Sample records for magma ocean combined

  1. Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

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


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

  2. Magma Oceans on Exoplanets and Early Earth

    Elkins-Tanton, Linda


    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.

  3. Geochemical Evidence for a Terrestrial Magma Ocean

    Agee, Carl B.


    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

  4. Experimental Constraints on a Vesta Magma Ocean

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


    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 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 MELTS calculation are clear

  5. The three stages of magma ocean cooling

    Warren, Paul H.


    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.

  6. Experimental Fractional Crystallization of the Lunar Magma Ocean

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


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

  7. Crystallization and Cooling of a Deep Silicate Magma Ocean

    Bower, Dan; Wolf, Aaron


    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 magma ocean that subsequently cooled and crystallised. Understanding the cooling process is critical to determining magma ocean lifetimes and recognising possible remnant signatures of the magma ocean in present-day mantle heterogeneities. Modelling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (magma 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) magma 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 magma 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.

  8. The magma ocean as an impediment to lunar plate tectonics

    Warren, Paul H.


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

  9. The magma ocean as an impediment to lunar plate tectonics

    Warren, Paul H.


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

  10. On the cooling of a deep terrestrial magma ocean

    Monteux, J.; Andrault, D.; Samuel, H.


    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 magma 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 magma ocean starts to crystallize rapidly after its formation. The cooling efficiency of the magma 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 magma 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.

  11. Exoplanet Magma Ocean Magnetic Fields may be Common

    Bourzutschky, Alexander; Stevenson, David


    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 magma ocean. In many cases, the resulting high internal temperatures are sufficient to allow for dynamo action in the magma. 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 magma 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 magma. Assuming a fully molten silicate magma 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 magma, 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.

  12. Atmosphere-magma ocean modeling of GJ 1132 b

    Schaefer, Laura; Wordsworth, Robin; Berta-Thompson, Zachory K.; Sasselov, Dimitar


    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-magma 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 magma 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 magma ocean on GJ 1132 b. Preliminary modeling with the addition of CO2 gas will be presented.

  13. The chlorine isotope fingerprint of the lunar magma ocean.

    Boyce, Jeremy W; Treiman, Allan H; Guan, Yunbin; Ma, Chi; Eiler, John M; Gross, Juliane; Greenwood, James P; Stolper, Edward M


    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 magma 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 magma ocean early in the Moon's history. Chlorine isotope variability is therefore an indicator of planetary magma ocean degassing, an important stage in the formation of terrestrial planets.

  14. Terrestrial magma ocean and core segregation in the earth

    Ohtani, Eiji; Yurimoto, Naoyoshi


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

  15. Advancing dynamic and thermodynamic modelling of magma oceans

    Bower, Dan; Wolf, Aaron; Sanan, Patrick; Tackley, Paul


    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 magma 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 magma 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 magma ocean, including within the ultra-thin thermal boundary layers (important for multi-component systems). Our new high P-T liquid EOS accurately captures the energetics and physical properties of the partially molten system whilst retaining the largest number of familiar EOS parameters. We demonstrate the power of our integrated dynamic and EOS model by exploring two crystallisation scenarios for Earth that are dictated by the coincidence of the liquid

  16. Dropping stones in magma oceans - Effects of early lunar cratering

    Hartmann, W. K.


    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 magma ocean. If a magma 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 magma. 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.

  17. Differentiation of Vesta: Implications for a shallow magma ocean

    Neumann, Wladimir; Spohn, Tilman


    The Dawn mission confirms predictions that the asteroid 4 Vesta is differentiated with an iron-rich core, a silicate mantle and a basaltic crust, and confirms Vesta as the parent body of the HED meteorites. To better understand its early evolution, we perform numerical calculations of the thermo-chemical evolution adopting new data obtained by the Dawn mission such as mass, bulk density and size of the asteroid. We have expanded the model of Neumann et al. (2012) that includes accretion, compaction, melting and associated changes of material properties and partitioning of 26Al, advective heat transport, and differentiation by porous flow, to include convection and effective cooling in a magma ocean. Depending on the melt fraction, the heat transport by melt segregation is modelled either by porous flow or by convection and heat flux of a magma ocean with a high effective thermal conductivity. We show that partitioning of 26Al and its transport with the silicate melt is crucial for the formation of a magma oce...

  18. The timescales of magma evolution at mid-ocean ridges

    Brandl, Philipp A.; Regelous, Marcel; Beier, Christoph; O'Neill, Hugh St. C.; Nebel, Oliver; Haase, Karsten M.


    Oceanic crust is continuously created at mid-ocean ridges by decompression melting of the upper mantle as it upwells due to plate separation. Decades of research on active spreading ridges have led to a growing understanding of the complex magmatic, tectonic and hydrothermal processes linked to the formation of new oceanic igneous crust. However, less is known about the timescales of magmatic processes at mid-ocean ridges, including melting in and melt extraction from the mantle, fractional crystallisation, crustal assimilation and/or magma mixing. In this paper, we review the timescales of magmatic processes by integrating radiometric dating, chemical and petrological observations of mid-ocean ridge basalts (MORBs) and geophysical models. These different lines of evidence suggest that melt extraction and migration, and crystallisation and mixing processes occur over timescales of 1 to 10,000 a. High-resolution geochemical stratigraphic profiles of the oceanic crust using drill-core samples further show that at fast-spreading ridges, adjacent flow units may differ in age by only a few 100 a. We use existing chemical data and new major- and trace-element analyses of fresh MORB glasses from drill-cores in ancient Atlantic and Pacific crust, together with model stratigraphic ages to investigate how lava chemistry changes over 10 to 100 ka periods, the timescale of crustal accretion at spreading ridges which is recorded in the basalt stratigraphy in drilled sections through the oceanic crust. We show that drilled MORBs have compositions that are similar to those of young MORB glasses dredged from active spreading ridges (lavas that will eventually be preserved in the lowermost part of the extrusive section covered by younger flows), showing that the dredged samples are indeed representative of the bulk oceanic crust. Model stratigraphic ages calculated for individual flows in boreholes, together with the geochemical stratigraphy of the drilled sections, show that at

  19. Formation of Oceanic Lithosphere by Basal Magma Accretion

    Hamza, V. M.; Cardoso, R. R.; Alexandrino, C. H.


    The thermal models of the lithosphere proposed to date have failed to provide satisfactory accounts of some of the important features in large-scale variations of ocean floor bathymetry and heat flow. The systematic difference between model calculations and observational data have given rise to the so-called “oceanic heat flow paradox”, for which no satisfactory solution has been found for over the last forty years. In the present work, we point out that this paradox is a consequence of the assumption that lateral temperature variations are absent in the sub-lithospheric mantle. In the present work we propose a simple magma accretion model and examine its implications for understanding the thermal field of oceanic lithosphere. The new model (designated VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere, similar in character to those observed in magma solidification processes in the upper crust. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer (the Peclet number) is considered a space dependent variable. The solution to the problem of variable basal heat input has been obtained by the method of integral transform. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling and Plate models. Another noteworthy feature of the new model is its ability to account for the main observational features in the thermal behavior of both young and old oceanic lithosphere. Thus, heat flow and bathymetry variations calculated on the basis of the VBA model provide vastly improved fits to respective observational datasets. More importantly, the improved fits to bathymetry and heat flow have been achieved for the entire age range of oceanic lithosphere and without the need to invoke

  20. Zinc and volatile element loss during planetary magma ocean phases

    Dhaliwal, Jasmeet K.; Day, James M. D.; Moynier, Frédéric


    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 magma ocean phase.We explore conditions of volatile element loss within a lunar magma ocean (LMO) using models of Zn isotopic fractionation that are widely applicable to planetary magma 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

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

    Mills, Ryan D.


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

  2. Chlorine and hydrogen degassing in Vesta's magma ocean

    Sarafian, Adam R.; John, Timm; Roszjar, Julia; Whitehouse, Martin J.


    The hydrophilic nature of halogens makes these elements ideal for probing potential hydrous geologic processes. Generally, in magmatic settings the stable isotopes of Cl may fractionate when H is in low concentrations and little fractionation occurs when the H concentration is high. We determined the Cl isotope composition and halogen content (F, Cl, Br, and I) of apatite and merrillite in seven basaltic eucrites, which are meteorites linked to the asteroid 4-Vesta, by using secondary ion mass spectrometry. We compare our halogen results with H isotope data, existing bulk rock concentrations, and petrologic models. The inferred Cl isotope composition of eucrites from this study, expressed in standard δ37 Cl notation, which ranges from -3.8 to 7.7‰, correlates with the bulk major- and trace-element content, e.g., the Cl isotope composition positively correlates with Mg and Sc, while Cl isotope composition negatively correlates with K, V, and Cr. Here we suggest that eucrites preserve evidence of a degassing magma ocean as evidenced by the decreasing bulk rock K content with increasing δ37 Cl . If the eucrite parent body, 4-Vesta, accreted with a negative δ37 Cl of - 3.8 ± 1.1 ‰, at least some parts of the solar nebula would have been isotopically light compared to most estimates of the Earth, which on average is close to 0‰.

  3. Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply

    Olive, Jean-Arthur; Behn, Mark; Ito, Garrett; Escartin, Javier; Buck, Roger; Howell, Samuel


    Abyssal hills are the most common topographic feature on the surface of the solid Earth, yet the detailed mechanisms through which they are formed remain a matter of debate. Classical seafloor observations suggest hills acquire their shape at mid-ocean ridges through a combination of normal faulting and volcanic accretion. However, recent studies have proposed that the fabric of the seafloor reflects rapid fluctuations in ridge magma supply caused by oscillations in sea level modulating the partial melting process beneath the ridge [Crowley et al., 2015, Science]. In order to move this debate forward, we propose a modeling framework relating the magma supply of a mid-ocean ridge to the morphology of the seafloor it produces, i.e., the spacing and amplitude of abyssal hills. We specifically assess whether fluctuations in melt supply of a given periodicity can be recorded in seafloor bathymetry through (1) static compensation of crustal thickness oscillations, (2) volcanic extrusion, and (3) fault growth modulated by dike injection. We find that topography-building processes are generally insensitive to fluctuations in melt supply on time scales shorter than ~50-100 kyr. Further, we show that the characteristic wavelengths found in seafloor bathymetry across all spreading rates are best explained by simple tectono-magmatic interaction models, and require no periodic (climatic) forcing. Finally, we explore different spreading regimes where a smaller amplitude sea-level signal super-imposed on the dominant faulting signal could be most easily resolved.

  4. Evidence for an early wet Moon from experimental crystallization of the lunar magma ocean

    Lin, Yanhao; Tronche, Elodie J.; Steenstra, Edgar S.; van Westrenen, Wim


    The Moon is thought to have been covered initially by a deep magma ocean, its gradual solidification leading to the formation of the plagioclase-rich highland crust. We performed a high-pressure, high-temperature experimental study of lunar mineralogical and geochemical evolution during magma ocean solidification that yields constraints on the presence of water in the earliest lunar interior. In the experiments, a deep layer containing both olivine and pyroxene is formed in the first ~50% of crystallization, β-quartz forms towards the end of crystallization, and the last per cent of magma remaining is extremely iron rich. In dry experiments, plagioclase appears after 68 vol.% solidification and yields a floatation crust with a thickness of ~68 km, far above the observed average of 34-43 km based on lunar gravity. The volume of plagioclase formed during crystallization is significantly less in water-bearing experiments. Using the relationship between magma water content and the resulting crustal thickness in the experiments, and considering uncertainties in initial lunar magma ocean depth, we estimate that the Moon may have contained at least 270 to 1,650 ppm water at the time of magma ocean crystallization, suggesting the Earth-Moon system was water-rich from the start.

  5. Can a fractionally crystallized magma ocean explain the thermo-chemical evolution of Mars?

    Plesa, A -C; Breuer, D


    The impact heat accumulated during the late stage of planetary accretion can melt a significant part or even the entire mantle of a terrestrial body, giving rise to a global magma ocean. [...] Assuming fractional crystallization of the magma ocean, dense cumulates are produced close to the surface, largely due to iron enrichment in the evolving magma ocean liquid (Elkins-Tanton et al., 2003). A gravitationally unstable mantle thus forms, which is prone to overturn. We investigate the cumulate overturn and its influence on the thermal evolution of Mars using mantle convection simulations in 2D cylindrical geometry. We present a suite of simulations using different initial conditions and a strongly temperature-dependent viscosity. We assume that all radiogenic heat sources have been enriched during the freezing-phase of the magma ocean in the uppermost 50 km and that the initial steam-atmosphere created by the degassing of the freezing magma ocean was rapidly lost, implying that the surface temperature is set t...

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

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


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

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

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


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

  8. Thermal evolution of an early magma ocean in interaction with the atmosphere: conditions for the condensation of a water ocean

    Lebrun T.


    Full Text Available The thermal evolution of magma oceans produced by collision with giant impactors late in accretion is xpected to depend on the composition and structure of the atmosphere through the greenhouse effect of CO2 and H2O released from the magma during its crystallization. We developed a 1D parameterized convection model of a magma ocean coupled with a 1D radiative convective model of the atmosphere. We conducted a parametric study and described the influences of some important parameters such as the Sun-planet distance. Our results suggest that a steam atmosphere delays the end of the magma ocean phase by typically 1 Myr. Water vapor condenses to an ocean after 0.1 Myr, 1.5 Myr and 10 Myr for, respectively, Mars, Earth and Venus. This time would be virtually infinite for an Earth-sized planet located at less than 0.66 AU from the Sun. So there are conditions such as no water ocean is formed on Venus. Moreover, for Mars and Earth, water ocean formation time scales are shorter than typical time gaps between major impacts. This implies that successive water oceans may have developed during accretion, making easier the loss of their atmospheres by impact erosion.

  9. Experimental Simulations of Lunar Magma Ocean Crystallization: The Plot (But Not the Crust) Thickens

    Draper, D. S.; Rapp, J. F.; Elardo, S. M.; Shearer, C. K., Jr.; Neal, C. R.


    Numerical models of differentiation of a global-scale lunar magma ocean (LMO) have raised as many questions as they have answered. Recent orbital missions and sample studies have provided new context for a large range of lithologies, from the comparatively magnesian "purest anorthosite" reported by to Si-rich domes and spinel-rich clasts with widespread areal distributions. In addition, the GRAIL mission provided strong constraints on lunar crustal density and average thickness. Can this increasingly complex geology be accounted for via the formation and evolution of the LMO? We have in recent years been conducting extensive sets of petrologic experiments designed to fully simulate LMO crystallization, which had not been attempted previously. Here we review the key results from these experiments, which show that LMO differentiation is more complex than initial models suggested. Several important features expected from LMO crystallization models have yet to be reproduced experimentally; combined modelling and experimental work by our group is ongoing.

  10. Asymmetric shock heating and the terrestrial magma ocean origin of the Moon.

    Karato, Shun-ichiro


    One of the difficulties of the current giant impact model for the origin of the Moon is to explain the marked similarity in the isotopic compositions and the substantial differences in the major element chemistry. Physics of shock heating is analyzed to show that the degree of heating is asymmetric between the impactor and the target, if the target (the proto-Earth) had a magma-ocean but the impactor did not. The magma ocean is heated much more than the solid impactor and the vapor-rich jets come mainly from the magma-ocean from which the Moon might have been formed. In this scenario, the similarity and differences in the composition between the Moon and Earth would be explained as a natural consequence of a collision in the later stage of planetary formation. Including the asymmetry in shock heating is the first step toward explaining the chemical composition of the Moon.

  11. Phase equilibria and trace element partitioning in a magma ocean to 260 kilobars

    Herzberg, Claude


    A magma ocean can solidify in a way that is intermediate between perfect equilibrium and perfect fractional crystallization. In order to model quantitatively any fractional crystallization scenario, it is necessary to understand the geochemical characteristics of the phases that crystallize from a magma ocean, and how they vary with pressure. The crystallizing phase is called the liquidus phase, and their identities were determined by numerous experiments utilizing the multianvil apparatus. For chondritic compositions the liquidus phases are as follows: olivine at 1 atmosphere to 100 kilobars; garnet from 100 to about 260 kilobars; silicate perovskite from 260 kilobars to possibly the core-mantle boundary in the Earth.

  12. Deep intrusions, lateral magma transport and related uplift at ocean island volcanoes

    Klügel, Andreas; Longpré, Marc-Antoine; García-Cañada, Laura; Stix, John


    Oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions. Dykes and other intrusive bodies within volcanic edifices are comparatively well studied, but intrusive processes deep beneath the volcanoes remain elusive. Although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift, this has rarely been demonstrated by real-time monitoring. Here we use geophysical and petrological data from El Hierro, Canary Islands, to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth. Seismicity and ground deformation associated with a submarine eruption in 2011-2012 reveal deep subhorizontal intrusive sheets (sills), which have caused island-scale uplift of tens of centimetres. The pre-eruptive intrusions migrated 15-20 km laterally within the lower oceanic crust, opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface. During six post-eruptive episodes between 2012 and 2014, further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally, resulting in magma accumulation exceeding that of the pre-eruptive phase. A comparison of geobarometric data for the 2011-2012 El Hierro eruption with data for other Atlantic intraplate volcanoes shows similar bimodal pressure distributions, suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport. These processes add significant material to the oceanic crust, cause uplift, and are thus fundamentally important for the growth and evolution of volcanic islands. We suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution, and is a consequence of increasing size and complexity of the mantle reservoir system, and potentially

  13. Changing depths of magma fractionation and stagnation during the evolution of an oceanic island volcano: La Palma (Canary Islands)

    Galipp, Karsten; Klügel, Andreas; Hansteen, Thor H.


    La Palma (Canary Islands) represents an oceanic island volcano with an active rift zone, inferred to have formed during the last 800 ka following southward growth of the former radial-symmetrical stratovolcano Taburiente. We carried out clinopyroxene-melt thermobarometry and microthermometry of fluid inclusions to reconstruct the evolution of the magma plumbing systems over time and to understand the genetic relationship between Taburiente and the presently active Cumbre Vieja rift zone. Clinopyroxene-melt equilibria of phenocryst rims and glassy groundmass indicate pressures of 0.60-1.04 GPa (˜19-34 km depth) for Taburiente, 0.47-1.17 GPa (16-40 km) for the former Cumbre Nueva rift arm of Taburiente, and 0.50-0.78 GPa (16-26 km) for Bejenado volcano that formed after collapse of the Cumbre Nueva rift. These pressures are interpreted to reflect depths of magma storage and major crystal fractionation. CO 2-dominated fluid inclusions hosted by clinopyroxenes and olivines indicate pressures of formation or re-equilibration within an overall range of 0.25-0.61 GPa (˜8-19 km depth). Respective frequency maxima are at 0.41-0.50 GPa for Taburiente dunite xenoliths, 0.26-0.43 GPa for Cumbre Nueva ankaramites, and 0.26-0.32 GPa for Bejenado cumulate xenoliths. These pressures are interpreted to reflect levels of temporary magma stagnation during ascent. Our data show that the magma pathways during all volcanic phases including the presently active Cumbre Vieja rift [Klügel, A., Hansteen, T.H., Galipp, K., 2005. Magma storage and underplating beneath Cumbre Vieja volcano, La Palma (Canary Islands). Earth and Planetary Science Letters 236, 211-226] are characterized by two distinct storage levels: a system of prolonged storage within the upper mantle, and a system of short-term stagnation within the lower crust or near to the Moho. Both the mantle and crustal storage systems show a migration to shallower levels from 1.0 Ma to present, probably as a result of changing

  14. Evidence for multiple magma ocean outgassing and atmospheric loss episodes from mantle noble gases

    Tucker, Jonathan M


    The energy associated with giant impacts is large enough to generate global magma oceans during Earth's accretion. However, geochemical evidence requiring a terrestrial magma ocean is scarce. Here we present evidence for at least two separate magma ocean outgassing episodes on Earth based on the ratio of primordial 3He to 22Ne in the present-day mantle. We demonstrate that the depleted mantle 3He/22Ne ratio is at least 10 while a more primitive mantle reservoir has a 3He/22Ne ratio of 2.3 to 3. The 3He/22Ne ratios of the mantle reservoirs are higher than possible sources of terrestrial volatiles, including the solar nebula ratio of 1.5. Therefore, a planetary process must have raised the mantle's 3He/22Ne ratio. We show that long-term plate tectonic cycling is incapable of raising the mantle 3He/22Ne ratio and may even lower it. However, ingassing of a gravitationally accreted nebular atmosphere into a magma ocean on the proto-Earth explains the 3He/22Ne and 20Ne/22Ne ratios of the primitive mantle reservoir....

  15. A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

    Hamza, V M; Alexandrino, C H


    A simple magma accretion model of the oceanic lithosphere is proposed and its implications for understanding the thermal field of oceanic lithosphere examined. The new model (designated VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. Heat flow and bathymetry variations calculated on the basis of the VBA model provide vastly improved fits to respective observational datasets. The improved fits have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation in stable ocean crust. The results suggest that estimates of global heat loss need to be downsized by at least 25%.

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

    Maas, C.; Hansen, U.


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

  17. Can Fractional Crystallization of a Lunar Magma Ocean Produce the Lunar Crust?

    Rapp, Jennifer F.; Draper, David S.


    New techniques enable the study of Apollo samples and lunar meteorites in unprecedented detail, and recent orbital spectral data reveal more about the lunar farside than ever before, raising new questions about the supposed simplicity of lunar geology. Nevertheless, crystallization of a global-scale magma ocean remains the best model to account for known lunar lithologies. Crystallization of a lunar magma ocean (LMO) is modeled to proceed by two end-member processes - fractional crystallization from (mostly) the bottom up, or initial equilibrium crystallization as the magma is vigorously convecting and crystals remain entrained, followed by crystal settling and a final period of fractional crystallization [1]. Physical models of magma viscosity and convection at this scale suggest that both processes are possible. We have been carrying out high-fidelity experimental simulations of LMO crystallization using two bulk compositions that can be regarded as end-members in the likely relevant range: Taylor Whole Moon (TWM) [2] and Lunar Primitive Upper Mantle (LPUM) [3]. TWM is enriched in refractory elements by 1.5 times relative to Earth, whereas LPUM is similar to the terrestrial primitive upper mantle, with adjustments made for the depletion of volatile alkalis observed on the Moon. Here we extend our earlier equilibrium-crystallization experiments [4] with runs simulating full fractional crystallization

  18. Rapid timescales for magma ocean crystallization on the howardite-eucrite-diogenite parent body

    Schiller, M.; Paton, C.; Bizzarro, Martin


    Asteroid 4 Vesta has long been postulated as the source for the howardite-eucrite-diogenite (HED) achondrite meteorites. Here we show that Al-free diogenite meteorites record variability in the mass-independent abundance of Mg ( Mg*) that is correlated with their mineral chemistry. This suggests...... occurred within the following 2-3Myr. Thermal models predict that such rapid cooling and magma ocean crystallization could only occur on small asteroids (...

  19. A crystallizing dense magma ocean at the base of the Earth's mantle.

    Labrosse, S; Hernlund, J W; Coltice, N


    The distribution of geochemical species in the Earth's interior is largely controlled by fractional melting and crystallization processes that are intimately linked to the thermal state and evolution of the mantle. The existence of patches of dense partial melt at the base of the Earth's mantle, together with estimates of melting temperatures for deep mantle phases and the amount of cooling of the underlying core required to maintain a geodynamo throughout much of the Earth's history, suggest that more extensive deep melting occurred in the past. Here we show that a stable layer of dense melt formed at the base of the mantle early in the Earth's history would have undergone slow fractional crystallization, and would be an ideal candidate for an unsampled geochemical reservoir hosting a variety of incompatible species (most notably the missing budget of heat-producing elements) for an initial basal magma ocean thickness of about 1,000 km. Differences in 142Nd/144Nd ratios between chondrites and terrestrial rocks can be explained by fractional crystallization with a decay timescale of the order of 1 Gyr. These combined constraints yield thermal evolution models in which radiogenic heat production and latent heat exchange prevent early cooling of the core and possibly delay the onset of the geodynamo to 3.4-4 Gyr ago.

  20. Differentiation of Asteroid 4 Vesta: Core Formation by Iron Rain in a Silicate Magma Ocean

    Kiefer, Walter S.; Mittlefehldt, David W.


    Geochemical observations of the eucrite and diogenite meteorites, together with observations made by NASA's Dawn spacecraft while orbiting asteroid 4 Vesta, suggest that Vesta resembles H chondrites in bulk chemical composition, possible with about 25 percent of a CM-chondrite like composition added in. For this model, the core is 15 percent by mass (or 8 percent by volume) of the asteroid, with a composition of 73.7 percent by weight Fe, 16.0 percent by weight S, and 10.3 percent by weight Ni. The abundances of moderately siderophile elements (Ni, Co, Mo, W, and P) in eucrites require that essentially all of the metallic phase in Vesta segregated to form a core prior to eucrite solidification. The combination of the melting phase relationships for the silicate and metal phases, together with the moderately siderophile element concentrations together require that complete melting of the metal phase occurred (temperature is greater than1350 degrees Centigrade), along with substantial (greater than 40 percent) melting of the silicate material. Thus, core formation on Vesta occurs as iron rain sinking through a silicate magma ocean.

  1. Coupled 142Nd-143Nd evidence for a protracted magma ocean in Mars.

    Debaille, V; Brandon, A D; Yin, Q Z; Jacobsen, B


    Resolving early silicate differentiation timescales is crucial for understanding the chemical evolution and thermal histories of terrestrial planets. Planetary-scale magma oceans are thought to have formed during early stages of differentiation, but the longevity of such magma oceans is poorly constrained. In Mars, the absence of vigorous convection and plate tectonics has limited the scale of compositional mixing within its interior, thus preserving the early stages of planetary differentiation. The SNC (Shergotty-Nakhla-Chassigny) meteorites from Mars retain 'memory' of these events. Here we apply the short-lived 146Sm-142Nd and the long-lived 147Sm-143Nd chronometers to a suite of shergottites to unravel the history of early silicate differentiation in Mars. Our data are best explained by progressive crystallization of a magma ocean with a duration of approximately 100 million years after core formation. This prolonged solidification requires the existence of a primitive thick atmosphere on Mars that reduces the cooling rate of the interior.

  2. From magma-poor Ocean Continent Transitions to steady state oceanic spreading: the balance between tectonic and magmatic processes

    Gillard, Morgane; Manatschal, Gianreto; Autin, Julia; Decarlis, Alessandro; Sauter, Daniel


    The evolution of magma-poor rifted margins is linked to the development of a transition zone whose basement is neither clearly continental nor oceanic. The development of this Ocean-Continent Transition (OCT) is generally associated to the exhumation of serpentinized mantle along one or several detachment faults. That model is supported by numerous observations (IODP wells, dredges, fossil margins) and by numerical modelling. However, if the initiation of detachment faults in a magma-poor setting tends to be better understood by numerous studies in various area, the transition with the first steady state oceanic crust and the associated processes remain enigmatic and poorly studied. Indeed, this latest stage of evolution appears to be extremely gradual and involves strong interactions between tectonic processes and magmatism. Contrary to the proximal part of the exhumed domain where we can observe magmatic activity linked to the exhumation process (exhumation of gabbros, small amount of basalts above the exhumed mantle), in the most distal part the magmatic system appears to be independent and more active. In particular, we can observe large amounts of extrusive material above a previously exhumed and faulted basement (e.g. Alps, Australia-Antarctica margins). It seems that some faults can play the role of feeder systems for the magma in this area. Magmatic underplating is also important, as suggested by basement uplift and anomalously thick crust (e.g. East Indian margin). It results that the transition with the first steady state oceanic crust is marked by the presence of a hybrid basement, composed by exhumed mantle and magmatic material, whose formation is linked to several tectonic and magmatic events. One could argue that this basement is not clearly different from an oceanic basement. However, we consider that true, steady state oceanic crust only exists, if the entire rock association forming the crust is created during a single event, at a localized

  3. Formation of anorthosite on the Moon through magma ocean fractional crystallization

    Tatsuyuki Arai


    Full Text Available Lunar anorthosite is a major rock of the lunar highlands, which formed as a result of plagioclase-floatation in the lunar magma ocean (LMO. Constraints on the sufficient conditions that resulted in the formation of a thick pure anorthosite (mode of plagioclase >95 vol.% is a key to reveal the early magmatic evolution of the terrestrial planets. To form the pure lunar anorthosite, plagioclase should have separated from the magma ocean with low crystal fraction. Crystal networks of plagioclase and mafic minerals develop when the crystal fraction in the magma (φ is higher than ca. 40–60 vol.%, which inhibit the formation of pure anorthosite. In contrast, when φ is small, the magma ocean is highly turbulent, and plagioclase is likely to become entrained in the turbulent magma rather than separated from the melt. To determine the necessary conditions in which anorthosite forms from the LMO, this study adopted the energy criterion formulated by Solomatov. The composition of melt, temperature, and pressure when plagioclase crystallizes are constrained by using MELTS/pMELTS to calculate the density and viscosity of the melt. When plagioclase starts to crystallize, the Mg# of melt becomes 0.59 at 1291 °C. The density of the melt is smaller than that of plagioclase for P > 2.1 kbar (ca. 50 km deep, and the critical diameter of plagioclase to separate from the melt becomes larger than the typical crystal diameter of plagioclase (1.8–3 cm. This suggests that plagioclase is likely entrained in the LMO just after the plagioclase starts to crystallize. When the Mg# of melt becomes 0.54 at 1263 °C, the density of melt becomes larger than that of plagioclase even for 0 kbar. When the Mg# of melt decreases down to 0.46 at 1218 °C, the critical diameter of plagioclase to separate from the melt becomes 1.5–2.5 cm, which is nearly equal to the typical plagioclase of the lunar anorthosite. This suggests that plagioclase could separate from the

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

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


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

  5. Active convection and magma dynamics at mid-ocean ridges

    Katz, Richard


    The role of buoyancy-driven, "active" upwelling beneath mid-ocean ridges has been long debated [1,2,3], with the naysayers holding sway in recent years. Recent work on tomographic imaging of the sub-ridge mantle has revealed patterns in velocity variation that seem inconsistent with what we expect of passive upwelling and melting [4]. The irregular distribution, asymmetry, and off-axis locations of slow regions in tomographic results are suggestive of time-dependent convective flow. Using 2D numerical simulations of internally consistent mantle and magmatic flow plus melting/freezing [5,6], I investigate the parametric subspace in which active convection is expected to occur. For low mantle viscosities, convection can break the symmetry of corner flow. This may help to explain the asymmetric distribution of shear-wave velocity beneath the MELT region of the East Pacific Rise. References: [1] Rabinowicz, et al., EPSL, 1984; [2] Buck & Su, GRL, 1989; [3] Scott & Stevenson, JGR, 1989; [4] Toomey et al., Nature, 2007; [5] McKenzie, J.Pet., 1984; [6] Katz, J.Pet., 2008;

  6. Tidal dissipation in the lunar magma ocean and its effect on the early evolution of the Earth-Moon system

    Chen, Erinna M. A.; Nimmo, Francis


    The present-day inclination of the Moon reflects the entire history of its thermal and orbital evolution. The Moon likely possessed a global magma ocean following the Moon-forming impact. In this work, we develop a coupled thermal-orbital evolution model that takes into account obliquity tidal heating in the lunar magma ocean. Dissipation in the magma ocean is so effective that it results in rapid inclination damping at semi-major axes beyond about 20 Earth radii (RE), because of the increase in lunar obliquity as the so-called Cassini state transition at ≈30 RE is approached. There is thus a "speed limit" on how fast the Moon can evolve outwards while maintaining its inclination: if it reaches 20 RE before the magma ocean solidifies, any early lunar inclination cannot be maintained. We find that for magma ocean lifetimes of 10 Myr or more, the Earth's tidal quality factor Q must have been >300 to maintain primordial inclination, implying an early Earth 1-2 orders of magnitude less dissipative than at present. On the other hand, if tidal dissipation on the early Earth was stronger, our model implies rapid damping of the lunar inclination and requires subsequent late excitation of the lunar orbit after the crystallization of the lunar magma ocean.

  7. Effect of planetary rotation on the differentiation of a terrestrial magma ocean in spherical geometry

    Hansen, Ulrich; Maas, Christian


    About 4.5 billion years ago the early Earth experienced several giant impacts that lead to one or more deep terrestrial magma oceans of global extent. The crystallization of these vigorously convecting magma oceans is of key importance for the chemical structure of the Earth, the subsequent mantle evolution as well as for the initial conditions for the onset of plate tectonics. Due to the fast planetary rotation of the early Earth and the small magma viscosity, rotation probably had a profound effect on early differentiation processes and could for example influence the presence and distribution of chemical heterogeneities in the Earth's mantle [e.g. Matyska et al., 1994, Garnero and McNamara, 2008]. Previous work in Cartesian geometry revealed a strong influence of rotation as well as of latitude on the crystal settling in a terrestrial magma ocean [Maas and Hansen, 2015]. Based on the preceding study we developed a spherical shell model that allows to study crystal settling in-between pole and equator as well as the migration of crystals between these regions. Further we included centrifugal forces on the crystals, which significantly affect the lateral and radial distribution of the crystals. Depending on the strength of rotation the particles accumulate at mid-latitude or at the equator. At high rotation rates the dynamics of fluid and particles are dominated by jet-like motions in longitudinal direction that have different directions on northern and southern hemisphere. All in all the first numerical experiments in spherical geometry agree with Maas and Hansen [2015] that the crystal distribution crucially depends on latitude, rotational strength and crystal density. References E. J. Garnero and A. K. McNamara. Structure and dynamics of earth's lower mantle. Science, 320(5876):626-628, 2008. C. Maas and U. Hansen. Eff ects of earth's rotation on the early di erentiation of a terrestrial magma ocean. Journal of Geophysical Research: Solid Earth, 120

  8. Experimental constraints on the solidification of a nominally dry lunar magma ocean

    Lin, Yanhao; Tronche, Elodie J.; Steenstra, Edgar S.; van Westrenen, Wim


    The lunar magma ocean (LMO) concept has been used extensively for lunar evolution models for decades, but to date the full cooling and crystallization path of the LMO has not been studied experimentally. Here we present results of a high-pressure, high-temperature experimental study of the mineralogical and geochemical evolution accompanying the full solidification of a nominally dry LMO. Experiments used a bulk composition based on geophysical data, and assumed an initial LMO depth of 700 km. The effect of pressure within a deep magma ocean on solidification at different levels in the ocean was explicitly taken into account, by performing experiments at multiple pressures and constant temperature during each solidification step. Results show formation of a deep harzburgite (olivine + low-Ca pyroxene) layer in the first ∼50% of equilibrium crystallization. The crystallising mineral assemblage does not change until plagioclase and clinopyroxene appear at 68 PCS (per cent solid by volume), while low-Ca pyroxene stops forming. Olivine disappears at 83 PCS, and ilmenite and β-quartz start crystallizing at 91 and 96 PCS, respectively. At 99 PCS, we observe an extremely iron-rich (26.5 wt.% FeO) residual LMO liquid. Our results differ substantially from the oft-cited LMO solidification study of Snyder et al. (1992), which was based on a limited number of experiments at a single pressure. Differences include the mineralogy of the deepest sections of the solidified LMO (harzburgitic instead of dunitic), the formation of SiO2 in the lunar interior, and the development of extreme iron enrichment in the last remaining dregs of the LMO. Our findings shed new light on several aspects of lunar petrology, including the formation of felsic and iron-rich magmas in the Moon. Finally, based on our experiments the lunar crust, consisting of the light minerals plagioclase and quartz, would reach a thickness of ∼67.5 km. This is far greater than crustal thickness estimates from

  9. Combined effect of permeability and crystallization on the explosive eruption of basaltic magma

    Moitra, P.; Gonnermann, H. M.; Houghton, B. F.; Crozier, J.


    Plinian eruptions are the most dangerous style of eruptive activity of basaltic magma. In this study, we focus on the two best studied Plinian eruptions of basaltic magma at Mt. Tarawera, New Zealand (1886 CE) and Mt. Etna, Italy (122 BCE). We measured and analyzed the porosity-permeability relationships of the pyroclasts from both eruptions. We then used numerical modeling to assess the relative importance of two competing processes during eruptive magma ascent, which are the syneruptive crystallization that increases viscosity, potentially increasing bubble overpressure, and the open-system degassing of the permeable magma that allows the pressurized gas to escape, potentially reducing bubble overpressure. We find that the onset of crystallization is likely to have occurred prior to the onset of magma percolation. The orders of magnitude increase in magma viscosity due to the nucleation and growth of microlites had the combined effect of rapidly increasing the decompression rate, due to viscous pressure losses associated with magma flow within the volcanic conduit, and decreasing the rates of bubble growth, thus building up large overpressures inside bubbles. Although measured permeabilities of the studied pyroclasts are 1-2 orders of magnitude higher than their silicic counterpart, our model results show that crystallization and subsequent increase in viscosity are likely to surpass the effect of open-system gas loss, thus increasing bubble overpressure, required for explosive magma fragmentation.

  10. Thermometry of the magma ocean: Controls on the metal-silicate partitioning of gold

    Bennett, N. R.; Brenan, J. M.; Fei, Y.


    We have performed experiments to investigate the solubility and metal-silicate partitioning of gold as a function of metal sulphur content (XS), silicate melt polymerization (NBO/T) and pressure (P). These experiments show that Au becomes less siderophile both with increasing pressure and as the metal phase becomes more sulphur-rich. For the studied range of compositions, melt polymerization has no effect on the solubility of Au. The reduction in the siderophile tendency of gold with increasing metal sulphur content is greater than expected on the basis of activity-composition relationships in the metal phase. This suggests a significant role for complexing between Au and S in the silicate melt. Our new experimental results are combined with literature data to yield a parameterisation for the exchange coefficient of Au (KdAuMet/Sil) as a function of P, T and XS: Using this relationship, alongside similar parameterisations for Ni and Co selected from the literature, we performed continuous accretion models to delineate regions of parameter space in which Au and moderately siderophile element (MSE) abundances in the primitive upper mantle (PUM) could be reproduced. These models suggest that for metal-silicate equilibrium at very high pressures, Au will be overabundant in the PUM if equilibrium also occurs at extreme temperatures. Instead, most successful models are found when equilibrium occurs at high pressure but sub-liquidus temperatures. This result is in keeping with the physical conditions expected for a scenario where core-forming metal ponds and equilibrates at the rheological base of a magma ocean (e.g. Wade and Wood, 2005).

  11. Chemical consequences of perovskite fractionation from an ultramafic liquid with application to the evolving composition of a basal magma ocean

    Jackson, Colin; Ziegler, Leah; Zhang, Hongluo; Jackson, Matt; Stegman, Dave


    Heterogeneity in the present day mantle is evidenced by seismology and geochemistry, with significant heterogeneity apparent in the lowermost mantle, just above the core-mantle boundary. Origins of this structure are hypothesized to be related to the initial solidification of a deep magma ocean. In particular, in a scenario where solidification begins mid-mantle, a resulting basal magma ocean could be long-lived and geochemically isolated, with the final crystallization products accumulating at the core mantle boundary. The geochemical makeup of the basal magma ocean products depends on fractionation of elements (major, minor, trace) by Mg-perovskite (MgPv), the dominant lower mantle mineral. Here we compile a comprehensive database of elemental partitioning by MgPv from published experimental studies and use it to generate a set of parameterized partition coefficients (f[melt composition]). Partition coefficients are then applied to a crystallization model. Uncertainty bounds are calculated from monte carlo methods. Partitioning of minor and trace elements (i.e. Fe, REE, HFSE, U+Th) depend significantly on melt composition, particularly Al and Ca content, due to charge coupled substitution and site size effects. After accounting for these effects through our parameterized partition coefficients, we present the resulting evolution of the melt and solid (MgPv) phases during magma ocean crystallization. Using a simple model of fractional crystallization, the chemical evolution is calculated until the liquid becomes saturated in a second solid phase (likely ferropericlase). The co-saturation point is uncertain but is estimated to be at ~50% crystallization of the magma ocean. During crystallization of MgPv, the melt phase becomes enriched in Fe, leading to compositionally denser products in the later stages of crystallization. The enrichment in Fe, however, is less extreme than predicted by recent experimental work (e.g. Nomura et al., 2011), bringing into question

  12. Investigating Compositional Links Between Arc Magmas And The Subducted Altered Oceanic Crust

    Straub, S. M.


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

  13. Post-magma ocean mixing of reservoirs inside the angrite parent body

    Golabek, Gregor; Bourdon, Bernard; Rozel, Antoine; Gerya, Taras


    Angrites are a rare group of mafic volcanic-plutonic meteorites with only 28 samples listed by the Meteoritical Society that formed within the first 10 Myr after the formation of the solar system. Studies of siderophile elements showed that core formation in the angrite parent body occurred at super liquidus temperatures. Despite experiencing an early magma ocean, Hf-W data suggest the presence of at least two distinct mantle reservoirs. A possible explanation for the isotopic variations (coupled with elemental variations) could be delivery of new planetesimal material during the post-magma ocean stage and imperfect mixing of the resulting mantle reservoirs. To test this theory we use the 2D/3D finite difference marker-in-cell code family I2ELVIS/I3ELVIS to study the mixing of reservoirs in bodies with radii ranging from 50 to 300 km. Numerical results show that mixing in 3D models is more efficient than in their 2D counterparts. Based on the numerical results we derive a semi-analytical scaling law describing the mixing efficiency. Using the available constraints on formation time of the angrites, the activity of an early dynamo and the modelled thermal evolution, we put constraints on the size of the angrite parent body.

  14. Moonage Daydream: Reassessing the Simple Model for Lunar Magma Ocean Crystallization

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


    Details of the differentiation of a global-scale lunar magma ocean (LMO) remain enigmatic, as the Moon is not simply composed of highlands anorthosite and a suite of mare basalts as inferred from early studies. Results from recent orbital missions, and the increasingly detailed study of lunar samples, have revealed a much larger range of lithologies, from relatively MgO-rich and "purest anorthosite" discovered on the lunar far side by the M3 instrument on Chandraayan-1 to more exotic lithologies such as Si-rich domes and spinel-rich clasts distributed globally. To understand this increasingly complex geology, we must understand the initial formation and evolution of the LMO, and the composition of the cumulates this differentiation could have produced. Several attempts at modelling such a crystallization sequence have been made, and have raised as many questions as they have answered. We present results from our ongoing experimental simulations of magma ocean crystallization, investigating two end-member bulk compositions (TWM and LPUM) under fully fractional crystallization conditions. These simulations represent melting of the entire silicate portion of the Moon, as an end-member starting point from which to begin assessing the evolution of the lunar interior and formation of the lunar crust.

  15. A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

    Valiya M. Hamza


    Full Text Available A magma accretion model of oceanic lithosphere is proposed and its implications for understanding its thermal field examined. The new model (designated Variable Basal Accretion—VBA assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer is considered a space dependent variable. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling models. Another noteworthy feature of the new model is its ability to account for the main features in the thermal behavior of oceanic lithosphere. The improved fits to bathymetry have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation. Also, use of VBA model does not lead to artificial discontinuities in the temperature field of the lithosphere, as is the case with GDH (Global Depth Heat Flow reference models. The results suggest that estimates of global heat loss need to be downsized by at least 25%.

  16. Emergence of two types of terrestrial planet on solidification of magma ocean.

    Hamano, Keiko; Abe, Yutaka; Genda, Hidenori


    Understanding the origins of the diversity in terrestrial planets is a fundamental goal in Earth and planetary sciences. In the Solar System, Venus has a similar size and bulk composition to those of Earth, but it lacks water. Because a richer variety of exoplanets is expected to be discovered, prediction of their atmospheres and surface environments requires a general framework for planetary evolution. Here we show that terrestrial planets can be divided into two distinct types on the basis of their evolutionary history during solidification from the initially hot molten state expected from the standard formation model. Even if, apart from their orbits, they were identical just after formation, the solidified planets can have different characteristics. A type I planet, which is formed beyond a certain critical distance from the host star, solidifies within several million years. If the planet acquires water during formation, most of this water is retained and forms the earliest oceans. In contrast, on a type II planet, which is formed inside the critical distance, a magma ocean can be sustained for longer, even with a larger initial amount of water. Its duration could be as long as 100 million years if the planet is formed together with a mass of water comparable to the total inventory of the modern Earth. Hydrodynamic escape desiccates type II planets during the slow solidification process. Although Earth is categorized as type I, it is not clear which type Venus is because its orbital distance is close to the critical distance. However, because the dryness of the surface and mantle predicted for type II planets is consistent with the characteristics of Venus, it may be representative of type II planets. Also, future observations may have a chance to detect not only terrestrial exoplanets covered with water ocean but also those covered with magma ocean around a young star.

  17. The oxygen isotope composition of earth's oldest rocks and evidence of a terrestrial magma ocean

    Rumble, D.; Bowring, S.; Iizuka, T.;


    Analysis of Hadean and Archean rocks for O-16-O-17-O-18 isotopes demonstrates that the Terrestrial Mass Fractionation Line of oxygen isotopes has had the same slope and intercept for at least the past 4.0 and probably for as long as 4.2Ga. The homogenization of oxygen isotopes required to produce...... such long-lived consistency was most easily established by mixing in a terrestrial magma ocean. The measured identical oxygen isotope mass fractionation lines for Earth and Moon suggest that oxygen isotope reservoirs of both bodies were homogenized at the same time during a giant moon-forming impact....... But other sources of heat for global melting cannot be excluded such as bolide impacts during early accretion of proto-Earth, the decay of short-lived radioactive isotopes, or the energy released during segregation of core from mantle....

  18. Crystallization and cooling conditions for diogenite formation in the turbulent magma ocean of asteroid 4 Vesta

    Kawabata, Yusuke; Nagahara, Hiroko


    Despite its small size, the asteroid 4 Vesta has been completely differentiated to core and mantle. Its composition is similar to howardite-eucrite-diogenite (HED) meteorites of which the detailed petrology is known. Therefore, 4 Vesta is a good target for understanding the differentiation of terrestrial planets. A new differentiation model for crust formation has been developed by taking magma ocean fluid dynamics, chemical equilibrium, the presence of 26Al, and cooling into consideration with a special focus on crystal separation. The role of crystal size, thickness of the conductive lid, and fO2 are evaluated as parameters. The results show that large crystals of at least 1 cm settled and formed a kilometer-thick cumulate layer of orthopyroxene with Mg # of 0.70-0.90 in ∼20 thousand years, which almost agrees with the Mg # of diogenites. Smaller grain sizes formed thinner layers.

  19. Turbulent metal-silicate mixing, fragmentation, and equilibration in magma oceans

    Deguen, Renaud; Olson, Peter


    Much of the Earth was built by high-energy impacts of planetesimals and embryos, many of these impactors already differentiated, with metallic cores of their own. Geochemical data provide critical information on the timing of accretion and the prevailing physical conditions, but their interpretation depends critically on the degree of metal-silicate chemical equilibration during core-mantle differentiation, which is poorly constrained. Efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal-silicate mass transfer. Here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment, with fragmentation into droplets eventually resulting from the entrainment process. In our experiments, fragmentation of the dense fluid occurs after falling a distance equal to 3-4 times its initial diameter, at which point a sizable volu...

  20. Interpretation of Ferroan Anorthosite Ages and Implications for the Lunar Magma Ocean

    Neal, C. R.; Draper, D. S.


    Ferroan Anorthosites (FANs) are considered to have purportedly crystallized directly from the lunar magma ocean (LMO) as a flotation crust. LMO modeling suggests that such anorthosites started to form only after greater than 70 percent of the LMO had crystallized. Recent age dates for FANs have questioned this hypothesis as they span too large of an age range. This means a younger age for the Moon-forming giant impact or the LMO hypothesis is flawed. However, FANs are notoriously difficult to age-date using the isochron method. We have proposed a mechanism for testing the LMO hypothesis through using plagioclase trace element abundances to calculate equilibrium liquids and compare them with LMO crystallization models. We now examine the petrography of the samples that have Sm-Nd (Samarium-Neodymium) age dates (Rb-Sr (Rubidium-Strontium) isotopic systematics may have been disturbed) and propose a relative way to age date FANs.

