The density, compressibility and seismic velocity of hydrous melts at crustal and upper mantle conditions

NASA Astrophysics Data System (ADS)

Ueki, K.; Iwamori, H.

2015-12-01

Various processes of subduction zone magmatism, such as upward migration of partial melts and fractional crystallization depend on the density of the hydrous silicate melt. The density and the compressibility of the hydrous melt are key factors for the thermodynamic calculation of phase relation of the hydrous melt, and the geophysical inversion to predict physicochemical conditions of the melting region based on the seismic velocity. This study presents a new model for the calculations of the density of the hydrous silicate melts as a function of T, P, H2O content and melt composition. The Birch-Murnaghan equation is used for the equation of state. We compile the experimentally determined densities of various hydrous melts, and optimize the partial molar volume, compressibility, thermal expansibility and its pressure derivative, and K' of the H2O component in the silicate melt. P-T ranges of the calibration database are 0.48-4.29 GPa and 1033-2073 K. As such, this model covers the P-T ranges of the entire melting region of the subduction zone. Parameter set provided by Lange and Carmichael [1990] is used for the partial molar volume and KT value of the anhydrous silicate melt. K' of anhydrous melt is newly parameterized as a function of SiO2 content. The new model accurately reproduces the experimentally determined density variations of various hydrous melts from basalt to rhyolite. Our result shows that the hydrous melt is more compressive and less dense than the anhydrous melt; with the 5 wt% of H2O in melt, density and KT decrease by ~10% and ~30% from those of the anhydrous melt, respectively. For the application of the model, we calculated the P-wave velocity of the hydrous melt. With the 5 wt% of H2O, P-wave velocity of the silicate melt decreases by >10%. Based on the melt P-wave velocity, we demonstrate the effect of the melt H2O content on the seismic velocity of the partially molten zone of the subduction zone.

Chondritic Meteorites: Nebular and Parent-Body Formation Processes

NASA Technical Reports Server (NTRS)

Rubin, Alan E.; Lindstrom, David (Technical Monitor)

2002-01-01

It is important to identify features in chondrites that formed as a result of parent-body modification in order to disentangle nebular and asteroidal processes. However, this task is difficult because unmetamorphosed chondritic meteorites are mixtures of diverse components including various types of chondrules, chondrule fragments, refractory and mafic inclusions, metal-sulfide grains and fine-grained matrix material. Shocked chondrites can contain melt pockets, silicate-darkened material, metal veins, silicate melt veins, and impact-melt-rock clasts. This grant paid for several studies that went far in helping to distinguish primitive nebular features from those produced during asteroidal modification processes.

Electrical conductivity of basaltic and carbonatite melt-bearing peridotites at high pressures: Implications for melt distribution and melt fraction in the upper mantle

NASA Astrophysics Data System (ADS)

Yoshino, Takashi; Laumonier, Mickael; McIsaac, Elizabeth; Katsura, Tomoo

2010-07-01

Electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a Kawai-type multi-anvil apparatus in order to investigate melt fraction-conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure. The silicate samples were composed of San Carlos olivine with various amounts of mid-ocean ridge basalt (MORB), and the carbonate samples were a mixture of San Carlos olivine with various amounts of carbonatite. High-pressure experiments on the silicate and carbonate systems were performed up to 1600 K at 1.5 GPa and up to at least 1650 K at 3 GPa, respectively. The sample conductivity increased with increasing melt fraction. Carbonatite-bearing samples show approximately one order of magnitude higher conductivity than basalt-bearing ones at the similar melt fraction. A linear relationship between log conductivity ( σbulk) and log melt fraction ( ϕ) can be expressed well by the Archie's law (Archie, 1942) ( σbulk/ σmelt = Cϕn) with parameters C = 0.68 and 0.97, n = 0.87 and 1.13 for silicate and carbonate systems, respectively. Comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry. The gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction. The melt fraction of the partial molten region in the upper mantle can be estimated to be 1-3% and ˜ 0.3% for basaltic melt and carbonatite melt, respectively.

Evidence of cross-cutting and redox reaction in Khatyrka meteorite reveals metallic-Al minerals formed in outer space.

PubMed

Lin, Chaney; Hollister, Lincoln S; MacPherson, Glenn J; Bindi, Luca; Ma, Chi; Andronicos, Christopher L; Steinhardt, Paul J

2017-05-09

We report on a fragment of the quasicrystal-bearing CV3 carbonaceous chondrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (Russia). We show higher melting-point silicate glass cross-cutting lower melting-point Al-Cu-Fe alloys, as well as unambiguous evidence of a reduction-oxidation reaction history between Al-Cu-Fe alloys and silicate melt. The redox reactions involve reduction of FeO and SiO 2 to Fe and Fe-Si metal, and oxidation of metallic Al to Al 2 O 3 , occurring where silicate melt was in contact with Al-Cu-Fe alloys. In the reaction zone, there are metallic Fe and Fe-Si beads, aluminous spinel rinds on the Al-Cu-Fe alloys, and Al 2 O 3 enrichment in the silicate melt surrounding the alloys. From this and other evidence, we demonstrate that Khatyrka must have experienced at least two distinct events: first, an event as early as 4.564 Ga in which the first Al-Cu-Fe alloys formed; and, second, a more recent impact-induced shock in space that led to transformations of and reactions between the alloys and the meteorite matrix. The new evidence firmly establishes that the Al-Cu-Fe alloys (including quasicrystals) formed in outer space in a complex, multi-stage process.

Float processing of high-temperature complex silicate glasses and float baths used for same

NASA Technical Reports Server (NTRS)

Cooper, Reid Franklin (Inventor); Cook, Glen Bennett (Inventor)

2000-01-01

A float glass process for production of high melting temperature glasses utilizes a binary metal alloy bath having the combined properties of a low melting point, low reactivity with oxygen, low vapor pressure, and minimal reactivity with the silicate glasses being formed. The metal alloy of the float medium is exothermic with a solvent metal that does not readily form an oxide. The vapor pressure of both components in the alloy is low enough to prevent deleterious vapor deposition, and there is minimal chemical and interdiffusive interaction of either component with silicate glasses under the float processing conditions. Alloys having the desired combination of properties include compositions in which gold, silver or copper is the solvent metal and silicon, germanium or tin is the solute, preferably in eutectic or near-eutectic compositions.

Dependence of Ru2O3 Activity on Composition of Silicate Melts: Using Statistical Correlations to Infer Thermodynamic Behavior in the Melt

NASA Technical Reports Server (NTRS)

Colson, R. O.; Malum, K. M.

2005-01-01

Understanding variations in activity with composition is an essential step in improving prediction of partition coefficients during magma evolution. Variations in activity with composition are complex and do not generally exhibit ideal behavior relative to a traditional melt-component set. Although deviations from component ideality can be modeled numerically by simply fitting to compositional variables (such as in a regular or subregular solution model), such models have not been particularly successful for describing variations in trace component activities. A better approach might be to try to identify components that do a better job of describing the behavior of the species in the melt. Electrochemical Measurement of Ru2O3 activities: Electrodes were inserted into silicate melt beads of various compositions (Table 1) suspended on Ptwire loops in a 1-atm gas mixing furnace. An electrical potential was imposed between the electrodes, the imposed potential increasing along a step ramp with a pulse imposed on each step (Fig. 1). Current flows between electrodes when electroactive species in the melt are oxidized or reduced at the electrodes. The resulting current was measured at the top and bottom of the voltage pulse, and the difference (the differential current) was plotted against potential. The peak of the resulting curve is related to the activity coefficient for the particular electroactive species (Ru2O3) in the melt [1, 2, 3]. A significant part of the nonideal contribution to activity is due not to intrinsic properties of the component in the melt, but to our ignorance about the state and mixing properties of the component in the melt.

Partial Melting of the Indarch (EH4) Meteorite : A Textural, Chemical and Phase Relations View of Melting and Melt Migration

NASA Technical Reports Server (NTRS)

McCoy, Timothy J.; Dickinson, Tamara L.; Lofgren, Gary E.

2000-01-01

To Test whether Aubrites can be formed by melting of enstatite Chondrites and to understand igneous processes at very low oxygen fugacities, we have conducted partial melting experiments on the Indarch (EH4) chondrite at 1000-1500 C. Silicate melting begins at 1000 C. Substantial melt migration occurs at 1300-1400 C and metal migrates out of the silicate change at 1450 C and approx. 50% silicate partial melting. As a group, our experiments contain three immiscible metallic melts 9Si-, and C-rich), two immiscible sulfide melts(Fe-and FeMgMnCa-rich) and Silicate melt. Our partial melting experiments on the Indarch (EH4) enstatite Chondrite suggest that igneous processes at low fO2 exhibit serveral unique features. The complete melting of sulfides at 1000 C suggest that aubritic sulfides are not relicts. Aubritic oldhamite may have crystallized from Ca and S complexed in the silicate melt. Significant metal-sulfide melt migration might occur at relatively low degrees of silicate partial melting. Substantial elemental exchange occurred between different melts (e.g., between sulfide and silicate, Si between silicate and metal), a feature not observed during experiments at higher fO2. This exchange may help explain the formation of aubrites from known enstatite chondrites.

Experimental simulation of the alkali-carbonate metasomatism

NASA Astrophysics Data System (ADS)

Gorbachev, Nikolay; Kostyuk, Anastasia

2010-05-01

Close association of alkaline and ultrabasic rocks, carbonatites, apatitic and sulfidic mineralization, features of structure testify about mantle a source and the important role alcalic-carbonaceous fluids in genesis of these rocks. Formation alkaline silicate, carbonaceous and sulfidic melts, phase relationship, behaviour of the ti-tan, phosphorus, sulphur and zircon has been experimentally studied at pressure 3.9 GPa, temperature 1250°С in system peridotit-basalt (eclogite)-alcalic-carbonaceous fluid with additives in quality acces-sory minerals, apatite, nickel-containing pyrrhotite, ilmenite, zircon. Experiments were carried out using of apparatus high pressure (piston cilinder and anvil with hole) by a quenching technique. It was used two ampoules (platinum and peridotite, content basalt powder) method. Duration of experiments was 6-8 hours. Products of experiments were studied on electronic scanning microscope Tescan VEGA TS 5130MM with YAG detector of secondary and reflected elec-tron and energy-dispersive the x-ray microanalyzer with semi-conductor Si (Li) detector INCA Energy 350. The morphology, structure and relationship of glass, inclusions of carbonatic and sulfidic globules specify in existence in the conditions of experiment immiscibility silicate, carbonate and sulfidic melts. The composition of silicate melt answered phonolite, carbonaceous melts it is essential calciferous composition with an impurity of alkaline metals and silicate components. Solubility of zircon in silicate melts reached 0.8 wt.% ZrO2, in co-existing carbonaceous melt - 1.5 wt.%. Concentration TiO2 and Р2О5 in silicate melt reached 2 wt.%, in carbonaceous melt - 1.7 wt.% TiO2 and up to 14 wt.% Р2О5. Concentration of sulphur in these melts did not exceed 0.2 мас. %. From minerals of liqudus the main concentrators of the titan and phosphorus were the X-phase and phlogopite - up to 8 wt.% TiO2 and up to 3 wt.% Р2О5 in the X-phase, up to 6 wt. % TiO2 and to 2.5 wt. % Р2О5 in phlogopite. Absence ilmenite and apatite in experimental samples under the studied conditions is obviously caused by their high solubility in co-existing phases. The composition of X-phase is similar to composition of Cpx, but X-phase enrich in TiO2 and de-plete in SiO2 . The partition coefficient of oxides some elements between silicate and carbonaceous melts Dka/si increasing from SiO2 (D<1) to CaO (D>10). Reduction of solubility of apatite in alkaline silicate melt at pressure decline promotes silicate-phosphate stratification and formation of apatite mineralization at introduction of mantle magmas into the earth crust. Supported by grant RFBR № 09-05-01131, ONZ th. 2

Composition of Impact Melt Debris from the Eltanin Impact Strewn Field, Bellingshausen Sea

NASA Technical Reports Server (NTRS)

Kyte, Frank T.

2002-01-01

The impact of the km-sized Eltanin asteroid into the Bellingshausen Sea produced mm- to cm-sized vesicular impact melt-rock particles found in sediment cores across a large area of the ocean floor. These particles are composed mainly of olivine and glass with minor chromite and traces of NiFe-sulfides. Some particles have inclusions of unmelted mineral and rock fragments from the precursor asteroid. Although all samples of melt rock examined have experienced significant alteration since their deposition in the late Pliocene, a significant portion of these particles have interiors that remain pristine and can be used to estimate the bulk composition of the impact melt. The bulk composition of the melt-rock particles is similar to the composition of basaltic meteorites such as howardites or mesosiderite silicates, with a contribution from seawater salts and a siderophile-rich component. There is no evidence that the Eltanin impact melt contains a significant terrestrial silicate component that might have been incorporated by mixing of the projectile with oceanic crust. If terrestrial silicates were incorporated into the melt, then their contribution must be much less than 10 wt%. Since excess K, Na, and CI are not present in seawater proportions, uptake of these elements into the melt must have been greatest for K and least for CI, producing a K/CI ratio about 4 times that in seawater. After correcting for the seawater component, the bulk composition of the Eltanin impact melt provides the best estimate of the bulk composition of the Eltanin asteroid. Excess Fe in the impact melt, relative to that in howardites, must be from a significant metal phase in the parent asteroid. Although the estimated Fe:Ni:Ir ratios (8:1:4 x 10(exp -5)) are similar to those in mesosiderite metal nodules (10:1:6 x 10(exp -5), excess Co and Au by factors of about 2 and 10 times, respectively, imply a metal component distinct from that in typical mesosiderites. An alternative interpretation, that siderophiles have been highly fractionated from a mesosiderite source, would require loss of about 90% of the original metal from the impact melt and the sediments, and is unsupported by any observational data. More likely, the excess Fe in the melt rocks is 'representative of the amount of metal in the impacting asteroid, which is estimated to be 4+/- 1 wt%.

Experimental determination of activities of FeO and Fe 2O 3 components in hydrous silicic melts under oxidizing conditions

NASA Astrophysics Data System (ADS)

Gaillard, Fabrice; Pichavant, Michel; Scaillet, Bruno

2003-11-01

The critical role of iron on crystal-silicate liquid relationships and melt differentiation is mainly controlled by the redox conditions prevailing in magmas, but the presently available database merely constrains the thermodynamic properties of iron-bearing components in strongly reduced and anhydrous molten silicate where iron is in the ferrous form. This paper provides new standard states for pure ferrous (FeOliq) and ferric (Fe2O3liq) molten iron oxides and extends the experimental database towards oxidizing and water-bearing domains. Iron-iridium, iron-platinum alloys, magnetite or hematite were equilibrated with synthetic silicic liquids at high temperature and high pressure under controlled oxygen fugacity (fO2) to determine activity-composition relationships for FeOliq and Fe2O3liq. Between 1000 and 1300°C, the fO2 ranges from that in air to 3-log units below that of the nickel-nickel oxide buffer (NNO). Experiments were performed on both anhydrous and hydrous melts containing up to 6-wt.% water. Incorporation of water under reducing conditions increases the activity coefficient of FeOliq but has an opposite effect on Fe2O3liq. As calcium is added to system, the effect of water becomes weaker and is inverted for Fe2O3liq. Under oxidizing conditions, water has a negligible effect on both activities of FeOliq and Fe2O3liq. In contrast, changes in redox conditions dominate the activity coefficients of both FeOliq and Fe2O3liq, which increase significantly with increasing fO2. The present results combined with the previous work provide a specific database on the energetics of iron in silicate melts that cover most of the condition prevailing in natural magmas.

Melting in super-earths.

PubMed

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

Partitioning of F and Cl Between Apatite and a Synthetic Shergottite Liquid (QUE 94201) at 4 Gpa from 1300 TO 1500 C

NASA Technical Reports Server (NTRS)

McCubbin, F. M.; Barnes, J. J.; Vander Kaaden, K. E.; Boyce, J. W.

2017-01-01

Apatite [Ca5(PO4)3(F,Cl,OH)] is present in a wide range of planetary materials. Due to the presence of volatiles within its crystal structure (Xsite), many recent studies have attempted to use apatite to constrain the volatile contents of planetary magmas and mantle sources. In order to use the volatile contents of apatite to accurately determine the abundances of volatiles in coexisting silicate melt or fluids, thermodynamic models for the apatite solid solution and for the apatite components in multicomponent silicate melts and fluids are required. Although some thermodynamic models for apatite have been developed, they are incomplete. Furthermore, no mixing model is available for all of the apatite components in silicate melts or fluids, especially for F and Cl components. Several experimental studies have investigated the apatite-melt and apatite-fluid partitioning behavior of F, Cl, and OH in terrestrial and planetary systems, which have determined that apatite-melt partitioning of volatiles are best described as exchange equilibria similar to Fe-Mg partitioning between olivine and silicate melt. However, McCubbin et al., recently reported that the exchange coefficients vary in portions of apatite compositional space where F, Cl, and OH do not mix ideally in apatite. In particular, solution calorimetry data of apatite compositions along the F-Cl join exhibit substantial excess enthalpies of mixing, and McCubbin et al. reported substantial deviations in the Cl-F exchange Kd along the F-Cl apatite join that could be explained by the preferential incorporation of F into apatite. In the present study, we assess the effect of apatite crystal chemistry on F-Cl exchange equilibria between apatite and melt at 4 GPa over the temperature range of 1300-1500 C. The goal of these experiments is to assess the variation in the Ap-melt Cl-F exchange Kd over a broad range of F:Cl ratios in apatite. The results of these experiments could be used to understand at what composition apatite shifts from a hexagonal unit cell with space group P63/m to a unit cell with monoclinic symmetry within space group P21/b. We anticipate that this transition occurs at >70% chlorapatite based on solution calorimetry data.

Core formation in the early solar system through percolation: 4-D in-situ visualization of melt migration

NASA Astrophysics Data System (ADS)

Bromiley, G.; Berg, M.; Le Godec, Y.; Mezouar, N.; Atwood, R. C.; Phillipe, J.

2015-12-01

Although core formation was a key stage in the evolution of terrestrial planets, the physical processes which resulted in segregation of iron and silicate remain poorly understood. Formation of a silicate magma oceans provides an obvious mechanism for segregation of core-forming liquids, although recent work has strengthened arguments for a complex, multi-stage model of core formation. Extreme pressure1 and the effects of deformation2 have both been shown to promote percolation of Fe-rich melts in a solid silicate matrix, providing mechanisms for early, low temperature core-formation. However, the efficiency of these processes remains untested and we lack meaningful experimental data on resulting melt segregation velocities. Arguments regarding the efficiency of core formation through percolation of Fe-rich melts in solid silicate are based on simple, empirical models. Here, we review textural evidence from recent experiments which supports early core formation driven by deformation-aided percolation of Fe-rich melts. We then present results of novel in-situ synchrotron studies designed to provide time-resolved 3-D microimaging of percolating melt in model systems under extreme conditions. Under low strain rates characteristic of deformation-aided core formation, segregation of metallic (core-forming) melts by percolation is driven by stress gradients. This is expected to ultimately result in channelization and efficient segregation of melts noted in high-strain, low pressure experiments3. In-situ visualization also demonstrates that percolation of viscous metallic melts is surprisingly rapid. A combination of melt channelization and hydraulic fracture results in rapid, episodic melt migration, even over the limited time scale of experiments. The efficiency of this process depends strongly on the geometry of the melt network and is scaled to grain size in the matrix. We use both in-situ visualization and high-resolution ex-situ analysis to provide accurate constraints on melt migration velocities via this combined mechanism and will propose a model by which results can be scaled to core formation in the early solar system. References[1] Shi et al. Nature GeoSc. 6, 971 (2013).[2] Bruhn et al. Nature 403, 883 (2000).[3] Kohlstedt & Holtzman Ann. Rev. Earth. Planet. Sci. 37, 561 (2009).

Carbon-bearing MgSiO3 melt at deep mantle conditions

NASA Astrophysics Data System (ADS)

Ghosh, D. B.; Bajgain, S. K.; Mookherjee, M.; Karki, B. B.

2016-12-01

Carbon di-oxide and water are two important volatiles that are often present in silicate magmas and volcanic eruptions. To address the influence of these volatiles in deep seated melts, their properties (e.g., structure, transport, thermodynamics) at relevant pressure-temperature (P-T) conditions along with compositional variance need to be explored. MgSiO3 being one of the major components of the mantle, the study of carbonated MgSiO3 melts is of great contextual relevance. In the present work we investigate the structure and thermodynamics of carbon bearing MgSiO3 melts under conditions of the entire mantle.Our first-principles molecular dynamics (MD) simulations of the MgSiO3-CO2 system show that pressure profoundly influences the behavior of carbon-bearing silicate melts. Our results encompassing from 5 - 30 wt.% CO2 in MgSiO3 demonstrate that: (1) carbon speciation consists of distinct molecular CO2 and carbonate ions ( (CO3)2-) below 15 GPa and interestingly almost all of the carbonate ions are bound to Mg polyhedra; (2) with compression they evolve to silicon-polyhedral bound carbonate (along with Mg polyhedra bound), CO4 , and di-carbonate species. Accordingly, carbon solubility in the silicate melt becomes nearly ideal and carbon remains completely miscible with increasing pressure. Carbon reduces the melt density modestly by 0.015 to 0.005 g cm-3 per wt.% CO2 between 15 and 140 GPa. These results imply that deep-seated silicate melts above and below the transition zone, and atop the core-mantle boundary may be able to sequester significant amounts of carbon without making melts gravitationally unstable.

Influence of Silicate Melt Composition on Metal/Silicate Partitioning of W, Ge, Ga and Ni

NASA Technical Reports Server (NTRS)

Singletary, S. J.; Domanik, K.; Drake, M. J.

2005-01-01

The depletion of the siderophile elements in the Earth's upper mantle relative to the chondritic meteorites is a geochemical imprint of core segregation. Therefore, metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle. The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. Several recent studies have shown the importance of silicate melt composition on the partitioning of siderophile elements between silicate and metallic liquids. It has been demonstrated that many elements display increased solubility in less polymerized (mafic) melts. However, the importance of silicate melt composition was believed to be minor compared to the influence of oxygen fugacity until studies showed that melt composition is an important factor at high pressures and temperatures. It was found that melt composition is also important for partitioning of high valency siderophile elements. Atmospheric experiments were conducted, varying only silicate melt composition, to assess the importance of silicate melt composition for the partitioning of W, Co and Ga and found that the valence of the dissolving species plays an important role in determining the effect of composition on solubility. In this study, we extend the data set to higher pressures and investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid.

The effects of sulfide composition on the solubility of sulfur in coexisting silicate melts

NASA Astrophysics Data System (ADS)

Smythe, Duane; Wood, Bernard; Kiseeva, Ekaterina

2016-04-01

The extent to which sulfur dissolves in silicate melts saturated in an immiscible sulfide phase is a fundamental question in igneous petrology and plays a primary role in the generation of magmatic ore deposits, volcanic degassing and planetary differentiation. Terrestrial sulfide melts often contain over 20 weight percent Ni + Cu, however, most experimental studies investigating sulfur solubility in silicate melt have been primarily concerned with the effects of silicate melt composition, and pure FeS has been use as the immiscible sulfide melt (O'Neill and Mavrogenes, 2002; Li and Ripley, 2005). To investigation of the effects of sulfide composition, in addition to those of temperature, pressure and silicate melt composition, on sulfur solubility in silicate melts, we have carried out a series of experiments done at pressures between 1.5 and 3 GPa and temperatures from 1400 to 1800C over a range of compositions of both the silicate and sulfide melt. We find that the solubility of sulfur in silicate melts drops significantly with the substitution of Ni and Cu for Fe in the immiscible sulfide melt, decreasing by approximately 40% at mole fractions of NiS + Cu2S of 0.4. Combining our results with those from the previous studies investigating sulfur solubility in silicate melts we have also found that solubility increases with increasing temperature and decreases pressure. These results show that without considering the composition of the immiscible sulfide phase the sulfur content of silicate melts can be significantly overestimated. This may serve to explain the relatively low sulfur concentrations in MORB melts, which previous models predict to be undersaturated in a sulfide phase despite showing chemical and textural evidence for sulfide saturation. Li, C. & Ripley, E. M. (2005). Empirical equations to predict the sulfur content of mafic magmas at sulfide saturation and applications to magmatic sulfide deposits. Mineralium Deposita 40, 218-230. O'Neill, H. S. C. & Mavrogenes, J. A. (2002). The Sulfide Capacity and the Sulfur Content at Sulfide Saturation of Silicate Melts at 1400°C and 1 bar. Journal of Petrology 43, 1049-1087.

A Non-Arrhenian Viscosity Model for Natural Silicate Melts with Applications to Volcanology

NASA Astrophysics Data System (ADS)

Russell, J. K.; Giordano, D.; Dingwell, D. B.

2005-12-01

Silicate melt viscosity is the most important physical property in volcanic systems. It governs styles and rates of flow, velocity distributions in flowing magma, rates of vesiculation, and, ultimately, sets limits on coherent(vs. fragmented or disrupted) flow. The prediction of melt viscosity over the range of conditions found on terrestrial planets remains a challenge. However, the extraordinary increase in number and quality of published measurements of melt viscosity suggests the possibility of new models. Here we review the attributes of previous models for silicate melt viscosity and, then, present a new predictive model natural silicate melts. The importance of silicate melt viscosity was recognized early [1] and culminated in 2 models for predicting silicate melt viscosity [2,3]. These models used an Arrhenian T-dependence; they were limited by a limited experimental database dominated by high-T measurements. Subsequent models have aimed to: i) extend the compositional range of Arrhenian T-dependent models [4,5]; ii) to develop non-Arrhenian models for limited ranges of composition [6,7,8], iii) to develop new strategies for modelling the composition and T-dependence of viscosity [9,10,11], and, finally, to create chemical models for the non-Arrhenian T-dependence of natural melts [12]. We present a multicomponent model for the compositional and T dependence of silicate melt viscosity based on data spanning a wide range of anhydrous melt compositions. The experimental data include micropenetration and concentric cylinder viscometry measurements covering a viscosity range of 10-1 to 1012 Pa s and a T-range from 700 to 1650°C. These published data provide a high- quality database comprising ~ 800 experimental data on 44 well-characterized melt compositions. Our model uses the Adam-Gibbs equation to capture T-dependence: log η = A + B/[T · log (T/C)] where A, B, and C are adjustable parameters that vary for different melt compositions. We assume that all silicate melts converge to a common, but unknown, high-T limit (e.g., A) and that all compositional dependence is accommodated for by B and C. We adopt a linear compositional dependence for B and C: B = σi=1..n [xi βi] C = σi=1..n [xi γi] where xi's are the mole fractions of oxide components (n=8) and βi and γi are adjustable parameters. The model, therefore, comprises 2 · n+1 adjustable parameters which are optimized for against the experimental database including a common value of A and compositional coefficeints for B and C. The new model reproduces the original database to within experimental uncertainty and can predict the viscosity of silicate melts across the full range of conditions found in Nature. References Cited: [1] Friedman et al., 1963. J Geophys Res 68, 6523-6535. [2] Bottinga Y & Weill D 1972. Am J Sci 272, 438- 475. [3] Shaw HR 1972. Am J Sci 272, 438- 475. [4] Persikov ES 1991. Adv Phys Geochem 9, 1-40. [5] Prusevich AA 1988. Geol Geofiz 29, 67-69. [6] Baker DR 1996. Am Min 81, 126-134. [7] Hess KU & Dingwell DB 1996. Am Min 81, 1297- 1300. [8] Zhang, et al. 2003. Am min 88, 1741- 1752. [9] Russell et al. 2002. Eur J Min 14, 417-428. [10] Russell et al. 2003. Am Min 8, 1390- 1394. [11] Russell JK & Giordano D In Press. Geochim Cosmochim Acta. [12] Giordano D & Dingwell DB 2003. Earth Planet. Sci. Lett. 208, 337-349.

Silicate melts density, buoyancy relations and the dynamics of magmatic processes in the upper mantle

NASA Astrophysics Data System (ADS)

Sanchez-Valle, Carmen; Malfait, Wim J.

2016-04-01

Although silicate melts comprise only a minor volume fraction of the present day Earth, they play a critical role on the Earth's geochemical and geodynamical evolution. Their physical properties, namely the density, are a key control on many magmatic processes, including magma chamber dynamics and volcanic eruptions, melt extraction from residual rocks during partial melting, as well as crystal settling and melt migration. However, the quantitative modeling of these processes has been long limited by the scarcity of data on the density and compressibility of volatile-bearing silicate melts at relevant pressure and temperature conditions. In the last decade, new experimental designs namely combining large volume presses and synchrotron-based techniques have opened the possibility for determining in situ the density of a wide range of dry and volatile-bearing (H2O and CO2) silicate melt compositions at high pressure-high temperature conditions. In this contribution we will illustrate some of these progresses with focus on recent results on the density of dry and hydrous felsic and intermediate melt compositions (rhyolite, phonolite and andesite melts) at crustal and upper mantle conditions (up to 4 GPa and 2000 K). The new data on felsic-intermediate melts has been combined with in situ data on (ultra)mafic systems and ambient pressure dilatometry and sound velocity data to calibrate a continuous, predictive density model for hydrous and CO2-bearing silicate melts with applications to magmatic processes down to the conditions of the mantle transition zone (up to 2773 K and 22 GPa). The calibration dataset consist of more than 370 density measurements on high-pressure and/or water-and CO2-bearing melts and it is formulated in terms of the partial molar properties of the oxide components. The model predicts the density of volatile-bearing liquids to within 42 kg/m3 in the calibration interval and the model extrapolations up to 3000 K and 100 GPa are in good agreement with results from ab initio calculations. The density model has been applied to examine the mineral-melt buoyancy relations at depth and the implications of these results for the dynamics of magma chambers, crystal settling and the stability and mobility of magmas in the upper mantle will be discussed.

Transport properties of carbonated silicate melt at high pressure

PubMed Central

Ghosh, Dipta B.; Karki, Bijaya B.

2017-01-01

Carbon dioxide, generally considered as the second most abundant volatile component in silicate magmas, is expected to significantly influence various melt properties. In particular, our knowledge about its dynamical effects is lacking over most of Earth’s mantle pressure regime. Here, we report the first-principles molecular dynamics results on the transport properties of carbonated MgSiO3 liquid under conditions of mantle relevance. They show that dissolved CO2 systematically enhances the diffusion rates of all elements and lowers the melt viscosity on average by factors of 1.5 to 3 over the pressure range considered. It is remarkable that CO2 has very little or no influence on the electrical conductivity of the silicate melt under most conditions. Simulations also predict anomalous dynamical behavior, increasing diffusivity and conductivity and decreasing viscosity with compression in the low-pressure regime. This anomaly and the concomitant increase of pressure and temperature with depth together make these transport coefficients vary modestly over extended portions of the mantle regime. It is possible that the melt electrical conductivity under conditions corresponding to the 410- and 660-km seismic discontinuities is at a detectable level by electromagnetic sounding observation. In addition, the low melt viscosity values of 0.2 to 0.5 Pa⋅s at these depths and near the core-mantle boundary may imply high mobility of possible melts in these regions. PMID:29226244

The opportunity of silicate product manufacturing with simultaneous pig iron reduction from slag technogenic formations

NASA Astrophysics Data System (ADS)

Sheshukov, O. Yu.; Lobanov, D. A.; Mikheenkov, M. A.; Nekrasov, I. V.; Egiazaryan, D. K.

2017-09-01

There are two main kinds of slag in modern steelmaking industry: the electric arc furnace slag (EAF slag) and ladle furnace slag (LF slag). The all known slag processing schemes provide the iron-containing component reduction while silicate component stays unprocessed. On the contrary, the silicate processing schemes doesn't provide the utilization of the iron-containing component. The present-day situation doesn't solve the problem of total slag utilization. The aim of this work is to investigate the opportunity of silicate product obtaining with simultaneous pig iron reduction from EAF and LF slags. The tests are conducted by the method of simplex-lattice design. The test samples are heated and melted under reductive conditions, slowly cooled and then analyzed by XRD methods. The experiment results prove the opportunity: the Portland clinker and pig iron can be simultaneously produced on the basis of these slags with a limestone addition.

Metamorphic reactions in mesosiderites - Origin of abundant phosphate and silica

NASA Technical Reports Server (NTRS)

Harlow, G. E.; Delaney, J. S.; Prinz, M.; Nehru, C. E.

1982-01-01

In light of a study of the Emery mesosiderite, it is determined that the high modal abundances of merrillite and tridymite in most mesosiderites are attributable to redox reactions between silicates and P-bearing Fe-Ni metal within a limited T-fO2 range at low pressure. The recalculated amounts of dissolved P and S in the metallic portion of Emery reduce the metal liquidus temperature to less than 1350 C, and the solidus to less than 800 C, so that the mixing of liquid metal with cold silicates would have resulted in silicate metamorphism rather than melting. This redox reaction and redistribution of components between metal and silicates illuminates the complexities of mesosiderite processing, with a view to the recalculation of their original components.

Understanding Vesuvius magmatic processes: Evidence from primitive silicate-melt inclusions in medieval scoria clinopyroxenes (Terzigno formation)

USGS Publications Warehouse

Lima, A.; Belkin, H.E.; Torok, K.

1999-01-01

Microthermometric investigations of silicate-melt inclusions and electron microprobe analyses were conducted on experimentally homogenized silicate-melt inclusions and on the host clinopyroxenes from 4 scoria samples of different layers from the Mt. Somma-Vesuvius medieval eruption (Formazione di Terzigno, 893 A.D.). The temperature of homogenization, considered the minimum trapping temperature, ranges from 1190 to 1260??5 ??C for all clinopyroxene-hosted silicate melt inclusions. The major and minor-element compositional trends shown by Terzigno scoria and matrix glass chemical analysis are largely compatible with fractional crystallization of clinopyroxene and Fe-Ti oxides. Sulfur contents of the homogenized silicate-melt inclusions in clinopyroxene phenocrysts compared with that in the host scoria show that S has been significantly degassed in the erupted products; whereas, Cl has about the same abundance in the inclusions and in host scoria. Fluorine is low (infrequently up to 800 ppm) in the silicate-melt inclusions compared to 2400 ppm in the bulk scoria. Electron microprobe analyses of silicate-melt inclusions show that they have primitive magma compositions (Mg# = 75-91). The composition of the host clinopyroxene phenocrysts varies from typical plinian-related (Mg#???85) to non-plinian related (Mg#???85). The mixed source of the host clinopyroxenes and primitive nature of the silicate-melt inclusions implies that these phenocrysts, in part, may be residual and/or have a polygenetic origin. The similar variation trends of major and minor-elements between homogenized silicate-melt inclusions from the Terzigno scoria, and silicate-melt inclusions in olivine and diopside phenocrysts from plinian eruptions (Marianelli et al., 1995) suggest that the trapped inclusions represent melts similar to those that supplied the plinian and sub-plinian magma chambers. These geochemical characteristics suggest that the Vesuvius magmatic system retained a vestige of the most recent plinian event.

Imaging the Mount St. Helens Magmatic Systems using Magnetotellurics

NASA Astrophysics Data System (ADS)

Hill, G. J.; Caldwell, T. G.; Heise, W.; Bibby, H. M.; Chertkoff, D. G.; Burgess, M. K.; Cull, J. P.; Cas, R. A.

2009-05-01

A detailed magnetotelluric survey of Mount St. Helens shows that a conduit like zone of high electrical conductivity beneath the volcano is connected to a larger zone of high conductivity at 15 km depth that extends eastward to Mount Adams. We interpret this zone to be a region of connected melt that acts as the reservoir for the silicic magma being extruded at the time of the magnetotelluric survey. This interpretation is consistent with a mid-crustal origin for the silicic component of the Mount St. Helens' magmas and provides an elegant explanation for a previously unexplained feature of the seismicity observed at the time of the catastrophic eruption in 1980. This zone of high mid-crustal conductivity extends northwards to near Mount Rainier suggesting a single region of connected melt comparable in size to the largest silicic volcanic systems known.

Uranium, thorium and REE partitioning into sulfide liquids at high pressure and high temperature: Implications for reduced, S-rich planetary bodies

NASA Astrophysics Data System (ADS)

Wohlers, A.; Wood, B. J.

2017-12-01

Based on models of the young solar nebula it is likely that the inner planets went through an early reduced phase of accretion with high metal/silicate ratio and low volatile element contents. Mercury is an existing example of a large planetary embryo with these characteristics but also with a very high S content. In order to investigate the geochemical evolution of Mercury-like bodies we experimentally determined the partitioning of lithophile elements (U, Th, Eu, Sm, Nd, Zr, La, Ce, Yb) between sulfide liquid, low-S metals and silicate melt at 1.5 GPa and 1400-2100˚C. Our results, when combined with those of Wohlers and Wood (2015) show that under highly reducing conditions (FeOsilicate<1wt%) U, Sm, Nd and other lithophile elements partition strongly into FeS liquids relative to silicate melts. The dependences of D's on the FeS contents of the metal and FeO contents of the silicate may be understood in terms of exchange reactions: UO2 + 2FeS = 2FeO + US2silicate sulfide silicate sulfideHigh concentrations of FeSmetal and low FeO contents of the silicate melts drive the reaction to the right, yielding high US2 in the sulfide and high DU. A second effect which raises DU (and other lithophile D's) is the S content of the silicate melt. The latter increases rapidly at low FeO contents and reaches 11wt %. This greatly reduces the activity coefficient of FeO, displacing the reaction further to the right. At 1.5GPa and 1400˚C we obtain sulfide-silicate partitioning with DNd/DSm 1.4 and DTh 0.1DU. As temperature increases to 2100˚C, DNd/DSm declines to 1.0 and DTh/DU increases to 0.3. We estimated the effects of accreting a reduced sulfur-rich component (with FeS core) added to early Earth. The results at 1400˚C imply the possibility of a significant ( 11ppm) 142Nd anomaly in silicate Earth and the addition of >8 ppb U to the core, but require an unreasonably high Th/U of silicate Earth (4.54). Results at 2100˚C lead to a 142Nd anomaly of 0 but addition of such a reduced sulfur-rich body could add up to 10 ppb of U to the core, together with 21 ppb Th. This combination would generate 3 TW of the energy required for the geodynamo. In this case, the Th/U ratio of silicate Earth would be 4.3, within the range of some estimates. Wohlers A. & Wood B.J. (2015) A Mercury-like component of early Earth yield uranium in the core and high mantle Nd142. Nature 520, 337-340

Partitioning of carbon between Fe-rich alloy melt and silicate melt in a magma ocean - Implications for the abundance and origin of volatiles in Earth, Mars, and the Moon

NASA Astrophysics Data System (ADS)

Chi, Han; Dasgupta, Rajdeep; Duncan, Megan S.; Shimizu, Nobumichi

2014-08-01

The budget and origin of carbon in Earth and other terrestrial planets are debated and one of the key unknowns is the fate of carbon during early planetary processes including accretion, core formation, and magma ocean (MO) crystallization. Here we determine, experimentally, the solubility of carbon in coexisting Fe-Ni alloy melt and basaltic silicate melt in shallow MO conditions, i.e., at 1-3 GPa, 1500-1800 °C. Oxygen fugacity of the experiments, estimated based on Fe (in metallic alloy melt)-FeO (in silicate melt) equilibrium, varied between ∼IW-0.4 and IW-1.0, where IW refers to the oxygen fugacity imposed by the coexistence of iron and wüstite. Four different starting mixes, each with 7:3 silicate:metal mass ratio and silicate melt NBO/T (estimated proportion of non-bridging oxygen with respect to tetrahedral cations; NBO/T=2×/total OT -4, where T = Si + Ti + Al + Cr + P) ranging from 0.81 to 1.54 were studied. Concentrations of carbon in the alloy melt were determined using electron microprobe whereas carbon contents of quenched basaltic glasses were determined using secondary ionization mass spectrometry (SIMS). Identification of carbon and hydrogen-bearing species in silicate glasses was performed using Raman and Fourier Transformed Infrared (FTIR) spectroscopy. Our results show that carbon in the metallic melt varies between 4.4 wt.% and 7.4 wt.% and increases with increasing temperature and modestly with increasing pressure but decreases with increasing Ni content of the alloy melt. Carbon concentration in the silicate melts, on the other hand, varies from 11 ± 1 ppm to 111 ± 7 ppm and is negatively correlated with pressure but positively correlated with temperature, the NBO/T, the oxygen fugacity and the water content of the silicate melts. Raman and FTIR results show that at our experimental conditions, carbon in silicate melt is dissolved both as hydrogenated species and CO32-. The calculated carbon partition coefficient DCmetal/silicate varies from 510 ± 53 to 5369 ± 217 and varies systematically as a function of P, T, fO2, water content, the composition of the silicate melt (expressed using NBO/T), and Ni content of alloy melt (XNi). The range of DCmetal/silicate measured in our study with carbonated and hydrogenated carbon species in silicate melt is similar to that reported in the literature for experiments where carbonyl complexes are the chief carbon species in silicate melts. A parameterization was derived using the data from this and existing studies such as lnDCmetal/silicate=a/T+b·P/T+c·ln(fO2)+d·(NBO/T)+e·ln(1-XNi)+f where a = -33,510, b = 1357, c = -0.596, d = -1.182, e = 4.15, f = 13.38, the temperature is in Kelvin, and the pressure is in gigapascal. Using this parameterization and the estimated conditions for the base of the MOs, the average DCmetal/silicate value for Earth, Mars, and the Moon can be predicted. The deep MO of Earth is predicted to cause the strongest depletion of its silicate carbon budget, closely followed by Mars with intermediate depth MO, and then the Moon with a shallow MO. We predict that the lunar mantle carbon budget, similar to that of the Earth’s present-day upper mantle, might have been set by equilibrium core-mantle fractionation in MO; whereas for Earth, later processes such as ingassing from a proto-atmosphere and late-stage accretion of volatile-rich material was necessary for delivery of carbon and other volatiles. Finally, the comparison of our measured and predicted value of DCmetal/silicate for terrestrial MO with similar constraints on DNmetal/silicate from the literature suggests that the apparent depletion of nitrogen relative to carbon for the bulk silicate Earth and the Earth’s upper mantle is unlikely to be caused by preferential partitioning of nitrogen to alloy melt during core formation.

Electrochemical Measurement of Activities for NiO, Ru2O3, and ZnO in a Lunar Volcanic Glass Analog

NASA Technical Reports Server (NTRS)

Colson, R. O.; Hendrickson, T. R.; Malum, K. M.; Floden, A. M.

2000-01-01

Differential Pulse Voltammetry is a fast in situ method for measuring component activities in silicate melts. We report methods for confirming equilibrium conditions and activities for oxide components in an Apollo 15 green glass analog composition.

Experimental constraints on mantle metasomatism caused by silicate and carbonate melts

NASA Astrophysics Data System (ADS)

Gervasoni, Fernanda; Klemme, Stephan; Rohrbach, Arno; Grützner, Tobias; Berndt, Jasper

2017-06-01

Metasomatic processes are responsible for many of the heterogeneities found in the upper mantle. To better understand the metasomatism in the lithospheric mantle and to illustrate the differences between metasomatism caused by hydrous silicate and carbonate-rich melts, we performed various interaction experiments: (1) Reactions between hydrous eclogite-derived melts and peridotite at 2.2-2.5 GPa and 900-1000 °C reproduce the metasomatism in the mantle wedge above subduction zones. (2) Reactions between carbonate-rich melts and peridotite at 2.5 GPa and 1050-1000 °C, and at 6 GPa and 1200-1250 °C simulate metasomatism of carbonatite and ultramafic silicate-carbonate melts in different regions of cratonic lithosphere. Our experimental results show that partial melting of hydrous eclogite produces hydrous Si- and Al-rich melts that react with peridotite and form bi-mineralic assemblages of Al-rich orthopyroxene and Mg-rich amphibole. We also found that carbonate-rich melts with different compositions react with peridotite and form new metasomatic wehrlitic mineral assemblages. Metasomatic reactions caused by Ca-rich carbonatite melt consume the primary peridotite and produce large amounts of metasomatic clinopyroxene; on the other hand, metasomatism caused by ultramafic silicate-carbonate melts produces less clinopyroxene. Furthermore, our experiments show that ultramafic silicate-carbonate melts react strongly with peridotite and cause crystallization of large amounts of metasomatic Fe-Ti oxides. The reactions of metasomatic melts with peridotite also change the melt composition. For instance, if the carbonatite melt is not entirely consumed during the metasomatic reactions, its melt composition may change dramatically, generating an alkali-rich carbonated silicate melt that is similar in composition to type I kimberlites.

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions.

PubMed

Bennett, Neil R; Brenan, James M; Fei, Yingwei

2015-06-13

Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from their extraction to the core during terrestrial accretion. Experiments to investigate the partitioning of these elements between metal and silicate melts suggest that the PUM composition is best matched if metal-silicate equilibrium occurred at high pressures and temperatures, in a deep magma ocean environment. The behavior of the most highly siderophile elements (HSEs) during this process however, has remained enigmatic. Silicate run-products from HSE solubility experiments are commonly contaminated by dispersed metal inclusions that hinder the measurement of element concentrations in the melt. The resulting uncertainty over the true solubility and metal-silicate partitioning of these elements has made it difficult to predict their expected depletion in PUM. Recently, several studies have employed changes to the experimental design used for high pressure and temperature solubility experiments in order to suppress the formation of metal inclusions. The addition of Au (Re, Os, Ir, Ru experiments) or elemental Si (Pt experiments) to the sample acts to alter either the geometry or rate of sample reduction respectively, in order to avoid transient metal oversaturation of the silicate melt. This contribution outlines procedures for using the piston-cylinder and multi-anvil apparatus to conduct solubility and metal-silicate partitioning experiments respectively. A protocol is also described for the synthesis of uncontaminated run-products from HSE solubility experiments in which the oxygen fugacity is similar to that during terrestrial core-formation. Time-resolved LA-ICP-MS spectra are presented as evidence for the absence of metal-inclusions in run-products from earlier studies, and also confirm that the technique may be extended to investigate Ru. Examples are also given of how these data may be applied.

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

PubMed Central

Bennett, Neil R.; Brenan, James M.; Fei, Yingwei

2015-01-01

Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from their extraction to the core during terrestrial accretion. Experiments to investigate the partitioning of these elements between metal and silicate melts suggest that the PUM composition is best matched if metal-silicate equilibrium occurred at high pressures and temperatures, in a deep magma ocean environment. The behavior of the most highly siderophile elements (HSEs) during this process however, has remained enigmatic. Silicate run-products from HSE solubility experiments are commonly contaminated by dispersed metal inclusions that hinder the measurement of element concentrations in the melt. The resulting uncertainty over the true solubility and metal-silicate partitioning of these elements has made it difficult to predict their expected depletion in PUM. Recently, several studies have employed changes to the experimental design used for high pressure and temperature solubility experiments in order to suppress the formation of metal inclusions. The addition of Au (Re, Os, Ir, Ru experiments) or elemental Si (Pt experiments) to the sample acts to alter either the geometry or rate of sample reduction respectively, in order to avoid transient metal oversaturation of the silicate melt. This contribution outlines procedures for using the piston-cylinder and multi-anvil apparatus to conduct solubility and metal-silicate partitioning experiments respectively. A protocol is also described for the synthesis of uncontaminated run-products from HSE solubility experiments in which the oxygen fugacity is similar to that during terrestrial core-formation. Time-resolved LA-ICP-MS spectra are presented as evidence for the absence of metal-inclusions in run-products from earlier studies, and also confirm that the technique may be extended to investigate Ru. Examples are also given of how these data may be applied. PMID:26132380

Preliminary results of sulfide melt/silicate wetting experiments in a partially melted ordinary chondrite

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1994-01-01

Recently, mechanisms for core formation in planetary bodies have received considerable attention. Most current theories emphasize the need for large degrees of silicate partial melting to facilitate the coalescence and sinking of sulfide-metal liquid blebs through a low strength semi-crystalline silicate mush. This scenario is based upon observations that sulfide-metal liquid tends to form circular blebs in partially molten meteorites during laboratory experiments. However, recent experimental work by Herpfer and Larimer indicates that some sulfide-Fe liquids have wetting angles at and slightly below 60 deg in an olivine aggregate, implying an interconnected melt structure at any melt fraction. Such melt interconnectivity provides a means for gravitational compaction and extraction of the majority of a sulfide liquid phase in small planetary bodies without invoking large degrees of silicate partial melting. Because of the important ramifications of these results, we conducted a series of experiments using H-chondrite starting material in order to evaluate sulfide-liquid/silicate wetting behavior in a more complex natural system.

Multi-stage mixing in subduction zone: Application to Merapi volcano, Indonesia

NASA Astrophysics Data System (ADS)

Debaille, V.; Doucelance, R.; Weis, D.; Schiano, P.

2003-04-01

Basalts sampling subduction zone volcanism (IAB) often show binary mixing relationship in classical Sr-Nd, Pb-Pb, Sr-Pb isotopic diagrams, generally interpreted as reflecting the involvement of two components in their source. However, several authors have highlighted the presence of minimum three components in such a geodynamical context: mantle wedge, subducted and altered oceanic crust and subducted sediments. The overlying continental crust can also contribute by contamination and assimilation in magma chambers and/or during magma ascent. Here we present a multi-stage model to obtain a two end-member mixing from three components (mantle wedge, altered oceanic crust and sediments). The first stage of the model considers the metasomatism of the mantle wedge by fluids and/or melts released by subducted materials (altered oceanic crust and associated sediments), considering mobility and partition coefficient of trace elements in hydrated fluids and silicate melts. This results in the generation of two distinct end-members, reducing the number of components (mantle wedge, oceanic crust, sediments) from three to two. The second stage of the model concerns the binary mixing of the two end-members thus defined: mantle wedge metasomatized by slab-derived fluids and mantle wedge metasomatized by sediment-derived fluids. This model has been applied on a new isotopic data set (Sr, Nd and Pb, analyzed by TIMS and MC-ICP-MS) of Merapi volcano (Java island, Indonesia). Previous studies have suggested three distinct components in the source of indonesian lavas: mantle wedge, subducted sediments and altered oceanic crust. Moreover, it has been shown that crustal contamination does not significantly affect isotopic ratios of lavas. The multi-stage model proposed here is able to reproduce the binary mixing observed in lavas of Merapi, and a set of numerical values of bulk partition coefficient is given that accounts for the genesis of lavas.

Core segregation mechanism and compositional evolution of terretrial planets

NASA Astrophysics Data System (ADS)

Petford, N.; Rushmer, T.

2009-04-01

A singular event in the formation of the earth and terrestrial planets was the separation iron-rich melt from mantle silicate to form planetary cores. On Earth, and by implication other rocky planets, this process induced profound internal chemical fractionation, with siderophile elements (Ni, Co, Au, Pt, W, Re) following Fe into the core, leaving the silicate crust and mantle with strong depletions of these elements relative to primitive planetary material. Recent measurements of radiogenic 182W anomalies in the silicate Earth, Mars and differentiated meteorites imply that planetesimals segregated metallic cores within a few Myr of the origin of the solar system. Various models have been put forward to explain the physical nature of the segregation mechanism (Fe-diapirs, ‘raining' through a magma ocean), and more recently melt flow via fractures. In this contribution we present the initial results of a numerical study into Fe segregation in a deforming silicate matrix that captures the temperature-dependent effect of liquid metal viscosity on the transport rate. Flow is driven by pressure gradients associated with impact deformation in a growing planetesimal and the fracture geometry is constrained by experimental data on naturally deformed H6 chondrite. Early results suggest that under dynamic conditions, fracture-driven melt flow can in principle be extremely rapid, leading to a significant draining of the Fe-liquid metal and siderophile trace element component on a timescale of hours to days. Fluid transport in planetesimals where deformation is the driving force provides an attractive and simple way of segregating Fe from host silicate as both precursor and primary agent of core formation. The potential for flow of metal-rich melt to induce local magnetic anomalies will also be addressed.

Study of diffusion and local structure of sodium-silicate liquid: the molecular dynamic simulation

NASA Astrophysics Data System (ADS)

Hung, Pham Khac; Noritake, Fumiya; San, Luyen Thi; Van, To Ba; Vinh, Le The

2017-10-01

A systematic analysis on sodium-silicate melt with various silica contents was carried out. The simulation revealed two diffusion mechanisms occurred in the melt: the bond-breaking and hopping between sites. The local structure was analyzed through T-simplexes. It was revealed that T-clusters have a non-spherical shape and represent the diffusion channel, in which Na atoms are dominant, but no any O atoms are located. The SiO2-poor melt acquires a long channel. In contrast, the SiO2-rich melt consists of unconnected short channels. The simulation also revealed the immobile and mobile regions which differ in local structure and constituent composition. We propose a new CL-function to characterizing the spatial distribution of different atom component. The spatial distribution of mobile and immobile atoms is found quite different. In particular, the immobile atoms are concentrated in high-density regions possessing very large density of immobile atoms. The spatial distribution of mobile atoms in contrast is more homogeneous.

Inclusions of Sulphide Immiscible Melts in Primitive Olivine Phenocrysts from Mantle-Derived Magmas; Preliminary Results

NASA Astrophysics Data System (ADS)

Danyushevsky, L.; Ryan, C.; Kamenetsky, V.; Crawford, A.

2001-12-01

Sulphide inclusions have been identified in olivine phenocrysts (and in one case in a spinel phenocryst) in primitive volcanic rocks from mid- ocean ridges, subduction-related island arcs and backarc basins. These inclusions represent droplets of an immiscible sulphide melt and are trapped by olivine crystals growing from silicate melts. Sulphide melt is usually trapped as separate inclusions, however combined inclusions of sulphide and silicate melts have also been observed. Sulphide inclusions have rounded shapes and vary in size from several up to 100 microns in diameter. At room temperature sulphide inclusions consist of several phases. These phases are formed as a result of crystallisation of the sulphide melt after it was trapped. Crystallisation occurs due to decreasing temperature in the magma chamber after trapping and/or when magma ascents from the magma chamber during eruptions. In all studied sulphides three different phases can be identified: a high- Fe, low-Ni, low-Cu phase; a high-Fe, high-Ni, low-Cu phase; and high-Fe, low-Ni, high-Cu phase. Low-Cu phases appear to be monomineralic, whereas the high-Cu phase is usually composed of a fine intergrowth of high- and low-Cu phases, resembling the quench 'spinifex' structure. Fe, Ni and Cu are the major elements in all sulphides studied. The amount of Ni decreases with decreasing forsterite content of the host olivine phenocryst, which is an index of the degree of silicate magma fractionation. Since Ni content of the silicate magma is decreasing during fractionation, this indicates either that the immiscible sulfide melt remains in equilibrium with the silicate melt continuously changing its composition during fractionation, or that the sulfide melt is continuously separated from the silicate melt during fractionation, with later formed droplets having lower Ni content due to the lower Ni content of the evolved, stronger fractionated silicate melt. Trace element contents of the sulfide inclusions have been analysed on the proton microprobe at CSIRO in Sydney. The main trace elements in the sulfide inclusions are Zn, Pb, Ag, and Se. Other trace elements are below detection limits, which are normally at a level of several ppm. Zn concentrations (120 +/- 40 ppm) in sulphides are similar to those in silicate melts. This indicates that separation of the sulfide melt does not affect Zn contents of silicate melts. On the contrary, Ag (30 +/- 10 ppm) and Pb (40 +/- 10 ppm) contents in sulphides are at least in order of magnitude higher than in the silicate melt, and thus separation of the immiscible sulfide melt can significantly decrease Pb and Ag contents of the silicate magma. The widespread occurrence of sulfide inclusions, which were also described in olivine phenocrysts from ocean island basalts, indicates common saturation at low pressure of mantle-derived magmas with reduced sulfur.

The distribution of chromium among orthopyroxene, spinel and silicate liquid at atmospheric pressure

NASA Technical Reports Server (NTRS)

Barnes, S. J.

1986-01-01

The Cr distributions for a synthetic silicate melt equilibrated with bronzitic orthopyroxene and chromite spinel between 1334 and 1151 C over a range of oxygen fugacities between the nickel-nickel oxide and iron-wuestite buffers are studied. The occurrence, chemical composition, and structure of the orthopyroxene-silicate melt and the spinel-silicate melt are described. It is observed that the Cr content between bronzite and the melt increases with falling temperature along a given oxygen buffer and decreases with falling oxygen fugacity at a given temperature; however, the Cr content of the melt in equilibrium with spinel decreases with falling temperature and increases with lower oxygen fugacity.

Impact-melt origin for the Simondium, Pinnaroo, and Hainholz mesosiderites: implicatiions for impact processes beyond the Earth--Moon system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Floran, R J; Caulfield, J B.D.; Harlow, G E

The Simondium, Pinnaroo, and Hainholz mesosiderites are interpreted to be clast-laden impact melts that crystallized from immiscible silicate, metallic (Fe-FeS) liquids. The existence of silicate melts is shown by intergranular basaltic textures. Metallic melts are inferred on the basis of smooth boundaries between metal and troilite and the occurrence of troilite as anastomosing areas that radiate outward into the silicate fractions. These relations suggest that troilite crystallized after silicates, concentrating as a late-stage residuum. Evidence for impact melting includes: diversity and abundance of clast types (mineral, metal, lithic) in various stages of recrystallization and assimilation; differences in mineral chemistries betweenmore » clasts and igneous-textured matrix silicates; unusual metal plus silicate bulk composition. Silicate clasts consist primarily of orthopyroxene and minor olivine with a range of Fe/Fe + Mg ratios, anorthitic plagioclase, and rare orthopyroxenite (diogenite) fragments. Substantial amounts of Fe-Ni metal were melted during the impact events and minor amounts were incorporated into the melts as clasts. The clast populations suggest that at least four rock types were melted and mixed: (a) diogenite, (b) a plagioclase-rich source, possibly cumulate eucrite, (c) dunite, and (d) metal. Most orthopyroxene appears to have been derived from fragmentation of diogenites. Orthopyroxene (En/sub 82-61/) and olivine (Fo/sub 86-67/) clasts include much material unsampled as individual meteorites and probably represent a variety of source rocks.« less

Seismic perspectives from the western U.S. on the evolution of magma reservoirs underlying major silicic eruptions

NASA Astrophysics Data System (ADS)

Schmandt, B.; Huang, H. H.; Farrell, J.; Hansen, S. M.; Jiang, C.

2017-12-01

The western U.S. Cordillera has hosted widespread magmatic activity since the Eocene including ≥1,000 km3 silicic eruptions since 1 Ma. A review of recent seismic constraints on relatively young (≤1.1 Ma) and old (Oligocene) magmatic systems provides insight into the heterogeneity among these systems and their temporal evolution. Local seismic data vary widely but all of these systems are covered by the USArray's 70-km spacing. Among 3 young systems with ≥300 km3 silicic eruptions (Yellowstone - 0.64 Ma; Long Valley - 0.76 Ma; Valles - 1.1 Ma) only Yellowstone shows sufficiently low seismic velocities to require partial melt in the upper crust at scales visible with USArray data. Finer-scale arrays refine the shape of large (>1,000 km3) partially molten volumes in the upper and lower crust at Yellowstone, and similar studies at Long Valley and Valles indicate much smaller volumes of partial melt. Notably, Long Valley Caldera is seismically active in the upper and lower crust, has a high flux of CO2 degassing, and multi-year geodetic transients consistent with an inflating upper crustal reservoir of 2-4 km radius (compared to 20x50x5 km at Yellowstone). Upper mantle seismic imaging finds strong low velocity anomalies that require some partial melt beneath Yellowstone and Long Valley, but more ambiguous results beneath Valles. Thus, the structures of the three young large-volume silicic systems are highly variable suggesting that large reservoirs of melt in the upper crust are short-lived with respect to the ≤1.1 Ma since the last major eruption, consistent with recent inferences from geochemically constrained thermal histories of erupted crystals. Among long-extinct silicic systems, most were severely overprinted by extensional deformation. The San Juan and Mogollon Datil are exceptions with only modest deformation. These systems show low-to-average velocity crust down to a sharp Moho and relatively thin crust for their elevations. Both are consistent with a felsic to intermediate crustal column, suggesting that mafic cumulates required to produce silicic magma from basaltic inputs are not present in large quantities (>5 km layers). We infer that post-eruption foundering of mafic cumulates into the mantle occurred and was not followed by another major episode of basaltic melt input.

Structure of Oxide Glass and Melts at High-Pressure: A View from Inelastic X-ray Scattering and 2D Solid-State NMR

NASA Astrophysics Data System (ADS)

Lee, S.; Mysen, B. O.; Fei, Y.; Cody, G. D.; Mao, H.; Eng, P.

2006-12-01

Full understanding of the atomic arrangement of oxides glasses and melts both at ambient and high-pressure has long been one of the fundamental and yet difficult problems in earth sciences, condensed matter physics as well as glass sciences. The structures of archetypal oxide glasses (e.g. SiO2 and B2O3) as well as complex silicate glasses (ternary and quaternary aluminosilicate glasses) at high pressure are essential to elucidate origins of anomalous macroscopic properties of melts and global geophysical processes in the Earth's interior. Recent progress in inelastic x-ray scattering (IXS) with high brilliance 3rd generation synchrotron x-rays combined with DAC techniques allows us to explore pressure-induced changes in the bonding nature of archetypal amorphous oxide, illustrating a new opportunity to study amorphous oxides with IXS (Lee SK et al. Nature Materials 2005, 4, p851). 2 dimensional solid-state NMR have offered much improved resolution over conventional 1D NMR, unveiling previously unknown structural details of amorphous silicates at high pressure (Lee SK. Geochim. Cosmochim. Acta 2005, 69, p3695; J. Phys. Chem. B. 2006, 110, p16408) Here, we report the synchrotron inelastic x-ray scattering results (oxygen and boron K-edge) for divers oxide glasses at pressure up to 40 GPa, revealing the nature of pressure-induced bonding changes and the structure. Direct in-situ measurements provide evidence for a continuous transformation with multiple densification mechanisms. 2D solid-state NMR spectra for silicate and germinate glasses shows detailed information about extent of disorder among framework units at high pressure. The chemical ordering among framework units leads to the formation of ^{[5,6]}Si-O-^{[4]}Si in silicates and ^{[5,6]}Al-O-^{[4]}Si in aluminosilicates. Whereas the densification mechanism can be dependent on the chemical composition and the fraction of non-bridging oxygen, the pressure dependence of both simple and complex multi-component silicate glasses showed similar characteristics: low pressure regime was marked with topological variation without coordination transformation and inter-mediate pressure region (about 5-10 GPa) was characterized by the largest (d(^{[4]}B or ^{[5,6]}Si)/dP) value. Finally high-pressure regime (above 10 GPa) was characterized by a larger energy penalty for coordination transformation than in intermediate pressure regime. These results provide improved prospect for the bonding nature of amorphous materials at high pressure using synchrotron inelastic x-ray scattering and 2D NMR and aid in understanding the microscopic origins of the properties of melts and geological processes in the Earth's interior.

Crystallization and Cooling of a Deep Silicate Magma Ocean

NASA Astrophysics Data System (ADS)

Wolf, A. S.; Bower, D. J.

2015-12-01

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 crystallized (e.g. Nakajima and Stevenson, 2015). Understanding the cooling process is critical to determining magma ocean lifetimes and recognizing possible remnant signatures of the magma ocean in present-day mantle heterogeneities (i.e. Labrosse et al., 2007). Modeling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (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 captures 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 (important for multi-component systems). We derive a new high P-T equation of state (EOS) formulation designed to capture the energetics and physical properties of the partially molten system using parameters that are readily interpreted in the context of magma ocean crystallization. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS (e.g., Mosenfelder et al., 2009; Stixrude et al., 2009).

Sulfur Saturation Limits in Silicate Melts and their Implications for Core Formation Scenarios for Terrestrial Planets

NASA Technical Reports Server (NTRS)

Holzheid, Astrid; Grove, Timothy L.

2002-01-01

This study explores the controls of temperature, pressure, and silicate melt composition on S solubility in silicate liquids. The solubility of S in FeO-containing silicate melts in equilibrium with metal sulfide increases significantly with increasing temperature but decreases with increasing pressure. The silicate melt structure also exercises a control on S solubility. Increasing the degree of polymerization of the silicate melt structure lowers the S solubility in the silicate liquid. The new set of experimental data is used to expand the model of Mavrogenes and O'Neill(1999) for S solubility in silicate liquids by incorporating the influence of the silicate melt structure. The expected S solubility in the ascending magma is calculated using the expanded model. Because the negative pressure dependence of S solubility is more influential than the positive temperature dependence, decompression and adiabatic ascent of a formerly S-saturated silicate magma will lead to S undersaturation. A primitive magma that is S-saturated in its source region will, therefore, become S-undersaturated as it ascends to shallower depth. In order to precipitate magmatic sulfides, the magma must first cool and undergo fractional crystallization to reach S saturation. The S content in a metallic liquid that is in equilibrium with a magma ocean that contains approx. 200 ppm S (i.e., Earth's bulk mantle S content) ranges from 5.5 to 12 wt% S. This range of S values encompasses the amount of S (9 to 12 wt%) that would be present in the outer core if S is the light element. Thus, the Earth's proto-mantle could be in equilibrium (in terms of the preserved S abundance) with a core-forming metallic phase.

Lunar and Planetary Science XXXV: Terrestrial Planets: Building Blocks and Differentiation

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Terrestrial Planets: Building Blocks and Differentiation: included the following topics:Magnesium Isotopes in the Earth, Moon, Mars, and Pallasite Parent Body: High-Precision Analysis of Olivine by Laser-Ablation Multi-Collector ICPMS; Meteoritic Constraints on Collision Rates in the Primordial Asteroid Belt and Its Origin; New Constraints on the Origin of the Highly Siderophile Elements in the Earth's Upper Mantle; Further Lu-Hf and Sm-Nd Isotopic Data on Planetary Materials and Consequences for Planetary Differentiation; A Deep Lunar Magma Ocean Based on Neodymium, Strontium and Hafnium Isotope Mass Balance Partial Resetting on Hf-W System by Giant Impacts; On the Problem of Metal-Silicate Equilibration During Planet Formation: Significance for Hf-W Chronometry ; Solid Metal-Liquid Metal Partitioning of Pt, Re, and Os: The Effect of Carbon; Siderophile Element Abundances in Fe-S-Ni-O Melts Segregated from Partially Molten Ordinary Chondrite Under Dynamic Conditions; Activity Coefficients of Silicon in Iron-Nickel Alloys: Experimental Determination and Relevance for Planetary Differentiation; Reinvestigation of the Ni and Co Metal-Silicate Partitioning; Metal/Silicate Paritioning of P, Ga, and W at High Pressures and Temperatures: Dependence on Silicate Melt Composition; and Closure of the Fe-S-Si Liquid Miscibility Gap at High Pressure and Its Implications for Planetary Core Formation.

Carbonate Mineral Assemblages as Inclusions in Yakutian Diamonds: TEM Verifications

NASA Astrophysics Data System (ADS)

Logvinova, A. M.; Wirth, R.; Sobolev, N. V.; Taylor, L. A.

2014-12-01

Carbonate mineral inclusions are quite rare in diamonds from the upper mantle, but are evidence for a carbonate abundance in the mantle. It is believed that such carbonatitic inclusions originated from high-density fluids (HDFs) that were enclosed in diamond during its growth. Using TEM and EPMA, several kinds of carbonate inclusions have been identified in Yakutian diamonds : aragonite, dolomite, magnesite, Ba-, Sr-, and Fe-rich carbonates. Most of them are represented by multi-phase inclusions of various chemically distinct carbonates, rich in Ca, Mg, and K and associated with minor amounts of silicate, oxide, saline, and volatile phases. Volatiles, leaving some porosity, played a significant role in the diamond growth. A single crystal of aragonite (60μm) is herein reported for the first time. This inclusion is located in the center of a diamond from the Komsomolskaya pipe. Careful CL imaging reveals the total absence of cracks around the aragonite inclusion - i.e., closed system. This inclusion has been identified by X-ray diffraction and microprobe analysis. At temperatures above 1000 0C, aragonite is only stable at high pressures of 5-6 GPa. Inside this aragonite, we observed nanocrystalline inclusions of titanite, Ni-rich sulfide, magnetite, water-bearing Mg-silicate, and fluid bubbles. Dolomite is common in carbonate multi-phase inclusions in diamonds from the Internatsionalnaya, Yubileinaya, and Udachnaya kimberlite pipes. Alluvial diamonds of the northeastern Siberian Platform are divided into two groups based on the composition of HDFs: 1) Mg-rich multi-phase inclusions (60% magnesite + dolomite + Fe-spinel + Ti-silicate + fluid bubbles); and 2) Ca-rich multi-phase inclusions (Ca,Ba-, Ca,Sr-, Ca,Fe-carbonates + Ti-silicate + Ba-apatite + fluid bubbles). High-density fluids also contain K. Volatiles in the fluid bubbles are represented by water, Cl, F, S, CO2, CH4, and heavy hydrocarbons. Origin of the second group of HDFs may be related to the non-silicate carbonatitic melt. We consider the primary hydrous, Сa-rich and Mg-poor carbonate melts as having formed in subducted oceanic crust. Variations of carbonate-inclusion compositions among diamonds indicate the variability in the source media during the formation of diamond and may be the result of metasomatic interaction with host rocks.

Configurational Heat Capacity of Na- and Ca-bearing Aluminosilicate Melts

NASA Astrophysics Data System (ADS)

Webb, S. L.

2006-12-01

The Na2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 systems are used as analogs for the more complex natural magmatic systems of the Earth in studies of the physical properties, structure and flow mechanisms of silicate melts. Although the description of flow in binary alkali-silicate melts is clear; that for multi-oxide compositions quickly becomes very complex. The addition of aluminium to melts creates the need for a charge-balancing cation for the tetrahedrally co-ordinated Al3+. With the presence of both mono- and di-valent ions there are questions about which atom is preferred as the charge balancer and which will create non-bridging oxygens. This study addresses the structure of peraluminous and peralkaline/metaluminous Na2O-CaO-Al2O3-SiO2 melts and the change in structure with composition via determination of their shear viscosity and heat capacity. Viscosity has been determined using the micropenetration technique and the heat capacity and configurational heat capacity have been determined by differential scanning calorimetry. While the viscosity of these melts indicates structural changes at the condition where there are no longer enough Na+ or Ca2+ to charge balance all of the Al3+ in tetrahedral co-ordination, it is the heat capacity data which provides more information about the energy required for flow to occur in the melts as the structure changes due to changing composition. The configurational heat capacity can be determined from the difference between the liquid (cpl) and the glass (cpg) heat capacity at the glass transition temperature. To a first approximation cpg can be calculated from a linear summation of the cps of the oxide components. Similarly, if there are no anomalous changes in melt structure upon heating through Tg, the cpl will be a linear sum of the contributions of the component oxides. Configurational entropy Sconf(Tg) has been calculated from the viscosity data using the Adam-Gibbs equation for viscosity as a function of configurational entropy and temperature. In addition to the change in structure implied from changes in the trends of the viscosity and heat capacity data when there are no longer enough charge balancers for all of the Al3+ in tetrahedral co-ordination, there also appears to be a change in structure at the composition where there are no longer enough Ca2+ in the melt that each Al3+ tetrahedron has its own charge balancer that is the composition at which pairs of Al3+ tetrahedra must share a Ca2+ as charge balancer.

