the density of the magma and thus increases its rate of ascent, the loss of volatiles from the magma, in general, results in an increase in the viscosity. This is the ideal scenario for the deformation rate of the magma crossing the relaxation timescale of the increasingly viscous magma which can result in the shattering of the magma in its unrelaxed (glassy) state; which results in an explosive eruption and pyroclastic flow. The effect of the volatiles H2O and F on magma viscosity and relaxation timescale have been extensively studied; with 1 mol% F2O-1 or H2O causing a 4 to 5 order of magnitude decrease in viscosity at ca. 800 C. Early determinations of the effect of chlorine on melt viscosity, however, indicated that chlorine increases the viscosity of Al-bearing melts (but decreases the viscosity of Al-free synthetic melts). Thus the degassing of chlorine would result in a decrease in magma viscosity and a distancing of the physical condition of the magma from the shattering of the magma as it rises to the surface. The viscosity of chlorine-bearing peralkaline Na2O-CaO-Al2O3-SiO2 melts has been investigated using micro-penetration techniques in the 108 - 1013 Pa s viscosity range. The presence of 0.5 mol% (0.6 wt%) Cl2O-1 increases viscosity by 0.5 log10 units. A similar amount of H2O or F2O-1 would decrease viscosity by 2.5 orders of magnitude in this viscosity range. More information about the relative solubility of Cl, F and H2O as a function of composition, temperature and pressure is needed before one can model the relative effects of degassing volatiles on the rheology of magmas. Very little is known about the structural role of chlorine in silicate melts. NMR studies of Na2O-CaO-Al2O3-SiO2 glasses have shown that chlorine does not bond to Al (in contrast to fluorine

  4. Process for forming hydrogen and other fuels utilizing magma

    DOEpatents

    Galt, John K.; Gerlach, Terrence M.; Modreski, Peter J.; Northrup, Jr., Clyde J. M.

    1978-01-01

    The disclosure relates to a method for extracting hydrogen from magma and water by injecting water from above the earth's surface into a pocket of magma and extracting hydrogen produced by the water-magma reaction from the vicinity of the magma.

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

    NASA Astrophysics Data System (ADS)

    Glazner, A. F.

    2015-12-01

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

  6. Linking enclave formation to magma rheology

    NASA Astrophysics Data System (ADS)

    Hodge, K. F.; Jellinek, A. M.

    2012-10-01

    Magmatic enclaves record the history of deformation and disaggregation (i.e., fragmentation) of relatively hot, compositionally more mafic magmas injected into actively convecting silicic magma chambers through dikes. Enclave size distributions may provide crucial clues for understanding the nature of this mechanical mixing process. Accordingly, we conduct a comprehensive field study to measure enclave size distributions in six Cascade lava flows. Using results from recent fluid dynamics experiments along with thermodynamic and modeling constraints on key physical properties of the injected and host magmas (i.e., temperature, density and effective viscosity), we use the size distributions of enclaves to characterize the magmatic flow regime governing enclave formation. Scaling arguments suggest that the viscous stresses related to magma chamber flow acting against the yield strength of a crystallizing injected magma control the breakup of 1 m-wide mafic dikes into millimeter- to centimeter-scale enclaves. Our data analysis identifies a characteristic length scale of breakup that constrains the yield strength of the injected magmas in a more restrictive way than existing empirical models for yield strength based on crystal content. In all six lava flows, we show that the progressive fragmentation of the injected magma is self-similar and characterized by a fractal dimensionDf ˜ 2, which is comparable to previous studies on enclaves. We also find a small but statistically significant dependence of Df on the effective viscosity ratio between host and enclave magmas, such that large variations in effective viscosity enhance breakup. This work demonstrates that field observations of enclave size distributions can reliably constrain the rheological and flow conditions in which enclaves form.

  7. Describing the chemical character of a magma

    NASA Astrophysics Data System (ADS)

    Duley, Soma; Vigneresse, Jean-Louis; Chattaraj, Pratim K.

    2010-05-01

    We introduce the concepts of hard-soft acid-base (HSAB) and derive parameters to characterize a magma that consists either of a solid rock, a melt or its exsolved gaseous phase. Those parameters are the electronegativity, hardness, electrophilicity, polarisability and optical basicity. They determine the chemical reactivity of each component individually, or its equivalence in the case of a complex system of elements or oxides. This results from equalization methods or from direct computation through density functional theory (DFT). Those global parameters help in characterizing magma, provide insights into the reactivity of the melt or its fluid phase when in contact with another magma, or when considering the affinity of each component for metals. In particular, the description leads to a better understanding on the mechanisms that control metal segregation and transportation during igneous activity. The trends observed during magma evolution, whether they follow a mafic or a felsic trend are also observed using these parameters and can be interpreted as approaching a greater stability. Nevertheless, the trend for felsic magma occurs at constant electrophilicity toward a silica pole of great hardness. Conversely, mafic magmas evolve at a constant hardness and decreasing electrophilicity

  8. Basaltic injections into floored silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Wiebe, R. A.

    Recent studies have provided compelling evidence that many large accumulations of silicic volcanic rocks erupted from long-lasting, floored chambers of silicic magma that were repeatedly injected by basaltic magma. These basaltic infusions are commonly thought to play an important role in the evolution of the silicic systems: they have been proposed as a cause for explosive silicic eruptions [Sparks and Sigurdsson, 1977], compositional variation in ash-flow sheets [Smith, 1979], mafic magmatic inclusions in silicic volcanic rocks [Bacon, 1986], and mixing of mafic and silicic magmas [Anderson, 1976; Eichelberger, 1978]. If, as seems likely, floored silicic magma chambers have frequently been invaded by basalt, then plutonic bodies should provide records of these events. Although plutonic evidence for mixing and commingling of mafic and silicic magmas has been recognized for many years, it has been established only recently that some intrusive complex originated through multiple basaltic injections into floored chambers of silicic magma [e.g., Wiebe, 1974; Michael, 1991; Chapman and Rhodes, 1992].

  9. Final report - Magma Energy Research Project

    SciTech Connect

    Colp, J.L.

    1982-10-01

    Scientific feasibility was demonstrated for the concept of magma energy extraction. The US magma resource is estimated at 50,000 to 500,000 quads of energy - a 700- to 7000-yr supply at the current US total energy use rate of 75 quads per year. Existing geophysical exploration systems are believed capable of locating and defining magma bodies and were demonstrated over a known shallow buried molten-rock body. Drilling rigs that can drill to the depths required to tap magma are currently available and experimental boreholes were drilled well into buried molten rock at temperatures up to 1100/sup 0/C. Engineering materials compatible with the buried magma environment are available and their performances were demonstrated in analog laboratory experiments. Studies show that energy can be extracted at attractive rates from magma resources in all petrologic compositions and physical configurations. Downhole heat extraction equipment was designed, built, and demonstrated successfully in buried molten rock and in the very hot margins surrounding it. Two methods of generating gaseous fuels in the high-temperature magmatic environment - generation of H/sub 2/ by the interaction of water with the ferrous iron and H/sub 2/, CH/sub 4/, and CO generation by the conversion of water-biomass mixtures - have been investigated and show promise.

  10. Hydroxyl speciation in felsic magmas

    NASA Astrophysics Data System (ADS)

    Malfait, Wim J.; Xue, Xianyu

    2014-09-01

    The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by 27Al-1H cross polarization and quantitative 1H MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its 1H NMR partial spectrum was derived from the 27Al-1H cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative 1H NMR spectra. The degree of aluminum avoidance and the relative tendency for Si-O-Si, Si-O-Al and Al-O-Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al-O-Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84-89% and 68-78%, respectively), but with a significant fraction of Al-OH (11-16% and 22-32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH + SiOH) ratio is likely smaller than the Al/(Al + Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al + Si) ratio at higher temperatures.

  11. Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

    NASA Astrophysics Data System (ADS)

    Dahren, Börje; Troll, Valentin R.; Andersson, Ulf B.; Chadwick, Jane P.; Gardner, Màiri F.; Jaxybulatov, Kairly; Koulakov, Ivan

    2012-04-01

    Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2-8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7-12 km, while plagioclase records both shallow crustal (3-7 km) and sub-Moho (23-28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.

  12. Rapid Crystallization of the Bishop Magma

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    Substantial effort has been made to understand the longevity of rhyolitic magmas, and particular attention has been paid to the systems in the Long Valley area (California). Recent geochronological data suggest discrete magma bodies that existed for hundreds of thousands of years. Zircon crystallization ages for the Bishop Tuff span 100-200 ka, and were interpreted to reflect slow crystallization of a liquid-rich magma. Here we use the diffusional relaxation of Ti zoning in quartz to investigate the longevity of the Bishop magma. We have used such an approach to show the short timescales of crystallization of Ti-rich rims on quartz from early- erupted Bishop Tuff. We have now recognized Ti-rich cores in quartz that can be used to derive the timescales of their crystallization. We studied four samples of the early-erupted Bishop. Hand-picked crystals were mounted on glass slides and polished. Cathodoluminescence (CL) images were obtained using the electron microprobe at the University of Chicago. Ti zoning was documented using the GeoSoilEnviroCARS x-ray microprobe at the Advanced Photon Source (Argonne National Lab). Quartz crystals in all 4 samples include up to 3 Ti-bearing zones: a central core (50-100 μm in diameter, ca. 50 ppm Ti), a volumetrically predominant interior (~40 ppm Ti), and in some crystals a 50-100 μm thick rim (50 ppm Ti). Maximum estimates of core residence times were calculated using a 1D diffusion model, as the time needed to smooth an infinitely steep profile to fit the observed profile. Surprisingly, even for the largest crystals studied - ca. 2 mm in diameter - core residence times are less than 1 ka. Calculated growth rates imply that even cm-sized crystals crystallized in less than 10 ka. Crystal size distribution data show that crystals larger than 3 mm are exceedingly rare, such that the important inference is that the bulk of the crystallization of the early-erupted Bishop magma occurred in only a few thousand years. This timescale

  13. Convective Regimes in Crystallizing Basaltic Magma Chambers

    NASA Astrophysics Data System (ADS)

    Gilbert, A. J.; Neufeld, J. A.; Holness, M. B.

    2015-12-01

    Cooling through the chamber walls drives crystallisation in crustal magma chambers, resulting in a cumulate pile on the floor and mushy regions at the walls and roof. The liquid in many magma chambers, either the bulk magma or the interstitial liquid in the mushy regions, may convect, driven either thermally, due to cooling, or compositionally, due to fractional crystallization. We have constructed a regime diagram of the possible convective modes in a system containing a basal mushy layer. These modes depend on the large-scale buoyancy forcing characterised by a global Rayleigh number and the proportion of the chamber height constituting the basal mushy region. We have tested this regime diagram using an analogue experimental system composed of a fluid layer overlying a pile of almost neutrally buoyant inert particles. Convection in this system is driven thermally, simulating magma convection above and within a porous cumulate pile. We observe a range of possible convective regimes, enabling us to produce a regime diagram. In addition to modes characterised by convection of the bulk and interstitial fluid, we also observe a series of regimes where the crystal pile is mobilised by fluid motions. These regimes feature saltation and scouring of the crystal pile by convection in the bulk fluid at moderate Rayleigh numbers, and large crystal-rich fountains at high Rayleigh numbers. For even larger Rayleigh numbers the entire crystal pile is mobilised in what we call the snowglobe regime. The observed mobilisation regimes may be applicable to basaltic magma chambers. Plagioclase in basal cumulates crystallised from a dense magma may be a result of crystal mobilisation from a plagioclase-rich roof mush. Compositional convection within such a mush could result in disaggregation, enabling the buoyant plagioclase to be entrained in relatively dense descending liquid plumes and brought to the floor. The phenocryst load in porphyritic lavas is often interpreted as a

  14. Radiographic visualization of magma dynamics in an erupting volcano

    PubMed Central

    Tanaka, Hiroyuki K. M.; Kusagaya, Taro; Shinohara, Hiroshi

    2014-01-01

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures. PMID:24614612

  15. Radiographic visualization of magma dynamics in an erupting volcano.

    PubMed

    Tanaka, Hiroyuki K M; Kusagaya, Taro; Shinohara, Hiroshi

    2014-03-10

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures.

  16. Pressure of Partial Crystallization of Katla Magmas: Implications for Magma Chamber Depth and for the Magma Plumbing System

    NASA Astrophysics Data System (ADS)

    Tenison, A.; Kelley, D. F.; Barton, M.

    2012-12-01

    Iceland is home to some of the most active volcanoes in the world, and recent eruptions emphasize the need for additional studies to better understand the volcanism and tectonics in this region. Historical patterns of eruptive activity and an increase in seismic activity suggest that Katla is showing signs of an impending eruption. The last major eruption in 1918 caused massive flooding and deposited enough sediment to extend part of Iceland's southern shoreline by 5 km. It also generated sufficient ash over many weeks to cause a brief drop in global temperature. A future eruption similar to the 1918 event could have serious global consequences, including severe disruptions in air travel, short-term global cooling, and shortened growing seasons. Relatively few studies have focused on establishing the depth of the main magma chamber beneath Katla, although knowledge of magma chamber depth is essential for constraining models for magma evolution and for understanding the eruption dynamics of this volcano. The results of seismic and geodetic studies suggest the presence of a shallow magma body at a depth of 2-4 km, but do not provide firm evidence for the presence of deeper chambers in contrast to results obtained for other volcanoes in Iceland. Studies of volcanic ash layers reveal a history of alternating cycles of basaltic and silicic eruptions. We suggest that the shallow magma chamber is primarily the source of silica-rich magma, and postulate that there must be one or more additional chambers in the middle or deep crust that serve as the storage site of the basaltic magma erupted as lava and ash. We have tested this proposal by calculating the pressures of partial crystallization for basalts erupted at Katla using petrological methods. These pressures can be converted to depths and the results provide insight into the likely configuration of the magma plumbing system. Published analyses of volcanic glasses (lava, ash and hyaloclastite) were used as input data

  17. Crystallization kinetics in magmas during decompression

    NASA Astrophysics Data System (ADS)

    Arzilli, Fabio; Burton, Mike; Carroll, Michael R.

    2016-04-01

    Many variables play a role during magma crystallization at depth or in a volcanic conduit, and through experimentally derived constraints we can better understand pre- and syn-eruptive magma crystallization behavior. The thermodynamic properties of magmas have been extensively investigated as a function of T, P, fO2 and magma composition [1], and this allows estimation of the stability of equilibrium phases and physical parameters (e.g., density, viscosity). However, many natural igneous rocks contain geochemical, mineralogical and textural evidence of disequilibrium, suggesting that magmas frequently follow non-equilibrium, time-dependent pathways that are recorded in the geochemical and petrographic characteristics of the rocks. There are currently no suitable theoretical models capable of calculating nucleation and growth rates in disequilibrium conditions without experimental constraints. The aim of this contribution is provide quantitative data on growth and nucleation rates of feldspar crystals in silicate melts obtained through decompression experiments, in order to determine the magma evolution in pre- and sin-eruptive conditions. Decompression is one of the main processes that induce the crystallization of feldspar during the magma ascent in the volcanic conduit. Decompression experiments have been carried out on trachytic and basaltic melts to investigate crystallization kinetics of feldspar as a function of the effect of the degassing, undercooling and time on nucleation and crystal growth process [2; 3]. Furthermore, feldspar is the main crystals phase present in magmas, and its abundance can strongly vary with small changes in pressure, temperature and water content in the melt, implying appreciable variations in the textures and in the crystallization kinetics. Crystallization kinetics of trachytic melts show that long experiment durations involve more nucleation events of alkali feldspar than short experiment durations [2]. This is an important

  18. Vesiculation of basaltic magma during eruption

    USGS Publications Warehouse

    Mangan, Margaret T.; Cashman, Katharine V.; Newman, Sally

    1993-01-01

    Vesicle size distributions in vent lavas from the Pu'u'O'o-Kupaianaha eruption of Kilauea volcano are used to estimate nucleation and growth rates of H2O-rich gas bubbles in basaltic magma nearing the earth's surface (≤120 m depth). By using well-constrained estimates for the depth of volatile exsolution and magma ascent rate, nucleation rates of 35.9 events ⋅ cm-3 ⋅ s-1 and growth rates of 3.2 x 10-4cm/s are determined directly from size-distribution data. The results are consistent with diffusion-controlled growth as predicted by a parabolic growth law. This empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings. In addition, perturbations in the measured size distributions are used to examine bubble escape, accumulation, and coalescence prior to the eruption of magma.

  19. A tale of two magmas, Fuego, Guatemala

    NASA Astrophysics Data System (ADS)

    Berlo, Kim; Stix, John; Roggensack, Kurt; Ghaleb, Bassam

    2012-03-01

    Fuego volcano in Guatemala erupted in 1974 in a basaltic sub-Plinian event, which has been well documented and studied. In 1999, after a period of quiescence lasting 20 years, Fuego erupted again, this time less violently, but with persistent low-level activity. This study investigates the link between these episodes. Previous melt inclusion studies have shown magma erupted in 1974 to have been a volatile-rich hybrid tapped from a vertically extensive system. By contrast, magma erupted in 1999 and 2003 is similar in composition to that erupted in 1974, but melt inclusions are more evolved. Although melt inclusions from the later period are CO2 rich (up to ˜1,500 ppm), they have low H2O concentration (max 1.5 wt.%, compared to ˜6 wt.% in 1974). These melt inclusions have a modified H2O concentration due to diffusive re-equilibration at shallow pressures. Despite this diffusive exchange, both eruptions show evidence of recent mingling of the same low and higher K melts, one of which was slightly cooler than the other and as a result traversed the amphibole stability field. (210Pb/226Ra) data on selected bulk rock samples from 1974 suggest that whereas the cooler, more evolved end-member may have been degassing since the last major eruption in the 1930s, the warmer end-member intruded at most a decade prior to the 1974 eruption. The two end-members are thus batches of the same magma emplaced shallowly ˜30 years apart during which time the older batch was cooled and differentiated before mixing with the younger influx. The presence of the same two melts in the later eruptions suggests that magma in 1999 and 2003 is partly residual from 1974. The current eruptive activity is clearing the system of this residual magma prior to an expected new magma batch.

  20. Volatile transport in subvolcanic magma reservoirs

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Volatiles exsolving from magma reservoirs within magmatic columns play a significant role in their thermo-mechanical state, impacting forthcoming eruptions. The transport of these volatiles across reservoirs and up to the surface is an essential component of volatile cycling between the earth's mantle and atmosphere, and also plays an important role for the formation of ore deposits. We focus here on three fundamental questions (1) how does magmatic vapor migrate in heterogeneous shallow magma reservoirs, (2) how does it influence the evolution of the reservoir itself and (3) what are the physical processes and optimal conditions that allow crystal-rich magma to outgas efficiently and become ultimately dry (< 1 wt% water) as they solidify to form plutons? We approach these questions by investigating the pore-scale fluid dynamics that controls the transport of the vapor in crystal-rich and crystal-poor magmas. We show how the interplay between capillary stresses and the viscosity contrast between the vapor phase and the host melt results in counterintuitive dynamics, whereby the vapor tends to migrate efficiently in crystal-rich parts of a magma reservoir and accumulate in crystal-poor regions. We find that outgassing by permeable buoyant migration is most efficient between 50 and 70 vol. % of crystals for typical magmatic conditions, and that subsequent outgassing is promoted by capillary fracturing to overcome the large capillary stresses. We implement these results in a magma chamber model to test several outgassing scenarios and to assess how macro-scale processes might control the efficiency of gas loss.

  1. Large-volume lateral magma transport from the Mull volcano: An insight to magma chamber processes

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Taylor, Rex N.; Geshi, Nobuo; Mochizuki, Nobutatsu

    2017-04-01

    Long-distance lateral magma transport within the crust has been inferred for various magmatic systems including oceanic island volcanoes, mid-oceanic ridges, and large igneous provinces. However, studying the physical and chemical properties of active fissure systems is difficult. Hence, this study investigates the movement of magma away from the Mull volcano in the North Atlantic Igneous Province, where erosion has exposed its upper crustal dike networks. Magmatic lineations within dikes indicate that the magma flow in the Mull dike suite changed from near vertical to horizontal within 30 km of the volcanic center. This implies that distal dikes were fed by lateral magma transport from Mull. Geochemical characteristics indicate that many <50 km long dikes have deep crustal signatures, reflecting storage and assimilation in Lewisian basement. Following crystallization and assimilation in the lower crust, magma fed an upper crustal reservoir, where further fractionation and incorporation of Moinian rocks generated felsic compositions. Distal dikes are andesitic and reflect events in which large volumes of mafic and felsic magma were combined by mixing between lower and upper crustal reservoirs to generate the 30-80 km3 required to supply the long-distance dikes. Once propagated, compositions along dikes were not significantly affected by assimilation and crystallization. Supplying the distal dikes with magma would have required a large-scale evacuation of the crustal reservoirs that acted as a potential trigger for explosive volcanism and the caldera formation recorded in Mull central complex.

  2. Interdisciplinary Studies of Magma-Tectonic Interactions

    NASA Astrophysics Data System (ADS)

    LaFemina, Peter; Stix, John; Saballos, Armando

    2013-08-01

    The Pan-American Advanced Studies Institute (PASI) Magma-Tectonic Interactions in the Americas brought together researchers, postdoctoral fellows, and graduate students from every country in the Americas with active volcanoes and one participant from Iceland. Lecturers presented the latest geochemical and geophysical approaches to studying magma-tectonic interactions. Participants were introduced to the tectonics and volcanism of Nicaragua through a daylong field trip and given opportunities to collect and analyze their own data, including seismic, geodetic, and geochemical data, at the Cerro Negro volcano.

  3. Evolution and Consequences of Magma Ocean Solidifcation

    NASA Astrophysics Data System (ADS)

    Maurice, Maxime; Tosi, Nicola; Ana-Catalina, Plesa; Breuer, Doris

    2015-04-01

    The various and intense energy sources involved in the early stages of planetary formation, such as kinetic energy of accretion, decay of short-lived radiogenics, release of gravitational potential energy upon core formation, and tidal effects, are thought to have caused partial or possibly entire melting of the mantle of terrestrial planets and moons [Elkins-Tanton2012]. Global or local liquid magma oceans could thus have formed, whose solidification upon planetary cooling could have exerted a significant impact on the differentiation and subsequent evolution of the interior of terrestrial bodies. The solidification of such magma oceans likely proceeds from the bottom upwards because of the steeper slope of the mantle adiabat with respect to the slope of the solidus, and controls the initial compositional stratification of the solid mantle, which, in turn, can play an important role in shaping the earliest forms of mantle convection and surface tectonics. We investigate the thermal evolution of a whole-mantle magma ocean using the finite-volume code Gaia [Huettig2013]. We run two-dimensional simulations of magma ocean cooling and crystallization and investigate in particular the conditions for which the onset of solid-state thermal convection is possible before mantle solidification has completed. We assume an adiabatic temperature profile in the magma ocean and various cooling rates of the surface temperature according to coupled magma ocean-atmosphere models [Lebrun2013]. Upon reaching a critical melt fraction that marks the formation of the so-called rheological front, [Solomatov2007], we self-consistently solve with Gaia the conservation equations of solid-state mantle convection in the partially molten domain assuming a viscosity strongly dependent on temperature and melt content. By varying the reference Rayleigh number and the magma ocean cooling rate, we show that, even for a surface temperature decreasing very rapidly at a rate of 1000 K/Myr, a

  4. Frozen magma lenses below the oceanic crust.

    PubMed

    Nedimović, Mladen R; Carbotte, Suzanne M; Harding, Alistair J; Detrick, Robert S; Canales, J Pablo; Diebold, John B; Kent, Graham M; Tischer, Michael; Babcock, Jeffrey M

    2005-08-25

    The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies.

  5. Iron Redox Systematics of Martian Magmas

    NASA Technical Reports Server (NTRS)

    Righter, K.; Danielson, L.; Martin, A.; Pando, K.; Sutton, S.; Newville, M.

    2011-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite [1]. Morris et al. [1] propose that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks [2,3]. Magnetite stability in terrestrial magmas is well understood, as are the stability of FeO and Fe2O3 in terrestrial magmas [4,5]. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas we have undertaken an experimental study with two emphases. First we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition. Second, we determine the FeO and Fe2O3 contents of the same shergottite bulk composition at 1 bar and variable fO2 at 1250 C, and at variable pressure. These two goals will help define not only magnetite stability, but pyroxene-melt equilibria that are also dependent upon fO2.

  6. Unusual Iron Redox Systematics of Martian Magmas

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  7. Unusual Iron Redox Systematics of Martian Magmas

    SciTech Connect

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

    2012-03-26

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite. Morris et al. proposed that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks. Magnetite stability in terrestrial magmas is well understood, as are the stabilities of FeO and Fe{sub 2}O{sub 3} in terrestrial magmas. In order to better understand the variation of FeO and Fe{sub 2}O{sub 3}, and the stability of magnetite (and other FeO-bearing phases) in martian magmas, we have undertaken an experimental study with two emphases. First, we determine the FeO and Fe{sub 2}O{sub 3} contents of super- and sub-liquidus glasses from a shergottite bulk composition at 1 bar to 4 GPa, and variable fO{sub 2}. Second, we document the stability of magnetite with temperature and fO{sub 2} in a shergottite bulk composition.

  8. Petrology and Physics of Magma Ocean Crystallization

    NASA Technical Reports Server (NTRS)

    Elkins-Tanton, Linda T.; Parmentier, E. M.; Hess, P. C.

    2003-01-01

    Early Mars is thought to have been melted significantly by the conversion of kinetic energy to heat during accretion of planetesimals. The processes of solidification of a magma ocean determine initial planetary compositional differentiation and the stability of the resulting mantle density profile. The stability and compositional heterogeneity of the mantle have significance for magmatic source regions, convective instability, and magnetic field generation. Significant progress on the dynamical problem of magma ocean crystallization has been made by a number of workers. The work done under the 2003 MFRP grant further explored the implications of early physical processes on compositional heterogeneity in Mars. Our goals were to connect early physical processes in Mars evolution with the present planet's most ancient observable characteristics, including the early, strong magnetic field, the crustal dichotomy, and the compositional characteristics of the SNC meteorite's source regions as well as their formation as isotopically distinct compositions early in Mars's evolution. We had already established a possible relationship between the major element compositions of SNC meteorite sources and processes of Martian magma ocean crystallization and overturn, and under this grant extended the analysis to the crucial trace element and isotopic SNC signatures. This study then demonstrated the ability to create and end the magnetic field through magma ocean cumulate overturn and subsequent cooling, as well as the feasibility of creating a compositionally- and volumetrically-consistent crustal dichotomy through mode-1 overturn and simultaneous adiabatic melting.

  9. Geology of magma systems: background and review

    SciTech Connect

    Peterfreund, A.R.

    1981-03-01

    A review of basic concepts and current models of igneous geology is presented. Emphasis is centered on studies of magma generation, ascent, emplacement, evolution, and surface or near-surface activity. An indexed reference list is also provided to facilitate future investigations.

  10. Loki Patera: A Magma Sea Story

    NASA Technical Reports Server (NTRS)

    Veeder, G. J.; Matson, D. L.; Rathbun, A. G.

    2005-01-01

    We consider Loki Patera on Io as the surface expression of a large uniform body of magma. Our model of the Loki magma sea is some 200 km across; larger than a lake but smaller than an ocean. The depth of the magma sea is unknown, but assumed to be deep enough that bottom effects can be ignored. Edge effects at the shore line can be ignored to first order for most of the interior area. In particular, we take the dark material within Loki Patera as a thin solidified lava crust whose hydrostatic shape follows Io's isostatic surface (approx. 1815 km radius of curvature). The dark surface of Loki appears to be very smooth on both regional and local (subresolution) scales. The thermal contrast between the low and high albedo areas within Loki is consistent with the observed global correlation. The composition of the model magma sea is basaltic and saturated with dissolved SO2 at depth. Its average, almost isothermal, temperature is at the liquidus for basalt. Additional information is included in the original extended abstract.

  11. Volcanology: Look up for magma insights

    USGS Publications Warehouse

    Segall, Paul; Anderson, Kyle

    2014-01-01

    Volcanic plumes can be hazardous to aircraft. A correlation between plume height and ground deformation during an eruption of Grímsvötn Volcano, Iceland, allows us to peer into the properties of the magma chamber and may improve eruption forecasts.

  12. Direct Observation of Rhyolite Magma by Drilling: The Proposed Krafla Magma Drilling Project

    NASA Astrophysics Data System (ADS)

    Eichelberger, J. C.; Sigmundsson, F.; Papale, P.; Markusson, S.; Loughlin, S.

    2014-12-01

    Remarkably, drilling in Landsvirkjun Co.'s geothermal field in Krafla Caldera, Iceland has encountered rhyolite magma or hypersolidus rhyolite at 2.1-2.5 km depth in 3 wells distributed over 3.5 km2, including Iceland Deep Drilling Program's IDDP-1 (Mortensen, 2012). Krafla's most recent rifting and eruption (basalt) episode was 1975-1984; deformation since that time has been simple decay. Apparently rhyolite magma was either emplaced during that episode without itself erupting or quietly evolved in situ within 2-3 decades. Analysis of drill cuttings containing quenched melt from IDDP-1 yielded unprecedented petrologic data (Zierenberg et al, 2012). But interpreting active processes of heat and mass transfer requires knowing spatial variations in physical and chemical characteristics at the margin of the magma body, and that requires retrieving core - a not-inconceivable task. Core quenched in situ in melt up to 1150oC was recovered from Kilauea Iki lava lake, Hawaii by the Magma Energy Project >30 years ago. The site from which IDDP-1 was drilled, and perhaps IDDP-1 itself, may be available to attempt the first-ever coring of rhyolite magma, now proposed as the Krafla Magma Drilling Project (KMDP). KMDP would also include geophysical and geochemical experiments to measure the response of the magma/hydrothermal system to fluid injection and flow tests. Fundamental results will reveal the behavior of magma in the upper crust and coupling between magma and the hydrothermal system. Extreme, sustained thermal power output during flow tests of IDDP-1 suggests operation of a Kilauea-Iki-like freeze-fracture-flow boundary propagating into the magma and mining its latent heat of crystallization (Carrigan et al, EGU, 2014). Such an ultra-hot Enhanced Geothermal System (EGS) might be developable beneath this and other magma-heated conventional hydrothermal systems. Additionally, intra-caldera intrusions like Krafla's are believed to produce the unrest that is so troubling in

  13. The mechanics of shallow magma reservoir outgassing

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

  14. Io: Loki Patera as a Magma Sea

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  15. Numerical simulation of magma energy extraction

    SciTech Connect

    Hickox, C.E.

    1991-01-01

    The Magma Energy Program is a speculative endeavor regarding practical utility of electrical power production from the thermal energy which reside in magma. The systematic investigation has identified an number of research areas which have application to the utilization of magma energy and to the field of geothermal energy. Eight topics were identified which involve thermal processes and which are areas for the application of the techniques of numerical simulation. These areas are: (1) two-phase flow of the working fluid in the wellbore, (2) thermodynamic cycles for the production of electrical power, (3) optimization of the entire system, (4) solidification and fracturing of the magma caused by the energy extraction process, (5) heat transfer and fluid flow within an open, direct-contact, heat-exchanger, (6) thermal convection in the overlying geothermal region, (7) thermal convection within the magma body, and (8) induced natural convection near the thermal energy extraction device. Modeling issues have been identified which will require systematic investigation in order to develop the most appropriate strategies for numerical simulation. It appears that numerical simulations will be of ever increasing importance to the study of geothermal processes as the size and complexity of the systems of interest increase. It is anticipated that, in the future, greater emphasis will be placed on the numerical simulation of large-scale, three-dimensional, transient, mixed convection in viscous flows and porous media. Increased computational capabilities, e.g.; massively parallel computers, will allow for the detailed study of specific processes in fractured media, non-Darcy effects in porous media, and non-Newtonian effects. 23 refs., 13 figs., 1 tab.

  16. Deep magma transport at Kilauea volcano, Hawaii

    USGS Publications Warehouse

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

    2006-01-01

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

  17. Outgassing of silicic magma through bubble and fracture networks (Invited)

    NASA Astrophysics Data System (ADS)

    Okumura, S.; Nakamura, M.; Uesugi, K.

    2013-12-01

    Outgassing of magma is a fundamental process that controls the style and explosivity of volcanic eruptions. Vesiculation during the ascent and decompression of magma results in the formation of bubble networks within the magma. The permeable gas escape through the bubble networks is an efficient way to induce the outgassing of silicic magma (Eichelberger et al., 1986). To understand magma ascent dynamics and predict the style and explosivity of eruptions, it is necessary to constrain the rate of magma outgassing as the magma ascends in a volcanic conduit. However, the gas permeability of natural samples should not be considered, because it reflects complicated processes involving vesiculation, deformation, outgassing, and compaction. Experimental studies have demonstrated that vesiculation and compaction processes show hysteresis behavior (Okumura et al., 2013). Thus, we have performed experiments to simulate magma decompression and the deformation of vesicular magmas (e.g., Okumura et al., 2009, 2012). A series of decompression and deformation experiments indicates that the gas permeability is less than the order of 10-15 m2 for isotropic vesiculation at vesicularity <60-80 vol%. When magma ascent is simulated with shear deformation, the gas permeability is much greater than that observed under isotropic conditions. Akin to bubble networks, permeable networks consisting of shear-induced brittle fractures are thought to be efficient outgassing pathways (Gonnermann and Manga, 2003). Our recent experiments demonstrated that fractured magma has a higher gas permeability than vesicular magma at least at vesicularities <~40 vol%. This indicates that fracture networks in magma become efficient parts for the outgassing. However, as shear fracturing results from high strain rates in highly viscous magma, outgassing via fracture networks can be enhanced in localized shear zones and shallow parts of the conduit. The permeable bubble and fracture networks are preferentially

  18. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2000-01-01

    The research described in this progress report involved the study of petrological, geochemical and volcanic processes that occur on the Moon and the SNC 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 role of volatiles in magmatic processes and on processes of magma evolution on these planets. The work on the lunar volcanic glasses has resulted in some exciting new discoveries over the years of this grant. During the tenure of the present grant, we discovered a variety of metal blebs in the A17 orange glass. Some of these Fe-Ni metal blebs occur in the glass; others were found in olivine phenocrysts which we find make up about 2 vol % 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 which drove the lunar fire-fountaining. In an Undergraduate senior thesis project, Nora Klein discovered a melt inclusion that remained in a glassy state in one of the olivine phenocrysts. Analyses of this inclusion gave additional information on the CO2, CO and S contents of the orange glass magma prior to its reaching the lunar surface. The composition of lunar volcanic gases has long been one of the puzzles of lunar magmatic processes. One of the more exciting findings in our research over the past year has been the study of magmatic processes linking the SNC meteorite source magma composition with the andesitic composition rocks found at the Pathfinder site. In this project, graduate student Michelle Minitti showed that there was a clear petrologic link between these two magma types via fractional removal of crystals from the SNC parent melt, but the process only worked if there was at least 1 wt

  19. Magma Dynamics in Dome-Building Volcanoes

    NASA Astrophysics Data System (ADS)

    Kendrick, J. E.; Lavallée, Y.; Hornby, A. J.; Schaefer, L. N.; Oommen, T.; Di Toro, G.; Hirose, T.

    2014-12-01

    The frequent and, as yet, unpredictable transition from effusive to explosive volcanic behaviour is common to active composite volcanoes, yet our understanding of the processes which control this evolution is poor. The rheology of magma, dictated by its composition, porosity and crystal content, is integral to eruption behaviour and during ascent magma behaves in an increasingly rock-like manner. This behaviour, on short timescales in the upper conduit, provides exceptionally dynamic conditions that favour strain localisation and failure. Seismicity released by this process can be mimicked by damage accumulation that releases acoustic signals on the laboratory scale, showing that the failure of magma is intrinsically strain-rate dependent. This character aids the development of shear zones in the conduit, which commonly fracture seismogenically, producing fault surfaces that control the last hundreds of meters of ascent by frictional slip. High-velocity rotary shear (HVR) experiments demonstrate that at ambient temperatures, gouge behaves according to Byerlee's rule at low slip velocities. At rock-rock interfaces, mechanical work induces comminution of asperities and heating which, if sufficient, may induce melting and formation of pseudotachylyte. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The bulk composition, mineralogy and glass content of the magma all influence frictional behaviour, which supersedes buoyancy as the controlling factor in magma ascent. In the conduit of dome-building volcanoes, the fracture and slip processes are further complicated: slip-rate along the conduit margin fluctuates. The shear-thinning frictional melt yields a tendency for extremely unstable slip thanks to its pivotal position with regard to the glass transition. This thermo-kinetic transition bestows the viscoelastic melt with the ability to either flow or

  20. Fractionation of a Basal Magma Ocean

    NASA Astrophysics Data System (ADS)

    Laneuville, M.; Hernlund, J. W.; Labrosse, S.

    2014-12-01

    Earth's magnetic field is thought to be sustained by dynamo action in a convecting metallic outer core since at least 3.45 Ga (Tarduno et al., 2010). Convection induces an isentropic temperature gradient that drains 13±3 TW of heat from the core by thermal conduction (de Koker et al., 2012; Pozzo et al., 2012; Gomi et al., 2013), and suggests that Earth's core has cooled by ˜1,000 K or more since Earth's formation (Gomi et al., 2013). However, models of Earth's initial thermal evolution following a giant-impact predict rapid cooling to the mantle melting temperature (e.g., Solomatov, 2007). In order to understand how the core could have retained enough heat to explain the age of the geodynamo, we relax a key assumption of the basal magma ocean model of (Labrosse et al., 2007) to allow for the possibility that the magma is stably stratified. Recent giant impact simulations suggest extensive core-mantle mixing (Saitoh and Makino, 2013), which could have produced such a large stratified magma layer at the core-mantle boundary. In the presence of a stable density gradient, heat transfer through the basal magma ocean occurs through conduction and therefore delays heat loss from the core. Partitioning of iron in the liquid phase upon crystallization changes the density profile and triggers convection in the upper part of the basal magma ocean. Our hypothesis suggests that early core cooling is dominated by the diffusion timescale through the basal magma ocean, and predicts a delayed onset of the geodynamo (i.e, during the late Headean/early Archean). This model can therefore be falsified if the existence of a geomagnetic field can be inferred from magnetization of inclusions in Hadean zircons. N. de Koker et al., Proc. Natl. Acad. Sci. 190, 4070-4073 (2012).H. Gomi et al., Phys. Earth Planet. Inter. 224, 88-103 (2013).S. Labrosse et al., Nature 450, 866-869 (2007).M. Pozzo et al., Nature 485, 355-358 (2012).T. Saitoh and J. Makino. Astrophys. J. 768, 44 (2013).V

  1. Deformation-induced magma degassing (Invited)

    NASA Astrophysics Data System (ADS)

    Caricchi, L.; Pommier, A.; Pistone, M.; Castro, J. M.; Burgisser, A.

    2009-12-01

    The style and rate of magma degassing during its rise in volcanic conduits controls the eruptive behavior of volcanoes. For example, the transition from extremely explosive to an effusive eruption of lava, as observed recently at Chaitén volcano, Chile, may be the consequence of efficient degassing of highly viscous magmas through a permeable bubble network. Magma experiences extensive shear deformation along conduit walls during its rise to the surface, which could enhance gas bubble coalescence and favor degassing of magma at depth. We performed a series of simple shear deformation experiments using an internally heated Paterson-type apparatus, on bubbly magmas at 100 MPa confining pressure and temperatures between 823 and 873K. Crystal free silicate-melt of tephri-phonolitic composition containing about 15 vol.% H2O-pressurized bubbles was used for the experiments. The experimental products were analyzed both in two and three-dimensions using an optical microscope and a X-ray nanotomographer respectively. The water content of the starting material and the deformed samples was measured by infrared spectroscopy (FTIR). The analyses of the samples after deformation show that simple shear enhances bubble coalescence and degassing, especially at high strain (gamma~10, about 2.5 rotations). The water content of the deformed glasses is equal to the starting material at relatively low gamma (~2) while it decreases dramatically at high strain, to a value (~0.1 wt.%) much lower than the H2O-saturation limit at 100 MPa (~4.2 wt.%). An additional static experiment was performed for the same duration as the high strain experiment to check if the samples were degassing with time. The FTIR analyses confirmed that the bulk water content of the sample remains constant in the absence of shear and over the timescale of the high strain experiments. The observation that the residual water content is lower than 100 MPa-saturation value, indicates that the degassing process is not

  2. Laguna del Maule magma feeding system and construction of a shallow silicic magma reservoir

    NASA Astrophysics Data System (ADS)

    Cáceres, Francisco; Castruccio, Ángelo; Parada, Miguel; Scheu, Bettina

    2017-04-01

    Laguna del Maule Volcanic Field is composed by at least 130 basaltic-to-rhyolitic eruptive vents that erupted more than 350 km3 of lavas and pyroclasts since Pleistocene in the Chilean Andes. It has captivated attention because of its current high accelerated uplift suggested to be formed by a growing shallow rhyolitic magma reservoir beneath the zone of deformation. Studying six Holocene post-glacial andesitic-to-rhyolitic lavas and one dome that partially overlap the ground-inflation zone, we determined the architecture and steps of construction of the magma feeding system that generated its post-glacial effusive volcanism. Further we suggest a possible origin for the rhyolitic magma that generated the ring of rhyolites encircling the lake and remain active causing the uplift. Mineral chemistry and textures suggest the same provenance of magma for the studied units, as well as complex magmatic history before eruptions. Similar temperatures, pressures, H2O and fO2 conditions for amphibole crystallisation in first stages indicate a common ˜17 km deep original reservoir that differentiated via in-situ crystallisation. The chemistry of the amphiboles present in all not-rhyolitic units shows trends that indicate a temperature domain on their crystallisation over other thermodynamic parameters such as pressure, water activity or chemistry of co-crystallising phases. All this supports a mush-like reservoir differentiating interstitial magma while crystallisation occurs. P-T conditions for amphibole crystallisation indicate that only amphiboles from rhyodacites show a non-adiabatic decompression that give rise to a polybaric and polythermal evolution trend from ˜450-200 MPa and ˜1030-900 ˚ C. In addition, unbuffered fO2 conditions were calculated for rhyodacite amphibole crystallisation upon cooling from melts with rather constant H2O contents. We propose that a large part of these rhyodacite amphiboles were formed during a non-adiabatic magma ascent similar to that

  3. Thermomechanics of Triggering the Eruption of Large Magma Reservoirs: The Effects of Buoyancy and Magma Recharge

    NASA Astrophysics Data System (ADS)

    Gregg, P. M.; Grosfils, E. B.; de Silva, S. L.

    2014-12-01

    The evacuation of large silicic magma reservoirs via catastrophic caldera forming eruptions that emplace 100s to 1000s of km3 of material is a devastating and rare natural disaster on Earth. Given the destructive nature of these eruptions, it is critical to better understand the evolution of large silicic systems and what parameters are responsible for either maintaining magma in storage conditions or triggering an eruption. The formation of large, shallow magma bodies requires thermal maturation of the upper crust through elevated magma fluxes over periods of 104-106 years. Once the crust is thermally primed, the viscoelastic response of the host rock buffers the reservoir and stifles the generation of significant overpressure, thus accommodating the accumulation of large magma volumes (103-104 km3). Given that overpressures are difficult to generate in magma reservoirs of this size, increasing attention has been focused on better understanding what mechanisms may trigger their eruption. Recent analytical models suggest that buoyancy may play a critical role in generating the necessary overpressures to trigger eruption of the largest systems. We build upon these findings and utilize numerical models to quantify overpressure generation due to buoyancy and magmatic recharge. Furthermore, the interplay between reservoir growth and fault formation is explored to determine whether eruption triggering is most likely to occur due to fault development within the overlying roof or due to rupture at the reservoir boundary. Specifically, we utilize viscoelastic finite element models with Mohr-Coulomb and von Mises failure criteria to explore foundering in the roof and failure development at the reservoir boundary during buoyant magma recharge. Presented results will compare temperature- and non-temperature dependent viscosities with elastic models to investigate end-member controls on fault formation and reservoir rupture.

  4. Krafla Magma Testbed: An International Project Crossing The Scientific Frontier From Geothermal System Into Magma

    NASA Astrophysics Data System (ADS)

    Eichelberger, J. C.; Dingwell, D. B.; Ludden, J. N.; Mandeville, C. W.; Markusson, S.; Papale, P.; Sigmundsson, F.

    2016-12-01

    Few Earth regimes are subject to as much inference and as little direct knowledge as magma. Among the most important mysteries is the transition from hydrothermal to magmatic, i.e. from aqueous fluid-present to silicate melt-present, regimes. Because solid rock is ductile at near-solidus temperature, fractures should have fleeting existence and therefore heat transfer should be by conduction. Heat and mass transport across this zone influences evolution of magma bodies. The hydrothermal regime influences eruptive behavior when magma intrudes it and propagation of the transition zone toward magma is demonstrated by physical and chemical evidence. Both drilling observations and heat-balance considerations indicate that the melt- and fluid-absent transition zone is thin. Drilling of Iceland Deep Drilling Project's IDDP-1, 2 km into Krafla Caldera, showed that the transition from deep-solidus fine-grained granite to liquidus rhyolite is less than 30 m thick, probably much less. For the first time, we have the opportunity to interrogate an entire system of heat and mass transport, from magmatic source through the hydrothermal zone to surface volcanism, and in so doing unite the disciplines of volcanology and geothermal energy. With support from industry, national geoscience agencies, community stakeholders, and the International Continental Scientific Drilling Program (ICDP), we are developing a broad program to push the limits of knowledge and technology in extremely hot Earth. We use the term "testbed" for two reasons: Surface and borehole observations used in volcano monitoring and geothermal exploration will be tested and reinterpreted in light of the first "ground-truth" about magma. More than "observing", magma and the transition zone will be manipulated through fluid injection and extraction to understand time-dependent behavior. Sensor technology will be pushed to measure magmatic conditions directly. Payoffs are in fundamental planetary science, volcano

  5. The location and timing of magma degassing during Plinian eruptions

    NASA Astrophysics Data System (ADS)

    Giachetti, T.; Gonnermann, H. M.

    2014-12-01

    Water is the most abundant volatile species in explosively erupting silicic magmas and significantly affects magma viscosity, magma fragmentation and the dynamics of the eruption column. The effect that water has on these eruption processes can be modulated by outgassing degassing from a permeable magma. The magnitude, rate and timing of outgassing during magma ascent, in particular in relation to fragmentation, remains a subject of debate. Here we constrain how much, how fast and where the erupting magma lost its water during the 1060 CE Plinian phase of the Glass Mountain eruption of Medicine Lake Volcano, California. Using thermogravimetric analysis coupled with numerical modeling, we show that the magma lost >90% of its initial water upon eruption. Textural analyses of natural pumices, together with numerical modeling of magma ascent and degassing, indicate that 65-90% of the water exsolved before fragmentation, but very little was able to outgas before fragmentation. The magma attained permeability only within about 1 to 10 seconds before fragmenting and during that time interval permeable gas flow resulted in only a modest amount of gas flux from the un-fragmented magma. Instead, most of the water is lost shortly after fragmentation, because gas can escape rapidly from lapilli-size pyroclasts. This results in an efficient rarefaction of the gas-pyroclast mixture above the fragmentation level, indicating that the development of magma permeability and ensuing permeable outgassing are a necessary condition for sustain explosive eruptions of silicic magma. Magma permeability is thus a double-edged sword, it facilitates both, the effusive and the explosive eruption of silicic magma.

  6. Magma vesiculation and pyroclastic volcanism on Venus

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Head, J. W.; Wilson, L.

    1982-01-01

    Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO2 is the primary magmatic volatile. However, the high surface atmospheric pressure (about 90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5-4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

  7. Magma vesiculation and pyroclastic volcanism on Venus

    NASA Astrophysics Data System (ADS)

    Garvin, J. B.; Head, J. W.; Wilson, L.

    1982-11-01

    Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO2 is the primary magmatic volatile. However, the high surface atmospheric pressure (about 90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5-4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

  8. Magma in forearcs: implication for ophiolite generation

    NASA Astrophysics Data System (ADS)

    Jakeŝ, Petr; Miyake, Yasuyuki

    1984-07-01

    Forearc areas ("non-volcanic" arcs) of contemporary island arcs at convergent plate boundaries contain magmatic rocks. Geological evidence, seismic profiles, heat flow data, density considerations and petrological and geochemical arguments suggest that a forearc tholeiitic association (FAT) (containing high-Mg calc-alkaline andesites) is present in "non-volcanic" arcs at some stage of island-arc development. The fractionated, as well as primitive magma, is unable to penetrate low-density sediments and underplates thick piles of unconsolidated accreting rocks. The underplating causes upwelling. The occurrence of magma in forearcs provides an alternative interpretation for the tectonic setting of some ophiolitic masses. Rather than "ocean-ridge formation" and later "obduction" it offers an autochthonous (island-arc bound and geologically-substantiated) interpretation for the ophiolite suite.

  9. Magma Oceans on Exoplanets and Early Earth

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, Linda

    2009-09-01

    Late, giant accretionary impacts likely form multiple magma oceans of some depth in young rocky planets. Models of magma ocean solidification that incorporate water, carbon, and other incompatible volatile elements in small amounts predict a range of first-order outcomes important to planetary evolution. First, initial planetary bulk composition and size determine the composition of the earliest degassed atmosphere. This early atmosphere appears in a rapid burst at the end of solidification, determined by the ability of nucleating bubbles to reach the surface. Larger planets will have briefer and more catastrophic atmospheric degassing during solidification of any magma ocean. Second, this early atmosphere is sufficiently insulating to keep the planetary surface hot for millions of years. Depending upon the atmospheric composition and temperature structure these hot young planets may be observable from Earth or from satellites. Third, small but significant quantities of volatiles remain in the planet's solid mantle, encouraging convection, plate tectonics, and later atmospheric degassing through volcanism. A critical outcome of magma ocean solidification is the development of a solid mantle density gradient with den-sity increasing with radius, which will flow to gravitational stability. Shallow, dense, damp material will carry its water content as it sinks into the perovskite stability zone and transforms into perovskite. Even in models with very low initial water contents, a large fraction of the sinking upper mantle material will be forced to dewater as it crosses the boundary into the relatively dry lower mantle, leaving its water behind in a rapid flux as it sinks. This water ad-dition could initiate or speed convection in planets in which perovskite is stable, that is, planets larger than Mars.

  10. Yamato 980459: Crystallization of Martian Magnesian Magma

    NASA Technical Reports Server (NTRS)

    Koizumi, E.; Mikouchi, T.; McKay, G.; Monkawa, A.; Chokai, J.; Miyamoto, M.

    2004-01-01

    Recently, several basaltic shergottites have been found that include magnesian olivines as a major minerals. These have been called olivinephyric shergottites. Yamato 980459, which is a new martian meteorite recovered from the Antarctica by the Japanese Antarctic expedition, is one of them. This meteorite is different from other olivine-phyric shergottites in several key features and will give us important clues to understand crystallization of martian meteorites and the evolution of Martian magma.

  11. Pressure waves in a supersaturated bubbly magma

    USGS Publications Warehouse

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

    2011-01-01

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

  12. Permeable Gas Flow Influences Magma Fragmentation Speed.

    NASA Astrophysics Data System (ADS)

    Richard, D.; Scheu, B.; Spieler, O.; Dingwell, D.

    2008-12-01

    Highly viscous magmas undergo fragmentation in order to produce the pyroclastic deposits that we observe, but the mechanisms involved remain unclear. The overpressure required to initiate fragmentation depends on a number of physical parameters, such as the magma's vesicularity, permeability, tensile strength and textural properties. It is clear that these same parameters control also the speed at which a fragmentation front travels through magma when fragmentation occurs. Recent mathematical models of fragmentation processes consider most of these factors, but permeable gas flow has not yet been included in these models. However, it has been shown that permeable gas flow through a porous rock during a sudden decompression event increases the fragmentation threshold. Fragmentation experiments on natural samples from Bezymianny (Russia), Colima (Mexico), Krakatau (Indonesia) and Augustine (USA) volcanoes confirm these results and suggest in addition that high permeable flow rates may increase the speed of fragmentation. Permeability from the investigated samples ranges from as low as 5 x 10-14 to higher than 9 x 10- 12 m2 and open porosity ranges from 16 % to 48 %. Experiments were performed for each sample series at applied pressures up to 35 MPa. Our results indicate that the rate of increase of fragmentation speed is higher when the permeability is above 10-12 m2. We confirm that it is necessary to include the influence of permeable flow on fragmentation dynamics.

  13. Native gold in Hawaiian alkalic magma

    USGS Publications Warehouse

    Sisson, T.W.

    2003-01-01

    Native gold found in fresh basanite glass from the early submarine phase of Kilauea volcano, Hawaii, may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle-derived magma. The gold-bearing glass is a grain in bedded volcanic glass sandstone (Japan Marine Science and Technology Center (JAMSTEC) sample S508-R3) collected by the submersible Shinkai 6500 at 3879 m depth off Kilauea's south flank. Extensive outcrops there expose debris-flow breccias and sandstones containing submarine-erupted alkalic rock fragments and glasses from early Kilauea. Precipitation of an immiscible gold liquid resulted from resorption of magmatic sulfides during crystallization-differentiation, with consequent liberation of sulfide-hosted gold. Elevated whole-rock gold concentrations (to 36 ppb) for fresh lavas and clasts from early Kilauea further show that some magmas erupted at the beginning stages of Hawaiian shield volcanoes were distinctly gold rich, most likely owing to limited residual sulfide in their mantle source. Alkalic magmas at other ocean islands may also be gold rich, and oceanic hot-spot provinces may contain underappreciated gold resources.

  14. Voluminous granitic magmas from common basaltic sources

    USGS Publications Warehouse

    Sisson, T.W.; Ratajeski, K.; Hankins, W.B.; Glazner, A.F.

    2005-01-01

    Granitic-rhyolitic liquids were produced experimentally from moderately hydrous (1.7-2.3 wt% H2O) medium-to-high K basaltic compositions at 700 MPa and f O2 controlled from Ni-NiO -1.3 to +4. Amount and composition of evolved liquids and coexisting mineral assemblages vary with fO2 and temperature, with melt being more evolved at higher fO2s, where coexisting mineral assemblages are more plagioclase- and Fe-Ti oxide-rich and amphibole-poor. At fO2 of Ni-NiO +1, typical for many silicic magmas, the samples produce 12-25 wt% granitic-rhyolitic liquid, amounts varying with bulk composition. Medium-to-high K basalts are common in subduction-related magmatic arcs, and near-solidus true granite or rhyolite liquids can form widely, and in geologically significant quantities, by advanced crystallization-differentiation or by low-degree partial remelting of mantle-derived basaltic sources. Previously differentiated or weathered materials may be involved in generating specific felsic magmas, but are not required for such magmas to be voluminous or to have the K-rich granitic compositions typical of the upper continental crust. ?? Springer-Verlag 2005.

  15. Viscosity of mafic magmas at high pressures

    NASA Astrophysics Data System (ADS)

    Cochain, B.; Sanloup, C.; Leroy, C.; Kono, Y.

    2017-01-01

    While it is accepted that silica-rich melts behave anomalously with a decrease of their viscosity at increased pressures (P), the viscosity of silica-poor melts is much less constrained. However, modeling of mantle melts dynamics throughout Earth's history, including the magma ocean era, requires precise knowledge of the viscous properties of silica-poor magmas. We extend here our previous measurements on fayalite melt to natural end-members pyroxenite melts (MgSiO3 and CaSiO3) using in situ X-ray radiography up to 8 GPa. For all compositions, viscosity decreases with P, rapidly below 5 GPa and slowly above. The magnitude of the viscosity decrease is larger for pyroxene melts than for fayalite melt and larger for the Ca end-member within pyroxene melts. The anomalous viscosity decrease appears to be a universal behavior for magmas up to 13 GPa, while the P dependence of viscosity beyond this remains to be measured. These results imply that mantle melts are very pervasive at depth.

  16. Volatile content of Hawaiian magmas and volcanic vigor

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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

  17. Geochemical Evidence for a Terrestrial Magma Ocean

    NASA Technical Reports Server (NTRS)

    Agee, Carl B.

    1999-01-01

    The aftermath of phase separation and crystal-liquid fractionation in a magma ocean should leave a planet geochemically differentiated. Subsequent convective and other mixing processes may operate over time to obscure geochemical evidence of magma ocean differentiation. On the other hand, core formation is probably the most permanent, irreversible part of planetary differentiation. Hence the geochemical traces of core separation should be the most distinct remnants left behind in the mantle and crust, In the case of the Earth, core formation apparently coincided with a magma ocean that extended to a depth of approximately 1000 km. Evidence for this is found in high pressure element partitioning behavior of Ni and Co between liquid silicate and liquid iron alloy, and with the Ni-Co ratio and the abundance of Ni and Co in the Earth's upper mantle. A terrestrial magma ocean with a depth of 1000 km will solidify from the bottom up and first crystallize in the perovskite stability field. The largest effect of perovskite fractionation on major element distribution is to decrease the Si-Mg ratio in the silicate liquid and increase the Si-Mg ratio in the crystalline cumulate. Therefore, if a magma ocean with perovskite fractionation existed, then one could expect to observe an upper mantle with a lower than chondritic Si-Mg ratio. This is indeed observed in modern upper mantle peridotites. Although more experimental work is needed to fully understand the high-pressure behavior of trace element partitioning, it is likely that Hf is more compatible than Lu in perovskite-silicate liquid pairs. Thus, perovskite fractionation produces a molten mantle with a higher than chondritic Lu-Hf ratio. Arndt and Blichert-Toft measured Hf isotope compositions of Barberton komatiites that seem to require a source region with a long-lived, high Lu-Hf ratio. It is plausible that that these Barberton komatiites were generated within the majorite stability field by remelting a perovskite

  18. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C. J.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-08-01

    In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be

  19. The Magma Chamber Simulator: Modeling Compositional, Temperature and Mass Variations in a Composite Magma-Wallrock System

    NASA Astrophysics Data System (ADS)

    Bohrson, W. A.; Spera, F. J.; Creamer, J. B.; Ghiorso, M. S.

    2012-12-01

    Elucidation of the spectrum of compositional and mineralogical characteristics that can be generated by assimilation-fractional crystallization (AFC) contributes to the goal of defining the thermal and mass characteristics required to develop and maintain magma storage and transport systems in a range of tectonic settings. The Magma Chamber Simulator (MCS) utilizes the thermodynamic functionality of MELTS (Ghiorso & Sack 1995) to assess thermal, compositional and mass variations that develop in a composite magma-wallrock (M-WR) system undergoing AFC. Wallrock of defined initial conditions (e.g., PTX) heats up and potentially melts as magma cools and crystallizes. Energy balance is maintained between magma and wallrock and informs the thermal condition of wallrock, which dictates the amount and composition of anatectic melt that is incorporated into magma. As magma cools through a defined T path, output includes thermal, mass, compositional, and physical parameters for melt and solids in magma and wallrock. The simulation is complete when thermal equilibrium between magma and wallrock is achieved. Key parameters that impact the bulk composition and mineralogy of magma undergoing AFC include the initial wallrock to magma mass ratio, wallrock initial T, and initial compositions of magma and wallrock. While other system parameters are held constant, assimilation of lherzolite vs. granite by high-alumina basalt (HAB) yields differences in the total mass of anatectic melt at thermal equilibrium (e.g., 4 vs. 12% of starting magma mass, respectively) but magma SiO2 range is similar (51-53 wt. %). Thus, basaltic samples with similar Si contents can have different assimilation histories and thus manifest different trace element/isotopic characteristics; caution is therefore required when interpreting the origin of compositional heterogeneity of basalts. Initial mass of wallrock impacts magma chemical evolution as illustrated by two cases in a HAB-granite M-WR system in which

  20. Oxidized sulfur-rich mafic magma at Mount Pinatubo, Philippines

    USGS Publications Warehouse

    de Hoog, J.C.M.; Hattori, K.H.; Hoblitt, R.P.

    2004-01-01

    Basaltic fragments enclosed in andesitic dome lavas and pyroclastic flows erupted during the early stages of the 1991 eruption of Mount Pinatubo, Philippines, contain amphiboles that crystallized during the injection of mafic magma into a dacitic magma body. The amphiboles contain abundant melt inclusions, which recorded the mixing of andesitic melt in the mafic magma and rhyolitic melt in the dacitic magma. The least evolved melt inclusions have high sulfur contents (up to 1,700 ppm) mostly as SO42, which suggests an oxidized state of the magma (NNO + 1.4). The intrinsically oxidized nature of the mafic magma is confirmed by spinel-olivine oxygen barometry. The value is comparable to that of the dacitic magma (NNO + 1.6). Hence, models invoking mixing as a means of releasing sulfur from the melt are not applicable to Pinatubo. Instead, the oxidized state of the dacitic magma likely reflects that of parental mafic magma and the source region in the sub-arc mantle. Our results fit a model in which long-lived SO2 discharge from underplated mafic magma accumulated in the overlying dacitic magma and immiscible aqueous fluids. The fluids were the most likely source of sulfur that was released into the atmosphere during the cataclysmic eruption. The concurrence of highly oxidized basaltic magma and disproportionate sulfur output during the 1991 Mt. Pinatubo eruption suggests that oxidized mafic melt is an efficient medium for transferring sulfur from the mantle to shallow crustal levels and the atmosphere. As it can carry large amounts of sulfur, effectively scavenge sulfides from the source mantle and discharge SO2 during ascent, oxidized mafic magma forms arc volcanoes with high sulfur fluxes, and potentially contributes to the formation of metallic sulfide deposits. ?? Springer-Verlag 2003.