  1. Geochemical investigation of Gabbroic Xenoliths from Hualalai Volcano: Implications for lower oceanic crust accretion and Hualalai Volcano magma storage system

    Gao, Ruohan; Lassiter, John C.; Barnes, Jaime D.; Clague, David A.; Bohrson, Wendy A.


    The patterns of axial hydrothermal circulation at mid-ocean ridges both affect and are influenced by the styles of magma plumbing. Therefore, the intensity and distribution of hydrothermal alteration in the lower oceanic crust (LOC) can provide constraints on LOC accretion models (e.g., "gabbro glacier" vs. "multiple sills"). Gabbroic xenoliths from Hualalai Volcano, Hawaii include rare fragments of in situ Pacific lower oceanic crust. Oxygen and strontium isotope compositions of 16 LOC-derived Hualalai gabbros are primarily within the range of fresh MORB, indicating minimal hydrothermal alteration of the in situ Pacific LOC, in contrast to pervasive alteration recorded in LOC xenoliths from the Canary Islands. This difference may reflect less hydrothermal alteration of LOC formed at fast ridges than at slow ridges. Mid-ocean ridge magmas from slow ridges also pond on average at greater and more variable depths and undergo less homogenization than those from fast ridges. These features are consistent with LOC accretion resembling the "multiple sills" model at slow ridges. In contrast, shallow magma ponding and limited hydrothermal alteration in LOC at fast ridges are consistent with the presence of a long-lived shallow magma lens, which limits the penetration of hydrothermal circulation into the LOC. Most Hualalai gabbros have geochemical and petrologic characteristics indicating derivation from Hualalai shield-stage and post-shield-stage cumulates. These xenoliths provide information on the evolution of Hawaiian magmas and magma storage systems. MELTS modeling and equilibration temperatures constrain the crystallization pressures of 7 Hualalai shield-stage-related gabbros to be ∼2.5-5 kbar, generally consistent with inferred local LOC depth. Therefore a deep magma reservoir existed within or at the base of the LOC during the shield stage of Hualalai Volcano. Melt-crust interaction between Hawaiian melts and in situ Pacific crust during magma storage partially

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

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


    Experiments establishing the effect of pressure on the Fe3+/ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO2 were performed from 100 kPa to 7 GPa and 1400–1750 °C. Fe3+/ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe3+/ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O’Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe3+ ions of ~5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe2+ ions, from ~5 to ~6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe3+/ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al., 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe3+/ΣFe applicable to high pressure glasses. Consistent with interpretations of the Mössbauer hyperfine parameters, XANES pre-edge peak features in high pressure glasses are owing chiefly to the effects of pressure on the coordination of Fe2+ ions from ~5.5 to ~6, with negligible effects evident for Fe3+ ions. We use the new data to construct a thermodynamic model relating the effects of oxygen fugacity and pressure on Fe3+/ΣFe. We apply this model to calculate variations in oxygen fugacity in isochemical (constant Fe3+/ΣFe) columns of magma representative of magma oceans, in which fO2 is fixed at the base by equilibration with molten Fe. These calculations

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

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


    Experiments establishing the effect of pressure on the Fe3+/ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO2 were performed from 100 kPa to 7 GPa and 1400-1750 °C. Fe3+/ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe3+/ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O'Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe3+ ions of ∼5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe2+ ions, from ∼5 to ∼6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe3+/ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al., 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe3+/ΣFe applicable to high pressure glasses. Consistent with interpretations of the Mössbauer hyperfine parameters, XANES pre-edge peak features in high pressure glasses are owing chiefly to the effects of pressure on the coordination of Fe2+ ions from ∼5.5 to ∼6, with negligible effects evident for Fe3+ ions. We use the new data to construct a thermodynamic model relating the effects of oxygen fugacity and pressure on Fe3+/ΣFe. We apply this model to calculate variations in oxygen fugacity in isochemical (constant Fe3+/ΣFe) columns of magma representative of magma oceans, in which fO2 is fixed at the base by equilibration with molten Fe. These calculations indicate that oxygen fugacities at the surface of shallow magma oceans are more reduced than at depth. For magma oceans in

  4. Magma plumbing system and seismicity of an active mid-ocean ridge volcano

    Schmid, Florian; Schlindwein, Vera; Koulakov, Ivan; Plötz, Aline; Scholz, John-Robert


    At mid-ocean ridges volcanism generally decreases with spreading rate but surprisingly massive volcanic centres occur at the slowest spreading ridges. These volcanoes can host unexpectedly strong earthquakes and vigorous, explosive submarine eruptions. Our understanding of the geodynamic processes forming these volcanic centres is still incomplete due to a lack of geophysical data and the difficulty to capture their rare phases of magmatic activity. We present a local earthquake tomographic image of the magma plumbing system beneath the Segment 8 volcano at the ultraslow-spreading Southwest Indian Ridge. The tomography shows a confined domain of partial melt under the volcano. We infer that from there melt is horizontally transported to a neighbouring ridge segment at 35 km distance where microearthquake swarms and intrusion tremor occur that suggest ongoing magmatic activity. Teleseismic earthquakes around the Segment 8 volcano, prior to our study, indicate that the current magmatic spreading episode may already have lasted over a decade and hence its temporal extent greatly exceeds the frequent short-lived spreading episodes at faster opening mid-ocean ridges.

  5. Magma plumbing system and seismicity of an active mid-ocean ridge volcano.

    Schmid, Florian; Schlindwein, Vera; Koulakov, Ivan; Plötz, Aline; Scholz, John-Robert


    At mid-ocean ridges volcanism generally decreases with spreading rate but surprisingly massive volcanic centres occur at the slowest spreading ridges. These volcanoes can host unexpectedly strong earthquakes and vigorous, explosive submarine eruptions. Our understanding of the geodynamic processes forming these volcanic centres is still incomplete due to a lack of geophysical data and the difficulty to capture their rare phases of magmatic activity. We present a local earthquake tomographic image of the magma plumbing system beneath the Segment 8 volcano at the ultraslow-spreading Southwest Indian Ridge. The tomography shows a confined domain of partial melt under the volcano. We infer that from there melt is horizontally transported to a neighbouring ridge segment at 35 km distance where microearthquake swarms and intrusion tremor occur that suggest ongoing magmatic activity. Teleseismic earthquakes around the Segment 8 volcano, prior to our study, indicate that the current magmatic spreading episode may already have lasted over a decade and hence its temporal extent greatly exceeds the frequent short-lived spreading episodes at faster opening mid-ocean ridges.

  6. Melting curve of the deep mantle applied to properties of early magma ocean and actual core-mantle boundary

    Andrault, Denis; Lo Nigro, Giacomo; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed


    Our planet experienced partial melting early in its history as a consequence of energy release due to accretion. Partial mantle melting could still happen today in the lowermost mantle. Occurrence of melting is primordial for the chemical segregation between the different Earth's reservoirs and for the dynamics of the whole planet. Melting of iron-alloys is relatively easy to achieve, but the silicated mantle happens to be more refractory. We investigated experimentally melting properties of two starting material, forsterite and chondritic-mantle, at pressures ranging from 25 to 140 GPa, using laser-heated diamond anvil cell coupled with synchrotron radiation. We show that partial melting in the lowermost mantle, as suggested by seismology on the basis of the ultra-low velocity zones (ULVZ), requires temperatures above 4200 K at the core-mantle boundary. At low pressures, our curve plots significantly lower than previous reports. Compared to recent estimates of mantle geotherm, while this temperature remains possible if the Earth's core is very hot, it is more likely that ULVZs correspond to high concentration of incompatible elements driven down to the D"-layer by subducting slabs or extracted out from the outer core. When our chondritic melting curve is coupled with recent isentropic temperature profiles for a magma ocean, we obtain a correlation between magma ocean depth and the potential temperature (Tp) at its surface; an ocean depth of 1000 km (equivalent to ~40 GPa) corresponds to Tp=2000 K, which happens to be significantly hotter than the estimated surface temperature of a sustained magma ocean. It emphasizes the importance of a lid at the magma ocean surface at an epoch as early as that of core-mantle segregation.

  7. A test for Io's magma ocean: Modeling tidal dissipation with a partially molten mantle

    Bierson, C. J.; Nimmo, F.


    Magnetic induction measurements and astrometry provide constraints on the internal structure of Io, a volcanically active moon of Jupiter. We model the tidal response of a partially molten Io using an Andrade rheology which is supported by silicate deformation experiments. This model uses material properties similar to the Earth's mantle and includes feedbacks between partial melting, tidal heat production, and melt transport. We are able to satisfy constraints provided by the measured imaginary part of the tidal Love number Im(k2), the inferred depth and melt fraction of a near-surface partially molten layer, and the observed equatorial concentration of volcanic landforms. We predict a value for the real part of the tidal Love number of Re(k2) = 0.09 ± 0.02, much smaller than the value of Re(k2)≈0.5 predicted for an Io with a fluid magma ocean. Future spacecraft observations should be able to measure this value and test which model is correct.

  8. Fast Spreading Mid Ocean Ridge Magma Chamber Processes: New Constraints from Hess Deep

    MacLeod, C. J.; Lissenberg, J. C.; Howard, K. A.; Ildefonse, B.; Morris, A.; JC21 Scientific Party


    Hess Deep, on the northern edge of the Galapagos Microplate, is a rift valley located at the tip of the Cocos Nazca spreading centre. It is actively propagating westwards into young lithosphere formed at the East Pacific Rise (EPR). Previous studies have shown that the centre of Hess Deep, in the vicinity of a horst block termed the intra-rift ridge (IRR), is characterised by outcrops of gabbro and (minor) peridotite that form the most extensive and complete exposure yet known of lower crust and shallow mantle from a fast spreading mid-ocean ridge. In the absence of a total crustal penetration borehole, the tectonic window of Hess Deep provides our best opportunity to study fast-spreading magma chamber processes and lower crustal accretion by direct observation. Using the Isis ROV we collected high-resolution bathymetry and video data from an 11 sq km area of seafloor, from the nadir of Hess Deep (5400 mbsl) up to the IRR, and sampled outcrops from the region in detail. Of 145 samples in total 94 were gabbro (s.l.). Accounting as much as possible for the complex tectonic disruption of the region we have reassembled these gabbros into a stratigraphic section through an EPR lower crust that we estimate to have been originally about 4350 m thick. The upper half of this plutonic section, which includes a dyke to gabbro transition at the top, is more or less intact on the IRR; however the lower half has been tectonically thinned by active gravity driven faulting and is incomplete. Within this lower section we nevertheless believe we have representative samples from the entire interval. At its base, in addition to primitive olivine gabbro we also recovered dunite, troctolite and residual mantle harzburgite. We here present a synthesis of the petrography and whole rock and mineral compositions of the gabbros from the reconstructed lower crustal section, coupled with a quantitative (electron backscatter diffraction and magnetic) study of their petrofabrics. From this, in

  9. Lifetime and Spectral Evolution of a Magma Ocean with a Steam Atmosphere: Its Detectability by Future Direct Imaging

    Hamano, Keiko; Abe, Yutaka; Onishi, Masanori; Hashimoto, George L


    We present the thermal evolution and emergent spectra of solidifying terrestrial planets along with the formation of steam atmospheres. The lifetime of a magma ocean and its spectra through a steam atmosphere depends on the orbital distance of the planet from the host star. For a type-I planet, which is formed beyond a certain critical distance from the host star, the thermal emission declines on a timescale shorter than approximately $10^6$ years. Therefore, young stars should be targets when searching for molten planets in this orbital region. In contrast, a type-II planet, which is formed inside the critical distance, will emit significant thermal radiation from near-infrared atmospheric windows during the entire lifetime of the magma ocean. The Ks and L bands will be favorable for future direct imaging because the planet-to-star contrasts of these bands are higher than approximately 10$^{-7}$-10$^{-8}$. Our model predicts that, in the type-II orbital region, molten planets would be present over the main s...

  10. Recycled oceanic crust and marine sediment in the source of alkali basalts in Shandong, eastern China: Evidence from magma water content and oxygen isotopes

    Liu, Jia; Xia, Qun-Ke; Deloule, Etienne; Chen, Huan; Feng, Min


    The magma water contents and cpx δ18O values in alkali basalts from the Fuyanyshan (FYS) volcano in Shandong, eastern China, were investigated by an inverse calculation based on the water content of clinopyroxene (cpx) phenocrysts, the ivAlcpx-dependent water partitioning coefficient Dwatercpx>/melt, and secondary ion mass spectrometer, respectively. The calculated water content (H2O wt.) of magma ranges from 0.58% to 3.89%. It positively correlates with heavy rare earth element concentrations and bulk rock 87Sr/86Sr ratios, and it negatively correlates with Nb/U ratios. However, it is not correlated with bulk Mg# (Mg# = 100 × Mg / (Mg + Fe)) and (La/Yb)n (n represents primitive mantle normalization). Combined with the rather homogenous distribution of water content within cpx grains, these correlations indicate that the water variations among different samples represent the original magma signature, rather than results of a shallow process, such as degassing and diffusion. The δ18O of cpx phenocrysts varies from 3.6‰ to 6.3‰ (±0.5‰, 2SD), which may be best explained by the involvement of components from the lower and upper oceanic crust with marine sediments within the mantle source. The H2O/Ce ratios of the calculated melts range from 113 to 696 and form a positive trend with bulk rock 87Sr/86Sr, which cannot be explained by the recycled Sulu eclogite or by the metasomatized lithospheric mantle. Our modeling calculation shows that the decoupling of ɛHf and ɛNd could be caused by the involvement of marine sediments. Combing the high Ba/Th ratios, positive Sr spikes, and low Ce/Pb ratios for the Fuyanshan basalts, we suggest that the hydrous nature of the FYS basalts was derived from the hydrous mantle transition zone with ancient sediments.

  11. Crystallization and cooling conditions for the diogenite formation in the turbulent magma ocean of the asteroid 4 Vesta

    Kawabata, Yusuke


    The asteroid 4 Vesta has been completely differentiated to core and mantle despite its small size, of which surface materials are howardite-eucrite-diogenite (HED) meteorites that we know the detailed petrology, and therefore, is a good target for understanding differentiation of terrestrial planets. A new differentiation model for crust formation was developed by taking magma ocean fluid dynamics, chemical equilibrium, presence of $^{26}$Al, and cooling into consideration with special care to crystal separation. The role of crystal size, thickness of the conductive lid, and fO2 are evaluated as parameters. The results show that large crystals (1cm) settle and form a km-thick cumulate layer of orthopyroxene with Mg# of 0.70-0.90 in ~20 thousand years, which almost agrees with the Mg# of diogenites, whereas thinner layers are formed if the grain size is smaller.


    Hamano, Keiko; Kawahara, Hajime; Abe, Yutaka [Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Onishi, Masanori [Department of Earth and Planetary Sciences, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan); Hashimoto, George L., E-mail: [Department of Earth Sciences, Okayama University, 3-1-1 Tsushima-Naka, Kita, Okayama, 700-8530 (Japan)


    We present the thermal evolution and emergent spectra of solidifying terrestrial planets along with the formation of steam atmospheres. The lifetime of a magma ocean and its spectra through a steam atmosphere depends on the orbital distance of the planet from the host star. For a Type I planet, which is formed beyond a certain critical distance from the host star, the thermal emission declines on a timescale shorter than approximately 10{sup 6} years. Therefore, young stars should be targets when searching for molten planets in this orbital region. In contrast, a Type II planet, which is formed inside the critical distance, will emit significant thermal radiation from near-infrared atmospheric windows during the entire lifetime of the magma ocean. The K{sub s} and L bands will be favorable for future direct imaging because the planet-to-star contrasts of these bands are higher than approximately 10{sup −7}–10{sup −8}. Our model predicts that, in the Type II orbital region, molten planets would be present over the main sequence of the G-type host star if the initial bulk content of water exceeds approximately 1 wt%. In visible atmospheric windows, the contrasts of the thermal emission drop below 10{sup −10} in less than 10{sup 5} years, whereas those of the reflected light remain 10{sup −10} for both types of planets. Since the contrast level is comparable to those of reflected light from Earth-sized planets in the habitable zone, the visible reflected light from molten planets also provides a promising target for direct imaging with future ground- and space-based telescopes.

  13. The Metal-Silicate Partitioning of Tungsten at Magma Ocean Conditions Using a Laser-Heated Diamond Anvil Cell

    Bennett, N.; Jackson, C.; Fei, Y.; Bullock, E. S.; Armstrong, J. T.


    The primitive upper mantle (PUM) represents the silicate residue of terrestrial core formation and should reflect element partitioning between metal and silicate melts that equilibrated in a magma ocean. Laboratory experiments suggest that the W/Mo ratio of PUM is only reproduced if S is added to the Earth during the late stages of accretion (Wade et al. 2012). Core-segregation, however, is posited to occur at >35 GPa and >3000 K; above the pressure range explored by existing W partitioning experiments and conditions under which O may also enter core-forming metal. The effect of light element solutes on a metallic Fe liquid can be modeled using experimentally determined interaction parameters (ɛ). On the basis of ɛ values determined at ambient pressure, both O and S should interact strongly with W (ɛw-o = 4.1, ɛw-s = 6.1), possibly complicating the history of W distribution during accretion. We have performed experiments to assess the metal-silicate partitioning of W at conditions directly relevant to those expected for the base of a magma ocean, under which O enters the metal phase. Experiments were performed at 15-50 GPa in a diamond anvil cell, using Re gaskets and an MgO pressure medium. In several instances, cells were loaded with two sample mixtures, containing W in either oxidized or reduced form. Heating spots subject to the same temperature and heating duration but different initial W oxidation state will be used to assess if heating times were sufficient to approach equilibrium. Samples were laser-heated at sector 13 of the Advanced Photon Source then recovered for analysis using a focused ion beam, to reveal cross-sections through the heated spot. Samples comprise a Fe-rich metal bleb, surrounded by silicate glass. The quenched metal contains exsolved spherules of a Si+O-rich phase, indicating significant solution of these elements at high pressure and temperature. Work is ongoing to quantify the element distribution between metal and silicate phases.

  14. A new view of the He-Ar-CO 2 degassing at mid-ocean ridges: Homogeneous composition of magmas from the upper mantle

    Paonita, Antonio; Martelli, Mauro


    Deep-sea exploration is rapidly improving our understanding of volatiles geochemistry in mid-ocean-ridge igneous products. It is also placing greater constraints on degassing processes of the Earth's mantle, with the result that degassing models based on vapour-melt equilibrium are no longer able to explain the increasing number of data. In fact, such models force to postulate an upper mantle strongly heterogeneous at any scale, and cannot account for the widespread carbon supersaturation of the recovered igneous products. Here we review the global He-Ar-CO 2 dataset of fluid inclusions in mid-ocean-ridge glasses using the framework of advanced modelling of multicomponent bubble growth in magmas. We display that non-equilibrium fractionations among He, Ar and CO 2, driven by their different diffusivities in silicate melts, are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing. Due to the comparable Ar and CO 2 diffusivity, magma degassing at low pressure fractionates both the He/Ar and He/CO 2 ratio by a similar extent, while the slower CO 2 diffusion at high pressure causes early kinetic effects on Ar/CO 2 ratio and dramatically changes the degassing path. On this ground, the very different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored. Besides, the variations inside a single suite highlight variable ascent speed and cooling rate of the emplaced lava. The large variations in both the He/CO 2 and Ar/CO 2 ratios at almost constant He/Ar, displayed in glasses coming from the Mid-Atlantic Ridge 24-30°N segment and the Rodriguez Triple Junction, are therefore interpreted as a high-pressure signature. In contrast, the simultaneous increase in both He/CO 2 and He/Ar of the East Pacific Rise, Pito Seamount and South-East Indian Ridge data sets suggests the dominance of low

  15. Magma storage and migration associated with the 2011-2012 El Hierro eruption: Implications for crustal magmatic systems at oceanic island volcanoes

    González, Pablo J.; Samsonov, Sergey V.; Pepe, Susi; Tiampo, Kristy F.; Tizzani, Pietro; Casu, Francesco; Fernández, José; Camacho, Antonio G.; Sansosti, Eugenio


    Starting in July 2011, anomalous seismicity was observed at El Hierro Island, a young oceanic island volcano. On 12 October 2011, the process led to the beginning of a submarine NW-SE fissural eruption at ~15 km from the initial earthquake loci, indicative of significant lateral magma migration. Here we conduct a multifrequency, multisensor interferometric analysis of spaceborne radar images acquired using three different satellite systems (RADARSAT-2, ENVISAT, and COSMO-SkyMed (Constellation of Small Satellites for Mediterranean Basin Observation)). The data fully captures both the pre-eruptive and coeruptive phases. Elastic modeling of the ground deformation is employed to constrain the dynamics associated with the magmatic activity. This study represents the first geodetically constrained active magmatic plumbing system model for any of the Canary Islands volcanoes, and one of the few examples of submarine volcanic activity to date. Geodetic results reveal two spatially distinct shallow (crustal) magma reservoirs, a deeper central source (9.5 ± 4.0 km), and a shallower magma reservoir at the flank of the southern rift (4.5 ± 2.0 km). The deeper source was recharged, explaining the relatively long basaltic eruption, contributing to the observed island-wide uplift processes, and validating proposed active magma underplating. The shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other Canary Islands. Data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long-term magma supply rate and oceanic lithospheric age. Such a relationship implies that a factor controlling the existence/depth of shallow (crustal) magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior.

  16. Fault Geometry Evolution and the Flexural Isostatic Response to Faulting in the Ocean-Continent Transition of Magma-Poor Rifted Margins

    Gómez-Romeu, J.; Kusznir, N.; Manatschal, G.; Roberts, A.


    Extensional fault geometry and the response to extensional faulting during rifted margin formation are controversial. During the formation of magma-poor rifted margins, lithosphere stretching and thinning progressively evolves through continental rifting, crustal necking, hyper-extension, mantle exhumation and eventual magmatic sea-floor spreading (Mohn et al., 2012). Initially lithosphere extensional faulting is achieved by steep normal faults rheologically decoupled from mantle deformation but, as crustal thickness decreases, extensional faults couple into the mantle. We use a kinematic forward model to examine the evolution of fault geometry and its flexural isostatic response during the formation of the ocean-continent transition at magma-poor rifted margins. In particular we study how this response controls the structural development of hyper-extended crust, exhumed mantle and the resulting sedimentary record. At slow spreading ocean ridges, large extensional faults lead to the isostatic rotation of exhumed footwall (Buck, 1988) and produce sub-horizontal fault footwall and low fault emergence angle (15°-20°). The same process (the rolling-hinge model) is used to explain the formation of extensional allochthon blocks at magma-poor rifted margins, which requires a very low flexural strength (Te < 1km) consistent with work at slow spreading ocean ridges (Smith et al., 2008; Schouten et al., 2010) and low fault footwall emergence angle. Field observations at magma-poor rifted margins suggest that the dimensions of allochthon blocks in the dip sense are not greater than approximately 2-3 km, which is supported by our modelling. One of many remaining questions concerns the geometry of extensional faults within distal hyper-extended continental crust is; are the seismically observed extensional fault blocks in this region allochthons underlain by extensional detachments or are the extensional faults coupled into the mantle?

  17. Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB

    Fischer, Lennart A.; Erdmann, Martin; France, Lydéric; Wolff, Paul E.; Deloule, Etienne; Zhang, Chao; Godard, Marguerite; Koepke, Jürgen


    At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 °C and 970 °C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.

  18. Magma Fragmentation

    Gonnermann, Helge M.


    Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.

  19. Combined ocean acidification and low temperature stressors cause coral mortality

    Kavousi, Javid; Parkinson, John Everett; Nakamura, Takashi


    Oceans are predicted to become more acidic and experience more temperature variability—both hot and cold—as climate changes. Ocean acidification negatively impacts reef-building corals, especially when interacting with other stressors such as elevated temperature. However, the effects of combined acidification and low temperature stress have yet to be assessed. Here, we exposed nubbins of the scleractinian coral Montipora digitata to ecologically relevant acidic, cold, or combined stress for 2 weeks. Coral nubbins exhibited 100% survival in isolated acidic and cold treatments, but ~30% mortality under combined conditions. These results provide further evidence that coupled stressors have an interactive effect on coral physiology, and reveal that corals in colder environments are also susceptible to the deleterious impacts of coupled ocean acidification and thermal stress.

  20. Genesis of andesitic boninitic magmas at mid-ocean ridges by melting of hydrated peridotites: Geochemical evidence from DSDP Site 334 gabbronorites

    Nonnotte, Philippe; Ceuleneer, Georges; Benoit, Mathieu


    The gabbronoritic cumulates drilled at DSDP Site 334 (Mid-Atlantic Ridge off the FAMOUS area) are neither crystallization products of the associated basalts, nor from any MORB composition documented along ocean ridges. Their parent melts are richer in SiO 2 than MORB at a given MgO content, as attested by the crystallization sequence starting with an olivine + calcic and sub-calcic pyroxene assemblages. These melts are issued from a source highly depleted in incompatible elements, likely residual peridotite left after MORB extraction. To understand the role of water in the genesis of these lithologies whose occurrence in a mid-ocean ridge setting is rather puzzling, we performed a geochemical study on clinopyroxene separates following an analytical protocol able to remove the effects of water rock interactions post-dating their crystallization. Accordingly, the measured isotopic signatures can be used to trace magma sources. We find that Site 334 clinopyroxenes depart from the global mantle correlation: normal MORB values for the 143Nd / 144Nd ratio (0.51307-0.51315) are associated to highly radiogenic 87Sr / 86Sr (0.7034-0.7067) ratios. This indicates that the parent melts of Site 334 cumulates are issued from a MORB source but that seawater contamination occurred at some stage of their genesis. The extent of contamination, traced by the Sr isotopic signature, is variable within all cumulates but more developed for gabbronorites sensus stricto, suggesting that seawater introduction was a continuous process during all the magmatic evolution of the system, from partial melting to fractional crystallization. Simple masse balance calculations are consistent with a contaminating agent having the characters of a highly hydrated (possibly water saturated) silica-rich melt depleted in almost all incompatible major, minor and trace elements relative to MORB. Mixing in various proportions of contaminated melts similar to the parent melts of Site 334 cumulates with MORB can

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

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


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

  2. Sediments overlying exhumed continental mantle: a proxy for the morphotectonic evolution of the Ocean Continent Transition in magma-poor rifted margins

    Karpoff, A. M.; Manatschal, G.; Bernoulli, D.; Lagabrielle, Y.


    Observations from ancient and present-day magma-poor rifted margins in the Alps and Iberia provide compelling evidence that within the ocean-continent transition (OCT) crustal and sub-continental mantle rocks were exhumed along downward-concave faults which were active during final rifting and accommodated high amounts of extension. The faults are overlain by stranded allochthons of continental origin, pillow basalts, and pelagic sediments, i.e. radiolarites and/or pelagic limestones, and hemipelagic shales. Associated with the faults are tectono-sedimentary breccias and various types of clastic sediments, ranging from debris flow deposits to laminated sandstone, and quartz-rich silt- and claystones. Mineralogical studies of the shales, red jaspers, and red cherts overlying mantle rocks in the Alps of eastern Switzerland are typically quartz-rich and contain variable amounts of phyllosilicates (chlorite and/or mica), feldspars, ± calcite, oxides, pyrite, and epidote. Their main geochemical characteristic is the high silica and low iron and manganese content, which contrasts with that of "metalliferous" Fe-Mn-Si-rich sediments overlying oceanic basalts. High Fe, Ba, REE, U/Th values measured in black shales overlying mantle rocks in the proximal OCT point to a strong hydrothermal activity associated with mantle exhumation. The clastic sediments in the OCT show a wide range of compositions related to mantle, continental crust, and/or pelagic contributions. In particular, the fact that these sediments contain abundant material derived from continental basement rocks seems at odds with their occurrence on top of tectonized mantle rocks. However, drilling in the Iberia margin, where tectonized mantle rocks are overlain by sedimentary breccias (e.g. ODP Sites 1068, 1070), shed new light on the observations in the Alps. Based on drill-hole and seismic data, the tectono-sedimentary breccias drilled in the OCT off Iberia may be interpreted to result from a conveyor

  3. Comparative Magma Oceanography

    Jones, J. H.


    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

  4. Lunar magma transport phenomena

    Spera, Frank J.


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

  5. Insights from geophysical monitoring into the volcano structure and magma supply systems at three very different oceanic islands in the Cape Verde archipelago

    Faria, B. V.; Day, S.; Fonseca, J. F.


    Three oceanic volcano islands in the west of the Cape Verde archipelago are considered to have the highest levels of volcanic hazard in the archipelago: Fogo, Brava, and Santo Antao. Fogo has had frequent mainly effusive eruptions in historic time, the most recent in 1995, whilst Brava and Santo Antao have ongoing geothermal activity and felt earthquakes, and have experienced geologically recent violent explosive eruptions. Therefore, these three islands have been the focus of recent efforts to set up seismic networks to monitor their activity. Here we present the first results from these networks, and propose interpretations of the monitored seismic activity in terms of subsurface volcano structures, near-surface intrusive activity and seasonal controls on geothermal activity. In Fogo, most recorded seismic events are hydrothermal events. These show a strong seasonal variation, increasing during the summer rain season and decreasing afterwards. Rare volcano-tectonic (VT) events (0.1scar. They are interpreted as shear failures between unconsolidated material at the base of the collapse scar fill and underlying more rigid pre-collapse rocks with abundant dikes, occuring as a result of long-term gravitational re-adjustment of the collapse scar fill after inflation of the island due to the 1995 eruption. Brava experiences frequent swarms of VT events. These are located mostly offshore, with a small proportion of on-shore events. The positions of offshore events are strongly correlated with seamounts and hence are interpreted as due to submarine volcanic processes. Onshore events (0.7magma reservoir in the edifice. S. Antão is characterized by frequent seismic swarms composed of VT earthquakes (0.1

  6. Slab melting and magma generation beneath the southern Cascade Arc

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


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

  7. Seismic evidence for a crustal magma reservoir beneath the upper east rift zoneof Kilauea volcano, Hawaii

    Lin, Guoqing; Amelung, Falk; Lavallee, Yan; Okubo, Paul G.


    An anomalous body with low Vp (compressional wave velocity), low Vs (shear wave velocity), and high Vp/Vs anomalies is observed at 8–11 km depth beneath the upper east rift zone of Kilauea volcano in Hawaii by simultaneous inversion of seismic velocity structure and earthquake locations. We interpret this body to be a crustal magma reservoir beneath the volcanic pile, similar to those widely recognized beneath mid-ocean ridge volcanoes. Combined seismic velocity and petrophysical models suggest the presence of 10% melt in a cumulate magma mush. This reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 M7.2 Kalapana earthquake.

  8. Digital images of combined oceanic and continental data sets and their use in tectonic studies

    Haxby, W. F.; Labrecque, J. L.; Weissel, J. K.; Karner, G. D.


    It is shown how crustal and lithospheric studies can benefit when continental and oceanic data sets are combined. It is also shown how digital imaging techniques provide an effective means for displaying the information contained in these combined data sets. The region of Australia, New Zealand, and the surrounding ocean is chosen for illustrating the advantages of combining continental and oceanic data sets. Here, the tectonic setting of Australia, a relatively stable continent in an intraplate environment, can be contrasted with New Zealand, which is traversed by one of the world's major plate boundaries. Simultaneous display and analysis of complementary data sets make possible a rapid geologic and tectonic interpretation of regional areas. It is shown, by way of example, that the relationship between topography and gravity anomalies in central Australia gives important new information concerning the state of isostasy of thrust terrains and their related sedimentary basins and hence provides a means of understanding the mechanical properties of the continental lithosphere.

  9. Ship detection in South African oceans using a combination of SAR and historic LRIT data

    Kleynhans, W


    Full Text Available International Geoscience and Remote Sensing Symposium, Melbourne, Australia, 21-26 July 2013 SHIP DETECTION IN SOUTH AFRICAN OCEANS USING A COMBINATION OF SAR AND HISTORIC LRIT DATA †‡W. Kleynhans, ‡B.P. Salmon, †‡C.P. Schwegmann, ♯‡M.V. Seotlo...

  10. Combined Effects of Ocean Acidification and Light or Nitrogen Availabilities on

    Hoins, M.; Eberlein, T.; Großmann, C.H.; Brandenburg, K.; Reichart, G.-J.; Rost, B.; Sluijs, A.; Van de Waal, D.B.


    Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractio

  11. Partial Melt Systems in Plate-Driven Corner Flow: Evaluating the Formation of Porosity Bands as a Mechanism for Magma Focusing at Mid-Ocean Ridges

    Gebhardt, D.; Butler, S. L.


    The imposition of an external shear on a system of partial melt will result in compaction of the solid matrix and concentration of the interstitial liquid melt leading to the formation of regions of contrasting high and low porosity. In experiments, direct and torsional shear geometries have demonstrated that these regions of varying porosity form in bands orientated at low angles relative to the shear plane. A variety of numerical models have been employed to recreate these experimental results. Simple shear, pure shear and torsional shear geometries have been used in both linear and nonlinear numerical settings to model the formation of the porosity bands. In this contribution the numerical models utilize a shear geometry derived from the velocity field of the plate-driven corner flow of a mid-ocean ridge. Motivation for using the velocity field of a mid-ocean ridge comes from evidence that suggests the existence of lateral melt channeling from either side of the ridge axis. Imposing the shear from a mid-ocean ridge corner flow allows for the evaluation of the resulting porosity bands in terms of suitability for channeling melt laterally toward the ridge axis. This is done using both slow and fast spreading ridge geometries. The degree of similarity between previous numerical and experimental results has been found to be greatly influenced by the imposed viscosity law of the solid matrix phase. In order to keep this in mind, the numerical models in this contribution use three different matrix viscosity laws: strain-rate independent, strain-rate dependent and anisotropic. Of these rheologies, strain-rate independence results in the poorest orientation for channeling melt directly to the ridge axis. The strain-rate dependent and anisotropic viscosities present more favorable direct-channeling orientations for the fastest growing porosity bands, but in both cases the background flow will rotate bands to less ideal orientations over time. However, these less

  12. Combining ocean sequestration of CO{sub 2} and OTEC; a win-win solution?

    Golmen, L.G.; Masutani, S.M. [NIVA, Regional Office Bergen, Bergen (Norway). Norwegian Institute for Water Research


    OTEC (Ocean Thermal Energy Conversion) and deep CO{sub 2} ocean sequestration share several technological similarities. OTEC uses cold deep sea water as a thermal sink for a heat engine that generates clean energy while ocean sequestration uses it as a sink for anthropogenic CO{sub 2}. Both technologies have the potential for application in the future but require additional technical development. Furthermore, the economics of dedicated OTEC and CO{sub 2} sequestration systems are currently unfavourable; so that co-products that jointly utilize the relatively expensive marine systems may be necessary to offset costs. This paper describes a new concept, 'CO{sub 2}TEC', in which the two systems are combined for mutual benefit. The proposed synergy includes the sharing of platforms and equipment; addition of CO{sub 2} to the warm water OTEC intakes to prevent biofouling of pipelines and heat exchangers; and exploiting the negatively buoyant CO{sub 2} enriched sea water to drive part of the upward water transport for OTEC. In the combined system, CO{sub 2} ocean sequestration contributes to the production of clean renewable energy which may enhance its chances to gain public acceptance. 12 refs., 2 figs.

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

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


    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). 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.

  14. Barometry of lavas from the 1951 eruption of Fogo, Cape Verde Islands: Implications for historic and prehistoric magma plumbing systems

    Hildner, Elliot; Klügel, Andreas; Hansteen, Thor H.


    Fogo is one of the most active oceanic volcanoes in the world. The island was affected by a prehistoric giant lateral collapse that decapitated the summit of the former Monte Amarelo volcano. Subsequent volcanism has partly filled the collapse scar and built up the present-day Cha das Caldeiras plain and the Pico do Fogo stratovolcano. We have conducted a thermobarometric study of historic and prehistoric, basanitic to tephritic rocks in order to gain insight into Fogo's magma plumbing system and the impact of the collapse event on fractionation depths. A main focus was the penultimate 1951 eruption, which produced basanites to tephrites (5.0-8.2 wt.% MgO) at two sites south and northwest of Pico do Fogo. Clinopyroxene-melt barometry of phenocrysts yields a well-confined pressure range of 480-650 MPa for the final crystallization level. Microthermometric data of CO2-dominated fluid inclusions in olivine and clinopyroxene phenocrysts yield systematically lower pressures of 250-430 MPa. Inclusions in cumulate xenoliths yield pressures of 100-290 MPa. The combined data indicate pre-eruptive magma storage in the uppermost mantle between 17 and 22 km depth and syn-eruptive short-term magma stalling within the lower crust at 8-13 km depth. The lower pressures revealed by fluid inclusions in xenoliths may indicate that they originate from pre-1951 magma pulses that stalled and crystallized at variable levels in the crust. There is, however, no petrologic evidence for persistent crustal magma chambers. Clinopyroxene-melt barometric data of other historic and prehistoric eruptions indicate that magma storage and differentiation occurred in the uppermost mantle at pressures between 420 and 870 MPa (15-30 km depth) throughout the subaerial evolution of Fogo. Our data indicate that fractionation depths decreased significantly during a period of about 100 ka representing a strong growth phase of Fogo edifice leading up to the giant Monte Amarelo flank collapse at 123-62 ka

  15. Combined Atmospheric and Ocean Profiling from an Airborne High Spectral Resolution Lidar

    Hair Johnathan


    Full Text Available First of its kind combined atmospheric and ocean profile data were collected by the recently upgraded NASA Langley Research Center’s (LaRC High Spectral Resolution Lidar (HSRL-1 during the 17 July – 7 August 2014 Ship-Aircraft Bio-Optical Research Experiment (SABOR. This mission sampled over a region that covered the Gulf of Maine, open-ocean near Bermuda, and coastal waters from Virginia to Rhode Island. The HSRL-1 and the Research Scanning Polarimeter from NASA Goddard Institute for Space Studies collected data onboard the NASA LaRC King Air aircraft and flight operations were closely coordinated with the Research Vessel Endeavor that made in situ ocean optical measurements. The lidar measurements provided profiles of atmospheric backscatter and particulate depolarization at 532nm, 1064nm, and extinction (532nm from approximately 9km altitude. In addition, for the first time HSRL seawater backscatter, depolarization, and diffuse attenuation data at 532nm were collected and compared to both the ship measurements and the Moderate Resolution Imaging Spectrometer (NASA MODIS-Aqua satellite ocean retrievals.

  16. Combining Satellite and in Situ Data with Models to Support Climate Data Records in Ocean Biology

    Gregg, Watson


    The satellite ocean color data record spans multiple decades and, like most long-term satellite observations of the Earth, comes from many sensors. Unfortunately, global and regional chlorophyll estimates from the overlapping missions show substantial biases, limiting their use in combination to construct consistent data records. SeaWiFS and MODIS-Aqua differed by 13% globally in overlapping time segments, 2003-2007. For perspective, the maximum change in annual means over the entire Sea WiFS mission era was about 3%, and this included an El NinoLa Nina transition. These discrepancies lead to different estimates of trends depending upon whether one uses SeaWiFS alone for the 1998-2007 (no significant change), or whether MODIS is substituted for the 2003-2007 period (18% decline, P less than 0.05). Understanding the effects of climate change on the global oceans is difficult if different satellite data sets cannot be brought into conformity. The differences arise from two causes: 1) different sensors see chlorophyll differently, and 2) different sensors see different chlorophyll. In the first case, differences in sensor band locations, bandwidths, sensitivity, and time of observation lead to different estimates of chlorophyll even from the same location and day. In the second, differences in orbit and sensitivities to aerosols lead to sampling differences. A new approach to ocean color using in situ data from the public archives forces different satellite data to agree to within interannual variability. The global difference between Sea WiFS and MODIS is 0.6% for 2003-2007 using this approach. It also produces a trend using the combination of SeaWiFS and MODIS that agrees with SeaWiFS alone for 1998-2007. This is a major step to reducing errors produced by the first cause, sensor-related discrepancies. For differences that arise from sampling, data assimilation is applied. The underlying geographically complete fields derived from a free-running model is unaffected

  17. The fate of volatiles in mid-ocean ridge magmatism

    Keller, Tobias; Hirschmann, Marc M


    Deep-Earth volatile cycles couple the mantle with near-surface reservoirs. Volatiles are emitted by volcanism and, in particular, from mid-ocean ridges, which are the most prolific source of basaltic volcanism. Estimates of volatile extraction from the asthenosphere beneath ridges typically rely on measurements of undegassed lavas combined with simple petrogenetic models of the mean degree of melting. Estimated volatile fluxes have large uncertainties; this is partly due to a poor understanding of how volatiles are transported by magma in the asthenosphere. Here, we assess the fate of mantle volatiles through numerical simulations of melting and melt transport at mid-ocean ridges. Our simulations are based on two-phase, magma/mantle dynamics theory coupled to an idealised thermodynamic model of mantle melting in the presence of water and carbon dioxide. We combine simulation results with catalogued observations of all ridge segments to estimate a range of likely volatile output from the global mid-ocean ridge...

  18. Self Sealing Magmas

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


    During ascent of magma, pressure decreases and bubbles form. If the volume increases more rapidly than the relaxation timescale, the magma fragments catastrophically. If a permeable network forms, the magma degasses non-violently. This process is generally assumed to be unidirectional, however, recent studies have shown how shear and compaction can drive self sealing. Here, we additionally constrain skin formation during degassing and sintering. We heated natural samples of obsidian in a dry atmosphere and monitored foaming and impermeable skin formation. We suggest a model for skin formation that is controlled by diffusional loss of water and bubble collapse at free surfaces. We heated synthetic glass beads in a hydrous atmosphere to measure the timescale of viscous sintering. The beads sinter at drastically shorter timescales as water vapour rehydrates an otherwise degassed melt, reducing viscosity and glass transition temperatures. Both processes can produce dense inhomogeneities within the timescales of magma ascent and effectively disturb permeabilities and form barriers, particularly at the margins of the conduit, where strain localisation takes place. Localised ash in failure zones (i.e. Tuffisite) then becomes associated with water vapour fluxes and alow rapid rehydration and sintering. When measuring permeabilities in laboratory and field, and when discussing shallow degassing in volcanoes, local barriers for degassing should be taken into account. Highlighting the processes that lead to the formation of such dense skins and sintered infills of cavities can help understanding the bulk permeabilities of volcanic systems.

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

    Schwindinger, Martin; Weinberg, Roberto F.


    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.

  20. Eruption and magma crystallization ages of Las Tres Vírgenes (Baja California) constrained by combined 230Th/ 238U and (U-Th)/He dating of zircon

    Schmitt, Axel K.; Stockli, Daniel F.; Hausback, Brian P.


    Las Tres Vírgenes volcano is a calc-alkaline composite cone located near the main Gulf of California escarpment on the E coast of the Baja California peninsula. High-sensitivity ion microprobe U-series ( 230Th/ 238U) ages for zircon from La Vírgen tephra average 121 - 10 + 12 ka (1σ; MSWD = 2.7), with discrete age peaks at ˜ 100 and 160 ka. The noble gas mass spectrometric (U-Th)/He zircon age, corrected for disequilibrium and pre-eruptive storage, is 36 ± 3 ka. This result for the eruption age of La Vírgen tephra is significantly older than previously postulated historic or Holocene ages that were based on an 18th century map reference and 14C dating of accidental charcoal, respectively. The new (U-Th)/He zircon age is consistent with a > 26 ± 4 ka age derived from cosmogenic He exposure dating of an overlying basaltic lava flow [Hausback, B.P. and Abrams, M.J., 1996. Plinian eruption of La Virgen Tephra, Volcán Las Tres Virgenes, Baja California Sur, Mexico. Eos, Transactions, American Geophysical Union, 77(46, Suppl.): 813-814.]. U-Pb zircon analysis of ignimbrites erupted from the adjacent Early Pleistocene La Reforma and El Aguajito calderas yielded ages of 1.38 ± 0.03 Ma ( n = 12; MSWD = 1.0) and 1.17 ± 0.07 Ma ( n = 23; MSWD = 1.3), respectively. No evidence for these ages is found among La Vírgen zircons, whereas pre-Quaternary zircon xenocrysts are common. The La Vírgen magma, therefore, evolved unrelated to Early Pleistocene magmatism in adjacent calderas, but assimilated local basement rocks. A gap between average Th-U and (U-Th)/He zircon ages suggests that zircon crystallization was discontinuous in the La Vírgen magma chamber. In addition, partial resorption of zircon suggests episodic thermal rejuvenation, most likely by basaltic recharge. Based on the zircon record, the > 100 ka lifetime of the thermal anomaly that sustained repeated intrusive pulses significantly exceeds the age of the last eruption. This strengthens the view that Tres

  1. Mush Column Magma Chambers

    Marsh, B. D.


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

  2. The combined effects of ocean warming and acidification on shallow-water meiofaunal assemblages.

    Lee, Matthew R; Torres, Rodrigo; Manríquez, Patricio H


    Climate change due to increased anthropogenic CO2 in the atmosphere is causing an increase in seawater temperatures referred to as ocean warming and a decrease in seawater pH, referred to as ocean acidification. The meiofauna play an important role in the ecology of marine ecosystems and the functions they provide. Using microcosms, meiofaunal assemblages were exposed to two temperatures (15 and 19 °C) and two pHs (pCO2 of 400 and 1000 ppm), both individually and in combination, for a period of 90 days. The hypothesis that increased temperature will increase meiofaunal abundance was not supported. The hypothesis that a reduced pH will reduce meiofaunal abundance and species richness was supported. The combination of future conditions of temperature and pH (19 °C and pCO2 of 1000 ppm) did not affect overall abundance but the structure of the nematode assemblage changed becoming dominated by a few opportunistic species. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. Formation of redox gradients during magma-magma mixing

    Ruprecht, P.; Fiege, A.; Simon, A. C.


    Magma-mixing is a key process that controls mass transfer in magmatic systems. The variations in melt compositions near the magma-magma interface potentially change the Fe oxidation state [1] and, thus, affect the solubility and transport of metals. To test this hypothesis, diffusion-couple experiments were performed at 1000 °C, 150 MPa and QFM+4. Synthesized crystal-bearing cylinders of hydrous dacite and hydrous basaltic andesite were equilibrated for up to 80 h. The run products show that mafic components (Fe, Mg, etc.) were transported from the andesite into the dacite, while Si, Na and K diffused from the dacite into the andesite. A crystal dissolution sequence in the order of cpx, opx, plag, and spl/il was observed for the andesite. We combined μ-XANES spectroscopy at Fe K-edge [2] with two-oxide oxybarometry [3] to measure redox profiles within our experiments. Here, fO2 decreased towards the interface within the dacite and increased towards the interface within the andesite. This discontinuous fO2 evolution, with a sharp redox gradient of ~1.8 log fO2 units at the interface was maintained throughout the time-series despite the externally imposed fO2 of the vessel. We propose a combination of two mechanisms that create and sustain this redox gradient: 1) The dissolution of cpx and opx in the andesite mainly introduced Fe2+ into the melt, which diffused towards the dacite, lowering Fe3+/SFe near the interface. 2) Charge balance calculations in the melt during diffusive exchange suggest net positive charge excess in the andesite near the interface (i.e., oxidation) and net negative charge excess in the dacite near the interface (i.e., reduction). We suggest that this (metastable) redox layer can help to explain the contrasting Au/Cu ratios observed for arc-related porphyry-type ore deposits. [1] Moretti (2005), Ann. Geophys. 48, 583-608. [2] Cottrell et al. (2009), Chem. Geol. 268, 167-179. [3] Ghiorso and Evans (2008), Am. J. Sci. 308, 957-1039.