Carbonate-silicate liquid immiscibility upon impact melting, Ries Crater, Germany

NASA Astrophysics Data System (ADS)

Graup, Guenther

1999-05-01

The 24-km-diameter Ries impact crater in southern Germany is one of the most studied impact structures on Earth. The Ries impactor struck a Triassic to Upper Jurassic sedimentary sequence overlying Hercynian crystalline basement. At the time of impact (14.87 +/- 0.36 Ma; Storzer et al., 1995), the 350 m thick Malm limestone was present only to the S and E of the impact site. To the N and W, the Malm had been eroded away, exposing the underlying Dogger and Lias. The largest proportion of shocked target material is in the impact melt-bearing breccia suevite. The suevite had been believed to be derived entirely from the crystalline basement. Calcite in the suevite has been interpreted as a post-impact hydrothermal deposit. From optical inspection of 540 thin sections of suevite from 32 sites, I find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt. Textural evidence of liquid immiscibility between silicate and carbonate melt in the Ries suevite includes: carbonate globules within silicate glass, silicate globules embedded in carbonate, deformable and coalescing carbonate spheres within silicate glass, sharp menisci or cusps and budding between silicate and carbonate melt, fluidal textures and gas vesicles in carbonate schlieren, a quench crystallization sequence of the carbonate, spinifex textured quenched carbonate, separate carbonate spherules in the suevite mineral-fragment-matrix, and inclusions of mineral fragments suspended in carbonate blebs. Given this evidence of liquid immiscibility, the carbonate in the suevite has, therefore, like the silicate melt a primary origin by impact shock melting. Evidence of carbonate-silicate liquid immiscibility is abundant in the suevites to the SW to E of the Ries crater. The rarer suevites to the W to NE of the crater are nearly devoid of carbonate melts. This correspondence between the occurrence of outcropping limestones at the target surface and the formation of carbonate melt, indicates that the Malm limestones are the source rocks of the carbonate impact melt. This correspondence shows that the suevites preserve a compositional memory of their source rocks. From the regional distribution of suevites with or without immiscible carbonate melts, it is inferred that the Ries impactor hit the steep Albtrauf escarpment at its toe, in an oblique impact from the north.

Partitioning of Mo, P and other siderophile elements (Cu, Ga, Sn, Ni, Co, Cr, Mn, V, and W) between metal and silicate melt as a function of temperature and silicate melt composition

NASA Astrophysics Data System (ADS)

Righter, K.; Pando, K. M.; Danielson, L.; Lee, Cin-Ty

2010-03-01

Metal-silicate partition coefficients can provide information about the earliest differentiation histories of terrestrial planets and asteroids. Systematic studies of the effects of key parameters such as temperature and melt composition are lacking for many elements. In particular, data for Mo is scarce, but given its refractory nature, is of great value in interpreting metal-silicate equilibrium. Two series of experiments have been carried out to study Mo and P partitioning between Fe metallic liquid and basaltic to peridotitic silicate melt, at 1 GPa and temperatures between 1500 and 1900 °C. Because the silicate melt utilized was natural basalt, there are also measurable quantities of 9 other siderophile elements (Ni, Co, W, Sn, Cu, Mn, V, Cr, Ga and Zn). The Ni and Co data can be used to assess consistency with previous studies. In addition, the new data also allow a first systematic look at the temperature dependence of Cu, Ga, Sn, Cr, Mn V and W for basaltic to peridotitic melts. Many elements exhibit an increase in siderophile behavior at higher temperature, contrary to popular belief, but consistent with predictions from thermodynamics. Using these new data we examine DMomet/sil and DPmet/sil in detail and show that increasing temperature causes a decrease in the former and an increase in the latter, whereas both increase with MgO content of the silicate melt. The depletions of Mo and P in the mantle of the Earth can be explained by metal-silicate equilibrium at magma ocean conditions — both elements are satisfied at PT conditions of an intermediate depth magma ocean for the Earth 22.5 GPa and 2400 °C.

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

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Mittlefehldt, David W.

2017-01-01

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.

Multiple enrichment of the Carpathian-Pannonian mantle: Pb-Sr-Nd isotope and trace element constraints

NASA Astrophysics Data System (ADS)

Rosenbaum, Jeffrey M.; Wilson, Marjorie; Downes, Hilary

1997-07-01

Pb isotope compositions of acid-leached clinopyroxene and amphibole mineral separates from spinel peridotite mantle xenoliths entrained in Tertiary-Quaternary alkali basalts from the Carpathian-Pannonian Region of eastern Europe provide important constraints on the processes of metasomatic enrichment of the mantle lithosphere in an extensional tectonic setting associated with recent subduction. Principal component analysis of Pb-Sr-Nd isotope and rare earth element compositions of the pyroxenes is used to identify the geochemical characteristics of the original lithospheric mantle protolith and a spectrum of infiltrating metasomatic agents including subduction-related aqueous fluids and silicate melts derived from a subduction-modified mantle wedge which contains a St. Helena-type (HIMU) plume component. The mantle protolith is highly depleted relative to mid-ocean ridge basalt-source mantle with Pb-Nd-Sr isotope compositions consistent with an ancient depletion event. Silicate melt infiltration into the protolith accounts for the primary variance in the Pb-Sr-Nd isotope compositions of the xenoliths and has locally generated metasomatic amphibole. Infiltration of aqueous fluids has introduced radiogenic Pb and Sr without significantly perturbing the rare earth element signature of the protolith. The Pb isotope compositions of the fluid-modified xenoliths suggest that they reacted with aqueous fluids released from a subduction zone which had equilibrated with sediment derived from an ancient basement terrain. We propose a model for mantle lithosphere evolution consistent with available textural and geochemical data for the xenolith population. The Pb-Sr-Nd isotope compositions of both alkaline mafic magmas and rare, subduction-related, calc-alkaline basaltic andesites from the region provide important constraints for the nature of the asthenospheric mantle wedge and confirm the presence of a HIMU plume component. These silicate melts contribute to the metasomatism of the mantle lithosphere rather than being derived therefrom.

Concentrations and behavior of oxygen and oxide ion in melts of composition CaO.MgO.xSiO2

NASA Technical Reports Server (NTRS)

Semkow, K. W.; Haskin, L. A.

1985-01-01

The behavior of oxygen and oxide ion in silicate melts was investigated through their electrochemical reactions at a platinum electrode. Values are given for the diffusion coefficient for molecular oxygen in diopside melt and the activation energy of diffusion. It is shown that molecular oxygen dissociates prior to undergoing reduction and that oxide ion reacts quickly with silicate polymers when it is produced. The concentration of oxide ion is kept low by a buffering effect of the silicate, the exact level being dependent on the silicate composition. Data on the kinetics of reaction of the dissociation of molecular oxygen and on the buffering reactions are provided. It is demonstrated that the data on oxygen in these silicate melts are consistent with those for solid buffers.

Solubilities of nitrogen and noble gases in basalt melt

NASA Technical Reports Server (NTRS)

Miyazaki, A.; Hiyagon, H.; Sugiura, N.

1994-01-01

Nitrogen and noble gases are important tracers in geochemistry and chosmochemistry. Compared to noble gases, however, physicochemical properties of nitrogen, such as solubility in melt or melt/silicate partition, are not well known. Solubility of nitrogen in basalt melt depends on redox condition of the atmosphere. For example, solubility of nitrogen in E chondrite melt under reducing conditions is as high as 2 mol percent at 1500 C, suggesting that nitrogen is chemically dissolved in silicate melts, i.e., being dissolved as free anions or replacing oxygen sites in silicate network. However, the solubility and the dissolution mechanism of nitrogen under oxidizing conditions are not well investigated. To obtain nitrogen solubility in silicate melts under various redox conditions and to understand its mechanism, we are conducting experiments by using (15)N(15)N-labeled nitrogen gas. This makes it easy to distinguish dissolved nitrogen from later contamination of atmospheric nitrogen, and hence enables us to measure the nitrogen solubility accurately. As a preliminary experiment, we have measured solubility of nitrogen in basalt melt under the atmospheric oxygen pressure.

Evidence for the presence of carbonate melt during the formation of cumulates in the Colli Albani Volcanic District, Italy

NASA Astrophysics Data System (ADS)

Shaw, Cliff S. J.

2018-06-01

Fergusite and syenite xenoliths and mafic lapilli from two locations in the Villa Senni ignimbrite of the Colli Albani Volcanic District show evidence for fractionation of a silicate magma that led to exsolution of an immiscible carbonate melt. The fergusite xenoliths are divided into two groups on the basis of their clinopyroxene compositions. Group 1 clinopyroxene records the crystallisation of a silicate melt and enrichment of the melt in Al, Ti and Mn and depletion in Si as well as enrichment in incompatible trace elements. The second group of clinopyroxene compositions (group 2) comes mainly from Ba-F-phlogopite- and Ti-andradite-bearing fergusites. They have significantly higher Si and lower Al and Ti and, like the coexisting phlogopite and garnet are strongly enriched in Mn. The minerals in the fergusites containing group 2 clinopyroxene are enriched in Ba, Sr, Cs, V and Li all of which are expected to partition strongly into a carbonate melt phase relative to the coexisting silicate melt. The compositional data suggest that the group 1 fergusites record sidewall crystallisation of CO2-rich silicate melt and that once the melt reached a critical degree of fractionation, carbonate melt exsolved. The group 2 fergusites record continued crystallisation in this heterogeneous silicate - carbonate melt system. Composite xenoliths of fergusite and thermometamorphic skarn record contact times of hundreds to a few thousand years indicating that fractionation and assimilation was relatively rapid.

Rapid thermal rejuvenation of high-crystallinity magma linked to porphyry copper deposit formation; evidence from the Koloula Porphyry Prospect, Solomon Islands

NASA Astrophysics Data System (ADS)

Tapster, S.; Condon, D. J.; Naden, J.; Noble, S. R.; Petterson, M. G.; Roberts, N. M. W.; Saunders, A. D.; Smith, D. J.

2016-05-01

Magmas containing the components needed to form porphyry copper deposits are relatively common within arcs, yet mineralising events are uncommon within the long-lived magmatic systems that host them. Understanding what causes the transition from barren to productive intrusions is critical to the development of conceptual deposit models. We have constrained the tempo of pre- and syn-mineralisation magmatic events in relationship to the thermal evolution of the plutonic body that underlies one of the world's youngest exposed plutonic-porphyry systems, the Inamumu Zoned Pluton, Koloula Porphyry Prospect, Solomon Islands. High precision ID-TIMS U-Pb dates of texturally and chemically characterised zircons indicate pluton emplacement over <150 kyr was superseded after ca. 50 kyr by two discrete episodes of mineralising porphyritic melt emplacement. Their associated hydrothermal systems initiated within ca. 30 kyrs of each other. Zircon populations within evolved intrusions contain resorbed cores that were recycled from the deeper magmatic system, yet their youngest dates are statistically indistinguishable from those yielded by crystals lacking resorption. Comparisons of Ti-in-zircon proxy temperatures, modelled zircon saturation temperatures and temperature-crystallinity relationships suggest that prior to being heated and emplaced within the shallow level pluton, magmas were stored at depth in a high-crystallinity (>50% crystals) state, past the point of rheological lock-up. We estimate that thermal rejuvenation of the deeper high-crystallinity magma and generation of a mobile melt fraction may have occurred ≤10 kyr before its transport and emplacement within the porphyry environment. The underlying pluton likely cooled and returned to high-crystallinity states prior to subsequent remobilisation-emplacement events. Titanium-in-zircon geothermometry and whole-rock geochemistry suggest pre-mineralisation intrusions were remobilised by mixing of a silicic magma with a high-temperature, less-evolved melt. In contrast, syn-mineralisation melts were most likely remobilised by the percolation of hot volatiles exsolved from contemporaneous less-evolved intrusions cooling beneath the crystalline silicic magma. The evidence for the rapid thermal rejuvenation and long term storage of highly crystalline silicic magmas is consistent with previous studies that indicate two components of exsolved volatiles contribute to ore forming fluids. We conclude that the liberation of crystal-rich porphyry copper deposit forming magmas, and the addition of the chemical components required for ore formation, are intrinsically linked to the volatiles released during the recharge of less-evolved melt into a highly crystalline silicic magma.

Experimental Investigation on the Topotaxy of Sulfide and Silicate Melts in Peridotite: Implications for the Origin of PGE-depleted Cu-Ni Sulfide Deposit

NASA Astrophysics Data System (ADS)

Wang, Z.; Zhang, J.; Jin, Z.

2016-12-01

Cu-Ni sulfide deposit is generally considered partial melt originated from the mantle which is usually PGE-enriched. However, the largest Cu-Ni sulfide deposits of China (the Jinchuan Cu-Ni deposit) is PGE-depleted. Comparing to silicate melt, the nature and topotaxy of sulfide melt have remained poorly understood. Here we report experimental investigation on the topotaxy of sulfide and silicate melts in peridotite using a piston-cylinder press and a 5GPa Griggs-type deformation apparatus. The starting material consists of polycrystalline olivine or pyrolite and 1 wt% Fe-Ni-Cu sulfide. Hydrostatic and deformation experiments were conducted at a pressure of 1.5 GPa and a temperature of 1250°. Under hydrostatic conditions, our results reveal that the apparent dihedral angle of sulfide melt in an olivine matrix( 96°) is much larger than that of silicate + sulfide melt in pyrolite(<60°) under hydrostatic conditions. The sulfide melt pockets appear mostly as blobs in triple junctions with an immiscible Ni-poor center surrounded by a Ni-rich layer. Under deformation conditions, olivine develops pronounced fabrics with the pole of the (010) forming high concentrations approximately normal to the foliation plane and the [100] axes forming a girdle in the foliation plane. EBSD phase mapping analyses reveal strong shape preferred orientations (SPO) of sulfide +silicate melt in the 45, 90, 135 degree directions for deformation experiments indicating complete wetting of grain boundaries and forming a favorable source for ore deposits. Deformation also causes mixing of the Ni-rich and the Ni-poor sulfide melts. As the platinum-group elements(PGE) prefer to concentrate in the Ni-rich sulfide melt at high temperatures, our results suggest that the metallogenetic source of the PGE-depleted Cu-Ni deposits may have formed under relatively intense deformation and low temperatures with a small fraction of mixed sulfide and silicate melts.

Si and O partitioning between core metal and lower mantle minerals during core formation

NASA Astrophysics Data System (ADS)

Nakajima, Y.; Frost, D. J.; Rubie, D. C.

2010-12-01

In addition to Fe and Ni, the Earth’s core contains light alloying elements (e.g., H, C, O, Si, and/or S) in order to explain the 10% core density deficit (e.g., Birch, 1964, JGR). Experimental data on the partitioning behavior of siderophile elements such as Ni and Co between liquid Fe and mantle minerals indicate that equilibration between core-forming metal and a silicate magma ocean likely occurred at lower-mantle pressures (e.g., Li and Agee, 1996 Nature). If core-mantle differentiation has occurred under such conditions, significant quantities of O or Si could have entered the core. At these conditions the nature of the dominant light element in the core will depend strongly on the oxygen fugacity at which equilibration occurred. High pressure experiments were carried out at 25 GPa and 2400-2950 K using a Kawai-type multi-anvil apparatus in order to investigate the partitioning of Si and O between liquid Fe and (Mg,Fe)SiO3 perovskite (Pv), silicate melt, and (Mg,Fe)O ferropericlace (Fp). Starting materials consisting of metallic Fe (+-Si) and olivine (Fo70-95) were contained in single-crystal MgO capsules. Over the oxygen fugacity range IW-0.5 to -3, the Si molar partition coefficient D* (= [Si]metal /[Si]silicate) between metal and Pv increases linearly with decreasing oxygen fugacity at a fixed given temperature. The partition coefficient between metal and silicate melt is of a similar magnitude but is less dependent on the oxygen fugacity. The obtained oxygen distribution coefficient Kd (= [Fe]metal[O]metal /[FeO]Fp) is in agreement with that determined in the Fe-Fp binary system (Asahara et al., 2007 EPSL) below the silicate liquidus temperature. In contrast, a correlation between the O partitioning and Si concentration in Fe is observed above 2700 K where liquid metal coexists with silicate melt + Fp. With an increasing concentration of Si in the liquid metal, O partitioning into Fp is strongly enhanced. Five atomic% Si in the metal reduces the metal-silicate O partition coefficient by about 1 order magnitude. Near the base of a deep magma ocean where pressures exceed 20 GPa, liquid metal could have coexisted with silicate melt, Pv, and Fp. Our results show that Si would readily partitioned into core-forming metal from both perovskite and silicate liquid at a relevant oxygen fugacity (e.g., IW-2). Simultaneously, the Si solubility would hinder the dissolution of O in the liquid metal. This implies that the presence of Si in liquid metal must be included in models of O partitioning.

Investigation of the noble gas solubility in H 2O-CO 2 bearing silicate liquids at moderate pressure II: the extended ionic porosity (EIP) model

NASA Astrophysics Data System (ADS)

Nuccio, P. M.; Paonita, A.

2000-12-01

A semi-theoretical model is proposed to predict partitioning of noble gases between any silicate liquid and a H 2O-CO 2 gas phase with noble gas as a minor component, in a large range of pressures (at least up to 300 MPa). The model is based on the relationship between the concentration of dissolved noble gas and ionic porosity of the melt, found by Carroll and Stolper [Geochim. Cosmochim. Acta 57 (1993) 5039-5051] for H 2O-CO 2 free melts. It evaluates the effect of dissolved H 2O and CO 2 on the melt ionic porosity and, consequently on Henry's constants of noble gases. The fugacities of the noble gases in the H 2O-CO 2-noble gas mixtures are also considered in our equilibrium calculations of dissolved gas by using a modified Redlich-Kwong equation of state for the H 2O-CO 2-noble gas system. The formulated model (referred to as the extended ionic porosity model) clearly predicts a positive dependence of noble gas solubility on dissolved H 2O in melt, which becomes negligible when water concentration is higher than 3 wt%. Oppositely, noble gas solubility decreases as a consequence of increasing CO 2 in both basaltic and rhyolitic melts. The increase of noble gas solubility as a consequence of H 2O addition to the melt grows exponentially with the increase of the noble gas atomic size. As a result, although xenon solubility is much lower than the helium solubility in anhydrous melts, they become almost comparable at several percent of dissolved H 2O in the melt. On this basis, an exponential augmentation of the number of large free spaces in silicate liquid can be inferred in relation to increasing dissolved H 2O. Comparison between our predicted values and available experimental data [A. Paonita et al., Earth Planet. Sci. Lett. 181 (2000) 595-604] shows good agreement. At present, the EIP model is the unique tool which predicts how the main volatiles in magmatic systems affect the noble gas solubility in silicate melts, therefore it should be taken into account for future studies of noble gas fractionation in degassing natural magmas.

Effect of pressure on the short-range structure and speciation of carbon in alkali silicate and aluminosilicate glasses and melts at high pressure up to 8 GPa: 13C, 27Al, 17O and 29Si solid-state NMR study

NASA Astrophysics Data System (ADS)

Kim, Eun Jeong; Fei, Yingwei; Lee, Sung Keun

2018-03-01

Despite the pioneering efforts to explore the nature of carbon in carbon-bearing silicate melts under compression, experimental data for the speciation and the solubility of carbon in silicate melts above 4 GPa have not been reported. Here, we explore the speciation of carbon and pressure-induced changes in network structures of carbon-bearing silicate (Na2O-3SiO2, NS3) and sodium aluminosilicate (NaAlSi3O8, albite) glasses quenched from melts at high pressure up to 8 GPa using multi-nuclear solid-state NMR. The 27Al triple quantum (3Q) MAS NMR spectra for carbon-bearing albite melts revealed the pressure-induced increase in the topological disorder around 4 coordinated Al ([4]Al) without forming [5,6]Al. These structural changes are similar to those in volatile-free albite melts at high pressure, indicating that the addition of CO2 in silicate melts may not induce any additional increase in the topological disorder around Al at high pressure. 13C MAS NMR spectra for carbon-bearing albite melts show multiple carbonate species, including [4]Si(CO3)[4]Si, [4]Si(CO3)[4]Al, [4]Al(CO3)[4]Al, and free CO32-. The fraction of [4]Si(CO3)[4]Al increases with increasing pressure, while those of other bridging carbonate species decrease, indicating that the addition of CO2 may enhance mixing of Si and Al at high pressure. A noticeable change is not observed for 29Si NMR spectra for the carbon-bearing albite glasses with varying pressure at 1.5-6 GPa. These NMR results confirm that the densification mechanisms established for fluid-free, polymerized aluminosilicate melts can be applied to the carbon-bearing albite melts at high pressure. In contrast, the 29Si MAS NMR spectra for partially depolymerized, carbon-bearing NS3 glasses show that the fraction of [5,6]Si increases with increasing pressure at the expense of Q3 species ([4]Si species with one non-bridging oxygen as the nearest neighbor). The pressure-induced increase in topological disorder around Si is evident from an increase in peak width of [4]Si with pressure. 17O NMR spectrum shows that the fraction of Na⋯Osbnd [5]Si in carbon-bearing NS3 glasses is less than that of carbon-free NS3 glasses at 6 GPa potentially due to the formation of bridging carbonate species. While its presence is not evident from the 17O NMR spectrum primarily due to low carbon concentration, 13C MAS NMR results imply the formation of bridging carbonates, [4]Si(CO3)[4]Si, above 6 GPa. The spin-lattice relaxation time (T1) of CO2 in albite melts increases with increasing pressure from 42 s (at 1.5 GPa) to 149 s (at 6 GPa). Taking the pressure-induced change in T1 of carbon species into consideration, total carbon content in carbon-bearing albite melts increases with pressure from ∼1 wt% at 1.5 GPa to ∼4.1 wt% at 6 GPa. The results also reveal a noticeable drop in the peak intensity of free carbonates in carbon-bearing NS3 melts at 6 GPa, implying a potential non-linear change in the carbon solubility with pressure. The current results of carbon speciation in the silicate melts above 4 GPa provide an improved link among the atomic configurations around carbon species, their carbon contents, and isotope composition of carbon-bearing melts in the upper mantle.

Material transport in laser-heated diamond anvil cell melting experiments

NASA Technical Reports Server (NTRS)

Campbell, Andrew J.; Heinz, Dion L.; Davis, Andrew M.

1992-01-01

A previously undocumented effect in the laser-heated diamond anvil cell, namely, the transport of molten species through the sample chamber, over distances large compared to the laser beam diameter, is presented. This effect is exploited to determine the melting behavior of high-pressure silicate assemblages of olivine composition. At pressures where beta-spinel is the phase melted, relative strengths of partitioning can be estimated for the incompatible elements studied. Iron was found to partition into the melt from beta-spinel less strongly than calcium, and slightly more strongly than manganese. At higher pressures, where a silicate perovskite/magnesiowuestite assemblage is melted, it is determined that silicate perovskite is the liquidus phase, with iron-rich magnesiowuestite accumulating at the end of the laser-melted stripe.

Properties of the Guin ungrouped iron meteorite - The origin of Guin and of group-IIE irons

NASA Astrophysics Data System (ADS)

Rubin, A. E.; Jerde, E. A.; Zong, P.; Wasson, J. T.; Westcott, J. W.; Mayeda, T. K.; Clayton, R. N.

1986-01-01

The composition and structure of the Guin ungrouped iron meteorite inclusions have been investigated experimentally. The structural characteristics of polished and etched slabs of the meteorite were studied microscopically in reflected light. Modal abundances of troilite nodules and silicate inclusions were determined by weighing paper traces. The bulk composition of the silicate inclusions was calculated by combining modal phase abundances and mineral compositions. It is found that the largest silicate inclusion (2 x 4 cm) consists mostly of a shock-melted plagioclase-rich matrix surrounding large, partly melted augite grains. The oxygen isotopic composition of the inclusion is near that of LL chondrites. The inclusion is found to be similar in composition to selected melt pocket glasses in ordinary chondrites produced in situ by preferential melting of plagioclase rock due to shock compression. It is suggested that the Guin assemblage was formed by impact melting on a chondritic parent body. Silicate inclusions in IIE irons share many of the compositional and petrological characteristics of the Guin inclusions, indicating that IIE irons also formed by impact-melting of chondritic materials. Black and white photomicrographs of the silicate inclusions are provided.

Ultrasonic Sound Velocity of Diopside Liquid Under High Pressure and High Temperature Conditions

NASA Astrophysics Data System (ADS)

Xu, M.; Jing, Z.; Chantel, J.; Yu, T.; Wang, Y.; Jiang, P.

2017-12-01

The equation of state (EOS) of silicate liquids is of great significance to the understanding of the dynamics and differentiation of the magmatic systems in Earth and other terrestrial planets. Sound velocity of silicate liquids measured at high pressure can provide direct information on the bulk modulus and its pressure derivative and hence tightly constrain the EOS of silicate liquids. In addition, the sound velocity data can be directly compared to seismic observations to infer the presence of melts in the mantle. While the sound velocity for silicate liquids at ambient pressure has been well established, the high-pressure sound velocity data are still lacking due to experimental challenges. In this study, we successfully determined the sound velocities of diopside (CaMgSi2O6) liquid in a multi-anvil apparatus under high pressure-high temperature conditions from 1 to 4 GPa and 1973 to 2473 K by the ultrasonic interferometry in conjunction with synchrotron X-ray techniques. Diopside was chosen to study because it is not only one of the most important phases in the Earth's upper mantle, but also an end-member composition of model basalt. It is thus an ideal simplified melt composition in the upper mantle. Besides, diopside liquid has been studied by ambient-pressure ultrasonic measurements (e.g., Ai and Lange, 2008) and shock-wave experiments at much higher pressure (e.g., Asimow and Ahrens, 2010), which allows comparison with our results over a large pressure range. Our high-pressure results on the sound velocity of Di liquid are consistent with the ambient-pressure data and show an increase of velocity with pressure (from 3039 m/s at 0.1 GPa to 4215 m/s at 3.5 GPa). Fitting to the Murnaghan EOS gives an isentropic bulk modulus (Ks) of 24.8 GPa and its pressure dependence (K'S) of 7.8. These are consistent with the results from shock-wave experiments on Di liquid (Asimow and Ahrens, 2010), indicating that the technique used in this study is capable to accurately determine the sound velocity of silicate liquids at high pressures. We will use these results to better constrain the hard sphere EOS model for silicate liquids (Jing and Karato, 2011), with implications to the stability of melt layers in the deep mantle under gravity and the presence of partial melts in low velocity zones in the mantle.

Thermal Constraints from Siderophile Trace Elements in Acapulcoite-Lodranite Metals

NASA Technical Reports Server (NTRS)

Herrin, Jason S.; Mittlefehldt, D. W.; Humayun, M.

2006-01-01

A fundamental process in the formation of differentiated bodies is the segregation of metal-sulfide and silicate phases, leading to the formation of a metallic core. The only known direct record of this process is preserved in some primitive achondrites, such as the acapulcoite-lodranites. Meteorites of this clan are the products of thermal metamorphism of a chondritic parent. Most acapulcoites have experienced significant partial melting of the metal-sulfide system but not of silicates, while lodranites have experienced partial melting and melt extraction of both. The clan has experienced a continuum of temperatures relevant to the onset of metal mobility in asteroidal bodies and thus could yield insight into the earliest stages of core formation. Acapulcoite GRA 98028 contains relict chondrules, high modal sulfide/metal, has the lowest 2-pyroxene closure temperature, and represents the least metamorphosed state of the parent body among the samples examined. Comparison of the metal-sulfide component of other clan members to GRA 98028 can give an idea of the effects of metamorphism.

Co-settling of Chromite and Sulfide Melt Droplets and Trace Element Partitioning between Sulfide and Silicate Melts

NASA Astrophysics Data System (ADS)

Manoochehri, S.; Schmidt, M. W.; Guenther, D.

2013-12-01

Gravitational settling of immiscible, dense sulfide melt droplets together with other cumulate phases such as chromite, combined with downward percolation of these droplets through a cumulate pile, is thought to be one of the possible processes leading to the formation of PGE rich sulfide deposits in layered mafic intrusions. Furthermore some chromitite seams in the Merensky Reef (Bushveld Complex) are considered to be acting as a filter or barrier for further downward percolation of sulfide melts into footwall layers. To investigate the feasibility of such mechanical processes and to study the partitioning behavior of 50 elements including transition metals and REEs (but not PGEs) between a silicate and a sulfide melt, two separate series of high temperature (1250-1380 °C) centrifuge-assisted experiments at 1000 g, 0.4-0.6 GPa were conducted. A synthetic silicate glass with a composition representative of the parental magma of the Bushveld Complex (~ 55 wt% SiO2) was mixed with pure FeS powder. For the first series of experiments, 15 or 25 wt% natural chromite with average grain sizes of ~ 5 or 31 μm were added to a mixture of silicate glass and FeS (10 wt%) adding 1 wt% water. For the second series, a mixture of the same glass and FeS was doped with 50 trace elements. These mixtures were first statically equilibrated and then centrifuged. In the first experimental series, sulfide melt droplets settled together with, but did not segregate from chromite grains even after centrifugation at 1000 g for 12 hours. A change in initial chromite grain size and proportions didn't have any effect on segregation. Without chromite, the starting mixture resulted in the formation of large sulfide melt pools together with finer droplets still disseminated through the silicate glass and both at the bottom of the capsule. The incomplete segregation of sulfide melt is interpreted as being due to high interfacial energies between sulfide and silicate melts/crystals which hinder both, the nucleation of newly formed sulfide droplets and the interconnectivity of separate droplets. The interfacial energies between sulfide melt and silicate or oxide crystals is even higher than for silicate melt, consequently in experiments with chromite, sulfide segregation is even more hindered. Partition coefficients of 50 elements between a sulfide and a silicate melt are determined as a function of differing temperature between 1250 - 1380 °C. As a proxy to investigate the bond strength of network modifier cations, the relation between the partition coefficients and ionic potentials of different groups of elements has been determined.

Chalcophile element partitioning in highly oxidised and highly reduced bodies.

NASA Astrophysics Data System (ADS)

Kiseeva, K.; Wood, B. J.

2015-12-01

In our recent studies [1-3] we showed that partitioning of many chalcophile elements could be described by a simple relationship as a function of the FeO content of the silicate liquid. LogDi ~= A-0.5nlog[FeO] where A is a constant, n is the constant related to the valency of element i and [FeO] is the concentration of FeO in the silicate melt. For many chalcophile and moderately chalcophile elements (e.g., Zn, Cr, Pb, Sb, In), the fitted slope n depends only on the valency of the element. More lithophile elements (e.g., Ti, Nb, Ce, Ga) exhibit concave upwards behavior on a plot of logD versus log[FeO] due to their strong interaction with oxygen in sulphide, which increases with the increasing FeO content of the silicate liquid. Strongly chalcophile elements, like Cu, Ag and Ni have the opposite trend (concave downwards) and their D decreases both at high (> 10-12wt %) and very low (< 1wt%) FeO contents of the silicate melt. These changes correlate with increasing S content of the silicate melt (up to 11 wt%) as the FeO content of the silicate melt declines to ~0.3wt%. An experiment at 1.5 GPa/1420oC having 4 wt% S and 0.28 wt% FeO in the silicate melt has DCu (sulf/sil) ~ 84, which is about 6 times lower than the DCu(sulf/sil) at identical p-T conditions but at 8 wt% FeO in the silicate melt. Our new experimental data on Re partitioning between sulphide and silicate melt in the CMAS+FeO system show that Re behaves similarly to the highly chalcophile elements and exhibits concave downwards behaviour on the LogD/LogFeO diagram. With the highest DRe (sulf/sil) at around 1.5-2.0x104 at 1.5-6.0 wt% FeO in the silicate melt, DRe (sulf/sil) declines to the values of 50-150 at ~0.5 wt% and > ~15 wt% FeO in the silicate melt, respectively. This means that at highly reducing conditions Re is similarly or less chalcophile than some of the highly lithophile elements, like Ta (D ≈ 9), Nb (D ≈ 600), Ti (D ≈ 6) [3]. The results mean that in oxidised bodies like Mars and reduced bodies like Mercury, most "lithophile" elements partition more strongly into sulphide than Re and Cu. [1] Kiseeva E. S., Wood B. J. (2013). EPSL 383, p. 68-81. [2] Kiseeva E. S., Wood B. J. (2015). EPSL 424, p. 280-294. [3] Wood B. J., Kiseeva E. S. (2015). AmMin (in press).

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

NASA Astrophysics Data System (ADS)

Keller, T.; Katz, R. F.

2015-12-01

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 & Kohlstedt (1996), EPSLDH06 Dasgupta & Hirschmann (2006), NatureH10 Hirschmann (2010), PEPI DH10 Dasgupta & Hirschmann (2010), EPSLMcK84 McKenzie (1984), J PetKW12 Katz & Weatherley (2012), EPSLRBS11 Rudge, Bercovici & Spiegelman (2011), GJI

Experimental segregation of iron-nickel metal, iron-sulfide, and olivine in a thermal gradient: Preliminary results

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, J. H.

1993-01-01

Speculation about the possible mechanisms for core formation in small asteroids raises more questions than answers. Petrologic evidence from iron meteorites, pallasites, and astronomical observations of M asteroids suggests that many small bodies were capable of core formation. Recent work by Taylor reviews the geochemical evidence and examines the possible physical/mechanical constraints on segregation processes. Taylor's evaluation suggests that extensive silicate partial melting (preferably 50 vol. percent or greater) is required before metal can segregate from the surrounding silicate and form a metal core. The arguments for large degrees of silicate partial melting are two-fold: (1) elemental trends in iron meteorites require that the metal was at is liquidus; and (2) experimental observations of metal/sulfide inclusions in partially molten silicate meteorites show that the metal/sulfide tends to form spherules in the liquid silicate due to surface tension effects. Taylor points out that for these metal spherules to sink through a silicate mush, high degrees of silicate partial melting are required to lower the silicate yield strength. Although some qualitative experimental data exists, little is actually known about the behavior of metals and liquid sulfides dispersed in silicate systems. In addition, we have been impressed with the ability of cumulative olivine to expel trapped liquid when placed in a thermal gradient. Consequently, we undertook to accomplish the following: (1) experimentally evaluate the potential for metal/sulfide/silicate segregation in a thermal gradient; and (2) obtain quantitative data of the wetting parameters of metal-sulfide melts among silicate grains.

Using MELTS to understand the evolution of silicic magmas: Challenges and successes in modeling the Highland Range Volcanic Sequence (NV)

NASA Astrophysics Data System (ADS)

Vaum, R. C.; Gualda, G. A.; Ghiorso, M. S.; Miller, C. F.; Colombini, L. L.

2009-12-01

The Highland Range near Searchlight, Nevada is comprised of mid-Miocene, intermediate to silicic volcanic rocks. This study focuses on the most silicic portion of the eruptive sequence (16.0-16.5 Ma). The first eruptions during this interval were effusive and produced trachydacite (66-70 wt% SiO2), but later the eruptive style shifted to explosive and compositions were more evolved (70-78 wt% SiO2). Glass compositions in rocks saturated in both quartz and sanidine align along the 150 MPa quartz+sanidine saturation surface, suggesting that the Highland Range magmas equilibrated in a single reservoir at that pressure. We are interested in better understanding this transition in eruptive style from effusive to eruptive, and our approach is based on modeling melt evolution using MELTS thermodynamic modeling software. We selected representative samples from key stratigraphic units, and focused on samples for which whole-rock and glass compositions, as well as mineral abundances, are available. This allows for direct comparison of simulation results with existing data. Initial simulations showed that MELTS predicts unrealistic paths of evolution when compared to the glass compositions and to the phase relations in the Qz-Ab-Or ternary. In particular, the stability field of quartz predicted by MELTS is much too small, causing melts to become exceedingly silicic (>80 wt% SiO2). Sanidine, on the other hand, has fairly sodic compositions and crystallizes too early in the sequence; therefore, simulated melt compositions are never as potassic as the analyzed glasses. Similar results are obtained when modeling the evolution of the Bishop and Campanian magmas, showing that these are systematic problems in MELTS calibration. Accordingly, we have adjusted the enthalpy of quartz and potassium end-member of the feldspar solid solution in MELTS so that the quartz-sanidine saturation surface is correctly predicted. We find that this modified version of MELTS much better models the evolution of silicic magmas. Sanidine begins to crystallize at lower temperatures, causing evolved melts to become significantly more potassic. Also, MELTS prediction of quartz saturation is in agreement with the position of the experimentally determined 150 MPa quartz+sanidine saturation surface. Importantly, the melt evolution that this modified version of MELTS predicts is very consistent with whole-rock data, glass chemistry, and mineral abundances in samples from the Highland Range. Simulations using the modified version of MELTS show that it works remarkably well, at least for relatively low degrees of crystallization. But a more reliable model to simulate the evolution of silicic magmas is necessary to more properly simulate the evolution of silicic systems, in particular at high degrees of crystallinity. We are currently working to create gMELTS, an associated solution model of the haplogranitic system, which, once completed, will be optimized to simulate the evolution of silicic systems.

Lunar production of oxygen by electrolysis

NASA Technical Reports Server (NTRS)

Keller, Rudolf

1991-01-01

Two approaches to prepare oxygen from lunar resources by direct electrolysis are discussed. Silicates can be melted or dissolved in a fused salt and electrolyzed with oxygen evolved at the anode. Direct melting and electrolysis is potentially a very simple process, but high temperatures of 1400-1500 C are required, which aggravates materials problems. Operating temperatures can be lowered to about 1000 C by employing a molten salt flux. In this case, however, losses of electrolyte components must be avoided. Experimentation on both approaches is progressing.

VOLATILECALC: A silicate melt-H2O-CO2 solution model written in Visual Basic for excel

USGS Publications Warehouse

Newman, S.; Lowenstern, J. B.

2002-01-01

We present solution models for the rhyolite-H2O-CO2 and basalt-H2O-CO2 systems at magmatic temperatures and pressures below ~ 5000 bar. The models are coded as macros written in Visual Basic for Applications, for use within MicrosoftR Excel (Office'98 and 2000). The series of macros, entitled VOLATILECALC, can calculate the following: (1) Saturation pressures for silicate melt of known dissolved H2O and CO2 concentrations and the corresponding equilibrium vapor composition; (2) open- and closed-system degassing paths (melt and vapor composition) for depressurizing rhyolitic and basaltic melts; (3) isobaric solubility curves for rhyolitic and basaltic melts; (4) isoplethic solubility curves (constant vapor composition) for rhyolitic and basaltic melts; (5) polybaric solubility curves for the two end members and (6) end member fugacities of H2O and CO2 vapors at magmatic temperatures. The basalt-H2O-CO2 macros in VOLATILECALC are capable of calculating melt-vapor solubility over a range of silicate-melt compositions by using the relationships provided by Dixon (American Mineralogist 82 (1997) 368). The output agrees well with the published solution models and experimental data for silicate melt-vapor systems for pressures below 5000 bar. ?? 2002 Elsevier Science Ltd. All rights reserved.

V OLATILEC ALC: a silicate melt-H 2O-CO 2 solution model written in Visual Basic for excel

NASA Astrophysics Data System (ADS)

Newman, Sally; Lowenstern, Jacob B.

2002-06-01

We present solution models for the rhyolite-H 2O-CO 2 and basalt-H 2O-CO 2 systems at magmatic temperatures and pressures below ˜5000 bar. The models are coded as macros written in Visual Basic for Applications, for use within Microsoft ® Excel (Office'98 and 2000). The series of macros, entitled V OLATILEC ALC, can calculate the following: (1) Saturation pressures for silicate melt of known dissolved H 2O and CO 2 concentrations and the corresponding equilibrium vapor composition; (2) open- and closed-system degassing paths (melt and vapor composition) for depressurizing rhyolitic and basaltic melts; (3) isobaric solubility curves for rhyolitic and basaltic melts; (4) isoplethic solubility curves (constant vapor composition) for rhyolitic and basaltic melts; (5) polybaric solubility curves for the two end members and (6) end member fugacities of H 2O and CO 2 vapors at magmatic temperatures. The basalt-H 2O-CO 2 macros in V OLATILEC ALC are capable of calculating melt-vapor solubility over a range of silicate-melt compositions by using the relationships provided by Dixon (American Mineralogist 82 (1997) 368). The output agrees well with the published solution models and experimental data for silicate melt-vapor systems for pressures below 5000 bar.

Experimental constraints on the degree of melting beneath tectonic plates

NASA Astrophysics Data System (ADS)

Clark, A. N.; Lesher, C. E.

2017-12-01

Determining the volume and geometric distribution of silicate melts is fundamentally important to understand the current structure of the Earth as well as the dynamics of the Earth's interior. Regions in the upper mantle and crust that have lower velocities than the 1D global average are commonly attributed to the presence of silicate melts. Constraining melt fraction and distribution from seismic data requires a robust equation of state for silicate melts. Commonly, silicate melts are modeled at high pressure using equations of state developed for crystalline materials (e.g. the Birch-Murnaghan equation of state). However, amorphous silicates (glasses and melts), which lack long-range ordering, violate Birch's law at high pressures and high temperatures (Clark et al., 2016). We present a new model for seismic velocity reductions that accounts for the violation of Birch's law (anomalous compressibility) observed in amorphous silicates, rendering compressional wave velocities more sensitive to melt fraction and distribution than previous estimates. Forward modeling that combines our experimental data with the analytical solution of Takei (2002) predicts comparable velocity reductions for compressional and shear waves for partially molten mantle. Additionally, models that use crystalline equations of state to determine melt fraction at high pressure may overestimate melt fraction by 20% at pressures corresponding to the lithosphere-asthenosphere boundary (LAB) with the overestimation increasing with depth (e.g. a factor of 2 at the transition zone). By applying our results to recent seismic studies below the western Pacific plate that have reported low velocity regions associated with the lithosphere - asthenosphere boundary (LAB), we predict melt present at <5% distributed in near-textural equilibrium. These findings reconcile seismic observations for the LAB regionally and locally, and favor models of strong coupling across the LAB rather than melt channeling due to shear deformation. Clark, A. N., Lesher, C. E., Jacobsen, S. D., and Wang, Y., 2016, Journal of Geophysical Research: Solid Earth, v. 121, no. 6, p. 4232-4248. Takei, Y., 2002, Journal of Geophysical Research: Solid Earth (1978-2012), v. 107, no. B2, p. 6-12.

An Iron-Rain Model for Core Formation on Asteroid 4 Vesta

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Mittlefehldt, David W.

2016-01-01

Asteroid 4 Vesta is differentiated into a crust, mantle, and core, as demonstrated by studies of the eucrite and diogenite meteorites and by data from NASA's Dawn spacecraft. Most models for the differentiation and thermal evolution of Vesta assume that the metal phase completely melts within 20 degrees of the eutectic temperature, well before the onset of silicate melting. In such a model, core formation initially happens by Darcy flow, but this is an inefficient process for liquid metal and solid silicate. However, the likely chemical composition of Vesta, similar to H chondrites with perhaps some CM or CV chondrite, has 13-16 weight percent S. For such compositions, metal-sulfide melting will not be complete until a temperature of at least 1350 degrees Centigrade. The silicate solidus for Vesta's composition is between 1100 and 1150 degrees Centigrade, and thus metal and silicate melting must have substantially overlapped in time on Vesta. In this chemically and physically more likely view of Vesta's evolution, metal sulfide drops will sink by Stokes flow through the partially molten silicate magma ocean in a process that can be envisioned as "iron rain". Measurements of eucrites show that moderately siderophile elements such as Ni, Mo, and W reached chemical equilibrium between the metal and silicate phases, which is an important test for any Vesta differentiation model. The equilibration time is a function of the initial metal grain size, which we take to be 25-45 microns based on recent measurements of H6 chondrites. For these sizes and reasonable silicate magma viscosities, equilibration occurs after a fall distance of just a few meters through the magma ocean. Although metal drops may grow in size by merger with other drops, which increases their settling velocities and decreases the total core formation time, the short equilibration distance ensures that the moderately siderophile elements will reach chemical equilibrium between metal and silicate before metal drop merger becomes important. In this model, there must be at least 30 percent melting of the silicate phase when metal melting is complete, corresponding to a crust thickness of at least 30 kilometers on Vesta, consistent with Dawn gravity observations. Greater degrees of silicate melting and a correspondingly thicker crust are possible if Vesta accreted sufficiently rapidly.

Computational and experimental studies of iron-bearing carbonates and silicate glasses at lower mantle pressures

NASA Astrophysics Data System (ADS)

Solomatova, N. V.; Jackson, J. M.; Asimow, P. D.; Sturhahn, W.; Rossman, G. R.; Roskosz, M.

2017-12-01

Decomposition of carbonates may be responsible for creating silicate melts within the lower mantle by lowering the melting temperature of surrounding rock. Identifying and characterizing the stability of carbonates is therefore a necessary step towards understanding the transport of carbon in Earth's interior. Dolomite is one of the major mineral forms in which carbon is subducted into the Earth's mantle. Although iron-free dolomite is expected to break down upon compression, high-pressure polymorphs of iron-bearing dolomite may resist decomposition. Using a genetic algorithm that predicts crystal structures, we found a monoclinic phase with space group C2/c that has a lower energy than all previously reported dolomite structures at pressures above 15 GPa, where the substitution of iron for magnesium stabilizes monoclinic dolomite at certain pressures of the lower mantle. Thus, an iron-bearing dolomite polymorph may be an important carbon carrier in regions of Earth's lower mantle. The depth at which carbonates will decompose is dependent on the age, temperature and density of subducting slabs. Decarbonation reactions may lower the melting temperature of surrounding rocks to produce silicate melts. In regions of the mantle where silicate melts may exist, it is important to understand the physical properties and dynamic behavior of the melts because they affect the chemical and thermal evolution of its interior. Composition, degree of polymerization, and iron's spin state affect such properties. The behavior of iron in silicate melts is poorly understood but, in some cases, may be approximated by iron-bearing glasses. We measured the hyperfine parameters of iron-bearing rhyolitic and basaltic glasses up to 120 GPa and 100 GPa, respectively, in a neon pressure medium using time-domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high-spin Fe2+-like sites with distinct quadrupole splittings, reflecting the influence of evolving coordination environments with pressure. With the assumption that coordination environments in silicate glasses may serve as a good indicator for those in a melt, this study suggests that ferrous iron in chemically-complex silicate melts likely exists in a high-spin state throughout most of Earth's mantle.

New findings for the equilibrated enstatite chondrite Grein 002

NASA Astrophysics Data System (ADS)

Patzer, Andrea; Schlüter, Jochen; Schultz, Ludolf; Tarkian, M.; Hill, Dolores H.; Boynton, William V.

2004-09-01

We report new petrographic and chemical data for the equilibrated EL chondrite Grein 002, including the occurrence of osbornite, metallic copper, abundant taenite, and abundant diopside. As inferred from low Si concentrations in kamacite, the presence of ferroan alabandite, textural deformation, chemical equilibration of mafic silicates, and a subsolar noble gas component, we concur with Grein 002's previous classification as an EL4-5 chondrite. Furthermore, the existence of pockets consisting of relatively coarse, euhedral enstatite crystals protruding large patches of Fe-Ni alloys suggests to us that this EL4-5 chondrite has been locally melted. We suspect impact induced shock to have triggered the formation of the melt pockets. Mineralogical evidence indicates that the localized melting of metal and adjacent enstatite must have happened relatively late in the meteorite's history. The deformation of chondrules, equilibration of mafic silicates, and generation of normal zoning in Fe, Zn-sulfides took place during thermal alteration before the melting event. Following parent body metamorphism, daubreelite was exsolved from troilite in response to a period of slow cooling at subsolidus temperatures. Exsolution of schreibersite from the coarse metal patches probably occurred during a similar period of slow cooling subsequent to the event that induced the formation of the melt pockets. Overall shock features other than localized melting correspond to stage S2 and were likely established by the final impact that excavated the Grein 002 meteoroid.

Experimental Partitioning of Chalcophile Elements between Mantle Silicate Minerals and Basaltic Melt at High Pressures and Temperatures - Implications for Sulfur Geochemistry of Mantle and Crust

NASA Astrophysics Data System (ADS)

Dasgupta, R.; Jego, S.; Ding, S.; Li, Y.; Lee, C. T.

2015-12-01

The behavior of chalcophile elements during mantle melting, melt extraction, and basalt differentiation is critical for formation of ore deposits and geochemical model and evolution of crust-mantle system. While chalcophile elements are strongly partitioned into sulfides, their behavior with different extent of melting, in particular, in the absence of sulfides, can only be modeled with complete knowledge of the partitioning behavior of these elements between dominant mantle minerals and basaltic melt with or without dissolved sulfide (S2-). However, experimental data on mineral-melt partitioning are lacking for many chalcophile elements. Crystallization experiments were conducted at 3 GPa and 1450-1600 °C using a piston cylinder and synthetic silicate melt compositions similar to low-degree partial melt of peridotite. Starting silicate mixes doped with 100-300 ppm of each of various chalcophile elements were loaded into Pt/graphite double capsules. To test the effect of dissolved sulfur in silicate melt on mineral-melt partitioning of chalcophile elements, experiments were conducted on both sulfur-free and sulfur-bearing (1100-1400 ppm S in melt) systems. Experimental phases were analyzed by EPMA (for major elements and S) and LA-ICP-MS (for trace elements). All experiments produced an assemblage of cpx + melt ± garnet ± olivine ± spinel and yielded new partition coefficients (D) for Sn, Zn, Mo, Sb, Bi, Pb, and Se for cpx/melt, olivine/melt, and garnet/melt pairs. Derived Ds (mineral/basalt) reveal little effect of S2- in the melt on mineral-melt partition coefficients of the measured chalcophile elements, with Ds for Zn, Mo, Bi, Pb decreasing by less than a factor of 2 from S-free to S-bearing melt systems or remaining similar, within error, between S-free and S-bearing melt systems. By combining our data with existing partitioning data between sulfide phases and silicate melt we model the fractionation of these elements during mantle melting and basalt crystallization. The model results are compared with the chalcophile element abundance in oceanic basalts. We will discuss the implications of our new partitioning data and model results on sulfur and chalcophile element geochemistry of mantle source regions of ocean floor basalts and the fate of sulfides during mantle melting.

Mg-perovskite/silicate melt and magnesiowuestite/silicate melt partition coefficients for KLB-1 at 250 Kbars

NASA Technical Reports Server (NTRS)

Drake, Michael J.; Rubie, David C.; Mcfarlane, Elisabeth A.

1992-01-01

The partitioning of elements amongst lower mantle phases and silicate melts is of interest in unraveling the early thermal history of the Earth. Because of the technical difficulty in carrying out such measurements, only one direct set of measurements was reported previously, and these results as well as interpretations based on them have generated controversy. Here we report what are to our knowledge only the second set of directly measured trace element partition coefficients for a natural system (KLB-1).

Pt, Au, Pd and Ru Partitioning Between Mineral and Silicate Melts: The Role of Metal Nanonuggets

NASA Technical Reports Server (NTRS)

Malavergne, V.; Charon, E.; Jones, J.; Agranier, A.; Campbell, A.

2012-01-01

The partition coefficients of Pt and other Pt Group Elements (PGE) between metal and silicate D(sub Metal-Silicate) and also between silicate minerals and silicate melts D(sub Metal-Silicate) are among the most challenging coefficients to obtain precisely. The PGE are highly siderophile elements (HSE) with D(sub Metal-Silicate) >10(exp 3) due to the fact that their concentrations in silicates are very low (ppb to ppt range). Therefore, the analytical difficulty is increased by the possible presence of HSE-rich-nuggets in reduced silicate melts during experiments). These tiny HSE nuggets complicate the interpretation of measured HSE concentrations. If the HSE micro-nuggets are just sample artifacts, then their contributions should be removed before calculations of the final concentration. On the other hand, if they are produced during the quench, then they should be included in the analysis. We still don't understand the mechanism of nugget formation well. Are they formed during the quench by precipitation from precursor species dissolved homogeneously in the melts, or are they precipitated in situ at high temperature due to oversaturation? As these elements are important tracers of early planetary processes such as core formation, it is important to take up this analytical and experimental challenge. In the case of the Earth for example, chondritic relative abundances of the HSE in some mantle xenoliths have led to the concept of the "late veneer" as a source of volatiles (such as water) and siderophiles in the silicate Earth. Silicate crystal/liquid fractionation is responsible for most, if not all, the HSE variation in the martian meteorite suites (SNC) and Pt is the element least affected by these fractionations. Therefore, in terms of reconstructing mantle HSE abundances for Mars, Pt becomes a very important player. In the present study, we have performed high temperature experiments under various redox conditions in order to determine the abundances of Pt, Au, Ru and Pd in minerals (olivine and diopside) and in silicate melts, but also to characterize the sizes, density and chemistry of HSE nuggets when present in the samples.

CO2-rich phonolitic melt and carbonatite immiscibility in melt inclusions in nephelinite (Hanang volcano, North Tanzanian Divergence, East African Rift).

NASA Astrophysics Data System (ADS)

Baudouin, C.; Parat, F.

2016-12-01

Hanang is the southern volcano of the East branch of the East African Rift and represents volcanic activity at early stage rifting (0.9 Ma). Lavas are highly alkaline Mg-poor nephelinites (Mg#=24.4-35.2) with cpx, garnet, nepheline, titanite, and apatite and result from fractional crystallisation of primary melilitite magmas (Parat et al. AGU2016). In this study, we investigate glassy melt inclusions at the rim of nepheline phenocrysts to constrain the late stage of nephelinite evolution and the behaviour of volatiles (CO2, H2O, S, F, Cl) during magma storage and ascent. The melt inclusions have a green silicate glass, a microcrystalline carbonate phase and a shrinkage bubble free of gas phase (Raman analyses) suggesting that carbonatite-silicate liquid immiscibility (85:15) occurred during nephelinite differentiation. The silicate glasses have trachytic composition (Na+K/Al=1.6-7.2, SiO2=54-65.5 wt%) with high CO2 (0.43 wt% CO2, SIMS analyses), sulfur (0.21-0.92 wt% S) and halogens (0.28-0.84 wt% Cl; 0.35-2.54 wt% F) content and very low H2O content (<0.1wt%, Raman analyses). The carbonate phase is an anhydrous Ca-Na±S,K- carbonate with 33 wt% CaO, 20 wt% Na2O, 3 wt% K2O, and 3 wt% S. The pre-immiscible silicate liquid (e.g. silicate melt + carbonatite) in equilibrium with nepheline and cpx phenocrysts has CO2-rich phonolitic composition (Na+K/Al=6.2-6.9) with 6 ± 1.5 wt% CO2 at pressure of 700-1100 MPa. The entrapped melt in nepheline corresponds to evolved interstitial silicate melt after crystallisation of cpx (16.7%), nepheline (40%) garnet (6.5%) and apatite (1.7%) from Mg-nephelinite magma. The immiscibility process leading to glassy silicate melt and microcrystalline carbonatitic melt occurred in closed system during rapid ascent at crustal level at 200-230 MPa. The absence of gas phase in shrinkage bubble in melt inclusions suggests CO2-undersaturated conditions during quenching. The absence of carbonatite lavas at Hanang volcano is then explained by open system differentiation with primary melilititic magma replenishment preventing alkaline enrichment and carbonatite-silicate liquid immiscibility at depth as observed for the nephelinite-natrocarbonatite Oldoinyo Lengai volcano in the Natron Basin (150 km north).

Distribution of some highly volatile elements in chondrules

NASA Astrophysics Data System (ADS)

Kim, J. S.; Marti, K.

1994-07-01

As chondrule apparently were melted before accretion into chondritic parent bodies, we carried out a N and Xe isotopic study to obtain information on the partitioning of some of the most volatile as well as incompatible elements: noble gases, N, I, REE, and Pu. In separated silicates in Forest Vale, consisting of mostly broken chondrules, we observed rather large Xe concentrations, and since noble gases in chondrites are associated with C-rich phases, we decided to study the core portion of a suite of chondrules after removing the chondrule rim portion and adhering matrix. We selected sets of rounded chondrules from four meteorites: Allende (CV3), Dhajala (H3.8), Forest Vale (H4), and Bjurbole (L4). We compare measured N and Xe concentrations and isotopic abundances in cores of chondrules to those obtained from unetched chondrules. We discuss results obtained from melting steps, because N and Xe in the silicate lattice are mostly released at T greater than 1000 C. All cores of chondrules contain less than 1% of the Xe in the respective bulk samples. Moreover, they released much less trapped Xe in the melting step than did untreated bulk chondrites. However, the radiogenic Xer-129 and fissiogenic Xef is not or is only slightly depleted, and spallogenic Xe is a major component, particularly in Forest Vale. We can not deduce the signature of trapped Xe in the chondrules. The release systematics are completely different from those observed in primitive achondrites, which contain noble gas in the 'dusty' silicate inclusions. Allende chondrules differ from those of ordinary chondrite in the N release pattern. This represents possibly a signature of the local environment during chondrule formation, since N may exist in chondrule minerals in chemically bound forms. In contrast, all three sets of ordinary chondrite chondrules released less than 0.6 ppm N in the melting step, and these signatures reveal substantial components of cosmic-ray-produced N.

Origin of silicic magmas along the Central American volcanic front: Genetic relationship to mafic melts

NASA Astrophysics Data System (ADS)

Vogel, Thomas A.; Patino, Lina C.; Eaton, Jonathon K.; Valley, John W.; Rose, William I.; Alvarado, Guillermo E.; Viray, Ela L.

2006-09-01

Silicic pyroclastic flows and related deposits are abundant along the Central American volcanic front. These silicic magmas erupted through both the non-continental Chorotega block to the southeast and the Paleozoic continental Chortis block to the northwest. The along-arc variations of the silicic deposits with respect to diagnostic trace element ratios (Ba/La, U/Th, Ce/Pb), oxygen isotopes, Nd and Sr isotope ratios mimic the along-arc variation in the basaltic and andesitic lavas. This variation in the lavas has been interpreted to indicate relative contributions from the slab and asthenosphere to the basaltic magmas [Carr, M.J., Feigenson, M.D., Bennett, E.A., 1990. Incompatible element and isotopic evidence for tectonic control of source mixing and melt extraction along the Central American arc. Contributions to Mineralogy and Petrology, 105, 369-380.; Patino, L.C., Carr, M.J. and Feigenson, M.D., 2000. Local and regional variations in Central American arc lavas controlled by variations in subducted sediment input. Contributions to Mineralogy and Petrology, 138 (3), 265-283.]. With respect to along-arc trends in basaltic lavas the largest contribution of slab fluids is in Nicaragua and the smallest input from the slab is in central Costa Rica — similar trends are observed in the silicic pyroclastic deposits. Data from melting experiments of primitive basalts and basaltic andesites demonstrate that it is difficult to produce high K 2O/Na 2O silicic magmas by fractional crystallization or partial melting of low-K 2O/Na 2O sources. However fractional crystallization or partial melting of medium- to high-K basalts can produce these silicic magmas. We interpret that the high-silica magmas associated Central America volcanic front are partial melts of penecontemporaneous, mantle-derived, evolved magmas that have ponded and crystallized in the mid-crust — or are melts extracted from these nearly completely crystallized magmas.

Synchrotron X-ray spectroscopic investigations of an Nb-bearing silicate melt in contact with an aqueous fluid

NASA Astrophysics Data System (ADS)

Mayanovic, R. A.; Anderson, A. J.; Bassett, W. A.; Chou, I.

2006-05-01

Understanding the structural properties of trace elements in hydrous silicate melts in contact with a hydrothermal fluid is fundamentally important for a better assessment of the role of such elements in silicate melts being subjected to hydrothermal processes. We describe the use of synchrotron x-ray microprobe techniques and the modified hydrothermal diamond-anvil cell for in-situ spectroscopic analysis of individual phases of a silicate-melt/fluid system. Synchrotron X-ray fluorescence (XRF) and Nb K-edge X-ray absorption fine structure (XAFS) measurements were made on sectors ID20 and ID13 at the Advanced Photon Source, at the Argonne National Laboratory, on a Nb-bearing granitic glass in H2O and separately in a 1 M Na2CO3 aqueous solution at temperatures ranging from 25 to 880 °C and at up to 700 MPa of pressure. Individual phases of the Nb-glass/fluid system (at low temperatures) or the hydrous-silicate-melt/fluid system (at elevated temperatures) were probed using an X-ray beam focused to a diameter of 5 μm at the location of the sample. XRF analysis shows that the Nb partitions selectively from the hydrous silicate melt into the aqueous fluid at high temperatures in the Nb-glass/Na2CO3/H2O system but not so in the Nb-glass/H2O system. Analysis of XAFS spectra measured from the hydrous silicate melt phase of the Nb-glass/H2O sample in the 450 to 700 °C range shows that the first shell contains six oxygen atoms at a distance of ~1.98 Å. Our results suggest that reorganization of the silicate structure surrounding Nb occurs in the melt when compared to that of the starting glass. The X-ray absorption near edge structure (XANES) spectra show a pre-edge peak feature located at ~18995 eV that exhibits sharpening and becomes more intensified in the 450 to 700 °C range. Fitting of the Nb K-edge XANES spectra measured from the melt is accomplished using FEFF8.28 and an atomic model NbSi4O6-4(Na, K). The model is based on the structure of fresnoite (Ba2TiSi2O8), in which an NbO6 octahedron unit is substituted for the TiO5 unit, four Na and four K atoms are placed alternately on nearby Ba atom sites, and four Si atoms are arranged in a single plane intersecting the NbO6 unit. The results from fitting indicate that the local structure of Nb in the silicate melt is altered from its local structure in the quenched glass before heating and in the glass after heating in the diamond anvil cell. The importance of in situ analysis of melts and hydrothermal fluids at various temperatures and pressures is discussed in the context of our study.

Metal/Silicate Partitioning of P, Ga, and W at High Pressures and Temperatures: Dependence on Silicate Melt Composition

NASA Technical Reports Server (NTRS)

Bailey, Edward; Drake, Michael J.

2004-01-01

The distinctive pattern of element concentrations in the upper mantle provides essential evidence in our attempts to understand the accretion and differentiation of the Earth (e.g., Drake and Righter, 2002; Jones and Drake, 1986; Righter et al., 1997; Wanke 1981). Core formation is best investigated through use of metal/silicate partition coefficients for siderophile elements. The variables influencing partition coefficients are temperature, pressure, the major element compositions of the silicate and metal phases, and oxygen fugacity. Examples of studies investigating the effects of these variables on partitioning behavior are: composition of the metal phase by Capobianco et al. (1999) and Righter et al. (1997); silicate melt composition by Watson (1976), Walter and Thibault (1995), Hillgren et al. (1996), Jana and Walker (1997), and Jaeger and Drake (2000); and oxygen fugacity by Capobianco et al. (1999), and Walter and Thibault (1995). Here we address the relative influences of silicate melt composition, pressure and temperature.

A carbon-rich region in Miller Range 091004 and implications for ureilite petrogenesis

NASA Astrophysics Data System (ADS)

Day, James M. D.; Corder, Christopher A.; Cartigny, Pierre; Steele, Andrew M.; Assayag, Nelly; Rumble, Douglas; Taylor, Lawrence A.

2017-02-01

Ureilite meteorites are partially melted asteroidal-peridotite residues, or more rarely, cumulates that can contain greater than three weight percent carbon. Here we describe an exceptional C-rich lithology, composed of 34 modal % large (up to 0.8 mm long) crystalline graphite grains, in the Antarctic ureilite meteorite Miller Range (MIL) 091004. This C-rich lithology is embedded within a silicate region composed dominantly of granular olivine with lesser quantities of low-Ca pyroxene, and minor FeNi metal, high-Ca pyroxene, spinel, schreibersite and troilite. Petrological evidence indicates that the graphite was added after formation of the silicate region and melt depletion. Associated with graphite is localized reduction of host olivine (Fo88-89) to nearly pure forsterite (Fo99), which is associated with FeNi metal grains containing up to 11 wt.% Si. The main silicate region is typical of ureilite composition, with highly siderophile element (HSE) abundances ∼0.3 × chondrite, 187Os/188Os of 0.1260-0.1262 and Δ17O of -0.81 ± 0.16‰. Mineral trace-element analyses reveal that the rare earth elements (REE) and the HSE are controlled by pyroxene and FeNi metal phases in the meteorite, respectively. Modeling of bulk-rock REE and HSE abundances indicates that the main silicate region experienced ∼6% silicate and >50% sulfide melt extraction, which is at the lower end of partial melt removal estimated for ureilites. Miller Range 091004 demonstrates heterogeneous distribution of carbon at centimeter scales and a limited range in Mg/(Mg + Fe) compositions of silicate grain cores, despite significant quantities of carbon. These observations demonstrate that silicate rim reduction was a rapid disequilibrium process, and came after silicate and sulfide melt removal in MIL 091004. The petrography and mineral chemistry of MIL 091004 is permissive of the graphite representing late-stage C-rich melt that pervaded silicates, or carbon that acted as a lubricant during anatexis and impact disruption in the parent body. Positive correlation of Pt/Os ratios with olivine core compositions, but a wide range of oxygen isotope compositions, indicates that ureilites formed from a compositionally heterogeneous parent body that experienced variable sulfide and metal melt-loss that is most pronounced in relatively oxidized ureilites with Δ17O between -1.5 and ∼0‰.

The Origin of Silicic Arc Crust - Insights from the Northern Pacific Volcanic Arcs through Space and Time

NASA Astrophysics Data System (ADS)

Straub, S. M.; Kelemen, P. B.

2016-12-01

The remarkable compositional similarities of andesitic crust at modern convergent margins and the continental crust has long evoked the hypothesis of similar origins. Key to understanding either genesis is understanding the mode of silica enrichment. Silicic crust cannot be directly extracted from the upper mantle. Hence, in modern arcs, numerous studies - observant of the pervasive and irrefutable evidence of melt mixing - proposed that arc andesites formed by mixing of mantle-derived basaltic melts and fusible silicic material from the overlying crust. Mass balance requires the amount of silicic crust in such hybrid andesites to be on the order to tens of percent, implying that their composition to be perceptibly influenced by the various crustal basements. In order to test this hypothesis, major and trace element compositions of mafic and silicic arc magmas with arc-typical low Ce/Pb< 10 of Northern Pacific arcs (Marianas through Mexico) were combined with Pb isotope ratios. Pb isotope ratios are considered highly sensitive to crustal contamination, and hence should reflect the variable composition of the oceanic and continental basement on which these arcs are constructed. In particular, in thick-crust continental arcs where the basement is isotopically different from the mantle and crustal assimilation thought to be most prevalent, silicic magmas must be expected to be distinct from those of the associated mafic melts. However, in a given arc, the Pb isotope ratios are constant with increasing melt silica regardless of the nature of the basement. This observation argues against a melt origin of silicic melts from the crustal basement and suggest them to be controlled by the same slab flux as their co-eval mafic counterparts. This inference is validated by the spatial and temporal pattern of arc Pb isotope ratios along the Northern Pacific margins and throughout the 50 million years of Cenozoic evolution of the Izu Bonin Mariana arc/trench system that are can be related to with systematic, `real-time' changes in the composition of the slab flux with no role of the crustal basement. In summary, these data suggest that that silicic melts are ultimately genetically linked to the mafic co-eval series from the mantle, by such mechanisms as fractional crystallization, or melt-rock reactions, or a combination of both.

Solubility of copper in silicate melts as function of oxygen and sulfur fugacities, temperature, and silicate composition

NASA Astrophysics Data System (ADS)

Holzheid, A.; Lodders, K.

2001-06-01

The solubility of Cu in silicate melts coexisting with liquid Cu(Fe) metal and liquid Cu(Fe) sulfide was determined experimentally at oxygen fugacities ranging from 10 -9.1 to 10 -13.6 bar and sulfur fugacities ranging from 10 -2.5 to 10 -6.3 bar at 1300°C. An iron oxide-free silicate of anorthite-diopside eutectic composition and a synthetic MgO-rich basaltic silicate (FeO-bearing) were used in the partitioning experiments. In S-containing systems, some of the metal reacted to metal sulfide. The silicates in the four systems investigated (Fe-free and S-free; Fe-containing and S-free; Fe-free and S-containing; Fe-containing and S-containing) had different colors depending on the dissolved Cu species and the presence of iron and/or sulfur. Irrespective of the presence of sulfur, the solubility of Cu in the silicate increases with increasing oxygen fugacity and metal/silicate partition coefficients for Cu decrease. Increasing the temperature from 1300°C to 1514°C increases the Cu solubility (decreases the metal/silicate partition coefficient) at an oxygen fugacity 0.5 log units below the iron-wüstite (IW) equilibrium in the Fe-free, S-free and Fe-containing, S-free systems. We infer the presence of monovalent Cu + ("CuO 0.5") in the silicate melt on the basis of the solubility of Cu as function of oxygen fugacity. Experiments containing iron yield a formal valence of ˜0.5 for Cu at very low oxygen fugacities, which is not observed in Fe-free systems. The low formal valence is explained by redox reactions between iron and copper in the silicate melts. There is no evidence for sulfidic dissolution of Cu in the silicates but sulfur has indirect effects on Cu partitioning. Iron metal/silicate partition coefficients depend on oxygen fugacity and on sulfur fugacity. Sulfidic dissolution of iron and oxide-sulfide exchange reactions with Cu cause a small increase in Cu metal/silicate partition coefficients. We derive an activity coefficient (γ CuO 0.5) of 10 ± 1 for liquid CuO 0.5 at 1300°C for the silicate melts used here. A comparison with literature data shows that log γ CuO 0.5 increases in proportion to the mass percentages [CaO +(Al 2O 3)/2] in silicate melts. We recommend the following equations for Cu metal/silicate and sulfide/silicate partitioning for geochemical and cosmochemical modeling if silicate composition and the activity of Cu in the metal or sulfide is known: log D met/sil = -0.48 - 0.25 · log fO 2 - log γ Cu metal + 0.02 · [CaO + (Al 2O 3)/2; wt%] silicate logD sul/sil=+0.76-0.25 · logfO 2+0.25logfS 2-logγ CS 0.5,sulfide +0.02 · [CaO+Al 2O 3/2;wt%] silicate. The derived Cu metal/silicate and metal/sulfide partition coefficients are applied to core formation in the Earth and Mars. The observed Cu abundances in the Earth cannot be easily explained by simple core-mantle equilibrium, but the observed Cu abundances for Mars are consistent with core-mantle equilibrium at low pressure and temperatures.

Evidence of denser MgSiO3 glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean.

PubMed

Murakami, Motohiko; Bass, Jay D

2011-10-18

Ultralow velocity zones are the largest seismic anomalies in the mantle, with 10-30% seismic velocity reduction observed in thin layers less than 20-40 km thick, just above the Earth's core-mantle boundary (CMB). The presence of silicate melts, possibly a remnant of a deep magma ocean in the early Earth, have been proposed to explain ultralow velocity zones. It is, however, still an open question as to whether such silicate melts are gravitationally stable at the pressure conditions above the CMB. Fe enrichment is usually invoked to explain why melts would remain at the CMB, but this has not been substantiated experimentally. Here we report in situ high-pressure acoustic velocity measurements that suggest a new transformation to a denser structure of MgSiO(3) glass at pressures close to those of the CMB. The result suggests that MgSiO(3) melt is likely to become denser than crystalline MgSiO(3) above the CMB. The presence of negatively buoyant and gravitationally stable silicate melts at the bottom of the mantle, would provide a mechanism for observed ultralow seismic velocities above the CMB without enrichment of Fe in the melt. An ultradense melt phase and its geochemical inventory would be isolated from overlying convective flow over geologic time.

Evidence of denser MgSiO3 glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

PubMed Central

Murakami, Motohiko; Bass, Jay D.