  1. Magma deformation and emplacement in rhyolitic dykes

    NASA Astrophysics Data System (ADS)

    McGowan, Ellen; Tuffen, Hugh; James, Mike; Wynn, Peter

    2016-04-01

    Silicic eruption mechanisms are determined by the rheological and degassing behaviour of highly-viscous magma ascending within shallow dykes and conduits. However, we have little knowledge of how magmatic behaviour shifts during eruptions as dykes and conduits evolve. To address this we have analysed the micro- to macro-scale textures in shallow, dissected rhyolitic dykes at the Tertiary Húsafell central volcano in west Iceland. Dyke intrusion at ~3 Ma was associated with the emplacement of subaerial rhyolitic pyroclastic deposits following caldera formation[1]. The dykes are dissected to ~500 m depth, 2-3 m wide, and crop out in two stream valleys with 5-30 m-long exposures. Dykes intrude diverse country rock types, including a welded ignimbrite, basaltic lavas, and glacial conglomerate. Each of the six studied dykes is broadly similar, exhibiting obsidian margins and microcrystalline cores. Dykes within pre-fractured lava are surrounded by external tuffisite vein networks, which are absent from dykes within conglomerate, whereas dykes failed to penetrate the ignimbrite. Obsidian at dyke margins comprises layers of discrete colour. These display dramatic thickness variations and collapsed bubble structures, and are locally separated by zones of welded, brecciated and flow-banded obsidian. We use textural associations to present a detailed model of dyke emplacement and evolution. Dykes initially propagated with the passage of fragmented, gas-charged magma and generation of external tuffisite veins, whose distribution was strongly influenced by pre-existing fractures in the country rock. External tuffisites retained permeability throughout dyke emplacement due to their high lithic content. The geochemically homogenous dykes then evolved via incremental magma emplacement, with shear deformation localised along emplacement boundary layers. Shear zones migrated between different boundary layers, and bubble deformation promoted magma mobility. Brittle

  2. Viscosity of Campi Flregrei (Italy) magmas

    NASA Astrophysics Data System (ADS)

    Misiti, Valeria; Vetere, Francesco; Scarlato, Piergiorgio; Behrens, Harald; Mangiacapra, Annarita; Freda, Carmela

    2010-05-01

    Viscosity is an important factor governing both intrusive and volcanic processes. The most important parameters governing silicate melts viscosity are bulk composition of melt and temperature. Pressure has only minor effect at crustal depths, whereas crystals and bubbles have significant influence. Among compositional parameters, the water content is critical above all in terms of rheological behaviour of melts and explosive style of an eruption. Consequently, without an appropriate knowledge of magma viscosity depending on the amount of dissolved volatiles, it is not possible to model the processes (i.e., magma ascent, fragmentation, and dispersion) required to predict realistic volcanic scenarios and thus forecast volcanic hazards. The Campi Flegrei are a large volcanic complex (~150 km2) located west of the city of Naples, Italy, that has been the site of volcanic activity for more than 60 ka and represents a potential volcanic hazard owing to the large local population. In the frame of a INGV-DPC (Department of Civil Protection) project devoted to design a multidisciplinary system for short-term volcano hazard evaluation, we performed viscosity measurements, under dry and hydrous conditions, of primitive melt compositions representative of two Campi Flegrei eruptions (Minopoli-shoshonite and Fondo Riccio-latite). Viscosity of the two melts have been investigated in the high temperature/low viscosity range at atmospheric pressure in dry samples and at 0.5 GPa in runs having water content from nominally anhydrous to about 3 wt%. Data in the low temperature/high viscosity range were obtained near the glass transition temperature at atmospheric pressure on samples whose water contents vary from 0.3 up to 2.43 wt%. The combination of high- and low-viscosity data permits a general description of the viscosity as a function of temperature and water content using a modified Tamman-Vogel-Fulcher equation. logν = a+ --b--+ --d--×exp(g × w-) (T - c) (T - e) T (1) where

  3. Stress modelling of magma storage zones and its implications for rapid kimberlitic magma ascent

    NASA Astrophysics Data System (ADS)

    Baruah, A.; Mandal, N.

    2012-12-01

    Rapid ascent of low viscous kimberlitic magmas is reflected from the presence of meta-stable diamond phenocrysts. Existing models suggest that high velocity magma ascent takes place as a mechanical coupling interaction between the CO2-rich volatile phase originating from the magma and the hydraulic fracture (Type-I). However, for such fracturing to occur at a depth of ~200 km, the system need to have a huge tensile stress to overcome the lithostatic pressure (~60 Kb) and the tensile strength of the rocks (0.4 - 0.5 Kb). The objective of the present work is to present a mechanical model and show the specific conditions in which the magma storage zone (MSZ) can build up such large tensile stresses to cause fracturing for magma ascent. Finite Element (FE) method was employed to map the stress field in the mantle rock around a magma chamber. MSZ was modeled as a semi-elliptical zone at bottom of the model of 150 km depth and 300 km width. Two types of FE modelling was performed considering two factors: (1) density contrast (Δρ) between magma and ambient mantle, and (2) shape (Ar: ratio of vertical and horizontal dimensions) of the MSZ. Figure 1 show the Δρ contrasts required for tensile fracturing to occur at the MSZ tip for different values of their Ar. Results reveal a distinct zone of maximum tensile stresses in the neighborhood of the MSZ, suggesting the potential locations of tensile fracturing. It shows that the tensile stress magnitude decreases exponentially away from the MSZ top vertically. The results illustrate a nonlinear relation of stress with increasing Δρ (Figure 1). We show that for models with Ar >1 there is a localization of tensile stress at the MSZ tip, and for the models with Ar << 1 it diffuse along the boundary (Figure 2). We also show that for a particular Δρ, tensile stress increases for increasing Ar. The results indicate that MSZ with large Ar are more potential for tensile fracturing to occur at their vertices. Considering the

  4. The influence of magma viscosity on convection within a magma chamber

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Magmatic-hydrothermal ore deposits are the most important sources of metals like Cu, Mo, W and Sn and a major resource for Au. It is well accepted that they are formed by the release of magmatic fluids from a batholith-sized magma body. Traditionally, it has been assumed that crystallization-induced volatile saturation (called "second boiling") is the main mechanism for fluid release, typically operating over thousands to tens of thousands of years (Candela, 1991). From an analysis of alteration halo geometries caused by magmatic fluids, Cathles and Shannon (2007) suggested much shorter timescales in the order of hundreds of years. Such rapid release of fluids cannot be explained by second boiling as the rate of solidification scales with the slow conduction of heat away from the system. However, rapid fluid release is possible if convection is assumed within the magma chamber. The magma would degas in the upper part of the magma chamber and volatile poor magma would sink down again. Such, the rates of degassing can be much higher than due to cooling only. We developed a convection model using Navier-Stokes equations provided by the computational fluid dynamics platform OpenFOAM that gives the possibility to use externally derived meshes with complex (natural) geometries. We implemented a temperature, pressure, composition and crystal fraction dependent viscosity (Ardia et al., 2008; Giordano et al., 2008; Moore et al., 1998) and a temperature, pressure, composition dependent density (Lange1994). We found that the new viscosity and density models strongly affect convection within the magma chamber. The dependence of viscosity on crystal fraction has a particularly strong effect as the steep viscosity increase at the critical crystal fraction leads to steep decrease of convection velocity. As the magma chamber is cooling from outside to inside a purely conductive layer is developing along the edges of the magma chamber. Convection continues in the inner part of the

  5. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Daniele, M.; Renggli, C.; Perugini, D.; De Campos, C.; Hess, K. U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2014-12-01

    Rising bubbles may significantly affect magma mixing paths as has been demonstrated by analogue experiments in the past. Here, bubble-advection experiments are performed for the first time employing natural materials at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears as efficient mechanism to mingle contrasting melt compositions. MicroCT imaging shows bubbles trailing each other and trails of multiple bubbles having converged. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that subsequent bubbles rising are likely to follow the same pathways that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Fundamental implications for the concept of bubble advection in magma mixing are thus a) an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and b) non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a filament. Inside these filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments are likely to have experienced multiple bubbles passing through

  6. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    1998-01-01

    The research described in this progress report involved the study of petrological, geochemical and volcanic processes that occur on the Moon and the SNC 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 role of volatiles in magmatic processes and on processes of magma evolution on these planets. The work on the lunar volcanic glasses has resulted in some exciting new discoveries over the years of this grant. We discovered small metal blebs initially in the Al5 green glass, and determined the significant importance of this metal in fixing the oxidation state of the parent magma (Fogel and Rutherford, 1995). More recently, we discovered a variety of metal blebs in the Al7 orange glass. Some of these Fe-Ni metal blebs were in the glass; others were in olivine phenocrysts. 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 (Weitz et al., 1997) They also yield important information about the composition of the gas phase present, the gas which drove the lunar fire-fountaining. One of the more exciting and controversial findings in our research over the past year has been the possible fractionation of H from D during shock (experimental) of hornblende bearing samples (Minitti et al., 1997). This research is directed at explaining some of the low H2O and high D/H observed in hydrous phases in the SNC meteorites.

  7. Differentiation of an Apollo 12 picrite magma

    NASA Technical Reports Server (NTRS)

    Walker, D.; Hays, J. F.; Longhi, J.; Kirkpatrick, R. J.

    1976-01-01

    The Apollo 12 olivine basalt suite shows a strong positive correlation of grain size with normative olivine content. This correlation is interpreted to mean that the suite of samples represents the basal portion of a cooling unit which differentiated by simple olivine settling. The grain size of plagioclase observed in the coarsest samples indicates the cooling unit may have been as much as 30 m thick. The amount of olivine concentration observed in the suite is quantitatively internally consistent with simple olivine settling in a magma body of this size which has the composition of the chill margin.

  8. Asteroid differentiation - Pyroclastic volcanism to magma oceans

    NASA Technical Reports Server (NTRS)

    Taylor, G. J.; Keil, Klaus; Mccoy, Timothy; Haack, Henning; Scott, Edward R. D.

    1993-01-01

    A summary is presented of theoretical and speculative research on the physics of igneous processes involved in asteroid differentiation. Partial melting processes, melt migration, and their products are discussed and explosive volcanism is described. Evidence for the existence of asteroidal magma oceans is considered and processes which may have occurred in these oceans are examined. Synthesis and inferences of asteroid heat sources are discussed under the assumption that asteroids are heated mainly by internal processes and that the role of impact heating is small. Inferences of these results for earth-forming planetesimals are suggested.

  9. Special Relativity Derived from Spacetime Magma

    PubMed Central

    Greensite, Fred

    2014-01-01

    We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid) existing on the union of spacetime frame components and Euclidean which is consistent with an “inversion symmetry” constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of “inverse norms” which play major roles with respect to various unital -algebras more generally. PMID:24959889

  10. Magma storage under Iceland's Eastern Volcanic Zone

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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

  11. Special relativity derived from spacetime magma.

    PubMed

    Greensite, Fred

    2014-01-01

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

  12. Asteroid differentiation - Pyroclastic volcanism to magma oceans

    NASA Technical Reports Server (NTRS)

    Taylor, G. J.; Keil, Klaus; Mccoy, Timothy; Haack, Henning; Scott, Edward R. D.

    1993-01-01

    A summary is presented of theoretical and speculative research on the physics of igneous processes involved in asteroid differentiation. Partial melting processes, melt migration, and their products are discussed and explosive volcanism is described. Evidence for the existence of asteroidal magma oceans is considered and processes which may have occurred in these oceans are examined. Synthesis and inferences of asteroid heat sources are discussed under the assumption that asteroids are heated mainly by internal processes and that the role of impact heating is small. Inferences of these results for earth-forming planetesimals are suggested.

  13. Role of Yield Stress in Magma Rheology

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Di Giuseppe, E.; Davaille, A.; Kurita, K.

    2012-04-01

    Magmas are essentially multiphase material composed of solid crystals, gaseous bubbles and silicate liquids. They exhibit various types of drastic change in rheology with variation of mutual volumetric fractions of the components. The nature of this variable rheology is a key factor in controlling dynamics of flowing magma through a conduit. Particularly the existence of yield stress in flowing magma is expected to control the wall friction and formation of density waves. As the volumetric fraction of solid phase increases yield stress emerges above the critical fraction. Several previous studies have been conducted to clarify this critical value of magmatic fluid both in numerical simulations and laboratory experiments ([Lejeune and Pascal, 1995], [Saar and Manga 2001], [Ishibashi and Sato 2010]). The obtained values range from 13.3 to 40 vol%, which display wide variation and associated change in rheology has not been clarified well. In this presentation we report physical mechanism of emergence of yield stress in suspension as well as the associated change in the rheology based on laboratory experiments using analog material. We utilized thermogel aqueous suspension as an analog material of multiphase magma. Thermogel, which is a commercial name for poly(N-isopropyl acrylamide) (PNIPAM) undergoes volumetric phase change at the temperature around 35C:below this temperature the gel phase absorbs water and swells while below this it expels water and its volume shrinks. Because of this the volumetric fraction of gel phase systematically changes with temperature and the concentration of gel powder. The viscosity measured at lower stress drastically decreases across this phase change with increasing temperature while the viscosity at higher stress does not exhibit large change across the transition. We have performed a series of rheological measurements focusing on the emergence of yield stress on this aqueous suspension. Since the definition of yield stress is not

  14. Using magma flow indicators to infer flow dynamics in sills

    NASA Astrophysics Data System (ADS)

    Hoyer, Lauren; Watkeys, Michael K.

    2017-03-01

    Fabrics from Anisotropy of Magnetic Susceptibility (AMS) analyses and Shape Preferred Orientation (SPO) of plagioclase are compared with field structures (such as bridge structures, intrusive steps and magma lobes) formed during magma intrusion in Jurassic sills. This is to constrain magma flow directions in the sills of the Karoo Igneous Province along the KwaZulu-Natal North Coast and to show how accurately certain structures predict a magma flow sense, thus improving the understanding of the Karoo sub-volcanic dynamics. The AMS fabrics are derived from magnetite grains and are well constrained, however the SPO results are commonly steeply inclined, poorly constrained and differ to the AMS fabrics. Both techniques resulted in asymmetrical fabrics. Successful relationships were established between the AMS fabric and the long axes of the magma flow indicators, implying adequate magma flow prediction. However, where numerous sill segments merge, either in the form of magma lobes or bridge structures, the coalescence process creates a new fabric between the segments preserving late-stage magma migration between the merged segments, overprinting the initial magma flow direction.

  15. Selection of promising sites for magma energy experiments

    SciTech Connect

    Carson, C.C.

    1985-01-01

    The Long Valley and Coso Hot Springs areas of California have been identified as the most promising sites for conducting a magma energy extraction experiment. These two locations were selected from among the potential sites on the basis of several factors that are critical to the success of the proposed long-term energy extraction experiment. These factors include the likelihood of the existence of shallow magma targets as well as several other drilling, energy extraction and programmatic considerations. As the magma energy extraction program continues, these sites will be analyzed in detail so that one can be selected as the site for the planned magma experiment.

  16. Evidence for magma mixing within the Laacher See magma chamber (East Eifel, Germany)

    USGS Publications Warehouse

    Worner, G.; Wright, T.L.

    1984-01-01

    The final pyroclastic products of the late Quaternary phonolitic Laacher See volcano (East Eifel, W.-Germany) range from feldspar-rich gray phonolite to dark olivine-bearing rocks with variable amounts of feldspar and Al-augite megacrysts. Petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite (MgO 0.9%) to mafic hybrid rock (MgO 7.0%) for all major and trace elements. Both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts. The phonolite-derived phenocrysts are characterized by glass inclusions of evolved composition, rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix. Basanitic (magnesian) clinopyroxene and olivine, in contrast, show skeletal (normally zoned) overgrowths indicative of post-mixing crystallization. In accord with petrographical and other chemical evidence, mass balance calculations suggest mixing of an evolved Laacher See phonolite containing variable amounts of mineral cumulates and a megacryst-bearing basanite magma. Magma mixing occurred just prior to eruption (hours) of the lowermost magma layer of the Laacher See magma chamber but did not trigger the volcanic activity. ?? 1984.

  17. Breaking the paradigm at magma-poor and magma-rich rifted margins

    NASA Astrophysics Data System (ADS)

    Tugend, Julie; Manatschal, Gianreto; Gillard, Morgane; Nirrengarten, Michael; Epin, Marie-Eva; Sauter, Daniel; Autin, Julia; Harkin, Caroline; Kusznir, Nick

    2017-04-01

    Rifted margins used to be classified into volcanic or non-volcanic passive margins. Because magmatism is evidenced even in so-called 'non-volcanic' settings, this terminology was later adjusted to magma-poor and magma-rich rifted margins. This classification represents a simplification into end-member magmatic types depending on the magmatic budget related to rifting and/or breakup processes. New observations derived from higher quality geophysical data sets and drill-hole data revealed the great diversity of rifted margin architecture and highly variable distribution of rift-related and/or breakup related magmatism. Recent studies suggest that rifted margins have a more complex tectono-magmatic evolution than previously assumed and cannot be characterized based on the observed volume of magma alone. In this study, we present seismic observations from 2D high resolution long-offset deep reflection seismic profiles across the East-Indian and South-Atlantic rifted margins. We aim to compare structural similarities between rifted margins with different magmatic budgets. We apply a systematic seismic interpretation approach to describe and characterize the first-order architecture and magmatic budget of our case examples. The identification of magmatic additions based on seismic observations only is indeed not unequivocal, in spite of the high-resolution dataset. Interpretations are related to large uncertainties in particular at ocean-continent transitions (i.e. outer highs) where most of the magmatism seems to be located. For each line, we present three different interpretations based on offshore and/or onshore field analogues. These interpretations illustrate scenarios for the nature of the outer highs that we believe are geologically meaningful and reasonable, and imply different magmatic budgets at breakup. Based on these interpretations we discuss different mechanisms for lithospheric breakup involving either a gradual or more instantaneous process independently

  18. Investigating magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions.

    NASA Astrophysics Data System (ADS)

    Dahren, Börje; Troll, Valentin R.; Andersson, Ulf-Bertil; Chadwick, Jane P.; Gardner, Mairi F.

    2010-05-01

    Improving our understanding of magma plumbing and storage remains one of the major challenges for petrologists and volcanologists today. This is especially true for explosive volcanoes, where constraints on magma plumbing are essential for predicting dynamic changes in future activity and thus for hazard mitigation. This study aims to investigate the magma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the 1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rate of ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry [1,2] b.) plagioclase-melt thermo-barometry [3] c.) clinopyroxene composition barometry [2,4] and d.) olivine-melt thermometry [5]. The minerals analysed are from basaltic-andesites erupted between 1990-2002, with an average modal composition of 70% groundmass, 25% plagioclase, 4% clinopyroxene and <1% olivine. Clinopyroxenes are homogenous and display no obvious zoning. Plagioclases are considerably more heterogenous, exhibiting complex zoning and An content between An45-80. In addition, mineral compositions of older clinopyroxenes, erupted between 1883-1981, are used for comparison [6,7]. Previously, both seismic [8] and petrological studies [6,7,9] have addressed the magma plumbing beneath Anak Krakatau. Interestingly, petrological studies indicate shallow magma storage in the region of 2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and 22 km respectively. Our results imply that clinopyroxene presently crystallizes in a mid-crustal storage region (8-12 km), a previously identified depth level for magma storage, using seismic methods [8]. Plagioclases, in turn, form at shallower depths (4-6 km), in concert with previous petrological studies [6,7,9]. Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km), indicating that there may have been an overall shallowing of the plumbing system over the last ~40 years

  19. Magma evolution inside the 1631 Vesuvius magma chamber and eruption triggering

    NASA Astrophysics Data System (ADS)

    Stoppa, Francesco; Principe, Claudia; Schiazza, Mariangela; Liu, Yu; Giosa, Paola; Crocetti, Sergio

    2017-03-01

    Vesuvius is a high-risk volcano and the 1631 Plinian eruption is a reference event for the next episode of explosive unrest. A complete stratigraphic and petrographic description of 1631 pyroclastics is given in this study. During the 1631 eruption a phonolite was firstly erupted followed by a tephritic phonolite and finally a phonolitic tephrite, indicating a layered magma chamber. We suggest that phonolitic basanite is a good candidate to be the primitive parental-melt of the 1631 eruption. Composition of apatite from the 1631 pyroclastics is different from those of CO2-rich melts indicating negligible CO2 content during magma evolution. Cross checking calculations, using PETROGRAPH and PELE software, accounts for multistage evolution up to phonolite starting from a phonolitic basanite melt similar to the Vesuvius medieval lavas. The model implies crystal settling of clinopyroxene and olivine at 6 kbar and 1220°C, clinopyroxene plus leucite at a pressure ranging from 2.5 to 0.5 kbar and temperature ranging from 1140 to 940°C. Inside the phonolitic magma chamber K-feldspar and leucite would coexist at a temperature ranging from from 940 to 840°C and at a pressure ranging from 2.5 to0.5 kbar. Thus crystal fractionation is certainly a necessary and probably a sufficient condition to evolve the melt from phono tephritic to phonolitic in the 1631 magma chamber. We speculate that phonolitic tephrite magma refilling from deeper levels destabilised the chamber and triggered the eruption, as testified by the seismic precursor phenomena before 1631 unrest.

  20. A felsic MASH zone of crustal magmas - Feedback between granite magma intrusion and in situ crustal anatexis

    NASA Astrophysics Data System (ADS)

    Schwindinger, Martin; Weinberg, Roberto F.

    2017-07-01

    Magma mixing and mingling are described from different tectonic environments and are key mechanisms in the evolution of granitoids. The literature focuses on the interaction between mafic and felsic magmas with only limited research on the interaction between similar magmas. Here, we investigate instead hybridization processes between felsic magmas formed during the 500 Ma Delamerian Orogeny on the south coast of Kangaroo Island. Field relations suggest that a coarse, megacrystic granite intruded and interacted with a fine-grained diatexite that resulted from combined muscovite dehydration and water-fluxed melting of Kanmantoo Group turbidites. The two magmas hybridized during syn-magmatic deformation, explaining the complexity of relationships and variability of granitoids exposed. We suggest that granite intrusion enhanced melting of the turbidites by bringing in heat and H2O. With rising melt fraction, intrusive magmas became increasingly unable to traverse the partially molten terrane, creating a positive feedback between intrusion and anatexis. This feedback loop generated the exposed mid-crustal zone where magmas mixed and homogenized. Thus, the outcrops on Kangaroo Island represent a crustal and felsic melting-assimilation-storage-homogenization (felsic MASH) zone where, instead of having direct mantle magma involvement, as originally proposed, these processes developed in a purely crustal environment formed by felsic magmas.

  1. Magma volumes and storage in the middle crust

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Barnes, C. G.; Paterson, S. R.

    2015-12-01

    Quantifying magma volumes in magma plumbing systems is mostly done through geophysical means or based on volcanic eruptions. Detailed studies of plutons, however, are useful in revealing depths and evolving volumes of stored magmas over variable lifetimes of magma systems. Knowledge of the location, volume, and longevity of stored magma is critical for understanding where in the crust magmas attain their chemical signature, how these systems physically behave and how source, storage levels, and volcanoes are connected. Detailed field mapping, combined with single mineral geochemistry and geochronology of plutons, allow estimates of size and longevity of melt-interconnected magma batches that existed during the construction of magma storage sites. The Tuolumne intrusive complex (TIC) recorded a 10 myr magmatic history. Detailed maps of the major units in different parts of the TIC indicate overall smaller scale (cm- to <1 km) compositional variation in the oldest, outer Kuna Crest unit and mainly larger scale (>10 km) changes in the younger Half Dome and Cathedral Peak units. Mineral-scale trace element data from hornblende of granodiorites to gabbros from the Kuna Crest lobe show distinct hornblende compositions and zoning patterns. Mixed hornblende populations occur only at the transition to the main TIC. This compositional heterogeneity in the first 1-2 myr points to low volume magmatism resulting in smaller, discrete and not chemically interacting magma bodies. Trace element and Sr- and Pb-isotope data from growth zones of K-feldspar phenocrysts from the two younger granodiorites indicate complex mineral zoning, but general isotopic overlap, suggesting in-situ, inter-unit mixing and fractionation. This is supported by hybrid zones between units, mixing of zircon, hornblende, and K-feldspar populations and late leucogranites. Thus, magma body sizes increased later resulting in overall more homogeneous, but complexly mixing magma mushes that fractionated locally.

  2. Open-system dynamics and mixing in magma mushes

    NASA Astrophysics Data System (ADS)

    Bergantz, G. W.; Schleicher, J. M.; Burgisser, A.

    2015-10-01

    Magma dominantly exists in a slowly cooling crystal-rich or mushy state. Yet, observations of complexly zoned crystals, some formed in just one to ten years, as well as time-transgressive crystal fabrics imply that magmas mix and transition rapidly from a locked crystal mush to a mobile and eruptable fluid. Here we use a discrete-element numerical model that resolves crystal-scale granular interactions and fluid flow, to simulate the open-system dynamics of a magma mush. We find that when new magma is injected into a reservoir from below, the existing magma responds as a viscoplastic material: fault-like surfaces form around the edges of the new injection creating a central mixing bowl of magma that can be unlocked and become fluidized, allowing for complex mixing. We identify three distinct dynamic regimes that depend on the rate of magma injection. If the magma injection rate is slow, the intruded magma penetrates and spreads by porous media flow through the crystal mush. With increasing velocity, the intruded magma creates a stable cavity of fluidized magma that is isolated from the rest of the reservoir. At higher velocities still, the entire mixing bowl becomes fluidized. Circulation within the mixing bowl entrains crystals from the walls, bringing together crystals from different parts of the reservoir that may have experienced different physiochemical environments and leaving little melt unmixed. We conclude that both granular and fluid dynamics, when considered simultaneously, can explain observations of complex crystal fabrics and zoning observed in many magmatic systems.

  3. Comparison of Magma Residence, Magma Ascent and Magma-Hydrothermal Interaction at EPR 9°N and Endeavour Segment

    NASA Astrophysics Data System (ADS)

    Michael, P. J.; Gill, J. B.; Ramos, F. C.

    2010-12-01

    We compare magmas’ temperatures (Mg#s), their degree of crustal assimilation (“excess” Chlorine) and their residence depth and ascent speed (dissolved CO2 content) at similar scales, using new data for Endeavour and new and published [1] data for EPR 9°N. We relate differences between the two segments to other differences, e.g., depth and width of the AMC reflector. Cl in glasses, and Cl/K or Cl/Nb ratios, are indicators of magma’s interaction with altered crust, probably at the roof of the AMC [1,2]. An excess Cl (in ppm) value for each glass can be calculated by subtracting mantle-derived Cl from measured Cl. At 9°N, excess Cl is negatively correlated with Mg#. Mg# is lower and excess Cl is higher off-axis (up to 4 km). At a given Mg#, Cl is higher off-axis [1]. Endeavour magmas on-axis have lower Mg# than EPR, while their ranges are similar off-axis. At Endeavour, there is no good correlation of excess Cl with Mg#, although glasses with high Mg# are found mostly on-axis. There is no trend of Mg# or excess Cl with distance from the axis. Excess Cl is similar on-axis between the two ridges. At both ridges, assimilation has a stochastic distribution, such that high- and low-Cl glasses are found in most locations. Because CO2 exsolution and bubble formation is slow compared to magma ascent and surface flow, many glasses are oversaturated compared to their eruption depth. Dissolved CO2 contents thus provide information about the duration of a magma’s transit between its last stopping point and final lava emplacement. If magma erupts and cools quickly, its dissolved CO2 should correspond to its last resting point, possibly the AMC. At EPR 9°N, maximum CO2 contents would be in equilibrium at the AMC roof, while minimum CO2 contents are nearly in equilibrium with collection depths. Glasses have high CO2 on-axis and low CO2 off-axis, and there is a negative correlation between CO2 and distance off-axis [1]. This is partly due to post-eruptive flow away from

  4. 75 FR 28778 - Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, AZ

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-24

    ... Natural Resources Conservation Service Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan... Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, Arizona. FOR FURTHER... needed for this project. The project proposes to rehabilitate the Magma FRS to provide for...

  5. Three Dimensional Magma Wagging: Seismic Diagnostics And Forcing Mechanism

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Jellinek, M.; Bercovici, D.

    2016-12-01

    Seismic tremor involving 0.5-7 Hz ground oscillations are common precursors of explosive sillicic volcanism. Here we present recent progress on the development and application of the three dimensional magma-wagging model, which is extended from the magma wagging model for tremor [Jellinek and Bercovici, 2011, Bercovici et al., 2013]. In our model, a stiff magma column rising in a vertical conduit oscillates against a surrounding foamy annulus of bubbly magma, giving rise to tremor. Inside the volcanic conduit, the magma column undergoes swirling motion, in which each horizontal section of the column can trace elliptical trajectories. We propose seismic diagnostics for the characteristics of the swirling motion using the time-lag between seismic stations, and test our model by analyzing pre-eruptive seismic data from the 2009 eruption of Redoubt Volcano. Our analysis demonstrates the existence of elliptical swirling motion more than one week before the eruption, and suggests that the 2009 eruption was accompanied by qualitative changes in the magma wagging behavior including fluctuations in eccentricity and a reversal in the direction of elliptical swirling motion when the eruption was immediately impending. We further explore the coupling between the dynamics of the gas flux in the foamy annulus and the wagging motion of the magma column. We show that the gas flux provides a driving force for the magma column to swirl against viscous damping. The coupling between gas flux and wagging motion also brings the possibility to link observation of out-gassing with seismic measurements.

  6. The role of volatiles in magma chamber dynamics.

    PubMed

    Huppert, Herbert E; Woods, Andrew W

    2002-12-05

    Many andesitic volcanoes exhibit effusive eruption activity, with magma volumes as large as 10(7)-10(9) m(3) erupted at rates of 1-10 m(3) x s(-1) over periods of years or decades. During such eruptions, many complex cycles in eruption rates have been observed, with periods ranging from hours to years. Longer-term trends have also been observed, and are thought to be associated with the continuing recharge of magma from deep in the crust and with waning of overpressure in the magma reservoir. Here we present a model which incorporates effects due to compressibility of gas in magma. We show that the eruption duration and volume of erupted magma may increase by up to two orders of magnitude if the stored internal energy associated with dissolved volatiles can be released into the magma chamber. This mechanism would be favoured in shallow chambers or volatile-rich magmas and the cooling of magma by country rock may enhance this release of energy, leading to substantial increases in eruption rate and duration.

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

    PubMed

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2014-07-24

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

  8. Magma mixing induced by particle settling

    NASA Astrophysics Data System (ADS)

    Renggli, Christian J.; Wiesmaier, Sebastian; De Campos, Cristina P.; Hess, Kai-Uwe; Dingwell, Donald B.

    2016-11-01

    A time series of experiments at high temperature have been performed to investigate the influence of particle settling on magma mixing. A natural rhyolite glass was held above a natural basalt glass in a platinum crucible. After melting of the glasses at superliquidus temperatures, a platinum sphere was placed on the upper surface of the rhyolitic melt and sank into the experimental column (rhyolitic melt above basaltic melt). Upon falling through the rhyolitic-basaltic melt interface, the Pt sphere entrained a filament of rhyolitic melt in its further fall. The quenched products of the experiments were imaged using X-ray microCT methods. The images of our time series of experiments document the formation of a rhyolite filament as it is entrained into the underlying basalt by the falling platinum sphere. When the Pt particle reached the bottom of the crucible, the entrained rhyolitic filament started to ascend buoyantly up to the initial rhyolitic-basaltic interface. This generated a significant thickness increase of a comingled "melange" layer at the interface due to "liquid rope coiling" and piling up of the filament. As a consequence, the basalt/rhyolite interface was greatly enlarged and diffusive hybridisation greatly accelerated. Further, bubbles, originating at the interface, are observed to have risen into the overlying rhyolite dragging basalt filaments with them. Upon crossing the basalt/rhyolite interface, the bubbles have non-spherical shapes as they adapt to the differing surface tensions of basaltic and rhyolitic melts. Major element profiles, measured across the rhyolite filaments, exhibit asymmetrical shapes from the rhyolite into the basalt. Na and Ti reveal uphill diffusion from the rhyolite towards the interface in the filament cross sections. These results reveal the potential qualitative complexity of the mingling process between rhyolitic and basaltic magmas in the presence of sinking crystals. They imply that crystal-rich magma mingling may

  9. Experimental Constraints on a Vesta Magma Ocean

    NASA Technical Reports Server (NTRS)

    Hoff, C.; Jones, J. H.; Le, L.

    2014-01-01

    A magma ocean model was devised to relate eucrites (basalts) and diogenites (orthopyroxenites), which are found mixed together as clasts in a suite of polymict breccias known as howardites. The intimate association of eucritic and diogenitic clasts in howardites argues strongly that these three classes of achondritic meteorites all originated from the same planetoid. Reflectance spectral evidence (including that from the DAWN mission) has long suggested that Vesta is indeed the Eucrite Parent Body. Specifically, the magma ocean model was generated as follows: (i) the bulk Vesta composition was taken to be 0.3 CV chondrite + 0.7 L chondrite but using only 10% of the Na2O from this mixture; (ii) this composition is allowed to crystallize at 500 bar until approx. 80% of the system is solid olivine + low-Ca pyroxene; (iii) the remaining 20% liquid crystallizes at one bar from 1250C to 1110C, a temperature slightly above the eucrite solidus. All crystallization calculations were performed using MELTS. In this model, diogenites are produced by cocrystallization of olivine and pyroxene in the >1250C temperature regime, with Main Group eucrite liquids being generated in the 1300-1250C temperature interval. Low-Ca pyroxene reappears at 1210C in the one-bar calculations and fractionates the residual liquid to produce evolved eucrite compositions (Stannern Trend). We have attempted to experimentally reproduce the <1250C portion of the MELTS Vesta magma ocean. In the MELTS calculation, the change from 500 bar to one bar results in a shift of the olivine:low-Ca pyroxene boundary so that the 1250C liquid is now in the olivine field and, consequently, olivine should be the first-crystallizing phase, followed by low-Ca pyroxene at 1210C, and plagioclase at 1170C. Because at one bar the olivine:low-Ca pyroxene boundary is a peritectic, fractional crystallization of the 1210C liquid proceeds with only pyroxene crystallization until plagioclase appears. Thus, the predictions of the

  10. Electrical conductivity of water-bearing magmas

    NASA Astrophysics Data System (ADS)

    Gaillard, F.

    2003-04-01

    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

  11. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-04-01

    That rising bubbles may significantly affect magma mixing paths has already been demon strated by analogue experiments. Here, for the first time, bubble-advection experiments are performed employing volcanic melts at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears to be an efficient mechanism for mingling volcanic melts of highly contrasting compositions and properties. MicroCT imaging reveals bubbles trailing each other and multiple filaments coalescing into bigger ones. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that bubbles rising successively are likely to follow this pathway of low resistance that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Inevitable implications for the concept of bubble advection in magma mixing include thereby both an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a material. Inside the filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments

  12. Flow in an experimental micro-magma chamber

    NASA Astrophysics Data System (ADS)

    Carroll, Michael R.; Wyllie, Peter J.

    The chemical evolution and eruptive behavior of magmas may be controlled largely by convective processes within magma chambers. According to a recent National Research Council Report [Committee on Physics and Chemistry of Earth Materials, 1987], “the style of convection itself, whether it is turbulent, laminar, large-scale, of multiple scales, tiered, or localized and intermittent, is very much at question.” In the U.S. National Report to the International Union of Geodesy and Geophysics, Marsh [1987] reviewed recent theoretical and experimental developments related to the style of convection in magma chambers, noting both significant quantitative advances and also the many remaining uncertainties. With regard to double-diffusive convection, he stated “as ever, the critical question concerns whether or not actual magma chambers convect in this style.” Similarly, Spera et al. [1986] , in discussion of double-diffusive convection, cautioned against “applying results from saltwater tanks to magma chambers.”

  13. Fate of a perched crystal layer in a magma ocean

    NASA Technical Reports Server (NTRS)

    Morse, S. A.

    1992-01-01

    The pressure gradients and liquid compressibilities of deep magma oceans should sustain the internal flotation of native crystals owing to a density crossover between crystal and liquid. Olivine at upper mantle depths near 250 km is considered. The behavior of a perched crystal layer is part of the general question concerning the fate of any transient crystal carried away from a cooling surface, whether this be a planetary surface or the roof of an intrusive magma body. For magma bodies thicker than a few hundred meters at modest crustal depths, the major cooling surface is the roof even when most solidification occurs at the floor. Importation of cool surroundings must also be invoked for the generation of a perched crystal layer in a magma ocean, but in this case the perched layer is deeply embedded in the hot part of the magma body, and far away from any cooling surface. Other aspects of this study are presented.

  14. Factors controlling the structures of magma chambers in basaltic volcanoes

    NASA Technical Reports Server (NTRS)

    Wilson, L.; Head, James W.

    1991-01-01

    The depths, vertical extents, and lateral extents of magma chambers and their formation are discussed. The depth to the center of a magma chamber is most probably determined by the density structure of the lithosphere; this process is explained. It is commonly assumed that magma chambers grow until the stress on the roof, floor, and side-wall boundaries exceed the strength of the wall rocks. Attempts to grow further lead to dike propagation events which reduce the stresses below the critical values of rock failure. The tensile or compressive failure of the walls is discussed with respect to magma migration. The later growth of magma chambers is accomplished by lateral dike injection into the country rocks. The factors controlling the patterns of growth and cooling of such dikes are briefly mentioned.

  15. Hydrogen isotopic fractionation during crystallization of the terrestrial magma ocean

    NASA Astrophysics Data System (ADS)

    Pahlevan, K.; Karato, S. I.

    2016-12-01

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

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

    PubMed

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-07

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

  17. Transition from magma dominant to magma poor rifting along the Nova Scotia Continental Margin

    NASA Astrophysics Data System (ADS)

    Lau, K. H.; Louden, K. E.; Nedimović, M. R.; Whitehead, M.; Farkas, A.; Watremez, L.; Dehler, S. A.

    2011-12-01

    Passive margins have been characterized as magma-dominant (volcanic) or magma-poor (non-volcanic). However, the conditions under which margins might switch states are not well understood as they typically have been studied as end member examples in isolation to each other. The Nova Scotia (NS) continental margin, however, offers an opportunity to study the nature of such a transition between the magma-dominant US East Coast margin to the south and the magma-poor Newfoundland margin to the north within a single rift segment. This transition is evidenced by a clear along-strike reduction in features characteristic of syn-rift volcanism from south-to-north along the NS margin, such as the weakening of the East Coast Magnetic Anomaly (ECMA) and the coincident disappearance of seaward dipping reflector sequences (SDRS) on multichannel seismic (MCS) reflection profiles. Results from recent industry MCS profiles along and across the margin suggest a potentially narrow magma-dominant to magma-poor along-strike transition between the southern and the central NS margin. Such a transition is broadly consistent with results of several widely-spaced, across-strike ocean bottom seismometer (OBS) wide-angle profiles. In the southern region, the crustal structure exhibits a narrow (~120-km wide) ocean-continent transition (OCT) with a high velocity (7.2 km/s) lower crust, interpreted as a gabbro-rich underplated melt, beneath the SDRS and the ECMA, similar to crustal models across the US East Coast. In contrast, profiles across the central and northern margin contain a much wider OCT (150-200-km wide) underlain by a low velocity mantle layer (7.3-7.9 km/s), interpreted as partially serpentinized olivine, which is similar to the magma-poor Newfoundland margin to the north. However, the central-to-northern OBS profiles also exhibit significant variations within the OCT and the along-strike continuity of these OCT structures is not yet clear. In November 2010, we acquired, in the

  18. Session 6: Magma Energy: Engineering Feasibility of Energy Extraction from Magma Bodies

    SciTech Connect

    Traeger, R.K.

    1983-12-01

    Extensive quantities of high-quality energy are estimated to be available from molten magma bodies existing within 10 Km of the US continent's surface. A five-year study sponsored by DOE/BES demonstrated that extraction of energy from these melts was scientifically feasible. The next stage of assessment is to evaluate the engineering feasibility of energy extraction and provide a preliminary economic evaluation. Should the second step demonstrate engineering feasibility, the third step would include detailed economic, market and commercialization endeavors. Evaluation of the engineering feasibility will be initiated in FY 84 in a program supported by DOE/GHTD and managed by Dave Allen. The project will be managed by Sandia Labs in James Kelsey's Geothermal Technology Development Division. The project will continue to draw on expertise throughout the country, especially the scientific base established in the previous BES Magma Energy Program.

  19. Intrusion of granitic magma into the continental crust facilitated by magma pulsing and dike-diapir interactions: Numerical simulations

    NASA Astrophysics Data System (ADS)

    Cao, Wenrong; Kaus, Boris J. P.; Paterson, Scott

    2016-06-01

    We conducted a 2-D thermomechanical modeling study of intrusion of granitic magma into the continental crust to explore the roles of multiple pulsing and dike-diapir interactions in the presence of visco-elasto-plastic rheology. Multiple pulsing is simulated by replenishing source regions with new pulses of magma at a certain temporal frequency. Parameterized "pseudo-dike zones" above magma pulses are included. Simulation results show that both diking and pulsing are crucial factors facilitating the magma ascent and emplacement. Multiple pulses keep the magmatic system from freezing and facilitate the initiation of pseudo-dike zones, which in turn heat the host rock roof, lower its viscosity, and create pathways for later ascending pulses of magma. Without diking, magma cannot penetrate the highly viscous upper crust. Without multiple pulsing, a single magma body solidifies quickly and it cannot ascent over a long distance. Our results shed light on the incremental growth of magma chambers, recycling of continental crust, and evolution of a continental arc such as the Sierra Nevada arc in California.

  20. Chemical diffusion during isobaric degassing of magma

    NASA Astrophysics Data System (ADS)

    von Aulock, Felix W.; Kennedy, Ben M.; Lavallée, Yan; Henton-de Angelis, Sarah; Oze, Christopher; Morgan, Daniel J.; Clesham, Steve

    2014-05-01

    During ascent of magma, volatiles exsolve and bubbles form. Volatiles can either escape through a permeable network of bubbles in an open system or be trapped in non-connected pores during closed system degassing. Geochemical studies have shown that in most cases both- open system and closed system degassing take place at the same time. During cooling of the melt, diffusion slows down and eventually diffusional gradients get frozen in, preserving a history of degassing and rehydration during bubble growth, bubble collapse and crystal growth. We present data from experiments in which natural obsidian was degassed at atmospheric pressures at 950ºC over timescales of 3-24h. During bubble growth, a skin formed, at the outer edge of the sample, effectively prohibiting any degassing of its interior. Diffusion gradients were measured across the glass surrounding vesicles, and across this impermeable skin. Water contents were analyzed with synchrotron sourced Fourier transform infrared spectroscopy and several major, minor and trace elements were mapped using synchrotron sourced X-ray fluorescence spectroscopy. The samples show a dimpled surface, as well as signs of oxidation and growth of submicroscopic crystals. Water contents around bubbles decrease in simple heating experiments (from ~0.13 wt. % down to ~0.1 wt. %), whereas slight rehydration of the vesicle wall can be observed when a second, cooler step at 850ºC follows the initial 950ºC. Water gradients towards the outside of the sample decrease linearly to a minimum of ~0.045 wt. %, far below the solubility of water in melts at these temperatures. We mapped the distribution of K, Ca, Fe, Ti, Mn, Rb, Sr, Y and Zr. Especially the trace elements show a decrease towards the outside of the sample, whereas K, Fe, Ca and Ti generally do not show significant partitioning between melt and gas/crystal phase. Several effects could attribute to the distribution of these elements, such as the crystal growth and exchange with

  1. The three stages of magma ocean cooling

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1992-01-01

    Models of magma ocean (MO) cooling and crystallization can provide important constraints on MO plausibility for a given planet, on the origin of long term, stable crusts, and even on the origin of the solar system. Assuming the MO is initially extensive enough to have a mostly molten surface, its first stage of cooling is an era of radiative heat loss from the surface, with extremely rapid convection below, and no conductive layer in between. The development of the chill crust starts the second stage of MO cooling. Heat loss is now limited by conduction through the crust. The third stage of cooling starts when the near surface MO evolves compositionally to the point of saturation with feldspar. At this point, the cooling rate again precipitously diminishes, the rate of crustal thickness growth as a function of temperature suddenly increases. More work on incorporating chemical constraints into the evolving physical models of MO solidification would be worthwhile.

  2. Magma mixing during caldera forming eruptions

    NASA Astrophysics Data System (ADS)

    Kennedy, B.; Jellinek, M.; Stix, J.

    2006-12-01

    During explosive caldera-forming eruptions magma erupts through a ring dyke. Flow is driven, in part, by foundering of a magma chamber roof into underlying buoyant magma. One intriguing and poorly understood characteristic of deposits from calderas is that bulk ignimbrite, pumices, and crystals can show complex stratigraphic zonation. We propose that zonation patterns can be explained by different, and temporally evolving subsidence styles, and that the geometry imposed by subsidence can affect flow and cause mixing in the chamber and ring dyke. We use two series of laboratory experiments to investigate aspects of the mixing properties of flow in the chamber and ring dike during caldera collapse. In the first series, cylindrical blocks of height, h, and diameter, d, are released into circular analog magma chambers of diameter D and height H, containing buoyant fluids with viscosities that we vary. Subsidence occurs as a result of flow through the annular gap (ring dike) between the block and the wall of the surrounding tank of width, w = D-d. Three dimensionless parameters characterize the nature and evolution of the subsidence, and the resulting flow: A Reynolds number, Re, a tilt number, T = w/h and a subsidence number, S = w/H. Whereas Re indicates the importance of inertia for flow and mixing, T and S are geometric parameters that govern the extent of roof tilting, the spatial variation in w during collapse and the wavelength and structure of fluid motions. On the basis of field observations and theoretical arguments we fix T ≍ 0.14 and characterize subsidence and the corresponding flow over a wide range of Re - S parameter space appropriate to silicic caldera systems. Where S < 2 and Re < 103 the roof can rotate or tilt as it sinks and a spectrum of fluid mechanical behavior within the ring dike are observed. The combination of roof rotation and tilting drives unsteady, 3D overturning motions within the ring dike that are inferred to cause extensive mixing

  3. The magma ocean concept and lunar evolution

    NASA Technical Reports Server (NTRS)

    Warren, P. H.

    1985-01-01

    The model of lunar evolution in which the anorthositic plagioclase-rich oldest crust of the moon is formed over a period of 300 Myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies. Consideration is given to the classification of lunar rocks, the evidence for primordial deep global differentiation, constraints on the depth of the molten zone, the effects of pressure on mineral stability relationships, mainly-liquid vs mainly-magmifer ocean models, and the evidence for multiple ancient differentiation episodes. A synthesis of the model of primordial differentiation and its aftereffects is presented, and the generalization of the model to the earth and to Mars, Mercury, Venus, and the asteroids is discussed.

  4. How did the Lunar Magma Ocean crystallize?

    NASA Astrophysics Data System (ADS)

    Davenport, J.; Neal, C. R.

    2012-12-01

    It is generally accepted that the lunar crust and at least the uppermost (500 km) mantle was formed by crystallization of a magma ocean. How the magma ocean cooled and crystallized is still under debate. Parameters such as bulk composition, lunar magma ocean (LMO) crystallization method (fractional vs. equilibrium), depth of the LMO, and time for LMO solidification (effects of tidal heating mechanisms, insulating crustal lid, etc.) are still under debate. Neal (2001, JGR 106, 27865-27885) argues for the presence of garnet in the deep lunar mantle via compositional differences between low- and high-Ti mare basalts and volcanic glasses. Neal (2001) suggests that these compositional differences are due to the presence of garnet in the source regions of certain volcanic glass bead groups. As Neal (2001, JGR 106, 27865-27885) points out, determining if there is garnet in the lunar mantle is important in determining if the LMO was a "whole-Moon" event or if it was limited to certain areas. In the latter case, garnet would have been preserved in the lunar mantle and would have been used in the source material for some of the volcanic glasses. High-pressure experimental work concludes that with the right T-P conditions (2.5-4.5 GPa and 1675-1800° C) there could be a garnet-bearing pyroxene rich protolith at ~500 km depth. This also has significant implications for the bulk Al2O3 composition of the initial bulk Moon. If the LMO was not global, the volcanic glass beads that show evidence of garnet in their sources were formed from the deep, primitive lunar mantle, it begs the questions how was the non-LMO regions of the Moon formed and what was it's bulk composition? To try to answer these questions, it is necessary to thoroughly model the evolution of the LMO and then use that work to model the sources and formation of mare basalts, the volcanic glass beads, and other regions in question. To begin to answer these questions, we developed a scenario we have termed reverse

  5. The Abundance of Sulfur in Venus Magmas

    NASA Astrophysics Data System (ADS)

    Bullock, M. A.; Grinspoon, D. H.

    1999-09-01

    Outgassing of sulfur gases due to volcanism within the past 100 My on Venus is probably responsible for the planet's globally encircling H2SO4 cloud layers. Dramatic changes in volcanic output on Venus would have altered the atmospheric inventory of sulfur gases, and hence the structure of its clouds (Bullock and Grinspoon, Icarus, submitted 1999). Although Magellan radar images provide some constraints on the magnitude of volcanism in the geologically recent past, little is known of the sulfur content of Venus lavas. In order to assess the effects that Venus' volcanic history may have had on cloud and therefore climate change, it is desirable to place some constraints on the abundance of sulfur in Venus magmas. The sulfur content of terrestrial volcanic lavas varies widely, depending upon the local sedimentary environment and the source and history of upwelling magmas. We estimate the average abundance of sulfur in Venus lavas from an analysis of the production and loss of atmospheric SO2. The volumetric rate of resurfacing on Venus in the recent past is approximately 0.1 to 2 km3/yr (Bullock et al., JGR 20, 1993, Basilevsky and Head, GRL 23, 1996). Outgassed SO2 reacts quickly with crustal carbonate -- residence times in the atmosphere with respect to the reaction SO2 + CaCO3 <=> CaSO4 + CO are about 2-30 My (Fegley and Prinn, Nature 337, 1989, Bullock and Grinspoon, Icarus, submitted 1999). Assuming steady state conditions and an abundance of 25-180 ppm of atmospheric SO2 (Oyama et al., JGR 85, 1980, Bertaux et al., JGR 101, 1996), we will discuss constraints on the abundance of this important greenhouse and cloud-precursor gas in Venus lavas.

  6. Crystal Histories and Crustal Magmas: Insights into Magma Storage from U-Series Crystal Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.

    2014-12-01

    The dynamic processes operating within crustal magma reservoirs control many aspects of the chemical composition of erupted magmas, and crystals in volcanic rocks can provide a temporally-constrained archive of these changing environments. A new compilation of 238U-230Th ages of accessory phases and 238U-230Th-226Ra ages of bulk mineral separates of major phases documents that crystals in individual samples often have ages spanning most of the history of a volcanic center. Somewhat surprisingly, this observation holds for surface analyses as well as interior analyses, indicating that the latest stages of growth took place at different times for different grains. Nevertheless, average ages of surfaces are younger than interiors (as expected), and the dominant surface age population is often within error of eruption age. In contrast to accessory phase ages, less than half of the bulk separate 238U-230Th-226Ra ages for major phases are more than 10 kyr older than eruption. This suggests that major phases may in general reflect a later stage of development of an eruptible magma body than do accessory phases, or that the extent of discordance between ages of major and accessory phases reflects the extent to which a crystal mush was remobilized during processes leading to eruption. Crystal ages are most useful for illuminating magmatic processes when combined with crystal-scale trace-element or isotopic data, and I will present several case studies where such combined data sets exist. For example, at Yellowstone and at Okataina Caldera Complex, New Zealand, the combination zircon surface and interior analyses (of age, Hf isotopic, and trace-element data) with bulk dating and in-situ trace-element and isotopic compositions of feldspar allows a comparison of the early history of storage in a crystal mush with the later history of melt extraction and further crystallization prior to eruption, thus tracking development of erupted magma bodies from storage through eruption.

  7. Controls on banded pumice and enclave formation during magma mixing

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.; Manga, M.

    2011-12-01

    The deformation causing magma mixing can occur in a fluid-like manner to produce banded pumice or in a brittle manner to form enclaves. X-ray computed tomography (XRCT) and numerical modeling suggest that mixing style is controlled by whether the or not the host magma begins to convect before the intruding magma solidifies; the same two host and intruding magmas can thus form either enclaves or banded pumice depending on the size of the intruding magma body and the temperatures of the magmas. The critical control on mixing is competition between development of crystal networks in the intruding magma and melting and disruption of networks in the host. Consequently, the size of the intruding dike influences mixing style. XRCT analysis demonstrates that banded pumice from the 1915 Mt. Lassen eruption lack crystal networks and hence experienced mixing dominated by fluid flow. In contrast, rhyodacites with mafic enclaves from Chaos Crags contain well-developed networks of large crystals. Our model relies on three assumptions: 1) when magma crystallinity exceeds a critical value, ~13 vol.%, the magma develops a yield strength; 2) when crystallinity exceeds 40 vol.% (depending on mineral phase) the magma has a crystal network and is effectively solid; and 3) mixing is initiated by the injection of a hot dike into a cooler magma body with a yield strength. We model the mixing process as a 1-dimensional conductive cooling problem, use MELTS to calculate magma density, phase assemblages, and melt composition, and calculate melt viscosity using the method of Giordano et al. (2008), bulk viscosity using the Einstein-Roscoe equation, and yield strength using the method of Hoover et al. (2001). Importantly, because the two magmas are of different compositions, their crystallinities and viscosities do not have the same variations with temperature. Modeling begins with the instantaneous emplacement of a hot, mafic dike with crystallinity below 30 vol.% in a cooler, more silicic

  8. The Perils of Partition: Erroneous Results from Applying D Mineral/Magma to Rocks that Equilibrated Without Magma

    NASA Astrophysics Data System (ADS)

    Treiman, A. H.

    1995-09-01

    Compositions of extraterrestrial magmas are commonly derived from mineral compositions using, using experimentally determined mineral/basalt partition coefficients, Dmineral/basalt [1]. However, Dmineral/basalts cannot be applied to minerals which have experienced post-magmatic (subsolidus or metamorphic) chemical equilibration [2]. A failure to recognize post-magmatic equilibration can lead to wildly erroneous estimates of magma compositions and unrealistic scenarios of magmatic and planetary evolution [3]. To judge the effects of subsolidus chemical equilibration, consider REE distributions in a eucrite basalt, formed from a magma with CREE = 10 x CI. Let this magma crystallize and chemically equilibrate just below its solidus to a rock consisting of 49.5% plagioclase, 49.5% pigeonite, 0.1% whitlockite (a Ca phosphate), and 0.9% minor phases no REE content (silica, Fe metal, troilite); exact proportions are not critical. The total REE content ofthe rock is unchanged at 10 x CI, and distributions of REE among its minerals can be calculated from solidus-temperature Ds, e.g., Dpigeonite/plagioclase = Dpigeonite/basalt / Dplagioclase/basalt (where Dmineral/basalts are chosen to reflect the same magma compositions and temperature). REE abundances in minerals of this equilibrated rock (Figure 1 [5]) are significantly higher than they would be in the presence of magma. For instance, if this eucrite basalt system consisted of 50% magma, 25% pigeonite, and 25% plagioclase, one calculates C(La)Pigeonite = 0 04 x CI and C(La)Plagioclase = 0.8 x CI; with no magma present (Figure 1), C(La)Pigeonite = 0.4 x CI and CLaPIagioclase = 9 x CI! In the absence of magma, the incompatible REE must go somewhere!! If a mineral grain from this rock were used with Dmineral/basalts to derive a magma composition, that "Hparent basalt" would be rich in REE (130-200 x CI), enrichmed in light REE (La/Lu = 1.6 x CI), and strongly depleted in Eu. Compare this to the original eucrite, with REE at

  9. Solidifying the lunar magma ocean: Model results and geochronology (Invited)

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L. T.; Burgess, S. D.; Meyer, J.; Wisdom, J.

    2009-12-01

    The Moon is posited to have formed by reconsolidation of materials produced during a giant impact with the Earth early in solar system evolution. The young Moon appears to have experienced a magma ocean of some depth, which resulted in the formation of an anorthosite flotation crust. There is no simple way to reconcile W-Hf results for the age of Moon formation, U-Pb and Sm-Nd ages of lunar crustal crystallization, and modeling results for magma ocean solidification. At the beginning of magma ocean solidification the dense iron- and magnesium-rich phases crystallizing from the cooling magma are believed to have sunk to the bottom of the magma ocean. When approximately 80% of the lunar magma ocean solidified, anorthite began to crystallize and float upward through the more dense magma ocean liquid; anorthite will continue to be added to this flotation crust until the last dregs of the magma ocean solidify. The crystallization times of the anorthite in the flotation crust, therefore, could span the range from about 80% solidification to what has been interpreted as the lunar magma ocean solidification age. Models including convection in the remaining magma ocean, conduction through the growing anorthosite lid, and radiation into space indicate that the magma ocean may freeze to the point of anorthosite formation in less than 104 years, and perhaps as little as 103 years. After this brief free-surface cooling period the growth of the anorthosite lid radically slows heat loss, and complete solidification of the magma ocean will require additional tens of millions of years. Young anorthosite crustal ages, far younger than models would predict possible, may be explained by further investigations into the evolution of the lunar orbit. Tidal heating of the anorthosite crust as the young Moon experiences a period of high eccentricity may delay closure of minerals with radiogenic phases; these late-closing minerals will then yield young ages, though they originally formed

  10. Limits to magma mixing based on chemistry and mineralogy of pumice fragments erupted from a chemically zoned magma body

    SciTech Connect

    Vogel, T.A.; Ryerson, F.J.; Noble, D.C.; Younker, L.W.

    1987-09-01

    The chemical variation among pumice fragments from the Pahute Mesa Member of the Thirsty Canyon Tuff (Black Mountain volcanic center, southwestern Nevada) is consistent with magma withdrawal from a chemically zoned magma body. The top of this magma body contained little chemical variations, the lowest concentration of light REEs, and the highest concentrations of SiO/sub 2/, heavy REEs, and Th. The pumice fragments derived from the top of the magma body contain nearly pure ferrohedenbergite and fayalite. The next discrete zone in the magma body contained lower SiO/sub 2/, heavy REEs, and Th concentrations, and very high concentrations of light REEs. The lowest erupted layer contained relatively low concentrations of SiO/sub 2/, Th, and light and heavy REEs. Pumice fragments with polymodal disequilibrium phenocryst populations are a priori evidence of magma mixing. The magma mixing process is constrained by: the systematic vertical distribution of chemically distinct pumice fragments throughout the ash-flow sheet; the presence of disequilibrium phenocrysts within some pumice fragments in all but the lowermost part of the sheet; and the presence of compositionally uniform glass in most pumice fragments, including those with widely varying phenocryst compositions. Negligible mixing occurred at the top of the magma body; limited mixing occurred in the second and third layers. Because mixing did not destroy the original layering, the amount of guest magma must have been small. In order for unzoned disequilibrium phenocrysts to not become zoned, they must have been preserved in the magma body only a short time. And yet, in order to produce the homogeneous liquid that surrounds these phenocrysts, mechanical mixing must have been very efficient. 44 references.

  11. Forecasting magma-chamber rupture at Santorini volcano, Greece

    PubMed Central

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-01-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011–2012 unrest period, that the measured 0.02% increase in volume of Santorini’s shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano. PMID:26507183

  12. Ultra-rapid formation of large volumes of evolved magma

    NASA Astrophysics Data System (ADS)

    Michaut, C.; Jaupart, C.

    2006-10-01

    We discuss evidence for, and evaluate the consequences of, the growth of magma reservoirs by small increments of thin (⋍ 1-2 m) sills. For such thin units, cooling proceeds faster than the nucleation and growth of crystals, which only allows a small amount of crystallization and leads to the formation of large quantities of glass. The heat balance equation for kinetic-controlled crystallization is solved numerically for a range of sill thicknesses, magma injection rates and crustal emplacement depths. Successive injections lead to the accumulation of poorly crystallized chilled magma with the properties of a solid. Temperatures increase gradually with each injection until they become large enough to allow a late phase of crystal nucleation and growth. Crystallization and latent heat release work in a positive feedback loop, leading to catastrophic heating of the magma pile, typically by 200 °C in a few decades. Large volumes of evolved melt are made available in a short time. The time for the catastrophic heating event varies as Q- 2 , where Q is the average magma injection rate, and takes values in a range of 10 5-10 6 yr for typical geological magma production rates. With this mechanism, storage of large quantities of magma beneath an active volcanic center may escape detection by seismic methods.

  13. MAGMA: analysis of two-channel microarrays made easy.

    PubMed

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph

    2007-07-01

    The web application MAGMA provides a simple and intuitive interface to identify differentially expressed genes from two-channel microarray data. While the underlying algorithms are not superior to those of similar web applications, MAGMA is particularly user friendly and can be used without prior training. The user interface guides the novice user through the most typical microarray analysis workflow consisting of data upload, annotation, normalization and statistical analysis. It automatically generates R-scripts that document MAGMA's entire data processing steps, thereby allowing the user to regenerate all results in his local R installation. The implementation of MAGMA follows the model-view-controller design pattern that strictly separates the R-based statistical data processing, the web-representation and the application logic. This modular design makes the application flexible and easily extendible by experts in one of the fields: statistical microarray analysis, web design or software development. State-of-the-art Java Server Faces technology was used to generate the web interface and to perform user input processing. MAGMA's object-oriented modular framework makes it easily extendible and applicable to other fields and demonstrates that modern Java technology is also suitable for rather small and concise academic projects. MAGMA is freely available at www.magma-fgcz.uzh.ch.

  14. Forecasting magma-chamber rupture at Santorini volcano, Greece.

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-28

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

  15. Numerical modeling of shallow magma intrusions with finite element method

    NASA Astrophysics Data System (ADS)

    Chen, Tielin; Cheng, Shaozhen; Fang, Qian; Zhou, Cheng

    2017-03-01

    A numerical approach for simulation of magma intrusion process, considering the couplings of the stress distribution, the viscous fluid flow of magma, and the fracturing of host rock, has been developed to investigate the mechanisms of fracture initiation and propagation in host rock during magma intrusion without pre-placing a set of fractures. The study focused on the dike intrusions filled with injected viscous magma in shallow sediments. A series of numerical modellings were carried out to simulate the process of magma intrusion in host rocks, with particular attention on the magma propagation processes and the formation of intrusion shapes. The model materials were Mohr-Coulomb materials with tension failure and shear failure. The scenarios of both stochastically heterogeneous host rocks and layered host rocks were analyzed. The injected magma formed intrusions shapes of (a) dyke, (b) sill, (c) cup-shaped intrusion, (d) saucer-shaped intrusion. The numerical results were in agreement with the experimental and field observed results, which confirmed the adequacy and the power of the numerical approach.

  16. MAGMA: analysis of two-channel microarrays made easy

    PubMed Central

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph

    2007-01-01

    The web application MAGMA provides a simple and intuitive interface to identify differentially expressed genes from two-channel microarray data. While the underlying algorithms are not superior to those of similar web applications, MAGMA is particularly user friendly and can be used without prior training. The user interface guides the novice user through the most typical microarray analysis workflow consisting of data upload, annotation, normalization and statistical analysis. It automatically generates R-scripts that document MAGMA's entire data processing steps, thereby allowing the user to regenerate all results in his local R installation. The implementation of MAGMA follows the model-view-controller design pattern that strictly separates the R-based statistical data processing, the web-representation and the application logic. This modular design makes the application flexible and easily extendible by experts in one of the fields: statistical microarray analysis, web design or software development. State-of-the-art Java Server Faces technology was used to generate the web interface and to perform user input processing. MAGMA's object-oriented modular framework makes it easily extendible and applicable to other fields and demonstrates that modern Java technology is also suitable for rather small and concise academic projects. MAGMA is freely available at www.magma-fgcz.uzh.ch. PMID:17517778

  17. Draining mafic magma from conduits during Strombolian eruption

    NASA Astrophysics Data System (ADS)

    Wadsworth, F. B.; Kennedy, B.; Branney, M. J.; Vasseur, J.; von Aulock, F. W.; Lavallée, Y.; Kueppers, U.