  4. Accretion and Subduction of Oceanic Lithosphere: 2D and 3D Seismic Studies of Off-Axis Magma Lenses at East Pacific Rise 9°37-40'N Area and Downgoing Juan de Fuca Plate at Cascadia Subduction Zone

    Han, Shuoshuo

    Two thirds of the Earth's lithosphere is covered by the ocean. The oceanic lithosphere is formed at mid-ocean ridges, evolves and interacts with the overlying ocean for millions of years, and is eventually consumed at subduction zones. In this thesis, I use 2D and 3D multichannel seismic (MCS) data to investigate the accretionary and hydrothermal process on the ridge flank of the fast-spreading East Pacific Rise (EPR) at 9°37-40'N and the structure of the downgoing Juan de Fuca plate at the Cascadia subduction zone offshore Oregon and Washington. Using 3D multichannel seismic (MCS) data, I image a series of off-axis magma lenses (OAML) in the middle or lower crust, 2-10 km from the ridge axis at EPR 9°37-40'N. The large OAMLs are associated with Moho travel time anomalies and local volcanic edifices above them, indicating off-axis magmatism contributes to crustal accretion though both intrusion and eruption (Chapter 1). To assess the effect of OAMLs on the upper crustal structure, I conduct 2-D travel time tomography on downward continued MCS data along two across-axis lines above a prominent OAML in our study area. I find higher upper crustal velocity in a region ~ 2 km wide above this OAML compared with the surrounding crust. I attribute these local anomalies to enhanced precipitation of alteration minerals in the pore space of upper crust associated with high-temperature off-axis hydrothermal circulation driven by the OAML (Chapter 2). At Cascadia, a young and hot end-member of the global subduction system, the state of hydration of the downgoing Juan de Fuca (JdF) plate is important to a number of subduction processes, yet is poorly known. As local zones of higher porosity and permeability, faults constitute primary conduits for seawater to enter the crust and potentially uppermost mantle. From pre-stack time migrated MCS images, I observe pervasive faulting in the sediment section up to 200 km from the deformation front. Yet faults with large throw and

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

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


    High-spatial resolution zircon geochronology was applied to constrain the timescales of volcanic eruptions of the youngest, mostly explosive volcanic phase of Ciomadul volcano (Carpathian-Pannonian region, Romania). Combined U-Th and (U-Th)/He zircon dating demonstrates that intermittent volcanic eruptions occurred in a time range of 56-32 ka. The reliability of the eruption dates is supported by concordant ages obtained from different dating techniques, such as zircon geochronology, radiocarbon analysis, and infrared stimulated luminescence dating for the same deposits. The new geochronological data suggest that volcanism at Ciomadul is much younger (volcanic phase occurred after an apparent lull in volcanism that lasted for several 10's of ka, after a period of lava dome extrusion that defines the onset of the known volcanism at Ciomadul. At least four major eruptive episodes can be distinguished within the 56-32 ka period. Among them, relatively large (sub-plinian to plinian) explosive eruptions produced distal tephra covering extended areas mostly southeast from the volcano. The 38.9 ka tephra overlaps the age of the Campanian Ignimbrite eruption and has an overlapping dispersion axis towards the Black Sea region. The wide range of U-Th model ages of the studied zircons indicates prolonged existence of a low-temperature (volcanism. Even the youngest U-Th model ages obtained for the outermost 4 μm rim of individual zircon crystals predate the eruption by several 10's of ka. The zircon age distributions suggest re-heating above zircon saturation temperatures via injection of hot mafic magmas prior to eruption. Intermittent intrusions of fresh magma could play a significant role in keeping the intrusive silicic magmatic reservoir in a partially melted for prolonged period. The previous history of Ciomadul suggests that melt-bearing crystal mush resided beneath the volcano, and was rapidly remobilized after a protracted (several 10's of ka) lull in volcanism to

  6. The magma plumbing system for the 1971 Teneguía eruption on La Palma, Canary Islands

    Barker, Abigail K.; Troll, Valentin R.; Carracedo, Juan Carlos; Nicholls, Peter A.


    The 1971 Teneguía eruption is the most recent volcanic event of the Cumbre Vieja rift zone on La Palma. The eruption produced basanite lavas that host xenoliths, which we investigate to provide insight into the processes of differentiation, assimilation and magma storage beneath La Palma. We compare our results to the older volcano magmatic systems of the island with the aim to reconstruct the temporal development of the magma plumbing system beneath La Palma. The 1971 lavas are clinopyroxene-olivine-phyric basanites that contain augite, sodic-augite and aluminium augite. Kaersutite cumulate xenoliths host olivine, clinopyroxene including sodic-diopside, and calcic-amphibole, whereas an analysed leucogabbro xenolith hosts plagioclase, sodic-augite-diopside, calcic-amphibole and hauyne. Mineral thermobarometry and mineral-melt thermobarometry indicate that clinopyroxene and plagioclase in the 1971 Teneguía lavas crystallised at 20-45 km depth, coinciding with clinopyroxene and calcic-amphibole crystallisation in the kaersutite cumulate xenoliths at 25-45 km and clinopyroxene, calcic-amphibole and plagioclase crystallisation in the leucogabbro xenolith at 30-50 km. Combined mineral chemistry and thermobarometry suggest that the magmas had already crystallised, differentiated and formed multiple crystal populations in the oceanic lithospheric mantle. Notably, the magmas that supplied the 1949 and 1971 events appear to have crystallised deeper than the earlier Cumbre Vieja magmas, which suggests progressive underplating beneath the Cumbre Vieja rift zone. In addition, the lavas and xenoliths of the 1971 event crystallised at a common depth, indicating a reused plumbing system and progressive recycling of Ocean Island plutonic complexes during subsequent magmatic activity.

  7. Determination of volatile concentrations in fluorapatite of Martian shergottite NWA 2975 by combining synchrotron FTIR, Raman spectroscopy, EMPA, and TEM, and inferences on the volatile budget of the apatite host-magma

    SłAby, Ewa; Koch-Müller, Monika; FöRster, Hans-Jürgen; Wirth, Richard; Rhede, Dieter; Schreiber, Anja; Schade, Ulrich


    We combined the focused ion beam sample preparation technique with polarized synchrotron-based FTIR (Fourier transform infrared) spectroscopy, laser-Raman spectroscopy, electron microprobe analysis (EMPA), and transmission electron microscope (TEM) analysis to identify and quantify structurally bound OH, F, Cl, and CO3 groups in fluorapatite from the Northwest Africa 2975 (NWA 2975) shergottite. In this study, the first FTIR spectra of the OH-stretching region from a Martian apatite are presented that show characteristic OH-bands of a F-rich, hydroxyl-bearing apatite. Depending on the method of apatite-formula calculation and whether charge balance is assumed or not, the FTIR-based quantification of the incorporated OH, expressed as wt% H2O, is in variably good agreement with the H2O concentration calculated from electron microprobe data. EMP analyses yielded between 0.35 and 0.54 wt% H2O, and IR data yielded an average H2O content of 0.31 ± 0.03 wt%, consistent with the lower range determined from EMP analyses. The TEM observations implied that the volatiles budget of fluorapatite is magmatic. The water content and the relative volatile ratios calculated for the NWA 2975 magma are similar to those established for other enriched or intermediate shergottites. It is difficult to define the source of enrichment: either Martian wet mantle or crustal assimilation. Comparing the environment of parental magma generation for NWA 2975 with the terrestrial mantle in terms of water content, it displays a composition intermediate between enriched and depleted MORB.

  8. Combined effects of iron and copper from atmospheric dry deposition on ocean productivity

    Wang, F. J.; Chen, Y.; Guo, Z. G.; Gao, H. W.; Mackey, K. R.; Yao, X. H.; Zhuang, G. S.; Paytan, A.


    Atmospheric deposition can provide nutrients and potential toxicants to marine ecosystem, hence affecting ocean net primary productivity (NPP). Nonetheless, the interactive effects of mixed aerosol components on phytoplankton have rarely been reported. Here we explored the combined effects of iron (Fe) and copper (Cu) on NPP over the East China Sea. In aerosol addition mesocosm experiments, phytoplankton growth was suppressed under high aerosol Cu but was increased when high Cu was accompanied by high Fe in aerosols. A time series of soluble aerosol Fe and Cu deposition was obtained and compared to regional chlorophyll a (Chl a) abundances from Moderate Resolution Imaging Spectroradiometer/Aqua. Strong positive correlations were observed between the dry flux ratios of soluble Fe/Cu and Chl a abundances in the large offshore area, whereas these variables were uncoupled in coastal regions where riverine input and upwelling dominated the biogeochemistry. Current work provides insight into the complex linkage between atmospheric deposition and marine productivity.

  9. Magma Rich Events at Magma-Poor Rifted Margins: A South-East Indian Example

    Harkin, Caroline; Kusznir, Nick; Tugend, Julie; Manatschal, Gianreto; Horn, Brian


    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 magma-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 magma-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 magma-poor rifted margins (e.g. NE Brazil). This interpretation of magma-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

  10. Viscosity of mafic magmas at high pressures

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


    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.

  11. Combined effects of warming and ocean acidification on coral reef Foraminifera Marginopora vertebralis and Heterostegina depressa

    Schmidt, Christiane; Kucera, Michal; Uthicke, Sven


    Warming and changes in ocean carbonate chemistry alter marine coastal ecosystems at an accelerating pace. The interaction between these stressors has been the subject of recent studies on reef organisms such as corals, bryozoa, molluscs, and crustose coralline algae. Here we investigated the combined effects of elevated sea surface temperatures and pCO2 on two species of photosymbiont-bearing coral reef Foraminifera: Heterostegina depressa (hosting diatoms) and Marginopora vertebralis (hosting dinoflagellates). The effects of single and combined stressors were studied by monitoring survivorship, growth, and physiological parameters, such as respiration, photochemistry (pulse amplitude modulation fluorometry and oxygen production), and chl a content. Specimens were exposed in flow-through aquaria for up to seven weeks to combinations of two pCO2 (~790 and ~490 µatm) and two temperature (28 and 31 °C) regimes. Elevated temperature had negative effects on the physiology of both species. Elevated pCO2 had negative effects on growth and apparent photosynthetic rate in H.depressa but a positive effect on effective quantum yield. With increasing pCO2, chl a content decreased in H. depressa and increased in M. vertebralis. The strongest stress responses were observed when the two stressors acted in combination. An interaction term was statistically significant in half of the measured parameters. Further exploration revealed that 75 % of these cases showed a synergistic (= larger than additive) interaction between the two stressors. These results indicate that negative physiological effects on photosymbiont-bearing coral reef Foraminifera are likely to be stronger under simultaneous acidification and temperature rise than what would be expected from the effect of each of the stressors individually.

  12. The simulation of gas production from oceanic gas hydrate reservoir by the combination of ocean surface warm water flooding with depressurization

    Hao Yang; Yu-Hu Bai; Qing-Ping Li


    A new method is proposed to produce gas from oceanic gas hydrate reservoir by combining the ocean surface warm water flooding with depressurization which can efficiently utilize the synthetic effects of thermal,salt and depressurization on gas hydrate dissociation.The method has the advantage of high efficiency,low cost and enhanced safety.Based on the proposed conceptual method,the physical and mathematical models are established,in which the effects of the flow of multiphase fluid,the kinetic process of hydrate dissociation,the endothermic process of hydrate dissociation,ice-water phase equilibrium,salt inhibition,dispersion,convection and conduction on the hydrate dissociation and gas and water production are considered.The gas and water rates,formation pressure for the combination method are compared with that of the single depressurization,which is referred to the method in which only depressurization is used.The results show that the combination method can remedy the deficiency of individual producing methods.It has the advantage of longer stable period of high gas rate than the single depressurization.It can also reduce the geologic hazard caused by the formation deformation due to the maintaining of the formation pressure by injected ocean warm water.

  13. Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes.

    Got, Jean-Luc; Monteiller, Vadim; Monteux, Julien; Hassani, Riad; Okubo, Paul


    Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate. Despite the apparent simplicity of the parent process--emission of magma onto the oceanic crust--the resulting edifices display some topographic complexity. Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown. Here we use seismological investigations and finite-element mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities. Further studies are needed to determine whether such processes occur in other active intraplate volcanoes.

  14. Mid-oceanic ridge system

    Ramprasad, T.

    cinders, followed by a rebuilding phase with hot magma. The entire Pacific Ocean boundary is surrounded by long stretches of volcanoes and is known collectively as The Ring of Fire. Continental / Continental Where two continental plates collide...

  15. Adakitic magmas: modern analogues of Archaean granitoids

    Martin, Hervé


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

  16. Combined effects of ocean acidification and light or nitrogen availabilities on 13C fractionation in marine dinoflagellates

    Hoins, M.; Eberlein, T.; Großmann, C.H.; Brandenburg, K.; Reichart, G.-J.|info:eu-repo/dai/nl/165599081; Rost, B.; Sluijs, A.|info:eu-repo/dai/nl/311474748; Van De Waal, D.B.


    Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractio

  17. Instability of combined gravity-inertial-Rossby waves in atmospheres and oceans

    J. F. McKenzie


    Full Text Available The properties of the instability of combined gravity-inertial-Rossby waves on a β-plane are investigated. The wave-energy exchange equation shows that there is an exchange of energy with the background stratified medium. The energy source driving the instability lies in the background enthalpy released by the gravitational buoyancy force.

    It is shown that if the phase speed of the westward propagating low frequency-long wavelength Rossby wave exceeds the Poincaré-Kelvin (or "equivalent" shallow water wave speed, instability arises from the merging of Rossby and Poincaré modes. There are two key parameters in this instability condition; namely, the equatorial/rotational Mach (or Froude number M and the latitude θ0 of the β-plane. In general waves equatorward of a critical latitude for given M can be driven unstable, with corresponding growth rates of the order of a day or so. Although these conclusions may only be safely drawn for short wavelengths corresponding to a JWKB wave packet propagating internally and located far from boundaries, nevertheless such a local instability may play a significant role in atmosphere-ocean dynamics.

  18. Mechanisms of magma degassing at mid-oceanic ridges and the local volatile composition (4He-40Ar*-CO2) of the mantle by laser ablation analysis of individual MORB vesicles

    Colin, A.; Burnard, P.; Marty, B.


    Individual vesicles in excimer laser. One sample shows evidence of syn-emplacement selective helium loss from the vesicles in the glass rim close to the crystallised zone of the pillow lava, proving that He contents and low He/Ar ratios do not always reflect mantle and/or magmatic processes. However the composition of the different vesicles of three of these samples covers large ranges in He/Ar and Ar/CO2 with linear variations in plots of ln(He/Ar) vs. ln(Ar/CO2) which are consistent with a Rayleigh distillation at equilibrium and allow the relative abundances of the volatiles in the MORB mantle source to be estimated by correcting for degassing processes on a sample-by-sample basis. This technique presents a new tool for characterising and correcting for volatile fractionation processes that have modified the initial mantle source composition. The results confirm a heterogeneous CO2/3He ratio in the MORB source regions with the Azores mantle source enriched in C/3He compared to that of N-MORBs. The considerable heterogeneity in vesicle compositions within such a small volume (<1 cm3) requires injection of less degassed magma at shallow level before eruption. The maximum time interval between magma mixing and quenching on the seafloor is of the order of a few hours.

  19. Thermal and mechanical evolution of magma reservoirs

    Bachmann, O.; Huber, C.; Dufek, J.


    Magmas spend most of their suprasolidus lifespan at high crystallinity. Crystal-rich mushes have a low thermal contrast with the surrounding crust and latent heat buffering is expected to decrease the cooling rate as they approach the solidus. The impact of latent buffering is phase-diagram dependent; massive crystallization over a short temperature interval, occurring near invariant points, can significantly increase the time a given magma spends above the solidus. This latent heat effect is likely to play an important role in the upper crust, as the typical upper crustal compositions (dacite) reach the haplogranite eutectic around 40-60 vol% crystals. As high crystallinity is the most probable state for magmas in the upper crust, the interaction between crystal mushes and hot recharges from below is common. Hence, the thermo-mechanical response of mushes to recharge is a central process in the rheological evolution of these systems. An important feedback following recharge is related to the reduction in density as solid phases melt, leading to the development of in-situ overpressures. The combined effect of melting and overpressurization has a two major consequences for magmatic systems, both commonly observed in the rock record: (1) it increases the likelihood for reactivation of locked crystal mushes, and (2) it enhances the assimilation of stoped blocks in the upper crust.

  20. The combined impact of CO2-dependent parameterisations of Redfield and Rain ratios on ocean carbonate saturation

    M. H. England


    Full Text Available Future changes to the organic carbon and carbonate pumps are likely to affect ocean ecosystem dynamics and the biogeochemical climate. Here, biological dependencies on the Rain and Redfield ratios on pCO2 are implemented in a coupled Biogeochemistry-Ocean Model, the CSIRO-Mk3L, to establish extreme-case carbonate saturation vulnerability to model parameterisation at year 2500 using IPCC Representative Concentration Pathway 8.5. Surface carbonate saturation is relatively insensitive to the combined effects of variable Rain and Redfield ratios (an anomaly of less than 10 % of the corresponding change in the control configuration by year 2500, but the global zonally-averaged ocean interior anomaly due to these feedbacks is up to 130 % by 2500. A non-linear interaction between organic and carbonate pumps is found in export production, where higher rates of photosynthesis enhance calcification by raising surface alkalinity. This non-linear effect has a negligible influence on surface carbonate saturation but does significantly influence ocean interior carbonate saturation fields (an anomaly of up to 45 % in 2500. The strongest linear and non-linear sensitivity to combined feedbacks occurs in low-latitude remineralisation zones below regions of enhanced biological production, where dissolved inorganic carbon rapidly accumulates.

  1. Low-(18)O Silicic Magmas: Why Are They So Rare?

    Balsley, S.D.; Gregory, R.T.


    LOW-180 silicic magmas 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 magma genesis for nearly all silicic magmas. The rarity of 10W-l `O magmas 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 magmas 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 magmas 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 magmas at Yellowstone produced small- volume, 10W-180 magmas directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.

  2. Magma production rate along the Ninetyeast Ridge and its relationship to Indian plate motion and Kerguelen hot spot activity

    Sreejith, K.M.; Krishna, K.S.

    The Ninetyeast Ridge, a linear trace of the Kerguelen hot spot in the Indian Ocean, was emplaced on a rapidly drifting Indian plate. Magma production rates along the ridge track are computed using gravity-derived excess crustal thickness data...

  3. Warm storage for arc magmas.

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


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

  4. Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model

    Cai, C.; Rignot, E. J.; Menemenlis, D.


    Zachariae Isstrom, a major ice stream in northeast Greenland, has lost its entire ice shelf in the past decade. Here, we study the evolution of subaqueous melting of its floating section during the transition. Observations show that the rate of ice shelf melting has doubled during 1999-2010 and is twice higher than that maintaining the ice shelf in a state of mass equilibrium. The ice shelf melt rate depends on the thermal forcing from warm, salty, subsurface ocean water of Atlantic origin (AW), and - in contrast with Antarctic ice shelves - on the mixing of AW with fresh buoyant subglacial discharge. Subglacial discharge has increased as result of enhanced ice sheet runoff driven by warmer air temperature; ocean thermal forcing has increased due enhanced advection of AW. Here, we employ the Massassuchetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution (1 m horizontal and 1 m vertical spacing near the grounding line) to simulate the melting process in 3-D. The model is constrained by ice thickness from mass conservation, oceanic bathymetry from NASA Operation IceBridge gravity data, in-situ ocean temperature/salinity data, ocean tide height and current from the Arctic Ocean Tidal Inverse Model (AOTIM-5) and subglacial discharge from output products of the Regional Atmospheric Climate Model (RACMO). We compare the results in winter (no runoff) with summer (maximum runoff) at two different stages with (prior to 2012) and without the ice shelf (after 2012) to subaqueous melt rates deduced from remote sensing observations. We show that ice melting by the ocean has increased by one order of magnitude as a result of the transition from ice shelf terminating to near-vertical calving front terminating. We also find that subglacial discharge has a significant impact on the ice shelf melt rates in Greenland. We conclude on the impact of ocean warming and air temperature warming on the melting regime of the ice margin of Zachariae

  5. Viscosity of Campi Flregrei (Italy) magmas

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


    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

  6. Experimental constraints on the outgassing dynamics of basaltic magmas

    Pioli, L.; Bonadonna, C.; Azzopardi, B. J.; Phillips, J. C.; Ripepe, M.


    The dynamics of separated two-phase flow of basaltic magmas 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 magma 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 magma in the column, and the gas rise speed of gas slugs. It predicts that magma 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 magma 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 magma 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 magma homogeneity and stable conditions.

  7. Insights into deep-sea sediment fungal communities from the East Indian Ocean using targeted environmental sequencing combined with traditional cultivation

    Zhang, Xiao-yong; Tang, Gui-ling; Xu, Xin-ya; Nong, Xu-hua; Qi, Shu-hua


    .... We investigated the fungal community structure in five sediments from a depth of ∼ 4000 m in the East India Ocean using a combination of targeted environmental sequencing and traditional cultivation...

  8. Magma mixing during the 2010 Eyjafjallajökull eruption

    Portnyagin, M.; Borisova, A. Y.; Plechov, P.; Shkurski, B.; Stefansson, A.


    We performed detailed study of matrix glasses, olivines and melt inclusions in 6 samples of tephras of the 2010 Eyjafjallajökull eruption. Tephras erupted during the early basaltic stage (March 20 - April 13) are very homogeneous with respect to matrix glass compositions and host assemblage of primitive phenocrysts (olivine Fo75-87, Cr-spinel Cr# = 0.14 - 0.55). The olivines have normal or rhythmic zoning which suggests multiple episodes of mixing with more primitive magmas and crystallization before eruption. Glasses of the initial andesitic stage (April 14 - 30) fall into three groups: basaltic (group 2a, andesitic (group 2b, >80% ) and dacitic (group 2c, andesitic stage (May 1 - 22, group 3) have exclusively andesitic composition, slightly more primitive than on the early stage. The compositions of olivine cores and Cr-spinel inclusions in olivine in the late stage andesites are identical to those in basalts and suggest injection of basaltic magma into silicic magma shortly before eruption of andesite. The composition of shallow magma reservoir before the 2010 eruption could have composition similar to the group 2c glasses. A remarkable peculiarity of silicic Eyjafjallajökull glasses is high Cl (0.2-0.45 wt%) and high Cl/K2O (0.07-0.13) which are higher compared to basaltic glasses and primitive inclusions in olivine (Cl=0.02-0.09 wt%, Cl/K2O=0.04-0.09). The Cl enrichment in silicic Eyjafjallajökull melts may be an indicator of assimilation of crustal rocks altered via interaction with Cl-rich surface or oceanic waters. To estimate the residence time of basaltic xenocrysts in andesitic magma erupted on May 11, we measured compositional profiles in olivine xenocrysts and calculated the time required to form such a zoning via Fe-Mg diffusion. Orientation of the studied olivine sections has been determined with universal table and verified by comparing the facet angles with the ideal olivine crystal shape. Our modeling indicates that the high-Mg olivine

  9. Magma flow through elastic-walled dikes

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


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

  10. Combined Effects of Ocean Warming and Acidification on Copepod Abundance, Body Size and Fatty Acid Content.

    Jessica Garzke

    Full Text Available Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1-5 and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA and arachidonic acid (ARA to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts.

  11. Combined Effects of Ocean Warming and Acidification on Copepod Abundance, Body Size and Fatty Acid Content

    Hansen, Thomas; Ismar, Stefanie M. H.; Sommer, Ulrich


    Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1–5) and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA) and arachidonic acid (ARA) to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts. PMID:27224476

  12. Utilising Geological Field Measurements and Historic Eruption Volumes to Estimate the Volume of Santorini's Magma Chamber

    Browning, J.; Drymoni, K.; Gudmundsson, A.


    An understanding of the amount of magma available to supply any given eruption is useful for determining the potential eruption magnitude and duration. Geodetic measurements and inversion techniques are often used to constrain volume changes within magma chambers, as well as constrain location and depth, but such models are incapable of calculating total magma storage. For example, during the 2012 unrest period at Santorini volcano, approximately 0.021 km3 of new magma entered a shallow chamber residing at around 4 km below the surface. This type of event is not unusual, and is in fact a necessary condition for the formation of a long-lived shallow chamber, of which Santorini must possess. The period of unrest ended without culminating in eruption, i.e the amount of magma which entered the chamber was insufficient to break the chamber and force magma further towards the surface. We combine previously published data on the volume of recent eruptions at Santorini together with geodetic measurements. Measurements of dykes within the caldera wall provide an estimate of the volume of magma transported during eruptions, assuming the dyke does not become arrested. When the combined volume of a dyke and eruption are known (Ve) they can be used to estimate using fracture mechanics principles and poro-elastic constraints the size of an underlying shallow magma chamber. We present field measurements of dykes within Santorini caldera and provide an analytical method to estimate the volume of magma contained underneath Santorini caldera. In addition we postulate the potential volume of magma required as input from deeper sources to switch the shallow magma chamber from an equilibrium setting to one where the pressure inside the chamber exceeds the surrounding host rocks tensile strength, a condition necessary to form a dyke and a possible eruption.

  13. Southeast Asia in the ancient Indian Ocean World; Combining historical linguistic and archaeological approaches

    Tom G. Hoogervorst


    Full Text Available This PhD dissertation examines the role of insular Southeast Asia in the trans-regional networks of maritime trade that shaped the history of Indian Ocean. The work brings together data and approaches from archaeology, historical linguistics and other disciplines, proposing a reconstruction of cultural and linguistic contact between Southeast Asia and its maritime neighbours to the west in order to advance our historical understanding of this part of the world. Numerous biological, commercial and technical items are examined. The study underlines that the analysis of lexical data is one of the strongest tools to detect and analyse contact between two or more speech communities. It demonstrates how Southeast Asian products and concepts were mainly dispersed by speakers of Malay varieties, although other communities played a role as well. Through an interdisciplinary approach, the study offers new perspectives on the role of insular Southeast Asian agents on cultural dynamism and interethnic contact in the pre-modern Indian Ocean World.

  14. Separation of atmospheric, oceanic and hydrological polar motion excitation mechanisms by a combination of geometric and gravimetric space observations

    Göttl, Franziska; Schmidt, Michael; Seitz, Florian; Blossfeld, Mathis


    Redistribution and motion of masses within and between the individual subsystems of the Earth cause variations of the orientation of the Earth axis with respect to an Earth-fixed reference frame (polar motion and length-of-day variations). Whereas the integral effect of Earth rotation is precisely measured by geometric space techniques, such as Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and Doppler Orbit determination and Radiopositioning Integrated on Satellite (DORIS), the separation into individual excitation mechanisms remains a challenge. Commonly, individual geophysical excitation mechanisms of Earth rotation are derived from geophysical models. Due to the fact that geophysical models are afflicted with uncertainties, results derived from different model show large discrepancies. Here we present an adjustment model which allows to combine precise observations from space geodetic observation systems (SLR, VLBI, GNSS, DORIS, satellite altimetry and satellite gravimetry) in order to separate geophysical excitation mechanisms of the Earth rotation. Time variable gravity field solutions from GRACE (Gravity Recovery and Climate Experiment) are used to determine not only the integral mass effect but also the oceanic and hydrological mass effects by applying suitable filter techniques and land-ocean-masks. Furthermore the oceanic mass effect is determined from sea level anomalies as observed by cross-calibrated multi-mission altimetry. Due to the fact that sea level anomalies are not only caused by mass variations but also by volume changes (steric effect), these steric sea level anomalies need to be reduced using appropriate models. We show that through the combination weaknesses of the individual processing strategies can be compensated and the technique specific strengths can be optimally accounted for. This way, excitation functions of atmospheric, oceanic and hydrological mass effects and

  15. Extension by faulting, stretching and magma intrusion in Ethiopia

    Bastow, I. D.; Keir, D.


    The 2001-2004 Ethiopia Afar Geoscientific Lithospheric Experiment showed that high seismic wavespeed, dense, mafic crustal intrusions exist beneath many zones of Quaternary magmatism in the Main Ethiopian rift, and that crustal thinning is minimal. From these observations, a consensus quickly emerged that extension presently occurs not by ductile stretching and brittle faulting but by magma intrusion. Striking InSAR images and accompanying seismic data from the 2005 Afar diking episode provided further compelling evidence in support of the magma assisted rifting hypothesis. Patterns of mantle seismic anisotropy, constrained by a combination of body and surface-wave analysis showed that melt intrusion likely also plays an important role in accommodating extension at greater depths in the extending plate. Evidence from further north in Afar, however, where crustal thickness decreases abruptly into the Danakil Depression, is not so easily explained by the magma assisted rifting hypothesis. Subsidence of the newly forming margin towards and below sea level, and eruption of voluminous basalt flows, is likely the result of late-stage thinning of the heavily intruded, weakened plate just before the onset of seafloor spreading. Faulting, stretching and magma intrusion are thus each important, but at different times during breakup. Combining, not isolating, these mechanisms of strain in new rifting models and appreciating how plate strength varies during rifting is essential in developing a clearer understanding of the incomplete geological record that documents continental breakup over time.

  16. Textural and chemical consequences of interaction between hydrous mafic and felsic magmas: an experimental study

    Pistone, Mattia; Blundy, Jonathan D.; Brooker, Richard A.


    Mantle-derived, hydrous mafic magmas are often invoked as a mechanism to transfer heat, mass and volatiles to felsic plutons in the Earth's crust. Field observations suggest that mafic, water-rich magmas often intrude viscous felsic crystal-rich mushes. This scenario can advect water from the crystallising mafic magma to the felsic magma, leading to an increase in melt fraction in the felsic mush and subsequent mobilisation, at the same time as the mafic magma becomes quenched through a combination of cooling and water loss. To investigate such a scenario, we conducted experiments on a water-undersaturated (4 wt% H2O in the interstitial melt) dacitic crystal mush (50-80 vol% quartz crystals) subject to volatile supply from a water-saturated (≥6 wt% H2O) andesite magma at 950 °C and 4 kbar. Our experimental run products show unidirectional solidification textures (i.e. comb layering) as crystals nucleate at the mafic-felsic interface and grow into the mafic end-member. This process is driven by isothermal and isobaric undercooling resulting from a change in liquidus temperature as water migrates from the mafic to the felsic magma. We refer to this process as "chemical quenching" and suggest that some textures associated with natural mafic-felsic interactions are not simply cooling-driven in origin, but can be caused by exsolution of volatiles adjacent to an interface, whether a water-undersaturated felsic magma (as in our experiments) or a fracture.

  17. Magma Mixing: Why Picrites are Not So Hot

    Natland, J. H.


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

  18. Combined Use of Polar and Geostationary Satellite Sensors For Aerosol Characterization Over The Ocean

    Costa, M. J.; Cervino, M.; Levizzani, V.; Silva, A. M.

    Aerosol particles play an important role in the Earth's climate due to their direct and indirect interaction with the atmosphere. Monitoring of the optical properties of atmospheric aerosol is thus crucial for a radiative forcing quantification at the lo- cal, regional and global scales. Ground-based measurements provide accurate aerosol properties. However, given the strong spatial and temporal variability of tropospheric aerosols ground measurements cannot cover the global scale. On the other hand, satellite-based algorithms for aerosol retrievals presently do not match the accuracy of ground-based results. Most satellite algorithms are based on a single sensor, thus often suffering from specific limitations (poor spatial or spectral resolution, long re- visitation time, poor cloud mask). A method to exploit the synergy between the polar orbiting Global Ozone Monitoring Experiment (GOME) onboard ERS-2 and the METEOSAT geostationary system was proposed (Costa et al., 2001), aiming at increasing the accuracy of the aerosol charac- terization and monitoring of the optical thickness. A validation of the algorithm is done by comparing satellite retrievals with results obtained via independent space-time co- located ground-based measurements from AERONET (Aerosol Robotic NETwork) and from other state of the art algorithms that make use of satellite measurements such as the MODIS official aerosol product. Results of the ongoing validation are pre- sented for relevant transport events of desert dust and biomass burning aerosol over the Atlantic and Indian Oceans during year 2000. References: Costa,M.J., M.Cervino, E.Cattani, F.Torricella, V.Levizzani, and A.M.Silva, 2001: "Aerosol characterization and optical thickness retrievals using GOME and METEOSAT satellite data". Meteor. Atmos. Phys., (in press). Acknowledgements: METEOSAT imagery was kindly made available by EUMET- SAT. We thank the AERONET investigators and their staff for establishing and main- taining the

  19. MAGMA: a multiagent architecture for metaheuristics.

    Milano, Michela; Roli, Andrea


    In this work, we introduce a multiagent architecture called the MultiAGent Metaheuristic Architecture (MAGMA) conceived as a conceptual and practical framework for metaheuristic algorithms. Metaheuristics can be seen as the result of the interaction among different kinds of agents: The basic architecture contains three levels, each hosting one or more agents. Level-0 agents build solutions, level-1 agents improve solutions, and level-2 agents provide the high level strategy. In this framework, classical metaheuristic algorithms can be smoothly accommodated and extended. The basic three level architecture can be enhanced with the introduction of a fourth level of agents (level-3 agents) coordinating lower level agents. With this additional level, MAGMA can also describe, in a uniform way, cooperative search and, in general, any combination of metaheuristics. We describe the entire architecture, the structure of agents in each level in terms of tuples, and the structure of their coordination as a labeled transition system. We propose this perspective with the aim to achieve a better and clearer understanding of metaheuristics, obtain hybrid algorithms, suggest guidelines for a software engineering-oriented implementation and for didactic purposes. Some specializations of the general architecture will be provided in order to show that existing metaheuristics [e.g., greedy randomized adaptive procedure (GRASP), ant colony optimization (ACO), iterated local search (ILS), memetic algorithms (MAs)] can be easily described in our framework. We describe cooperative search and large neighborhood search (LNS) in the proposed framework exploiting level-3 agents. We show also that a simple hybrid algorithm, called guided restart ILS, can be easily conceived as a combination of existing components in our framework.

  20. Shallow magma targets in the western US

    Hardee, H.C.


    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.

  1. Linking magma composition with volcano size and eruptive style in basaltic monogenetic systems

    Smith, I. E.; McGee, L. E.; Cronin, S. J.


    Magma composition, volcano size and eruptive style (together with vent locations) are the definitive parameters of basaltic monogenetic systems. These variables are not independent, but the relationships between them are complex. Monogenetic volcano fields that episodically erupt small-volume, discrete magma batches such as the Auckland Volcanic Field (AVF, northern New Zealand), typically represent primary mantle melts variably modified by near source processes. In such cases, where the volume of magma is small, eruption styles are strongly controlled by the interaction of magma with the surficial environment and this is determined by both magma volume and its rise rate. The magmatic compositional extremes of primitive magmas in the AVF define a spectrum ranging from strongly silica-undersaturated nephelinite to sub-alkalic basalt. Nephelinites are low SiO2 (~40 wt.%), highly incompatible-element enriched compositions, representing very low degrees of partial melting (indicates that all of these magmas are sourced within the same general mantle region at depths of 80-70 km. The two compositional extremes also define extremes in volume of magma and ultimately magma flux at the surface. The surficial environment of the AVF is characterized by highly water saturated sediments of variable competency and many pressurized aquifer systems. Where there is a combination of small volumes and low flux rates, environmental factors dominate and phreatomagmatic explosive eruptions ensue, forming tuff cones, rings and maars. Larger volumes and flux rates result in dry eruptions forming cinder cones and lava fields. Thus at a fundamental level defining magma source characteristics and temporal or spatial variation in these (such as cyclic or evolutionary trends) can inform better long term forecasts of surface eruption processes and thus should be more closely examined in hazard studies of monogentic fields.

  2. Numerical Simulation of Magma Effects on Hydrothermal Venting at Ultra-Slow Spreading Southwest Indian Ridge

    Zang, Hong; Niu, Xiongwei; Ruan, Aiguo; Li, Jiabiao; Meng, Lin


    Finite element method is used to numerically simulate oceanic crust thermal dynamics in order to understand the hydrothermal venting mechanism at ultra-slow spreading ridge, whether is the ancient magma chamber still living and supplying hot magma for vents or have surrounding hotspots been affecting on the ridge continually with melting and hot magma. Two models are simulated, one is a horizontal layered oceanic crust model and the other is a model derived from wide angle seismic experiment of OBS at the ultra-slow spreading Southwest Indian Ridge (50°E, Zhao et al., 2013; Li et al., 2015; Niu et al., 2015). For the former two cases are simulated: without magma from upper mantel or with continuous magma supply, and for the latter supposing magma supply occurs only once in short period. The main conclusions are as follows: (1) Without melt magma supply at the oceanic crust bottom, a magma chamber can live only thousands ten thousand years. According to the simulated results in this case, the magma chamber revealed by seismic data at the mid-east shallow section of the Southwest Indian Ridge could only last 0.8Ma, the present hydrothermal venting is impossible to be the caused by the magma activity occurred during 8-11Ma (Sauter et al., 2009). (2) The magma chamber can live long time with continuous hot magma supply beneath the oceanic crust due to the melting effects of surrounding ridge hotspots, and would result hydrothermal venting with some tectonic structures condition such as detachment faults. We suggest that the present hydrothermal activities at the mid-east shallow section of the Southwest Indian Ridge are the results of melting effects or magma supply from surrounding hotspots. This research was granted by the National Basic Research program of China (grant 2012CB417301) and the National Natural Science Foundation of China (grants 41176046, 91228205). References Zhao, M., Qiu, X., Li, J., et al., 2013. Three-dimensional seismic structure of the Dragon

  3. Why do Martian Magmas erupt?

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


    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. The larvae of congeneric gastropods showed differential responses to the combined effects of ocean acidification, temperature and salinity.

    Zhang, Haoyu; Cheung, S G; Shin, Paul K S


    The tolerance and physiological responses of the larvae of two congeneric gastropods, the intertidal Nassarius festivus and subtidal Nassarius conoidalis, to the combined effects of ocean acidification (pCO2 at 380, 950, 1250 ppm), temperature (15, 30°C) and salinity (10, 30 psu) were compared. Results of three-way ANOVA on cumulative mortality after 72-h exposure showed significant interactive effects in which mortality increased with pCO2 and temperature, but reduced at higher salinity for both species, with higher mortality being obtained for N. conoidalis. Similarly, respiration rate of the larvae increased with temperature and pCO2 level for both species, with a larger percentage increase for N. conoidalis. Larval swimming speed increased with temperature and salinity for both species whereas higher pCO2 reduced swimming speed in N. conoidalis but not N. festivus. The present findings indicated that subtidal congeneric species are more sensitive than their intertidal counterparts to the combined effects of these stressors.

  5. Primary magmas and mantle temperatures through time

    Ganne, Jérôme; Feng, Xiaojun


    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.abstract type="synopsis">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 (>22,000 samples formed in

  6. Staged storage and magma convection at Ambrym volcano, Vanuatu

    Sheehan, Fionnuala; Barclay, Jenni


    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 magma plumbing system of Ambrym volcano. Pressures and temperatures of magma crystallisation at Ambrym are poorly constrained. This study focuses on characterising the magma conditions underlying the quasi-permanent lava lakes at the basaltic central vents, and examines petrological evidence for magma 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 magma 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.

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

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


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

  8. Magma Energy Research Project, FY80 annual progress report

    Colp, J.L. (ed.)


    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.

  9. Petrology of ocean floor rocks from Central Indian Ocean basin

    Iyer, S.D.; Karisiddaiah, S.M.

    on the pumice is also a possibility IQ. The influence ofsubmarine volca noes as sources for pumice may be possible for CIOO samples, similar to those reported for the Atlantic Ocean 20 . It is envisaged that the uprising magma was basic and highly fluid...

  10. More Evidence for Multiple Meteorite Magmas

    Taylor, G. J.


    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.

  11. Depth of origin of magma in eruptions.

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


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

  12. Time Evolution of Thermo-Mechanically and Chemically Coupled Magma Chambers

    Ozimek, C.; Karlstrom, L.; Erickson, B. A.


    Complexity in the volcanic eruption cycle reflects time variation both of magma inputs to the crustal plumbing system and of crustal melt storage zones (magma chambers). These data include timing and volumes of eruptions, as well as erupted compositions. Thus models must take into account the coupled nature of physical attributes. Here we combine a thermo-mechanical model for magma chamber growth and pressurization with a chemical model for evolving chamber compositions, in the limit of rapid mixing, to study controls on eruption cycles and compositions through time. We solve for the mechanical evolution of a 1D magma chamber containing melt, crystals and bubbles, in a thermally evolving and viscoelastic crust. This pressure and temperature evolution constrains the input values of a chemical box model (Lee et al., 2013) that accounts for recharge, eruption, assimilation and fractional crystallization (REAFC) within the chamber. We plan to study the influence of melt supply, input composition, and chamber depth eruptive fluxes and compositions. Ultimately we will explore multiple chambers coupled by elastic-walled dikes. We expect that this framework will facilitate self-consistent inversion of long-term eruptive histories in terms of magma transport physics. Lee, C.-T. A., Lee, T.-C., Wu, C.-T., 2013. Modeling the compositional evolution of recharging, evacuating, and fractionating (REFC) magma chambers: Implications for differentiationof arc magmas. Geochemica Cosmochimica Acta,

  13. Lifetime and size of shallow magma bodies controlled by crustal-scale magmatism

    Karakas, Ozge; Degruyter, Wim; Bachmann, Olivier; Dufek, Josef


    Magmatic processes on Earth govern the mass, energy and chemical transfer between the mantle, crust and atmosphere. To understand magma storage conditions in the crust that ultimately control volcanic activity and growth of continents, an evaluation of the mass and heat budget of the entire crustal column during magmatic episodes is essential. Here we use a numerical model to constrain the physical conditions under which both lower and upper crustal magma bodies form. We find that over long durations of intrusions (greater than 105 to 106 yr), extensive lower crustal mush zones develop, which modify the thermal budget of the upper crust and reduce the flux of magma required to sustain upper crustal magma reservoirs. Our results reconcile physical models of magma reservoir construction and field-based estimates of intrusion rates in numerous volcanic and plutonic localities. Young igneous provinces (less than a few hundred thousand years old) are unlikely to support large upper crustal reservoirs, whereas longer-lived systems (active for longer than 1 million years) can accumulate magma and build reservoirs capable of producing super-eruptions, even with intrusion rates smaller than 10-3 to 10-2 km3 yr-1. Hence, total duration of magmatism should be combined with the magma intrusion rates to assess the capability of volcanic systems to form the largest explosive eruptions on Earth.

  14. A mantle-driven surge in magma supply to Kīlauea Volcano during 2003--2007

    Poland, Michael P.; Miklius, Asta; Sutton, A. Jeff; Thornber, Carl R.


    The eruptive activity of a volcano is fundamentally controlled by the rate of magma supply. At Kīlauea Volcano, Hawai‘i, the rate of magma rising from a source within Earth’s mantle, through the Hawaiian hotspot, was thought to have been relatively steady in recent decades. Here we show that the magma supply to Kīlauea at least doubled during 2003–2007, resulting in dramatic changes in eruptive activity and the formation of new eruptive vents. An initial indication of the surge in supply was an increase in CO2 emissions during 2003–2004, combined with the onset of inflation of Kīlauea’s summit, measured using the Global Positioning System and interferometric synthetic aperture radar. Inflation was not limited to the summit magma reservoirs, but was recorded as far as 50 km from the summit, implying the existence of a connected magma system over that distance. We also record increases in SO2 emissions, heightened seismicity, and compositional and temperature variations in erupted lavas. The increase in the volume of magma passing through and stored within Kīlauea, coupled with increased CO2 emissions, indicate a mantle source for the magma surge. We suggest that magma supply from the Hawaiian hotspot can vary over timescales of years, and that CO2 emissions could be a valuable aid for assessing variations in magma supply at Kīlauea and other volcanoes.

  15. Combination of TOPEX/POSEIDON Data with a Hydrographic Inversion for Determination of the Oceanic General Circulation and its Relation to Geoid Accuracy

    Ganachaud, Alexandre; Wunsch, Carl; Kim, Myung-Chan; Tapley, Byron


    A global estimate of the absolute oceanic general circulation from a geostrophic inversion of in situ hydrographic data is tested against and then combined with an estimate obtained from TOPEX/POSEIDON altimetric data and a geoid model computed using the JGM-3 gravity-field solution. Within the quantitative uncertainties of both the hydrographic inversion and the geoid estimate, the two estimates derived by very different methods are consistent. When the in situ inversion is combined with the altimetry/geoid scheme using a recursive inverse procedure, a new solution, fully consistent with both hydrography and altimetry, is found. There is, however, little reduction in the uncertainties of the calculated ocean circulation and its mass and heat fluxes because the best available geoid estimate remains noisy relative to the purely oceanographic inferences. The conclusion drawn from this is that the comparatively large errors present in the existing geoid models now limit the ability of satellite altimeter data to improve directly the general ocean circulation models derived from in situ measurements. Because improvements in the geoid could be realized through a dedicated spaceborne gravity recovery mission, the impact of hypothetical much better, future geoid estimates on the circulation uncertainty is also quantified, showing significant hypothetical reductions in the uncertainties of oceanic transport calculations. Full ocean general circulation models could better exploit both existing oceanographic data and future gravity-mission data, but their present use is severely limited by the inability to quantify their error budgets.

  16. Combined Effects of Ocean Acidification and Light or Nitrogen Availabilities on 13C Fractionation in Marine Dinoflagellates

    Hoins, Mirja; Eberlein, Tim; Groβmann, Christian H.; Brandenburg, Karen; Reichart, Gert-Jan; Rost, Björn; Sluijs, Appy; Van de Waal, Dedmer B.


    Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractionation (εp) in four dinoflagellate species. We cultured Gonyaulax spinifera and Protoceratium reticulatum in dilute batches under low-light (‘LL’) and high-light (‘HL’) conditions, and grew Alexandrium fundyense and Scrippsiella trochoidea in nitrogen-limited continuous cultures (‘LN’) and nitrogen-replete batches (‘HN’). The observed CO2-dependency of εp remained unaffected by the availability of light for both G. spinifera and P. reticulatum, though at HL εp was consistently lower by about 2.7‰ over the tested CO2 range for P. reticulatum. This may reflect increased uptake of (13C-enriched) bicarbonate fueled by increased ATP production under HL conditions. The observed CO2-dependency of εp disappeared under LN conditions in both A. fundyense and S. trochoidea. The generally higher εp under LN may be associated with lower organic carbon production rates and/or higher ATP:NADPH ratios. CO2-dependent εp under non-limiting conditions has been observed in several dinoflagellate species, showing potential for a new CO2-proxy. Our results however demonstrate that light- and nitrogen-limitation also affect εp, thereby illustrating the need to carefully consider prevailing environmental conditions. PMID:27153107

  17. The X-43A/Pegasus combination dropped into the Pacific Ocean after losing control early in the first


    The first X-43A hypersonic research aircraft and its modified Pegasus booster rocket were carried aloft by NASA's NB-52B carrier aircraft from Dryden Flight Research Center at Edwards Air Force Base, Calif., on June 2, 2001 for the first of three high-speed free flight attempts. About an hour and 15 minutes later the Pegasus booster was released from the B-52 to accelerate the X-43A to its intended speed of Mach 7. Before this could be achieved, the combined Pegasus and X-43A 'stack' lost control about eight seconds after ignition of the Pegasus rocket motor. The mission was terminated and explosive charges ensured the Pegasus and X-43A fell into the Pacific Ocean in a cleared Navy range area. A NASA investigation board is being assembled to determine the cause of the incident. Work continues on two other X-43A vehicles, the first of which could fly by late 2001. Central to the X-43A program is its integration of an air-breathing 'scramjet' engine that could enable a variety of high-speed aerospace craft, and promote cost-effective access to space. The 12-foot, unpiloted research vehicle was developed and built for NASA by MicroCraft Inc., Tullahoma, Tenn. The booster was built by Orbital Sciences Corp. at Chandler, Ariz. The X-43A flights are the first actual flight tests of an aircraft powered by a scramjet engine capable of operating at hypersonic speeds (above Mach 5, or five times the speed of sound). Some 90 minutes after takeoff, the Pegasus will launch from a B-52, rocketing the X-43A to Mach 7 at 95,000 feet altitude, or Mach 10 at 105,000 feet altitude. The X-43A will be powered by its revolutionary air-breathing supersonic-combustion ramjet or 'scramjet' engine. The X-43A will then fly a pre-programmed trajectory, conducting aerodynamic and propulsion experiments as it descends until it splashes into the Pacific Ocean.