2011-01-01

Ultralow velocity zones are the largest seismic anomalies in the mantle, with 10–30% seismic velocity reduction observed in thin layers less than 20–40 km thick, just above the Earth’s core-mantle boundary (CMB). The presence of silicate melts, possibly a remnant of a deep magma ocean in the early Earth, have been proposed to explain ultralow velocity zones. It is, however, still an open question as to whether such silicate melts are gravitationally stable at the pressure conditions above the CMB. Fe enrichment is usually invoked to explain why melts would remain at the CMB, but this has not been substantiated experimentally. Here we report in situ high-pressure acoustic velocity measurements that suggest a new transformation to a denser structure of MgSiO3 glass at pressures close to those of the CMB. The result suggests that MgSiO3 melt is likely to become denser than crystalline MgSiO3 above the CMB. The presence of negatively buoyant and gravitationally stable silicate melts at the bottom of the mantle, would provide a mechanism for observed ultralow seismic velocities above the CMB without enrichment of Fe in the melt. An ultradense melt phase and its geochemical inventory would be isolated from overlying convective flow over geologic time. PMID:21969547

Carbonatite and silicate melt metasomatism of the mantle surrounding the Hawaiian plume: Evidence from volatiles, trace elements, and radiogenic isotopes in rejuvenated-stage lavas from Niihau, Hawaii

NASA Astrophysics Data System (ADS)

Dixon, Jacqueline; Clague, David A.; Cousens, Brian; Monsalve, Maria Luisa; Uhl, Jessika

2008-09-01

We present new volatile, trace element, and radiogenic isotopic compositions for rejuvenated-stage lavas erupted on Niihau and its submarine northwest flank. Niihau rejuvenated-stage Kiekie Basalt lavas are mildly alkalic and are isotopically similar to, though shifted to higher 87Sr/86Sr and lower 206Pb/204Pb than, rejuvenated-stage lavas erupted on other islands and marginal seafloor settings. Kiekie lavas display trace element heterogeneity greater than that of other rejuvenated-stage lavas, with enrichments in Ba, Sr, and light-rare earth elements resulting in high and highly variable Ba/Th and Sr/Ce. The high Ba/Th lavas are among the least silica-undersaturated of the rejuvenated-stage suite, implying that the greatest enrichments are associated with the largest extents of melting. Kiekie lavas also have high and variable H2O/Ce and Cl/La, up to 620 and 39, respectively. We model the trace element concentrations of most rejuvenated-stage lavas by small degrees (˜1% to 9%) of melting of depleted peridotite recently metasomatized by a few percent of an enriched incipient melt (0.5% melting) of the Hawaiian plume. Kiekie lavas are best explained by 4% to 13% partial melting of a peridotite source metasomatized by up to 0.2% carbonatite, similar in composition to oceanic carbonatites from the Canary and Cape Verde Islands, with lower proportion of incipient melt than that for other rejuvenated-stage lavas. Primary H2O and Cl of the carbonatite component must be high, but variability in the volatile data may be caused by heterogeneity in the carbonatite composition and/or interaction with seawater. Our model is consistent with predictions based on carbonated eclogite and peridotite melting experiments in which (1) carbonated eclogite and peridotite within the Hawaiian plume are the first to melt during plume ascent; (2) carbonatite melt metasomatizes plume and surrounding depleted peridotite; (3) as the plume rises, silica-undersaturated silicate melts are also produced and contribute to the metasomatic signature. The metasomatic component is best preserved at the margins of the plume, where low extents of melting of the metasomatized depleted mantle surrounding the plume are sampled during flexural uplift. Formation of carbonatite melts may provide a mechanism to transfer plume He to the margins of the plume.

Thermodynamic Model of the Na-Al-Si-O-F Melts

NASA Astrophysics Data System (ADS)

Dolejs, D.; Baker, D. R.

2004-05-01

Fluorine is a common volatile element in magmatic-hydrothermal systems, but its solution mechanisms in highly polymerized silicate melts are poorly known. We have developed a thermodynamic model for fluorosilicate liquids which links experimentally determined phase equilibria and spectroscopic information on melt structure. The model is applicable to crystallization of fluoride minerals or fluoride-silicate immiscibility in natural felsic melts. Configurational properties of the liquid are defined by mixing of alkali fluoride, polyhedral aluminofluoride and silicofluoride species and non-bridging terminations of the silicate network. Abundances of individual structural species are described by a homogeneous equilibrium, representing melt depolymerization: F- (free) + O0 (bridging) = F0 (terminal) + O- (non-bridging), which is a replacement of one oxygen bridge, Si-O-Si, by two terminations, Si-F | Na-O-Si. In cryolite-bearing systems, the self-dissociation of octahedral aluminofluoride complexes: Na3[AlF6] = Na[AlF4] + 2 NaF, and the short-range order between (O,F)-corners and (Si,NaAl)-centers of tetrahedra: Si-O-Si + 2 [NaAl]-F = [NaAl]-O-[NaAl] + 2 Si-F, represent two additional interaction mechanisms. Portrayal of these equilibria in ternary Thompson reaction space allows to decrease the number of interaction mechanisms by linearly combining melt depolymerization with tetrahedral short-range order. In this formulation, the interaction parameters are incorporated directly in configurational properties, thus the complete melt speciation can be calculated, and the activities of any macroscopic species are readily derived. The model has been applied to subsystems of the Na2O-NaAlO2-SiO2-F2O-1 compositional space. Activity-composition relationships in the villiaumite-sodium silicate binaries require clustering of silicate tetrahedra in fluoride solvent. Phase-equilibria in cryolite-nepheline and cryolite-albite systems illustrate an overall increase of Na3AlF6 self-association in both joins. On the other hand, melt depolymerization by fluorine controls depression of silicate liquidi. The present model is useful for modeling the differentiation of peralkaline fluorine-bearing magmas and provides a starting point for predicting halide, carbonate, sulfide or sulfate saturation in natural melts.

Smyer H-Chondrite Impact-Melt Breccia and Evidence for Sulfur Vaporization

NASA Technical Reports Server (NTRS)

Rubin, Alan E.

2002-01-01

Smyer is an H-chondrite impact-melt breccia containing approx.20 vol% 0.5- to 13-mm-thick silicate-rich melt veins surrounding unmelted subrounded chondritic clasts up to 7 cm in maximum dimension. At the interface between some of the melt veins and chondritic clasts, there are troilite-rich regions consisting of unmelted. crushed 0.2- to 140-micron-size angular silicate grains and chondrule fragments surrounded by troilite and transected by thin troilite veins. Troilite fills every available fracture in the silicates. including some as thin as 0.1 microns. Little metallic Fe-Ni is present in these regions: the FeS/Fe modal ratio ranges from -25: 1 to approx.500: 1, far higher than the eutectic weight ratio of 7.5: 1. The texture of these regions indicates that the sulfide formed from a fluid of very low viscosity. The moderately high viscosity (0.2 poise) and large surface tension of liquid FeS, its inability to wet silicate grain surfaces at low oxygen fugacities. and the supereutectic FeS/Fe ratios in the troilite-rich regions indicate that the fluid was a vapor. It seems likely that during the shock event that melted Smyer, many silicates adjacent to the melt veins were crushed. Upon release of shock pressure. some of the troilite evaporated and dissociated. Molecules of S2 were transported and condensed into fractures and around tiny silicate grains: there, they combined with Fe from small adjacent metallic Fe-Ni grains to form troilite. The Ni content at the edges of some of these metal grains increased significantly; Co from these Ni-rich grains diffused into nearby kamacite. Impact-induced S volatilization may have played a major role in depleting the surface of 433 Eros (and other chondritic asteroids) in S.

An early geodynamo driven by exsolution of mantle components from Earth’s core

PubMed Central

Badro, James; Siebert, Julien; Nimmo, Francis

2016-01-01

Terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, stripping iron-loving elements from the silicate mantle to the metallic core1–3, and leaving rock-loving components behind. Here we performed experiments showing that at high enough temperature, Earth’s major rock-loving component, magnesium oxide, can also dissolve in core-forming metallic melts. Our data clearly point to a dissolution reaction, and are in agreement with recent DFT calculations4. Using core formation models5, we further show that a high-temperature event during Earth’s accretion (such as the Moon-forming giant impact6) can contribute significant amounts of magnesium to the early core. As it subsequently cools, the ensuing exsolution7 of buoyant magnesium oxide generates a substantial amount of gravitational energy. This energy is comparable to if not significantly higher than that produced by inner core solidification8 — the primary driver of the Earth’s current magnetic field9–11. Since the inner core is too young12 to explain the existence of an ancient field prior to ~1 billion years, our results solve the conundrum posed by the recent paleomagnetic observation13 of an ancient field at least 3.45 Gyr old. PMID:27437583

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

NASA Astrophysics Data System (ADS)

Jackson, Matthew; Blundy, Jon; Sparks, Steve

2017-04-01

Increasing geological and geophysical evidence suggests that crustal magma reservoirs are normally low melt fraction 'mushes' rather than high melt fraction 'magma chambers'. Yet high melt fractions must form within these mush reservoirs to explain the observed flow and eruption of low crystallinity magmas. In many models, crystallinity is linked directly to temperature, with higher temperature corresponding to lower crystallinity (higher melt fraction). However, increasing temperature yields less evolved (silicic) melt composition for a given starting material. If mobile, low crystallinity magmas require high temperature, it is difficult to explain how they can have evolved composition. Here we use numerical modelling to show that reactive melt flow in a porous and permeable mush reservoir formed by the intrusion of numerous basaltic sills into the lower continental crust produces magma in high melt fraction (> 0.5) layers akin to conventional magma chambers. These magma-chamber-like layers contain evolved (silicic) melt compositions and form at low (close to solidus) temperatures near the top of the mush reservoir. Evolved magma is therefore kept in 'cold storage' at low temperature, but also at low crystallinity so the magma is mobile and can leave the mush reservoir. Buoyancy-driven reactive flow and accumulation of melt in the mush reservoir controls the temperature and composition of magma that can leave the reservoir. The modelling also shows that processes in lower crustal mush reservoirs produce mobile magmas that contain melt of either silicic or mafic composition. Intermediate melt compositions are present but are not within mobile magmas. Silicic melt compositions are found at high melt fraction within the magma-chamber like layers near the top of the mush reservoir. Mafic melt compositions are found at high melt fraction within the cooling sills. Melt elsewhere in the reservoir has intermediate composition, but remains trapped in the reservoir because the local melt fraction is too low to form a mobile magma. The model results are consistent with geochemical data suggesting that lower crustal magma reservoirs supply silicic and mafic melts to arc volcanoes, but intermediate magmas are formed by mixing in shallower reservoirs. We suggest here that lower crustal magma chambers primarily form in response to changes in bulk composition caused by melt migration and chemical reaction in a mush reservoir. This process is different to the conventional and widely applied models of magma chamber formation. Similar processes are likely to operate in shallow mush reservoirs, but will likely be further complicated by the presence of volatile phases, and mixing of different melt compositions sourced from deeper mush reservoirs.

Silicate and Carbonatite Melts in the Mantle: Adding CO2 to the pMELTS Thermodynamic Model of Silicate Phase Equilibria

NASA Astrophysics Data System (ADS)

Antoshechkina, P. M.; Shorttle, O.

2016-12-01

The current rhyolite-MELTS algorithm includes a mixed H2O-CO2 vapor phase, and a self-consistent speciation model for CO2 and CaCO3 in the silicate liquid (Ghiorso & Gualda 2012; 2015). Although intended primarily to model crustal differentiation and degassing, GG15 captures much of the experimentally-observed melting behavior of CO2-rich mafic lithologies, including generation of small-degree carbonatite melts, a miscibility gap between carbonatite and silicate liquids at low P and a smooth transition to a single carbonated-silicate melt at high P (e.g. Dasgupta et al. 2007). However, solid and liquid carbonate phases were not used in calibration of GG15, and it is suitable only for P < 3 GPa. We present a preliminary model, based on pMELTS (Ghiorso et al. 2002), for melting of nominally-anhydrous carbonated peridotite and pyroxenite. In Antoshechkina et al. (2015; and references therein) we developed a scheme for calibration of molar volumes that directly interfaces with a MySQL database, adapted from LEPR (Hirschmann et al. 2008). Here, we further extend our database, e.g. to include multiple carbonate phases, and combine the calibration scheme with the libalphaMELTS interface to the rhyolite-MELTS, pMELTS, and H2O-CO2 fluid thermodynamic models (see magmasource.caltech.edu/alphamelts). We use a Monte-Carlo type calibration approach to fit the observed phases and compositions, though stop short of a fully Bayesian formulation. The CO2-fluid experimental database has been updated to include more recent and higher P studies, adding approximately 40 pure fluid plus liquid constraints that conform to the selection criteria used in GG15. To further expand the database, we plan to use some or all of: solid carbonate-bearing experiments; coexisting silicate and carbonatite liquids; phase-present, and phase-absent constraints. As a first approximation, we include four carbonate phases: pure calcite and aragonite, and binary solutions for dolomite-ankerite and magnesite-siderite. Following GG15, we have adopted the CO2 fluid model of Duan & Zhang (2006) and added CO2 and CaCO3 species to the pMELTS liquid model. A key question that we hope to address during calibration is whether a Na2CO3 liquid species is justified instead of, or in addition to, CaCO3 for the range over which pMELTS is calibrated (1 < P < 4 GPa).

Anionic Pt in Silicate Melts at Low Oxygen Fugacity: Speciation, Partitioning and Implications for Core Formation Processes on Asteroids

NASA Technical Reports Server (NTRS)

Medard, E.; Martin, A. M.; Righter, K.; Malouta, A.; Lee, C.-T.

2017-01-01

Most siderophile element concentrations in planetary mantles can be explained by metal/ silicate equilibration at high temperature and pressure during core formation. Highly siderophile elements (HSE = Au, Re, and the Pt-group elements), however, usually have higher mantle abundances than predicted by partitioning models, suggesting that their concentrations have been set by late accretion of material that did not equilibrate with the core. The partitioning of HSE at the low oxygen fugacities relevant for core formation is however poorly constrained due to the lack of sufficient experimental constraints to describe the variations of partitioning with key variables like temperature, pressure, and oxygen fugacity. To better understand the relative roles of metal/silicate partitioning and late accretion, we performed a self-consistent set of experiments that parameterizes the influence of oxygen fugacity, temperature and melt composition on the partitioning of Pt, one of the HSE, between metal and silicate melts. The major outcome of this project is the fact that Pt dissolves in an anionic form in silicate melts, causing a dependence of partitioning on oxygen fugacity opposite to that reported in previous studies.

Magma Electrolysis: An update

NASA Technical Reports Server (NTRS)

Colson, Russell O.; Haskin, Larry A.

1991-01-01

Electrolytic extraction of O2 from molten lunar soil is conceptually simple and thus a candidate process for producing O2 on the Moon. Possible container and electrode materials are being tested for durability in corrosive high-temperature silicate melts and looking for complications that might increase energy requirements. Gaseous oxygen is being produced by electrolysis of 1-2 gram quantities of silicate melts in spinel (MgAl2O4) crucibles; in these melts, spinel is a stable phase. The concentration of FeO was kept low because FeO decrease O2 production efficiency. Platinum electrodes were placed about 0.5 cm apart in the melt. The spinel crucible was still intact after 40 minutes of electrolysis, when the experiment was halted for examination. The Pt anode was also intact; its Pt was maintained in a dynamci state in which the anode was continuously oxidized but quickly reduced again by the silicate melt, inhibiting migration of Pt away from the anode. In melts with low concentrations of Al2O3 + SiO2 (2 wt percent), the energy of resistance heating was only approximately equal to 10 to 20 percent of the theoretical amount required to produce O2. In melts substantially more concentrated in Al2O3 + SiO2, higher melt viscosity resulted in frothing that, in the worst case, caused high enough melt resistivities to raise the energy requirements to nearly 10 times theoretical. Both Fe and Si are produced at the cathode; in iron-rich melts, a- and c-iron and molten ferrosilicon were observed. Production was also observed at the cathode of a previously unrecognized gas; which is not yet identified. The solubility of metallic species was measured in silicate melts. They are too low to reduce significantly the efficiency of O2 production.

Oxygen and iron production by electrolytic smelting of lunar soil

NASA Technical Reports Server (NTRS)

Colson, R. O.; Haskin, L. A.

1991-01-01

Oxygen, present in abundance in nearly all lunar materials, can theoretically be extracted by molten silicate electrolysis from any known lunar rock. Derivation of oxygen by this method has been amply demonstrated experimentally in silicate melts of a variety of compositions. This work can be divided into three categories: (1) measurement of solubilities of metals (atomic) in silicate melts; (2) electrolysis experiments under various conditions of temperature, container material, electrode configuration, current density, melt composition, and sample mass (100 to 2000 mg) measuring energy required and character of resulting products; and (3) theoretical assessment of compositional requirements for steady state operations of an electrolysis cell.

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

NASA Astrophysics Data System (ADS)

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

2015-02-01

We have reconstructed the compositional evolution of the silicate and carbonate melt, and various crystalline phases in the subvolcanic reservoir of Kerimasi Volcano in the East African Rift. Trace element concentrations of silicate and carbonate melt inclusions trapped in nepheline, apatite and magnetite from plutonic afrikandite (clinopyroxene-nepheline-perovskite-magnetite-melilite rock) and calciocarbonatite (calcite-apatite-magnetite-perovskite-monticellite-phlogopite rock) show that liquid immiscibility occurred during the generation of carbonatite magmas from a CO2-rich melilite-nephelinite magma formed at relatively high temperatures (1,100 °C). This carbonatite magma is notably more calcic and less alkaline than that occurring at Oldoinyo Lengai. The CaO-rich (32-41 wt%) nature and alkali-"poor" (at least 7-10 wt% Na2O + K2O) nature of these high-temperature (>1,000 °C) carbonate melts result from strong partitioning of Ca (relative to Mg, Fe and Mn) in the immiscible carbonate and the CaO-rich nature (12-17 wt%) of its silicate parent (e.g., melilite-nephelinite). Evolution of the Kerimasi carbonate magma can result in the formation of natrocarbonatite melts with similar composition to those of Oldoinyo Lengai, but with pronounced depletion in REE and HFSE elements. We suggest that this compositional difference results from the different initial parental magmas, e.g., melilite-nephelinite at Kerimasi and a nephelinite at Oldoinyo Lengai. The difference in parental magma composition led to a significant difference in the fractionating mineral phase assemblage and the element partitioning systematics upon silicate-carbonate melt immiscibility. LA-ICP-MS analysis of coeval silicate and carbonate melt inclusions provides an opportunity to infer carbonate melt/silicate melt partition coefficients for a wide range of elements. These data show that Li, Na, Pb, Ca, Sr, Ba, B, all REE (except Sc), U, V, Nb, Ta, P, Mo, W and S are partitioned into the carbonate melt, whereas Mg, Mn, Fe, Co, Cu, Zn, Al, Sc, Ti, Hf and Zr are partitioned into the silicate melt. Potassium and Rb show no preferential partitioning. Kerimasi melt inclusions show that the immiscible calcic carbonate melt is strongly enriched in Sr, Ba, Pb, LREE, P, W, Mo and S relative to other trace elements. Comparison of our data with experimental results indicates that preferential partitioning of oxidized sulfur (as SO4 2-), Ca and P (as PO4 3-) into the carbonate melt may promote the partitioning of Nb, Ta, Pb and all REE, excluding Sc, into this phase. Therefore, it is suggested that P and S enrichment in calcic carbonate magmas promotes the genesis of REE-rich carbonatites by liquid immiscibility. Our study shows that changes in the partition coefficients of elements between minerals and the coexisting melts along the liquid line of descent are rather significant at Kerimasi. This is why, in addition to the REE, Nb, Ta and Zr are also enriched in Kerimasi calciocarbonatites. We consider significant amounts of apatite and perovskite precipitated from melilite-nephelinite-derived carbonate melt as igneous minerals can have high LREE, Nb and Zr contents relative to other carbonatite minerals.

Can Suspended Iron-Alloy Droplets Explain the Origin, Composition and Properties of Large Low Shear Velocity Provinces?

NASA Astrophysics Data System (ADS)

Zhang, Z.; Dorfman, S. M.; Labidi, J.; Zhang, S.; Manga, M.; Stixrude, L. P.; McDonough, W. F.; Williams, Q. C.

2014-12-01

The enigmatic large low shear velocity provinces (LLSVPs) identified by seismic tomography at the base of the Earth's mantle have been proposed to be reservoirs of primordial mantle composition tapped by hot spot volcanism. The LLSVPs are characterized by anomalously low shear wave speed, VS, slightly elevated bulk sound speed, VB, and high density, ρ, in piles as thick as 1000 km above the core-mantle boundary. This combination of properties could be explained by a few percent dense melt, but the solidus of the lower mantle silicate and oxide assemblage may be too high to produce melt over the large extent of these regions. Iron-rich sulfur-bearing alloy may be molten at the conditions of the LLSVPs and ~1-2% of this component could satisfy both constraints on VS and ρ. An Fe alloy phase in the LLSVPs also has the potential to explain geochemical anomalies associated with hot spot volcanism, and its existence can be constrained by geochemical mass balance. Primordial noble gases such as 3He would be preferentially dissolved in Fe-rich melt rather than crystalline silicates. The reconstructed abundances of the moderately siderophile/chalcophile elements S, Cu and Pb in iron-alloy-bearing LLSVPs do not exceed predicted losses from volatilization, though this depends on the S-content of the alloy. The alloy phase would also be expected to incorporate W, and W isotope anomalies associated with hot spots are thus expected to have important implications for the timing of LLSVP formation. We have developed a model, via CIDER-2014, for the origin and properties of LLSVPs incorporating geochemistry, mineral physics, and fluid dynamic constraints on the generation, capture, and thermoelastic properties of Fe-rich melt droplets. The solidification of a basal magma ocean would produce both solid silicates and metallic melt. The bulk of the alloy generated by this process would sink to merge with the core. However, once the density of the remnant liquid exceeds that of the solid, newly-formed crystals floating at the crystallization front may trap droplets of Fe-rich melt as inclusions or at grain boundaries. We find that a mixture of mantle silicates and ~1-2% molten Fe-rich droplets matches constraints on density and seismic velocities and could host the hidden 3He and other elements of the primordial mantle reservoir.

Constraints on Ureilite Petrogenesis and Carbon-Metal-Silicate Equilibria on the UPB

NASA Astrophysics Data System (ADS)

Goodrich, C. A.; Holloway, J. R.

1992-07-01

The most important constraints on models of ureilite petrogenesis are 1) Ureilites have lost a basaltic complement (they are ultramafic, extremely depleted in plagiophile elements, enriched in HREE, and have negative Eu anomalies and superchondritic Ca/Al ratios). 2) Ureilites experienced long equilibration times at high T (indicated by coarse grain size, extreme homogeneity of core crystals, correlations between olivine and pyroxene compositions, and metamorphic-like textures), followed by rapid cooling (indicated by structural features of pyroxene and narrow reduction rims on olivine). 3) Ureilites are probably residues (based on mass balance) but partly crystallized from melts. 4) Ureilites are derived from a minimum of six reservoirs that were distinct in oxygen isotopic composition and did not equilibrate with one another (this is consistent with the observation that olivine and pyroxene cores do not show correlations of mg with MnO, Cr2O3, Sm/Eu or Lu/Eu). 5) There is a correlation between oxygen isotopic composition and mg ratio in ureilites. Similar correlations are observed for Allende chondrules and group means of H3-L3-LL3 chondrites (Fig. 1), and are argued to result from nebular processes [1]. 6) If graphite-metal-silicate-CO/CO2 equilibrium was established during melting, then mg ratios of ureilites were determined by depth because CCO redox reactions are strongly pressure-dependent. Cohenite-bearing metallic spherule inclusions in the silicates and euhedral shapes of large graphite crystals in low-shock ureilites have been taken as evidence of equilibrium. Olivine reduction rims, highly variable interstitial metal compositions, and a lack of correlation between mg and metal content argue against equilibrium. 7) Ureilites either lost a low melting-T metal fraction or gained a refractory-rich metal component. (they have high abundances of siderophile elements but show fractionation between [Os, Ir, W, Re] and [Ni, Ga, Ge, Au]). 8) Primordial noble gases were retained in some carbon phases. 9) Ureilites formed at ~4.55 Ga but both Sm-Nd and Rb-Sr isotopic systematics have been subsequently disturbed. Constraints 1-4 are best met if ureilites are partial melt residues produced by ~25% equilibrium partial melting on an oxygen-isotopically heterogeneous parent body in >=6 distinct melting zones. If there was no global magma ocean, km-sized melting zones would not equilibrate oxygen with one another in 10 m.y. Constraints 5 and 6 appear difficult to reconcile. If the UPB inherited a nebular oxygen isotope-mg correlation how could this correlation have survived partial melting? If the melting zones all experienced approximately the same degree of melting (Mn/Mg, Cr/Mg, and HRE provide evidence for this), and silicate equilibria determined mg, then the original correlation may simply have shifted to higher mg, consistent with the position of the ureilite trend relative to the Allende trends (Fig. 1). However, if mg was depth-dependent then it is unlikely that any oxygen isotope-mg correlation would remain. Also, noble gases in carbon would be lost (violating constraint 8) during carbon redox reactions. All constraints would be better met if graphite-metal-silicate-CO/CO2 equilibrium was not established during partial melting. If graphite was primary but a CO/CO2 fluid phase was not present then there would have been no pressure/depth dependence of fO(sub)2. As long as the pressure was sufficiently high (~100-200 bars) to stabilize the most ferroan ureilite (Fo 76) then the more magnesian ureilites would have been stable in the presence of graphite and metal. On the other hand, constraints 7, 8, and 9 could be neatly met if most of the carbon was not primary but a carbon-metal-noble gas assemblage was added as a late component to the ultramafic rocks. The cohenite-bearing metallic spherules are rare and tiny (10-50 micrometers) compared to interstitial metal (mm-sized irregular grains). They appear to have been droplets of immiscible, hypereutectic Fe(Ni)-C liquids that were trapped by crystallizing silicates. In contrast, the interstitial metal and graphite show no evidence of having been a liquid Fe-C alloy and their confinement to grain boundaries and reduction rims is consistent with late addition. Goodrich and Berkley (2) argued that the spherules were carbon-saturated at 1200-1225 degrees C and therefore that the silicate liquid must have contained graphite. However, in the Fe-C system the stable graphite liquidus is much steeper than the metastable cohenite liquidus, and although these alloys were cohenite-saturated, they were not graphite-saturated. Hence, the silicate magma probably did not contain graphite and carbon was not the dominant control on fO(sub)2. Thus, it may be possible to reconcile the main constraints on ureilite petrogenesis without high pressures. [1] R.N. Clayton & T.K. Mayeda (1988] GCA 52, 1313. [2] C.A. Goodrich & J.L. Berkely (1986) GCA 50, 681.

Residual stresses and phase transformations in Ytterbium silicate environmental barrier coatings

NASA Astrophysics Data System (ADS)

Stolzenburg, Fabian

Due to their high melting temperature, low density, and good thermomechanical stability, silicon-based ceramics (SiC, Si3N4) are some of the most promising materials systems for high temperature structural applications in gas turbine engines. However, their silica surface layer reacts with water vapor contained in combustion environments. The resulting hydroxide layer volatilizes, leading to component recession. Environmental barrier coatings (EBCs) have been developed to shield the substrate from degradation. Next generation coatings for silicon-based ceramics based on ytterbium silicates have shown a promising combination of very low and good thermomechanical properties. The focus of this thesis is threefold: In the first part, phase transformations in plasma sprayed ytterbium silicates were investigated. Plasma sprayed materials are known to contain large amounts of amorphous material. Phase changes during the conversion from amorphous to crystalline materials were investigated as they have been known to lead to failure in many coatings. The second part of this work focused on measuring residual stresses in multilayer EBCs using synchrotron X-ray diffraction (XRD). Strains were resolved spatially, with probe sizes as small as 20 um. Stresses were calculated using mechanical properties of ytterbium silicates, determined with in-situ loading and heating experiments. In-situ and ex-situ heating experiments allowed for the study of changes in stress states that occur in these EBC materials during heating and cooling cycles. Lastly, the interaction of ytterbium silicates with low-melting environmental calcium-magnesium-aluminosilicate (CMAS) glasses was studied. Synchrotron XRD was used to study the influence of CMAS on the stress state in the coating, X-ray computed tomography was used to provide 3D images of coatings, and EDS and TEM analysis were used to study the interactions at the CMAS/ytterbium silicate interface in detail.

Veins in Silicates of IIE Iron Mont Dieu II: Melt Migration Caused by Impact?

NASA Astrophysics Data System (ADS)

Van Roosbroek, N.; Debaille, V.; Pittarello, L.; Hecht, L.; Claeys, Ph.

2014-09-01

Mont Dieu II is a ~450kg meteorite classified as IIE iron. The primitive silicate inclusions can be linked to the H-chondrites. Thick metal veins with angular clasts crosscut these inclusions and could point to an impact-melt migration formation.

The thermodynamic activity of ZnO in silicate melts

NASA Astrophysics Data System (ADS)

Reyes, R. A.; Gaskell, D. R.

1983-12-01

The activity of ZnO in ZnO-SiO2 and CaO-ZnO-SiO2 melts has been measured at 1560 °C using a transpiration technique with CO-CO2 mixtures as the carrier gas. The activities of ZnO in dilute solution in 42 wt pct SiO2-38 wt pct CaO-20 wt pct A12O3 in the range 1400° to 1550 °C and in 62 wt pct SiO2-23.3 wt pct CaO-14.7 wt pct A12O3 at 1550 °C have also been measured. The measured free energies of formation of ZnO-SiO2 melts are significantly more negative than published estimated values and this, together with the behavior observed in the system CaO-Al2O3-SiO2, indicate that ZnO is a relatively basic oxide. The results are discussed in terms of the polymerization model of binary silicate melts and ideal silicate mixing in ternary silicate melts. The behavior of ZnO in dilute solution in CaO-Al2O3-SiO2 melts is discussed in terms of the possibility of the fluxing of ZnO by iron blast furnace slags.

Melting and reactive flow of a volatilized mantle beneath mid-ocean ridges: theory and numerical models

NASA Astrophysics Data System (ADS)

Keller, Tobias; Katz, Richard F.

2015-04-01

Laboratory experiments indicate that even small concentrations volatiles (H2O or CO2) in the upper mantle significantly affect the silicate melting behavior [HK96,DH06]. The presence of volatiles stabilizes volatile-rich melt at high pressure, thus vastly increasing the volume of the upper mantle expected to be partially molten [H10,DH10]. These small-degree melts have important consequences for chemical differentiation and could affect the dynamics of mantle flow. 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+volatilized MORB) physical model. The fluid dynamics is based on McKenzie's equations [McK84], while the thermo-chemical formulation of the system is represented by a novel disequilibrium multi-component melting model based on thermo-dynamic theory [RBS11]. This physical model is implemented as a parallel, two-dimensional, finite-volume code that leverages tools from the PETSc toolkit. Application of this simulation code to a mid-ocean ridge system suggests that the methodology captures the leading-order features of both hydrated and carbonated mantle melting, including deep, low-degree, volatile-rich melt formation. Melt segregation leads to continuous dynamic thermo-chemical dis-equilibration, while phenomenological reaction rates are applied to continually move the system towards re-equilibration. The simulations will be used first to characterize volatile extraction from the MOR system assuming a chemically homogeneous mantle. Subsequently, simulations will be extended to investigate the consequences of heterogeneity in lithology [KW12] and volatile content. These studies will advance our understanding of the role of volatiles in the dynamic and chemical evolution of the upper mantle. Moreover, they will help to gauge the significance of the coupling between the deep carbon cycle and the ocean/atmosphere system. REFERENCES HK96 Hirth & Kohlstedt (1996), Earth Planet Sci Lett DH06 Dasgupta & Hirschmann (2006), doi:10.1038/nature04612. H10 Hirschmann (2010), doi:10.1016/j.pepi.2009.12.003. DH10 Dasgupta & Hirschmann (2010), doi:10.1016/j.epsl.2010.06.039. McK84 McKenzie (1984), J Pet KW12 Katz & Weatherley (2012), doi: 10.1016/j.epsl.2012.04.042. RBS11 Rudge, Bercovici & Spiegelman (2011), doi: 10.1111/j.1365-246X.2010.04870.x

Theoretical Prediction of Melting Relations in the Deep Mantle: the Phase Diagram Approach

NASA Astrophysics Data System (ADS)

Belmonte, D.; Ottonello, G. A.; Vetuschi Zuccolini, M.; Attene, M.

2016-12-01

Despite the outstanding progress in computer technology and experimental facilities, understanding melting phase relations in the deep mantle is still an open challenge. In this work a novel computational scheme to predict melting relations at HP-HT by a combination of first principles DFT calculations, polymer chemistry and equilibrium thermodynamics is presented and discussed. The adopted theoretical framework is physically-consistent and allows to compute multi-component phase diagrams relevant to Earth's deep interior in a broad range of P-T conditions by a convex-hull algorithm for Gibbs free energy minimisation purposely developed for high-rank simplexes. The calculated phase diagrams are in turn used as a source of information to gain new insights on the P-T-X evolution of magmas in the deep mantle, providing some thermodynamic constraints to both present-day and early Earth melting processes. High-pressure melting curves of mantle silicates are also obtained as by-product of phase diagram calculation. Application of the above method to the MgO-Al2O3-SiO2 (MAS) ternary system highlights as pressure effects are not only able to change the nature of melting of some minerals (like olivine and pyroxene) from eutectic to peritectic (and vice versa), but also simplify melting relations by drastically reducing the number of phases with a primary phase field at HP-HT conditions. It turns out that mineral phases like Majorite-Pyrope garnet and Anhydrous Phase B (Mg14Si5O24), which are often disregarded in modelling melting processes of mantle assemblages, are stable phases at solidus or liquidus conditions in a P-T range compatible with the mantle transition zone (i.e. P = 16 - 23 GPa and T = 2200 - 2700 °C) when their thermodynamic and thermophysical properties are properly assessed. Financial support to the Senior Author (D.B.) during his stay as Invited Scientist at the Institut de Physique du Globe de Paris (IPGP, Paris) is warmly acknowledged.

Contribution of early impact events to metal-silicate separation, thermal annealing, and volatile redistribution: Evidence in the Pułtusk H chondrite

NASA Astrophysics Data System (ADS)

Krzesińska, Agata M.

2017-11-01

Three-dimensional X-ray tomographic reconstructions and petrologic studies reveal voluminous accumulations of metal in Pułtusk H chondrite. At the contact of these accumulations, the chondritic rock is enriched in troilite. The rock contains plagioclase-rich bands, with textures suggesting crystallization from melt. Unusually large phosphates are associated with the plagioclase and consist of assemblages of merrillite, and fluorapatite and chlorapatite. The metal accumulations were formed by impact melting, rapid segregation of metal-sulfide melt and the incorporation of this melt into the fractured crater basement. The impact most likely occurred in the early evolution of the H chondrite parent body, when post-impact heat overlapped with radiogenic heat. This enabled slow cooling and separation of the metallic melt into metal-rich and sulfide-rich fractions. This led to recrystallization of chondritic rock in contact with the metal accumulations and the crystallization of shock melts. Phosphorus was liberated from the metal and subsumed by the silicate shock melt, owing to oxidative conditions upon slow cooling. The melt was also a host for volatiles. Upon further cooling, phosphorus reacted with silicates leading to the formation of merrillite, while volatiles partitioned into the residual halogen-rich, dry fluid. In the late stages, the fluid altered merrillite to patchy Cl/F-apatite. The above sequence of alterations demonstrates that impact during the early evolution of chondritic parent bodies might have contributed to local metal segregation and silicate melting. In addition, postshock conditions supported secondary processes: compositional/textural equilibration, redistribution of volatiles, and fluid alterations.

Immiscible Transition from Carbonate-rich to Silicate-rich Melts in Eclogite+CO2 and Genesis of Ocean Island Melilitite

NASA Astrophysics Data System (ADS)

Dasgupta, R.; Stalker, K.; Hirschmann, M. M.

2004-12-01

Derivation of highly silica-undersaturated lavas such as olivine melilitites and melilite nephelinites from the mantle has been attributed to the effects of CO2. However, experimental studies have so far failed to demonstrate equilibrium of melilititic melts with a four-phase peridotite assemblage. Instead, the liquidus mineralogy of these silica-undersaturated magmas at high-pressures appears to be dominated by cpx1. Although, experimental partial melts from natural peridotite+CO2 span a continuum from carbonatite to alkali-basalts2, ocean-island melilitites have distinctly higher TiO2, FeO*, and CaO/(CaO+MgO)3,4 than compositions derived thus far from a carbonated lherzolite source. Partial melting experiments of a nominally anhydrous, natural eclogite with a small amount of added carbonate (SLEC1; 5 wt.% bulk CO2) were performed to investigate the transition between carbonate and silicate melts with increasing temperature. Experiments were conducted in a piston cylinder at 3 GPa from 1050 to 1400 ° C. Garnet and cpx appear in all the experiments and ilmenite is observed from 1075 to ˜1200 ° C. An Fe-bearing calcio-dolomitic melt is present from the solidus (1050-1075 ° C) up to 1375 ° C. Beginning at 1275 ° C, it coexists with a silica-poor silicate melt. Textural criteria indicate only a single CO2-rich silicate melt phase at 1400 ° C, coexisting with garnet and minor cpx. The liquidus temperature is estimated to be ˜1415 ° C from the melt fraction-temperature trend. With increasing temperature, the carbonate melt becomes richer in SiO2 ( ˜2 to 5 wt.%) and Al2O3 ( ˜0.75 to 2.25 wt.%) and poorer in CaO ( ˜30 to 25 wt.% from ˜1200 to 1375 ° C). Compositions of silicate partial melts change systematically with increasing temperature, increasing in SiO2 ( ˜36 to 41 wt.%), Al2O3 ( ˜4.5 to 9.5 wt.%), MgO ( ˜9.5 to 13 wt.%), CaO ( ˜8 to 14 wt.%) and decreasing in TiO2 ( ˜14 to 2.5 wt.%), FeO ( ˜20 to 13 wt.%), Na2O ( ˜3.3 to 1.7 wt.%). A wide temperature interval of coexisting carbonate and silicate partial melts of carbonated eclogite is distinct from the continuous transition from carbonate to silicate melts observed in carbonated peridotite systems2,5. At high-temperature, the silicate melts generated from SLEC1 are comparable to strongly silica-undersaturated, alkalic OIB lavas and closely resembles ocean island melilitite and nepheline melilitite3,4 in its SiO2, FeO*, MgO, CaO, TiO2, and Na2O content. They are also similar to melilite bearing lavas of continental affinity, though the match is not as close. Although the SLEC1 derived immiscible silicate melts are lower in Al2O3 than primitive alkalic OIB lavas, liquids richer in Al2O3 may be produced at slightly lower pressures. Geochemical and geodynamical investigations of carbonated eclogite sources for melilitic volcanic series thus merit consideration. 1. Brey, G and Green, D. H. 1977, CMP 61, 141-162. 2. Hirose, K. 1997, GRL 24, 2837-2840. 3. Clague, D. A. and Frey, F. A. 1982, JP 23, 447-504. 4. Hoernle, K. and Schmincke, H.-U. 1993, JP 34, 573-597. 5. Moore, K. R. and Wood, B. J. 1998, JP 39, 1943-1951.

The solubility of carbon monoxide in silicate melts at high pressures and its effect on silicate phase relations. [in terrestrial and other planetary interiors

NASA Technical Reports Server (NTRS)

Eggler, D. H.; Mysen, B. O.; Hoering, T. C.; Holloway, J. R.

1979-01-01

Autoradiographic analysis and gas chromatography were used to measure the solubility in silicate melts of CO-CO2 vapors (30 to 40% CO by thermodynamic calculation) in equilibrium with graphite at temperatures up to 1700 deg C and pressures to 30 kbar. At near-liquidus temperatures CO-CO2 vapors were found to be slightly more soluble than CO2 alone. As a result of the apparently negative temperature dependence of CO solubility, the solubility of CO-CO2 at superliquidus temperatures is less than that of CO2. Melting points of two silicates were depressed more by CO than by CO2. Phase boundary orientations suggest that CO/CO + CO2 is greater in the liquid than in the vapor. The effect of the presence of CO on periodotite phase relations was investigated, and it was found that melts containing both CO and CO2 are nearly as polymerized as those containing only CO2. These results suggest that crystallization processes in planetary interiors can be expected to be about the same, whether the melts contain CO2 alone or CO2 and CO.

Petrologically-based Electrical Profiles vs. Geophysical Observations through the Upper Mantle (Invited)

NASA Astrophysics Data System (ADS)

Gaillard, F.; Massuyeau, M.; Sifre, D.; Tarits, P.

2013-12-01

Mineralogical transformations in the up-welling mantle play a critical role on the dynamics of mass and heat transfers at mid-ocean-ridgeS. The melting event producing ridge basalts occur at 60 km depth below the ridge axis, but because of small amounts of H2O and CO2 in the source region of MOR-basalts, incipient melting can initiate at much greater depth. Such incipient melts concentrate incompatible elements, and are particularly rich in volatile species. These juices evolve from carbonatites, carbonated basalts, to CO2-H2O-rich basalts as recently exposed by petrological surveys; the passage from carbonate to silicate melts is a complex pathway that is strongly non-linear. This picture has recently been complicated further by studies showing that oxygen increasingly partitions into garnet as pressure increases; this implies that incipient melting may be prevented at depth exceeding 200 km because not enough oxygen is available in the system to stabilize carbonate melts. The aim of this work is twofold: - We modelled the complex pathway of mantle melting in presence of C-O-H volatiles by adjusting the thermodynamic properties of mixing in the multi-component C-O-H-melt system. This allows us to calculate the change in melt composition vs. depth following any sortS of adiabat. - We modelled the continuous change in electrical properties from carbonatites, carbonated basalts, to CO2-H2O-rich basalts. We then successfully converted this petrological evolution along a ridge adiabat into electrical conductivity vs. depth signal. The discussion that follows is about comparison of this petrologically-based conductivity profile with the recent profiles obtained by inversion of the long-period electromagnetic signals from the East-Pacific-Rise. These geophysically-based profiles reveal the electrical conductivity structure down to 400 km depth and they show some intriguing highly conductive sections. We will discuss heterogeneity in electrical conductivity of the upper mantle underneath the ridge in terms of melting processes. Our prime conclusion is that the redox melting process, universally predicted by petrological models, might not be universal and that incipient melting can extend down to the transition zone.

Syntectic Reactions involving Limestones and Limestone-Derived Carbonatitic Melts in the Generation of some Peralkalic Magmas: Reflections on Reginald Daly's Insights 100 Years Later

NASA Astrophysics Data System (ADS)

Lentz, D.

2017-12-01

The theoretical analysis of how sedimentary limestones and marbles could melt as a result of infiltrative contact metasomatism associated with silicate magmas, enables reconsideration of the limestone syntectic (assimilation) hypothesis for the origin of some peralkalic rocks. Reginald Daly's syntectic model published in detail in early 1918 fell out of favor because experimental evidence from the early 1960's suggested; 1) that limestone assimilation would increase P(CO2) and cause solidification of the silicate intrusion, 2) that there is a thermal barrier between silica-saturated and undersaturated magmas that would inhibit extensive desilication of the magma, and 3) the endothermic decarbonation reactions would require heat via magmatic crystallization of near-solidus magmas. However, these concerns were not as critical for high-T mafic melts relative to more low-T silicic melts, although most subsequent researchers dismissed syntexis as isotopic arguments also seemed robust. However, skarn-related limestone melts can interact much more easily with silicate magma, resulting in calc-silicate-forming (endoskarn-like) limestone syntectic (desilication - calcification-magnesification processes) decarbonation reactions with compositional evolution into the silica-undersaturated field. If mafic in composition originally when syntectically modified, then the CO2-bearing derivative peralkalic melt may subsequently react with the dominant volume magma or fractionate separately into a more evolved composition. As well, an increase in P(CO2) within the modified silicate fraction coupled with compositional evolution to more silica-undersaturated compositions enhances the stability of the immiscible, extremely low viscosity carbonate melt fraction. In addition, dynamic interaction of these co-existing immiscible melts (analogous to the current hypothesis) would partition elements, as well as isotopic signatures, such that they would be virtually unrecognizable as having a crustal level syntectic origin, based on mass-balance principles and Rayleigh decarbonation isotopic equilibria, as they do in many infiltrative skarn systems. Essentially, this partly vindicates the basic premise of Daly's limestone syntectic hypothesis for the origin of some peralkalic igneous rocks.

Method for the production of mineral wool and iron from serpentine ore

DOEpatents

O'Connor, William K [Albany, OR; Rush, Gilbert E [Scio, OR; Soltau, Glen F [Lebanon, OR

2011-10-11

Magnesium silicate mineral wools having a relatively high liquidus temperature of at least about 1400.degree. C. and to methods for the production thereof are provided. The methods of the present invention comprise melting a magnesium silicate feedstock (e.g., comprising a serpentine or olivine ore) having a liquidus temperature of at least about 1400.degree. C. to form a molten magnesium silicate, and subsequently fiberizing the molten magnesium silicate to produce a magnesium silicate mineral wool. In one embodiment, the magnesium silicate feedstock contains iron oxide (e.g., up to about 12% by weight). Preferably, the melting is performed in the presence of a reducing agent to produce an iron alloy, which can be separated from the molten ore. Useful magnesium silicate feedstocks include, without limitation, serpentine and olivine ores. Optionally, silicon dioxide can be added to the feedstock to lower the liquidus temperature thereof.

Siderophile Element Partitioning between Sulfide- and Silicate melts.

NASA Astrophysics Data System (ADS)

Hackler, S.; Rohrbach, A.; Loroch, D. C.; Klemme, S.; Berndt, J.

2017-12-01

Different theories concerning the formation of the Earth are debated. Either Earth accreted mostly `dry' or volatile elements were delivered late after core formation was largely inactive [1, 2], or volatile rich material was accreted during the main stages of accretion and core formation [3, 4, 5]. The partitioning behavior of siderophile volatile elements (SVE; S, Se, Te, Tl, Ag, Au, Cd, Bi, Pb, Sn, Cu, Ge, and In) may provide first order constraints whether these element concentrations in Earth's mantle were established before or after core-mantle differentiation or perhaps during both periods by multi stage core formation [6]. A special interest is laid into chalcophile element behavior with respective to the possible formation and segregation of a hadean matte [7]. To examine the influence of sulfur on SVE partitioning between metal-silicate melts, we performed experiments simulating a magma ocean stage evolving from sulfur poor- (low fO2) to more oxidizing sulfur rich- (Fe, Ni)-S melts ( 20 wt% S) towards the end of accretion. We carried out partitioning experiments under various P-T-fO2 conditions with a Bristol type end loaded piston cylinder apparatus (<3 GPa) and a 1000 t walker-type multi-anvil press (3-20 GPa). Our results will be presented at the meeting. References: [1] Albarède F. (2009) Nature, 461, 1227-1233. [2] Ballhaus C. et al. (2013) EPSL, 362, 237-245. [3] Fischer-Gödde M. and Kleine T. (2017) Nature, 541, 525 527. [4] Wade J. and Wood B. J. (2005) EPSL, 236, 78-95. [5] Rubie D. et al. (2016) Science, 253, 1141-1144. [6] Rubie D. et al. (2011) EPSL, 301, 31-42. [7] O'Neill H. St. C. (1991) GCA, 55, 1159-1172.

Experimentally determined sulfur isotope fractionation between metal and silicate and implications for planetary differentiation

NASA Astrophysics Data System (ADS)

Labidi, J.; Shahar, A.; Le Losq, C.; Hillgren, V. J.; Mysen, B. O.; Farquhar, J.

2016-02-01

The Earth's mantle displays a subchondritic 34S/32S ratio. Sulfur is a moderately siderophile element (i.e. iron-loving), and its partitioning into the Earth's core may have left such a distinctive isotope composition on the terrestrial mantle. In order to constrain the sulfur isotope fractionation occurring during core-mantle differentiation, high-pressure and temperature experiments were conducted with synthetic mixtures of metal and silicate melts. With the purpose to identify the mechanism(s) responsible for the S isotope fractionations, we performed our experiments in different capsules - namely, graphite and boron nitride capsules - and thus at different fO2, with varying major element chemistry of the silicate and metal fractions. The S isotope fractionations Δ34Smetal-silicate of equilibrated metal alloys versus silicate melts is +0.2 ± 0.1‰ in a boron-free and aluminum-poor system quenched at 1-1.5 GPa and 1650 °C. The isotope fractionation increases linearly with increasing boron and aluminum content, up to +1.4 ± 0.2‰, and is observed to be independent of the silicon abundance as well as of the fO2 over ∼3.5 log units of variations explored here. The isotope fractionations are also independent of the graphite or nitride saturation of the metal. Only the melt structural changes associated with aluminum and boron concentration in silicate melts have been observed to affect the strength of sulfur bonding. These results establish that the structure of silicate melts has a direct influence on the S2- average bonding strengths. These results can be interpreted in the context of planetary differentiation. Indeed, the structural environments of silicate evolve strongly with pressure. For example, the aluminum, iron or silicon coordination numbers increase under the effect of pressure. Consequently, based on our observations, the sulfur-bonding environment is likely to be affected. In this scheme, we tentatively hypothesize that S isotope fractionations between the silicate mantle and metallic core of terrestrial planetary bodies would depend on the average pressure at which their core-mantle differentiation occurred.

A multi-component evaporation model for beam melting processes

NASA Astrophysics Data System (ADS)

Klassen, Alexander; Forster, Vera E.; Körner, Carolin

2017-02-01

In additive manufacturing using laser or electron beam melting technologies, evaporation losses and changes in chemical composition are known issues when processing alloys with volatile elements. In this paper, a recently described numerical model based on a two-dimensional free surface lattice Boltzmann method is further developed to incorporate the effects of multi-component evaporation. The model takes into account the local melt pool composition during heating and fusion of metal powder. For validation, the titanium alloy Ti-6Al-4V is melted by selective electron beam melting and analysed using mass loss measurements and high-resolution microprobe imaging. Numerically determined evaporation losses and spatial distributions of aluminium compare well with experimental data. Predictions of the melt pool formation in bulk samples provide insight into the competition between the loss of volatile alloying elements from the irradiated surface and their advective redistribution within the molten region.

Sulfur Solubility In Silicate Melts: A Thermochemical Model

NASA Astrophysics Data System (ADS)

Moretti, R.; Ottonello, G.

A termochemical model for calculating sulfur solubility of simple and complex silicate melts has been developed in the framework of the Toop-Samis polymeric approach combined with a Flood - Grjotheim theoretical treatment of silicate slags [1,2]. The model allows one to compute sulfide and sulfate content of silicate melts whenever fugacity of gaseous sulphur is provided. "Electrically equivalent ion fractions" are needed to weigh the contribution of the various disproportion reactions of the type: MOmelt + 1/2S2 ,gas MSmelt+1/2O2 ,gas (1) MOmelt + 1/2S2 ,gas + 3/2O2 ,gas MSO4 ,melt (2) Eqs. 1 and 2 account for the oxide-sulfide and the oxide-sulfate disproportiona- tion in silicate melt. Electrically equivalent ion fractions are computed, in a fused salt Temkin notation, over the appropriate matrixes (anionic and cationic). The extension of such matrixes is calculated in the framework of a polymeric model previously developed [1,2,3] and based on a parameterization of acid-base properties of melts. No adjustable parameters are used and model activities follow the raoultian behavior implicit in the ion matrix solution of the Temkin notation. The model is based on a huge amount of data available in literature and displays a high heuristic capability with virtually no compositional limits, as long as the structural role assigned to each oxide holds. REFERENCES: [1] Ottonello G., Moretti R., Marini L. and Vetuschi Zuccolini M. (2001), Chem. Geol., 174, 157-179. [2] Moretti R. (2002) PhD Thesis, University of Pisa. [3] Ottonello G. (2001) J. Non-Cryst. Solids, 282, 72-85.

Pyroxene-melt equilibria. [for lunar maria basalts

NASA Technical Reports Server (NTRS)

Nielsen, R. L.; Drake, M. J.

1979-01-01

A thermodynamic analysis of pyroxene-melt equilibria is performed through use of a literature survey of analyses of high-Ca pyroxene and coexisting silicate melt pairs and analyses of low-Ca pyroxene silicate melt pairs. Reference is made to a modified version of a model developed by Bottinga and Weill (1972) which more successfully accounts for variations in melt composition than does a model which considers the melt to be composed of simple oxides which mix ideally. By using a variety of pyroxene melt relations, several pyroxene-melt and low-Ca pyroxene-high-Ca pyroxene geothermometers are developed which have internally consistant precisions of approximately + or - 20 C. Finally, it is noted that these equations may have application in modeling the evolution of mineral compositions during differentiation of basaltic magmas.

Experimental investigations of influence of pressure on the solubility of sulfur in silicate melts.

NASA Astrophysics Data System (ADS)

Kostyuk, Anastasia; Gorbachev, Nikolay

2010-05-01

Sulfide-silicate demixing of silicate melts on immiscible silicate and sulfide liquids occurs at magma sulfur saturation. This type of liquation plays an important role in geochemistry of mantle magmas, in processes of magmatic differentiation, and in ore deposit formation. The major parameter defining sulfide-silicate stratification of silicate melts is solubility of sulfur in magmas. It is considered that «solubility of sulfur» is concentration of sulfur in silicate melts. The previous researches have established positive dependence of solubility of sulphur on temperature [1, 2], melt composition [3, 4], oxidation-reduction conditions [5, 6] and our experimental data confirm it. However, available data does not give a simple answer about dependence of solubility of sulfur from pressure in modelling and natural "dry" sulfide-saturated silicate melts. The reason of difference in experiments remains not clear and further work is needed on this topic. In this paper, we report our findings on the influence of pressure on the solubility of sulfur in hydrous magnesian melts. This melts are represent by olivine basalt - picrite, coexisting with Fe-Cu-Ni sulfide melt and harzburgite (Ol+Opx) and it was investigated in a temperature range from 1200 to 1350°С and a pressure range from 0.2 to 2.5 GPa. Experiments were carried out on the piston-cylinder at Р=1-2.5GPa and in an internal-heated pressure vessels at P=0.2-0.6 GPa by a quenching technique. Our findings disagree with all previous studies demonstrating the positive [7] or negative [8, 9] influence of pressure on the solubility of sulfur in silicate melts. Our researches have shown complicated influence of pressure. Concentration of sulfur in glasses increases with increase in pressure from 0.2 to 0.6 GPa in experiments where andesite was used as a starting material. The sulfur concentration increases from 0.09 wt.% at 0.2 GPa to 0.4 wt.% at 0.6 GPa and Т=1200°С. In hydrous magnesian basalts (12-18 % MgO), we observe an extremum around 1.5 GPa. Solubility of sulfur increases from 0.31 wt.% to 1.01 wt.% at P=1-1.5 GPa, T=1300°С and decreases till 0.19 wt.% at P=2.5 GPa, T=1350°С. At ultrahigh (>4GPa) pressure concentration of sulfur in magmas will change slightly, considering increase of magnesian basalt liquidus in temperature and positive influence of temperature on the solubility of sulfur. Extreme character of the pressure dependences plays an important role in transportation of sulfide-silicate melts from the deep magmatic centers into the modern magmatic chambers where most of open deposits of hypabyssal ore-bearing magmas are localized. Possible explanation of an extremum in the field of 1.5-2.0 GPa is character of dissolution of water in silicate melts. Supported by grant RFBR 09-05-01131, 10-05-00928. References: 1.Luhr, J. F. Experimental phase relations of water- and sulphur-saturated arc magmas and the 1982 eruptions of El Chichòn Volcano. Journal of Petrology 31, 1990, p. 1071-1114. 2.Carroll, M. R. & Rutherford, M. J. The stability of igneous anhydrite: experimental results and implications for sulphur behavior in the 1982 El Chichòn trachyandesite and other evolved magmas. Journal of Petrology 28, 1987. p. 781-801. 3.Haughton, D. R., Roeder, P. L. & Skinner, B. J. Solubility of sulphur in mafic magmas. Economic Geology 69, 1974. p. 451-466 4.Wallace P., and Carmachael L.S.E. Sulfur in basaltic magmas. Geochim. Cosmochim. Acta 56, 1992. p. 1863-1874. 5.Fincham, C. J. B. & Richardson, F. D. Behaviour of sulphur in silicate and aluminate melts. Proceedings of the Royal Society of London 223, 1954. p. 40-62. 6.Carroll M.R. and Webster J.D. Solubilities of sulfur, noble gases, nitrogen, chlorine and fluorine in magmas. In Volatiles in Magmas (1994); pp. 231-279. Rev. mineral. 30, Mineralogical Society of America. 7.Mysen B.O., Popp R.N. Amer.J.Sci. V. 280. № 2. 1980 P.788-792. 8.Wendlandt R.F. Sulfide saturation of basalt and andesite melts at high pressure and temperature. Amer. Mineral. V. 67. № 7. 1982 P. 877-885. 9.Mavrogenes J.A., O'Neill H.S. The relative effects of pressure, temperature and oxygen fugacity on the solubility of sulfide in mafic magmas // Geochim. Cosmochim. Acta. 1999. V.63. № 7/8. P.1173-1180.

Coordination chemistry of titanium (IV) in silicate glasses and melts: IV. XANES studies of synthetic and natural volcanic glasses and tektites at ambient temperature and pressure

NASA Astrophysics Data System (ADS)

Farges, François; Brown, Gordon E.

1997-05-01

The coordination environment of Ti(IV) in seven natural and synthetic glasses of basaltic, trachytic, rhyolitic composition as well as four tektites has been studied using high-resolution Ti K-edge x-ray absorption near edge structure (XANES) spectroscopy at ambient temperature and pressure. Pre-edge features of Ti K-edge XANES spectra for these glasses suggest that [5]Ti is the dominant Ti coordination in all volcanic glasses. However, in the less polymerized glasses studied (basaltic and trachytic), [6]Ti is also important (30-50% of the total Ti) but [4]Ti was not detected. In contrast, [4]Ti is important in the most polymerized glasses (rhyolites and tektites) (from 30 to 60% of the total Ti depending on NBO/T) with [6]Ti below the detection level (≈10 at%). The local structure around Ti in the natural volcanic glasses is similar to that observed in compositionally similar synthetic silicate glasses and also in Ti-bearing silicate glass and melts with simpler compositions. The presence of F, Cl, and H 2O does not appear to affect the coordination of Ti, based on Ti K-edge XANES measurements of natural glasses bearing these volatile components. In contrast, the presence of nonbridging oxygens (produced by network modifiers) favors [5]Ti in these glass/melts. In parallel, [4]Ti is important when nonbridging oxygens are at small concentrations (NBO/T < 0.1). [6]Ti is detected (i.e., when present >10% of the total Ti) when alkaline-earths are dominant over alkalis, in agreement with bond-valence predictions for Ti-bearing silicate glass/melts below TiO 2 saturation. The abundance of [5]Ti in these silicate glasses (and presumably their melts) is in sharp contrast with the rarity of this Ti coordination state in common rock-forming minerals. Titanium cannot readily enter the structure of most rock-forming minerals, because it is present dominantly as titanyl-bearing ( [5]TiO) units in most natural magmas. In contrast, [6]Ti and [4]Ti (present, respectively, in basic and acidic magmas) are better able to enter inosilicates, but these coordination states represent only a fraction of the Ti in basalts, explaining the usually moderate level of incompatibility of Ti during magmatic differentiation. Finally, [5]Ti transforms to [6]Ti during crystallization of Ti-rich minerals (ilmenite, rutile, pyrochlore).

CUMULATE ROCKS ASSOCIATED WITH CARBONATE ASSIMILATION, HORTAVÆR COMPLEX, NORTH-CENTRAL NORWAY

NASA Astrophysics Data System (ADS)

Barnes, C. G.; Prestvik, T.; Li, Y.

2009-12-01

The Hortavær igneous complex intruded high-grade metamorphic rocks of the Caledonian Helgeland Nappe Complex at ca. 466 Ma. The complex is an unusual mafic-silicic layered intrusion (MASLI) because the principal felsic rock type is syenite and because the syenite formed in situ rather than by deep-seated partial melting of crustal rocks. Magma differentiation in the complex was by assimilation, primarily of calc-silicate rocks and melts with contributions from marble and semi-pelites, plus fractional crystallization. The effect of assimilation of calcite-rich rocks was to enhance stability of fassaitic clinopyroxene at the expense of olivine, which resulted in alkali-rich residual melts and lowering of silica activity. This combination of MASLI-style emplacement and carbonate assimilation produced three types of cumulate rocks: (1) Syenitic cumulates formed by liquid-crystal separation. As sheets of mafic magma were loaded on crystal-rich syenitic magma, residual liquid was expelled, penetrating the overlying mafic sheets in flame structures, and leaving a cumulate syenite. (2) Reaction cumulates. Carbonate assimilation, illustrated by a simple assimilation reaction: olivine + calcite + melt = clinopyroxene + CO2 resulted in cpx-rich cumulates such as clinopyroxenite, gabbro, and mela-monzodiorite, many of which contain igneous calcite. (3) Magmatic skarns. Calc-silicate host rocks underwent partial melting during assimilation, yielding a Ca-rich melt as the principal assimilated material and permitting extensive reaction with surrounding magma to form Kspar + cpx + garnet-rich ‘cumulate’ rocks. Cumulate types (2) and (3) do not reflect traditional views of cumulate rocks but instead result from a series of melt-present discontinuous (peritectic) reactions and partial melting of calc-silicate xenoliths. In the Hortavær complex, such cumulates are evident because of the distinctive peritectic cumulate assemblages. It is unclear whether assimilation of ‘normal’ silicate rocks results in peritectic assemblages, or whether they could be identified as such if they exist.

Identification of Gravity-Related Effects on Crystal Growth From Melts With an Immiscibility Gap

NASA Technical Reports Server (NTRS)

Kassemi, M.; Sayir, A.; Farmer, S.

1999-01-01

This work involves an experimental-numerical approach to study the effects of natural and Marangoni convections on solidification of single crystals from a silicate melt with a liquid-liquid immiscibility gap. Industrial use of crystals grown from silicate melts is becoming increasingly important in electronic, optical, and high temperature structural applications. Even the simplest silicate systems like Al203-SiO2 have had, and will continue to have, a significant role in the development of traditional and advanced ceramics. A unique feature of crystals grown from the silicate systems is their outstanding linear electro-optic properties. They also exhibit exceptionally high optical rotativity. As a result, these crystals are attractive materials for dielectric, optical, and microwave applications. Experimental work in our laboratory has indicated that directional solidification of a single crystal mullite appears to be preceded by liquid-liquid phase separation in the melt. Disruption of the immiscible state results in crystallization of a two phase structure. There is also evidence that mixing in the melt caused by density-driven convection can significantly affect the stability of the immiscible liquid layers and result in poly-crystalline growth. On earth, the immiscible state has only been observed for small diameter crystals grown in float zone systems where natural convection is almost negligible. Therefore, it is anticipated that growth of large single crystals from silicate melts would benefit from microgravity conditions because of the reduction of the natural convective mixing. The main objective of this research is to determine the effects of transport processes on the phase separation in the melt during growth of a single crystal while addressing the following issues: (1) When do the immiscible layers form and are they real?; (2) What are the main physical characteristics of the immiscible liquids?; and (3) How mixing by natural or Marangoni convection affects the stability of the phase separated melt.

Molybdenum Valence in Basaltic Silicate Melts

NASA Technical Reports Server (NTRS)

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

2010-01-01

The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

The electronic structure of iron in rhyolitic and basaltic glasses at high pressure

NASA Astrophysics Data System (ADS)

Solomatova, N. V.; Jackson, J. M.; Sturhahn, W.; Roskosz, M.

2016-12-01

The physical properties of silicate melts within the Earth's mantle affect the chemical and thermal evolution of the Earth's interior. To understand melting processes within the Earth, it is imperative to determine the structure of silicate melts at high pressure. It has been proposed that iron-bearing silicate melts may exist in the lower mantle just above the core-mantle boundary [1]. The behavior of iron in mantle melts is poorly understood, but can be experimentally approximated by iron-bearing silicate glasses. Previous studies have conflicting conclusions on whether iron in lower mantle silicate melts goes through a high-spin to low-spin transition [2-4]. Additionally, the average coordination environment of iron in glasses is poorly constrained. XANES experiments on basaltic glasses have demonstrated that both four and six-fold coordinated iron may exist in significant amounts regardless of oxidation state [5] while conventional Mössbauer experiments have observed five-fold coordinated Fe2+ with small amounts of four and six-fold coordinated Fe2+ [6]. In an attempt to resolve these discrepancies, we have measured the hyperfine parameters of iron-bearing rhyolitic glass up to 115 GPa and basaltic glass up to 92 GPa in a neon pressure medium using time-resolved synchrotron Mössbauer spectroscopy at the Advanced Photon Source (Argonne National Laboratory, IL). We observed changes in the hyperfine parameters likely due to coordination changes as a result of increasing pressure. Our results indicate that iron does not undergo a high-spin to low-spin transition within the pressure range investigated. Changes in the electronic configuration, such as the spin state of iron affects the compressibility and thermal properties of melts. With the assumption that silica glasses can be used to model structural behavior in silicate melts, our study predicts that iron in chemically-complex silica-rich melts in the lower mantle likely exists in a high-spin state. Select references: [1] Williams and Garnero, Science 273, 1528-1530 (1996). [2] Nomura et al., Nature 473, 199-202 (2011). [3] Gu et al., Geophys. Res. Lett. 39 (2012). [4] Mao et al., Am. Mineral. 99, 415-423 (2014). [5] Wilke et al., Chem. Geology 220, 143-161 (2005). [6] Cottrell and Kelley Earth Planet. Sci. Lett. 305, 270-282 (2011).

Precise new shock temperatures in forsterite and in silicate liquids: phase transitions and heat capacity at high pressure

NASA Astrophysics Data System (ADS)

Asimow, P. D.; Fat'yanov, O. V.; Su, C.; Ma, X. J.

2017-12-01

Shock temperature measurements in transparent samples provide key constraints on the phase transitions and thermodynamic properties of materials at high pressure and temperature. Such measurements are necessary, for example, to allow equation of state measurements taken along the Hugoniot to be translated to P-V-T space. We have recently completed a detailed study of the accuracy and reproducibility of calibration of our 6-channel fast pyrometer. We have also introduced improved analysis procedures of the time-dependent multi-wavelength radiance signal that avoid the need for a greybody assumption and therefore have better precision than earlier results. This has motivated (a) renewed study of the shock temperature of forsterite in the superheating, partial melting, and complete melting regimes, (b) pre-heated diopside-anorthite glass shock temperature experiments for comparison to pre-heated silicate liquid equation of state results, and (c) new soda-lime glass shock temperature experiments. Single-crystal synthetic forsterite samples were shocked along (100) to pressures between 120 and 210 GPa on the Caltech two-stage light gas gun. Uncertainties on most results are 50 K. Results above the onset of partial melting at 130 GPa are consistent with Lyzenga and Ahrens (1980) data and show a low P-T slope consistent with a partial melting interval. Complete melting may occur, given sufficient time, at about 210 GPa. The experiment at 120-130 GPa is anomalous, showing two-wave structure and time- and wavelength-dependent scattering suggesting a subsolidus phase transition behind the shock front. The amount of super-heating, if any, is far smaller than claimed by Holland and Ahrens (1997). Steady radiation profiles, high emissivity, and consistency from channel to channel provide high precision (±40 K) in diopside-anorthite liquid shocked from just above the glass transition to high pressure. Temperatures are colder than expected for a model with constant heat capacity, providing direct evidence that multicomponent silicate liquids show a major increase in heat capacity in the P-T range appropriate to terrestrial magma oceans (<150 GPa, <5000 K).

Sulfide Melts and Chalcophile Element Behavior in High Temperature Systems

NASA Astrophysics Data System (ADS)

Wood, B. J.; Kiseeva, K.

2016-12-01

We recently found that partition coefficients (Di) of many weakly and moderately chalcophile elements (e.g., Cd, Zn, Co, Cr, Pb, Sb, In) between sulfide and silicate melts are simple functions of the FeO content of the silicate liquid: logDi A-Blog[FeO] where [FeO] is the FeO concentration in the silicate, A and B are constants and the latter is related to the valency of the element of interest. In contrast, some strongly chalcophile (e.g Cu, Ni, Ag) and lithophile elements (e.g Mn) show marked deviations from linearity on a plot of logDi vs log[FeO]. More recent experiments show that linear behavior is confined to elements whose affinities for S and O are similar to those of Fe. In the case of elements more strongly lithophile than Fe (Ti, U, REE, Zr, Nb, Ta, Mn) a plot of logDi versus log[FeO] describes a U-shape with the element partitioning strongly into the sulfide at very low FeO and again at very high FeO content of the silicate melt. In contrast, strongly chalcophile elements (Cu, Ni, Ag) describe an n-shape on the plot of logD vs log[FeO]. The result is that lithophile elements such as Nb become more "chalcophile" than Cu at very low and very high FeO contents of the silicate melt. The reasons for this surprising behavior are firstly that, at very low FeO contents the silicate melt dissolves substantial amounts of sulfur, which drives down the activity of FeO and, from mass-action "pulls" the lihophile element into the sulfide. At high FeO contents of the silicate the sulfide itself starts to dissolve substantial amounts of oxygen and lithophile elements follow the oxygen into the sulfide. Given the principles which we have established, we are able to describe the patterns of chalcophile element behavior during partial melting and fractional crystallisation on Earth and also on bodies such as Mercury and Mars which are, respectively, strongly reduced relative to Earth and more oxidised than Earth.

Water speciation in sodium silicate glasses (quenched melts): A comprehensive NMR study

NASA Astrophysics Data System (ADS)

Xue, X.; Kanzaki, M.; Eguchi, J.

2012-12-01

Dissolution mechanism of water is an important factor governing how the dissolved water affects the physical and thermodynamic properties of silicate melts and glasses. Our previous studies have demonstrated that 1H MAS NMR in combination with 29Si-1H and 27Al-1H double-resonance NMR experiments is an effective approach for unambiguously differentiating and quantifying different water species in quenched silicate melts (glasses). Several contrasting dissolution mechanisms have been revealed depending on the melt composition: for relatively polymerized melts, the formation of SiOH/AlOH species (plus molecular H2O) and depolymerization of the network structure dominate; whereas for depolymerized Ca-Mg silicate melts, free OH (e.g. MgOH) become increasingly important (cf. [1]). The proportion of free OH species has been shown to decrease with both increasing melt polymerization (silica content) and decreasing field strength of the network modifying cations (from Mg to Ca). Our previous 1H and 29Si MAS NMR results for hydrous Na silicate glasses of limited compositions (Na2Si4O9 and Na2Si2O5) were consistent with negligible free OH (NaOH) species and depolymerizing effect of water dissolution [2]. On the other hand, there were also other studies that proposed the presence of significant NaOH species in hydrous glasses near the Na2Si2O5 composition. The purpose of this study is apply the approach of combined 1H MAS NMR and double-resonance (29Si-1H and 23Na-1H) NMR to gain unambiguous evidence for the OH speciation in Na silicate glasses (melts) as a function of composition. Hydrous Na silicate glasses containing mostly ≤ 1 wt% H2O for a range of Na/Si ratios from 0.33 to 1.33 have been synthesized by rapidly quenching melts either at 0.2 GPa using an internally heated gas pressure vessel or at 1 GPa using a piston cylinder high-pressure apparatus. NMR spectra have been acquired using a 9.4 T Varian Unity-Inova spectrometer. The 29Si and 1H chemical shifts are reported relative to TMS. The 1H MAS NMR spectra show broad peaks covering a chemical shift range of 1 to 17 ppm, with peak maxima near 4 and 15 ppm for more Si-rich compositions and near 12 ppm for less Si-rich compositions. The 1H-29Si-1H and 23Na-1H cross-polarization (CP) MAS NMR spectra for all the hydrous Na silicate glasses suggest negligible NaOH species, which, if present, should show enhanced relative intensity with 23Na-1H CP and the opposite with 1H-29Si-1H CP. All the observed 1H NMR intensities can be attributed to SiOH species of a range of hydrogen-bonding distances, plus a small amount of molecular H2O for higher water-content samples that contribute to intensities around 6 ppm. In conclusion, our combined 1H MAS NMR and double-resonance (1H-29Si-1H and 23Na-1H CP) MAS NMR study on Na silicate glasses of a range of Na/Si ratios has confirmed that water dissolves predominantly as SiOH and molecular H2O species in Na silicate melts (glasses), consistent with the trend predicted from studies on the Ca-Mg silicate system [1,2]. References:[1] Xue, X. Y.; Kanzaki, M. J. Am. Ceram. Soc. 2009, 92, 2803-2830. [2] Xue, X. Y.; Kanzaki, M. Geochim. Cosmochim. Acta 2004, 68, 5027-5057.