    2014-12-01

    During and following eruption, mafic magmas can readily drain downward in conduits, dykes and lakes producing complex and coincident up-flow and down-flow textures. This process can occur at the top of the plumbing system if the magma outgases as slugs or through porous foam, causing the uppermost magma surface to descend and the magma to densify. In this scenario the draining volume is limited by the gas volume outgassed. Additionally, magma can undergo wholesale backflow when the pressure at the base of the conduit or feeder dyke exceeds the driving pressure in the chamber beneath. This second scenario will continue until pressure equilibrium is established. These two scenarios may occur coincidently as local draining of uppermost conduit magma by outgassing can lead to wholesale backflow because the densification of magma is an effective way to modify the vertical pressure profile in a conduit. In the rare case where conduits are preserved in cross section, the textural record of draining is often complex and great care should be taken in interpreting bimodal kinematic trends in detail. Lateral cooling into country rock leads to lateral profiles of physical and flow properties and, ultimately, outgassing potential, and exploration of such profiles elucidates the complexity involved. We present evidence from Red Crater volcano, New Zealand, and La Palma, Canary Islands, where we show that at least one draining phase followed initial ascent and eruption. We provide a rheological model approach to understand gravitational draining velocities and therefore, the timescales of up- and down-flow cycles predicted. These timescales can be compared with observed geophysical signals at monitored mafic volcanoes worldwide. Finally, we discuss the implications of shallow magma draining for edifice stability, eruption longevity and magma-groundwater interaction.

  18. Insights Into Magma Mixing from Bimodal Volcanic Centers

    NASA Astrophysics Data System (ADS)

    Hudgins, T.

    2016-12-01

    Magma mixing has been described as ubiquitous by some, and unlikely by others. Intermediate magmas in arc environments are oft attributed to magma mixing, however critics of magma mixing point to bimodal volcanic centers as evidence that magma mixing is not a plausible mechanism to generate intermediate magmas, given the large volumes of mafic and felsic lavas and the absence of intermediate lavas. Here we present a model that investigates the physical plausibility of mixing mafic and felsic magmas at bimodal volcanic centers. To do this we utilize the chemical and thermodynamic output of MELTS (Ghiorso and Sack, 1995) to constrain the changes in chemistry, crystallinity, viscosity, and enthalpy for mafic and felsic lavas erupted from the Trans-Mexican Volcanic Belt. The Trans-Mexican Volcanic Belt is an ideal place for this investigation as it erupted abundant mafic and felsic lavas from 7.5 - 3.0 Ma and has been well studied, providing a wealth of well characterized samples to work with. Using the MELTS output of these data we can assess under what conditions the viscosities (η) of the mafic and felsic magmas satisfy the experimentally constrained Δlog η (log(ηmafic/ηfelsic)) < 0.5 threshold for mixing. Variations between magma chamber conditions such as pressure, temperature, and composition in the Trans-Mexican Volcanic Belt and volcanic centers where mixing is proposed and has been modeled (e.g. Mt. Hood, Oregon; Mutnovsky, Kamchatka) are used to provide insight into why intermediate lavas are not present in bimodal volcanic centers.

  19. The Role and Behavior of Exsolved Volatiles in Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Edmonds, M.; Woods, A.

    2016-12-01

    There is an abundance of evidence for complex, vertically protracted and frequently recharged magma reservoirs in a range of tectonic settings. Geophysical evidence suggests that vertically protracted mushy zones with liquid-rich regions may extend throughout much of the crust and even beyond the Moho. Geochemical evidence suggests that magma mixing, as well as extensive fractional crystallization, dominates the differentiation of crystal-rich magmas. These magmas may reside for long timescales close to their solidus temperatures in the crust before being recharged by mafic magmas, which supply heat and volatiles. The volatile budgets and gas emissions associated with eruptions from these long-lived reservoirs typically show that there is an abundance of magmatic vapor emitted, far above that expected from syn-eruptive degassing of the erupted, crystal-rich intermediate or evolved melts. Eruptions are often associated with muted ground deformation, far less than expected to account for the volumes erupted, suggesting a compressible magma. Breccia pipes in a number of mafic layered intrusion settings, thought to be the expression of diatreme-like volcanism, testify to the importance of gas overpressure in slowly crystallizing magmas. These observations are all consistent with the existence of a substantial fraction of exsolved magmatic vapor throughout much of the upper crustal zones of the magma reservoir, which holds much of the sulfur, as well as carbon dioxide, chlorine and metal species. Reconstruction of the distribution and form of this exsolved vapor phase is a challenge, as there is little geochemical record in the erupted rocks, beyond that which may be established from melt inclusion studies. The most promising approach to understand the distribution and role of exsolved vapor in magma reservoir dynamics is through analogue experiments, which have yielded valuable insights into the role of crystals in modulating gas storage and flow in the plutonic and

  20. Diatexite Deformation and Magma Extraction on Kangaroo Island, South Australia

    NASA Astrophysics Data System (ADS)

    Hasalova, P.; Weinberg, R. F.; Ward, L.; Fanning, C. M.

    2012-12-01

    Migmatite terranes are structurally complex. We have investigated the relationships between deformation and magma extraction in migmatites formed during the Delamerian orogeny on Kangaroo Island. Several phases of deformation occurred in the presence of melt (D1-D4) and we describe how magma segregation, accumulation and extraction changes with deformation style. During an early upright folding event (D2), magma was channelled towards the hinge of antiforms. Funnel-shaped networks of leucosomes form a root that link towards a central axial planar channel, marking the main magma extraction paths. Extraction was associated with limb collapse, and antiformal hinge disruption. During a later deformation phase (D4), diatexites were sheared so that schollen were disaggregated into smaller blocks and schlieren, and deformed into asymmetric, sigmoidal shapes. Foliations in the magmatic matrix and schollen asymmetry indicate dextral shearing. During flow, magma accumulated in shear planes, indicating a dilational component during shearing (transtension) and on strain shadows of schollen. As deformation waned (post-D4), magma extraction from these diatexites gave rise to steeply dipping, funnel-shaped channels, similar to those developed during folding. The funnel-shape networks are interpreted as magma extraction networks and indicate magma flow direction. Structures developed during this phase are comparable with those developed during dewatering of soft sediments. The magmatic rocks from migmatites formed early, during folding, and formed late after deformation waned were dated. Both have two monazite (U-Pb, SHRIMP) age groups of ~490Ma and ~505-520Ma. The older sample has a well-defined peak at 505-510Ma and trails into the younger ages. The younger sample has the opposite, with few old spots and a well-defined young peak at ~490Ma. The age range indicates the duration of anatexis, and well-defined peaks are interpreted to mark the age of individual magma batch

  1. Magma energy extraction - Annual Report for FY88

    SciTech Connect

    Dunn, J.C.

    1989-08-01

    Thermal energy contained in magmatic systems represents a huge potential resource. In the US, useful energy contained in molten and partially-molten magma within the upper 10 km of the crust has been estimated at 50,000 to 500,000 Quads. The objective of the Magma Energy Extraction Program is to determine engineering feasibility of locating, accessing and utilizing magma as a viable energy resource. Engineering feasibility will depend on size and depth of the resource; extraction rates; and material life times. 11 refs., 29 figs., 1 tab.

  2. Mechanisms for the generation of compositional heterogeneities in magma chambers

    NASA Technical Reports Server (NTRS)

    Trial, Alain F.; Spera, Frank J.

    1990-01-01

    The two main hypotheses concerning the origin of compositional heterogeneities in magma chambers are discussed: (1) models in which the development of compositional zonation is simultaneous with the birth and growth of the magma body and (2) models in which zonation develops within an initially homogeneous batch of magma. The paper presents an overview of the geological possibilities and evaluates them on the basis of current research. Calculations are presented for boundary-layer flow in isothermal ternary component systems, and it is demonstrated that multicomponent diffusion effects may be very significant, as was earlier suggested by Trial and Spera (1988).

  3. How do crystal-rich magmas outgas?

    NASA Astrophysics Data System (ADS)

    Oppenheimer, Julie; Cashman, Katharine V.; Rust, Alison C.; Sandnes, Bjornar

    2014-05-01

    Crystals can occupy ~0 to 100% of the total magma volume, but their role in outgassing remains poorly understood. In particular, the upper half of this spectrum - when the particles touch - involves complex flow behaviours that inevitably affect the geometry and rate of gas migration. We use analogue experiments to examine the role of high particle concentrations on outgassing mechanisms. Mixtures of sugar syrup and glass beads are squeezed between two glass plates to allow observations in 2D. The experiments are performed horizontally, so buoyancy does not intervene, and the suspensions are allowed to expand laterally. Gas flow regimes are mapped out for two sets of experiments: foams generated by chemical reactions, and single air bubbles injected into the particle suspension. Chemically induced bubble nucleation and growth throughout the suspension gradually generated a foam and allowed observations of bubble growth and migration as the foam developed. High particle fractions, close to the random maximum packing, reduced foam expansion (i.e. promoted outgassing). In the early phases of the experiments, they caused a flushing of bubbles from the system which did not occur at low crystal contents. High particle fractions also led to melt segregation and phase re-arrangements, eventually focusing gas escape through connected channels. A more in-depth study of particle-bubble interactions was carried out for single bubbles expanding in a mush. These show a clear change in behaviour close to the limit for loose maximum packing of dry beads, determined experimentally. At concentrations below loose packing, gas expands in a fingering pattern, characterized by a steady advance of widening lobes. This transits to a 'pseudo-fracturing' regime at or near loose packing, whereby gas advances at a point, often in an episodic manner, and outgases with little to no bulk expansion. However, before they can degas, pseudo-fractures typically build up larger internal gas pressures

  4. Primary magmas and mantle temperatures through time

    NASA Astrophysics Data System (ADS)