  18. The impacts of pharmaceutical drugs under ocean acidification: New data on single and combined long-term effects of carbamazepine on Scrobicularia plana.

    Freitas, Rosa; Almeida, Ângela; Calisto, Vânia; Velez, Cátia; Moreira, Anthony; Schneider, Rudolf J; Esteves, Valdemar I; Wrona, Frederick J; Figueira, Etelvina; Soares, Amadeu M V M


    Ocean acidification and increasing discharges of pharmaceutical contaminants into aquatic systems are among key and/or emerging drivers of environmental change affecting marine ecosystems. A growing body of evidence demonstrates that ocean acidification can have direct and indirect impacts on marine organisms although combined effects with other stressors, namely with pharmaceuticals, have received very little attention to date. The present study aimed to evaluate the impacts of the pharmaceutical drug Carbamazepine and pH 7.1, acting alone and in combination, on the clam Scrobicularia plana. For this, a long-term exposure (28 days)was conducted and a set of oxidative stress markers was investigated. The results obtained showed that S. plana was able to develop mechanisms to prevent oxidative damage when under low pH for a long period, presenting higher survival when exposed to this stressor compared to CBZ or the combination of CBZ with pH 7.1. Furthermore, the toxicity of CBZ on S. plana was synergistically increased under ocean acidification conditions (CBZ + pH 7.1): specimens survival was reduced and oxidative stress was enhanced when compared to single exposures. These findings add to the growing body of evidence that ocean acidification will act to increase the toxicity of CBZ to marine organisms,which has clear implications for coastal benthic ecosystems suffering chronic pollution from pharmaceutical drugs.

  19. A model to forecast magma chamber rupture

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust


    An understanding of the amount of magma available to supply any given eruption is useful for determining the potential eruption magnitude and duration. Geodetic measurements and inversion techniques are often used to constrain volume changes within magma chambers, as well as constrain location and depth, but such models are incapable of calculating total magma storage. For example, during the 2012 unrest period at Santorini volcano, approximately 0.021 km3 of new magma entered a shallow chamber residing at around 4 km below the surface. This type of event is not unusual, and is in fact a necessary condition for the formation of a long-lived shallow chamber. The period of unrest ended without culminating in eruption, i.e the amount of magma which entered the chamber was insufficient to break the chamber and force magma further towards the surface. Using continuum-mechanics and fracture-mechanics principles, we present a model to calculate the amount of magma contained at shallow depth beneath active volcanoes. Here we discuss our model in the context of 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.

  20. Experimental Study of Lunar and SNC Magmas

    Rutherford, Malcolm J.


    The research described in this progress report involved the study of petrological, geochemical, and volcanic processes that occur on the Moon and the SNC meteorite parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the types of magmas (magma compositions) present, the role of volatiles in magmatic processes, and on processes of magma evolution on these planets. We are also interested in how these processes and magma types varied over time.In earlier work on the A15 green and A17 orange lunar glasses, we discovered a variety of metal blebs. Some of these Fe-Ni metal blebs occur in the glass; others (in A17) were found in olivine phenocrysts that we find make up about 2 vol 96 of the orange glass magma. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption . They also yield important information about the composition of the gas phase present, the gas that drove the lunar fire-fountaining. During the tenure of this grant, we have continued to work on the remaining questions regarding the origin and evolution of the gas phase in lunar basaltic magmas, what they indicate about the lunar interior, and how the gas affects volcanic eruptions. Work on Martian magmas petrogenesis questions during the tenure of this grant has resulted in advances in our methods of evaluating magmatic oxidation state variations in Mars and some new insights into the compositional variations that existed in the SNC magmas over time . Additionally, Minitti has continued to work on the problem of possible shock effects on the abundance and distribution of water in Mars minerals.

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

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


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

  2. Magma production rate along the Ninetyeast Ridge and its relationship to Indian plate motion and Kerguelen hot spot activity

    Sreejith, K. M.; Krishna, K. S.


    The Ninetyeast Ridge, a linear trace of the Kerguelen hot spot in the Indian Ocean, was emplaced on a rapidly drifting Indian plate. Magma production rates along the ridge track are computed using gravity-derived excess crustal thickness data. The production rates change between 2 and 15 m3/s over timescales of 3-16 Myr. Major variations in magma production rates are primarily associated with significant changes in the Indian plate velocity with low-production phases linked to high plate velocity periods. The lowest magma production rate (2 m3/s) at 62 Ma is associated with the rapid northward drift of Indian plate under the influence of the Reunion mantle plume. The contemporaneous slowing of the African plate coincides with increase in magma production rate along the Walvis Ridge in the Atlantic Ocean. The present study suggests that variations in the Indian plate motion and frequent ridge jumps have a major role in controlling the magma production, particularly on long-period cycles (~16 Myr). Short-period variations (~5 Myr) in magma productions may be associated with intrinsic changes in the plume, possibly due to the presence of solitary waves in the plume conduit.

  3. Tidal Heating in a Magma Ocean within Jupiter's Moon Io

    Tyler, Robert H.; Henning, Wade G.; Hamilton, Christopher W.


    Active volcanism observed on Io is thought to be driven by the temporally periodic, spatially differential projection of Jupiter's gravitational field over the moon. Previous theoretical estimates of the tidal heat have all treated Io as essentially a solid, with fluids addressed only through adjustment of rheological parameters rather than through appropriate extension of the dynamics. These previous estimates of the tidal response and associated heat generation on Io are therefore incomplete and possibly erroneous because dynamical aspects of the fluid behavior are not permitted in the modeling approach. Here we address this by modeling the partial-melt asthenosphere as a global layer of fluid governed by the Laplace Tidal Equations. Solutions for the tidal response are then compared with solutions obtained following the traditional solid-material approach. It is found that the tidal heat in the solid can match that of the average observed heat flux (nominally 2.25 W m-2), though only over a very restricted range of plausible parameters, and that the distribution of the solid tidal heat flux cannot readily explain a longitudinal shift in the observed (inferred) low-latitude heat fluxes. The tidal heat in the fluid reaches that observed over a wider range of plausible parameters, and can also readily provide the longitudinal offset. Finally, expected feedbacks and coupling between the solid/fluid tides are discussed. Most broadly, the results suggest that both solid and fluid tidal-response estimates must be considered in exoplanet studies, particularly where orbital migration under tidal dissipation is addressed.

  4. Magma beneath Yellowstone National Park

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


    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

  5. Volatiles Which Increase Magma Viscosity

    Webb, S.


    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.

  6. Oxidation of shallow conduit magma: Insight from μ-XANES analysis on volcanic ash particle

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


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

  7. Enhanced volcanic CO2 degassing at oceanic hotspots and mid-ocean ridges in response to falling sea level

    Hasenclever, Jörg; Knorr, Gregor; Rüpke, Lars; Köhler, Peter; Morgan, Jason; Garofalo, Kristin; Barker, Stephen; Lohmann, Gerrit; Hall, Ian


    Evidence from paleo-climate proxy data as well as results from geodynamical and biogeochemical modelling point to complex interactions between sea level variations, pressure-release melting of oceanic mantle, associated volcanic degassing, and atmospheric CO2 concentrations. Ice core data shows that the orbital component in global temperature records gradually declined between ˜85,000-70,000 yr BP, while atmospheric CO2 - instead of continuing its long-term correlation with Antarctic temperatures - remained relatively stable for several thousand years. Based on 2-D and 3-D geodynamical models we show that the massive (60-100 m) sea level drop during this period of Earth history led to a significant increase in magma and possibly CO2 fluxes along mid-ocean ridges (MOR) and especially oceanic hotspot volcanoes. We assess the MOR magma and CO2 fluxes using 2-D thermo-mechanical models that solve for wet melting of the mantle and the partitioning of highly incompatible carbon dioxide into the melt. These models have been run at various MOR opening rates, and we integrate these results with the global distribution of spreading rates to compute baseline fluxes as well as enhanced fluxes during the sea level fall. Furthermore we conducted more than 120 3-D simulations of rising and melting mantle plumes to construct a four-dimensional parameter space that covers a wide range of plume buoyancy fluxes, plume excess temperatures, lithosphere thicknesses and plate speeds. Using published data on 43 oceanic hotspots and locating them in the parameter space we derive a global hotspot-melting model that predicts magma and CO2 fluxes before and during the sea level drop. We find that, during a 80 m sea level drop over 10 kyr, global degassing at MOR and oceanic hotspots increases by 26 % and 36 %, respectively. Biogeochemical carbon cycle modelling further shows that the combined predicted increase in volcanic emissions along the global mid-ocean ridge system and at oceanic

  8. On the Interaction of a Vigorous Hydrothermal System with an Active Magma Chamber: The Puna Magma Chamber, Kilauea East Rift, Hawaii

    Gregory, R. T.; Marsh, B. D.; Teplow, W.; Fournelle, J.


    of dacitic composition of ~67 wt.% SiO2. The melt flowed up the borehole, quenched, and was repeatedly re-drilled over a depth interval of ~8 m, producing several kilograms of clear, colorless vitric cuttings. The melt is of low crystallinity, vesicle-free, at a minimum temperature of ~865°C, and with an apparent viscosity of ~106.5 Pa-s. The magma is separated from the deepest hydrothermal regime at 356°C by 526 m of sealed rock. Heat flux from the magma into the overlying geothermal reservoir at ~2784 mW/m2 is an order of magnitude greater than that for mid-ocean ridges. Typical Hawaiian basalt contains ~0.25 wt.% water. The dacite melt contains ~2.44 wt.% water, and is of normal magmatic δ18O (5.4 ‰) and δD (-61.8‰), which is in contrast to the surrounding hydrothermal waters. A similar preliminary analysis of the water content in the altered basalt just outside the sealed zone shows it to heavily hydrated (~4.94 wt.%) and altered by the hydrothermal field. This suggests that volatile under-saturated magmas are sealed with respect to hydrothermal fields and deeper systems may be even more strongly sealed.

  9. Layered basic complex in oceanic crust, romanche fracture, equatorial atlantic ocean.

    Melson, W G; Thompson, G


    A layered, basic igneous intrusion, analogous in mineralogy and texture to certain large, continental layered complexes, is exposed in the Romanche Fracture, equatorial Atlantic Ocean. Crustal intrusion of large masses of basic magmas with their subsequent gravity differentiation is probably one of a number of major processes involved in the formation of new oceanic crust during sea-floor spreading.

  10. Differentiation Mechanism and Evolution of High-level Magma Chamber at Xiangshan,China


    The calc-alkaline volcanic magmas,which formed the Mesozoic uraniferous volcanic complex of Xiangshan,resulted from partial melting of the mixture of lower crust and enriched mantle with a high mixing proportion in a specific tectonic setting such as active continental margin or ocean-continent collision zone.The preliminary concentrations of Uand Th occur in low-degree par-tial melts.Only small part of these melts was rapidly extracted and erupted and most intruded into the high-level magma chamber(depth:12-13 km) of the compressed upper lithosphere ,in which occurred a strong differentiation which would resulted in strong preconcentrations of the high-hygromagmaphile elements U and Th associated with strong depletion of the 3-d transition ele-ments Ti,Sc,Co,Zr,etc.At the final stage of subduction of the West-Pacific-Kula plate towards the Asian continental plate,the regional tectonic environment was transformed from a compressive in-to a tensional setting.The strongly differentiated,U(and Th) enriched silicic alkalic magmas in high level magma chamber extensively erupted,extruded and intruded.The hydrothermal fluids released as a result of late volcano-degassing and dewatering during crystallization-solidification of magmas,re-sulted in the remobilization,leaching,migration and reconcentration of uranium ,which had been preconcentrated in volcanic rocks.Therefore,specific regional petrogeochemical criteria are expected for the uraniferous volcanic series.

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

    Glazner, A. F.


    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

  12. Understanding individual and combined effects of ocean acidification, warming and coastal runoff on marine calcifying organisms on tropical coral reefs

    Vogel, Nikolas


    Anthropogenically induced greenhouse gas emissions result in two major environmental changes on the global scale for coral reefs: ocean acidification (OA) and ocean warming (OW). Additionally, increasing levels of terrestrial runoff, that introduce fertilizer, sewage, sediments and other contaminants into coastal areas, can decrease water quality on the local scale. Consequently, photosynthesizing and calcifying coral reef organisms are affected by OA, OW and coastal runoff, but knowledge abo...

  13. Combining Satellite Ocean Color Imagery and Circulation Modeling to Forecast Bio-Optical Properties: Comparison of Models and Advection Schemes


    Remote sensing of ocean color provides synoptic surface ocean bio -optical properties but is limited to real-time or climatological applications. Many...this, we couple satellite imagery with numerical circulation models to provide short-term (24-48 hr) forecasts of bio -optical properties. These are...physical processes control the bio -optical distribution patterns. We compare optical forecast results from three Navy models and two advection

  14. Slab melting and magma formation beneath the southern Cascade arc

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


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

  15. Experiments on the rheology of vesicle-bearing magmas

    Vona, Alessandro; Ryan, Amy G.; Russell, James K.; Romano, Claudia


    We present a series of high temperature uniaxial deformation experiments designed to investigate the effect of bubbles on the magma 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 magmas and lavas as a function of melt viscosity, vesicularity, strain rate, and geological condition. Increasing vesicularity in magmas can initiate non-Newtonian behaviour at constant strain rates. Lower melt viscosity sustains homogeneous Newtonian flow in vesiculated magmas even at relatively high strain rates.

  16. Mineralogical evidence for lamproite magma mixing and storage at mantle depths: Socovos fault lamproites, SE Spain

    Cambeses, A.; Garcia-Casco, A.; Scarrow, J. H.; Montero, P.; Pérez-Valera, L. A.; Bea, F.


    Detailed textural and mineral chemistry characterisation of lamproites from the Socovos fault zone, SE Spain Neogene Volcanic Province (NVP) combining X-ray element maps and LA-ICP-MS spot analyses has provided valuable information about mantle depth ultrapotassic magma mixing processes. Despite having similar whole-rock compositions, rocks emplaced in the Socovos fault are mineralogically varied: including type-A olivine-phlogopite lamproites; and type-B clinopyroxene-phlogopite lamproites. The Ol-lacking type-B predates Ol-bearing type-A by c. 2 million years. We propose that the mineralogical variations, which are representative of lamproites in the NVP as a whole, indicate mantle source heterogeneities. Major and trace element compositions of mineral phases suggest both metasomatised harzburgite and veined pyroxenite sources that were most likely closely spatially related. Thin section scale textural and compositional variations in mineral phases reveal heterogeneous mantle- and primitive magma-derived crystals. The variety of crystals points to interaction and mingling-mixing of ultrapotassic magma batches at mantle depths prior crustal emplacement. The mixing apparently occurred in a mantle melting zone with a channelised flow regime and localised magma chambers-reservoirs. Magma interaction was interrupted when the Socovos and other lithosphere-scale faults tore down to the mantle source region, triggering rapid ascent of the heterogeneous lamproite magma.

  17. Genesis and open-system evolution of Quaternary magmas beneath southeastern margin of Tibet: Constraints from Sr-Nd-Pb-Hf isotope systematics

    Zou, Haibo; Ma, Mingjia; Fan, Qicheng; Xu, Bei; Li, Shuang-Qing; Zhao, Yongwei; King, David T.


    Post-collisional volcanic rocks on the Tibetan Plateau and its margins contain valuable information about the geodynamic processes associated with this Cenozoic continent-continent collision. The Quaternary Tengchong volcanic field at the southeastern margin of the Tibetan Plateau formed high-potassium calc-alkaline volcanic rocks. Herein, we present comprehensive Nd-Sr-Pb-Hf isotopic and elemental data for trachybasalts, basaltic trachyandesites, and trachyandesites from four Quaternary Tengchong volcanoes (Maanshan, Dayingshan, Heikongshan, and Laoguipo) in order to understand their magma genesis and evolution as well as tectonic significance. Good correlations between SiO2 content and the ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 177Hf/176Hf for these Quaternary volcanics strongly suggest that the combined assimilation and fractional crystallization (AFC) was an important process in the origin of basaltic trachyandesites and trachyandesites. High Y and Yb contents and low Sr/Y ratios of these basaltic trachyandesites and trachyandesites are uncharacteristic of adakites that formed by partial melting of eclogitic lower crust or partial melting of basaltic oceanic crust with eclogite as a restite. A combined assimilation-fractional crystallization model is proposed for these basaltic trachyandesites and trachyandesites. Nd-Sr-Pb-Hf isotopes for the uncontaminated Tengchong magma (trachybasalts with SiO2 5.5% wt.%) reflect a heterogeneous enriched mantle source. High Th/U, Th/Ta, and Rb/Nb ratios and Nd-Sr-Pb-Hf isotope characteristics of the uncontaminated magmas suggest that the enriched mantle beneath Tengchong formed as a result of subduction of clay-rich sediments, which probably came from the Indian continental plate. Partial melting of the enriched mantle was generated by deep continental subduction coupled with recent regional extension in the Tengchong area.

  18. Convective Regimes in Crystallizing Basaltic Magma Chambers

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


    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

  19. Remnants of a Late Triassic ocean island in the Gufeng area, northern Tibet: Implications for the opening and early evolution of the Bangong-Nujiang Tethyan Ocean

    Fan, Jian-Jun; Li, Cai; Wang, Ming; Liu, Yi-Ming; Xie, Chao-Ming


    In this paper we present new major and trace element compositions of basaltic rocks in the Gufeng ocean island (GFOI) area in the western segment of the Bangong-Nujiang Suture Zone, northern Tibet. Our aim was to assess the genesis of these rocks and discuss the implications of this new dataset for the evolution of the Bangong-Nujiang Tethyan Ocean. An ocean-island-type double-layer structure comprising a basaltic basement and an oceanic sedimentary cover sequence found within the GFOI provides direct evidence for the interpretation that the assemblage is a typical ocean island. The basalts in the GFOI can be divided into three types (named G1, G2 and G3 basalts), and these basalts range in composition from MORB to OIB types, which is typical of ocean islands. The G1 basalts have MORB-type affinities, possibly indicating the existence of MORB oceanic crust under the GFOI. The G2 basalts represent the early stage of formation of the GFOI, and are produced by the interaction of rising OIB-type basaltic magma and the existing MORB oceanic crust. The G3 basalts are typical OIB basalts and they are the products of the direct eruption of OIB-type basaltic magmas. The G3 basalts have high (La/Yb)N (12.3-14.4), (Ce/Yb)N (10.8-11.8), (La/Sm)N (2.39-2.76), and (Sm/Yb)N (4.89-5.23) ratios, indicating the presence of oceanic lithosphere below the GFOI with a thickness of 50-60 km. Geochemical analyses of the GFOI cherts show that they contain terrigenous material, indicating the GFOI formed close to a continental margin. Norian conodont fossils within the GFOI limestones indicate the GFOI formed during the Late Triassic. These data, combined with geological evidence and a half-space model of lithosphere cooling, where the thickness of the oceanic lithosphere is determined from the age of the lithosphere, indicate that the western segment of the Bangong-Nujiang Tethyan Ocean opened initially in the late Permian, expanded rapidly during the Early-Middle Triassic, and was a

  20. The parent magmas of the SNC meteorites

    Longhi, J.; Pan, V.


    Mineral compositions, partition coefficients, and computer-graphic representations of liquidus phase boundaries are used here to calculate parent magma compositions for Nakhla, Chassigny, and the xenocryst assemblage in EETA79001B, ALHA77005, and the EETA79001A groundmass. The calculated SNC parent magma compositions have low concentrations of Al2O3 and widely varying wollastonitite (CaO) component. In this regard they resemble basaltic komatiites, but their range of Wo is more extensive than that of basaltic komatiites and trace element characteristics are different. The calculated Nakhla parent magma has an unusually high Wo content and does not resemble any other known magmatic composition. A model of SNC petrogenesis is proposed.

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

    Xu, Wenbin; Rivalta, Eleonora; Li, Xing


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

  2. Yanshanian Magma-Tectonic-Metallogenic Belt in East China of Circum-Pacific Domain (Ⅰ):Igneous Rocks and Orogenic Processes


    Yanshanian igneous rocks in the East China, on an orogenic belt scale, are characterized by the continental marginal arc in petrology and geochemistry as Andes and West USA, except for the Hercyn-type biotite-two mica-muscovite granite belt in the Nanling region. Three segments of the Yanshanian igneous rocks along the belt are recognized. In terms of magma-tectonic event sequence, the north, middle and south segments have counter-clockwise (ccw), clockwise (cw) and ccw+cw pTt paths of the orogenic process, respectively. A genetic model of the lithospheric delamination (loss of the lithospheric root in about 120 km) in combination with the oceanic subduction for the Yanshanian Andes-like orogenic belt and both the crust and lithosphere thickening for the Yanshanian Hercyn-type Nanling orogenic belt in the East China is suggested.

  3. Dacite petrogenesis on mid-ocean ridges: Evidence for oceanic crustal melting and assimilation

    Wanless, V.D.; Perfit, M.R.; Ridley, W.I.; Klein, E.


    Whereas the majority of eruptions at oceanic spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, the formation of tholeiitic andesites and dacites at mid-ocean ridges (MORs) is a petrological enigma. Eruptions of MOR high-silica lavas are typically associated with ridge discontinuities and have produced regionally significant volumes of lava. Andesites and dacites have been observed and sampled at several locations along the global MOR system; these include propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Gal??pagos spreading center, and at the 9??N overlapping spreading center on the East Pacific Rise. Despite the formation of these lavas at various ridges, MOR dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes are controlling their chemistry. Although most geochemical variability in MOR basalts is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical data for MOR dacitic glasses suggest that contamination from a seawater-altered component is important in their petrogenesis. MOR dacites are characterized by elevated U, Th, Zr, and Hf, low Nb and Ta concentrations relative to rare earth elements (REE), and Al2O3, K2O, and Cl concentrations that are higher than expected from low-pressure fractional crystallization alone. Petrological modeling of MOR dacites suggests that partial melting and assimilation are both integral to their petrogenesis. Extensive fractional crystallization of a MORB parent combined with partial melting and assimilation of amphibole-bearing altered crust produces a magma with a geochemical signature similar to a MOR dacite. This supports the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas and may be significant in the generation of evolved MORB in

  4. Silicic Arc Magmas And Silicic Slab Melts: The Melt-Rock Reaction Link

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


    mantle and slab-derived crustal components (trench sediment, altered oceanic crust, eroded crust) instead as melt contamination by the overlying crust. Despite the ˜45 km thick continental basement, crustal extension in the central MVB likely facilitates the ascent of high-Mg# magmas with such strong source signatures. In contrast, more intense crustal processing in other arcs may overprint and erase such source signatures when producing a broader spectrum of low Mg# magmas.

  5. Geology of magma systems: background and review

    Peterfreund, A.R.


    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.

  6. Unusual Iron Redox Systematics of Martian Magmas

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


    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. Iron Redox Systematics of Martian Magmas

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


    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.

  8. Two-dimensional magma-repository interactions

    Bokhove, O.


    Two-dimensional simulations of magma-repository interactions reveal that the three phases --a shock tube, shock reflection and amplification, and shock attenuation and decay phase-- in a one-dimensional flow tube model have a precursor. This newly identified phase ``zero'' consists of the impact of

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

    John Browning; Kyriaki Drymoni; Agust Gudmundsson


    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 techni...

  10. Modeling the Daly Gap: The Influence of Latent Heat Production in Controlling Magma Extraction and Eruption

    Nelson, B. K.; Ghiorso, M. S.; Bachmann, O.; Dufek, J.


    A century-old issue in volcanology is the origin of the gap in chemical compositions observed in magmatic series on ocean islands and arcs - the "Daly Gap". If the gap forms during differentiation from a mafic parent, models that predict the dynamics of magma extraction as a function of chemical composition must simulate a process that results in volumetrically biased, bimodal compositions of erupted magmas. The probability of magma extraction is controlled by magma dynamical processes, which have a complex response to magmatic heat evolution. Heat loss from the magmatic system is far from a simple, monotonic function of time. It is modified by the crystallization sequence, chamber margin heat flux, and is buffered by latent heat production. We use chemical and thermal calculations of MELTS (Ghiorso & Sack, 1995) as input to the physical model of QUANTUM (Dufek & Bachmann, 2010) to predict crystallinity windows of most probable magma extraction. We modeled two case studies: volcanism on Tenerife, Canary Islands, and the Campanian Ignimbrite (CI) of Campi Flegrei, Italy. Both preserve a basanitic to phonolitic lineage and have comparable total alkali concentrations; however, CI has high and Tenerife has low K2O/Na2O. Modeled thermal histories of differentiation for the two sequences contrast strongly. In Tenerife, the rate of latent heat production is almost always greater than sensible heat production, with spikes in the ratio of latent to sensible heats of up to 40 associated with the appearance of Fe-Ti oxides at near 50% crystallization. This punctuated heat production must cause magma temperature change to stall or slow in time. The extended time spent at ≈50% crystallinity, associated with dynamical processes that enhance melt extraction near 50% crystallinity, suggests the magma composition at this interval should be common. In Tenerife, the modeled composition coincides with that of the first peak in the bimodal frequency-composition distribution. In our

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

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


    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

  12. Linking magma reservoir processes to the frequency and magnitude of volcanic eruptions

    Sheldrake, Tom; Caricchi, Luca


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

  13. The mechanics of shallow magma reservoir outgassing

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


    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. RNA-seq reveals a diminished acclimation response to the combined effects of ocean acidification and elevated seawater temperature in Pagothenia borchgrevinki.

    Huth, Troy J; Place, Sean P


    The IPCC has reasserted the strong influence of anthropogenic CO2 contributions on global climate change and highlighted the polar-regions as highly vulnerable. With these predictions the cold adapted fauna endemic to the Southern Ocean, which is dominated by fishes of the sub-order Notothenioidei, will face considerable challenges in the near future. Recent physiological studies have demonstrated that the synergistic stressors of elevated temperature and ocean acidification have a considerable, although variable, impact on notothenioid fishes. The present study explored the transcriptomic response of Pagothenia borchgrevinki to increased temperatures and pCO2 after 7, 28 and 56days of acclimation. We compared this response to short term studies assessing heat stress alone and foretell the potential impacts of these stressors on P. borchgrevinki's ability to survive a changing Southern Ocean. P. borchgrevinki did demonstrate a coordinated stress response to the dual-stressor condition, and even indicated that some level of inducible heat shock response may be conserved in this notothenioid species. However, the stress response of P. borchgrevinki was considerably less robust than that observed previously in the closely related notothenioid, Trematomus bernacchii, and varied considerably when compared across different acclimation time-points. Furthermore, the molecular response of these fish under multiple stressors displayed distinct differences compared to their response to short term heat stress alone. When exposed to increased sea surface temperatures, combined with ocean acidification, P. borchgrevinki demonstrated a coordinated stress response that has already peaked by 7days of acclimation and quickly diminished over time. However, this response is less dramatic than other closely related notothenioids under identical conditions, supporting previous research suggesting that this notothenioid species is less sensitive to environmental variation. Copyright

  15. Combined impact of ocean acidification and corrosive waters in a river-influenced coastal upwelling area off Central Chile

    Vargas, C.; De La Hoz, M.; San Martin, V.; Contreras, P.; Navarro, J. M.; Lagos, N. A.; Lardies, M.; Manríquez, P. H.; Torres, R.


    Elevated CO2 in the atmosphere promotes a cascade of physical and chemical changes affecting all levels of biological organization, and the evidence from local to global scales has shown that such anthropogenic climate change has triggered significant responses in the Earth's biota. The increased concentration of CO2 is likely to cause a corresponding increase in ocean acidification (OA). In addition, economically valuable shellfish species predominantly inhabit coastal regions both in natural stocks and/or in managed stocks and farming areas. Many coastal ecosystems may experience seawater pCO2 levels significantly higher than expected from equilibrium with the atmosphere, which in this case are strongly linked to biological processes and/or the impact of two important processes; river plumes and coastal upwelling events, which indeed interplay in a very dynamic way on continental shelves, resulting in both source or sink of CO2 to the atmosphere. Coastal ecosystems receive persistent acid inputs as a result of freshwater discharges from river basins into the coastal domain. In this context, since shellfish resources and shellfish aquaculture activities predominantly occur in nearshore areas, it is expected that shellfish species inhabiting river-influenced benthic ecosystems will be exposed persistently to acidic conditions that are suboptimal for its development. In a wider ecological context, little is also known about the potential impacts of acid waters on the performance of larvae and juveniles of almost all the marine species inhabiting this benthic ecosystem in Eastern Southern Pacific Ocean. We present here the main results of a research study aimed to investigate the environmental conditions to which economically valuable calcifiers shellfish species are exposed in a river-influenced continental shelf off Central Chile. By using isotopic measurements in the dissolved inorganic carbon (DIC) pool (d13C-DIC) we showed the effect of the remineralization of

  16. The origin of a zoned ignimbrite: Insights into the Campanian Ignimbrite magma chamber (Campi Flegrei, Italy)

    Forni, Francesca; Bachmann, Olivier; Mollo, Silvio; De Astis, Gianfilippo; Gelman, Sarah E.; Ellis, Ben S.


    Caldera-forming eruptions, during which large volumes of magma are explosively evacuated into the atmosphere from shallow crustal reservoirs, are one of the most hazardous natural events on Earth. The Campanian Ignimbrite (CI; Campi Flegrei, Italy) represents a classical example of such events, producing a voluminous pyroclastic sequence of trachytic to phonolitic magma that covered several thousands of squared kilometers in the south-central Italy around 39 ka ago. The CI deposits are known for their remarkable geochemical gradients, attributed to eruption from a vertically zoned magma chamber. We investigate the relationships between such chemical zoning and the crystallinity variations observed within the CI pyroclastic sequence by combining bulk-rock data with detailed analyses of crystals and matrix glass from well-characterized stratigraphic units. Using geothermometers and hygrometers specifically calibrated for alkaline magmas, we reconstruct the reservoir storage conditions, revealing the presence of gradients in temperature and magma water content. In particular, we observe a decrease in crystallinity and temperature and an increase in magma evolution and water content from the bottom to the top of the magma chamber. We interpret these features as the result of protracted fractional crystallization leading to the formation of a cumulate crystal mush at the base of the eruptible reservoir, from which highly evolved, crystal-poor, water-rich and relatively cold melts were separated. The extracted melts, forming a buoyant, easily eruptible cap at the top of the magma chamber, fed the initial phases of the eruption, until caldera collapse and eruption of the deeper more crystalline part of the system. This late-erupted, crystal-rich material represents remobilized portions of the cumulate crystal mush, partly melted following hotter recharge. Our interpretation is supported by: 1) the positive bulk-rock Eu anomalies and the high Ba and Sr contents observed in

  17. Differentiation mechanism of frontal-arc basalt magmas

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


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

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

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


    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

  19. Zircon from historic eruptions in Iceland: Reconstructing storage and evolution of silicic magmas

    Carley, T.L.; Miller, C.F.; Wooden, J.L.; Bindeman, I.N.; Barth, A.P.


    Zoning patterns, U-Th disequilibria ages, and elemental compositions of zircon from eruptions of Askja (1875 AD), Hekla (1158 AD), ??r??faj??kull (1362 AD) and Torfaj??kull (1477 AD, 871 AD, 3100 BP, 7500 BP) provide insights into the complex, extended, histories of silicic magmatic systems in Iceland. Zircon compositions, which are correlated with proximity to the main axial rift, are distinct from those of mid-ocean ridge environments and fall at the low-Hf edge of the range of continental zircon. Morphology, zoning patterns, compositions, and U-Th ages all indicate growth and storage in subvolcanic silicic mushes or recently solidified rock at temperatures above the solidus but lower than that of the erupting magma. The eruptive products were likely ascending magmas that entrained a zircon "cargo" that formed thousands to tens of thousands of years prior to the eruptions. ?? 2011 Springer-Verlag.

  20. Combining local lithofacies and global geochemical signals to test the acidification hypothesis for the onset of Oceanic Anoxic Event 2 in the U.S. Western Interior Basin

    Jones, M. M.; Sageman, B. B.; Selby, D. S.; Oakes, R. L.; Bralower, T. J.; Parker, A. L.; Leckie, R. M.; Sepulveda, J.


    igneous province volcanism and enhanced global organic matter burial, respectively. By combining a refined knowledge of local depositional environments with isotope geochemistry it is better possible to evaluate the impact of ocean acidification on the stratigraphic record through this critical Earth-life transition.

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

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


    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

  2. Transfer of volatiles and metals from mafic to felsic magmas in composite magma chambers: An experimental study

    Guo, Haihao; Audétat, Andreas


    In order to determine the behavior of metals and volatiles during intrusion of mafic magma into the base of silicic, upper crustal magma 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 magma. 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 magma 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

  3. Short-lived radioactivity and magma genesis

    Gill, James; Condomines, Michel


    Short-lived decay products of uranium and thorium have half-lives and chemistries sensitive to the processes and time scales of magma genesis, including partial melting in the mantle and magmatic differentiation in the crust. Radioactive disequilibrium between U-238, Th-230, and Ra-226 is widespread in volcanic rocks. These disequilibria and the isotopic composition of thorium depend especially on the extent and rate of melting as well as the presence and composition of vapor during melting. The duration of mantle melting may be several hundred millennia, whereas ascent times are a few decades to thousands of years. Differentiation of most magmas commonly occurs within a few millennia, but felsic ones can be tens of millennia old upon eruption.

  4. Ocean Robotic Networks

    Schofield, Oscar [Rutgers University


    We live on an ocean planet which is central to regulating the Earth’s climate and human society. Despite the importance of understanding the processes operating in the ocean, it remains chronically undersampled due to the harsh operating conditions. This is problematic given the limited long term information available about how the ocean is changing. The changes include rising sea level, declining sea ice, ocean acidification, and the decline of mega fauna. While the changes are daunting, oceanography is in the midst of a technical revolution with the expansion of numerical modeling techniques, combined with ocean robotics. Operating together, these systems represent a new generation of ocean observatories. I will review the evolution of these ocean observatories and provide a few case examples of the science that they enable, spanning from the waters offshore New Jersey to the remote waters of the Southern Ocean.

  5. Pressure waves in a supersaturated bubbly magma

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


    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.

  6. Volatile content of Hawaiian magmas and volcanic vigor

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


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

  7. Magma deformation and emplacement in rhyolitic dykes

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


    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

  8. Primitive layered gabbros from fast-spreading lower oceanic crust.

    Gillis, Kathryn M; Snow, Jonathan E; Klaus, Adam; Abe, Natsue; Adrião, Alden B; Akizawa, Norikatsu; Ceuleneer, Georges; Cheadle, Michael J; Faak, Kathrin; Falloon, Trevor J; Friedman, Sarah A; Godard, Marguerite; Guerin, Gilles; Harigane, Yumiko; Horst, Andrew J; Hoshide, Takashi; Ildefonse, Benoit; Jean, Marlon M; John, Barbara E; Koepke, Juergen; Machi, Sumiaki; Maeda, Jinichiro; Marks, Naomi E; McCaig, Andrew M; Meyer, Romain; Morris, Antony; Nozaka, Toshio; Python, Marie; Saha, Abhishek; Wintsch, Robert P


    Three-quarters of the oceanic crust formed at fast-spreading ridges is composed of plutonic rocks whose mineral assemblages, textures and compositions record the history of melt transport and crystallization between the mantle and the sea floor. Despite the importance of these rocks, sampling them in situ is extremely challenging owing to the overlying dykes and lavas. This means that models for understanding the formation of the lower crust are based largely on geophysical studies and ancient analogues (ophiolites) that did not form at typical mid-ocean ridges. Here we describe cored intervals of primitive, modally layered gabbroic rocks from the lower plutonic crust formed at a fast-spreading ridge, sampled by the Integrated Ocean Drilling Program at the Hess Deep rift. Centimetre-scale, modally layered rocks, some of which have a strong layering-parallel foliation, confirm a long-held belief that such rocks are a key constituent of the lower oceanic crust formed at fast-spreading ridges. Geochemical analysis of these primitive lower plutonic rocks--in combination with previous geochemical data for shallow-level plutonic rocks, sheeted dykes and lavas--provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust so far. Simple crystallization models using this bulk crustal composition as the parental melt accurately predict the bulk composition of both the lavas and the plutonic rocks. However, the recovered plutonic rocks show early crystallization of orthopyroxene, which is not predicted by current models of melt extraction from the mantle and mid-ocean-ridge basalt differentiation. The simplest explanation of this observation is that compositionally diverse melts are extracted from the mantle and partly crystallize before mixing to produce the more homogeneous magmas that erupt.

  9. Non-additive effects of ocean acidification in combination with warming on the larval proteome of the Pacific oyster, Crassostrea gigas.

    Harney, Ewan; Artigaud, Sébastien; Le Souchu, Pierrick; Miner, Philippe; Corporeau, Charlotte; Essid, Hafida; Pichereau, Vianney; Nunes, Flavia L D


    Increasing atmospheric carbon dioxide results in ocean acidification and warming, significantly impacting marine invertebrate larvae development. We investigated how ocean acidification in combination with warming affected D-veliger larvae of the Pacific oyster Crassostrea gigas. Larvae were reared for 40h under either control (pH8.1, 20 °C), acidified (pH7.9, 20 °C), warm (pH8.1, 22 °C) or warm acidified (pH7.9, 22 °C) conditions. Larvae in acidified conditions were significantly smaller than in the control, but warm acidified conditions mitigated negative effects on size, and increased calcification. A proteomic approach employing two-dimensional electrophoresis (2-DE) was used to quantify proteins and relate their abundance to phenotypic traits. In total 12 differentially abundant spots were identified by nano-liquid chromatography-tandem mass spectrometry. These proteins had roles in metabolism, intra- and extra-cellular matrix formations, stress response, and as molecular chaperones. Seven spots responded to reduced pH, four to increased temperature, and six to acidification and warming. Reduced abundance of proteins such as ATP synthase and GAPDH, and increased abundance of superoxide dismutase, occurred when both pH and temperature changes were imposed, suggesting altered metabolism and enhanced oxidative stress. These results identify key proteins that may be involved in the acclimation of C. gigas larvae to ocean acidification and warming. Increasing atmospheric CO2 raises sea surface temperatures and results in ocean acidification, two climatic variables known to impact marine organisms. Larvae of calcifying species may be particularly at risk to such changing environmental conditions. The Pacific oyster Crassostrea gigas is ecologically and commercially important, and understanding its ability to acclimate to climate change will help to predict how aquaculture of this species is likely to be impacted. Modest, yet realistic changes in pH and

  10. The Santander Atlantic Time-Series Station (SATS): A Time Series combination of a monthly hydrographic Station and The Biscay AGL Oceanic Observatory.

    Lavin, Alicia; Somavilla, Raquel; Cano, Daniel; Rodriguez, Carmen; Gonzalez-Pola, Cesar; Viloria, Amaia; Tel, Elena; Ruiz-Villareal, Manuel


    Long-Term Time Series Stations have been developed in order to document seasonal to decadal scale variations in key physical and biogeochemical parameters. Long-term time series measurements are crucial for determining the physical and biological mechanisms controlling the system. The Science and Technology Ministers of the G7 in their Tsukuba Communiqué have stated that 'many parts of the ocean interior are not sufficiently observed' and that 'it is crucial to develop far stronger scientific knowledge necessary to assess the ongoing changes in the ocean and their impact on economies.' Time series has been classically obtained by oceanographic ships that regularly cover standard sections and stations. From 1991, shelf and slope waters of the Southern Bay of Biscay are regularly sampled in a monthly hydrographic line north of Santander to a depth of 1000 m in early stages and for the whole water column down to 2580 m in recent times. Nearby, in June 2007, the IEO deployed an oceanic-meteorological buoy (AGL Buoy, 43° 50.67'N; 3° 46.20'W, and 40 km offshore, The Santander Atlantic Time Series Station is integrated in the Spanish Institute of Oceanography Observing Sistem (IEOOS). The long-term hydrographic monitoring has allowed to define the seasonality of the main oceanographic facts as the upwelling, the Iberian Poleward Current, low salinity incursions, trends and interannual variability at mixing layer, and at the main water masses North Atlantic Central Water and Mediterranean Water. The relation of these changes with the high frequency surface conditions recorded by the Biscay AGL has been examined using also satellite and reanalysis data. During the FIXO3 Project (Fixed-point Open Ocean Observatories), and using this combined sources, some products and quality controled series of high interest and utility for scientific purposes has been developed. Hourly products as Sea Surface Temperature and Salinity anomalies, wave significant

  11. Formation and evolution of magma-poor margins, an example of the West Iberia margin

    Perez-Gussinye, Marta; Andres-Martinez, Miguel; Morgan, Jason P.; Ranero, Cesar R.; Reston, Tim


    The West Iberia-Newfoundland (WIM-NF) conjugate margins have been geophysically and geologically surveyed for the last 30 years and have arguably become a paradigm for magma-poor extensional margins. Here we present a coherent picture of the WIM-NF rift to drift evolution that emerges from these observations and numerical modeling, and point out important differences that may exist with other magma-poor margins world-wide. The WIM-NF is characterized by a continental crust that thins asymmetrically and a wide and symmetric continent-ocean transition (COT) interpreted to consist of exhumed and serpentinised mantle with magmatic products increasing oceanward. The architectural evolution of these margins is mainly dominated by cooling under very slow extension velocities (crust that most probably was not extremely weak at the start of rifting. These conditions lead to a system where initially deformation is distributed over a broad area and the upper, lower crust and lithosphere are decoupled. As extension progresses upper, lower, crust and mantle become tightly coupled and deformation localizes due to strengthening and cooling during rifting. Coupling leads to asymmetric asthenospheric uplift and weakening of the hanginwall of the active fault, where a new fault forms. This continued process leads to the formation of an array of sequential faults that dip and become younger oceanward. Here we show that these processes acting in concert: 1) reproduce the margin asymmetry observed at the WIM-NF, 2) explain the fault geometry evolution from planar, to listric to detachment like by having one common Andersonian framework, 3) lead to the symmetric exhumation of mantle with little magmatism, and 4) explain the younging of the syn-rift towards the basin centre and imply that unconformities separating syn- and post-rift may be diachronous and younger towards the ocean. Finally, we show that different lower crustal rheologies lead to different patterns of extension and to an

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

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


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

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

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


    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

  14. Tectonic focusing of voluminous basaltic eruptions in magma-deficient backarc rifts

    Anderson, Melissa O.; Hannington, Mark D.; Haase, Karsten; Schwarz-Schampera, Ulrich; Augustin, Nico; McConachy, Timothy F.; Allen, Katie


    The Coriolis Troughs of the New Hebrides subduction zone are among the youngest backarc rifts in the world. They reach depths of >3 km, despite their small size (Pacific, occur on the youngest lava flows. Comparison with similar axial volcanoes on the mid-ocean ridges suggests that the 46 ×106 m3 of sheet flows in the caldera could have been erupted in ridge. This study shows that the upper plate stresses can result in dramatic variability in magma supply and hydrothermal activity at the earliest stages of arc rifting and could explain the wide range of melt compositions, volcanic styles and mineral deposit types found in nascent backarc rifts.

  15. The geology and geochemistry of Isla Marchena, Galapagos Archipelago: An ocean island adjacent to a mid-ocean ridge

    Vicenzi, E. P.; McBirney, A. R.; White, W. M.; Hamilton, M.


    Isla Marchena is the subaerial exposure of a shield volcano located between the Galapagos Platform and the Galapagos Spreading Center. The geologic evolution of the island can be divided into two lava series separated by formation of a cadera and a period of explosive activity. Both lava series contain evolved alkali olivine and tholeiitic basalts (average mg # = 55.2) and are virtually aphyric with the exception of a plagioclase-rich horizon in the pre-caldera section. Although the major-element compositions of the two series are similar, the abundances of incompatible elements and ratios of highly/moderately incompatible elements increase systematically with decreasing stratigraphic age. These compositional differences, together with textural and mineral chemical evidence for disequilibrium, are not easily explained by any single petrologic mechanism. The combined effects of a periodically replenished magma chamber, assimilation-fractionation, and in situ crystallization of a solidification zone are possible mechanisms that may be responsible for the temporal changes in lava composition. MORB-like abundances of trace elements, in addition to unusually depleted 87Sr/ 86Sr and 143Nd/ 144Nd ratios for ocean-island basalts, suggest that magmas associated with the Galapagos plume interacted with those of the Galapagos Spreading Center.

  16. Outgassing from Open and Closed Magma Foams

    Felix W. von Aulock


    Full Text Available During magma ascent, bubbles nucleate, grow, coalesce, and form a variably permeable porous network. The reorganization, failing and sealing of bubble walls may contribute to the opening and closing of the volcanic system. In this contribution we cause obsidian to nucleate and grow bubbles to high gas volume fraction at atmospheric pressure by heating samples to 950°C for different times and we image the growth through a furnace. Following the experiment, we imaged the internal pore structure of selected samples in 3D and then dissected for analysis of textures and dissolved water content remnant in the glass. We demonstrate that in these high viscosity systems, during foaming and subsequent foam-maturation, bubbles near a free surface resorb via diffusion to produce an impermeable skin of melt around a foam. The skin thickens non-linearly through time. The water concentrations at the outer and inner skin margins reflect the solubility of water in the melt at the partial pressure of water in atmospheric and water-rich bubble conditions, respectively. In this regime, mass transfer of water out of the system is diffusion limited and the sample shrinks slowly. In a second set of experiments in which we polished off the skin of the foamed samples and placed them back in the furnace to allow open system outgassing, we observe rapid sample contraction and collapse of the connected pore network under surface tension as the system efficiently outgasses. In this regime, mass transfer of water is permeability limited. We conclude that diffusion-driven skin formation can efficiently seal connectivity in foams. When rupture of melt film around gas bubbles (i.e., skin removal occurs, then rapid outgassing and consequent foam collapse modulate gas pressurization in the vesiculated magma. The mechanisms described here are relevant to the evolution of pore network heterogeneity in permeable magmas.

  17. Chlorine solubility in evolved alkaline magmas

    M. R. Carroll


    Full Text Available Experimental studies of Cl solubility in trachytic to phonolitic melts provide insights into the capacity of alkaline magmas to transport Cl from depth to the earth?s surface and atmosphere, and information on Cl solubility variations with pressure, temperature and melt or fluid composition is crucial for understanding the reasons for variations in Cl emissions at active volcanoes. This paper provides a brief review of Cl solubility experiments conducted on a range of trachytic to phonolitic melt compositions. Depending on the experimental conditions the melts studied were in equilibrium with either a Cl-bearing aqueous fluid or a subcritical assemblage of low- Cl aqueous fluid + Cl-rich brine. The nature of the fluid phase(s was identified by examination of fluid inclusions present in run product glasses and the fluid bulk composition was calculated by mass balance. Chlorine concentrations in the glass increase with increasing Cl molality in the fluid phase until a plateau in Cl concentration is reached when melt coexists with aqueous fluid + brine. With fluids of similar Cl molality, higher Cl concentrations are observed in peralkaline phonolitic melts compared with peraluminous phonolitic melts; overall the Cl concentrations observed in phonolitic and trachytic melts are approximately twice those found in calcalkaline rhyolitic melts under similar conditions. The observed negative pressure dependence of Cl solubility implies that Cl contents of melts may actually increase during magma decompression if the magma coexists with aqueous fluid and Cl-rich brine (assuming melt-vapor equilibrium is maintained. The high Cl contents (approaching 1 wt% Cl observed in some melts/glasses from the Vesuvius and Campi Flegrei areas suggest saturation with a Cl-rich brine prior to eruption.