Slab-derived metasomatism in the Carpathian-Pannonian mantle revealed by investigations of mantle xenoliths from the Bakony-Balaton Highland Volcanic Field

NASA Astrophysics Data System (ADS)

Créon, Laura; Delpech, Guillaume; Rouchon, Virgile; Guyot, François

2017-08-01

A suite of fifteen peridotite xenoliths from the Bakony-Balaton Highland Volcanic Field (BBHVF, Pannonian Basin, Central Europe) that show abundant petrographic evidence of fluid and melt percolation were studied in order to decipher the formation of their melt pockets and veins. The suite mainly consists of "fertile" lherzolites (5.8-19.9 vol.% clinopyroxene) and a few harzburgites (1.9-5.4 vol.% clinopyroxene) from well-known localities (Szentbékkálla, Szigliget) and two previously unreported localities (Füzes-tó and Mindszentkálla). Major and trace element data indicate that most of the peridotites record variable degrees of partial melt extraction, up to > 15% for the harzburgites. Subsequently, the xenoliths experienced at least two stages of metasomatic modification. The first stage was associated with percolation of a volatile-bearing silicate melt and resulted in crystallization of amphibole, enrichment in the most incompatible trace elements (Ba, Th, U, Sr), and development of negative Nb-Ta anomalies in clinopyroxene. The second and last metasomatic event, widespread beneath the BBHVF, is associated with the formation of silicate melt pockets, physically connected to a network of melt veins, with large and abundant CO2 vesicles. The glass in these veins has sub-alkaline trachy-andesitic composition and displays an OIB-like trace element signature. Its composition attests to the migration through a supra-subduction zone mantle wedge of silicic melt highly enriched in volatiles (CO2, H2O, Cl, F), LILE, REE and HFSE and consistent with compositions of natural and experimental examples of slab melting-derived magma. In the present case, however, melt was likely derived from melting of oceanic crust and carbonated sediments under conditions where Nb-rich mineral phases were not stable in the residue. A likely scenario for the origin such melts involves melting after subduction ceased as the slab thermally equilibrated with the asthenosphere. Melt-rock reactions due to ascent of hot, CO2-rich, siliceous melt to near-Moho depths triggered destabilization of amphibole and primary clinopyroxene, spinel, and possibly olivine. The resulting andesitic glass in melt pockets evolved to more mafic compositions due to mantle mineral assimilation but has heterogeneous trace element signatures mostly inherited from preexisting amphibole. The present example of melt-rock reactions between highly volatile-enriched siliceous slab-derived melt and peridotite from the upper part of the lithospheric mantle ultimately produced derivative melt with major element composition akin to calc-alkaline basaltic andesite, with generally low trace elements concentrations but selective pronounced enrichments in LILE's such as Ba, Sr, Pb.

Silicate melts: The “anomalous” pressure dependence of the viscosity

NASA Astrophysics Data System (ADS)

Bottinga, Y.; Richet, P.

1995-07-01

The decrease of the specific volume, when the extent of polymerization diminishes, is a cause of the pressure sensitivity of the viscosity of silicate melts. This effect can be explained by means of the Adam and Gibbs (1965) theory, taking into account the pressure dependence of the degree of polymerization of the melt and its influence on the configurational entropy. At temperatures close to their glass transitions, liquid silica and SiO2sbnd Na2O melts have configurational entropies that are probably due to the mixing of their bridging and nonbridging oxygen atoms.

Early metal-silicate differentiation during planetesimal formation revealed by acapulcoite and lodranite meteorites

NASA Astrophysics Data System (ADS)

Dhaliwal, Jasmeet K.; Day, James M. D.; Corder, Christopher A.; Tait, Kim T.; Marti, Kurt; Assayag, Nelly; Cartigny, Pierre; Rumble, Doug; Taylor, Lawrence A.

2017-11-01

In order to establish the role and expression of silicate-metal fractionation in early planetesimal bodies, we have conducted a highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and 187Re-187Os study of acapulcoite-lodranite meteorites. These data are reported with new petrography, mineral chemistry, bulk-rock major and trace element geochemistry, and oxygen isotopes for Acapulco, Allan Hills (ALHA) 81187, Meteorite Hills (MET) 01195, Northwest Africa (NWA) 2871, NWA 4833, NWA 4875, NWA 7474 and two examples of transitional acapulcoite-lodranites, Elephant Moraine (EET) 84302 and Graves Nunataks (GRA) 95209. These data support previous studies that indicate that these meteorites are linked to the same parent body and exhibit limited degrees (<2-7%) of silicate melt removal. New HSE and osmium isotope data demonstrate broadly chondritic relative and absolute abundances of these elements in acapulcoites, lower absolute abundances in lodranites and elevated (>2 × CI chondrite) HSE abundances in transitional acapulcoite-lodranite meteorites (EET 84302, GRA 95209). All of the meteorites have chondritic Re/Os with measured 187Os/188Os ratios of 0.1271 ± 0.0040 (2 St. Dev.). These geochemical characteristics imply that the precursor material of the acapulcoites and lodranites was broadly chondritic in composition, and were then heated and subject to melting of metal and sulfide in the Fe-Ni-S system. This resulted in metallic melt removal and accumulation to form lodranites and transitional acapulcoite-lodranites. There is considerable variation in the absolute abundances of the HSE, both among samples and between aliquots of the same sample, consistent with both inhomogeneous distribution of HSE-rich metal, and of heterogeneous melting and incomplete mixing of silicate material within the acapulcoite-lodranite parent body. Oxygen isotope data for acapulcoite-lodranites are also consistent with inhomogeneous melting and mixing of accreted components from different nebular sources, and do not form a well-defined mass-dependent fractionation line. Modeling of HSE inter-element fractionation suggests a continuum of melting in the Fe-Ni-S system and partitioning between solid metal and sulfur-bearing mineral melt, where lower S contents in the melt resulted in lower Pt/Os and Pd/Os ratios, as observed in lodranites. The transitional meteorites, EET 84302 and GRA 95209, exhibit the most elevated HSE abundances and do not follow modelled Pt/Os and Pd/Os solid metal-liquid metal partitioning trends. We interpret this to reflect metal melt pooling into domains that were sampled by these meteorites, suggesting that they may originate from deeper within the acapulcoite-lodranite parent body, perhaps close to a pooled metallic 'core' region. Petrographic examination of transitional samples reveals the most extensive melting, pooling and networking of metal among the acapulcoite-lodranite meteorites. Overall, our results show that solid metal-liquid metal partitioning in the Fe-Ni-S system in primitive achondrites follows a predictable sequence of limited partial melting and metal melt pooling that can lead to significant HSE inter-element fractionation effects in proto-planetary materials.

Metal/silicate partitioning of Pt and the origin of the "late veneer"

NASA Astrophysics Data System (ADS)

Ertel, W.; Walter, M. J.; Drake, M. J.; Sylvester, P. J.

2002-12-01

Highly siderophile elements (HSEs) are perfect tools for investigating core forming processes in planetary bodies due to their Fe-loving (siderophile) geochemical behavior. Tremendous scientific effort was invested into this field during the past 10 years - mostly in 1 atm experiments. However, little is known about their high-pressure geochemistry and partitioning behavior between core and mantle forming phases. This knowledge is essential to distinguish between equilibrium (Magma Ocean) and non-equilibrium (heterogeneous accretion, late veneer) models for the accretion history for the early Earth. We therefore chose to investigate the partitioning behavior of Pt up to pressures of 140 kbar (14 GPa) and temperatures of 1950°C. The used melt composition - identical to melt systems used in 1 atm experiments - is the eutectic composition of Anorthite-Diopside (AnDi), a pseudo-basalt. A series of runs were performed which were internaly buffered by the piston cylinder apparatus, and were followed by duplicate experiments buffered in the AnDi-C-CO2 system. These experiments constitute reversals since they approach equilibrium from an initially higher and lower Pt solubility (8 ppm in the non-buffered runs, and essentially Pt free in the buffered runs). Experimental charges were encapsulated in Pt capsules which served as source for Pt. Experiments up to 20 kbar were performed in a Quickpress piston cylinder apparatus, while experiments at higher pressures were performed in a Walker-type (Tucson, AZ) and a Kawai-type (Misasa, Japan) multi anvil apparatus. Time series experiments were performed in piston-cylinder runs to determine minimum run durations for the achievement of equilibrium, and to guarantee high-quality partitioning data. 6 hours was found to be sufficient to obtain equilibrium. In practice, all experiments exceeded 12 hours to assure equilibrium. In a second set of runs the temperature dependence of the partitioning behavior of Pt was investigated between the melting point of the 1 atm, AnDi system and the melting point of the Pt capsule material. Over 150 piston cylinder and 12 multi anvil experiments have been performed. Pt solubility is only slightly dependent on temperature, decreasing between 1800 and 1400°C by less than an order of magnitude. In consequence, the partitioning behavior of Pt is mostly determined by its oxygen fugacity dependence, which has only been determined in 1 atm experiments. At 10 kbar, metal/silicate partition coefficients (D's) decrease by about 3 orders of magnitude. The reason for this is not understood, but might be attributed to a first order phase transition as found for, e.g., SiO2 or H2O. Above 10 kbar any increase in pressure does not lead to any further significant decrease in partition coefficients. Solubilities stay roughly constant up to 140 kbar. Abundances of moderately siderophile elements were possibly established by metal/silicate equilibrium in a magma ocean. These results for Pt suggest that the abundances of HSEs were most probably established by the accretion of a chondritic veneer following core formation, as metal/silicate partition coefficients are too high to be consistent with metal/silicate equilibrium in a magma ocean.

Novel Experimental Simulations of the Atmospheric Injection of Meteoric Metals

NASA Astrophysics Data System (ADS)

Gómez Martín, J. C.; Bones, D. L.; Carrillo-Sánchez, J. D.; James, A. D.; Trigo-Rodríguez, J. M.; Fegley, B., Jr.; Plane, J. M. C.

2017-02-01

A newly developed laboratory, Meteoric Ablation Simulator (MASI), is used to test model predictions of the atmospheric ablation of interplanetary dust particles (IDPs) with experimental Na, Fe, and Ca vaporization profiles. MASI is the first laboratory setup capable of performing time-resolved atmospheric ablation simulations, by means of precision resistive heating and atomic laser-induced fluorescence detection. Experiments using meteoritic IDP analogues show that at least three mineral phases (Na-rich plagioclase, metal sulfide, and Mg-rich silicate) are required to explain the observed appearance temperatures of the vaporized elements. Low melting temperatures of Na-rich plagioclase and metal sulfide, compared to silicate grains, preclude equilibration of all the elemental constituents in a single melt. The phase-change process of distinct mineral components determines the way in which Na and Fe evaporate. Ca evaporation is dependent on particle size and on the initial composition of the molten silicate. Measured vaporized fractions of Na, Fe, and Ca as a function of particle size and speed confirm differential ablation (I.e., the most volatile elements such as Na ablate first, followed by the main constituents Fe, Mg, and Si, and finally the most refractory elements such as Ca). The Chemical Ablation Model (CABMOD) provides a reasonable approximation to this effect based on chemical fractionation of a molten silicate in thermodynamic equilibrium, even though the compositional and geometric description of IDPs is simplistic. Improvements in the model are required in order to better reproduce the specific shape of the elemental ablation profiles.

Partitioning of copper between olivine, orthopyroxene, clinopyroxene, spinel, garnet and silicate melts at upper mantle conditions

NASA Astrophysics Data System (ADS)

Liu, Xingcheng; Xiong, Xiaolin; Audétat, Andreas; Li, Yuan; Song, Maoshuang; Li, Li; Sun, Weidong; Ding, Xing

2014-01-01

Previously published Cu partition coefficients (DCu) between silicate minerals and melts cover a wide range and have resulted in large uncertainties in model calculations of Cu behavior during mantle melting. In order to obtain true DCumineral/melt values, this study used Pt95Cu05 alloy capsules as the source of Cu to experimentally determine the DCu between olivine (ol), orthopyroxene (opx), clinopyroxene (cpx), spinel (spl), garnet (grt) and hydrous silicate melts at upper mantle conditions. Three synthetic silicate compositions, a Komatiite, a MORB and a Di70An30, were used to produce these minerals and melts. The experiments were conducted in piston cylinder presses at 1.0-3.5 GPa, 1150-1300 °C and oxygen fugacities (fO2) of from ∼2 log units below to ∼5 log units above fayalite-magnetite-quartz (FMQ). The compositions of minerals and quenched melts in the run products were measured with EMP and LA-ICP-MS. Attainment of equilibrium is verified by reproducible DCu values obtained at similar experimental conditions but different durations. The results show that DCu for ol/, opx/, spl/ and possibly cpx/melt increase with increasing fO2 when fO2 > FMQ + 1.2, while DCu for cpx/ and spl/melt also increase with increasing Na2O in cpx and Fe2O3 in spinel, respectively. In the investigated P-T-fO2 conditions, the DCumineral/melt values are 0.04-0.14 for ol, 0.04-0.09 for opx, 0.02-0.23 for cpx, 0.19-0.77 for spl and 0.03-0.05 for grt. These results confirm that Cu is highly incompatible (DCu < ∼0.2) in all the silicate minerals and oxides of the upper mantle with the exception of the high-Fe spinel, in which Cu is moderately incompatible (DCu = 0.4-0.8) and thus Cu will be enriched in the derived melts during mantle partial melting and magmatic differentiation if sulfide is absent. These experimental DCu values are used to assess the controls on Cu behavior during mantle melting. The model results suggest that MORBs and most arc basalts must form by sulfide-present melting at relatively reduced conditions, while high Cu (>70 ppm) arc basalts may form at oxidized, sulfide-absent conditions, which is consistent with the possibility of some high fO2 regions present in the arc mantle.

Determination of calcium carbonate and sodium carbonate melting curves up to Earth's transition zone pressures with implications for the deep carbon cycle

NASA Astrophysics Data System (ADS)

Li, Zeyu; Li, Jie; Lange, Rebecca; Liu, Jiachao; Militzer, Burkhard

2017-01-01

Melting of carbonated eclogite or peridotite in the mantle influences the Earth's deep volatile cycles and bears on the long-term evolution of the atmosphere. Existing data on the melting curves of calcium carbonate (CaCO3) and sodium carbonate (Na2CO3) are limited to 7 GPa and therefore do not allow a full understanding of carbon storage and cycling in deep Earth. We determined the melting curves of CaCO3 and Na2CO3 to the pressures of Earth's transition zone using a multi-anvil apparatus. Melting was detected in situ by monitoring a steep and large increase in ionic conductivity, or inferred from sunken platinum markers in recovered samples. The melting point of CaCO3 rises from 1870 K at 3 GPa to ∼2000 K at 6 GPa and then stays within 50 K of 2000 K between 6 and 21 GPa. In contrast, the melting point of Na2CO3 increases continuously from ∼1123 K at 3 GPa to ∼1950 K at 17 GPa. A pre-melting peak in the alternating current through solid CaCO3 is attributed to the transition from aragonite to calcite V. Accordingly the calcite V-aragonite-liquid invariant point is placed at 13 ± 1 GPa and 1970 ± 40 K, with the Clapeyron slope of the calcite V to aragonite transition constrained at ∼70 K/GPa. The experiments on CaCO3 suggest a slight decrease in the melting temperature from 8 to 13 GPa, followed by a slight increase from 14 to 21 GPa. The negative melting slope is consistent with the prediction from our ab initio simulations that the liquid may be more compressible and become denser than calcite V at sufficiently high pressure. The positive melting slope at higher pressures is supported by the ab initio prediction that aragonite is denser than the liquid at pressures up to 30 GPa. At transition zone pressures the melting points of CaCO3 are comparable to that of Na2CO3 but nearly 400 K and 500 K lower than that of MgCO3. The fusible nature of compressed CaCO3 may be partially responsible for the majority of carbonatitic melts found on Earth's surface being highly calcic. It also provides a plausible explanation for low-degree melts of carbonated silicate rocks being particularly calcic at these depths. The melting curves of CaCO3 and Na2CO3 overlap with the estimated ocean-island geotherm at transition zone pressures, indicating that carbonatitic melt is readily generated from multi-component carbonate systems in the transition zone. The occurrence of such melt between the 410 and 660 km depths may facilitate the formation of ultradeep diamonds, produce low-velocity regions within the transition zone, and create a barrier to carbonate subduction into the lower mantle.

Constraints on the origin of Os-isotope disequilibrium in included and interstitial sulfides in mantle peridotites: Implications for the interpretation of Os-isotope signatures in MORB and Abyssal Peridotites

NASA Astrophysics Data System (ADS)

Lassiter, J. C.

2016-12-01

The use of isotope variations in basalts to probe the composition and evolution of the mantle is predicated on the assumption of local (i.e., grain-scale) isotopic equilibrium during mantle melting (Hofmann & Hart, 1978). However, several studies report Os-isotope disequilibrium in distinct populations of sulfides in some peridotites. In principle, grain-scale isotopic heterogeneity could reflect variable radiogenic ingrowth in ancient sulfides with variable Re/Os, or partial re-equilibration of low-Re/Os sulfides with high-Re/Os silicate phases along grain boundaries during mantle melting (e.g., Alard et al., 2005). Both cases require that sulfides fail to maintain isotopic equilibrium with neighboring phases over geologically long ( Ga) time scales. The preservation of Os-isotope disequilibrium in peridotites has been ascribed to the armoring effect of low-[Os] silicates, which limit diffusive exchange between isolated Os-rich phases. This raises the prospect that peridotite-derived melts may not inherit the Os-isotope composition of their source. The timescale required for diffusive equilibration between separate sulfide grains or between Os-rich sulfides and Os-poor silicates is a function of average sulfide size and spacing, Os diffusivity in armoring silicate minerals, and Os partitioning between silicate and sulfide phases. For typical sulfide abundances and sizes in mantle peridotites, neighboring sulfides are expected to re-equilibrate in less than a few 10s of m.y. at adiabatic mantle temperatures, even for very high (>106) sulfide/silicate KD values. Maintenance of disequilibrium requires very large sulfides (>100 um) separated by several mm and diffusion rates (D < 10-20 m2/s) slower than for most other elements in olivine. Equilibration timescales between sulfides and surrounding silicates are similar, so that large-scale isotopic disequilibrium between sulfides and silicates is also unlikely within the convecting mantle. Instead, observed grain-scale Os-isotope disequilibrium in mantle peridotites likely reflects recent sulfide metasomatism linked to interaction with eclogite- or pyroxenite-derived melts. Interstitial sulfides with radiogenic Os-isotopes provide further evidence for a role of eclogite melting in MORB genesis.

Aqueous Silicate Polymers: An Alternative to `Supercritical' Fluids as Transport Agents in Subduction Zones

NASA Astrophysics Data System (ADS)

Mannig, C. E.

2005-12-01

The chemistry of subduction-zone fluids is complicated by melt-vapor miscibility and the existence of critical end-points in rock-H2O systems. It is commonly assumed that fluids in subduction zones attain properties intermediate in composition between hydrous silicate liquid and H2O, and that such fluids possess enhanced material transport capabilities. However, the relevance of supercritical, intermediate fluids to subduction zones presents four problems. (1) Albite-H2O is typically used as an analogue system, but the favorable position of its critical curve is not representative; critical curves for polymineralic subduction-zone lithologies lie at substantially higher P. (2) Even if albite-H2O is relevant, jadeite may interfere because of its different solubility and the positive clapeyron slope of its solidus, which points to liquid-structure changes that could cause reappearance of the liquid+vapor field. (3) Critical curves are features of very H2O-rich compositions; low-porosity, H2O-poor natural systems will coexist with intermediate fluids only over a narrow PT interval. (4) Intermediate fluids are expected only over short length scales because their migration will likely result in compositional shifts via reaction and mineral precipitation in the mantle wedge. Although supercritical, intermediate fluids are probably relatively unimportant in subduction zones, they reflect a chemical process that may hold the key to understanding high- P mass transfer. Miscibility in melt-vapor systems is a consequence of polymerization of dissolved components, primarily Si ± Al, Na and Ca. This behavior yields, e.g., aqueous Si-Si, Si-Al, Si-Na-Al, and Si-Ca oxide dimers and other multimers of varying stoichiometry (silicate polymers), even in subcritical, dilute, H2O-rich vapor. Silicate polymers in subcritical aqueous solutions have been inferred from high- P mineral-solubility experiments. The abundance of these species at high P shows that the chemistry of aqueous fluids in subduction-zones differs fundamentally from the more familiar ionic solutions of the upper crust. This has important consequences for minor element transport. Measurements of Fe, phosphorous and Ti solubility reveal that dissolved concentrations rise with increased aqueous albite content at fixed P and T, with maximum enhancements exceeding 10X at melt saturation. Subcritical silicate polymerization thus permits transport of low solubility components via their substitution into sites on aqueous multimers constructed of "polymer formers" such as Na, Al, and Si, even in dilute solutions. The partitioning of elements between the bulk fluid, the polymer network, and the rock matrix likely controls the overall compositional evolution of subduction-zone fluids. Because they form over a wider PT and bulk X range, subcritical silicate polymers in dilute solutions are likely responsible for more mass transfer in subduction zones than intermediate, supercritical fluids.

New poly(butylene succinate)/layered silicate nanocomposites: preparation and mechanical properties.

PubMed

Ray, Suprakas Sinha; Okamoto, Kazuaki; Maiti, Pralay; Okamoto, Masami

2002-04-01

New poly(butylene succinate) (PBS)/layered silicate nanocomposites have been successfully prepared by simple melt extrusion of PBS and octadecylammonium modified montmorillonite (C18-mmt) at 150 degrees C. The d-spacing of both C18-mmt and intercalated nanocomposites was investigated by wide-angle X-ray diffraction analysis. Bright-field transmission electron microscopic study showed several stacked silicate layers with random orientation in the PBS matrix. The intercalated nanocomposites exhibited remarkable improvement of mechanical properties in both solid and melt states as compared with that of PBS matrix without clay.

Transport and thermodynamic properties of hydrous melts in the system An-Di.

NASA Astrophysics Data System (ADS)

Giordano, D.; Potuzak, M.; Romano, C.; Russell, J. K.; Nowak, M.; Dingwell, D. B.

2006-12-01

The thermodynamic and transport properties hydrous silicate melts are of fundamental importance for characterization of the dynamics and energetics associated with silicate melts in the Earth. The literature concerning the transport and calorimetric properties of hydrous silicate melts remains scarce. With few exceptions little has been effectively done in order to provide chemical models that bridge the gap between the description of both complex and simple systems. The An-Di system is of general interest to geochemists as well as petrologists because it serves as a simple analogue for basaltic compositions. It was chosen here due to the combination of its simple chemical description and the presence of an extensive database of published experimental data on both its transport and thermodynamic properties. We have measured the viscosity (η)), the glass transition temperatures (Tg) and the heat capacity (Cp) of silicate melts in the An-Di system containing up to 3 wt.% of dissolved H2O. Viscosity data were obtained by using the dilatometric method of micropenetration, whereas a differential scanning calorimeter (DSC) was employed to determine the glass transition temperatures and the heat capacities. In order to characterize the well-known cooling/heating rate dependence of the glass transition temperatures the calorimetric measurements were performed at heating/cooling rate of 5, 10, 15 and 20 K/min. These results together with those of previous experimental studies have been used to provide a compositional model capable of calculating the Newtonian viscosity of melts as well as the Tg and Cp values for the An- Di+H2O system. The non-Arrhenian T-dependence of viscosity is accounted for by the Vogel-Fulcher- Tammann (VFT) and the Adam Gibbs (AG) equations. Our optimizations assume a common, high-T limit (A) for silicate melt viscosity, consistent with values provided by both theoretical and experimental studies. In particular, we also show that glass transition temperatures taken at each single heating/cooling rate are associated to single viscosity values. The equivalence of the activation energy associated to viscous and enthalpic relaxation process at specific temperatures also allow us to calibrate a tool to predict the viscosity of silicate melts by using specific heat curves. The effect of water on the heat capacity of the glass (Cpglass), from dry to nearly 3 wt% H2O, ranges from almost absent up to 20% of the measured Cp,glass values.

Investigation of the H7 ordinary chondrite, Watson 012: Implications for recognition and classification of Type 7 meteorites

NASA Astrophysics Data System (ADS)

Tait, Alastair W.; Tomkins, Andrew G.; Godel, Bélinda M.; Wilson, Siobhan A.; Hasalova, Pavlina

2014-06-01

Despite the fact that the number of officially classified meteorites is now over 45,000, we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting. Here, we conduct a detailed analysis of Watson 012, an H7 ordinary chondrite, to generate some clarity on the textural and chemical changes associated with equilibrium-based silicate partial melting in chondritic meteorites. To do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on Earth. The most distinctive texture generated by the partial melting that affected Watson 012 is an extensively interconnected plagioclase network, which is clearly observable with a petrographic microscope. Enlarged metal-troilite grains are encapsulated at widenings in this plagioclase network, and this is clearly visible in reflected light. Together with these features, we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic Type 7. To provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites, we use high-resolution X-ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large (cm-scale) skeletal crystals within an olivine-orthopyroxene-clinopyroxene framework, essentially pseudomorphing a melt network. Back-scattered electron imaging and element mapping are used to show that some of the clino- and orthopyroxene in Watson 012 also crystallised from silicate melt, and the order of crystallisation was orthopyroxene → clinopyroxene → plagioclase. X-ray diffraction data, supported by bulk geochemistry, are used to show that plagioclase and ortho- and clinopyroxene were added to the Watson 012 sample by through-flowing basaltic melt. Along with the absence of glass and granophyre, this interconnected network of coarse-grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body. The evidence of melt flux indicates that Watson 012 formed in the presence of a gravitational gradient, and thus at significant distance from the centre of the H chondrite parent body (the gravitational gradient at the centre would be zero). Our interpretation is that incipient silicate partial melting in Watson 012 occurred when a region of radiogenically heated H6 material located at considerable depth (possibly at ∼15-20 km from surface) was heated by an additional ca. 200-300 °C in association with a large shock event. Due to insulation at depth within an already hot parent body, the post-shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium-based silicate partial melting, and for melt to migrate. Although the observed melting may have been facilitated by additional heating from an impact event, this is not an example of instantaneous shock melting, which produces thermal disequilibrium at short length scales and distinctly different textures. A small number of H, L and LL chondrites have been previously classified as being of petrologic Type 7; with our new criteria to support that classification, these represent our best opportunity to explore the transition from high temperature sub-solidus metamorphism through the onset of silicate partial melting in three different parent bodies.

Spade: An H Chondrite Impact-melt Breccia that Experienced Post-shock Annealing

NASA Technical Reports Server (NTRS)

Rubin, Alan E.; Jones, Rhian H.

2006-01-01

The low modal abundances of relict chondrules (1.8 Vol%) and of coarse (i.e. >= 2200 micron-size) isolated mafic silicate grains (1.8 Vol%) in Spade relative to mean H6 chondrites (11.4 and 9.8 vol%, respectively) show Spade to be a rock that has experienced a significant degree of melting. Various petrographic features (e.g., chromite-plagioclase assemblages, chromite veinlets, silicate darkening) indicate that melting was caused by shock. Plagioclase was melted during the shock event and flowed so that it partially to completely surrounded nearby mafic silicate grains. During crystallization, plagioclase developed igneous zoning. Low-Ca pyroxene that crystallized from the melt (or equilibrated with the melt at high temperatures) acquired relatively high amounts of CaO. Metallic Fe-Ni cooled rapidly below the Fe-Ni solws and transformed into martensite. Subsequent reheating of the rock caused transformation of martensite into abundant duplex plessite. Ambiguities exist in the shock stage assignment of Spade. The extensive silicate darkening, the occurrence of chromite-plagioclase assemblages, and the impact-melted characteristics of Spade are consistent with shock stage S6. Low shock (stage S2) is indicated by the undulose extinction and lack of planar fractures in olivine. This suggests that Spade reached a maximum prior shock level equivalent to stage S6 and then experienced post-shock annealing (probably to stage Sl). These events were followed by a less intense impact that produced the undulose extinction in the olivine, characteristic of shock stage S2. Annealing could have occurred if Spade were emplaced near impact melts beneath the crater floor or deposited in close proximity to hot debris within an ejecta blanket. Spade firmly establishes the case for post-shock annealing. This may have been a common process on ordinary chondrites (OC) asteroids.

Partitioning of Moderately Siderophile Elements Among Olivine, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars

NASA Technical Reports Server (NTRS)

Gaetani, Glenn A.; Grove, Timothy L.

1997-01-01

This study investigates the effects of Variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals (V, Cr, Mn, Fe, Co, Ni. and Cu) and W among coexisting sulfide melt, silicate melt, and olivine. Experiments were performed at 1 atm pressure, 1350 C, with the fugacities of oxygen and sulfur controlled by mixing CO2, CO, and SO2 gases. Starting compositions consisted of a CaO-MgO-Al2O3-SiO2-FeO-Na2O analog for a barred olivine chondrule from an ordinary chondrite and a synthetic komatiite. The f(sub O2)/f(sub S2), conditions ranged from log of f(sub O2) = -7.9 to - 10.6, with log of f(sub S2) values ranging from - 1.0 to -2.5. Our experimental results demonstrate that the f(sub O2)/f(sub S2) dependencies of sulfide melt/silicate melt partition coefficients for the first series transition metals arc proportional to their valence states. The f(sub O2)/f(sub S2) dependencies for the partitioning of Fe, Co, Ni, and Cu are weaker than predicted on the basis of their valence states. Variations in conditions have no significant effect on olivine/melt partitioning other than those resulting from f(sub O2)-induced changes in the valence state of a given element. The strong f(sub O2)/f(sub S2) dependence for the olivine/silicate melt partitioning of V is attributable to a change of valence state, from 4+ to 3+, with decreasing f(sub O2). Our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early Earth and the Shergottite parent body (Mars). We find that the influence of S is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the Earth following core formation. Important constraints on core formation in Mars are provided by our experimental determination of the partitioning of Cu between silicate and sulfide melts. When combined with existing estimates for siderophile element abundances in the Martian mantle and a mass balance constraint from Fe, the experiments allow a determination of the mass of the Martian core (approx. 17 to 22 wt% of the planet) and its S content (approx.0.4 wt%). These modeling results indicate that Mars is depleted in S, and that its core is solid.

The system CaO-MgO-SiO2-CO2 at 1 GPa, metasomatic wehrlites, and primary carbonatite magmas

NASA Astrophysics Data System (ADS)

Lee, W. J.; Wyllie, P. J.

New experimental data in CaO-MgO-SiO2-CO2 at 1GPa define the vapor-saturated silicate-carbonate liquidus field boundary involving primary minerals calcite, forsterite and diopside. The eutectic reaction for melting of model calcite (1% MC)-wehrlite at 1GPa is at 1100°C, with liquid composition (by weight) 72% CaCO3 (CC), 9% MgCO3 (MC), and 18% CaMgSi2O6 (Di). These data combined with previous results permit construction of the isotherm-contoured vapor-saturated liquidus surface for the calcite/dolomite field, and part of the adjacent forsterite and diopside fields. Nearly pure calcite crystals in mantle xenoliths cannot represent equilibrium liquids. We recently determined the complete vapor-saturated liquidus surface between carbonates and model peridotites at 2.7GPa the peritectic reaction for dolomite (25% MC)-wehrlite at 2.7GPa occurs at 1300°C, with liquid composition 60% CC, 29% MC, and 11% Di. The liquidus field boundaries on these two surfaces provide the road-map for interpretation of magmatic processes in various peridotite-CO2 systems at depths between the Moho and about 100km. Relationships among kimberlites, melilitites, carbonatites and the liquidus phase boundaries are discussed. Experimental data for carbonatite liquid protected by metasomatic wehrlite have been reported. The liquid trends directly from dolomitic towards CaCO3 with decreasing pressure. The 1.5GPa liquid contains 87% CC and 4% Di, much lower in silicate components than our phase boundary. However, the liquids contain approximately the same CaCO3 (90+/- 1wt%) in terms of only carbonate components. For CO2-bearing mantle, all magmas at depth must pass through initial dolomitic compositions. Rising dolomitic carbonatite melt will vesiculate and may erupt as primary magmas through cracks from about 70km. If it percolates through metasomatic wehrlite from 70km toward the Moho at 35-40km, primary calcic siliceous carbonatite magma can be generated with silicate content at least 11-18% (70-40km) on the silicate-carbonate boundary.

Platinum and Palladium Exsolution Textures in Quenched Sulfide Melts

NASA Astrophysics Data System (ADS)

Reo, G.; Frank, M. R.; Loocke, M. P.; Macey, C. J.

2017-12-01

Magmatic sulfide ore deposits account for over 80% of the world's platinum group element (PGE) reserves. Layered mafic intrusions (LMIs), a type of magmatic sulfide ore deposit, contain alternating layers of silicate and sulfide mineralization that are thought to have coexisted as an immiscible silicate + sulfide melt pair. Platinum and palladium, the most common PGEs found in LMIs, heavily favor the sulfide melt. Nernst partition coefficients for Pt (D = wt% of Pt in sulfide/wt% of Pt in silicate) range from 102 to 109. This study examined the Pt- and Pd-bearing phases that formed from the quenched sulfide melts to better constrain the PGE-rich sulfide layers of LMIs system. Experiments were conducted with a basalt melt, sulfide melt, and Pt-Pd metal in a vertical tube furnace at 1100°C and 1 atm and with oxygen fugacity buffered to QFM (quartz-fayalite-magnetite). Following the experiments, run products containing both sulfide and silicate glasses (quenched melts) were analyzed by a Shimadzu EPMA-1720HT Electron Probe Microanalyzer. The focus here is on the quenched Fe-rich sulfides whereas data on the partitioning of Pt and Pd between the coexisting silicate and sulfide melts will be presented in the future. The sulfide samples were imaged in back-scattering mode and major and trace element concentrations of separate metal-rich phases in the sulfide matrix were ascertained through wavelength-dispersive x-ray spectroscopy. Three discernable PGE-rich phases were found to have exsolved from the sulfide matrix upon quenching of the sulfide melt. All of these phases had Fe and S of 21-24 and 16-22 wt.%, respectively. An irregularly shaped Pd- and Cu-rich sulfide phase ( 36 and 14 wt.%, respectively) makes up the majority of the exsolution product. A separate Pd- and Ni-rich phase ( 22 and 14 wt%, respectively) can be found as grains or rims adjacent to the exsolved Pd- and Cu-rich phase. A third Pd- and Pt-rich phase ( 26 and 18 wt.%, respectively) exhibits a dendritic quench texture and is usually surrounded by the sulfide matrix. These data indicate that multiple phases, each with a different Pt:Pd ratio can form upon quench of a homogenous sulfide melt. Thus, the analysis of PGE-rich sulfide domains within LMI may be best considered as a single phase when conducting exploration efforts.

Experimental Behavior of Sulfur Under Primitive Planetary Differentiation Processes, the Sulfide Formations in Enstatite Meteorites and Implications for Mercury.

NASA Technical Reports Server (NTRS)

Malavergne, V.; Brunet, F.; Righter, K.; Zanda, B.; Avril, C.; Borensztajn, S.; Berthet, S.

2012-01-01

Enstatite meteorites are the most reduced naturally-occuring materials of the solar system. The cubic monosulfide series with the general formula (Mg,Mn,Ca,Fe)S are common phases in these meteorite groups. The importance of such minerals, their formation, composition and textural relationships for understanding the genesis of enstatite chondrites (EC) and aubrites, has long been recognized (e.g. [1]). However, the mechanisms of formation of these sulfides is still not well constrained certainly because of possible multiple ways to produce them. We propose to simulate different models of formation in order to check their mineralogical, chemical and textural relevancies. The solubility of sulfur in silicate melts is of primary interest for planetary mantles, particularly for the Earth and Mercury. Indeed, these two planets could have formed, at least partly, from EC materials (e.g. [2, 3, 4]). The sulfur content in silicate melts depends on the melt composition but also on pressure (P), temperature (T) and oxygen fugacity fO2. Unfortunately, there is no model of general validity in a wide range of P-T-fO2-composition which describes precisely the evolution of sulfur content in silicate melts, even if the main trends are now known. The second goal of this study is to constrain the sulfur content in silicate melts under reducing conditions and different temperatures.

Apatite-hosted melt inclusions in Damiao massif anorthosite complex, North China

NASA Astrophysics Data System (ADS)

Wang, M.; Veksler, I. V.; Zhang, Z.

2014-12-01

Models for the nelsonite formation are currently highly contentious, with liquid immiscibility and fractional crystallization as frequently proposed formation mechanisms. The nelsonites in the Damiao massif anorthosite complex in the North China Craton and experimental evidence are revisited for the existence of silica-free CaO-FeO-Fe2O3-TiO2-P2O5 immiscible nelsonitic liquids. Our results of differential scanning calorimetry (DSC) demonstrate that nelsonite with the composition of one-third apatite and two-thirds Fe-Ti oxides by weight completely melts well above 1450 ºC, which is in good agreement with numerous experimental studies of the CaO-P2O5-FexO system in connection to metallurgy. Thus, the composition cannot be molten at temperatures relevant for crystallization of the Damiao magma. A review of experimental studies of liquid immiscibility and analyses of natural immiscible glasses show that all the liquids on the Fe- and P-rich side of the miscibility gap have at least 20 wt. % of aluminosilicate components. Main results of this study come from the analyses of apatite-hosted melt inclusions in Damiao nelsonite. The inclusions range from ~3 to 200 μm in diameter. They are ubiquitous and meet all the morphological criteria of primary melt inclusions crystallised into assemblages of daughter minerals. Almost all of them contain vermiculite and chlorite, and some contain biotite, amphibole, phlogopite and Fe-Ti oxides. Out of dozens analysed inclusions, only three have high contents of SiO2 (62.1-73.8 wt. %) and low contents of FeO (0.25-2.35 wt. %). Bulk compositions of other inclusions show large variations in SiO2 (20.79-50.16 wt. %) and FeOt (13.44-32.78 wt. %). With a few exceptions, the inclusions are very low in CaO (0.04-1.51 wt. %, and high in Al2O3 (10-21.17 wt. %). Despite the high Fe content, the compositions differ from those of the typical immiscible Fe-rich melts. It appears that the cumulus apatite crystallised from Fe-rich, hydrated silicate melt. We propose that the inclusions at Damiao record a trend of intercumulus melt evolution, which was strongly affected by separation of a hydrothermal fluid phase and the losses of alkali and Ca silicate components from the melt into the fluid.

Melt segregation from partially molten source regions - The importance of melt density and source region size

NASA Technical Reports Server (NTRS)

Stolper, E.; Hager, B. H.; Walker, D.; Hays, J. F.

1981-01-01

An investigation is conducted regarding the changes expected in the density contrast between basic melts and peridotites with increasing pressure using the limited data available on the compressibilities of silicate melts and data on the densities of mantle minerals. It is concluded that since compressibilities of silicate melts are about an order of magnitude greater than those of mantle minerals, the density contrast between basic melts and mantle minerals must diminish significantly with increasing pressure. An earlier analysis regarding the migration of liquid in partially molten source regions conducted by Walker et al. (1978) is extended, giving particular attention to the influence of the diminished density contrast between melt and residual crystals with increasing source region depth and to the influence of source region size. This analysis leads to several generalizations concerning the factors influencing the depths at which magmas will segregate from their source regions and the degrees of partial melting that can be achieved in these source regions before melt segregation occurs.

Oceanic slab melting and mantle metasomatism.

PubMed

Scaillet, B; Prouteau, G

2001-01-01

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (< 50 Ma) subducted plates. Slab melts are silicic and strongly sodic (trondhjemitic). They are produced at low temperatures (< 1000 degrees C) and under water excess conditions. Their interaction with mantle peridotite produces hydrous metasomatic phases such as amphibole and phlogopite that can be more or less sodium rich. Upon interaction the slab melt becomes less silicic (dacitic to andesitic), and Mg, Ni and Cr richer. Virtually all exposed slab melts display geochemical evidence of ingestion of mantle material. Modern slab melts are thus unlike Archean Trondhjemite-Tonalite-Granodiorite rocks (TTG), which suggests that both types of magmas were generated via different petrogenetic pathways which may imply an Archean tectonic model of crust production different from that of the present-day, subduction-related, one.

Ar-Ar and I-Xe Ages of Caddo County and Thermal History of IAB Iron Meteorites

NASA Technical Reports Server (NTRS)

Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

2005-01-01

Inclusions in IAB iron meteorites include non-chondritic silicate and those with more primitive chondritic silicate composition. Coarse-grained gabbroic material rich in plagioclase and diopside occurs in the Caddo County IAB iron meteorite and represents a new type of chemically differentiated, extra-terrestrial, andesitic silicate. Other parts of Caddo contain mostly andesitic material. Caddo thus exhibits petrologic characteristics of parent body metamorphism of a chondrite-like parent and inhomogeneous segregation of melts. Proposed IAB formation models include parent body partial melting and fractional crystallization or incomplete differentiation due to internal heat sources, and impact/induced melting and mixing. Benedix et al. prefer a hybrid model whereby the IAB parent body largely melted, then underwent collisional breakup, partial mixing of phases, and reassembly. Most reported 129I- Xe-129 ages of IABs are greater than 4.56 Gyr and a few are greater than or = 4.567 Gyr. These oldest ages exceed the 4.567 Gyr Pb-Pb age of Ca, Al-rich inclusions in primitive meteorites,

Superheat in magma oceans

NASA Technical Reports Server (NTRS)

Jakes, Petr

1992-01-01

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

Experimental investigation on V isotope equilibrium fractionation factor between metal and silicate melt

NASA Astrophysics Data System (ADS)

Zhang, S.; Zhang, H.; Huang, F.

2017-12-01

Equilibrium fractionation factors of stable isotopes between metal and silicate melt are of vital importance for understanding the isotope variations within meteorites and planetary bodies. The V isotope composition (reported as δ51V = 1000 × [(51V/50Vsample/51V/50VAA)-1] ) of the bulk silicate Earth (BSE) has been estimated as δ51V = -0.7 ± 0.2‰ (2sd) [1], which is significantly heavier than most meteorites by 1‰ [2]. Such isotopic offset may provide insights for the core formation and core-mantle segregation. Therefore, it is important to understand V isotope equilibrium fractionation factor between silicate melt and metal. Nielsen et al. (2014) [2] had performed 3 experiments using starting materials of pure Fe metal and An50Di28Fo22 composition, revealing no resolvable V isotope fractionation. However, it is not clear whether chemical compositions in the melts can affect V isotope fractionations. Therefore, we experimentally calibrated equilibrium V isotope fractionation between Fe metallic and basaltic melt, with particular focus on the effect of Ni and other light elements. Experiments were performed at 1 GPa and 1600 oC using a 3/4″ end-loaded piston cylinder. The starting materials consisted of 1:1 mixture of pure Fe metal and basaltic composition [3]. The isotope equilibrium was assessed using time series experiments combined with the reverse reaction method. Carbon saturation and C-free experiments were achieved by using graphite and silica capsules, respectively. The Ni series experiments were doped with 6 wt% Ni into the starting Fe metal. The metal and silicate phases of samples were mechanically separated, V was purified using a chromatographic technique, and V isotope ratios were measured using MC-ICP-MS [4]. Carbon saturation, C-free experiments and Ni series experiment all show non-resolvable V isotope fractionation between metal and basaltic melt, which indicates that the presence of C and Ni could not affect V isotope fractionation during core formation. More experiments will be performed to explore the effect of Si and S in the metal on V isotope fractionation between metal and silicate melt.References: [1] Prytulak et al. (2013) EPSL 365, 177-189 [2] Nielsen et al. (2014) EPSL 389, 167-175 [3] Cottrell et al. (2009) CG 268, 167-179 [4] Wu et al. (2016) CG 421, 17-25

Osmium mass balance in peridotite and the effects of mantle-derived sulphides on basalt petrogenesis

NASA Astrophysics Data System (ADS)

Harvey, J.; Dale, C. W.; Gannoun, A.; Burton, K. W.

2011-10-01

Analyses of enriched mantle (EM)-basalts, using lithophile element-based isotope systems, have long provided evidence for discrete mantle reservoirs with variable composition. Upon partial melting, the mantle reservoir imparts its isotopic fingerprint upon the partial melt produced. However, it has increasingly been recognised that it may not be simple to delimit these previously well-defined mantle reservoirs; the "mantle zoo" may contain more reservoirs than previously envisaged. Here we demonstrate that a simple model with varying contributions from two populations of compositionally distinct mantle sulphides can readily account for the observed heterogeneities in Os isotope systematics of such basalts without additional mantle reservoirs. Osmium elemental and isotopic analyses of individual sulphide grains separated from spinel lherzolites from Kilbourne Hole, New Mexico, USA demonstrate that two discrete populations of mantle sulphide exist in terms of both Re-Os systematics and textural relationship with co-existing silicates. One population, with a rounded morphology, is preserved in silicate grains and typically possesses high [Os] and low [Re] with unradiogenic, typically sub-chondritic 187Os/ 188Os attributable to long term isolation in a low-Re environment. By contrast, irregular-shaped sulphides, preserved along silicate grain boundaries, possess low [Os], higher [Re] and a wider range of, but generally supra-chondritic 187Os/ 188Os ([Os] typically ⩽ 1-2 ppm, 187Os/ 188Os ⩽ 0.3729; this study). This population is thought to represent metasomatic sulphide. Uncontaminated silicate phases contain negligible Os (<100 ppt) therefore the Os elemental and isotope composition of basalts is dominated by volumetrically insignificant sulphide ([Os] ⩽ 37 ppm; this study). During the early stages of partial melting, supra-chondritic interstitial sulphides are mobilised and incorporated into the melt, adding their radiogenic 187Os/ 188Os signature. Only when sulphides armoured within silicates are exposed to the melt through continued partial melting will enclosed sulphides add their high [Os] and unradiogenic 187Os/ 188Os to the aggregate melt. Platinum-group element data for whole rocks are also consistent with this scenario. The sequence of (i) addition of all of the metasomatic sulphide, followed by (ii) the incorporation of small amounts of armoured sulphide can thus account for the range of both [Os] and 187Os/ 188Os of EM-basalts worldwide without the need for contributions from additional silicate mantle reservoirs.

A IAB-Complex Iron Meteorite Containing Low-Ca Clinopyroxene: Northwest Africa 468 and its Relationship to Iodranites and Formation by Impact Melting

NASA Technical Reports Server (NTRS)

Rubin, Alan E.; Kallemeyn, Gregory W.; Wasson, John T.

2002-01-01

Northwest Africa 468 (NWA 468) is a new ungrouped, silicate-rich member of the IAB complex of nonmagmatic iron meteorites. The silicates contain relatively coarse (approximately 300 micron-size) grains of low-Ca clinopyroxene with polysynthetic twinning and inclined extinction. Low-Ca clinopyroxene is indicative of quenching from high temperatures (either from protoenstatite in a few seconds or high-temperature clinoenstatite in a few hours). It seems likely that NWA 468 formed by impact melting followed by rapid cooling to less than or equal to 660 C. After the loss of a metal-sulfide melt from the silicates, sulfide was reintroduced, either from impact-mobilized FeS or as an S2 vapor that combined with metallic Fe to produce FeS. The O-isotopic composition (delta O-17 = -1.39 %) indicates that the precursor material of NWA 468 was a metal-rich (e.g., CR) carbonaceous chondrite. Lodranites are similar in bulk chemical and O-isotopic composition to the silicates in NWA 468; the MAC 88177 lodranite (which also contains low-Ca clinopyroxene) is close in bulk chemical composition. Both NWA 468 and MAC 88177 have relatively low abundances of REE (rare earth elements) and plagiophile elements. Siderophiles in the metal-rich areas of NWA 468 are similar to those in the MAC 88177 whole rock; both samples contain low Ir and relatively high Fe, Cu and Se. Most unweathered lodranites contain approximately 20 - 38 wt. % metallic Fe-Ni. These rocks may have formed in an analogous manner to NWA 468 (i.e., by impact melting of metal-rich carbonaceous-chondrite precursors) but with less separation of metal-rich melts from silicates.

Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for early core-mantle differentiation

NASA Astrophysics Data System (ADS)

Cerantola, V.; Walte, N. P.; Rubie, D. C.

2015-05-01

Deformation-assisted segregation of metallic and sulphidic liquid from a solid peridotitic matrix is a process that may contribute to the early differentiation of small planetesimals into a metallic core and a silicate mantle. Here we present results of an experimental study using a simplified system consisting of a polycrystalline Fo90-olivine matrix containing a small percentage of iron sulphide and a synthetic primitive MORB melt, in order to investigate whether the silicate melt enhances the interconnection and segregation of FeS liquid under deformation conditions at varying strain rates. The experiments have been performed at 2 GPa, 1450 °C and strain rates between 1 ×10-3s-1 to 1 ×10-5s-1. Our results show that the presence of silicate melt actually hinders the migration and segregation of sulphide liquid by reducing its interconnectivity. At low to moderate strain rates the sulphide liquid pockets preserved a roundish shape, showing the liquid behavior is governed mainly by surface tension rather than by differential stress. Even at the highest strain rates, insignificant FeS segregation and interconnection were observed. On the other hand the basaltic melt was very mobile during deformation, accommodating part of the strain, which led to its segregation from the matrix at high bulk strains leaving the sulphide liquid stranded in the olivine matrix. Hence, we conclude that deformation-induced percolation of sulphide liquid does not contribute to the formation of planetary cores after the silicate solidus is overstepped. A possible early deformation enhanced core-mantle differentiation after overstepping the Fe-S solidus is not possible between the initial formation of silicate melt and the formation of a widespread magma ocean.

Novel Experimental Simulations of the Atmospheric Injection of Meteoric Metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez Martín, J. C.; Bones, D. L.; Carrillo-Sánchez, J. D.

2017-02-20

A newly developed laboratory, Meteoric Ablation Simulator (MASI), is used to test model predictions of the atmospheric ablation of interplanetary dust particles (IDPs) with experimental Na, Fe, and Ca vaporization profiles. MASI is the first laboratory setup capable of performing time-resolved atmospheric ablation simulations, by means of precision resistive heating and atomic laser-induced fluorescence detection. Experiments using meteoritic IDP analogues show that at least three mineral phases (Na-rich plagioclase, metal sulfide, and Mg-rich silicate) are required to explain the observed appearance temperatures of the vaporized elements. Low melting temperatures of Na-rich plagioclase and metal sulfide, compared to silicate grains, precludemore » equilibration of all the elemental constituents in a single melt. The phase-change process of distinct mineral components determines the way in which Na and Fe evaporate. Ca evaporation is dependent on particle size and on the initial composition of the molten silicate. Measured vaporized fractions of Na, Fe, and Ca as a function of particle size and speed confirm differential ablation (i.e., the most volatile elements such as Na ablate first, followed by the main constituents Fe, Mg, and Si, and finally the most refractory elements such as Ca). The Chemical Ablation Model (CABMOD) provides a reasonable approximation to this effect based on chemical fractionation of a molten silicate in thermodynamic equilibrium, even though the compositional and geometric description of IDPs is simplistic. Improvements in the model are required in order to better reproduce the specific shape of the elemental ablation profiles.« less

Fracture-induced flow and liquid metal transport during core formation

NASA Astrophysics Data System (ADS)

Jones, V.; Petford, N.; Rushmer, T.; Wertheim, D.

2008-12-01

The most important event in the early history of the earth was the separation of its iron-rich core. Core formation induced profound chemical fractionations and extracted into the core most of Earth's iron and siderophile elements (Ni, Co, Au, Pt, W, Re), leaving the silicate crust and mantle with strong depletions of these elements relative to primitive planetary material. Recent measurements of radiogenic 182W anomalies in the silicate Earth, Mars and differentiated meteorites imply that planetesimals segregated metallic cores within a few Myr of the origin of the solar system. Various models have been put forward to explain the physical nature of the segregation mechanism (Fe-diapirs, 'raining' through a magma ocean), and more recently melt flow via fractures. In this contribution we present the initial results of a numerical study into Fe segregation in a deforming silicate matrix that captures the temperature-dependent effect of liquid metal viscosity on the transport rate. Flow is driven by pressure gradients associated with impact deformation in a growing planetesimal and the fracture geometry is constrained by experimental data on naturally deformed H6 chondrite. Early results suggest that under dynamic conditions, fracture-driven melt flow can in principle be extremely rapid, leading to a significant draining of the Fe-liquid metal and siderophile trace element component on a timescale of hours to days. Fluid transport in planetesimals where deformation is the driving force provides an attractive and simple way of segregating Fe from host silicate as both precursor and primary agent of core formation

Barrier Properties of Layered-Silicate Reinforced Ethylenepropylenediene Monomer/Chloroprene Rubber Nanorubbers.

PubMed

Wu, Chang Mou; Hsieh, Wen Yen; Cheng, Kuo Bin; Lai, Chiu-Chun; Lee, Kuei Chi

2018-05-09

The triacetin and nitroglycerin barrier properties of layered-silicate reinforced ethylenepropylenediene monomer/chloroprene rubber (EPDM/CR) nanorubbers were investigated as rocket-propellant inhibitors. EPDM/CR nanorubbers with intercalated structures were formulated and prepared by the melt-compounding method. The triacetin permeability and nitroglycerin absorption were observed to decrease with increasing layered-silicate content. The layered silicates also improved the flame retardancies of the nanorubbers by forming silicate reinforced carbonaceous chars. Layered-silicate reinforced EPDM/CR nanorubbers are potentially effective rocket propellant-inhibiting materials.

Eclogite-associated potassic silicate melts and chloride-rich fluids in the mantle: a possible connection

NASA Astrophysics Data System (ADS)

Safonov, O.; Butvina, V.

2009-04-01

Relics of potassium-rich (4-14 wt. % of K2O and K2O/Na2O > 1.0) melts are a specific features of some partially molten diamondiferous eclogite xenoliths in kimberlites worldwide [1, 2]. In addition, potassic silicic melt inclusions with up to 16 wt. % of K2O are associated with eclogite phases in kimberlitic diamonds (O. Navon, pers. comm.). According to available experimental data, no such potassium contents can be reached by "dry" and hydrous melting of eclogite. These data point to close connection between infiltration of essentially potassic fluids, partial melting and diamond formation in mantle eclogites [2]. Among specific components of these fluids, alkali chlorides, apparently, play an important role. This conclusion follows from assemblages of the melt relics with chlorine-bearing phases in eclogite xenoliths [1], findings of KCl-rich inclusions in diamonds from the xenoliths [3], and concentration of Cl up to 0.5-1.5 wt. % in the melt inclusions in diamonds. In this presentation, we review our experimental data on reactions of KCl melts and KCl-bearing fluids with model and natural eclogite-related minerals and assemblages. Experiments in the model system jadeite(±diopside)-KCl(±H2O) at 4-7 GPa showed that, being immiscible, chloride liquids provoke a strong K-Na exchange with silicates (jadeite). As a result, low-temperature ultrapotassic chlorine-bearing (up to 3 wt. % of Cl) aluminosilicate melts form. These melts is able to produce sanidine, which is characteristic phase in some partially molten eclogites. In addition, in presence of water Si-rich Cl-bearing mica (Al-celadonite-phlogopite) crystallizes in equilibrium with sanidine and/or potassic melt and immiscible chloride liquid. This mica is similar to that observed in some eclogitic diamonds bearing chloride-rich fluid inclusions [4], as well as in diamonds in partially molten eclogites [2]. Interaction of KCl melt with pyrope garnet also produce potassic aluminosilicate melt because of high affinity of Al and Si to potassium. Additional products of this interaction are spinel and, possibly, olivine. These minerals are common products of garnet breakdown within the zones of partial melting of eclogite xenoliths [1, 2]. It is evident that simultaneous action of fluid species (H2O, CO2) and chlorides would produce much stronger effect. Following to this assumption, we further performed experiments on melting of model and natural eclogites with participation of the H2O-CO2-KCl fluids at 5 GPa. Comparison with the KCl-free melting (i.e. H2O-CO2 fluid only) shows that addition of KCl to the fluid intensifies melting. This effect is related both to high Cl content (up to 3-5.5 wt. %) in the newly formed silicate melt and its enrichment in K2O via K-Na exchange reactions with the immiscible chloride melt. Owing to these reactions, the ratio K2O/Cl in the melts increases with the increase of the KCl content in the system and reaches 2.5-3.5 in the melts coexisting with immiscible chloride liquids. However, the KCl/(H2O+CO2) ratio in the fluid does not influence on the K2O/Cl ratio in the melts suggesting that solubility of KCl in the melts practically does not depends on a presence of the H2O-CO2 fluid. Thus, the experiments imply that the KCl-bearing fluids or aqueous(±carbonic) KCl liquids could serve as a possible factor assisting to formation of the K-rich Cl-bearing aluminosilicate melts during the eclogite melting in the mantle. In turn, it means that the KCl content in such rock-melt-fluid systems could exceed 5 wt. %. The study is supported by the RFBR (07-05-00499), the Leading Scientific Schools Program (1949.2008.5), Russian President Grant MD-130.2008.5, and Russian Science Support Foundation. References: [1] Misra et al. (2004) Contrib. Mineral. Petrol. V. 146. P. 696-714; [2] Shatsky et al. (2008) Lithos. 105. 289-300; [3] Zedgenizov et al. (2007) Doklady Earth Sci. 415. 961-964; [4] Izraeli et al. (2001) Earth Planet. Sci. Lett. 5807. 1-10.

High chloride content calcium silicate glasses.

PubMed

Chen, Xiaojing; Karpukhina, Natalia; Brauer, Delia S; Hill, Robert G

2017-03-08

Chloride is known to volatilize from silicate glass melts and until now, only a limited number of studies on oxychloride silicate glasses have been reported. In this paper we have synthesized silicate glasses that retain large amounts of CaCl 2 . The CaCl 2 has been added to the calcium metasilicate composition (CaO·SiO 2 ). Glasses were produced via a melt quench route and an average of 70% of the chloride was retained after melting. Up to 31.6 mol% CaCl 2 has been successfully incorporated into these silicate glasses without the occurrence of crystallization. 29 Si MAS-NMR spectra showed the silicon being present mainly as a Q 2 silicate species. This suggests that chloride formed Cl-Ca(n) species, rather than Si-Cl bonds. Upon increasing the CaCl 2 content, the T g reduced markedly from 782 °C to 370 °C. Glass density and glass crystallization temperature decreased linearly with an increase in the CaCl 2 content. However, both linear regressions revealed a breakpoint at a CaCl 2 content just below 20 mol%. This might be attributed to a significant change in the structure and is also correlated with the nature of the crystallizing phases formed upon heat treatment. The glasses with less than 19.2 mol% CaCl 2 crystallized to wollastonite, whilst the compositions with CaCl 2 content equal to or greater than 19.2 mol% are thought to crystallize to CaCl 2 . In practice, the crystallization of CaCl 2 could not occur until the crystallization temperature fell below the melting point of CaCl 2 . The implications of the results along with the high chloride retention are discussed.

Velocity of a freely rising gas bubble in a soda-lime silicate glass melt

NASA Technical Reports Server (NTRS)

Hornyak, E. J.; Weinberg, M. C.

1984-01-01

A comparison is conducted between measured velocities for the buoyant rise of single bubbles of varying size and composition, in a soda-lime silicate glass melt, with the steady state velocities predicted by the Stokes and Hadamard-Rybczynski formulas. In all cases, the data are noted to fit the Hadamard-Rybczynski expression for steady state rise speed considerably better than the Stokes formula.

Phosphorus Equilibria Among Mafic Silicate Phases

NASA Technical Reports Server (NTRS)

Berlin, Jana; Xirouchakis, Dimitris

2002-01-01

Phosphorus incorporation in major rock-forming silicate minerals has the following implications: (1) Reactions between phosphorus-hosting major silicates and accessory phosphates, which are also major trace element carriers, may control the stability of the latter and thus may affect the amount of phosphorus and other trace elements released to the coexisting melt or fluid phase. (2) Less of a phosphate mineral is needed to account for the bulk phosphorus of planetaty mantles. (3) During partial melting of mantle mineral assemblages or equilibrium fractional crystallization of basaltic magmas, and in the absence or prior to saturation with a phosphate mineral, silicate melts may become enriched in phosphorus, especially in the geochemically important low melt fraction regime, Although the small differences in the ionic radii of IVp5+, IVSi4+, and IV Al3+ makes phosphoms incorporation into crystalline silicates perhaps unsurprising, isostructural silicate and phosphate crystalline solids do not readily form solutions, e.g., (Fe, Mg)2SiO4 vs. LiMgPO4, SiO)2 VS. AlPO4. Nonetheless, there are reports of, poorly characterized silico-phosphate phases in angrites , 2-4 wt% P2O5 in olivine and pyroxene grains in pallasites and reduced terestrial basalts which are little understood but potentially useful, and up to 17 wt% P2O5 in olivine from ancient slags. However, such enrichments are rare and only underscore the likelihood of phosphoms incorporation in silicate minerals. The mechanisms that allow phosphorus to enter major rock-forming silicate minerals (e.g., Oliv, Px, Gt) remain little understood and the relevant data base is limited. Nonetheless, old and new high-pressure (5-10 GPa) experimental data suggest that P2O5 wt% decreases from silica-poor to silica-rich compositions or from orthosilicate to chain silicate structures (garnet > olivine > orthopyroxene) which implies that phosphorus incorporation in silicates is perhaps more structure-than site-specific. The data also indicate that DXVliQP2O5 decrease in the same order, but DOVLiQP2O5 and DOpx/LiQP205 are likely constant, respectively equal to 0.08(3) and 0.007(4), in contrast, DG1ILiQP205 increases from 0.15(3) to 0.36(10) as garnet becomes majoritic, thus silica-enriched, and may also depend on liquid composition (SiO2, P2O5 and Na2O wt%).

Planetesimal core formation with partial silicate melting using in-situ high P, high T, deformation x-ray microtomography

NASA Astrophysics Data System (ADS)

Anzures, B. A.; Watson, H. C.; Yu, T.; Wang, Y.

2017-12-01

Differentiation is a defining moment in formation of terrestrial planets and asteroids. Smaller planetesimals likely didn't reach high enough temperatures for widescale melting. However, we infer that core formation must have occurred within a few million years from Hf-W dating. In lieu of a global magma ocean, planetesimals likely formed through inefficient percolation. Here, we used in-situ high temperature, high pressure, x-ray microtomography to track the 3-D evolution of the sample at mantle conditions as it underwent shear deformation. Lattice-Boltzmann simulations for permeability were used to characterize the efficiency of melt percolation. Mixtures of KLB1 peridotite plus 6.0 to 12.0 vol% FeS were pre-sintered to achieve an initial equilibrium microstructure, and then imaged through several consecutive cycles of heating and deformation. The maximum calculated melt segregation velocity was found to be 0.37 cm/yr for 6 vol.% FeS and 0.61 cm/year for 12 vol.% FeS, both below the minimum velocity of 3.3 cm/year required for a 100km planetesimal to fully differentiate within 3 million years. However, permeability is also a function of grain size and thus the samples having smaller grains than predicted for small planetesimals could have contributed to low permeability and also low migration velocity. The two-phase (sulfide melt and silicate melt) flow at higher melt fractions (6 vol.% and 12 vol.% FeS) was an extension of a similar study1 containing only sulfide melt at lower melt fraction (4.5 vol.% FeS). Contrary to the previous study, deformation did result in increased permeability until the sample was sheared by twisting the opposing Drickamer anvils by 360 degrees. Also, the presence of silicate melt caused the FeS melt to coalesce into less connected pathways as the experiment with 6 vol.% FeS was found to be less permeable than the one with 4.5 vol.% FeS but without any partial melt. The preliminary data from this study suggests that impacts as well as higher temperature leading to partial melting of the silicate portion of the mantle could have contributed to fast enough core formation. 1. Todd, K.A., Watson, H.C., Yu, T., Wang, Y., American Mineralogist, 101.9, 1996-2004, 2016

Reactive Transport of Slab-Derived Carbonatitic Melts in the Deep Upper Mantle and Generation of Kimberlites

NASA Astrophysics Data System (ADS)

Sun, C.; Dasgupta, R.

2017-12-01

Kimberlite is a diamond-bearing CO2-rich ultramafic magma from the mantle at depths of >200 km, featured by enrichment of incompatible elements [1]. It has been considered significant for understanding mantle geochemistry and particularly for providing information of deep carbon cycle. Recent experimental studies suggested that partial melts of carbonated peridotites at high pressures and temperatures could resemble the MgO (>20 wt%) and enriched incompatible elements in kimberlites only when the source experienced refertilization with perhaps prior depletion (e.g., [2]). Although addition of CO2 and incompatible elements in the deep mantle is often linked to subducted components, partial melts directly from carbonated oceanic crusts do not have high enough MgO (e.g., ≤8.2 wt%; [3]). A crucial question is how slab-derived CO2-rich melt evolves in reaction with ambient mantle, which may provide a feasible mechanism for kimberlite generation. To investigate the fate of slab-derived carbonatitic melt in the deep ambient mantle, we have performed multi-anvil experiments at 7-10 GPa and 1400-1450 °C. The starting compositions were synthesized by mixing a fertile peridotite composition, KLB-1, with variable proportions (0-45 wt.%) of Ca-rich carbonatitic melt similar to those derived from a carbonated ocean crust at 13-21 GPa [3]. Experiments were performed in Pt, Pt/Gr, Au-Pd and Au-Pd/Gr capsules, and the experimental phases include olivine ± opx + cpx + majoritic garnet ± carbonated silicate melt. With the increase of melt-rock ratios, experimental melts become progressively enriched in CaO (13.0-23.1 wt%) and CO2 (14.2-38.7 wt%) but depleted in MgO (28.9-19.9 wt%), SiO2 (33.1-7.9 wt%), and Al2O3 (2.7-0.2 wt%). The net flux of melt increases with the increase of infiltrating carbonatitic melt proportion and with the decrease of pressure. Kimberlite melts were produced from experiments with 5-25 wt% infiltrating carbonatitic melts by dissolution of olivine and orthopyroxene and precipitation of clinopyroxene. Thus, a localized influx of slab-derived CO2-rich melts can enlarge the mantle porosity, enhance melt focusing, and initiate a channelized flow of kimberlite melts. [1] Becker & Le Roex (2006) J. Pet. 47: 673-703; [2] Brey et al. (2008) J. Pet. 49: 797-821; [3] Thomson et al. (2016) Nature 529: 76-79.

Simulation of the planetary interior differentiation processes in the laboratory.

PubMed

Fei, Yingwei

2013-11-15

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

PubMed Central

Fei, Yingwei

2013-01-01

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process. PMID:24326245

Fractionation products of basaltic komatiite magmas at lower crustal pressures: implications for genesis of silicic magmas in the Archean

NASA Astrophysics Data System (ADS)

Mandler, B. E.; Grove, T. L.

2015-12-01

Hypotheses for the origin of crustal silicic magmas include both partial melting of basalts and fractional crystallization of mantle-derived melts[1]. Both are recognized as important processes in modern environments. When it comes to Archean rocks, however, partial melting hypotheses dominate the literature. Tonalite-trondhjemite-granodiorite (TTG)-type silicic magmas, ubiquitous in the Archean, are widely thought to be produced by partial melting of subducted, delaminated or otherwise deeply buried hydrated basalts[2]. The potential for a fractional crystallization origin for TTG-type magmas remains largely unexplored. To rectify this asymmetry in approaches to modern vs. ancient rocks, we have performed experiments at high pressures and temperatures to closely simulate fractional crystallization of a basaltic komatiite magma in the lowermost crust. These represent the first experimental determinations of the fractionation products of komatiite-type magmas at elevated pressures. The aim is to test the possibility of a genetic link between basaltic komatiites and TTGs, which are both magmas found predominantly in Archean terranes and less so in modern environments. We will present the 12-kbar fractionation paths of both Al-depleted and Al-undepleted basaltic komatiite magmas, and discuss their implications for the relative importance of magmatic fractionation vs. partial melting in producing more evolved, silicic magmas in the Archean. [1] Annen et al., J. Petrol., 47, 505-539, 2006. [2] Moyen J-F. & Martin H., Lithos, 148, 312-336, 2012.

First finding of impact melt in the IIE Netschaëvo meteorite

NASA Astrophysics Data System (ADS)

Roosbroek, N.; Pittarello, L.; Greshake, A.; Debaille, V.; Claeys, P.

2016-02-01

About half of the IIE nonmagmatic iron meteorites contain silicate inclusions with a primitive to differentiated nature. The presence of preserved chondrules has been reported for two IIE meteorites so far, Netschaëvo and Mont Dieu, which represent the most primitive silicate material within this group. In this study, silicate inclusions from two samples of Netschaëvo were examined. Both silicate inclusions are characterized by a porphyritic texture dominated by clusters of coarse-grained olivine and pyroxene, set in a fine-grained groundmass that consists of new crystals of olivine and a glassy appearing matrix. This texture does not correspond to the description of the previously examined pieces of Netschaëvo, which consist of primitive chondrule-bearing angular clasts. Detailed petrographic observations and geochemical analyses suggest that the investigated samples of Netschaëvo consist of quenched impact melt. This implies that Netschaëvo is a breccia containing metamorphosed and impact-melt rock (IMR) clasts and that collisions played a major role in the formation of the IIE group.

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

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Mittlefehldt, David W.

2017-01-01

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.

Redox state of recycled crustal lithologies in the convective upper mantle constrained using oceanic basalt CO2-trace element systematics

NASA Astrophysics Data System (ADS)

Eguchi, J.; Dasgupta, R.

2017-12-01

Investigating the redox state of the convective upper mantle remains challenging as there is no way of retrieving samples from this part of the planet. Current views of mantle redox are based on Fe3+/∑Fe of minerals in mantle xenoliths and thermodynamic calculations of fO2 [1]. However, deep xenoliths are only recoverable from continental lithospheric mantle, which may have different fO2s than the convective oceanic upper mantle [1]. To gain insight on the fO2 of the deep parts of the oceanic upper mantle, we probe CO2-trace element systematics of basalts that have been argued to receive contributions from subducted crustal lithologies that typically melt deeper than peridotite. Because CO2 contents of silicate melts at graphite saturation vary with fO2 [2], we suggest CO2-trace element systematics of oceanic basalts which sample deep heterogeneities may provide clues about the fO2 of the convecting mantle containing embedded heterogeneities. We developed a new model to predict CO2 contents in nominally anhydrous silicate melts from graphite- to fluid-saturation over a range of P (0.05- 5 GPa), T (950-1600 °C), and composition (foidite-rhyolite). We use the model to calculate CO2 content as a function of fO2 for partial melts of lithologies that vary in composition from rhyolitic sediment melt to silica-poor basaltic melt of pyroxenites. We then use modeled CO2 contents in mixing calculations with partial melts of depleted mantle to constrain the fO2 required for partial melts of heterogeneities to deliver sufficient CO2 to explain CO2-trace element systematics of natural basalts. As an example, Pitcairn basalts, which show evidence of a subducted crustal component [3] require mixing of 40% of partial melts of a garnet pyroxenite at ΔFMQ -1.75 at 3 GPa. Mixing with a more silicic composition such as partial melts of a MORB-eclogite cannot deliver enough CO2 at graphite saturation, so in this scenario fO2 must be above the EMOG/D buffer at 4 GPa. Results suggest convecting upper mantle may be more oxidized than continental lithospheric mantle, and fO2 profiles of continental lithospheric mantle may not be applicable to convective upper mantle.[1] Frost, D, McCammon, C. 2008. An Rev E & P Sci. (36) p.389-420; [2] Holloway, J, et al. 1992. Eu J. Min. (4) p. 105-114; [3] Woodhead, J, Devey C. 1993. EPSL. (116) p. 81-99.

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

NASA Astrophysics Data System (ADS)

Le Losq, Charles; Dalou, Célia; Mysen, Bjorn O.

2017-07-01

The bonding and speciation of water dissolved in Na silicate and Na and Ca aluminosilicate melts were inferred from in situ Raman spectroscopy of the samples, in hydrothermal diamond anvil cells, while at crustal temperature and pressure conditions. Raman data were also acquired on Na silicate and Na and Ca aluminosilicate glasses, quenched from hydrous melts equilibrated at high temperature and pressure in a piston cylinder apparatus. In the hydrous melts, temperature strongly influences O-H stretching ν(O-H) signals, reflecting its control on the bonding of protons between different molecular complexes. Pressure and melt composition effects are much smaller and difficult to discriminate with the present data. However, the chemical composition of the melt + fluid system influences the differences between the ν(O-H) signals from the melts and the fluids and, hence, between their hydrogen partition functions. Quenching modifies the O-H stretching signals: strong hydrogen bonds form in the glasses below the glass transition temperature Tg, and this phenomenon depends on glass composition. Therefore, glasses do not necessarily record the O-H stretching signal shape in melts near Tg. The melt hydrogen partition function thus cannot be assessed with certainty using O-H stretching vibration data from glasses. From the present results, the ratio of the hydrogen partition functions of hydrous silicate melts and aqueous fluids mostly depends on temperature and the bulk melt + fluid system chemical composition. This implies that the fractionation of hydrogen isotopes between magmas and aqueous fluids in water-saturated magmatic systems with differences in temperature and bulk chemical composition will be different.