    Ganne, Jérôme; Feng, Xiaojun

    2017-03-01

    Chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2 = 0.5) or constant redox condition (Fe2+/∑Fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal "horizons" (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (ΔTp) observed between Tp maxima and minima did not change significantly with time (˜170°C). Conversely, a progressive but limited cooling of ˜150°C is proposed since ˜2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al. [2010] (˜150-250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.Plain Language SummaryThe Earth's upper mantle constitutes a major interface between inner and outer envelops of the planet. We explore at high resolution its thermal state evolution (potential temperature of the ambient mantle, Tp) in depth and time using a multi-dimensional database of mafic lavas chemistry (>22</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Litho.155..272C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Litho.155..272C"><span>Assembly of a zoned volcanic <span class="hlt">magma</span> chamber from multiple <span class="hlt">magma</span> batches: The Cerberean Cauldron, Marysville Igneous Complex, Australia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Clemens, J. D.; Birch, W. D.</p> <p>2012-12-01</p> <p>The Late Devonian (374 Ma) Cerberean Cauldron forms the northern part of the Marysville Igneous Complex, in Central Victoria, Australia, filled with around 900 km3 of intra-caldera ignimbrites. The basal volcanic formation is the rhyolitic high-Al Rubicon Ignimbrite, overlain by a larger volume of crystal-rich rhyolitic low-Al Rubicon Ignimbrite, which grades upward into the voluminous, rhyodacitic Lake Mountain Ignimbrite. The rocks are S-type in character, with initial 87Sr/86Sr around 0.709 to 0.710 and ɛNdt varying from - 4.7 to - 6.0, suggesting metagreywacke protoliths. The chemistry of the volcanic rocks is incompatible with formation by a differentiation mechanism. Experimentally determined phase relations of a low-Al Rubicon Ignimbrite and a Lake Mountain Ignimbrite show that early crystallisation of the Lake Mountain <span class="hlt">magma</span> began at > 450 MPa and at > 875 °C (possibly up to 940 °C), with an initial <span class="hlt">magma</span> H2O content of 4.1 to 5.3 wt.%. In the pre-eruption <span class="hlt">magma</span> chamber, the Rubicon Ignimbrite <span class="hlt">magma</span> had a temperature of ≥ 780 °C and contained ≥ 4 wt.% H2O. Each formation, and indeed smaller volumes of rock, appears to have been produced by partial melting of slightly contrasting greywackes in a protolith with spatial variations in its chemistry and mineralogy, with the <span class="hlt">magma</span> delivered in batches to a high-level chamber. The Rubicon Ignimbrite <span class="hlt">magmas</span> underwent some internal differentiation, probably by crystal settling, prior to eruption, and variations in the Lake Mountain Ignimbrite are most probably due to small but variable degrees of peritectic phase entrainment. The limited gradation between the Rubicon Ignimbrite and Lake Mountain Ignimbrite is due to minor, pre-eruption mixing across the <span class="hlt">magma</span> interface. Such limited mixing between individual <span class="hlt">magma</span> batches appears typical of anatectic granitic <span class="hlt">magmas</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005E%26PSL.236..654B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005E%26PSL.236..654B"><span><span class="hlt">Magma</span> differentiation rates from ( 226Ra / 230Th) and the size and power output of <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blake, Stephen; Rogers, Nick</p> <p>2005-08-01</p> <p>We present a mathematical model for the evolution of the ( 226Ra / 230Th) activity ratio during simultaneous fractional crystallization and ageing of <span class="hlt">magma</span>. The model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization. These are tholeiitic basalt from Ardoukoba, Djibouti, MORB from the East Pacific Rise, alkali basalt to mugearite from Vestmannaeyjar, Iceland, and basaltic andesites from Miyakejima, Izu-Bonin arc. In all cases ( 226Ra / 230Th) correlates with indices of fractional crystallization, such as Th, and the data fall close to model curves of constant fractional crystallization rate. The best fit rates vary from 2 to 6 × 10 - 4 yr - 1 . Consequently, the time required to generate moderately evolved <span class="hlt">magmas</span> ( F ≤ 0.7) is of the order of 500 to 1500 yrs and closed <span class="hlt">magma</span> chambers will have lifetimes of 1700 to 5000 yrs. These rates and timescales are argued to depend principally on the specific power output (i.e., power output per unit volume) of the <span class="hlt">magma</span> chambers that are the sites of fractional crystallization. Equating the heat flux at the EPR to the heat flux from the sub-axial <span class="hlt">magma</span> chamber that evolves at a rate of ca. 3 × 10 - 4 yr - 1 implies that the <span class="hlt">magma</span> body is a sill of ca. 100 m thickness, a value which coincides with independent estimates from seismology. The similarity of the four inferred differentiation rates suggests that the specific power output of shallow <span class="hlt">magma</span> chambers in a range of tectonic settings covers a similarly narrow range of ca. 10 to 50 MW km - 3 . Their differentiation rates are some two orders of magnitude slower than that of the basaltic Makaopuhi lava lake, Hawaii, that cooled to the atmosphere. This is consistent with the two orders of magnitude difference in heat flux between Makaopuhi and the East Pacific Rise. ( 226Ra / 230Th) data for <span class="hlt">magma</span> suites related by fractional crystallization allow the <span class="hlt">magma</span> differentiation rate to be estimated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1111985B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1111985B"><span>Halogen behaviours during andesitic <span class="hlt">magma</span> degassing: from <span class="hlt">magma</span> chamber to volcanic plume</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balcone-Boissard, H.; Villemant, B.; Boudon, G.; Michel, A.</p> <p>2009-04-01</p> <p>Halogen (F, Cl, Br and I) behaviours during degassing of H2O-rich silicic <span class="hlt">magmas</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magmas</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/859089','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/859089"><span><span class="hlt">Magma</span> Dynamics at Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>D. Krier</p> <p>2005-08-29</p> <p>Small-volume basaltic volcanic activity at Yucca Mountain has been identified as one of the potential events that could lead to release of radioactive material from the U.S. Department of Energy (DOE) designated nuclear waste repository at Yucca Mountain. Release of material could occur indirectly as a result of magmatic dike intrusion into the repository (with no associated surface eruption) by changing groundwater flow paths, or as a result of an eruption (dike intrusion of the repository drifts, followed by surface eruption of contaminated ash) or volcanic ejection of material onto the Earth's surface and the redistribution of contaminated volcanic tephra. Either release method includes interaction between emplacement drifts and a magmatic dike or conduit, and natural (geologic) processes that might interrupt or halt igneous activity. This analysis provides summary information on two approaches to evaluate effects of disruption at the repository by basaltic igneous activity: (1) descriptions of the physical geometry of ascending basaltic dikes and their interaction with silicic host rocks similar in composition to the repository host rocks; and (2) a summary of calculations developed to quantify the response of emplacement drifts that have been flooded with <span class="hlt">magma</span> and repressurized following blockage of an eruptive conduit. The purpose of these analyses is to explore the potential consequences that could occur during the full duration of an igneous event.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5718994','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5718994"><span>Preliminary considerations for extraction of thermal energy from <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hickox, C.E.; Dunn, J.C.</p> <p>1985-01-01</p> <p>Simplified mathematical models are developed to describe the extraction of thermal energy from <span class="hlt">magma</span> based on the concept of a counterflow heat exchanger inserted into the <span class="hlt">magma</span> body. Analytical solutions are used to investigate influence of the basic variables on electric power production. Calculations confirm that the proper heat exchanger flow path is down the annulus with hot fluid returning to the surface through the central core. The core must be insulated from the annulus to achieve acceptable wellhead temperatures, but this insulation thickness can be quite small. The insulation is effective in maintaining the colder annular flow below expected formation temperatures so that a net heat gain from the formation above a <span class="hlt">magma</span> body is predicted. The analyses show that optimum flow rates exist that maximize electric power production. These optimum flow rates are functions of the heat transfer coefficients that describe <span class="hlt">magma</span> energy extraction. 15 refs., 3 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016LPICo1921.6148F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016LPICo1921.6148F"><span>Steam Atmosphere — <span class="hlt">Magma</span> Ocean Chemistry on the Early Earth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fegley, B.; Lodders, K.</p> <p>2016-08-01</p> <p>We use experimental data from the literature to calculate chemistry of the steam atmosphere — <span class="hlt">magma</span> ocean system on the early Earth. Our results show partitioning of rocky elements into the steam atmosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T11F..05D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T11F..05D"><span>The Role of <span class="hlt">Magma</span> Mixing in Creating Magmatic Diversity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davidson, J. P.; Collins, S.; Morgan, D. J.</p> <p>2012-12-01</p> <p>Most <span class="hlt">magmas</span> derived from the mantle are fundamentally basaltic. An assessment of actual magmatic rock compositions erupted at the earth's surface, however, shows greater diversity. While still strongly dominated by basalts, magmatic rock compositions extend to far more differentiated (higher SiO2, LREE enriched) compositions. Magmatic diversity is generated by differentiation processes, including crystal fractionation/ accumulation, crustal contamination and <span class="hlt">magma</span> mixing. Among these, <span class="hlt">magma</span> mixing is arguably inevitable in <span class="hlt">magma</span> systems that deliver <span class="hlt">magmas</span> from source-to-surface, since <span class="hlt">magmas</span> will tend to multiply re-occupy plumbing systems. A given mantle-derived <span class="hlt">magma</span> type will mix with any residual <span class="hlt">magmas</span> (and crystals) in the system, and with any partial melts of the wallrock which are generated as it is repeatedly flushed through the system. Evidence for <span class="hlt">magma</span> mixing can be read from the petrography (identification of crystals derived from different <span class="hlt">magmas</span>), a technique which is now well-developed and supplemented by isotopic fingerprinting (1,2) As a means of creating diversity, mixing is inevitably not efficient as its tendency is to blend towards a common composition (i.e. converging on homogeneity rather than diversity). It may be surprising then that many systems do not tend to homogenise with time, meaning that the timescales of mixing episodes and eruption must be similar to external <span class="hlt">magma</span> contributions of distinct composition (recharge?). Indeed recharge and mixing/ contamination may well be related. As a result, the consequences of <span class="hlt">magma</span> mixing may well bear on eruption triggering. When two <span class="hlt">magmas</span> mix, volatile exsolution may be triggered by retrograde boiling, with crystallisation of anhydrous phase(s) in either of the <span class="hlt">magmas</span> (3) or volatiles may be generated by thermal breakdown of a hydrous phase in one of the <span class="hlt">magmas</span> (4). The generation of gas pressures in this way probably leads to geophysical signals too (small earthquakes). Recent work pulling</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoRL..43.1543S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..43.1543S"><span>Time scales of crystal mixing in <span class="hlt">magma</span> mushes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schleicher, Jillian M.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain</p> <p>2016-02-01</p> <p><span class="hlt">Magma</span> mixing is widely recognized as a means of producing compositional diversity and preconditioning <span class="hlt">magmas</span> for eruption. However, the processes and associated time scales that produce the commonly observed expressions of <span class="hlt">magma</span> mixing are poorly understood, especially under crystal-rich conditions. Here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal-rich <span class="hlt">magma</span> mush that is subject to open-system reintrusion events. Our approach includes novel numerical simulations that resolve multiphase particle-fluid interactions. It also quantifies the crystal mixing by calculating both the local and system-wide progressive loss of the spatial correlation of individual crystals throughout the mixing region. Both inertial and viscous time scales for bulk mixing are introduced. Estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V13G2697J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V13G2697J"><span>The <span class="hlt">Magma</span> Transport System of the Mono Craters, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, M. R.; Putirka, K. D.</p> <p>2013-12-01</p> <p>The Mono Craters are a series of 28 volcanic domes, coulees, and craters, just 16 km north of Long Valley. The magmatic products of the Mono Craters include mostly small magmatic bodies, sills, and dikes set in a transtensional tectonic setting. New high-density sampling of the domes reveals a wider range of <span class="hlt">magma</span> compositions than heretofore recognized, and thus reveals what is likely a more complex magmatic system, involving a greater number of batches of <span class="hlt">magma</span> and a more complex <span class="hlt">magma</span> storage/delivery system. Here, we present a model for the <span class="hlt">magma</span> plumbing system based on space-composition patterns and preliminary estimates of crystallization temperatures and pressures based on olivine-, feldspar- and clinopyroxene-liquid equilibria. Whole rock analyses show three compositionally distinct batches of <span class="hlt">magma</span> within the Mono Craters proper: a felsic (73-78.4% SiO2), intermediate (64.4-68% SiO2) and mafic (52.7-61% SiO2) group. The Mono Lake Islands (Paoha and Negit) fall into the intermediate group, but contain distinctly lower TiO2 and Fe2O3 at a given SiO2 compared to all other Mono Craters; on this basis, we surmise that the Paoha and Negit eruptions represent a distinct episode of magmatism that is not directly related to the magmatic activity that created the Mono Craters proper. The discontinuous nature of the three groups indicates that <span class="hlt">magma</span> mixing, while evident to some degree within and between certain domes, did not encompass the entire range of compositions at any given time. The three groups, however, do form a rough linear trend, and some subsets of domes have compositions that fall on distinctly linear (if still discontinuous) trends that cannot be reproduced by fractional crystallization, but rather are indicative of <span class="hlt">magma</span> mixing. Our high-density sampling also reveals interesting geographical patterns: for example, felsic <span class="hlt">magmas</span> erupt throughout the entire Mono Craters chain, erupting at a wide range of temperatures, ranging from 650-995°C, but</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V23A3071L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V23A3071L"><span>Seismic Tremors and Three-Dimensional <span class="hlt">Magma</span> Wagging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liao, Y.; Bercovici, D.</p> <p>2015-12-01</p> <p>Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the <span class="hlt">magma</span>-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici et.al. 2013) that the <span class="hlt">magma</span> column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the <span class="hlt">magma</span> inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the <span class="hlt">magma</span> column is restricted to one vertical plane, the three-dimensional model we employ allows the <span class="hlt">magma</span> column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the <span class="hlt">magma</span> column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the <span class="hlt">magma</span> column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the <span class="hlt">magma</span> column leading to a coiled wagging motion. For the viscous-<span class="hlt">magma</span> model, we predict a similar damping rate for the uncoiled <span class="hlt">magma</span> column as in the two-dimensional model, and faster damping for the coiled <span class="hlt">magma</span> column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/884943','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/884943"><span>CONDITIONS LEADING TO SUDDEN RELEASE OF <span class="hlt">MAGMA</span> PRESSURE</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>B. Damjanac; E.S. Gaffney</p> <p>2005-08-26</p> <p>Buildup of magmatic pressures in a volcanic system can arise from a variety of mechanisms. Numerical models of the response of volcanic structures to buildup of pressures in <span class="hlt">magma</span> in dikes and conduits provide estimates of the pressures needed to reopen blocked volcanic vents. They also can bound the magnitude of sudden pressure drops in a dike or conduit due to such reopening. Three scenarios are considered: a dike that is sheared off by covolcanic normal faulting, a scoria cone over a conduit that is blocked by in-falling scoria and some length of solidified <span class="hlt">magma</span>, and a lava flow whose feed has partially solidified due to an interruption of <span class="hlt">magma</span> supply from below. For faulting, it is found that <span class="hlt">magma</span> would be able to follow the fault to a new surface eruption. A small increase in <span class="hlt">magma</span> pressure over that needed to maintain flow prior to faulting is required to open the new path, and the <span class="hlt">magma</span> pressure needed to maintain flow is lower but still greater than for the original dike. The <span class="hlt">magma</span> pressure needed to overcome the other types of blockages depends on the details of the blockage. For example, for a scoria cone, it depends on the depth of the slumped scoria and on the depth to which the <span class="hlt">magma</span> has solidified in the conduit. In general, failure of the blockage is expected to occur by radial hydrofracture just below the blocked length of conduit at <span class="hlt">magma</span> pressures of 10 MPa or less, resulting in radial dikes. However, this conclusion is based on the assumption that the fluid <span class="hlt">magma</span> has direct access to the rock surrounding the conduit. If, on the other hand, there is a zone of solidified basalt, still hot enough to deform plastically, surrounding the molten <span class="hlt">magma</span> in the conduit, this could prevent breakout of a hydrofracture and allow higher pressures to build up. In such cases, pressures could build high enough to deform the overlying strata (scoria cone or lava flow). Models of such deformations suggest the possibility of more violent eruptions resulting from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.7236P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.7236P"><span>A cellular automaton model for the rise of <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Piegari, Ester; di Maio, Rosa; Milano, Leopoldo; Scandone, Roberto</p> <p>2010-05-01</p> <p>Eruptions of volcanoes are complex natural events highly variable in size and time. Over the last couple of decades, statistical analyses of erupted volume and repose time catalogues have been performed for a large number of volcanoes. The aim of such analyses is either to predict future eruptive events or to define physical models for improving our understanding of the volcanic processes that cause eruptions. In particular, for this latter purpose we study a statistical model of eruption triggering caused by the fracturing of the crust above a <span class="hlt">magma</span> reservoir residing in the crust. When the fracturing reaches the reservoir, <span class="hlt">magma</span> is allowed to ascend because of its buoyancy. It will be found in batches along the transport region and it will ascend as long as fractures are developed to its tip; when a path is opened to the surface, an eruption occurs involving all batches connected to the opening. We model the vertical section of a volcanic edifice by means of a two-dimensional grid and characterize the state of each cell of the grid by assigning the values of two dynamical variables: a time dependent variable e describing the status of the local stress and a time-dependent variable n describing the presence of <span class="hlt">magma</span>. At first step of approximation, we treat the <span class="hlt">magma</span> presence field n as a diffusing lattice gas, and, therefore, we assume its value to be either zero or one if the corresponding cell is empty or filled by <span class="hlt">magma</span>, respectively. We study the probability distribution, P(V), of eruptions of volume V and the probability distribution, P(t), of inter-event time t and find that the model is able to reproduce, at least in a descriptive way, the essential statistical features of the activity of volcanoes. A key component of <span class="hlt">magma</span> is the quantity of dissolved gas as it gives <span class="hlt">magma</span> its explosive character, because the volume of gas expands as the pressure decreases on raising towards the surface. Then, to more accurately describe the rise of <span class="hlt">magma</span> in a volcanic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.V51B..07M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.V51B..07M"><span>The role of turbulence in explosive <span class="hlt">magma</span>-water mixing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mastin, L. G.; Walder, J. S.; Stern, L. A.</p> <p>2003-12-01</p> <p>Juvenile tephra from explosive hydromagmatic eruptions differs from that of dry magmatic eruptions by its fine average grain size and highly variable vesicularity. These characteristics are generally interpreted to indicate that fragmentation, which occurs in dry <span class="hlt">magmas</span> by bubble growth, is supplemented in hydromagmatic eruptions by quench-fracturing. Quench fragmentation is thought to accelerate heat transfer to water, driving violent steam expansion and increasing eruptive violence. Although some observed hydromagmatic events (e.g. at Surtsey) are indeed violent, others (e.g. quiescent entry of lava into the ocean at Kilauea) are not. We suggest that the violence of <span class="hlt">magma</span>-water mixing and the grain size and dispersal of hydromagmatic tephras are controlled largely by the turbulence of <span class="hlt">magma</span>-water mixing. At Surtsey, fine-grained, widely dispersed hydromagmatic tephras were produced primarily during continuous uprush events in which turbulent jets of <span class="hlt">magma</span> and gas passed through shallow water (Thorarinsson, 1967). During Kilauea's current eruption, videos show generation of fine-grained tephras when turbulent jets of <span class="hlt">magma</span>, steam, and seawater exited through skylights at the coastline. Turbulence intensity, or the fraction of total jet kinetic energy contained in fine-scale turbulent velocity oscillations, has long been known to control the scale of atomization in spray nozzles and the rate of heat transfer and chemical reaction in fuel injectors. We hypothesize that turbulence intensity also influences grain size and heat transfer rate in <span class="hlt">magma</span>-water mixing, though such processes are complicated by boiling (in water) and quench fracturing (in <span class="hlt">magma</span>). We are testing this hypothesis in experiments involving turbulent injection of water (a <span class="hlt">magma</span> analog) into liquid nitrogen (a water analog). We also suggest that turbulent mixing influences relative proportions of <span class="hlt">magma</span> and water in hydromagmatic eruptions. Empirical studies indicate that pressure-neutral turbulent</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013E%26PSL.383..182L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013E%26PSL.383..182L"><span>Crystallization and saturation front propagation in silicic <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lake, Ethan T.</p> <p>2013-12-01</p> <p>The cooling and crystallization style of silicic <span class="hlt">magma</span> bodies in the upper crust falls on a continuum between whole-chamber processes of convection, crystal settling, and cumulate formation and interface-driven processes of conduction and crystallization front migration. In the end-member case of vigorous convection and crystal settling, volatile saturation advances downward from the roof and upward from the floor throughout the chamber. In the end-member case of stagnant <span class="hlt">magma</span> bodies, volatile saturation occurs along an inward propagating front from all sides of the chamber. Ambient thermal gradient primarily controls the propagation rate; warm (⩾40 °C/km) geothermal gradients lead to thick (1200+ m) crystal mush zones and slow crystallization front propagation. Cold (<40 °C/km) geothermal gradients lead to rapid crystallization front propagation and thin (<1000 m) mush zones. <span class="hlt">Magma</span> chamber geometry also exerts a first-order control on propagation rates; bodies with high surface to <span class="hlt">magma</span> volume ratio and large Earth-surface-parallel faces exhibit more rapid propagation and thinner mush zones. Crystallization front propagation occurs at speeds of greater than 10 cm/yr (rhyolitic <span class="hlt">magma</span>; 1 km thick sill geometry in a 20 °C/km geotherm), far faster than diffusion of volatiles in <span class="hlt">magma</span> and faster than bubbles can nucleate, grow, and ascend through the chamber. Numerical simulations indicate saturation front propagation is determined primarily by pressure and <span class="hlt">magma</span> crystallization rate; above certain initial water contents (4.4 wt.% in a dacite) the mobile <span class="hlt">magma</span> is volatile-rich enough above 10 km depth to always contains a saturation front. Saturation fronts propagate down from the <span class="hlt">magma</span> chamber roof at lower water contents (3.3 wt.% in a dacite at 5 km depth), creating an upper saturated interface for most common (4-6 wt.%) <span class="hlt">magma</span> water contents. This upper interface promotes the production of a fluid pocket underneath the apex of the <span class="hlt">magma</span> chamber. If the fluid</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.6524H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.6524H"><span>Diatexite Deformation and <span class="hlt">Magma</span> Extraction on Kangaroo Island, South Australia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hasalova, Pavlina; Weinberg, Roberto; Ward, Lindsay; Fanning, Mark</p> <p>2013-04-01</p> <p>Migmatite terranes are structurally complex because of strong rheological contrast between layers with different melt contents and because of <span class="hlt">magma</span> migration leading to volume changes. Migmatite deformation is intimately linked with <span class="hlt">magma</span> extraction and the origin of granitoids. We investigate here the relationships between an evolving deformation and <span class="hlt">magma</span> extraction in migmatites formed during the ca. 500Ma Delamerian orogeny, exposed on Kangaroo Island, South Australia. Here, several phases of deformation occurred in the presence of melt. During an early upright, non-cylindrical folding event, <span class="hlt">magma</span> was channeled towards the hinge zones of antiforms. Funnel-shaped networks of leucosomes form a root zone that link up towards a central axial planar channel, forming the main <span class="hlt">magma</span> extraction paths during folding. Extraction was associated with fold limb collapse, and antiformal hinge disruption by <span class="hlt">magma</span> accumulation and transfer. During a later deformation phase, melt-rich diatexites were deformed, and schollen were disaggregated into smaller blocks and schlieren, and deformed into asymmetric, sigmoidal shapes indicative of dextral shearing flow. During flow, <span class="hlt">magma</span> accumulated preferentially along shear planes, indicating a dilatational component during shearing (transtension) and in strain shadows of schollen. As deformation waned, <span class="hlt">magma</span> extraction from these diatexites gave rise to N-trending, steeply dipping, funnel-shaped channels not associated to any deformational feature. The funnel-shape of these structures indicates the direction of <span class="hlt">magma</span> flow. Structures developed during this phase are comparable with those formed during dewatering of soft sediments. Despite a high degree of complexity, <span class="hlt">magma</span> migration and extraction features record distinct responses to the evolving deformation which can be used to understand deformation, and nature and direction of melt extraction. The oldest and youngest magmatic rocks from migmatites were dated (U-Pb monazite, SHRIMP</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V12B..07G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V12B..07G"><span>Tracking <span class="hlt">Magma</span> Degassing and Changes in <span class="hlt">Magma</span> Rheology Between Major Dome Collapse Events</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Genareau, K.; Cronin, S. J.; Lube, G.</p> <p>2012-12-01</p> <p>Merapi volcano, Java, Indonesia, produced two particularly large dome collapse events on 26 October and 5 November 2010, during its largest eruption since 1872. These were accompanied by explosive eruptions and highly destructive pyroclastic density currents that killed several hundred people in villages on the southern flanks. Previous work revealed that the tephras from the 26 October surges were dominated by free crystals liberated from a vesicular melt, while the 5 November tephras were dominated by juvenile lava fragments as the result of the development of permeable pathways for gas escape caused by vesicle coalescence and collapse. Scanning electron microscopic (SEM) examination of lava clasts from the 2010 surge-producing events at Merapi revealed differences in the groundmass crystallinities as a result of decompression-induced crystallization during <span class="hlt">magma</span> ascent over a time period of ten days. Lava clasts from the 5 November event contain microlite number densities over an order of magnitude higher than lava clasts from the 26 October collapse, 7.6 x 104 per mm2 versus 5.7 x 103 per mm2, respectively. The number density of plagioclase feldspar microlites is ten times higher in the 5 November event, while the number of pyroxene/Fe-oxide microlites is fifteen times higher compared to the 26 October event. Additionally, textures of the microlites provide information on <span class="hlt">magma</span> ascent rates during the two phases of <span class="hlt">magma</span> extrusion. 26 October lava clasts display euhedral and tabular plagioclase microlites with an average area of 133 μm2(n=100). 5 November lava clasts contain plagioclase microlites with lath-shaped and swallowtail morphologies and pyroxene/Fe-oxide microlites with anhedral, skeletal, and hopper morphologies, with most of the latter on the order of 1 μm in diameter. These variations in groundmass textures indicate that the lava extruded prior to the 5 November collapse event experienced a significant amount of decompression</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMOS43A1886A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMOS43A1886A"><span>A large <span class="hlt">magma</span> chamber and complex <span class="hlt">magma</span> delivery system revealed beneath Axial volcano</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arnulf, A. F.; Harding, A. J.; Kent, G.</p> <p>2013-12-01</p> <p>Axial volcano is located at 46N, 130W at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg seamount chain. It is the most recent eruptive center of the Cobb hotspot, which last erupted in 2011. The volcano rises ~700 m above the adjacent ridge axis, has two major rift zones extending ~50 km to the north and south and its summit features a 8-km-long, U-shaped caldera with an opening to the southeast where there is an active hydrothermal field and young lava flows. Located at the junction of a mid-ocean ridge and a volcanic hotspot, Axial volcano is part of an atypical segment of the intermediate spreading Juan de Fuca Ridge and its internal structure remains poorly understood. In this study, we have applied an accurate solution for imaging an active volcano combining full waveform inversion (FWI) with reverse time migration (RTM) imaging. Our approach produces images of the magmatic system at Axial volcano with spatial resolutions on the order of ~50 meters, at least an order of magnitude better resolution than traditional tomographic images of active magmatic systems. We show the clearest example to date of an unambiguous basal reflector from a melt lens system beneath a spreading centre. We find that the <span class="hlt">magma</span> reservoir is up to 1 km thick, the thickest <span class="hlt">magma</span> reservoir observed beneath a spreading centre to date. Interestingly, the amplitude of the <span class="hlt">magma</span> reflector is stronger to the southeast of Axial volcano, between 0 and 6 km off axis, which might reflect an offset between the Cobb hotspot at depth and Axial volcano; if this is correct, the narrow ribbon of melt extending away from the caldera may actually funnel melt from a decoupled hotspot toward Axial caldera. In addition, we present a unique image of the magmatic plumbing system underlying an active volcano that appears to be composed of a network of sub-horizontal to shallow dipping features (planes of weakness), which might cyclically be reactivated to transport melt from the <span class="hlt">magma</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8990H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8990H"><span><span class="hlt">Magma</span> Rich Events at <span class="hlt">Magma</span>-Poor Rifted Margins: A South-East Indian Example</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harkin, Caroline; Kusznir, Nick; Tugend, Julie; Manatschal, Gianreto; Horn, Brian</p> <p>2016-04-01</p> <p>The south-east Indian continental rifted margin, as imaged by the INE1-1000 deep long-offset seismic reflection section by ION Geophysical, is a classic example of a <span class="hlt">magma</span>-poor rifted margin, showing highly thinned continental crust, or possibly exhumed mantle, within the ocean-continent transition (OCT). Outboard, the steady-state oceanic crust is between 4 and 5 km thickness, consistent with <span class="hlt">magma</span>-poor continental breakup and sea-floor spreading. It is therefore surprising that between the hyper-extended crust showing thin or absent continental crust (of approximately 75 km width) and the anomalously thin steady-state oceanic crust, there appears to be a region of thicker magmatic crust of approximately 11 km thickness and 100 km width. Magmatic events, at or just after continental breakup, have also been observed at other <span class="hlt">magma</span>-poor rifted margins (e.g. NE Brazil). This interpretation of <span class="hlt">magma</span>-poor OCT structure and thinner than global average oceanic crust separated by thicker magmatic crust on the SE Indian margin is supported by gravity inversion; which uses a 3D spectral technique and includes a lithosphere thermal gravity anomaly correction. Residual depth anomaly (RDA) analysis corrected for sediment loading using flexural backstripping, gives a small negative value (approximately -0.1 km) over the steady-state oceanic crust compared with a positive value (approximately +0.3 km) over the thicker magmatic crust. This RDA difference is consistent with the variation in crustal thickness seen by the seismic reflection interpretation and gravity inversion. We use joint inversion of the time domain seismic reflection and gravity data to investigate the average basement density and seismic velocity of the anomalously thick magmatic crust. An initial comparison of Moho depth from deep long-offset seismic reflection data and gravity inversion suggests that its basement density and seismic velocity are slightly less than that of the outboard steady-state oceanic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1370','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1370"><span>Low-(18)O Silicic <span class="hlt">Magmas</span>: Why Are They So Rare?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Balsley, S.D.; Gregory, R.T.</p> <p>1998-10-15</p> <p>LOW-180 silicic <span class="hlt">magmas</span> are reported from only a small number of localities (e.g., Yellowstone and Iceland), yet petrologic evidence points to upper crustal assimilation coupled with fractional crystallization (AFC) during <span class="hlt">magma</span> genesis for nearly all silicic <span class="hlt">magmas</span>. The rarity of 10W-l `O <span class="hlt">magmas</span> in intracontinental caldera settings is remarkable given the evidence of intense 10W-l*O meteoric hydrothermal alteration in the subvolcanic remnants of larger caldera systems. In the Platoro caldera complex, regional ignimbrites (150-1000 km3) have plagioclase 6180 values of 6.8 + 0.1%., whereas the Middle Tuff, a small-volume (est. 50-100 km3) post-caldera collapse pyroclastic sequence, has plagioclase 8]80 values between 5.5 and 6.8%o. On average, the plagioclase phenocrysts from the Middle Tuff are depleted by only 0.3%0 relative to those in the regional tuffs. At Yellowstone, small-volume post-caldera collapse intracaldera rhyolites are up to 5.5%o depleted relative to the regional ignimbrites. Two important differences between the Middle Tuff and the Yellowstone 10W-180 rhyolites elucidate the problem. Middle Tuff <span class="hlt">magmas</span> reached water saturation and erupted explosively, whereas most of the 10W-l 80 Yellowstone rhyolites erupted effusively as domes or flows, and are nearly devoid of hydrous phenocrysts. Comparing the two eruptive types indicates that assimilation of 10W-180 material, combined with fractional crystallization, drives silicic melts to water oversaturation. Water saturated <span class="hlt">magmas</span> either erupt explosively or quench as subsurface porphyrins bejiire the magmatic 180 can be dramatically lowered. Partial melting of low- 180 subvolcanic rocks by near-anhydrous <span class="hlt">magmas</span> at Yellowstone produced small- volume, 10W-180 <span class="hlt">magmas</span> directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AREPS..31..399P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AREPS..31..399P"><span>Rheology of Granitic <span class="hlt">Magmas</span> During Ascent and Emplacement</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petford, Nick</p> <p></p> <p>Considerable progress has been made over the past decade in understanding the static rheological properties of granitic <span class="hlt">magmas</span> in the continental crust. Changes in H2O content, CO2 content, and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid/fluid mixture. Although the strengths of granitic <span class="hlt">magmas</span> over the crystallization interval are still poorly constrained, theoretical investigations suggest that during <span class="hlt">magma</span> ascent, yield strengths of the order of 9 kPa are required to completely retard the upward flow in meter-wide conduits. In low Bagnold number <span class="hlt">magma</span> suspensions with moderate crystal contents (solidosities 0.1 0.3), viscous fluctuations may lead to flow differentiation by shear-enhanced diffusion. AMS and microstructural studies support the idea that granite plutons are intruded as crystal-poor liquids ( 50%), with fabric and foliation development restricted to the final stages of emplacement. If so, then these fabrics contain no information on the ascent (vertical transport) history of the <span class="hlt">magma</span>. Deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt, resulting in a range of local macroscopic flow structures, including layering, crystal alignment, and other mechanical instabilities such as shear zones. As the suspension viscosity varies with stress rate, it is not clear how the timing of proposed rheological transitions formulated from simple equations for static <span class="hlt">magma</span> suspensions applies to mixtures undergoing shear. New theories of <span class="hlt">magmas</span> as multiphase flows are required if the full complexity of granitic <span class="hlt">magma</span> rheology is to be resolved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120003028','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120003028"><span>Experimental Fractional Crystallization of the Lunar <span class="hlt">Magma</span> Ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rapp, J. F.; Draper, D. S.</p> <p>2012-01-01</p> <p>The current paradigm for lunar evolution is of crystallization of a global scale <span class="hlt">magma</span> ocean, giving rise to the anorthositic crust and mafic cumulate interior. It is thought that all other lunar rocks have arisen from this differentiated interior. However, until recently this paradigm has remained untested experimentally. Presented here are the first experimental results of fractional crystallization of a Lunar <span class="hlt">Magma</span> Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V33E3164C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V33E3164C"><span>Crystalline heterogeneities and instabilities in thermally convecting <span class="hlt">magma</span> chamber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Culha, C.; Suckale, J.; Qin, Z.</p> <p>2016-12-01</p> <p>A volcanic vent can supply different densities of crystals over an eruption time period. This has been seen in Hawai'i's Kilauea Iki 1959 eruption; however it is not common for all Kilauea or basaltic eruptions. We ask the question: Under what conditions can homogenous <span class="hlt">magma</span> chamber cultivate crystalline heterogeneities? In some laboratory experiments and numerical simulations, a horizontal variation is observed. The region where crystals reside is identified as a retention zone: convection velocity balances settling velocity. Simulations and experiments that observe retention zones assume crystals do not alter the convection in the fluid. However, a comparison of experiments and simulations of convecting <span class="hlt">magma</span> with crystals suggest that large crystal volume densities and crystal sizes alter fluid flow considerably. We introduce a computational method that fully resolves the crystalline phase. To simulate basaltic <span class="hlt">magma</span> chambers in thermal convection, we built a numerical solver of the Navier-Stoke's equation, continuity equation, and energy equation. The modeled <span class="hlt">magma</span> is assumed to be a viscous, incompressible fluid with a liquid and solid phase. Crystals are spherical, rigid bodies. We create Rayleigh-Taylor instability through a cool top layer and hot bottom layer and update <span class="hlt">magma</span> density while keeping crystal temperature and size constant. Our method provides a detailed picture of <span class="hlt">magma</span> chambers, which we compare to other models and experiments to identify when and how crystals alter <span class="hlt">magma</span> chamber convection. Alterations include stratification, differential settling and instabilities. These characteristics are dependent on viscosity, convection vigor, crystal volume density and crystal characteristics. We reveal that a volumetric crystal density variation may occur over an eruption time period, if right conditions are met to form stratifications and instabilities in <span class="hlt">magma</span> chambers. These conditions are realistic for Kilauea Iki's 1959 eruption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70011752','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70011752"><span>Solidification of basaltic <span class="hlt">magma</span> during flow in a dike.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Delaney, P.T.; Pollard, D.D.</p> <p>1982-01-01</p> <p>A model for time-dependent unsteady heat transfer from <span class="hlt">magma</span> flowing in a dyke is developed. The ratio of solidification T to <span class="hlt">magma</span> T is the most important parameter. Observations of volcanic fissure eruptions and study of dykes near Ship Rock, New Mexico, show that the low T at dyke margins and the rapidly advancing solidification front predicted by the model are qualitatively correct.-M.S.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010820','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010820"><span>Composition and origin of basaltic <span class="hlt">magma</span> of the Hawaiian Islands</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Powers, H.A.</p> <p>1955-01-01</p> <p>Silica-saturated basaltic <span class="hlt">magma</span> is the source of the voluminous lava flows, erupted frequently and rapidly in the primitive shield-building stage of activity, that form the bulk of each Hawaiian volcano. This <span class="hlt">magma</span> may be available in batches that differ slightly in free silica content from batch to batch both at the same and at different volcanoes; differentiation by fractionation of olivine does not occur within this primitive <span class="hlt">magma</span>. Silica-deficient basaltic <span class="hlt">magma</span>, enriched in alkali, is the source of commonly porphyritic lava flows erupted less frequently and in relatively negligible volume during a declining and decadent stage of activity at some Hawaiian volcanoes. Differentiation by fractionation of olivine, plagioclase and augite is evident among these lavas, but does not account for the silica deficiency or the alkali enrichment. Most of the data of Hawaiian volcanism and petrology can be explained by a hypothesis that batches of <span class="hlt">magma</span> are melted from crystalline paridotite by a recurrent process (distortion of the equatorial bulge by forced and free nutational stresses) that accomplishes the melting only of the plagioclase and pyroxene component but not the excess olivine and more refractory components within a zone of fixed and limited depth. Eruption exhausts the supply of meltable <span class="hlt">magma</span> under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. ?? 1955.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.9373C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.9373C"><span>Non-Newtonian flow of bubbly <span class="hlt">magma</span> in volcanic conduits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Colucci, Simone; Papale, Paolo; Montagna, Chiara Paola</p> <p>2017-04-01</p> <p>The dynamics of <span class="hlt">magma</span> ascent along volcanic conduits towards the Earth's surface affects eruptive styles and contributes to volcanic hazard. The rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent, even determining effusive vs explosive eruptive behaviour. In this work we explore the effects of bubble-induced non-Newtonian rheology on the dynamics of <span class="hlt">magma</span> flow in volcanic conduits. We develop a quasi-2D model of <span class="hlt">magma</span> ascent that incorporates a rheological constitutive equation describing the strain-dependent effect of gas bubbles on the viscosity of the multiphase <span class="hlt">magma</span>. Non-Newtonian <span class="hlt">magma</span> flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges. Our results show that non-Newtonian rheology leads to greater exit velocity, mass flow, and density. The pressure distribution along the conduit remains very similar to the Newtonian case, deviating only at the conduit exit. Plug-like velocity profiles develop approaching the conduit exit, when mixture velocity is high, and are favored by smaller liquid viscosity. Since the mass flow rate, the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics, neglecting the non-Newtonian effect of bubble-bearing <span class="hlt">magmas</span> may result in misinterpretation of the deposit and, consequently, eruptive behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRB..122.1789C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRB..122.1789C"><span>Non-Newtonian flow of bubbly <span class="hlt">magma</span> in volcanic conduits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Colucci, S.; Papale, P.; Montagna, C. P.</p> <p>2017-03-01</p> <p>The dynamics of <span class="hlt">magma</span> ascent along volcanic conduits toward the Earth's surface affects eruptive styles and contributes to volcanic hazard. The rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent, even determining effusive versus explosive eruptive behavior. In this work we explore the effects of bubble-induced non-Newtonian rheology on the dynamics of <span class="hlt">magma</span> flow in volcanic conduits. We develop a quasi 2-D model of <span class="hlt">magma</span> ascent that incorporates a rheological constitutive equation describing the strain-dependent effect of gas bubbles on the viscosity of the multiphase <span class="hlt">magma</span>. Non-Newtonian <span class="hlt">magma</span> flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges. Our results show that non-Newtonian rheology leads to greater exit velocity, mass flow, and density. The pressure distribution along the conduit remains very similar to the Newtonian case, deviating only at the conduit exit. Plug-like velocity profiles develop approaching the conduit exit, when mixture velocity is high, and are favored by smaller liquid viscosity. Since the mass flow rate, the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics, neglecting that the non-Newtonian effect of bubble-bearing <span class="hlt">magmas</span> may result in misinterpretation of the deposit and, consequently, eruptive behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=Evolution+theory+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DEvolution%2Btheory%2Bevidence','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=Evolution+theory+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DEvolution%2Btheory%2Bevidence"><span>Geophysical and geochemical evolution of the lunar <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Herbert, F.; Drake, M. J.; Sonett, C. P.</p> <p>1978-01-01</p> <p>There is increasing evidence that at least the outer few hundred kilometers of the moon were melted immediately following accretion. This paper studies the evolution of this lunar <span class="hlt">magma</span> ocean. The long time scale for solidification leads to the inference that the plagioclase-rich (ANT) lunar crust began forming, perhaps preceded by local accumulations termed 'rockbergs', at the very beginning of the <span class="hlt">magma</span> ocean epoch. In this view the cooling and solidification of the <span class="hlt">magma</span> ocean was primarily controlled by the rate at which heat could be conducted across the floating ANT crust. Thus the thickness of the crust was the factor controlling the lunar solidification time. Heat arising from enthalpy of crystallization was transported in the <span class="hlt">magma</span> by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The <span class="hlt">magma</span> ocean is deduced to have been turbulent down to a characteristic length scale of the order of 100 m, and to have overturned on a time scale of the order of 1 yr for most of the <span class="hlt">magma</span> ocean epoch.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016BVol...78...78V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016BVol...78...78V"><span>Tracking dynamics of <span class="hlt">magma</span> migration in open-conduit systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Valade, Sébastien; Lacanna, Giorgio; Coppola, Diego; Laiolo, Marco; Pistolesi, Marco; Donne, Dario Delle; Genco, Riccardo; Marchetti, Emanuele; Ulivieri, Giacomo; Allocca, Carmine; Cigolini, Corrado; Nishimura, Takeshi; Poggi, Pasquale; Ripepe, Maurizio</p> <p>2016-11-01</p> <p>Open-conduit volcanic systems are typically characterized by unsealed volcanic conduits feeding permanent or quasi-permanent volcanic activity. This persistent activity limits our ability to read changes in the monitored parameters, making the assessment of possible eruptive crises more difficult. We show how an integrated approach to monitoring can solve this problem, opening a new way to data interpretation. The increasing rate of explosive transients, tremor amplitude, thermal emissions of ejected tephra, and rise of the very-long-period (VLP) seismic source towards the surface are interpreted as indicating an upward migration of the <span class="hlt">magma</span> column in response to an increased <span class="hlt">magma</span> input rate. During the 2014 flank eruption of Stromboli, this <span class="hlt">magma</span> input preceded the effusive eruption by several months. When the new lateral effusive vent opened on the Sciara del Fuoco slope, the effusion was accompanied by a large ground deflation, a deepening of the VLP seismic source, and the cessation of summit explosive activity. Such observations suggest the drainage of a superficial <span class="hlt">magma</span> reservoir confined between the crater terrace and the effusive vent. We show how this model successfully reproduces the measured rate of effusion, the observed rate of ground deflation, and the deepening of the VLP seismic source. This study also demonstrates the ability of the geophysical network to detect superficial <span class="hlt">magma</span> recharge within an open-conduit system and to track <span class="hlt">magma</span> drainage during the effusive crisis, with a great impact on hazard assessment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.5543B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.5543B"><span>Crystallization and Cooling of a Deep Silicate <span class="hlt">Magma</span> Ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bower, Dan; Wolf, Aaron</p> <p>2016-04-01</p> <p>Impact and accretion simulations of terrestrial planet formation suggest that giant impacts are both common and expected to produce extensive melting. The moon-forming impact, for example, likely melted the majority of Earth's mantle to produce a global <span class="hlt">magma</span> ocean that subsequently cooled and crystallised. Understanding the cooling process is critical to determining <span class="hlt">magma</span> ocean lifetimes and recognising possible remnant signatures of the <span class="hlt">magma</span> ocean in present-day mantle heterogeneities. Modelling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (<span class="hlt">magma</span> ocean) and viscous creep (present-day mantle), in addition to uncertainties in material properties and chemical partitioning. We consider a simplified spherically-symmetric (1-D) <span class="hlt">magma</span> ocean to investigate both its evolving structure and cooling timescale. Extending the work of Abe (1993), mixing-length theory is employed to determine convective heat transport, producing a high resolution model that parameterises the ultra-thin boundary layer (few cms) at the surface of the <span class="hlt">magma</span> ocean. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985RpESc....Q.101K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985RpESc....Q.101K"><span>Thermohydrodynamic model: Hydrothermal system, shallowly seated <span class="hlt">magma</span> chamber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kiryukhin, A. V.</p> <p>1985-02-01</p> <p>The results of numerical modeling of heat exchange in the Hawaiian geothermal reservoir demonstrate the possibility of appearance of a hydrothermal system over a <span class="hlt">magma</span> chamber. This matter was investigated in hydrothermal system. The equations for the conservation of mass and energy are discussed. Two possible variants of interaction between the <span class="hlt">magma</span> chamber and the hydrothermal system were computated stationary dry <span class="hlt">magma</span> chamber and dry <span class="hlt">magma</span> chamber changing volume in dependence on the discharge of <span class="hlt">magma</span> and taking into account heat exchange with the surrounding rocks. It is shown that the thermal supplying of the hydrothermal system can be ensured by the extraction of heat from a <span class="hlt">magma</span> chamber which lies at a depth of 3 km and is melted out due to receipt of 40 cubic km of basalt melt with a temperature of 1,300 C. The initial data correspond with computations made with the model to the temperature values in the geothermal reservoir and a natural heat transfer comparable with the actually observed values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=ants&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dants','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=ants&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dants"><span>Geophysical and geochemical evolution of the lunar <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Herbert, F.; Drake, M. J.; Sonett, C. P.</p> <p>1978-01-01</p> <p>There is increasing evidence that at least the outer few hundred kilometers of the moon were melted immediately following accretion. This paper studies the evolution of this lunar <span class="hlt">magma</span> ocean. The long time scale for solidification leads to the inference that the plagioclase-rich (ANT) lunar crust began forming, perhaps preceded by local accumulations termed 'rockbergs', at the very beginning of the <span class="hlt">magma</span> ocean epoch. In this view the cooling and solidification of the <span class="hlt">magma</span> ocean was primarily controlled by the rate at which heat could be conducted across the floating ANT crust. Thus the thickness of the crust was the factor controlling the lunar solidification time. Heat arising from enthalpy of crystallization was transported in the <span class="hlt">magma</span> by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The <span class="hlt">magma</span> ocean is deduced to have been turbulent down to a characteristic length scale of the order of 100 m, and to have overturned on a time scale of the order of 1 yr for most of the <span class="hlt">magma</span> ocean epoch.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813444H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813444H"><span>Thermal and mechanical controls on <span class="hlt">magma</span> supply and volcanic deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hickey, James; Gottsmann, Jo; Nakamichi, Haruhisa; Iguchi, Masato</p> <p>2016-04-01</p> <p>Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rock. Geodetic models aimed at constraining source processes consequently require the implementation of realistic mechanical and thermal rock properties. However, most generic models ignore this requirement and employ oversimplified mechanical assumptions without regard for thermal effects. Here we show how spatio-temporal deformation and <span class="hlt">magma</span> reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that despite on-going eruptions <span class="hlt">magma</span> is accumulating faster than it can be ejected, and the current uplift is approaching the level inferred prior to the 1914 Plinian eruption. Our results from inverse and forward numerical models are consistent with petrological constraints and highlight how the location, volume, and rate of <span class="hlt">magma</span> supply, 0.014 km3/yr, are thermomechanically controlled. <span class="hlt">Magma</span> storage conditions coincide with estimates for the caldera-forming reservoir ˜29,000 years ago, and the inferred <span class="hlt">magma</span> supply rate indicates a ˜130-year timeframe to amass enough <span class="hlt">magma</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PEPI..229...55X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PEPI..229...55X"><span>Constraints on volatile concentrations of pre-eruptive lunar <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Yingkui; Zhu, Dan; Wang, Shijie</p> <p>2014-04-01</p> <p>Until recently, the Moon had long been thought to be depleted of volatiles such as H2O, S, COx and Cl2. Researchers have recently measured volatile concentrations in the minerals, glasses and inclusions of lunar samples, and the results show that lunar rocks contain volatiles that are more similar to terrestrial materials than was previously thought. Mare basalts are located on the Earth-facing hemisphere in large impact basins, and they are not representative of the feldspathic highlands. Thus, it is likely that the density of lunar mafic <span class="hlt">magma</span> exceeds that of the highland rocks based on buoyancy alone. According to this observational fact, we calculate the density of mare basalt to give a constraint for the maximum amount of water mare basalt can contain because water can effectively decrease the density of mare <span class="hlt">magma</span>. Our result shows that water contained in the pre-eruptive <span class="hlt">magma</span> could not have been more than 1000 ppm; otherwise, the density of very-low-Ti basaltic <span class="hlt">magma</span> would be less than that of the highland rocks. Additionally, if <span class="hlt">magma</span> contains other species of volatiles such as C-O, S, F, or Cl2, the water in the pre-eruptive <span class="hlt">magma</span> would have to be much less than 1000 ppm because volatiles such as CO2 can effectively decrease the solubility of water in silicate melts. Based on these calculations on densities and a comparison with water in MORB, we conclude that the moon's water is not as great as has been recently suggested.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.V41F..02Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.V41F..02Z"><span>Why do <span class="hlt">magmas</span> stall? Insights from petrologic and geodetic data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zimmer, M. M.; Plank, T.; Freymueller, J.; Hauri, E. H.; Larsen, J. F.; Nye, C. J.</p> <p>2007-12-01</p> <p><span class="hlt">Magmas</span> stall at various depths in the crust due to their internal properties (<span class="hlt">magma</span> viscosity, buoyancy) and external crustal controls (local stress regime, wallrock strength). Annen et al. (JPet 2006) propose a petrological model in which buoyant <span class="hlt">magma</span> ascends through the crust until the depth of water saturation, after which it crystallizes catastrophically and stalls due to the large increase in <span class="hlt">magma</span> viscosity. <span class="hlt">Magmas</span> may erupt from this storage region, or viscous death may result in pluton formation. In order to test this model, and constrain <span class="hlt">magma</span> storage depths, we combine petrological and geodetic data for several active volcanoes along the Aleutian-Alaska arc. We analyzed glassy, primarily olivine-hosted melt inclusions by SIMS in tephra samples for their pre-eruptive volatile contents, which can be related to the depth of entrapment via pressure-dependent H2O-CO2 solubility models (e.g., VolatileCalc). Melt inclusions are not in equilibrium with pure water vapor (all will contain S and C species), but >50% of the inclusion population are in equilibrium with a vapor containing >85% H2O. Geodetic data (InSAR, GPS) record surface deformation related to volcano inflation/deflation, and can be inverted to solve for the depths of volume change (<span class="hlt">magma</span> storage) in the crust. In the Aleutians, we find that the maximum melt inclusion trapping depths and geodetic depths correlate, suggesting both techniques record crustal <span class="hlt">magma</span> storage and crystallization. Melt inclusions from the 1997 Okmok eruption are trapped at ≤3 km; deformation during the eruption and subsequent inflation occurred at 3±0.5 km (Miyagi et al., EPSL 2004; Lu & Masterlark, JGR 2005). At Akutan, melt inclusions and GPS data indicate <span class="hlt">magma</span> storage at ~5-7 km. Inclusions from flank cones of Makushin yield depths of 7 km, similar to inflation observed beneath the main edifice (6.8 km, Lu et al., JGR 2002). Pleistocene inclusions from Augustine volcano indicate <span class="hlt">magma</span> storage at 10-18 km, in accord</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.158...79M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.158...79M"><span>Anhydrite solubility in differentiated arc <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masotta, M.; Keppler, H.</p> <p>2015-06-01</p> <p>The solubility of anhydrite in differentiated arc <span class="hlt">magmas</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1818532H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1818532H"><span>The rheology of crystal-rich <span class="hlt">magmas</span> (Kuno Award Lecture)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim</p> <p>2016-04-01</p> <p>The rheology of <span class="hlt">magmas</span> controls not only eruption dynamics but also the rate of transport of <span class="hlt">magmas</span> through the crust and to a large extent the rate of <span class="hlt">magma</span> differentiation and degassing. <span class="hlt">Magma</span> bodies stalled in the upper crust are known to spend most of their lifespan above the solidus at a high crystal content (Cooper and Kent, 2014; Huber et al., 2009), where the probability of melt extraction (crystal fractionation) is the greatest (Dufek and Bachmann, 2010). In this study, we explore a new theoretical framework to study the viscosity of crystal bearing <span class="hlt">magmas</span>. Since the seminal work of A. Einstein and W. Sutherland in the early 20th century, it has been shown theoretically and tested experimentally that a simple self-similar behavior exist between the relative viscosity of dilute (low crystal content) suspensions and the particle volume fraction. The self-similar nature of that relationship is quickly lost as we consider crystal fractions beyond a few volume percent. We propose that the relative viscosity of crystal-bearing <span class="hlt">magmas</span> can be fully described by two state variables, the intrinsic viscosity and the crowding factor (a measure of the packing threshold in the suspension). These two state variables can be measured experimentally under different conditions, which allows us to develop closure relationships in terms of the applied shear stress and the crystal shape and size distributions. We build these closure equations from the extensive literature on the rheology of synthetic suspensions, where the nature of the particle shape and size distributions is better constrained and apply the newly developed model to published experiments on crystal-bearing <span class="hlt">magmas</span>. We find that we recover a self-similar behavior (unique rheology curve) up to the packing threshold and show that the commonly reported break in slope between the relative viscosity and crystal volume fraction around the expected packing threshold is most likely caused by a sudden change in the state</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.277..109G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.277..109G"><span>Phase equilibrium modelling of granite <span class="hlt">magma</span> petrogenesis: B. An evaluation of the <span class="hlt">magma</span> compositions that result from fractional crystallization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garcia-Arias, Marcos; Stevens, Gary</p> <p>2017-04-01</p> <p>Several fractional crystallization processes (flow segregation, gravitational settling, filter-pressing), as well as batch crystallization, have been investigated in this study using thermodynamic modelling (pseudosections) to test whether they are able to reproduce the compositional trends shown by S-type granites. Three starting compositions comprising a pure melt phase and variable amounts of entrained minerals (0, 20 and 40 wt.% of the total <span class="hlt">magma</span>) have been used to study a wide range of likely S-type <span class="hlt">magma</span> compositions. The evolution of these <span class="hlt">magmas</span> was investigated from the segregation from their sources at 0.8 GPa until emplacement at 0.3 GPa in an adiabatic path, followed by isobaric cooling until the solidus was crossed, in a closed-system scenario. The modelled <span class="hlt">magmas</span> and the fractionated mineral assemblages are compared to the S-type granites of the Peninsula pluton, Cape Granite Suite, South Africa, which have a composition very similar to most of the S-type granites. The adiabatic ascent of the <span class="hlt">magmas</span> digests partially the entrained mineral assemblage of the <span class="hlt">magmas</span>, but unless this entrained assemblage represents less than 1 wt.% of the original <span class="hlt">magma</span>, part of the mineral fraction survives the ascent up to the chosen pressure of emplacement. At the level of emplacement, batch crystallization produces <span class="hlt">magmas</span> that only plot within the composition of the granites of the Peninsula pluton if the bulk composition of the original <span class="hlt">magmas</span> already matched that of the granites. Flow segregation of crystals during the ascent and gravitational settling fractional crystallization produce bodies that are generally more mafic than the most mafic granites of the pluton and the residual melts have an almost haplogranitic composition, producing a bimodal compositional distribution not observed in the granites. Consequently, these two processes are ruled out. Filter-pressing fractional crystallization produces bodies in an onion-layer structure that become more felsic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V11C2771C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V11C2771C"><span>The <span class="hlt">Magma</span> Chamber Simulator: Modeling the Impact of Wall Rock Composition on Mafic <span class="hlt">Magmas</span> during Assimilation-Fractional Crystallization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Creamer, J. B.; Spera, F. J.; Bohrson, W. A.; Ghiorso, M. S.</p> <p>2012-12-01</p> <p>Although stoichiometric titration is often used to model the process of concurrent Assimilation and Fractional Crystallization (AFC) within a compositionally evolving <span class="hlt">magma</span> body, a more complete treatment of the problem involves simultaneous and self-consistent determination of stable phase relationships and separately evolving temperatures of both <span class="hlt">Magma</span> (M) and Wall Rock (WR) that interact as a composite M-WR system. Here we present results of M-WR systems undergoing AFC forward modeled with the <span class="hlt">Magma</span> Chamber Simulator (MCS), which uses the phase modeling capabilities of MELTS (Ghiorso & Sack 1995) as the thermodynamic basis. Simulations begin with one of a variety of mafic <span class="hlt">magmas</span> (e.g. HAB, MORB, AOB) intruding a set mass of Wall Rock (e.g. lherzolite, gabbro, diorite, granite, metapelite), and heat is exchanged as the M-WR system proceeds towards thermal equilibrium. Depending on initial conditions, the early part of the evolution can involve closed system FC while the WR heats up. The WR behaves as a closed system until it is heated beyond the solidus to critical limit for melt fraction extraction (fc), ranging between 0.08 and 0.12 depending on WR characteristics including composition and, rheology and stress field. Once fc is exceeded, a portion of the anatectic liquid is assimilated into the <span class="hlt">Magma</span>. The MCS simultaneously calculates mass and composition of the mineral assemblage (<span class="hlt">Magma</span> cumulates and WR residue) and melt (anatectic and <span class="hlt">Magma</span>) at each T along the equilibration trajectory. Sensible and latent heat lost or gained plus mass gained by the <span class="hlt">Magma</span> are accounted for by the MCS via governing Energy Constrained- Recharge Assimilation Fractional Crystallization (EC-RAFC) equations. In a comparison of two representative MCS results, consider a granitic WR intruded by HAB melt (51 wt. % SiO2) at liquidus T in shallow crust (0.1 GPa) with a WR/M ratio of 1.25, fc of 0.1 and a QFM oxygen buffer. In the first example, the WR begins at a temperature of 100o</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V44A..01N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V44A..01N"><span>When <span class="hlt">Magma</span> Might but Doesn't Erupt</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newhall, C.</p> <p>2008-12-01</p> <p>If we define failed eruptions as those in which <span class="hlt">magma</span> seemingly comes close to erupting but doesn't, 3 main variants are seen: (1) where volcanoes exhibit only fumarolic changes (strong steaming, sometimes but not always with high SO2 emission or fumarole temperatures) without notable other unrest (e.g,, Baker 1975; Fourpeaked 2006; Kudriavy, Satsuma-Iwojima, and Momotombo); (2) where seismic swarms, inflation, and other evidence of stress buildup simply stop, abruptly or slowly (e.g., Akutan 1996, Iliamna 1996); and (3) where unrest culminates in phreatic explosions (e.g., Soufrière Guadeloupe 1976, Bulusan-1980'-2000's, Canlaon 1990's-2000's, Iwo-Jima 2001, Huila 2007) A special case of (2) and (3) is when swarms of high-frequency earthquakes under or just off volcano flanks (distal volcano-tectonic earthquakes or DVT's) dominate seismicity (e.g., Tacana 1986, Guagua Pichincha 1998-99 during its phreatic phase); Another category, where deep LP earthquakes and/or deep-focus inflation stop after little or no shallow unrest (e.g., Three Sisters, Fuji), should not be called "failed" because <span class="hlt">magma</span> isn't (yet) close to erupting. Unrest with or without eruption is especially common at large <span class="hlt">magma</span>-hydrothermal systems beneath calderas (e.g., Rabaul 1982-84; Campi Flegrei 1969-70, 1982-85, 2004-06; Long Valley 1979-present). These are large, metastable systems that can buffer small incoming intrusions. Unrest is often prolonged. At Rabaul unrest died back but then resurged and <span class="hlt">magma</span> finally erupted in 1994. At Campi Flegrei and Long Valley, unrest still occurs intermittently as of 2008. Most failed eruptions involve <span class="hlt">magma</span> intrusion and/or acceleration of <span class="hlt">magma</span> convection in a conduit; a few may involve late-stage second boiling. The final step to magmatic eruption can be aborted by (a) loss of driving force (gas pressure, <span class="hlt">magma</span> supply) or (b) a physical barrier (solid; viscous or low-density <span class="hlt">magma</span>). Degassing diminishes driving force AND increases viscosity - a double</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5809540','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5809540"><span>Modelling of a <span class="hlt">magma</span> energy geothermal power plant</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Boehm, R.F.; Berg, D.L.; Jr.; Ortega, A.</p> <p>1987-01-01</p> <p>We are currently investigating the engineering feasibility of drilling into an active <span class="hlt">magma</span> body at a depth of roughly 5 km from the earth's surface, establishing a downhole heat exchange region, and extracting thermal energy from the <span class="hlt">magma</span> body by circulating fluid through this heat exchange region. In the present paper, we evaluate the overall thermodynamic performance of various conceptual <span class="hlt">magma</span> energy systems in which energy is added as heat to the fluid within the <span class="hlt">magma</span> region and is converted to useful work in a power conversion cycle at the surface. Unusually high return temperatures and pressures may be available at the wellhead of such a circulating well. Cycles investigated here are an open Rankine power system in which steam from the <span class="hlt">magma</span> well is circulated directly through a power conversion cycle and a closed Rankine cycle where the heated fluid from downhole is circulated through an aboveground heat exchanger to heat the cycle fluid. The downhole heat exchange region is established during the drilling process. As drilling proceeds into the <span class="hlt">magma</span>, a solidified layer forms about the drilling tube due to heat exchange to the fluid. This solidified layer thermally fractures because of large temperature gradients between the cooled inner region and the heated outer region, thereby opening secondary flow paths. Two models of the downhole behavior have been used. In the simplest approach, denoted as the ''infinite area model,'' the water entering the pipe to return to the surface is assumed to be always at the temperature of the <span class="hlt">magma</span>, independent of mass flow rate and other parameters. The other model is more detatiled and the fractured heat exchange region is modelled as a cylindrical porous layer through which fluid flows vertically. The net power and the performance aspects for the systems are investigated in terms of various parameters, including the characteristics of the downhole heat transfer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024098','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024098"><span><span class="hlt">Magma</span> storage prior to the 1912 eruption at Novarupta, Alaska</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hammer, J.E.; Rutherford, M.J.; Hildreth, W.</p> <p>2002-01-01</p> <p>New analytical and experimental data constrain the storage and equilibration conditions of the <span class="hlt">magmas</span> erupted in 1912 from Novarupta in the 20th century's largest volcanic event. Phase relations at H2O+CO2 fluid saturation were determined for an andesite (58.7 wt% SiO2) and a dacite (67.7 wt%) from the compositional extremes of intermediate <span class="hlt">magmas</span> erupted. The phase assemblages, matrix melt composition and modes of natural andesite were reproduced experimentally under H2O-saturated conditions (i.e., PH2O=PTOT) in a negatively sloping region in T-P space from 930 ??C/100 MPa to 960 ??C/75 MPa with fO2???N NO + 1. The H2O-saturated equilibration conditions of the dacite are constrained to a T-P region from 850 ??C/ 50 MPa to 880 ??C/25 MPa. If H2O-saturated, these <span class="hlt">magmas</span> equilibrated at (and above) the level where coerupted rhyolite equilibrated (???100 MPa), suggesting that the andesite-dacite <span class="hlt">magma</span> reservoir was displaced laterally rather than vertically from the rhyolite <span class="hlt">magma</span> body. Natural mineral and melt compositions of intermediate <span class="hlt">magmas</span> were also reproduced experimentally under saturation conditions with a mixed (H2O + CO2) fluid for the same range in PH2O. Thus, a storage model in which vertically stratified mafic to silicic intermediate <span class="hlt">magmas</span> underlay H2O-saturated rhyolite is consistent with experimental findings only if the intermediates have XH2Ofl=0.7 and 0.9 for the extreme compositions, respectively. Disequilibrium features in natural pumice and scoria include pristine minerals existing outside their stability fields, and compositional zoning of titanomagnetite in contact with ilmenite. Variable rates of chemical equilibration which would eliminate these features constrain the apparent thermal excursion and re-distribution of minerals to the time scale of days.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.413....1M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.413....1M"><span>Megacrystals track <span class="hlt">magma</span> convection between reservoir and surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moussallam, Yves; Oppenheimer, Clive; Scaillet, Bruno; Buisman, Iris; Kimball, Christine; Dunbar, Nelia; Burgisser, Alain; Ian Schipper, C.; Andújar, Joan; Kyle, Philip</p> <p>2015-03-01</p> <p>Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such <span class="hlt">magma</span> chambers may lead to vigorous convection as inferred from theoretical models and evidence for <span class="hlt">magma</span> mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of <span class="hlt">magma</span> transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk <span class="hlt">magma</span> flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of ∼150 days at a speed of ∼0.5 mm s-1) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic <span class="hlt">magma</span> is likely sustained by CO2 fluxing, suggesting that accumulation of mafic <span class="hlt">magma</span> in the lower crust is volumetrically more significant than that of evolved <span class="hlt">magma</span> within the edifice.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMDI11A2569W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMDI11A2569W"><span>Crystallization and Cooling of a Deep Silicate <span class="hlt">Magma</span> Ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolf, A. S.; Bower, D. J.</p> <p>2015-12-01</p> <p>Impact and accretion simulations of terrestrial planet formation suggest that giant impacts are both common and expected to produce extensive melting. The moon-forming impact, for example, likely melted the majority of Earth's mantle to produce a global <span class="hlt">magma</span> ocean that subsequently cooled and crystallized (e.g. Nakajima and Stevenson, 2015). Understanding the cooling process is critical to determining <span class="hlt">magma</span> ocean lifetimes and recognizing possible remnant signatures of the <span class="hlt">magma</span> ocean in present-day mantle heterogeneities (i.e. Labrosse et al., 2007). Modeling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (<span class="hlt">magma</span> ocean) and viscous creep (present-day mantle), in addition to uncertainties in material properties and chemical partitioning. We consider a simplified spherically-symmetric (1-D) <span class="hlt">magma</span> ocean to investigate both its evolving structure and cooling timescale. Extending the work of Abe (1993), mixing-length theory is employed to determine convective heat transport, producing a high resolution model that captures the ultra-thin boundary layer (few cms) at the surface of the <span class="hlt">magma</span> ocean. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting (important for multi-component systems). We derive a new high P-T equation of state (EOS) formulation designed to capture the energetics and physical properties of the partially molten system using parameters that are readily interpreted in the context of <span class="hlt">magma</span> ocean crystallization. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS (e.g., Mosenfelder et al., 2009; Stixrude et al., 2009).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V13B3102I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V13B3102I"><span>Linking Plagioclase Zoning Patterns to Active <span class="hlt">Magma</span> Processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Izbekov, P. E.; Nicolaysen, K. P.; Neill, O. K.; Shcherbakov, V.; Plechov, P.; Eichelberger, J. C.</p> <p>2015-12-01</p> <p>Plagioclase, one of the most common and abundant mineral phases in volcanic products, will vary in composition in response to changes in temperature, pressure, composition of the ambient silicate melt, and melt H2O concentration. Changes in these parameters may cause dissolution or growth of plagioclase crystals, forming characteristic textural and compositional variations (zoning patterns), the complete core-to-rim sequence of which describes events experienced by an individual crystal from its nucleation to the last moments of its growth. Plagioclase crystals in a typical volcanic rock may look drastically dissimilar despite their spatial proximity and the fact that they have erupted together. Although they shared last moments of their growth during <span class="hlt">magma</span> ascent and eruption, their prior experiences could be very different, as plagioclase crystals often come from different domains of the same <span class="hlt">magma</span> system. Distinguishing similar zoning patterns, correlating them across the entire population of plagioclase crystals, and linking these patterns to specific perturbations in the magmatic system may provide additional perspective on the variety, extent, and timing of <span class="hlt">magma</span> processes at active volcanic systems. Examples of <span class="hlt">magma</span> processes, which may be distinguished based on plagioclase zoning patterns, include (1) cooling due to heat loss, (2) heating and/or pressure build up due to an input of new magmatic material, (3) pressure drop in response to <span class="hlt">magma</span> system depressurization, and (4) crystal transfer between different <span class="hlt">magma</span> domains/bodies. This review will include contrasting examples of zoning patters from recent eruptions of Karymsky, Bezymianny, and Tolbachik Volcanoes in Kamchatka, Augustine and Cleveland Volcanoes in Alaska, as well as from the drilling into an active <span class="hlt">magma</span> body at Krafla, Iceland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JGRB..117.3204P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JGRB..117.3204P"><span>Experimental constraints on the outgassing dynamics of basaltic <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pioli, L.; Bonadonna, C.; Azzopardi, B. J.; Phillips, J. C.; Ripepe, M.</p> <p>2012-03-01</p> <p>The dynamics of separated two-phase flow of basaltic <span class="hlt">magmas</span> in cylindrical conduits has been explored combining large-scale experiments and theoretical studies. Experiments consisted of the continuous injection of air into water or glucose syrup in a 0.24 m diameter, 6.5 m long bubble column. The model calculates vesicularity and pressure gradient for a range of gas superficial velocities (volume flow rates/pipe area, 10-2-102 m/s), conduit diameters (100-2 m), and <span class="hlt">magma</span> viscosities (3-300 Pa s). The model is calibrated with the experimental results to extrapolate key flow parameters such as Co (distribution parameter) and Froude number, which control the maximum vesicularity of the <span class="hlt">magma</span> in the column, and the gas rise speed of gas slugs. It predicts that <span class="hlt">magma</span> vesicularity increases with increasing gas volume flow rate and decreases with increasing conduit diameter, until a threshold value (45 vol.%), which characterizes churn and annular flow regimes. Transition to annular flow regimes is expected to occur at minimum gas volume flow rates of 103-104 m3/s. The vertical pressure gradient decreases with increasing gas flow rates and is controlled by <span class="hlt">magma</span> vesicularity (in bubbly flows) or the length and spacing of gas slugs. This study also shows that until conditions for separated flow are met, increases in <span class="hlt">magma</span> viscosity favor stability of slug flow over bubbly flow but suggests coexistence between gas slugs and small bubbles, which contribute to a small fraction of the total gas outflux. Gas flow promotes effective convection of the liquid, favoring <span class="hlt">magma</span> homogeneity and stable conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V31B3032L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V31B3032L"><span><span class="hlt">Magma</span> Storage Conditions, Eruption Initiation and <span class="hlt">Magma</span> Evolution Over Time: Investigating the Eruptions of Organ Caldera, Southern NM</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lente, J. L.; Johnson, E. R.</p> <p>2015-12-01</p> <p>The Organ caldera in southern New Mexico formed ~36 Ma from a series of three explosive, voluminous eruptions. The volcanic deposits are now exposed in the Organ Mountains and have a combined thickness of nearly 3 km and an estimated volume between 500 and1000 km3 (Seager & McCurry, 1988). This research uses analyses of quartz-hosted melt inclusions from the first- and last-erupted units to study the storage and differentiation of the <span class="hlt">magma</span> body prior-to and during the initial eruption, as well as changes in the <span class="hlt">magma</span> chamber over time as the eruptions progressed and ultimately ceased. Previous work suggests the Organ <span class="hlt">magma</span> chamber was compositionally stratified (Seager, 1981) erupting top-down and tapping less-evolved <span class="hlt">magmas</span> over time. However, preliminary results suggest a more complex system; possibly a convecting, homogenized <span class="hlt">magma</span> chamber or a series of dykes and sills. Results obtained using FTIR analyses of H2O and CO2 in melt inclusions have shown variable volatile contents from the first erupted unit (~2.3 to 6.8 weight percent H2O, 0-118 ppm CO2). Using these values, saturation pressures of 45 to 266 MPa were calculated, indicating a minimum pressure at which the melt inclusion was trapped. These pressures suggest <span class="hlt">magma</span> storage depths for the first erupted <span class="hlt">magmas</span> of ~2 to 9 km (with most inclusions trapped between 4 and 8 km) which is inconsistent with the initial eruption coming from the top of a normally stratified chamber. The large variation in volatile contents and storage depths can have many explanations, such as degassing and shallow crystallization during ascent, or perhaps a more complex, elongate <span class="hlt">magma</span> storage system. These possibilities, and whether or not <span class="hlt">magma</span> mixing/rejuvenation triggered the initial eruption, will be explored with the acquisition of major and trace element compositions of melt inclusions. Additionally, analyses of melt inclusions from the last erupted ignimbrite, which erupted ~0.5 Ma after the first eruption, will enable</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.V51E..08R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.V51E..08R"><span>On the Itinerant History of Crystals in <span class="hlt">Magma</span> Reservoirs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reid, M. R.; Cooper, K. M.; Vazquez, J. A.; Simon, J. I.