  18. Magma storage under Iceland's Eastern Volcanic Zone

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


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

  19. Role of Yield Stress in Magma Rheology

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


    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

  20. Special relativity derived from spacetime magma.

    Greensite, Fred


    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.

  1. Special relativity derived from spacetime magma.

    Fred Greensite

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

  2. The role of magma mixing in the evolution of the Early Paleozoic calc-alkaline granitoid suites. Eastern magmatic belt, Puna, NW Argentina

    Suzaño, Néstor; Becchio, Raúl; Sola, Alfonso; Ortiz, Agustín; Nieves, Alexis; Quiroga, Mirta; Fuentes, Gabriela


    The outcrops of the Eastern magmatic belt in Puna, NW Argentina, offer an excellent field laboratory to study the interaction processes between magmas of contrasting composition in a plutonic environment. We evaluate the genesis of Cambrian-Ordovician intermediate to acid rocks from the Diablillos Intrusive Complex and the Cerro Bayo area, through detailed geological, petrographic, mineralogical, geochemical, and Nd isotopic analyses in combination with published data. These localities display a great variety of magmatic rocks from diorite/Qz-diorite to two-mica syenogranites with tonalite, granodiorite, monzogranite and Bt-Ttn-leucogranites as mixed products. Major, trace element and whole-rock Nd isotope modeling and petrological data, suggests that magma mixing between hydrous juvenile mantle- and crustal-derived magmas contributed significantly to the geochemical variation of these granites. The estimated proportion of mafic component 0.40-0.67 and 0.14-0.35 in the mixtures may produce the tonalite-granodiorites and monzogranites magmas. The mixing model excludes the predominant influence of fractional crystallization from a mafic magma and local assimilation-fractional-crystallization processes. Isotopic and geochemical comparison between the studied rocks and the magmatic belts in Puna and Tastil batholith suites reveals a marked resemblance. The data suggests that those rocks were probably generated by magma mixing and denotes a regionally and continuous process in a long-lasting (∼540-440 Ma) active continental margin. We propose that partial melting of the crust and magma mixing occurred in the lower crust and was possibly triggered by underplated and intraplated hydrous (4.37-5.91 wt% H2O) mafic magmas. The hybrid magmas were emplaced at shallow depth (∼8-9 km, 684-727 °C) and occasionally injected either by synplutonic-to late successive pulses of mafic magmas.

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

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


    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.

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

    Stoppa Francesco


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

  5. Physiological responses and scope for growth upon medium-term exposure to the combined effects of ocean acidification and temperature in a subtidal scavenger Nassarius conoidalis.

    Zhang, Haoyu; Shin, Paul K S; Cheung, S G


    Physiological responses (ingestion rate, absorption rate and efficiency, respiration, rate, excretion rate) and scope for growth of a subtidal scavenging gastropod Nassarius conoidalis under the combined effects of ocean acidification (pCO2 levels: 380, 950, 1250 μatm) and temperature (15, 30 °C) were investigated for 31 days. There was a significant reduction in all the physiological rates and scope for growth following short-term exposure (1-3 days) to elevated pCO2 except absorption efficiency at 15 °C and 30 °C, and respiration rate and excretion rate at 15 °C. The percentage change in the physiological rates ranged from 0% to 90% at 15 °C and from 0% to 73% at 30 °C when pCO2 was increased from 380 μatm to 1250 μatm. The effect of pCO2 on the physiological rates was enhanced at high temperature for ingestion, absorption, respiration and excretion. When the exposure period was extended to 31 days, the effect of pCO2 was significant on the ingestion rate only. All the physiological rates remained unchanged when temperature increased from 24 °C to 30 °C but the rates at 15 °C were significantly lower, irrespective of the duration of exposure. Our data suggested that a medium-term exposure to ocean acidification has no effect on the energetics of N. conoidalis. Nevertheless, the situation may be complicated by a longer term of exposure and/or a reduction in salinity in a warming world.

  6. Open-system dynamics and mixing in magma mushes

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


    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.

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

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


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

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

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


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

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

    Iyer, H. M.


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

  10. Discovering Mathematics with Magma Reducing the Abstract to the Concrete

    Bosma, Wieb


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

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

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


    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.

  12. Magma mixing enhanced by bubble segregation

    S. Wiesmaier


    Full Text Available 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

  13. Electrical conductivity of water-bearing magmas

    Gaillard, F.


    Phase diagrams and chemical analyzes of crystals and glass inclusions of erupted lavas tell us that most explosive volcanic eruptions were caused by extremely water-rich pre-eruptive conditions. Volcanologists estimate volcanic hazards by the pre-eruptive water content of lavas erupted in the past and they hypothesize that future eruptions should show similar features. Alternatively, the development of methods allowing direct estimation of water content of magmas stored in the Earth’s interior would have the advantage of providing direct constraints about upcoming rather than past eruptions. Geoelectrical sounding, being the most sensitive probe to the chemical state of the Earth’s interior, seems a promising tool providing that its interpretation is based on relevant laboratory constraints. However, the current database of electrical conductivity of silicate melt merely constrains anhydrous composition. We have therefore undertaken an experimental program aiming at elucidating the effect of water on the electrical conductivity of natural magmas. Measurements (impedance spectroscopy) are performed using a two electrodes set-up in an internally heated pressure vessel. The explored temperature and pressure range is 25-1350°C and 0.1-400MPa. The material used is a natural rhyolitic obsidian. Hydration of this rhyolite is first performed in Pt capsules with 0.5, 1, 2 and 6wt% of water. In a second step, the conductivity measurements are performed at pressure and temperature in a modified Pt capsule. One end of the capsule is arc-welded whereas the other end is closed with the help of a BN cone and cement through which an inner electrode is introduced in the form a Pt wire. The capsule is used as outer electrode. The electrical cell has therefore a radial geometry. The rhyolite is introduced in the cell in the form of a cylinder drilled in the previously hydrated glass. At dwell condition, the melt is sandwiched between two slices of quartz avoiding any deformation

  14. Magma mixing induced by particle settling

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


    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

  15. A possible model for initiationof ULF oscillation in magma

    L.V. Nikitina


    Full Text Available During the period just prior to an earthquake, an electomagnetic emission develops over seismic zones. In this paper, a model of excitation of magnetic fields over zones of volcanic activity is proposed. Movement of magma along volcanic channels precedes an earthquake, hydrodynamic processes in the moving magma can lead to formation of waves and vortices in the flow which, in turn, can cause development of magnetic fields in conducting magma. During this period, the movement of the magma intensifies leading to a corresponding intensification of the magnetic fields. In this paper, different possible sources of ULF pulsation in magma are examined,and the variable geomagnetic fields induced by this pulsation are estimated.

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

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine


    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. The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny

    Richards, Jeremy P.


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

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

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


    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.

  19. A decadal view of magma fragmentation

    Cashman, K. V.; Rust, A.


    Although the past decade has seen fundamental advances in studies of explosive volcanism, the disruption to air traffic caused by the 2010 eruption of Eyjafjallajökull, Iceland, highlights the need for improved understanding of magmatic fragmentation in general, and of fine ash generation in particular. To develop a theoretical basis for predicting the fine ash content of eruptive plumes, we need to understand not only fragmentation mechanisms but also the dependence of those mechanisms on conditions of magma ascent and degassing. Experimental and analytical approaches to this problem include experimental studies of vesiculation and permeability development in silicic melts, quantitative textural studies of pyroclasts to constrain conditions that reduce fragmentation efficiency (that is, allow vesicular clasts to be preserved), direct experiments on fragmentation in both natural and analog materials, and determination of total grain size distributions (TGSDs) of pyroclastic deposits. Experiments on silicic melts have demonstrated that very high supersaturations (overpressures ΔP) may be achieved in silicic melts prior to homogeneous bubble nucleation, and that the high bubble number densities of silicic pumice require not only homogeneous nucleation but also nucleation of a mixed H2O-CO2 gas phase. In most pumice and scoria clasts, resulting vesicle populations form power law size distributions; power law exponents >3 in silicic tephras indicate that small vesicles comprise most of the vesicle volume (consistent with rapid late-stage vesiculation at high ΔP), while exponents 60-70%) and show no dependence on either melt composition or mass eruption rate; this suggests that melt porosity is more important than either decompression rate or magma rheology for clast preservation. These pyroclasts also have uniformly high permeabilities, high pore connectivity, and simple porous pathways, all of which suggest that ease of gas escape also contributed to clast

  20. Crustal Assimilation and Magma Recharge in the Recent Mt. Etna Magma Plumbing System: Evidence from In Situ Plagioclase Textural and Compositional Data

    Pitcher, B. W.; Bohrson, W. A.; Viccaro, M.


    Mt. Etna is Europe's largest and most active volcano, and as a result of its proximity to populated areas, understanding the structure of its magma plumbing system and the nature of its magmatic processes is essential for better predicting eruptive hazards. The aim of this study is to document core to rim textural, chemical, and isotopic variations in plagioclase, in order to investigate the physical characteristics of the subvolcanic magma system and processes by which magmas evolve. Nomarski Differential Interference Contrast (NDIC) imaging was used to characterize the complex textures of plagioclase crystals in six trachybasaltic samples from eruption years 1974, 1981, 2001, and 2004. Approximately 30 NDIC images per sample revealed 6 textural categories defined by combinations of monotonous, oscillatory, sieve, and patchy zoning. Core to rim electron microprobe analyses carried out at distinct textural boundaries revealed variable anorthite (An) (mol %) values ranging from 92 to 44. In most phenocrysts, An decreases non-monotonically from core to rim, and simple correlations among An, FeO (wt. %), textural type, and eruption year are lacking, indicating intricate crystallization histories that likely reflect changing magma chamber conditions. Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS) 87Sr/86Sr analyses were performed on cores and rims of selected crystals from each textural type within each sample. Phenocryst 87Sr/86Sr values ranged from ~0.70300 to 0.70370 (±.00002), and were significantly lower than preliminary groundmass 87Sr/86Sr values, which ranged from ~0.70466 to 0.70498. Whole-rock 87Sr/86Sr values are between groundmass and crystal values. The Δ87Sr/86Sr within each crystal, defined as rim minus core, varied from -0.00030 to +0.00011; while most crystals exhibit a core to rim increase, some showed a decrease and some had constant 87Sr/86Sr. The prevalence of core to rim increases, combined with whole rock and preliminary

  1. Magma-poor and magma-rich segments along the hyperextended, pre-Caledonian passive margin of Baltica

    Andersen, Torgeir B.; Alsaif, Manar; Corfu, Fernando; Jakob, Johannes; Planke, Sverre; Tegner, Christian


    The Scandinavian Caledonides constitute a more than 1850 km long 'Himalayan-type' orogen, formed by collision between Baltica-Avalonia and Laurentia. Subduction-related magmatism in the Iapetus ended at ~430 Ma and continental convergence continued for ~30 Myr until ~400 Ma. The collision produced a thick orogenic wedge comprising the stacked remnants of the rifted to hyperextended passive Baltican margin (Andersen et al. 2012), as well as suspect, composite and outboard terranes, which were successively emplaced as large-scale nappe complexes onto Baltica during the Scandian collision (see Corfu et al. 2014 for a recent review). Large parts (~800 km) of the mountain-belt in central Scandinavia, particularly in the Särv and Seve Nappes and their counterparts in Troms, are characterised by spectacular dyke complexes emplaced into continental sediments (e.g. Svenningsen 2001, Hollocher et al. 2007). These constitute a magma-rich segment formed along the margin of Baltica or within hyperextended continental slivers outboard of Baltica. The intensity of the pre-Caledonian magmatism is comparable to that of the present NE-Atlantic and other volcanic passive margins. The volumes and available U-Pb ages of 610-597 Ma (Baird et al. 2014 and refs therein) suggest that the magmatism was short lived, intense and therefore compatible with a large igneous province (LIP). By analogy with present-day margins this LIP may have been associated with continental break-up and onset of sea-floor spreading. The remnants of the passive margin both north and south of the magma-rich segment have different architectures, and are almost devoid of rift/drift related magmatic rocks. Instead, these magma-poor segments are dominated by heterogeneous sediment-filled basins characterised by the abundant presence of solitary bodies of variably altered mantle peridotites, also commonly present as detrital serpentinites. These basins are interpreted to have formed by hyperextension. We suggest that

  2. The effect of nonlinear decompression history on H2O/CO2 vesiculation in rhyolitic magmas

    Su, Yanqing; Huber, Christian


    Magma ascent rate is one of the key parameters that control volcanic eruption style, tephra dispersion, and volcanic atmospheric impact. Many methods have been employed to investigate the magma ascent rate in volcanic eruptions, and most rely on equilibrium thermodynamics. Combining the mixed H2O-CO2 solubility model with the diffusivities of both H2O and CO2 for normal rhyolitic melt, we model the kinetics of H2O and CO2 in rhyolitic eruptions that involve nonlinear decompression rates. Our study focuses on the effects of the total magma ascent time, the nonlinearity of decompression paths, and the influence of different initial CO2/H2O content on the posteruptive H2O and CO2 concentration profiles around bubbles within the melt. Our results show that, under most circumstances, volatile diffusion profiles do not constrain a unique solution for the decompression rate of magmas during an eruption, but, instead, provide a family of decompression paths with a well-defined trade-off between ascent time and nonlinearity. An important consequence of our analysis is that the common assumption of a constant decompression rate (averaged value) tends to underestimate the actual magma ascent time.

  3. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran

    K. Jamshidi


    Full Text Available Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468–130 MPa, while amphiboles record both low pressures (~ 300 MPa and very high pressures (> 700 MPa of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa. The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  4. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, northeast Iran

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~350 (130 to 468) MPa, while amphiboles record both low pressures (~300 MPa) and very high pressures (>700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process in intensifying adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, implies that final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  5. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468-130) MPa, while amphiboles record both low pressures (~ 300 MPa) and very high pressures (> 700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  6. Mineralogy and composition of the oceanic mantle

    Putirka, Keith; Ryerson, F.J.; Perfit, Michael; Ridley, W. Ian


    The mineralogy of the oceanic basalt source region is examined by testing whether a peridotite mineralogy can yield observed whole-rock and olivine compositions from (1) the Hawaiian Islands, our type example of a mantle plume, and (2) the Siqueiros Transform, which provides primitive samples of normal mid-ocean ridge basalt. New olivine compositional data from phase 2 of the Hawaii Scientific Drilling Project (HSDP2) show that higher Ni-in-olivine at the Hawaiian Islands is due to higher temperatures (T) of melt generation and processing (by c. 300°C) related to the Hawaiian mantle plume. DNi is low at high T, so parental Hawaiian basalts are enriched in NiO. When Hawaiian (picritic) parental magmas are transported to shallow depths, olivine precipitation occurs at lower temperatures, where DNi is high, leading to high Ni-in-olivine. Similarly, variations in Mn and Fe/Mn ratios in olivines are explained by contrasts in the temperatures of magma processing. Using the most mafic rocks to delimit Siqueiros and Hawaiian Co and Ni contents in parental magmas and mantle source compositions also shows that both suites can be derived from natural peridotites, but are inconsistent with partial melting of natural pyroxenites. Whole-rock compositions at Hawaii and Siqueiros are also matched by partial melting experiments conducted on peridotite bulk compositions. Hawaiian whole-rocks have elevated FeO contents compared with Siqueiros, which can be explained if Hawaiian parental magmas are generated from peridotite at 4-5 GPa, in contrast to pressures of slightly greater than 1 GPa for melt generation at Siqueiros; these pressures are consistent with olivine thermometry, as described in an earlier paper. SiO2-enriched Koolau compositions are reproduced if high-Fe Hawaiian parental magmas re-equilibrate at 1-1·5 GPa. Peridotite partial melts from experimental studies also reproduce the CaO and Al2O3 contents of Hawaiian (and Siqueiros) whole-rocks. Hawaiian magmas have TiO2

  7. Formation of Early Water Oceans on Rocky Planets

    Elkins-Tanton, Linda T


    Terrestrial planets, with silicate mantles and metallic cores, are likely to obtain water and carbon compounds during accretion. Here I examine the conditions that allow early formation of a surface water ocean (simultaneous with cooling to clement surface conditions), and the timeline of degassing the planetary interior into the atmosphere. The greatest fraction of a planet's initial volatile budget is degassed into the atmosphere during the end of magma ocean solidification, leaving only a small fraction of the original volatiles to be released into the atmosphere through later volcanism. Rocky planets that accrete with water in their bulk mantle have two mechanisms for producing an early water ocean: First, if they accrete with at least 1 to 3 mass% of water in their bulk composition, liquid water may be extruded onto the planetary surface at the end of magma ocean solidification. Second, at initial water contents as low as 0.01 mass% or lower, during solidification a massive supercritical fluid and steam ...

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

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust


    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.

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

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph


    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

  10. Continental crust generated in oceanic arcs

    Gazel, Esteban; Hayes, Jorden L.; Hoernle, Kaj; Kelemen, Peter; Everson, Erik; Holbrook, W. Steven; Hauff, Folkmar; van den Bogaard, Paul; Vance, Eric A.; Chu, Shuyu; Calvert, Andrew J.; Carr, Michael J.; Yogodzinski, Gene M.


    Thin oceanic crust is formed by decompression melting of the upper mantle at mid-ocean ridges, but the origin of the thick and buoyant continental crust is enigmatic. Juvenile continental crust may form from magmas erupted above intra-oceanic subduction zones, where oceanic lithosphere subducts beneath other oceanic lithosphere. However, it is unclear why the subduction of dominantly basaltic oceanic crust would result in the formation of andesitic continental crust at the surface. Here we use geochemical and geophysical data to reconstruct the evolution of the Central American land bridge, which formed above an intra-oceanic subduction system over the past 70 Myr. We find that the geochemical signature of erupted lavas evolved from basaltic to andesitic about 10 Myr ago--coincident with the onset of subduction of more oceanic crust that originally formed above the Galápagos mantle plume. We also find that seismic P-waves travel through the crust at velocities intermediate between those typically observed for oceanic and continental crust. We develop a continentality index to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust globally. We conclude that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone--a process probably more common in the Archaean--can produce juvenile continental crust.

  11. Draining mafic magma from conduits during Strombolian eruption

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


    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.

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

    Igan S. Sutawidjaja


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

  13. Petrology of continental tholeiitic magmas forming a 350-km-long Mesozoic dyke swarm in NE Brazil: Constraints of geochemical and isotopic data

    Ngonge, Emmanuel Donald; de Hollanda, Maria Helena Bezerra Maia; Archanjo, Carlos José; de Oliveira, Diógenes Custódio; Vasconcelos, Paulo Marcosde Paula; Muñoz, Patrício Rodrigo Montecinos


    The Ceará Mirim dyke swarm (northeastern Brazil) is composed of Cretaceous tholeiites with plagioclase, clinopyroxene (± olivine), Fe-Ti oxides and pigeonite in their groundmass. These tholeiites have been subdivided into three groups: high-Ti olivine tholeiites, evolved high-Ti tholeiites (TiO2 ≥ 1.5 wt.%; Ti/Y > 360), and low-Ti tholeiites (TiO2 ≤ 1.5 wt%; Ti/Y ≤ 360), with all exhibiting distinct degrees of enrichment in incompatible elements relative to Primitive Mantle. Negative Pb anomalies are found in all three groups, while Nb-Ta abundances similar to those of OIB-type magmas are found in the olivine tholeiites, with moderate to high depletions being observed, respectively, in the evolved high-Ti and low-Ti tholeiites. The low-Ti tholeiites exhibit some contamination with crustal (felsic) materials during ascent. The initial isotopic compositions of the olivine tholeiites show uniform and unradiogenic 87Sr/86Sr (~ 0.7035-0.7039) combined with (in part) radiogenic 143Nd/144Nd and 206Pb/204Pb (> 19.1) ratios, which together reveal a likely contribution of FOZO (FOcalZOne) component in their genesis. The other tholeiite groups show variable Sr-Nd ratios with relatively consistent 206Pb/204Pb ratios clustering towards an isotopically enriched mantle (EM1) component. Taken in conjunction with the Nb, this enriched signature reflects the involvement of a subduction-modified lithospheric mantle in the source of the evolved high-Ti and low-Ti tholeiites. Thus, we propose that FOZO and EMI components coexisted (including minor mixing with E-MORB magmas) and contributed in varying extents to the generation of the Ceará-Mirim dyke swarm primary melts, which segregated at 75 to 60 km in depth around the garnet-spinel facies transition zone. The mechanism that promoted melting was most likely non-plume related. We suggest that plate-boundary forces linked to the opening of the Atlantic Ocean promoted passive rifting and that the resulting asthenospheric

  14. Appinite suites: A record of the role of water in the genesis, transport, emplacement and crystallization of magma

    Murphy, J. Brendan


    The appinite suite of rocks offers a unique opportunity to study the effect of water on the generation, emplacement and crystallization history of mafic to felsic magma. The suite consists of a group of coeval plutonic and/or hypabyssal rocks, ranging from ultramafic to felsic in composition in which hornblende is the dominant mafic mineral, and typically occurs both as large prismatic phenocrysts and in the finer grained matrix. The suite is also characterized by abundant evidence for mixing and mingling between diverse magma types and variable degrees of contamination by host rock. Field observations corroborate experimental and theoretical studies that the hornblende stability field expands at the expense of olivine and pyroxene with increasing pH2O in the magma. Textures characteristic of appinites are consistent with rapid growth and with experimental evidence for the reduced viscosity of melts allowing efficient migration of ions to the sites of mineral growth. The appinite suite was originally defined in the Paleozoic Caledonide orogen in Scotland, where it occurs as a number of small shallow crustal bodies that were emplaced after the cessation of subduction and in the immediate aftermath of terrane collision and closure of the Iapetus Ocean. The mafic component is thought to have been triggered by asthenospheric upwelling following stab break-off, and magmas produced have both juvenile and sub-continental lithospheric mantle components. Its compositions have affinities with shoshonites. The felsic components include large batholiths that were probably derived by fractional crystallization. Other appinite suites share some, but not all of these characteristics. Appinite suites apparently range in age from Neo-Archean to Recent, and occur at all crustal levels, at depths of up to 40 km. In addition to shoshonites, appinite suites share some similar geochemical features with high-Mg andesites, sanukitoids and adakites. Some common tectonic traits include a

  15. Mantle to surface degassing of carbon- and sulphur-rich alkaline magma at El Hierro, Canary Islands

    Longpré, Marc-Antoine; Stix, John; Klügel, Andreas; Shimizu, Nobumichi


    Basaltic volcanoes transfer volatiles from the mantle to the surface of the Earth. The quantification of deep volatile fluxes relies heavily on estimates of the volatile content of primitive magmas, the best archive of which is provided by melt inclusions. Available data from volcanoes producing mafic alkaline lavas in a range of tectonic settings suggest high volatile fluxes, but information remains sparse, particularly for intraplate ocean islands. Here we present measurements of volatile and trace element concentrations, as well as sulphur speciation, in olivine-hosted melt inclusions and matrix glasses from quenched basanite lava balloon samples from the 2011-2012 submarine eruption at El Hierro, Canary Islands. The results reveal remarkably high concentrations of dissolved volatiles and incompatible trace elements in this magma, with ∼80 ppm Nb and up to 3420 ppm CO2, 3.0 wt.% H2O and 5080 ppm S. Reconstructed primitive CO2 contents, considering CO2/Nb systematics and possible CO2 sequestration in shrinkage bubbles, reach weight percent levels, indicating that carbon is a major constituent of Canary Island magmas at depth and that exsolution of a CO2-rich fluid begins in the mantle at pressures in excess of 1 GPa. Correlations between sulphur concentration, sulphur speciation and water content suggest strong reduction of an initially oxidised mantle magma, likely controlled by coupled H2O and S degassing. This late-stage redox change may have triggered sulphide saturation, recorded by globular sulphide inclusions in clinopyroxene and ulvöspinel. The El Hierro basanite thus had a particularly high volatile-carrying capacity and released a minimum of 1.3-2.1 Tg CO2 and 1.8-2.9 Tg S to the environment, causing substantial stress on the local submarine ecosystem. These results highlight the important contribution of alkaline ocean island volcanoes, such as the Canary Islands, to volatile fluxes from the mantle.

  16. Halogen behaviours during andesitic magma degassing: from magma chamber to volcanic plume

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


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

  17. Magma Dynamics at Yucca Mountain, Nevada

    D. Krier


    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 magma 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.

  18. Time scales of crystal mixing in magma mushes

    Schleicher, Jillian M.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain


    Magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption. However, the processes and associated time scales that produce the commonly observed expressions of magma 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 magma 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.

  19. Magma chamber processes in central volcanic systems of Iceland

    Þórarinsson, Sigurjón Böðvar; Tegner, Christian


    New field work and petrological investigations of the largest gabbro outcrop in Iceland, the Hvalnesfjall gabbro of the 6-7 Ma Austurhorn intrusive complex, have established a stratigraphic sequence exceeding 800 m composed of at least 8 macrorhythmic units. The bases of the macrorhythmic units......3 of clinopyroxene and magnetite indicative of magma replenishment. Some macrorhythmic units show mineral trends indicative of up-section fractional crystallisation over up to 100 m, whereas others show little variation. Two populations of plagioclase crystals (large, An-rich and small, less An...... olivine basalts from Iceland that had undergone about 20% crystallisation of olivine, plagioclase and clinopyroxene and that the macrorhythmic units formed from thin magma layers not exceeding 200-300 m. Such a "mushy" magma chamber is akin to volcanic plumbing systems in settings of high magma supply...

  20. The Role of Magma Mixing in Creating Magmatic Diversity

    Davidson, J. P.; Collins, S.; Morgan, D. J.


    Most magmas 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 magma mixing. Among these, magma mixing is arguably inevitable in magma systems that deliver magmas from source-to-surface, since magmas will tend to multiply re-occupy plumbing systems. A given mantle-derived magma type will mix with any residual magmas (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 magma mixing can be read from the petrography (identification of crystals derived from different magmas), 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 magma contributions of distinct composition (recharge?). Indeed recharge and mixing/ contamination may well be related. As a result, the consequences of magma mixing may well bear on eruption triggering. When two magmas mix, volatile exsolution may be triggered by retrograde boiling, with crystallisation of anhydrous phase(s) in either of the magmas (3) or volatiles may be generated by thermal breakdown of a hydrous phase in one of the magmas (4). The generation of gas pressures in this way probably leads to geophysical signals too (small earthquakes). Recent work pulling

  1. Seismic Tremors and Three-Dimensional Magma Wagging

    Liao, Y.; Bercovici, D.


    Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the magma-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici 2013) that the magma column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the magma inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the magma column is restricted to one vertical plane, the three-dimensional model we employ allows the magma column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the magma column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the magma column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the magma column leading to a coiled wagging motion. For the viscous-magma model, we predict a similar damping rate for the uncoiled magma column as in the two-dimensional model, and faster damping for the coiled magma column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3

  2. NVP melt/magma viscosity: insight on Mercury lava flows

    Rossi, Stefano; Morgavi, Daniele; Namur, Olivier; Vetere, Francesco; Perugini, Diego; Mancinelli, Paolo; Pauselli, Cristina


    After more than four years of orbiting Mercury, NASA's MESSENGER spacecraft came to an end in late April 2015. MESSENGER has provided many new and surprising results. This session will again highlight the latest results on Mercury based on MESSENGER observations or updated modelling. The session will further address instrument calibration and science performance both retrospective on MESSENGER and on the ESA/JAXA BepiColombo mission. Papers covering additional themes related to Mercury are also welcomed. Please be aware that this session will be held as a PICO session. This will allow an intensive exchange of expertise and experience between the individual instruments and mission. NVP melt/magma viscosity: insight on Mercury lava flows S. Rossi1, D. Morgavi1, O. Namur2, D. Perugini1, F.Vetere1, P. Mancinelli1 and C. Pauselli1 1 Dipartimento di Fisica e Geologia, Università di Perugia, piazza Università 1, 06123 Perugia, Italy 2 Uni Hannover Institut für Mineralogie, Leibniz Universität Hannover, Callinstraβe 3, 30167 Hannover, Germany In this contribution we report new measurements of viscosity of synthetic komatitic melts, used the behaviour of silicate melts erupted at the surface of Mercury. Composition of Mercurian surface magmas was calculated using the most recent maps produced from MESSENGER XRS data (Weider et al., 2015). We focused on the northern hemisphere (Northern Volcanic Province, NVP, the largest lava flow on Mercury and possibly in the Solar System) for which the spatial resolution of MESSENGER measurements is high and individual maps of Mg/Si, Ca/Si, Al/Si and S/Si were combined. The experimental starting material contains high Na2O content (≈7 wt.%) that strongly influences viscosity. High temperature viscosity measurements were carried out at 1 atm using a concentric cylinder apparatus equipped with an Anton Paar RheolabQC viscometer head at the Department of Physics and Geology (PVRG_lab) at the University of Perugia (Perugia, Italy

  3. Il magma costitutivo dell'immaginario sociale contemporaneo: vivere e pensare il magma

    Orazio Maria Valastro


    Full Text Available La figura dell’Etna, sede della redazione di M@gm@, ha sollecitato un’immaginazione straordinaria durante la creazione del progetto editoriale avviato nel 2002, stimolando il coraggio di un’esperienza entusiasmante e appassionata dalla logica del magma del vulcano fonte di una poetica che ha alimentato, grazie alla sua sintassi metaforica, la costituzione di un progetto e di spazi alternativi. Celebriamo in quest’occasione il sesto anniversario della rivista, dedicando un numero ai contributi proposti dagli associati d’ (il progetto dell’Osservatorio dei Processi Comunicativi, l’Associazione culturale scientifica che pubblica la rivista ed i membri della redazione.

  4. Tracking Magma Degassing and Changes in Magma Rheology Between Major Dome Collapse Events

    Genareau, K.; Cronin, S. J.; Lube, G.


    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 magma 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 magma ascent rates during the two phases of magma 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

  5. Diapiric ascent of silicic magma beneath the Bolivian Altiplano

    Del Potro, R.; M. Díez; Blundy, J.; Camacho, Antonio G.; Gottsmann, Joachim


    The vertical transport of large volumes of silicic magma, which drives volcanic eruptions and the long-term compositional evolution of the continental crust, is a highly debated problem. In recent years, dyking has been favored as the main ascent mechanism, but the structural connection between a distributed configuration of melt-filled pores in the source region and shallow magma reservoirs remains unsolved. In the Central Andes, inversion of a new high-resolution Bouguer anomaly data over t...

  6. Evaluating Complex Magma Mixing via Polytopic Vector Analysis (PVA in the Papagayo Tuff, Northern Costa Rica: Processes that Form Continental Crust

    Guillermo E. Alvarado


    Full Text Available Over the last forty years, research has revealed the importance of magma mixing as a trigger for volcanic eruptions, as well as its role in creating the diversity of magma compositions in arcs. Sensitive isotopic and microchemical techniques can reveal subtle evidence of magma mixing in igneous rocks, but more robust statistical techniques for bulk chemical data can help evaluate complex mixing relationships. Polytopic vector analysis (PVA is a multivariate technique that can be used to evaluate suites of samples that are produced by mixing of two or more magma batches. The Papagayo Tuff of the Miocene-Pleistocene Bagaces Formation in northern Costa Rica is associated with a segment of the Central American Volcanic Arc. While this segment of the arc is located on oceanic plateau, recent (<8 Ma ignimbrites bear the chemical signatures of upper continental crust, marking the transition from oceanic to continental crust. The Papagayo Tuff contains banded pumice fragments consistent with one or more episodes of mixing/mingling to produce a single volcanic deposit. The PVA solution for the sample set is consistent with observations from bulk chemistry, microchemistry and petrographic data from the rocks. However, without PVA, the unequivocal identification of the three end-member solution would not have been possible.

  7. Tracking dynamics of magma migration in open-conduit systems

    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


    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 magma column in response to an increased magma input rate. During the 2014 flank eruption of Stromboli, this magma 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 magma 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 magma recharge within an open-conduit system and to track magma drainage during the effusive crisis, with a great impact on hazard assessment.

  8. H Diffusion in Olivine and Pyroxene from Peridotite Xenoliths and a Hawaiian Magma Speedometer

    Peslier, A. H.; Bizimis, M.


    Hydrogen is present as a trace element in olivine and pyroxene and its content distribution in the mantle results from melting and metasomatic processes. Here we examine how these H contents can be disturbed during decompression. Hydrogen was analyzed by FTIR in olivine and pyroxene of spinel peridotite xenoliths from Salt Lake Crater (SLC) nephelinites which are part of the rejuvenated volcanism at Oahu (Hawaii) [1,2]. H mobility in pyroxene resulting from spinel exsolution during mantle upwelling Most pyroxenes in SLC peridotites exhibit exsolutions, characterized by spinel inclusions. Pyroxene edges where no exsolution are present have less H then their core near the spinel. Given that H does not enter spinel [3], subsolidus requilibration may have concentrated H in the pyroxene adjacent to the spinel exsolution during mantle upwelling. H diffusion in olivine during xenolith transport by its host magma and host magma ascent rates Olivines have lower water contents at the edge and near fractures compared to at their core, while the concentrations of all other chemical elements appear homogeneous. This suggests that some of the initial water has diffused out of the olivine. Water loss from the olivine is thought to occur during host-magma ascent and xenolith transport to the surface [4-6]. Diffusion modeling matches best the data when the initial water content used is that measured at the core of the olivines, implying that mantle water contents are preserved at the core of the olivines. The 3225 cm(sup -1) OH band at times varies independantly of other OH bands, suggesting uneven H distribution in olivine defects likely acquired during mantle metasomatism just prior to eruption and unequilibrated. Diffusion times (1-48 hrs) combined with depths of peridotite equilibration or of magma start of degassing allow to calculate ascent rates for the host nephelinite of 0.1 to 27 m/s.

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

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


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

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

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


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

  11. Global Ocean Phytoplankton

    Franz, B. A.; Behrenfeld, M. J.; Siegel, D. A.; Werdell, P. J.


    Marine phytoplankton are responsible for roughly half the net primary production (NPP) on Earth, fixing atmospheric CO2 into food that fuels global ocean ecosystems and drives the ocean's biogeochemical cycles. Phytoplankton growth is highly sensitive to variations in ocean physical properties, such as upper ocean stratification and light availability within this mixed layer. Satellite ocean color sensors, such as the Sea-viewing Wide Field-of-view Sensor (SeaWiFS; McClain 2009) and Moderate Resolution Imaging Spectroradiometer (MODIS; Esaias 1998), provide observations of sufficient frequency and geographic coverage to globally monitor physically-driven changes in phytoplankton distributions. In practice, ocean color sensors retrieve the spectral distribution of visible solar radiation reflected upward from beneath the ocean surface, which can then be related to changes in the photosynthetic phytoplankton pigment, chlorophyll- a (Chla; measured in mg m-3). Here, global Chla data for 2013 are evaluated within the context of the 16-year continuous record provided through the combined observations of SeaWiFS (1997-2010) and MODIS on Aqua (MODISA; 2002-present). Ocean color measurements from the recently launched Visible and Infrared Imaging Radiometer Suite (VIIRS; 2011-present) are also considered, but results suggest that the temporal calibration of the VIIRS sensor is not yet sufficiently stable for quantitative global change studies. All MODISA (version 2013.1), SeaWiFS (version 2010.0), and VIIRS (version 2013.1) data presented here were produced by NASA using consistent Chla algorithms.

  12. Anhydrite solubility in differentiated arc magmas

    Masotta, M.; Keppler, H.


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

  13. The rheology of crystal-rich magmas (Kuno Award Lecture)

    Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim


    The rheology of magmas controls not only eruption dynamics but also the rate of transport of magmas through the crust and to a large extent the rate of magma differentiation and degassing. Magma 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 magmas. 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 magmas 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 magmas. 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

  14. Plagioclase in Dacites of the Current Mt. St. Helens Eruption: Constraints for Magma Origin and Dynamics

    Streck, M. J.; Broderick, C.; Thornber, C. R.; Clynne, M. A.; Pallister, J. S.


    The current, now year-long eruption of Mt. St. Helens is remarkable for a variety of reasons. Nearly solid, gas-poor dacite lava is extruding at the surface. Earthquakes are limited to the upper 3 km with most occurring less than 1 km below the surface; no deeper seismicity has been observed. Emissions of SO2, H2S, CO2 are extremely low, suggesting eruption of degassed magma. No direct evidence for mingling of more mafic magma has been observed. We investigated plagioclase crystals in 2004-5 dacite and 1980-86 dacite dome rocks to shed light on the nature and origin of the current magma. Polarized light and Nomarski microscopy in combination with detailed microprobe traverses were used to characterize single plagioclase crystals, focusing on areas near their rims. In addition, we mapped all plagioclase crystals within an area of ~1/3 of each thin section and grouped them according to easily distinguishable mineral features. Although labor-intensive, this new approach was devised to generate data statistically significant enough to compare plagioclase crystal populations of crystal-rich samples. Mappable features within crystals include: i) zones of acicular opx microlitic inclusions (commonly occurring near the rim), ii) resorption surfaces, iii) spatial association of i) and ii). Our key results from the crystal mapping indicate that sequential samples of 2004/5 have remained comparable, but are distinct from 1980-86 dacite dome samples. We interpret this result as strong evidence that the 2004-5 dacite is new magma and not 'left-over' 1980's dacite. The most interesting result from combining compositional profiling with texture is that acicular opx inclusions occur at the lowest observed An content of 40-33 regardless of position within crystal and that overgrowth on resorption surfaces are typically 10-20 mol% higher in An than within opx-rich zones resulting in single to multiple oscillations of An content towards the rim. These features could possibly be

  15. Phase equilibrium modelling of granite magma petrogenesis: B. An evaluation of the magma compositions that result from fractional crystallization

    Garcia-Arias, Marcos; Stevens, Gary


    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 magma) have been used to study a wide range of likely S-type magma compositions. The evolution of these magmas 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 magmas 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 magmas digests partially the entrained mineral assemblage of the magmas, but unless this entrained assemblage represents less than 1 wt.% of the original magma, part of the mineral fraction survives the ascent up to the chosen pressure of emplacement. At the level of emplacement, batch crystallization produces magmas that only plot within the composition of the granites of the Peninsula pluton if the bulk composition of the original magmas 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

  16. Sr-O isotope systematics in the Campi Flegrei magma systems

    Wörner, Gerhard; Iovine, Raffaella; Carmine Mazzeo, Fabio; D'Antonio, Massimo; Arienzo, Ilenia; Civetta, Lucia; Orsi, Giovanni


    Combined radiogenic Sr- and stable O-isotopes are a powerful tool to distinguish between (a) contamination of mantle magma sources by fluids and subducted sediment and (b) assimilation of magmas during ascent through the crust. Advance in laser fluorination mass spectrometry permits to measure small samples and single mineral grains. This allows to directly link Sr- and O-isotope measurements practically for the same sample material. Although isotopic heterogeneity remains a problem even at this level, this approach avoids problems of weathering and mineral-melt disequilibria. We analysed mineral separates (feldspar, Fe-cpx, Mg-cpx, magnetite, olivine) from 37 samples covering the stratigraphic sequence of the Campi Flegrei volcanic field: Pre-Campanian Ignimbrite (Pre CI; >39.28 ka), Campanian Ignimbrite (CI; 39.28 ka), Post Campanian Ignimbrite/Pre Neapolitan Yellow Tuff (Post CI/pre NYT; 14.90 ka), Neapolitan Yellow Tuff (NYT; 14.90 ka), and Post-Neapolitan Yellow Tuff (Post NYT; 12.8 ka-1538 A.D.) deposits. Sr isotopic compositions were determined using standard cation-exchange methods on separated hand-picked feldspar, clinopyroxene and olivine phenocrysts (~300mg) and on whole rocks, in case of not enough amount of crystals. By infrared laser fluorination was, instead, measured the oxygen isotopic composition of ~0.3 mg of hand-picked phenocrysts. Recalculating measured mineral O-isotope values to magmatic values to account for mineral-melt 18O/16O-fractionation at various SiO2-contens of the melt should provide a data set that better constrains magma isotope compositions and magma sources. Sr-isotopes span a range from 0.7069 to 0.7082 that exceed the variations in the bulk rock samples (0.7071-0.7081). However, these ranges vary significantly between eruptive periods. For example the Sr-isotope variation in the Neapolitan Yellow Tuff is only between 0.70750 and 0.70754 for minerals and whole rocks. Similarly, recalculated δ18O-melt values show a large

  17. The buoyancy of large siliceous magma chambers is sufficient to initiate supereruptions

    Malfait, W.; Sanchez-Valle, C.; Seifert, R.; Petitgirard, S.; Perrillat, J.; Ota, T.; Nakamura, E.; Lerch, P.; Mezouar, M.


    The geological record shows abundant evidence for rare, but extremely large caldera-forming eruptions of siliceous magmas that dwarf all historical volcanic episodes in erupted volume [1] and environmental impact [2, 3]. Because of the large size of the magma chambers that feed these eruptions, the overpressure generated by magma recharge is insufficient to fracture the cap rock and trigger an eruption [4]. For these thick magma chambers, the buoyancy of the magma potentially creates a sufficient overpressure capable of fracturing the cap rock, but the lack of data on the density of rhyolite melts precludes the appropriate estimation of the overpressure and the role of buoyancy in initiating supervolcano eruptions. The density of rhyolite melts has not been determined at super-liquidus temperatures or elevated pressures because traditional techniques, including Archimedean methods, sink/float experiments and acoustic measurements, are limited by the high melt viscosity. Here, we measured the density of rhyolitic/granitic melts with 0, 4.5 and 7.7 wt% of dissolved water at geologically relevant conditions: 0.9 to 3.6 GPa, 1270 to 1950 K. High pressure and temperature conditions were generated in a Paris-Edinburgh large volume press. Before and after each density measurement, the molten state of the sample was verified by X-ray diffraction. The density of the melt (ρPT) was determined from the X-ray attenuation coefficient of the sample, determined in situ (μPT) and at room conditions (μ0), and the density at room conditions (ρ0): ρPT=ρ0.(μPT/μ0). The acquired data were combined with available ambient pressure data on super-cooled liquids [5, 6] to derive a third order Birch-Murnaghan equation of state that accurately predicts the density of rhyolite melts as a function of pressure, temperature and water content, and the partial molar volume of dissolved water. Application of the melt equation of state to calculate the overpressure at the roof of supervolcano

  18. Comparisons of venus surface compositions with terrestrial ocean floor rocks

    Garvin, J.B.; Bryan, W.B.


    Statistical comparison of Venera and Vega lander x-ray fluorescence spectrometer measurements of the composition of the Venus surface with an extensive database of compositional data for terrestrial ocean floor rocks indicates that the Venera 14 data matches certain tholeiitic basalts from the Kane Fracture Zone (KFZ) in the Mid-Atlantic Ridge (22-25/sup 0/N) at high confidence levels. The tholeiites most similar to the Venera measurements are very primitive, low-calcium, high-alumina pillow basalts depleted in clinopyroxene, and are relatively unique to certain fracture zones in oceanic regions. If the Venera 14 analogy is valid, the implication is that certain Venus basaltic magmas have lost clinopyroxene at relatively high pressures by fractionation, perhaps within a deep source region. Comparisons of Venera 13 and Vega 2 data with oceanic rocks yield poorer matches. Venera 13 matches Loihi seamount alkali basalts, as well as potassic mafic rocks from oceanic island such as Tristan de Cunha. The best analogy to Vega 2 may be altered gabbros or basic lavas from terrestrial basic intrusions such as the Troodos ophiolite. The close similarity of a representative sample of Venera 14 material with distinctive ocean floor tholeiitic basalts suggests that deep magma storage regions exist on Venus, and that derivation of both tholeiitic and alkalic magmas from a single primitive parent may be an important process on Venus.

  19. Evolution of magma-poor continental margins from rifting to seafloor spreading.

    Whitmarsh, R B; Manatschal, G; Minshull, T A


    The rifting of continents involves faulting (tectonism) and magmatism, which reflect the strain-rate and temperature dependent processes of solid-state deformation and decompression melting within the Earth. Most models of this rifting have treated tectonism and magmatism separately, and few numerical simulations have attempted to include continental break-up and melting, let alone describe how continental rifting evolves into seafloor spreading. Models of this evolution conventionally juxtapose continental and oceanic crust. Here we present observations that support the existence of a zone of exhumed continental mantle, several tens of kilometres wide, between oceanic and continental crust on continental margins where magma-poor rifting has taken place. We present geophysical and geological observations from the west Iberia margin, and geological mapping of margins of the former Tethys ocean now exposed in the Alps. We use these complementary findings to propose a conceptual model that focuses on the final stage of continental extension and break-up, and the creation of a zone of exhumed continental mantle that evolves oceanward into seafloor spreading. We conclude that the evolving stress and thermal fields are constrained by a rising and narrowing ridge of asthenospheric mantle, and that magmatism and rates of extension systematically increase oceanward.

  20. Solidification fronts in large magma chambers: insights from the anomalies

    VanTongeren, J. A.


    The emplacement of hot viscous magma into the cold rigid crust causes a thermal disturbance within both the country rock and the magma. With time, heat loss from the molten interior to the walls causes solidification at the floor, roof and margins of the magma chamber. As is observed in both experiment and theory, in the absence of hydrothermal convection, the majority of heat is lost via conduction through the roof of the intrusion. In basaltic sills and layered mafic intrusions (LMIs), this solidification front is manifest in the deposition of mineral assemblages and compositions that become progressively more evolved from the floor of the intrusion upwards (the 'Layered Series'; LS) and from the roof downwards (the UBS) such that the most chemically evolved rocks are found in the interior of the magma body at a 'Sandwich Horizon'. The formation of a UBS, as typified by the Skaergaard Intrusion, is a natural outcome of the progression of the solidification front from the cold roof to the hot center of the magma chamber. There are, however, a few unique LMIs for which little or no UBS exists. Convection of the molten magma, reinjection and mixing of new magma, compaction of cumulates, and porous flow of interstitial liquid, among other processes, can affect the final location and composition of the most differentiated liquids; but ultimately, all are linked to the nature of heat loss from the magma chamber. In this study, I examine the thermal evolution of several classic LMIs as it is recorded in the extent of the preserved upper solidification front (or Upper Border Series; 'UBS'). For those intrusions that have experienced crystallization at the roof, such as the Skaergaard Intrusion, the development of a UBS reduces the temperature gradient at the roof and effectively slows the rate of heat loss from the main magma body. However, for those intrusions that do not have an UBS, such as the Bushveld Complex, the cooling rate is controlled only by the maximum rate

  1. Laboratory studies of crystal growth in magma

    Hammer, J. E.; Welsch, B. T.; First, E.; Shea, T.


    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 magmas 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

  2. Eddy Flow during Magma Emplacement: The Basemelt Sill, Antarctica

    Petford, N.; Mirhadizadeh, S.


    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 magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle macrostructure of a congested magma 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 magma 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 magma at a later time according to their mass density. This trapping mechanism has potential to develop local variations in structure (layering) and magma chemistry that may otherwise not occur where the contact between magma and country rock is linear. Simulations indicate that eddy formation is best developed where magma 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

  3. Slab Contributions to Cascades Magmas: Constraints from Central Oregon and Northern California

    Ruscitto, D. M.; Wallace, P. J.


    The Cascades arc is the global end member, warm-slab subduction zone (slab thermal parameter ~200 km) resulting from the slow subduction of young oceanic crust beneath North America. Significant slab dehydration is predicted to occur beneath the forearc (high-Mg andesite (HMA) and primitive basaltic andesite (PBA) with 3.3 and 5.6 wt.% H2Omax, respectively. Three distinct primitive melt compositions were calculated using inclusions from Central Oregon: calc-alkaline basalt, Sr-rich basalt, and depleted basaltic andesite (1.6, 2.3, and 3.0 wt.% H2Omax, respectively). We calculated extents of mantle melting for each primitive magma composition using Ti, Y, Gd, Dy, Er, and Yb contents (i.e., assuming negligible contributions from the slab). Based on these calculations, we infer Central Oregon and Shasta magmas to represent 8-15% and 14-20% partial melts (respectively) of variably depleted sources. Major elements in preliminary slab components from Central Oregon are H2O (~39-45 wt.%), Na2O (~36-47 wt.%), K2O (~8-15 wt.%), and Cl (~1.0-3.8 wt.%) and similar to the slab component calculated for Shasta HMA. The slab component calculated for Shasta PBA is more volatile-rich with ~62 wt.% H2O, ~28 wt.% Na2O, ~5.3 wt.% K2O, and 4.6 wt.% Cl. Calculated slab components are similar to previously published estimates from the Shasta region and experimental high temperature (>800 °C) fluids/melts derived from altered oceanic crust and/or sediments. Compositional proxies for slab surface temperatures (H2O/K2O and H2O/Ce) are at the high temperature range of the global arc spectrum, corresponding to temperatures of 850-950 °C, and are consistent with a young, hot incoming plate.