Nanoscale Origin of the Dichotimous Viscosity-Pressure Behavior in Silicate Melts

NASA Astrophysics Data System (ADS)

Wang, Y.; Sakamaki, T.; Skiner, L.; Jing, Z.; Yu, T.; Kono, Y.; Park, C.; Shen, G.; Rivers, M. L.; Sutton, S. R.

2013-12-01

A defining characteristic of silicate melts is the degree of polymerization (tetrahedral connectivity), which dictates physical properties such as viscosity and density. While viscosity of depolymerized silicate melts increases with pressure consistent with free volume theory, isothermal viscosity of polymerized melts decreases with pressure up to ~3 - 5 GPa, above which it turns over to normal (positive) pressure dependence. We conducted high-pressure melt structure studies along the jadeite (Jd) - diopside (Di) join, using a Paris-Edinburgh Press at the HPCAT beamline 16-BM-B and measured Jd melt density using a DIA type apparatus based on x-ray absorption at GSECARS beamline 13-BM-D. Structures of polymerized (Jd and Jd50Di50) and depolymerized (Di) melts show distinct responses to pressure. For Jd melt, T-O, T-T bond lengths (where T denotes tetrahedrally coordinated Al and Si) and T-O-T angle all exhibit rapid, sometimes non-linear decrease with increasing pressure to ~3 GPa. For Di melt, these parameters vary linearly with pressure and change very little. Molecular dynamics calculations, constrained by the x-ray structural data, were employed to examine details of structural evolution in polymerized and depolymerized liquids. A structural model is developed to link structural evolution to changes in melt properties, such as density and viscosity, with pressure. We show that the pressure of the viscosity turnover corresponds to the tetrahedral packing limit, below which the structure is compressed through tightening of the inter-tetrahedral bond angle, resulting in continual breakup of tetrahedral connectivity and viscosity decrease. Above the turnover pressure, Si and Al coordination increases to allow further packing, with increasing viscosity. This structural response prescribes the distribution of melt viscosity and density with depth, and may be the main controlling factor for magma transport rates in terrestrial planetary interiors.

The solubility of Pd and Au in hydrous intermediate silicate melts: The effect of oxygen fugacity and the addition of Cl and S

NASA Astrophysics Data System (ADS)

Sullivan, Neal A.; Zajacz, Zoltan; Brenan, James M.

2018-06-01

The solubilities of Pd and Au in a hydrous trachyandesitic melt were experimentally determined at 1000 °C and 200 MPa at oxygen fugacity (ƒO2) from 0.45 log units below to 6.55 log units above the Ni-NiO buffer (NNO). The effect of adding metal-binding ligands (i.e. Cl and S) to the silicate melt was also studied. The solubility of Au increases from 0.15 ± 0.1 to 3.85 ± 1.48 ppm in Cl- and S-free melts with ƒO2 increasing from NNO-0.45 to NNO+6.55 with a slope that suggests that it is present in 1+ oxidation state over the entire studied ƒO2 range. On the other hand, Pd solubility, shows a more moderate increase with ƒO2, especially in the lower half of the studied range, increasing from 2.66 ± 0.25 ppm at NNO-0.45 to only 3.62 ± 0.38 ppm at NNO+1.72 in Cl- and S-free melts. Overall, the variation in Pd solubility as a function of ƒO2 indicates Pd being dissolved in the silicate melt in both zero and 1+ oxidation state, with the former being dominant below NNO+4.5. At NNO-0.45 to +3.48, the addition of 3170-4060 ppm Cl to the silicate melt increased the solubility of Au by an average factor of 1.5, in comparison to Cl-free melts. However, at NNO+6.55, Au solubility increased by a factor of 2.5. The addition of Cl had a negligible effect on the solubility of Pd except for a large increase (factor of 2.4) at NNO+6.55. At reducing conditions (NNO-0.45), the addition of 170 ppm S to the silicate melt increased the solubility of Au by a factor of ∼4 but did not change the solubility of Pd in comparison to S-free melts. The observation that Pd is dominantly present as Pd0 at NNO < +4.5 may explain the lack of complexation with potential reduced sulfur-bearing and chloride ligands. As one may expect similar behavior in fluids degassing from magmas at depth, the lack of oxidized Pd species could be an important factor behind the scarcity of economically viable Pd-rich magmatic-hydrothermal deposits observed in nature.

Solubility, Partitioning, and Speciation of Carbon in Shallow Magma Oceans of Terrestrial Planets Constrained by High P-T Experiments

NASA Astrophysics Data System (ADS)

Chi, H.; Dasgupta, R.; Shimizu, N.

2011-12-01

Deep planetary volatile cycles have a critical influence on planetary geodynamics, atmospheres, climate, and habitability. However, the initial conditions that prevailed in the early, largely molten Earth and other terrestrial planets, in terms of distribution of volatiles between various reservoirs - metals, silicates, and atmosphere - remains poorly constrained. Here we investigate the solubility, partitioning, and speciation of carbon-rich volatile species in a shallow magma ocean environment, i.e., in equilibrium with metallic and silicate melts. A series of high pressure-temperature experiments using a piston cylinder apparatus were performed at 1-3 GPa, 1500-1800 °C on synthetic basaltic mixtures + Fe-Ni metal powders contained in graphite capsules. All the experiments produced glassy silicate melt pool in equilibrium with quenched metal melt composed of dendrites of cohenite and kamacite. Major element compositions of the resulting phases and the carbon content of metallic melts were analyzed by EPMA at NASA-JSC. Carbon and hydrogen concentrations of basaltic glasses were determined using Cameca IMS 1280 SIMS at WHOI and speciation of dissolved volatiles was constrained using FTIR and Raman spectroscopy at Rice University. Based on the equilibria - FeO (silicate melt) = Fe (metal alloy melt) + 1/2O2, we estimate the oxygen fugacity of our experiments in the range of ΔIW of -1 to -2. FTIR analysis on doubly polished basaltic glass chips suggests that the concentrations of dissolved CO32- or molecular CO2 are negligible in graphite and metal saturated reduced conditions, whereas the presence of dissolved OH- is evident from the asymmetric peak at 3500 cm-1. Collected Raman spectra of basaltic glasses in the frequency range of 200-4200 cm-1 suggest that hydrogen is present both as dissolved OH- species (band at 3600 cm-1) and as molecular H2 (band near 4150 cm-1) for all of our experiments. Faint peaks near 2915 cm-1 and consistent peaks near 740 cm-1 suggest that possible carbon species in our reduced glasses are likely minor CH4 and Si-C, respectively and are consistent with the recent solubility studies at reduced conditions [1,2]. Carbon solubility (calibrated using 12C/30Si) at graphite saturation in our reduced basaltic glasses is only in the range 20-100 ppm C, with H2O contents in the range of 0.2-0.7 wt.%. In contrast to the low dissolved carbon concentration in the basaltic silicate melts, carbon solubility in quenched metallic melts vary in the range of 5-7 wt.%. Our preliminary work indicates that the solubility of carbon in reduced basaltic melts relevant for early magma conditions may be several orders of magnitude lower compared to the solubility of carbon in modern terrestrial basalts. This coupled with significant solubility of carbon in Fe-Ni metallic melt suggests that most of magma ocean carbon was likely partitioned into deep metallic melts. Further metal-silicate experiments with more depolymerized basaltic melts of variable compositions are underway and will be presented. [1] Kadik et al. JPetrol 45, 1297-1310, 2004; [2] Kadik et al. Geochem Int 44, 33-47, 2006.

Highly CO2-supersaturated melts in the Pannonian lithospheric mantle - A transient carbon reservoir?

NASA Astrophysics Data System (ADS)

Créon, Laura; Rouchon, Virgile; Youssef, Souhail; Rosenberg, Elisabeth; Delpech, Guillaume; Szabó, Csaba; Remusat, Laurent; Mostefaoui, Smail; Asimow, Paul D.; Antoshechkina, Paula M.; Ghiorso, Mark S.; Boller, Elodie; Guyot, François

2017-08-01

Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0-0.25 wt.% CO2), whereas the H2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9-6.3 wt.% H2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions determined by Raman spectroscopy and microthermometry (0.1-1.1 GPa). The CO2/silicate melt mass ratios in the metasomatic agent that percolated through the lithospheric mantle below the Pannonian Basin are estimated to be between 9.0 and 25.4 wt.%, values consistent with metasomatism either by (1) silicate melts already supersaturated in CO2 before reaching lithospheric depths or (2) carbonatite melts that interacted with mantle peridotite to generate carbonated silicic melts. Taking the geodynamical context of the Pannonian Basin and our calculations of the CO2/silicate melt mass ratios in the metasomatic agent into account, we suggest that slab-derived melts initially containing up to 25 wt.% of CO2 migrated into the lithospheric mantle and exsolved CO2-rich fluid that became trapped in secondary fluid inclusions upon fracturing of the peridotite mineral matrix. We propose a first-order estimate of 2000 ppm as the minimal bulk CO2 concentration in the lithospheric mantle below the Pannonian Basin. This transient carbon reservoir is believed to be degassed through the Pannonian Basin due to volcanism and tectonic events, mostly focused along the lithospheric-scale regional Mid-Hungarian shear Zone.

Sources and mobility of carbonate melts beneath cratons, with implications for deep carbon cycling, metasomatism and rift initiation

NASA Astrophysics Data System (ADS)

Tappe, Sebastian; Romer, Rolf L.; Stracke, Andreas; Steenfelt, Agnete; Smart, Katie A.; Muehlenbachs, Karlis; Torsvik, Trond H.

2017-05-01

Kimberlite and carbonatite magmas that intrude cratonic lithosphere are among the deepest probes of the terrestrial carbon cycle. Their co-existence on thick continental shields is commonly attributed to continuous partial melting sequences of carbonated peridotite at >150 km depths, possibly as deep as the mantle transition zone. At Tikiusaaq on the North Atlantic craton in West Greenland, approximately 160 Ma old ultrafresh kimberlite dykes and carbonatite sheets provide a rare opportunity to study the origin and evolution of carbonate-rich melts beneath cratons. Although their Sr-Nd-Hf-Pb-Li isotopic compositions suggest a common convecting upper mantle source that includes depleted and recycled oceanic crust components (e.g., negative ΔεHf coupled with > + 5 ‰ δ7Li), incompatible trace element modelling identifies only the kimberlites as near-primary low-degree partial melts (0.05-3%) of carbonated peridotite. In contrast, the trace element systematics of the carbonatites are difficult to reproduce by partial melting of carbonated peridotite, and the heavy carbon isotopic signatures (-3.6 to - 2.4 ‰ δ13C for carbonatites versus -5.7 to - 3.6 ‰ δ13C for kimberlites) require open-system fractionation at magmatic temperatures. Given that the oxidation state of Earth's mantle at >150 km depth is too reduced to enable larger volumes of 'pure' carbonate melt to migrate, it is reasonable to speculate that percolating near-solidus melts of carbonated peridotite must be silicate-dominated with only dilute carbonate contents, similar to the Tikiusaaq kimberlite compositions (e.g., 16-33 wt.% SiO2). This concept is supported by our findings from the North Atlantic craton where kimberlite and other deeply derived carbonated silicate melts, such as aillikites, exsolve their carbonate components within the shallow lithosphere en route to the Earth's surface, thereby producing carbonatite magmas. The relative abundances of trace elements of such highly differentiated 'cratonic carbonatites' have only little in common with those of metasomatic agents that act on the deeper lithosphere. Consequently, carbonatite trace element systematics should only be used with caution when constraining carbon mobility and metasomatism at mantle depths. Regardless of the exact nature of carbonate-bearing melts within the mantle lithosphere, they play an important role in enrichment processes, thereby decreasing the stability of buoyant cratons and promoting rift initiation - as exemplified by the Mesozoic-Cenozoic breakup of the North Atlantic craton.

Al Speciation in Silicate Melts: AlV a new Network Former?

NASA Astrophysics Data System (ADS)

Neuville, D. R.; Florian, P.; de Ligny, D.; Montouillout, V.; Massiot, D.

2009-05-01

The first human glasses were made 3500 BC. It was essentially sodo-lime silicate glass. To improve the chemical resistance, the thermal properties and increase the viscosity it is interesting to add aluminum in these silicates. But what is the speciation of the aluminum and how it varies according to the chemical composition and to the temperature? The aluminum appears essentially in four or five fold coordination in glasses and melts melted. The proportion of [5]Al varies according to the alkaline or to the earth-alkaline content and to the temperature. We shall present in a first part the influence of the network-modifier on the proportion of [5]Al and then we shall present some new results of absorption of high-temperature using NMR and XANES spectroscopy at the Al K-edge. Finally, from glass transition temperature measurements we propose to explain that [5]Al can be a new network former.

Experimental modeling of the interaction of subducted carbonates and sulfur with mantle silicates

NASA Astrophysics Data System (ADS)

Bataleva, Yu. V.; Palyanov, Yu. N.; Borzdov, Yu. M.; Zdrokov, E. V.; Sobolev, N. V.

2016-09-01

Experimental studies in the system Fe,Ni-olivine-carbonate-S ( P = 6.3 GPa, T = 1050-1550°C, t = 40-60 h) aimed at modeling of the interaction of subducted carbonates and sulfur with rocks of the silicate mantle and at investigation of the likely mechanism of the formation of mantle sulfides were performed. It is shown that an association of olivine + orthopyroxene + magnesite + pyrite coexisting with a sulfur melt/fluid with dissolved Fe, Ni, and O is formed at T ≤ 1250°C. An association of low-Fe olivine, orthopyroxene, and magnesite and two immiscible melts of the carbonate and S-Fe-Ni-O compositions are formed at T ≥ 1350°C. It is shown that the reduced S-bearing fluids may transform silicates and carbonates, extract metals from the solid-phase matrix, and provide conditions for generation of sulfide melts.

Iron metal production in silicate melts through the direct reduction of Fe/II/ by Ti/III/, Cr/II/, and Eu/II/. [in lunar basalts

NASA Technical Reports Server (NTRS)

Schreiber, H. D.; Balazs, G. B.; Shaffer, A. P.; Jamison, P. L.

1982-01-01

The production of metallic iron in silicate melts by chemical reactions of Ti(3+), Cr(2+), and Eu(2+) with Fe(2+) is demonstrated under experimental conditions in a simplified basaltic liquid. These reactions form a basis for interpreting the role of isochemical valency exchange models in explanations for the reduced nature of lunar basalts. The redox couples are individually investigated in the silicate melt to ascertain reference redox ratios that are independent of mutual interactions. These studies also provide calibrations of spectral absorptions of the Fe(2+) and Ti(2+) species in these glasses. Subsequent spectrophotometric analyses of Fe(2+) and Ti(2+) in glasses doped with both iron and titanium and of Fe(2+) in glasses doped with either iron and chromium or iron and europium ascertain the degree of mutual interactions in these dual-doped glasses.

Thermodynamic modeling of melts in the system Na 2O-NaAlO 2-SiO 2-F 2O -1

NASA Astrophysics Data System (ADS)

Dolejš, David; Baker, Don R.

2005-12-01

Fluorine is a common volatile element in magmatic-hydrothermal systems, but its solution mechanisms and thermodynamic description in highly polymerized silicate melts are poorly known. We have developed a thermodynamic model for fluorosilicate liquids that links experimentally determined phase equilibria and spectroscopic information on melt structure. The model is applicable to crystallization of fluoride minerals, fluoride-silicate immiscibility in natural felsic melts, and metallurgical processes. Configurational properties of fluorosilicate melts are described by mixing on three site levels (sublattices): (1) alkali fluoride, polyhedral aluminofluoride and silicofluoride species and nonbridging terminations of the aluminosilicate network, (2) alkali-aluminate and silicate tetrahedra within the network and (3) bridging oxygen, nonbridging oxygen and terminal fluorine atoms on tetrahedral apices of the network. Abundances of individual chemical species are described by a homogeneous equilibrium representing melt depolymerization: F - (free) + O 0 (bridging) = F 0 (terminal) + O - (nonbridging) which corresponds to a replacement of an oxygen bridging two tetrahedra by a pair of terminations, one with F and the other with an O and a charge-balancing Na. In cryolite-bearing systems two additional interaction mechanisms occur: (1) the self-dissociation of octahedral aluminofluoride complexes: [AlF 6] = [AlF 4] + 2 [F], and (2) the short-range order between (O,F)-corners and (Si,NaAl)-centers of tetrahedra: Si-O-Si + 2 [NaAl]-F = [NaAl]-O-[NaAl] + 2 Si-F. Portrayal of these equilibria in ternary Thompson reaction space allows for the decrease in the number of interaction mechanisms by linearly combining melt depolymerization with tetrahedral short-range order. In this formulation, the nonideal thermodynamic properties are represented by reaction energies of homogeneous equilibria, thus defining directly individual chemical species concentrations and configurational properties. Thermodynamic expressions for the activity-composition relationships are simplified if all entities are expressed using symbolic molecular notation (e.g., SiO 2, SiF 4, [NaAl]O 2, [NaAl]F 4, NaF etc.) with corresponding nonfractional site multiplicities (1, 2 or 4). The model has been applied to three subsystems of the Na 2O-NaAlO 2-SiO 2-F 2O -1 compositional space. Activity-composition relationships in the villiaumite-sodium silicate binaries require clustering of silicate tetrahedra and only negligible interaction between fluoride species and silicate polymer. Phase equilibria in the cryolite-albite system with a large depression of albite liquidus are interpreted via complete substitution of O 0 by O - and F 0 in the silicate framework. With increasing fluorine content, initial Al-F and Si-O short-range order evolves into the partial O-F disorder. The present model provides a useful relationship between experimental equilibria, macroscopic thermodynamics and melt speciation, thus it facilitates comparisons with, and interpretations of, spectroscopic and molecular simulation data.

A geochemical study of the winonaites: Evidence for limited partial melting and constraints on the precursor composition

NASA Astrophysics Data System (ADS)

Hunt, Alison C.; Benedix, Gretchen K.; Hammond, Samantha J.; Bland, Philip A.; Rehkämper, Mark; Kreissig, Katharina; Strekopytov, Stanislav

2017-02-01

The winonaites are primitive achondrites which are associated with the IAB iron meteorites. Textural evidence implies heating to at least the Fe, Ni-FeS cotectic, but previous geochemical studies are ambiguous about the extent of silicate melting in these samples. Oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites. Here we analysed a suite of winonaites for modal mineralogy and bulk major- and trace-element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite-IAB parent asteroid. Modal mineralogy and geochemical data are presented for eight winonaites. Textural analysis reveals that, for our sub-set of samples, all except the most primitive winonaite (Northwest Africa 1463) reached the Fe, Ni-FeS cotectic. However, only one (Tierra Blanca) shows geochemical evidence for silicate melting processes. Tierra Blanca is interpreted as a residue of small-degree silicate melting. Our sample of Winona shows geochemical evidence for extensive terrestrial weathering. All other winonaites studied here (Fortuna, Queen Alexander Range 94535, Hammadah al Hamra 193, Pontlyfni and NWA 1463) have chondritic major-element ratios and flat CI-normalised bulk rare-earth element patterns, suggesting that most of the winonaites did not reach the silicate melting temperature. The majority of winonaites were therefore heated to a narrow temperature range of between ∼1220 (the Fe, Ni-FeS cotectic temperature) and ∼1370 K (the basaltic partial melting temperature). Silicate inclusions in the IAB irons demonstrate partial melting did occur in some parts of the parent body (Ruzicka and Hutson, 2010), thereby implying heterogeneous heat distribution within this asteroid. Together, this indicates that melting was the result of internal heating by short-lived radionuclides. The brecciated nature of the winonaites suggests that the parent body was later disrupted by a catastrophic impact, which allowed the preservation of the largely unmelted winonaites. Despite major-element similarities to both ordinary and enstatite chondrites, trace-element analysis suggests the winonaite parent body had a carbonaceous chondrite-like precursor composition. The parent body of the winonaites was volatile-depleted relative to CI, but enriched compared to the other carbonaceous classes. The closest match are the CM chondrites; however, the specific precursor is not sampled in current meteorite collections.

Volatile Element Behavior During Melting and Vaporisation on Earth and Protoplanets.

NASA Astrophysics Data System (ADS)

Wood, B. J.; Norris, C. A.

2017-12-01

During accretion the Earth and many of the smaller bodies which were added to it, underwent periods of partial melting, vaporisation and re-condensation. This resulted in patterns of volatile element depletion relative to CI chondrite which are difficult to interpret. The behavior of moderately volatile elements (Pb, Cd, Zn,Cu, In,Tl etc) during these melting, vaporisation and condensation processes is usually approximated by the temperature of condensation from a gas of solar composition. Thus, Tl and In have low condensation temperatures and are regarded as the most volatile of this group. In order to test this volatility approximation we have studied the vaporisation behavior of 13 elements (Ag,Bi,Cd,Cr,Cu,Ga,Ge,In,Pb,Sb,Sn,Tl,Zn) from molten basalt at 1 atm pressure and oxygen fugacities between Ni-NiO and 2 log units below Fe-FeO. The relative volatilities of the elements turn out to be only weakly correlated with condensation temperature, indicating that the latter is a poor proxy for volatility on molten bodies. Cu, Zn and In for example all have similar volatility in the oxygen fugacity range of concern, despite the condensation temperature of Cu (1037K at 10-4bar) being 500K greater than that of In. The oxygen fugacity dependence of volatility indicates that the volatile species are, for all elements more reduced than the melt species. We addressed the differences between condensation temperature and relative volatility in 2 steps. Firstly we used metal-silicate partitioning experiments to estimate the activity coefficients of the trace element oxides in silicate melts. We then used available thermodynamic data to compute the vapor pressures of the stable species of these 13 elements over the silicate melt at oxygen fugacities ranging from Ni-NiO to about 6 log units below Fe-FeO, which approximates the solar gas. Thus we find that presence of Cl and S in the solar gas and the stable Cl and S species of In,Tl Ga Ge Cd and Sn are important contributing factors to volatility in the solar nebula. Our measured volatilities from silicate melt under reducing (S and Cl-absent) conditions are consistent with abundances in the silicate Earth, indicating that these moderately volatile elements were added to Earth in bodies which had undergone episodes of melting and vaporisation.

Tonalites in crustal evolution

USGS Publications Warehouse

Barker, F.; Arth, Joseph G.; Hudson, T.

1981-01-01

Tonalites, including trondhjemite as a variety, played three roles through geological time in the generation of Earth's crust. Before about 2.9 Ga ago they were produced largely by simple partial melting of metabasalt to give the dominant part of Archaean grey gneiss terranes. These terranes are notably bimodal; andesitic rocks are rare. Tonalites played a crucial role in the generation of this protocontinental and oldest crust 3.7-2.9 Ga ago in that they were the only low-density, high-SiO2 rocks produced directly from basaltic crust. In the enormous event giving the greenstone-granite terranes, mostly 2.8-2.6 Ga ago, tonalites formed in lesser but still important proportions by partial melting of metabasalt in the lower regions of down-buckled greenstone belts and by remobilization of older grey gneisses. Tectonism in the Archaean (3.9-2.5 Ga ago) perhaps was controlled by small-cell convection (McKenzie & Weiss I975). Little or no ophiolite or eclogite formed, and only minor andesite. Plate tectonics of modern type (involving large, rigid plates) commenced in the early Proterozoic. Uniformitarianism thus goes back one-half of the age of the earth. Tonalites compose about 5-10 % of crust generated in Proterozoic and Phanerozoic time at convergent oceanic-continental margins. They occur here as minor to prominent members of the compositionally continuous continental-margin batholiths. A simple model of generation of these batholiths is offered: mantle-derived mafic magma pools in the lower crust above a subduction zone reacts with and incorporates wall-rock components (Bowen I922), and breaches its roof rocks as an initial diapir. This mantle magma also develops a gradient of partial melting in its wall rocks. This wall-rock melt accretes in the collapsed chamber and moves up the conduit broached by the initial diapir, the higher, less siliceous fractions of melting first, the lower, more siliceous (and further removed) fractions of melting last. The process gives in the optimum case a mafic-to-siliceous sequence of diorite or quartz diorite through tonalite or quartz monzodiorite to granodiorite and granite. The model implies that great masses of cumulate phases and refractory wall rock form the roots of continental- margin batholiths, and that migmatites overlie that residuum and underlie the batholiths.

Modelling of multi-vortex convection of fine alloying components in the molten pool under the laser radiation

NASA Astrophysics Data System (ADS)

Gurin, A. M.; Kovalev, O. B.

2013-06-01

The work is devoted to the mathematical modelling and numerical solution of the problems of conjugate micro-convection, which arises under the laser radiation action in the metal melt with surface-active refractory disperse components added for the modification, hardening, and doping of the treated surface. A multi-vortex structure of the melt flow has been obtained, the number of vortices in which depends on the surface tension variation, on the temperature and power of laser radiation. Special attention is paid to the numerical modelling of the behavior in the melt of the substrate of disperse admixture consisting of the tungsten carbide particles. The role of microconvection in the distribution of powder particles in the surface layer of the substrate after its cooling is shown.

Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur

NASA Astrophysics Data System (ADS)

Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.

2008-07-01

Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between< 0.5 to ˜ 1% in Albian rocks, and between ˜ 1 and 2% in succeeding Cenomanian to Campanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average < 16%), low Mg-number (molar Mg/Mg + Fe < 0.5), TiO 2 (< 1.0%), and Sr/Y (< 10), oceanic or arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (< 20%) of silicic lavas were erupted. The systematic variation of both sediment flux and abundance of crustally derived silicic lavas are consistent with current tectonic models of Caribbean evolution involving approximately perpendicular subduction of the Caribbean spur of the mid-Atlantic Ridge, which was located approximately midway between North and South America until Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment flux was limited. Conversely, toward the west in central Puerto Rico, which was consistently more remote from the subducting ridge, heat flow was relatively low and produced limited crustal melting, while the sediment flux was comparatively elevated.

Barrier Properties of Layered-Silicate Reinforced Ethylenepropylenediene Monomer/Chloroprene Rubber Nanorubbers

PubMed Central

Hsieh, Wen Yen; Cheng, Kuo Bin; Lai, Chiu-Chun; Lee, Kuei Chi

2018-01-01

The triacetin and nitroglycerin barrier properties of layered-silicate reinforced ethylenepropylenediene monomer/chloroprene rubber (EPDM/CR) nanorubbers were investigated as rocket-propellant inhibitors. EPDM/CR nanorubbers with intercalated structures were formulated and prepared by the melt-compounding method. The triacetin permeability and nitroglycerin absorption were observed to decrease with increasing layered-silicate content. The layered silicates also improved the flame retardancies of the nanorubbers by forming silicate reinforced carbonaceous chars. Layered-silicate reinforced EPDM/CR nanorubbers are potentially effective rocket propellant-inhibiting materials. PMID:29747427

Metal/Silicate Partitioning, Melt Speciation, Accretion, and Core Formation in the Earth

NASA Astrophysics Data System (ADS)

Drake, M. J.; Hillgren, V. J.; Dearo, J. A.; Capobianco, C. J.

1993-07-01

Core formation in terrestrial planets was concomitant with accretion. Siderophile and chalcophile element signatures in the mantles of planets are the result of these processes. For Earth, abundances of most siderophile and chalcophile elements are elevated relative to predictions from simple metal/silicate equilibria at low pressures [1]. This observation has led to three hypotheses for how these abundances were established: heterogeneous accretion [2], inefficient core formation [3], and metal/silicate equilibria at magma ocean pressures and temperatures [4]. Knowledge of speciation of siderophile elements in silicate melts in equilibrium with metal may help distinguish between these hypotheses. But there is some uncertainty regarding speciation. For example, Ni and Co have been reported to be present as 1+ or zero valence species in silicate melts at redox states appropriate to planetary accretion, rather than the expected 2+ state [5-7]. Independent metal/silicate partitioning experiments by three members of this group using two different experimental designs on both synthetic and natural compositions do not show evidence for Ni and Co in valence states other than 2+ over a wide range of redox states. For example, solid metal/silicate melt partition coefficients for Ni at 1260 degrees C obtained by VJH from experiments investigating the partitioning of Ni, Co, Mo, W, and P are indistinguishable from those obtained by JAD in similar experiments investigating the partitioning of Ni, Ge, and Sn. Both datasets define a line with the equation: log D(Ni) = - 0.54log fO2 - 3.14 with r^2 > 0.995. (Note that fO2 was calculated in both studies from thermodynamic data and phase compositions. A small, systematic offset from the true fO2 as measured by a solid electrolyte cell affects both equations similarly, but does not diminish their close agreement.) The valence of Ni in the silicate melt is obtained by multiplying the slope of the line by -4, indicating divalent Ni in both studies. Experiments by [8] between 1300 degrees C and 1550 degrees C and fO2 from air to just below iron-wustite in which Ni and Co are partitioned between Pt metal and CaO-Al2O3-SiO2 silicate melt also show evidence only for 2+ valence. Capobianco et al. [1] have noted that reliable extrapolation from current laboratory temperatures (1190 degrees C-1600 degrees C) to magma ocean temperatures is not possible. The hypothesis that siderophile and chalcophile element abundances in the mantle of Earth were established by metal/silicate equilibria at magma ocean pressures and temperatures needs to be tested using direct experimental measurements at magma ocean temperatures and pressures. Such experiments are currently being conducted. References: [1] Capobianco et al. (1993) J. Geophys. Res., 98, 5433. [2] Wanke (1981) Phil. Trans. R. Soc. London, A303, 287. [3] Jones and Drake (1986) Nature, 322, 221. [4] Murthy (1991) Science, 253, 303. [5] Schmitt et al. (1989) GCA, 53, 173. [6] Ehlers et al. (1993) GCA, 56, 3733. [7] Colson (1992) Nature, 357, 65. [8] Capobianco and Amelin (1993) GCA, 56 (in press).

Deep-Earth Equilibration between Molten Iron and Solid Silicates

NASA Astrophysics Data System (ADS)

Brennan, M.; Zurkowski, C. C.; Chidester, B.; Campbell, A.

2017-12-01

Elemental partitioning between iron-rich metals and silicate minerals influences the properties of Earth's deep interior, and is ultimately responsible for the nature of the core-mantle boundary. These interactions between molten iron and solid silicates were influential during planetary accretion, and persist today between the mantle and liquid outer core. Here we report the results of diamond anvil cell experiments at lower mantle conditions (40 GPa, >2500 K) aimed at examining systems containing a mixture of metals (iron or Fe-16Si alloy) and silicates (peridotite). The experiments were conducted at pressure-temperature conditions above the metallic liquidus but below the silicate solidus, and the recovered samples were analyzed by FIB/SEM with EDS to record the compositions of the coexisting phases. Each sample formed a three-phase equilibrium between bridgmanite, Fe-rich metallic melt, and an oxide. In one experiment, using pure Fe, the quenched metal contained 6 weight percent O, and the coexisting oxide was ferropericlase. The second experiment, using Fe-Si alloy, was highly reducing; its metal contained 10 wt% Si, and the coexisting mineral was stishovite. The distinct mineralogies of the two experiments derived from their different starting metals. These results imply that metallic composition is an important factor in determining the products of mixed phase iron-silicate reactions. The properties of deep-Earth interfaces such as the core-mantle boundary could be strongly affected by their metallic components.

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

PubMed

Reubi, Olivier; Blundy, Jon

2009-10-29

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

High temperature calorimetric studies of heat of solution of NiO, CuO, La2O3, TiO2, HfO2 in sodium silicate liquids

NASA Astrophysics Data System (ADS)

Linard, Yannick; Wilding, Martin C.; Navrotsky, Alexandra

2008-01-01

The enthalpies of solution of La2O3, TiO2, HfO2, NiO and CuO were measured in sodium silicate melts at high temperature. When the heat of fusion was available, we derived the corresponding liquid-liquid enthalpies of mixing. These data, combined with previously published work, provide insight into the speciation reactions in sodium silicate melts. The heat of solution of La2O3 in these silicate solvents is strongly exothermic and varies little with La2O3 concentration. The variation of heat of solution with composition of the liquid reflects the ability of La(III) to perturb the transient silicate framework and compete with other cations for oxygen. The enthalpy of solution of TiO2 is temperature-dependent and indicates that the formation of Na-O-Si species is favored over Na-O-Ti at low temperature. The speciation reactions can be interpreted in terms of recent spectroscopic studies of titanium-bearing melts which identify a dual role of Ti4+ as both a network-former end network-modifier. The heats of solution of oxides of transition elements (Ni and Cu) are endothermic, concentration-dependent and reach a maximum with concentration. These indicate a charge balanced substitution which diminishes the network modifying role of Na+ by addition of Ni2+ or Cu2+. The transition metal is believed to be in tetrahedral coordination, charge balanced by the sodium cation in the melts.

Two-phase convection in Ganymede's high-pressure ice layer - Implications for its geological evolution

NASA Astrophysics Data System (ADS)

Kalousová, Klára; Sotin, Christophe; Choblet, Gaël; Tobie, Gabriel; Grasset, Olivier

2018-01-01

Ganymede, the largest moon in the solar system, has a fully differentiated interior with a layer of high-pressure (HP) ice between its deep ocean and silicate mantle. In this paper, we study the dynamics of this layer using a numerical model of two-phase ice-water mixture in two-dimensional Cartesian geometry. While focusing on the generation of water at the silicate/HP ice interface and its upward migration towards the ocean, we investigate the effect of bottom heat flux, the layer thickness, and the HP ice viscosity and permeability. Our results suggest that melt can be generated at the silicate/HP ice interface for small layer thickness ( ≲ 200 km) and high values of heat flux ( ≳ 20 mW m-2) and viscosity ( ≳ 1015 Pa s). Once generated, the water is transported through the layer by the upwelling plumes. Depending on the vigor of convection, it stays liquid or it may freeze before melting again as the plume reaches the temperate (partially molten) layer at the boundary with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the permeability of the HP ice. This process constitutes a means of transporting volatiles and salts that might have dissolved into the melt present at the silicate/HP ice interface. As the moon cools down, the HP ice layer becomes less permeable because the heat flux from the silicates decreases and the HP ice layer thickens.

An Interconnected Network of Core-Forming Melts Produced by Shear Deformation

NASA Technical Reports Server (NTRS)

Bruhn, D.; Groebner, N.; Kohlstedt, D. L.

2000-01-01

The formation mechanism of terrestrial planetary is still poorly understood, and has been the subject of numerous experimental studies. Several mechanisms have been proposed by which metal-mainly iron with some nickel-could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle that is often referred to as a'magma ocean. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix. But experimental studies performed at high pressures have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (nonhydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.

Power supplies for dual-frequency induction melting of metals

NASA Astrophysics Data System (ADS)

Lusgin, V. I.; Koptyakov, A. S.; Petrov, A. U.; Zinovev, K. A.; Kamaev, D. A.

2018-02-01

The article discusses the benefits of multi frequency induction melting in the production of synthetic cast iron, structural (electric circuit) principles of dual frequency Power supplies of melting systems. The ways of electric power regulation of low frequency and high frequency components of the current in the inductor sections of furnace are demonstrated, namely power rescheduling at the metal melting stage, alloying stage and decarburizing of synthetic cast iron.

Evolution of melt-vapor surface tension in silicic volcanic systems: Experiments with hydrous melts

USGS Publications Warehouse

Mangan, M.; Sisson, T.

2005-01-01

We evaluate the melt-vapor surface tension (??) of natural, water-saturated dacite melt at 200 MPa, 950-1055??C, and 4.8-5.7 wt % H2O. We experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for ?? at those conditions using classical nucleation theory. The solutions obtained give dacite melt-vapor surface tensions that vary inversely with dissolved water from 0.042 (??0.003) J m-2 at 5.7 wt% H2O to 0.060 (??0.007) J m-2 at 5.2 wt% H2O to 0.073 (??0.003) J m-2 at 4.8 wt% H2O. Combining our dacite results with data from published hydrous haplogranite and high-silica rhyolite experiments reveals that melt-vapor surface tension also varies inversely with the concentration of mafic melt components (e.g., CaO, FeOtotal, MgO). We develop a thermodynamic context for these observations in which melt-vapor surface tension is represented by a balance of work terms controlled by melt structure. Overall, our results suggest that cooling, crystallization, and vapor exsolution cause systematic changes in ?? that should be considered in dynamic modeling of magmatic processes.

Platinum Partitioning at Low Oxygen Fugacity: Implications for Core Formation Processes

NASA Technical Reports Server (NTRS)

Medard, E.; Martin, A. M.; Righter, K.; Lanziroti, A.; Newville, M.

2016-01-01

Highly siderophile elements (HSE = Au, Re, and the Pt-group elements) are tracers of silicate / metal interactions during planetary processes. Since most core-formation models involve some state of equilibrium between liquid silicate and liquid metal, understanding the partioning of highly siderophile elements (HSE) between silicate and metallic melts is a key issue for models of core / mantle equilibria and for core formation scenarios. However, partitioning models for HSE are still inaccurate due to the lack of sufficient experimental constraints to describe the variations of partitioning with key variable like temperature, pressure, and oxygen fugacity. In this abstract, we describe a self-consistent set of experiments aimed at determining the valence of platinum, one of the HSE, in silicate melts. This is a key information required to parameterize the evolution of platinum partitioning with oxygen fugacity.

Experimental Constraints on Silicic Slab Melt and Depleted Mantle Reaction in the Presence of CO2-H2O: Implications for the Origin of Mid Lithospheric Discontinuity

NASA Astrophysics Data System (ADS)

Saha, S.; Dasgupta, R.; Tsuno, K.

2016-12-01

Seismic shear wave velocity, VS drop (upto 24% and mostly 2-7%) observed globally beneath continents at depths of 60-160 km, known as the Mid Lithospheric Discontinuity (MLD) [e.g., 1], is an enigmatic feature of cratons whose origin is highly debated [e.g., 2, 3]. One of the mechanisms that can explain the MLD is the presence of volatile bearing phases such as partial melts and/or hydrous or carbonate minerals at depths. However, the compositional vector and geodynamic scenario required for their formation and the proportion and composition of infiltrating melt or fluid that may lead to their stability is poorly known at present. We performed high P-T experiments equilibrating a depleted peridotite (Mg# 92) with variable proportion of a H2O-CO2 bearing silicic melt, interaction that could occur during the formation of continents by imbrication of slabs. The first set of experiments were performed with 10 wt.% melt (0.9 wt.% H2O and 0.5 wt.% CO2 in the bulk) at 950-1175 °C at 3 GPa using a piston cylinder and 950-1150 °C at 4 GPa using a multi anvil apparatus. Olivine, opx, cpx, garnet/spinel and phlogopite (5-6%) are present in all runs. Amphibole (3.5-9.5%) is present at 3 GPa and ≤1050 °C. Magnesite ( 1%) is present at ≤1000 °C at 3 and ≤1050 °C at 4 GPa. Trace melt is observed along the grain boundaries above 1000 °C at 3 GPa and 1050 ° C at 4 GPa, respectively. Mineral modes obtained by mass balance calculations, ignoring the presence of melts, were used to calculate VS of the resulting assemblages [4]. The calculated drops in VS at 3 GPa (3.8-4.5%) and 4 GPa (1.6-3.2%) are well within the range of velocity drops for MLDs observed globally. Further experiments on different melt-rock ratios are underway and will constrain how modal proportion of hydrous and carbonate minerals varies as a function of melt:rock ratio and bulk volatile contents. [1] Abt et al., 2010, JGR; [2] Rader et al., 2015, G3; [3] Karato et al., 2015, NatGeo [4] Abers & Hacker, 2016, G3

XANES evidence for sulphur speciation in Mn-, Ni- and W-bearing silicate melts

NASA Astrophysics Data System (ADS)

Evans, K. A.; O'Neill, H. St. C.; Mavrogenes, J. A.; Keller, N. S.; Jang, L.-Y.; Lee, J.-F.

2009-11-01

S K-edge XANES and Mn-, W- and Ni-XANES and EXAFS spectra of silicate glasses synthesised at 1400 °C and 1 bar with compositions in the CaO-MgO-Al 2O 3-SiO 2-S plus MnO, NiO, or WO 3 systems were used to investigate sulphur speciation in silicate glasses. S K-edge spectra comprised a composite peak with an edge between 2470 and 2471.4 eV, which was attributed to S 2-, and a peak of variable height with an edge at 2480.2-2480.8 eV, which is consistent with the presence of S 6+. The latter peak was attributed to sample oxidation during sample storage. W-rich samples produced an additional lower energy peak at 2469.8 eV that is tentatively attributed to the existence of S 3p orbitals hybridised with the W 5d states. Deconvolution of the composite peak reveals that the composite peak for Mn-bearing samples fits well to a model that combines three Lorentzians at 2473.1, 2474.9 and 2476.2 eV with an arctan edge step. The composite peak for W-bearing samples fits well to the same combination plus an additional Lorentzian at 2469.8 eV. The ratio of the proportions of the signal accounted for by peaks at 2473.1 and 2476.2 eV correlates with Mn:Ca molar ratios, but not with W:Ca ratios. Spectra from Ni-bearing samples were qualitatively similar but S levels were too low to allow robust quantification of peak components. Some part of the signal accounted for by the 2473.1 eV peak was therefore taken to record the formation of Mn-S melt species, while the 2469.8 peak is interpreted to record the formation of W-S melt species. The 2474.9 and 2476.2 eV peaks were taken to be dominated by Ca-S and Mg-S interactions. However, a 1:1 relationship between peak components and specific energy transitions is not proposed. This interpretation is consistent with known features of the lower parts of the conduction band in monosulphide minerals and indicates a similarity between sulphur species in the melts and the monosulphides. S-XANES spectra cannot be reproduced by a combination of the spectra of the component element monosulphides. Mn-, W- and Ni-XANES and EXAFS for synthetic glasses without sulphide exsolution did not show any sensitivity to the presence of sulphur, which is unsurprising as S:O ratios were sufficiently low that metals would be mostly co-ordinated by O. Mn EXAFS spectra were consistent with divalent Mn in 5 co-ordinated Mn-O melt species. W spectra were consistent with tetrahedrally co-ordinated hexavalent W, most likely in scheelite-like melt species, and Ni spectra were consistent with [4] co-ordinated divalent Ni. These results indicate lower co-ordinations for both W and Ni than those inferred by some previous workers. Cation co-ordination may reflect the proportion of non-bridging oxygens, which is lower in the Ca-rich and Al-poor samples investigated here than for previous studies.

Spectroscopy `outside the box': Towards wider application of NMR to minerals and glasses with abundant paramagnetic cations - Fe, Ni, Co, and Cu silicates

NASA Astrophysics Data System (ADS)

Stebbins, J. F.

2017-12-01

Since the early applications of solid-state NMR (Nuclear Magnetic Resonance) to silicates in the early 1980's, this powerful method has been widely applied to problems of short- to medium-range structure, particularly for materials in which order/disorder is critical, such as crystalline solid solutions, glasses, and even melts. However, almost all such work has been on materials with low (< a few %) contents of ions with unpaired electron spins. Such spins interact strongly with NMR-observed nuclear spins, and can cause severe line broadening and loss of information, in some cases making spectra nearly unobservable. Many groups of minerals with abundant, paramagnetic transition metals (notably Fe2+) and rare earth cations, as well as wide, petrologically important ranges of glass composition have thus been excluded. Inspired by in-depth NMR studies of 31P, 7Li, and other nuclides in lithium-transition metal oxide and phosphate battery materials (C. Grey and others), and with some serendipitous discovery plus persistence to look far outside of "normal" parameter space, we have recently shown that high resolution, structurally informative spectra can actually be obtained for silicate, oxide, and phosphate solid solutions with moderate (0.1 up to 10%) contents of paramagnetic cations such as Fe2+, Ni2+, Co2+ and REE3+. Very recently we have extended this to observe some of the first quantitative NMR spectra of silicate minerals in which a paramagnetic transition metal is the major cation, obtaining useful data for a series of Cu2+ silicates, fayalite (Fe2SiO4) and Ni- and Co- equivalents of diopside (CaMSi2O6). New data for glasses of the latter compositions may be the first such accurate results for any transition metal-rich glass. Although we are still far from a detailed theoretical understanding of these data, the spectra for the glasses are quite different from those of the crystals, suggesting the possibility of medium-range ordering and clustering of NiO and CoO-rich regions. If this conclusion holds up, it may have major implications for thermodynamic models of activities of such components in melts, which in turn are important for a number of geothermometers and barometers based on mineral-melt partitioning.

Advancing dynamic and thermodynamic modelling of magma oceans

NASA Astrophysics Data System (ADS)

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

2017-04-01

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 (< 2 cm thickness) at the core-mantle boundary and surface. PETSc also enables our code to support a parallel implementation and quad-precision calculations for future modelling capabilities. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting (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 adiabat and melting curve. Experiments on melting of primitive chondrite composition predict that crystallisation occurs from the "bottom-up", whereas molecular dynamics simulations of MgSiO3 perovskite suggest crystallisation occurs from the "middle-out". In each case, we evaluate the lifetime of the magma ocean using our model and find that in both scenarios, initial cooling is rapid and the rheological transition (boundary between melt- and solid-like behaviour) is reached within a few kyrs. During this stage efficient mixing prevents the establishment of thermal and chemical heterogeneity, so it may be challenging to locate a signature of the earliest phase of magma ocean evolution. At the rheological transition, cooling is governed by gravitational separation and viscous creep, and even in the absence of iron partitioning our models predict long-lasting (> 500 Myr) melt at the base of the mantle.

Generation of Silicic Melts in the Early Izu-Bonin Arc Recorded by Detrital Zircons in Proximal Arc Volcaniclastic Rocks From the Philippine Sea

NASA Astrophysics Data System (ADS)

Barth, A. P.; Tani, K.; Meffre, S.; Wooden, J. L.; Coble, M. A.; Arculus, R. J.; Ishizuka, O.; Shukle, J. T.

2017-10-01

A 1.2 km thick Paleogene volcaniclastic section at International Ocean Discovery Program Site 351-U1438 preserves the deep-marine, proximal record of Izu-Bonin oceanic arc initiation, and volcano evolution along the Kyushu-Palau Ridge (KPR). Pb/U ages and trace element compositions of zircons recovered from volcaniclastic sandstones preserve a remarkable temporal record of juvenile island arc evolution. Pb/U ages ranging from 43 to 27 Ma are compatible with provenance in one or more active arc edifices of the northern KPR. The abundances of selected trace elements with high concentrations provide insight into the genesis of U1438 detrital zircon host melts, and represent useful indicators of both short and long-term variations in melt compositions in arc settings. The Site U1438 zircons span the compositional range between zircons from mid-ocean ridge gabbros and zircons from relatively enriched continental arcs, as predicted for melts in a primitive oceanic arc setting derived from a highly depleted mantle source. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic melts that evolved toward more Th and U-rich compositions with time. Th, U, and light rare earth element enrichments beginning about 35 Ma are consistent with detrital zircons recording development of regional arc asymmetry and selective trace element-enriched rear arc silicic melts as the juvenile Izu-Bonin arc evolved.

Evaporation and Accompanying Isotopic Fractionation of Sulfur from FE-S Melt During Shock Wave Heating

NASA Technical Reports Server (NTRS)

Tachibana, S.; Huss, G. R.; Miura, H.; Nakamoto, T.

2004-01-01

Chondrules probably formed by melting and subsequent cooling of solid precursors. Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. It is known that kinetic evaporation, especially evaporation from a melt, often leads to enrichment of heavy isotopes in an evaporation residue. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules for K, Mg, Si, and Fe (as FeO). The lack of isotopic fractionation has also been found for sulfur in troilites (FeS) within Bishunpur (LL3.1) and Semarkona (LL3.0) chondrules by an ion microprobe study. The largest fractionation, found in only one grain, was 2.7 +/- 1.4 %/amu, while all other troilite grains showed isotopic fractionations of <1 %/amu. The suppressed isotopic fractionation has been interpreted as results of (i) rapid heating of precursors at temperatures below the silicate solidus and (ii) diffusion-controlled evaporation through a surrounding silicate melt at temperatures above the silicate solidus. The kinetic evaporation model suggests that a rapid heating rate of >10(exp 4)-10(exp 6) K/h for a temperature range of 1000-1300 C is required to explain observed isotopic fractionations. Such a rapid heating rate seems to be difficult to be achieved in the X-wind model, but can be achieved in shock wave heating models. In this study, we have applied the sulfur evaporation model to the shock wave heating conditions of to evaluate evaporation of sulfur and accompanying isotopic fractionation during shock wave heating at temperatures below the silicate solidus.

Intrusive rocks of the Wadi Hamad Area, North Eastern Desert, Egypt: Change of magma composition with maturity of Neoproterozoic continental island arc and the role of collisional plutonism in the differentiation of arc crust

NASA Astrophysics Data System (ADS)

Basta, Fawzy F.; Maurice, Ayman E.; Bakhit, Bottros R.; Azer, Mokhles K.; El-Sobky, Atef F.

2017-09-01

The igneous rocks of the Wadi Hamad area are exposed in the northernmost segment of the Arabian-Nubian Shield (ANS). These rocks represent part of crustal section of Neoproterozoic continental island arc which is intruded by late to post-collisional alkali feldspar granites. The subduction-related intrusives comprise earlier gabbro-diorites and later granodiorites-granites. Subduction setting of these intrusives is indicated by medium- to high-K calc-alkaline affinity, Ta-Nb troughs on the spider diagrams and pyroxene and biotite compositions similar to those crystallized from arc magmas. The collisional alkali feldspar granites have high-K highly fractionated calc-alkaline nature and their spider diagrams almost devoid of Ta-Nb troughs. The earlier subduction gabbro-diorites have lower alkalis, LREE, Nb, Zr and Hf values compared with the later subduction granodiorites-granites, which display more LILE-enriched spider diagrams with shallower Ta-Nb troughs, reflecting variation of magma composition with arc evolution. The later subduction granitoids were generated by lower degree of partial melting of mantle wedge and contain higher arc crustal component compared with the earlier subduction gabbro-diorites. The highly silicic alkali feldspar granites represent extensively evolved melts derived from partial melting of intermediate arc crustal sources during the collisional stage. Re-melting of arc crustal sources during the collisional stage results in geochemical differentiation of the continental arc crust and the silicic collisional plutonism drives the composition of its upper part towards that of mature continental crust.

Chemical Zoning of Feldspars in Lunar Granitoids: Implications for the Origins of Lunar Silicic Magmas

NASA Technical Reports Server (NTRS)

Mills, R. D; Simon, J. I.; Alexander, C.M. O'D.; Wang, J.; Christoffersen, R.; Rahman, Z..

2014-01-01

Fine-scale chemical and textural measurements of alkali and plagioclase feldspars in the Apollo granitoids (ex. Fig. 1) can be used to address their petrologic origin(s). Recent findings suggest that these granitoids may hold clues of global importance, rather than of only local significance for small-scale fractionation. Observations of morphological features that resemble silicic domes on the unsampled portion of the Moon suggest that local, sizable net-works of high-silica melt (>65 wt % SiO2) were present during crust-formation. Remote sensing data from these regions suggest high concentrations of Si and heat-producing elements (K, U, and Th). To help under-stand the role of high-silica melts in the chemical differentiation of the Moon, three questions must be answered: (1) when were these magmas generated?, (2) what was the source material?, and (3) were these magmas produced from internal differentiation. or impact melting and crystallization? Here we focus on #3. It is difficult to produce high-silica melts solely by fractional crystallization. Partial melting of preexisting crust may therefore also have been important and pos-sibly the primary mechanism that produced the silicic magmas on the Moon. Experimental studies demonstrate that partial melting of gabbroic rock under mildly hydrated conditions can produce high-silica compositions and it has been suggested by that partial melting by basaltic underplating is the mechanism by which high-silica melts were produced on the Moon. TEM and SIMS analyses, coordinated with isotopic dating and tracer studies, can help test whether the minerals in the Apollo granitoids formed in a plutonic setting or were the result of impact-induced partial melting. We analyzed granitoid clasts from 3 Apollo samples: polymict breccia 12013,141, crystalline-matrix breccia 14303,353, and breccia 15405,78

Density Measurement for MORB Melts by X-ray Absorption Method

NASA Astrophysics Data System (ADS)

Sakamaki, T.; Urakawa, S.; Suzuki, A.; Ohtani, E.; Katayama, Y.

2006-12-01

Density of silicate melts at high pressure is one of the most important properties to understand magma migration in the planetary interior and the differentiation of the terrestrial planets. The density measurements of silicate melts have been carried out by several methods (shock compression experiments and sink-float method in static experiments, etc.). However, since these methods have difficulties in acquisition of data at a desired pressure and temperature, the density of the silicate melt have been measured under only a few conditions. Recently a new density measurement was developed by the X-ray absorption method. Advantage of this method is to measure density of liquids at a desired pressure and temperature. In the present study we measured the density of MORB melt by X-ray absorption method. Experiments were carried out at the BL22XU beamline at SPring-8. A DIA-type cubic anvil apparatus was used for generation of high pressure and temperature. We used tungsten carbide anvils with the top anvil sizes of 6 mm and 4 mm. The energy of monochromateized X-ray beam was 23 keV. The intensities of incident and transmitted X-ray were measured by ion chambers. The density of the melt was calculated on the basis of Beer-Lambert law. The starting material was a glass with the MORB composition. Experiments were made from 1 atm to 5 GPa, from 300 to 2000 K. We compared the density of MORB melt with the compression curve of the melt in previous works. The density measured by this study is lower than that expected from the compression curve determined at higher pressures by the sink-float method. Structural change of the MORB melt with increasing pressure might be attributed to this discrepancy.

Density Measurement for MORB Melts by X-ray Absorption Method

NASA Astrophysics Data System (ADS)

Sakamaki, T.; Urakawa, S.; Ohtani, E.; Suzuki, A.; Katayama, Y.

2005-12-01

Density of silicate melts at high pressure is one of the most important properties to understand magma migration in the planetary interior and the differentiation of the terrestrial planets. The density measurements of silicate melts have been carried out by several methods (shock compression experiments and sink-float method in static experiments, etc.). However, since these methods have difficulties in acquisition of data at a desired pressure and temperature, the density of the silicate melt have been measured under only a few conditions. Recently a new density measurement was developed by the X-ray absorption method. Advantage of this method is to measure density of liquids at a desired pressure and temperature. In the present study we measured the density of MORB melt by X-ray absorption method. Experiments were carried out at the BL22XU beamline at SPring-8. A DIA-type cubic anvil apparatus was used for generation of high pressure and temperature. We used tungsten carbide anvils with the edge-length of 6 mm. The energy of monochromateized X-ray beam was 23 keV. The intensities of incident and transmitted X-ray were measured by ion chambers. The density of the melt was calculated on the basis of Beer-Lambert law. The starting material was a glass with the MORB composition. Experiments were made from 1 atm to 4 GPa, from 300 to 2200 K. We compared the density of MORB melt with the compression curve of the melt in previous works. The density measured by this study is lower than that expected from the compression curve determined at higher pressures by the sink-float method. Structural change of the MORB melt with increasing pressure might be attributed to this discrepancy.

An electrochemical series of redox couples in silicate melts - A review and applications to geochemistry

NASA Technical Reports Server (NTRS)

Schreiber, Henry D.

1987-01-01

An electrochemical series for redox couples in a glass-forming oxide melt is developed. This series is a quantitative numerical scale of reference reduction potentials of the redox couples in a silicate melt that is a model for basaltic magmas. The redox couples are ordered in terms of their reference reduction potentials; the order appears to be relatively independent of the exact melt composition and temperature. Thus, upon calibration to a desired composition, oxygen fugacity, and temperature, this electrochemical series can provide estimates of redox state proportions in basaltic magmas on different planetary bodies. The geochemical electrochemical series can also be used to understand the interrelationship of the redox state of the magma and the presence of volatile species such as oxygen, water, sulfur gases, and carbon gases.

Experimental Determination of Spinel/Melt, Olivine/Melt, and Pyroxene/Melt Partition Coefficients for Re, Ru, Pd, Au, and Pt

NASA Technical Reports Server (NTRS)

Righter, K.; Campbell, A. J.; Humayun, M.

2003-01-01

Experimental studies have identified spinels as important hosts phases for many of the highly siderophile elements (HSE). Yet experimental studies involving chromite or Cr-rich spinel have been lacking. Experimental studies of partitioning of HSEs between silicate, oxides and silicate melt are plagued by low solubilities and the presence of small metallic nuggets at oxygen fugacities relevant to magmas, which interfere with analysis of the phases of interest. We have circumvented these problems in two ways: 1) performing experiments at oxidized conditions, which are still relevant to natural systems but in which nuggets are not observed, and 2) analysis of run products with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), allowing a combination of high sensitivity and good spatial resolution.

Isotope geochemistry and fluid inclusion study of skarns from Vesuvius

USGS Publications Warehouse

Gilg, H.A.; Lima, A.; Somma, R.; Belkin, H.E.; de Vivo, B.; Ayuso, R.A.

2001-01-01

We present new mineral chemistry, fluid inclusion, stable carbon and oxygen, as well as Pb, Sr, and Nd isotope data of Ca-Mg-silicate-rich ejecta (skarns) and associated cognate and xenolithic nodules from the Mt. Somma-Vesuvius volcanic complex, Italy. The typically zoned skarn ejecta consist mainly of diopsidic and hedenbergitic, sometimes "fassaitic" clinopyroxene, Mg-rich and Ti-poor phlogopite, F-bearing vesuvianite, wollastonite, gehlenite, meionite, forsterite, clinohumite, anorthite and Mg-poor calcite with accessory apatite, spinell, magnetite, perovskite, baddeleyite, and various REE-, U-, Th-, Zr- and Ti-rich minerals. Four major types of fluid inclusions were observed in wollastonite, vesuvianite, gehlenite, clinopyroxene and calcite: a) primary silicate melt inclusions (THOM = 1000-1050??C), b) CO2 ?? H2S-rich fluid inclusions (THOM = 20-31.3??C into the vapor phase), c) multiphase aqueous brine inclusions (THOM = 720-820??C) with mainly sylvite and halite daughter minerals, and d) complex chloride-carbonate-sulfate-fluoride-silicate-bearing saline-melt inclusions (THOM = 870-890??C). The last inclusion type shows evidence for immiscibility between several fluids (silicate melt - aqueous chloride-rich liquid - carbonate/sulfate melt?) during heating and cooling below 870??C. There is no evidence for fluid circulation below 700??C and participation of externally derived meteoric fluids in skarn formation. Skarns have considerably variable 206Pb/204Pb (19.047-19.202), 207Pb/204Pb (15.655-15.670), and 208Pb/204Pb (38.915-39.069) and relatively low 143Nd/144Nd (0.51211-0.51244) ratios. The carbon and oxygen isotope compositions of skarn calcites (??13CV-PDB = -5.4 to -1.1???; ??18OV-SMOW = 11.7 to 16.4???) indicate formation from a 18O- and 13C-enriched fluid. The isotope composition of skarns and the presence of silicate melt inclusion-bearing wollastonite nodules suggests assimilation of carbonate wall rocks by the alkaline magma at moderate depths (< 5 km) and consequent exsolution of CO2-rich vapor and complex saline melts from the contaminated magma that reacted with the carbonate rocks to form skarns.

Water in silicate melts

NASA Astrophysics Data System (ADS)

McMillan, Paul; Stolper, Edward

Water is one of the more important volatile species in magmas, both in terms of its abundance and its influence on the properties of a given magma. Many workers in the geological sciences have measured, modeled, and speculated on the interaction of water with silicate melts as a function of pressure. At the same time, glass and materials scientists have collected a considerable body of data on the effect of water on the properties of liquid and glassy silicates at 1 atmosphere (1.01325×105 N m-2) and below. A special session on “Solubility and Transport Properties of Water in Silicate Melts” was held during the 1983 AGU Spring Meeting, May 30-June 3, in Baltimore. The session had three main objectives: (1) review the present data base and discuss the status of current models in order to identify areas where further work is needed; (2) introduce interested geologists to the large body of work being carried out in the glass and materials sciences; and (3) consider static properties, such as thermodynamic relations, structure of hydrous melts, and dynamic properties including diffusion and viscosity. This report summarizes the major topics discussed. More detailed information may be found in the published abstracts (Eos, May 3, 1983, pp. 338-343).

Kinetics and mechanism of corrosion of SiC by molten salts

NASA Technical Reports Server (NTRS)

Jacobson, N. S.

1986-01-01

Corrosion of sintered alpha-SiC under thin films of Na2CO3/CO2, Na2SO4/O2, and Na2SO4/SO3 was investigated at 1000 C. Chemical analysis was used to follow silicate and silica evolution as a function of time. This information coupled with morphology observations leads to a detailed corrosion mechanism. In all cases the corrosion reactions occur primarily in the first few hours. In the Na2CO3/CO2 case, rapid oxidation and dissolution lead to a thick layer of silicate melt in about 0.25 h. After this, silica forms a protective layer on the carbide. In the Na2SO4/O2 case, a similar mechanism occurs. In the Na2SO4/SO3 case, a porous nonprotective layer of SiO2 grows directly on the carbide, and a silicate melt forms above this. In addition, SiO2 and regenerated Na2SO4 form at the melt/gas interface due to reaction of silicate with SO3 and SO2 + O2. The reaction slows when the lower silica layer becomes nonporous.

The Partial Molar Volume and Compressibility of FeO in CaO-SiO2 Liquids: Systematic Variation with Fe2+ Coordination Change

NASA Astrophysics Data System (ADS)

Guo, X.; Lange, R. A.; Ai, Y.

2009-12-01

Iron is an important element in magmatic liquid, since its concentration can range up to 18% in some basaltic liquids, and it has two oxidation states. In order to model magmatic processes, thermodynamic descriptions of silicate melts must include precise information for both the FeO and Fe2O3 components. Currently, the partial molar volume of FeO is not as well known as that for Fe2O3 because of the difficulty of performing double-bob density measurements under reducing conditions. Yet these data are required in order to convert sound speed measurements on FeO-bearing liquids into compressibility data, which in turn are needed extend density models for magmatic liquids to elevated pressures. Moreover, there is growing evidence from the spectroscopic literature that Fe2+ occurs in 4, 5, and 6-fold coordination in silicate melts, and thus it is possible that the partial molar volume and compressibility of FeO may vary with Fe2+ coordination, and thus with melt composition. To explore these issues, we have conducted both density and relaxed sound speed measurements on liquids in the CaO-FeO-SiO2 system, where the CaO/SiO2 ratio was systematically varied at constant FeO concentration (40 mol%). Density was measured between 1594 and 1813K with the double-bob Archimedean method using molybdenum bobs and crucible in a reducing gas (1%CO-99%Ar) environment. The sounds speeds were measured under similar conditions with a frequency-sweep acoustic interferometer. The derived partial molar volume of FeO increases systematically from 13.7 to 15.2 cm3/mol at 1673 K as the CaO/SiO2 ratio increases and the Fe2+ coordination number decreases. From a comparison with the crystalline volume of FeO (halite structure; 12.06 cm3/mol), which serves as a lower limit for VFeO in silicate liquids when Fe2+ is in 6-fold coordination, we estimate that the average Fe2+ coordination in our experimental melts extends up to values between 5 and 4, consistent with the spectroscopic literature. The partial molar compressibility of FeO also increases systematically as Fe2+ coordination decreases, and its maximum measured value (7.01 x 10-2 GPa-1) is nearly identical to that for the SiO2 component in 4-fold coordination (7.14 x 10-2 GPa-1) and is considerably larger than that for the relatively incompressible component MgO (0.65 x 10-2 GPa-1). Thus, our data indicate that the volumetric properties of FeO component have more in common with those for SiO2 than for MgO.

Experimental study of the electrolysis of silicate melts

NASA Technical Reports Server (NTRS)

Keller, Rudolf

1992-01-01

Melting and electrolyzing lunar silicates yields oxygen gas and potentially can be practiced in situ to produce oxygen. With the present experiments conducted with simulant oxides at 1425-1480 C, it was ascertained that oxygen can be obtained anodically at feasible rates and current efficiencies. An electrolysis cell was operated with platinum anodes in a sealed vessel, and the production of gas was monitored. In these electrolysis experiments, stability of anodes remained a problem, and iron and silicon did not reduce readily into the liquid silver cathode.

Magmatic evolution of lunar highland rocks estimated from trace elements in plagioclase: A new bulk silicate Moon model with sub-chondritic Ti/Ba, Sr/Ba, and Sr/Al ratios

NASA Astrophysics Data System (ADS)

Togashi, Shigeko; Kita, Noriko T.; Tomiya, Akihiko; Morishita, Yuichi

2017-08-01

The compositions of host magmas of ferroan anorthosites (FAN-host magmas) were estimated from secondary ion mass spectrometry analyses of plagioclase in lunar highland rocks. The evolution of the magmas was investigated by considering phase relations based on the MELTS algorithm and by re-examining partition coefficients for trace elements between plagioclase and melts. Data little affected by post-magmatic processes were selected by using plagioclase with relatively primitive Sc and Co contents. The FAN-host magma contained 90-174 ppm Sr, 40-119 ppm Ba and 0.5-1.3% TiO2, and had sub-chondritic Sr/Ba and Ti/Ba ratios. It is difficult to account for the formation of FAN-host magma on the basis of magma evolution processes of previously proposed bulk silicate Moon models with chondritic ratios for refractory elements at global scale. Therefore, the source of the FAN-host magma must have had primordial sub-chondritic Sr/Ba and Ti/Ba ratios. The FAN-host magmas were consistent in refractory elements with the estimated host mafic magma for feldspathic crust based on lunar meteorites, and some very-low-Ti mare rocks from lunar meteorites. Here, we propose an alternative bulk silicate Moon model (the cBSM model), which is enriched in crustal components of proto-bodies relative to the present whole Earth-Moon system.

Shock recovery of a magnesium-silicate spinelloid

NASA Astrophysics Data System (ADS)

Tschauner, O. D.; Asimow, P. D.; Ahrens, T. J.; Kostandova, N.

2009-12-01

Previously it was believed that some high pressure polymorphs (e.g. of framework silicates) form under shock via growth from shock-induced precursor microscopic melt zones. Since diffusion in the melt was assumed to control crystallization rates, absence of shock recovery of any of those minerals was attributed to the short duration of laboratory shock (0.1 to 1 microsecond) experiments. In contrast to laboratory experiments, grains of high pressure polymorphs of 1 - 100 micrometer diameter have been found in melt veins of shocked meteorites and were widely believed to have formed via diffusion-controlled growth that occurred over seconds to minute time scales. Recently we reported formation of wadsleyite from a shock-generated melt in a laboratory shock experiment by analysis of the recovery products [1]. The growth rate of wadsleyite crystals at the experimental temperature of 2000 to 3000 K was estimated to be several m/s suggesting that diffusion was not the dominant factor in this ultra-rapid crystal growth. Consequently, S6 shock events in chondrites may not always be related to long shock duration and large impactors. Here we report formation of another high-pressure magnesium silicate polymorph in a shock experiment. The starting materials for this 30 GPa shot was single-crystal synthetic forsterite in a NIST 1157 tool-steel chamber. The recovered material was analyzed by micro-Raman spectroscopy and by synchrotron-based micro-X ray diffraction. Diffraction experiments were conducted in Gandolfi-geometry at station B2, CHESS, using a MAR345 image plate detector and a primary beam of 25 keV energy. Melted regions of the sample contained a spinelloid isotypic to a magnesium-gallium germanate spinelloid synthesized at ambient pressure [2]. As in the previous study [1] we observe oxidation of iron from melted metal of the recovery chamber wall entrained by the silicate melt while silicon is partially reduced. The new high-pressure silicate may have formed at less than the peak pressure experienced by the sample. [1]: O.Tschauner, P.D. Asimow, N. Kostandova,T.J. Ahrens, C. Ma, S. Sinogeikin, Z. Liu, S. Fakra, N. Tamura, Proc. Nat. Acad. Sci. USA 106, 13691-5 (2009) , [2]: Barbier, J., Hyde, B.G.,Acta Cryst. B 43, 34-40 (1987).

Melt segregation from silicic crystal mushes: a critical appraisal of possible mechanisms and their microstructural record

NASA Astrophysics Data System (ADS)

Holness, Marian B.

2018-06-01

One of the outstanding problems in understanding the behavior of intermediate-to-silicic magmatic systems is the mechanism(s) by which large volumes of crystal-poor rhyolite can be extracted from crystal-rich mushy storage zones in the mid-deep crust. The mechanisms commonly invoked are hindered settling, micro-settling, and compaction. The concept of micro-settling involves extraction of grains from a crystal framework during Ostwald ripening and has been shown to be non-viable in the metallic systems for which it was originally proposed. Micro-settling is also likely to be insignificant in silicic mushes, because ripening rates are slow for quartz and plagioclase, contact areas between grains in a crystal mush are likely to be large, and abundant low-angle grain boundaries promote grain coalescence rather than ripening. Published calculations of melt segregation rates by hindered settling (Stokes settling in a crystal-rich system) neglect all but fluid dynamical interactions between particles. Because tabular silicate minerals are likely to form open, mechanically coherent, frameworks at porosities as high as 75%, settling of single crystals is only likely in very melt-rich systems. Gravitationally-driven viscous compaction requires deformation of crystals by either dissolution-reprecipitation or dislocation creep. There is, as yet, no reported microstructural evidence of extensive, syn-magmatic, internally-generated, viscous deformation in fully solidified silicic plutonic rocks. If subsequent directed searches do not reveal clear evidence for internally-generated buoyancy-driven melt segregation processes, it is likely that other factors, such as rejuvenation by magma replenishment, gas filter-pressing, or externally-imposed stress during regional deformation, are required to segregate large volumes of crystal-poor rhyolitic liquids from crustal mushy zones.

Processes Influencing the Timing and Volume of Eruptions From the Youngest Supervolcano on Earth

NASA Astrophysics Data System (ADS)

Wilson, C. J. N.; Barker, S. J.; Morgan, D. J.; Rowland, J. V.; Schipper, I.

2015-12-01

In their stratigraphic records, silicic caldera volcanoes display wide ranges of eruptive styles and volumes. However, relationships between frequency and magnitude are often complex, and the forecasting of future activity is inherently problematic. Taupo volcano, New Zealand, provides a unique opportunity to investigate eruptive histories from a hyperactive, large silicic magmatic system with eruptive volumes that span 3-4 orders of magnitude, and show no clear relationships with the repose period. Taupo hosted the world's most recent supereruption at 25.4 ka, which discharged 530 km3 of magma in the episodic 10-phase Oruanui event. Only 5 kyr later, Taupo revived, with 3 dacitic eruptions from 21.5-17 ka and 25 rhyolite eruptions from 12-1.7 ka. Here we use trends in whole rock, glass and mineral chemistry to show how the magma system reestablished following the Oruanui event, and to consider what processes influence the state of the modern volcano. The post-Oruanui dacites reflect the first products of the rebuilding silicic magma system, as most of the Oruanui mush was reconfigured or significantly modified in composition following thermal fluxing accompanying post-caldera collapse readjustment. Compositional variations within the younger rhyolites at <12 ka reflect fine-scale temporal changes in mineral phase stability, closely linked to the development, stabilization and maturation of a new silicic mush system. For the most recent eruptions, the system underwent destabilization, resulting in increased volumes of melt extraction from the silicic mush. Orthopyroxene Fe-Mg diffusion timescales indicate that the onset of rapid heating and priming of the silicic mush occurred <100 years prior to the <2.15 ka eruptions, with subsequent melt accumulation occurring in only decades. The largest post-Oruanui eruption at 232 AD culminated from elevated mafic magma supply to the silicic mush pile, rapid melt accumulation and high differential tectonic stress build up, leading to one of the largest and most violent Holocene eruptions globally. The latest eruptions of Taupo highlight the multiple controls on the timing of eruptions, and demonstrate how the magmatic system can rapidly change behavior to generate large eruptible melt bodies on timescales of direct relevance to humans and monitoring initiatives.

Experimental Constraints on the Partitioning Behavior of F, Cl, and OH Between Apatite and Basaltic Melt

NASA Technical Reports Server (NTRS)

McCubbin, Francis M.; Barnes, Jessica J.; Vander Kaaden, Kathleen E.; Boyce, Jeremy W.; Ustunisik, Gokce; Whitson, Eric S.