</p> <p>2004-12-01</p> <p>The storage times of <span class="hlt">magma</span> systems have been imaged by a variety of geophysical and geochemical approaches, each of which provides different insights because each is necessarily biased in some fashion. Perhaps the most fundamental bias is the predominance of <span class="hlt">magma</span> storage records based on extrusive rocks. This, in turn, implies some bias towards imaging of the most-fluid portions of a <span class="hlt">magma</span> reservoir. Factors that may affect the probability of eruption and therefore apparent storage intervals are the frequency and interplay between <span class="hlt">magma</span> replenishment and <span class="hlt">magma</span> arrest in the crust, the volatile content of the <span class="hlt">magma</span>, and the tectonic regime of magmatic activity. In situ Pb and Th isotopic analyses of the accessory phases zircon and allanite from rhyolites show 1) that successive eruptions can apparently sample the same crystal populations and 2) that crystal growth may occur intermittently, separated by up to tens of k.y. These results provide evidence for discontinuous crystal growth and for the rejuvenation of growth at least in part by <span class="hlt">magma</span> mixing and <span class="hlt">magma</span> replenishment. Chemical analyses suggest that these same observations also broadly apply to the major mineral phases but the chronological details could differ if crystals are selectively preserved during <span class="hlt">magma</span> ascent and/or mixing, and/or due to differential buoyancy between phases. Our work on the age and compositional zoning of allanite might be particularly revealing in this respect since the buoyancy of allanite is similar to those of major phases. Radiometric methods generally give older crystallization ages than those determined by kinetic considerations (e.g., CSD, diffusional relaxation). Accepting the kinetic ages at face value, crystallization appears to typically require <100 y. with a maximum duration of ˜s1 k.y. for major phenocryst phases. In apparent corroboration of these timescales, many <span class="hlt">magmas</span> have 226Ra excesses that are difficult to reconcile with <span class="hlt">magma</span> storage times of >few k.y. 230Th</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V54A..02H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V54A..02H"><span>Laboratory studies of crystal growth in <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hammer, J. E.; Welsch, B. T.; First, E.; Shea, T.</p> <p>2012-12-01</p> <p>The proportions, compositions, and interrelationships among crystalline phases and glasses in volcanic rocks cryptically record pre-eruptive intensive conditions, the timing of changes in crystallization environment, and the devolatilization history of eruptive ascent. These parameters are recognized as important monitoring tools at active volcanoes and interpreting geologic events at prehistoric and remote eruptions, thus motivating our attempts to understand the information preserved in crystals through an experimental appoach. We are performing laboratory experiments in mafic, felsic, and intermediate composition <span class="hlt">magmas</span> to study the mechanisms of crystal growth in thermochemical environments relevant to volcanic environments. We target features common to natural crystals in igneous rocks for our experimental studies of rapid crystal growth phenomena: (1) Surface curvature. Do curved interfaces and spongy cores represent evidence of dissolution (i.e., are they corrosion features), or do they record the transition from dendritic to polyhedral morphology? (2) Trapped melt inclusions. Do trapped liquids represent bulk (i.e., far-field) liquids, boundary layer liquids, or something intermediate, depending on individual species diffusivity? What sequence of crystal growth rates leads to preservation of sealed melt inclusions? (3) Subgrain boundaries. Natural phenocrysts commonly exhibit tabular subgrain regions distinguished by small angle lattice misorientations or "dislocation lamellae" and undulatory extinction. Might these crystal defects be produced as dendrites undergo ripening? (4) Clusters. Contacting clusters of polymineralic crystals are the building blocks of cumulates, and are ubiquitous features of mafic volcanic rocks. Are plagioclase and clinopyroxene aligned crystallographically, suggesting an epitaxial (surface energy) relationship? (5) Log-normal size distribution. What synthetic cooling histories produce "natural" distributions of crystal sizes, and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70023045','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70023045"><span>Carbon dioxide in <span class="hlt">magmas</span> and implications for hydrothermal systems</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lowenstern, J. B.</p> <p>2001-01-01</p> <p>This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in <span class="hlt">magma</span>-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and <span class="hlt">magma</span> alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle <span class="hlt">magmas</span>. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc <span class="hlt">magmas</span> via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to <span class="hlt">magmas</span> during <span class="hlt">magma</span>-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many <span class="hlt">magmas</span> are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic <span class="hlt">magmas</span>. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host <span class="hlt">magma</span>. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V34A..04M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V34A..04M"><span>Crystallization processes and 'adakitic' <span class="hlt">magmas</span>: mutually exclusive ? (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muntener, O.; Ulmer, P.</p> <p>2009-12-01</p> <p>There are at least 6 different processes that contribute to the genesis of so-called ‘adakitic’ <span class="hlt">magmas</span> (see session description V05) that all require some sort of (partial) melting of crustal lithologies. Since subduction zone geotherms derived from more complex numerical models that include temperature dependent viscosity became higher, partial melting of subducted crustal rocks is an attractive model to explain a wide variety of geochemical observations in arcs. Melting models plausibly explain highly incompatible elements in arcs such as Th, but probably less so major and moderately incompatible elements. Here we ask if the formation of ‘adakitic’ <span class="hlt">magmas</span> requires polybaric crystal fractionation at all, and if so, what are the potential consequences for 'adakite' genesis. We review the results of crystallization experiments of primary, mantle-derived hydrous <span class="hlt">magmas</span> and their derivatives under conditions prevailing in the uppermost mantle, at the base and in the lower part of island arc crust (0.8-1.5 GPa) and compare them to the results of partial melting experiments of metabasalts. We consider the mutual phase relations of the principal phases olivine, cpx, opx, garnet, amphibole, plagioclase and spinel at variable water contents and their bearing on the control of important trace elements and trace element ratios of arc <span class="hlt">magmas</span>. At pressures exceeding 0.8 GPa (25km), between 45 and 70% of the initial liquid mass produced ultramafic, garnet- bearing, clinopyroxene and amphibole dominated cumulates and derivative andesitic to dacitic <span class="hlt">magmas</span> that are typical for evolved island-arc <span class="hlt">magmas</span> and plutonic rocks (tonalites) forming the upper part of the igneous arc crust. Delayed plagioclase crystallization at the expense of early amphibole saturation shifts derivative liquids close to or even into the peraluminous field, so peraluminous compositions are not a straightforward criterion for melting. Based on well studied and relatively complete arc sections, we</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V43F..04P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V43F..04P"><span>Eddy Flow during <span class="hlt">Magma</span> Emplacement: The Basemelt Sill, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petford, N.; Mirhadizadeh, S.</p> <p>2014-12-01</p> <p>The McMurdo Dry Valleys magmatic system, Antarctica, forms part of the Ferrar dolerite Large Igneous Province. Comprising a vertical stack of interconnected sills, the complex provides a world-class example of pervasive lateral <span class="hlt">magma</span> flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle macrostructure of a congested <span class="hlt">magma</span> slurry1. Image-based numerical modelling where the intrusion geometry defines its own unique finite element mesh allows simulations of the flow regime to be made that incorporate realistic <span class="hlt">magma</span> particle size and flow geometries obtained directly from field measurements. One testable outcome relates to the origin of rhythmic layering where analytical results imply the sheared suspension intersects the phase space for particle Reynolds and Peclet number flow characteristic of macroscopic structures formation2. Another relates to potentially novel crystal-liquid segregation due to the formation of eddies locally at undulating contacts at the floor and roof of the intrusion. The eddies are transient and mechanical in origin, unrelated to well-known fluid dynamical effects around obstacles where flow is turbulent. Numerical particle tracing reveals that these low Re number eddies can both trap (remove) and eject particles back into the <span class="hlt">magma</span> at a later time according to their mass density. This trapping mechanism has potential to develop local variations in structure (layering) and <span class="hlt">magma</span> chemistry that may otherwise not occur where the contact between <span class="hlt">magma</span> and country rock is linear. Simulations indicate that eddy formation is best developed where <span class="hlt">magma</span> viscosity is in the range 1-102 Pa s. Higher viscosities (> 103 Pa s) tend to dampen the effect implying eddy development is most likely a transient feature. However, it is nice to think that something as simple as a bumpy contact could impart physical and by implication chemical diversity in igneous rocks. 1Marsh, D.B. (2004), A</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V52B..03G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V52B..03G"><span>Experimental Constraints on the Bishop Tuff <span class="hlt">Magma</span> Body</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gardner, J. E.; Befus, K. S.; Gualda, G. A.; Ghiorso, M. S.</p> <p>2013-12-01</p> <p>Hundreds to thousands of cubic kilometers of <span class="hlt">magma</span> must accumulate just before immense "super volcano" eruptions. The petrology and geochemistry of the giant <span class="hlt">magma</span> body that erupted to form the Bishop Tuff has served for decades as a cornerstone for petrologic models of such large accumulations of <span class="hlt">magma</span>. A benchmark for those models has been the thermal gradient of over 100° C thought to be preserved by the compositional variations of magnetite and ilmenite throughout the Bishop Tuff. Yet, despite the importance of the Bishop Tuff in our community's thinking about large <span class="hlt">magma</span> bodies, little experimental work has been carried out on its products to help constrain its pre-eruptive storage conditions. We have thus carried hydrothermal experiments using representative samples of the Bishop Tuff, all of which were run at conditions near the Ni-NiO oxygen buffer, equivalent to those recorded by magnetite-ilmenite equilibrium. Our results agree well with those predicted by the Rhyolite-MELTS thermodynamic model, including finding a narrow temperature range separating the crystallization of the first felsic mineral and the onset of the ternary minimum (quartz plus two feldspars), and extensive crystallization over a narrow temperature range once that minimum is reached. The hottest parts of the Bishop Tuff <span class="hlt">magma</span>, the so-called Late Bishop Tuff (LBT), crystallized two feldspars and quartz at water pressures of 100-120 MPa, based on water contents dissolved in quartz glass inclusions. Given those constraints, our results indicate that the LBT <span class="hlt">magma</span> was colder than about 740° C. Such low temperatures conflict with the much hotter ones purportedly preserved by magnetite-ilmenite compositions in the LBT (785° C for the sample used in the experiments). Experimentally, however, ilmenite and magnetite coexist only at temperatures below 750° C. The composition of clinopyroxene in LBT is homogeneous, and matches that of experimental clinopyroxene grown only at high temperature</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V41A3105M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V41A3105M"><span><span class="hlt">Magma</span> ascent and magmatism controlled by cratering on the Moon</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michaut, C.; Pinel, V.</p> <p>2016-12-01</p> <p>The lunar primary crust was formed by flotation of light plagioclase minerals on top of the lunar <span class="hlt">magma</span> ocean, resulting in a relatively light and thick crust. This crust acted as a barrier for the denser primary mantle melts: mare basalts erupted primarily within large impact basins where at least part of this crust was removed. Thus, lunar <span class="hlt">magmas</span> likely stored at the base of or deep in the lunar crust and the ascent of <span class="hlt">magma</span> to shallow depths probably required local or regional tensional stresses. On the Moon, evidences of shallow sites of magmatism are mostly concentrated within old and degraded simple and complex craters that surround the Mare basalts. Impacts, that were numerous in the early times of the Moon, created depressions at the lunar surface that induced specific states of stress. Below a crater, <span class="hlt">magma</span> ascent is helped by the tensional stresses caused by the depression up to a depth that is close to the crater radius. However, many craters that are the sites of shallow magmatism are less than 10 to 20 km in radius and are equally situated in regions of thin (i.e. 20 km) or thick (i.e. 60km) crust suggesting that the depression, although significant enough to control <span class="hlt">magma</span> emplacement, was not large enough to induce it. Since the sites of magmatism surround the mare basalts, we explore the common idea that the weight of the Mare induced a tensile state of stress in the surrounding regions. We constrain the regional state of stress that was necessary to help <span class="hlt">magma</span> ascent to shallow depths but was low enough for the local depression due to a crater to control <span class="hlt">magma</span> emplacement. This state of stress is consistent with a relatively thin but extended mare load. We also show that the depression due to the crater probably caused the horizontalization and hence the storage of the magmatic intrusion at shallow depth below the crater. In the end, because of the neutral buoyancy of <span class="hlt">magmas</span> in the crust and the lack of tectonic processes, impact processes largely</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V31F..01C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V31F..01C"><span><span class="hlt">Magmas</span>, Mushes and Mobility: Thermal Histories of <span class="hlt">Magma</span> Reservoirs from Combined U-Series and Diffusion Ages</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cooper, K. M.; Rubin, A. E.; Schrecengost, K.; Kent, A. J.; Huber, C.</p> <p>2014-12-01</p> <p>The thermal conditions of <span class="hlt">magma</span> storage control many aspects of the dynamics of a <span class="hlt">magma</span> reservoir system. For example, the temperature of <span class="hlt">magma</span> storage directly relates to the crystallinity, and <span class="hlt">magmas</span> stored at relatively low temperatures in a crystal mush (more than 40-50% crystalline) must be remobilized (e.g., by heating) before they can be erupted. A better understanding of the duration of <span class="hlt">magma</span> storage at largely-liquid vs. largely-solid conditions is thus critical to understanding crustal magmatic processes such as <span class="hlt">magma</span> mixing and for quantifying the hazard potential of a given volcano. Although mineral thermometry reflects the conditions of crystal growth or equilibration, these may not correspond to the thermal conditions of crystal storage. The duration of crystal storage at high temperatures can be quantified by comparing U-series crystal ages with the time scales over which disequilibrium trace-element profiles in the same crystals would be erased by diffusion. In the case of Mount Hood, OR, such a comparison for the two most recent eruptions shows that <12% of the total lifetime of plagioclase crystals (minimum 21 kyr) was spent at temperatures high enough that the <span class="hlt">magma</span> would be easily mobilized. Partial data sets for other systems suggest such behavior is common, although the diffusion and U-series ages in these cases are from different samples and may not be directly comparable. We will present preliminary data combining U-series dating and diffusion timescales on the same samples for other volcanic systems (e.g., Lassen Volcanic Center, Mount St. Helens, Okataina Volcanic Center, New Zealand). Combining these data with numerical models offers additional insights into the controls on the conditions of storage. In addition, extension of this approach to combining U-Th ages with time scales of Li diffusion in zircon offers a promising new method to quantify thermal histories of silicic reservoir systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoRL..42.7090W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoRL..42.7090W"><span>Linking <span class="hlt">magma</span> transport structures at Kīlauea volcano</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wech, Aaron G.; Thelen, Weston A.</p> <p>2015-09-01</p> <p>Identifying <span class="hlt">magma</span> pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long-period (LP) events dominate the shallow (5-10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending <span class="hlt">magma</span>. Using envelope cross-correlation, we systematically catalog non-earthquake seismicity between 2008 and 2014. We find that the LPs and deep tremor are spatially distinct, separated by the 15-25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader band (0.5-20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to <span class="hlt">magma</span> intruding from the mantle plume beneath the MFZ. We propose that the overlying MFZ promotes lateral <span class="hlt">magma</span> transport, linking this deep intrusion with Kīlauea's shallow <span class="hlt">magma</span> plumbing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70168969','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70168969"><span>Linking <span class="hlt">magma</span> transport structures at Kīlauea volcano</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Wech, Aaron G.; Thelen, Weston A.</p> <p>2015-01-01</p> <p>Identifying <span class="hlt">magma</span> pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long-period events (LPs) dominate the shallow (5-10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending <span class="hlt">magma</span>. Using envelope cross-correlation, we systematically catalog non-earthquake seismicity between 2008-2014. We find the LPs and deep tremor are spatially distinct, separated by the 15-25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader-band (0.5-20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to <span class="hlt">magma</span> intruding from the mantle plume beneath the MFZ. We propose the overlying MFZ promotes lateral <span class="hlt">magma</span> transport, linking this deep intrusion with Kīlauea’s shallow <span class="hlt">magma</span> plumbing.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.457..313D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.457..313D"><span>Imaging a <span class="hlt">magma</span> plumbing system from MASH zone to <span class="hlt">magma</span> reservoir</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Delph, Jonathan R.; Ward, Kevin M.; Zandt, George; Ducea, Mihai N.; Beck, Susan L.</p> <p>2017-01-01</p> <p>The Puna Plateau of the Central Andes is a well-suited location to investigate the processes associated with the tectono-magmatic development of a Cordilleran system. These processes include long-lived subduction (including shallow and steep phases), substantial crustal thickening, the emplacement of large volumes of igneous rocks, and probably delamination. To elucidate the processes associated with the development of a Cordilleran system, we pair Common Conversion Point-derived receiver functions with Rayleigh wave dispersion data from Ambient Noise Tomography. The resulting high-resolution shear wave velocity model of the southern Puna Plateau reveals the details of a lithospheric-scale <span class="hlt">magma</span> plumbing system. Slow velocities near the crust-mantle transition are interpreted as a MASH zone (a partially molten zone where mantle-derived melts interact with the lithosphere and undergo density differentiation) with ∼ 4- 9% melt. After differentiation, less dense and presumably more felsic melts propagate to shallower depths within the crust (∼20 km below surface) and comprise vertically (∼10 km) and laterally (∼75 km) extensive slow velocity bodies that span the frontal arc and plateau interior. These large slow velocity bodies represent a partially molten mid-crust (up to 22%) where <span class="hlt">magma</span> can further evolve to higher silica concentrations. The periodic influx of melt from the underlying MASH zone into these mid-crustal bodies may serve as a trigger to the eruption of the voluminous ignimbrites observed in the southern Puna Plateau. Many of the active tectonic processes operating along the southern Puna Plateau are thought to be analogous to the processes that formed the North American Cordillera. Thus, these results could provide insight into some of the processes associated with the development of a Cordilleran margin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120007400','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120007400"><span>Iron Redox Systematics of Shergottites and Martian <span class="hlt">Magmas</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Righter, Kevin; Danielson, L. R.; Martin, A. M.; Newville, M.; Choi, Y.</p> <p>2010-01-01</p> <p>Martian meteorites record a range of oxygen fugacities from near the IW buffer to above FMQ buffer [1]. In terrestrial <span class="hlt">magmas</span>, Fe(3+)/ SigmaFe for this fO2 range are between 0 and 0.25 [2]. Such variation will affect the stability of oxides, pyroxenes, and how the melt equilibrates with volatile species. An understanding of the variation of Fe(3+)/SigmaFe for martian <span class="hlt">magmas</span> is lacking, and previous work has been on FeO-poor and Al2O3-rich terrestrial basalts. We have initiated a study of the iron redox systematics of martian <span class="hlt">magmas</span> to better understand FeO and Fe2O3 stability, the stability of magnetite, and the low Ca/high Ca pyroxene [3] ratios observed at the surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4961867','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4961867"><span><span class="hlt">Magma</span> storage in a strike-slip caldera</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.</p> <p>2016-01-01</p> <p>Silicic calderas form during explosive volcanic eruptions when <span class="hlt">magma</span> withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of <span class="hlt">magma</span> reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of <span class="hlt">magma</span> constrains potential vent locations for future eruptions. PMID:27447932</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5598305','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5598305"><span>Origin of silicic <span class="hlt">magma</span> in Iceland revealed by Th isotopes</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sigmarsson, O.; Condomines, M. ); Hemond, C. ); Fourcade, S. ); Oskarsson, N. )</p> <p>1991-06-01</p> <p>Th, Sr, Nd, and O isotopes have been determined in a suite of volcanic rocks from Hekla and in a few samples from Askja and Krafla volcanic centers in Iceland. Although {sup 87}Sr/{sup 86}Sr and {sup 143}Nd/{sup 144}Nd ratios are nearly the same for all compositions at Hekla, the ({sup 230}Th/{sup 232}Th) ratios differ and thus clearly show that the silicic rocks cannot be derived from fractional crystallization of a more primitive <span class="hlt">magma</span>. Similar results are obtained for the Krafla and Askja volcanic centers, where the {delta}{sup 18}O values are much lower in the silicic <span class="hlt">magma</span> than in the mafic <span class="hlt">magma</span>. These data suggest that large volumes of silicic rocks in central volcanoes of the neovolcanic zones in Iceland are produced by partial melting of the underlying crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatCo...713744K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatCo...713744K"><span>Observing eruptions of gas-rich compressible <span class="hlt">magmas</span> from space</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kilbride, Brendan Mccormick; Edmonds, Marie; Biggs, Juliet</p> <p>2016-12-01</p> <p>Observations of volcanoes from space are a critical component of volcano monitoring, but we lack quantitative integrated models to interpret them. The atmospheric sulfur yields of eruptions are variable and not well correlated with eruption magnitude and for many eruptions the volume of erupted material is much greater than the subsurface volume change inferred from ground displacements. Up to now, these observations have been treated independently, but they are fundamentally linked. If <span class="hlt">magmas</span> are vapour-saturated before eruption, bubbles cause the <span class="hlt">magma</span> to become more compressible, resulting in muted ground displacements. The bubbles contain the sulfur-bearing vapour injected into the atmosphere during eruptions. Here we present a model that allows the inferred volume change of the reservoir and the sulfur mass loading to be predicted as a function of reservoir depth and the <span class="hlt">magma</span>'s oxidation state and volatile content, which is consistent with the array of natural data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28000791','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28000791"><span>Observing eruptions of gas-rich compressible <span class="hlt">magmas</span> from space.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kilbride, Brendan McCormick; Edmonds, Marie; Biggs, Juliet</p> <p>2016-12-21</p> <p>Observations of volcanoes from space are a critical component of volcano monitoring, but we lack quantitative integrated models to interpret them. The atmospheric sulfur yields of eruptions are variable and not well correlated with eruption magnitude and for many eruptions the volume of erupted material is much greater than the subsurface volume change inferred from ground displacements. Up to now, these observations have been treated independently, but they are fundamentally linked. If <span class="hlt">magmas</span> are vapour-saturated before eruption, bubbles cause the <span class="hlt">magma</span> to become more compressible, resulting in muted ground displacements. The bubbles contain the sulfur-bearing vapour injected into the atmosphere during eruptions. Here we present a model that allows the inferred volume change of the reservoir and the sulfur mass loading to be predicted as a function of reservoir depth and the <span class="hlt">magma</span>'s oxidation state and volatile content, which is consistent with the array of natural data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930049223&hterms=Plate+Tectonics&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DPlate%2BTectonics','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930049223&hterms=Plate+Tectonics&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DPlate%2BTectonics"><span>The <span class="hlt">magma</span> ocean as an impediment to lunar plate tectonics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Warren, Paul H.</p> <p>1993-01-01</p> <p>The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the <span class="hlt">magma</span> ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the <span class="hlt">magma</span> ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the <span class="hlt">magma</span> ocean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatCo...712295S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatCo...712295S"><span><span class="hlt">Magma</span> storage in a strike-slip caldera</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.</p> <p>2016-07-01</p> <p>Silicic calderas form during explosive volcanic eruptions when <span class="hlt">magma</span> withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of <span class="hlt">magma</span> reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of <span class="hlt">magma</span> constrains potential vent locations for future eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V11C2770A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V11C2770A"><span>Deep-level <span class="hlt">magma</span> ascent rates at Mt. Etna (Italy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Armienti, P.; Perinelli, C.; Putirka, K. D.</p> <p>2012-12-01</p> <p>Deep-level ascent rates are related to the triggering mechanisms of volcanic eruptions. Recent models and experimental studies have focused on the very shallow parts of <span class="hlt">magma</span> plumbing systems, mostly the upper few km, and have thus far emphasized that volatile contents and volatile exsolution, are key to understanding eruption dynamics and its fingerprint in the rock texture. Massive volatile loss induces a dramatic change in the liquidus temperature, thus producing observable effects on the rates of nucleation and growth of minerals . Volatile saturation, however, may well occur at greater depths, which means that initial stages of <span class="hlt">magma</span> ascent may be triggered by events taking place at much greater depths than those recorded by melt inclusions, likely captured at shallow levels. We present a method to evaluate ascent rates deep in a volcano plumbing system, discussing the implications for <span class="hlt">magma</span> dehydration and using Mt. Etna as case a study. We investigate the deeper levels of <span class="hlt">magma</span> transport by presenting detailed P-T paths for Etnean <span class="hlt">magmas</span>, and combining these with Crystal Size Distribution (CSD)-derived cooling rates. The key to this analysis is the recognition that the slope of a P-T path, as determined from mineral-melt thermobarometry, is a result of <span class="hlt">magma</span> cooling rate, which is in turn a function of <span class="hlt">magma</span> ascent via the effect of pressure on volatile solubility. We also rely on a thermodynamic treatment of exsolution of non-ideal H2O-CO2 mixtures, based on the Kerric & Jacobs (1981) model, and the simplified solubility model of CO2 (Spera & Bergman, 1980) and H2O (Nicholls, 1980), recalibrated with experimental and melt inclusions data from Mt. Etna. Our modeling is able to decipher <span class="hlt">magma</span> ascent velocity, v (dH/dt; H = depth, t = time), from ascent rate (dP/dt), and rate of cooling (dT/dt), where ρ is <span class="hlt">magma</span> density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/976355','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/976355"><span>Phenomena associated with <span class="hlt">magma</span> expansion into a drift</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gaffney, E. S.</p> <p>2002-01-01</p> <p>One of the significant threats to the proposed Yucca Mountain nuclear waste repository has been identified as the possibility of intersection of the underground structure by a basaltic intrusion. Based on the geology of the region, it is assumed that such an intrusion would consist of an alkali basalt similar to the nearby Lathrop Wells cone, which has been dated at about 78 ka. The threat of radioactive release may be either from eruption through the surface above the repository of basalt that had been contaminated or from migration through ground water of radionucleides released as a result of damage to waste packages that interact with the <span class="hlt">magma</span>. As part of our study of these threats, we are analyzing the phenomena associated with <span class="hlt">magma</span> expansion into drifts in tuff. The early phenomena of the encounter of volatile-rich basaltic <span class="hlt">magma</span> with a drift are discussed here.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27447932','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27447932"><span><span class="hlt">Magma</span> storage in a strike-slip caldera.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E</p> <p>2016-07-22</p> <p>Silicic calderas form during explosive volcanic eruptions when <span class="hlt">magma</span> withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of <span class="hlt">magma</span> reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of <span class="hlt">magma</span> constrains potential vent locations for future eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V44B..01T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V44B..01T"><span>Deep <span class="hlt">magma</span> feeding system of Fuji volcano, Japan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takahashi, E.; Asano, K.; Nakajima, J.</p> <p>2012-12-01</p> <p>Fuji volcano is known for its perfect cone shape and it is the largest among Japanese Quaternary volcanoes. For the last 100kya, Fuji has erupted dominantly basalt <span class="hlt">magma</span> (>>99 vol%), but its eruption style changed (from debris flow and tephra dominant Ko-Fuji or Older Fuji, to lava flow dominant Shin-Fuji or Younger Fuji) at ~15 kya BP. The incompatible trace element composition of the <span class="hlt">magma</span> changed abruptly between Ko-Fuji and Shin-Fuji. The origin of the voluminous yet monotonous basalt production and the simultaneous changes in volcanic style and <span class="hlt">magma</span> chemistry in Fuji volcano have been discussed but remain unanswered. Here we report the first high-pressure melting experimental results on Fuji Basalt (Hoei-IV, AD1707) and demonstrate that its main <span class="hlt">magma</span> chamber is located at ca.25km depth (Asano et al, this conference). We also show seismic tomographic images of Fuji volcano for the first time, which reveal the existence of strong upwelling flow in the mantle and its connection to the voluminous lower crustal <span class="hlt">magma</span> chamber (Fig.1). The chemistry of Fuji <span class="hlt">magma</span> is buffered by a lower crustal AFC <span class="hlt">magma</span> chamber located at 25-35km depth. Mantle derived primitive basalt (FeO/MgO~1.0, saturated with mantle peridotite assemblage, oliv+opx+cpx) changes to evolved basalt (FeO/MgO~2.0, saturated with lower crustal gabbroic assemblage, opx+cpx+pl) by the AFC process. Very frequent low frequency earthquakes just above the <span class="hlt">magma</span> chamber (red circles in Fig.1) may be due to the injection of basalt <span class="hlt">magma</span> and/or fluids (Ukawa, 2007). The total lack of silica-rich rocks (basaltic andesite and andesite) in Fuji volcano must be due to the special location of the volcano. As shown in Fig.1 (solid line), the plate boundary between the Eurasia plate and the subducting Phillipine sea plate is located just beneath Fuji volcano (~5 km depth). Large tectonic stress and deformation associated with the plate boundary inhibit the survival of a shallow level <span class="hlt">magma</span> chamber, which would allow</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5187499','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5187499"><span>Observing eruptions of gas-rich compressible <span class="hlt">magmas</span> from space</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kilbride, Brendan McCormick; Edmonds, Marie; Biggs, Juliet</p> <p>2016-01-01</p> <p>Observations of volcanoes from space are a critical component of volcano monitoring, but we lack quantitative integrated models to interpret them. The atmospheric sulfur yields of eruptions are variable and not well correlated with eruption magnitude and for many eruptions the volume of erupted material is much greater than the subsurface volume change inferred from ground displacements. Up to now, these observations have been treated independently, but they are fundamentally linked. If <span class="hlt">magmas</span> are vapour-saturated before eruption, bubbles cause the <span class="hlt">magma</span> to become more compressible, resulting in muted ground displacements. The bubbles contain the sulfur-bearing vapour injected into the atmosphere during eruptions. Here we present a model that allows the inferred volume change of the reservoir and the sulfur mass loading to be predicted as a function of reservoir depth and the <span class="hlt">magma</span>'s oxidation state and volatile content, which is consistent with the array of natural data. PMID:28000791</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JVGR..338...25S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JVGR..338...25S"><span>Decoding <span class="hlt">magma</span> plumbing and geochemical evolution beneath the Lastarria volcanic complex (Northern Chile)-Evidence for multiple <span class="hlt">magma</span> storage regions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stechern, André; Just, Tobias; Holtz, François; Blume-Oeste, Magdalena; Namur, Olivier</p> <p>2017-05-01</p> <p>The petrology of quaternary andesites and dacites from Lastarria volcano was investigated to reconstruct the <span class="hlt">magma</span> plumbing and storage conditions beneath the volcano. The mineral phase compositions and whole-rock major and trace element compositions were used to constrain temperature, pressure and possible mechanisms for <span class="hlt">magma</span> differentiation. The applied thermobarometric models include two-pyroxene thermobarometry, plagioclase-melt thermometry, amphibole composition thermobarometry, and Fe-Ti oxide thermo-oxybarometry. The overall temperature estimation is in the range 840 °C to 1060 °C. Calculated oxygen fugacity ranges between NNO to NNO + 1. Results of the geo-barometric calculations reveal multiple <span class="hlt">magma</span> storage regions, with a distinct storage level in the uppermost crust ( 6.5-8 km depth), a broad zone at mid-crustal levels ( 10-18 km depth), and a likely deeper zone at intermediate to lower crustal levels (> 20 km depth). The highest temperatures in the range 940-1040 °C are recorded in minerals stored in the mid-crustal levels ( 10-18 km depth). The whole-rock compositions clearly indicate that <span class="hlt">magma</span> mixing is the main parameter controlling the general differentiation trends. Complex zoning patterns and textures in the plagioclase phenocrysts confirm reheating and remobilization processes due to <span class="hlt">magma</span> replenishment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70035149','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70035149"><span>Molybdenite saturation in silicic <span class="hlt">magmas</span>: Occurrence and petrological implications</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Audetat, A.; Dolejs, D.; Lowenstern, J. B.</p> <p>2011-01-01</p> <p>We identified molybdenite (MoS2) as an accessory magmatic phase in 13 out of 27 felsic <span class="hlt">magma</span> systems examined worldwide. The molybdenite occurs as small (<20 ??m) triangular or hexagonal platelets included in quartz phenocrysts. Laser-ablation inductively coupled plasma mass spectrometry analyses of melt inclusions in molybdenite-saturated samples reveal 1-13 ppm Mo in the melt and geochemical signatures that imply a strong link to continental rift basalt-rhyolite associations. In contrast, arc-associated rhyolites are rarely molybdenite-saturated, despite similar Mo concentrations. This systematic dependence on tectonic setting seems to reflect the higher oxidation state of arc <span class="hlt">magmas</span> compared with within-plate <span class="hlt">magmas</span>. A thermodynamic model devised to investigate the effects of T, f O2 and f S2 on molybdenite solubility reliably predicts measured Mo concentrations in molybdenite-saturated samples if the <span class="hlt">magmas</span> are assumed to have been saturated also in pyrrhotite. Whereas pyrrhotite microphenocrysts have been observed in some of these samples, they have not been observed from other molybdenite-bearing <span class="hlt">magmas</span>. Based on the strong influence of f S2 on molybdenite solubility we calculate that also these latter <span class="hlt">magmas</span> must have been at (or very close to) pyrrhotite saturation. In this case the Mo concentration of molybdenite-saturated melts can be used to constrain both magmatic f O2 and f S2 if temperature is known independently (e.g. by zircon saturation thermometry). Our model thus permits evaluation of magmatic f S2, which is an important variable but is difficult to estimate otherwise, particularly in slowly cooled rocks. ?? The Author 2011. Published by Oxford University Press. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150007318','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150007318"><span>Lunar <span class="hlt">Magma</span> Ocean Crystallization: Constraints from Fractional Crystallization Experiments</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rapp, J. F.; Draper, D. S.</p> <p>2015-01-01</p> <p>The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale <span class="hlt">magma</span> ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar <span class="hlt">magma</span> ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep <span class="hlt">magma</span> ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow <span class="hlt">magma</span> ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper <span class="hlt">magma</span> ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after <span class="hlt">magma</span> ocean crystallization and the nature of KREEP</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006DPS....38.3001M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006DPS....38.3001M"><span>Tidal Dissipation in the Loki Patera <span class="hlt">Magma</span> Sea on Io</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matson, Dennis; Castillo, J.; Davies, A. G.; Veeder, G. J.; Johnson, T. V.</p> <p>2006-09-01</p> <p>We compute how tidal energy may be dissipated in the Loki Patera <span class="hlt">magma</span> sea using different models to describe the frequency-dependent response of the <span class="hlt">magma</span> in the sea. Our objective is to determine what role tidal dissipation may play in maintaining Loki Patera's thermal emission, some10-20% of Io's heat flow. We first model the Loki region as a Maxwell body. Such a model is governed by the silicate viscosity-temperature relationship. However, <span class="hlt">magma</span> is a non-newtonian liquid with a complex rheology dependent on interactions between the different phases present: liquid, crystals and bubbles form a slurry with each component responding differently to changing temperature and stress. The behaviour of cyclically stressed basalt has been observed in laboratory for frequencies between 0.005 and 1 Hz (periods of 1 to 200 s). Bagdassarov et al. show that models including a structural component are more appropriate to describe the behaviour of a multiphase medium. From the trend observed at low frequencies we extrapolate these data to tidal frequencies encountered at Io and combine them with field measurements of terrestrial <span class="hlt">magma</span> viscosity and crystal content as a function of temperature. From this modelling we derive bounds on Loki's volumetric heating. We also compute heating per unit area at the bottom of the <span class="hlt">magma</span> sea. We demonstrate that the system is self-regulated and stable in the long-term (≥106 years). Comparison between this model and observations allows the inference of constraints on the characteristics of the Loki <span class="hlt">magma</span> sea (e.g., depth). This work was performed at the Jet Propulsion Laboratory-California Institute of Technology under contract to NASA.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V13E2071A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V13E2071A"><span>Dike injection and <span class="hlt">magma</span> mixing in Kenya rift volcanoes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anthony, E. Y.; Espejel, V.; Biggs, J.</p> <p>2009-12-01</p> <p>A nexus of volcanoes in the rift graben at approximately the latitude of Nairobi consist of central vent trachyte, phonolite, and peralkaline rhyolite and cinder cone and fissure-fed flows of basalt to benmoreite. The volcanoes are referred to as the Central Kenya Peralkaline Province (CKPP, Macdonald and Scaillet, 2006, Lithos 91, 59-73) and formed by a combination of processes including fractional crystallization, <span class="hlt">magma</span> mixing, and volatile transport (Ren et al., 2006, Lithos 91, 109-124; Macdonald et al., 2008, JPet 49, 1515-1547). This presentation focuses on <span class="hlt">magma</span> mixing for trachytes and phonolites for Suswa rocks, which are the southernmost part of the CKPP. We also explore the contribution of <span class="hlt">magma</span> process studies to the interpretation of recent geodetic data, which indicate inflation/deflation of up to 21 cm for Kenyan volcanoes from 1997 to present (Biggs et al., 2009, Geology, in press). Incontrovertible evidence for <span class="hlt">magma</span> mixing is found in field evidence, where a basaltic trachyandesite ash horizon is found interbedded with syncaldera trachyte (Skilling, 1993, J. Geol. Society London 150, 885-896), hand-specimen and thin-section petrography, and disequilibrium mineral chemistry. Precaldera lavas contain a homogeneous group of anorthoclase crystals with An content 6% or less. Syncaldera samples contain this same group and two other populations: polysynthetic twinned labradorite and andesine and anorthoclase with An content of 17%. Textures for all three groups indicate disequilibrium. Postcaldera flows contain the high and low An anorthoclase populations but lack the polysynthetic twinned labradorite and andesine. These observations suggest a model of injection of mafic <span class="hlt">magmas</span> via diking into shallow trachtytic <span class="hlt">magma</span> systems. Recent geodetic studies of dike injection and subsequent seismic/volcanic activity in both Ethiopia and Lengai point to the ongoing importance of these processes to rift evolution in East Africa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015DPS....4740405B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015DPS....4740405B"><span>Exoplanet <span class="hlt">Magma</span> Ocean Magnetic Fields may be Common</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bourzutschky, Alexander; Stevenson, David</p> <p>2015-11-01</p> <p>Kepler data suggest that many exoplanets have low densities for their mass, and therefore probably have hydrogen-rich atmospheres. For all but very thin atmospheres, these have a convective zone beneath the radiative outer region, and as a consequence have high temperatures at the assumed silicate surface, usually above the liquidus, implying a <span class="hlt">magma</span> ocean. In many cases, the resulting high internal temperatures are sufficient to allow for dynamo action in the <span class="hlt">magma</span>. There, the electrical conductivities are high enough to support such a dynamo but not so high that the thermal conductivity favors conduction over convection. High conductivity is bad for a dynamo so this lower thermal conductivity makes such <span class="hlt">magma</span> ocean dynamos preferable to a putative iron core dynamo.In our simple models, the atmospheres of exoplanets will contain a convective zone beneath a radiative zone if sufficiently thick. We develop a simple model for the surface temperature of a rocky exoplanet with atmosphere-to-planet mass ratios 0.001% to 10%, planet masses 1-10 M⊕, and effective temperatures 150-1000 K. In most models with atmosphere mass ratios greater than 0.1% the rocky surface is above 1500 K, above the liquidus for silicate <span class="hlt">magma</span>. Assuming a fully molten silicate <span class="hlt">magma</span> ocean planet of Earthlike composition, the primary mode of heat transport is convection except at the high-temperature, high atmosphere mass ratio end. From that, even with conservative estimates of the electrical conductivity of the liquid silicate <span class="hlt">magma</span>, the nominal magnetic Reynolds number at the surface seldom falls below 10. Thus the tentative conclusion is that rocky exoplanets with sufficiently thick atmospheric envelopes to melt the surface can generate magnetic fields irrespective of their putative cores. Estimates of the magnetic field were done following Christensen, yielding surface values in the range of 0.1 to 0.5 Gauss.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70036578','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70036578"><span>Failed magmatic eruptions: Late-stage cessation of <span class="hlt">magma</span> ascent</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Moran, S.C.; Newhall, C.; Roman, D.C.</p> <p>2011-01-01</p> <p>When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: "deep intrusion", "shallow intrusion", "sluggish/viscous magmatic eruption", and "rapid, often explosive magmatic eruption". We define "failed eruptions" as instances in which <span class="hlt">magma</span> reaches but does not pass the "shallow intrusion" stage, i. e., when <span class="hlt">magma</span> gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a <span class="hlt">magma</span> intrusion. Fresh intrusion from depth, high <span class="hlt">magma</span> gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased <span class="hlt">magma</span> supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause <span class="hlt">magma</span> to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.9610G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.9610G"><span>Imaging <span class="hlt">magma</span> plumbing beneath Askja volcano, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greenfield, Tim; White, Robert S.</p> <p>2015-04-01</p> <p>Volcanoes during repose periods are not commonly monitored by dense instrumentation networks and so activity during periods of unrest is difficult to put in context. We have operated a dense seismic network of 3-component, broadband instruments around Askja, a large central volcano in the Northern Volcanic Zone, Iceland, since 2006. Askja last erupted in 1961, with a relatively small basaltic lava flow. Since 1975 the central caldera has been subsiding and there has been no indication of volcanic activity. Despite this, Askja has been one of the more seismically active volcanoes in Iceland. The majority of these events are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the <span class="hlt">magma</span> plumbing system. More intriguing are the less numerous deeper earthquakes at 12-24km depth, situated in three distinct areas within the volcanic system. These earthquakes often show a frequency content which is lower than the shallower activity, but they still show strong P and S wave arrivals indicative of brittle failure, despite their location being well below the brittle-ductile boundary, which, in Askja is ~7km bsl. These earthquakes indicate the presence of melt moving or degassing at depth while the volcano is not inflating, as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. The lower frequency content must be the result of a slower source time function as earthquakes which are both high frequency and low frequency come from the same cluster, thereby discounting a highly attenuating lower crust. To image the plumbing system beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.272..261R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.272..261R"><span>Silicic <span class="hlt">magma</span> differentiation in ascent conduits. Experimental constraints</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rodríguez, Carmen; Castro, Antonio</p> <p>2017-02-01</p> <p>Crystallization of water-bearing silicic <span class="hlt">magmas</span> in a dynamic thermal boundary layer is reproduced experimentally by using the intrinsic thermal gradient of piston-cylinder assemblies. The standard AGV2 andesite under water-undersaturated conditions is set to crystallize in a dynamic thermal gradient of about 35 °C/mm in 10 mm length capsules. In the hotter area of the capsule, the temperature is initially set at 1200 °C and decreases by programmed cooling at two distinct rates of 0.6 and 9.6 °C/h. Experiments are conducted in horizontally arranged assemblies in a piston cylinder apparatus to avoid any effect of gravity settling and compaction of crystals in long duration runs. The results are conclusive about the effect of water-rich fluids that are expelled out the crystal-rich zone (mush), where water saturation is reached by second boiling in the interstitial liquid. Expelled fluids migrate to the <span class="hlt">magma</span> ahead of the solidification front contributing to a progressive enrichment in the fluxed components SiO2, K2O and H2O. The composition of water-rich fluids is modelled by mass balance using the chemical composition of glasses (quenched melt). The results are the basis for a model of granite <span class="hlt">magma</span> differentiation in thermally-zoned conduits with application of in-situ crystallization equations. The intriguing textural and compositional features of the typical autoliths, accompanying granodiorite-tonalite batholiths, can be explained following the results of this study, by critical phenomena leading to splitting of an initially homogeneous <span class="hlt">magma</span> into two <span class="hlt">magma</span> systems with sharp boundaries. <span class="hlt">Magma</span> splitting in thermal boundary layers, formed at the margins of ascent conduits, may operate for several km distances during <span class="hlt">magma</span> transport from deep sources at the lower crust or upper mantle. Accordingly, conduits may work as chromatographic columns contributing to increase the silica content of ascending <span class="hlt">magmas</span> and, at the same time, leave behind residual mushes that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.448..140M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.448..140M"><span>On the cooling of a deep terrestrial <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Monteux, J.; Andrault, D.; Samuel, H.</p> <p>2016-08-01</p> <p>Several episodes of complete melting have probably occurred during the first stages of the Earth's evolution. We have developed a numerical model to monitor the thermal and melt fraction evolutions of a cooling and crystallizing <span class="hlt">magma</span> ocean from an initially fully molten mantle. For this purpose, we numerically solve the heat equation in 1D spherical geometry, accounting for turbulent heat transfer, and integrating recent and strong experimental constraints from mineral physics. We have explored different initial <span class="hlt">magma</span> ocean viscosities, compositions, thermal boundary layer thicknesses and initial core temperatures. We show that the cooling of a thick terrestrial <span class="hlt">magma</span> ocean is a fast process, with the entire mantle becoming significantly more viscous within 20 kyr. Due to the slope difference between the adiabats and the melting curves, the solidification of the molten mantle occurs from the bottom up. In the meantime, a crust forms due to the high surface radiative heat flow, the last drop of fully molten silicate is restricted to the upper mantle. Among the studied parameters, the <span class="hlt">magma</span> ocean lifetime is primarily governed by its viscosity. Depending on the thermal boundary layer thickness at the core-mantle boundary, the thermal coupling between the core and <span class="hlt">magma</span> ocean can either insulate the core during the <span class="hlt">magma</span> ocean solidification and favor a hot core or drain the heat out of the core simultaneously with the cooling of the <span class="hlt">magma</span> ocean. Reasonable thickness for the thermal boundary layer, however, suggests rapid core cooling until the core-mantle boundary temperature results in a sluggish lowermost mantle. Once the crystallization of the lowermost mantle becomes significant, the efficiency of the core heat loss decreases. Since a hotter liquidus favors crystallization at hotter temperatures, a hotter deep mantle liquidus favors heat retention within the core. In the context of an initially fully molten mantle, it is difficult to envision the formation of a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V53C3139G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V53C3139G"><span>Determining the <span class="hlt">Magma</span> Genesis of Mo Porphyry Deposits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaynor, S.; Coleman, D. S.; Rosera, J.</p> <p>2015-12-01</p> <p>The high flux of <span class="hlt">magma</span> associated with super eruptions is hypothesized to rebuild the deep crust, altering the source(s) of subsequent magmatism. Climax-type Mo deposits are commonly generated immediately after eruption of large ignimbrites within a volcanic field, and provide an opportunity to understand the evolution of <span class="hlt">magma</span> sources following high flux events. The Questa caldera of the Latir volcanic field, NM exposes a 10 Ma long record of pre-, syn- and post-ignimbrite intrusive and extrusive rocks, and hosts the Questa Climax-type Mo deposit. New detailed geochronology and geochemistry from Questa (including extensive sampling of subsurface rocks in the mine) permit detailed reconstruction of the temporal evolution of <span class="hlt">magma</span> sources through the waxing and waning stages of super eruption magmatism. Comparison of chemical and isotopic data waxing, ignimbrite, Mo-mineralizing and waning stage <span class="hlt">magmas</span> reveals several patterns. Waxing and waning <span class="hlt">magmas</span> (waxing: 29-25.7 Ma; waning: 24.5-19 Ma) have intermediate trace elements and radiogenic isotopes relative to other magmatism (87Sr/86Sri=0.7050 to 0.7070, ɛNd=-5.2 to -7.2). Ignimbrite magmatism (25.5 Ma) is depleted in incompatible elements, enriched in MREE and HREE's and has more evolved radiogenic isotopes (87Sr/86Sri=0.7095, ɛNd=-8.0). Molybdenum mineralizing <span class="hlt">magmas</span> (24.9-24.5 Ma), are enriched in incompatible elements, depleted in MREE and HREE's and have distinct radiogenic isotopes (87Sr/86Sri=0.7055 to 0.7075, ɛNd=-4.2 to -5.7). We suggest the lower crustal source of <span class="hlt">magmas</span> changed during ignimbrite generation, and as a result, subsequent mineralizing <span class="hlt">magmas</span> incorporated more juvenile, mafic components. This mantle influence is the metallogenesis for Climax-type deposits and indicates that deep crustal hybridization, rather than upper crustal differentiation, is pivotal in their generation. These results indicate that a lower crustal source of magmatism for a volcanic field is altered due to super</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/890512','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/890512"><span>Summary - <span class="hlt">Magma</span> Energy R&D Strategies and Applications</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tennyson, George P. Jr.</p> <p>1989-03-21</p> <p>In this session, this vast resource of thermal energy was described by Dr. James C. Dunn (SNLA) as an estimated 500,000 quads in U.S. crustal <span class="hlt">magma</span> bodies with temperatures in excess of 600 degrees Celsius and at depths of less than 10 km. The aim is to develop technology which can experimentally extract energy from a silicic <span class="hlt">magma</span> body to demonstrate the feasibility of utilizing this resource. Energy extraction from molten rock has been demonstrated in Hawaii at the Kilauea Iki lava lake. The program is showing significant progress in Geophysics and Site Selection, Energy Extraction Processes, and Geochemistry/Materials. The next major step is to drill and evaluate a deep exploratory well at the Long Valley caldera in California. Extensive analyses by the program and from previous work indicate that active <span class="hlt">magma</span> may be expected. John T. Finger (SNLA) then summarized the proposed four-phase drilling plan. The four phases will be approximately one year apart, and are expected to result in a large diameter well to a total depth of about 20,000 feet. The well design (by Livesay, Inc.) was described in considerable detail, together with predictions of the expected drilling problems. The well design and schedule includes accommodation of not only a substantial time for both program and outside experiments, but also the restrictions imposed by regulatory agencies including noise, disposal of wastes, and consideration of wildlife migratory patterns. Last, but hardly least, was a relation of the well and its drilling to the benefits to be accrued to the <span class="hlt">magma</span> energy technology. The deep borehole measurements which can, and will be taken at the Long Valley well present a unique opportunity to test and validate geophysical techniques for locating <span class="hlt">magma</span>, analyzing the geophysical parameters of the site and testing the theory that <span class="hlt">magma</span> is still present at drillable depths within the central portion of the caldera. Assuming the drilling indicates that there is <span class="hlt">magma</span> present</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/890517','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/890517"><span>Drilling Operations Plan for the <span class="hlt">Magma</span> Energy Exploratory Well</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Finger, John T.; Livesay, Bill J.; Ash, Don</p> <p>1989-03-21</p> <p>This paper is a summary of the proposed drilling plan for the first phase (to 2500 feet depth) of the <span class="hlt">Magma</span> Energy Exploratory Well. The drilling program comprises four phases, spaced approximately one year apart, which culminate in a large-diameter well to a total depth near 20,000 feet. Included here are descriptions of the well design, predictions of potential drilling problems, a list of restrictions imposed by regulatory agencies, an outline of Sandia's management structure, and an explanation of how the <span class="hlt">magma</span> energy technology will benefit from this drilling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6429716','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6429716"><span>Drilling operations plan for the <span class="hlt">Magma</span> Energy Exploratory Well</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Finger, J.T.; Livesay, B.J.; Ash, D.</p> <p>1989-01-01</p> <p>This paper is a summary of the proposed drilling plan for the first phase (to 2500 feet depth) of the <span class="hlt">Magma</span> Energy Exploratory Well. The drilling program comprises four phases, spaced approximately one year apart, which culminate in a large-diameter well to a total depth near 20,000 feet. Included here are descriptions of the well design, predictions of potential drilling problems, a list of restrictions imposed by regulatory agencies, an outline of Sandia's management structure, and an explanation of how the <span class="hlt">magma</span> energy technology will benefit from this drilling. 3 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.7077F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.7077F"><span><span class="hlt">Magma</span> dynamics above the Karoo plume, South Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ferre, Eric; Geissman, John; Stephanie, Maes; Aneesa, Gillum; Julian, Marsh</p> <p>2015-04-01</p> <p>Mantle plumes produce voluminous amounts of <span class="hlt">magma</span> (106 km3) during a short period of time (106 years). The heat input of such plumes into sedimentary basins has been proposed as a significant factor in several global climatic crises. Indeed heat transfer through conductive and advective processes is likely to bake organic matter-rich sediments, which in turn may release greenhouse gases (CO2 and CH4). One of the yet poorly understood aspects of this model is the regional pattern of <span class="hlt">magma</span> flow. The objective of this study is to constrain <span class="hlt">magma</span> dynamics in the Karoo Large Igneous Province (LIP) intruded in a continental basin of South Africa. Magnetic fabrics provide an efficient and accurate mean to determine <span class="hlt">magma</span> flow direction in gabbroic rocks. The anisotropy of magnetic susceptibility (AMS) is particularly suited for this type of study. A previous study had shown that the AMS fabric is a reliable proxy for <span class="hlt">magma</span> flow as long as samples are collected from the upper chilled margin of a sill. The central part is more complex due to interference caused by thermal convection. Oriented core samples were collected from 30 different sills and yielded 1598 specimens for AMS measurements. The low-field magnetic susceptibility Km ranges widely from about 100 to 20,000 . 10-6 [SI], while the degree of anisotropy P' ranges from 1.01 to 1.10. Thermomagnetic experiments reveal that the main magnetic carrier is titanomagnetite with variable ulvöspinel content. This is confirmed by measurement of hysteresis properties that also indicate that titanomagnetite in general has a pseudo-single domain grain size. The results of this study clearly indicate that <span class="hlt">magma</span> flow followed a main NW-SE direction in the studied area. The AMS directional data is consistent with the nearly horizontal attitude of the sill in 23 out of 30 cases, with subvertical K3 axes. In 5 out of 30 sills, K3 axes are subhorizontal, characterized by scattered directional data and are considered anomalous AMS</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V53A2750B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V53A2750B"><span><span class="hlt">Magmas</span> and reservoirs beneath the Rabaul caldera (Papua New Guinea)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bouvet de Maisonneuve, C.; Costa Rodriguez, F.; Huber, C.</p> <p>2013-12-01</p> <p>The area of Rabaul (Papua New Guinea) consists of at least seven - possibly nine - nested-calderas that have formed over the past 200 ky. The last caldera-forming eruption occurred 1400 y BP, and produced about 10 km3 of crystal-poor, two-pyroxene dacite. Since then, five effusive and explosive eruptive episodes have occurred from volcanic centres along the caldera rim. The most recent of these was preceded by decade-long unrest (starting in 1971) until the simultaneous eruption of Vulcan and Tavurvur, two vents on opposite sides of the caldera in 1994. Most eruptive products are andesitic in composition and show clear signs of mixing/mingling between a basalt and a high-K2O dacite. The hybridization is in the form of banded pumices, quenched mafic enclaves, and hybrid bulk rock compositions. In addition, the 1400 y BP caldera-related products show the presence of a third mixing component; a low-K2O rhyodacitic melt or <span class="hlt">magma</span>. Geochemical modeling considering major and trace elements and volatile contents shows that the high-K2O dacitic <span class="hlt">magma</span> can be generated by fractional crystallization of the basaltic <span class="hlt">magma</span> at shallow depths (~7 km, 200 MPa) and under relatively dry conditions (≤3 wt% H2O). The low-K2O rhyodacitic melt can either be explained by extended crystallization at low temperatures (e.g. in the presence of Sanidine) or the presence of an additional, unrelated <span class="hlt">magma</span>. Our working model is therefore that basalts ascend to shallow crustal levels before intruding a main silicic reservoir beneath the Rabaul caldera. Storage depths and temperatures estimated from volatile contents, mineral-melt equilibria and rock densities suggest that basalts ascend from ~20 km (~600 MPa) to ~7 km (200 MPa) and cool from ~1150-1100°C before intruding a dacitic <span class="hlt">magma</span> reservoir at ~950°C. Depending on the state of the reservoir and the volumes of basalt injected, the replenishing <span class="hlt">magma</span> may either trigger an eruption or cool and crystallize. We use evidence from major and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810029485&hterms=Active+volcano&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DActive%2Bvolcano','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810029485&hterms=Active+volcano&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DActive%2Bvolcano"><span>Output rate of <span class="hlt">magma</span> from active central volcanoes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wadge, G.</p> <p>1980-01-01</p> <p>For part of their historic records, nine of the most active volcanoes on earth have each erupted <span class="hlt">magma</span> at a nearly constant rate. These output rates are very similar and range from 0.69 to 0.26 cu m/s. The volcanoes discussed - Kilauea, Mauna Loa, Fuego, Santiaguito, Nyamuragira, Hekla, Piton de la Fournaise, Vesuvius and Etna - represent almost the whole spectrum of plate tectonic settings of volcanism. A common mechanism of buoyantly rising <span class="hlt">magma</span>-filled cracks in the upper crust may contribute to the observed restricted range of the rates of output.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810029485&hterms=kilauea+volcano&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dkilauea%2Bvolcano','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810029485&hterms=kilauea+volcano&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dkilauea%2Bvolcano"><span>Output rate of <span class="hlt">magma</span> from active central volcanoes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wadge, G.</p> <p>1980-01-01</p> <p>For part of their historic records, nine of the most active volcanoes on earth have each erupted <span class="hlt">magma</span> at a nearly constant rate. These output rates are very similar and range from 0.69 to 0.26 cu m/s. The volcanoes discussed - Kilauea, Mauna Loa, Fuego, Santiaguito, Nyamuragira, Hekla, Piton de la Fournaise, Vesuvius and Etna - represent almost the whole spectrum of plate tectonic settings of volcanism. A common mechanism of buoyantly rising <span class="hlt">magma</span>-filled cracks in the upper crust may contribute to the observed restricted range of the rates of output.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5595011','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5595011"><span>Drilling fluid temperatures in a <span class="hlt">magma</span> - penetrating wellbore</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Finger, J.T.</p> <p>1986-01-01</p> <p>This paper describes the numerical modeling of the drilling fluid temperatures in a deep well that penetrates a <span class="hlt">magma</span> body. The basic assumptions for the model are listed, the importance of the fluid temperature is considered, and the effect of changing the model parameters is assessed. The stratigraphy and formation temperature profile assumed for this hypothetical well are similar to Long Valley, CA, where a relatively shallow <span class="hlt">magma</span> body is believed to exist. A major result of this modeling is demonstration of the benefit of insulated drillpipe.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920001570','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920001570"><span><span class="hlt">Magma</span> generation on Mars: Estimated volumes through time</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greeley, Ronald; Schneid, B.</p> <p>1991-01-01</p> <p>Images of volcanoes and lava flows, chemical analysis by the Viking landers, and studies of meteorites show that volcanism has played an important role in the evolution of Mars. Photogeologic mapping suggests that half of Mars' surface is covered with volcanic materials. Here, researchers present results from new mappings, including estimates of volcanic deposit thicknesses based on partly buried and buried impact craters using the technique of DeHon. The researchers infer the volumes of possible associated plutonic rocks and derive the volumes of <span class="hlt">magmas</span> on Mars generated in its post-crustal formation history. Also considered is the amount of juvenile water that might have exsolved from the <span class="hlt">magma</span> through time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V31B1963R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V31B1963R"><span>The Relationship Between Amphibole Cumulates and Adakite <span class="hlt">Magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rooney, T. O.</p> <p>2009-12-01</p> <p>Amphibole, while uncommon as a primary fractioning phase is increasingly recognized as a key constituent in the petrogenesis of arc <span class="hlt">magmas</span>. Fractional crystallization of water-saturated arc <span class="hlt">magmas</span> in the lower crust can yield substantial volumes amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production adakite <span class="hlt">magmas</span>. The origin of adakites, defined by their heavy REE and Y depletion and Sr enrichments, have vigorously debated since their re-discovery in Panama two decades ago. In addition to widespread modern adakitic volcanism, the Panamanian portion of the Central American Arc preserves the magmatic record of arc development in close spatial association with younger magmatism. Late-Oligocene hypabyssal crystal-rich andesites from Cerro Patacon are preserved near the Panama Canal region. These contain nodules of amphibole cumulates, and may be used to examine the amphibole-fractionation model for adakite origin. The cumulate nodules are ~6 cm in diameter and are almost entirely composed of 5-10mm amphibole crystals (dominantly ferri-tschermakite), and are accompanied in the host andesites by amphibole phenocrysts, antecrysts and megacryts. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of the array defined by similarly differentiated (58-60% SiO2) Central American Arc <span class="hlt">magmas</span>, and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite. Sr/Y which is used as a geochemical tool for discriminating adakites from other arc magams, is transitional in the Cerro Patcon andesites. However La/Yb is within the range for ‘normal’ arc <span class="hlt">magmas</span> and shows that amphibole fractionation alone is insufficient to generate adakite <span class="hlt">magmas</span> - some garnet</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016FrEaS...4...99G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016FrEaS...4...99G"><span>Orientation of the eruption fissures controlled by a shallow <span class="hlt">magma</span> chamber in Miyakejima</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Geshi, Nobuo; Oikawa, Teruki</p> <p>2016-11-01</p> <p>Orientation of the eruption fissures and composition of the lavas of the Miyakejima volcano indicate tectonic influence of a shallow <span class="hlt">magma</span> chamber on the distribution of eruption fissures. We examined the distributions and magmatic compositions of 23 fissures that formed within the last 2800 years, based on a field survey and a new dataset of 14C ages. The dominant orientation of the eruption fissures in the central portion of the volcano was found to be NE-SW, which is perpendicular to the direction of regional maximum horizontal compressive stress (σHmax). <span class="hlt">Magmas</span> that show evidences of <span class="hlt">magma</span> mixing between basaltic and andesitic <span class="hlt">magmas</span> erupted mainly from the eruption fissures with a higher offset angle from the regional σHmax direction. The presence of a shallow dike-shaped <span class="hlt">magma</span> chamber controls the distribution of the eruption fissures. The injection of basaltic <span class="hlt">magma</span> into the shallow andesitic <span class="hlt">magma</span> chamber caused the temporal rise of internal magmatic pressure in the shallow <span class="hlt">magma</span> chamber. Dikes extending from the andesitic <span class="hlt">magma</span> chamber intrude along the local compressive stress field which is generated by the internal excess pressure of the andesitic <span class="hlt">magma</span> chamber. As the result, the eruption fissures trend parallel to the elongation direction of the shallow <span class="hlt">magma</span> chamber. Injection of basaltic <span class="hlt">magma</span> into the shallow andesitic <span class="hlt">magma</span> chamber caused the <span class="hlt">magma</span> mixing. Some basaltic dikes from the deep-seated <span class="hlt">magma</span> chamber reach the ground surface without intersection with the andesitic <span class="hlt">magma</span> chamber. The patterns of the eruption fissures can be modified in the future as was observed in the case of the destruction of the shallow <span class="hlt">magma</span> chamber during the 2000 AD eruption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014NatGe...7..122M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014NatGe...7..122M"><span>Supervolcano eruptions driven by melt buoyancy in large silicic <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Malfait, Wim J.; Seifert, Rita; Petitgirard, Sylvain; Perrillat, Jean-Philippe; Mezouar, Mohamed; Ota, Tsutomu; Nakamura, Eizo; Lerch, Philippe; Sanchez-Valle, Carmen</p> <p>2014-02-01</p> <p>Super-eruptions that dwarf all historical volcanic episodes in erupted volume and environmental impact are abundant in the geological record. Such eruptions of silica-rich <span class="hlt">magmas</span> form large calderas. The mechanisms that trigger these super-eruptions are elusive because the processes occurring in conventional volcanic systems cannot simply be scaled up to the much larger <span class="hlt">magma</span> chambers beneath supervolcanoes. Over-pressurization of the <span class="hlt">magma</span> reservoir, caused by <span class="hlt">magma</span> recharge, is a common trigger for smaller eruptions, but is insufficient to generate eruptions from large supervolcano <span class="hlt">magma</span> chambers. <span class="hlt">Magma</span> buoyancy can potentially create sufficient overpressure, but the efficiency of this trigger mechanism has not been tested. Here we use synchrotron measurements of X-ray absorption to determine the density of silica-rich <span class="hlt">magmas</span> at pressures and temperatures of up to 3.6GPa and 1,950K, respectively. We combine our results with existing measurements of silica-rich <span class="hlt">magma</span> density at ambient pressures to show that <span class="hlt">magma</span> buoyancy can generate an overpressure on the roof of a large supervolcano <span class="hlt">magma</span> chamber that exceeds the critical overpressure of 10-40MPa required to induce dyke propagation, even when the <span class="hlt">magma</span> is undersaturated in volatiles. We conclude that <span class="hlt">magma</span> buoyancy alone is a viable mechanism to trigger a super-eruption, although <span class="hlt">magma</span> recharge and mush rejuvenation, volatile saturation or tectonic stress may have been important during specific eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T13G2710C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T13G2710C"><span>Numerical Simulations of the Incremental Intrusion of Granitic <span class="hlt">Magma</span> into Continental Crust</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cao, W.; Kaus, B. J.; Paterson, S. R.</p> <p>2012-12-01</p> <p>We have employed the visco-elasto-plastic Finite-Element & Marker-in-cell code, MILAMIN_VEP, to carry out a 2D modeling study of the incremental intrusion of granitic <span class="hlt">magma</span> into continental crust. Algorithms of multiple pulses of <span class="hlt">magma</span> and pseudo-diking are implemented into the code. New <span class="hlt">magma</span> of an initial circular shape is regularly replenished at "<span class="hlt">magma</span> source" regions at sub-crustal depths. Pseudo-dikes of rectangular shapes are added at location where the maximum differential stress along the melt-solid interface is greater than an assigned tensile strength of the surrounding solid host rock. Preliminary results show that when diking and multiple pulses of <span class="hlt">magma</span> are included, later pulses of <span class="hlt">magma</span> rise higher and faster and even reach the Earth's surface in some cases by taking advantage of the pre-heated low-viscosity pathways created by earlier dikes and pulses of <span class="hlt">magma</span>. Host rocks display bedding rotation, and downward flow at two sides of a growing <span class="hlt">magma</span> chamber but show discordantly truncation when <span class="hlt">magma</span> ascend through the weak channels made by dikes. The effect of the thermal structure of the crust was tested as well. In a cold crust, "diking" is critical in breaking the high-viscosity crust, guiding the direction of <span class="hlt">magma</span> rising, and facilitating later <span class="hlt">magma</span> pulses to form chambers. In a warmer crust, <span class="hlt">magma</span> rises in the form of diapirs, after which dikes take over in transporting later pulses of <span class="hlt">magma</span> to the surface. The simulations also suggest that a <span class="hlt">magma</span> chamber incrementally constructed by multiple <span class="hlt">magma</span> bathes is a very dynamic environment featuring intra-chamber convection and recycling previous batches of <span class="hlt">magma</span>. In simulations without diking and multiple pulses, <span class="hlt">magma</span> is unable to reach the shallow crust. Instead, it is stuck in the middle crust, as the viscosity of the upper crust is too large to permit rapid motion, and at the same time <span class="hlt">magma</span>-induced stresses are insufficient to deform the upper crust in a plastic manner. Intra</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V21B2724O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V21B2724O"><span>Conduit <span class="hlt">Magma</span> Storage during the 800 BP Quilotoa Eruption, Ecuador</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ort, M. H.; Cashman, K. V.; Di Muro, A.; Best, J. A.; Rosi, M.; Mothes, P. A.; Bustillos, J.</p> <p>2013-12-01</p> <p>The 800 BP eruption of Quilotoa produced two large ignimbrites, U1 (~5.8 km3 DRE) and U3 (~1.8 km3 DRE). These eruptions were separated by a series of much smaller eruptions over one to several weeks, as inferred from 1) the intercalation of secondary pyroclastic and debris flow deposits between U1 and U3, 2) deposits from phreatic explosions from the U1 ignimbrite surface, 3) oxidation of the upper 2 m of U1, and 4) a lack of erosion of the U1 surface. Why did the main phase of the eruption (U1) stall when eruptable <span class="hlt">magma</span> was available? How did explosive activity stop and restart? We address these questions by examining deposits (U2) emplaced during the 'hiatus' that provide information on the conditions in the conduit and vent area between explosive episodes. The lowest sub-unit, U2a, forms a series of pumiceous surge deposits found only within 5 km of the crater rim. U2b is a vitric-poor, crystal- and lithic-rich fall deposit distributed to about 15 km from the crater. U2c is a thin gray fine ash containing 2-5-mm-diameter rhyolite lapilli that is present within 6 km of the vent. Similar lapilli also occur in the lowermost few centimeters of U3 and appear to be from a dome that exploded as the new <span class="hlt">magma</span> arrived at the surface; their presence as small ballistic fragments ties U2c to lowermost U3 in time. U2a appears to have been emplaced by episodic surges and weak fallout plumes, whereas U2b and U2c were deposited from a series of sustained eruption columns. Moreover, the lack of U2b grain-size variation with distance suggests that the grain size was determined at the vent, not by transport. FTIR analysis of CO2 and H2O in melt inclusions (MIs) indicates that a deep <span class="hlt">magma</span> chamber (>400 MPa; ~12 km) fed U1. U2a and U2b MIs plot along vapor isopleths, suggesting equilibration at pressures to about 300 MPa as CO2 outgassed. U2b MIs have lower CO2 than U2a, perhaps indicating continued degassing during the 'hiatus'. MIs from the lower few centimeters of U3 lie along</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.V31E..01C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.V31E..01C"><span>A cinder cone perspective on <span class="hlt">magma</span> ascent and eruption (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cashman, K. V.; Ruscitto, D.; McKay, D.; Wallace, P. J.; Johnson, E. R.</p> <p>2010-12-01</p> <p>Cinder cone eruptions provide unique perspectives on <span class="hlt">magma</span> transport because they are often monogenetic (single events) and must therefore create their own pathways through the crust. Here we contrast conditions of <span class="hlt">magma</span> ascent in the Trans-Mexican Volcanic Belt and the central Oregon Cascades by combining volcanological studies of cinder cone deposits with petrologic studies of constituent tephra to link <span class="hlt">magma</span> ascent paths to eruption conditions. Recent cinder cone eruptions in the Trans-Mexican Volcanic Belt (TMVB; e.g., Parícutin, 1943-1952) have been long-lived (years), have generated abundant tephra (108-109 m3), and have melt inclusion volatile contents that record extensive gas fluxing and development of shallow (1-2 km) storage regions over the time period of eruptive activity. Compositional variations within individual deposits indicate both crystal fractionation in the lower crust and shallow (probably syn-eruptive) assimilation. In contrast, recent cinder cone eruptions in the central Oregon Cascades appear to have lasted for months, have produced smaller tephra deposits, have olivine-hosted melt inclusions that record <span class="hlt">magma</span> storage at 100-200 MPa (4-8 km), and typically show evidence of only limited fractionation and/or assimilation. We suggest that differences in the petrologic evolution of these cinder cone products can be explained by (1) relatively rapid transfer of <span class="hlt">magma</span> from the lower to uppermost crust in Mexico as compared to (2) protracted pre-eruptive accumulation and storage of <span class="hlt">magma</span> in the upper crust in the Oregon Cascades. Rapid <span class="hlt">magma</span> transport through the crust in central Mexico would explain the high variability of olivine crystallization pressures recorded by the melt inclusions, the relatively high explosivity of the eruptions (as illustrated by the extensive tephra deposits) and temporary generation of through-going pathways for magmatic volatiles as required by evidence of fluxing with deep (CO2-rich) gases. Subsequent ponding of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V43H..01B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V43H..01B"><span>Constraints on the Physiochemical Evolution of Crustal <span class="hlt">Magma</span> Bodies (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bohrson, W. A.; Spera, F. J.</p> <p>2009-12-01</p> <p>Crustal <span class="hlt">magma</span> bodies chemically differentiate via complex combinations of relatively simple processes dominated by recharge, assimilation and reaction, and fractional crystallization (RAFC). A multitude of data, including field, whole rock and in situ crystal chemistry, provides constraints on the efficacy of such processes. Because each <span class="hlt">magma</span> body is subjected to unique thermal and chemical conditions, it is critical is to quantify the fundamental physiochemical conditions governing <span class="hlt">magma</span> diversification. In order to combine thermal, chemical, and mass constraints, we have developed Energy-Constrained Recharge, Assimilation, Fractional Crystallization (EC-RAFC), a tool to track the physiochemical evolution of melt and associated solids. EC-RAFC can address broad questions about crustal <span class="hlt">magma</span> bodies, including (1) How much differentiation occurs in deep vs. shallow reservoirs? and (2) What controls the growth of giant <span class="hlt">magma</span> reservoirs? The distinct signatures that may develop during lower vs. upper crustal RAFC can be simulated by varying initial wallrock (WR) temperature (T) (e.g., 600, 300°C) and initial WR 87Sr/86Sr (e.g., 0.710, 0.722). Comparison of lower vs. upper RAFC cases suggests that the record of assimilation initially will be recorded in higher T phases in the lower crust because assimilation initiates at higher <span class="hlt">magma</span> T. Because the upper crust is generally more radiogenic, as assimilation progresses, upper crustal melt and solid 87Sr/86Sr typically will be more radiogenic. Because a record of RAFC processes may be preserved as solid phases grow, inverse EC-RAFC modeling of crystal stratigraphy may yield a family of solutions, which include masses of all subsystems (e.g., cumulates, recharge <span class="hlt">magma</span>) and compositional predictions for melt and solids. Best-fit models may then be chosen by integrating information from field, geophysical and other studies. As suggested by a number of workers (e.g., DeSilva & Gosnold 2007), aggregation of large volumes of</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011CoMP..161..373R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011CoMP..161..373R"><span>Water-saturated <span class="hlt">magmas</span> in the Panama Canal region: a precursor to adakite-like <span class="hlt">magma</span> generation?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rooney, Tyrone O.; Franceschi, Pastora; Hall, Chris M.</p> <p>2011-03-01</p> <p>Amphibole, while uncommon as a phenocryst in arc lavas, is increasingly recognized as a key constituent in the petrogenesis of arc <span class="hlt">magmas</span>. Fractional crystallization of water-saturated arc <span class="hlt">magmas</span> in the lower crust can yield substantial volumes of amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of <span class="hlt">magmas</span> that contain an adakitic signature. This study examines newly dated Late-Oligocene (25.37 ± 0.13 Ma) hypabyssal amphibole-rich andesites from Cerro Patacon in the Panama Canal region. These andesites contain nodules of amphibole cumulates that are ~4-6 cm in diameter and are almost entirely composed of 5-10-mm amphibole crystals (dominantly ferri-tschermakite). Geochemical variations, optical and chemical zoning of the Cerro Patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite. Amphiboles hosted within the cumulate nodules differ from those hosted in the Cerro Patacon andesite and contain consistently higher values of Ti. We suggest these nodules represent the early stages of fractionation from a water-saturated <span class="hlt">magma</span>. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of Central American Arc <span class="hlt">magmas</span> and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite, consistent with the petrographic evidence. Fractionation of water-saturated <span class="hlt">magmas</span> is a mechanism by which adakitic compositions may be produced, and the Cerro Patacon andesites do exhibit adakite-like geochemical characteristics (e.g., elevated Sr/Y; 28-34). However, the relatively elevated concentrations of Y and HREE indicate garnet was not stable in the fractionating</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017DokES.474..535P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017DokES.474..535P"><span>Processes of the formation of mugearitic and benmoreitic <span class="hlt">magmas</span> on Nemrut Volcano (East Turkey)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peretyazhko, I. S.; Savina, E. A.</p> <p>2017-05-01</p> <p>The samples of trachybasalt, mugearite, benmoreite, trachydacite, and comendite from Nemrut Volcano (East Turkey) were studied. Except for trachybasalt, each sample contains partly dissolved mineral xenocrysts from <span class="hlt">magmas</span> with different compositions. At the precaldera stage of volcanic evolution fractional crystallization of the alkali basaltic melt contaminated with a small amount of material of the upper crust, as well as mixing of trachybasaltic and trachydacitic <span class="hlt">magmas</span>, could result in the formation of mugearitic <span class="hlt">magma</span>. At the precaldera stage benmoreitic <span class="hlt">magma</span> formed as a result of the evolution of trachybasaltic and mugearitic <span class="hlt">magmas</span>, while at the postcaldera stage—after the mixing of trachybasaltic <span class="hlt">magma</span> and low-Fe comenditic melt. The presence of relics of postcaldera benmoreitic <span class="hlt">magma</span> in comendite (glass of trachyrhyodacite-trachyrhyolite composition, xenocrysts of Mg-rich olivine, plagioclase, and augite) allows us to assume that repeated eruptions at the postcaldera stage of volcanic evolution were caused by its eruptions into the low-Fe comenditic <span class="hlt">magma</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5528222','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5528222"><span><span class="hlt">Magma</span> energy research project: state-of-the-project report, October 1, 1978</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Colp, J.L.; Traeger, R.K.</p> <p>1980-02-01</p> <p>The feasibility of extracting energy from <span class="hlt">magma</span> bodies is investigated. The work done in FY 76, 77, and 78 in the following tasks are summarized; resource location and definition, source tapping, <span class="hlt">magma</span> characterization and materials compatibility, and energy extraction. (MHR)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JVGR..304...62T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JVGR..304...62T"><span>Evolution of <span class="hlt">magma</span> feeding system in Kumanodake agglutinate activity, Zao Volcano, northeastern Japan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takebe, Yoshinori; Ban, Masao</p> <p>2015-10-01</p> <p>The Kumanodake agglutinate of Zao Volcano in northeastern Japan consists of pyroclastic surge layers accumulated during the early part of the newest stage of activity (ca. 33 ka to present). Our petrologic study of this agglutinate based on systematically collected samples aims to reveal the evolution of <span class="hlt">magma</span> feeding system. To understand the <span class="hlt">magma</span> evolution, we have examined samples from the agglutinate by using petrologic data including, petrography, analysis of minerals (plagioclase, pyroxene, and olivine), glass compositions, and whole rock major element and trace element (Ba, Sr, Cr, Ni, V, Rb, Zr, Nb, and Y) compositions. Agglutinate are mixed, medium-K, calc-alkaline olv-cpx-opx basaltic andesite (55.2-56.2% SiO2). Results show that the <span class="hlt">magma</span> feeding system comprised a shallow felsic chamber injected by mafic <span class="hlt">magma</span> from depth. The felsic <span class="hlt">magma</span> (59-62% SiO2, 950-990 °C), which was stored at a shallower depth, had orthopyroxene (Mg# = 60-69), clinopyroxene (Mg# = 65-71), and low-An plagioclase (Anca. 58-70). The mafic <span class="hlt">magma</span> is further divisible into two types: less-differentiated and more-differentiated, designed respectively as an initial mafic <span class="hlt">magma</span>-1 and a second mafic <span class="hlt">magma</span>-2. The original mafic <span class="hlt">magma</span>-1 was olivine (Fo 84) basalt (ca. 48-51% SiO2, 1110-1140 °C). The second mafic <span class="hlt">magma</span>-2, stored occasionally at 4-6 km depth, was basalt (1070-1110 °C) having Foca. 80 olivine and high-An (Anca. 90) plagioclase phenocrysts. These two <span class="hlt">magmas</span> mixed (first mixing) to form hybrid mafic <span class="hlt">magma</span>. The forced injections of the hybrid mafic <span class="hlt">magmas</span> activated the felsic <span class="hlt">magma</span>, and these two were mixed (second mixing) shortly before eruptions. The explosivity is inferred to have increased over time because the abundance of large scoria increased. Furthermore, the erupted <span class="hlt">magma</span> composition became more mafic, which reflects increased percentage of the hybrid mafic <span class="hlt">magma</span> involved in the second mixing. At the beginning of activity, the mafic <span class="hlt">magma</span> also acted as a heat</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6834226','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6834226"><span>Geologic evidence for a <span class="hlt">magma</span> chamber beneath Newberry Volcano, Oregon</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Macleod, N.S.; Sherrod, D.R.</p> <p>1988-09-10</p> <p>At Newberry Volcano, central Oregon, more than 0.5 m.y. of magmatic activity, including caldera collapse and renewed caldera-filling volcanism, has created a structural and thermal chimney that channels <span class="hlt">magma</span> ascent. Holocene rhyolitic eruptions (1) have been confined mainly within the caldera in an area 5 km in diameter, (2) have been very similar in chemical composition, phenocryst mineralogy, and eruptive style, and (3) have occurred as recently as 1300 years ago, with repose periods of 2000--3000 years between eruptions. Holocene basaltic andesite eruptions are widespread on the flanks but are excluded from the area of rhyolitic volcanism. Basaltic andesite in fissures at the edge of the rhyolite area has silicic inclusions and shows mixed basalt-rhyolite <span class="hlt">magma</span> relations. These geologic relations and the high geothermal gradient that characterizes the lower part of a drill hole in the caldera (U.S. Geological Survey Newberry 2) indicate that a rhyolitic <span class="hlt">magma</span> chamber has existed beneath the caldera throughout the Holocene. Its longevity probably is a result of intermittent underplating by basaltic <span class="hlt">magma</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V22B..01T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V22B..01T"><span>Evaluating the Controls on <span class="hlt">Magma</span> Ascent Rates Through Numerical Modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thomas, M. E.; Neuberg, J. W.</p> <p>2015-12-01</p> <p>The estimation of the <span class="hlt">magma</span> ascent rate is a key factor in predicting styles of volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. The ability to link potential changes in such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk <span class="hlt">magma</span> composition on the <span class="hlt">magma</span> flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. The results indicate that potential changes to conduit geometry and excess pressure in the <span class="hlt">magma</span> chamber are amongst the dominant controlling variables that effect ascent rate, but the single most important parameter is the volatile content (assumed in this case as only water). Modelling this parameter across a range of reported values causes changes in the calculated ascent velocities of up to 800%, triggering fluctuations in ascent rates that span the potential threshold between effusive and explosive eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GGG....17.2953G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GGG....17.2953G"><span><span class="hlt">Magma</span> plumbing for the 2014-2015 Holuhraun eruption, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Geiger, Harri; Mattsson, Tobias; Deegan, Frances M.; Troll, Valentin R.; Burchardt, Steffi; Gudmundsson, Ólafur; Tryggvason, Ari; Krumbholz, Michael; Harris, Chris</p> <p>2016-08-01</p> <p>The 2014-2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was accompanied by caldera subsidence in the Bárðarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Bárðarbunga to the Holuhraun eruption site over the course of two weeks. In order to better understand this lateral connection between Bárðarbunga and Holuhraun, we present mineral textures and compositions, mineral-melt-equilibrium calculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraun samples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from the Bárðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system. Thermobarometry calculations indicate a polybaric <span class="hlt">magma</span> plumbing system for the Holuhraun eruption, wherein clinopyroxene and plagioclase crystallized at average depths of ˜17 km and ˜5 km, respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbing system facilitated <span class="hlt">magma</span> mixing and assimilation of low-δ18O Icelandic crust prior to eruption. In conjunction with the existing geophysical evidence for lateral migration, our results support a model of initial vertical <span class="hlt">magma</span> ascent within the Bárðarbunga plumbing system followed by lateral transport of aggregated <span class="hlt">magma</span> batches within the upper crust to the Holuhraun eruption site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRB..119.8667G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRB..119.8667G"><span>On depressurization of volcanic <span class="hlt">magma</span> reservoirs by passive degassing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Girona, Társilo; Costa, Fidel; Newhall, Chris; Taisne, Benoit</p> <p>2014-12-01</p> <p>Many active volcanoes around the world alternate episodes of unrest and mildly explosive eruptions with quiescent periods dominated by abundant but passive gas emissions. These are the so-called persistently degassing volcanoes, and well-known examples are Mayon (Philippines) and Etna (Italy). Here, we develop a new lumped-parameter model to investigate by how much the gas released during quiescence can decrease the pressure within persistently degassing volcanoes. Our model is driven by the gas fluxes measured with monitoring systems and takes into account the size of the conduit and reservoir, the viscoelastic response of the crust, the <span class="hlt">magma</span> density change, the bubble exsolution and expansion at depth, and the hydraulic connectivity between reservoirs and deeper <span class="hlt">magma</span> sources. A key new finding is that, for a vast majority of scenarios, passive degassing reduces the pressure of shallow <span class="hlt">magma</span> reservoirs by several MPa in only a few months or years, that is, within the intereruptive timescales of persistently degassing volcanoes. Degassing-induced depressurization could be responsible for the subsidence observed at some volcanoes during quiescence (e.g., at Satsuma-Iwojima and Asama, in Japan; Masaya, in Nicaragua; and Llaima, in Chile), and could play a crucial role in the onset and development of the physical processes which may in turn culminate in new unrest episodes and eruptions. For example, degassing-induced depressurization could promote <span class="hlt">magma</span> replenishment, induce massive and sudden gas exsolution at depth, and trigger the collapse of the crater floor and reservoir roof.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6935617','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6935617"><span>Degassing of rhyolitic <span class="hlt">magma</span> during ascent and emplacement</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Westrich, H.R.; Stockman, H.W.; Eichelberger, J.</p> <p>1988-06-10</p> <p>The degassing history of a rhyolitic igneous system was documented from analyses of drill core samples through the extrusive and intrusive portions of Obsidian Dome and of surface samples of associated tephra. The initial volatile composition of the Inyo <span class="hlt">magma</span> was estimated to be 4.0 wt % H/sub 2/O, 500 ppm F, 800 ppm Cl, and 80 ppm S. Retained volatile contents of glassy and crystalline samples reflect the effects of decompression and second boiling. Decompression is rapid and involves loss of water-rich fluid until a close approach to lithostatic equilibrium is achieved. Second boiling is a slower process and produces a chlorine-rich fluid, some of which can be trapped during development of extremely fine crystallization textures. Nearly complete dewatering during decompression of surface-extruded <span class="hlt">magma</span> strongly undercools the system (..delta..Tapprox. =175 /sup 0/C), suppressing crystallization and yielding glassy rhyolitic lava. Partial degassing of shallowly intruded <span class="hlt">magma</span> permits pervasive crystallization even at high cooling rates. The subvolcanic intrusive regime is the zone of maximum volatile release because second boiling is incomplete in extrusives, and volatile-bearing crystalline phases are stable in <span class="hlt">magma</span> crystallized at greater depth. copyright Amierican Geophysical Union 1988</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040058026&hterms=loki&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dloki','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040058026&hterms=loki&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dloki"><span>Loki Patera as the Surface of a <span class="hlt">Magma</span> Sea</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Matson, D. L.; Davies, A. G.; Veeder, G. J.; Rathbun, J. A.; Johnson, T. V.</p> <p>2004-01-01</p> <p>Inspired by the finding of Schubert et al that Io's figure is consistent with a hydrostatic shape, we explore the consequences of modeling Loki Patera as the surface of a large <span class="hlt">magma</span> sea. This model is attractive because of its sheer simplicity and its usefulness in interpreting and predicting observations. Here, we report on that work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatGe..10..604K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatGe..10..604K"><span>A reverse energy cascade for crustal <span class="hlt">magma</span> transport</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karlstrom, Leif; Paterson, Scott R.; Jellinek, A. Mark</p> <p>2017-08-01</p> <p>Direct constraints on the ascent, storage and eruption of mantle melts come primarily from exhumed, long-frozen intrusions. These structures, relics of a dynamic <span class="hlt">magma</span> transport network, encode how Earth's crust grows and differentiates over time. Furthermore, they connect mantle melting to an evolving distribution of surface volcanism. Disentangling <span class="hlt">magma</span> transport processes from the plutonic record is consequently a seminal but unsolved problem. Here we use field data analyses, scaling theory and numerical simulations to show that the size distribution of intrusions preserved as plutonic complexes in the North American Cordillera suggests a transition in the mechanical response of crustal rocks to protracted episodes of magmatism. Intrusion sizes larger than about 100 m follow a power-law scaling expected if energy delivered from the mantle to open very thin dykes and sills is transferred to intrusions of increasing size. Merging, assimilation and mixing of small intrusions into larger ones occurs until irreversible deformation and solidification dissipate available energy. Mantle <span class="hlt">magma</span> supply over tens to hundreds of thousands of years will trigger this regime, a type of reverse energy cascade, depending on the influx rate and efficiency of crustal heating by intrusions. Identifying regimes of <span class="hlt">magma</span> transport provides a framework for inferring subsurface magmatic processes from surface patterns of volcanism, information preservation in the plutonic record, and related effects including climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED224699.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED224699.pdf"><span>Crystallization of <span class="hlt">Magma</span>. CEGS Programs Publication Number 14.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Berry, R. W.</p> <p></p> <p>Crystallization of <span class="hlt">Magma</span> is one of a series of single-topic problem modules intended for use in undergraduate geology and earth science courses. Through problems and observations based on two sets of experiments, this module leads to an understanding of how an igneous rock can form from molten material. Environmental factors responsible for…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000JVGR...95....1B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000JVGR...95....1B"><span>On the deformation and freezing of enclaves during <span class="hlt">magma</span> mixing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blake, S.; Fink, J. H.</p> <p>2000-01-01</p> <p>Mixing of an enclave of hot mafic <span class="hlt">magma</span> into cooler silicic <span class="hlt">magma</span> involves the competing effects of heat transfer acting to rigidify the enclave and viscous shearing imposed by a flowing host <span class="hlt">magma</span> acting to deform and disperse the enclave. We model the time required to grow a rigid chilled margin and compare this with the time required to deform the initially hot enclave. Whether an enclave will deform before it freezes depends on the ratio of the thermal and deformation timescales Pe= σapp3a2/( κμsσr2) and the dimensionless rigidification temperature θ=( Tr- Ts)/( Tm- Ts) where σapp is the applied shear stress, a is the enclave radius, κ is the thermal diffusivity, μs is the viscosity of the host, σr is the strength of the chilled rind, Tr is the temperature at which the enclave attains strength σr and Tm and Ts are the initial temperatures of the mafic enclave and silicic host. According to the model, small values of Pe and large values of θ promote rapid rigidification. The model is verified by laboratory experiments on the flow and freezing of polyglycol wax droplets in cold water. Geological observations show that correlations between enclave size, degree of deformation and local shear stress match the model's predictions. Studies of enclave size and shape as functions of eruption rate and position within lava flows and minor intrusions offer a new technique for studying <span class="hlt">magma</span> flow processes during eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28801635','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28801635"><span>Thermally-assisted <span class="hlt">Magma</span> Emplacement Explains Restless Calderas.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Amoruso, Antonella; Crescentini, Luca; D'Antonio, Massimo; Acocella, Valerio</p> <p>2017-08-11</p> <p>Many calderas show repeated unrest over centuries. Though probably induced by <span class="hlt">magma</span>, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei caldera, Italy. Campi Flegrei experienced at least 4 major unrest episodes in the last decades. Our results indicate that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated <span class="hlt">magma</span> emplacement requires a persistently hot crust. Our thermal models show that this repeated emplacement was assisted by the thermal anomaly created by <span class="hlt">magma</span> that was intruded at shallow depth ~3 ka before the last eruption. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct <span class="hlt">magmas</span> recorded in young volcanic rocks. Our model of thermally-assisted unrest may have a wider applicability, possibly explaining also the dynamics of other restless calderas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010281','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010281"><span><span class="hlt">Magma</span> supply rate at Kilauea volcano, 1952-1971</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Swanson, D.A.</p> <p>1972-01-01</p> <p>The three longest Kilauea eruptions since 1952 produced lava at an overall constant rate of about 9 ?? 106 cubic meters per month (vesicle-free). This is considered to represent the rate of <span class="hlt">magma</span> supply from a deep source, probably the mantle, because little or no summit deformation indicating high-level storage accompanied any of the three eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040058026&hterms=Loki&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DLoki','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040058026&hterms=Loki&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DLoki"><span>Loki Patera as the Surface of a <span class="hlt">Magma</span> Sea</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Matson, D. L.; Davies, A. G.; Veeder, G. J.; Rathbun, J. A.; Johnson, T. V.</p> <p>2004-01-01</p> <p>Inspired by the finding of Schubert et al that Io's figure is consistent with a hydrostatic shape, we explore the consequences of modeling Loki Patera as the surface of a large <span class="hlt">magma</span> sea. This model is attractive because of its sheer simplicity and its usefulness in interpreting and predicting observations. Here, we report on that work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17771801','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17771801"><span><span class="hlt">Magma</span> supply rate at kilauea volcano, 1952-1971.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Swanson, D A</p> <p>1972-01-14</p> <p>The three longest Kilauea eruptions since 1952 produced lava at an overall constant rate of about 9 x 10(6) cubic meters per month (vesicle-free). This is considered to represent the rate of <span class="hlt">magma</span> supply from a deep source, probably the mantle, because little or no summit deformation indicating high-level storage accompanied any of the three eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.P11A2062M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.P11A2062M"><span>On the cooling of a deep terrestrial <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Monteux, J.; Andrault, D.; Samuel, H.</p> <p>2015-12-01</p> <p>In its early evolution, the Earth mantle likely experienced several episodes of complete melting enhanced by giant impact heating, short-lived radionuclides heating and viscous dissipation during the metal/silicate separation. We have developed numerical models to monitor the thermo-chemical evolution of a cooling and crystallizing <span class="hlt">magma</span> ocean from an initially fully molten mantle. For this purpose, we use a 1D approach accounting for turbulent convective heat transfer. Our numerical model benchmarked with analytical solutions solves the heat equation in spherical geometry. This model also integrates recent and strong experimental constraints from mineral physics such as adiabatic temperature profiles and liquidus/solidus up 140 GPa for different mantle compositions. Our preliminary results show that a deep <span class="hlt">magma</span> ocean starts to crystallize rapidly after its formation. The cooling efficiency of the <span class="hlt">magma</span> ocean is strongly dependent on the coupling with the core cooling. Hence, depending on the thermal boundary layer thickness at the CMB, the thermal coupling between the core and <span class="hlt">magma</span> ocean can either insulate the core during the MO solidification and favor a hot core, generate the formation of a thin basal molten layer or empty the heat from the core. Then, once the melt fraction reaches a critical value, the cooling efficiency becomes limited.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016475','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016475"><span>Modelling the petrogenesis of high Rb/Sr silicic <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Halliday, A.N.; Davidson, J.P.; Hildreth, W.; Holden, P.</p> <p>1991-01-01</p> <p>Rhyolites can be highly evolved with Sr contents as low as 0.1 ppm and Rb Sr > 2,000. In contrast, granite batholiths are commonly comprised of rocks with Rb Sr 100. Mass-balance modelling of source compositions, differentiation and contamination using the trace-element geochemistry of granites are therefore commonly in error because of the failure to account for evolved differentiates that may have been erupted from the system. Rhyolitic <span class="hlt">magmas</span> with very low Sr concentrations (???1 ppm) cannot be explained by any partial melting models involving typical crustal source compositions. The only plausible mechanism for the production of such rhyolites is Rayleigh fractional crystallization involving substantial volumes of cumulates. A variety of methods for modelling the differentiation of <span class="hlt">magmas</span> with extremely high Rb/Sr is discussed. In each case it is concluded that the bulk partition coefficients for Sr have to be large. In the simplest models, the bulk DSr of the most evolved types is modelled as > 50. Evidence from phenocryst/glass/whole-rock concentrations supports high Sr partition coefficients in feldspars from high silica rhyolites. However, the low modal abundance of plagioclase commonly observed in such rocks is difficult to reconcile with such simple fractionation models of the observed trace-element trends. In certain cases, this may be because the apparent trace-element trend defined by the suite of cognetic rhyolites is the product of different batches of <span class="hlt">magma</span> with separate differentiation histories accumulating in the <span class="hlt">magma</span> chamber roof zone. ?? 1991.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.V43B2382K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.V43B2382K"><span>Mapping the ductile-brittle transition of <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kendrick, J. E.; Lavallee, Y.; Dingwell, D. B.</p> <p>2010-12-01</p> <p>During volcanic unrest, eruptive activity can switch rapidly from effusive to explosive. Explosive eruptions require the fragmentation of <span class="hlt">magma</span>, in which, if deformation rate is too fast to be relaxed, <span class="hlt">magma</span> undergoes a transition in deformation mechanism from viscous and/or ductile to brittle. Our knowledge of the deformation mechanisms of <span class="hlt">magma</span> ascent and eruption remains, to date, poor. Many studies have constrained the glass transition (Tg) of the interstitial melt phase; yet the effect of crystals and bubbles are unresolved. During ascent, <span class="hlt">magma</span> undergoes P-T changes which induce crystallization, thereby inducing a transition from viscous to ductile and, in some cases, to brittle deformation. Here, we explore the deformation mechanisms of <span class="hlt">magma</span> involved in the dome-building eruptions and explosions that occurred at Volcán de Colima (Mexico) since 1998. For this purpose, we investigated the rheology of dome lavas, containing 10-45 vol.% rhyolitic interstitial melt, 55-90 vol.% crystals and 5-20 vol.% bubbles. The interstitial glass is characterized by electron microprobe and Tg is characterized using a differential scanning calorimeter and a dilatometer. The population of crystals (fraction, shape and size distribution) is described optically and quantified using ImageJ and AMOCADO. The rheological effects of crystals on the deformation of <span class="hlt">magmas</span> are constrained via acoustic emission (AE) and uniaxial deformation experiments at temperature above Tg (900-980 °C) and at varied applied stresses (and strain rates: 10-6 to 10-2 s-1). The ratio of ductile to brittle deformation across the ductile-brittle transition is quantified using the output AE energy and optical and SEM analysis. We find that individual dome lava sample types have different mechanical responses, yielding a significant range of measured strain rates under a given temperature and applied stress. Optical analysis suggests that at low strain rates, ductile deformation is mainly controlled by the</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V41D..07C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V41D..07C"><span>The crystal's view of upper-crustal <span class="hlt">magma</span> reservoirs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cooper, K. M.; Kent, A. J.; Huber, C.; Stelten, M. E.; Rubin, A. E.; Schrecengost, K.</p> <p>2015-12-01</p> <p>Upper-crustal <span class="hlt">magma</span> reservoirs are important sites of <span class="hlt">magma</span> mixing, crustal refining, and <span class="hlt">magma</span> storage. Crystals residing in these reservoirs have been shown to represent valuable archives of the chemical and physical evolution of reservoirs, and the time scales of this evolution. This presentation addresses the question of "What do crystals "see" and record about processes within the upper crust? And how is that view similar or different between plutonic and volcanic records?" Three general observations emerge from study of the ages of crystals, combined with crystal-scale geochemical data: 1) Patterns of isotopic and trace-element data over time in zircon crystals from a given magmatic system (e.g., Yellowstone, WY, and Taupo Volcanic Zone, New Zealand) can show systematic changes in the degree of heterogeneity, consistent with extraction of melts from a long-lived (up to 100s of kyr), heterogeneous crystal mush and in some cases continued crystallization and homogenization of the <span class="hlt">magma</span> during a short period (< a few kyr) preceding eruption. 2) Thermal histories of <span class="hlt">magma</span> storage derived from crystal records also show that the vast majority of time recorded by major phases was spent in storage as a crystal mush, perhaps at near-solidus conditions. 3) Comparison of ages of accessory phases in both plutonic blocks and host <span class="hlt">magmas</span> that brought them to the surface do not show a consistent relationship between the two. In some cases, zircons from plutonic blocks have age spectra much older than zircon in the host <span class="hlt">magma</span>. In other cases, host and plutonic block zircons have similar age spectra and chemical characteristics, suggesting a closer genetic connection between the two. These observations suggest that crystals in plutonic bodies, if examined at similar spatial and temporal scales to those in volcanic rocks, would show records that are highly heterogeneous in chemistry and age on the scale of a pluton or a lobe of a pluton, but that local regions of limited</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.252..216E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.252..216E"><span>Extensive, water-rich <span class="hlt">magma</span> reservoir beneath southern Montserrat</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.</p> <p>2016-05-01</p> <p>South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their <span class="hlt">magmas</span> are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of <span class="hlt">magmas</span> and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of <span class="hlt">magma</span> storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible <span class="hlt">magma</span>. The high water contents of the <span class="hlt">magmas</span> suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during <span class="hlt">magma</span> ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1211515D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1211515D"><span>Oxygen isotope geochemistry of mafic <span class="hlt">magmas</span> at Mt. Vesuvius</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano</p> <p>2010-05-01</p> <p>Pumice and scoria from different eruptive layers of Mt. Vesuvius volcanic products contain mafic minerals consisting of High-Fo olivine and Diopsidic Pyroxene. These phases were crystallized in unerupted trachibasaltic to tephritic <span class="hlt">magmas</span>, and were brought to surface by large phonolitic/tephri-phonolitic (e.g. Avellino and Pompei) and/or of tephritic and phono-tephritic (Pollena) eruptions. A large set of these mm-sized crystals was accurately separated from selected juvenile material and measured for their chemical compositions (EPMA, Laser Ablation ICP-MS) and 18O/16O ratios (conventional laser fluorination) to constrain the nature and evolution of the primary <span class="hlt">magmas</span> at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary <span class="hlt">magmas</span>, mostly due to the widespread occurrence of crustal contamination of the primary melts during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). At Mt. Vesuvius, measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic <span class="hlt">magmas</span>. Trace element composition constrains the near primary nature of the phases. Published data on volatile content of melt inclusions hosted in these crystals reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth occurred in a reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali <span class="hlt">magmas</span> from trachybasaltic melts. Accordingly, the δ18O variability and the trace element content of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. Low, nearly primitive δ18O values are observed for olivine from Pompeii eruption, although still</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001E%26PSL.186..297P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001E%26PSL.186..297P"><span>Bubble plumes generated during recharge of basaltic <span class="hlt">magma</span> reservoirs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Phillips, Jeremy C.; Woods, Andrew W.</p> <p>2001-03-01</p> <p>CO 2 is relatively insoluble in basaltic <span class="hlt">magma</span> at low crustal pressures. It therefore exists as a gas phase in the form of bubbles in shallow crustal reservoirs. Over time these bubbles may separate gravitationally from the <span class="hlt">magma</span> in the chamber. As a result, any new <span class="hlt">magma</span> which recharges the chamber from deeper in the crust may be more bubble-rich and hence of lower density than the <span class="hlt">magma</span> in the chamber. Using scaling arguments, we show that for typical recharge fluxes, such a source of low-viscosity, bubble-rich basalt may generate a turbulent bubble plume within the chamber. We also show that the bubbles are typically sufficiently small to have a low Reynolds number and to remain in the flow. We then present a series of analogue laboratory experiments which identify that the motion of such a turbulent bubble-driven line plume is well described by the classical theory of buoyant plumes. Using the classical plume theory we then examine the effect of the return flow associated with such bubble plumes on the mixing and redistribution of bubbles within the chamber. Using this model, we show that a relatively deep bubbly layer of <span class="hlt">magma</span> may form below a thin foam layer at the roof. If, as an eruption proceeds, there is a continuing influx at the base of the chamber, then our model suggests that the bubble content of the bubbly layer may gradually increase. This may lead to a transition from lava flow activity to more explosive fire-fountaining activity. The foam layer at the top of the chamber may provide a flux for the continual outgassing from the flanks of the volcano [Ryan, Am. Geophys. Union Geophys. Monogr. 91 (1990)] and if it deepens sufficiently it may contribute to the eruptive activity [Vergniolle and Jaupart, J. Geophys. Res. 95 (1990) 2793-3001].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.V33F..06J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.V33F..06J"><span>Seismic Tremors and <span class="hlt">Magma</span> Wagging During Explosive Volcanism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jellinek, M.; Bercovici, D.</p> <p>2010-12-01</p> <p>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 <span class="hlt">magma</span>. Because neither the initial structure nor the evolution of the <span class="hlt">magma</span>-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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> column will oscillate or "wag" against the restoring "gas-spring" force of the annulus at observed tremor frequencies. In contrast to previous models, the <span class="hlt">magma</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21350484','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21350484"><span>Seismic tremors and <span class="hlt">magma</span> wagging during explosive volcanism.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jellinek, A Mark; Bercovici, David</p> <p>2011-02-24</p> <p>Volcanic tremor is a ubiquitous feature of explosive eruptions. This oscillation persists for minutes to weeks and is characterized by a remarkably narrow band of frequencies from about 0.5 Hz to 7 Hz (refs 1-4). Before major eruptions, tremor can occur in concert with increased gas flux and related ground deformation. Volcanic tremor is thus of particular value for eruption forecasting. Most models for volcanic tremor rely on specific properties of the geometry, structure and constitution of volcanic conduits as well as the gas content of the erupting <span class="hlt">magma</span>. Because neither the initial structure nor the evolution of the <span class="hlt">magma</span>-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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> column will oscillate or 'wag' against the restoring 'gas-spring' force of the annulus at observed tremor frequencies. In contrast to previous models, the <span class="hlt">magma</span>-wagging oscillation is relatively insensitive to the conduit structure and geometry, which explains the narrow band of tremor frequencies observed around the world. Moreover, the model predicts that as an eruption proceeds there will be an upward drift in both the maximum frequency and the total signal frequency bandwidth, the nature of which depends on the explosivity of the eruption, as is often observed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..322..144S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..322..144S"><span>Staged storage and <span class="hlt">magma</span> convection at Ambrym volcano, Vanuatu</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sheehan, Fionnuala; Barclay, Jenni</p> <p>2016-08-01</p> <p>New mineral-melt thermobarometry and mineral chemistry data are presented for basaltic scoriae erupted from the Mbwelesu crater of Ambrym volcano, Vanuatu, during persistent lava lake activity in 2005 and 2007. These data reveal crystallisation conditions and enable the first detailed attempt at reconstruction of the central <span class="hlt">magma</span> plumbing system of Ambrym volcano. Pressures and temperatures of <span class="hlt">magma</span> crystallisation at Ambrym are poorly constrained. This study focuses on characterising the <span class="hlt">magma</span> conditions underlying the quasi-permanent lava lakes at the basaltic central vents, and examines petrological evidence for <span class="hlt">magma</span> circulation. Mineral-melt equilibria for clinopyroxene, olivine and plagioclase allow estimation of pressures and temperatures of crystallisation, and reveal two major regions of crystallisation, at 24-29 km and 11-18 km depth, in agreement with indications from earthquake data of crustal storage levels at c. 25-29 km and 12-21 km depth. Temperature estimates are 1150-1170 °C for the deeper region, and 1110-1140 °C in the mid-crustal region, with lower temperatures of 1090-1100 °C for late-stage crystallisation. More primitive plagioclase antecrysts are thought to sample a slightly more mafic melt at sub-Moho depths. Resorption textures combined with effectively constant mafic mineral compositions suggest phenocryst convection in a storage region of consistent <span class="hlt">magma</span> composition. In addition, basalt erupted at Ambrym has predominantly maintained a constant composition throughout the volcanic succession. This, coupled with recurrent periods of elevated central vent activity on the scale of months, suggest frequent magmatic recharge via steady-state melt generation at Ambrym.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V13G..04S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V13G..04S"><span>Bubble nucleation in <span class="hlt">magmas</span>: a dominantly heterogeneous process?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shea, T.; Hammer, J. E.; Brachfeld, S. A.</p> <p>2016-12-01</p> <p>The processes governing volatile exsolution, and particularly the timing of initial vapor phase nucleation with respect to depth in the conduit, control a <span class="hlt">magma</span>'s explosive potential. Experimental studies have shown that nucleation kinetics exert the dominant control on degassing efficiency in silicate melts. Homogeneous nucleation (i.e. without assistance from crystal substrates or other phases) often requires attainment of large supersaturation pressures (ΔPN, the change in pressure required for nucleation), while heterogeneous nucleation on pre-existing crystals can occur at significantly lower ΔPN (<50 MPa). Crystal-poor rhyolites have therefore been largely regarded as the type example of homogeneous bubble nucleation, disequilibrium degassing and heightened explosivity. while other less viscous <span class="hlt">magmas</span> (dacite, phonolite, basalt) are thought to more often foster heterogeneous nucleation with variable departures from equilibrium. Distinguishing between the two nucleation mechanisms is vital for applications that employ classical nucleation theory and its derivatives: for instance, Toramaru's increasingly used decompression-rate meter (Toramaru 2006) links the number density of bubbles per unit volume melt (NV) of pyroclasts - a readily obtained textural characteristic - to rates of pressure change (dP/dt) during ascent. These formulations require an explicit or implicit decision as to whether <span class="hlt">magma</span> degassing was dominated by homogeneous or heterogeneous nucleation. This study exploits the large number of textural datasets available for eruptions involving various <span class="hlt">magma</span> compositions to examine the dominant nucleation mechanism in natural melts. Because Fe-Ti oxides are unrivaled in their capacity to favor heterogeneous nucleation, the absence of high concentrations of petrographically-observable Fe-Ti oxide crystals in erupted pyroclasts is often taken as an indicator that homogeneous nucleation dominated bubble vesiculation in rhyolites. This contribution</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030111250&hterms=feeding&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dfeeding','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030111250&hterms=feeding&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dfeeding"><span><span class="hlt">Magma</span> Reservoirs Feeding Giant Radiating Dike Swarms: Insights from Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grosfils, E. B.; Ernst, R. E.</p> <p>2003-01-01</p> <p>Evidence of lateral dike propagation from shallow <span class="hlt">magma</span> reservoirs is quite common on the terrestrial planets, and examination of the giant radiating dike swarm population on Venus continues to provide new insight into the way these complex magmatic systems form and evolve. For example, it is becoming clear that many swarms are an amalgamation of multiple discrete phases of dike intrusion. This is not surprising in and of itself, as on Earth there is clear evidence that formation of both <span class="hlt">magma</span> reservoirs and individual giant radiating dikes often involves periodic <span class="hlt">magma</span> injection. Similarly, giant radiating swarms on Earth can contain temporally discrete subswarms defined on the basis of geometry, crosscutting relationships, and geochemical or paleomagnetic signatures. The Venus data are important, however, because erosion, sedimentation, plate tectonic disruption, etc. on Earth have destroyed most giant radiating dike swarm's source regions, and thus we remain uncertain about the geometry and temporal evolution of the <span class="hlt">magma</span> sources from which the dikes are fed. Are the reservoirs which feed the dikes large or small, and what are the implications for how the dikes themselves form? Does each subswarm originate from a single, periodically reactivated reservoir, or do subswarms emerge from multiple discrete geographic foci? If the latter, are these discrete foci located at the margins of a single large <span class="hlt">magma</span> body, or do multiple smaller reservoirs define the character of the magmatic center as a whole? Similarly, does the locus of magmatic activity change with time, or are all the foci active simultaneously? Careful study of giant radiating dike swarms on Venus is yielding the data necessary to address these questions and constrain future modeling efforts. Here, using giant radiating dike swarms from the Nemesis Tessera (V14) and Carson (V43) quadrangles as examples, we illustrate some of the dike swarm focal region diversity observed on Venus and briefly explore some</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GGG....11.9005B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GGG....11.9005B"><span>Behavior of halogens during the degassing of felsic <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balcone-Boissard, H.; Villemant, B.; Boudon, G.</p> <p>2010-09-01</p> <p>Residual concentrations of halogens (F, Cl, Br, I) and H2O in glass (matrix glass and melt inclusions) have been determined in a series of volcanic clasts (pumice and lava-dome fragments) of plinian, vulcanian and lava dome-forming eruptions. Felsic <span class="hlt">magmas</span> from calc-alkaline, trachytic and phonolitic systems have been investigated: Montagne Pelée and Soufrière Hills of Montserrat (Lesser Antilles), Santa Maria-Santiaguito (Guatemala), Fogo (Azores) and Vesuvius (Italy). The behavior of halogens during shallow H2O degassing primarily depends on their incompatible character and their partitioning between melt and exsolved H2O vapor. However, variations in pre-eruptive conditions, degassing kinetics, and syn-eruptive melt crystallization induce large variations in the efficiency of halogen extraction. In all systems studied, Cl, Br and I are not fractionated from each other by differentiation or by degassing processes. Cl/Br/I ratios in melt remain almost constant from the <span class="hlt">magma</span> reservoir to the surface. The ratios measured in erupted clasts are thus characteristic of pre-eruptive <span class="hlt">magma</span> compositions and may be used to trace deep magmatic processes. F behaves as an incompatible element and, unlike the other halogens, is never significantly extracted by degassing. Cl, Br and I are efficiently extracted from melts at high pressure by H2O-rich fluids exsolved from <span class="hlt">magmas</span> or during slow effusive <span class="hlt">magma</span> degassing, but not during rapid explosive degassing. Because H2O and halogen mobility depends on their speciation, which strongly varies with pressure in both silicate melts and exsolved fluids, we suggest that the rapid pressure decrease during highly explosive eruptions prevents complete equilibrium between the diverse species of the volatiles and consequently limits their degassing. Conversely, degassing in effusive eruptions is an equilibrium process and leads to significant halogen output in volcanic plumes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995IJEaS..84..359C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995IJEaS..84..359C"><span>Unstable flow, <span class="hlt">magma</span> mixing and <span class="hlt">magma</span>-rock deformation in a deep-seated conduit: the Gil-Márquez Complex, south-west Spain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Castro, A.; la Rosa, J. D. De; Fernández, C.; Moreno-Ventas, I.</p> <p></p> <p>The Gil-Márquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of <span class="hlt">magma</span> transport through the continental crust. This conduit allowed the intrusion of <span class="hlt">magmas</span> of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic <span class="hlt">magma</span> generated by partial melting of a depleted-mantle source. Both <span class="hlt">magmas</span> rose through a common channel in which favorable conditions for unstable flow and <span class="hlt">magma</span> mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid <span class="hlt">magmas</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995GeoRu..84..359C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995GeoRu..84..359C"><span>Unstable flow, <span class="hlt">magma</span> mixing and <span class="hlt">magma</span>-rock deformation in a deep-seated conduit: the Gil-Márquez Complex, south-west Spain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Castro, A.; de La Rosa, J. D.; Fernández, C.; Moreno-Ventas, I.</p> <p>1995-06-01</p> <p>The Gil-Marquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of <span class="hlt">magma</span> transport through the continental crust. This conduit allowed the intrusion of <span class="hlt">magmas</span> of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic <span class="hlt">magma</span> generated by partial melting of a depletedmantle source. Both <span class="hlt">magmas</span> rose through a common channel in which favorable conditions for unstable flow and <span class="hlt">magma</span> mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid <span class="hlt">magmas</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993Geo....21.1083H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993Geo....21.1083H"><span>High-sulfur <span class="hlt">magma</span>, a product of fluid discharge from underlying mafic <span class="hlt">magma</span>: Evidence from Mount Pinatubo, Philippines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hattori, Keiko</p> <p>1993-12-01</p> <p>Beneath Mount Pinatubo in the Philippines, a hot mafic melt ascended, releasing supercritical fluids rich in SO2into an overlying semisolidified dacitic <span class="hlt">magma</span>. The SO2 was reduced to H2S in the cool, wet dacite, causing oxidation of this <span class="hlt">magma</span>. H2S thus formed was initially precipitated in the dacite as sulfides, which were high in Cu, Cd, Zn, and Se/S, elements also introduced by the fluids. Continued influx of SO2 and oxidation of the dacite led to an increase in the S solubility of the melt, causing partial resorption of sulfide minerals. Further addition of SO2 then led to excess S, which, in part, was precipitated as anhydrite. High S contents and the oxidized nature of the eruption products were due to the conjunction of an overlying, cool dacitic <span class="hlt">magma</span> and ascending hot mafic melt. The 1982 eruption products of El Chichón (Mexico) and those from the 1985 eruption of Nevado del Ruiz (Colombia) have features similar to Pinatubo, suggesting that these high-S <span class="hlt">magmas</span> may have formed by a similar process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.8146G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.8146G"><span>Subsurface <span class="hlt">magma</span> pathways inferred from statistical analysis of volcanic vent distribution and numerical model of <span class="hlt">magma</span> ascent</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Germa, Aurelie; Connor, Laura; Connor, Chuck; Malservisi, Rocco</p> <p>2015-04-01</p> <p>One challenge of volcanic hazard assessment in distributed volcanic fields (large number of small-volume basaltic volcanoes along with one or more silicic central volcanoes) is to constrain the location of future activity. Although the extent of the source of melts at depth can be known using geophysical methods or the location of past eruptive vents, the location of preferential pathways and zones of higher <span class="hlt">magma</span> flux are still unobserved. How does the spatial distribution of eruptive vents at the surface reveal the location of <span class="hlt">magma</span> sources or focusing? When this distribution is investigated, the location of central polygenetic edifices as well as clusters of monogenetic volcanoes denote zones of high <span class="hlt">magma</span> flux and recurrence rate, whereas areas of dispersed monogenetic vents represent zones of lower flux. Additionally, central polygenetic edifices, acting as <span class="hlt">magma</span> filters, prevent dense mafic <span class="hlt">magmas</span> from reaching the surface close to their central silicic system. Subsequently, the spatial distribution of mafic monogenetic vents may provide clues to the subsurface structure of a volcanic field, such as the location of <span class="hlt">magma</span> sources, preferential <span class="hlt">magma</span> pathways, and flux distribution across the field. Gathering such data is of highly importance in improving the assessment of volcanic hazards. We are developing a modeling framework that compares output of statistical models of vent distribution with outputs form numerical models of subsurface <span class="hlt">magma</span> transport. Geologic data observed at the Earth's surface are used to develop statistical models of spatial intensity (vents per unit area), volume intensity (erupted volume per unit area) and volume-flux intensity (erupted volume per unit time and area). Outputs are in the form of probability density functions assumed to represent volcanic flow output at the surface. These are then compared to outputs from conceptual models of the subsurface processes of <span class="hlt">magma</span> storage and transport. These models are using Darcy's law</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V52B..06Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V52B..06Z"><span>Pressure effect on Fe3+/FeT in silicate melts and applications to <span class="hlt">magma</span> redox, particularly in <span class="hlt">magma</span> oceans</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, H.; Hirschmann, M. M.</p> <p>2014-12-01</p> <p>The proportions of Fe3+ and Fe2+ in <span class="hlt">magmas</span> reflect the redox conditions of their origin and influence the chemical and physical properties of natural silicate liquids, but the relationship between Fe3+/FeT and oxygen fugacity depends on pressure owing to different molar volumes and compressibilities of Fe3+ and Fe2+ in silicates. An important case where the effect of pressure effect may be important is in <span class="hlt">magma</span> oceans, where well mixed (and therefore potentially uniform Fe3+/FeT) experiencses a wide range of pressures, and therefore can impart different ƒO2 at different depths, influencing <span class="hlt">magma</span> ocean degassing and early atmospheres, as well as chemical gradients within <span class="hlt">magma</span> oceans. To investigate the effect of pressure on magmatic Fe3+/FeT we conducted high pressure expeirments on ƒO2-buffered andestic liquids. Quenched glasses were analyzed by Mössbauer spectroscopy. To verify the accuracy of Mössbauer determinations of Fe3+/FeT in glasses, we also conducted low temperature Mössbauer studies to determine differences in the recoilless fraction (ƒ) of Fe2+ and Fe3. These indicate that room temperature Mössbauer determinations of on Fe3+/FeT glasses are systematically high by 4% compared to recoilless-fraction corrected ratios. Up to 7 GPa, pressure decreases Fe3+/FeT, at fixed ƒO2 relative to metal-oxide buffers, meaning that an isochemical <span class="hlt">magma</span> will become more reduced with decreasing pressure. Consequently, for small planetary bodies such as the Moon or Mercury, atmospheres overlying their MO will be highly reducing, consisting chiefly of H2 and CO. The same may also be true for Mars. The trend may reverse at higher pressure, as is the case for solid peridotite, and so for Earth, Venus, and possibly Mars, more oxidized atmospheres above MO are possible. Diamond anvil experiments are underway to examine this hypothesis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/137954','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/137954"><span>Nd isotopic gradients in upper crustal <span class="hlt">magma</span> chambers: Evidence for in situ <span class="hlt">magma</span>-wall-rock interaction</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Farmer, G.L.; Tegtmeyer, K.J.</p> <p>1990-01-01</p> <p>Multiple Nd isotopic analyses were obtained for one metaluminous and two peralkaline Tertiary rhyolitic ash-flow tuffs in the Great Basin to determine whether upper crustal silici <span class="hlt">magmas</span> chemically evolve under closed- or open-system conditions. All the ash-flow tuffs analyzed show significant internal Nd isotopic variations. The largest variations occur within the peralkaline Double-H Mountains Tuff ({epsilon}{sub Nd} = +2.0 to +6.4) at the McDermitt volcanic field in north-central Nevada, and the smallest within the metaluminous Topopah Spring Tuff ({epsilon}{sub Nd} = {minus}10.6 to {minus}11.7) at the southwestern Nevada volcanic field. In all cases the isotopic variation are correlated with magmatic Nd contents, even though the Nd concentrations decreased roofward for the metaluminous rhyolite and increased for the peralkaline rhyolites. The consistent positive correlation between [Nd] and {epsilon}{sub Nd} provides strong evidence for in situ open-system addition of low {epsilon}{sub Nd} wall-rock material to the silicic <span class="hlt">magmas</span> during their residence in the upper crust. The proportion of wall-rock Nd required to produce the isotopic zonations is small (1 to 15 mol%) for both the peralkaline and metaluminous rhyolites. All levels of the parental <span class="hlt">magmas</span> sampled by the ash-flow tuffs, and not just <span class="hlt">magma</span> occupying the roof zone, were open to wall-rock interaction. These results suggest that upper crustal silicic <span class="hlt">magma</span> bodies evolve under open-system conditions and the effects of such processes should be addressed in models for their chemical differentiation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V21D2034D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V21D2034D"><span>Oxygen isotope composition of mafic <span class="hlt">magmas</span> at Vesuvius</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.</p> <p>2009-12-01</p> <p>The oxygen isotope composition of olivine and clinopyroxene from four plinian (AD 79 Pompeii, 3960 BP Avellino), subplinian (AD 472 Pollena) and violent strombolian (Middle Age activity) eruptions were measured to constrain the nature and evolution of the primary <span class="hlt">magmas</span> of the last 4000 years of Mt. Vesuvius activity. A large set of mm-sized crystals was accurately separated from selected juvenile material of the four eruptions. Crystals were analyzed for their major and trace element compositions (EPMA, Laser Ablation ICP-MS), and for 18O/16O ratios. As oxygen isotope composition of uncontaminated mantle rocks on world-wide scale is well constrained (δ18Oolivine = 5.2 ± 0.3; δ18Ocpx = 5.6 ± 0.3 ‰), the measured values can be conveniently used to monitor the effects of assimilation/contamination of crustal rocks in the evolution of the primary <span class="hlt">magmas</span>. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary <span class="hlt">magmas</span>, mostly due to the widespread occurrence of crustal contamination of the primary <span class="hlt">magmas</span> during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). Low δ18O values have been measured in olivine from Pompeii eruption (δ18Oolivine = 5.54 ± 0.03‰), whereas higher O-compositions are recorded in mafic minerals from pumices or scoria of the other three eruptions. Measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic <span class="hlt">magmas</span>, as also constrained by their trace element compositions. Data on melt inclusions hosted in crystals of these compositions have been largely collected in the past demonstrating that they crystallized from mafic melt, basaltic to tephritic in composition. Published data on volatile content of these melt inclusions reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70041368','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70041368"><span>Ground surface deformation patterns, <span class="hlt">magma</span> supply, and <span class="hlt">magma</span> storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997–2008</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lu, Zhong; Dzurisin, Daniel; Biggs, Juliet; Wicks, Charles; McNutt, Steve</p> <p>2010-01-01</p> <p>Starting soon after the 1997 eruption at Okmok volcano and continuing until the start of the 2008 eruption, <span class="hlt">magma</span> accumulated in a storage zone centered ~3.5 km beneath the caldera floor at a rate that varied with time. A Mogi-type point pressure source or finite sphere with a radius of 1 km provides an adequate fit to the deformation field portrayed in time-sequential interferometric synthetic aperture radar images. From the end of the 1997 eruption through summer 2004, <span class="hlt">magma</span> storage increased by 3.2–4.5 × 107 m3, which corresponds to 75–85% of the <span class="hlt">magma</span> volume erupted in 1997. Thereafter, the average <span class="hlt">magma</span> supply rate decreased such that by 10 July 2008, 2 days before the start of the 2008 eruption, <span class="hlt">magma</span> storage had increased by 3.7–5.2 × 107 m3 or 85–100% of the 1997 eruption volume. We propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper <span class="hlt">magma</span> source region. Eventually the effects of continuing <span class="hlt">magma</span> supply and vesiculation of stored <span class="hlt">magma</span> caused a critical pressure threshold to be exceeded, triggering the 2008 eruption. A similar pattern of initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption. In both cases, withdrawal of <span class="hlt">magma</span> during the eruptions depressurized the shallow storage zone, causing significant volcano-wide subsidence and initiating a new intereruption deformation cycle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.2647P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.2647P"><span>Permeability of alkaline <span class="hlt">magmas</span>: a study from Campi Flegrei, Italy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Polacci, M.; Bouvet de Maissoneuve, C.; Giordano, D.; Piochi, M.; Degruyter, W.; Bachmann, O.; Mancini, L.</p> <p>2012-04-01</p> <p>Knowledge of permeability is of paramount importance for understanding the evolution of <span class="hlt">magma</span> degassing during pre-, syn- and post-eruptive volcanic processes. Most permeability estimates existing to date refer to <span class="hlt">magmas</span> of calc-alkaline compositions. We report here the preliminary results of permeability measurements performed on alkali-trachyte products erupted from the Campanian Ignimbrite (CI) and Monte Nuovo (MTN), two explosive eruptions from Campi Flegrei (CF), an active, hazardous caldera west of Naples, Southern Italy. Darcian (viscous) permeability spans a wide range between 10^-11 and 10^-14 m^2. We observe that the most permeable samples are the scoria clasts from the upper units of MTN; pumice samples from the Breccia Museo facies of CI are instead the least permeable. Non-Darcian (inertial) permeability follows the same trend as Darcian permeability. The first implication of this study is that porosity in alkaline as well as calc-alkaline <span class="hlt">magmas</span> does not exert a first order control on permeability (e.g. the MTN samples are the most permeable but not the most porous). Second, sample geometry exhibits permeability anisotropy (higher permeability in the direction of vesicle elongation), suggesting stronger degassing in the vertical direction in the conduit. In addition, inertial effects are higher across the sample. As inertial effects are potentially generated by tortuosity (or tortuous vesicle paths), tortuosity is likely higher horizontally than vertically in the conduit. Finally, the measured CF permeability values overlap with those of rhyolitic pumice clasts from the Kos Plateau Tuff (Bouvet de Maisonneuve et al., 2009), together with CI one of the major Quaternary explosive eruptions of the Mediterranean region. This indicates that gas flow is strongly controlled by the geometry of the porous media, which is generated by the bubble dynamics during <span class="hlt">magma</span> ascent. Therefore, permeability will depend on composition through the rheological properties</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920019363&hterms=Earth+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DEarth%2Bcore','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920019363&hterms=Earth+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DEarth%2Bcore"><span>Terrestrial <span class="hlt">magma</span> ocean and core segregation in the earth</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ohtani, Eiji; Yurimoto, Naoyoshi</p> <p>1992-01-01</p> <p>According to the recent theories of formation of the earth, the outer layer of the proto-earth was molten and the terrestrial <span class="hlt">magma</span> ocean was formed when its radius exceeded 3000 km. Core formation should have started in this <span class="hlt">magma</span> ocean stage, since segregation of metallic iron occurs effectively by melting of the proto-earth. Therefore, interactions between <span class="hlt">magma</span>, mantle minerals, and metallic iron in the <span class="hlt">magma</span> ocean stage controlled the geochemistry of the mantle and core. We have studied the partitioning behaviors of elements into the silicate melt, high pressure minerals, and metallic iron under the deep upper mantle and lower mantle conditions. We employed the multi-anvil apparatus for preparing the equilibrating samples in the ranges from 16 to 27 GPa and 1700-2400 C. Both the electron probe microanalyzer (EPMA) and the Secondary Ion Mass spectrometer (SIMS) were used for analyzing the run products. We obtained the partition coefficients of various trace elements between majorite, Mg-perovskite, and liquid, and magnesiowustite, Mg-perovskite, and metallic iron. The examples of the partition coefficients of some key elements are summarized in figures, together with the previous data. We may be able to assess the origin of the mantle abundances of the elements such as transition metals by using the partitioning data obtained above. The mantle abundances of some transition metals expected by the core-mantle equilibrium under the lower mantle conditions cannot explain the observed abundance of some elements such as Mn and Ge in the mantle. Estimations of the densities of the ultrabasic <span class="hlt">magma</span> Mg-perovskite at high pressure suggest existence of a density crossover in the deep lower mantle; flotation of Mg-perovskite occurs in the deep <span class="hlt">magma</span> ocean under the lower mantle conditions. The observed depletion of some transition metals such as V, Cr, Mn, Fe, Co, and Ni in the mantle may be explained by the two stage process, the core-mantle equilibrium under the lower</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.7508M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.7508M"><span>Effects of Earth's rotation on the early differentiation of a terrestrial <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maas, Christian; Hansen, Ulrich</p> <p>2015-11-01</p> <p>Similar to other terrestrial planets like Moon and Mars, Earth experienced a <span class="hlt">magma</span> ocean period about 4.5 billion years ago. On Earth differentiation processes in the <span class="hlt">magma</span> ocean set the initial conditions for core formation and mantle evolution. During the <span class="hlt">magma</span> ocean period Earth was rotating significantly faster than today. Further, the viscosity of the <span class="hlt">magma</span> was low, thus that planetary rotation potentially played an important role for differentiation. However, nearly all previous studies neglect rotational effects. All in all, our results suggest that planetary rotation plays an important role for <span class="hlt">magma</span> ocean crystallization. We employ a 3-D numerical model to study crystal settling in a rotating and vigorously convecting early <span class="hlt">magma</span> ocean. We show that crystal settling in a terrestrial <span class="hlt">magma</span> ocean is crucially affected by latitude as well as by rotational strength and crystal density. Due to rotation an inhomogeneous accumulation of crystals during <span class="hlt">magma</span> ocean solidification with a distinct crystal settling between pole and equator could occur. One could speculate that this may have potentially strong effects on the <span class="hlt">magma</span> ocean solidification time and the early mantle composition. It could support the development of a basal <span class="hlt">magma</span> ocean and the formation of anomalies at the core-mantle boundary in the equatorial region, reaching back to the time of <span class="hlt">magma</span> ocean solidification.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780057200&hterms=oxygen+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Doxygen%2Btheory','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780057200&hterms=oxygen+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Doxygen%2Btheory"><span>Oxygen fugacity of basaltic <span class="hlt">magmas</span> and the role of gas-forming elements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sato, M.</p> <p>1978-01-01</p> <p>It is suggested that major variations in the relative oxygen fugacity of a basaltic <span class="hlt">magma</span> are caused primarily by gas-forming elements, especially carbon and hydrogen. According to this theory, carbon, present in the source region of a basaltic <span class="hlt">magma</span>, reduces the host <span class="hlt">magma</span> during ascent, as isothermally carbon becomes more reducing with decreasing pressure. For an anhydrous <span class="hlt">magma</span> such as lunar basalts, this reduction continues through the extrusive phase and the relative oxygen fugacity decreases rapidly until buffered by the precipitation of a metallic phase. For hydrous <span class="hlt">magmas</span> such as terrestrial basalts, reduction by carbon is eventually superceded by oxidation due to loss of H2 generated by the reaction of C with H2O and by thermal dissociation of H2O. The relative oxygen fugacity of a hydrous <span class="hlt">magma</span> initially decreases as a <span class="hlt">magma</span> ascends from the source region and then increases until magnetite crystallization curbs the rising trend of the relative oxygen fugacity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18.1214P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18.1214P"><span>Pressure evolution in shallow <span class="hlt">magma</span> chambers upon buoyancy-driven replenishment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Papale, P.; Montagna, C. P.; Longo, A.</p> <p>2017-03-01</p> <p>The invasion of active <span class="hlt">magma</span> chambers by primitive <span class="hlt">magma</span> of deeper provenance is a frequent occurrence in volcanic systems, and it is commonly associated with pressurization. Chamber replenishment is driven by pressure and buoyancy forces that cause <span class="hlt">magma</span> ascent towards shallow depths. We examine the end-member case of pure buoyancy-driven (natural) convection in crustal reservoirs deriving from the presence of degassed, dense <span class="hlt">magma</span> at shallow level, that can originate a gravitational instability. Space-time-dependent numerical simulations of <span class="hlt">magma</span> dynamics in composite underground systems reveal highly nonlinear pressure evolution dominated by decompression at shallow depths. This counterintuitive result originates from the compressible nature of multiphase <span class="hlt">magmas</span> and their complex convection and mixing dynamics. Shallow <span class="hlt">magma</span> chamber decompression on replenishment is favored by large volatile contents of the uprising <span class="hlt">magma</span>, resulting in large density contrasts among the resident and the incoming components. These results show that the intuitive concept of <span class="hlt">magma</span> chamber pressurization upon replenishment may not always hold in real situations dominated by buoyancy, and provide new perspectives for the interpretation of geophysical records at active volcanoes.<abstract type="synopsis"><title type="main">Plain Language SummaryA common process at active volcanoes worldwide is the arrival of <span class="hlt">magma</span> from depth of tens of kilometers into shallower (depths of some km) reservoirs ("<span class="hlt">magma</span> chambers"), containing themselves <span class="hlt">magma</span> that can be different in terms of gas content and composition. We present numerical simulations that describe this process, with particular reference to the Campi Flegrei volcano in Italy. Our results show that, depending on the specific conditions and the gas contents of the two <span class="hlt">magma</span> types, this process can lead to a decrease in pressure of the shallow chamber. When interpreting ground deformation signals, very often <span class="hlt">magma</span> rise toward shallow depths</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17794034','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17794034"><span>Origin of High-Alumina Basalt, Andesite, and Dacite <span class="hlt">Magmas</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hamilton, W</p> <p>1964-10-30</p> <p>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 <span class="hlt">magmas</span> may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite <span class="hlt">magma</span> may represent more complete melting beneath it.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.2325R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.2325R"><span>Oxygen regime of Siberian alkaline-ultramafic <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ryabchikov, Igor; Kogarko, Liya</p> <p>2017-04-01</p> <p>Regimes of S2 and O2 are decisive factors controlling behavior of chalcophile and siderophile elements in magmatic processes. These parameters play important role during magmagenesis and in the course of crystallization and fluid mass transfer in <span class="hlt">magma</span> chamber. Alkaline-ultramafic magmatism in Maymecha-Kotuy Province (Polar Siberia) is represented by giant intrusive complexes as well as by volcanics and dyke rocks, which include a well-known variety - meimechites. The latter are considered primary <span class="hlt">magmas</span> of alkaline-ultramafic plutons in the region like for instance Guli intrusive complex. Sulfur content in primitive <span class="hlt">magmas</span> estimated from the analyses of melt inclusions in olivine megacrysts from meimechites is close to 0.1 %. fO2 values calculated using olivine+clinopyroxene+spinel and spinel+melt oxygen barometers (1, 2) are 2-3 log units above QFM buffer. The relatively high oxygen potential at the early magmatic stage of alkaline-ultramafic Guli pluton provide predominance of sulfates among other forms of sulfur in the melt. This leads to the almost complete absence of sulfides in highly magnesian rocks. The oxidizing conditions exert important effect on behavior of many ore metals. At the stage of <span class="hlt">magma</span> generation absence of sulfides in mantle materialresults in the presence of siderophile elements in metallic form and saturation of primary <span class="hlt">magmas</span> in respect of metallic phases at an early stage of injection of the melt into the <span class="hlt">magma</span> chamber. Later, under favorable circumstances during <span class="hlt">magma</span> crystallization nuggets of precious metals may be formed. During further evolution of magmatic system fO2 and activity of oxidized sulfur decrease due to intensive crystallization of magnetite during the formation of koswites, then oxygen fugacity becomes even lower as a result serpentinization at a postmagmatic stage. These serpentization processes are caused by the displacement of reactions in the aqueous phase due to cooling towards the formation of methane and other</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5598959','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5598959"><span>Finite difference seismic modeling of axial <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Swift, S.A.; Dougherty, M.E.; Stephen, R.A. )</p> <p>1990-11-01</p> <p>The authors tested the feasibility of using finite difference methods to model seismic propagation at {approximately}10 Hx through a two-dimensional representation of an axial <span class="hlt">magma</span> chamber with a thin, liquid lid. This technique produces time series of displacement or pressure at seafloor receivers to mimic a seismic refraction experiment and snapshots of P and S energy propagation. The results indicate that the implementation is stable for models with sharp velocity contrasts and complex geometries. The authors observe a high-energy, downward-traveling shear phase, observable only with borehole receivers, that would be useful in studying the nature and shape of <span class="hlt">magma</span> chambers. The ability of finite difference methods to model high-order wave phenomena makes this method ideal for testing velocity models of spreading axes and for planning near-axis drilling of the East Pacific Rise in order to optimize the benefits from shear wave imaging of sub-axis structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780057784&hterms=parental+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dparental%2Bpressure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780057784&hterms=parental+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dparental%2Bpressure"><span>Chemical variation and fractionation of KREEP basalt <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Irving, A. J.</p> <p>1977-01-01</p> <p>The fact that 53 Apollo 15 igneous KREEP basalts show a range of 100 Mg/(Mg + Fe) from 73 to 35, and that there are systematic variations in K2O and trace element abundances with the Mg/(Mg + Fe) ratio, suggests that the KREEP basalts are a <span class="hlt">magma</span> series generated by fractional crystallization processes. Experimental and chemical evidence indicate that this <span class="hlt">magma</span> series results from low-pressure, possibly subvolcanic, fractional crystallization of a magnesian parental liquid (100 Mg/(Mg + Fe) equal to approximately 72) by removal of low-Ca pyroxene and plagioclase, with eventual production of liquids similar in composition to 15405 quartz-monozodiorites. One soil sample, SAO 465-11, corresponds to the postulated parental liquid, which might have been a direct partial melt of troctolitic materials in the deep lunar crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017182','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017182"><span>Dissolved volatile concentrations in an ore-forming <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lowenstern, J. B.</p> <p>1994-01-01</p> <p>Infrared spectroscopic measurements of glass inclusions within quartz phenocrysts from the Plinian fallout of the 22 Ma tuff of Pine Grove show that the trapped silicate melt contained high concentrations of H2O and CO2. Intrusive porphyries from the Pine Grove system are nearly identical in age, composition, and mineralogy to the tephra, and some contain high-grade Mo mineralization. Assuming that the porphyry <span class="hlt">magmas</span> originally contained similar abundances of volatile components as the erupted rocks, they would have been saturated with fluid at pressures far greater than those at which the porphyries were emplaced and mineralized. The data are consistent with formation of Climax-type Mo porphyry deposits by prolonged fluid flux from a large volume of relatively Mo-poor (1-5 ppm) <span class="hlt">magma</span>. -from Author</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920019347&hterms=pac&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dpac','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920019347&hterms=pac&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dpac"><span>A <span class="hlt">magma</span> ocean and the Earth's internal water budget</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ahrens, Thomas J.</p> <p>1992-01-01</p> <p>There are lines of evidence which relate bounds on the primordial water content of the Earth's mantle to a <span class="hlt">magma</span> ocean and the accompanying Earth accretion process. We assume initially (before a <span class="hlt">magma</span> ocean could form) that as the Earth accreted, it grew from volatile- (H2O, CO2, NH3, CH4, SO2, plus noble) gas-rich planetesimals, which accreted to form an initial 'primitive accretion core' (PAC). The PAC retained the initial complement of planetesimal gaseous components. Shock wave experiments in which both solid, and more recently, the gaseous components of materials such as serpentine and the Murchison meteorite have demonstrated that planetesimal infall velocities of less than 0.5 km/sec, induce shock pressures of less than 0.5 GPa and result in virtually complete retention of planetary gases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUSM.U22A..04E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUSM.U22A..04E"><span>Using Intensive Variables to Constrain <span class="hlt">Magma</span> Source Regions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edwards, B. R.; Russell, J. K.</p> <p>2006-05-01</p> <p>In the modern world of petrology, <span class="hlt">magma</span> source region characterization is commonly the realm of trace element and isotopic geochemistry. However, major element analyses of rocks representing magmatic compositions can also be used to constrain source region charactertistics, which enhance the results of isotopic and trace element studies. We show examples from the northern Cordilleran volcanic province (NCVP), in the Canadian Cordillera, where estimations of thermodynamic intensive variables are used to resolve different source regions for mafic alkaline <span class="hlt">magmas</span>. We have taken a non-traditional approach to using the compositions of three groups of mafic, alkaline rocks to characterize the source regions of <span class="hlt">magmas</span> erupted in the NCVP. Based on measured Fe2O3 and FeO in rocks from different locations, the Atlin volcanic district (AVD), the Fort Selkirk volcanic complex (FSVC), the West Tuya volcanic field, (WTVF), we have estimated oxygen fugacities (fO2) for the source regions of <span class="hlt">magmas</span> based on the model of Kress and Carmichael (1991) and the computational package MELTS/pMelts (Ghiorso and Sack, 1995; Ghiorso et al., 2002). We also have used Melts/pMelts to estimate liquidus conditions for the compositions represented by the samples as well as activities of major element components. The results of our calculations are useful for distinguishing between three presumably different <span class="hlt">magma</span> series: alkaline basalts, basanites, and nephelinites (Francis and Ludden, 1990; 1995). Calculated intensive variables (fO2, activities SiO2, KAlSiO4, Na2SiO3) show clear separation of the samples into two groups: i) nephelinites and ii) basanites/alkaline basalts. The separation is especially evident on plots of log fO2 versus activity SiO2. The source region for nephelinitic <span class="hlt">magmas</span> in the AVD is up to 2 log units more oxidized than that for the basanites/basalts as well as having a distinctly lower range of activities of SiO2. Accepting that our assumptions about the <span class="hlt">magmas</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018090','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018090"><span>Degassing during <span class="hlt">magma</span> ascent in the Mule Creek vent (USA)</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Stasiuk, M.V.; Barclay, J.; Carroll, M.R.; Jaupart, Claude; Ratte, J.C.; Sparks, R.S.J.; Tait, S.R.</p> <p>1996-01-01</p> <p>The structures and textures of the rhyolite in the Mule Creek vent (New Mexico, USA) indicate mechanisms by which volatiles escape from silicic <span class="hlt">magma</span> during eruption. The vent outcrop is a 300-m-high canyon wall comprising a section through the top of a feeder conduit, vent and the base of an extrusive lava dome. Field relations show that eruption began with an explosive phase and ended with lava extrusion. Analyses of glass inclusions in quartz phenocrysts from the lava indicate that the <span class="hlt">magma</span> had a pre-eruptive dissolved water content of 2.5-3.0 wt% and, during eruption, the <span class="hlt">magma</span> would have been water-saturated over the vertical extent of the present outcrop. However, the vesicularity of the rhyolite is substantially lower than that predicted from closed-system models of vesiculation under equilibrium conditions. At a given elevation in the vent, the volume fraction of primary vesicles in the rhyolite increases from zero close to the vent margin to values of 20-40 vol.% in the central part. In the centre the vesicularity increases upward from approximately 20 vol.% at 300 m below the canyon rim to approximately 40 vol.% at 200 m, above which it shows little increase. To account for the discrepancy between observed vesicularity and measured water content, we conclude that gas escaped during ascent, probably beginning at depths greater than exposed, by flow through the vesicular <span class="hlt">magma</span>. Gas escape was most efficient near the vent margin, and we postulate that this is due both to the slow ascent of <span class="hlt">magma</span> there, giving the most time for gas to escape, and to shear, favouring bubble coalescence. Such shear-related permeability in erupting <span class="hlt">magma</span> is supported by the preserved distribution of textures and vesicularity in the rhyolite: Vesicles are flattened and overlapping near the dense margins and become progressively more isolated and less deformed toward the porous centre. Local zones have textures which suggest the coalescence of bubbles to form permeable</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.V33F..06C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.V33F..06C"><span>Sulfate Saturated Hydrous <span class="hlt">Magmas</span> Associated with Hydrothermal Gold Ores</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chambefort, I.; Dilles, J. H.; Kent, A. J.</p> <p>2007-12-01</p> <p>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 <span class="hlt">magma</span>-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 <span class="hlt">magma</span>'s liquidus at P(H2O)> 3kbar and 950 to 1000°C of a basaltic, basaltic andesite ascending <span class="hlt">magma</span>. Low Al amphibole presents an REE pattern with negative anomalies in Sr, Ti and Eu, characteristic of plagioclase and titanite fractionation in the <span class="hlt">magma</span>. 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V33D2905M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V33D2905M"><span>Simulation of pre-eruptive <span class="hlt">magma</span> migration and accumulation based on hydrokinetic modeling of <span class="hlt">magma</span> plumbing system beneath Sakurajima Volcano (Japan)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Minami, S.; Iguchi, M.; Mikada, H.; Goto, T.; Takekawa, J.</p> <p>2012-12-01</p> <p>We numerically simulated a transient <span class="hlt">magma</span> accumulating process in the <span class="hlt">magma</span> plumbing system beneath an active Showa crater of Sakurajima Volcano (Japan). Our objective is to find dominant geophysical parameters in the accumulating process before eruption. Geodetic observations showed that a periodic inflation and deflation event had lasted 30 hours before an explosive eruption. Our model consists of shallower gas and deeper <span class="hlt">magma</span> reservoirs connected by a volcanic conduit as inferred from the past geophysical observations. A pressure difference between the two reservoirs forces the <span class="hlt">magma</span> to move from the deeper up to the shallower reservoir. We assumed a constant rate of <span class="hlt">magma</span> supply to the deeper reservoir as an input to the <span class="hlt">magma</span> plumbing system. In a cylindrical volcanic conduit, a viscous multiphase <span class="hlt">magma</span> flow is demonstrated by 1-dimentional transient flow simulations with the effects of the relative motion of gas in <span class="hlt">magma</span>, the exsolution of volatiles in melt, the crystallization of microlites in groundmass, the change in height of <span class="hlt">magma</span> head, etc. As a result, we found that the radius of the volcanic conduit, the <span class="hlt">magma</span> supply rate and the compressibility of the deeper reservoir are key parameters to reproduce the observed volumetric variations before the eruption. These three parameters are estimated about 13 m, 3.5 m3/s and 10 GPa, respectively by means of a least squares method. Finally, the inflation and deflation event observed before the eruption are well reproduced. We would like to propose our numerical model as one of quantitative simulation methods that could be applied to the future eruptive events not only at Sakurajima Volcano but for the other volcanoes. Some of parameters of the <span class="hlt">magma</span> plumbing system need to be fixed as in this study should be discussed in terms of the sensitivity in the analysis at the time of the application.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V53A2130V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V53A2130V"><span>The Primary <span class="hlt">Magma</span> Composition of the Bushveld Upper Zone: Implications for <span class="hlt">Magma</span> Loss and Connection to Overlying Rooiberg Lavas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vantongeren, J. A.; Mathez, E. A.