  4. Mantle decarbonation and Archean high-Mg magmas

    Edwards, Garth R.


    Magnesium-rich mane to ultramafic extrusions were most common in the Archean and pose interesting petrological problems. The high Mg content of komatiites (>18 wt%, for example, is usually interpreted as indicating an origin at higher temperatures than exist in mantle melting zones in the modern Earth. Current contrasting models for the origin of komatiites in the mantle require either high degrees of melting or lower degrees of melting at great depth. A potential complementary mechanism for Mg enrichment in magmas involves the melting of magnesite-bearing garnet Iherxolite. In this model, the ascending primary mafic or ultramafic magma is enriched in MgO by the loss of some off the CO2 to the adjacent mantle at pressures of ˜2.2 GPa, where the magma becomes saturated with CO2. To generate komatiite in this way from a picritelike parent, for example, requires that the primary magma lose some of its major and trace element components to the adjacent mantle concurrently with the CO2. Production of magnesian magmas by magnesite breakdown may not have required the heat or depth of those produced by other means; this mechanism may help to explain some apparently low Archean geothermal gradients, as well as the contemporaneity of Archean diamonds and komatites. The mantle magnesite could have formed by direct reaction of primordial CO2 or CO with hot, protomantle material during Earth's accretionary period.

  5. The Inclusion of Raman Scattering Effects in the Combined Ocean-Atmosphere Radiative Transfer Model MOMO to Estimate the Influence of Raman Scattering in Case 1 Waters on Satellite Ocean Remote Sensing Applications

    von Bismarck, J.; Fischer, J.


    Raman scattering of the solar lightfield, due to energy absorption by vibrational modes of water molecules, may contribute significantly to the signals observed by remote sensing satellites over water. The inelastic fraction of the water-leaving radiance for clear water reaches values of 30% in the red part of the visible spectrum, and still reaches values of several percent in moderately turbid waters. Furthermore, inelastic scattering due to chlorophyll and yellow substance fluorescence adds to this fraction. For these reasons the inclusion of inelastic scattering sources into radiative-transfer models, used in ocean remote sensing applications or atmosphere remote sensing over the ocean, can be important. MOMO is a computer code based on the matrix-operator method designed to calculate the lightfield in the stratified atmosphere-ocean system. It has been developed at the Institute for Space Sciences of the Freie Universität Berlin and provides the full polarization state (in the newest version) and an air-sea interface accounting for radiative effects of the wind roughened water surface. The inclusion of Raman scattering effects is done by a processing module, that starts a primary MOMO program run with a high spectral resolution, to calculate the radiative energy available for inelastic scattering at each model layer boundary. The processing module then calculates the first order Raman source-terms for every observation wavelength at every layer boundary, accounting for the non-isotropicity (including the azimuthal dependence) of the Raman phase-function, the spectral redistribution, and the spectral dependence of the Raman scattering coefficient. These elementary source-terms then serve as input for the second program run, which then calculates the source-terms of all model layers, using the doubling-adding method, and the resulting radiance field. Higher orders of the Raman contribution can be computed with additional program runs. Apart from the Raman

  6. Magma chamber history related to the shield building stage of Piton des Neiges volcano, La Réunion Island

    Berthod, Carole; Michon, Laurent; Famin, Vincent; Bascou, Jérôme; Bachelery, Patrick


    Piton des Neiges volcano (La Réunion hotspot) experienced a long-lasting shield building stage before entering its degenerative stage 0.4 my ago. The deep edifice incision due to the intense tropical erosion allowed the description for several decades of a layered gabbroic complex interpreted as a piece of magma chamber, which has been tectonically displaced (Chevallier & Vatin-Perignon, 1982; Upton & Wadsworth, 1972). Here, we combine field investigations, petrographic, mineralogical, geochemical and anisotropy of magnetic susceptibility (AMS) studies to constrain the spatial distribution of the plutonic complex, to identify the physical and chemical processes and to integrate this complex in the evolution of Piton des Neiges (PdN). Field investigations allowed us to discover three additional massifs of gabbro and peridotite along the Mât River. The four massifs are overlaid by a pile of basic sills and a breccia interpreted as a debris avalanche deposit. Albeit spatially disconnected, the massifs show a relatively constant dip of the magnetic foliation toward the current summit of the volcano (i.e. toward the SSE). The two massifs cropping in the upper Mât River are exclusively composed of massive dunite and wherlite units with a cumulate texture and no visible dynamic structures. The two massifs located in the lower Mât River are made of olivine-gabbro, ferrogabbro and gabbro showing numerous flow structures and synmagmatic faults that indicates instabilities which trend NNW-SSE. Minerals (olivine, clinopyroxene and oxide) present primitive compositions in the two upper massifs and slightly differentiated ones in the lower massif. Given the consistency of our dataset, we propose that the four massifs correspond to outcrops of a unique chemically stratified magma chamber, whose center would have been located about 4 km North of the current summit of PdN. The existence of an initial PdN, North of the current edifice, is supported by morphological

  7. Constraints on the Rates of Replenishment, Magma Mixing, and Crystal Recycling at Santorini Volcano, Greece

    Martin, V. M.; Davidson, J. P.; Morgan, D. J.; Jerram, D. A.


    ratios of plagioclase xenocryst cores suggest crystal recycling from a pre-Minoan source is probable. Olivine xenocrysts in the enclaves possess narrow (10-30 μm) Fe-Mg diffusion profiles, due to interaction with enclave magma groundmass, which can be used to estimate the interval between entrainment and eruption. Initial modelling of diffusion profiles from more than 60 crystals suggests short timescales, from 15 to 45 days, for the combined migration-replenishment-eruption cycle at Kameni.

  8. Silica-enriched mantle sources of subalkaline picrite-boninite-andesite island arc magmas

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


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

  9. Melting and Reactive Flow of Carbonated Peridotite Beneath Mid-Ocean Ridges

    Keller, T.; Katz, R. F.


    The mantle carbon reservoir is four orders of magnitude more massive than that of the atmosphere and ocean combined. The behaviour of carbon in the mantle, especially its transport and extraction, is thus of crucial importance to understanding the coupling between the deep interior and the surface environment of Earth. Laboratory experiments indicate that even small concentrations of carbon dioxide (and other volatiles like H2O) in the upper mantle significantly affect silicate melting [HK96,DH06] by stabilising carbon-rich melt at high pressure. The presence of carbon in the mantle substantially extends the region where partial melt is stable and has important consequences for the dynamics of magma transport and chemical differentiation [H10,DH10]. We have developed theory and numerical implementation to simulate thermo-chemically coupled magma/mantle dynamics in terms of a two-phase (rock+melt), three component (dunite+MORB+carbonated MORB) physical model. The fluid dynamics is based on McKenzie's equations [McK84]. The thermo-chemical formulation of the system is represented by a novel, disequilibrium, multi-component melting model based on thermodynamic theory [RBS11]. This physical model is implemented as a parallel, two-dimensional, finite-volume code that leverages tools from the PETSc toolkit. First results show that carbon and other volatiles cause a qualitative difference to the style of melt transport, potentially enhancing its extraction efficiency - measured in the carbon mass flux arriving at the mid-ocean ridge axis - by at least an order of magnitude. The process that controls magma transport in our models is a volatile flux-induced reactive infiltration instability, causing carbonated melt to rise from depth in localized channels. These results add to our understanding of melt formation and transport at mid-ocean ridges (the most important magmatic system in the mantle) and may have important implications for subduction zones. REFERENCESHK96 Hirth

  10. Andean Adakites: Products of Slab Melting, Magma Evolution in Thickened Crust and Crustal Recycling by Forearc Subduction Erosion

    Kay, S. M.; Kay, R. W.; Goss, A.


    Adakites in the southern and central Andes show a residual garnet signature that can variously be related to local slab melting associated with subduction of hot oceanic crust at the Chile Triple Junction, widespread interaction of mafic magmas in regions of thickened crust, and episodic melting of crust removed by forearc subduction erosion, particularly at times of frontal arc migration. Among the most convincing slab-melt adakites on Earth are the late Miocene Cerro Pampa type dacitic adakites east of the Chile Triple Junction whose low 87Sr/86Sr ratios (0.7028-0.7033) and high Sr contents (up to 2300 ppm) are difficult to explain by any other mechanism. Elsewhere the appearance of transient extreme adakitic signatures at times of frontal arc migration can be explained by forearc subduction erosion and the evolution of magmas at deep crustal levels in a contractional regime provided the crust is thick. Transient steep adakitic-like REE patterns at times of arc migration fit with forearc crust being transported down the subduction channel, entering the tip of the asthenospheric wedge and being incorporated into the arc mantle source. Evidence for a genetic link for transient adakite signatures, arc migration and forearc subduction erosion comes from changing isotopic ratios in mafic magmas erupted before and after arc migration on the edges of the Chilean flat-slab near 27°S and 34°S (Kay et al 2005) where the arc front has migrated up to 50 km eastward in the last 8 Ma. The chemistry of these mafic magmas cannot be explained by enriched mantle or incorporation of subducted sediments or in situ crust. Sharp increases in 87Sr/86Sr ratios and transient steep REE patterns in Andean arc rocks erupted in the final stages of Cretaceous to early Tertiary magmatic cycles at 21°S to 26°S (see Haschke et al. 2002) can also be attributed to forearc subduction erosion. Forearc subduction erosion provides a better explanation for the formation of Aleutian and Central

  11. Assessing chromophoric dissolved organic matter (CDOM) distribution, stocks, and fluxes in Apalachicola Bay using combined field, VIIRS ocean color, and model observations

    Joshi, Ishan D.; D' Sa, Eurico J.; Osburn, Christopher L.; Bianchi, Thomas S.; Ko, Dong S.; Oviedo-Vargas, Diana; Arellano, Ana R.; Ward, Nicholas D.


    Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. The chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412 nm (ag412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processes using satellite ocean color imagery necessitates the removal of atmospheric contribu- tion (~90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R2 = 0.95, N = 25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R2 = 0.87, N = 9) and validated (R2 = 0.76, N = 20, RMSE = 0.29 m-1) against in situ observations. Subsequently, ag412 was used as a proxy ofDOCinMarch(DOC=1.08+0.94×ag412,R2 =0.88,N=13)andinNovember(DOC= 1.61 + 1.33 × ag412, R2 = 0.83, N = 24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~3.71 × 106 kg C in March and ~4.07 × 106 kg C in November over an area of ~560 km2. Volume flux (out of the bay) almost doubled for March 24 (735 m3

  12. Imaging magma storage reservoirs beneath Sierra Negra volcano, Galápagos, Ecuador

    Tepp, G.; Belachew, M.; Ebinger, C. J.; Seats, K.; Ruiz, M. C.; Lawrence, J. F.


    Ocean island volcanoes initiate and grow through repeated eruptions and intrusions of primarily basaltic magma that thicken the oceanic crust above melt production zones within the mantle. The movement of oceanic plates over the hot, melt-rich upwellings produces chains of progressively younger basaltic volcanoes, as in the Galapagos Islands. Rates of surface deformation along the chain of 7 active volcanoes in the western Galápagos are some of the most rapid in the world, yet little is known of the subsurface structure of the active volcanic systems. The 16-station SIGNET array deployed between July 2009 and June 2011 provides new insights into the time-averaged structure beneath Sierra Negra, Cerro Azul, and Alcedo volcanoes, and the ocean platform. We use wavespeed tomography to image volcanic island structure, with focus on the magmatic plumbing system beneath Sierra Negra volcano, which has a deep, ~10 km-wide caldera and last erupted in 2005. We compare our results to those of ambient noise tomography. Our 120 x 100 km grid has a variable mesh of 2.5 - 10 km. We have good resolution at depths between 3 and 15 km, with poorer resolution beneath Cerro Azul volcano. Events from Alcedo volcano, which is just outside our array, cause some N-S smearing. Results from wavespeed tomography provide insights into the major island building processes: accretion through extrusive magmatism, magma chamber geometry and depth, radial dike intrusions, and magmatic underplating/sill emplacement. The wide caldera of Sierra Negra is underlain by high velocity (~7 %) material from depths of 5 - 15, and the flanks correspond to low velocity material at all depths. A high velocity zone corresponds to Cerro Azul (~3%). Aligned chains of eruptive centers correlate with elongate high velocity zones, suggesting that radial dikes are the sites of repeated dike intrusions. These chains are preferentially located along ridges linking nearby volcanoes. A comparison of well-resolved zones

  13. Iron Redox Systematics of Shergottites and Martian Magmas

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


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

  14. Magma storage in a strike-slip caldera

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


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

  15. Magma storage in a strike-slip caldera.

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


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

  16. Efficiency of differentiation in the Skaergaard magma chamber

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


    Although it is largely agreed that crystallization occurs inwardly in crystal mushes along the margins of magma chambers, the efficiency and mechanisms of differentiation are not well constrained. The fractionation paradigm hinges on mass exchange between the crystal mush and the main magma reservoir resulting in coarse-grained, refractory (cumulate) rocks of primary crystals, and complementary enrichment of incompatible elements in the main reservoir of magma. Diffusion, convection, liquid immiscibility and compaction have been proposed as mechanisms driving this mass exchange. Here we examine the efficiency of differentiation in basaltic crystal mushes in different regions of the Skaergaard magma chamber. The contents of incompatible elements such as phosphorus and calculated residual porosities are high in the lowermost cumulate rocks of the floor (47-30%) and decrease upsection, persisting at low values in the uppermost two-thirds of the floor rock stratigraphy (~5% residual porosity). The residual porosity is intermediate at the walls (~15%) and highest and more variable at the roof (10-100%). This is best explained by compaction and expulsion of interstitial liquid from the accumulating crystal mush at the floor and the inefficiency of these processes elsewhere in the intrusion. In addition, the roof data imply upwards infiltration of interstitial liquid. Remarkably uniform residual porosity of ~15% for cumulates formed along the walls suggest that their preservation is related to the rheological properties of the mush, i.e. at ≤ 15% porosity the mush is rigid enough to adhere to the wall, while at higher porosity it is easily swept away. We conclude that the efficiency of compaction and differentiation can be extremely variable along the margins of magma chambers. This should be taken into account in models of magma chamber evolution.

  17. Tectono-magmatic evolution at distal magma-poor rifted margins: insights of the lithospheric breakup at the Australia-Antarctica margins.

    Gillard, Morgane; Autin, Julia; Manatschal, Gianreto


    The discovery of large domains of hyper-extended continental crust and exhumed mantle along many present-day magma-poor rifted margins questions the processes that play during the lithospheric breakup and the onset of seafloor spreading. In particular, the amount of magma and its relation to tectonic structures is yet little understood. Trying to find answers to these questions asks to work at the most distal parts of rifted margins where the transition from rifting to steady state seafloor spreading occurred. The Australian-Antarctic conjugated margins provide an excellent study area. Indeed, the central sector of the Great Australian Bight/Wilkes Land developed in a magma-poor probably ultra-slow setting and displays a complex and not yet well understood Ocean-Continent Transition (OCT). This distal area is well imaged by numerous high quality seismic lines covering the whole OCT and the steady-state oceanic crust. The deformation recorded in the sedimentary units along these margins highlights a migration of the deformation toward the ocean and a clear polyphase evolution. In particular, the observation that each tectono-sedimentary unit downlaps oceanwards onto the basement suggests that final rifting is associated with the creation of new depositional ground under conditions that are not yet those of a steady state oceanic crust. These observations lead to a model of evolution for these distal margins implying the development of multiple detachment systems organizing out-of-sequence, each new detachment fault developing into the previously exhumed basement. This spatial and temporal organization of fault systems leads to a final symmetry of exhumed domains at both conjugated margins. Magma appears to gradually increase during the margin development and is particularly present in the more distal domain where we can observe clear magma/fault interactions. We propose that the evolution of such rifted margins is linked to cycles of delocalisation

  18. Imaging magma plumbing beneath Askja volcano, Iceland

    Greenfield, Tim; White, Robert S.


    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 magma 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

  19. Output rate of magma from active central volcanoes

    Wadge, G.


    For part of their historic records, nine of the most active volcanoes on earth have each erupted magma 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 magma-filled cracks in the upper crust may contribute to the observed restricted range of the rates of output.

  20. Silicic magma differentiation in ascent conduits. Experimental constraints

    Rodríguez, Carmen; Castro, Antonio


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

  1. Ocean technology

    Peshwe, V.B.

    stream_size 2 stream_content_type text/plain stream_name Voices_Oceans_1996_113.pdf.txt stream_source_info Voices_Oceans_1996_113.pdf.txt Content-Encoding ISO-8859-1 Content-Type text/plain; charset=ISO-8859-1 ...

  2. Oceanic archipelagos

    Triantis, Kostas A.; Whittaker, Robert James; Fernández-Palacios, José María;


    Since the contributions of Charles Darwin and Alfred Russel Wallace, oceanic archipelagos have played a central role in the development of biogeography. However, despite the critical influence of oceanic islands on ecological and evolutionary theory, our focus has remained limited to either the i...

  3. Ocean acidification

    Gattuso, J.P; Hansson, L


    The fate of much of the CO 2 we produce will be to enter the ocean. In a sense, we are fortunate that ocean water is endowed with the capacity to absorb far more CO 2 per litre than were it salt free...

  4. Conduit Magma Storage during the 800 BP Quilotoa Eruption, Ecuador

    Ort, M. H.; Cashman, K. V.; Di Muro, A.; Best, J. A.; Rosi, M.; Mothes, P. A.; Bustillos, J.


    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 magma 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 magma 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 magma 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

  5. Cyclic Explosivity in High Elevation Phreatomagmatic Eruptions at Ocean Island Volcanoes: Implications for Aquifer Pressurization and Volcano Flank Destabilization.

    Tarff, R.; Day, S. J.; Downes, H.; Seghedi, I.


    Groundwater heating and pressurization of aquifers trapped between dikes in ocean island volcanoes has been proposed as a mechanism for destabilizing and triggering large-volume flank collapses. Previous modelling has indicated that heat transfer from sustained magma flow through dikes during eruption has the potential to produce destabilizing levels of pressure on time scales of 4 to 400 days, if the aquifers remain confined. Here we revisit this proposal from a different perspective. We examine evidence for pressure variations in dike-confined aquifers during eruptions at high elevation vents on ocean island volcanoes. Initially magmatic, these eruptions change to mostly small-volume explosive phreatomagmatic activity. A recent example is the 1949 eruption on La Palma, Canary Islands. Some such eruptions involve sequences of larger-volume explosive phases or cycles, including production of voluminous low-temperature, pyroclastic density currents (PDC). Here we present and interpret data from the Cova de Paul crater eruption (Santo Antao, Cape Verde Islands). The phreatomagmatic part of this eruption formed two cycles, each culminating with eruption of PDCs. Compositional and textural variations in the products of both cycles indicate that the diatreme fill began as coarse-grained and permeable which allowed gas to escape. During the eruption, the fill evolved to a finer grained, poorly sorted, less permeable material, in which pore fluid pressures built up to produce violent explosive phases. This implies that aquifers adjacent to the feeder intrusion were not simply depressurized at the onset of phreatomagmatic explosivity but experienced fluctuations in pressure throughout the eruption as the vent repeatedly choked and emptied. In combination with fluctuations in magma supply rate, driving of aquifer pressurization by cyclical vent choking will further complicate the prediction of flank destabilization during comparable eruptions on ocean island volcanoes.

  6. Magma energy research project: state-of-the-project report, October 1, 1978

    Colp, J.L.; Traeger, R.K.


    The feasibility of extracting energy from magma bodies is investigated. The work done in FY 76, 77, and 78 in the following tasks are summarized; resource location and definition, source tapping, magma characterization and materials compatibility, and energy extraction. (MHR)

  7. 3D numerical modeling of mantle flow, crustal dynamics and magma genesis associated with slab roll-back and tearing: The eastern Mediterranean case

    Menant, Armel; Sternai, Pietro; Jolivet, Laurent; Guillou-Frottier, Laurent; Gerya, Taras


    Interactions between subduction dynamics and magma genesis have been intensely investigated, resulting in several conceptual models derived from geological, geochemical and geophysical data. To provide physico-chemical constraints on these conceptual models, self-consistent numerical simulations containing testable thermo-mechanical parameters are required, especially considering the three-dimensional (3D) natural complexity of subduction systems. Here, we use a 3D high-resolution petrological and thermo-mechanical numerical model to quantify the relative contribution of oceanic and continental subduction/collision, slab roll-back and tearing to magma genesis and transport processes. Our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3D slab dynamics and related asthenospheric flow. Moreover, the decrease of the bulk lithospheric strength induced by mantle- and crust-derived magmas promotes the propagation of strike-slip and extensional fault zones through the overriding crust as response to slab roll-back and continental collision. Reduction of the lithosphere/asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust. Similarities between our modeling results and the late Cenozoic tectonic and magmatic evolution across the eastern Mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region, which in turn promotes lithospheric deformation by mantle drag via melt-induced weakening effects.

  8. Evolution of magma feeding system in Kumanodake agglutinate activity, Zao Volcano, northeastern Japan

    Takebe, Yoshinori; Ban, Masao


    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 magma feeding system. To understand the magma 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 magma feeding system comprised a shallow felsic chamber injected by mafic magma from depth. The felsic magma (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 magma is further divisible into two types: less-differentiated and more-differentiated, designed respectively as an initial mafic magma-1 and a second mafic magma-2. The original mafic magma-1 was olivine (Fo 84) basalt (ca. 48-51% SiO2, 1110-1140 °C). The second mafic magma-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 magmas mixed (first mixing) to form hybrid mafic magma. The forced injections of the hybrid mafic magmas activated the felsic magma, 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 magma composition became more mafic, which reflects increased percentage of the hybrid mafic magma involved in the second mixing. At the beginning of activity, the mafic magma also acted as a heat

  9. Electrical conductivity of intermediate magmas from Uturuncu Volcano (Bolivia)

    Laumonier, Mickael; Gaillard, Fabrice; Sifre, David


    Magmas erupted at Uturuncu volcano (South Bolivia) comes from the Altiplano-Puna Magma Body (APMB, Chile-Bolivia), a crustal massive body of 80 km long by 10 km thick located at ~ 35 km depth named. Recent magneto telluric surveys reveal a resistivity lower than 1 ohm.m due to the presence of melt which could result in the reactivation of the volcano. In order to better constrain the resistivity profiles and thus the conditions of magma storage of the APMB, we have performed in situ electrical measurements on natural dacites and andesites from Uturuncu with a 4-wire set up in a piston cylinder and internally heated pressure vessel. The range of temperature (500 to 1300°C), pressure (0.3 to 2 Gpa), and the various water contents covers the respective ranges occurring at natural conditions. The results show that the conductivity increases with the temperature and the water content but slightly decreases with the pressure. Then a model was built from these results so as to help in (i) interpreting the electrical signature of natural magmas, (ii) constraining their conditions (chemical composition, temperature, pressure, water content, melt fraction) from the source to the storage location and (iii) providing information on the interior structure of a volcano and its reservoir.

  10. Magma plumbing for the 2014-2015 Holuhraun eruption, Iceland

    Geiger, Harri; Mattsson, Tobias; Deegan, Frances M.; Troll, Valentin R.; Burchardt, Steffi; Gudmundsson, Ólafur; Tryggvason, Ari; Krumbholz, Michael; Harris, Chris


    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 magma 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 magma 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 magma ascent within the Bárðarbunga plumbing system followed by lateral transport of aggregated magma batches within the upper crust to the Holuhraun eruption site.

  11. Crystallization of Magma. CEGS Programs Publication Number 14.

    Berry, R. W.

    Crystallization of Magma 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…

  12. A reverse energy cascade for crustal magma transport

    Karlstrom, Leif; Paterson, Scott R.; Jellinek, A. Mark


    Direct constraints on the ascent, storage and eruption of mantle melts come primarily from exhumed, long-frozen intrusions. These structures, relics of a dynamic magma 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 magma 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 magma 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 magma 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.

  13. Oxygen isotope geochemistry of mafic magmas at Mt. Vesuvius

    Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano


    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 magmas, 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 magmas at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary magmas, 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 magmas. 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 magmas 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

  14. JPL Ecco Ocean Data Assimilation

    National Aeronautics and Space Administration — ECCO was established in 1998 as part of the World Ocean Circulation Experiment (WOCE) with the goal of combining a general circulation model (GCM) with diverse...

  15. Behavior of halogens during the degassing of felsic magmas

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


    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 magmas 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 magma reservoir to the surface. The ratios measured in erupted clasts are thus characteristic of pre-eruptive magma 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 magmas or during slow effusive magma 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.

  16. Mezcla de magmas en Vulcanello (Isla Vulcano, Italia

    Aparicio, A.


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

  17. Bubble plumes generated during recharge of basaltic magma reservoirs

    Phillips, Jeremy C.; Woods, Andrew W.


    CO 2 is relatively insoluble in basaltic magma 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 magma in the chamber. As a result, any new magma which recharges the chamber from deeper in the crust may be more bubble-rich and hence of lower density than the magma 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 magma 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].

  18. Seismic Tremors and Magma Wagging During Explosive Volcanism

    Jellinek, M.; Bercovici, D.


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

  19. Sulfur isotopic zoning in apatite crystals: A new record of dynamic sulfur behavior in magmas

    Economos, Rita; Boehnke, Patrick; Burgisser, Alain


    The mobility and geochemical behavior of sulfur in magmas is complex due to its multi-phase (solid, immiscible liquid, gaseous, dissolved ions) and multi-valent (from S2- to S6+) nature. Sulfur behavior is closely linked with the evolution of oxygen fugacity (fO2) in magmas; the record of fO2 evolution is often enigmatic to extract from rock records, particularly for intrusive systems. We apply a novel method of measuring S isotopic ratios in zoned apatite crystals that we interpret as a record of open-system magmatic processes. We interrogate the S concentration and isotopic variations preserved in multiple apatite crystals from single hand specimens from the Cadiz Valley Batholith, CA via electron microprobe and ion microprobe. Isotopic variations in single apatite crystals ranged from 0 to 3.8‰ δ34S and total variation within a single hand sample was 6.1‰ δ34S. High S concentration cores yielded high isotopic ratios while low S concentration rims yielded low isotopic ratios. We discuss a range of possible natural scenarios and favor an explanation of a combination of magma mixing and open-system, ascent-driven degassing under moderately reduced conditions: fO2 at or below NNO+1, although the synchronous crystallization of apatite and anhydrite is also a viable scenario. Our conclusions have implications for the coupled S and fO2 evolution of granitic plutons and suggest that in-situ apatite S isotopic measurements could be a powerful new tool for evaluating redox and S systematics in magmatic systems.

  20. Magma mixing and high fountaining during the 1959 Kīlauea Iki eruption, Hawai‘i

    Sides, I.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Swanson, Don; Steele-MacInnis, M.J.


    The 1959 Kīlauea Iki eruption provides a unique opportunity to investigate the process of shallow magma mixing, its impact on the magmatic volatile budget and its role in triggering and driving episodes of Hawaiian fountaining. Melt inclusions hosted by olivine record a continuous decrease in H2O concentration through the 17 episodes of the eruption, while CO2 concentrations correlate with the degree of post-entrapment crystallization of olivine on the inclusion walls. Geochemical data, when combined with the magma budget and with contemporaneous eruption observations, show complex mixing between episodes involving hot, geochemically heterogeneous melts from depth, likely carrying exsolved vapor, and melts which had erupted at the surface, degassed and drained-back into the vent. The drained-back melts acted as a coolant, inducing rapid cooling of the more primitive melts and their olivines at shallow depths and inducing crystallization and vesiculation and triggering renewed fountaining. A consequence of the mixing is that the melts became vapor-undersaturated, so equilibration pressures cannot be inferred from them using saturation models. After the melt inclusions were trapped, continued growth of vapor bubbles, caused by enhanced post-entrapment crystallization, sequestered a large fraction of CO2 from the melt within the inclusions. This study, while cautioning against accepting melt inclusion CO2 concentrations “as measured” in mixed magmas, also illustrates that careful analysis and interpretation of post-entrapment modifications can turn this apparent challenge into a way to yield novel useful insights into the geochemical controls on eruption intensity.

  1. Water-magma interaction and plume processes in the 2008 Okmok eruption, Alaska

    Unema, Joel; Ort, Michael H.; Larsen, Jessica D; Neal, Christina; Schaefer, Janet R.


    Eruptions of similar explosivity can have divergent effects on the surroundings due to differences in the behavior of the tephra in the eruption column and atmosphere. Okmok volcano, located on Umnak Island in the eastern Aleutian Islands, erupted explosively between 12 July and 19 August 2008. The basaltic andesitic eruption ejected ∼0.24 km3dense rock equivalent (DRE) of tephra, primarily directed to the northeast of the vent area. The first 4 h of the eruption produced dominantly coarse-grained tephra, but the following 5 wk of the eruption deposited almost exclusively ash, much of it very fine and deposited as ash pellets and ashy rain and mist. Meteorological storms combined with abundant plume water to efficiently scrub ash from the eruption column, with a rapid decrease in deposit thickness with distance from the vent. Grain-size analysis shows that the modes (although not their relative proportions) are very constant throughout the deposit, implying that the fragmentation mechanisms did not vary much. Grain-shape features consistent with molten fuel-coolant interaction are common. Surface and groundwater drainage into the vents provided the water for phreatomagmatic fragmentation. The available water (water that could reach the vent area during the eruption) was ∼2.8 × 1010 kg, and the erupted magma totaled ∼7 × 1011 kg, which yield an overall water:magma mass ratio of ∼0.04, but much of the water was not interactive. Although magma flux dropped from 1 × 107 kg/s during the initial 4 h to 1.8 × 105 kg/s for the remainder of the eruption, most of the erupted material was ejected during the lower-mass-flux period due to its much greater length, and this tephra was dominantly deposited within 10 km downwind of the vent. This highlights the importance of ash scrubbing in the evaluation of hazards from explosive eruptions.

  2. Magma genesis and chamber processes at Los Humeros caldera, Mexico-Nd and Sr isotope data

    Verma, Surendra P.


    The Mexican volcanic belt (MVB), a roughly east-west structure, consists of many late Tertiary and Quaternary cindercones, domes, calderas and stratovolcanoes1,2. Los Humeros caldera (approximately 19°40' N latitude, 97°25' W longitude) lies on the northeastern part of the MVB where the belt overlaps with another major volcanic province, the Eastern cordillera3 (Fig. 1). A compilation6 of the bulk chemical analyses of the two major volcanic provinces indicates that the MVB is characterized largely by calc-alkaline series whereas rocks of the alkaline series dominate the Eastern cordiliera (EC). Pleistocene to Recent basaltic to rhyolitic volcanism in Los Humeros caldera, one of the best known examples of a well-developed caldera in Mexico7-9, presumably associated with the subduction of Cocos plate along the Middle America trench, shows that the initial 87Sr/86Sr ratios range from 0.7039 to 0.7048 and the initial 143Nd/144Nd ratios from 0.5126 to 0.5129. We show here that these isotope ratios are negatively correlated and lie on the mantle array defined by MORB and oceanic island rocks; implying that Los Humeros magmas were generated in the upper mantle with very little, if any, contribution from the subducted oceanic crust, sediments or continental crust.

  3. Magma dynamics at shield-volcanoes: New insights from Hualalai oceanites

    Welsch, B. T.; Hammer, J. E.; Hellebrand, E.


    Oceanites are olivine-rich basalts generally interpreted as resulting from the dismantling of a dunitic cumulate by percolating magmas. To constrain the possible origins of olivine forming during the shield stage of an ocean island volcano, we studied the texture and the composition of oceanite samples collected from the submarine extension of Hualalai volcano's NW rift zone (2002 JAMSTEC dive S690). These oceanites contain abundant magnesian olivine macrocrysts (Ø>0.5 mm, Fo90-86), mesocrysts (0.1Welsch et al., 2009; Welsch et al., submitted). Evidence of initial olivine crystallization at high undercooling (with dendrite formation) followed by low undercooling (and planar crystal faceting) in the shallow reservoirs of both ocean island volcanoes suggests this olivine growth history may be the rule rather than the exception. Welsch, B, F Faure, P Bachèlery, V Famin (2009). Microcrysts record convection at Piton de la Fournaise volcano (La Réunion hotspot). J Petrol. 50, 2287-2305.

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

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


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

  5. Oceanic archipelagos

    Triantis, Kostas A.; Whittaker, Robert James; Fernández-Palacios, José María


    Since the contributions of Charles Darwin and Alfred Russel Wallace, oceanic archipelagos have played a central role in the development of biogeography. However, despite the critical influence of oceanic islands on ecological and evolutionary theory, our focus has remained limited to either...... the island-level of specific archipelagos or single archipelagos. Recently, it was proposed that oceanic archipelagos qualify as biotic provinces, with diversity primarily reflecting a balance between speciation and extinction, with colonization having a minor role. Here we focus on major attributes...... of the archipelagic geological dynamics that can affect diversity at both the island and the archipelagic level. We also reaffirm that oceanic archipelagos are appropriate spatiotemporal units to frame analyses in order to understand large scale patterns of biodiversity....

  6. Ocean Acidification

    Ocean and coastal acidification is an emerging issue caused by increasing amounts of carbon dioxide being absorbed by seawater. Changing seawater chemistry impacts marine life, ecosystem services, and humans. Learn what EPA is doing and what you can do.

  7. Ocean Color

    National Aeronautics and Space Administration — Satellite-derived Ocean Color Data sets from historical and currently operational NASA and International Satellite missions including the NASA Coastal Zone Color...

  8. Volatile abundances and oxygen isotopes in basaltic to dacitic lavas on mid-ocean ridges: The role of assimilation at spreading centers

    Wanless, V.D.; Perfit, M.R.; Ridley, W.I.; Wallace, P.J.; Grimes, Craig B.; Klein, E.M.


    Most geochemical variability in MOR basalts is consistent with low- to moderate-pressure fractional crystallization of various mantle-derived parental melts. However, our geochemical data from MOR high-silica glasses, including new volatile and oxygen isotope data, suggest that assimilation of altered crustal material plays a significant role in the petrogenesis of dacites and may be important in the formation of basaltic lavas at MOR in general. MOR high-silica andesites and dacites from diverse areas show remarkably similar major element trends, incompatible trace element enrichments, and isotopic signatures suggesting similar processes control their chemistry. In particular, very high Cl and elevated H2O concentrations and relatively light oxygen isotope ratios (~ 5.8‰ vs. expected values of ~ 6.8‰) in fresh dacite glasses can be explained by contamination of magmas from a component of ocean crust altered by hydrothermal fluids. Crystallization of silicate phases and Fe-oxides causes an increase in δ18O in residual magma, but assimilation of material initially altered at high temperatures results in lower δ18O values. The observed geochemical signatures can be explained by extreme fractional crystallization of a MOR basalt parent combined with partial melting and assimilation (AFC) of amphibole-bearing altered oceanic crust. The MOR dacitic lavas do not appear to be simply the extrusive equivalent of oceanic plagiogranites. The combination of partial melting and assimilation produces a distinct geochemical signature that includes higher incompatible trace element abundances and distinct trace element ratios relative to those observed in plagiogranites.

  9. The deep ocean under climate change

    Levin, Lisa A.; Le Bris, Nadine


    The deep ocean absorbs vast amounts of heat and carbon dioxide, providing a critical buffer to climate change but exposing vulnerable ecosystems to combined stresses of warming, ocean acidification, deoxygenation, and altered food inputs. Resulting changes may threaten biodiversity and compromise key ocean services that maintain a healthy planet and human livelihoods. There exist large gaps in understanding of the physical and ecological feedbacks that will occur. Explicit recognition of deep-ocean climate mitigation and inclusion in adaptation planning by the United Nations Framework Convention on Climate Change (UNFCCC) could help to expand deep-ocean research and observation and to protect the integrity and functions of deep-ocean ecosystems.

  10. The deep ocean under climate change.

    Levin, Lisa A; Le Bris, Nadine


    The deep ocean absorbs vast amounts of heat and carbon dioxide, providing a critical buffer to climate change but exposing vulnerable ecosystems to combined stresses of warming, ocean acidification, deoxygenation, and altered food inputs. Resulting changes may threaten biodiversity and compromise key ocean services that maintain a healthy planet and human livelihoods. There exist large gaps in understanding of the physical and ecological feedbacks that will occur. Explicit recognition of deep-ocean climate mitigation and inclusion in adaptation planning by the United Nations Framework Convention on Climate Change (UNFCCC) could help to expand deep-ocean research and observation and to protect the integrity and functions of deep-ocean ecosystems.

  11. Oxygen isotope composition of mafic magmas at Vesuvius

    Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.


    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 magmas 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 magmas. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary magmas 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 magmas, 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

  12. Does sea level influence mid-ocean ridge magmatism on Milankovitch timescales?

    Lund, David C.; Asimow, Paul D.


    Magma production at mid-ocean ridges is driven by seafloor spreading and decompression melting of the upper mantle. In the special case of Iceland, mantle melting may have been amplified by ice sheet retreat during the last deglaciation, yielding anomalously high rates of subaerial volcanism. For the remainder of the global mid-ocean ridge system, the ocean may play an analogous role, with lowering of sea level during glacial maxima producing greater magma flux to ridge crests. Here we show that the mantle decompression rate associated with changes in sea level is a substantial fraction of that from plate spreading. Modeled peaks in magma flux occur after sea level drops rapidly, including the Marine Isotope Stage (MIS) 5/4 and 3/2 transitions. The minimum in simulated flux occurs during the mid-Holocene, due to the rapid sea level rise at the MIS 2/1 boundary. The model results are highly sensitive to melt migration rate; rates of ˜1 m/yr produce small signals, while those >5 m/yr yield substantial anomalies. In the latter case, sea level-driven magma flux varies by 15-100% relative to the long-term average, with the largest effect occurring at slow-spreading ridges. We suggest that sedimentary time series of hydrothermal particle flux, oceanic Os isotopic ratio, and oceanic radiocarbon may serve as proxies for magma-flux variations at mid-ocean ridges. Although well-dated records are rare, preliminary data from the Pacific and Atlantic suggest hydrothermal metal flux was elevated during MIS 2 and 4, broadly consistent with our modeling results.

  13. Magma Energy Research Project. Project summary, July 1, 1974--June 30, 1975

    Colp, J.L.; Davis, M.J.; Graeber, E.J.; Hardee, H.C.


    The objective of the Magma Energy Research Project now under way at Sandia Laboratories is to investigate the feasibility of extracting energy directly from deeply buried circulating magma sources. Project plans describe a concept whereby a fully closed heat exchanger system is inserted directly into such a magma source to allow the heat energy to be brought to the surface with minimal environmental impact. A summary of previous efforts is given. The achievements and future plans for source location and definition, source tapping, magma characterization, magma materials compatibilities studies, and energy extraction studies are outlined. (LBS)

  14. Permeability of alkaline magmas: a study from Campi Flegrei, Italy

    Polacci, M.; Bouvet de Maissoneuve, C.; Giordano, D.; Piochi, M.; Degruyter, W.; Bachmann, O.; Mancini, L.


    Knowledge of permeability is of paramount importance for understanding the evolution of magma degassing during pre-, syn- and post-eruptive volcanic processes. Most permeability estimates existing to date refer to magmas 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 magmas 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 magma ascent. Therefore, permeability will depend on composition through the rheological properties

  15. Layering in peralkaline magmas, Ilímaussaq Complex, S Greenland

    Hunt, Emma J.; Finch, Adrian A.; Donaldson, Colin H.


    The peralkaline to agpaitic Ilímaussaq Complex, S. Greenland, displays spectacular macrorhythmic (> 5 m) layering via the kakortokite (agpaitic nepheline syenite), which outcrops as the lowest exposed rocks in the complex. This study applies crystal size distribution (CSD) analyses and eudialyte-group mineral chemical compositions to study the marker horizon, Unit 0, and the contact to the underlying Unit - 1. Unit 0 is the best-developed unit in the kakortokites and as such is ideal for gaining insight into processes of crystal formation and growth within the layered kakortokite. The findings are consistent with a model whereby the bulk of the black and red layers developed through in situ crystallisation at the crystal mush-magma interface, whereas the white layer developed through a range of processes operating throughout the magma chamber, including density segregation (gravitational settling and flotation). Primary textures were modified through late-stage textural coarsening via grain overgrowth. An open-system model is proposed, where varying concentrations of halogens, in combination with undercooling, controlled crystal nucleation and growth to form Unit 0. Our observations suggest that the model is applicable more widely to the layering throughout the kakortokite series and potentially other layered peralkaline/agpaitic rocks around the world.

  16. Nyamulagira’s magma plumbing system inferred from 15 years of InSAR

    Wauthier, Christelle; Cayol, Valerie; Poland, Michael; Kervyn, François; D'Oreye, Nicolas; Hooper, Andrew; Samsonov, Sergei; Tiampo, Kristy; Smets, Benoit; Pyle, D. M.; Mather, T.A.; Biggs, J.


    Nyamulagira, located in the east of the Democratic Republic of Congo on the western branch of the East African rift, is Africa’s most active volcano, with an average of one eruption every 3 years since 1938. Owing to the socio-economical context of that region, the volcano lacks ground-based geodetic measurements but has been monitored by interferometric synthetic aperture radar (InSAR) since 1996. A combination of 3D Mixed Boundary Element Method and inverse modelling, taking into account topography and source interactions, is used to interpret InSAR ground displacements associated with eruptive activity in 1996, 2002, 2004, 2006 and 2010. These eruptions can be fitted by models incorporating dyke intrusions, and some (namely the 2006 and 2010 eruptions) require a magma reservoir beneath the summit caldera. We investigate inter-eruptive deformation with a multi-temporal InSAR approach. We propose the following magma plumbing system at Nyamulagira by integrating numerical deformation models with other available data: a deep reservoir (c. 25 km depth) feeds a shallower reservoir (c. 4 km depth); proximal eruptions are fed from the shallow reservoir through dykes while distal eruptions can be fed directly from the deep reservoir. A dyke-like conduit is also present beneath the upper southeastern flank of Nyamulagira.

  17. Hydrogen isotope investigation of amphibole and glass in dacite magmas erupted in 1980-1986 and 2005 at Mount St. Helens, Washington

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


    In active, shallow, sub-volcanic magma conduits the extent of the dehydrogenation–oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases. Amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at Mount St. Helens (MSH) were analyzed for δD, water content and Fe3+/Fe2+, and fragments of glassy groundmass were analyzed for δD and water content. Changes in amphibole δD values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations. Driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity, decrease in amphibole hydrogen fugacity, or both. The phenocryst amphibole (δD value c. –57‰ and 2 wt % H2O) in the white fallout pumice of the May 18, 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an ∼7 km conduit. Younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses, based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation. Pyroclastic rocks from explosive eruptions in June–October 1980 have elevated abundances of mottled amphibole phenocrysts (peaking in some pyroclastic rocks erupted on July 22, 1980), and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole. Multiple amphibole δD populations in many 1980 pyroclastic rocks combined with their groundmass characteristics (e.g. mixed pumice textures) support models of shallow mixing prior to, or during, eruption as new, volatile-rich magma pulses blended with more oxidized, degassed magma. Amphibole dehydrogenation is quenched at the top surface of MSH dacite lava lobes, but the diversity in the

  18. Melt focusing and CO2 extraction at mid-ocean ridges: simulations of reactive two-phase flow

    Keller, T.; Katz, R. F.; Hirschmann, M. M.


    The deep CO2 cycle is the result of fluxes between near-surface and mantle reservoirs. Outgassing from mid-ocean ridges is one of the primary fluxes of CO2 from the asthenosphere into the ocean-atmosphere reservoir. Focusing of partial melt to the ridge axis crucially controls this flux. However, the role of volatiles, in particular CO2 and H2O, on melt transport processes beneath ridges remains poorly understood. We investigate this transport using numerical simulations of two-phase, multi-component magma/mantle dynamics. The phases are solid mantle and liquid magma; the components are dunite, MORB, hydrated basalt, and carbonated basalt. These effective components capture accepted features of mantle melting with volatiles. The fluid-dynamical model is McKenzie's formulation [1], while melting and reactive transport use the R_DMC method [2,3]. Our results indicate that volatiles cause channelized melt transport, which leads to significant variability in volume and composition of focused melt. The volatile-induced expansion of the melting regime at depth, however, has no influence on melt focusing; distal volatile-rich melts are not focused to the axis. Up to 50% of these melts are instead emplaced along the oceanic LAB. There, crystallization of accumulated melt leads to enrichment of CO2 and H2O in the deep lithosphere, which has implications for LAB rheology and volatile recycling by subduction. Results from a suite of simulations, constrained by catalogued observational data [4,5,6] enable predictions of global MOR CO2 output. By combining observational constraints with self-consistent numerical simulations we obtain a range of CO2 output from the global ridge system of 28-110 Mt CO2/yr, corresponding to mean CO2 contents of 50-200 ppm in the mantle. REFERENCES[1] McKenzie (1984), doi:10.1093/petrology/25.3.713.[2] Rudge, Bercovici & Spiegelman (2011), doi:10.1111/j.1365-246X.2010.04870.x.[3] Keller & Katz (2016), doi:10.1093/petrology/egw030.[4] Dalton

  19. Large-scale magmatic layering in the Main Zone of the Bushveld Complex and episodic downward magma infiltration

    Hayes, Ben; Ashwal, Lewis D.; Webb, Susan J.; Bybee, Grant M.


    The Bellevue drillcore intersects 3 km of Main and Upper Zone cumulates in the Northern Limb of the Bushveld Complex. Main Zone cumulates are predominately gabbronorites, with localized layers of pyroxenite and anorthosite. Some previous workers, using bulk rock major, trace and isotopic compositions, have suggested that the Main Zone crystallized predominantly from a single pulse of magma. However, density measurements throughout the Bellevue drillcore reveal intervals that show up-section increases in bulk rock density, which are difficult to explain by crystallization from a single batch of magma. Wavelet analysis of the density data suggests that these intervals occur on length-scales of 40 to 170 m, thus defining a scale of layering not previously described in the Bushveld Complex. Upward increases in density in the Main Zone correspond to upward increases in modal pyroxene, producing intervals that grade from a basal anorthosite (with 5% pyroxene) to gabbronorite (with 30-40% pyroxene). We examined the textures and mineral compositions of a 40 m thick interval showing upwardly increasing density to establish how this type of layering formed. Plagioclase generally forms euhedral laths, while orthopyroxene is interstitial in texture and commonly envelops finer-grained and embayed plagioclase grains. Minor interstitial clinopyroxene was the final phase to crystallize from the magma. Plagioclase compositions show negligible change up-section (average An62), with local reverse zoning at the rims of cumulus laths (average increase of 2 mol%). In contrast, interstitial orthopyroxene compositions become more primitive up-section, from Mg# 57 to Mg# 63. Clinopyroxene similarly shows an up-section increase in Mg#. Pyroxene compositions record the primary magmatic signature of the melt at the time of crystallization and are not an artefact of the trapped liquid shift effect. Combined, the textures and decoupled mineral compositions indicate that the upward density

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

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


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

  1. Using Intensive Variables to Constrain Magma Source Regions

    Edwards, B. R.; Russell, J. K.