2017-01-01

The mineral apatite is present in a wide range of planetary materials. The presence of volatiles (F, Cl, and OH) within its crystal structure (X-site) have motivated numerous studies to investigate the partitioning behavior of F, Cl, and OH between apatite and silicate melt with the end goal of using apatite to constrain the volatile contents of planetary magmas and mantle sources. A number of recent experimental studies have investigated the apatite-melt partitioning behavior of F, Cl, and OH in magmatic systems. Apatite-melt partitioning of volatiles are best described as exchange equilibria similar to Fe-Mg partitioning between olivine and silicate melt. However, the partitioning behavior is likely to change as a function of temperature, pressure, oxygen fugacity, apatite composition, and melt composition. In the present study, we have conducted experiments to assess the partitioning behavior of F, Cl, and OH between apatite and silicate melt over a pressure range of 0-6 gigapascals, a temperature range of 950-1500 degrees Centigrade, and a wide range of apatite ternary compositions. All of the experiments were conducted between iron-wustite oxidation potentials IW minus 1 and IW plus 2 in a basaltic melt composition. The experimental run products were analyzed by a combination of electron probe microanalysis and secondary ion mass spectrometry (NanoSIMS). Temperature, apatite crystal chemistry, and pressure all play important roles in the partitioning behavior of F, Cl, and OH between apatite and silicate melt. In portions of apatite ternary space that undergo ideal mixing of F, Cl, and OH, exchange coefficients remain constant at constant temperature and pressure. However, exchange coefficients vary at constant temperature (T) and pressure (P) in portions of apatite compositional space where F, Cl, and OH do not mix ideally in apatite. The variation in exchange coefficients exhibited by apatite that does not undergo ideal mixing far exceeds the variations induced by changes in temperature (T) or pressure (P) . In regions where apatite undergoes ideal mixing of F, Cl, and OH, temperature has a stronger effect than pressure on the partitioning behavior, but both are important. Furthermore, fluorine becomes less compatible in apatite with increasing pressure and temperature. We are still in the process of analyzing our experimental run products, but we plan to quantify the effects of P and T on apatite-melt partitioning of F, Cl, and OH.

Diffusive exchange of trace elements between basaltic-andesite and dacitic melt: Insights into potential metal fractionation during magma mixing

NASA Astrophysics Data System (ADS)

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

2017-12-01

Mafic magma recharge is a common process that triggers physical and chemical mixing in magmatic systems and drives their evolution, resulting in, e.g., hybridization and volcanic eruptions. Once magma-magma contact is initiated, rapid heat-flux commonly leads to the formation of a cooling-induced crystal mush on the mafic side of the interface. Here, on a local scale (µm to cm), at the magma-magma interface, melt-melt diffusive exchange is required to approach equilibrium. Significant chemical potential gradients drive a complex, multi-element mass flux between the two systems (Liang, 2010). This diffusive-equilibration often controls crystal dissolution rates within the boundary layers and, thus, the formation of interconnected melt or fluid networks. Such networks provide important pathways for the transport of volatiles and trace metals from the mafic recharge magma to the felsic host magma, where the latter may feed volcanic activities and ore deposits. While major element diffusion in silicate melts is mostly well understood, even in complex systems, the available data for many trace element metals are limited (Liang, 2010; Zhang et al., 2010). Differences in diffusivity in a dynamic, mixing environment can cause trace element fractionation, in particular during crystallization and volatile exsolution and separation. This may affect trace element signatures in phenocrysts and magmatic volatile phases that can form near a magma-magma boundary. As a result, the chemistry of volcanic gases and magmatic-hydrothermal ore deposits may be partially controlled by such mixing phenomena. We performed melt-melt diffusion-couple experiments at 150 MPa, 1100°C, FMQ, FMQ+1 and FMQ+3 (FMQ: fayalite-magnetite-quartz oxygen fugacity buffer). Hydrated, sulfur-bearing cylinders of dacite and basaltic andesite were equilibrated for up to 20 h. Major and trace element gradients were measured by using laser-ablation ICP-MS and electron microprobe analyses. The results we will present will help to fill data gaps for the diffusivity of certain metals in silicate melts (e.g., V, Mo, W). First data analyses indicate a higher diffusivity of V when compared to W . Liang (2010) Rev Mineral Geochem 72, 409-446; Zhang et al. (2010) Rev Mineral Geochem 72, 311-408.

Multiphotonic Confocal Microscopy 3D imaging: Application to mantle sulfides in sub-arc environment (Avacha Volcano, Kamchatka)

NASA Astrophysics Data System (ADS)

Antoine, Bénard; Luc-Serge, Doucet; Sabine, Palle; Dmitri A., Ionov

2010-05-01

Petrogenetic relations in igneous rocks are usually studied in natural samples using classical optical microscopy and subsequent geochemical data acquisition. Multiphotonic Laser Scanning Confocal Microscopy (MLSCM) can be a powerful tool to section geological materials optically with sub-micrometric resolution and then generate a three-dimensional (3D) reconstruction (ca. 106 μm3 stack). MLSCM is used here to investigate textural relations of Monosulfide Solid Solution (MSS) with silicate phases in fresh spinel harzburgite xenoliths from the andesitic Avacha volcano (Kamchatka, Russia). The xenoliths contain MSS disseminated in olivine and orthopyroxene (opx) neoblasts as well as MSS-rich quenched magmatic opx veins [1]. First, Reflection Mode (RM) was tested on vein sulfides in resin-impregnated thick (120 μm) polished rock sections. Then we used a combination of Differential Interference Contrast (DIC) with a transmitted light detector, two photons-excited fluorescence (2PEF) and Second Harmonic Generation (SHG). Sequential imaging feature of the Leica TCS-SP2 software was applied. The excitation laser used for 2PEF was a COHERENT MIRA 900 with a 76Hz repetition rate and 800nm wavelength. Image stacks were analysed using ImageJ software [2]. The aim of the tests was to try to discriminate sulfides in silicate matrix as a tool for a better assessment of equilibrium conditions between the two phases. Preliminary results show that Fe-Ni rich MSS from vein and host rock have a strong auto-fluorescence in the Near UV-VIS domain (392-715 nm) whereas silicate matrix is only revealed through DIC. SHG is obtained only from dense nanocentrosymmetrical structures such as embedded medium (organic matter like glue and resin). The three images were recorded sequentially enabling efficient discrimination between the different components of the rock slices. RM permits reconstruction of the complete 3D structure of the rock slice. High resolution (ca. 0.2 μm along X-Y axis vs. 0.4 along Z axis) 2PEF enables analysis of 3D textural relations of tiny individual MSS globules (˜10 μm) in their various habitus. Statistical microgeometric descriptions can be derived from volumetric image data. These results may permit refinement of models concerning (re-) crystallisation kinetics and miscibility conditions of sulphur species in various media likely to act in different mantle environments: silicate melt, fluid-rich silicate melt, silicate-rich fluid. Furthermore, this study provides 3D images with improved resolution of several components (silicate phases, sulfides, silicate glass) over the full thickness (>100 μm) of rock slices which cannot be done with classical methods. Besides 3D imaging of ‘hidden' phases in mantle rocks, it opens up new possibilities for other domains in geosciences like crystallography or petrophysics. [1] Bénard & Ionov (2010) GRA, this volume [2] Abramoff, M.D., Magelhaes, P.J. & Ram, S.J. (2004) Image processing with ImageJ. Biophoton. Int., 11, 36-42

Experimental determination of the partitioning of gallium between solid iron metal and synthetic basaltic melt Electron and ion microprobe study

NASA Technical Reports Server (NTRS)

Drake, M. J.; Newsom, H. E.; Reed, S. J. B.; Enright, M. C.

1984-01-01

The distribution of Ga between solid Fe metal and synthetic basaltic melt is investigated experimentally at temperatures of 1190 and 1330 C, and over a narrow range of oxygen fugacities. Metal-silicate reversal experiments were conducted, indicating a close approach to equilibrium. The analysis of the partitioned products was performed using electron and ion microprobes. At one bar total pressure, the solid metal/silicate melt partition coefficient D(Ga) is used to evaluate metal-silicate fractionation processes in the earth, moon, and Eucrite Parent Body (EPB). It is found that the depletion of Ga abundances in the EPB is due to the extraction of Ga into a metallic core. Likewise, the depletion of Ga in the lunar mantle is consistent with the extraction of Ga into a smaller lunar core if Ga was originally present in a subchondritic concentration. The relatively high Ga abundances in the earth's mantle are discussed, with reference to several theoretical models.

Siderophile Volatile Element Partitioning during Core Formation.

NASA Astrophysics Data System (ADS)

Loroch, D. C.; Hackler, S.; Rohrbach, A.; Klemme, S.

2017-12-01

Since the nineteen sixties it is known, that the Earth's mantle is depleted relative to CI chondrite in numerous elements as a result of accretion and core-mantle differentiation. Additionally, if we take the chondritic composition as the initial solar nebular element abundances, the Earth lacks 85 % of K and up to 98 % of other volatiles. However one potentially very important group of elements has received considerably less attention in this context and these elements are the siderophile but volatile elements (SVEs). SVEs perhaps provide important information regarding the timing of volatile delivery to Earth. Especially for the SVEs the partitioning between metal melt and silicate melt (Dmetal/silicate) at core formation conditions is poorly constrained, never the less they are very important for most of the core formation models. This study is producing new metal-silicate partitioning data for a wide range of SVEs (S, Se, Te, Tl, Ag, As, Au, Cd, Bi, Pb, Sn, Cu, Ge, Zn, In and Ga) with a focus on the P, T and fO2dependencies. The initial hypothesis that we are aiming to test uses the accretion of major portions of volatile elements while the core formation was still active. The key points of this study are: - What are the effects of P, T and fO2 on SVE metal-silicate partioning? - What is the effect of compositional complexity on SVE metal-silicate partioning? - How can SVE's D-values fit into current models of core formation? The partitioning experiments will be performed using a Walker type multi anvil apparatus in a pressure range between 10 and 20 GPa and temperatures of 1700 up to 2100 °C. To determine the Dmetal/silicate values we are using a field emission high-resolution JEOL JXA-8530F EPMA for major elements and a Photon Machines Analyte G2 Excimer laser (193 nm) ablation system coupled to a Thermo Fisher Element 2 single-collector ICP-MS (LA-ICP-MS) for the trace elements. We recently finished the first sets of experiments and can provide the corresponding datasets. Based on the general understanding of Dmetal/silicate values we expect to depend on the composition, in this particular case this means a variation in sulfur and carbon content of the core composition, and also a change of the redox conditions. The major goal however is to derive a model of core formation on Earth that includes and also explains the SVEs.

Extraction of trace metals from fly ash

DOEpatents

Blander, M.; Wai, C.M.; Nagy, Z.

1983-08-15

A process is described for recovering silver, gallium and/or other trace metals from a fine grained industrial fly ash associated with a process for producing phosphorous. The fly ash has a silicate base and contains surface deposits of the trace metals as oxides, chlorides or the like. The process is carried out by contacting the fly ash with AlCl/sub 3/ in an alkali halide melt to react the trace metals with the AlCl/sub 3/ to form compositions soluble in the melt and a residue containing the silicate and aluminum oxide or other aluminum precipitate, and separating the desired trace metal or metals from the melt by electrolysis or other separation techniques.

Extraction of trace metals from fly ash

DOEpatents

Blander, Milton; Wai, Chien M.; Nagy, Zoltan

1984-01-01

A process for recovering silver, gallium and/or other trace metals from a fine grained industrial fly ash associated with a process for producing phosphorous, the fly ash having a silicate base and containing surface deposits of the trace metals as oxides, chlorides or the like, with the process being carried out by contacting the fly ash with AlCl.sub.3 in an alkali halide melt to react the trace metals with the AlCl.sub.3 to form compositions soluble in the melt and a residue containing the silicate and aluminum oxide or other aluminum precipitate, and separating the desired trace metal or metals from the melt by electrolysis or other separation techniques.

Effect of Sulfur on Siderophile Element Partitioning Between Olivine and Martian Primary Melt

NASA Technical Reports Server (NTRS)

Usui, T.; Shearer, C. K.; Righter, K.; Jones, J. H.

2011-01-01

Since olivine is a common early crystallizing phase in basaltic magmas that have produced planetary and asteroidal crusts, a number of experimental studies have investigated elemental partitioning between olivine and silicate melt [e.g., 1, 2, 3]. In particular, olivine/melt partition coefficients of Ni and Co (DNi and DCo) have been intensively studied because these elements are preferentially partitioned into olivine and thus provide a uniquely useful insight into the basalt petrogenesis [e.g., 4, 5]. However, none of these experimental studies are consistent with incompatible signatures of Co [e.g., 6, 7, 8] and Ni [7] in olivines from Martian meteorites. Chemical analyses of undegassed MORB samples suggest that S dissolved in silicate melts can reduce DNi up to 50 % compared to S-free experimental systems [9]. High S solubility (up to 4000 ppm) for primitive shergottite melts [10] implies that S might have significantly influenced the Ni and Co partitioning into shergottite olivines. This study conducts melting experiments on Martian magmatic conditions to investigate the effect of S on the partitioning of siderophile elements between olivine and Martian primary melt.

Silicate glasses and sulfide melts in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure, Virginia, USA

USGS Publications Warehouse

Belkin, H.E.; Horton, J. Wright

2009-01-01

Optical and electron-beam petrography of melt-rich suevite and melt-rock clasts from selected samples from the Eyreville B core, Chesapeake Bay impact structure, reveal a variety of silicate glasses and coexisting sulfur-rich melts, now quenched to various sulfi de minerals (??iron). The glasses show a wide variety of textures, fl ow banding, compositions, devitrifi cation, and hydration states. Electron-microprobe analyses yield a compositional range of glasses from high SiO2 (>90 wt%) through a range of lower SiO2 (55-75 wt%) with no relationship to depth of sample. Some samples show spherical globules of different composition with sharp menisci, suggesting immiscibility at the time of quenching. Isotropic globules of higher interfacial tension glass (64 wt% SiO2) are in sharp contact with lower-surface-tension, high-silica glass (95 wt% SiO2). Immiscible glass-pair composition relationships show that the immiscibility is not stable and probably represents incomplete mixing. Devitrifi cation varies and some low-silica, high-iron glasses appear to have formed Fe-rich smectite; other glass compositions have formed rapid quench textures of corundum, orthopyroxene, clinopyroxene, magnetite, K-feldspar, plagioclase, chrome-spinel, and hercynite. Hydration (H2O by difference) varies from ~10 wt% to essentially anhydrous; high-SiO2 glasses tend to contain less H2O. Petrographic relationships show decomposition of pyrite and melting of pyrrhotite through the transformation series; pyrite? pyrrhotite? troilite??? iron. Spheres (~1 to ~50 ??m) of quenched immiscible sulfi de melt in silicate glass show a range of compositions and include phases such as pentlandite, chalcopyrite, Ni-As, monosulfi de solid solution, troilite, and rare Ni-Fe. Other sulfi de spheres contain small blebs of pure iron and exhibit a continuum with increasing iron content to spheres that consist of pure iron with small, remnant blebs of Fe-sulfi de. The Ni-rich sulfi de phases can be explained by melting and/or concentrating targetderived Ni without requiring an asteroid impactor source component. The presence of locally unaltered glasses in these rocks suggests that in some rock volumes, isolation from postimpact hydrothermal systems was suffi cient for glass preservation. Pressure and temperature indicators suggest that, on a thin-section scale, the suevites record rapid mixing and accumulation of particles that sustained widely different peak temperatures, from clasts that never exceeded 300 ?? 50 ??C, to the bulk of the glasses where melted sulfi de and unmelted monazite suggest temperatures of 1500 ?? 200 ??C. The presence of coesite in some glass-bearing samples suggests that pressures exceeded ~3 GPa. ?? 2009 Geological Society of America.

The viscosity of magmatic silicate liquids: A model for calculation

NASA Technical Reports Server (NTRS)

Bottinga, Y.; Weill, D. F.

1971-01-01

A simple model has been designed to allow reasonably accurate calculations of viscosity as a function of temperature and composition. The problem of predicting viscosities of anhydrous silicate liquids has been investigated since such viscosity numbers are applicable to many extrusive melts and to nearly dry magmatic liquids in general. The fluidizing action of water dissolved in silicate melts is well recognized and it is now possible to predict the effect of water content on viscosity in a semiquantitative way. Water was not incorporated directly into the model. Viscosities of anhydrous compositions were calculated, and, where necessary, the effect of added water and estimated. The model can be easily modified to incorporate the effect of water whenever sufficient additional data are accumulated.

An interconnected network of core-forming melts produced by shear deformation

PubMed

Bruhn; Groebner; Kohlstedt

2000-02-24

The formation mechanism of terrestrial planetary cores is still poorly understood, and has been the subject of numerous experimental studies. Several mechanisms have been proposed by which metal--mainly iron with some nickel--could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle that is often referred to as a 'magma ocean'. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix. But experimental studies performed at high pressures have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (non-hydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.

Rapid high-silica magma generation in basalt-dominated rift settings

NASA Astrophysics Data System (ADS)

Berg, Sylvia E.; Troll, Valentin R.; Burchardt, Steffi; Deegan, Frances M.; Riishuus, Morten S.; Whitehouse, Martin J.; Harris, Chris; Freda, Carmela; Ellis, Ben S.; Krumbholz, Michael; Gústafsson, Ludvik E.

2015-04-01

The processes that drive large-scale silicic magmatism in basalt-dominated provinces have been widely debated for decades, with Iceland being at the centre of this discussion [1-5]. Iceland hosts large accumulations of silicic rocks in a largely basaltic oceanic setting that is considered by some workers to resemble the situation documented for the Hadean [6-7]. We have investigated the time scales and processes of silicic volcanism in the largest complete pulse of Neogene rift-related silicic magmatism preserved in Iceland (>450 km3), which is a potential analogue of initial continent nucleation in early Earth. Borgarfjörður Eystri in NE-Iceland hosts silicic rocks in excess of 20 vol.%, which exceeds the ≤12 vol% usual for Iceland [3,8]. New SIMS zircon ages document that the dominantly explosive silicic pulse was generated within a ≤2 Myr window (13.5 ± 0.2 to 12.2 ± 03 Ma), and sub-mantle zircon δ18O values (1.2 to 4.5 ± 0.2‰, n=337) indicate ≤33% assimilation of low-δ18O hydrothermally-altered crust (δ18O=0‰), with intense crustal melting at 12.5 Ma, followed by rapid termination of silicic magma production once crustal fertility declined [9]. This silicic outburst was likely caused by extensive rift flank volcanism due to a rift relocation and a flare of the Iceland plume [4,10] that triggered large-scale crustal melting and generated mixed-origin silicic melts. High-silica melt production from a basaltic parent was replicated in a set of new partial melting experiments of regional hydrated basalts, conducted at 800-900°C and 150 MPa, that produced silicic melt pockets up to 77 wt.% SiO2. Moreover, Ti-in-zircon thermometry from Borgarfjörður Eystri give a zircon crystallisation temperature ~713°C (Ti range from 2.4 to 22.1 ppm, average=7.7 ppm, n=142), which is lower than recorded elsewhere in Iceland [11], but closely overlaps with the zircon crystallisation temperatures documented for Hadean zircon populations [11-13], hinting at crustal recycling as a key process. Our results therefore provide a mechanism and a time-scale for rapid, voluminous silicic magma generation in modern and ancient basalt-dominated rift setting, such as Afar, Taupo, and potentially early Earth. The Neogene plume-related rift flank setting of NE-Iceland may thus constitute a plausible geodynamic and compositional analogue for generating silicic (continental) crust in the subduction-free setting of a young Earth (e.g. ≥3 Ga [14]). [1] Bunsen, R. 1851. Ann. Phys. Chem. 159, 197-272. [2] MacDonald R., et al., 1987. Mineral. Mag. 51, 183-202. [3] Jonasson, K., 2007. J. Geodyn. 43, 101-117. [4] Martin, E., et al., 2011. Earth Planet. Sci. Lett. 311, 28-38. [5] Charreteur, G., et al., 2013.Contrib. Mineral. Petr. 166, 471- 490. [6] Willbold, E., et al., 2009. Earth Planet. Sci. Lett. 279, 44-52. [7] Reimink, J.R., et al., 2014. Nat. Geosci. 7, 529-533. [8] Gústafsson, L.E., et al., 1989. Jökull 39, 75-89. [9] Meade, F.C., et al., 2014. Nat. comm. 5. [10] Óskarsson, B.V., Riishuus, M.S., 2013. J. Volcanol. Geoth. Res. 267, 92-118. [11] Carley, T.L., et al., 2014. Earth Planet. Sci. Lett. 405, 85-97. [12] Trail, D., et al., 2007. Geochem. Geophys. Geosyst.8, Q06014. [13] Harrison, T.M. et al., 2008. Earth Planet. Sci. Lett.268, 476-486. [14] Kamber, B. S., et al., 2005. Earth Planet. Sci. Lett. 240, 276-290.

Shock melting and vaporization of lunar rocks and minerals.

NASA Technical Reports Server (NTRS)

Ahrens, T. J.; O'Keefe, J. D.

1972-01-01

The entropy associated with the thermodynamic states produced by hypervelocity meteoroid impacts at various velocities are calculated for a series of lunar rocks and minerals and compared with the entropy values required for melting and vaporization. Taking into account shock-induced phase changes in the silicates, we calculate that iron meteorites impacting at speeds varying from 4 to 6 km/sec will produce shock melting in quartz, plagioclase, olivine, and pyroxene. Although calculated with less certainty, impact speeds required for incipient vaporization vary from 7 to 11 km/sec for the range of minerals going from quartz to periclase for aluminum (silicate-like) projectiles. The impact velocities, which are required to induce melting in a soil, are calculated to be in the range of 3 to 4 km/sec, provided thermal equilibrium is achieved in the shock state.

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

One of the current stakes in modern volcanology is the definition of magma storage conditions which has direct implications on the eruptive style and thus on the associated risks and the management of likely related crisis. In alkaline differentiated magmas, chlorine (Cl), contrary to H2O, occurs as a minor volatile species but may be used as a geobarometer. Numerous experimental studies on Cl solubility have highlighted its saturation conditions in alkaline silicate melts. The NaCl-H2O system is characterized by immiscibility under wide ranges of pressure, temperature and NaCl content (< 200 MPa, < 1000°C). The addition of the silicate melt to the system does not rule out this property. These P-T conditions are very common for alkaline magmas evolving in shallow reservoirs, and they strongly affect the evolution of sin-eruptive magmatic melts and fluids. In H2O-bearing systems, the Cl concentration in the exsolved H2O vapour phase may increase with that of Cl in the silicate melt. Yet this system becomes strongly non-Henryan at high Cl concentration, depending on P-T conditions: the exsolved fluid phase unmixes to form a low-density, Cl-poor and H2O -rich vapour phase, and a dense hypersaline brine. In such a subcritical domain, as the composition of both vapour phase and brine is fixed, also the Cl concentration in the silicate melt is invariant, as expected from the Gibb's phase rule. The Cl buffer value will depend on the silicate melt composition, being higher in alkali-rich melts. The achievement of the Cl buffer value is so explained by the equilibrium of the silicate melt with a two-phase fluid in the reservoir. As this equilibrium is generally inherited from conditions established in the reservoir rather than during magma ascent, Cl buffering effect can be evidenced through the analysis of the residual glass. Here we applied systematically this methodology to the large explosive eruptions of Monte Somma-Vesuvius: We have analysed the products of 13 explosive eruptions of Monte Somma-Vesuvius, including four Plinian (Pomici di Base, Mercato, Avellino, Pompeii), five sub-Plinian (Verdoline, AP1, AP2, Pollena, 1631 AD) and four violent strombolian to ash emission events (AP3, 1822, 1906, 1944). We have focussed our research on the earliest emitted, most evolved products of each eruption, likely representing the shallower, H2O-saturated portion of the reservoir. We highlighted two magma ponding zones, at ~170-200 MPa and ~105-115 MPa. We have also estimated maximum pre-eruptive H2O content for the different magma compositions, varying between 3.5 and 7 wt%. The results, in large agreement with literature, are very promising. The Cl geobarometer may help scientists to define the reservoir dynamics through time and provide strong constraints on pre-eruptive conditions, of outmost importance for the interpretation of the monitoring data and the identification of precursory signals.

Making Earth's earliest continental crust - an analogue from voluminous Neogene silicic volcanism in NE-Iceland

NASA Astrophysics Data System (ADS)

Berg, Sylvia E.; Troll, Valentin R.; Burchardt, Steffi; Riishuus, Morten S.; Deegan, Frances M.; Harris, Chris; Whitehouse, Martin J.; Gústafsson, Ludvik E.

2014-05-01

Borgarfjörður Eystri in NE-Iceland represents the second-most voluminous exposure of silicic eruptive rocks in Iceland and is a superb example of bimodal volcanism (Bunsen-Daly gap), which represents a long-standing controversy that touches on the problem of crustal growth in early Earth. The silicic rocks in NE-Iceland approach 25 % of the exposed rock mass in the region (Gústafsson et al., 1989), thus they significantly exceed the usual ≤ 12 % in Iceland as a whole (e.g. Walker, 1966; Jonasson, 2007). The origin, significance, and duration of the voluminous (> 300 km3) and dominantly explosive silicic activity in Borgarfjörður Eystri is not yet constrained (c.f. Gústafsson, 1992), leaving us unclear as to what causes silicic volcanism in otherwise basaltic provinces. Here we report SIMS zircon U-Pb ages and δ18O values from the region, which record the commencement of silicic igneous activity with rhyolite lavas at 13.5 to 12.8 Ma, closely followed by large caldera-forming ignimbrite eruptions from the Breiðavik and Dyrfjöll central volcanoes (12.4 Ma). Silicic activity ended abruptly with dacite lava at 12.1 Ma, defining a ≤ 1 Myr long window of silicic volcanism. Magma δ18O values estimated from zircon range from 3.1 to 5.5 (± 0.3; n = 170) and indicate up to 45 % assimilation of a low-δ18O component (e.g. typically δ18O = 0 ‰, Bindeman et al., 2012). A Neogene rift relocation (Martin et al., 2011) or the birth of an off-rift zone to the east of the mature rift associated with a thermal/chemical pulse in the Iceland plume (Óskarsson & Riishuus, 2013), likely brought mantle-derived magma into contact with fertile hydrothermally-altered basaltic crust. The resulting interaction triggered large-scale crustal melting and generated mixed-origin silicic melts. Such rapid formation of silicic magmas from sustained basaltic volcanism may serve as an analogue for generating continental crust in a subduction-free early Earth (e.g. ≥ 3 Ga, Kamber et al., 2005). REFERENCES: Bindeman, I.N., et al., 2012. Terra Nova 24, 227-232. Gústafsson, L.E., et al., 1989. Jökull, v. 39, 75-89. Gústafsson, L.E., 1992. PhD dissertation, Freie Universität Berlin. Jonasson, K., 2007. Journal of Geodynamics, 43, 101-117. Kamber, B.S., et al., 2005. Earth Planet. Sci. Lett., Vol. 240 (2), 276-290. Martin, E., et al., 2011. Earth Planet. Sc. Lett., 311, 28-38. Óskarsson, B.V., & Riishuus, M.S., 2013. J. Volcanol. Geoth.Res., 267, 92-118. Walker, G.P.L., 1966. Bull. Volcanol., 29 (1), 375-402.

Nitrogen partitioning during core-mantle differentiation

NASA Astrophysics Data System (ADS)

Speelmanns, I. M.; Schmidt, M. W.; Liebske, C.

2016-12-01

This study investiagtes nitrogen partitioing between metal and silicate melts as relevant for core segregation during the accretion of planetesimals into the Earth. On present day Earth, N belongs to the most important elements, as it is one of the key constituents of our atmosphere and forms the basis of life. However, the geochemistry of N, i.e. its distribution and isotopic fractionation between Earth's deep reservoirs is not well constrained. In order to determine the partitioning behaviour of N, a centrifuging piston cylinder was used to euqilibrate and then gravitationally separate metal-silicate melt pairs at 1250 °C, 1 GPa over the range of oxygen fugacities thought to have prevailied druing core segreagtion (IW-4 to IW). Complete segregation of the two melts was reached within 3 hours at 1000 g, the interface showing a nice meniscus The applied double capsule technique, using an outer metallic and inner non-metallic (mostly graphite) capsule, minimizes volatile loss over the course of the experiment compared to single non-metallic capsules. The two quenched melts were cut apart, cleaned at the outside and N concentrations of the melts were analysed on bulk samples by an elemental analyser. Nevertheless, the low amount of sample material and the N yield in the high pressure experiments required the developement of new analytical routines. Despite these experimental and analytical difficulties, we were able to determine a DNmetal/silicateof 13±0.25 at IW-1, N partitioning into the core froming metal. The few availible literature data [1],[2] suggest that N changes its compatibility favoring the silicate melt or magma ocean at around IW-2.5. In order to asses how much N may effectively be contained in the core and the silicate Earth, experiments characterizing N behaviour over the entire range of core formation condtitions are well under way. [1] Kadik et al., (2011) Geochemistry International 49.5: 429-438. [2] Roskosz et al., (2013) GCA 121: 15-28.

Silica-rich orthopyroxenite in the Bovedy chondrite

NASA Technical Reports Server (NTRS)

Ruzicka, Alex; Kring, David A.; Hill, Dolores H.; Boynton, William V.; Clayton, Robert N.; Mayeda, Toshiko K.

1995-01-01

A large (greater than 4.5 x 7 x 4 mm), igneous-textured clast in the Bovedy (L3) chondrite is notable for its high bulk SiO2 content (is approximately equal to 57.5 wt%). The clast consists of normally zoned orthopyroxene (83.8 vol%), tridymite (6.2%), an intergrowth of feldspar (5.8%) and sodic glass (3.1%), pigeonite (1.0%), and small amounts of chromite (0.2%), augite, and Fe,Ni-metal; it is best described as a silica-rich orthopyroxenite. The oxygen-isotopic composition of the clast is similar, but not identical, to Bovedy and other ordinary chondrites. The clast has a superchondritic Si/Mg ratio, but has Mg/(Mg + Fe) and Fe/Mn ratios that are similar to ordinary chondrite silicate. The closest chemical analogues to the clast are radial-pyroxene chondrules, diogenites, pyroxene-silica objects in ordinary chondrites, and silicates in the IIE iron meteorite Weekeroo Station. The clast crystallized from a siliceous melt that cooled fast enough to prevent complete attainment of equilibrium but slow enough to allow nearly complete crystallization. The texture, form, size and composition of the clast suggestion that it is an igneous differentiate from an asteroid or planetesimal that formed in the vicinity of ordinary chondrites. The melt probably cooled in the near-surface region of the parent object. It appears that in the source region of the clast, metallic and silicate partial melt were largely-to-completely lost during a relatively low degree of melting, and that during a higher degree of melting, olivine and low-Ca pyroxene separated from the remaining liquid, which ultimately solidified to form the clast. While these fractionation steps could not have all occurred at the same temperature, they could have been accomplished in a single melting episode, possibly as a result of heating by radionuclides or by electromagnetic induction. Fractionated magmas can also account for other Si-rich objects in chondrites.

Redox dependent behaviour of molybdenum during magmatic processes in the terrestrial and lunar mantle: Implications for the Mo/W of the bulk silicate Moon

NASA Astrophysics Data System (ADS)

Leitzke, F. P.; Fonseca, R. O. C.; Sprung, P.; Mallmann, G.; Lagos, M.; Michely, L. T.; Münker, C.

2017-09-01

We present results of high-temperature olivine-melt, pyroxene-melt and plagioclase-melt partitioning experiments aimed at investigating the redox transition of Mo in silicate systems. Data for a series of other minor and trace elements (Sc, Ba, Sr, Cr, REE, Y, HFSE, U, Th and W) were also acquired to constrain the incorporation of Mo in silicate minerals. All experiments were carried out in vertical tube furnaces at 1 bar and temperatures ranging from ca. 1220 to 1300 °C. Oxygen fugacity was controlled via CO-CO2 gas mixtures and varied systematically from 5.5 log units below to 1.9 log units above the fayalite-magnetite-quartz (FMQ) redox buffer thereby covering the range in oxygen fugacities of terrestrial and lunar basalt genesis. Molybdenum is shown to be volatile at oxygen fugacities above FMQ and that its compatibility in pyroxene and olivine increases three orders of magnitude towards the more reducing conditions covered in this study. The partitioning results show that Mo is dominantly tetravalent at redox conditions below FMQ-4 and dominantly hexavalent at redox conditions above FMQ. Given the differences in oxidation states of the terrestrial (oxidized) and lunar (reduced) mantles, molybdenum will behave significantly differently during basalt genesis in the Earth (i.e. highly incompatible; average DMoperidotite/melt ∼ 0.008) and Moon (i.e. moderately incompatible/compatible; average DMoperidotite/melt ∼ 0.6). Thus, it is expected that Mo will strongly fractionate from W during partial melting in the lunar mantle, given that W is broadly incompatible at FMQ-5. Moreover, the depletion of Mo and the Mo/W range in lunar samples can be reproduced by simply assuming a primitive Earth-like Mo/W for the bulk silicate Moon. Such a lunar composition is in striking agreement with the Moon being derived from the primitive terrestrial mantle after core formation on Earth.

The effect of melt composition on the partitioning of trace elements between titanite and silicate melt

NASA Astrophysics Data System (ADS)

Prowatke, S.; Klemme, S.

2003-04-01

The aim of this study is to systematically investigate the influence of melt composition on the partitioning of trace elements between titanite and different silicate melts. Titanite was chosen because of its important role as an accessory mineral, particularly with regard to intermediate to silicic alkaline and calc-alkaline magmas [e.g. 1] and of its relative constant mineral composition over a wide range of bulk compositions. Experiments at atmospheric pressure were performed at temperatures between 1150°C and 1050°C. Bulk compositions were chosen to represent a basaltic andesite (SH3 - 53% SiO2), a dacite (SH2 - 65 SiO2) and a rhyolite (SH1 - 71% SiO2). Furthermore, two additional experimental series were conducted to investigate the effect of Al-Na and the Na-K ratio of melts on partitioning. Starting materials consisted of glasses that were doped with 23 trace elements including some selected rare earth elements (La, Ce, Pr, Sm, Gd, Lu), high field strength elements (Zr, Hf, Nb, Ta) and large ion lithophile elements (Cs, Rb, Ba) and Th and U. The experimental run products were analysed for trace elements using secondary ion mass spectrometry at Heidelberg University. Preliminary results indicate a strong effect of melt composition on trace element partition coefficients. Partition coefficients for rare-earth elements uniformly show a convex-upward shape [2, 3], since titanite accommodates the middle rare-earth elements more readily than the light rare-earth elements or the heavy rare-earth elements. Partition coefficients for the rare-earth elements follow a parabolic trend when plotted against ionic radius. The shape of the parabola is very similar for all studied bulk compositions, the position of the parabola, however, is strongly dependent on bulk composition. For example, isothermal rare-earth element partition coefficients (such as La) are incompatible (D<1) in alkali-rich silicate melts and strongly compatible (D>>1) in alkali-poor melt compositions. From our experimental data we present an model that combines the influence of the crystal lattice on partitioning with the effect of melt composition on trace element partition coefficients. [1] Nakada, S. (1991) Am. Mineral. 76: 548-560 [2] Green, T.H. and Pearson, N.J. (1986) Chem. Geol. 55: 105-119 [3] Tiepolo, M.; Oberti, R. and Vannucci, R. (2002) Chem. Geol. 191: 105-119

Partitioning of V, Mn, Co, Ni, Cu, Zn, As, Mo, Ag, Sn, Sb, W, Au, Pb, and Bi between sulfide phases and hydrous basanite melt at upper mantle conditions

NASA Astrophysics Data System (ADS)

Li, Yuan; Audétat, Andreas

2012-11-01

The partitioning of 15 major to trace metals between monosulfide solid solution (MSS), sulfide liquid (SL) and mafic silicate melt (SM) was determined in piston-cylinder experiments performed at 1175-1300 °C, 1.5-3.0 GPa and oxygen fugacities ranging from 3.1 log units below to 1.0 log units above the quartz-fayalite-magnetite fO2 buffer, which conditions are representative of partial melting in the upper mantle in different tectonic settings. The silicate melt was produced by partial melting of a natural, amphibole-rich mantle source rock, resulting in hydrous (˜5 wt% H2O) basanitic melts similar to low-degree partial melts of metasomatized mantle, whereas the major element composition of the starting sulfide (˜52 wt% Fe; 39 wt% S; 7 wt% Ni; 2 wt% Cu) was similar to the average composition of sulfides in this environment. SL/SM partition coefficients are high (≥100) for Au, Ni, Cu, Ag, Bi, intermediate (1-100) for Co, Pb, Sn, Sb (±As, Mo), and low (≤1) for the remaining elements. MSS/SM partition coefficients are generally lower than SL/SM partition coefficients and are high (≥100) for Ni, Cu, Au, intermediate (1-100) for Co, Ag (±Bi, Mo), and low (≤1) for the remaining elements. Most sulfide-silicate melt partition coefficients vary as a function of fO2, with Mo, Bi, As (±W) varying by a factor >10 over the investigated fO2 range, Sb, Ag, Sn (±V) varying by a factor of 3-10, and Pb, Cu, Ni, Co, Au, Zn, Mn varying by a factor of 3-10. The partitioning data were used to model the behavior of Cu, Au, Ag, and Bi during partial melting of upper mantle and during fractional crystallization of primitive MORB and arc magmas. Sulfide phase relationships and comparison of the modeling results with reported Cu, Au, Ag, and Bi concentrations from MORB and arc magmas suggest that: (i) MSS is the dominant sulfide in the source region of arc magmas, and thus that Au/Cu ratios in the silicate melt and residual sulfides may decrease with increasing degree of partial melting, (ii) both MSS and sulfide liquid are precipitated during fractional crystallization of MORB, and (iii) fractional crystallization of arc magmas is strongly dominated by MSS.

Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

USGS Publications Warehouse

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

2005-01-01

Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850??C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635-661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486-1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening. ?? Springer-Verlag 2005.

In-situ determination of the oxidation state of iron in Fe-bearing silicate melts

NASA Astrophysics Data System (ADS)

Courtial, P.; Wilke, M.; Potuzak, M.; Dingwell, D. B.

2005-12-01

Terrestrial lavas commonly contain up to 10 wt% of iron. Furthermore, rocks returned from the Moon indicate lunar lava containing up to 25 wt% of iron and planetary scientists estimated that the martian mantle has about 18 wt% of iron. An experimental challenge in dealing with Fe-bearing silicate melts is that the oxidation state, controlling the proportions of ferric and ferrous iron, is a function of composition, oxygen fugacity and temperature and may vary significantly. Further complications concerning iron originate from its potential to be either four-, six- or even five-fold coordinated in both valence states. Therefore, the oxidation state of iron was determined in air for various Fe-bearing silicate melts. Investigated samples were Na-disilicate (NS), one atmosphere anorthite-diopside eutectic (AD) and haplogranitic (HPG8) melts containing up to 20, 20 and 10 wt% of iron, respectively. XANES spectra at the Fe K-edge were collected for all the melts at beamline A1, HASYLAB, Hamburg, using a Si(111) 4-crystal monochromator. Spectra were collected for temperatures up to 1573 K using a Pt-Rh loop as heating device. The Fe oxidation state was determined from the centroid position of the pre-edge feature using the calibration of Wilke et al. (2004). XANES results suggest that oxidation state of iron does not change within error for NS melts with addition of Fe, while AD and HPG8 melts become more oxidised with increasing iron content. Furthermore, NS melts are well more oxidised than AD and HPG8 melts that exhibit relatively similar oxidation states for identical iron contents. The oxidation state of iron for NS melts appears to be slightly temperature-dependent within the temperature range investigated (1073-1573 K). However, this trend is stronger for AD and HPG8 melts. Assuming that glass reflects a picture of the homogeneous equilibria of the melt, the present in-situ Fe-oxidation states determined for these melts were compared to those obtained on quenched glasses from different temperatures, when possible, using wet-chemical analysis (i.e., K-dichromate potentiometry). Both datasets agree reasonably well (within 10 %). References: Wilke et al. (2004) Chemical Geology, 213, 71-87.

Melt inclusions in alluvial sapphires from Montana, USA: Formation of sapphires as a restitic component of lower crustal melting?

NASA Astrophysics Data System (ADS)

Palke, Aaron C.; Renfro, Nathan D.; Berg, Richard B.

2017-05-01

We report here compositions of glassy melt inclusions hosted in sapphires (gem quality corundum) from three alluvial deposits in Montana, USA including the Rock Creek, Dry Cottonwood Creek, and Missouri River deposits. While it is likely that sapphires in these deposits were transported to the surface by Eocene age volcanic events, their ultimate origin is still controversial with many models suggesting the sapphires are xenocrysts with a metamorphic or metasomatic genesis. Melt inclusions are trachytic, dacitic, and rhyolitic in composition. Microscopic observations allow separation between primary and secondary melt inclusions. The primary melt inclusions represent the silicate liquid that was present at the time of sapphire formation and are enriched in volatile components (8-14 wt.%). Secondary melt inclusions analyzed here for Dry Cottonwood Creek and Rock Creek sapphires are relatively volatile depleted and represent the magma that carried the sapphires to the surface. We propose that alluvial Montana sapphires from these deposits formed through a peritectic melting reaction during partial melting of a hydrated plagioclase-rich protolith (e.g. an anorthosite). The heat needed to drive this reaction was likely derived from the intrusion of mantle-derived mafic magmas near the base of the continental lithosphere during rollback of the Farallon slab around 50 Ma. These mafic magmas may have ended up as the ultimate carrier of the sapphires to the surface as evidenced by the French Bar trachybasalt near the Missouri River deposit. Alternatively, the trachytic, rhyolitic, and dacitic secondary melt inclusions at Rock Creek and Dry Cottonwood Creek suggests that the same magmas produced during the partial melting event that generated the sapphires may have also transported them to the surface. Determining the genesis of these deposits will further our understanding of sapphire deposits around the world and may help guide future sapphire prospecting techniques. This work is also important to help reveal the history of mantle-derived mafic magmas as they pass through the continental crust.

Melting Processes at the Base of the Mantle Wedge: Melt Compositions and Melting Reactions for the First Melts of Vapor-Saturated Lherzolite

NASA Astrophysics Data System (ADS)

Grove, T. L.; Till, C. B.

2014-12-01

Vapor-saturated melting experiments have been performed at pressures near the base of the mantle wedge (3.2 GPa). The starting composition is a metasomatized lherzolite containing 3 wt. % H2O. Near-solidus melts and coexisting mineral phases have been characterized in experiments that span 925 to 1100 oC with melt % varying from 6 to 9 wt. %. Olivine, orthopyroxene, clinopyroxene and garnet coexist with melt over the entire interval and rutile is also present at < 1000 oC. Melt is andesitic in composition and varies from 60 wt. % SiO2 at 950 oC to 52 wt. % at 1075 oC. The Al2O3 contents of the melt are 13 to 14 wt. %, and CaO contents range from 1 and 4 wt. %. Melting is peritectic with orthopyroxene + liquid produced by melting of garnet + olivine + high-Ca pyroxene. In addition to quenched melt, we observe a quenched silicate component that is rhyolitic (>72 % SiO2) that we interpret as a precipitate from the coexisting supercritical H2O-rich vapor. Extrapolation of the measured compositional variation toward the solidus suggests that the first melt may be very SiO2 rich (i.e., granitic). We suggest that these granitic melts are the first melts of the mantle near the slab-wedge interface. As these SiO2-rich melts ascend into shallower, hotter overlying mantle, they continue to interact with the surrounding mantle and evolve in composition. These first melts may elucidate the geochemical and physical processes that accompany the beginnings of H2O flux melting.

A Model for Siderophile Element Distribution in Planetary Differentiation

NASA Technical Reports Server (NTRS)

Humayun, M.; Rushmer, T.; Rankenburg, K.; Brandon, A. D.

2005-01-01

Planetary differentiation begins with partial melting of small planetesimals. At low degrees of partial melting, a sulfur-rich liquid segregates by physical mechanisms including deformation-assisted porous flow. Experimental studies of the physical mechanisms by which Fe-S melts segregate from the silicate matrix of a molten H chondrite are part of a companion paper. Geochemical studies of these experimental products revealed that metallic liquids were in equilibrium with residual metal in the H chondrite matrix. This contribution explores the geochemical signatures produced by early stages of core formation. Particularly, low-degree partial melt segregation of Fe-S liquids leaves residual metal in the silicate matrix. Some achondrites appear to be residues of partial melting, e.g., ureilites, which are known to contain metal. The metal in these achondrites may show a distinct elemental signature. To quantify the effect of sulfur on siderophile element contents of residual metal we have developed a model based on recent parametrizations of equilibrium solid metal-liquid metal partitioning experiments.

Coordinated Hard Sphere Mixture (CHaSM): A fast approximate model for oxide and silicate melts at extreme conditions

NASA Astrophysics Data System (ADS)

Wolf, A. S.; Asimow, P. D.; Stevenson, D. J.

2015-12-01

Recent first-principles calculations (e.g. Stixrude, 2009; de Koker, 2013), shock-wave experiments (Mosenfelder, 2009), and diamond-anvil cell investigations (Sanloup, 2013) indicate that silicate melts undergo complex structural evolution at high pressure. The observed increase in cation-coordination (e.g. Karki, 2006; 2007) induces higher compressibilities and lower adiabatic thermal gradients in melts as compared with their solid counterparts. These properties are crucial for understanding the evolution of impact-generated magma oceans, which are dominated by the poorly understood behavior of silicates at mantle pressures and temperatures (e.g. Stixrude et al. 2009). Probing these conditions is difficult for both theory and experiment, especially given the large compositional space (MgO-SiO2-FeO-Al2O3-etc). We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme P-T conditions (Wolf et al., 2015). The Coordinated Hard Sphere Mixture (CHaSM) extends the Hard Sphere mixture model, accounting for the range of coordination states for each cation in the liquid. Using approximate analytic expressions for the hard sphere model, this fast statistical method compliments classical and first-principles methods, providing accurate thermodynamic and structural property predictions for melts. This framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide P-T range. Typical Mg-coordination numbers are predicted to evolve continuously from 5.25 (0 GPa) to 8.5 (250 GPa), comparing favorably with first-principles Molecular Dynamics (MD) simulations. We begin extending the model to a simplified mantle chemistry using empirical potentials (generally accurate over moderate pressure ranges, <~30 GPa), yielding predictions rooted in statistical representations of melt structure that compare well with more time-consuming classical MD calculations. This approach also sheds light on the universality of the increasing Grüneisen parameter trend for liquids (opposite that of solids), which directly reflects their progressive evolution toward more compact solid-like structures upon compression.

Genesis of IIICD Iron Meteorites: Evidence From Silicate Inclusions

NASA Astrophysics Data System (ADS)

McCoy, T. J.; Keil, K.; Scott, E. R. D.; Haack, H.

1992-07-01

The IAB and IIICD iron meteorite groups exhibit much larger ranges in siderophile concentrations than other groups and commonly contain silicate inclusions. Extensive studies of metal in both groups and silicates in IAB irons have led to a variety of ideas to explain the genesis of these groups. Wasson et al. (1980) envision each meteorite forming in a separate impact melt pool. Kracher (1982, 1985) suggested that the siderophile trends might result from fractional crystallization of both metal and troilite in a S-saturated magma. A role for oxidation-reduction in these groups has been proposed by Scott and Bild (1974). Similarities in siderophile elemental trends indicate that IIICD metal has a similar origin, although data on silicate inclusions in IIICD irons are scarce (Ramdohr, 1973; Scott and Bild, 1974; Kracher and Kurat, 1977; Prinz et al., 1982; Clayton et al., 1983). We report the first detailed study of silicate inclusions in IIICD iron meteorites in an attempt to elucidate their history. We have studied the only silicate-bearing IIICD irons - Carlton, Dayton, and the recently reported Maltahohe. Silicate-graphite-phosphate inclusions comprise at most a few percent of the bulk meteorite, and silicates comprise <25 vol% of the inclusion. Silicate mineralogy and chemistry vary systematically with increasing M content of the metal. Maltahohe (10.7 wt% Ni) and Carlton (13.0%) contain olivine, pyroxene, and plagioclase, whereas Dayton (17.0%) contains pyroxene, plagioclase, and SiO2. Pyroxene becomes more FeO-rich from Maltahohe (FS(sub)7.8) to Carlton (Fs(sub)9.7) to Dayton (Fs(sub)11.6). Inverse FeO zoning in silicates and lower Fa than Fs indicate reduction in all three meteorites. Plagioclase compositions in IIICD (An(sub)1.1-4.9) are lower than IAB (An(sub)9.2-2l.5) and uncorrelated with Ni content. The abundances of associated phases also vary. Graphite comprises ~25 vol% of Maltahohe silicate inclusions, but only a few percent in Carlton, and is absent in Dayton silicate inclusions. Phosphate mineralogy and modal abundance also vary, with phosphates absent in Maltahohe, chlorapatite comprising 0-70 vol% of inclusions in Carlton, and the unusual phosphates brianite and panethite, along with whitlockite, comprising up to 55 vol% of Dayton's inclusions. The small number of silicate-bearing IIICD irons require that any conclusions must be considered tentative. The precursor silicate assemblage was similar for IAB and IIICD, as suggested by the general similarity between Maltahohe and IAB silicate inclusions. With increasing Ni contents, however, IIICD and IAB silicate inclusions become dramatically different, as indicated by the mineralogical and chemical trends present in IIICD and absent in IAB silicate inclusions. Silicate inclusions in the Ni-rich IAB irons (e.g., San Cristobal, 25 wt% Ni) do not resemble the phosphate-rich, evolved-silicate assemblages observed in Dayton. It is clear that one or more processes were capable of producing changes in metal compositions and silicate inclusion mineralogy, which correlated with one another. None of the observed trends in silicate mineralogy are predicted by the impact-melt model, although impact might have played a role in mixing silicates into the metallic magma. Some trends are consistent with oxidation-reduction, but variations in some siderophiles (e.g., Ir, Cu) cannot be explained easily by this mechanism. We believe that solid silicates must have been mixed with an evolving metallic melt, with the metallic magma dramatically influencing the mineralogy and chemistry of the inclusion, similar to the fractional crystallization model of Kracher (1982,1985). However, many details of this process remain obscure, including the mechanism that concentrated a S-rich melt, the mixing of metal and silicates, and the fractionation of S. References: Clayton et al. (1983) EPSL 65, 229-232. Kracher (1982) GRL 9, 412-415. Kracher (1985) PLPSC 15, C689-C698. Kracher and Kurat (1977) Meteoritics 12, 282-283. Scott and Bild (1974) GCA 38, 1379-1391. Prinz et al. (1982) LPSC XIlI, 632-633. Ramdohr (1973) Elsevier Pub. Co. Wasson et al. (1980) Z. Naturforsch. 35a, 781-795.

Shock compression of stishovite and melting of silica at planetary interior conditions

NASA Astrophysics Data System (ADS)

Millot, M.; Dubrovinskaia, N.; Černok, A.; Blaha, S.; Dubrovinsky, L.; Braun, D. G.; Celliers, P. M.; Collins, G. W.; Eggert, J. H.; Jeanloz, R.

2015-01-01

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets.

Planetary science. Shock compression of stishovite and melting of silica at planetary interior conditions.

PubMed

Millot, M; Dubrovinskaia, N; Černok, A; Blaha, S; Dubrovinsky, L; Braun, D G; Celliers, P M; Collins, G W; Eggert, J H; Jeanloz, R

2015-01-23

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet's internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets. Copyright © 2015, American Association for the Advancement of Science.

Sulfur and sulfides in chondrules

NASA Astrophysics Data System (ADS)

Marrocchi, Yves; Libourel, Guy

2013-10-01

The nature and distribution of sulfides within type I PO, POP and PP chondrules of the carbonaceous chondrite Vigarano (CV3) have been studied by secondary electron microscopy and electron microprobe. They occur predominantly as spheroidal blebs composed entirely of low-Ni iron sulfide (troilite, FeS) or troilite + magnetite but in less abundance in association with metallic Fe-Ni beads in opaque assemblages. Troilites are mainly located within the low-Ca pyroxene outer zone and their amounts increase with the abundance of low-Ca pyroxene within chondrules, suggesting co-crystallization of troilite and low-Ca pyroxene during high-temperature events. We show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws. Depending on the fS2 and fO2 of the surrounding gas and on the melt composition, mainly the FeO content, sulfur dissolved in chondrule melts may eventually reach a concentration limit, the sulfur content at sulfide saturation (SCSS), at which an immiscible iron sulfide liquid separates from the silicate melt. The occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non-wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron-sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule-forming event. The evolution of chondrule melts from PO to PP towards more silicic compositions, very likely due to high PSiO(g) of the surrounding nebular gas, induces saturation of FeS at much lower S content in PP than in PO chondrules, leading to the co-crystallization of iron sulfides and low-Ca pyroxenes. Conditions of co-saturation of low-Ca pyroxene and FeS are only achieved in non canonical environments characterized by high partial pressures of sulfur and SiO and redox conditions more oxidizing than IW-3. Fe and S mass balance calculations also suggest the occurrence of an external source of iron, very likely gaseous, during chondrule formation. We therefore propose that enrichments in sulfur (and other volatile and moderately volatile elements) from PO to PP type I bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine-bearing precursors and a volatile-rich gas phase.

Assessing the Behavior of Typically Lithophile Elements Under Highly Reducing Conditions Relevant to the Planet Mercury

NASA Technical Reports Server (NTRS)

Rowland, Rick, II; Vander Kaaden, Kathleen E.; McCubbin, Francis M.; Danielson, Lisa R.

2017-01-01

With the data returned from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (lvtESSENGER) mission, there are now numerous constraints on the physical and chemical properties of Mercury, including its surface composition. The high S and low FeO contents observed from MESSENGER suggest a low oxygen fugacity of the present materials on the planet's surface. Most of our understanding of elemental partitioning behavior comes from observations made on terrestrial rocks, but Mercury's oxygen fugacity is far outside the conditions of those samples, estimated at approximately 3-7 log units below the Iron-Wustite (lW) oxygen buffer, several orders of magnitude more reducing than other terrestrial bodies we have data from. With limited oxygen available, lithophile elements may instead exhibit chalcophile, halophile, or siderophile behaviors. Furthermore, very few natural samples of rocks that formed under reducing conditions (e.g., enstatite chondrites, achondrites, aubrites) are available in our collections for examination of this change in geochemical affinity. Our goal is to determine the elemental partitioning behavior of typically lithophile elements at lower oxygen fugacity as a function of temperature and pressure. Experiments were conducted at I GPa in a 13 mm QUICKpress piston cylinder and at 4 GPa in an 880-ton multi-anvil press, at temperatures up to 1850 C. The composition of starting materials for the experiments were designed so the final run products contained metal, silicate melt, and sulfide melt phases. Oxygen fugacity was controlled in the experiments by adding silicon metal to the samples, in order to utilize the Si-Si02 buffer, which is approx. 5 log units more reducing than the IW buffer at our temperatures of interest. The target silicate melt composition was diopside (CaMgSi206) because measured surface compositions indicate partial melting of a pyroxene-rich mantle. The results of our experiments will aid in our understanding of the fate of elements during the differentiation and thermal evolution of Mercury and other highly reducing planetary bodies.

The oxidation state of the mantle and the extraction of carbon from Earth's interior.

PubMed

Stagno, Vincenzo; Ojwang, Dickson O; McCammon, Catherine A; Frost, Daniel J

2013-01-03

Determining the oxygen fugacity of Earth's silicate mantle is of prime importance because it affects the speciation and mobility of volatile elements in the interior and has controlled the character of degassing species from the Earth since the planet's formation. Oxygen fugacities recorded by garnet-bearing peridotite xenoliths from Archaean lithosphere are of particular interest, because they provide constraints on the nature of volatile-bearing metasomatic fluids and melts active in the oldest mantle samples, including those in which diamonds are found. Here we report the results of experiments to test garnet oxythermobarometry equilibria under high-pressure conditions relevant to the deepest mantle xenoliths. We present a formulation for the most successful equilibrium and use it to determine an accurate picture of the oxygen fugacity through cratonic lithosphere. The oxygen fugacity of the deepest rocks is found to be at least one order of magnitude more oxidized than previously estimated. At depths where diamonds can form, the oxygen fugacity is not compatible with the stability of either carbonate- or methane-rich liquid but is instead compatible with a metasomatic liquid poor in carbonate and dominated by either water or silicate melt. The equilibrium also indicates that the relative oxygen fugacity of garnet-bearing rocks will increase with decreasing depth during adiabatic decompression. This implies that carbon in the asthenospheric mantle will be hosted as graphite or diamond but will be oxidized to produce carbonate melt through the reduction of Fe(3+) in silicate minerals during upwelling. The depth of carbonate melt formation will depend on the ratio of Fe(3+) to total iron in the bulk rock. This 'redox melting' relationship has important implications for the onset of geophysically detectable incipient melting and for the extraction of carbon dioxide from the mantle through decompressive melting.

Structural Integration of Sensors/Actuators by Laser Beam Melting for Tailored Smart Components

NASA Astrophysics Data System (ADS)

Töppel, Thomas; Lausch, Holger; Brand, Michael; Hensel, Eric; Arnold, Michael; Rotsch, Christian

2018-03-01

Laser beam melting (LBM), an additive laser powder bed fusion technology, enables the structural integration of temperature-sensitive sensors and actuators in complex monolithic metallic structures. The objective is to embed a functional component inside a metal part without losing its functionality by overheating. The first part of this paper addresses the development of a new process chain for bonded embedding of temperature-sensitive sensor/actuator systems by LBM. These systems are modularly built and coated by a multi-material/multi-layer thermal protection system of ceramic and metallic compounds. The characteristic of low global heat input in LBM is utilized for the functional embedding. In the second part, the specific functional design and optimization for tailored smart components with embedded functionalities are addressed. Numerical and experimental validated results are demonstrated on a smart femoral hip stem.

In Situ XANES of U and Th in Silicate Liquids at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

Mallmann, G.; Wykes, J.; Berry, A.; O'Neill, H. S.; Cline, C. J., II; Turner, S.; Rushmer, T. A.

2016-12-01

Although the chemical environments of elements in silicate melts at specific conditions of temperature, pressure and oxygen fugacity (fO2) are often inferred from measurements after quenching the melts to glasses, it is widely recognized that changes may occur during the quenching process, making measurements in situ at high pressure and temperature highly desirable. A case of importance in geochemistry is the speciation of uranium in silicate melts as a function of pressure. Evidence from mineral-melt partitioning and XANES (X-ray Absorption Near-Edge Structure) spectroscopy of glasses suggests that U5+ may be stable at low pressures in the Earth's crust (along with U4+ or U6+, depending on fO2) where basaltic liquids crystallize, but not in the Earth's upper mantle where peridotite partially melts to produce such liquids. To test these observations we recorded in situ transmission U and Th L3-edge XANES spectra of U and Th-doped silicate liquids at 1.6 GPa and 1350°C using the D-DIA apparatus at the X-ray Absorption Spectroscopy Beamline of the Australian Synchrotron. Data for thorium, which occurs exclusively as a tetravalent cation under terrestrial fO2 conditions, were collected as a `control' to monitor for changes in coordination. The cell assembly consisted of a boron-epoxy cube as pressure medium, alumina sleeve and cylindrical graphite heater. The starting mix, a powdered synthetic average MORB silicate glass doped with 2 wt.% of U and Th, was loaded into San Carlos olivine capsules along with solid oxygen buffers (either Re-ReO2 or Ru-RuO2) in a sandwich arrangement. The capsule was then placed inside the graphite heater and insulated with crushable MgO powder. Temperature was monitored using a type D thermocouple. U and Th L3-edge XANES spectra were recorded throughout the heating/compression cycle and then after quenching. Our preliminary assessment indicates that the U-XANES spectra recorded for the liquid in situ at high pressure and temperature and subsequently for the quenched glass are very similar, which would suggest no apparent change in uranium coordination and/or valence state on cooling/decompression.

Metal/sulfide-silicate intergrowth textures in EL3 meteorites: Origin by impact melting on the EL parent body

NASA Astrophysics Data System (ADS)

van Niekerk, Deon; Keil, Klaus

2011-10-01

We document the petrographic setting and textures of Fe,Ni metal, the mineralogy of metallic assemblages, and the modal mineral abundances in the EL3 meteorites Asuka (A-) 881314, A-882067, Allan Hills 85119, Elephant Moraine (EET) 90299/EET 90992, LaPaz Icefield 03930, MacAlpine Hills (MAC) 02635, MAC 02837/MAC 02839, MAC 88136, Northwest Africa (NWA) 3132, Pecora Escarpment 91020, Queen Alexandra Range (QUE) 93351/QUE 94321, QUE 94594, and higher petrologic type ELs Dar al Gani 1031 (EL4), Sayh al Uhaymir 188 (EL4), MAC 02747 (EL4), QUE 94368 (EL4), and NWA 1222 (EL5). Large metal assemblages (often containing schreibersite and graphite) only occur outside chondrules and are usually intergrown with silicate minerals (euhedral to subhedral enstatite, silica, and feldspar). Sulfides (troilite, daubréelite, and keilite) are also sometimes intergrown with silicates. Numerous authors have shown that metal in enstatite chondrites that are interpreted to have been impact melted contains euhedral crystals of enstatite. We argue that the metal/sulfide-silicate intergrowths in the ELs we studied were also formed during impact melting and that metal in EL3s thus does not retain primitive (i.e., nebular) textures. Likewise, the EL4s are also impact-melt breccias. Modal abundances of metal in the EL3s and EL4s range from approximately 7 to 30 wt%. These abundances overlap or exceed those of EL6s, and this is consistent either with pre-existing heterogeneity in the parent body or with redistribution of metal during impact processes.

A review of the contrasting behavior of two magmatic volatiles: Chlorine and carbon dioxide

USGS Publications Warehouse

Lowenstern, J. B.

2000-01-01

Chlorine (Cl) and carbon dioxide (CO2) are common magmatic volatiles with contrasting behaviors. CO2 solubility increases with pressure whereas Cl solubility shows relatively little pressure or temperature effect. CO2 speciation changes with silicate melt composition, dissolving as carbonate in basaltic magmas and molecular CO2 in more silicic compositions. In H2O-bearing systems, the strongly non-ideal behavior of alkali chlorides causes unmixing of the volatile phase to form a H2O-rich vapor and a hydrosaline phase with important implications for the maximum concentration of Cl in magmas. Addition of CO2 to magma hastens immiscibility at crustal pressures (<500 MPa), inducing the formation of CO2-rich vapors and Cl-rich hydrosaline melts. (C) 2000 Elsevier Science B.V. All rights reserved.Chlorine (Cl) and carbon dioxide (CO2) are common magmatic volatiles with contrasting behaviors. CO2 solubility increases with pressure whereas Cl solubility shows relatively little pressure or temperature effect. CO2 speciation changes with silicate melt composition, dissolving as carbonate in basaltic magmas and molecular CO2 in more silicic compositions. In H2O-bearing systems, the strongly non-ideal behavior of alkali chlorides causes unmixing of the volatile phase to form a H2O-rich vapor and a hydrosaline phase with important implications for the maximum concentration of Cl in magmas. Addition of CO2 to magma hastens immiscibility at crustal pressures (<500 MPa), inducing the formation of CO2-rich vapors and Cl-rich hydrosaline melts.

High-temperature apparatus for chaotic mixing of natural silicate melts.

PubMed

Morgavi, D; Petrelli, M; Vetere, F P; González-García, D; Perugini, D

2015-10-01

A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10(6) Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.

Equation of state of molten fayalite (Fe2SiO4)

NASA Astrophysics Data System (ADS)

Waller, C.; Liu, Q.; Agee, C. B.; Asimow, P. D.; Lange, R. A.

2010-12-01

We have conducted new equation of state measurements on liquid fayalite (Fe2SiO4) in a collaborative, multi-technique study. Using a shared bulk starting material, we have measured the liquid density, the bulk modulus (K), and its pressure derivative (K’) from 1 atm to 163 GPa using 1-atm double-bob Archimedean and ultrasonic, sink/float, and shock wave techniques to form a coherent, internally consistent equation of state. Previous shock studies of liquid fayalite were conducted up to pressures of 40 GPa1; we extended this data set with two additional pre-heated, molten (1573 K) fayalite shock compression experiments at 121 and 163 GPa. Linear fitting of this data in shock velocity (US)-particle velocity (up) space defines a Hugoniot with an unconstrained zero-pressure intercept that crosses within error at the bulk sound speed (Co) determined by ultrasonic techniques. Fixing the intercept at this ultrasonic value reduces the error on the linear fit and yields the relation: US =1.65(0.02)up+ 2.4377(0.006) km/s. This relationship indicates that the behavior of the liquid is relaxed during shock compression and demonstrates consistency across experimental methods. Likewise, results from new static compression sink/float experiments conducted in piston-cylinder and multi-anvil devices are in agreement with shock wave and ultrasonic data, consistent with an isothermal K=19.4 and K’=5.57 at 1500°C. In solid materials, the Grüneisen parameter (γ) generally decreases upon compression. However, preliminary calculations for γ of this liquid using additional initially solid shock data from Chen et al.(2002) indicate that γ increases upon compression. Using the functional form γ = γo(ρo/ρ)q at a density of 7.65 Mg/m3 yields a q value of -1.77 (γo = 0.41 is known from low-pressure data), which is similar to the reported q values of forsterite2, enstatite3, and anorthite-diopside liquids4. This result shows that iron-bearing mafic to ultramafic silicate liquids follow the same general behavior as iron-free liquids such that -2.0 ≤ q ≤ -1.5 for the compression range 1 ≥ ρo/ρ ≥ 0.50. We will be performing an additional shock wave experiment on initially solid (300 K) fayalite to confirm this result. We will be continuing collaborative equation of state measurements on additional iron-bearing silicate liquids, working to further clarify the properties of melts and their importance to understanding the dynamics of the early magma ocean and of melt migration within the mantle. In particular, understanding the properties of iron-rich silicates and their melts will constrain hypotheses of melting and of iron enrichment for explaining the occurrence and characteristics of ultra-low velocity zones near the CMB.

Fe-Ti-oxide textures and microstructures in shear zones from oceanic gabbros at Atlantis Bank, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Till, Jessica; Morales, Luiz F. G.; Rybacki, Erik

2016-04-01

Ocean drilling expeditions at several oceanic core complexes formed at slow- and ultra-slow-spreading ridges have recovered cores containing numerous zones of oxide-rich gabbros containing ilmenite and magnetite. In these cores, high modal concentrations of Fe-Ti-oxides are systematically associated with high-temperature plastic deformation features in silicates. We present observations of Fe-Ti-oxide mineral structures and textural characteristics from a series of oxide-rich shear zones from Atlantis Bank (ODP Site 735B) on the Southwest Indian Ridge aimed at determining how oxide mineral abundances relate to strain localization. Fe-Ti-oxide minerals in undeformed oxide gabbros and in highly deformed samples from natural shear zones generally have morphologies characteristic of crystallized melt, including highly cuspate grains and low dihedral angles. Anisotropy of magnetic susceptibility in oxide-rich shear zones is very strong, with fabrics mainly characterized by strong magnetic foliations parallel to the macroscopic foliation. Crystallographic preferred orientations (CPO) in magnetite are generally weak, with occasionally well-defined textures. Ilmenite typically displays well-developed CPOs, however, the melt-like ilmenite grain shapes indicate that at least part of the crystallographic texture results from oriented ilmenite growth during post-deformation crystallization. The oxides are hypothesized to have initially been present as isolated pockets of trapped melt (intercumulus liquid) in a load-bearing silicate framework. Progressive plastic deformation of silicate phases at high-temperature mainly produced two features: (i) elongated melt pockets, which crystallized to form strings of opaque minerals and (ii), interconnected networks of melt regions. The latter lead to intense strain localization of the rock, which appears as oxide-rich mylonites in the samples. In some samples, abundant low-angle grain boundaries in both magnetite and ilmenite suggest that deformation may have continued after crystallization of the late melt, imposing a weak strain on the oxides. Recent experimental deformation results indicate that magnetite and ilmenite should be weaker than most mafic silicates under anhydrous conditions. However, melt-like oxide morphologies observed in Atlantis Bank shear zones indicate that the redistribution of Fe-Ti-oxide melts may have more influence on the strength and strain localization behavior of oceanic gabbros than their solid-state rheology.

Crystallization and Cooling of a Deep Silicate Magma Ocean

NASA Astrophysics Data System (ADS)

Bower, Dan; Wolf, Aaron

2016-04-01

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.

High-temperature rapid pyrometamorphism induced by a charcoal pit burning: The case of Ricetto, central Italy

NASA Astrophysics Data System (ADS)

Capitanio, Flavio; Larocca, Francesco; Improta, Salvatore

Bulk chemistry and mineralogy of the peculiar rock of Ricetto (Carseolani Mts., Central Apennines, Italy) was studied to resolve its controversial origin: igneous dyke or anthropic product. This hybrid rock consists of a colorless, felsic component made up of glass plus quartz, and a brown, femic component made up of fans and spherulites of diopside, calcic plagioclase, wollastonite, and melilite. Textural relationships indicate very rapid cooling and immiscibility phenomena. The bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone. The 14C analysis of a coal fragment from bottom of the body yields the conventional age of 227(+/-50) years. The Ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning. The small size of the heat source at Ricetto caused an intense but short-lived melting of the country rock. Prograde metamorphism caused a temperature increase up to 1,000-1,100 °C when melilite crystallization conditions were reached at appreciable P(CO2) and high f(O2). Melting occurred in a close system represented by the simplified equation: 3Cal+16.5Qtz+Ms+Bt-->Mel+Melt+2H2O+3CO2+0.5O2. Diopside+calcic plagioclase+wollastonite formed by melilite breakdown during rapid cooling, through the reaction: 6Mel+6Qtz+0.5O2-->3Di+2An+7Wo. Liquid immiscibility caused the separation between the felsic melt component and the femic melilite-bearing component. Immiscibility was characterized by different fractionation of alumina and alkalies between these two phases. Differences in bulk, glass, and mineral chemistry between the Ricetto and other melilite-bearing pyrometamorphic rocks can be attributed mainly to different protoliths.

Trace element distribution in peridotite xenoliths from Tok, SE Siberian craton: A record of pervasive, multi-stage metasomatism in shallow refractory mantle

NASA Astrophysics Data System (ADS)

Ionov, Dmitri A.; Chazot, Gilles; Chauvel, Catherine; Merlet, Claude; Bodinier, Jean-Louis

2006-03-01

Spinel peridotite xenoliths in alkali basalts at Tok, SE Siberian craton range from fertile lherzolites to harzburgites and wehrlites; olivine-rich (70-84%) rocks are dominant. REE patterns in the lherzolites range from nearly flat for fertile rocks (14-17% cpx) to LREE-enriched; the enrichments are positively correlated with modal olivine, consistent with high-permeability of olivine-rich rocks during melt percolation. Clinopyroxene in olivine-rich Tok peridotites typically has convex-upward trace element patterns (La/Nd PM < 1 and Nd/Yb PM ≫ 1), which we consider as evidence for equilibration with evolved silicate liquids (with higher REE and lower Ti contents than in host basalts). Whole-rock patterns of the olivine-rich xenoliths range from convex-upward to LREE-enriched (La/Nd PM > 1); the LREE-enrichments are positively correlated with phosphorus abundances and are mainly hosted by accessory phosphates and P-rich cryptocrystalline materials. In addition to apatite, some Tok xenoliths contain whitlockite (an anhydrous, halogen-poor and Na-Mg-rich phosphate), which is common in meteorites and lunar rocks, but has not been reported from any terrestrial mantle samples. Some olivine-rich peridotites have generations of clinopyroxene with distinct abundances of Na, LREE, Sr and Zr. The mineralogical and trace element data indicate that the lithospheric mantle section represented by the xenoliths experienced a large-scale metasomatic event produced by upward migration of mafic silicate melts followed by percolation of low- T, alkali-rich melts and fluids. Chromatographic fractionation and fractional crystallisation of the melts close to the percolation front produced strong LREE-enrichments, which are most common in the uppermost mantle and are related to carbonate- and P 2O 5-rich derivatives of the initial melt. Reversal and gradual retreat of the percolation front during thermal relaxation to ambient geotherm ("retrograde" metasomatism) caused local migration and entrapment of small-volume residual fluids and precipitation of volatile-rich accessory minerals. A distinct metasomatic episode, which mainly produced "anhydrous" late-stage interstitial materials was concomitant with the alkali basaltic magmatism, which brought the xenoliths to the surface.