</p> <p>2008-12-01</p> <p>The Upper Zone of the 8 km thick Bushveld Complex is critical to understanding the petrologic evolution of the entire <span class="hlt">magma</span> body and its thermal and chemical interactions with its roof. Despite its central importance, little is known about the Upper Zone <span class="hlt">magma</span> composition or how it was related to the rest of the intrusion. Published estimates of the initial Upper Zone composition have relied on analysis of marginal sills or infer the addition of an escaped component for which there is no natural representative [e.g., Tegner et al., 2006 J. Pet. 47, 2257]. Application of MELTS thermodynamic modeling, however, shows that all of these estimates fail to account for the presence of primary orthopyroxene or the observed mineral compositions near the base of the Upper Zone, i.e., the inferred <span class="hlt">magma</span> compositions cannot be related to the lower section of the Upper Zone by fractional crystallization. Immediately overlying the Upper Zone is a 6 km thick series of basaltic-andesite to rhyolitic lavas of the Rooiberg Group. Despite nearly identical ages of approximately 2.06 Ga, the relationship between the Bushveld Complex and Rooiberg lavas remains unclear. Our MELTS results suggest that some of the Upper Zone rocks and Rooiberg lavas may be co-genetic. In particular, a mixture of 60% bulk Upper Zone cumulate composition plus 40% Rooiberg Damwal Formation results in an initial <span class="hlt">magma</span> composition that is able to reproduce the observed Upper Zone cumulate sequence and mineral composition. Equilibrium liquid compositions calculated from 2 pyroxenes and plagioclase throughout the stratigraphy are consistent with this result. Also, initial Sr isotopes for the Upper Zone are within error of those measured in the Damwal formation [Buchanan et al., 2004, Lithos 75, 373; Kruger et al., 1987, EPSL, 84, 51]. Our calculations not only place constraints on the primary Upper Zone <span class="hlt">magma</span> composition but also the amount and composition of the "missing liquid" at the top of the Upper Zone. If</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....6051L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....6051L"><span><span class="hlt">Magma</span> mixing and degassing recorded in plagioclase from the shallow <span class="hlt">magma</span> body at Stromboli (Aeolian Archypelago, Italy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Landi, P.; Metrich, N.; Bertagnini, A.; Rosi, M.</p> <p>2003-04-01</p> <p>Stromboli has produced nearly-aphyric pumice and crystal-rich scoriae since the beginning of its persistent strombolian activity, 1400-1800 years ago. In spite of their contrasting texture, the highly vesiculated pumice and the dense scoriae rich in mm-sized crystals have virtually the same bulk rock composition, ranging from HK-basaltic andesite to HK-basalt. It is thought that the crystal-rich <span class="hlt">magma</span> at the origin of the dense scoriae derives from the volatile-rich melt, emitted as pumice, via low pressure crystallization induced by water loss. Such characteristics make the shallow, crystal-rich body, a study-case to investigate the mechanisms of crystallization during rapid degassing. We have studied different crystal-rich products, both scoriae and lavas, of the 1985-2000 period of activity. All of them, contain 47-55 vol% euhedral phenocrysts of plagioclase, the dominant phase, clinopyroxene and olivine embedded in a glassy to hypocrystalline, homogeneous shoshonitic groundmass. Crystallization history and <span class="hlt">magma</span> dynamics are mainly discussed on the basis of the chemical and textural zoning of the plagioclase phenocrysts. They consist of alternating, concentric layers of An-rich and Ab-rich plagioclase. The Ab-rich layers (An64-An70) are characterized by a small-scale (1-5 mm) oscillatory zoning and appear to be in equilibrium with a liquid with the composition of the glassy matrix. The An-rich zones (An70-An88) are patchy zoned, show sieve texture with abundant micrometric glass inclusions and voids, and overgrow on dissolution surfaces. We propose that zoning of the plagioclase reflects successive intrusions of volatile-rich melts in the shallow crystal-rich mush. The high H_2O content of ascending melt blobs stabilizes An-rich plagioclase. Sieve textures result from rapid crystallization occurring under supercooling conditions, which are induced by rapid degassing of the volatile-rich <span class="hlt">magma</span> blobs when they react with the shallow crystal-rich <span class="hlt">magma</span>, at low</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53A3077L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53A3077L"><span>Petrologic Constraints on <span class="hlt">Magma</span> Plumbing Systems Beneath Hawaiian Volcanoes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Y.; Peterman, K. J.; Scott, J. L.; Barton, M.</p> <p>2016-12-01</p> <p>We have calculated the pressures of partial crystalliztion of basaltic <span class="hlt">magmas</span> from Hawaii using a petrological method. A total of 1576 major oxide analyses of glasses from four volcanoes (Kilauea and the Puna Ridge, Loihi, Mauna Loa, and Mauna Kea, on the Big Island) were compiled and used as input data. Glasses represent quenched liquid compositions and are ideal for calculation of pressures of partial crystallization. The results were filtered to exclude samples that yielded unrealistic high errors associated with the calculated pressure or negative value of pressure, and to exclude samples with non-basaltic compositions. Calculated pressures were converted to depths of partial crystallization. The majority (68.2%) of pressures for the shield-stage subaerial volcanoes Kilauea, Mauna Loa, and Mauna Kea, fall in the range 0-140 MPa, corresponding to depths of 0-5 km. Glasses from the Puna Ridge yield pressures ranging from 18 to 126 MPa and are virtually identical to pressures determined from glasses from Kilauea (0 to 129 MPa). These results are consistent with the presence of <span class="hlt">magma</span> reservoirs at depths of 0-5 km beneath the large shield volcanoes. The inferred depth of the <span class="hlt">magma</span> reservoir beneath the summit of Kilauea (average = 1.8 km, maximum = 5 km) agrees extremely well with depths ( 2-6 km) estimated from seismic studies. The results for Kilauea and Mauna Kea indicate that significant partial crystallization also occurs beneath the summit reservoirs at depths up to 11 km. These results are consistent with seismic evidence for the presence of a <span class="hlt">magma</span> reservoir at 8-11 km beneath Kilauea at the base of the volcanic pile. The results for Loihi indicate crystallization at higher average pressures (100-400 MPa) and depths (3-14 km) than the large shield volcanoes, suggesting that the plumbing system is not yet fully developed, and that the Hawaiian volcanic plumbing systems evolve over time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V33D2240H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V33D2240H"><span>Depths of <span class="hlt">Magma</span> Storage Beneath Fogo Volcano, Cape Verde Islands</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hildner, E.; Klügel, A.</p> <p>2008-12-01</p> <p>Fogo is one of the most active oceanic volcanoes of the world in present time and the only island of the Cape Verde archipelago with historic volcanic activity. We have carried out a barometric study of basanitic to tephriphonolitic volcanic rocks of the 1995 eruption of Fogo in order to reconstruct the depths of <span class="hlt">magma</span> reservoirs and <span class="hlt">magma</span> pathways prior to eruption. The pyroclastic rocks and lavas studied span the whole temporal and compositional range of this eruption. Clinopyroxene-melt thermobarometry of 75 clinopyroxenes in 9 samples yields a well-defined pressure range of 500-630 MPa (average 550 MPa). This pressure range is interpreted to reflect a major fractionation level at ca. 17-22 km depth, within the uppermost mantle, where melt and phenocrysts last equilibrated. Microthermometry of CO2-rich fluid inclusions in clinopyroxene and olivine phenocrysts indicates a broader pressure range with two apparent frequency maxima. The higher pressure range, between 430 and 510 MPa (average 480 MPa), partly overlaps with the clinopyroxene-melt barometry data. The lower pressure range, between 250 and 430 MPa (average 375 MPa), is within the lower crust to Moho and may reflect short-term stagnation of <span class="hlt">magma</span> at 9-16 km depth prior to eruption. Our data suggest that the 1995 <span class="hlt">magmas</span> ascended from mantle depth to the surface with residence times at shallow levels probably being restricted to less than a day. This conclusion is in accordance with the absence of plagioclase phenocrysts and microphenocrysts in the 1995 and most other recent lavas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4401657','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4401657"><span><span class="hlt">MAGMA</span>: Generalized Gene-Set Analysis of GWAS Data</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>de Leeuw, Christiaan A.; Mooij, Joris M.; Heskes, Tom; Posthuma, Danielle</p> <p>2015-01-01</p> <p>By aggregating data for complex traits in a biologically meaningful way, gene and gene-set analysis constitute a valuable addition to single-marker analysis. However, although various methods for gene and gene-set analysis currently exist, they generally suffer from a number of issues. Statistical power for most methods is strongly affected by linkage disequilibrium between markers, multi-marker associations are often hard to detect, and the reliance on permutation to compute p-values tends to make the analysis computationally very expensive. To address these issues we have developed <span class="hlt">MAGMA</span>, a novel tool for gene and gene-set analysis. The gene analysis is based on a multiple regression model, to provide better statistical performance. The gene-set analysis is built as a separate layer around the gene analysis for additional flexibility. This gene-set analysis also uses a regression structure to allow generalization to analysis of continuous properties of genes and simultaneous analysis of multiple gene sets and other gene properties. Simulations and an analysis of Crohn’s Disease data are used to evaluate the performance of <span class="hlt">MAGMA</span> and to compare it to a number of other gene and gene-set analysis tools. The results show that <span class="hlt">MAGMA</span> has significantly more power than other tools for both the gene and the gene-set analysis, identifying more genes and gene sets associated with Crohn’s Disease while maintaining a correct type 1 error rate. Moreover, the <span class="hlt">MAGMA</span> analysis of the Crohn’s Disease data was found to be considerably faster as well. PMID:25885710</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V11F..02A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V11F..02A"><span>Dynamic Heating and Decompression Experiments on Dacite and Rhyolite <span class="hlt">Magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andrews, B. J.; Waters, L.; Grocke, S. B.</p> <p>2015-12-01</p> <p>Mineral reaction rims, zoned crystals, and myriad growth or dissolution textures provide evidence for changes in <span class="hlt">magma</span> pressure, temperature, or composition. Quantifying the magnitudes, timescales and length scales of those variations is a fundamental challenge of volcanology and igneous petrology; experiments provide quantitative insights into how <span class="hlt">magmas</span> react to changes in pressure and temperature that can be used to address that challenge. We use single-step and dynamic experiments conducted in cold seal pressure vessels to study the responses of dacite and rhyolite <span class="hlt">magmas</span> to heating and decompression events. During single-step decompression (or heating) experiments, conditions are changed nearly instantaneously from the initial to final state in one step, or several smaller steps, whereas "dynamic experiments" have continuous variation in pressure and/or temperature. These two types of experiments yield useful and complementary information describing crystal nucleation, growth, and reaction rates in response to changing (as opposed to steady state) conditions. Here we discuss isothermal decompression experiments that show substantial path-dependence for runs with equivalent time-averaged decompression rates as slow as 0.27 MPa/h for >500 h. Continuous decompression experiments often contain fewer but larger plagioclase crystals than are present in single-step runs, and those new crystals often show complex growth textures. Our results suggest that even slow changes in storage conditions can disrupt melt structure and greatly retard nucleation provided the changes are steady. We hypothesize that if the decompression path remains steady and continuous (absent a stall on and/or rapid decompression), the <span class="hlt">magma</span> can remain in a growth-dominated regime even though it is far from equilibrium.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920048256&hterms=JOHN+green&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DJOHN%2Bgreen','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920048256&hterms=JOHN+green&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DJOHN%2Bgreen"><span>Origin of picritic green glass <span class="hlt">magmas</span> by polybaric fractional fusion</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Longhi, John</p> <p>1992-01-01</p> <p>A preliminary presentation is given of a model which explains the picritic lunar mare green glass compositions as composites or <span class="hlt">magmas</span> derived by polybaric fractional melting. The model accommodates changes in source composition and solidus temperature. As in the Klein and Langmuir model, the final compositions of the melts signify only average depths of melting. The onset of melting is deeper, final segregation is shallower.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25885710','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25885710"><span><span class="hlt">MAGMA</span>: generalized gene-set analysis of GWAS data.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>de Leeuw, Christiaan A; Mooij, Joris M; Heskes, Tom; Posthuma, Danielle</p> <p>2015-04-01</p> <p>By aggregating data for complex traits in a biologically meaningful way, gene and gene-set analysis constitute a valuable addition to single-marker analysis. However, although various methods for gene and gene-set analysis currently exist, they generally suffer from a number of issues. Statistical power for most methods is strongly affected by linkage disequilibrium between markers, multi-marker associations are often hard to detect, and the reliance on permutation to compute p-values tends to make the analysis computationally very expensive. To address these issues we have developed <span class="hlt">MAGMA</span>, a novel tool for gene and gene-set analysis. The gene analysis is based on a multiple regression model, to provide better statistical performance. The gene-set analysis is built as a separate layer around the gene analysis for additional flexibility. This gene-set analysis also uses a regression structure to allow generalization to analysis of continuous properties of genes and simultaneous analysis of multiple gene sets and other gene properties. Simulations and an analysis of Crohn's Disease data are used to evaluate the performance of <span class="hlt">MAGMA</span> and to compare it to a number of other gene and gene-set analysis tools. The results show that <span class="hlt">MAGMA</span> has significantly more power than other tools for both the gene and the gene-set analysis, identifying more genes and gene sets associated with Crohn's Disease while maintaining a correct type 1 error rate. Moreover, the <span class="hlt">MAGMA</span> analysis of the Crohn's Disease data was found to be considerably faster as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.9602V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.9602V"><span>Experiments on the rheology of vesicle-bearing <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia</p> <p>2016-04-01</p> <p>We present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the <span class="hlt">magma</span> bulk viscosity. Starting materials having variable vesicularity (φ = 0 - 66%) were synthesized by high-temperature foaming (T = 900 - 1050 ° C and P = 1 bar) of cores of natural rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland. These cores were subsequently deformed using a high-temperature uniaxial press at dry atmospheric conditions. Each experiment involved deforming vesicle-bearing cores isothermally (T = 750 ° C), at constant displacement rates (strain rates between 0.5-1 x 10-4 s-1), and to total strains (ɛ) of 10-40%. The viscosity of the bubble-free melt (η0) was measured by micropenetration and parallel plate methods and establishes a baseline for comparing data derived from experiments on vesicle rich cores. At the experimental conditions, the presence of vesicles has a major impact on the rheological response, producing a marked decrease of bulk viscosity (maximum decrease of 2 log units Pa s) that is best described by a two-parameter empirical equation: log ηBulk = log η0 - 1.47 * [φ/(1-φ)]0.48. Our model provides a means to compare the diverse behaviour of vesicle-bearing melts reported in the literature and reflecting material properties (e.g., analogue vs. natural), geometry and distribution of pores (e.g. foamed/natural vs. unconsolidated/sintered materials), and flow regime. Lastly, we apply principles of Maxwell relaxation theory, combined with our parameterization of bubble-melt rheology, to map the potential onset of non-Newtonian behaviour (strain localization) in vesiculated <span class="hlt">magmas</span> and lavas as a function of melt viscosity, vesicularity, strain rate, and geological condition. Increasing vesicularity in <span class="hlt">magmas</span> can initiate non-Newtonian behaviour at constant strain rates. Lower melt viscosity sustains homogeneous Newtonian flow in vesiculated <span class="hlt">magmas</span> even at relatively high strain rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6239899','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6239899"><span><span class="hlt">Magmas</span> and magmatic rocks: An introduction to igneous petrology</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Middlemost, E.A.K.</p> <p>1986-01-01</p> <p>This book melds traditional igneous petrology with the emerging science of planetary petrology to provide an account of current ideas on active magmatic and volcanic processes, drawing examples from all igneous provinces of the world as well as from the moon and planets. It reviews the history and development of concepts fundamental to modern igneous petrology and includes indepth sections on <span class="hlt">magmas</span>, magnetic differentiation and volcanology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AAS...22940106S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AAS...22940106S"><span>Atmosphere-<span class="hlt">magma</span> ocean modeling of GJ 1132 b</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schaefer, Laura; Wordsworth, Robin; Berta-Thompson, Zachory K.; Sasselov, Dimitar</p> <p>2017-01-01</p> <p>GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly characterizable small exoplanets currently known. Using a coupled atmosphere-<span class="hlt">magma</span> ocean model, we determine that GJ 1132 b must have begun with more than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the amount of O2 that can build up in the atmosphere as a result of hydrogen dissociation and loss. We find that the <span class="hlt">magma</span> ocean absorbs at most ~ 10% of the O2 produced, whereas more than 90% is lost to space through hydrodynamic drag. The results of the model depend strongly on the initial water abundance and the XUV model. The most common outcome for GJ 1132 b from our simulations is a tenuous atmosphere dominated by O2, although for very large initial water abundances, atmospheres with several thousands of bars of O2 are possible. A substantial steam envelope would indicate either the existence of an earlier H2 envelope or low XUV flux over the system's lifetime. A steam atmosphere would also imply the continued existence of a <span class="hlt">magma</span> ocean on GJ 1132 b. Preliminary modeling with the addition of CO2 gas will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.V43A1767N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.V43A1767N"><span>Viscosity of bubble- and crystal- bearing <span class="hlt">magmas</span>: Analogue results</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Namiki, A.; Manga, M.</p> <p>2006-12-01</p> <p>Natural <span class="hlt">magmas</span> often include both phenocrysts and bubbles. Such <span class="hlt">magmas</span> can be regarded as suspensions including particles and bubbles and should have a viscosity different from the particle- and bubble- free melt. Viscosity is one of the key physical properties that affects eruption dynamics and <span class="hlt">magma</span> flow. To understand the relation between the viscosity and the volume fraction of bubbles and particles, we directly measure the viscosity of suspensions with both particles and bubbles. Measurements are performed with the 4 degree cone-and-plate type rheometer (Thermo HAAKE Rheoscope 1), which allows us to observe the samples in situ during the measurement. The suspending fluid is corn syrup whose viscosity is 1.7 Pa·s at 23 °C. Particles are Techpolymer (polymethylmethacrylate) 40 μm diameter spheres. Bubbles are made by dissolving baking soda and citric acid; reaction between them generates carbon dioxide. No surfactant is added. The Peclet number is sufficiently large that Brownian motion does not influence our results. The measured viscosity for the suspensions with particles, and with both particles and bubbles, show strong shear thinning. The measured viscosities during increasing and decreasing shear rate differ from each other, indicating that the microstructure is modified by flow. When the deformation of bubbles is not significant, the measured viscosity with bubbles is higher than that without bubbles, and vice versa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998E%26PSL.160..709M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998E%26PSL.160..709M"><span>Open-system degassing of sulfur from Krakatau 1883 <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mandeville, Charles W.; Sasaki, Akira; Saito, Genji; Faure, Kevin; King, Robert; Hauri, Erik</p> <p>1998-08-01</p> <p>We present the first sulfur and oxygen isotopic data for tephra from the catastrophic 1883 eruption of Krakatau. Sulfur isotopic ratios in unaltered Krakatau tephra erupted August 26-27, 1883 are markedly enriched in 34S relative to mantle sulfur. High δ34S values of +6.3 to +16.4‰ can best be explained by open-system or multi-stage degassing of SO 2 from the oxidized rhyodacitic and gray dacitic <span class="hlt">magmas</span> with 34S enrichment of SO 2-4 remaining in the melt. Lower whole-rock δ34S values of +2.6‰ and +4.0‰ in two oxidized gray dacitic samples indicate more primitive subarc mantle sulfur in the 1883 <span class="hlt">magma</span> chamber. Initial δ34S of the rhyodacitic <span class="hlt">magma</span> was probably in the +1.5‰ to +4.0‰ range and similar to δ34S values measured in arc volcanic rocks from the Mariana Arc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V21D2031B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V21D2031B"><span><span class="hlt">Magma</span> differentiation and volatile evolution at Fuego Volcano, Guatemala</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Berlo, K.; Stix, J.; Roggensack, K.</p> <p>2009-12-01</p> <p>Fuego is an active stratovolcano in Guatemala that has erupted mainly basaltic <span class="hlt">magma</span> in recent times. The last large eruption, a subplinian (VEI 4), occurred in 1974 and produced pyroclastic flows and ash fall for 10 days. Many smaller eruptions with pyroclastic, lava and lahars flows have occurred since then and activity is intermittently ongoing. Melt inclusions in olivine phenocrysts from the 1974 eruption testify to the presence of variably crystallized <span class="hlt">magma</span> over a range of depths. Melt inclusions from 1999 and 2004 overlap and extend the 1974 fractional crystallization trend to lower pressure. Melt inclusions from 1974 record high H2O (~6 wt %) and high CO2 (~2500 ppm) concentrations. In contrast the later eruptions have much lower H2O (maximum observed 1 wt %), but CO2 concentrations up to ~1500 ppm. Whereas melts recorded by the later eruptions could be residual from the <span class="hlt">magma</span> erupted in 1974, these high CO2 concentrations combined with a somewhat higher alkali concentration point to a more complex process or combination of processes. This contribution will examine the origin and associated implications of these later melts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/59926','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/59926"><span><span class="hlt">Magma</span> mixing due to disruption of a compositional interface</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Flood, T.P.; Schuraytz, B.C.; Vogel, T.A.</p> <p>1986-07-15</p> <p>The chemical compositions of glassy pumices are used to investigate the relationship between two ash-flow sheets that were erupted from the same volcanic center. The first ash-flow sheet, the large volume (>1200 km{sup 3}) Topopah Spring Member, represents an eruption from a <span class="hlt">magma</span> body that contained a sharp compositional interface between a high-silica rhyolite and a lower-silica quartz latite. The second ash-flow sheet is the smaller volume (<40 km{sup 3}) Pah Canyon Member. It represents an eruption of a relatively homogenous <span class="hlt">magma</span> that is intermediate in composition to the compositions of the Topopah Spring Member. Mixing of the quartz latite and rhyolite <span class="hlt">magmas</span> to produce the Pah Canyon Member is evaluated using variation diagrams of the major and trace elements, ratio-ratio plots, and least-squares multiple linear regression. The latter includes two independent tests, one using the major elements, and the other using selected trace elements. Fractional crystallization of the quartz latite to produce the Pah Canyon Member is evaluated using multiple linear regression with both the major elements and selected trace elements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006PCE....31..223F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006PCE....31..223F"><span>Earliest detection of <span class="hlt">magma</span> movements by measuring transient streaming potential</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fujinawa, Yukio; Matsumoto, Takumi; Iitaka, Hiroshi; Takahashi, Kozo; Nakano, Hiroshi; Doi, Takuya; Saito, Toshiyuki; Kasai, Naoko; Sato, Sohjun</p> <p></p> <p>Volcanic eruptions are generally preceded by <span class="hlt">magma</span> intrusion. Volcanic forecasting is sure to make considerable progress if we have a practical means to detect <span class="hlt">magma</span> movements. Electric potential variations have been observed since April 1999 at Miyake Island, a volcanic island in Japan. Measurements have been conducted by a special long vertical antenna using a steel casing pipe and a short horizontal dipole. Beginning about half a day before as well as at the time period of the largest eruption in 2000 of Miyake-jima volcano on August 18, 2000, conspicuous electric field variations were observed on the horizontal and vertical components in the frequency bands of DC, ULF and ELF/VLF. And several types of anomalies were found to occur in association with different stage of volcanic activities. We suggest that transient self-potential variations are induced by confined ground water pressure fluctuations through interaction between intruding <span class="hlt">magma</span> and hydrothermal circulation through electro-kinetic effect. Subsurface transient self-potential measurement has been suggested to be useful means for monitoring volcanic eruption and to provide an efficient window for looking into modification of hydrothermal circulation induced by the volcanic activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26601265','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26601265"><span>The chlorine isotope fingerprint of the lunar <span class="hlt">magma</span> ocean.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Boyce, Jeremy W; Treiman, Allan H; Guan, Yunbin; Ma, Chi; Eiler, John M; Gross, Juliane; Greenwood, James P; Stolper, Edward M</p> <p>2015-09-01</p> <p>The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free ("dry") Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because (37)Cl/(35)Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, (37)Cl/(35)Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high (37)Cl/(35)Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar <span class="hlt">magma</span> ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar <span class="hlt">magma</span> ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary <span class="hlt">magma</span> ocean degassing, an important stage in the formation of terrestrial planets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4585707','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4585707"><span>Concentration variance decay during <span class="hlt">magma</span> mixing: a volcanic chronometer</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Perugini, Diego; De Campos, Cristina P.; Petrelli, Maurizio; Dingwell, Donald B.</p> <p>2015-01-01</p> <p>The mixing of <span class="hlt">magmas</span> is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of <span class="hlt">magma</span> mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of <span class="hlt">magma</span> mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing – a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical “mixing to eruption” time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest. PMID:26387555</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015NatSR...514225P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015NatSR...514225P"><span>Concentration variance decay during <span class="hlt">magma</span> mixing: a volcanic chronometer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perugini, Diego; de Campos, Cristina P.; Petrelli, Maurizio; Dingwell, Donald B.</p> <p>2015-09-01</p> <p>The mixing of <span class="hlt">magmas</span> is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of <span class="hlt">magma</span> mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of <span class="hlt">magma</span> mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing - a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical “mixing to eruption” time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V31B3027P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V31B3027P"><span>Concentration variance decay during <span class="hlt">magma</span> mixing: a volcanic chronometer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perugini, D.; De Campos, C. P.; Petrelli, M.; Dingwell, D. B.</p> <p>2015-12-01</p> <p>The mixing of <span class="hlt">magmas</span> is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of <span class="hlt">magma</span> mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of <span class="hlt">magma</span> mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing - a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical "mixing to eruption" time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Icar..272..246M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Icar..272..246M"><span><span class="hlt">Magma</span> ascent pathways associated with large mountains on Io</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McGovern, Patrick J.; Kirchoff, Michelle R.; White, Oliver L.; Schenk, Paul M.</p> <p>2016-07-01</p> <p>While Jupiter's moon Io is the most volcanically active body in the Solar System, the largest mountains seen on Io are created by tectonic forces rather than volcanic construction. Pervasive compression, primarily brought about by subsidence induced by sustained volcanic resurfacing, creates the mountains, but at the same time inhibits <span class="hlt">magma</span> ascent in vertical conduits (dikes). We superpose stress solutions for subsidence, along with thermal stress, (both from the "crustal conveyor belt" process of resurfacing) in Io's lithosphere with stresses from Io mountain-sized loads (in a shallow spherical shell solution) in order to evaluate <span class="hlt">magma</span> ascent pathways. We use stress orientation (least compressive stress horizontal) and stress gradient (compression decreasing upwards) criteria to identify ascent pathways through the lithosphere. There are several configurations for which viable ascent paths transit nearly the entire lithosphere, arriving at the base of the mountain, where <span class="hlt">magma</span> can be transported through thrust faults or perhaps thermally eroded flank sections. The latter is consistent with observations of some Io paterae in close contact with mountains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.412..143B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.412..143B"><span>Estimation of <span class="hlt">magma</span> depth for resurgent domes: An experimental approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brothelande, Elodie; Merle, Olivier</p> <p>2015-02-01</p> <p>Post-collapse resurgence is a phenomenon affecting many calderas. Attributed to a renewed <span class="hlt">magma</span> rise, the process is still poorly understood and the associated source parameters remain poorly constrained. A set of experiments has been conducted to gain insight into the structural evolution of caldera resurgent domes. A sand-plaster mixture was chosen as an analogue for the brittle pile of volcanic rocks, and silicone putty simulates the ductile behavior of the intruding <span class="hlt">magma</span>. Resurgence is driven by the vertical uplift of the silicone, with variable shape and depth. Similarity conditions are achieved through eight dimensionless numbers, which are of the same order of magnitude in both nature and experiments. Results show that extension due to doming is, in many cases, accommodated by one axial graben. Opposite master faults of this graben intersect at depth at the junction with the rising viscous silicone. The simplicity of the geometry of the whole analogue system provides equations which allow the estimation of the silicone depth from surface parameters. These equations are then used in some field examples to assess the <span class="hlt">magma</span> depth beneath natural resurgent domes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4643783','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4643783"><span>The chlorine isotope fingerprint of the lunar <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Boyce, Jeremy W.; Treiman, Allan H.; Guan, Yunbin; Ma, Chi; Eiler, John M.; Gross, Juliane; Greenwood, James P.; Stolper, Edward M.</p> <p>2015-01-01</p> <p>The Moon contains chlorine that is isotopically unlike that of any other body yet studied in the Solar System, an observation that has been interpreted to support traditional models of the formation of a nominally hydrogen-free (“dry”) Moon. We have analyzed abundances and isotopic compositions of Cl and H in lunar mare basalts, and find little evidence that anhydrous lava outgassing was important in generating chlorine isotope anomalies, because 37Cl/35Cl ratios are not related to Cl abundance, H abundance, or D/H ratios in a manner consistent with the lava-outgassing hypothesis. Instead, 37Cl/35Cl correlates positively with Cl abundance in apatite, as well as with whole-rock Th abundances and La/Lu ratios, suggesting that the high 37Cl/35Cl in lunar basalts is inherited from urKREEP, the last dregs of the lunar <span class="hlt">magma</span> ocean. These new data suggest that the high chlorine isotope ratios of lunar basalts result not from the degassing of their lavas but from degassing of the lunar <span class="hlt">magma</span> ocean early in the Moon’s history. Chlorine isotope variability is therefore an indicator of planetary <span class="hlt">magma</span> ocean degassing, an important stage in the formation of terrestrial planets. PMID:26601265</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810041805&hterms=Stone+Age&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DStone%2BAge','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810041805&hterms=Stone+Age&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DStone%2BAge"><span>Dropping stones in <span class="hlt">magma</span> oceans - Effects of early lunar cratering</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hartmann, W. K.</p> <p>1980-01-01</p> <p>A new methodology is used to calculate the accumulation rate of megaregolith materials for two models of early lunar cratering, both with and without episodes of late cataclysmic cratering. Results show that the pulverization of early rock layers was an important process competing with the formation of a coherent rock lithosphere at the surface of the hypothetical lunar <span class="hlt">magma</span> ocean. If a <span class="hlt">magma</span> ocean existed, then its initial cooling was marked by a period of pre-lithospheric chaos in which impacts punched through the initially thin rocky skin, mixing rock fragments with splashed <span class="hlt">magma</span>. Furthermore, the results show that intense brecciation and pulverization of rock materials must have occurred to a depth of at least tens of kilometers in the first few hundred years of lunar history regardless of whether a 'terminal lunar cataclysm' occurred around 4.0 G.y. ago. The predicted pattern of brecciation and the ages of surviving rock fragments is similar to that actually observed among lunar samples. More reliable dating of basin-forming events and models of rock exhumation and survival are needed in order to understand better the relation between the early intense bombardment of the moon and the samples collected on the moon today.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810041805&hterms=Stone+Age&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DStone%2BAge','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810041805&hterms=Stone+Age&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DStone%2BAge"><span>Dropping stones in <span class="hlt">magma</span> oceans - Effects of early lunar cratering</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hartmann, W. K.</p> <p>1980-01-01</p> <p>A new methodology is used to calculate the accumulation rate of megaregolith materials for two models of early lunar cratering, both with and without episodes of late cataclysmic cratering. Results show that the pulverization of early rock layers was an important process competing with the formation of a coherent rock lithosphere at the surface of the hypothetical lunar <span class="hlt">magma</span> ocean. If a <span class="hlt">magma</span> ocean existed, then its initial cooling was marked by a period of pre-lithospheric chaos in which impacts punched through the initially thin rocky skin, mixing rock fragments with splashed <span class="hlt">magma</span>. Furthermore, the results show that intense brecciation and pulverization of rock materials must have occurred to a depth of at least tens of kilometers in the first few hundred years of lunar history regardless of whether a 'terminal lunar cataclysm' occurred around 4.0 G.y. ago. The predicted pattern of brecciation and the ages of surviving rock fragments is similar to that actually observed among lunar samples. More reliable dating of basin-forming events and models of rock exhumation and survival are needed in order to understand better the relation between the early intense bombardment of the moon and the samples collected on the moon today.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V13D2885S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V13D2885S"><span>Timescales of <span class="hlt">magma</span> residence at Campi Flegrei, Italy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, V. C.; Saunders, K.; Isaia, R.</p> <p>2012-12-01</p> <p>Campi Flegrei caldera has produced many large explosive eruptions, including the largest in Europe in the last 200 kyrs. There have been more than 60 violent Strombolian-Vulcanian through to Plinian eruptions in the last 15 kyrs. Recent changes in ground displacement and composition of fumarole fluids indicate the caldera is still active and suggest that <span class="hlt">magma</span> resides in the upper crust (Chiodini et al., 2012). Here we used zoned crystals within the post-15 ka eruption deposits to assess the timescales of upper crustal <span class="hlt">magma</span> residence at Campi Flegrei. We present details of the major and trace element composition of the crystals, and diffusion chronometry results. These data provide detail on the crystallisation timescales and the changing nature of the magmatic system. It is clear that the <span class="hlt">magmas</span> that fuel the eruptions are assembled in an open system and that upper crustal residence for most of the melt is short. Chiodini, G., Caliro, S., De Martino, P., Avino, R., Gherardi, F. 2012. Early signals of new volcanic unrest at Campi Flegrei caldera? Insights from geochemical data and physical simulations. Geology. http://dx.doi.org/10.1130/G33251.1</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900046412&hterms=glass+evidence&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dglass%2Bevidence','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900046412&hterms=glass+evidence&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dglass%2Bevidence"><span>Parental <span class="hlt">magmas</span> of Mare Fecunditatis - Evidence from pristine glasses</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jin, Y.; Taylor, L. A.</p> <p>1990-01-01</p> <p>Results are presented on the petrography and electron microprobe analyses of 14 discrete glass beads from the Luna 16 core sample (21036,15) from Mare Fecunditatis regolith, that were previously characterized as representing pristine glasses. Compared to Apollo pristine glasses analyzed by Delano (1986), the Luna 16 pristine glasses have higher CaO and Al2O3 contents but lower MgO and Ni. On the basis of their contents of MgO, FeO, Al2O3, and CaO, these pristine glasses could be divided into two groups, A and B. It is suggested that at least two parental <span class="hlt">magmas</span> are needed to explain the chemical variations among these glasses. The Group B glasses appear to represent primitive parental <span class="hlt">magma</span> that evolved by olivine fractionation to the compositions of the Luna 16 aluminous mare basalts, whereas the Group A volcanic glasses may represent an unusual new basalt <span class="hlt">magma</span> type that contains a high plagioclase component.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T21A1784H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T21A1784H"><span>Petrogenesis of mafic <span class="hlt">magma</span> and associated silicic <span class="hlt">magma</span> for calk-alkaline rocks in the Shirataka volcano, NE Japan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hirotani, S.; Ban, M.; Nakagawa, M.</p> <p>2009-12-01</p> <p>Eruptive products of Shirataka volcano (0.9-0.7 Ma) in NE Japan are calc-alkaline andesite-dacite (57-66% SiO2), and are divided into six petrologic groups (G1-6). Mafic inclusions (48-58% SiO2) are always observed in G1, G2, G5 and G6. The host rocks as well as inclusions are mixed rocks formed between mafic and silicic end-members judging from many petrologic aspects. Based on petrologic data of more than 30 mafic inclusion-host pairs in these groups, we revealed the petrologic features of the end-member <span class="hlt">magmas</span> and examined their petrogenesis. The mixing trends defined by hosts and inclusions are divided into high- and low-Cr types. Both types coexist in G1, G2 and G5, while G6 lacks high-Cr type. In the same group, the mafic end-member for high-Cr type shows more primitive features (e.g. in G5; 1140-1160°C, 50% SiO2, Fo-rich olv + Mg-rich cpx + An-rich plg phenocrysts) than that for the low-Cr type (e.g. in G5; c. 1100°C, 51% SiO2, Mg-rich cpx + An-rich plg phenocrysts). The silicic end-members for the two types show similar mineral assemblage (e.g. in G5; hbl + qtz + Mg-poor px + An-poor plg phenocrysts) but are different in bulk compositions (e.g. in G5; high-Cr type, 67% SiO2; low-Cr type, 66% SiO2). Significantly, in a petrologic group, the high-Cr type mafic and corresponding silicic end-members have lower values in 87Sr/86Sr ratio than the low-Cr type ones. Further, the bulk compositions of each type end-members show slight variability among petrologic groups. For example, Sr isotopic ratios and SiO2 contents of high-Cr type mafic end-members are 0.7037 and 48% in G1, 0.7039 and 51% in G2, and 0.7042 and 50% in G5, respectively. The MELTS and geochemical model calculations have shown that the low-Cr type mafic end-member <span class="hlt">magma</span> can be produced through c. 20% fractional crystallization (olv + plg) from the high-Cr type mafic end-member <span class="hlt">magma</span> accompanied with the assimilation of basement plutonic rocks (r=0.02-0.05) in the case of G5. In terms of associated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930072214&hterms=scottish&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dscottish','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930072214&hterms=scottish&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dscottish"><span>Buffered and unbuffered dike emplacement on Earth and Venus - Implications for <span class="hlt">magma</span> reservoir size, depth, and rate of <span class="hlt">magma</span> replenishment</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Parfitt, E. A.; Head, J. W., III</p> <p>1993-01-01</p> <p>Models of the emplacement of lateral dikes from <span class="hlt">magma</span> chambers under constant (buffered) driving pressure conditions and declining (unbuffered) driving pressure conditions indicate that the two pressure scenarios lead to distinctly different styles of dike emplacement. In the unbuffered case, the lengths and widths of laterally emplaced dikes will be severely limited and the dike lengths will be highly dependent on chamber size; this dependence suggests that average dike length can be used to infer the dimensions of the source <span class="hlt">magma</span> reservoir. On Earth, the characteristics of many mafic-dike swarms suggest that they were emplaced in buffered conditions (e.g., the Mackenzie dike swarm in Canada and some dikes within the Scottish Tertiary). On Venus, the distinctive radial fractures and graben surrounding circular to oval features and edifices on many size scales and extending for hundreds to over a thousand km are candidates for dike emplacement in buffered conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/842661','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/842661"><span>A model for the origin of large silicic <span class="hlt">magma</span> chambers: precursors of caldera-forming eruptions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jellinek, A. Mark; DePaolo, Donald J.</p> <p>2002-01-02</p> <p>The relatively low rates of <span class="hlt">magma</span> production in island arcs and continental extensional settings require that the volume of silicic <span class="hlt">magma</span> involved in large catastrophic caldera-forming (CCF) eruptions must accumulate over periods of 10(5) to 10(6) years. We address the question of why buoyant and otherwise eruptible high silica <span class="hlt">magma</span> should accumulate for long times in shallow chambers rather than erupt more continuously as <span class="hlt">magma</span> is supplied from greater depths. Our hypothesis is that the viscoelastic behavior of <span class="hlt">magma</span> chamber wall rocks may prevent an accumulation of overpressure sufficient to generate rhyolite dikes that can propagate to the surface and cause an eruption. The critical overpressure required for eruption is based on the model of Rubin (1995a). An approximate analytical model is used to evaluate the controls on <span class="hlt">magma</span> overpressure for a continuously or episodically replenished spherical <span class="hlt">magma</span> chamber contained in wall rocks with a Maxwell viscoelastic rheology. The governing parameters are the long-term <span class="hlt">magma</span> supply, the <span class="hlt">magma</span> chamber volume, and the effective viscosity of the wall rocks. The long-term <span class="hlt">magma</span> supply, a parameter that is not typically incorporated into dike formation models, can be constrained from observations and melt generation models. For effective wall-rock viscosities in the range 10(18) to 10(20) Pa s(-1), dynamical regimes are identified that lead to the suppression of dikes capable of propagating to the surface. Frequent small eruptions that relieve <span class="hlt">magma</span> chamber overpressure are favored when the chamber volume is small relative to the <span class="hlt">magma</span> supply and when the wall rocks are cool. <span class="hlt">Magma</span> storage, leading to conditions suitable for a CCF eruption, is favored for larger <span class="hlt">magma</span> chambers (>10(2) km(3)) with warm wall rocks that have a low effective viscosity. <span class="hlt">Magma</span> storage is further enhanced by regional tectonic extension, high <span class="hlt">magma</span> crystal contents, and if the effective wall-rock viscosity is lowered by microfracturing, fluid</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989JGR....94.6041V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989JGR....94.6041V"><span>Evolution of a Chemically Zoned <span class="hlt">Magma</span> Body: Black Mountain Volcanic Center, southwestern Nevada</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vogel, Thomas A.; Noble, Donald C.; Younker, Leland W.</p> <p>1989-05-01</p> <p>Rocks of the Black Mountain volcanic center consist of four ash flow sheets and units of lava that underlie, interfinger with, and overlie the sheets. Rocks from the center represent three <span class="hlt">magma</span> types. <span class="hlt">Magma</span> type c was present through the history of the center, whereas types a and b were available after the eruption of the Rocket Wash Member, during the eruptions of the Pahute Mesa and Trail Ridge members. The <span class="hlt">magma</span> types are defined by trace element ratios; for example, <span class="hlt">magma</span> types a, b, and c have La/Th values of 1.0-3.5, >7.5, and 3.5-7.5. Silica contents in the <span class="hlt">magma</span> types a, b, and c range from 71.5 to 74.1, from 65.8 to 69.2, and from 55.6 to 73.8 wt %, respectively. The stratigraphic distribution of chemically distinct pumice fragments within the ash flow sheets is used to show that <span class="hlt">magma</span> type a was located in the uppermost part of the chamber and was underlain successively by <span class="hlt">magma</span> types b and c. Because pumice fragments that belong to all three <span class="hlt">magma</span> types occur in individual cooling units, a zoned <span class="hlt">magma</span> body must have existed during this period. <span class="hlt">Magma</span> mixing is indicated by the disequilibrium phenocrysts which are common in pumice fragments from all <span class="hlt">magma</span> types; however, this mixing did not destroy the original zoning of the upper part of the <span class="hlt">magma</span> body. Most of the chemical variation of <span class="hlt">magma</span> type c is consistent with fractionation of feldspar, olivine, and pyroxene, but abundant disequilibrium, mafic phenocrysts indicate that <span class="hlt">magma</span> replenishment and mixing were common. <span class="hlt">Magma</span> type b had much higher La/Th and light rare earth element (LREE)/heavy rare earth element values and must have originated independently from <span class="hlt">magma</span> type c. Most likely the two types were derived from different source material. The low La/Th values of <span class="hlt">magma</span> type a can be explained by separation of a phenocryst assemblage containing both a LREE-bearing phase and zircon from either <span class="hlt">magma</span> types b or c, or possibly by the partial melting of source material containing these phases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.429..223H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.429..223H"><span>Timescales for permeability reduction and strength recovery in densifying <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heap, M. J.; Farquharson, J. I.; Wadsworth, F. B.; Kolzenburg, S.; Russell, J. K.</p> <p>2015-11-01</p> <p>Transitions between effusive and explosive behaviour are routine for many active volcanoes. The permeability of the system, thought to help regulate eruption style, is likely therefore in a state of constant change. Viscous densification of conduit <span class="hlt">magma</span> during effusive periods, resulting in physical and textural property modifications, may reduce permeability to that preparatory for an explosive eruption. We present here a study designed to estimate timescales of permeability reduction and strength recovery during viscous <span class="hlt">magma</span> densification by coupling measurements of permeability and strength (using samples from a suite of variably welded, yet compositionally identical, volcanic deposits) with a rheological model for viscous compaction and a micromechanical model, respectively. Bayesian Information Criterion analysis confirms that our porosity-permeability data are best described by two power laws that intersect at a porosity of 0.155 (the ;changepoint; porosity). Above and below this changepoint, the permeability-porosity relationship has a power law exponent of 8.8 and 1.0, respectively. Quantitative pore size analysis and micromechanical modelling highlight that the high exponent above the changepoint is due to the closure of wide (∼200-300 μm) inter-granular flow channels during viscous densification and that, below the changepoint, the fluid pathway is restricted to narrow (∼50 μm) channels. The large number of such narrow channels allows porosity loss without considerable permeability reduction, explaining the switch to a lower exponent. Using these data, our modelling predicts a permeability reduction of four orders of magnitude (for volcanically relevant temperatures and depths) and a strength increase of a factor of six on the order of days to weeks. This discrepancy suggests that, while the viscous densification of conduit <span class="hlt">magma</span> will inhibit outgassing efficiency over time, the regions of the conduit prone to fracturing, such as the margins, will</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815195K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815195K"><span>The non-isothermal rheology of low viscosity <span class="hlt">magmas</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kolzenburg, Stephan; Giordano, Daniele; Dingwell, Donald B.</p> <p>2016-04-01</p> <p>Accurate prediction of the run-out distance of lava flows, as well as the understanding of <span class="hlt">magma</span> migration in shallow dyke systems is hampered by an incomplete understanding of the transient, sub-liquidus rheology of crystallizing melts. This sets significant limits to physical property based modelling of lava flow (especially flow width, length and advancement rate) and <span class="hlt">magma</span> migration behaviour and the resulting accuracy of volcanic hazard assessment The importance of the dynamic rheology of a lava / <span class="hlt">magma</span> on its emplacement style becomes especially apparent in towards later stages of flow and dyke emplacement, where the melt builds increasing resistance to flow, entering rheologic regimes that determine the halting of lava flows and sealing of dykes. Thermal gradients between the interior of a melt body and the contact with air or the substratum govern these rheologic transitions that give origin to flow directing or impeding features like levees, tubes and chilled margins. Besides the critical importance of non-isothermal and sub-liquidus processes for the understanding of natural systems, accurate rheologic data at these conditions are scarce and studies capturing the transient rheological evolution of lavas at conditions encountered during emplacement virtually absent. We describe the rheologic evolution of a series of natural, re-melted lava samples during transient and non-equilibrium crystallization conditions characteristic of lava flows and shallow magmatic systems in nature. The sample suite spans from foidites to basalts; the dominant compositions producing low viscosity lava flows. Our data show that all melts undergo one or more change zones in effective viscosity when subjected to sub liquidus temperatures. The apparent viscosity of the liquid-crystal suspension increases drastically from the theoretical temperature-viscosity relationship of a pure liquid once cooled below the liquidus temperature. We find that: 1) Both cooling rate and shear rate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V41B2778F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V41B2778F"><span>The Yellowstone <span class="hlt">magma</span> reservoir is 50% larger than previously imaged</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Farrell, J.; Smith, R. B.; Husen, S.</p> <p>2013-12-01</p> <p>Earlier tomographic studies of the Yellowstone crustal <span class="hlt">magma</span> system have revealed a low P-wave crustal anomaly beneath the 0.64 Ma Yellowstone caldera that has been interpreted to be the <span class="hlt">magma</span> reservoir of partial melt that provides the thermal energy for Yellowstone's youthful volcanic and hydrothermal systems. The Yellowstone seismic network has evolved over the last decade into a modern real-time volcano monitoring system that consists of 36 short-period, broadband, and borehole seismometers that cover the entire Yellowstone volcanic field and surrounding tectonic areas. Until recently, limited seismograph coverage did not provide for adequate resolution of the velocity structure northeast of the caldera, an area of the largest negative Bouguer gravity field of -60 mGal whose 3D density model reveals a shallow, low density body that extends ~20 km northeast of the caldera. Recent upgrades to the Yellowstone Seismic Network (YSN), including the addition of nine 3-component and broadband seismic stations providing much better ray coverage of the entire Yellowstone area with greater bandwidth data. This allows much-expanded and improved resolution coverage of the Yellowstone crustal velocity structure. We have compiled waveforms for the Yellowstone earthquake catalog from 1984-2011 with 45,643 earthquakes and 1,159,724 waveforms to analyze P-wave arrival times with an automatic picker based on an adaptive high-fidelity human mimicking algorithm. Our analysis reduced the data to the 4,520 best-located earthquakes with 48,622 P-wave arrival times to invert for the velocity structure. The resulting 3D P-wave model reveals a low Vp body (up to -7% ΔVp) that is interpreted to be the Yellowstone crustal <span class="hlt">magma</span> reservoir and is ~50% larger than previously imaged. It extends as an oblong shaped anomalous body ~90 km NE-SW, ~20 km NE of the 0.64 Ma caldera, and up to 30 km wide and markedly shallowing from 15 km depth beneath the caldera to less than ~2 km deep northeast of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.V11A0365G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.V11A0365G"><span>Deformation of <span class="hlt">Magma</span>-Filled Bodies during Solidification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaffney, E. S.; Damjanac, B.</p> <p>2007-12-01</p> <p>As <span class="hlt">magma</span> or lava solidifies, volatiles are concentrated in the residual liquid. The result will be expansion (including venting) or pressurization. The mechanism behind this is well-described. A rough hand calculation indicates that an alkali basalt with 4 wt% volatiles would attain attain 12 MPa with 50% crystallization at constant volume. Such pressures would easily be enough to break through the roof of a typical lava tube. If confined in a tunnel deeper in the ground, even in a relatively weak rock, crystallization would be virtually isochoric. However, in a sill at depths of only a few hundred meters, expansion could result in more nearly isobaric crystallization. In either event, before cooling enough to become a brittle solid, the outer portions of the <span class="hlt">magma</span> would reach a viscoplastic state that could seal in any remaining vapor phase. This would allow pressures to increase further as solidification progressed. Using PELE, a computer code developed to calculate the progress of solidification (Boudreau, 2005), we calculate isochoric and isobaric equilibrium crystallization of alkali basalt and obtain pressures and viscosities as a function of temperature. For an initial pressure of 6 MPa and 0.85 weight percent water, the liquidus is 1433 K. The isochoric pressure reaches 11 MPa at 1293 K with 57% of the mass crystallized; the bulk viscosity is about 3 MPa-s, but that of the residual liquid is only 1 kPa-s. At the same temperature, the isobaric path results in 60% crystallization and a viscosity on the order of 10 kPa-s. A tabular body with these properties would be easily deformed by sagging of the roof if the viscoplastic seal were breached, resulting in a saucer shape. With 91% of the mass crystallized, the isochoric pressure exceeds 28 MPa at 1173 K. By that time, the bulk viscosity of the nearly crystallized mass is on the order of 1025 Pa-s, effectively solid, and the viscosity of the residual liquid (there is also a vapor phase) is about 50 k</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....3295N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....3295N"><span>Melt production and <span class="hlt">magma</span> emplacement: What use are they?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nimmo, F.</p> <p>2003-04-01</p> <p>I will review the processes of melt production and <span class="hlt">magma</span> emplacement and address two questions: how do these processes affect planetary evolution?; and what can we learn from observing them, both now and in the future? Melt production is primarily controlled by the temperature of the planetary interior. The extraction of melt from silicate mantles has a number of effects. Firstly, it advects heat (e.g. Io, Venus?). Secondly, it segregates radiogenic materials into the crust, thus cooling the mantle (e.g. Mars, Earth). Thirdly, it removes volatiles from the interior (e.g. Venus, Mars). Recognition that melting is occurring gives us information about likely conditions inside the planet. Models of melt generation by convective upwelling have been used to constrain the interior properties of the Earth, Venus and Mars. Melting during tidal heating (Io) or accretion is less well understood. <span class="hlt">Magma</span> emplacement is primarily controlled by the density of the <span class="hlt">magma</span> and the surrounding material. Extrusive activity is likely for high volatile concentrations or low crustal densities. Water is particularly difficult to erupt, since (unlike silicates) the melt is denser than the solid. Different styles of <span class="hlt">magma</span> emplacement are observed: voluminous surface flows and volcanic edifices of various kinds (ubiquitous); giant radiating dyke swarms (Earth, Venus, Mars); intrusive sills and diapirs (Earth, Venus?, Mars?, Europa?). The extrusive emplacement of <span class="hlt">magma</span> will cause resurfacing, and is thus easily detected. The release of volatiles during emplacement may have local (e.g. Laki) or global (Venus? Mars?) effects on climate and atmosphere. Intrusive emplacement is harder to detect, but may interact with local volatiles to create unusual landforms (Earth, Mars). The style and volume of emplacement is a useful diagnostic tool. The morphology of lava flows gives information about the rheology and composition of the flow material (e.g. Venus, Miranda). Observations of dykes may be used to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V11E..08L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V11E..08L"><span>Reconciling Volatile Outputs with Heat Flow and <span class="hlt">Magma</span> Intrusion Rates at the Yellowstone <span class="hlt">Magma</span>-Hydrothermal System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lowenstern, J. B.; Hurwitz, S.</p> <p>2012-12-01</p> <p>The Yellowstone hydrothermal system releases hundreds of millions of liters of water on a daily basis. Gigawatts of heat and kilotons of magmatic volatiles (CO2, S, Cl, F and He) are discharged by these waters. By quantifying the relative contributions of crustal, meteoric, and mantle-derived components, we can estimate the rate at which <span class="hlt">magma</span> is fed to the crust from below (1). Combining isotopic studies with mass discharge rates of geothermal gases and aqueous dissolved solids, we recognize that over 20,000 tons of CO2 is released from basaltic <span class="hlt">magmas</span> ponding beneath any silicic <span class="hlt">magma</span> reservoir in the mid to shallow crust (1,2). In contrast, silicic <span class="hlt">magma</span> provides significantly less volatiles than what emerges from the hydrothermal system. Estimates of heat flow range from ~3 to 8 GW (1,3,4), derived from satellite, surface geophysics and geochemical methods. Such values, combined with estimates from gas flux, imply prolific basalt intrusion rates between 0.05 and 0.3 cubic kilometers per year (1). Over the history of the Yellowstone Plateau Volcanic Field, a picture emerges where the lower crust is converted from Precambrian metasediments and silicic intrusions into a thick gabbroic batholith similar to that envisioned by some to reside beneath the Snake River Plain along the ancestral track of the Yellowstone Hot Spot (5). (1) Lowenstern and Hurwitz, 2008, Elements 4: 35-40. (2) Werner and Brantley, 2003, G-Cubed 4;7: 1061 (3) Vaughan and others, 2012, JVGR 233-234: 72-89. (4) Hurwitz and others, in press, JGR (5) Shervais and others, 2006, Geology 34:365-368.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24019580','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24019580"><span>Origin of <span class="hlt">magmas</span> in subduction zones: a review of experimental studies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kushiro, Ikuo</p> <p>2007-02-01</p> <p>Studies of the origin of <span class="hlt">magmas</span> in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years. Kuno's original model(1)) for <span class="hlt">magma</span> generation in the Japanese island arc, that tholeiite <span class="hlt">magmas</span> are formed at relatively shallow levels in the mantle on the Pacific Ocean side whereas alkali basalt <span class="hlt">magmas</span> are formed in deeper levels on the Japan Sea side, stimulated subsequent studies, particularly high-pressure experimental studies in which the author participated. Recent seismic tomographic studies of regions beneath the Japanese island arc demonstrate that seismic low-velocity zones where primary <span class="hlt">magmas</span> are formed have finger-like shapes and rise obliquely from the Japan Sea side toward the Pacific Ocean side. Based on experimental studies, it is suggested that the compositions of primary <span class="hlt">magmas</span> depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite <span class="hlt">magmas</span> are formed by 10-25% melting of the source mantle containing less than 0.2 wt.% H2O. High-alumina basalt and alkali basalt <span class="hlt">magmas</span> are formed by smaller degrees of melting of similar mantle, whereas primary boninite <span class="hlt">magmas</span> are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite <span class="hlt">magmas</span> are formed by smaller degrees of melting of similar mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3756732','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3756732"><span>Origin of <span class="hlt">magmas</span> in subduction zones: a review of experimental studies</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kushiro, Ikuo</p> <p>2007-01-01</p> <p>Studies of the origin of <span class="hlt">magmas</span> in subduction zones, particularly in the Japanese island arc, have been significantly advanced by petrological, geochemical, geophysical and experimental studies during last 50 years. Kuno’s original model1) for <span class="hlt">magma</span> generation in the Japanese island arc, that tholeiite <span class="hlt">magmas</span> are formed at relatively shallow levels in the mantle on the Pacific Ocean side whereas alkali basalt <span class="hlt">magmas</span> are formed in deeper levels on the Japan Sea side, stimulated subsequent studies, particularly high-pressure experimental studies in which the author participated. Recent seismic tomographic studies of regions beneath the Japanese island arc demonstrate that seismic low-velocity zones where primary <span class="hlt">magmas</span> are formed have finger-like shapes and rise obliquely from the Japan Sea side toward the Pacific Ocean side. Based on experimental studies, it is suggested that the compositions of primary <span class="hlt">magmas</span> depend mainly on the H2O content and degree of melting in the melting zones, and that primary tholeiite <span class="hlt">magmas</span> are formed by 10–25% melting of the source mantle containing less than 0.2 wt.% H2O. High-alumina basalt and alkali basalt <span class="hlt">magmas</span> are formed by smaller degrees of melting of similar mantle, whereas primary boninite <span class="hlt">magmas</span> are formed by more than 20% melting of the source mantle with more than 0.2 wt.% H2O, and finally, high-magnesia andesite <span class="hlt">magmas</span> are formed by smaller degrees of melting of similar mantle. PMID:24019580</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970022595','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970022595"><span>The Perils of Partition: Difficulties in Retrieving <span class="hlt">Magma</span> Compositions from Chemically Equilibrated Basaltic Meteorites</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Treiman, Allan H.</p> <p>1996-01-01</p> <p>The chemical compositions of <span class="hlt">magmas</span> can be derived from the compositions of their equilibrium minerals through mineral/<span class="hlt">magma</span> partition coefficients. This method cannot be applied safely to basaltic rocks, either solidified lavas or cumulates, which have chemically equilibrated or partially equilibrated at subsolidus temperatures, i.e., in the absence of <span class="hlt">magma</span>. Applying mineral/ melt partition coefficients to mineral compositions from such rocks will typically yield '<span class="hlt">magma</span> compositions' that are strongly fractionated and unreasonably enriched in incompatible elements (e.g., REE's). In the absence of <span class="hlt">magma</span>, incompatible elements must go somewhere; they are forced into minerals (e.g., pyroxenes, plagioclase) at abundance levels far beyond those established during normal mineral/<span class="hlt">magma</span> equilibria. Further, using mineral/<span class="hlt">magma</span> partition coefficients with such rocks may suggest that different minerals equilibrated with different <span class="hlt">magmas</span>, and the fractionation sequence of those melts (i.e., enrichment in incompatible elements) may not be consistent with independent constraints on the order of crystallization. Subsolidus equilibration is a reasonable cause for incompatible- element-enriched minerals in some eucrites, diogenites, and martian meteorites and offers a simple alternative to petrogenetic schemes involving highly fractionated <span class="hlt">magmas</span> or <span class="hlt">magma</span> infiltration metasomatism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V21B2714S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V21B2714S"><span>Eruptive dynamics during <span class="hlt">magma</span> decompression: a laboratory approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spina, L.; Cimarelli, C.; Scheu, B.; Wadsworth, F.; Dingwell, D. B.</p> <p>2013-12-01</p> <p>A variety of eruptive styles characterizes the activity of a given volcano. Indeed, eruptive styles can range from effusive phenomena to explosive eruptions, with related implications for hazard management. Rapid changes in eruptive style can occur during an ongoing eruption. These changes are, amongst other, related to variations in the <span class="hlt">magma</span> ascent rate, a key parameter affecting the eruptive style. Ascent rate is in turn dependent on several factors such as the pressure in the <span class="hlt">magma</span> chamber, the physical properties of the <span class="hlt">magma</span> and the rate at which these properties change. According to the high number of involved parameters, laboratory decompression experiments are the best way to achieve quantitative information on the interplay of each of those factors and the related impact on the eruption style, i.e. by analyzing the flow and deformation behavior of the transparent volatile-bearing analogue fluid. We carried out decompression experiments following different decompression paths and using silicone oil as an analogue for the melt, with which we can simulate a range of melt viscosity values. For a set of experiments we added rigid particles to simulate the presence of crystals in the <span class="hlt">magma</span>. The pure liquid or suspension was mounted into a transparent autoclave and pressurized to different final pressures. Then the sample was saturated with argon for a fixed amount of time. The decompression path consists of a slow decompression from the initial pressure to the atmospheric condition. Alternatively, samples were decompressed almost instantaneously, after established steps of slow decompression. The decompression path was monitored with pressure transducers and a high-speed video camera. Image analysis of the videos gives quantitative information on the bubble distribution with respect to depth in the liquid, pressure and time of nucleation and on their characteristics and behavior during the ongoing <span class="hlt">magma</span> ascent. Furthermore, we also monitored the evolution of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V11A2515V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V11A2515V"><span>Sulfur evolution of the 1991 Pinatubo <span class="hlt">magmas</span> based on apatite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Van Hoose, A. E.; Streck, M. J.; Pallister, J. S.</p> <p>2011-12-01</p> <p>The 1991 eruptions of Mt. Pinatubo, Philippines, were triggered by basaltic recharge into the 50 km3 dacitic <span class="hlt">magma</span> reservoir, and released 20 million tonnes of SO2 into the stratosphere. Three primary juvenile products erupted: dacite, hybrid andesite, and basaltic inclusions. Sulfur bearing apatites occur in all three juvenile components, yet observed S content is variable. Basaltic <span class="hlt">magma</span> includes only high-S (>0.7 wt.% SO3) apatites, while dacitic and hybrid andesitic <span class="hlt">magmas</span> carry low- (<0.3 wt.% SO3), med.- (0.3-0.7 wt.% SO3), and high-S apatites. Pre-eruption conditions (~780°C, 220 MPa, NNO+1.7, and 77 ppm S) (Rutherford & Devine, 1996; Scaillet & Evans, 1999) and a partition coefficient of 13 (Baker & Rutherford, 1996) could yield only low-S apatite containing up to 0.25 wt.% SO3, which is consistent with the SO3 concentrations found in large (≤200 μm) apatite microphenocrysts in glass. Med.-S apatite would still be consistent with pre-eruption conditions if melt sulfur was once at the solubility maximum of ~350 ppm (cf., Clemente et al., 2004). However, concentrations of SO3 in nearly 30% of dacite-hosted apatites analyzed exceeded 0.7 wt.%, which is much higher than can be achieved through apatite/melt equilibrium partitioning. Such high-S apatite of dacite occur only as inclusions in other phenocrysts (anhydrite, plagioclase, hornblende, and Fe-Ti oxide) and were likely generated during conditions leading to accumulation of the pre-eruptive, separate S gas phase responsible for the "excess sulfur" at Pinatubo. Other explanations, such as inheritance from mafic <span class="hlt">magmas</span> or diffusional exchange with closely associated anhydrite, can be ruled out. Evidence against the former is found in distinct crystal populations based on major (e.g. Mg, Cl) and trace elements (e.g. total REE, Eu/Eu*, Sr), separating "silicic" apatites (i.e. those hosted in dacite or andesite, irrespective of S content) from basalt apatites. S element maps of apatites hosted by anhydrite</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1511520W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1511520W"><span>The role of bubble ascent in <span class="hlt">magma</span> mixing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wiesmaier, Sebastian; Morgavi, Daniele; Perugini, Diego; De Campos, Cristina; Hess, Kai-Uwe; Lavallée, Yan; Dingwell, Donald B.</p> <p>2013-04-01</p> <p>Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic homogenization is divided into a) the mechanical interaction of <span class="hlt">magma</span> batches (mingling) and b) the diffusive equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive mechanical interaction [1]. The mechanical interaction between two distinct batches of <span class="hlt">magma</span> has commonly been attributed to shear and folding movements between two distinct liquids. A mode of mechanical interaction scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments with analogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical component of <span class="hlt">magma</span> mixing [2]. Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) basalt were drilled with a cavity of defined volume and placed underneath cylinders of SRP rhyolite. Upon melting, the gas pocket (=bubble) trapped within the cavity, rose into the rhyolite, and thus entraining a portion of basaltic material in the shape of a plume trail. These plume-like structures that the advected basalt formed within the rhyolite were characterized by microCT and subsequent high-resolution EMP analyses. Single protruding filaments at its bottom end show a composite structure of many smaller plume tails, which may indicate the opening of a preferential pathway for bubbles after a first bubble has passed. The diffusional gradient around the plume tail showed a progressive evolution of equilibration from bottom to top of the plume tail</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/160064','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/160064"><span>Origin of compositional heterogeneities in tuffs of the Timber Mountain Group: The relationship between <span class="hlt">magma</span> batches and <span class="hlt">magma</span> transfer and emplacment in an extenional enviroment</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cambray, F.W.; Vogel, T.A.</p> <p>1995-08-10</p> <p>Compositionally zoned ash flow sheets provide convincing evidence for chemically zoned <span class="hlt">magma</span> bodies. Most workers have assumed that the high-silica portions of these <span class="hlt">magma</span> bodies evolved largely by differentiation processes that occurred within the <span class="hlt">magma</span> chamber. However, chemical heterogeneities within some ash flow sheets are not consistent with these diferentiation processes. The chemical variation of pumice fragments in the large volume (>1200 km{sup 3}), Rainier Mesa ash flow sheet ranges from 55 to 76.3% silica. These pumice fragments occur in three distinct chemical groups. A low- and high-silica group is separated by a compositional gap at about 72% silica, and within the high-silica group there are two distinct populations based on trace element variations. There is little overlap between populations. These three <span class="hlt">magma</span> types have been resident in same <span class="hlt">magma</span> chamber at the same time and cannot be produced by any differentiation process of a single <span class="hlt">magma</span> body. They must reflect discrete <span class="hlt">magma</span> batches generated in the source area. Furthermore, the lower silica portion (<72% SiO{sub 2}) of the Rainer Mesa ash flow sheet is chemically distinct from the lower silica portion of the overlying Ammonia Tanks ash flow sheet, even though they erupted within 200,000 years of each other. These ash flow sheets from the SW Nevada volcanic field are associated in time and place with Basin and Range extension, and all models for extension involve detachment surfaces that extend to great depth. A model for the relationship of these compositional heterogeneities and the regional extension involves (1) the generation of <span class="hlt">magma</span> batches by either continuous melting of the source at different temperatures, or by melting of different sources, (2) the use of faults (shears) as conduits for transport of <span class="hlt">magma</span>, and (3) the use of a dilatant releasing step on a detachment as storage chamber for the <span class="hlt">magma</span>. 80 refs., 12 figs., 1 tab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1210844L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1210844L"><span>Mathematical and numerical modelling of fractional crystallization coupled with chemical exchanges and differential <span class="hlt">magma</span>-solid transport in <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lakhssassi, Morad; Guy, Bernard; Cottin, Jean-Yves; Touboul, Eric</p> <p>2010-05-01</p> <p>The knowledge of the chemical evolution of <span class="hlt">magmas</span> is a major concern in geochemistry and petrology. The jumps (or discontinuities) of chemical composition observed in volcanic series from the same province are also the subject of many studies. In particular the phenomenon of "Daly gap" (Daly 1910, 1925), the name given to the jump in chemical composition between the mafic rocks (basalt) and felsic rocks (trachyte, rhyolite, phonolite), corresponding to the absence or scarcity of rocks of intermediate composition (andesite), in both ocean and continental series. Some authors explain these compositional jumps thanks to the intervention of various geological phenomena which follow in time. For example, when a <span class="hlt">magma</span> chamber turns from a closed to an open system, the lava of a specific composition is ejected to the surface, favoring the rise of the lightest, the most volatile-rich and the less sticky <span class="hlt">magmas</span> to the surface of the earth (Geist et al., 1995, Thompson et al., 2001). The various explanations offered, although they agree satisfactorily with the natural data, most often lead us away from basic phenomena of melting / solidification, relative migration and chemical equilibrium between solid and liquid and involve various additional phenomena. In our study, we propose a numerical modelling of the crystallization of a closed <span class="hlt">magma</span> chamber. The physical and mathematical model distinguishes three main classes of processes occurring simultaneously: - heat transfer and solidification, - relative migration between the solid and the liquid <span class="hlt">magma</span>, - chemical reactions between the two (solid and liquid) phases. Writing the partial differential equations with dimensionless numbers makes two parameters appear, they express the respective ratios of the solidification velocity on the transport velocity, and the kinetics of chemical exchange on the transport velocity. The speed of relative movement between the solid and the liquid, the solidification velocity and the chemical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998Geo....26..523S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998Geo....26..523S"><span>Sulfur evolution of oxidized arc <span class="hlt">magmas</span> as recorded in apatite from a porphyry copper batholith</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Streck, Martin J.; Dilles, John H.</p> <p>1998-06-01</p> <p>Uniformly sulfur-rich cores abruptly zoned to sulfur-poor rims (˜1 to <0.2 wt% SO3) in apatite from the Yerington batholith, Nevada, indicate that early <span class="hlt">magma</span> that is crystal poor, oxidizing, and sulfate rich evolved to sulfate-poor <span class="hlt">magma</span> via crystallization of anhydrite, a mineral observed in <span class="hlt">magmas</span> from Pinatubo and El Chichón. We predict that the characteristic zonation to sulfur-poor rims of apatite in the Yerington batholith is common in other oxidized, hydrous, calc-alkaline <span class="hlt">magmas</span>, and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution. Sulfate-rich arc <span class="hlt">magmas</span> such as Yerington <span class="hlt">magmas</span> may crystallize to produce hydrothermal fluids rich in chlorine, copper, and sulfur and porphyry copper ores.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V12C..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V12C..01M"><span>Lithological controls on shallow-level <span class="hlt">magma</span> emplacement (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Magee, C.; Jackson, C. A.; Schofield, N.; Briggs, F.</p> <p>2013-12-01</p> <p>The emplacement of <span class="hlt">magma</span> within the upper crust requires space to be generated by the deformation or assimilation of the host rock. Intrusion morphologies, <span class="hlt">magma</span> reservoir locations and the architecture of interconnecting <span class="hlt">magma</span> conduits are therefore strongly influenced by the behaviour of the host rock during emplacement. Importantly, monitoring host rock deformation affects (e.g., surface uplift) can provide invaluable insights into the potential timing, location and magnitude of future volcanic eruptions. This has led to significant advances in the inversion of host rock deformation patterns, acquired from geophysical and geodetic data, to elucidate sub-volcanic plumbing systems. However, the link between the shape and size of intrusion and the style and magnitude of the ground deformation is non-unique. While numerical and physical models have been developed to test plausible intrusion-deformation scenarios, they cannot explicitly incorporate complex host rock stratigraphies, temperature-driven intrusion-host rock interactions or brittle faulting. We advocate that three-dimensional seismic reflection data, which provide unparalleled images of entire volcanic plumbing systems, can be used to enhance our understanding of the intrusive networks and to test hypotheses concerning syn-emplacement host rock deformation. We use 3D seismic reflection data from the Exmouth Sub-basin, offshore NW Australia, to examine the link between a saucer-shaped sill and an overlying, dome-shaped fold developed at the contemporaneous palaeosurface. Our results highlight a disparity in size (e.g., areal coverage, thickness/amplitude) between the sill and fold, which we attribute to the initial accommodation of <span class="hlt">magma</span> by fluid expulsion from the poorly consolidated claystone host rock, prior to a period of (forced) folding. This is supported by field observations, which indicate ';triggered' or ';thermal' fluidisation of the host rock may occur during sill emplacement. In such cases</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V24C..05J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V24C..05J"><span><span class="hlt">Magma</span> ascent, degassing, and crystallization in monogenetic volcanoes (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, E. R.; Wallace, P. J.; Cashman, K. V.</p> <p>2009-12-01</p> <p>Monogenetic basaltic volcanoes, although small in volume, exhibit wide ranges of eruptive styles and durations. Factors that affect eruption style include <span class="hlt">magma</span> supply rate, volatile content, degassing conditions, and the presence of external H2O. We investigate the complexities of monogenetic eruptions, with a focus on the volatile contents, ascent, degassing and crystallization of the basaltic melts. We have studied basaltic cinder cones and a tuff ring from Mexico and a maar from the Oregon Cascades. Olivine-hosted melt inclusions (MI) from basaltic cinder cones in Mexico trapped volatile-rich melts (<5.75 wt% H2O, <2000 ppm CO2). Volatiles in MI from individual eruptions are highly variable, suggesting that degassing and olivine crystallization occurred over a wide range of pressures (<400 MPa). Gas-fluxing, or the upward percolation of a CO2-rich vapor (40-75 mol% CO2) from depth, can be recognized by MI that contain higher CO2 for a given H2O content. Conversely, MI trapped during a maar-forming eruption in Oregon show a very restricted range in volatiles (3-4 wt% H2O, 800-900ppm CO2), suggesting that these melts underwent very little degassing and crystallized over a narrow range of pressures (200-300 MPa). Magmatic crystallization also occurs at variable depths beneath monogenetic volcanoes. <span class="hlt">Magma</span> erupted during the long-lived (15 year) eruption of Volcán Jorullo underwent a multi-stage crystallization process. <span class="hlt">Magma</span> initially ponded in the lower crust and fractionated amphibole + olivine +/- clinopyroxene. The fractionated melts then ascended and crystallized olivine over a wide range of pressures (400-50 MPa), probably as a consequence of both fluxing and dehydration of the melt by CO2-rich gas and by H2O exsolution during decompression. As the eruption progressed, crystallization shifted to a shallow sill-like region beneath the volcano. Additionally, low pressure (< 50 MPa) degassing drove extensive crystallization of the melts, visible in the high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V24C..01F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V24C..01F"><span>Volcanic gas emissions: constraining <span class="hlt">magma</span> degassing and volatile sources (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, T. P.; de Moor, M. J.</p> <p>2013-12-01</p> <p>Approximately 70 volcanoes erupt per year and about 500 emit gases through vents or hydrothermal systems. The global volcanic sulfur flux is dominated by passively degassing volcanoes and only 1-10% of the total SO2 flux is emitted during eruptions [1, 2] - likely also the case for other volatiles. <span class="hlt">Magmas</span> lose their volatiles during ascent from the mantle and <span class="hlt">magma</span> with 7 wt% water will become saturated at 15-17 km depth [3]. Volcanic eruptions commonly release more gas into the atmosphere than could have been dissolved in the erupted <span class="hlt">magma</span>, first recognized by Rose [4]. Volcanic gases provide information on magmatic volatiles. Sampling of high temperature (> 400°C) volcanic gases emitted from crater fumaroles provide complete information on gas chemistry and isotopic ratios that are generally unaffected by low-temperature processes [5]. Complete gas compositions can be evaluated for equilibrium and corrected for modifications due to atmospheric contamination to obtain near-pristine magmatic gas compositions. In cases where gas and <span class="hlt">magma</span> have been evaluated for fO2 both generally agree. Oxygen fugacities calculated using gas equilibria (H2/H2O; CO2/CO) show that the highest temperature (>800C) gases from rifts (Erta Ale) are close to QFM, arc volcanoes record oxygen fugacities above QFM (ΔQFM +6 to +8 based on H2O/H2; +0.2 to +3.7 based on CO2/CO) consistent with a more oxidized nature of the subarc-mantle. H-based gas equilibria show significantly higher oxygen fugacities than C-based values. This may be related to surfical water in the system or oxidation of H, which can be tracked by stable isotopes. H2O/CO2 values vary between arcs where Kuriles, Japan and Kamchatka show higher ratios (40 to 800) than Cascades, Central America, S. America, Java, and Aeolian (1 to 70). Erta Ale gases have H2O/CO2 of 3. Order of magnitude changes in H2O/CO2 ratios (2 to 20) due to <span class="hlt">magma</span> degassing have been unequivocally documented by Gerlach [6] at Kilauea. H2O/CO2 ratios in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..321..158P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..321..158P"><span>Rheological flow laws for multiphase <span class="hlt">magmas</span>: An empirical approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pistone, Mattia; Cordonnier, Benoît; Ulmer, Peter; Caricchi, Luca</p> <p>2016-07-01</p> <p>The physical properties of <span class="hlt">magmas</span> play a fundamental role in controlling the eruptive dynamics of volcanoes. <span class="hlt">Magmas</span> are multiphase mixtures of crystals and gas bubbles suspended in a silicate melt and, to date, no flow laws describe their rheological behaviour. In this study we present a set of equations quantifying the flow of high-viscosity (> 105 Pa·s) silica-rich multiphase <span class="hlt">magmas</span>, containing both crystals (24-65 vol.%) and gas bubbles (9-12 vol.%). Flow laws were obtained using deformation experiments performed at high temperature (673-1023 K) and pressure (200-250 MPa) over a range of strain-rates (5 · 10- 6 s- 1 to 4 · 10- 3 s- 1), conditions that are relevant for volcanic conduit processes of silica-rich systems ranging from crystal-rich lava domes to crystal-poor obsidian flows. We propose flow laws in which stress exponent, activation energy, and pre-exponential factor depend on a parameter that includes the volume fraction of weak phases (i.e. melt and gas bubbles) present in the <span class="hlt">magma</span>. The bubble volume fraction has opposing effects depending on the relative crystal volume fraction: at low crystallinity bubble deformation generates gas connectivity and permeability pathways, whereas at high crystallinity bubbles do not connect and act as ;lubricant; objects during strain localisation within shear bands. We show that such difference in the evolution of texture is mainly controlled by the strain-rate (i.e. the local stress within shear bands) at which the experiments are performed, and affect the empirical parameters used for the flow laws. At low crystallinity (< 44 vol.%) we observe an increase of viscosity with increasing strain-rate, while at high crystallinity (> 44 vol.%) the viscosity decreases with increasing strain-rate. Because these behaviours are also associated with modifications of sample textures during the experiment and, thus, are not purely the result of different deformation rates, we refer to ;apparent shear-thickening; and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1612687D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1612687D"><span>Snapshots from deep <span class="hlt">magma</span> chambers: decoding field observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>De Campos, Cristina P.</p> <p>2014-05-01</p> <p>During the post-orogenic stage of a Neoproterozoic orogen (Araçuaí-West Congo), inversely zoned calc-alkaline to alkaline plutonic structures intruded previous geologic units. Structural measurements, mapping of flow patterns and additional geochemical and isotopic data point towards different compositional domains which have been generated during a time span between 20 to 30 Ma. The result from decades of mapping revealed the architecture of ca. 10 large plutons in more détail. This work will focus on the dynamics of magmatic interaction for six different plutons ranging from c.20 to 200 km2 in outcropping area. Conclusions are based on already published and new unpublished data aiming the state of the art. In the silica-richer structures concentric fragmented and folded layers of granite in a K-basaltic matrix contrast with predominant more homogeneous K-basaltic to gabbroic regions. These may be separated by stretched filament regions (magmatic shear zones) where mixing has been enhanced resulting in hybrid compositions. Locally sharp and pillow-like contacts between granitic and K-basaltic rocks depict a frozen-in situation of different intrusive episodes. In the silica-poorer plutonic bodies gradational contacts are more frequent and may be the result of convection enhanced diffusion. For all plutons, however, mostly sub-vertical internal contacts between most- and least-differentiated rocks suggest generation from predominat large <span class="hlt">magma</span> bodies of variable composition which crystallized while crossing the middle to lower crust (< 25 km depth). They have been catch in the act on their way up. Accordingly mushroom- to funnel-like <span class="hlt">magma</span>-chambers and/or conduits could register snapshots of the interaction dynamics between granitic and noritic/dioritic or syeno-monzonitic and gabbroic <span class="hlt">magmas</span>. Different compositional domains within different plutons suggest distinct kinematics. Nevertheless all studied plutons provide outstanding evidence for mixing, not only</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984RSPTA.310..535K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984RSPTA.310..535K"><span>Elemental Abundances Relevant to Identification of <span class="hlt">Magma</span> Sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kay, R. W.</p> <p>1984-04-01</p> <p>The search for chemical characteristics of <span class="hlt">magma</span> sources is usually done by analysing the <span class="hlt">magmas</span> themselves. This indirect approach has limitations: clearly the <span class="hlt">magma</span> has only some of the source's characteristics. What we require are process-independent chemical characteristics, analogous to the isotopic abundance of radiogenic daughter isotopes that have been used so successfully in defining <span class="hlt">magma</span> sources. Process-independent chemical characteristics in mid-oceanic ridge, oceanic island and island-arc basalts (m.o.r.b., o.i.b., i.a.b.) have been used to identify contrasting chemical characteristics of mantle peridotite from these three tectonically distinct regions. As an example, the abundance ratios of one group of elements (e.g. Cs, K, Rb, Ba, U, and perhaps Th) relative to another group (e.g. light r.e.e., Zr, Hf) are found to be fractionation-independent during most shallow-level basalt fractionation. These ratios are presumed to reflect the chemical characteristics of the mantle source of basalt from the three tectonic environments. In particular the ratios indicate the large cation-depleted nature of all m.o.r.b. and most o.i.b. peridotite sources. In common with many other island arcs, the abundance ratios are consistently higher in mantle under the Aleutian arc than in adjacent non-arc mantle represented by oceanic ridge, oceanic island, and back-arc basalts. The contention that subduction of sediment could result in arc mantle sources with these high ratios is substantiated by trace element analyses of Ba and Cs-rich deep sea sediments of the type that are being subducted at present at the Aleutian trench. The importance of recycling of sediment into the mantle at island arcs as an important control on the trace element (and isotopic) evolution of the mantle is indicated. Trace element heterogeneity in the source regions of <span class="hlt">magmas</span> as diverse as basalts and leucogranites can be established using analyses of fractionation-independent elements of the <span class="hlt">magmas</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016BVol...78...47G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016BVol...78...47G"><span>Abrupt transition from fractional crystallization to <span class="hlt">magma</span> mixing at Gorely volcano (Kamchatka) after caldera collapse</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gavrilenko, Maxim; Ozerov, Alexey; Kyle, Philip R.; Carr, Michael J.; Nikulin, Alex; Vidito, Christopher; Danyushevsky, Leonid</p> <p>2016-07-01</p> <p>A series of large caldera-forming eruptions (361-38 ka) transformed Gorely volcano, southern Kamchatka Peninsula, from a shield-type system dominated by fractional crystallization processes to a composite volcanic center, exhibiting geochemical evidence of <span class="hlt">magma</span> mixing. Old Gorely, an early shield volcano (700-361 ka), was followed by Young Gorely eruptions. Calc-alkaline high magnesium basalt to rhyolite lavas have been erupted from Gorely volcano since the Pleistocene. Fractional crystallization dominated evolution of the Old Gorely <span class="hlt">magmas</span>, whereas <span class="hlt">magma</span> mixing is more prominent in the Young Gorely eruptive products. The role of recharge-evacuation processes in Gorely <span class="hlt">magma</span> evolution is negligible (a closed magmatic system); however, crustal rock assimilation plays a significant role for the evolved <span class="hlt">magmas</span>. Most Gorely <span class="hlt">magmas</span> differentiate in a shallow magmatic system at pressures up to 300 MPa, ˜3 wt% H2O, and oxygen fugacity of ˜QFM + 1.5 log units. <span class="hlt">Magma</span> temperatures of 1123-1218 °C were measured using aluminum distribution between olivine and spinel in Old and Young Gorely basalts. The crystallization sequence of major minerals for Old Gorely was as follows: olivine and spinel (Ol + Sp) for mafic compositions (more than 5 wt% of MgO); clinopyroxene and plagioclase crystallized at ˜5 wt% of MgO (Ol + Cpx + Plag) and magnetite at ˜3.5 wt% of MgO (Ol + Cpx + Plag + Mt). We show that the shallow <span class="hlt">magma</span> chamber evolution of Old Gorely occurs under conditions of decompression and degassing. We find that the caldera-forming eruption(s) modified the <span class="hlt">magma</span> plumbing geometry. This led to a change in the dominant <span class="hlt">magma</span> evolution process from fractional crystallization to <span class="hlt">magma</span> mixing. We further suggest that disruption of the <span class="hlt">magma</span> chamber and accompanying change in differentiation process have the potential to transform a shield volcanic system to that of composite cone on a global scale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V44C..02G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V44C..02G"><span>Reconstructing <span class="hlt">Magma</span> Degassing and Fragmentation: The 1060 CE Plinian Eruption of Medicine Lake Volcano, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giachetti, T.; Gonnermann, H. M.; Crozier, J.</p> <p>2015-12-01</p> <p><span class="hlt">Magma</span> fragmentation during explosive volcanic eruptions occurs when the bubble overpressure exceeds some threshold. Because bubble coalescence and ensuing permeable outgassing allow partial release of bubble overpressure, high <span class="hlt">magma</span> permeabil