    In the modern world of petrology, magma 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 magmas. We have taken a non-traditional approach to using the compositions of three groups of mafic, alkaline rocks to characterize the source regions of magmas 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 magmas 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 magma 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 magmas 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 magmas

  2. Origin of High-Alumina Basalt, Andesite, and Dacite Magmas.

    Hamilton, W


    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it.

  3. Isotopic evidence for multiple contributions to felsic magma chambers

    Waight, Tod Earle; Wiebe, R.A.; Krogstad, E.J.


    by contemporaneous mafic magmas; the transition between the two now preserved as a zone of chilled mafic sheets and pillows in granite. Mafic components have highly variably isotopic compositions as a result of contamination either at depth or following injection into the magma chamber. Intermediate dikes...... with identical isotopic compositions to more mafic dikes suggest that closed system fractionation may be occurring in deeper level chambers prior to injection to shallower levels. The granitic portion of the pluton has the highest Nd isotopic composition (eNd=+3.0) of plutons in the region whereas the mafic...... lithologies have Nd isotopic compositions (eNd=+3.5) that are the lowest in the region and similar to the granite and suggestive of prolonged interactions and homogenization of the two components. Sr and Nd isotopic data for felsic enclaves are inconsistent with previously suggested models of diffusional...

  4. Sulfate Saturated Hydrous Magmas Associated with Hydrothermal Gold Ores

    Chambefort, I.; Dilles, J. H.; Kent, A. J.


    Hydrothermal ore deposits associated with arc magmatism represent important sulfur anomalies. During degassing of magmatic systems the volatile may transport metals and sulfur and produce deposits. The ultimate origin of the magma-derived sulfur is still uncertain. The Yanacocha high-sulfidation epithermal Au deposit, Peru, is hosted by a Miocene volcanic succession (ca. 16 to 8 Ma). Magmatic rocks are highly oxidized >NNO+2 and show a range of composition from andesite to dacite. Two populations of amphibole occur in the Yanacocha dacitic ignimbrite deposits (~7 and 12 wt% Al2O3). Low Al amphiboles crystallized at ~ 1.5-2 kbar and 800°C (Plag-Hb thermobarometry) in equilibrium with plagioclase and pyroxene. High Al amphiboles only contain inclusions of anhydrite associated with apatite (up to 1.2 wt% SO3), and have a higher Cr2O3 content (up to 1000 ppm). We estimate these amphiboles form near the magma's liquidus at P(H2O)> 3kbar and 950 to 1000°C of a basaltic, basaltic andesite ascending magma. Low Al amphibole presents an REE pattern with negative anomalies in Sr, Ti and Eu, characteristic of plagioclase and titanite fractionation in the magma. High Al amphiboles are less enriched in REE and have no Sr, Ti, or Eu anomaly. Rare crystals of high Al amphibole display a low Al rim marked by higher REE contents compared to the core and a negative Eu anomaly. Magmatic sulfate occurrences have been discovered through the 8 m.y. volcanic sequence. Rounded anhydrite crystals are found included within clinopyroxene and both high and low Al amphibole. The rare high Al amphiboles (from the sample RC6) contain up to ~10 vol.%, ~5-80 micrometer-long anhydrite as irregularly shaped (amoeboid) blebs that do not show crystallographic forms and do not follow host cleavages. Extremely rare sulfide inclusions are found in plagioclase (Brennecka, 2006). The major and trace element contents of Yanacocha magmatic anhydrite have been analyzed by electron microprobe and LA

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

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


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


    Tyler, Robert H.; Henning, Wade G. [Department of Astronomy, University of Maryland College Park (United States); Hamilton, Christopher W., E-mail: [Lunar and Planetary Laboratory, University of Arizona, AZ, Tuscon, 85721 (United States)


    Active volcanism observed on Io is thought to be driven by the temporally periodic, spatially differential projection of Jupiter's gravitational field over the moon. Previous theoretical estimates of the tidal heat have all treated Io as essentially a solid, with fluids addressed only through adjustment of rheological parameters rather than through appropriate extension of the dynamics. These previous estimates of the tidal response and associated heat generation on Io are therefore incomplete and possibly erroneous because dynamical aspects of the fluid behavior are not permitted in the modeling approach. Here we address this by modeling the partial-melt asthenosphere as a global layer of fluid governed by the Laplace Tidal Equations. Solutions for the tidal response are then compared with solutions obtained following the traditional solid-material approach. It is found that the tidal heat in the solid can match that of the average observed heat flux (nominally 2.25 W m{sup −2}), though only over a very restricted range of plausible parameters, and that the distribution of the solid tidal heat flux cannot readily explain a longitudinal shift in the observed (inferred) low-latitude heat fluxes. The tidal heat in the fluid reaches that observed over a wider range of plausible parameters, and can also readily provide the longitudinal offset. Finally, expected feedbacks and coupling between the solid/fluid tides are discussed. Most broadly, the results suggest that both solid and fluid tidal-response estimates must be considered in exoplanet studies, particularly where orbital migration under tidal dissipation is addressed.

  7. Initiation of Plate Tectonics from Post-Magma Ocean Thermo-Chemical Convection

    Foley, Bradford J; Elkins-Tanton, Linda T


    Leading theories for the presence of plate tectonics on Earth typically appeal to the role of present day conditions in promoting rheological weakening of the lithosphere. However, it is unknown whether the conditions of the early Earth were favorable for plate tectonics, or any form of subduction, and thus how subduction begins is unclear. Using physical models based on grain-damage, a grainsize-feedback mechanism capable of producing plate-like mantle convection, we demonstrate that subduction was possible on the Hadean Earth (hereafter referred to as proto-subduction or proto-plate tectonics), that proto-subduction differed from modern day plate tectonics, and that it could initiate rapidly. Scaling laws for convection with grain-damage show that, though either higher mantle temperatures or higher surface temperatures lead to slower plates, proto-subduction, with plate speeds of $\\approx 1.75$ cm/yr, can still be maintained in the Hadean, even with a CO$_2$ rich primordial atmosphere. Furthermore, when the...

  8. Core Formation on Asteroid 4 Vesta: Iron Rain in a Silicate Magma Ocean

    Kiefer, Walter S.; Mittlefehldt, David W.


    Geochemical observations of the eucrite and diogenite meteorites, together with observations made by NASA's Dawn spacecraft, suggest that Vesta resembles H chondrites in bulk chemical composition, possibly with about 25% of a CM-chondrite like composition added in. For this model, the core is 15% by mass (or 8 volume %) of the asteroid. The abundances of moderately siderophile elements (Ni, Co, Mo, W, and P) in eucrites require that essentially all of the metallic phase in Vesta segregated to form a core prior to eucrite solidification. Melting in the Fe-Ni-S system begins at a cotectic temperature of 940 deg. C. Only about 40% of the total metal phase, or 3-4 volume % of Vesta, melts prior to the onset of silicate melting. Liquid iron in solid silicate initially forms isolated pockets of melt; connected melt channels, which are necessary if the metal is to segregate from the silicate, are only possible when the metal phase exceeds about 5 volume %. Thus, metal segregation to form a core does not occur prior to the onset of silicate melting.

  9. Magma genesis, plate tectonics, and chemical differentiation of the Earth

    Wyllie, Peter J.


    Magma genesis, migration, and eruption have played prominent roles in the chemical differentiation of the Earth. Plate tectonics has provided the framework of tectonic environments for different suites of igneous rocks and the dynamic mechanisms for moving masses of rock into melting regions. Petrology is rooted in geophysics. Petrological and geophysical processes are calibrated by the phase equilibria of the materials. The geochemistry of basalts and mantle xenoliths demonstrates that the m...

  10. Ecocrítica e erotismo nos poemas de Magma

    Santana, Patricia Maria dos Santos; UFRJ


    Olga Savary nos mostra, através da poesia registrada no livro Magma, que a força erótica e a interdependência do homem com a Natureza são fatores que regem seu trabalho criativo no que tange a valorização da mulher como um ser que tem domínio de seu próprio corpo e que sabe muito bem o que realmente quer. 

  11. Arctic Ocean

    Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)


    The Arctic Ocean is the smallest of the Earth's four major oceans, covering 14x10(exp 6) sq km located entirely within the Arctic Circle (66 deg 33 min N). It is a major player in the climate of the north polar region and has a variable sea ice cover that tends to increase its sensitivity to climate change. Its temperature, salinity, and ice cover have all undergone changes in the past several decades, although it is uncertain whether these predominantly reflect long-term trends, oscillations within the system, or natural variability. Major changes include a warming and expansion of the Atlantic layer, at depths of 200-900 m, a warming of the upper ocean in the Beaufort Sea, a considerable thinning (perhaps as high as 40%) of the sea ice cover, a lesser and uneven retreat of the ice cover (averaging approximately 3% per decade), and a mixed pattern of salinity increases and decreases.

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

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


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

  13. Juvenile magma recognition and eruptive dynamics inferred from the analysis of ash time series: The 2015 reawakening of Cotopaxi volcano

    Gaunt, H. Elizabeth; Bernard, Benjamin; Hidalgo, Silvana; Proaño, Antonio; Wright, Heather; Mothes, Patricia; Criollo, Evelyn; Kueppers, Ulrich


    Forecasting future activity and performing hazard assessments during the reactivation of volcanoes remain great challenges for the volcanological community. On August 14, 2015 Cotopaxi volcano erupted for the first time in 73 years after approximately four months of precursory activity, which included an increase in seismicity, gas emissions, and minor ground deformation. Here we discuss the use of near real-time petrological monitoring of ash samples as a complementary aid to geophysical monitoring, in order to infer eruption dynamics and evaluate possible future eruptive activity at Cotopaxi. Twenty ash samples were collected between August 14 and November 23, 2015 from a monitoring site on the west flank of the volcano. These samples contain a range of grain types that we classified as: hydrothermal/altered, lithic, juvenile, and free crystals. The relative proportions of theses grains evolved as the eruption progressed, with increasing amounts of juvenile material and a decrease in hydrothermally altered material. In samples from the initial explosion, juvenile grains are glassy, microlite-poor and contain hydrothermal minerals (opal and alunite). The rising magma came in contact with the hydrothermal system under confinement, causing hydro-magmatic explosions that cleared the upper part of the plumbing system. Subsequently, the magmatic column produced a thermal aureole in the conduit and dried out the hydrothermal system, allowing for dry eruptions. Magma ascent rates were low enough to allow for efficient outgassing and microlite growth. Constant supply of magma from below caused quasi-continuous disruption of the uppermost magma volume through a combination of shear-deformation and gas expansion. The combination of increasing crystallinity of juvenile grains, and high measured SO2 flux indicate decreasing integrated magma ascent rates and clearing of the hydrothermal system along transport pathways in a system open to gas loss. The near real-time monitoring

  14. Juvenile magma recognition and eruptive dynamics inferred from the analysis of ash time series: The 2015 reawakening of Cotopaxi volcano

    Gaunt, H. Elizabeth; Bernard, Benjamin; Hidalgo, Silvana; Proano, Antonio; Wright, Heather M.; Mothes, Patricia; Criollo, Evelyn; Kueppers, Ulrich


    Forecasting future activity and performing hazard assessments during the reactivation of volcanoes remain great challenges for the volcanological community. On August 14, 2015 Cotopaxi volcano erupted for the first time in 73 years after approximately four months of precursory activity, which included an increase in seismicity, gas emissions, and minor ground deformation. Here we discuss the use of near real-time petrological monitoring of ash samples as a complementary aid to geophysical monitoring, in order to infer eruption dynamics and evaluate possible future eruptive activity at Cotopaxi. Twenty ash samples were collected between August 14 and November 23, 2015 from a monitoring site on the west flank of the volcano. These samples contain a range of grain types that we classified as: hydrothermal/altered, lithic, juvenile, and free crystals. The relative proportions of theses grains evolved as the eruption progressed, with increasing amounts of juvenile material and a decrease in hydrothermally altered material. In samples from the initial explosion, juvenile grains are glassy, microlite-poor and contain hydrothermal minerals (opal and alunite). The rising magma came in contact with the hydrothermal system under confinement, causing hydro-magmatic explosions that cleared the upper part of the plumbing system. Subsequently, the magmatic column produced a thermal aureole in the conduit and dried out the hydrothermal system, allowing for dry eruptions. Magma ascent rates were low enough to allow for efficient outgassing and microlite growth. Constant supply of magma from below caused quasi-continuous disruption of the uppermost magma volume through a combination of shear-deformation and gas expansion. The combination of increasing crystallinity of juvenile grains, and high measured SO2 flux indicate decreasing integrated magma ascent rates and clearing of the hydrothermal system along transport pathways in a system open to gas loss. The near real

  15. Search for shallow magma accumulations at Augustine Volcano

    Kienle, J.; Lalla, D.J.; Pearson, C.F.; Barrett, S.A.


    A search was made for shallow magma accumulations beneath Augustine Volcano using primarily three geophysical techniques: (1) temperature and heat flow measurements, (2) active and passive seismic refraction, and (3) three-dimensional modeling of aeromagnetic data. With these studies it was hoped to gain insight into the interval structure of Augustine Volcano, to delineate, if possible, the size and shape of near surface magma bodies and to assess the potential of the volcano as a natural laboratory for hot rock and magma geothermal energy research. Augustine was chosen because it is a very young and very active volcano with several historic eruptions in 1812, 1883, 1935, 1964/64. One of the main targets for the geophysical studies was a summit lava dome of about 0.05 km/sup 3/ volume, extruded in 1963/64 and suspected to still contain considerable residual heat, perhaps be still partially molten years after its intrusion. Five months after the field work in 1975 this dome was exploded in January 1976. One month later, a hot (about 650 to 800/sup 0/C) viscous dome was intruded into the January summit crater.

  16. Influence of Non-Newtonian rheology on magma degassing

    Divoux, Thibaut; Ripepe, Maurizio; Géminard, Jean-Christophe


    Many volcanoes exhibit temporal changes in their degassing process, from rapid gas puffing to lava fountaining and long-lasting quiescent passive degassing periods. This range of behaviors has been explained in terms of changes in gas flux and/or magma input rate. We report here a simple laboratory experiment which shows that the non- Newtonian rheology of magma can be responsible, alone, for such intriguing behavior, even in a stationary gas flux regime. We inject a constant gas flow-rate Q at the bottom of a non-Newtonian fluid column, and demonstrate the existence of a critical flow rate Q* above which the system spontaneously alternates between a bubbling and a channeling regime, where a gas channel crosses the entire fluid column. The threshold Q* depends on the fluid rheological properties which are controlled, in particular, by the gas volume fraction (or void fraction) {\\phi}. When {\\phi} increases, Q* decreases and the degassing regime changes. Non-Newtonian properties of magma might therefore play a...

  17. Magma ascent pathways associated with large mountains on Io

    McGovern, Patrick J.; Kirchoff, Michelle R.; White, Oliver L.; Schenk, Paul M.


    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 magma 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 magma 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 magma 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.

  18. Earliest detection of magma movements by measuring transient streaming potential

    Fujinawa, Yukio; Matsumoto, Takumi; Iitaka, Hiroshi; Takahashi, Kozo; Nakano, Hiroshi; Doi, Takuya; Saito, Toshiyuki; Kasai, Naoko; Sato, Sohjun

    Volcanic eruptions are generally preceded by magma intrusion. Volcanic forecasting is sure to make considerable progress if we have a practical means to detect magma 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 magma 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.

  19. Oceans Past

    Based on research for the History of Marine Animal Populations project, Oceans Past examines the complex relationship our forebears had with the sea and the animals that inhabit it. It presents eleven studies ranging from fisheries and invasive species to offshore technology and the study of marine...... environmental history, bringing together the perspectives of historians and marine scientists to enhance understanding of ocean management of the past, present and future. In doing so, it also highlights the influence that changes in marine ecosystems have upon the politics, welfare and culture of human...

  20. Unraveling the unusual morphology of the Cretaceous Dirck Hartog extinct mid-ocean ridge

    Watson, S. J.; Whittaker, J. M.; Halpin, J.; Williams, S.; Milan, L. A.; Daczko, N. R.; Wyman, D. A.


    The Perth Abyssal Plain (PAP), offshore southwest Australia formed during Mesozoic East Gondwana breakup and Kerguelen plume activity. This study combines petrographic and geochemical data from the first samples ever to be dredged from the flanks of the Dirck Hartog Ridge (DHR), a prominent linear bathymetric feature in the central PAP, with new bathymetric profiles across the PAP to better constrain the formation of the early Indian Ocean floor. The DHR exhibits high relief and distinctive asymmetry that is unusual compared to most active or extinct spreading centres and likely results from compression and deformation of the recently extinct DHR during changes in relative motion of the Indian plate (110 - 100 Ma). Exhumation of gabbros in the southern DHR and an increase in seafloor roughness towards the centre of the PAP, likely result from a half spreading rate decrease from 35 mm/yr (based on magnetic reversals) to 24 mm/yr at ~114 Ma. The results support a slowdown of spreading prior to full cessation at ~102 Ma. The composition of basaltic samples varies along the DHR: from sub-alkaline dolerites with incompatible element concentrations most similar to depleted-to-normal mid-ocean ridge basalts in the south, to alkali basalts similar to ocean island basalts in the north. Therefore, magma sources and degrees of partial melting varied in space and time, a result supporting the interpretation that the DHR is an extinct spreading ridge rather than a pseudofault. The enriched alkali basalt signatures may be attributed to melting of a heterogeneous mantle or to the influence of the Kerguelen plume over distances greater than 1000 km. The results demonstrate the significance of regional tectonic plate motions on the formation and deformation of young ocean crust, and provide insight into the unique DHR morphology.

  1. Role of mantle-derived magma in genesis of early Yanshanian granites in the Nanling Range, South China: in situ zircon Hf-O isotopic constraints


    Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived magmas were involved in granites. We carried out in this study a systematic analysis of in situ zircon Hf-O isotopes for three early Yanshanian intrusions dated at ca. 160 Ma from the Nanling Range of Southeast China. The Qinghu monzonite has very homogeneous zircon Hf-O isotopic compositions, εHf(t) =11.6±0.3 and δ18O=5.4‰±0.3‰. In combination with whole-rock geochemical and Sr-Nd isotopic data, the parental magma of the Qinghu monzonite were likely derived from the partial melting of recently-metasomatized, phlogopite-bearing lithospheric mantle without appreciable crustal contamination. The Lisong and Fogang granites and the mafic microgranular enclaves (MME) within the Lisong granites have a wide range of zircon Hf-O isotopic compositions, with Hf and O isotopes being negatively correlated within each pluton. The Lisong MMEs were crystallized from a mantle-derived magma, similar to the parental magma of the Qinghu monzonite, with small amount of crustal assimilation. The Lisong and Fogang granites were formed by reworking of meta-sedimentary materials by mantle-derived magmas and mixing of the mantle-and sediment-derived melts to varying degrees. It is thus concluded that these two Yanshanian granites in the Nanling Range were formed associated with growth and differentiation of continental crust.

  2. Magma displacements under insular volcanic fields, applications to eruption forecasting: El Hierro, Canary Islands, 2011-2013

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


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

  3. Rb—Sr Geochronology and Magma Source of the Mesozoic Fault—Granite Belt,East Shandong

    迟效国; 林景仟


    Developed in the southeast coast of te East Shandong Peninsula,the Mesozoic fault-magma belt consists of five rock series:the syenite series;the monzonite series;the megaporphyritic monzogranite series;the biotite-granite series;and the alkali granite seres.Based on their Rb-Sr isochron ages(122-220Ma),these rock series may be divided into three magma subcycles dated at Triassic,Late Jurassic and Early Cretaceous.The initial 87Sr/86Sr ration in these rock series range from 0.70436 to 0.7155.The starting points of the Rb-Sr isochrons exhibit four different distribution trends on the(87Sr/86Sr)i-87Rb/86Sr diagram.These characteristics show that the multiple granitic rock series are different in genesis and derivation.The syenite series might be derived from the combination of mantle-derived magma and crustal material,and the others could be derived from granulite-facies and amphibilite-facies rocks in the deep crust.

  4. Oceanic plateau model for continental crustal growth in the Archaean: A case study from the Kostomuksha greenstone belt, NW Baltic Shield

    Samsonov, A. V.; Shchipansky, A. A.; Jochum, K. P.; Mezger, K.; Hofmann, A. W.; Puchtel, I. S.


    Field studies combined with chemical and isotope data indicate that the Kostomuksha greenstone belt in the NW Baltic Shield consists of two lithotectonic terranes, one mafic igneous and the other sedimentary, separated by a major shear zone. The former contains submarine komatiite-basalt lavas and volcaniclastic lithologies, and the latter is composed of shelf-type rocks and BIF. Komatiitic and basaltic samples yield Sm-Nd and Pb-Pb isochron ages of 2843+/-39 and 2813+/-78 Ma, respectively. Their trace-element compositions resemble those of recent Pacific oceanic flood basalts with primitive-mantle normalized Nb/Th of 1.5-2.1 and Nb/La of 1.0-1.5. This is in sharp contrast with island arc and most continental magmas, which are characterized by Nb/(Th,La)N≪1. Calculated initial Nd-isotope compositions (ɛNd(T)=+2.8 to +3.4) plot close to an evolution line previously inferred for major orogens (``MOMO''), which is also consistent with the compositions of recent oceanic plateaux. The high liquidus temperatures of the komatiite magmas (1550°C) and their Al-depleted nature require an unusually hot (1770°C) mantle source for the lavas (>200°C hotter than the ambient mantle at 2.8 Ga), and are consistent with their formation in a deep mantle plume in equilibrium with residual garnet. This plume had the thermal potential to produce oceanic crust with an average thickness of ~30 km underlain by a permanently buoyant refractory lithospheric mantle keel. Nb/U ratios in the komatiites and basalts calculated on the basis of Th-U-Pb relationships range from 35 to 47 and are thus similar to those observed in modern MORB and OIB. This implies that some magma source regions of the Kostomuksha lavas have undergone a degree of continental material extraction comparable with those found in the modern mantle. The mafic terrane is interpreted as a remnant of the upper crustal part of an Archaean oceanic plateau. When the newly formed plateau reached the active continental margin

  5. Generation of continental crust in intra-oceanic arcs

    Gazel, E.; Hayes, J. L.; Kelemen, P. B.; Everson, E. D.; Holbrook, W. S.; Vance, E.


    The origin of continental crust is still an unsolved mystery in the evolution of our planet. Although the best candidates to produce juvenile continental crust are intra-oceanic arcs these systems are dominated by basaltic lavas, and when silicic magmas are produced, the incompatible-element compositions are generally too depleted to be a good match for continental crust estimates. Others, such as the W. Aleutians, are dominated by andesitic melts with trace element compositions similar to average continental crust. In order to evaluate which intra-oceanic arcs produced modern continental crust, we developed a geochemical continental index (CI) through a statistical analysis that compared all available data from modern intra-oceanic arcs with global estimates of continental crust. Our results suggest that magmas from Costa Rica (100 have the least continent-like geochemical signatures. In these arcs the subducting plate is old (>100 Ma), not overprinted by enriched intraplate volcanism and the geochemistry may be dominated by slab-derived, aqueous fluids. We also found a strong correlation between the CI and average crustal P-wave velocity, validating the geochemical index with the available seismic data for intra-oceanic arcs. In conclusion, the production of young continental crust with compositions similar to Archean continental crust is an unusual process, limited to locations where there are especially voluminous partial melts of oceanic crust.

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

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


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

  7. Geochemical and isotopic profile of Pico de Orizaba (Citlaltépetl) volcano, Mexico: Insights for magma generation processes

    Schaaf, Peter; Carrasco-Núñez, Gerardo


    Pico de Orizaba or Citlaltépetl volcano is the easternmost and highest stratovolcano of the subduction-related Mexican Volcanic Belt (MVB) located > 400 km NNE of the Middle America Trench. This active volcano comprises four evolutionary stages, ranging in age from 0.65 Ma to the Holocene, and is surrounded by Quaternary monogenetic scoria cones and maar volcanoes. Magmatic products of the stratocone range from basaltic andesites to rhyolites and the cinder cones erupted basalts and basaltic andesites. All rock compositions form a continuous calc-alkaline suite. Petrogenetic processes involved in magma generation and evolution include fractional crystallization and mid-crustal assimilation. Trace element patterns with elevated Ba/Nb, positive Pb spikes, and Th enrichments indicate contributions from subducted sediment. Low Ba/Th ratios suggest melting of hydrous sediment without significant loss of fluid-mobile elements prior to melting. Sr-Nd isotopic ratios of Pico de Orizaba and cinder cones are nearly chondritic and are located on a mixing curve between Pacific MORB and Paleozoic crust of SE Mexico. However, vertical Nd distributions in an 87Sr/ 86Sr vs. ɛNd diagram cannot be explained by crustal assimilation and indicate contributions of a sedimentary component with unradiogenic Nd. In contrast to other eastern MVB volcanic centres, Pico de Orizaba magmas are derived almost exclusively from a depleted mantle source. Compared to other MVB stratocones, Pico de Orizaba shows the least radiogenic Nd isotope ratios at nearly identical 87Sr/ 86Sr. Steep trends in a 206Pb/ 204Pb vs. 207Pb/ 204Pb diagram favour the involvement of young, 207Pb-enriched oceanic sediments in magma generation processes of Pico de Orizaba volcano. The Pb isotope data do not support any assimilation of lower crustal Grenvillian basement.

  8. Timescales for permeability reduction and strength recovery in densifying magma

    Heap, M. J.; Farquharson, J. I.; Wadsworth, F. B.; Kolzenburg, S.; Russell, J. K.


    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 magma 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 magma 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 magma will inhibit outgassing efficiency over time, the regions of the conduit prone to fracturing, such as the margins, will

  9. Melt production and magma emplacement: What use are they?

    Nimmo, F.


    I will review the processes of melt production and magma 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. Magma emplacement is primarily controlled by the density of the magma 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 magma 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 magma 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

  10. Ocean circulation and freshwater pathways in the Arctic Mediterranean based on a combined Nd isotope, REE and oxygen isotope section across Fram Strait

    Laukert, Georgi; Frank, Martin; Bauch, Dorothea; Hathorne, Ed C.; Rabe, Benjamin; von Appen, Wilken-Jon; Wegner, Carolyn; Zieringer, Moritz; Kassens, Heidemarie


    The water masses passing the Fram Strait are mainly responsible for the exchange of heat and freshwater between the Nordic Seas and the Arctic Ocean (the Arctic Mediterranean, AM). Disentangling their exact sources, distribution and mixing, however, is complex. This work provides new insights based on a detailed geochemical tracer inventory including dissolved Nd isotope (εNd), rare earth element (REE) and stable oxygen isotope (δ18O) data along a full water depth section across Fram Strait. We find that Nd isotope and REE distributions in the open AM primarily reflect lateral advection of water masses and their mixing. Seawater-particle interactions exert important control only above the shelf regions, as observed above the NE Greenland Shelf. Advection of northward flowing warm Atlantic Water (AW) is clearly reflected by an εNd signature of -11.7 and a Nd concentration ([Nd]) of 16 pmol/kg in the upper ∼500 m of the eastern and central Fram Strait. Freshening and cooling of the AW on its way trough the AM are accompanied by a continuous change towards more radiogenic εNd signatures (e.g. -10.4 of dense Arctic Atlantic Water). This mainly reflects mixing with intermediate waters but also admixture of dense Kara Sea waters and Pacific-derived waters. The more radiogenic εNd signatures of the intermediate and deep waters (reaching -9.5) are mainly acquired in the SW Nordic Seas through exchange with basaltic formations of Iceland and CE Greenland. Inputs of Nd from Svalbard are not observed and surface waters and Nd on the Svalbard shelf originate from the Barents Sea. Shallow southward flowing Arctic-derived waters (freshwater of up to ∼6%. In addition to these observations, this study shows that the pronounced gradients in εNd signatures and REE characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the AM.

  11. Garnet-bearing tonalitic porphyry from East Kunlun, Northeast Tibetan Plateau: implications for adakite and magmas from the MASH Zone

    Yuan, Chao; Sun, Min; Xiao, Wenjiao; Wilde, Simon; Li, Xianhua; Liu, Xiaohan; Long, Xiaoping; Xia, Xiaoping; Ye, Kai; Li, Jiliang


    A garnet-bearing tonalitic porphyry from the Achiq Kol area, northeast Tibetan Plateau has been dated by SHRIMP U-Pb zircon techniques and gives a Late Triassic age of 213 ± 3 Ma. The porphyry contains phenocrysts of Ca-rich, Mn-poor garnet (CaO > 5 wt%; MnO 17 wt%) contents, and is metaluminous to slightly peraluminous (ACNK = 0.89-1.05). The rock samples are enriched in LILE and LREE but depleted in Nb and Ti, showing typical features of subduction-related magmas. The relatively high Sr/Y (~38) ratios and low HREE (Yb residual phase, while suppressed crystallization of plagioclase and lack of negative Eu anomalies indicate a high water fugacity in the magma. Nd-Sr isotope compositions of the rock (ɛNdT = -1.38 to -2.33; 87Sr/86Sri = 0.7065-0.7067) suggest that both mantle- and crust-derived materials were involved in the petrogenesis, which is consistent with the reverse compositional zoning of plagioclase, interpreted to indicate magma mixing. Both garnet phenocrysts and their ilmenite inclusions contain low MgO contents which, in combination with the oxygen isotope composition of garnet separates (+6.23‰), suggests that these minerals formed in a lower crust-derived felsic melt probably in the MASH zone. Although the rock samples are similar to adakitic rocks in many aspects, their moderate Sr contents (residual melt. It is suggested that extensive crystallization of apatite as an early phase may prevent some arc magmas from evolving into adakitic rocks even under high water fugacity.

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

    Allard, Patrick


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

  13. The relative roles of boundary layer fractionation and homogeneous fractionation in cooling basaltic magma chambers

    Kuritani, Takeshi


    In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from low-temperature mush zones (boundary layer fractionation). In this study, the relative roles of boundary layer fractionation and homogeneous fractionation in basaltic magma bodies were examined using a thermodynamics-based mass balance model. Model calculations show that boundary layer fractionation cannot be a dominant fractionation mechanism when magma chambers are located at low pressures (magmatic evolution. On the other hand, boundary layer fractionation can occur effectively when magmas are hydrous (> ~ 2 wt.%), such as arc basalt, and the magma chambers are located at depth (> ~ 100 MPa). Because the melt derived from mush zones is enriched in alkalis and H 2O, crystallization from the main magma is suppressed by mixing with the mush melt as a consequence of depression of the liquidus temperature. Therefore, homogeneous fractionation is more effectively suppressed in magma chambers in which boundary layer fractionation is more active. If magmatic differentiation proceeds primarily by boundary layer fractionation, magmas can remain free of crystals for long periods during magmatic evolution.

  14. Storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of Augustine Volcano, Alaska

    Roman, Diana C.; Cashman, Katharine V.; Gardner, Cynthia A.; Wallace, Paul J.; Donovan, John J.


    Compositional heterogeneity (56–64 wt% SiO2 whole-rock) in samples of tephra and lava from the 1986 eruption of Augustine Volcano, Alaska, raises questions about the physical nature of magma storage and interaction beneath this young and frequently active volcano. To determine conditions of magma storage and evolutionary histories of compositionally distinct magmas, we investigate physical and chemical characteristics of andesitic and dacitic magmas feeding the 1986 eruption. We calculate equilibrium temperatures and oxygen fugacities from Fe-Ti oxide compositions and find a continuous range in temperature from 877 to 947°C and high oxygen fugacities (ΔNNO=1–2) for all magmas. Melt inclusions in pyroxene phenocrysts analyzed by Fourier-transform infrared spectroscopy and electron probe microanalysis are dacitic to rhyolitic and have water contents ranging from Augustine, and we interpret the mafic endmember to have been intruded from depth. Mixing appears to have continued as magmas ascended towards the vent. We suggest that the physical structure of the magma storage system beneath Augustine contributed to the sustained compositional heterogeneity of this eruption, which is best explained by magma storage and interaction in a vertically extensive system of interconnected dikes rather than a single coherent magma chamber and/or conduit. The typically short repose period (∼10 years) between Augustine's recent eruptive pulses may also inhibit homogenization, as short repose periods and chemically heterogeneous magmas are observed at several volcanoes in the Cook Inlet region of Alaska.

  15. Influence of ocean acidification on the organic complexation of iron and copper in Northwest European shelf seas; a combined observational and model study

    Lizeth eAvendaño


    Full Text Available The pH of aqueous solutions is known to impact the chemical speciation of trace metals. In this study we conducted titrations of coastal seawaters with iron and copper at pH 7.91, 7.37 and 6.99 (expressed on the total pH scale. Changes in the concentration of iron and copper that complexed with the added ligands 1-nitroso-2-napthol and salicylaldoxime respectively were determined by adsorptive cathodic stripping voltammetry - competitive ligand equilibrium (AdCSV-CLE. Interpretation of the results, assuming complexation by a low concentration of discrete ligands, showed that conditional stability constants for iron complexes increased relative to inorganic iron complexation as pH decreased by approximately 1 log unit per pH unit, whilst those for copper did not change. No trend was observed for concentrations of iron and copper complexing ligands over the pH range examined. We also interpreted our titration data by describing chemical binding and polyelectrolytic effects using non-ideal competitive adsorption in Donnan-like gels (NICA-Donnan model in a proof of concept study. The NICA-Donnan approach allows for the development of a set of model parameters that are independent of ionic strength and pH, and thus calculation of metal speciation can be undertaken at ambient sample pH or the pH of a future, more acidic ocean. There is currently a lack of basic NICA-Donnan parameters applicable to marine dissolved organic matter (DOM so we assumed that the measured marine dissolved organic carbon could be characterized as terrestrial fulvic acids. Generic NICA-Donnan parameters were applied within the framework of the software program visual MINTEQ and the metal –added ligand concentrations [MeAL] calculated for the AdCSV-CLE conditions. For copper, calculated [MeAL] using the NICA-Donnan model for DOM were consistent with measured [MeAL], but for iron an inert fraction with kinetically inhibited dissolution was required in addition to the NICA

  16. Titanite-scale insights into multi-stage magma mixing in Early Cretaceous of NW Jiaodong terrane, North China Craton

    Jiang, Peng; Yang, Kui-Feng; Fan, Hong-Rui; Liu, Xuan; Cai, Ya-Chun; Yang, Yue-Heng


    REEs contents, and Th/U ratios, but reveal high F contents (0.35-0.76 wt.%) and extreme high Nb/Ta ratios (up to 65.6). Such titanites are perceived to record late-stage mingling, during which F-rich and REE-poor hybrid granodioritic magma squeezed into the incompletely consolidated dioritic enclaves with accompanying fluid-rock interaction. Combining our results with previous isotopic studies, a new genetic model for Guojialing-type granodiorites is envisaged, which involves multi-stage magma mixing between Archean lower crust-derived felsic magma and mafic lower crust-derived dioritic magma, triggered by mantle-derived mafic magma underplating during the course of asthenospheric upwelling in Early Cretaceous. Such process further implicates the reactivation of Jiaodong lower crust during the destruction of NCC.

  17. Calc-alkali rocks derived from tholeiite magma in Hakone volcano; pyroxene crystallization trends and pyroxene geothermometry to estimate the magma temperature

    Ishii, T.


    Calc-alkali rocks are widely distributed in the island arcs. The several models of their magma-genesis were proposed by many geoscientists (e.g. Kuno 1950, Osborn 1959, Sakuyama 1981, Tatsumi 2011) on the bases of precise petrological investigations. Crystallization trends of rock forming minerals (pyroxene, feldspar etc.) in the individual lava flow of the hydrous tholeiitic magma are represented by chemical zoning from phenocryst through microphenocryst to the groundmass in each lava. Those trends indicate degassing (or dehydrating) trends of erupted lava (Ishii 1991). Crystallization trend of minerals of hydrous magma in the subvolcanic magma reservoir is represented by core of phenocrysts throughout lava-flow strata in each volcano. Those trends indicate water-enrichment (or hydrating) trend in the magma reservoir. On the bases of the detailed analyses of the pyroxene crystallization sequences as well as estimated magmatic temperatures using pyroxene geothermometer, for calc-alkali rocks from the Central Cone (CC) in the Hakone volcano, the following working hypothesis is suggested, i.e. those calc-alkali rocks are induced by magma mixing between high temperature (about 1120 Degree Centigrade) tholeiite magma and low temperature (about 970 Degree Centigrade) magma, the latter is originated from fractional crystallization of the primitive high temperature hydras island-arc tholeiite magma within magma reservoir under closed environment for water. Reference Ishii, T., 1991. Lava-flow and subvolcanic magma reservoir composition trends in the Ca-poor pyroxenes of Hakone Volcano, Japan. Jour. Petrol., 32, 429-450 Kuno, H., 1950. Petrology of Hakone volcano and the adjacent areas, Japan. Bull. Geol. Soc. Am., 61, 957-1019. Sakuyama, M., 1981. Petrological study of the Myoko and Kurohime volcanoes, Japan: crystallization sequence and evidence for magma mixing. Jour. Petrol., 22, 553-583. Osborn, E. F., 1959. Role of oxygen pressure in the crystallization and

  18. Rheological flow laws for multiphase magmas: An empirical approach

    Pistone, Mattia; Cordonnier, Benoît; Ulmer, Peter; Caricchi, Luca


    The physical properties of magmas play a fundamental role in controlling the eruptive dynamics of volcanoes. Magmas 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 magmas, 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 magma. 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.%) 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 "apparent shear-thinning" for the behaviours observed at low and high crystallinity, respectively. At low

  19. Reconstructing Magma Degassing and Fragmentation: The 1060 CE Plinian Eruption of Medicine Lake Volcano, California

    Giachetti, T.; Gonnermann, H. M.; Crozier, J.


    Magma 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 magma permeabil
ity is thought to adversely affect magma fragmentation and the ability of magma 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 magma ascent and bubble growth to predict the development of magma 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 magma degassing and fragmentation. Our results show that the porosity and permeability of pyroclasts coincide with the conditions required for fragmentation of the erupting magma. 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 magma 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 magma that fragmented over a depth range of several tens of meters, probably reflecting some degree of lateral variability in magma porosity in the conduit. The model also indicates that, even if the magma 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.

  20. Abrupt transition from fractional crystallization to magma mixing at Gorely volcano (Kamchatka) after caldera collapse

    Gavrilenko, Maxim; Ozerov, Alexey; Kyle, Philip R.; Carr, Michael J.; Nikulin, Alex; Vidito, Christopher; Danyushevsky, Leonid


    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 magma 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 magmas, whereas magma mixing is more prominent in the Young Gorely eruptive products. The role of recharge-evacuation processes in Gorely magma evolution is negligible (a closed magmatic system); however, crustal rock assimilation plays a significant role for the evolved magmas. Most Gorely magmas differentiate in a shallow magmatic system at pressures up to 300 MPa, ˜3 wt% H2O, and oxygen fugacity of ˜QFM + 1.5 log units. Magma 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 magma chamber evolution of Old Gorely occurs under conditions of decompression and degassing. We find that the caldera-forming eruption(s) modified the magma plumbing geometry. This led to a change in the dominant magma evolution process from fractional crystallization to magma mixing. We further suggest that disruption of the magma 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.

  1. The Implications of Petit-Spot Volcanism for the Origin of Alkaline Intraplate Magmas

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


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

  2. Copper isotope behavior during extreme magma differentiation and degassing: a case study on Laacher See phonolite tephra (East Eifel, Germany)

    Huang, Jian; Liu, Sheng-Ao; Wörner, Gerhard; Yu, Huimin; Xiao, Yilin


    Copper (Cu) isotopic analyses were performed on a set of samples from the Laacher See tephra (LST) (Eifel, Germany) to investigate whether Cu isotopes are fractionated during extreme magma differentiation and degassing. The LST represents a continuous fractional crystallization series from parental basanite through mafic to highly differentiated phonolites. Samples analyzed here include phonolites of variable degrees of differentiation, phonolite-basanite hybrid rocks formed by mixing basanite and phonolite magmas, and basanite-derived mega-crystals (i.e., clinopyroxene, amphibole, phlogopite). In addition, we analyzed a series of mafic parental lavas from surrounding volcanic centers to constrain the Cu isotopic features of the Eifel mantle. Mafic phonolites show strong depletion in Cu compared to their parental basanites from ~50 to ~3 ppm, indicating sulfide fractionation during the basanite-to-phonolite differentiation. Mass balance calculations, based on the most Cu-rich hybrid rock (δ65Cu = -0.21 ‰, [Cu] = 46.2 ppm), show that the parental basanite magmas have δ65Cu of ca. -0.21 ‰, lighter than those of the mafic phonolites (~0.11 ‰). This suggests that sulfide fractionation preferentially removes the lighter Cu isotope (63Cu) in S-saturated magmas. By contrast, all phonolites have a limited range of Cu contents (1.1 to 4.0 ppm) with no systematic variations with S, suggesting that Cu is not controlled by sulfide fractionation during the evolution of mafic to highly differentiated phonolites. The identical δ65Cu values (0.11 ± 0.03 ‰, 2SD, n = 10) of the phonolites, irrespective of highly diverse composition and extents of differentiation, indicate that fractional crystallization of silicates (e.g., plagioclase, sanidine, amphibole, pyroxene, olivine), Fe-Ti-oxides and phosphate (e.g., apatite) generates insignificant Cu isotope fractionation. The lack of correlations between δ65Cu and volatile contents (e.g., S, Cl) in the LST sequence implies

  3. Códigos binarios no lineales en MAGMA

    Ovalle Arce, Víctor


    La finalitat d'aquest projecte és aconseguir representar codis binaris no lineals de manera eficient en un ordinador. Per fer-ho, hem desenvolupat funcions per representar un codi binari a partir del super dual. Hem millorat la funció de càlcul del kernel d'un codi binari, implementada en projectes d'anys anteriors. També hem desenvolupat un paquet software per l'intèrpret MAGMA. Aquest paquet ens proveeix d'eines per al tractament de codis binaris no necessàriament lineals. La finalidad d...

  4. Temporal magma source changes at Gaua volcano, Vanuatu island arc

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


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

  5. Codis Z2Z4-additius en Magma

    Gastón Brasó, Bernat


    En aquest projecte es presenta el desenvolupament d'un paquet d'aplicacions en l'entorn de programació matemàtica Magma, per al tractament dels codis anomenats Z2Z4-additius. Els codis Z2Z4-additius permeten representar alguns codis binaris, com a codis lineals en l'espai dels codis Z2Z4-additius. Aquest fet permetrà l'estudi de tota una sèrie de codis binaris no lineals que fins ara eren intractables. En este proyecto se presenta el desarrollo de un paquete de aplicaciones en el entorno d...

  6. Role of magma-water interaction in very large explosive eruptions

    Valentine, G.A.


    An important class of explosive eruptions, involving large-scale magma-water interaction during the discharge of hundreds to thousands of cubic kilometers of magma, 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 magma properties and gas bubbles on magma-water interaction, and hazards associated with the eruptions.

  7. Growth rates of lava domes with respect to viscosity of magmas

    I. Yokoyama


    Full Text Available In the discussion of lava dome formation, viscosity of magma plays an important role. Measurements of viscosity of magmas in field and laboratory are briefly summarized. The types of lava dome emplacements are classified into two, squeeze- and spine-type, by kinetic processes. The squeeze-type is the formation of a dome as a result of squeezes of magma through conduits and the latter is solidified magma forced to ascend by underlying fluid magma. An important parameter in the formation of such lava domes is their growth rates. Lava domes of squeeze-type are governed by the Hagen-Poiseuille Law which involves their viscosoties and other eruption parameters. At present, the real viscosity of magmas at the site of lava dome is still inaccessible. In order to avoid uncertainty in viscosity of magmas, a conception of «macroscopic viscosity» is proposed, which involves effects of chemical components, mainly SiO2 and volatile material, crystals and temperature, and their changes with time. Lava dome formations during the 20th century are briefly examined and their growth rates are estimated. The relationship between the growth rates and the SiO2 content of the magma is statistically studied, and the macroscopic viscosity is empirically expressed as a function of SiO2 content. The linearity between the two parameters is reasonably interpreted. This means that formation processes of lava domes are dominantly controlled by macroscopic viscosity of magma.

  8. Magma Generation and Transport in Subduction Zones: Numerical Simulations of Chemical, Thermal and Mechanical Coupling During Magma Ascent by Porous Flow

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


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

  9. Deep crustal structure and continent-ocean boundary along the Galicia continental margin (NW Iberia)

    Druet, María; Muñoz-Martín, Alfonso; Carbó, Andrés; Acosta, Juan; Granja Bruña, José Luis; Llanes, Pilar; Vázquez, Juan-Tomás; Ercilla, Gemma


    The Galicia continental margin is a magma-poor rifted margin with an extremely complex structure. Its formation involves several rifting episodes during the Mesozoic in the vicinity of a ridge triple junction, which produces a change in the orientation of the main structures. In addition, there is an overimposed Cenozoic partial tectonic inversion along its northern border. Although this continental margin has been widely studied since the 70's, most studies have focused on its western part in the transition to the Iberia Abyssal Plain, and there is a significant lack of information on the north and northwestern flanks of this margin. This fact, along with its great structural complexity, has resulted in the absence of a previous comprehensive regional geodynamic model integrating all the processes observed. In the present study we integrate a large volume of new geophysical data (gravity, swath bathymetry and 2D multichannel reflection seismic). Data come from the systematic mapping of the Spanish EEZ project which provides a dense grid of gravity data and full seafloor coverage with swath bathymetry, and from the ERGAP project which provides serially-arranged 2D seismic reflection profiles across the NW Iberia margin. The combined interpretation and modelling of this new information has arisen significant constraints on the origin, the deep crustal structure and the physiographic complexity of the margin, as well as on the characterization of the along- and across-strike variation of the ocean-continent transition along NW Iberia margin. The analysis of this information leads us to propose a conceptual model for the initiation of the tectonic inversion of a magma-poor rifted margin. Finally, a framework for the geodynamic evolution of the Galicia margin has been constructed, involving three main stages: A) an early stage from the end of rifting and oceanic drift in the Bay of Biscay (Santonian); B) an intermediate stage with the beginning of tectonic inversion in

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

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


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

  11. Temperature profile data collected using XBTs from the ENDEAVOR from the Atlantic Ocean during the International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE (IDOE/POLYMODE) project, 1978-05-08 to 1978-05-25 (NCEI Accession 8000135)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature profile data were collected using bathythermograph (BT/XBT) casts from ENDEAVOR in the Atlantic Ocean from May 8, 1978 to May 25, 1978. Data were...

  12. Temperature, pressure, and other data collected using tide gauge and CTD casts from the Northwest Atlantic Ocean in part of the IDOE/POLYMODE (International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE) from 06 October 1976 to 05 July 1977 (NODC Accession 7900243)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature, pressure, and other data were collected using tide gauge and CTD casts from the Northwest Atlantic Ocean from October 6, 1976 to July 5, 1977. Data were...

  13. Temperature profile data from STD/CTD casts from the KNORR from the Atlantic Ocean during the International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE (IDOE/POLYMODE) project, 03 October 1976 to 19 October 1976 (NODC Accession 7800010)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature and conductivity profile data were collected using STD/CTD casts from KNORR in the Atlantic Ocean from October 3, 1976 to October 19, 1976. Data were...

  14. Temperature and pressure data collected using drifting buoy and profiling floats from the North Atlantic Ocean in part of the IDOE/POLYMODE (International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE) from 10 January 1975 to 31 May 1981 (NODC Accession 8700121)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature and pressure data were collected using drifting buoy and profiling floats from CHAIN, GILLISS, OCEANUS, and ENDEAVOR from the North Atlantic Ocean from...

  15. Temperature profile data from STD/CTD casts from the OCEANUS from the Atlantic Ocean during the International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE (IDOE/POLYMODE) project, 06 June 1978 to 22 June 1978 (NODC Accession 8200056)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature, depth, salinity, and sigma-T data were collected using STD/CTD casts from OCEANUS in the Atlantic Ocean from June 6, 1978 to June 22, 1978. Data were...