187Os/188Os in Spinel Peridotites from Borée, Massif Central, France: Seeing through the Effects of Melt Infiltration in the Sub-continental Lithospheric Mantle

NASA Astrophysics Data System (ADS)

Barnett, C. J.; Harvey, J.

2015-12-01

The Re-Os isotope system can be used to model the timing of melt extraction in peridotites, although secondary metasomatic processes can obscure primary melt depletion signatures, implying that bulk-rock Os model ages should be treated with caution.1Spinel peridotites from the volcanic Maar de Borée (French Massif Central) have equigranular to protogranular and occasionally poikilitic textures. Their bulk-rock chemistry are consistent with moderate degrees of partial melting, but elevated incompatible trace element ratios (e.g. La/YbN) are indicative of subsequent secondary processes. Petrographic observation reveals no infiltration of host basalt, but melt infiltration unrelated to the host basalt has occurred, most likely within the sub-continental lithospheric mantle prior to entrainment as xenoliths. The peridotites have a mean [Os] concentration of 2.35 ng g-1 and 187Os/188Os values from 0.12081 ± 16 to 0.12639 ± 14 (cf. PUM = 0.1296 ± 00082), with rhenium depletion model ages (TRD) ranging from 0.48 to 1.30 Ga. Silicate melt contains up to 2 orders of magnitude less Os than peridotites3 but the 187Os/188Os of melt infiltrated peridotite can be skewed by the precipitation of immiscible sulfide when an infiltrating melt reaches S-saturation4. The Borée peridotites retain an unradiogenic Os-isotope signature despite silicate melt infiltration; this may be due to primary base metal sulfides enclosed in silicate minerals and therefore protected from interaction with infiltrating melts. TRD of enclosed sulphides should therefore be able to 'see through' any secondary metasomatic events and reveal melt depletion ages significantly older than those obtained from bulk-rock analyses (cf. 4). 1. Rudnick & Walker (2009) Lithos 112S, 1083-1095. 2. Meisel et al. (2001) Geochim Cosmochim Ac 65, 1311-1323. 3. Day, J.M.D. (2013) Chem Geol 341, 50-74. 4. Harvey et al. (2010) Geochim Cosmochim Acta 74, 293-320.

Thermodynamic controls on element partitioning between titanomagnetite and andesitic-dacitic silicate melts

NASA Astrophysics Data System (ADS)

Sievwright, R. H.; Wilkinson, J. J.; O'Neill, H. St. C.; Berry, A. J.

2017-08-01

Titanomagnetite-melt partitioning of Mg, Mn, Al, Ti, Sc, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Hf and Ta was investigated experimentally as a function of oxygen fugacity ( fO2) and temperature ( T) in an andesitic-dacitic bulk-chemical compositional range. In these bulk systems, at constant T, there are strong increases in the titanomagnetite-melt partitioning of the divalent cations (Mg2+, Mn2+, Co2+, Ni2+, Zn2+) and Cu2+/Cu+ with increasing fO2 between 0.2 and 3.7 log units above the fayalite-magnetite-quartz buffer. This is attributed to a coupling between magnetite crystallisation and melt composition. Although melt structure has been invoked to explain the patterns of mineral-melt partitioning of divalent cations, a more rigorous justification of magnetite-melt partitioning can be derived from thermodynamic principles, which accounts for much of the supposed influence ascribed to melt structure. The presence of magnetite-rich spinel in equilibrium with melt over a range of fO2 implies a reciprocal relationship between a(Fe2+O) and a(Fe3+O1.5) in the melt. We show that this relationship accounts for the observed dependence of titanomagnetite-melt partitioning of divalent cations with fO2 in magnetite-rich spinel. As a result of this, titanomagnetite-melt partitioning of divalent cations is indirectly sensitive to changes in fO2 in silicic, but less so in mafic bulk systems.

Rhenium - osmium heterogeneity of enriched mantle basalts explained by composition and behaviour of mantle-derived sulfides

NASA Astrophysics Data System (ADS)

Harvey, J.; Dale, C. W.; Gannoun, A.; Burton, K. W.

2010-12-01

Analyses of enriched mantle (EM) -basalts, using lithophile element-based isotope systems have long provided evidence for discrete, but variable mantle reservoirs [1]. Upon partial melting, the isotopic fingerprint of each reservoir is imparted upon the partial melt produced. However, recent work involving the Re-Os isotope systematics of EM-basalts [2] suggests that it may not be so simple to delimit these previously well defined mantle reservoirs; the “mantle zoo” [3] may contain more reservoirs than previously envisaged. However, a simple model, with varying contributions from two populations of compositionally distinct mantle sulfides can readily account for the observed heterogeneities in Re-Os isotope systematics of such basalts without additional mantle reservoirs. Rhenium-osmium elemental and isotopic analyses of individual sulfide grains separated from spinel lherzolites from Kilbourne Hole, NM, USA demonstrate that two discrete populations of mantle sulfide exist in terms of both Re-Os systematics and textural relationship with co-existing silicates. One population, with a rounded morphology, is preserved in silicate grains and typically possesses high [Os], low [Re] with unradiogenic, typically sub-chondritic, 187Os/188Os attributable to long term isolation in a low-Re environment. By contrast, irregular-shaped sulfides, preserved along silicate grain boundaries, possess low [Os], higher [Re] and a wider range of, but generally supra-chondritic, 187Os/188Os ([Os] typically ≤ 1-2 ppm, 187Os/188Os ≤ 0.3729; this study). This population is thought to represent metasomatic sulfide (e.g. [4,5]). Uncontaminated silicate phases contain negligible Os (<100 ppt) therefore the Os elemental and isotope composition of basalts is dominated by volumetrically insignificant sulfide ([Os] ≤ 37 ppm, this study). During the early stages of partial melting, supra-chondritic interstitial sulfides are mobilized and incorporated into the melt, adding their radiogenic 187Os/188Os signature. Only when sulfides armored within silicates are exposed to the melt through continued partial melting will enclosed sulfides add their high [Os] and unradiogenic 187Os/188Os to the aggregate melt. Platinum-group element data for whole rocks are also consistent with this scenario. The sequence of (i) addition of all the metasomatic sulfide, followed by (ii) the incorporation of small amounts of armored sulfide can thus account for the range of both [Os] and 187Os/188Os of EM-basalts worldwide without the need for contributions from additional silicate mantle reservoirs. References: [1] Zindler & Hart, (1986) Annu. Rev. Earth Planet. Sci. 14, 493-571. [2] Class et al. (2009) Earth Planet. Sci. Lett. 284, 219-227. [3] Stracke, et al. (2005) Geochem., Geophys., Geosys. 6, doi:10.1029/2004GC000824. [4] Burton et al., Earth Planet. Sci. Lett. (1999) 172, 311-322. [5] Alard et al., (2002) Earth Planet. Sci. Lett. 203, 651-663

Natural occurrence and significance of fluids indicating high pressure and temperature

USGS Publications Warehouse

Roedder, E.

1981-01-01

Most natural minerals have formed from a fluid phase such as a silicate melt or a saline aqueous solution. Fluid inclusions are tiny volumes of such fluids that were trapped within the growing crystals. These inclusions can provide valuable but sometimes ambiguous data on the temperature, pressure, and composition of these fluids, many of which are not available from any other source. They also provide "visual autoclaves" in which it is possible to watch, through the microscope, the actual phase changes take place as the inclusions are heated. This paper reviews the methods of study and the results obtained, mainly on inclusions formed from highly concentrated solutions, at temperatures ???500??C. Many such fluids have formed as a result of immiscibility with silicate melt in igneous or high-temperature metamorphic rocks. These include fluids consisting of CO2, H2O, or hydrosaline melts that were <50% H2O. From the fluid inclusion evidence it is clear that a boiling, very hot, very saline fluid was present during the formation of most of the porphyry copper deposits in the world. Similarly, from the inclusion evidence it is clear that early (common) pegmatites formed from essentially silicate melts and that the late, rare-element-bearing and chamber-type pegmatites formed from a hydrosaline melt or a more dilute water solution. The evidence on whether this change in composition from early to late solutions was generally continuous or involved immiscibility is not as clear. ?? 1981.

Pressure-induced coordination changes in alkali-germanate melts - An in situ spectroscopic investigation

NASA Technical Reports Server (NTRS)

Farber, Danial L.; Williams, Quentin

1992-01-01

The structure of liquid Na2Ge2O5-H2O, a silicate melt analog, has been studied with Raman spectroscopy to pressures of 2.2 gigapascals. Upon compression, a peak near more than 240 wavenumbers associated with octahedral GeO6 groups grows relative to a peak near 500 wavenumbers associated with tetrahedral GeO4 groups. This change corresponds to an increase in octahedral germanium in the liquid from near 0 percent at ambient pressures to more than 50 percent at a pressure of 2.2 gigapascals. Silicate liquids pausibly undergo similar coordination changes at depth in the earth. Such structural changes may generate decreases in the fusion slopes of silicates at high pressures as well as neutrally buoyant magmas within the transition zone of the earth's mantle.

Electrochemistry of lunar rocks

NASA Technical Reports Server (NTRS)

Lindstrom, D. J.; Haskin, L. A.

1979-01-01

Electrolysis of silicate melts has been shown to be an effective means of producing metals from common silicate materials. No fluxing agents need be added to the melts. From solution in melts of diopside (CaMgSi2O6) composition, the elements Si, Ti, Ni, and Fe have been reduced to their metallic states. Platinum is a satisfactory anode material, but other cathode materials are needed. Electrolysis of compositional analogs of lunar rocks initially produces iron metal at the cathode and oxygen gas at the anode. Utilizing mainly heat and electricity which are readily available from sunlight, direct electrolysis is capable of producing useful metals from common feedstocks without the need for expendable chemicals. This simple process and the products obtained from it deserve further study for use in materials processing in space.

Copper Diffusion in Silicate Melts and Melt Inclusion Study on Volatiles in The Lunar Interior

NASA Astrophysics Data System (ADS)

Ni, Peng

This thesis focuses on the application of diffusion kinetics to both terrestrial and lunar geochemistry. In Chapters II and III, diffusivities of Cu in silicate melts were experimentally determined and used to discuss the role of Cu diffusion in formation of Cu ore deposits and also Cu isotope fractionation in tektites. In Chapters IV and V, lunar olivine-hosted melt inclusions are studied to understand their volatile loss during homogenization in lab, to estimate cooling rate for lunar Apollo sample 74220, and to estimate volatile abundance in the lunar mantle. Magmatic sulfide deposits and porphyry-type Cu deposits are two major types of Cu deposits that supply the world's Cu. In particular, porphyry-type Cu deposits provide ˜57% of the world's total discovered Cu. Recent studies suggest a potential role of diffusive transport of metals (e.g. Cu, Au, PGE, Mo) in the formation of magmatic sulfide deposits and porphyry-type deposits. Diffusivities of Cu in silicate melts, however, are poorly determined. In Chapters II and III of this thesis, Cu diffusion in basaltic melt and rhyolitic melts are studied by diffusion couple and chalcocite "dissolution" methods. Our results indicate high diffusivities of Cu and a general equation for Cu diffusion in silicate melts is obtained. The high diffusivity of Cu indicate that partition of Cu between the silicate phase and the sulfide or fluid phase can be assumed to be in equilibrium during the formation of magmatic sulfide deposits or porphyry-type deposits. In addition, our Cu diffusion data helps explain why Cu isotopes are more fractionated than Zn isotopes in tektites. Volatile abundances in the lunar mantle have profound implications for the origin of the Moon, which was thought to be bone-dry till about a decade ago, when trace amounts of H2O were detected in various types of lunar samples. In particular, high H2O concentrations comparable to mid-ocean ridge basalts were reported in lunar melt inclusions. There are still uncertainties, however, for lunar melt inclusion studies in at least two aspects. One is whether the low H2O/Ce ratios measured in homogenized crystalline inclusions are affected by the homogenization process. The other is that current estimation of volatile abundances in lunar mantle relies heavily on 74220, which is argued to be a local anomaly by some authors. In order to reach a conclusive answer on volatile abundances in lunar mantle, the above two questions have to be answered. To improve our understanding about these questions, in Chapter IV of this thesis, a series of experiments are carried out to understand possible volatile loss from lunar melt inclusions during homogenization. Our results indicate significant H2O loss from inclusions during homogenization in minutes, whereas loss of F, Cl or S is unlikely a concern under our experimental conditions. The most applicable way to preserve H2O during homogenization is to use large inclusions. In Chapter V of this thesis, volatile, trace and major element data for melt inclusions from 10020, 12040, 15016, 15647 and 74235 are reported. Our new data indicate large variation in H2O/Ce ratios from ˜77 to ˜1 across different lunar samples, which is at least partially due to H2O loss on lunar surface during cooling. In addition, evidences were found in F/Nd and S/Dy ratios that might suggest lunar mantle heterogeneity in terms of its volatile abundances.

XANES study on Fe, U and Th in hydrous melts at high temperature and pressure

NASA Astrophysics Data System (ADS)

Wilke, M.; Schmidt, C.; Farges, F.; Borchert, M.; Simionovici, A.; Hahn, M.

2005-12-01

Insight to the structural units of melts is an important key to model properties of magmas. The effect of water and pressure on the local structure around minor to trace elements in silicate melts was investigated at in-situ conditions. The study was performed using XANES spectroscopy and a diamond anvil-cell. This was done to characterize spurious effects observed on glasses that are potentially invoked by quenching [1] and to understand better the processes occurring during the quench. We present results of in-situ XANES measurements on iron, uranium and thorium in hydrous silicate melt up to 1 GPa and 700° C. In-situ XANES spectra were recorded at the ESRF (Grenoble, France), beamline ID 22, using a hydrothermal diamond anvil cell with a design optimized for such measurements [2], i.e. recesses on the front and the back-side of one of the diamond anvils that provide the possibility to collect spectra at relatively low energies (down to 7 keV) and relatively low concentrations (0.1-1 wt%). In-situ Fe K-edge XANES spectra of Fe(II) in hydrous haplogranitic melt at 700° C and 500 MPa suggests that the local structure around Fe in hydrous glass observed previously is probably due to ordering during the quench. Additionally, the XANES is very similar to in-situ spectra taken on Fe(II) in anhydrous haplogranitic melt at 1150° C and ambient pressure. This indicates that the combined effect of water and pressure (0-500 MPa range) does not influence drastically the local structure of Fe in this type of melt composition. In-situ LIII-edge XANES of U in hydrous haplogranitic melt (1 wt% U) at 700° C and 620 MPa show that, upon reduction, U precipitated as uraninite. This suggests a low amount of NBO's (to which tetravalent actinides preferentially bond [3]) in this water-saturated melt. In contrast, U-bearing (1000 ppm) hydrous sodium-tri-silicate melt shows the presence of U(IV) dissolved in the melt as 6-7 coordinated species, as in dry glasses [3]. Similar structural information is obtained for Th(IV). Spectra taken above and below the complete miscibility of the silicate and aqueous phase (ca. 460° C) also reveal no difference in speciation. The aqueous fluid measured at ambient conditions after the run did not show any significant amount of dissolved tetravalent actinides [1] Wilke et al. (2002) Chem. Geol., 189, 55-67. [2] Schmidt C., Rickers K. (2003) Am. Mineral., 88, 288-292. [3] Farges F. (1991) Geochim. Cosmochim. Acta, 55, 3303-3319.

Calcium-Magnesium-Aluminosilicate (CMAS) Reactions and Degradation Mechanisms of Advanced Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Ahlborg, Nadia L.; Zhu, Dongming

2013-01-01

The thermochemical reactions between calcium-magnesium-aluminosilicate- (CMAS-) based road sand and several advanced turbine engine environmental barrier coating (EBC) materials were studied. The phase stability, reaction kinetics and degradation mechanisms of rare earth (RE)-silicates Yb2SiO5, Y2Si2O7, and RE-oxide doped HfO2 and ZrO2 under the CMAS infiltration condition at 1500 C were investigated, and the microstructure and phase characteristics of CMAS-EBC specimens were examined using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Experimental results showed that the CMAS dissolved RE-silicates to form crystalline, highly non-stoichiometric apatite phases, and in particular attacking the silicate grain boundaries. Cross-section images show that the CMAS reacted with specimens and deeply penetrated into the EBC grain boundaries and formed extensive low-melting eutectic phases, causing grain boundary recession with increasing testing time in the silicate materials. The preliminary results also showed that CMAS reactions also formed low melting grain boundary phases in the higher concentration RE-oxide doped HfO2 systems. The effect of the test temperature on CMAS reactions of the EBC materials will also be discussed. The faster diffusion exhibited by apatite and RE-doped oxide phases and the formation of extensive grain boundary low-melting phases may limit the CMAS resistance of some of the environmental barrier coatings at high temperatures.

Mix or un-mix? Trace element segregation from a heterogeneous mantle, simulated.

NASA Astrophysics Data System (ADS)

Katz, R. F.; Keller, T.; Warren, J. M.; Manley, G.

2016-12-01

Incompatible trace-element concentrations vary in mid-ocean ridge lavas and melt inclusions by an order of magnitude or more, even in samples from the same location. This variability has been attributed to channelised melt flow [Spiegelman & Kelemen, 2003], which brings enriched, low-degree melts to the surface in relative isolation from depleted inter-channel melts. We re-examine this hypothesis using a new melting-column model that incorporates mantle volatiles [Keller & Katz 2016]. Volatiles cause a deeper onset of channelisation: their corrosivity is maximum at the base of the silicate melting regime. We consider how source heterogeneity and melt transport shape trace-element concentrations in basaltic lavas. We use both equilibrium and non-equilibrium formulations [Spiegelman 1996]. In particular, we evaluate the effect of melt transport on probability distributions of trace element concentration, comparing the inflow distribution in the mantle with the outflow distribution in the magma. Which features of melt transport preserve, erase or overprint input correlations between elements? To address this we consider various hypotheses about mantle heterogeneity, allowing for spatial structure in major components, volatiles and trace elements. Of interest are the roles of wavelength, amplitude, and correlation of heterogeneity fields. To investigate how different modes of melt transport affect input distributions, we compare melting models that produce either shallow or deep channelisation, or none at all.References:Keller & Katz (2016). The Role of Volatiles in Reactive Melt Transport in the Asthenosphere. Journal of Petrology, http://doi.org/10.1093/petrology/egw030. Spiegelman (1996). Geochemical consequences of melt transport in 2-D: The sensitivity of trace elements to mantle dynamics. Earth and Planetary Science Letters, 139, 115-132. Spiegelman & Kelemen (2003). Extreme chemical variability as a consequence of channelized melt transport. Geochemistry Geophysics Geosystems, http://doi.org/10.1029/2002GC000336

Determining the Metal/Silicate Partition Coefficient of Germanium: Implications for Core and Mantle Differentiation.

NASA Technical Reports Server (NTRS)

King, C.; Righter, K.; Danielson, L.; Pando, K.; Lee, C.

2010-01-01

Currently there are several hypotheses for the thermal state of the early Earth. Some hypothesize a shallow magma ocean, or deep magma ocean, or heterogeneous accretion which requires no magma ocean at all. Previous models are unable to account for Ge depletion in Earth's mantle relative to CI chondrites. In this study, the element Ge is used to observe the way siderophile elements partition into the metallic core. The purpose of this research is to provide new data for Ge and to further test these models for Earth's early stages. The partition coefficients (D(sub Ge) = c(sub metal)/c(sub silicate), where D = partition coefficient of Ge and c = concentration of Ge in the metal and silicate, respectively) of siderophile elements were studied by performing series of high pressure, high temperature experiments. They are also dependent on oxygen fugacity, and metal and silicate composition. Ge is a moderately siderophile element found in both the mantle and core, and has yet to be studied systematically at high temperatures. Moreover, previous work has been limited by the low solubility of Ge in silicate melts (less than 100 ppm and close to detection limits for electron microprobe analysis). Reported here are results from 14 experiments studying the partitioning of Ge between silicate and metallic liquids. The Ge concentrations were then analyzed using Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) which is sensitive enough to detect ppm levels of Ge in the silicate melt.

Experimental Constraints on Fe Isotope Fractionation in Carbonatite Melt Systems

NASA Astrophysics Data System (ADS)

Stuff, M.; Schuessler, J. A.; Wilke, M.

2015-12-01

Iron isotope data from carbonatite rocks show the largest variability found in igneous rocks to date [1]. Thus, stable Fe isotopes are promising tracers for the interaction of carbonate and silicate magmas in the mantle, particularly because their fractionation is controlled by oxidation state and bonding environment. The interpretation of Fe isotope data from carbonatite rocks remains hampered, since Fe isotope fractionation factors between silicate and carbonate melts are unknown and inter-mineral fractionation can currently only be assessed by theoretical calculations [1;2]. We present results from equilibration experiments in three natrocarbonatite systems between immiscible silicate and carbonate melts, performed at 1200°C and 0.7 GPa in an internally heated gas pressure vessel at intrinsic redox conditions. The Fe isotope compositions of the silicate melt (sil.m.), quenched to a glass, and the carbonate melt (carb.m.), forming fine-grained quench crystals, were analysed by solution MC-ICP-MS. Our first data indicate a remarkable fractionation of Δ56Fesil.m.‒carb.m.= 0.29 ±0.07 ‰ near equilibrium. At short run durations, even stronger fractionation up to Δ56Fesil.m.‒carb.m. = 0.41 ±0.07 ‰ occurs, due to kinetic effects. Additionally, Δ56Fesil.m.‒carb.m. changes with bulk chemical composition, likely reflecting considerable differences between the studied systems in terms of the Fe3+/Fe2+-ratios in the two immiscible liquids. Our findings provide experimental support for a carbonatite genesis model, in which extremely negative δ56Fe values in carbonatites result from differentiation processes, such as liquid immiscibility [1]. This effect can be enhanced by disequilibrium during fast ascent of carbonatite magmas. Their sensitivity to chemical and redox composition makes Fe isotopes a potential tool for constraining the original compositions of carbonatite magmas. [1] Johnson et al. (2010) Miner. Petrol. 98, 91-110. [2] Polyakov & Mineev (2000) Geochim. Cosmochim. Acta 64, 849-865.

Tin isotope fractionation during magmatic processes and the isotope composition of the bulk silicate Earth

NASA Astrophysics Data System (ADS)

Wang, Xueying; Amet, Quentin; Fitoussi, Caroline; Bourdon, Bernard

2018-05-01

Tin is a moderately volatile element whose isotope composition can be used to investigate Earth and planet differentiation and the early history of the Solar System. Although the Sn stable isotope composition of several geological and archaeological samples has been reported, there is currently scarce information about the effect of igneous processes on Sn isotopes. In this study, high-precision Sn isotope measurements of peridotites and basalts were obtained by MC-ICP-MS with a double-spike technique. The basalt samples display small variations in δ124/116Sn ranging from -0.01 ± 0.11 to 0.27 ± 0.11‰ (2 s.d.) relative to NIST SRM 3161a standard solution, while peridotites have more dispersed and more negative δ124Sn values ranging from -1.04 ± 0.11 to -0.07 ± 0.11‰ (2 s.d.). Overall, basalts are enriched in heavy Sn isotopes relative to peridotites. In addition, δ124Sn in peridotites become more negative with increasing degrees of melt depletion. These results can be explained by different partitioning behavior of Sn4+ and Sn2+ during partial melting. Sn4+ is overall more incompatible than Sn2+ during partial melting, resulting in Sn4+-rich silicate melt and Sn2+-rich residue. As Sn4+ has been shown experimentally to be enriched in heavy isotopes relative to Sn2+, the effect of melting is to enrich residual peridotites in relatively more compatible Sn2+, which results in isotopically lighter peridotites and isotopically heavier mantle-derived melts. This picture can be disturbed partly by the effect of refertilization. Similarly, the presence of enriched components such as recycled oceanic crust or sediments could explain part of the variations in Sn isotopes in oceanic basalts. The most primitive peridotite analyzed in this study was used for estimating the Sn isotope composition of the BSE, with δ124Sn = -0.08 ± 0.11‰ (2 s.d.) relative to the Sn NIST SRM 3161a standard solution. Altogether, this suggests that Sn isotopes may be a powerful probe of redox processes in the mantle.

Redox equilibria and the structural role of iron in alumino-silicate melts

NASA Astrophysics Data System (ADS)

Dickenson, M. P.; Hess, P. C.

1982-01-01

The relationship between the redox ratio Fe+2/(Fe+2+Fe+3) and the K2O/(K2O + Al2O3) ratio (K2O*) were experimentally investigated in silicate melts with 78 mol% SiO2 in the system SiO2-Al2O3-K2O-FeO-Fe2O3, in air at 1,400° C. Quenched glass compositions were analyzed by electron microprobe and wet chemical microtitration techniques. Minimum values of the redox ratio were obtained at K2O*≈0.5. The redox ratio in peralkaline melts (K2O*>0.5) increases slightly with K2O* whereas this ratio increases dramatically in peraluminous melts (K2O*<0.5) as K2O is replaced by Al2O3. These data indicate that all Fe+3 (and Al+3) occur as tetrahedral species charge balanced with K+ in peralkaline melts. In peraluminous melts, Fe+3 (and Al+3) probably occur as both tetrahedral species using Fe+2 as a charge-balancing cation and as network-modifying cations associated with non-bridging oxygen.

Silicate Inclusions in IAB Irons: Correlations Between Metal Composition and Inclusion Properties, and Inferences for Their Origin

NASA Astrophysics Data System (ADS)

Benedix, G. K.; McCoy, T. J.; Keil, K.

1995-09-01

IAB irons are the largest group of iron meteorites, exhibit a large range of siderophile element concentrations in their metal, and commonly contain silicate inclusions with roughly chondritic composition. They are closely related to IIICD irons [1,2] and their inclusions resemble winonaites [3]. It has been suggested that IAB's and IIICD's formed in individual impact melt pools [4,2] on a common parent body. However, it has also been suggested that fractional crystallization [5,6] of a S-saturated core could produce the observed siderophile element trends. Metal composition is correlated with silicate inclusion mineralogy in IIICD's [1], indicating reactions between solid silicates and the metallic magma in a core. These trends observed in IIICD's differ from those in IAB's, suggesting different parent bodies. A bi-modal grouping, based primarily on mineralogy and mineral abundances, was suggested for IAB inclusions [7]. However, recent recoveries of several new silicate-bearing IAB's, along with the emergence of new ideas on their origins, prompted a comprehensive study to document more fully the range of inclusions within IAB irons, to examine possible correlations between the compositions of the metallic host and the silicate inclusions, and to elucidate the origin of IAB irons. We are studying troilite-graphite-silicate inclusions in 24 IAB irons with Ni concentrations ranging from 6.6-25.0%. These include Odessa and Copiapo types [7], newly recovered meteorites (e.g., Lueders [8]) and meteorites with extreme Ni contents (e.g., Jenny's Creek, 6.8%; San Cristobal, 25.0% [9]). The inclusions exhibit a range of textures from recrystallized to partial melts (e.g., Caddo County [10]). Rigorous classification [7] is hampered by heterogeneities between group meteorites, between different samples of distinct meteorites, and within individual inclusions. While intergroup heterogeneities make comparisons between the suite of IAB's somewhat difficult, some general trends do exist. Inclusion mineralogy progresses from graphite-troilite nodules in low Ni IAB's, to silicate-dominated inclusions in high Ni IAB's. With increasing Ni abundance in the metal, systematic variations are found in several properties. Two groups are delineated on a Ni vs Fa content plot and both are positively correlated with Ni content. Graphite abundance noticeably decreases with increasing Ni content [7]. Graphite location also varies with Ni: graphite is primarily found interstitial to the silicates in low Ni IAB's, but is located at metal-silicate boundaries in those with higher Ni abundances. With increasing Ni, daubreelite disappears. Inclusion shape also varies [7]: more angular inclusions are associated with low Ni, while more rounded inclusions exist at high Ni contents. These systematic changes suggest interaction between the silicate inclusions and an evolving metallic magma. Troilite and graphite abundances may be related to early nucleation on silicates, hence their depletion in high Ni (later crystallizing) irons. The presence of abundant graphite creates reducing conditions which would result in the formation of daubreelite. Conditions become more oxidizing with loss of graphite, evidenced by lack of daubreelite and more FeO-rich silicates in high Ni irons. Although an overall trend exists, the story is complicated by heterogeneities. Significant variations are found between paired samples (e.g., Toluca and Tacubaya), as well as within individual inclusions (daubreelite and chromite in same inclusion). Local oxidation conditions may be controlled by graphite abundance. Heterogeneities within specific meteorites need documentation. Most of the inclusions exhibit similar textural (metamorphic) features, but a few show evidence of partial melting and melt migration, further complicating the parent body history. While a variety of processes (oxidation-reduction, metamorphism, partial melting) affected the inclusions during formation, systematic changes observed here indicate that the silicates were interacting with a single evolving metallic magma. We suggest that the requirement for a common system is more compatible with core formation [5,6] than with impact-melt pools [2,4]. References: [1] McCoy T. J. et al. (1993) Meteoritics, 28, 552-560. [2] Choi B.-G. et al. (1995) GCA, 59, 593-612. [3] Benedix G. K. et al. (1995) LPS XXVI, 99-100. [4] Wasson J. T. et al. (1980) Z. Naturforsch., 35a, 781-795. [5] Kracher A. (1982) GRL, 9, 412-415. [6] Kracher A. (1985) Proc. LPSC 15th, in JGR, 90, C689-C698. [7] Bunch T. E. et al. (1970) Contrib. Mineral. Petrol., 25, 297-340. [8] McCoy et al. (1995) Meteoritics, in preparation. [9] Scott E. R. D. and Bild R. W. (1974) GCA, 38, 1379-1391. [10] Takeda H. et al. (1993) Meteoritics, 28, 447.

High-temperature apparatus for chaotic mixing of natural silicate melts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgavi, D.; Petrelli, M.; Vetere, F. P.

2015-10-15

A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10{sup 6} Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed atmore » 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.« less

Experimental calibration of a new oxybarometer for silicic magmas based on the partitioning of vanadium between magnetite and silicate melt

NASA Astrophysics Data System (ADS)

Arató, Róbert; Audétat, Andreas

2016-04-01

Oxygen fugacity is an important parameter in magmatic systems that affects the stability of mineral phases and fluid species. However, there is no well-established method to reconstruct the oxygen fugacity of slowly cooled magmas such as granite, for example, because existing oxybarometers (e.g., magnetite-ilmenite method) are susceptible to re-equilibration processes during slow cooling and thus lead to erroneous results when applied for granitic rocks. In this study, we aim at developing an oxybarometer that is based on the partitioning of vanadium (a redox-sensitive element) between magnetite inclusions and silicate melt inclusions preserved in quartz phenocrysts, where they were protected from subsolidus alteration and can be measured as entities by LA-ICP-MS. In the first - experimental - part of this study we investigated the effects of temperature (800-950 ° C), pressure (1-2 kbar), oxygen fugacity (from ΔFMQ+0.7 to ΔFMQ+4.0), magnetite composition, and melt composition on the partition coefficient of vanadium between magnetite and melt (DVmgt-melt). The experiments were carried out in cold-seal pressure vessels and the starting material was a mixture of V-doped haplogranite glasses or natural obsidian powder with variable aluminum saturation index (ASI), and synthetic, V-free magnetite of 10-20 μm grain size. The vanadium partition coefficient was found to depend strongly on oxygen fugacity, and to lesser (but still considerable) degrees on melt composition and temperature. A more than 1.5 log unit decrease in DVmgt-melt values with increasing oxygen fugacity can be explained by a change of the dominant valence state of V in the silicate melt. For a given oxygen fugacity buffer DVmgt-melt decreases with increasing temperature, but this reflects mostly the change in absolute fO2 values while the net temperature effect is in fact positive. DVmgt-melt depends significantly on melt composition, resulting in higher D-values with increasing aluminum saturation index (ASI). This seems to reflect less favorable incorporation of V into peraluminous melts compared to depolymerized, peralkaline melts. Changing pressure from 1 to 2 kbar had an effect only at NNO, causing 0.3 log unit increase in D, whereas the Ti-content of magnetite turned out to have negligible effect on the V partitioning. In summary, the dependence of DVmgt-melt on temperature, ASI and oxygen fugacity can be described by the following regression equation: logD(V)mgt/melt=-1.22+0.31*10^5/T(° K) +1.73*ASI -0.49*ΔFMQ First tests of the equation on natural samples were carried out on rapidly cooled tuffs and vitrophyres from variable tectonic settings, for which fO2 could be constrained independently by the magnetite-ilmenite method. All calculated fO2 values fall within ± 0.75 log unit within those suggested by the Fe-Ti oxybarometer, whereas 12 out of 16 samples agree within 0.5 log units .

Silicic melt evolution in the early Izu-Bonin arc recorded in detrital zircons: Zircon U-Pb geochronology and trace element geochemistry for Site U1438, Amami Sankaku Basin

NASA Astrophysics Data System (ADS)

Barth, A. P.; Tani, K.; Meffre, S.; Wooden, J. L.; Coble, M. A.

2016-12-01

Understanding the petrologic evolution of oceanic arc magmas through time is important because these arcs reveal the processes of formation and the early evolution of juvenile continental crust. The Izu-Bonin (IB) arc system has been targeted because it is one of several western Pacific intraoceanic arcs initiated at 50 Ma and because of its prominent spatial asymmetry, with widespread development of relatively enriched rear arc lavas. We examined Pb/U and trace element compositions in zircons recovered at IODP Site 351-U1438 and compared them to regional and global zircon suites. These new arc zircon data indicate that detrital zircons will yield new insights into the generation of IB silicic melts and form a set of useful geochemical proxies for interpreting ancient arc detrital zircon provenance. Project IBM drilling target IBM1 was explored by Expedition 351 at Site U1438, located in the proximal back-arc of the northern Kyushu-Palau Ridge (KPR) at 27.3°N. A 1.2 km thick section of Paleogene volcaniclastic rocks, increasingly lithified and hydrothermally altered with depth, constitutes a proximal rear arc sedimentary record of IB arc initiation and early arc evolution. The ages and compositions of U1438 zircons are compatible with provenance in one or more edifices of the northern KPR and are incompatible with drilling contamination. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic KPR melts. The abundances of selected trace elements with high native concentrations provide insight into the petrogenesis of U1438 detrital zircon host melts, and may be useful indicators of both short and long-term variations in melt compositions in arc settings. The U1438 zircons are slightly enriched in U and LREE and are depleted in Nb compared to zircons from mid-ocean ridges and the Parece-Vela Basin, as predicted for melts in a primitive oceanic arc setting with magmas derived from a highly depleted mantle source. Close age and geochemical affinity of U1438 detrital zircons to igneous zircons in Eocene leucotonalite from the partially exhumed intrusive suite at Komahashi-Daini Seamount in the northernmost KPR suggests that these zircons also can yield insight into the link between silicic volcanism and evolving tonalitic intrusions in the Paleogene IB arc.

Partial melting of carbonated pelite at 3-7 GPa and deep cycling of CO2 and H2O in subduction zones

NASA Astrophysics Data System (ADS)

Tsuno, K.; Dasgupta, R.; Danielson, L. R.; Righter, K.

2011-12-01

The exchange of water and carbon dioxide between the Earth's crustal rocks and the interior is important for understanding geochemical and geophysical evolution of the planet on geologic timescale. Subduction of pelitic sediments is a key mechanism for volatile introduction to the mantle but the high-pressure behavior of H2O+ CO2 bearing sediments is only constrained for alumina-rich, low-Mg# bulk compositions [1, 2]. However, the ocean-floor sediments for many subduction zones that contain both water and CO2 are alumina-poor and have higher Mg#. To constrain the melting behavior of a model alumina poor carbonated pelite, we performed new experiments. Piston cylinder (3 GPa) and multianvil (5 and 7 GPa) experiments were conducted between 800 and 1150 °C, using a model sediment composition containing 1 wt.% H2O and 5 wt.% CO2 (trace vapor-present at subsolidus conditions). The choice of the bulk composition was aimed to model the loss of siliceous hydrous fluid during the shallow part of subduction. We determined the solidus temperatures between 800 and 850 °C at 3 GPa, 900 and 950 °C at 5 GPa, and <1000 °C at 7 GPa. The subsolidus phases include cpx, garnet, coesite, rutile, phengite, and calcitess at 3 GPa, and kyanite comes in at 5 GPa. Hydrous rhyolitic silicate melt was observed at 3 GPa and up to 1150 °C. The near-solidus melt at 5-7 GPa was K-rich and calcio-carbonatitic, in contrast to the previous experimental results in alumina-rich and low Mg# bulk composition [1, 2], which showed the stability of Al-rich trachyitic silicate melt at near-solidus temperatures up to 5 GPa, and replaced by carbonate melt only at ≥5.5 GPa. Carbonate-silicate melt immiscibility was observed at 5 GPa, 1100 °C in our study. The phengite-out boundary is located between 850 and 900 °C at 3 GPa, between 1000 and 1100 °C at 5 GPa, and <1000 °C at 7 GPa. The crystalline carbonate-out boundary is between 950 and 1000 °C at 3 and 5 GPa, and <1000 °C at 7 GPa. Comparison of our results, in terms of the P-T locations of the solidus, phengite- and carbonate-out boundaries, to the thermal structures of the slab-surface in cold-intermediate subduction zones indicates that most of the phengite-bound H2O and carbonate-bound CO2 are recycled into the deep upper mantle (~200 km depth). On the other hand, substantial amounts of C-O-H volatiles, in the form of either hydrous silicate melt or K-rich calcio-carbonatitic melt, are likely to be released from relatively hot subducting slabs. The observation of carbonate melt inclusion in cpx and garnet in deeply subducted carbonate-rich sediments [3] might be explained by our experimental results that carbonatite is the stable near-solidus sediment melt at deep sub-arc depths. [1] Thomsen, T.B. and Schmidt, M.W. 2008, EPSL 267, 17-31. [2] Grassi, D. and Schmidt, M.W. 2011, J. Petrol. 52, 765-789. [3] Korsakov, A.V., and Hermann, J. 2006, EPSL, 104-118.

Poly(ethylene glycol) layered silicate nanocomposites for retarded drug release prepared by hot-melt extrusion.

PubMed

Campbell, Kayleen; Craig, Duncan Q M; McNally, Tony

2008-11-03

Composites of paracetamol loaded poly(ethylene glycol) (PEG) with a naturally derived and partially synthetic layered silicate (nanoclay) were prepared using hot-melt extrusion. The extent of dispersion and distribution of the paracetamol and nanoclay in the PEG matrix was examined using a combination of field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and wide-angle X-ray diffraction (WAXD). The paracetamol polymorph was shown to be well dispersed in the PEG matrix and the nanocomposite to have a predominately intercalated and partially exfoliated morphology. The form 1 monoclinic polymorph of the paracetamol was unaltered after the melt mixing process. The crystalline behaviour of the PEG on addition of both paracetamol and nanoclay was investigated using differential scanning calorimetry (DSC) and polarised hot-stage optical microscopy. The crystalline content of PEG decreased by up to 20% when both drug and nanoclay were melt blended with PEG, but the average PEG spherulite size increased by a factor of 4. The time taken for 100% release of paracetamol from the PEG matrix and corresponding diffusion coefficients were significantly retarded on addition of low loadings of both naturally occurring and partially synthetic nanoclays. The dispersed layered silicate platelets encase the paracetamol molecules, retarding diffusion and altering the dissolution behaviour of the drug molecule in the PEG matrix.

Nitrogen partitioning during Earth's accretion and core-mantle differentiation

NASA Astrophysics Data System (ADS)

Speelmanns, I. M.; Schmidt, M. W.; Liebske, C.

2017-12-01

On present day Earth, N is one of the key constituents of our atmosphere and forms the basis of life. However, the deep Earth geochemistry of N, i.e. its distribution and isotopic fractionation between Earth's deep reservoirs is not well constrained. This study investigates nitrogen partitioning between metal and silicate melts as relevant for core segregation during the accretion of planetesimals into the Earth. We have determined N-partitioning coefficients over a wide range of temperatures (1250-2000 °C), pressures (15-35 kbar) and oxygen fugacity's, the latter in the relevant range of core segregation (IW-5 to IW). Centrifuging piston cylinders were used to equilibrate and then gravitationally separate metal-silicate melt pairs. Separation of the two melts is necessary to avoid micro nugget contamination in the silicate melt at reducing conditions < IW-2.5. Complete segregation of the two melts was reached within 1 to 3 hours at 1000 g and 1600-1250 °C respectively, the interface showing a proper meniscus. The applied double capsule technique in all experiments, using an outer metallic (Pt) and inner non-metallic capsule (graphite or Al2O3), minimizes N-loss over the course of the experiments compared to single non-metallic capsules. The two quenched melts were cut apart mechanically, cleaned at the outside, their N concentrations were then analysed on bulk samples by an elemental analyser, the low abslute masses requiring careful development of analytical routines. Despite these difficulties, we were able to determine a DNmetal/silicate of 13±0.3 at IW-1 decreasing to 2.0±0.2 at IW-5.5, at 1250°C and 15 kbar, N partitioning into the core forming metal. Increasing temperature dramatically lowers the DNmetal/silicate to e.g. 0.5±0.15 at IW-4, during early core formation N was hence mildly incompatible in the metal. The results suggest that under magma ocean conditions (> 2000 oC and fO2 IW-2.5), N-partition coefficents were within a factor of 2 of unity. Hence, N did not partition into the core, which should contain negliligible quantities of N. The few available literature data [1],[2],[3] support N changing compatibility with decreasing fO2. [1] Kadik et al., (2011) Geochem Int 49.5: 429-438. [2] Roskosz et al., (2013) GCA 121: 15-28. [3] Dalou et al., (2017) EPSL 458: 141-151

Experimental observations on noble metal nanonuggets and Fe-Ti oxides, and the transport of platinum group elements in silicate melts

NASA Astrophysics Data System (ADS)

Anenburg, Michael; Mavrogenes, John A.

2016-11-01

Platinum group element (PGE) nanonuggets are a nuisance in experimental studies designed to measure solubility or partitioning of noble metals in silicate melts. Instead of treating nanonuggets as experimental artifacts, we studied their behaviour motivated by recent discoveries of PGE nanonuggets in a variety of natural settings. We used an experimental setup consisting of AgPd, Pt or AuPd capsules and Fe(-Ti) oxide-saturated hydrous peralkaline silicate melts to maximise nanonugget production. TABS (Te, As, Bi, Sb, Sn) commonly occur in PGM (platinum group minerals), prompting addition of Bi to our experiments to investigate its properties as well. Three-dimensional optical examination by 100× objective and immersion oil reveals variable colour which correlates with nanonugget size and shape due to plasmon resonance effects. We observe two textural types: (1) intermediate-sized nanonuggets dispersed in the glass and adhering to oxides, and (2) abundant fine nanonuggets dispersed in the glass with coarse euhedral crystals in contact with oxides. Slow cooling removes dispersed nanonuggets and greatly coarsens existing oxide-associated metal crystals. Nanonugget-free halos are commonly observed around oxide grains. All metal phases are composed of major (Ag, Pd) and trace (Pt, Ir, Au) capsule material. Our results show reduction processes, imposed by growing oxides, causing local metal saturation in the oxide rich zones with preferential nucleation on smaller oxide grains. The redox gradient then blocks additional metals from diffusing into oxide rich zones, forming halos. As the entire experimental charge is reduced throughout the run, nanonuggets form in the distal glass. Bismuth contents of metal phases do not depend on Bi2O3 amounts dissolved in the melt. Further PGM crystallisation consumes nanonuggets as feedstock. We conclude that the appearance of metallic PGE phases happens in two stages: first as nanonuggets and then as larger PGM. Once formed, nanonuggets cannot be removed by oxidation or dissolution, but only by PGM coarsening. Sulfur-poor PGE ore deposits commonly contain more PGE than permitted by existing estimates of equilibrium solubility in silicate melts. This is commonly explained by initial scavenging of PGE by sulfide liquids followed by S-loss, but evidence for S-loss is not conclusive. We suggest that nanonuggets may be a means to transport PGE from source regions to form ore deposits, followed by direct PGM crystallisation from silicate melt without intermediate concentration by sulfide liquids.

The solubility of gold in silicate melts: First results

NASA Technical Reports Server (NTRS)

Borisov, A.; Palme, H.; Spettel, B.

1993-01-01

The effects of oxygen fugacity and temperature on the solubility of Au in silicate melts were determined. Pd-Au alloys were equilibrated with silicate of anorthite-diopside eutectic composition at different T-fO2 conditions. The behavior of Au was found to be similar to that of Pd reported recently. Au solubilities for alloys with 30 to 40 at. percent Au decrease at 1400 C from 12 ppm in air to 160 ppb at a log fO2 = -8.7. The slope of the log(Me-solubility) vs. log(fO2) curve is close to 1/4 for Au and the simultaneously determined Pd suggesting a formal valence of Au and Pd of 1+. Near the IW buffer Pd and Au solubilities become even less dependent on fO2 perhaps reflecting the presence of some metallic Au and Pd.

Melting phase relations in the MgSiO3-CaSiO3 system at 24 GPa

NASA Astrophysics Data System (ADS)

Nomura, Ryuichi; Zhou, Youmo; Irifune, Tetsuo

2017-12-01

The Earth's lower mantle is composed of bridgmanite, ferropericlase, and CaSiO3-rich perovskite. The melting phase relations between each component are key to understanding the melting of the Earth's lower mantle and the crystallization of the deep magma ocean. In this study, melting phase relations in the MgSiO3-CaSiO3 system were investigated at 24 GPa using a multi-anvil apparatus. The eutectic composition is (Mg,Ca)SiO3 with 81-86 mol% MgSiO3. The solidus temperature is 2600-2620 K. The solubility of CaSiO3 component into bridgmanite increases with temperature, reaching a maximum of 3-6 mol% at the solidus, and then decreases with temperature. The same trend was observed for the solubility of MgSiO3 component into CaSiO3-rich perovskite, with a maximum of 14-16 mol% at the solidus. The asymmetric regular solutions between bridgmanite and CaSiO3-rich perovskite and between MgSiO3 and CaSiO3 liquid components well reproduce the melting phase relations constrained experimentally. [Figure not available: see fulltext.

Core Formation: an Experimental Study of Metallic Melt-Silicate Segregation

NASA Astrophysics Data System (ADS)

Herpfer, M. A.; Larimer, J. W.

1993-07-01

To a large extent, the question of how metallic cores form reduces to the problem of understanding the surface tension between metallic melts and silicates [1]. This problem was addressed by performing experiments to determine the surface tensions between metallic melts with variable S contents and the silicate phases (olivine and orthopyroxene) expected in planetary mantles. The experiments were conducted in a piston-cylinder apparatus at P = 1GPa and T = 1250-1450 degrees C. Textural and chemical equilibration was confirmed in several ways: theoretical estimates were checked by conducting a series of experiments at progressively longer times (up to 72 hrs) until phase composition and dihedral angle ceased to change and the distribution of measured "apparent" angles matched the standard cumulative frequency curve. The dihedral "wetting" angles (theta) were measured from high resolution photomicrgraphs using a 10X optical protractor; 100-400 measurements were made for most experiments. The dihedral angle is related to the ratio of interfacial energies: gamma(sub)ss/gamma(sub)sl = 2 cos(theta/2), where gamma(sub)ss and gamma(sub)sl are the interfacial energies between solid-solid and liquid-solid. Since data exist for the pertinent solid-solid energies, the liquid-solid interfacial energies can be computed from measured theta values. However, the important relations are best expressed in terms of theta values. The extent to which a melt is interconnected along grain boundaries, and hence able to flow and segregate depends on the value of theta and the fraction of melt present. When theta < 60 degrees, the liquid can be interconnected at all melt fractions but when theta > 60 degrees, the melt fraction must be at least 1 vol% and increses as theta increases. Actually there is a predicted effect, analogous to a hysteresis effect, where for a given theta value the amount of melt that needs to be added for interconnection is greater than the amount left when the melt disconnects (pinches off). In our experiments, where dense metallic melt drained away, the disconnect theta values match the theoretical predictions. The composition of the metallic melt in the experiments was varied from stoichiometric FeS to Fe/S ratios near the the eutectic and on to more Fe rich compositons. The theta values vary in a systematic manner; for example, for melts in contact with olivine at 1300 degrees C the theta values range from 67 degrees for FeS to 55 degrees at the eutectic and back toward higher values at higher Fe contents. Theoretical considerations indicate that eutectic compositions are expected to have the lowest theta values, just as observed. The theta values indicate that melts with eutectic composition can interconnect and segregate at 1-2 vol% melt fraction at 1300 degrees C. Some previous estimates of the melt fraction required for interconnection are much higher [2,3], but the inferences were drawn from experiments that were not designed to test for textural equilibrium, fraction of melt present, etc. The present experiments clearly show that metallic melts can readily segregate from solid silicates. Simple extrapolations to other phases, compositions and PT conditions provide a rather complete picture of how the "plumbing" worked in the mantles of planetary objects during the initial stages of core segregation. References: [1] Stevenson D. J. (1990) In Origin of the Earth, 231-249. [2] Taylor G. J. (1989) LPSC XX, 1109. [3] Walker D. and Agee C. B. Meteor. 23, 81-91.

Shock compression of preheated silicate liquids: 30 years of progress

NASA Astrophysics Data System (ADS)

Asimow, Paul

2011-06-01

Tom Ahrens and his students pioneered, beginning around 1981, the technique of determining silicate liquid equations of state for geophysical applications using shock compression of pre-heated, encapsulated samples. In the last decade, we have ported this technique to the Caltech two-stage light gas gun and extended several pre-heated liquid Hugoniots to over 125 GPa. We now have enough compositions studied to perform several tests of the theory of linear mixing or, assuming linear mixing, to describe any liquid in the five-component CaO-MgO-FeO-Al2O3-SiO2 system. This data allows us to identify liquid compositions likely to be negatively or neutrally buoyant in the lower mantle and to form a preliminary description of the dynamics of partial melting of solid lower mantle or initial crystallization of a deep mantle magma ocean. The most robust and surprising feature of all studied liquids, which places very strong constraints on microscopic models for silicate liquid compression behavior, is anomalous increase of the Grüneisen parameter upon compression, with remarkably consistent q = dln γ/dlnV = -1.75 +/- 0.25. Thanks to long-term support by the National Science Foundation.

Highly Reducing Partitioning Experiments Relevant to the Planet Mercury

NASA Technical Reports Server (NTRS)

Rowland, Rick, II; Vander Kaaden, Kathleen E.; McCubbin, Francis M.; Danielson, Lisa R.

2017-01-01

With the data returned from the MErcury Surface Space ENvironment GEochemistry and Ranging (MESSENGER) mission, there are now numerous constraints on the physical and chemical properties of Mercury, including its surface composition. The high S and low FeO contents observed from MESSENGER on the planet's surface suggests a low oxygen fugacity of the present planetary materials. Estimates of the oxygen fugacity for Mercurian magmas are approximately 3-7 log units below the Iron-Wüstite (Fe-FeO) oxygen buffer, several orders of magnitude more reducing than other terrestrial bodies we have data from such as the Earth, Moon, or Mars. Most of our understanding of elemental partitioning behavior comes from observations made on terrestrial rocks, but Mercury's oxygen fugacity is far outside the conditions of those samples. With limited oxygen available, lithophile elements may instead exhibit chalcophile, halophile, or siderophile behaviors. Furthermore, very few natural samples of rocks that formed under reducing conditions are available in our collections (e.g., enstatite chondrites, achondrites, aubrites). With this limited amount of material, we must perform experiments to determine the elemental partitioning behavior of typically lithophile elements as a function of decreasing oxygen fugacity. Experiments are being conducted at 4 GPa in an 880-ton multi-anvil press, at temperatures up to 1850degC. The composition of starting materials for the experiments were selected for the final run products to contain metal, silicate melt, and sulfide melt phases. Oxygen fugacity is controlled in the experiments by adding silicon metal to the samples, using the Si-SiO2 oxygen buffer, which is approximately 5 log units more reducing than the Fe-FeO oxygen buffer at our temperatures of interest. The target silicate melt compositional is diopside (CaMgSi2O6) because measured surface compositions indicate partial melting of a pyroxene-rich mantle. Elements detected on Mercury's surface by MESSENGER (K, Na, Fe, Ti, Cl, Al, Cr, Mn, U, Th) and other geochemically relevant elements (P, F, H, N, C, Co, Ni, Mo, Ce, Nd, Sm, Eu, Gd, Dy, Yb) are added to the starting composition at trace abundances (approximately 500 ppm) so that they are close enough to infinite dilution to follow Henry's law of trace elements, and their partitioning behavior can be measured between the metal, silicate, and sulfide phases. The results of these experiments will allow us to assess the thermal and magmatic evolution of the planet Mercury from a geochemical standpoint.

The origin of chondrules - Experimental investigation of metastable liquids in the system Mg2SiO4-SiO2

NASA Technical Reports Server (NTRS)

Blander, M.; Planner, H. N.; Keil, K.; Nelson, L. S.; Richardson, N. L.

1976-01-01

Laser-melted magnesium silicate droplets were supercooled 400-750 C below their equilibrium liquidus temperatures before crystallization and their texture was compared with that of meteoritic and lunar chondrules. Crystal morphology, width and texture were studied in relation to nucleation temperature and bulk composition. It was found that the only phase to nucleate from the forsterite-enstatite normative melts was forsterite. Highly siliceous glass, about 65% SiO2 by weight, was identified interstitially to the forsterite crystals in seven of the MgSiO4 spherules and was thought to be present in all.

Water generation and transport through the high-pressure ice layers of Titan and Ganymede

NASA Astrophysics Data System (ADS)

Kalousova, K.; Sotin, C.; Choblet, G.; Tobie, G.; Grasset, O.

2017-09-01

We investigate the generation and transport of water through the high-pressure (HP) ice layers of Ganymede and Titan using a numerical model of two-phase convection in 2D geometry. Our results suggest that water can be generated at the silicate/HP ice interface for small to intermediate values of Rayleigh number (Ra 1.e8-1.e10) while no melt is generated for the higher values (Ra 1.e11). If generated, water is transported through the layer by the upwelling plumes and, depending on the vigor of convection, it stays liquid (smaller Ra) or it may freeze (intermediate Ra) before melting again as the plume reaches the temperate layer at the interface with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the HP ice permeability. This process may enable the transfer of volatiles and salts that might have been leached from silicates by the meltwater. Since the HP ice layer is much thinner on Titan than on Ganymede, it is probably more permeable for volatiles and salts leached from the silicate core.

Aluminum enrichment in silicate melts by fractional crystallization: some mineralogic and petrographic constraints.

USGS Publications Warehouse

Zen, E.

1986-01-01

The degree of Al saturation of an igneous rock may be given by its aluminium saturation index (ASI), defined as the molar ratio Al2O3/(CaO+K2O+Na2O). One suggested origin for mildly peraluminous granites (ASI 1-1.1) is fractional crystallization of subaluminous magmas (ASI 1. For hornblende to effectively cause a melt to evolve into a peraluminous composition, it must be able to coexist with peraluminous magmas; e.g. at = or <5 kbar hornblende can coexist with strongly peraluminous melts (ASI approx 1.5). Potentials and problems of using coarse-grained granitic rocks to prove courses of magmatic evolution are illustrated by a suite of samples from the Grayling Lake pluton, SW Montana. Such rocks generally contain a large cumulate component and should not be used as a primary test for the occurrence or efficacy of a fractionation process that might lead to peraluminous melts. The process is unlikely to give rise to peraluminous plutons of batholithic dimensions. A differential equation is presented which allows the direct use of mineral chemistry and modal abundance to predict the path of incremental evolution of a given magma.-R.A.H.

Density calculations for silicate liquids: Reply to a Critical Comment by Ghiorso and Carmichael

NASA Astrophysics Data System (ADS)

Bottinga, Y.; Weill, D. F.; Richet, P.

1984-02-01

The analysis of the liquid silicate density model recently proposed in BOTTINGAet al. (1982) by GHIORSO and CARMICHAEL (1984) is shown to be based on a combination of unwarranted mathematical assumptions, refusal to recognize experimental and theoretical evidence for the non-linear effect of composition on liquid silicate density, and a totally unrealistic view of the accuracy with which the thermal expansion of silicate liquids can be measured. As a consequence, none of the general or specific points raised by Ghiorso and Carmichael are relevant to the issue of which of the existing calculation models ( BOTTINGA and WEILL, 1970; NELSON and CARMICHAEL, 1979; MOet al., 1982; or BOTTINGAet al., 1982, 1983) should be used. As stated in BOTTINGA, RICHET and WEILL (1983), there is a problem in using a combination of the molar volume parameters from the first three of these models because they are not mutually independent. However, the set of partial molar volumes and thermal expansion constants given in BOTTINGAet al. (1982, 1983) are internally consistent and mutually compatible. We remain firmly of the opinion that our latest model is an improvement over previous attempts because it conforms to a much wider set of observations, it incorporates a larger set of melt components, it calculates density and thermal expansion more accurately, and it points the way to one possible method of accommodating a non-linear phenomenon into a nonlinear model.

Chlorine as a geobarometer tool: Application to the explosive eruptions of the Volcanic Campanian District (Mount Somma-Vesuvius, Phlegrean Fields, Ischia)

NASA Astrophysics Data System (ADS)

Balcone-Boissard, Hélène; Boudon, Georges; Zdanowicz, Géraldine; Orsi, Giovanni; Civetta, Lucia; Webster, Jim D.; Cioni, Raffaello; D'Antonio, Massimo

2016-04-01

One of the current stakes in modern volcanology is the definition of magma storage conditions which has direct implications on the eruptive style and thus on the associated risks and the management of likely related crisis. In alkaline differentiated magmas, chlorine (Cl), contrary to H2O, occurs as a minor volatile species but may be used as a geobarometer. Numerous experimental studies on Cl solubility have highlighted its saturation conditions in silicate melts. The NaCl-H2O system is characterized by immiscibility under wide ranges of pressure, temperature and NaCl content (< 200 MPa, < 1000°C). The addition of the silicate melt to the system does not rule out this property. These P-T conditions are very common for alkaline magmas evolving in shallow reservoirs, and they strongly affect the evolution of sin-eruptive magmatic melts and fluids. In alkali magmas, the Cl concentration in the exsolved fluid phase may increase with that of Cl in the silicate melt. Yet this system becomes strongly non-Henryan at high Cl concentration, depending on P-T conditions: the exsolved fluid phase unmixes to form a low-density, Cl-poor and H2O-rich vapour phase, and a dense hypersaline brine. In such a subcritical domain, as the composition of both vapour phase and brine is fixed, also the Cl concentration in the silicate melt is invariant, as expected from the Gibb's phase rule. The Cl buffer value will depend on the silicate melt composition, being higher in alkali-rich melts. In addition, we also underline the importance of considering the general HCOSClF system to well decipher pressure information from Cl buffering effect. As the equilibrium between the silicate melt and the fluid phase is generally inherited from conditions established in the reservoir rather than during magma ascent, Cl buffering effect can be evidenced through the analysis of the residual glass. Here we applied systematically this methodology to the explosive eruptions of the three threatening volcanoes of the Neapolitan area: Mount Somma-Vesuvius, Phlegrean Fields and Ischia. We have analysed the products of the representative explosive eruptions of each volcano, including Plinian, sub-Plinian and strombolian events. We have focussed our research on the earliest emitted, most evolved products of each eruption, likely representing the shallower, fluid-saturated portion of the reservoir. As the studied eruptions cover the entire eruptive history of each volcanic system, the results allow better constraining the evolution through time of the shallow plumbing system. We highlighted for Mount Somma - Vesuvius two magma ponding zones, at ~170-200 MPa and ~105-115 MPa, alternatively active in time. For Phlegrean Fields, we evidence a progressive deepening of the shallow reservoirs, from the Campanian Ignimbrite (30-50 MPa) to the Monte Nuovo eruption (115 MPa). Only one eruption was studied for Ischia, the Cretaio eruption, that shows a reservoir at 140 MPa. The results on pressure are in large agreement with literature. The Cl geobarometer may help scientists to define the reservoir dynamics through time and provide strong constraints on pre-eruptive conditions, of utmost importance for the interpretation of the monitoring data and the identification of precursory signals.

Low-δ13C carbonates in the Miocene basalt of the northern margin of the North China Craton: Implications for deep carbon recycling

NASA Astrophysics Data System (ADS)

Zhang, Huiting; Liu, Yongsheng; Hu, Zhaochu; Zong, Keqing; Chen, Haihong; Chen, Chunfei

2017-08-01

Three types of carbonates have been found in the Miocene basalt in the Dongbahao area (Inner Mongolia), including wide veins and veinlets of carbonate in basalt and carbonates in peridotite xenoliths. Except for the dolomitic zonation in the basalt, all of the carbonates are calcite. Despite their different appearances, they share almost identical geochemical characteristics of low LILE (low large ion lithophile element), HFSE (high field strength element), and REE (rare earth elements) contents (ΣREE = 0.51-137 ppm); negative Ce anomalies; and low Ce/Pb ratios (0.51-74.5). Moreover, they show high δ18OSMOW values (20.95-22.61‰) and 87Sr/86Sr ratios (0.7087 ± 0.0003 (1σ, n = 17)). These characteristics indicate a sedimentary precursor for these carbonates. However, the occurrence and petrographic characteristics imply an igneous origin for the carbonates rather than a hypergene process. Further, the trace element compositions of the silicate melt and carbonate melt in the calcite-dolomite-silicate zonations fall on the same variation lines in the plots of Y-Ho, La-Yb, Li-Pb and Ba-Cu. It is suggested that these melts could have evolved from one magma system or could have been equilibrated. Given the partition coefficients of REEs and alkali elements (Cs, Rb, and K) between the carbonate melt and silicate melt, it can be inferred that these melts could have been formed from a primary H2O-Si-bearing Mg-Ca-carbonate melt by an immiscibility process at 1-3 GPa. Considering the southward subduction of the Paleo-Asian ocean along the northern margin of the North China Craton (NCC), these carbonate melts could have been derived from the melting of subducted sedimentary carbonate rocks. Interestingly, these carbonates have quite depleted carbon isotopic compositions (δ13CPDB = -8.23‰ to -11.76‰) but moderate δ18OSMOW values, implying coupled H2O-CO2 degassing during subduction and/or recycling to the Earth's surface. Low-δ13CPBD carbonates appearing at the global scale may suggest an underestimated path of CO2 emission back to the atmosphere.

In-situ Pb isotope analysis of Fe-Ni-Cu sulphides by laser ablation multi-collector ICPMS: New insights into ore formation in the Sudbury impact melt sheet

NASA Astrophysics Data System (ADS)

Darling, J. R.; Storey, C. D.; Hawkesworth, C. J.; Lightfoot, P. C.

2012-12-01

Laser-ablation (LA) multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) is ideally suited to in situ determination of isotope ratios in sulphide minerals. Using samples of magmatic sulphide ore from the Sudbury impact structure, we test LA-MC-ICPMS analytical protocols that aim to meet a range of analytical challenges in the analysis of Pb isotopes. These include: potential matrix sensitive isotopic fractionation; interferences on Pb isotopes; low melting points of many sulphide minerals; the availability of standards. Magmatic sulphides of wide ranging mineralogy (pyrrhotite, pentlandite, chalcopyrite, pyrite and sphalerite) were analysed for Pb isotopic composition, using the silicate glass NIST SRM 610 as an external standard to correct for instrumental mass-fractionation. Despite matrix sensitive melting and re-deposition around ablation pits, several lines of evidence indicate that all analyses are accurate, within typical analytical uncertainties of 0.003-2% (2σ), and that the defined approach is insensitive to compositional diversity in sample matrix: (a) laser ablation and dissolution based measurements of sulphide powders are in agreement; (b) analyses from each sample define isochron ages within uncertainty of the known crystallization age (1850 Ma); (c) the results of sulphide measurements by laser ablation are consistent with age-corrected feldspar analyses from the same samples. The results have important implications for ore formation in Sudbury. The Pb isotope data regressions are consistent with age corrected feldspar analyses from each respective sample, which together with time integrated Th/U ratios that match whole rock values (3.1, 4.0 and 6.1 for the Worthington, Copper Cliff and Parkin Offset Dykes, respectively) indicate chemical equilibrium between the silicate and sulphide systems during ore formation. The sulphides within each respective sample have indistinguishable model initial Pb isotope ratios (207Pb/204Pbm), irrespective of mineralogy or texture, indicating a common origin for ores within each of three different Offset Dykes. Furthermore, variations between Offset Dykes (e.g., 207Pb/204Pbm = 15.514 ± 0.012, 15.399 ± 0.009 and 15.275 ± 0.003) show that the ores have differing crustal sources on previously unrecognized scales. Mass balance considerations, particularly for MgO, Ni and Cu, indicate that the spatial distribution of mafic target rocks played a significant role in controlling the mineralization potential in different parts of the melt sheet.

Transport properties of CO2-bearing MgSiO3 melt at mantle conditions

NASA Astrophysics Data System (ADS)

Ghosh, D. B.; Karki, B. B.

2017-12-01

Carbon dioxide, generally considered as the second most abundant volatile component in silicate magmas, is expected to significantly influence various melt properties. In particular, our knowledge about its dynamical effects is lacking over most of the Earth's mantle pressure regime. Here we report the first-principles molecular dynamics results on the transport properties of carbonated MgSiO3 liquid under the conditions of mantle relevance. They show that dissolved CO2 systematically enhances the diffusion rates of all elements and the associated electrical conductivity and lowers the melt viscosity on average by factors of 1.5 to 3 over the pressure range considered. They also predict anomalous dynamical behavior - increasing diffusivity and conductivity, and decreasing viscosity with compression in the low pressure regime. We attempt to link the predicted transport coefficients to the microsocopic structural changes that occur in response to pressure and temperature. This anomaly and the concomitant increase of pressure and temperature with depth together make these transport coefficients vary modestly over extended portions of the mantle regime. It is possible that the melt electrical conductivity at conditions corresponding to the 410 and 660 km seismic discontinuities is at a detectable level by electromagnetic sounding observation. Also, the low melt viscosity values 0.2-0.5 Pa s at these depths and near the core-mantle boundary may imply high mobility of possible melts in these regions.

Copper solubility in a basaltic melt and sulfide liquid/silicate melt partition coefficients of Cu and Fe

NASA Astrophysics Data System (ADS)

Ripley, Edward M.; Brophy, James G.; Li, Chusi

2002-09-01

The solubility of copper in a sulfur-saturated basaltic melt has been determined at 1245°C as a function of fO 2 and fS 2. Copper solubilities at log fO 2 values between -8 and -11 fall into two distinct populations as a function of fS 2. At log fS 2 values < -1.65, sulfide liquid that coexists with the basaltic glass quenches to sulfur-poor bornite solid solution. At log fS 2 values in excess of -1.65, the sulfide liquid quenches to a complex intergrowth of sulfur-rich bornite and intermediate solid solution. Copper solubilities in the low-fS 2 population range from 594 to 1550 ppm, whereas those in the high-fS 2 population range from 80 to 768 ppm. Sulfide liquid/silicate liquid partition coefficients (D) for Cu and Fe range from 480 to 1303 and 0.7 to 13.6, respectively. Metal-sulfur complexing in the silicate liquid is shown to be insignificant relative to metal-oxide complexing for Fe but permissible for Cu at high fS 2 values. On log D Fe (sulfide-silicate) and log D Cu (sulfide-silicate) vs. 1/2 (log fS 2 - log fO 2) diagrams, both fS 2 populations show distinct but parallel trends. The observation of two D values for any fS 2/fO 2 ratio indicates nonideal mixing of species involved in the exchange reaction. The two distinct trends observed for both Cu and Fe are thought to be due to variations in activity coefficient ratios (e.g., γ FeO/γ FeS and γ CuO 0.5/γ CuS 0.5). Results of the experiments suggest that accurate assessments of fS 2/fO 2 ratios are required for the successful numerical modeling of processes such as the partial melting of sulfide-bearing mantle and the crystallization of sulfide-bearing magmas, as well as the interpretation of sulfide mineralogical zoning. In addition, the experiments provide evidence for oxide or oxy-sulfide complexing for Cu in silicate magmas and suggest that the introduction of externally derived sulfur to mafic magma may be an important process for the formation of Cu-rich disseminated magmatic sulfide ore deposits.

First in-situ monitoring of CO2 delivery to the mantle followed by compression melting, using synchrotron generated X-ray diffraction.

NASA Astrophysics Data System (ADS)

Hammouda, Tahar; Chantel, Julien; Manthilake, Geeth; Guignard, Jérémy; Crichton, Wilson; Gaillard, Fabrice

2014-05-01

Melting of peridotite + CO2 upon compression has been directly monitored in situ, for the first time. We have combined high pressure experiments in the multianvil apparatus with synchrotron-generated X-ray diffraction, in order to monitor sample decarbonation upon heating, followed by melting upon compression. Experiments were performed in the model system CaO-MgO-SiO2+CO2, using dolomite and silicates contained in graphite capsules as starting material. Save Al, starting composition was aimed at reproducing peridotitic system. The sample was first compressed at room temperature, then heated. Decarbonation was observed at 2.2 GPa and 1100°C. After further heating to 1300°C, pressure was increased. Melting was observed at 2.7 GPa, while temperature was kept at 1300°C. All transformations were followed using X-ray diffraction. Starting with silicate + carbonate mixtures, we were thus able to keep CO2 fluid in the experimental sample at high P and T, up to the solidus. Concerning carbon recycling at subduction zones, it is known that CO2 is a non-wetting fluid in silicate aggregates. Therefore, any CO2 resulting from carbonate breakdown likely remains trapped at grain corners either in the subducted lithosphere or in the mantle wedge before eventually being trapped in mantle minerals as fluid inclusions, due to dynamic recrystallization. In this way, CO2 released from the slab may be spread laterally due to mantle convection. Entrainment to further depths by deep subduction or in convection cells induces CO2 introduction to depth wherein the solidus can be crossed, due to pressure increase. The solidus corresponds to the so-called carbonate ledge, beyond which carbonatitic melts are produced. Therefore, compression melting of CO2-bearing lithologies is a way to produce carbonatitic melts at depths corresponding to about 80 km. This mechanism is a viable explanation for the observed geophysical anomalies, such as those revealed by electrical conductivity measurements.

Ferrobasalt-rhyolite immiscibility in tholeiitic volcanic and plutonic series (Invited)

NASA Astrophysics Data System (ADS)

Charlier, B.; Namur, O.; Kamenetsky, V. S.; Grove, T. L.