ity is thought to adversely affect <span class="hlt">magma</span> fragmentation and the ability of <span class="hlt">magma</span> to erupt explosively. We used the Plinian phase of the 1060 CE Glass Mountain eruption of Medicine Lake Volcano, California, to show that this is not necessarily the case. We performed numerical modeling of eruptive <span class="hlt">magma</span> ascent and bubble growth to predict the development of <span class="hlt">magma</span> porosity, permeability, and the built-up of gas pressure inside bubbles. We explicitly took into account permeable outgassing in the model. We used the measured porosity and permeability of the Plinian pyroclasts, together with percolation modeling, to reconstruct the conditions for <span class="hlt">magma</span> degassing and fragmentation. Our results show that the porosity and permeability of pyroclasts coincide with the conditions required for fragmentation of the erupting <span class="hlt">magma</span>. The onset of fragmentation occurs when the decompression rate reaches about 2 MPa.s-1, corresponding to a constant melt viscosity of ˜107 Pa.s and a <span class="hlt">magma</span> porosity of approximately 0.75, conditions met for a mass discharge rate of about 107 kg.s-1, a cross sectional area of about 2,000 m2, and at a depth of approximately 1 km. Pyroclasts formed from <span class="hlt">magma</span> that fragmented over a depth range of several tens of meters, probably reflecting some degree of lateral variability in <span class="hlt">magma</span> porosity in the conduit. The model also indicates that, even if the <span class="hlt">magma</span> was highly permeable at the onset of fragmentation, permeable outgassing did not affect fragmentation. The transition to an effusive activity and the emission of obsidian after the Plinian phase of the Glass Mountain eruption is most probably due to a decrease in decompression rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..44.6589P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.6589P"><span>The shallow <span class="hlt">magma</span> chamber of Stromboli Volcano (Italy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Patanè, D.; Barberi, G.; De Gori, P.; Cocina, O.; Zuccarello, L.; Garcia-Yeguas, A.; Castellano, M.; D'Alessandro, A.; Sgroi, T.</p> <p>2017-07-01</p> <p>In this work, we integrate artificial and natural seismic sources data to obtain high-resolution images of the shallow inner structure of Stromboli Volcano. Overall, we used a total of 21,953 P readings from an active seismic experiment and an additional 2731 P and 992 S readings deriving from 269 local events. The well-defined Vp, Vs, and Vp/Vs tomograms have highlighted the following: (i) the region where <span class="hlt">magma</span> cumulates at shallow depths (2-4 km below sea level (bsl)), forming an elongated NE-SW high-velocity body (Vp ≥ 6.0 km/s and Vs ≥ 3.5 km/s), with a very fast velocity core (6.5 ≤ Vp < 7.0 km/s) of 2 km3; (ii) the presence of some near-vertical pipe-like structures, characterized by relatively high P velocities values, mainly linked to past activity (e.g., Strombolicchio); and (iii) a near-vertical pipe-like volume with high Vp/Vs (1.78 ÷ 1.85), located beneath to the craters (down to 1.0 km bsl), overlying a deeper region (1.0 to 3.0 km bsl) with low Vp/Vs (1.64 ÷ 1.69), interpreted as the actual and preferential pathway of <span class="hlt">magma</span> toward the surface. Our results demonstrate the importance of combining passive and active seismic data to improve, in a tomographic inversion, the resolution of the volcanic structures and to discover where <span class="hlt">magma</span> may be stored.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53C3121K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53C3121K"><span><span class="hlt">Magma</span>-tectonic Interaction at Laguna del Maule, Chile</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keranen, K. M.; Peterson, D. E.; Miller, C. A.; Garibaldi, N.; Tikoff, B.; Williams-Jones, G.</p> <p>2016-12-01</p> <p>The Laguna del Maule Volcanic Field (LdM), Chile, the largest concentration of rhyolite <20 kyr globally, exhibits crustal deformation at rates higher than any non-erupting volcano. The interaction of large magmatic systems with faulting is poorly understood, however, the Chaitén rhyolitic system demonstrated that faults can serve as <span class="hlt">magma</span> pathways during an eruption. We present a complex fault system at LdM in close proximity to the <span class="hlt">magma</span> reservoir. In March 2016, 18 CHIRP seismic reflection lines were acquired at LdM to identify faults and analyze potential spatial and temporal impacts of the fault system on volcanic activity. We mapped three key horizons on each line, bounding sediment packages between Holocene onset, 870 ybp, and the present date. Faults were mapped on each line and offset was calculated across key horizons. Our results indicate a system of normal-component faults in the northern lake sector, striking subparallel to the mapped Troncoso Fault SW of the lake. These faults correlate to prominent magnetic lineations mapped by boat magnetic data acquired February 2016 which are interpreted as dykes intruding along faults. We also imaged a vertical fault, interpreted as a strike-slip fault, and a series of normal faults in the SW lake sector near the center of magmatic inflation. Isochron and fault offset maps illuminate areas of growth strata and indicate migration and increase of fault activity from south to north through time. We identify a domal structure in the SW lake sector, coincident with an area of low magnetization, in the region of maximum deformation from InSAR results. The dome experienced 10 ms TWT ( 10 meters) of uplift throughout the past 16 kybp, which we interpret as magmatic inflation in a shallow <span class="hlt">magma</span> reservoir. This inflation is isolated to a 1.5 km diameter region in the hanging wall of the primary normal fault system, indicating possible fault-facilitated inflation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70186536','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70186536"><span>Deep volcanic tremor and <span class="hlt">magma</span> ascent mechanism under Kilauea, Hawaii</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Aki, Keiiti; Koyanagi, Robert Y</p> <p>1981-01-01</p> <p>Deep harmonic tremor originating at depths around 40 km under Kilauea was studied using records accumulated since 1962 at the Hawaii Volcano Observatory of the U.S. Geological Survey. The deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island-wide network of seismometers. The period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode. The tremor appeared to be primarily composed of P waves. We interpret the observed period and amplitude in terms of the stationary crack model of Aki et al. (1977) and find that the seismic moment rates for deep tremors are considerably larger than those for shallow-tremors suggesting more vigorous transport for the former. We propose a kinematic source model which may be more appropriate for deep tremor. According to this model, a measurable quantity called ‘reduced displacement’ is directly proportional to the rate of <span class="hlt">magma</span> flow. A systematic search for deep tremor episodes was made for the period from 1962 through 1979, and the amplitude, period, and duration of the tremor were tabulated. We then constructed a cumulative reduced-displacement plot over the 18-year period. The result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface. The total <span class="hlt">magma</span> flow estimated from the reduced displacement is however, one order of magnitude smaller than that estimated by Swanson (1972). It may be that most channels transport <span class="hlt">magma</span> aseismically, and only those with strong barriers generate tremor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006psrd.reptE.103T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006psrd.reptE.103T"><span>A Primordial and Complicated Ocean of <span class="hlt">Magma</span> on Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taylor, G. J.</p> <p>2006-03-01</p> <p>It seems almost certain that the Moon was surrounded by an ocean of <span class="hlt">magma</span> when it formed. This important idea has been applied to the other terrestrial planets and even to asteroids. Linda (Lindy) Elkins-Tanton and colleagues Mark Parmentier, Paul Hess, and Sarah Zaranek at Brown University, and Lars Borg and David Draper (University of New Mexico) have examined the chemical and physical consequences of <span class="hlt">magma</span> ocean crystallization on Mars. Elkins-Tanton has focused on the fate of the pile of crystals created during solidification of a <span class="hlt">magma</span> ocean over a thousand kilometers thick. Crystallization causes the minerals that form first to lie beneath those formed later. The deepest minerals are also less dense than the overlying minerals. This is an unstable situation: the low-density rocks would have a tendency to rise while the high-density rocks would have a tendency to sink. Although we think of rocks as solid and hard, when hot and under pressure, they flow like liquids. They do not flow fast, but they do flow like ultra-gooey liquids (about a factor of 100 million billion times gooier than ketchup at room temperature). Thus, the heavy layers sink and the light layers rise, producing a complicated Martian mantle with chemical characteristics like those cosmochemists infer from studies of Martian meteorites. The sinking of relatively cool rocks from the top of the crystallized pile cools the boundary between the metallic core and the mantle, causing motions inside the core to produce the early, strong magnetic field of Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1510680T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1510680T"><span>Predicting changes in volcanic activity through modelling <span class="hlt">magma</span> ascent rate.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thomas, Mark; Neuberg, Jurgen</p> <p>2013-04-01</p> <p>It is a simple fact that changes in volcanic activity happen and in retrospect they are easy to spot, the dissimilar eruption dynamics between an effusive and explosive event are not hard to miss. However to be able to predict such changes is a much more complicated process. To cause altering styles of activity we know that some part or combination of parts within the system must vary with time, as if there is no physical change within the system, why would the change in eruptive activity occur? What is unknown is which parts or how big a change is needed. We present the results of a suite of conduit flow models that aim to answer these questions by assessing the influence of individual model parameters such as the dissolved water content or <span class="hlt">magma</span> temperature. By altering these variables in a systematic manner we measure the effect of the changes by observing the modelled ascent rate. We use the ascent rate as we believe it is a very important indicator that can control the style of eruptive activity. In particular, we found that the sensitivity of the ascent rate to small changes in model parameters surprising. Linking these changes to observable monitoring data in a way that these data could be used as a predictive tool is the ultimate goal of this work. We will show that changes in ascent rate can be estimated by a particular type of seismicity. Low frequency seismicity, thought to be caused by the brittle failure of melt is often linked with the movement of <span class="hlt">magma</span> within a conduit. We show that acceleration in the rate of low frequency seismicity can correspond to an increase in the rate of <span class="hlt">magma</span> movement and be used as an indicator for potential changes in eruptive activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5939866','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5939866"><span>Deep volcanic tremor and <span class="hlt">magma</span> ascent mechanism under Kilauea, Hawaii</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Aki, K.; Koyanagi, R.</p> <p>1981-08-10</p> <p>Deep harmonic tremor originating at depths around 40 km under Kilauea was studied using records accumulated since 1962 at the Hawaii Volcano Observatory of the U. S. Geological Survey. The deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island-wide network of seismometers. The period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode. The tremor appeared to be primarily composed of P waves. We interpret the observation period and amplitude in terms of the stationary crack model of Aki et al. (1977) and find that the seismic moment rates for deep tremors are considerably larger than those for shallow-tremors suggesting mor vigorous transport for the former. We propose a kinematic source model which may be more appropriate for deep tremor. According to this model, a measurable quantity called 'reduced displacement' is directly proportional to the rate of <span class="hlt">magma</span> flow. A systematic search for deep tremor episodes was made for the period from 1962 through 1979, and the amplitude, period, and duration of the tremor were tabulated. We then constructed a cumulative reduced-displacement plot over the 18-year period. The result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface. The total <span class="hlt">magma</span> flow estimated from the reduced displacement is however, one order of magnitude smaller than that estimated by Swanson (1972). It may be that most channels transport <span class="hlt">magma</span> aseismically, and only those with strong barriers generate tremor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.470...37B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.470...37B"><span>The percolation threshold and permeability evolution of ascending <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burgisser, Alain; Chevalier, Laure; Gardner, James E.; Castro, Jonathan M.</p> <p>2017-07-01</p> <p>The development of gas permeability in <span class="hlt">magmas</span> is a complex phenomenon that directly influences the style of a volcanic eruption. The emergence of permeability is linked to the concept of percolation threshold, which is the point beyond which gas bubbles are connected in a continuous network that allows gas escape. Measurements of the percolation threshold, however, range from ∼30 to 78 vol%. No known combination of parameters can explain such a wide range of threshold values, which affects our understanding of the relationship between percolation and permeability. We present permeability calculations on bubble-bearing rhyolitic melts that underwent experimental decompression. Samples were analyzed by X-ray microtomography to image the bubble networks in 3D. We develop a percolation threshold for <span class="hlt">magmas</span> that depends on the bubble network characteristics of this sample set. This relationship recovers the behavior of a wide range of volcanic samples by separating permeable samples from impermeable ones with a success rate of 88%. We use this percolation threshold to propose simplified permeability relationships that rely on parameters widely used in numerical modeling of <span class="hlt">magma</span> flow. These relationships are valid within one order of magnitude for the viscous permeability coefficient and within two orders of magnitude for the inertial coefficient. They recover the ranges of values previously covered by isolated relationships, reassembling them within a single framework. We test the implications of such unification on eruptive dynamics with a 1D, two-phase conduit flow model. This test shows that varying the percolation threshold has little influence on vertical gas loss and ascent dynamics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DPS....4810903D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DPS....4810903D"><span>Zinc and volatile element loss during planetary <span class="hlt">magma</span> ocean phases</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dhaliwal, Jasmeet K.; Day, James M. D.; Moynier, Frédéric</p> <p>2016-10-01</p> <p>Zinc is a moderately volatile element and a key tracer of volatile depletion on planetary bodies due to lack of significant isotopic fractionation under high-temperature processes. Terrestrial basalts have δ66Zn values similar to some chondrites (+ 0.15 to 0.3‰ where [{66Zn/64Znsample/66Zn/64ZnJMC-Lyon-1} × 1000]) and elevated Zn concentrations (100 ppm). Lunar mare basalts yield a mean δ66Zn value of +1.4 ± 0.5‰ and have low Zn concentrations (~2 ppm). Late-stage lunar magmatic products, such as ferroan anorthosite, Mg-suite and Alkali suite rocks exhibit heavier δ66Zn values (+3 to +6‰). The heavy δ66Zn lunar signature is thought to reflect evaporative loss and fractionation of zinc, either during a giant impact or in a <span class="hlt">magma</span> ocean phase.We explore conditions of volatile element loss within a lunar <span class="hlt">magma</span> ocean (LMO) using models of Zn isotopic fractionation that are widely applicable to planetary <span class="hlt">magma</span> oceans. For the Moon, our objective was to identify conditions that would yield a δ66Zn signature of ~ +1.4‰ within the mantle, assuming a terrestrial mantle zinc starting composition.We examine two cases of zinc evaporative fractionation: (1) lunar surface zinc fractionation that was completed prior to LMO crystallization and (2) lunar surface zinc fractionation that was concurrent with LMO crystallization. The first case resulted in a homogeneous lunar mantle and the second case yielded a stratified lunar mantle, with the greatest zinc isotopic enrichment in late-stage crystallization products. This latter case reproduces the distribution of zinc isotope compositions in lunar materials quite well.We find that hydrodynamic escape was not a dominant process in losing Zn, but that erosion of a nascent lunar atmosphere, or separation of condensates into a proto-lunar crust are possible. While lunar volatile depletion is still possible as a consequence of the giant impact, this process cannot reproduce the variable δ66Zn found in the Moon. Outgassing</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EOSTr..95R.100S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EOSTr..95R.100S"><span>Migrating quake swarm may indicate <span class="hlt">magma</span> conduit clog</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schultz, Colin</p> <p>2014-03-01</p> <p>On 13 January 2006, Augustine Volcano, a towering volcano offshore from the Alaska Peninsula, erupted explosively. In the days leading up to the eruption, a series of explosions and earthquake swarms had warned of the impending activity. On 12 January, 36 hours before the first magmatic explosions, a swarm of 54 earthquakes was detected across the 13-station seismic network on Augustine Island. Analyzing the seismic waves produced by the earthquakes, Buurman and West found that the earthquakes were being triggered from point sources within the <span class="hlt">magma</span> conduit itself.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..322...30B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..322...30B"><span>Temporal <span class="hlt">magma</span> source changes at Gaua volcano, Vanuatu island arc</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Beaumais, Aurélien; Bertrand, Hervé; Chazot, Gilles; Dosso, Laure; Robin, Claude</p> <p>2016-08-01</p> <p>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 <span class="hlt">magmas</span>. 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 <span class="hlt">magma</span> issued from a separate <span class="hlt">magma</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.P51C1752M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.P51C1752M"><span><span class="hlt">Magma</span> ascent pathways associated with large mountains on Io</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McGovern, P. J.; Kirchoff, M. R.; White, O. L.; Schenk, P.</p> <p>2013-12-01</p> <p>While Jupiter's moon Io is the most volcanically active body in the solar system, the largest mountains seen on Io are created by tectonic forces rather than volcanic construction. Pervasive compression, brought about by subsidence induced by sustained volcanic resurfacing and aided by thermal stress, creates the mountains, but at the same time inhibits <span class="hlt">magma</span> ascent in vertical conduits (dikes). We superpose stress solutions for subsidence and thermal stress (from the 'crustal conveyor belt' resurfacing) in Io's lithosphere with stresses from Io mountain-sized loads (in a shallow spherical shell solution) in order to evaluate <span class="hlt">magma</span> ascent pathways. We use stress orientation (least compressive stress horizontal) and stress gradient (compression decreasing upwards) criteria to identify ascent pathways through the lithosphere. For nominal 'conveyor belt' stress states, the ascent criteria are satisfied only in a narrow (5 km or so), roughly mid-lithosphere band. Superposed stresses from loading of a 150-km wide mountain (comparable to Boösaule Mons) on a lithosphere with thickness Te = 50 km results in a thickening of the ascent-favorable (AF) zone beneath the center of the edifice, with a total thickness of 38 km for an 18 km tall (post-flexure) edifice. Most of the thickening is upward, although some is downward. Widening the edifice to 200 km produces a 'U-shaped' AF zone, thin and depressed at r = 0 but intersecting the surface at distances of about 20 to 40 km from the center. Increasing edifice width increases the radial distance at which the AF zone intersects the surface. Thinner lithospheres create generally thinner AF zones, and U-shaped AF zones for narrower edifices. There are several configurations for which viable ascent paths transit nearly the entire lithosphere, arriving at the base of the mountain, where <span class="hlt">magma</span> can be transported through thrust faults or perhaps thermally erode flank sections, the latter consistent with observations of paterae in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V33F..03I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V33F..03I"><span>Self-Potential Changes Caused by <span class="hlt">Magma</span> Ascent and Degassing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ishido, T.</p> <p>2009-12-01</p> <p>The self-potential (SP) distributions have similar features on a number of volcanoes: SP first decreases several hundred millivolts to more than one volts as one climbs the slopes of the volcano, then rapidly recovers to the level measured on the flank of volcano as the summit crater is approached. Consequently, the entire SP profile along a survey line starting from the foot, passing near the summit and reaching the foot on the opposite side often has the shape of the letter "W". Numerical simulations by Ishido (2004; see, Geophys. Res. Lett., doi:10.1029/2004GL020409) showed that the primary cause of the "W"-shaped SP distribution is a combination of the electrokinetic drag current associated with the downward liquid flow in the unsaturated and underlying saturated layers and the presence of a shallow conductor near the volcano summit. If the shallow conductor contacts a deep conductive layer, this conductive structure provides a current path between the low-potential shallow and high-potential deep regions, resulting in substantial increase in SP around the summit. The calculated amplitude of high SP around the summit is sensitive to the conductivity structure, which is thought to change over time due to volcanic activities such as <span class="hlt">magma</span> ascent, degassing, development of hydrothermal convection, etc. Evolution of high SP near the summit crater due to ascent of <span class="hlt">magma</span> and associated degassing is expected to be largely affected by the continuity of the pre-existing conductive structure between the near surface and deep regions. In the present study, the effects of high temperature acidic gas emanated from <span class="hlt">magma</span> into surrounding country rocks are discussed based upon the results of numerical simulation. In case that the permeability of the country rock is relatively high, the volcanic gas diffuses into the country rock over a substantial distance, creates a dry-out region adjacent to the volcanic conduit where <span class="hlt">magma</span> is ascending and condenses into acidic water in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....2458S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....2458S"><span>Melt segregation and <span class="hlt">magma</span> movement in the crust.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sawyer, E. W.; Bonnay, M.</p> <p>2003-04-01</p> <p>Melt flow out of rocks undergoing partial melting occurs in three stages. 1) A short distance of porous flow along grain boundaries and grain edges from the site of melt generation, followed by, 2) channel flow through an interconnected network of short linked segments of shear bands, boudin necks, dilatant foliation or bedding planes. Melt accumulates in this network, dilating foliation and bedding planes and forming stromatic leucosomes until, 3) melt escapes out of the source layers by a more focussed channel flow along fewer, but larger, oblique dilatant fractures. Steps 1 and 2 constitute the draining network and 3 the melt-transfer network. When the transfer network forms, the drainage network collapses and channels may disappear; the observed leucosome network no longer represents that of peak melt extraction. The result is a melt-depleted rock with few leucosomes. The geometry of the channel network by which melt passes through the middle crust above melt source is less well known, consequently we have studied several intermediate level transfer networks from localities in central Australia. Our analysis reveals that two, or in some cases three, <span class="hlt">magmas</span> from different sources passed through these fracture arrays and that locally they mixed forming hybrids. These particular vein networks may have been fed from a small volume source and represent the level at which fracture propagation stopped, rather than a slice through the feeder network to plutons higher in the crust. The rate of <span class="hlt">magma</span> influx at plutons has been considered rapid. However, plots of melt fraction vs temperature for biotite dehydration melting show a uniform rate of melt generation over 100 to150 degrees. If this temperature interval corresponds to millions or 10's of millions of years, then the melt flux out of the source is a continuous dribble, or as many small batches, over that period. Rapid pluton formation then requires pooling of melt somewhere in the crust. Furthermore, many granites</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.121..436B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.121..436B"><span>Element variations in rhyolitic <span class="hlt">magma</span> resulting from gas transport</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Berlo, K.; Tuffen, H.; Smith, V. C.; Castro, J. M.; Pyle, D. M.; Mather, T. A.; Geraki, K.</p> <p>2013-11-01</p> <p>Tuffisite veins are glass-filled fractures formed when <span class="hlt">magma</span> fragments during degassing within the conduit. These veins form transient channels through which exsolved gases can escape from <span class="hlt">magma</span>. The purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport, and assess how this can be used to study <span class="hlt">magma</span> degassing. Two tuffisite veins from contrasting rhyolitic eruptions at Torfajökull (Iceland) and Chaitén (Chile) were studied in detail. The tuffisite vein from Torfajökull is from a shallow dissected conduit (∼70 ka) that fed a degassed lava flow, while the sample from Chaitén was a bomb ejected during the waning phases of Plinian activity in May 2008. The results of detailed in situ chemical analyses (synchrotron XRF, FTIR, LA-ICP-MS) show that in both veins larger vesiculated fragments are enriched in volatile elements (Torfajökull: H, Li, Cl; Chaitén: Li, Cl, Cu, Zn, As, Sn, Sb) compared to the host, while the surrounding smaller particles are depleted in the Torfajökull vein (Li, Cl, Zn, Br, Rb, Pb), but enriched in the Chaitén vein (K, Cu, Zn, As, Mo, Sb, Pb). The lifespans of both veins and the fluxes of gas and particles through them can be estimated using diffusion profiles and enrichment factors. The Torfajökull vein had a longer lifespan (∼a day) and low particle velocities (∼cm/s), while the Chaitén vein was shorter lived (<1 h) with a high gas velocity (∼m/s). These differences are consistent with the contrasting eruption mechanisms (effusive vs. explosive). The amount of <span class="hlt">magma</span> that degassed through the Chaitén vein is more than ten times the volume of the vein itself, requiring the vein to tap into pre-exsolved gas pockets. This study highlights that tuffisite veins are highly efficient gas pathways and thereby impart chemical diversity in volatile elements on the melt.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53D3144A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53D3144A"><span>Timescales of Processes Related to the Socorro <span class="hlt">Magma</span> Body (SMB)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Axen, G. J.; Yao, S.; Sion, B.; van Wijk, J.</p> <p>2016-12-01</p> <p>The seismically imaged SMB (central Rio Grande rift) is a N-S elongate elliptical sill 130 m thick at 19 km depth with area of 3500 km2. Surface uplift over the north 2/3 of the SMB is circular with time-average maximum of 2.5 mm/yr ( 1911 to now). Episodic earthquake swarms in the shallower, wider co-located Socorro seismic anomaly may reflect episodic inflation or episodic release of related stress on a decadal scale, possibly modulated by migration of volatiles and/or groundwater flow. 2D numerical models (elastic host rocks, heat conduction, inflation and thermal expansion treated separately) yield uplift patterns and evolution. Preliminary results are: 1. Without <span class="hlt">magma</span> injection the SMB should solidify in ≤500 yrs. 2. SMB inflation drives uplift rates proportional to <span class="hlt">magma</span> pressure increase rate. 3. The inflation-driven uplift profile is pseudo-conical in cross section with a narrow flat top, similar to the observed profile. Width of uplift that is measurable geodetically (> 0.5-1 mm/yr) is similar to the SMB width. 4. Thermal expansion causes uplift soon after heating begins, driven initially by expansion of rocks close enough to the SMB that T increase is fast and large. Uplift rate stays nearly constant while heating continues, is similar to the measured average rate and drops to near zero soon after heating ends. Thermal expansion due to episodic inflation events would drive less strongly punctuated uplift events: previously fully expanded rocks near the SMB and slow heat conduction smooth the surface response. Advective heat loss (e.g., groundwater flow) would lower expansion-driven uplift rates. 5. Expansion-driven uplift is plateau-shaped, wider than the SMB, wider than that due to inflation, and unlike the observed profile. We infer that the northern SMB is actively inflating and the whole SMB is old enough that the expansion-driven uplift profile is subdued. River terrace studies suggest an earlier surface doming event between 10 and 50 ka</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/887061','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/887061"><span>Long-Term Volumetric Eruption Rates and <span class="hlt">Magma</span> Budgets</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Scott M. White Dept. Geological Sciences University of South Carolina Columbia, SC 29208; Joy A. Crisp Jet Propulsion Laboratory, California Institute of Technology Pasadena, CA 91109; Frank J. Spera Dept. Earth Science University of California, Santa Barbara Santa Barbara, CA 93106</p> <p>2005-01-01</p> <p>A global compilation of 170 time-averaged volumetric volcanic output rates (Qe) is evaluated in terms of composition and petrotectonic setting to advance the understanding of long-term rates of <span class="hlt">magma</span> generation and eruption on Earth. Repose periods between successive eruptions at a given site and intrusive:extrusive ratios were compiled for selected volcanic centers where long-term (>104 years) data were available. More silicic compositions, rhyolites and andesites, have a more limited range of eruption rates than basalts. Even when high Qe values contributed by flood basalts (9 ± 2 Å~ 10-1 km3/yr) are removed, there is a trend in decreasing average Qe with lava composition from basaltic eruptions (2.6 ± 1.0 Å~ 10-2 km3/yr) to andesites (2.3 ± 0.8 Å~ 10-3 km3/yr) and rhyolites (4.0 ± 1.4 Å~ 10-3 km3/yr). This trend is also seen in the difference between oceanic and continental settings, as eruptions on oceanic crust tend to be predominately basaltic. All of the volcanoes occurring in oceanic settings fail to have statistically different mean Qe and have an overall average of 2.8 ± 0.4 Å~ 10-2 km3/yr, excluding flood basalts. Likewise, all of the volcanoes on continental crust also fail to have statistically different mean Qe and have an overall average of 4.4 ± 0.8 Å~ 10-3 km3/yr. Flood basalts also form a distinctive class with an average Qe nearly two orders of magnitude higher than any other class. However, we have found no systematic evidence linking increased intrusive:extrusive ratios with lower volcanic rates. A simple heat balance analysis suggests that the preponderance of volcanic systems must be open magmatic systems with respect to heat and matter transport in order to maintain eruptible <span class="hlt">magma</span> at shallow depth throughout the observed lifetime of the volcano. The empirical upper limit of Å`10-2 km3/yr for <span class="hlt">magma</span> eruption rate in systems with relatively high intrusive:extrusive ratios may be a consequence of the fundamental parameters</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006Geo....34..937M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006Geo....34..937M"><span><span class="hlt">Magma</span> chamber of the Campi Flegrei supervolcano at the time of eruption of the Campanian Ignimbrite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marianelli, Paola; Sbrana, Alessandro; Proto, Monica</p> <p>2006-11-01</p> <p>A supereruption that occurred in the Campi Flegrei area, Italy, ca. 39 ka had regional- and global-scale environmental impacts and deposited the Campanian Ignimbrite (CI). We attempt to shed light on critical aspects of the eruption (depth of <span class="hlt">magma</span> chamber, intensive pre-eruptive <span class="hlt">magma</span> conditions) and the large-volume <span class="hlt">magma</span> plumbing system on the basis of information derived from analyzing melt inclusion (MI) data. To achieve these aims, we provide new measurements of homogenization temperatures and values of dissolved H2O within phenocryst-hosted MIs from pumices erupted during different phases of the CI eruption. The MI data indicate that a relatively homogeneous overheated trachytic <span class="hlt">magma</span> resided within a relatively deep <span class="hlt">magma</span> chamber. Dissolved water contents in MIs indicate that prior to the eruption the <span class="hlt">magma</span> chamber underwent radical changes related to differential upward movement of <span class="hlt">magma</span>. Decompression of the rising trachytic <span class="hlt">magma</span> caused a decrease in water solubility and crystallization, and trachytic bodies were emplaced at very shallow depths. The proposed eruptive model links portions of the main <span class="hlt">magma</span> chamber and apophyses with specific eruptive units.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53B3085T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53B3085T"><span><span class="hlt">Magma</span> plumbing in the Grímsvötn volcanic system, Iceland: an overview</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thordarson, T.</p> <p>2016-12-01</p> <p>The basaltic Grímsvötn volcanic system (GVS) consists of Grímsvötn central volcano (GCV) and an immature fissure swarm extending 70 km to the southwest from GCV. The GCV has the highest eruption frequency of all central volcanos in Iceland, or 7 events per 100 years. In contrast, the GVS fissure swarm has only featured two events in postglacial times, the 1783-4 Laki and the prehistoric Lambavatnsgígar fissure eruptions. These two events account for 25% of the total Holocene <span class="hlt">magma</span> output from the GVS and 80% of the output in historic time (i.e. last 1100 years). Although GVS <span class="hlt">magma</span> plumbing has been a topic of research for four decades, its general structure, extent and geometry is still deliberated. Is mantle-derived <span class="hlt">magma</span> delivered straight up beneath the GCV to an upper crustal <span class="hlt">magma</span> chamber and then vertically to eruptions at the GCV and laterally to eruption on the GVS fissure swarm? Or does the system feature two levels of crustal storage, one in the upper crust beneath GCV and another at mid-crustal depth? Or is the structure of the GVS plumbing more complex? The data that we have so far and is pertinent to GVS <span class="hlt">magma</span> plumbing is summarised below: Geophysical measurements imply that shallowest <span class="hlt">magma</span> storage beneath GCV is at 3-4 km. The Zr and Nb concentrations in the tephra from the 1998 and 2004 GCV plus Laki eruptions show that the parent <span class="hlt">magmas</span> for each was produced by different degrees of partial melting of a similar mantle source. It also demonstrates transport to the surface via separate pathways and that neither <span class="hlt">magma</span> can be derived by fractional crystallization from a Laki-like <span class="hlt">magma</span>. Detailed petrological studies on the Laki tephra and lava indicate polybaric <span class="hlt">magma</span> evolution within the mid-crust (at 6 to 15 km depth), with further evolution at shallower depths induced either by disequilibrium crystal growth during ascent of <span class="hlt">magma</span> from the mid-crust storage or a brief residence at 3-6 km depths. The Laki <span class="hlt">magma</span> contains significant abundances of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/144909','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/144909"><span>Role of <span class="hlt">magma</span>-water interaction in very large explosive eruptions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Valentine, G.A.</p> <p>1993-11-01</p> <p>An important class of explosive eruptions, involving large-scale <span class="hlt">magma</span>-water interaction during the discharge of hundreds to thousands of cubic kilometers of <span class="hlt">magma</span>, is discussed. Geologic evidence for such eruptions is summarized. Case studies from New Zealand, Australia, England, and the western United States are described, focusing on inferred eruption dynamics. Several critical problems that need theoretical and experimental research are identified. These include rates at which water can flow into a volcanic vent or plumbing system, entrainment of water by explosive eruptions through lakes and seas, effects of <span class="hlt">magma</span> properties and gas bubbles on <span class="hlt">magma</span>-water interaction, and hazards associated with the eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.V43D1638A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.V43D1638A"><span><span class="hlt">Magma</span> Generation and Transport in Subduction Zones: Numerical Simulations of Chemical, Thermal and Mechanical Coupling During <span class="hlt">Magma</span> Ascent by Porous Flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arcay, D.; Gerya, T.; Tackley, P.</p> <p>2007-12-01</p> <p>Most subduction zones are characterized by significant magmatic activity responsible for building trench-parallel volcanic arcs above descending slabs. High <span class="hlt">magma</span> 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 <span class="hlt">magma</span> transport from the melt generation region located above the hydrated slab surface at 100-300 km depth to the <span class="hlt">magma</span> 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 <span class="hlt">magma</span> generation and transport in subduction zones, that simulates chemical, thermal, and mechanical interactions between fluids and solid rocks along the <span class="hlt">magma</span> ascent pathway. <span class="hlt">Magma</span> 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. <span class="hlt">Magma</span> productivity rates, varying along the <span class="hlt">magma</span> ascent path way, will be discussed as a function of <span class="hlt">magma</span> viscosity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.198..360G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.198..360G"><span>Transfer of volatiles and metals from mafic to felsic <span class="hlt">magmas</span> in composite <span class="hlt">magma</span> chambers: An experimental study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guo, Haihao; Audétat, Andreas</p> <p>2017-02-01</p> <p>In order to determine the behavior of metals and volatiles during intrusion of mafic <span class="hlt">magma</span> into the base of silicic, upper crustal <span class="hlt">magma</span> chambers, fluid-rock partition coefficients (Dfluid/rock) of Li, B, Na, S, Cl, K, Mn, Fe, Rb, Sr, Ba, Ce, Cu, Zn, Ag, Cd, Mo, As, Se, Sb, Te, W, Tl, Pb and Bi were determined experimentally at 2 kbar and 850 °C close to the solidus of mafic <span class="hlt">magma</span>. In a first step, volatile-bearing mafic glasses were prepared by melting a natural basaltic trachyandesite in the presence of volatile-bearing fluids at 1200 °C/10 kbar in piston cylinder presses. The hydrous glasses were then equilibrated in subsequent experiments at 850 °C/2 kbar in cold-seal pressure vessels, which caused 80-90% of the melt to crystallize. After 0.5-2.0 days of equilibration, the exsolved fluid was trapped by means of in-situ fracturing in the form of synthetic fluid inclusions in quartz. Both the mafic rock residue and the fluid inclusions were subsequently analyzed by laser-ablation ICP-MS for major and trace elements. Reverse experiments were conducted by equilibrating metal-bearing aqueous solutions with rock powder and then trapping the fluid. In two additional experiments, information on relative element mobilities were obtained by reacting fluids that exsolved from crystallizing mafic <span class="hlt">magma</span> with overlying silicic melts. The combined results suggest that under the studied conditions S, Cl, Cu, Se, Br, Cd and Te are most volatile (Dfluid/rock >10), followed by Li, B, Zn, As, Ag, Sb, Cs, W, Tl, Pb and Bi (Dfluid/rock = 1-10). Less volatile are Na, Mg, K, Ca, Mn, Fe, Rb, Sr, Mo and Rb (Dfluid/rock 0.1-1), and the least fluid-mobile elements are Al, Si, Ti, Zr, Ba and Ce (Dfluid/rock <0.1). This trend is broadly consistent with relative element volatilities determined on natural high-temperature fumarole gases, although some differences exist. Based on the volatility data and measured mineral-melt and sulfide-melt partition coefficients, volatile fluxing in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.203...89H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.203...89H"><span>Iron isotopic compositions of adakitic and non-adakitic granitic <span class="hlt">magmas</span>: <span class="hlt">Magma</span> compositional control and subtle residual garnet effect</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>He, Yongsheng; Wu, Hongjie; Ke, Shan; Liu, Sheng-Ao; Wang, Qiang</p> <p>2017-04-01</p> <p>Here we present iron (Fe) isotopic compositions of 51 well-characterized adakitic and non-adakitic igneous rocks from the Dabie orogen, Central China and Panama/Costa Rica, Central America. Twelve I-type non-adakitic granitoid samples from the Dabie orogen yield δ56Fe ranging from -0.015‰ to 0.184‰. The good correlations between δ56Fe and indices of <span class="hlt">magma</span> differentiation (e.g., SiO2, FeOt, Mg#, and Fe3+/ΣFe) suggest Fe2+-rich silicate and oxide minerals dominated fractional crystallization with Δ56Femelt-crystal ∼ 0.06‰ may account for the δ56Fe variation in these samples. One A-type granite sample from the Dabie orogen has δ56Fe as high as 0.447‰, likely indicating less magnetite crystallization and an increase in 103lnβmelt with <span class="hlt">magma</span> (Na + K)/(Ca + Mg). Combined with the literature data, most high silica (SiO2 ⩾ 71 wt.%) granitic rocks define a good positive linear correlation between δ56Fe and (Na + K)/(Ca + Mg): δ56Fe = 0.0062‰ × (Na + K)/(Ca + Mg) + 0.130‰ (R2 = 0.66). Given that fractional crystallization also tends to increase δ56Fe with (Na + K)/(Ca + Mg), this correlation can serve as the maximum estimate of the <span class="hlt">magma</span> compositional control on Fe isotope fractionation. Low-Mg adakitic samples (LMA) have δ56Fe ranging from 0.114‰ to 0.253‰. The melt compositional control on LMA δ56Fe could be insignificant due to their limited (Na + K)/(Ca + Mg) variation. Except for one sample that may be affected by late differentiation, 14 out of 15 LMA have δ56Fe increasing with (Dy/Yb)N, reflecting a subtle but significant effect of residual garnet proportion. This serves as evidence for that source mineralogy may play an important role in fractionating Fe isotopes during partial melting. Dabie and Central America high-Mg adakitic samples have homogeneous Fe isotopic compositions with mean δ56Fe of 0.098 ± 0.038‰ (2SD, N = 11) and 0.085 ± 0.045‰ (2SD, N = 11), respectively. These samples have undergone melt-mantle interaction</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014402','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014402"><span>MAGMIX: a basic program to calculate viscosities of interacting <span class="hlt">magmas</span> of differing composition, temperature, and water content</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Frost, T.P.; Lindsay, J.R.</p> <p>1988-01-01</p> <p>MAGMIX is a BASIC program designed to predict viscosities at thermal equilibrium of interacting <span class="hlt">magmas</span> of differing compositions, initial temperatures, crystallinities, crystal sizes, and water content for any mixing proportion between end members. From the viscosities of the end members at thermal equilibrium, it is possible to predict the styles of <span class="hlt">magma</span> interaction expected for different initial conditions. The program is designed for modeling the type of <span class="hlt">magma</span> interaction between hypersthenenormative <span class="hlt">magmas</span> at upper crustal conditions. Utilization of the program to model <span class="hlt">magma</span> interaction at pressures higher than 200 MPa would require modification of the program to account for the effects of pressure on heat of fusion and <span class="hlt">magma</span> density. ?? 1988.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7004210','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7004210"><span>Oxygen isotope constraints on the petrogenesis of Aleutian arc <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Singer, B.S.; O'Neil, J.R. ); Brophy, J.G. )</p> <p>1992-04-01</p> <p>The first measurement of {sup 18}O/{sup 16}O ratios of plagioclase, clinopyroxene, orthopyroxene, and titanomagnetite phenocrysts from modern Aleutian island-arc lavas provides new insight and independent constraints on <span class="hlt">magma</span> sources and intracrustal processes. Basalts are heterogeneous on the scale of the entire arc and individual volcanic centers. Combined with Sr isotope and trace element data {delta}{sup 18}O{sub plag} values suggest a variable <span class="hlt">magma</span> source characterized by differences in the mantle wedge or the subducted sediment component along the volcanic front. Seven tholeiitic basalt to rhyodacite lavas from the Seguam volcanic center have nearly identical {delta}{sup 18}O{sub plag} values of 6.0{per thousand} {plus minus} 0.2{per thousand}, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1,150 {plus minus} 100C (basalt) and 950 {plus minus} 100C (rhyodacite). In contrast, {delta}{sup 18}O{sub plag} values of 12 calc-alkalic basaltic andesites and andesites from the smaller Kanaga volcanic center span a broader range of 5.9{per thousand}-6.6{per thousand}, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting {delta}{sup 18}O values occur in one andesite, and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetite oxygen isotope temperatures are inconsistent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4973271','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4973271"><span>Boron isotope fractionation in <span class="hlt">magma</span> via crustal carbonate dissolution</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela</p> <p>2016-01-01</p> <p>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 <span class="hlt">magma</span> at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc <span class="hlt">magmas</span> could flag shallow-level additions to the subduction cycle. PMID:27488228</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70032797','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70032797"><span>Pre-eruption recharge of the Bishop <span class="hlt">magma</span> system</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Wark, D.A.; Hildreth, W.; Spear, F.S.; Cherniak, D.J.; Watson, E.B.</p> <p>2007-01-01</p> <p>The 650 km3 rhyolitic Bishop Tuff (eastern California, USA), which is stratigraphically zoned with respect to temperatures of mineral equilibration, reflects a corresponding thermal gradient in the source <span class="hlt">magma</span> chamber. Consistent with previous work, application of the new TitaniQ (Ti-in-quartz) thermometer to quartz phenocryst rims documents an ???100 ??C temperature increase with chamber depth at the time of eruption. Application of TitaniQ to quartz phenocryst cores, however, reveals lower temperatures and an earlier gradient that was less steep, with temperature increasing with depth by only ???30 ??C. In many late-erupted crystals, sharp boundaries that separate low-temperature cores from high-temperature rims cut internal cathodoluminescent growth zoning, indicating partial phenocryst dissolution prior to crystallization of the high-temperature rims. Rimward jumps in Ti concentration across these boundaries are too abrupt (e.g., 40 ppm across a distance of <10 ??m) to have survived magmatic temperatures for more than ???100 yr. We interpret these observations to indicate heating-induced partial dissolution of quartz, followed by growth of high-temperature rims (made possible by lowering of water activity due to addition of CO2) within 100 yr of the climactic 760 ka eruption. Hot mafic melts injected into deeper parts of the <span class="hlt">magma</span> system were the likely source of heat and CO2, raising the possibility that eruption and caldera collapse owe their origin to a recharge event. ?? 2007 Geological Society of America.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.142..314D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.142..314D"><span>Heat capacity, configurational heat capacity and fragility of hydrous <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Di Genova, D.; Romano, C.; Giordano, D.; Alletti, M.</p> <p>2014-10-01</p> <p>The glassy and liquid heat capacities of four series of dry and hydrous natural glasses and <span class="hlt">magma</span> as a function of temperature and water content (up to 19.9 mol%) were investigated using differential scanning calorimetry (DSC). The analyzed compositions are basalt, latite, trachyte and pantellerite. The results of this study indicate that the measured heat capacity of glasses (Cpg) is a linear function of composition and is well reproduced by the empirical model of Richet (1987). For the investigated glasses, the partial molar heat capacity of water can be considered as independent of composition, in agreement with Bouhifd et al. (2006). For hydrous liquids, the heat capacity (Cpliq) decreases nonlinearly with increasing water content. Previously published models, combined with the partial molar heat capacity of water from the literature, are not able to reproduce our experimental data in a satisfactory way. We estimated the partial molar heat capacity of water (CpH2O) in hydrous <span class="hlt">magma</span> over a broad compositional range. The proposed value is 41 ± 3 J mol-1 K-1. Water strongly affects the configurational heat capacity at the glass transition temperature [Cpconf (Tg)]. An increases of Cpconf (Tg) with water content was measured for the polymerized liquids (trachyte and pantellerite), while the opposite behavior was observed for the most depolymerized liquids (basalt and latite). Structural and rheological implications of this behavior are discussed in light of the presented results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53D3160C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53D3160C"><span><span class="hlt">Magma</span> interaction in the root of an arc batholith</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chapman, T.; Robbins, V.; Clarke, G. L.; Daczko, N. R.; Piazolo, S.</p> <p>2016-12-01</p> <p>Fiordland, New Zealand, preserves extensive Cretaceous arc plutons, emplaced into parts of the Delamerian/Ross Orogen. Dioritic to gabbroic material emplaced at mid to lower crustal levels are exposed in the Malaspina Pluton (c. 1.2 GPa) and the Breaksea Orthogneiss (c. 1.8 GPa). Distinct magmatic pulses can be mapped in both of these plutons consistent with cycles of melt advection. Relationships are consistent with predictions from lower crustal processing zones (MASH and hot zones) considered important in the formation of Cordilleran margins. Metamorphic garnet growth is enhanced along magmatic contacts, such as where hornblende gabbronorite is cut by garnet-clinopyroxene-bearing diorite. Such features are consistent with cycles of incremental emplacement, younger <span class="hlt">magma</span> having induced localised garnet granulite metamorphism in wall rock of older material. Temperature estimates and microstructures preserved in garnet granulite are consistent with sub-solidus, water-poor conditions in both the Malaspina and Breaksea Orthogneiss. The extent and conditions of the metamorphism implies conditions and duration was incapable of partially melting older wall rock material. The nature of interactions in intermediate to basic compositions are assessed in terms of <span class="hlt">magma</span> genesis in the Cretaceous batholith. Most of the upper crustal felsic I-type magmatism along the margin being controlled by high-pressure garnet-clinopyroxene fractionation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27488228','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27488228"><span>Boron isotope fractionation in <span class="hlt">magma</span> via crustal carbonate dissolution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela</p> <p>2016-08-04</p> <p>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 <span class="hlt">magma</span> 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 <span class="hlt">magmas</span> could flag shallow-level additions to the subduction cycle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1917096S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1917096S"><span>Electrical conductivity of silicate liquids and a <span class="hlt">magma</span> ocean dynamo</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stixrude, Lars; Scipioni, Roberto</p> <p>2017-04-01</p> <p>Are silicate dynamos possible? So far planetary dynamos seated in silicate material are unknown. Several lines of evidence motivate the consideration of a silicate dynamo in the early Earth: 1) Paleomagnetic evidence of a very early dynamo-generated field 2) models of the early thermal state of Earth in which the mantle may have been too hot to permit a core-generated magnetic field, and 3) the possibility of a deep and thick basal <span class="hlt">magma</span> ocean. The key requirement is that the electrical conductivity σ of silicate liquids be sufficiently large at the relevant high pressure-temperature conditions (σ > 1000 S/m). Despite its importance, σ of silicate liquids is unknown above a few GPa in pressure, and measured values at low pressure are far too small to support a dynamo. However, observations of reflectivity from oxide liquids in shock wave experiments suggest a different mechanism of conductivity at high pressure (electrons, rather than ions). We have used ab initio molecular dynamics simulations to compute from first principles the value of σ at extreme conditions in systems with compositions that are simple (SiO2) and rich (MgO-FeO-CaO-Al2O3-Na2O-SiO2). We use DFT+U with and without spin polarization combined with the Kubo-Greenwood formula. We find that the value of σ exceeds the minimum requirements and that a silicate dynamo seated in a basal <span class="hlt">magma</span> ocean is viable.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940023347','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940023347"><span>Experimental study of lunar and SNC (Mars) <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rutherford, Malcolm J.</p> <p>1994-01-01</p> <p>The overall objectives of this research were to evaluate the role of C-O-S-Cl degassing processes in explaining vesiculation, oxidation state and fire-fountaining of lunar <span class="hlt">magmas</span> by analysis of individual lunar glass spherules, and by experimental determination of equilibrium abundances and diffusion rates of C, S and Cl melt species in lunar glass compositions; and to determine possible primitive SNC <span class="hlt">magma</span> compositions and the mineralogy of the mantle from which they were derived, and to evaluate P, T, XH2O etc. conditions at which they crystallize to form the SNC meteorites. After funding for one year, a project on the A15 volcanic green glass has been completed to the point of writing a first manuscript. Carbon-oxygen species C-O and CO2 are below detection limits (20 ppm) in these glasses, but there is up to 500 ppm S with concentrations both increasing and decreasing toward the spherule margins. Calculations and modeling indicate that C species could have been present in the volcanic gases, however. In a second project, experiments with low PH2O have resulted in refined estimates of the early intercumulus melt composition in the Chassigny meteorite which is generally accepted as a sample from Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V53A2749O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V53A2749O"><span>Crystal textures produced by <span class="hlt">magma</span> mixing at Chokai, northern Honshu, Japan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ohba, T.; Hayashi, S.; Ban, M.</p> <p>2013-12-01</p> <p>Thermal equilibration during <span class="hlt">magma</span> mingling between hot mafic <span class="hlt">magma</span> and cold felsic <span class="hlt">magma</span> results in rapid cooling of the mafic <span class="hlt">magma</span> and in rapid heating of the felsic <span class="hlt">magma</span>. In the mafic <span class="hlt">magma</span>, minerals would quickly crystallize to grow, whereas minerals would dissolve in the felsic <span class="hlt">magma</span>. As these suspended solid minerals are able to freely move in the liquids, they could enter the liquid which is not their original host. Every crystal would undergo complex chemical fluctuation of surrounding liquid during the dynamic mingling process, forming a wide variety of complex intracrystal textures. The complex mineralogy in a mixed lava (Saruana Lava) from Chokai, northern Honshu, Japan, is completely accounted for by crystallization and resorption induced by <span class="hlt">magma</span> mixing. The lava is compositionally heterogeneous, as silica contents in whole rocks ranges from 54 to 60 % in the single lava flow. Regardless of the heterogeneity, these rocks exhibit similar mineralogical features, e.g. coexistence of reversely zoned pyroxene and normally zoned pyroxenes. In addition to whole rocks chemistry, extensive petrographical study with SEM-EDS revealed original mineralogy and compositions of the endmembers. The felsic endmember is the andesitic crystal mush consisting of 46% rhyolite melt, 38% plagioclase, 11% pyroxenes, 5% magnetite, and trace of hornblende. The mafic endmember is magnesian basalt <span class="hlt">magma</span> containing small amount of magnesian olivine (Fo87), picotite, and calcic plagioclase (An90). Reversely zoned minerals consist of relatively uniform cores derived from felsic endmember and surrounding mafic margins that exhibit normal zoning imposed by fine rectilinear oscillatory zones. Innermost margin ranges mafic to intermediate in composition, depending on the thickness of the margin which broadly ranges from 1 to 100 micrometer. The cores exhibit resorption textures such as rounded shape, irregular shape, or dusty zones. Normally zoned crystals exhibit the similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5022700','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5022700"><span>Isotopic evidence of source variations in commingled <span class="hlt">magma</span> systems: Colorado River extensional corridor, Arizona and Nevada</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Metcalf, R.V.; Smith, E.I.; Martin, M.W. . Dept. of Geoscience); Gonzales, D.A.; Walker, J.D. . Isotope Geochronology Lab.)</p> <p>1993-04-01</p> <p>Mixing of mantle derived mafic and crustal derived felsic <span class="hlt">magmas</span> is a major Province-wide process forming Tertiary intermediate <span class="hlt">magmas</span> within the Basin and Range. Major variations in <span class="hlt">magma</span> sources, however, may exist in temporally and spatially related systems. Such variations are exemplified by two closely spaced plutons within the northern Colorado River extensional corridor. The 15.96 Ma Mt. Perkins pluton (MPP) was emplaced in three major phases: phase 1 (oldest) gabbro; phase 2 quartz diorite to hornblende granodiorite; and phase 3 biotite granodiorite ([+-]hbld). Phases 2 and 3 contain mafic microgranitoid enclaves (MME) that exhibit evidence of <span class="hlt">magma</span> mingling. Combined data from phase 2 and 3 rocks, including MMW, shows positive [sup 87]Sr/[sup 86]Sr and negative [var epsilon]Nd correlations vs. SiO[sub 2] (50--72 wt %). Phase 2 rocks, which plot between phase 2 MME and MME-free phase 3 granodiorite, represent hybrid <span class="hlt">magmas</span> formed by mixing of mantle and crustal derived <span class="hlt">magmas</span>. Phase 1 gabbro falls off isotope-SiO[sub 2] trends and represents a separate mantle derived <span class="hlt">magma</span>. The 13.2 Ma Wilson Ridge pluton (WRP), <20 km north of MPP, is cogenetic with the river Mountains volcano (RMV). In WRP an early diorite was intruded by a suite of monzodiorite to quartz monzonite. The monzodiorite portion contains MME and mafic schlieren representing mingled and mixed mafic <span class="hlt">magmas</span>. The WRP and MPP represent two closely spaced isotopically distinct and separate <span class="hlt">magma</span> systems. There are five <span class="hlt">magma</span> sources. The two felsic mixing end members represent two different crustal <span class="hlt">magma</span> sources. Two mantle sources are presented by MPP phase 1 gabbro and phase 2 MME, reflecting lithospheric and asthenospheric components, respectively. The latter represents the oldest reported Tertiary asthenospheric component within the region. A single lithospheric mantle source, different from the MPP gabbro, is indicated for the mafic mixing end member in the WRP-RMV suite.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021972','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021972"><span>A complex <span class="hlt">magma</span> mixing origin for rocks erupted in 1915, Lassen Peak, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Clynne, M.A.</p> <p>1999-01-01</p> <p>The eruption of Lassen Peak in May 1915 produced four volcanic rock types within 3 days, and in the following order: (1) hybrid black dacite lava containing (2) undercooled andesitic inclusions, (3) compositionally banded pumice with dark andesite and light dacite bands, and (4) unbanded light dacite. All types represent stages of a complex mixing process between basaltic andesite and dacite that was interrupted by the eruption. They contain disequilibrium phenocryst assemblages characterized by the co-existence of magnesian olivine and quartz and by reacted and unreacted phenocrysts derived from the dacite. The petrography and crystal chemistry of the phenocrysts and the variation in rock compositions indicate that basaltic andesite intruded dacite <span class="hlt">magma</span> and partially hybridized with it. Phenocrysts from the dacite <span class="hlt">magma</span> were reacted. Cooling, cyrstallization, and vesiculation of the hybrid andesite <span class="hlt">magma</span> converted it to a layer of mafic foam. The decreased density of the andesite <span class="hlt">magma</span> destabilized and disrupted the foam. Blobs of foam rose into and were further cooled by the overlying dacite <span class="hlt">magma</span>, forming the andesitic inclusions. Disaggregation of andesitic inclusions in the host dacite produced the black dacite and light dacite <span class="hlt">magmas</span>. Formation of foam was a dynamic process. Removal of foam propagated the foam layer downward into the hybrid andesite <span class="hlt">magma</span>. Eventually the thermal and compositional contrasts between the hybrid andesite and black dacite <span class="hlt">magmas</span> were reduced. Then, they mixed directly, forming the dark andesite <span class="hlt">magma</span>. About 40-50% andesitic inclusions were disaggregated into the host dacite to produce the hybrid black dacite. Thus, disaggregation of inclusions into small fragments and individual crystals can be an efficient <span class="hlt">magma</span>-mixing process. Disaggregation of undercooled inclusions carrying reacted host-<span class="hlt">magma</span> phenocrysts produces co-existing reacted and unreacted phenocrysts populations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5243897','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5243897"><span>Analysis of <span class="hlt">magma</span>-thermal conversion of biomass to gaseous fuel</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gerlach, T.M.</p> <p>1982-02-01</p> <p>A wide range of <span class="hlt">magma</span> types and pluton geometries believed to occur within the upper 10 km of the crust provide suitable sources of thermal energy for conversion of water-biomass mixtures to higher quality gaseous fuel. Gaseous fuel can be generated within a <span class="hlt">magma</span> body, within the hot subsolidus margins of a <span class="hlt">magma</span> body, or within surface reaction vessels heated by thermal energy derived from a <span class="hlt">magma</span> body. The composition, amount, and energy content of the fuel gases generated from water-biomass mixtures are not sensitive to the type, age, depth, or temperature of a <span class="hlt">magma</span> body thermal source. The amount and energy content of the generated fuel is almost entirely a function of the proportion of biomass in the starting mixture. CH/sub 4/ is the main gas that can be generated in important quantities by <span class="hlt">magma</span> thermal energy under most circumstances. CO is never an important fuel product, and H/sub 2/ generation is very limited. The rates at which gaseous fuels can be generated are strongly dependent on <span class="hlt">magma</span> type. Fuel generation rates for basaltic <span class="hlt">magmas</span> are at least 2 to 3 times those for andesitic <span class="hlt">magmas</span> and 5 to 6 times those for rhyolitic <span class="hlt">magmas</span>. The highest fuel generation rates, for any particular <span class="hlt">magma</span> body, will be achieved at the lowest possible reaction vessel operating temperature that does not cause graphite deposition from the water-biomass starting mixture. The energy content of the biomass-derived fuels is considerably greater than that consumed in the generation and refinement process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.9549P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.9549P"><span>Geodesy - the key for constraining rates of <span class="hlt">magma</span> supply, storage, and eruption</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Poland, Michael; Anderson, Kyle</p> <p>2016-04-01</p> <p>Volcanology is an inherently interdisciplinary science that requires joint analysis of diverse physical and chemical datasets to infer subsurface processes from surface observations. Among the diversity of data that can be collected, however, geodetic data are critical for elucidating the main elements of a magmatic plumbing system because of their sensitivity to subsurface changes in volume and mass. In particular, geodesy plays a key role in determining rates of <span class="hlt">magma</span> supply, storage, and eruption. For example, surface displacements are critical for estimating the volume changes and locations of subsurface <span class="hlt">magma</span> storage zones, and remotely sensed radar data make it possible to place significant bounds on eruptive volumes. Combining these measurements with geochemical indicators of <span class="hlt">magma</span> composition and volatile content enables modeling of <span class="hlt">magma</span> fluxes throughout a volcano's plumbing system, from source to surface. We combined geodetic data (particularly InSAR) with prior geochemical constraints and measured gas emissions from Kīlauea Volcano, Hawai`i, to develop a probabilistic model that relates <span class="hlt">magma</span> supply, storage, and eruption over time. We found that the <span class="hlt">magma</span> supply rate to Kīlauea during 2006 was 35-100% greater than during 2000-2001, with coincident increased rates of subsurface <span class="hlt">magma</span> storage and eruption at the surface. By 2012, this surge in supply had ended, and supply rates were below those of 2000-2001; <span class="hlt">magma</span> storage and eruption rates were similarly reduced. These results demonstrate the connection between <span class="hlt">magma</span> supply, storage, and eruption, and the overall importance of <span class="hlt">magma</span> supply with respect to volcanic hazards at Kīlauea and similar volcanoes. Our model also confirms the importance of geodetic data in modeling these parameters - rates of storage and eruption are, in some cases, almost uniquely constrained by geodesy. Future modeling efforts along these lines should also seek to incorporate gravity data, to better determine <span class="hlt">magma</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4479I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4479I"><span>Triple oxygen isotope composition of the Campi Flegrei <span class="hlt">magma</span> systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Iovine, Raffaella Silvia; Wörner, Gerhard; Pack, Andreas; Sengupta, Sukanya; Carmine Mazzeo, Fabio; Arienzo, Ilenia; D'Antonio, Massimo</p> <p>2017-04-01</p> <p>Sr-O isotope relationships in igneous rocks are a powerful tool to distinguish <span class="hlt">magma</span> 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 <span class="hlt">magmas</span> 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 <span class="hlt">magmas</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JVGR..125..107M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JVGR..125..107M"><span>Timing <span class="hlt">magma</span> ascent at Popocatepetl Volcano, Mexico, 2000-2001</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin-Del Pozzo, A. L.; Cifuentes, G.; Cabral-Cano, E.; Bonifaz, R.; Correa, F.; Mendiola, I. F.</p> <p>2003-07-01</p> <p>Magnetic anomalies may be used to constrain <span class="hlt">magma</span> ascent and are useful as precursors to eruptions especially when correlated with other geophysical and geochemical data. In this paper we present multiparameter data on the magnetics, dome morphology, geochemistry and seismicity associated with the December 2000-January 2001 eruptions, the largest of the recent eruptions at Popocatepetl Volcano. A 6-month data period was studied in order to evaluate the precursors and post-eruption processes. Several cycles of dome construction and destruction occurred from September 2000 through February 2001. In December, large amplitude tremor associated with a higher effusion rate resulted in the formation of a large dome which filled the crater to within about 50 m of the lowest part of the crater rim. Seismic activity in December was marked by many volcanotectonic earthquakes and both high frequency and harmonic tremor. On December 12 and 13, an increase in the tremor amplitude was followed by ash eruptions with 1.7-5-km-high columns. Tremor amplitude increased again on December 15 and oscillated for the next four days. Activity remained high until the end of the month. On January 22, an 18-km-high plume produced ash and pumice fall to the east as well as pyroclastic flows and mudflows which reached 6 km from the crater. The eruption left three concentric explosion pits, partially destroying the December dome. Mixing of a mafic olivine-bearing melt with a more evolved <span class="hlt">magma</span> triggered the larger eruption on January 22 as can be seen from the higher MgO concentrations in some of the ejecta and the presence of a dark andesitic scoria with lower silica content and a white andesitic pumice with higher silica content. Precursory negative magnetic anomalies up to 5 nT (-3.2 nT, -5 nT, -2.9 nT) were associated with the ascent of the larger batches of <span class="hlt">magma</span> which preceded the increases in seismicity, before the December 2000-January 22 VEI 3-4 eruptions. No significant increases in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4038B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4038B"><span>Advancing dynamic and thermodynamic modelling of <span class="hlt">magma</span> oceans</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bower, Dan; Wolf, Aaron; Sanan, Patrick; Tackley, Paul</p> <p>2017-04-01</p> <p>The techniques for modelling low melt-fraction dynamics in planetary interiors are well-established by supplementing the Stokes equations with Darcy's Law. But modelling high-melt fraction phenomena, relevant to the earliest phase of <span class="hlt">magma</span> ocean cooling, necessitates parameterisations to capture the dynamics of turbulent flow that are otherwise unresolvable in numerical models. Furthermore, it requires knowledge about the material properties of both solid and melt mantle phases, the latter of which are poorly described by typical equations of state. To address these challenges, we present (1) a new interior evolution model that, in a single formulation, captures both solid and melt dynamics and hence charts the complete cooling trajectory of a planetary mantle, and (2) a physical and intuitive extension of a "Hard Sphere" liquid equation of state (EOS) to describe silicate melt properties for the pressure-temperature (P-T) range of Earth's mantle. Together, these two advancements provide a comprehensive and versatile modelling framework for probing the far-reaching consequences of <span class="hlt">magma</span> ocean cooling and crystallisation for Earth and other rocky planets. The interior evolution model accounts for heat transfer by conduction, convection, latent heat, and gravitational separation. It uses the finite volume method to ensure energy conservation at each time-step and accesses advanced time integration algorithms by interfacing with PETSc. This ensures it accurately and efficiently computes the dynamics throughout the <span class="hlt">magma</span> ocean, including within the ultra-thin thermal boundary layers (< 2 cm thickness) at the core-mantle boundary and surface. PETSc also enables our code to support a parallel implementation and quad-precision calculations for future modelling capabilities. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..325..203A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..325..203A"><span>Variable H2O content in <span class="hlt">magmas</span> from the Tongariro Volcanic Centre and its relation to crustal storage and <span class="hlt">magma</span> ascent</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Auer, A.; White, J. D. L.; Tobin, M. J.</p> <p>2016-10-01</p> <p>The water content of crystal-hosted glass inclusions from Mt. Ruapehu has been determined by Fourier transform infrared spectroscopy (FTIR) at the IR beamline of the Australian Synchrotron. The results are compared with those from previous investigations as well as with calculated melt water concentrations in other <span class="hlt">magmas</span> from the Tongariro Volcannic Center (TgVC). It is shown that low and high water content in different <span class="hlt">magmas</span> can be related to distinct styles of <span class="hlt">magma</span> ascent and intermittent crustal storage. The first style is related to frequent small <span class="hlt">magma</span> batches erupted from the central volcanoes of Mt. Tongariro and Mt. Ruapehu. It produces highly porphyritic two-pyroxene-plagioclase andesites which generally show water contents below 3 wt%. The second style is sourced from mid-crustal intrusions which are characterized by highly differentiated hornblende dacites with dissolved water concentrations of up to 6 wt% H2O.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JVGR..257..184S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JVGR..257..184S"><span>Syneruptive deep <span class="hlt">magma</span> transfer and shallow <span class="hlt">magma</span> remobilization during the 2011 eruption of Shinmoe-dake, Japan—Constraints from melt inclusions and phase equilibria experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Suzuki, Yuki; Yasuda, Atsushi; Hokanishi, Natsumi; Kaneko, Takayuki; Nakada, Setsuya; Fujii, Toshitsugu</p> <p>2013-05-01</p> <p>The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic <span class="hlt">magma</span> mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are <span class="hlt">magma</span> mixing products (SiO2 = 57-58 wt.%; 960-980 °C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) <span class="hlt">magmas</span> at a fixed ratio (40%-30% SA and 60%-70% BA). The SA <span class="hlt">magma</span> had SiO2 = 62-63 wt.% and a temperature of 870 °C, and contains 43 vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA <span class="hlt">magma</span> had SiO2 = 55 wt.% and a temperature of 1030 °C, and contains 9 vol.% phenocrysts of olivine and plagioclase. The SA <span class="hlt">magma</span> partly erupted without mixing as white parts of pumices and juvenile particles. The two magmatic end-members crystallized at different depths, requiring the presence of two separate <span class="hlt">magma</span> reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA <span class="hlt">magma</span> had been stored at a pressure of 125 MPa, corresponding to a depth of 5 km. The textures and forms of phenocrysts from the BA <span class="hlt">magma</span> indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6 wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤ 250 MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of < 5 km is consistent with the proposed <span class="hlt">magma</span> system model, because olivine crystallization ceased after <span class="hlt">magma</span> mixing. Our petrological</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1044426','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1044426"><span>Timescales of Quartz Crystallization and the Longevity of the Bishop Giant <span class="hlt">Magma</span> Body</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gualda, Guilherme A.R.; Pamukcu, Ayla S.; Ghiorso, Mark S.; Anderson, Jr. , Alfred T.; Sutton, Stephen R.; Rivers, Mark L.</p> <p>2013-04-08</p> <p>Supereruptions violently transfer huge amounts (100 s-1000 s km{sup 3}) of <span class="hlt">magma</span> to the surface in a matter of days and testify to the existence of giant pools of <span class="hlt">magma</span> at depth. The longevity of these giant <span class="hlt">magma</span> bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant <span class="hlt">magma</span> body, which erupted {approx}760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop <span class="hlt">magma</span> body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of <10,000 years, more typically within 500-3,000 years before eruption. We conclude t