  16. Temperature profile and pressure data collected using moored buoy from the Atlantic Ocean with support from the IDOE/POLYMODE (International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE) from 04 May to 18 December 1975 (NODC Accession 7601247)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature profile and pressure data were collected using moored buoy from the Atlantic Ocean from May 4, 1975 to December 18, 1975. Data were submitted by...

  17. Temperature, pressure, and other data collected using tide gauge and CTD casts from the Northwest Atlantic Ocean as part of the IDOE/POLYMODE (International Decade of Ocean Exploration / combination of USSR POLYGON project and US MODE) from 01 May 1977 to 31 May 1978 (NODC Accession 7900244)

    National Oceanic and Atmospheric Administration, Department of Commerce — Temperature, pressure, and other data were collected using tide gauge and CTD casts from the Northwest Atlantic Ocean from May 1, 1977 to May 31, 1978. Data were...

  18. Combining ocean numerical model and SAR imagery to investigate the occurrence of oil pollution, a case study for the Java Sea

    Setiawan, A.; Putri, M. R.; Gade, M.; Pohlmann, T.; Mayer, B.


    IndoNACE is an abbreviation of Indo nesian Seas N umerical A ssessment of the C oastal E nvironment, a pilot study between Indonesia and Germany that combining analysis of oil spills from SAR images and numerical tracer studies from 3-D numerical model. Aim of this study is to understand the observed seasonal variations in marine oil pollution. Within this study, a visual inspection of all available SAR images is performed in order to generate maps of oil pollution occurrence in the Java Sea. Afterward, a set of numerical models is applied to trace back the origin of oil pollution. Our results showed that by analysing 706 ENVISAT ASAR images, the highest number of oil spills occurrence in the Java Sea was found during the transition monsoons, i.e. March to May and September to November. Assuming Marine Protected Area (MPA) of Seribu Islands as the end position of oil trajectory, we found that the origins of oil pollutions in that area were mostly from north and east.

  19. Temporal evolution of granitic magmas in the Luanchuan metallogenic belt, east Qinling Orogen, central China: Implications for Mo metallogenesis

    Li, Dong; Han, Jiangwei; Zhang, Shouting; Yan, Changhai; Cao, Huawen; Song, Yaowu


    The Luanchuan metallogenic belt, located within the eastern part of the Qinling Orogen, central China, hosts a number of world-class Mo deposits that are closely related to small late Mesozoic granitic plutons. Zircon U-Pb dating of distinct plutons in the Luanchuan metallogenic belt has yielded ages of 153 ± 1, 154 ± 2, 152 ± 2, and 148 ± 1 Ma. Molybdenite Re-Os isotopic compositions of Yuku ore district in the southern part of Luanchuan metallogenic belt has yielded an isochron age of 146 ± 1 Ma, which is consistent with the large-scale mineralization ages in the northern part of the Luanchuan metallogenic belt. A combination of previous studies and new geochronological and isotopic data show a concordant temporal and genetic link between granitic magmatism and Mo mineralization in the Luanchuan metallogenic belt, suggesting that this mineralization episode formed the most extensive Mo mineralization belt in the east Qinling Orogen. Zircon grains from Mo-related granitic plutons show similar trace element distributions. High-precision Multi Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS) Pb isotope analysis of K-feldspar megacrysts from mineralization-related granites suggest that they were derived from the lower crust. Similarly, the Pb isotopic compositions of pyrite coprecipitated with molybdenite also suggest that the metals were derived form the lower crust, with probably minor mantle contribution. A continuum mineralization model that describes the sourcing of Mo from an evolving granitic magma over successive differentiation events, possibly in separate but connected magma chambers, could explain the remarkable Mo enrichment in the Luanchuan metallogenic belt. The volatile- and Mo-bearing granitic magmas ascended as diapirs from the deep crust, and were emplaced as dikes in the upper crust. Lithological differences between these Mo-bearing granites may relate to different stages in the evolution of individual magmas. Finally, ore

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

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


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

  1. Precaldera lavas of the southeast San Juan Volcanic Field: Parent magmas and crustal interactions

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


    . Chemical and isotope correlations within each member indicate Conejos magmas differentiated via staged polybaric, multiprocess evolutionary paths. Stage I occurred near the base of the crust as mantle-derived basalt evolved to basaltic andesite by the MASH mechanism. Stage II followed ascent to shallower crustal levels where basaltic andesite differentiated to more evolved compositions by combined fractionation and assimilation of heterogeneous crust.

  2. Grain to outcrop-scale frozen moments of dynamic magma mixing in the syenite magma chamber, Yelagiri Alkaline Complex, South India

    M.L. Renjith


    Full Text Available Magma mixing process is unusual in the petrogenesis of felsic rocks associated with alkaline complex worldwide. Here we present a rare example of magma mixing in syenite from the Yelagiri Alkaline Complex, South India. Yelagiri syenite is a reversely zoned massif with shoshonitic (Na2O + K2O=5–10 wt.%, Na2O/K2O = 0.5–2, TiO2 <0.7 wt.% and metaluminous character. Systematic modal variation of plagioclase (An11–16 Ab82–88, K-feldspar (Or27–95 Ab5–61, diopside (En34–40Fs11–18Wo46–49, biotite, and Ca-amphibole (edenite build up three syenite facies within it and imply the role of in-situ fractional crystallization (FC. Evidences such as (1 disequilibrium micro-textures in feldspars, (2 microgranular mafic enclaves (MME and (3 synplutonic dykes signify mixing of shoshonitic mafic magma (MgO = 4–5 wt.%, SiO2 = 54–59 wt.%, K2O/Na2O = 0.4–0.9 with syenite. Molecular-scale mixing of mafic magma resulted disequilibrium growth of feldspars in syenite. Physical entity of mafic magma preserved as MME due to high thermal-rheological contrast with syenite magma show various hybridization through chemical exchange, mechanical dilution enhanced by chaotic advection and phenocryst migration. In synplutonic dykes, disaggregation and mixing of mafic magma was confined within the conduit of injection. Major-oxides mass balance test quantified that approximately 0.6 portions of mafic magma had interacted with most evolved syenite magma and generated most hybridized MME and dyke samples. It is unique that all the rock types (syenite, MME and synplutonic dykes share similar shoshonitic and metaluminous character; mineral chemistry, REE content, coherent geochemical variation in Harker diagram suggest that mixing of magma between similar composition. Outcrop-scale features of crystal accumulation and flow fabrics also significant along with MME and synplutonic dykes in syenite suggesting that Yelagiri syenite magma chamber had evolved

  3. MAGMIX: a basic program to calculate viscosities of interacting magmas of differing composition, temperature, and water content

    Frost, T.P.; Lindsay, J.R.


    MAGMIX is a BASIC program designed to predict viscosities at thermal equilibrium of interacting magmas 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 magma interaction expected for different initial conditions. The program is designed for modeling the type of magma interaction between hypersthenenormative magmas at upper crustal conditions. Utilization of the program to model magma 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 magma density. ?? 1988.

  4. Pre-eruption recharge of the Bishop magma system

    Wark, D.A.; Hildreth, W.; Spear, F.S.; Cherniak, D.J.; Watson, E.B.


    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 magma 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 magma 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.

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

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


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

  6. Experimental study of lunar and SNC (Mars) magmas

    Rutherford, Malcolm J.


    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 magmas 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 magma 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.

  7. Assessing land-ocean connectivity via submarine groundwater discharge (SGD) in the Ria Formosa Lagoon (Portugal): combining radon measurements and stable isotope hydrology

    Rocha, Carlos; Veiga-Pires, Cristina; Scholten, Jan; Knoeller, Kay; Gröcke, Darren R.; Carvalho, Liliana; Anibal, Jaime; Wilson, Jean


    Natural radioactive tracer-based assessments of basin-scale submarine groundwater discharge (SGD) are well developed. However, SGD takes place in different modes and the flow and discharge mechanisms involved occur over a wide range of spatial and temporal scales. Quantifying SGD while discriminating its source functions therefore remains a major challenge. However, correctly identifying both the fluid source and composition is critical. When multiple sources of the tracer of interest are present, failure to adequately discriminate between them leads to inaccurate attribution and the resulting uncertainties will affect the reliability of SGD solute loading estimates. This lack of reliability then extends to the closure of local biogeochemical budgets, confusing measures aiming to mitigate pollution.Here, we report a multi-tracer study to identify the sources of SGD, distinguish its component parts and elucidate the mechanisms of their dispersion throughout the Ria Formosa - a seasonally hypersaline lagoon in Portugal. We combine radon budgets that determine the total SGD (meteoric + recirculated seawater) in the system with stable isotopes in water (δ2H, δ18O), to specifically identify SGD source functions and characterize active hydrological pathways in the catchment. Using this approach, SGD in the Ria Formosa could be separated into two modes, a net meteoric water input and another involving no net water transfer, i.e., originating in lagoon water re-circulated through permeable sediments. The former SGD mode is present occasionally on a multi-annual timescale, while the latter is a dominant feature of the system. In the absence of meteoric SGD inputs, seawater recirculation through beach sediments occurs at a rate of ˜ 1.4 × 106 m3 day-1. This implies that the entire tidal-averaged volume of the lagoon is filtered through local sandy sediments within 100 days ( ˜ 3.5 times a year), driving an estimated nitrogen (N) load of ˜ 350 Ton N yr-1 into the system

  8. Analysis of magma-thermal conversion of biomass to gaseous fuel

    Gerlach, T.M.


    A wide range of magma 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 magma body, within the hot subsolidus margins of a magma body, or within surface reaction vessels heated by thermal energy derived from a magma 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 magma 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 magma 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 magma type. Fuel generation rates for basaltic magmas are at least 2 to 3 times those for andesitic magmas and 5 to 6 times those for rhyolitic magmas. The highest fuel generation rates, for any particular magma 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.

  9. The Role of KREEP in the Production of Mg-Suite Magmas and Its Influence on the Extent of Mg-Suite Magmatism in the Lunar Crust

    Elardo, S. M.; Shearer, C. K.; McCubbin, F. M.


    The lunar magnesian-suite, or Mg-suite, is a series of ancient plutonic rocks from the lunar crust. They have received a considerable amount of attention from lunar scientists since their discovery for three primary reasons: 1) their ages and geochemistry indicate they represent pristine magmatic samples that crystallized very soon after the formation of the Moon; 2) their ages often overlap with ages of the ferroan anorthosite (FAN) crust; and 3) planetary-scale processes are needed in formation models to account for their unique geochemical features. Taken as a whole, the Mg-suite samples, as magmatic cumulate rocks, approximate a fractional crystallization sequence in the low-pressure forsterite-anorthite-silica system, and thus these samples are generally thought to be derived from layered mafic intrusions which crystallized very slowly from magmas that intruded the anorthositic crust. However, no direct linkages have been established between different Mg-suite samples based either on field relationships or geochemistry.The model for the origin of the Mg-suite, which best fits the limited available data, is one where Mg-suite magmas form from melting of a hybrid cumulate package consisting of deep mantle dunite, crustal anorthosite, and KREEP (potassium-rare earth elements-phosphorus) at the base of the crust under the Procellarum KREEP Terrane (PKT). In this model, these three LMO (Lunar Magma Ocean) cumulate components are brought into close proximity by the cumulate overturn process. Deep mantle dunitic cumulates with an Mg number of approximately 90 rise to the base of the anorthositic crust due to their buoyancy relative to colder, more dense Fe- and Ti-rich cumulates. This hybridized source rock melts to form Mg-suite magmas, saturated in Mg-rich olivine and anorthitic plagioclase, that have a substantial KREEP component.

  10. Mid-crustal magmatic sheets in the Cascades Mountains, Washington: implications for magma ascent

    Paterson, Scott R.; Miller, Robert B.


    Diking, diapirism, ascent along faults, and ascent during heterogeneous ductile flow have all been championed as the most important means of magma ascent in the crust. We suggest that these mechanisms are end-members in a complex spectrum of ascent processes. In an attempt to evaluate which combination of ascent processes formed sheet-like bodies in the mid-crustal (20-25 km) Entiat pluton, Washington, we examined the tip regions of these sheets. The sheets have length/width ratios ranging from ˜6 to >75, with increasing ratios strongly correlated to decreasing sheet tip radii (from 850 to 100 m) and decreasing ratios of tip diameter/sheet width (from 0.66 to 0.33). Thus, these bodies have geometries falling between those of dikes and those associated with elliptical diapirs. The sheets are not associated with faults or fracture zones extending from their tips. Instead, sheet walls are oriented parallel to the axial planes of upright, syn-emplacement folds. In sheets with high length/width ratios, magmatic foliations in sheets are folded or parallel to axial planes of host rock folds. With decreasing length/width ratios, margin parallel foliations in both sheet and host rock are increasingly common. Our studies indicate that the sheets are emplaced at high angles to σ1, not σ3 as proposed in elastic dike models, and are always associated with complex, viscoelastic flow of host rock. These observations rule out elastic dike and fault models, and instead favor diapiric rise of magma sheets during viscoelastic behavior of host rock.

  11. Triple oxygen isotope composition of the Campi Flegrei magma systems

    Iovine, Raffaella Silvia; Wörner, Gerhard; Pack, Andreas; Sengupta, Sukanya; Carmine Mazzeo, Fabio; Arienzo, Ilenia; D'Antonio, Massimo


    Sr-O isotope relationships in igneous rocks are a powerful tool to distinguish magma sources and quantify assimilation processes in magmatic rocks. Isotopic (87Sr/86Sr and 18O/16O-17O/16O) data have been acquired on whole rocks and separated minerals (feldspar, Fe-cpx, Mg-cpx, olivine phenocrysts) from pyroclastic products of the Campi Flegrei volcanic complex (Gulf of Naples, Southern Italy). Oxygen isotope ratios were measured by infrared laser fluorination using a Thermo MAT253 gas source isotope ratio mass spectrometer in dual inlet mode, on ˜2 mg of hand-picked phenocrysts. Variations in triple oxygen isotope ratios (17O/16O, 18O/16O) are expressed as the δ notation relative to VSMOW. Sr isotopic compositions were determined by thermal ionization mass spectrometry after standard cation-exchange methods on separated hand-picked phenocrysts (˜300 mg), and on whole rocks, in case of insufficient sample size to separate crystals. Sr-isotopes in Campi Flegrei minerals range from 0.707305 to 0.707605 and δ18O varies from 6.5 to 8.3‰ . Recalculated δ18Omelt values accordingly show a large range between 7.2 and 8.6‰ . Our data, compared with published δ18O-isotope data from other Italian volcanic centers (Alban Hills, Mts. Ernici, Ischia, Mt. Vesuvius, Aeolian Islands, Tuscany and Sardinia) and from subduction zones worldwide (Kamchatka, Lesser Antilles, Indonesia and Central Andean ignimbrites), show compositions that are very different from typical mantle values. Distinct trends and sources are recognized in our compilation from global data: (1) serpentinized mantle (Kamchatka), (2) sediment-enrichment in the mantle source (Indonesia, Lesser Antilles, Eolian arc), (3) assimilation of old radiogenic continental crust affecting magmas derived from sediment-modified mantle sources (Tuscany, Sardinia), (4) assimilation of lower crustal lithologies (Central Andes, Alban Hills, Mts. Ernici, Ischia). Sr-O-isotope values of Campi Flegrei and Vesuvius magmas

  12. Timing magma ascent at Popocatepetl Volcano, Mexico, 2000-2001

    Martin-Del Pozzo, A. L.; Cifuentes, G.; Cabral-Cano, E.; Bonifaz, R.; Correa, F.; Mendiola, I. F.


    Magnetic anomalies may be used to constrain magma 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 magma 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 magma which preceded the increases in seismicity, before the December 2000-January 22 VEI 3-4 eruptions. No significant increases in

  13. Earth science: role of fO2 on fluid saturation in oceanic basalt.

    Scaillet, Bruno; Pichavant, Michel


    Assessing the conditions under which magmas become fluid-saturated has important bearings on the geochemical modelling of magmas because volatile exsolution may profoundly alter the behaviour of certain trace elements that are strongly partitioned in the coexisting fluid. Saal et al. report primitive melt inclusions from dredged oceanic basalts of the Siqueiros transform fault, from which they derive volatile abundances of the depleted mantle, based on the demonstration that magmas are not fluid-saturated at their eruption depth and so preserve the mantle signature in terms of their volatile contents. However, in their analysis, Saal et al. consider only fluid-melt equilibria, and do not take into account the homogeneous equilibria between fluid species, which, as we show here, may lead to a significant underestimation of the pressure depth of fluid saturation.

  14. Fifty Shades of Grey: Zircon Perspectives on the Timing and Chemistry of Magma Interactions Reflected in the Bishop Tuff

    Chamberlain, K. J.; Wilson, C. J.; Wooden, J. L.; Baker, J. A.; Charlier, B. L.


    The ~0.76 Ma Bishop Tuff eruption in eastern California is an archetypal example of the products of a compositionally stratified magma chamber. Key issues regarding the melt-dominant magma body that have arisen from recent studies include the role of horizontal variability versus vertical stratification, and the nature and timing of a late-stage ingress of compositionally contrasting melt. The latter is reflected in, for example, CL-bright rims on quartz, and Sr- and Ba-rich rims on sanidines, both of which are reported in samples from ignimbrite erupted from vents along the northern caldera rim. Various studies have placed contrasting temporal constraints on assembly and evacuation of the Bishop Tuff magma body and the processes occurring within it from one or two mineral phases. Although the overall crystal specific record is more complex, it has the potential to distinguish between mixing, in-situ crystallisation and other magmatic processes, and resolve the associated timings of these events. Zircon has been widely utilised in the Bishop Tuff and other silicic systems because of its unique records of information about the ages and P-T-X environments of growth. Here we present SHRIMP-RG ion probe data from Bishop Tuff zircons, collected from samples spanning the full eruptive sequence. A combination of age data, textural analysis and trace element analysis is used to yield insights into magma chamber development and the pre-eruptive state of the melt-dominant magma body, as evidenced in material erupted from different vent areas around what became the Long Valley caldera. U-Pb dating of 307 spots from all zones in crystals from all samples yields a strongly unimodal age spectrum, with a mean age of 794+/-3 ka (10 spots rejected, MSWD = 2.0). CL images of the dated zircon suites show the appearance of bright-rimmed zircons in later-erupted ignimbrite packages (accompanied generally by bright-rimmed sanidine and quartz crystals), but with diversity in the

  15. Tectonic analysis and paleo-stress determination of the upper lava section at ODP/IODP site 1256 (East Pacific Ocean)

    Fontana, Emanuele


    Research on the deep sea is of great importance for a better understanding of the mechanism of magma emplacement and the tectonic evolution of oceanic crust. However, details of the internal structure in the upper levels of the oceanic crust are much less complete than that of the more fully studied sub-aerial areas. For the first time, this study proposes a dynamic analysis using the inversion method on core data derived from the drilled basement of the present-day intact oceanic crust at ODP/IODP Site 1256 in the Cocos plate. The research is based on an innovative core reorientation process and combines different stress hypothesis approaches for the analysis of heterogeneous failure-slip data via exploitation of two distinct techniques. From the analysis of the failure-slip data, both techniques produce 5 distinct subsystem datasets. All calculated subsystems are mechanically and geometrically admissible. Interpretation of the results allows the researchers to note a complex local and regional tectonic evolution deriving from the interplay of (1) the ridge push and rotation of both the East Pacific Rise and the Cocos-Nazca Spreading Center, (2) the effect of the slab pull of the Middle America Trench, (3) the influence of lava emplacement mechanisms, and (4) intra-plate deformation.

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

    Clément Ganino


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

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

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


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

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

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


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

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

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


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

  20. The roles of fractional crystallization, magma mixing, crystal mush remobilization and volatile-melt interactions in the genesis of a young basalt-peralkaline rhyolite suite, the greater Olkaria volcanic complex, Kenya Rift valley

    Macdonald, R.; Belkin, H.E.; Fitton, J.G.; Rogers, N.W.; Nejbert, K.; Tindle, A.G.; Marshall, A.S.


    The Greater Olkaria Volcanic Complex is a young (???20 ka) multi-centred lava and dome field dominated by the eruption of peralkaline rhyolites. Basaltic and trachytic magmas have been erupted peripherally to the complex and also form, with mugearites and benmoreites, an extensive suite of magmatic inclusions in the rhyolites. The eruptive rocks commonly represent mixed magmas and the magmatic inclusions are themselves two-, three- or four-component mixes. All rock types may carry xenocrysts of alkali feldspar, and less commonly plagioclase, derived from magma mixing and by remobilization of crystal mushes and/or plutonic rocks. Xenoliths in the range gabbro-syenite are common in the lavas and magmatic inclusions, the more salic varieties sometimes containing silicic glass representing partial melts and ranging in composition from anorthite ?? corundum- to acmite-normative. The peralkaline varieties are broadly similar, in major element terms, to the eruptive peralkaline rhyolites. The basalt-trachyte suite formed by a combination of fractional crystallization, magma mixing and resorption of earlier-formed crystals. Matrix glass in metaluminous trachytes has a peralkaline rhyolitic composition, indicating that the eruptive rhyolites may have formed by fractional crystallization of trachyte. Anomalous trace element enrichments (e.g. ??? 2000 ppm Y in a benmoreite) and negative Ce anomalies may have resulted from various Na- and K-enriched fluids evolving from melts of intermediate composition and either being lost from the system or enriched in other parts of the reservoirs. A small group of nepheline-normative, usually peralkaline, magmatic inclusions was formed by fluid transfer between peralkaline rhyolitic and benmoreitic magmas. The plumbing system of the complex consists of several independent reservoirs and conduits, repeatedly recharged by batches of mafic magma, with ubiquitous magma mixing. ?? The Author 2008. Published by Oxford University Press. All

  1. Preliminary insights into a model for mafic magma fragmentation

    Edwards, Matt; Pioli, Laura; Andronico, Daniele; Cristaldi, Antonio; Scollo, Simona


    Fragmentation of mafic magmas remains a poorly understood process despite the common occurrence of low viscosity explosive eruptions. In fact, it has been commonly overlooked based on the assumption that low viscosity magmas have very limited explosivity and low potential to undergo brittle fragmentation. However, it is now known that highly explosive, ash forming eruptions can be relatively frequent at several mafic volcanoes. Three questions arise due to this - What is the specific fragmentation mechanism occuring in these eruptions? What are the primary factors controlling fragmentation efficiency? Can a link between eruption style and fragmentation efficiency be quantified? We addressed these questions by coupling theoretical observations and field analysis of the recent May 2016 eruption at Mount Etna volcano. Within this complex 10-day event three paroxysmal episodes of pulsating basaltic lava jets alternating with small lava flows were recorded from a vent within the Voragine crater. The associated plumes which were produced deposited tephra along narrow axes to the east and south east. Sampling was done on the deposits associated with the first two plumes and the third one. We briefly characterise the May 2016 eruption by assessing plume height, eruption phases, total erupted masses and fallout boundaries and comparing them to previous eruptions. We also analyse the total grainsize distribution (TGSD) of the scoria particles formed in the jets. Conventional methods for obtaining grainsize and total distributions of an eruption are based on mass and provide limited information on fragmentation though. For this reason, the TGSD was assessed by coupling particle analyser data and conventional sieving data to assess both particle size and number of particle distributions with better precision. This allowed for more accurate testing of several existing models describing the shape of the TGSD. Coupled further with observations on eruption dynamics and eruption

  2. The Influence of Phenocrysts on Magma Degassing in Rhyolitic Systems

    deGraffenried, R.; Larsen, J. F.; Lindoo, A. N.


    The kinetics of volatile exsolution and magma degassing control volcanic eruption styles, but the role of phenocrysts in the degassing process is poorly understood. The focus of this study is two series of decompression experiments examining how phenocrysts may or may not influence vesicle structures leading to permeability development and degassing in magmas with rhyolitic matrix melts. Powdered rhyolite obsidian (75 SiO2 wt. %; Mono Craters, CA) was seeded with 20 and 40 vol. % euhedral corundum crystals (350 μm) to approximate phenocrysts. Experiments were run using TZM (Ti-Zr-Mo alloy) vessels fitted with a water-cooled rapid quench top in a vertical Deltech furnace. Each run was held at 110 MPa and 900OC for 24 hours then decompressed continuously at a rate of 0.25 MPa/s to a final pressure (Pf) between 75 and 15 MPa. Permeability was measured using a bench-top permeameter constructed for the small experimental samples. Porosity was obtained from reflected light images using NIH Image J. The porosity of the samples increased from 11.0±1.7 to 73.3±3.1 vol % at Pf of 75 to 15 MPa for crystal free samples, 30.1±6.9 to 62.2±2.6 vol % at Pf of of 75 to 25 MPa for 20 vol % crystal samples, and 13.3±2.5 to 41.2±9.6 vol % at Pf of 75 to 50 MPa for 40 vol % crystal samples. The 20 vol % samples are impermeable up to at least 50 MPa Pf. The 40 vol % samples are impermeable up to 25 MPa Pf, with one sample having a measured Darcian permeability of -13.93±0.05 m2 at 25 MPa Pf. Comparatively, the crystal free samples were mostly impermeable up to 15 MPa, with one sample having a measured Darcian permeability of -14.41±0.04 m2 at 15 MPa Pf and 73.3 vol % porosity. Although preliminary, our permeable 40 vol % experiment suggests the phenocrysts help the samples develop permeability at a higher ending pressure and potentially lower porosity. Differences in the porosity curve as a function of pressure between the 20 and 40 vol % series indicate phenocrysts influence

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

    Mccallum, I. S.


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

  4. Degassing-induced crystallization of basaltic magma and effects on lava rheology

    Lipman, P.W.; Banks, N.G.; Rhodes, J.M.


    During the north-east rift eruption of Mauna Loa volcano, Hawaii, on 25 March-14 April 1984 (Fig. 1), microphenocryst contents of erupted lava increased from 0.5 to 30% without concurrent change in either bulk magma composition or eruption temperature (1,140 ?? 3 ??C). The crystallization of the microphenocrysts is interpreted here as being due to undercooling of the magma 20-30 ??C below its liquidas; the undercooling probably resulted from separation and release of volatiles as the magma migrated 12 km from the primary summit reservoir to the eruption site on the north-east rift zone. Such crystallization of magma during an eruption has not been documented previously. The undercooling and crystallization increased the effective viscosity of the magma, leading to decreased eruption rates and stagnation of the lava flow. ?? 1985 Nature Publishing Group.

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

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


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

  6. Planet Ocean

    Afonso, Isabel


    A more adequate name for Planet Earth could be Planet Ocean, seeing that ocean water covers more than seventy percent of the planet's surface and plays a fundamental role in the survival of almost all living species. Actually, oceans are aqueous solutions of extraordinary importance due to its direct implications in the current living conditions of our planet and its potential role on the continuity of life as well, as long as we know how to respect the limits of its immense but finite capacities. We may therefore state that natural aqueous solutions are excellent contexts for the approach and further understanding of many important chemical concepts, whether they be of chemical equilibrium, acid-base reactions, solubility and oxidation-reduction reactions. The topic of the 2014 edition of GIFT ('Our Changing Planet') will explore some of the recent complex changes of our environment, subjects that have been lately included in Chemistry teaching programs. This is particularly relevant on high school programs, with themes such as 'Earth Atmosphere: radiation, matter and structure', 'From Atmosphere to the Ocean: solutions on Earth and to Earth', 'Spring Waters and Public Water Supply: Water acidity and alkalinity'. These are the subjects that I want to develop on my school project with my pupils. Geographically, our school is located near the sea in a region where a stream flows into the sea. Besides that, our school water comes from a borehole which shows that the quality of the water we use is of significant importance. This project will establish and implement several procedures that, supported by physical and chemical analysis, will monitor the quality of water - not only the water used in our school, but also the surrounding waters (stream and beach water). The samples will be collected in the borehole of the school, in the stream near the school and in the beach of Carcavelos. Several physical-chemical characteristics related to the quality of the water will

  7. Timescales of magma processes occurred prior to recent Campi Flegrei caldera eruptions: first results from diffusion profiles on plagioclase phenocrysts

    D'Antonio, Massimo; Arienzo, Ilenia; Fedele, Lorenzo; Iovine, Raffaella; Carmine Mazzeo, Fabio; Civetta, Lucia; Orsi, Giovanni; Wörner, Gerhard


    Knowledge of the timescales of magma rising and stagnation, as well as mingling/mixing processes occurring in the shallow plumbing system of an active volcano is crucial for volcanic hazard assessment and risk mitigation. Among few recently developed methodologies, high-precision, high spatial resolution analysis of major-, minor- and trace elements on zoned phenocrysts through electron microprobe techniques represents a powerful tool to provide good estimates of timescales of pre-eruptive magma rising, stagnation and/or mingling/mixing processes. To this purpose, volcanic rock samples of trachytic composition representative of the Agnano-Monte Spina eruption (4.7 ka CAL BP) occurred at the Campi Flegrei caldera (southern Italy) have been selected. The investigation has been carried out in the framework of Project V2 - Precursori di Eruzioni, funded by the Italian Dipartimento per la Protezione Civile - Istituto Nazionale di Geofisica e Vulcanologia. The investigated rock samples are pumice fragments from which double-polished, 100 µm thick thin sections have been prepared for analytical purposes. Back-scattered electrons (BSE) images have been acquired at the scanning electron microscope (SEM), in order to identify the plagioclase phenocrysts suitable to be analyzed successively, selected among those that best display their zoning. After a careful observation of the BSE images, major-, minor- and selected trace element contents have been determined through combined energy-dispersive and wavelength-dispersive system electron microprobe analyses (EDS-WDS-EMPA) on transects crossing the growth zones of the selected phenocrysts. This methodology has allowed reconstructing the diffusion profile of some key-elements through the growth zones of the investigated phenocrysts. Successively, the diffusion profiles have been combined with textural features obtained through BSE images in order to obtain diffusion models aimed at estimating the timescales of crystals

  8. Determination of crystal residence timescales in magma reservoirs by diffusion modeling of dendritic phosphorus zoning patterns in olivine

    Chakraborty, S.; Potrafke, A.


    Deciphering the early stages of crystallization and the chronological evolution of phenocrysts in magma reservoirs is one of the main goals in volcanology. Established approaches that model the concentration evolution of fast diffusing elements like Fe/Mg carry limited information on timescales once the concentration gradients are homogenized. Elements that diffuse more slowly, such as P and Al, become useful in these cases. We present a novel modeling tool that combines high-resolution EMP mapping of slow diffusing phosphorus in olivine with 2D kinetic modeling of the diffusive relaxation of initial chemical zoning pattern of P as well as Fe/Mg. The modeling approach offers a new possibility for determining crystal residence times in magma reservoirs. P diffusion coefficients from the experimental determination of [1] and Fe/Mg diffusion coefficients from [2] were used. The method yields a time-bracket between the minimum time required to homogenize the zoning of fast-diffusing Fe/Mg and the maximum time period for which details of chemical zoning of slow-diffusing P may be retained. To illustrate the approach we have studied the compositional zoning patterns of 7 olivine crystals from Piton de la Fournaise volcano, La Réunion. All crystals show a narrow range of forsterite contents (=Fo82-84) with fully homogenized Fe/Mg distribution, whereas P-mapping reveals oscillatory to dendritic zoning patterns [3]. P concentrations scatter in the range of 0.4 wt-% to below detection limit. Revealed phosphorus zoning patterns were considered to display the initial crystal architecture, whereas Fe and Mg zoning has been wiped out due to faster diffusion. For La Réunion magmas at 1453 K, timescales between few days to weeks were determined to be the time brackets for growth and residence of the olivine crystals in the magmas. These short residence times combined with knowledge of very fast developing dendritic crystals that have recently been revealed worldwide [e.g. 3

  9. Does Cooling Magma Drive Deep Low-Frequency Earthquakes?

    Aso, N.; Ide, S.; Tsai, V. C.


    = Introduction = One major type of deep low-frequency earthquakes (LFEs) is tectonic LFEs that locate around plate boundaries, and are thought to be slip events. Another type of LFEs is volcanic LFEs that locate around the Moho mostly beneath active or Quaternary volcanoes, and their physical mechanism is not well established. We recently suggested that the volcanic LFEs in eastern Shimane can be interpreted as a resonant oscillation within an old magma conduit of 1600 m in length, which produces a focal mechanism that is equivalent to a compensated linear vector dipole (CLVD) oriented in the direction of the conduit [Aso et al., in prep. for re-submission]. However, a remaining question is what excites the resonance. In the present study, we suggest that cooling magma acts as a trigger for the resonant oscillation of volcanic LFEs, with the idea that thermal contraction of magma produces an anisotropic strain rate and the resulting brittle failure would trigger oscillation. To verify this, we calculated strain rates produced by this effect both analytically and numerically. = Model Setting and Method = We set the initial extent of magma as a 1600-m-long 400-m-wide pipe as is inferred from the distribution of hypocenters in eastern Shimane. The initial perturbation is set to be 400 K uniformly within the pipe. Thermal strain rate is calculated using the thermal stress potential of Timoshenko and Goodier [1970]. First, we estimated the strain rate without the effect of latent heat release. Assuming a cuboid pipe, it can be solved easily analytically. Next, to account for latent heat release, we use the enthalpy method [Eyres et al., 1946] to numerically solve the problem, assuming a cylindrical pipe. = Results = For the case without latent heat release, the strain rate remains higher than than 10-14/s for 600 years at the center of the pipe. For the case with latent heat release, although the latent heat delays the thermal evolution and decreases the strain rate, it

  10. An experimental tool to look in a magma chamber

    Gonde, C.; Massare, D.; Bureau, H.; Martel, C.; Pichavant, M.; Clocchiatti, R.


    Understanding the physical and geochemical processes occurring in the volcanoes roots is one of the fundamental tasks of research in the experimental petrology community. This requires experimental tools able to create confining conditions appropriate for magma chambers and conduits. However, the characterization of some natural magmatic processes requires more than a blink experimental approach, to be rigorously studied. In some cases, the in situ approach is the only one issue, because it permits the observation of processes (crystallization of mineral phases, bubble growth.) and their kinetic studies. Here we present a powerful tool, a transparent internally heated autoclave. With this apparatus, pressures (up to 0.3 GPa) and temperatures (up to 900°C) appropriate for subvolcanic magma reservoirs can be obtained. Because it is equipped with transparent sapphire windows, either images or movies can be recorded during an experiment. The pressure medium is Argon, and heating is achieved by a W winding placed into the pressure vessel. Pressure and temperature are calibrated using both well known melting points (eg. salts, metals) and phase transitions (AgI), either at room temperature or at medium and high temperatures. During an experiment, the experimental charge is held between two thick windows of diamond, placed in the furnace cylinder. The experimental volume is about 1 mm3. The observation and numeric record are made along the horizontal axis, through the windows. This apparatus is currently used for studies of nucleation and growth of gas bubbles in a silicate melt. The first results will be presented at the meeting.

  11. Experimental modelling of ground deformation associated with shallow magma intrusions

    Galland, O.


    Active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems. The analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems. Nevertheless, these analyses usually take into account simplistic shapes (sphere, dykes, sills) and the results cannot be verified as the modelled systems are buried. In this contribution, I will present new results from experimental models of magma intrusion, in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored in 3D. The models consisted of a molten vegetable oil, simulating low viscosity magma, injected into cohesive fine-grained silica flour, simulating the brittle upper crust; oil injection resulted is sheet intrusions (dykes, sills and cone sheets). The initial topography in the models was flat. While the oil was intruding, the surface of the models slightly lifted up to form a smooth relief, which was mapped through time. After an initial symmetrical development, the uplifted area developed asymmetrically; at the end of the experiments, the oil always erupted at the steepest edge of the uplifted area. After the experiment, the oil solidified, the intrusion was excavated and the shape of its top surface mapped. The comparison between the uplifted zone and the underlying intrusions showed that (1) the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions, (2) the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion, and (3) the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil. The experimental results also suggest that complex intrusion shapes (inclined sheet, cone sheet, complex sill) may have to be considered more systematically in analyses of ground deformation patterns on volcanoes.

  12. Mechanisms of differentiation in the Skaergaard magma chamber

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


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

  13. Ocean Uses: Hawaii (PROUA)

    National Oceanic and Atmospheric Administration, Department of Commerce — This Pacific Regional Ocean Uses Atlas (PROUA) Project is an innovative partnership between NOAA and the Bureau of Ocean Energy Management (BOEM) designed to...

  14. Optimal Combining Data for Improving Ocean Modeling


    fluxes (in presence of radar). Right: Same with no radar. Finally, we tested the algorithm on a velocity field immitating the Bodega Bay...parameter space, Geophys. J. Int., 138 , 479-494. 2. Sambridge M., (1999b), Geophysical Inversion with a Neighbourhood Algorithm - II . Appraising

  15. Optimal Combining Data for Improving Ocean Modeling


    uniformly distributaed over a circle . Figure 5. 1) Dependence of estimation error for circulation parameters in a vicinity of a saddle point, 2...Submesoscale physical- biogeochemical coupling across the Ligurian Current (northwestern Mediterranean) using a bio- optical glider, Limnol. Oceanogr

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

    Johnson, E. R.


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

  17. Magma Supply at the Arctic Gakkel Ridge: Constraints from Peridotites and Basalts

    Sun, C.; Dick, H. J.; Hellebrand, E.; Snow, J. E.


    Crustal thickness in global ridge systems is widely believed to be nearly uniform (~7 km) at slow- and fast-spreading mid-ocean ridges, but appears significantly thinner (ancient mantle depletion, lower mantle temperature, ridge obliquity, and melt retention/focusing. To better understand the magma supply at ultraslow-spreading ridges, we examined melting dynamics by linking peridotites and basalts dredged along the Gakkel Ridge. We analyzed rare earth elements in clinopyroxene from 84 residual peridotites, and estimated melting parameters for individual samples through nonlinear least squares analyses. The degrees of melting show a large variation but mainly center at around 7% assuming a somewhat arbitrary but widely used depleted MORB mantle starting composition. Thermobarometry on published primitive basaltic glasses from [2] indicates that the mantle potential temperature at the Gakkel Ridge is ~50°C cooler than that at the East Pacific Rise. The ridge-scale low-degree melting and lower mantle potential temperature place the final depth of melting at ~30 km and a melt thickness of 1.0 or 2.9 km for a triangular or trapezoidal melting regime, respectively. The final melting depth is consistent with excess conductive cooling and lithosphere thickening suggested by geodynamic models, while the estimated melt thickness is comparable to the seismic crust (1.4 - 2.9 km; [1]). The general agreement among geochemical analyses, seismic measurements, and geodynamic models supports that lower mantle potential temperature and thick lithosphere determine the ridge-scale low-degree melting and thin crust at the Gakkel Ridge, while melt retention/focusing and excess ancient mantle depletion are perhaps locally important at short length scales (e.g., < 50 - 100 km). [1] Jokat and Schmidt-Aursch (2007) Geophys. J. Int. (2007) 168, 983-998. [2] Gale et al. (2012) J. Petrology, 55, 1051-1082.

  18. The record of magma chamber processes in plagioclase phenocrysts at Thera Volcano, Aegean Volcanic Arc, Greece

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


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

  19. Rheology of phonolitic magmas - the case of the Erebus lava lake

    Le Losq, Charles; Neuville, Daniel R.; Moretti, Roberto; Kyle, Philip R.; Oppenheimer, Clive


    Long-lived active lava lakes are comparatively rare and are typically associated with low-viscosity basaltic magmas. Erebus volcano, Antarctica, is unique today in hosting a phonolitic lava lake. Phonolitic magmas can erupt explosively, as in the 79 CE Plinian eruption of Vesuvius volcano, Italy, and it is therefore important to understand their physical properties. The phonolite at Erebus has slightly higher silica content than that at Vesuvius yet its present activity is predominantly non-explosive. As a contribution to understanding such contrasting eruptive behaviour, we focus on the rheological differences between these comparable magmas. In particular, we evaluate the viscosity of the Erebus phonolite magma by integrating new experimental data within a theoretical and empirical framework. The resulting model enables estimation of the Erebus melt viscosity as a function of temperature, crystal and water concentrations, with an uncertainty of, at most, ± 0.45 log (Pa s). Using reported ranges for these parameters, we predict that the magma viscosity in the upper region of the plumbing system of Erebus ranges between 105 and 107 Pas. This is substantially higher than has been hitherto considered with significant implications for modelling the dynamics of the lava lake, conduit and magma reservoir system. Our analysis highlights the generic challenges encountered in calculation of magma viscosity and presents an approach that can be applied to other cases.

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

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


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

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

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


    Mt. Cameroon is one of the most active volcanoes in Africa and poses a possible threat to about half a million people in the area, yet knowledge of the volcano’s underlying magma supply system is sparse. To characterize Mt. Cameroon’s magma plumbing system, we employed mineral-melt equilibrium thermobarometry on the products of the volcano’s two most recent eruptions of 1999 and 2000. Our results suggest pre-eruptive magma storage between 20 and 39 km beneath Mt. Cameroon, which corresponds to the Moho level and below. Additionally, the 1999 eruption products reveal several shallow magma pockets between 3 and 12 km depth, which are not detected in the 2000 lavas. This implies that small-volume magma batches actively migrate through the plumbing system during repose intervals. Evolving and migrating magma parcels potentially cause temporary unrest and short-lived explosive outbursts, and may be remobilized during major eruptions that are fed from sub-Moho magma reservoirs. PMID:27713494

  2. Internal triggering of volcanic eruptions: tracking overpressure regimes for giant magma bodies

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


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

  3. The Campi Flegrei Deep Drilling Project `CFDDP': Understanding the Magma-Aquifers Interaction at Large Calderas

    de Natale, G.; Troise, C.; Sacchi, M.


    Campi Flegrei caldera is a good example of the most explosive volcanism on the Earth, a potential source of global catastrophes. Alike several similar volcanic areas (Yellowstone and Long Valley, USA; Santorini, Greece; Iwo Jima, Japan, etc.) its volcanic activity, i.e. eruptions and unrests, is dominated by physical mechanisms involving the strict interaction between shallow magma sources and geothermal systems. Furthermore, just like similar areas, it should be characterised by very large shallow magma chambers, filled by residual magma left after the ignimbritic caldera forming eruptions. However, neither the physical mechanisms of magma-water interaction, nor the evidence for such large magma chamber, have been ever clear enough to be used for detailed volcanological interpretation and eruption forecast. The CFDDP project aims to understand, for the first time, the location and rehology of large residual magma chambers and the mechanisms of interaction between magma and aquifer systems to generate eruptions and unrests. CFDDP is then structured as a large multidisciplinary project, with a main volcanological aim and with a further goal to launch a geothermal energy exploitation project in the area. A larger goal of the CFDDP project is to establish at Campi Flegrei, a densely urbanised area in a developed western country, a natural laboratory to study volcanic risk, environmental issues, monitoring technologies, geothermal energy exploitation.

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

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


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

  5. Ocean optics

    Spinard, R.W.; Carder, K.L.; Perry, M.J.


    This volume is the twenty fifth in the series of Oxford Monographs in Geology and Geophysics. The propagation off light in the hydra-atmosphere systems is governed by the integral-differential Radiative Transfer Equation (RTE). Closure and inversion are the most common techniques in optical oceanography to understand the most basic principles of natural variability. Three types of closure are dealt with: scale closure, experimental closure, and instrument closure. The subject is well introduced by Spinard et al. in the Preface while Howard Gordon in Chapter 1 provides an in-depth introduction to the RTE and its inherent problems. Inherent and apparent optical properties are dealt with in Chapter 2 by John Kirk and the realities of optical closure are presented in the following chapter by Ronald Zaneveld. The balance of the papers in this volume is quite varied. The early papers deal in a very mathematical manner with the basics of radiative transfer and the relationship between inherent and optical properties. Polarization of sea water is discussed in a chapter that contains a chronological listing of discoveries in polarization, starting at about 1000 AD with the discovery of dichroic properties of crystals by the Vikings and ending with the demonstration of polarotaxis in certain marine organisms by Waterman in 1972. Chapter 12 on Raman scattering in pure water and the pattern recognition techniques presented in Chapter 13 on the optical effects of large particles may be of relevance to fields outside ocean optics.

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

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


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

  7. How do granitoid magmas mix with each other? Insights from textures, trace element and Sr-Nd isotopic composition of apatite and titanite from the Matok pluton (South Africa)

    Laurent, Oscar; Zeh, Armin; Gerdes, Axel; Villaros, Arnaud; Gros, Katarzyna; Słaby, Ewa


    In plutonic systems, magma mixing is often modelled by mass balance based on whole-rock geochemistry. However, magma mixing is a chaotic process and chemical equilibration is controlled by non-linear diffusive-advective processes unresolved by the study of bulk samples. Here we present textural observations, LA-(MC-)ICP-MS trace element and Sr-Nd isotopic data of accessory apatites and titanites from a hybrid granodiorite of the Neoarchean Matok pluton (South Africa), collected in a zone of conspicuous mixing between mafic and felsic magmas. Apatite grains mostly show a pronounced zoning in CL images, corresponding to abrupt changes in REE and HFSE concentrations recording their transfer through compositionally different melt domains during mixing. These grains crystallized early, at temperatures of 950-1000 °C. Titanite grains crystallized at temperatures of 820-900 °C (Zr-in-sphene thermometry). They show limited intra-grain chemical variations but huge inter-grain compositional scatter in REE and HFSE, pinpointing crystallization within a crystal mush, from isolated melt pockets having different composition from one another owing to incomplete chemical homogenization and variable Rayleigh fractionation. These chemical-textural characteristics, in combination with partitioning models and Polytopic Vector Analysis, point to "self-mixing" between co-genetic dioritic and granodioritic/granitic magmas. Both resulted from differentiation of mantle-derived mafic melts, showing that mixing does not necessarily involve magmas from contrasted (crust vs. mantle) sources. Systematic variations in ɛNd t (-4.5 to -2.5) and 87Sr/86Sr(i) (0.703-0.707) of titanite and apatite grains/domains crystallized from the two magmas point to an isotopically inhomogeneous mantle source, which is not resolved by bulk-rock isotopic data. Interaction between the two magmas must have occurred at relatively high temperatures (ca. 900°C) so that their viscosity contrast remained low

  8. The parent magma of the Nakhla (SNC) meteorite: Reconciliation of composition estimates from magmatic inclusions and element partitioning

    Treiman, A. H.


    The composition of the parent magma of the Nakhla meteorite was difficult to determine, because it is accumulate rock, enriched in olivine and augite relative to a basalt magma. A parent magma composition is estimated from electron microprobe area analyses of magmatic inclusions in olivine. This composition is consistent with an independent estimate based on the same inclusions, and with chemical equilibria with the cores of Nakhla's augites. This composition reconciles most of the previous estimates of Nakhla's magma composition, and obviates the need for complex magmatic processes. Inconsistency between this composition and those calculated previously suggests that magma flowed through and crystallized into Nakhla as it cooled.

  9. Location and Pressures Change Prediction of Bromo Volcano Magma Chamber Using Inversion Scheme

    Kumalasari, Ratih; Srigutomo, Wahyu


    Bromo volcano is one of active volcanoes in Indonesia. It has erupted at least 50 times since 1775 and has been monitored by Global Positioning System (GPS) since 1989. We applied the Levenberg-Marquardt inversion scheme to estimate the physical parameters contributing to the surface deformation. Physical parameters obtained by the inversion scheme such as magma chamber location and volume change are useful in monitoring and predicting the activity of Bromo volcano. From our calculation it is revealed that the depth of the magma chamber d = 6307.6 m, radius of magma chamber α = 1098.6 m and pressure change ΔP ≈ 1.0 MPa.

  10. Sloshing of a bubbly magma reservoir as a mechanism of triggered eruptions

    Namiki, Atsuko; Rivalta, Eleonora; Woith, Heiko; Walter, Thomas R.


    Large earthquakes sometimes activate volcanoes both in the near field as well as in the far field. One possible explanation is that shaking may increase the mobility of the volcanic gase