2013-12-01

One atmosphere experiments show that silicate liquid immiscibility develops between Fe-rich and Si-rich melts below 1000-1020°C in compositionally diverse lavas that represent classical tholeiitic trends, such as Mull, Iceland, Snake River Plain and Sept Iles. Extreme iron enrichment along the evolution trend is not necessary; immiscibility also develops during iron depletion and silica enrichment after Fe-Ti oxide saturation. Natural liquid lines of descent for major tholeiitic series also approach or intersect the experimentally-defined compositional space of immiscibility. The importance of ferrobasalt-rhyolite unmixing in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts, and by unmixed melt inclusions in cumulus phases of major layered intrusions such as Sept Iles, Skaergaard and Sudbury. A clear case of liquid immiscibility is also recorded in intrusive tholeiitic gabbros from the Siberian Large Igneous Province and is evidenced by textures and compositions of millimeter-sized silicate melt pools trapped in native iron. An important implication of immiscibility in natural ferrobasaltic provinces is the development of a compositional gap characterized by the absence of intermediate compositions, a major feature observed in many tholeiitic provinces and referred to as the Daly gap. The compositions of experimental silica-rich immiscible melts coincide with those of natural rhyolites with high FeOtot and low Al2O3, which suggests a potential role for large-scale immiscibility in the petrogenesis of late-stage ferroan silicic melts. No evidence for the paired ferrobasaltic melt is observed in volcanic provinces, probably because of its uneruptable characteristics. Instead, Fe-Ti×P-rich gabbros crystallized at depth and are the cumulate products of immiscible Fe-rich melts in plutonic settings, a feature clearly evidenced in the Sept Iles intrusion. The production of immiscible Fe-Ti-Ca-P liquids has also important implications for the formation of some iron deposits associated with alkaline lavas.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solomatova, Natalia V.; Jackson, Jennifer M.; Sturhahn, Wolfgang

The physical properties of silicate melts within Earth's mantle affect the chemical and thermal evolution of its interior. Chemistry and coordination environments affect such properties. We have measured the hyperfine parameters of iron-bearing rhyolitic and basaltic glasses up to ~120 GPa and ~100 GPa, respectively, in a neon pressure medium using time domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high-spin Fe2+-like sites with distinct quadrupole splittings. Absence of detectable ferric iron was confirmed with optical absorption spectroscopy. The sites with relatively high and intermediate quadrupole splittings are likely a result ofmore » fivefold and sixfold coordination environments of ferrous iron that transition to higher coordination with increasing pressure. The ferrous site with a relatively low quadrupole splitting and isomer shift at low pressures may be related to a fourfold or a second fivefold ferrous iron site, which transitions to higher coordination in basaltic glass, but likely remains in low coordination in rhyolitic glass. These results indicate that iron experiences changes in its coordination environment with increasing pressure without undergoing a high-spin to low-spin transition. We compare our results to the hyperfine parameters of silicate glasses of different compositions. With the assumption that coordination environments in silicate glasses may serve as a good indicator for those in a melt, this study suggests that ferrous iron in chemically complex silicate melts likely exists in a high-spin state throughout most of Earth's mantle.« less

Battery components employing a silicate binder

DOEpatents

Delnick, Frank M [Albuquerque, NM; Reinhardt, Frederick W [Albuquerque, NM; Odinek, Judy G [Rio Rancho, NM

2011-05-24

A battery component structure employing inorganic-silicate binders. In some embodiments, casting or coating of components may be performed using aqueous slurries of silicates and electrode materials or separator materials.

Thermal evolution and core formation of planetesimals

NASA Astrophysics Data System (ADS)

Suwa, Taichi; Nagahara, Hiroko

2017-04-01

Planetesimals did not get an adequate thermal energy by accretion to form large scale magma ocean because of smaller radii, masses, gravity and accretion energy, however, there are various evidences for the presence of core in planetesimals: 4-Vesta has a core and non-magmatic iron meteorites were segregated metal in bodies that did not experience silicate melting. It has been pointed out that accretion time of planetesimals controls melting and differentiation, because short lived nuclides are plausible heat source. Other factors such as radiative cooling from the surface and thermal conductivity, would also affect thermal evolution of planetesimals. Furthermore, percolation of Fe-S melt through silicate matrix is controlled by the porosity and grain size of silicates and dihedral angle between the melt and silicates. Therefore, the interior structure of planetesimals should be considered by taking the accretion, growth, and thermal evolution of the interior simultaneously. We make a numerical simulation with a spherical 1D model on the basis of the model by Neuman, which is a non-stationary heat conduction equation. We specifically pay attention to the process at temperatures between eutectic temperature Fe-FeS (1213K) and silicate solidus (1425K) and the surface tension of the melt that governs percolation. The model contains three free parameters, formation time, accretion duration, and final size of the planetesimals. The results show that the interior structure can be divided to four types: Type A is undifferentiated, Type B is differentiated to core and mantle of which core was formed by Fe-S melt percolation, Type C is partially differentiated to FeS core and mantle, where mantle retains residual Fe metal, and Type D is differentiated to core and mantle by metal separation in silicate magma. Type A would correspond to the parent bodies of chondrites, and Type B (and Type C?) core would be the source of non-magmatic iron meteorites. Type D would be parent bodies for 4 Vesta and angrites. The conditions for the four types of planetesimals are throuly investigated as a function of the three parameters, accretion time, accreting duration, and palnetesimal size. We found that the planetesimal interior is strongly controlled by the formation time: planetesimals formed after 3 Ma after CAIs would be undifferentiated (Type A) regardless of the planetary size, whereas most of them formed within 1 Ma are Type D (differentiated bodies with magmatically formed core). Types B and C bodies are preferentially formed between 1 and 3 Ma after CAIs. Longer accretion duration tends to be resulted in formation of Types A, B and C. The present work predicts the planetesimal interior structure if we know the formation age with the isotopic measurements of samples and the size of the body, which would be a very powerful tool for future explorations of small bodies except for very small (< 20 km) bodies.

Diffusion of major and trace elements in natural silicate melts as a tool to investigate timescales in magma mixing

NASA Astrophysics Data System (ADS)

González-García, Diego; Zezza, Angela; Behrens, Harald; Vetere, Francesco; Petrelli, Maurizio; Morgavi, Daniele; Perugini, Diego

2016-04-01

New melt injection into a shallow magma chamber is regarded as one of the potential triggers for explosive volcanic eruptions. Chemical diffusion occurring between the two mixing melts is a time-dependent process, and thus has the potential to shed light on the timescales involved in magma mixing events leading to an eruption. In order to achieve this, a complete database of diffusion coefficients in natural melts is a necessary prerequisite. We have carried out a set of 12 diffusion couple experiments in order to determine diffusion coefficients (D) of major and trace elements in two natural silicate melts. Two end-members from the Vulcano island (Aeolian archipelago, Italy) have been chosen for the experiments: a shoshonite (Vulcanello lava platform) and a rhyolitic obsidian (Pietre Cotte lava flow, La Fossa cone). Glasses from each end-member with added water contents of 0 wt%, 1 wt% and 2 wt% were produced in an Internally Heated Pressure Vessel (IHPV). Two glass cylinders with similar water content but different base composition are inserted in Au-Pd capsules and experiments are run in the IHPV at 1200° C with pressure from 0.5 to 3 kbar. Experiment capsules are rapidly quenched and analyzed by FTIR, EPMA and LA-ICP-MS for H2O, major and trace elements, respectively, along 2 mm linear profiles extending across the interface. A Boltzmann-Matano approach is used to obtain concentration-dependent diffusivities. The obtained concentration-distance profiles are asymmetric and extend deeper into the shoshonite relative to the rhyolite, indicating that diffusion is slower in the latter. Results show that diffusivities are notably accelerated by the presence of H2O in the melt. Experiments performed by using water-free glass show diffusivities one order of magnitude lower compared to glasses containing up to 2 wt% H2O. The effect of pressure, in the investigated range, is negligible and falls within measurement error. Among major elements, Si and Ti are the slowest diffusing components, while Na is the fastest. Uphill diffusion minima are observed in Al, Na and some trace elements (Y, Nb, Pb). In contrast to other trace elements, light REE show prominent minima next to the interface between the two melts, with the minimum depth diminishing towards HREE.

A volatile-rich Earth's core inferred from melting temperature of core materials

NASA Astrophysics Data System (ADS)

Morard, G.; Andrault, D.; Antonangeli, D.; Nakajima, Y.; Auzende, A. L.; Boulard, E.; Clark, A. N.; Lord, O. T.; Cervera, S.; Siebert, J.; Garbarino, G.; Svitlyk, V.; Mezouar, M.

2016-12-01

Planetary cores are mainly constituted of iron and nickel, alloyed with lighter elements (Si, O, C, S or H). Understanding how these elements affect the physical and chemical properties of solid and liquid iron provides stringent constraints on the composition of the Earth's core. In particular, melting curves of iron alloys are key parameter to establish the temperature profile in the Earth's core, and to asses the potential occurrence of partial melting at the Core-Mantle Boundary. Core formation models based on metal-silicate equilibration suggest that Si and O are the major light element components1-4, while the abundance of other elements such as S, C and H is constrained by arguments based on their volatility during planetary accretion5,6. Each compositional model implies a specific thermal state for the core, due to the different effect that light elements have on the melting behaviour of Fe. We recently measured melting temperatures in Fe-C and Fe-O systems at high pressures, which complete the data sets available both for pure Fe7 and other binary alloys8. Compositional models with an O- and Si-rich outer core are suggested to be compatible with seismological constraints on density and sound velocity9. However, their crystallization temperatures of 3650-4050 K at the CMB pressure of 136 GPa are very close to, if not higher than the melting temperature of the silicate mantle and yet mantle melting above the CMB is not a ubiquitous feature. This observation requires significant amounts of volatile elements (S, C or H) in the outer core to further reduce the crystallisation temperature of the core alloy below that of the lower mantle. References 1. Wood, B. J., et al Nature 441, 825-833 (2006). 2. Siebert, J., et al Science 339, 1194-7 (2013). 3. Corgne, A., et al Earth Planet. Sc. Lett. 288, 108-114 (2009). 4. Fischer, R. a. et al. Geochim. Cosmochim. Acta 167, 177-194 (2015). 5. Dreibus, G. & Palme, H. Geochim. Cosmochim. Acta 60, 1125-1130 (1995). 6. McDonough, W. F. Treatise in Geochemistry 2, 547-568 (2003). 7. Anzellini, S., et al Science 340, 464-6 (2013). 8. Morard, G. et al. Phys. Chem. Miner. 38, 767-776 (2011). 9. Badro, J., et al Proc. Natl. Acad. Sci. U. S. A. 111, 7542-5 (2014).

The Garnet to Majorite Transformation in Mafic Compositions

NASA Technical Reports Server (NTRS)

Xirouchakis, D.; Draper, David S.; Agee, C. B.

2002-01-01

The garnet to majorite transformation in mafic compositions is controlled by bulk composition and the presence of silicate melt, clinopyroxene, and silicate perovskite as well as pressure. Thus, the use of empirical geobarometers based on garnet Si(4+) and/or [Al(3+) +/- Cr(3+)] (p.f.u) seems unjustified. Additional information is contained in the original extended abstract.

Composition, Temperature, and Pressure Dependence of the Phonon (Thermal) Conductivity of Silicate Geoliquids

NASA Astrophysics Data System (ADS)

Tikunoff, Dane Michael

The study of geoliquids and their transport properties is a burgeoning field that sheds light on many critical geological problems. One such property, the thermal conductivity, measures the heat conduction capacity of a material and plays an important role in mantle and crust dynamics. Previous research has suggested that an increased insulation factor in rocks of the crust, regulated by relatively small values of the thermal conductivity, promotes anatexis and alleviates radiogenic heating requirements for the inducement of dehydration-triggered partial melting (Whittington et al., 2009). At greater depths, the proposed existence of melt patches along and immediately above the Core-Mantle Boundary (CMB) at ~2900 km depth could explain the discrete rather than graduated thermal gradient seen across the CMB (Murakami and Bass, 2011). This thesis describes the use of Molecular Dynamics (MD) simulations to compute thermal conductivity for three liquid silicates: CaMgSi2O6, NaAlSi3 O8 and MgSi2O4. The motivation for this study was to examine the temperature, pressure and compositional dependencies of thermal conductivity approximating conditions in the upper mantle (0-30 GPa, 2000-4500 K) for a few end member geosilicate liquids of natural importance. Results at low pressure and temperature show good agreement with recent laboratory measurements on CaMgSi2O6 and NaAlSi3O8 suggesting that MD simulation can provide realistic values at elevated pressure and temperature, conditions not readily accessible without great expense and time in the laboratory. For example, simulation results for molten diopside at 1763+/-13 K and 0.36+/-0.017 GPa provide a thermal conductivity value of k=1.186+/-0.019 W/m K while laser-flash data from Hofmeister et al. (2009) provides a value of k=1.178 +/-0.06 W/m K, agreement to within a percent. Further, a positive correlation between atomic structure and thermal conductivity is confirmed. At low pressure, the polymeric liquid NaAlSi3O8, in which each oxygen atom is surrounded by two nearest neighbors of either Si or Al, is expected to possess a longer phonon mean free path, and thus higher conductivity, than the less polymerized liquid CaMgSi2O6, in which each oxygen atom, on average, is surrounded by only 4/3 nearest neighbors of Si. Simulation results for diopside melt at 2059+/-12 K and 0.04+/-0.14 GPa and albite melt at 2090+/-20 K and 0.20+/-0.23 GPa give values of k=1.143+/-0.004 W/m K and k=1.498+/-0.147 W/m K, respectively. Thus, this expectation based on empirical results has been faithfully captured by MD simulation. A modified Arrhenian expression was found to fit all liquids over the temperature and pressure range of the simulations (2000-4500 K and 0-30 GPa) reasonably well (correlation coefficient R2 ≈ 0.9). Activation energies are around 20 kJ/mol and activation volume is of order a few cm3/mol. A good correlation between the coordination numbers (CN) of Ca, Mg, Na, Al and Si around oxygen and by oxygen around the cations and thermal conductivity may be used semi-quantitatively to predict thermal conductivity in multi-component silicate liquids.

Effusive silicic volcanism in the Paraná Magmatic Province, South Brazil: Evidence for locally-fed lava flows and domes from detailed field work

NASA Astrophysics Data System (ADS)

Polo, L. A.; Janasi, V. A.; Giordano, D.; Lima, E. F.; Cañon-Tapia, E.; Roverato, M.

2018-04-01

Lava flows and dome complexes of silicic composition were identified in the Lower Cretaceous Paraná Magmatic Province (PMP) at Rio Grande do Sul state, southern Brazil. Detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments, likely representing the fissural systems that fed the three Palmas-type silicic units. Different structures indicative of effusive emplacement (lava domes, lobated flows, sheet flows and autobreccias) are very common in the study area, and are probably also more abundant than previously thought in whole PMP silicic magmatism. In fact, effusive deposits seem predominant in the three distinct silicic units identified in the area, since no remnants of pyroclastic components have been identified. The vitreous dacites that make up the upper flows of the basaltic andesite to dacite Barros Cassal sequence are clearly effusive, as indicated by their occurrence as thin sheet flows. The much thicker early Caxias do Sul dacites occur mostly as lava flow lobes and pancake-like, of low to moderate viscosity, and lava domes. The younger, high SiO2 Santa Maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion, as lobated flows formed by vesicle-rich obsidian. In spite of higher viscosities relative to the previous units ( 106 Pa·s), it is probable that the very low H2O contents 1 wt% of these rhyolite melts, associated with high discharge rates, resulted in an effusive nature in most to this unit.

A multi-species exchange model for fully fluctuating polymer field theory simulations.

PubMed

Düchs, Dominik; Delaney, Kris T; Fredrickson, Glenn H

2014-11-07

Field-theoretic models have been used extensively to study the phase behavior of inhomogeneous polymer melts and solutions, both in self-consistent mean-field calculations and in numerical simulations of the full theory capturing composition fluctuations. The models commonly used can be grouped into two categories, namely, species models and exchange models. Species models involve integrations of functionals that explicitly depend on fields originating both from species density operators and their conjugate chemical potential fields. In contrast, exchange models retain only linear combinations of the chemical potential fields. In the two-component case, development of exchange models has been instrumental in enabling stable complex Langevin (CL) simulations of the full complex-valued theory. No comparable stable CL approach has yet been established for field theories of the species type. Here, we introduce an extension of the exchange model to an arbitrary number of components, namely, the multi-species exchange (MSE) model, which greatly expands the classes of soft material systems that can be accessed by the complex Langevin simulation technique. We demonstrate the stability and accuracy of the MSE-CL sampling approach using numerical simulations of triblock and tetrablock terpolymer melts, and tetrablock quaterpolymer melts. This method should enable studies of a wide range of fluctuation phenomena in multiblock/multi-species polymer blends and composites.

Oxygen production by electrolysis of molten lunar regolith

NASA Technical Reports Server (NTRS)

Haskin, Larry A.

1990-01-01

The goal of this study was threefold. First, the theoretical energy requirements of the process were to be defined. This includes studies of the relevant oxidation-reduction reactions in the melt, their kinetics and energies of reaction, and experimental determination of production efficiencies and melt resistivities as functions of melt composition and applied potential. Second, the product(s) of silicate electrolysis were to be characterized. This includes: (1) evaluating the phase relationships in the systems SiO2-TiO2-Al2O3-MgO-FeO-CaO and Fe-Si; (2) estimating the compositions of the metal products as a function of applied potential and feedstock composition based on phase equilibria in the Fe-Si system and free energy values for SiO2 and FeO reported in the literature; (3) definition of compositions of products in actual experiments; and (4) definition of the form the product takes (whether phases separate or remain fixed, whether crystals settle or float in the remaining melt, and how large crystals form). Third, materials for these highly corrosive high-temperature silicate melts were to be identified. This includes identifing materials that may be either inert or thermodynamically stable in these melts, and experimental testing of the materials to confirm that they do not deteriorate. The results are discussed within this framework.

Silicate Inclusions in the Kodaikanal IIE Iron Meteorite

NASA Technical Reports Server (NTRS)

Kurat, G.; Varela, M. E.; Zinner, E.

2005-01-01

Silicate inclusions in iron meteorites display an astonishing chemical and mineralogical variety, ranging from chondritic to highly fractionated, silica- and alkali-rich assemblages. In spite of this, their origin is commonly considered to be a simple one: mixing of silicates, fractionated or unfractionated, with metal. The latter had to be liquid in order to accommodate the former in a pore-free way which all models accomplish by assuming shock melting. II-E iron meteorites are particularly interesting because they contain an exotic zoo of silicate inclusions, including some chemically strongly fractionated ones. They also pose a formidable conundrum: young silicates are enclosed by very old metal. This and many other incompatibilities between models and reality forced the formulation of an alternative genetic model for irons. Here we present preliminary findings in our study of Kodaikanal silicate inclusions.

The Effect of fO2 on Partition Coefficients of U and Th between Garnet and Silicate Melt

NASA Astrophysics Data System (ADS)

Huang, F.; He, Z.; Schmidt, M. W.; Li, Q.

2014-12-01

Garnet is one of the most important minerals controlling partitioning of U and Th in the upper mantle. U is redox sensitive, while Th is tetra-valent at redox conditions of the silicate Earth. U-series disequilibria have provided a unique tool to constrain the time-scales and processes of magmatism at convergent margins. Variation of garnet/meltDU/Th with fO2 is critical to understand U-series disequilibria in arc lavas. However, there is still no systematic experimental study about the effect of fO2 on partitioning of U and Th between garnet and melt. Here we present experiments on partitioning of U, Th, Zr, Hf, Nb, Ta, and REE between garnet and silicate melts at various fO2. The starting material was hydrous haplo-basalt. The piston cylinder experiments were performed with Pt double capsules with C-CO, MnO-Mn3O4 (MM), and hematite-magnetite (HM) buffers at 3 GPa and 1185-1230 oC. The experiments produced garnets with diameters > 50μm and quenched melt. Major elements were measured by EMPA at ETH Zurich. Trace elements were determined using LA-ICP-MS at Northwestern University (Xi'an, China) and SIMS (Cameca1280 at the Institute of Geology and Geophysics, Beijing, China), producing consistent partition coefficient data for U and Th. With fO2 increasing from CCO to MM and HM, garnet/meltDU decreases from 0.041 to 0.005, while garnet/meltDTh ranges from 0.003 to 0.007 without correlation with fO2. Notably, garnet/meltDTh/U increases from 0.136 at CCO to 0.41 at HM. Our results indicate that U is still more compatible than Th in garnet even at the highest fO2 considered for the subarc mantle wedge (~NNO). Therefore, we predict that if garnet is the dominant phase controlling U-Th partitioning during melting of the mantle wedge, melts would still have 230Th excess over 238U. This explains why most young continental arc lavas have 230Th excess. If clinopyroxene is the dominant residual phase during mantle melting, U could be more incompatible than Th at high fO2 because increasing fO2 can increase clinopyroxene/meltDTh/U by more than two magnitudes (Lundstrom et al. 1994). In this case, in-growth melting of the mantle can produce 238U excess over 230Th observed in the oceanic arc lavas.

A Low O/Si Ratio on the Surface of Mercury: Evidence for Silicon Smelting?

NASA Astrophysics Data System (ADS)

McCubbin, Francis M.; Vander Kaaden, Kathleen E.; Peplowski, Patrick N.; Bell, Aaron S.; Nittler, Larry R.; Boyce, Jeremy W.; Evans, Larry G.; Keller, Lindsay P.; Elardo, Stephen M.; McCoy, Timothy J.

2017-10-01

Data from the Gamma-Ray Spectrometer (GRS) that flew on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft indicate that the O/Si weight ratio of Mercury's surface is 1.2 ± 0.1. This value is lower than any other celestial surface that has been measured by GRS and suggests that 12-20% of the surface materials on Mercury are composed of Si-rich, Si-Fe alloys. The origin of the metal is best explained by a combination of space weathering and graphite-induced smelting. The smelting process would have been facilitated by interaction of graphite with boninitic and komatiitic parental liquids. Graphite entrained at depth would have reacted with FeO components dissolved in silicate melt, resulting in the production of up to 0.4-0.9 wt % CO from the reduction of FeO to Fe0—CO production that could have facilitated explosive volcanic processes on Mercury. Once the graphite-entrained magmas erupted, the tenuous atmosphere on Mercury prevented the buildup of CO over the lavas. The partial pressure of CO would have been sufficiently low to facilitate reaction between graphite and SiO2 components in silicate melts to produce CO and metallic Si. Although exotic, Si-rich metal as a primary smelting product is hypothesized on Mercury for three primary reasons: (1) low FeO abundances of parental magmas, (2) elevated abundances of graphite in the crust and regolith, and (3) the presence of only a tenuous atmosphere at the surface of the planet within the 3.5-4.1 Ga timespan over which the planet was resurfaced through volcanic processes.

How Does Enceladus do it?

NASA Astrophysics Data System (ADS)

Stevenson, D. J.

2006-12-01

Tidal heating is surely central to understanding the remarkable observations of Enceladus (Porco et al, 2006; Spencer et al, 2006) because: (a) It can set this body apart from others of similar or larger radius and composition; (b) It can break symmetry more strongly than mere thermal convection; (c) It introduces a complex temporal aspect to the response ;(d) It allows for the possibility of a non-monotonic history on longer timescales. In a "global" (and inadequate) view of tidal heating, the imaginary part of the Love number for Enceladus can vary by as much a six orders of magnitude depending on assumptions made, but localized heating may matter more (cf. the great Bolivian earthquake; Kanamori et al Science Vol. 279. 839 842 , 1998; or a model of tidal heating that involves lubricated blocks). The North-South asymmetry is not then puzzling. A full understanding also requires consideration of radiogenic heating (to "prime the pump") and composition. Ammonia may be good for getting things started (because it allows onset of melting) but might be irrelevant or even undesirable for how venting works now; carbon dioxide (or some other relatively insoluble component) may be irrelevant at first but important now. The tidal heating and energy budget does necessarily implicate the silicate component (except in the context of particular choices of ice rheology; something that we clearly do not know well enough). Any ongoing role of the silicates may perhaps be the chemistry question: Is there anything in the composition of expelled material that demands present day temperatures well in excess of the melting point of water? This talk may not answer the questions (especially the title!), but it may provide a framework for assessing the merits of different alternatives.

Molten salt corrosion of SiC: Pitting mechanism

NASA Technical Reports Server (NTRS)

Jacobson, N. S.; Smialek, J. L.

1985-01-01

Thin films of Na2SO4 and Na2CO3 at 1000 C lead to severe pitting of sintered alpha-SiC. These pits are important as they cause a strength reduction in this material. The growth of product layers is related to pit formation for the Na2CO3 case. The early reaction stages involve repeated oxidation and dissolution to form sodium silicate. This results in severe grain boundary attack. After this a porous silica layer forms between the sodium silicate melt and the SiC. The pores in this layer appear to act as paths for the melt to reach the SiC and create larger pits.

Effect of water on the composition of partial melts of greenstone and amphibolite

NASA Technical Reports Server (NTRS)

Beard, James S.; Lofgren, Gary E.

1989-01-01

Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich, anhydrous restites, and have compositions like island arc tonalites. In contrast, water-saturated melting at water pressures of 3 kilobars yields strongly peraluminous, low iron melts that coexist with an amphibole-bearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of pressures in the crust of island arcs is a plausible mechanism for the petrogenesis of islands arc tonalite, whereas water-saturated melting at pressure of 3 kilobars and above is not.

Assessing the Behavior of Typically Lithophile Elements Under Highly Reducing Conditions Relevant to the Planet Mercury

NASA Astrophysics Data System (ADS)

Rowland, R. L., II; Vander Kaaden, K. E.; McCubbin, F. M.; Danielson, L. R.

2017-12-01

With the data returned from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, there are now numerous constraints on the physical and chemical properties of Mercury, including its surface composition. The high S and low FeO contents observed from MESSENGER suggest a low oxygen fugacity of the present materials on the planet's surface. Most of our understanding of elemental partitioning behavior comes from observations made on terrestrial rocks, but Mercury's oxygen fugacity is far outside the conditions of those samples, estimated at approximately 3-7 log units below the Iron-Wüstite (IW) oxygen buffer, several orders of magnitude more reducing than other terrestrial bodies we have data from. With limited oxygen available, lithophile elements may instead exhibit chalcophile, halophile, or siderophile behaviors. Furthermore, very few natural samples of rocks that formed under reducing conditions (e.g., enstatite chondrites, achondrites, aubrites) are available in our collections for examination of this change in geochemical affinity. Our goal is to determine the elemental partitioning behavior of typically lithophile elements at lower oxygen fugacity as a function of temperature and pressure. Experiments were conducted at 1 GPa in a 13 mm QUICKpress piston cylinder and at 4 GPa in an 880-ton multi-anvil press, at temperatures up to 1850°C. The composition of starting materials for the experiments were designed so the final run products contained metal, silicate melt, and sulfide melt phases. Oxygen fugacity was controlled in the experiments by adding silicon metal to the samples, in order to utilize the Si-SiO2 buffer, which is 5 log units more reducing than the IW buffer at our temperatures of interest. The target silicate melt composition was diopside (CaMgSi2O6) because measured surface compositions indicate partial melting of a pyroxene-rich mantle. The results of our experiments will aid in our understanding of the fate of elements during the differentiation and thermal evolution of Mercury and other highly reducing planetary bodies.

The Diversity and Evolution of Different type Granitoids in Eastern Dharwar Craton: Evidence from "Arc-Plume" Collision in Neoarchaean

NASA Astrophysics Data System (ADS)

Nandy, J.; Dey, S.

2017-12-01

Neoarchaean crustal growth, role of plate tectonics and potential secular changes is still disoriented in Dharwar craton. To provide constraints on these questions, geochronological and geochemical data are presented on the unstudied granitoids associated with Kadiri greenstone belt, eastern Dharwar craton. Five diverse type of granitoids suites are identified in that area. Field setting, petrography, whole rock geochemistry study with Sm-Nd isotopes and zircon dates help to identify their source and petrogenesis. Along the eastern margin of the Kadiri belt a sanukitoid-like granitoid body is exposed which was probably derived from a metasomatised mantle wedge above a subduction zone followed by some older crustal contamination. Along the western margin transitional TTG is exposed displaying an intrusive relation with Kadiri dacite-rhyolite. This suite is interpreted to be derived from a mafic source with some enriched crustal component. Further east and west vast area is occupied highly silicic biotite monzogranite which is enriched in LILE, high K2O/Na2O. These granitoids are product of intracrustal shallow melting. At the south-eastern tip of the Kadiri belt occurs a well-foliated and banded transitional TTG which was probably derived from melting of mafic source with some contribution of felsic crustal material. At the north-eastern tip of the belt a highly silicic ferroan granitoid is exposed. Geochemical characteristics indicate that it is A-type granite, produced from shallow melting of a felsic crustal source. The basalt in greenstone belt is generated in oceanic plateau setting and granitoids in arc setting in different time. A tectonic scenario envisaging collision between an arc and oceanic plateau followed by repeated slab break-off and crustal recycling is proposed to explain the evolution of the terrain.

Improved Cook-off Modeling of Multi-component Cast Explosives

NASA Astrophysics Data System (ADS)

Nichols, Albert

2017-06-01

In order to understand the hazards associated with energetic materials, it is important to understand their behavior in adverse thermal environments. These processes have been relatively well understood for solid explosives, however, the same cannot be said for multi-component melt-cast explosives. Here we describe the continued development of ALE3D, a coupled thermal/chemical/mechanical code, to improve its description of fluid explosives. The improved physics models include: 1) Chemical potential driven species segregation. This model allows us to model the complex flow fields associated with the melting and decomposing Comp-B, where the denser RDX tends to settle and the decomposing gasses rise, 2) Automatically scaled stream-wise diffusion model for thermal, species, and momentum diffusion. These models add sufficient numerical diffusion in the direction of flow to maintain numerical stability when the system is under resolved, as occurs for large systems. And 3) a slurry viscosity model, required to properly define the flow characteristics of the multi-component fluidized system. These models will be demonstrated on a simple Comp-B system. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Metal-silicate partitioning of U: Implications for the heat budget of the core and evidence for reduced U in the mantle

NASA Astrophysics Data System (ADS)

Chidester, Bethany A.; Rahman, Zia; Righter, Kevin; Campbell, Andrew J.

2017-02-01

Earth's core might require an internal heat source, such as radioactive decay, to explain the presence of the magnetic field through geologic time. To investigate whether U would be an important heat source in the core, we performed metal-silicate partitioning experiments of U at P-T (up to 67 GPa and 5400 K) conditions more relevant to a magma ocean scenario than has previously been reported. This study finds the partitioning of U to be strongly dependent on ƒO2, temperature, the S content of the metal and the SiO2 content of the silicate during core-mantle differentiation. Differentiation at mean conditions of 42-58 GPa and 3900-4200 K would put 1.4-3.5 ppb U (2-8 wt% S) in the core, amounting to a maximum of 1.4 (+1/-0.7) TW of heat 4.5 billion years ago. This is likely not enough heat to mitigate early widespread mantle melting. It was also found that U likely exists in the 2+ oxidation state in silicate melts in the deep Earth, a state which has not been previously observed in nature.

Calcio-carbonatite melts and metasomatism in the mantle beneath Mt. Vulture (Southern Italy)

NASA Astrophysics Data System (ADS)

Rosatelli, Gianluigi; Wall, Frances; Stoppa, Francesco

2007-12-01

At Mt. Vulture volcano (Basilicata, Italy) calcite globules (5-150 μm) are hosted by silicate glass pools or veins cross-cutting amphibole-bearing, or more common spinel-bearing mantle xenoliths and xenocrysts. The carbonate globules are rounded or elongated and are composed of a mosaic of 2-20 μm crystals, with varying optical orientation. These features are consistent with formation from a quenched calciocarbonatite melt. Where in contact with carbonate amphibole has reacted to form fassaitic pyroxene. Some of these globules contain liquid/gaseous CO 2 bubbles and sulphide inclusions, and are pierced by quench microphenocrysts of silicate phases. The carbonate composition varies from calcite to Mg-calcite (3.8-5.0 wt.% MgO) both within the carbonate globules and from globule to globule. Trace element contents of the carbonate, determined by LAICPMS, are similar to those of carbonatites worldwide including ΣREE up to 123 ppm. The Sr-Nd isotope ratios of the xenolith carbonate are similar to the extrusive carbonatite and silicate rocks of Mt. Vulture testifying to derivation from the same mantle source. Formation of immiscibile silicate-carbonatite liquids within mantle xenoliths occurred via disequilibrium immiscibility during their exhumation.

Chicxulub ejecta at the Cretaceous-Paleogene (K-P) boundary in Northeastern Mexico

NASA Astrophysics Data System (ADS)

Schulte, Peter; Kontny, Agnes

2005-04-01

The combined petrological and rock magnetic study of the Cretaceous-Paleogene (K-P) boundary in northeastern Mexico revealed compositionally and texturally complex Chicxulub ejecta deposits. The predominant silicic ejecta components are Fe-Mg-rich chlorite and Si-Al-K-rich glass spherules with carbonate inclusions and schlieren. Besides these silica phases, the most prominent ejecta component is carbonate. Carbonate occurs as lithic clasts, accretionary lapilli, melt globules (often with quench textures), and as microspar. The composition of the spherules provides evidence for a range of target rocks of mafic to intermediate composition, presumably situated in the northwestern sector of the Chicxulub impact structure. The abundance of carbonate ejecta suggests that this area received ejecta mainly from shallow, carbonate-rich lithologies. Rare µm-sized metallic and sulfidic Ni-Co-rich inclusions in the spherules indicate a possible contamination by meteoritic material. This complex composition underlines the similarities of ejecta in NE Mexico to Chicxulub ejecta from K-P sections worldwide. Although the ejecta display a great variability, the magnetic susceptibility, remanence, and hysteresis properties of the ejecta deposits are fairly homogeneous, with dominantly paramagnetic susceptibilities and a weak ferromagnetic contribution from hematite and goethite. The absence of spinels and the ubiquitous presence of hematite and goethite points to high oxygen fugacity during the impact process. The microfacies and internal texture of the ejecta deposits show welding and fusing of components, as well as evidence for liquid immiscibility between silicic and carbonate melts. No evidence for binary mixing of ejecta phases was found. Therefore, Chicxulub ejecta in NE Mexico probably derived from less energetic parts of the ejecta curtain. However, welding features of ejecta particles and enclosed marl clasts and/or benthic foraminifera from a siliciclastic environment suggest interaction of the - still hot - ! ejecta curtain with northern Mexican shelf sediments. In addition, an initial ground surge-like ejecta-dispersion mode seems possible.

Coordinated Hard Sphere Mixture (CHaSM): A simplified model for oxide and silicate melts at mantle pressures and temperatures

NASA Astrophysics Data System (ADS)

Wolf, Aaron S.; Asimow, Paul D.; Stevenson, David J.

2015-08-01

We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme temperatures and pressures, including deep mantle conditions like those in the early Earth magma ocean. The Coordinated Hard Sphere Mixture (CHaSM) is based on an extension of the hard sphere mixture model, accounting for the range of coordination states available to each cation in the liquid. By utilizing approximate analytic expressions for the hard sphere model, this method is capable of predicting complex liquid structure and thermodynamics while remaining computationally efficient, requiring only minutes of calculation time on standard desktop computers. This modeling framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide range of pressures and temperatures. We find that the typical coordination number of the Mg cation evolves continuously upward from 5.25 at 0 GPa to 8.5 at 250 GPa. The results produced by CHaSM are evaluated by comparison with predictions from published first-principles molecular dynamics calculations, indicating that CHaSM is accurately capturing the dominant physics controlling the behavior of oxide melts at high pressure. Finally, we present a simple quantitative model to explain the universality of the increasing Grüneisen parameter trend for liquids, which directly reflects their progressive evolution toward more compact solid-like structures upon compression. This general behavior is opposite that of solid materials, and produces steep adiabatic thermal profiles for silicate melts, thus playing a crucial role in magma ocean evolution.

Kinetic D/H fractionation during hydration and dehydration of silicate glasses, melts and nominally anhydrous minerals

NASA Astrophysics Data System (ADS)

Roskosz, M.; Deloule, E.; Ingrin, J.; Depecker, C.; Laporte, D.; Merkel, S.; Remusat, L.; Leroux, H.

2018-07-01

The distribution of hydrogen isotopes during diffusion-driven aqueous processes in silicate glasses, melts and crystals was investigated. Hydration/dehydration experiments were performed on silica glasses at 1000 °C and 1 bar total pressure. Dehydration triggered by decompression-driven bubble nucleation and growth was performed on rhyolitic melts at 800 °C and a few hundred MPa. Hydrogen extraction from a nominally anhydrous mineral (grossular) single crystal was carried out at 800 °C and ambient pressure. After these three series of experiments, pronounced water (sensu lato) concentration profiles were observed in all recovered samples. In the grossular single-crystal, a large spatial variation in H isotopes (δD variation > 550‰) was measured across the sample. This isotopic distribution correlates with the hydrogen extraction profile. The fit to the data suggests an extreme decoupling between hydrogen and deuterium diffusion coefficients (DH and DD respectively), akin to the decoupling expected in a dilute ideal gas (DH/DD ≈ 1.41). Conversely, no measurable spatially- and time-resolved isotopic variations were measured in silicate glasses and melts. This contrasted behavior of hydrogen isotopes likely stands in the different water speciation and solution mechanisms in the three different materials. Glasses and melts contain essentially hydroxyl and molecular water groups but the mobile species is molecular water in both cases. Protonated defects make up most of the water accommodated in grossular and other nominally anhydrous minerals (NAM). These defects are also the mobile species that diffuse against polarons. These results are crucial to accurately model the degassing behavior of terrestrial and lunar magmas and to derive the initial D/H of water trapped in fluid inclusions commonly analyzed in mantle NAMs, which suffered complex geological histories.

Mineralogy, Reflectance Spectra, and Physical Properties of the Chelyabinsk LL5 Chondrite - Insight Into Shock Induced Changes in Asteroid Regoliths

NASA Astrophysics Data System (ADS)

Gritsevich, Maria; Muinonen, Karri; Kohout, Tomas; Grokhovsky, Victor; Yakovlev, Grigoriy; Haloda, Jakub; Halodova, Patricie; Michallik, Radoslaw; Penttilä, Antti

On February 15, 2013, at 9:22 am, an exceptionally bright and long duration fireball was observed by many eyewitnesses in the Chelyabinsk region, Russia. Two days later the first fragments of the Chelyabinsk meteorite were reported to be found in the area, located approximately 40 km south of Chelyabinsk. We have examined a large number of the recovered Chelyabinsk meteorite fragments. Three lithologies, the light-colored, dark-colored, and impact melt, were found within the recovered meteorites. The light colored lithology is a LL5 ordinary chondrite (Fa 28, Fs 23) shocked to S4 level. The dark colored lithology is of identical LL5 composition (Fa 28, Fs 23). However, it is shocked to higher level (shock-darkened) with fine grained metal and sulfide-rich melt forming a dense network of fine veins impregnating the inter- and intra-granular pore space within crushed silicate grains. The impact melt lithology is a whole-rock melt derived from the same LL5 source material and is present within the light-colored and dark-colored lithology as inter-granular veins. The measured bulk and grain densities and the porosity closely resemble other LL chondrites. Based on the magnetic susceptibility, the Chelyabinsk meteorites are richer in metallic iron as compared to database of other LL chondrites. All three Chelyabinsk lithologies are of identical LL5 composition and origin. Both impact melting and shock darkening cause a decrease in reflectance and a suppression of the silicate absorption bands in the reflectance spectra. Such spectral changes are similar to the space weathering effects observed on asteroids. However, space weathering of chondritic materials is often accompanied with a significant spectral slope change (reddening). In our case, only negligible to minor change in the spectral slope is observed. Thus, it is possible that some dark asteroids with invisible silicate absorption bands may be composed of relatively fresh shock-darkened chondritic material. The main spectral difference of chondritic asteroid surfaces dominated by impact melt, shock darkening, or space weathering, is a significant spectral slope change in the latter case. Thus, shock does not have significant effect on meteorite properties, but causes spectral darkening and suppression of silicate absorption bands.

Generation of volcanic ash: a textural study of ash produced in various laboratory experiments

NASA Astrophysics Data System (ADS)

Lavallée, Yan; Kueppers, Ulrich; Dingwell, Donald B.

2010-05-01

In volcanology, ash is commonly understood as a fragment of a bubble wall that gets disrupted during explosive eruptions. Most volcanic ashes are indeed the product of explosive eruptions, but the true definition is however that of a particle size being inferior to 2 mm. The term does not hold any information about its genesis. During fragmentation, particles of all sizes in various amounts are generated. In nature, fragmentation is a brittle response of the material (whether a rock or magma) caused by changes in 1) strain rate and 2) temperature, and/or 3) chemical composition. Here we used different experimental techniques to produce ash and study their physical characteristics. The effects of strain rate were investigated by deforming volcanic rocks and magma (pure silicate melt and crystal-bearing magma) at different temperatures and stresses in a uniaxial compression apparatus. Failure of pure silicate melts is spontaneous and generates more ash particles than fragmentation of crystal-bearing melts. In the latter, the abundance of generated ash correlates positively with the strain rate. We complemented this investigation with a study of particles generated during rapid decompression of porous rocks, using a fragmentation apparatus. Products of decompression experiments at different initial applied pore pressure show that the amount of ash generated by bubble burst increase with the initial applied pressure and the open porosity. The effects of temperature were investigated by dropping pure silicate melts and crystal-bearing magma at 900 and 1100°C in water at room temperature. Quenching of the material is accompanied by rapid contraction and near instantaneous fragmentation. Pure silicate melts respond more violently to the interaction with water and completely fragmented into small particles, including a variety of ash morphologies and surface textures. Crystal-bearing magmas however fragmented only very partially when in contact with water and produced a few ash particles (< 0.05 g). The morphology and surface textures of the experimentally generated ash particles were imaged through scanning electron microscopy, and the observations will be discussed in terms of fragmentation processes.

The Effect of Pressure on Iron Speciation in Silicate Melts at a Fixed Oxygen Fugacity: The Possibility of a Redox Profile Through a Terrestrial Magma Ocean

NASA Astrophysics Data System (ADS)

Armstrong, K.; Frost, D. J.; McCammon, C. A.; Rubie, D. C.; Boffa Ballaran, T.

2017-12-01

As terrestrial planets accreted, mantle silicates equilibrated with core-forming metallic iron, which would have imposed a mantle oxygen fugacity below the iron-wüstite oxygen buffer. Throughout Earth's history, however, the oxygen fugacity of at least the accessible portions of the upper mantle has been 4-5 orders of magnitude higher. The process that caused the rapid increase in the redox state of the mantle soon after core formation is unclear. Here we test the possibility that pressure stabilises ferric iron in silicate melts, as has been observed in silicate minerals. A deep magma ocean, which would have likely existed towards the end of accretion, could then develop a gradient in oxygen fugacity for a fixed ferric-ferrous ratio as a result of pressure. We have equilibrated an andesitic melt with a Ru-RuO2 buffer in a multianvil press between 5 and 24 GPa. Further experiments were performed on the same melt in equilibrium with iron metal. The recovered melts were then analysed using Mössbauer spectroscopy to determine the ferric/ferrous ratio. The results show that for the Ru-RuO2 buffer at lower pressures, the ferric iron content decreases with pressure, due to a positive volume change of the reaction FeO + 1/4O2 = FeO1.5. Ferric iron content also appears to be sensitive to water content at lower pressures. However, above 15 GPa this trend apparently reverses and the ferric iron content increases with pressure. This reversal in pressure dependence would drive the oxygen fugacity of a deep magma ocean with a fixed ferric/ferrous ratio down with increasing depth. This would create a redox gradient, where the magma ocean could potentially be in equilibrium with metallic iron at its base but more oxidised in its shallower regions. Crystallisation of this magma ocean could render an upper mantle oxygen fugacity similar to that in the Earth's accessible mantle today.

Nitrogen solubility in the deep mantle and the origin of Earth's primordial nitrogen budget

NASA Astrophysics Data System (ADS)

Yoshioka, Takahiro; Wiedenbeck, Michael; Shcheka, Svyatoslav; Keppler, Hans

2018-04-01

The solubility of nitrogen in the major minerals of the Earth's transition zone and lower mantle (wadsleyite, ringwoodite, bridgmanite, and Ca-silicate perovskite) coexisting with a reduced, nitrogen-rich fluid phase was measured. Experiments were carried out in multi-anvil presses at 14 to 24 GPa and 1100 to 1800 °C close to the Fe-FeO buffer. Starting materials were enriched in 15N and the nitrogen concentrations in run products were measured by secondary ion mass spectrometry. Observed nitrogen (15N) solubilities in wadsleyite and ringwoodite typically range from 10 to 250 μg/g and strongly increase with temperature. Nitrogen solubility in bridgmanite is about 20 μg/g, while Ca-silicate perovskite incorporates about 30 μg/g under comparable conditions. Partition coefficients of nitrogen derived from coexisting phases are DNwadsleyite/olivine = 5.1 ± 2.1, DNringwoodite/wadsleyite = 0.49 ± 0.29, and DNbridgmanite/ringwoodite = 0.24 (+ 0.30 / - 0.19). Nitrogen solubility in the solid, iron-rich metal phase coexisting with the silicates was also measured and reached a maximum of nearly 1 wt.% 15N at 23 GPa and 1400 °C. These data yield a partition coefficient of nitrogen between iron metal and bridgmanite of DNmetal/bridgmanite ∼ 98, implying that in a lower mantle containing about 1% of iron metal, about half of the nitrogen still resides in the silicates. The high nitrogen solubility in wadsleyite and ringwoodite may be responsible for the low nitrogen concentrations often observed in ultradeep diamonds from the transition zone. Overall, the solubility data suggest that the transition zone and the lower mantle have the capacity to store at least 33 times the mass of nitrogen presently residing in the atmosphere. By combining the nitrogen solubility data in minerals with data on nitrogen solubility in silicate melts, mineral/melt partition coefficients of nitrogen can be estimated, from which the behavior of nitrogen during magma ocean crystallization can be modeled. Such models show that if the magma ocean coexisted with a primordial atmosphere having a nitrogen partial pressure of just a few bars, several times the current atmospheric mass of nitrogen must have been trapped in the deep mantle. It is therefore plausible that the apparent depletion of nitrogen relative to other volatiles in the near-surface reservoirs reflects the storage of a larger reservoir of nitrogen in the solid Earth. Dynamic exchange between these reservoirs may have induced major fluctuations of bulk atmospheric pressure over Earth's history.

Spin-polarized Molecular Dynamics simulations of liquid iron silicate at high pressures.

NASA Astrophysics Data System (ADS)

Munoz Ramo, David; Stixrude, Lars

2010-05-01

Liquid iron silicate (Fe2SiO4) is an important component of natural silicate liquids appearing in Earth's interior. The effect of iron in the properties of these melts is a crucial issue, as it displays a high-spin to low-spin transition at high pressures which is accompanied by volume reduction and changes in the optical absorption spectrum. This phenomenon has a major influence on properties like the buoyancy or the thermal conductivity of the melt, and ultimately on the chemical and thermal evolution of our planet. Computer simulations using ab initio methods have proven to be a powerful approach to the study of liquid silicate systems[1,2], although not yet including Fe. In this paper, we report ab initio molecular dynamics studies of liquid iron silicate at high pressure (up to 400 GPa) and high temperatures (from 3000K to 6000K) that allow us to predict different properties of the system. We use the spin-polarized formalism and the GGA+U density functional for a better treatment of the iron magnetic moments in the system. Previous studies in the solid phase have shown that GGA predicts fayalite as a metal, while the introduction of U leads to a correct description of the band gap and the magnetic ordering of the system. We extend this analysis to the liquid phase. By means of these simulations we predict the liquid structure and thermodynamic properties of the liquid. We compute the theoretical Hugoniot for the system and find good agreement with values obtained from shock experiments [3]. Our calculations show large differences in the magnitude and orientation of the magnetic moments depending on the choice of functional; the GGA+U functional consistently provides larger values of the individual moments (about 1 unit larger) and of the total magnetization of the system. The high-spin to low-spin transition is predicted to take place at pressures from around 260GPa at 3000K to around 280GPa at 6000K in this iron-rich system. [1] N. P. de Koker, L. Stixrude, B. B. Karki, Geochim Cosmochim Acta 2008, 72, 1427. [2] B. B. Karki, D. Bhattarai, L. Stixrude, Phys. Rev. B 2007, 76, 104205. [3] G. Q. Chen, T. J. Ahrens, E. M. Stolper, Phys. Earth Planet. Inter. 2002, 134, 35.

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

USGS Publications Warehouse

Macdonald, R.; Belkin, H.E.; Fitton, J.G.; Rogers, N.W.; Nejbert, K.; Tindle, A.G.; Marshall, A.S.

2008-01-01

The Greater Olkaria Volcanic Complex is a young (???20 ka) multi-centred lava and dome field dominated by the eruption of peralkaline rhyolites. Basaltic and trachytic magmas have been erupted peripherally to the complex and also form, with mugearites and benmoreites, an extensive suite of magmatic inclusions in the rhyolites. The eruptive rocks commonly represent mixed magmas and the magmatic inclusions are themselves two-, three- or four-component mixes. All rock types may carry xenocrysts of alkali feldspar, and less commonly plagioclase, derived from magma mixing and by remobilization of crystal mushes and/or plutonic rocks. Xenoliths in the range gabbro-syenite are common in the lavas and magmatic inclusions, the more salic varieties sometimes containing silicic glass representing partial melts and ranging in composition from anorthite ?? corundum- to acmite-normative. The peralkaline varieties are broadly similar, in major element terms, to the eruptive peralkaline rhyolites. The basalt-trachyte suite formed by a combination of fractional crystallization, magma mixing and resorption of earlier-formed crystals. Matrix glass in metaluminous trachytes has a peralkaline rhyolitic composition, indicating that the eruptive rhyolites may have formed by fractional crystallization of trachyte. Anomalous trace element enrichments (e.g. ??? 2000 ppm Y in a benmoreite) and negative Ce anomalies may have resulted from various Na- and K-enriched fluids evolving from melts of intermediate composition and either being lost from the system or enriched in other parts of the reservoirs. A small group of nepheline-normative, usually peralkaline, magmatic inclusions was formed by fluid transfer between peralkaline rhyolitic and benmoreitic magmas. The plumbing system of the complex consists of several independent reservoirs and conduits, repeatedly recharged by batches of mafic magma, with ubiquitous magma mixing. ?? The Author 2008. Published by Oxford University Press. All rights reserved.

The Extent of Disorder among Charge-balancing Cations in Silicate Glasses and Melts: Spectroscopic Analysis and ab initio Molecular Orbital Calculations

NASA Astrophysics Data System (ADS)

Lee, S.; Doyle, C. S.; Stebbins, J. F.

2001-12-01

Aluminosilicate melts are one of the dominant components in upper mantle and crust. Essential to the thermodynamic and transport properties of these systems is the full understanding on the atomic arrangements and the extent of disorder. Recent quantification of the extent of disorder among 'framework cations' in silicate melts using NMR provided improved prospects on the atomic structure of the glasses and melt and their corresponding properties and allowed the degree of randomness to be evaluated in terms of the degree of Al-avoidance (Q) and degree of phase separations (P) (Lee and Stebbins, J. Phys. Chem. B 104, 4091; Lee and Stebbins, GCA in press). Quantitative estimation of the extent of disorder among 'charge-balancing cations' including Na in aluminosilicate glasses, however, has remained an unsolved problem and these cations have often been assumed to be randomly distributed. Here, we explore the intermediate range order around Na in charge-balanced aluminosilicate glasses using Na-23 NMR and Near-edge X-ray absorption fine structure (NEXAFS) with full multiple scattering (FMS) simulations combined with ab initio molecular orbital calculations. We also quantify the extent of disorder in charge balancing cations as a function of Na-O bond length (d(Na-O)) distribution with composition and present a structural model favoring ordered Na distributions. Peak position in Na-23 magic angle spinning (MAS) spectra of aluminosilicate glasses with varying R (Si/Al) at 14.1 T varies from -10.28 ppm (R = 0.7) to -19.98 ppm (R = 6). These results suggest that average d(Na-O) increases with increasing R, which is confirmed by Na-23 multiple quantum MAS spectra where the chemical shift moves toward lower frequency with increasing Si and shows the individual Gaussian components of Na-O distributions such as Na-(Al-O-Al), Na-(Si-O-Al) and Na-(Si-O-Si). Calculated d(Na-(Al-O-Al)) of 2.57 Å is shorter than d(Na-(Si-O-Si)) of 2.88 Å. Strong compositional dependence is further manifested in Na K-edge NEXAFS spectra for aluminosilicate glasses that are characterized by two main peaks at about 1057 ev (A) and 1062 ev (B). The intensity ratio between peak A and B increases with increasing R, which is consistent with our FMS simulations of model clusters with R and implies that the Na has rather well ordered oxygen coordination and Na-O distribution depends on the types of nearby framework cations. The potential energy surfaces for model six-member rings (NaAl2Si4O6(OH)12, with and without Al-O-Al) were calculated using ab initio calculations at the HF/6-311G(d) level in order to investigate the equilibrium atomic configurations around Na. The results manifest the varying bonding preference of Na to different framework oxygens. Na is located at single deep and narrow basin in potential energy surfaces. The motion of Na is therefore restricted to near equilibrium position even at higher temperature contrary to conventional random distribution model with moderate Na mobility, demonstrating that dynamics of Na should be associated with the collective motions of framework cations and oxygens. In this study, we provide new insights into the nature of disorder in charge-balancing cations in silicate glasses using spectroscopy combined with simulations, highlighting more complete, atomic-level understanding on the dynamic processes in silicate magmas.

Chloride-bearing liquids and partial melting of mantle eclogites: experimental study and application to the diamond-forming processes.

NASA Astrophysics Data System (ADS)

Safonov, Oleg

2010-05-01

Recent studies prove that the partial melting in some eclogite xenoliths in kimberlites is closely related to formation of diamonds in these rocks at 4-6 GPa and 1150-12500C [e.g. 1, 2]. Along with specific mineral assemblages, the products of the eclogite partial melting commonly include relics of potassium-rich silicic melts (45-65 wt. % of SiO2, 4-14 wt. % of K2O and K2O/Na2O > 1.0) [1, 2]. Available experimental data, however, demonstrate that such melts can not be produced by 'dry' or hydrous melting of a common eclogite. It implies that partial melting and conjugate diamond formation in mantle eclogites was triggered by infiltration of potassic fluids/melts. Assemblages of Cl-bearing phases and carbonates in eclogite xenoliths [1], and eclogitic diamonds [3-6] suggest that these agents were chloride-carbonate-H2O melts or/and chloride-H2O-CO2 fluids. In order to characterize interaction of both types of liquids with eclogites and their minerals, experiments in the eclogite-related systems with participation of CaCO3-Na2CO3-KCl-H2O or H2O-CO2-KCl are reviewed. Melting relations in the system eclogite-CaCO3-Na2CO3-KCl-H2O follow the general scheme proposed earlier for chloride-carbonate-silicate systems [7]. Below 12000C, Grt, Cpx and phlogopite (Phl) coexist with LCC only. Formation of Phl and Ca-rich Grt after Cpx indicate active reactions of Cpx with LCC accompanied by CO2 degassing and depletion of the clinopyroxene in jadeite. Subsequent dissolution of silicates in LCC at >1200OC results in formation of potassic silica-undersaturated carbonate and Cl-bearing melt (LCS) (37-40 wt. % of SiO2, 10-12 wt. % of K2O, ~3.5 wt. % of Cl) immiscible with the LCC. Compositional feature of this melt is very comparable to those of low-Mg carbonate-silicate melt inclusions in diamonds [6]. However, it is not relevant to the melt relics preserved in the partially molten eclogite xenoliths. Melting of eclogites with participation of the H2O-CO2-KCl fluid at 5 GPa at 1200-13000C [8] produces CO2-depleted aluminosilicate melts with up to 46 wt. % of SiO2, 9-10 wt. % of K2O, 2-5 wt. % of Cl, whose SiO2 and K2O contents resemble the silica-poor varieties of melt relics in the eclogite xenoliths [1, 2]. Presence of KCl in the fluid intensifies melting, that is related both to high Cl content in the melt and its enrichment in K2O via K-Na exchange reactions with the immiscible chloride melt. The ratio K2O/Cl in the melts increases with the increase of the KCl content in the system and reaches 2.5-3.5 in the melts coexisting with immiscible chloride liquids. No additional crystalline phases, except Grt, Cpx, and Phl, were observed in the above experiments. However, experiments in the model system jadeite-diopside-KCl(±H2O) at 4-5 GPa shows, that KCl liquids provoke formation of ultrapotassic Cl-bearing silica-rich (i.e. 63-65 wt. % of SiO2) melt, which is able to produce sanidine and Al-celadonite-phlogopite mica, which are observed in partially molten eclogites [2]. Dissolution of pyrope in KCl-rich liquids results in formation of spinel and olivine, which are also common products of garnet breakdown within the zones of partial melting in eclogite xenoliths [1, 2]. Thus, the reviewed experiments imply that the KCl-bearing liquids could serve as triggers for formation of the wide varieties of K-rich aluminosilicate and carbonate-silicate melts during the eclogite melting in the mantle. Nevertheless, compositional variability of the produced melts, as well as formation of some crystalline phases (sanidine, mica, spinel, olivine) during this process could be a result of highly localized action of these liquids. The study is supported by the RFBR (10-05-00040), Russian President Grant (MD-130.2008.5) and Russian Science Support Foundation. References: [1] Misra et al. (2004) Contrib. Mineral. Petrol., V. 146, P. 696-714; [2] Shatsky et al. (2008) Lithos, 105, 289-300; [3] Izraeli et al. (2001) Earth Planet. Sci. Lett., 5807, 1-10; [3] Zedgenizov et al. (2007) Doklady Earth Sci., 415, 961-964; [5] Tomlinson et al. (2006), Earth Planet. Sci. Lett., 250, 581-585; [6] Weiss et al. (2009), Lithos, 112S, 660-674; [7] Safonov et al. (2009), Lithos, 112S, 260-273; [8] Butvina et al. (2009), Doklady Earth Sci., 427A, 956-960.

Composition of primary fluid and melt inclusions in regenerated olivines from hypabyssal kimberlites of the Malokuonapskaya pipe (Yakutia)

NASA Astrophysics Data System (ADS)

Tomilenko, A. A.; Kuzmin, D. V.; Bulbak, T. A.; Timina, T. Yu.; Sobolev, N. V.

2015-11-01

The primary fluid and melt inclusions in regenerated zonal crystals of olivine from kimberlites of the Malokuonapskaya pipe were first examined by means of microthermometry, optic and scanning electron microscopy, and Raman spectroscopy. The high-pressure genesis of homogenous central parts of the olivines was revealed, probably under intense metasomatism at early hypogene stages with subsequent regeneration in the kimberlitic melt. The olivine crystals were regenerated from silicate-carbonate melts at about 1100°C. The composition of the kimberlitic melt was changed by way of an increase in the calcium content.

Surface-structural Control on Minor Element Zoning and Growth Mechanism in Synthetic Magmatic Clinopyroxene

NASA Astrophysics Data System (ADS)

Paquette, J.; Deakin, M.; Baker, D. R.

2006-12-01

Because in situ observations of actively growing surfaces are technically impractical, our understanding of crystal growth mechanisms at hydrothermal and magmatic conditions lags behind that of minerals that can be grown from aqueous solutions at or near room temperature. Growing silicate minerals from hydrous synthetic carbonate melts offers the opportunity to relate directly minor element incorporation to their surface microtopography. Natural hydrothermal diopside was used to seed experiments in which synthetic clinopyroxene crystals were grown at 800 degrees C and 10 kbars for 24 hours, from alkaline melts modelled after the lavas of the Tanzanian volcano Oldoinyo Lengai. The melts were prepared from Na2CO3, K2CO3, CaCO3, MgCO3 and Fe3O4 reagents. One run was anhydrous and the others contained either 2.5 or 5 wt. % H2O. Euhedral tabular crystals ranging in size from 100 to 300 ìm across were found in all three runs, hand-picked and freed from their carbonate matrix by overnight immersion in dilute acetic acid. The crystals consist of \\{110\\} prism, \\{100\\} and \\{001\\} pinacoids and a \\{111\\} dipyramid. AFM images resolved a distinct surface microtopography on each form: arrays of broad macrosteps on \\{100\\}, lens- shaped islands on \\{001\\} facets and striated fiber-like crystallites on \\{110\\}. EMP analyses of polished grain mounts show that compositional zoning of Na and Fe occurs not only among non-equivalent growth sectors but also within single \\{100\\} sectors. Electron microprobe maps of sequentially polished sections indicate that zoning within \\{100\\} sectors reflects differential uptake of Na and Fe on symmetrically non-equivalent steps. Near the crystal surface, the non- equivalent coeval vicinal faces of growth hillocks on \\{100\\} are either diopside-like, Na.007Ca1.00(Mg0.754Fe2+0.22Mn2+0.013Al_{0.003)Si2.00O6 , or acmitic, Ca0.63Na0.35(Mg0.64Fe3+ 0.36)Al0.01Si1.99O6 in composition. Step-specific incorporation of minor elements in a clinopyroxene face has only been documented once, in a hydrothermal diopside from Orford (Quebec), where Fe(II) and Mn(II) were differentially incorporated on steps oriented parallel to [010] on \\{100\\} faces. This natural example and our synthetic crystals reflect growth regimes where minor element incorporation was limited by surface-structural kinetics rather than diffusion- controlled kinetics. Such step-specific surface-structural control has never been reported in clinopyroxenes grown from silicate melts. Is it present, but more subtle, or do silicate melts promote a significantly different growth regime? Comparing zoning patterns in synthetic silicates grown from carbonate versus silicate melts could put new constraints on current models of element partitioning.

Effect of water on the fluorine and chlorine partitioning behavior between olivine and silicate melt.

PubMed

Joachim, Bastian; Stechern, André; Ludwig, Thomas; Konzett, Jürgen; Pawley, Alison; Ruzié-Hamilton, Lorraine; Clay, Patricia L; Burgess, Ray; Ballentine, Christopher J

2017-01-01

Halogens show a range from moderate (F) to highly (Cl, Br, I) volatile and incompatible behavior, which makes them excellent tracers for volatile transport processes in the Earth's mantle. Experimentally determined fluorine and chlorine partitioning data between mantle minerals and silicate melt enable us to estimate Mid Ocean Ridge Basalt (MORB) and Ocean Island Basalt (OIB) source region concentrations for these elements. This study investigates the effect of varying small amounts of water on the fluorine and chlorine partitioning behavior at 1280 °C and 0.3 GPa between olivine and silicate melt in the Fe-free CMAS+F-Cl-Br-I-H 2 O model system. Results show that, within the uncertainty of the analyses, water has no effect on the chlorine partitioning behavior for bulk water contents ranging from 0.03 (2) wt% H 2 O (D Cl ol/melt = 1.6 ± 0.9 × 10 -4 ) to 0.33 (6) wt% H 2 O (D Cl ol/melt = 2.2 ± 1.1 × 10 -4 ). Consequently, with the effect of pressure being negligible in the uppermost mantle (Joachim et al. Chem Geol 416:65-78, 2015), temperature is the only parameter that needs to be considered for the determination of chlorine partition coefficients between olivine and melt at least in the simplified iron-free CMAS+F-Cl-Br-I-H 2 O system. In contrast, the fluorine partition coefficient increases linearly in this range and may be described at 1280 °C and 0.3 GPa with ( R 2  = 0.99): [Formula: see text]. The observed fluorine partitioning behavior supports the theory suggested by Crépisson et al. (Earth Planet Sci Lett 390:287-295, 2014) that fluorine and water are incorporated as clumped OH/F defects in the olivine structure. Results of this study further suggest that fluorine concentration estimates in OIB source regions are at least 10% lower than previously expected (Joachim et al. Chem Geol 416:65-78, 2015), implying that consideration of the effect of water on the fluorine partitioning behavior between Earth's mantle minerals and silicate melt is vital for a correct estimation of fluorine abundances in OIB source regions. Estimates for MORB source fluorine concentrations as well as chlorine abundances in both mantle source regions are within uncertainty not affected by the presence of water.

Elasticity of MgSiO3 glass to pressures of the transition zone

NASA Astrophysics Data System (ADS)

Speziale, S.; Reichmann, H. J.; Marquardt, H.; Shim, S.-H.

2009-04-01

Geophysical observations suggest the presence of liquid silicates in regions at the top of the transition zone and at the core-mantle boundary. In addition, a mainly silicate magma ocean probably played a crucial role in the evolution of the early Earth. For these reasons understanding the physical behavior of silicates melts at high pressures is important. In situ experimental investigation of the physical properties of silicate melts at high pressures poses substantial technical difficulties, and computer simulations are nowadays the most effective method to explore the elasticity and the density of such material at relevant conditions of the deep Earth. Due to these difficulties, glasses are often used as "frozen" proxies of melts for experimental studies of their physical properties. Here we present the pressure dependence of sound velocity of MgSiO3 glass measured by Brillouin spectroscopy in the diamond-anvil cell across the whole pressure range of the upper mantle and transition zone. We measured both compressional and shear velocity at 36 different pressures both on compression and decompression. Fixing the starting density to 2.742 ± 0.003 g/cm3, we determined both bulk modulus KS0 and shear modulus G0, and their pressure derivatives at ambient conditions to be KS0 = 76.2 ± 1.0 GPa, G0 = 40.11 ± 0.32 GPa, (‚KS/‚P)0 = 3.04 ± 0.23, and (‚G/‚P )0 = 0.46 ± 0.06. We observe two discontinuities of the pressure dependence of both compressional and shear velocity at 7 ± 2 GPa and at 21 ± 1 GPa. These two discontinuities take place at pressures at which: (a) changes in the pressure dependence of both Si-O-Si bending and Si-O stretching vibrations of the polymerized SiO4 network were observed in the same glass by laser Raman scattering [1], and (b) new spectral features were observed by X-ray Raman scattering [2].The velocities measured upon decompression are significantly different from those measured during compression. The whole of our velocity measurements in compression and decompression suggest that MgSiO3 glass is subject to a multi-step pressure-induced irreversible densification. We estimate that the overall density increase is of the order of 2 percent after complete decompression. We will discuss issues related to the accuracy of density determination from high-pressure Brillouin scattering measurements of glasses at ambient temperature. References [1] Grocholski B., et al. (2008) Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abs. DI41A-1746. [2] Lee S.K., et al. (2008) Proc. Natl. Acad. Sci. U.S.A., 105(23), 7925-7929.

Viscosity of rock-ice mixtures and applications to the evolution of icy satellites

NASA Technical Reports Server (NTRS)

Friedson, A. J.; Stevenson, D. J.

1983-01-01

Theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix. A rheological model for rock-ice mixtures is described, establishing bounds for the range of possible viscosity enhancements provided by a suspension of silicate spheres in an ice matrix. A parametrized thermal convection model is described and used to determine a criterion for criticality, defined as the heat flow and/or silicate volume fraction for which the satellite temperature profile intercepts the melting curve of water ice. The consequences of achieving this critical state are examined, and it is shown that under certain circumstances a 'runaway' differentiation can occur in which the silicates settle to form a core and extensive melting of water ice takes place, the latent heat being supplied by the gravitational energy of differentiation. A possible application of these results to Ganymede and Callisto is described.

Paleoproterozoic mantle enrichment beneath the Fennoscandian Shield: Isotopic insight from carbonatites and lamprophyres

NASA Astrophysics Data System (ADS)

Woodard, Jeremy; Huhma, Hannu

2015-11-01

The isotope geochemistry of carbonatite from Naantali, southwest Finland as well as lamprophyres from North Savo, eastern Finland and the NW Ladoga region, northwest Russia has been investigated. These Paleoproterozoic dykes represent melting of an enriched mantle source spread over a 96,000 km2 area within the Fennoscandian Shield and intruded during post-collisional extension. The carbonatites have εNd(T) ranging from -0.8 to + 0.4, while lamprophyres have εNd(T) between -0.8 and + 0.3. 87Sr/86Sr ratios from the primary carbonatite samples from Naantali form a tight cluster between 0.70283 and 0.70303. For the lamprophyres, 87Sr/86Sr ratios range from 0.70327-0.70339 from NW Ladoga and 0.70316-0.70327 from North Savo. These characteristics are consistent with derivation from an enriched mantle showing an EMII trend, formed when sediments of mixed Archean and Proterozoic provenance were recycled back into the mantle via subduction during the preceding Svecofennian orogeny. Linear mixing of these subducted sediments and depleted mantle shows that a multistage process of enrichment is required to produce the observed isotope compositions. Batch melting of the subducted sediment first generated hydrous alkaline silicate melt, which crystallised as mica- and amphibole-rich veins in the mantle wedge. Continued melting of the subducted material under higher P-T conditions produced carbonatite melt, which infiltrated preferentially into this vein network. Assuming the silicate melt exerts greater influence on 87Sr/86Sr ratios while the carbonatite more greatly affects 143Nd/144Nd ratios, the model predicts significant regional variation in the silicate metasomatism with more consistent carbonatite metasomatism throughout the Fennoscandian subcontinental lithospheric mantle. The subducted sediments were likely also rich in organic matter, resulting in highly negative δ13C in mantle carbonates. The model predicts a higher content of organic carbon in the sediments in close proximity to the Archean continent, decreasing with distance.

Chemistry of uranium in aluminophosphate glasses

NASA Technical Reports Server (NTRS)

Schreiber, H. D.; Balazs, G. B.; Williams, B. J.

1982-01-01

The U(VI)-U(V)-U(IV) redox equilibria are investigated in two sodium aluminophosphate base compositions at a variety of melt temperatures, imposed oxygen fugacities, and uranium contents. Results show that the higher redox states of uranium are quite soluble in the phosphate glasses, although U(IV) readily precipitates from the melts as UO2. In addition, comparisons of the uranium redox equilibria established in phosphate melts versus those in silicate melts shows that the coordination sites of the individual uranium species are generally the same in both solvent systems although they differ in detail.

Primary melt and fluid inclusions in regenerated crystals and phenocrysts of olivine from kimberlites of the Udachnaya-East Pipe, Yakutia: The problem of the kimberlite melt

NASA Astrophysics Data System (ADS)

Tomilenko, A. A.; Kuzmin, D. V.; Bul'bak, T. A.; Sobolev, N. V.

2017-08-01

The primary melt and fluid inclusions in regenerated zonal crystals of olivine and homogeneous phenocrysts of olivine from kimberlites of the Udachnaya-East pipe, were first studied by means of microthermometry, optic and scanning electron microscopy, electron and ion microprobe analysis (SIMS), inductively coupled plasma mass-spectrometry (ICP MSC), and Raman spectroscopy. It was established that olivine crystals were regenerated from silicate-carbonate melts at a temperature of 1100°C.

Zircon solubility and of Zr species in subduction zone fluids

NASA Astrophysics Data System (ADS)

Wilke, M.; Schmidt, C.; Rickers, K.; Pascarelli, S.; Manning, C. E.; Stechern, A.

2009-12-01

The geochemical signature of igneous rocks at convergent plate margins is thought to result from complex melt formation processes involving aqueous solutions derived from dehydration of the subducted slab. In these processes, the depletion of high-field-strength elements (HFSE) may be controlled by the presence of accessory phases such as zircon and rutile, which can strongly fractionate these elements; however, the stability and solubility of these phases depends strongly on the fluid composition, including concentration and stoichiometry of Na-Al silicate components. Here we present new data on the influence of the fluid composition on zircon solubility as well as data on the Zr complexation in these fluids at P&T. Experiments were conducted using a modified hydrothermal diamond-anvil cell (HDAC). Zr contents at P&T were determined using SR-µXRF spectra. Zr K-edge X-ray Absorption Fine Structure (XAFS) spectra were acquired to investigate the Zr complexation in-situ at P&T. A grain of synthetic crystalline zircon was equilibrated with an aqueous fluid containing Na2Si2O5 or Na2Si2O5 + Al2O3 components. XAFS and SR-µXRF spectra were taken at the dispersive beamline ID24 of the ESRF, Grenoble, France. Some additional SR-µXRF spectra were taken at HASYLAB, Hamburg, beamline L. The observed Zr concentrations in fluids containing 7-33 wt% Na2Si2O5 and variable Al contents were between 75 and 720 ppm at 500 to 750°C and ~300 MPa to ~700 MPa. These values match expected solubilities calculated from linear interpolation of the maximum solubility in pure H2O (from the detection limit) and the solubility in the most alkaline high-silica melts reported by Ellison and Hess (1986, CMP, 94, 343). The high Zr solubility in sodium silicate-bearing solutions signifies that aqueous fluids with alkali silicates offer an efficient mechanism for HFSE transport. This can be explained by complexation of HFSE with Si, Na, and perhaps also Al, via formation of polymerized solutes. The XAFS results show clear differences between spectra of Zr in an HCl solution and in H2O-Na2Si2O5 (±Al2O3) aqueous fluid, implying considerable differences in Zr complexation. The latter spectra display similarities to spectra of Zr in Na2Si2O5 glass. This may indicate a similar structural environment for the two examined states, and thus point to Zr in (alumino)-silicate-based polymeric units in the aqueous solutions.

Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

NASA Astrophysics Data System (ADS)

Hoernle, Kaj; Tilton, George; Le Bas, Mike; Duggen, Svend; Garbe-Schönberg, Dieter

Major and trace element and Sr-Nd-Pb-O-C isotopic compositions are presented for carbonatites from the Cape Verde (Brava, Fogo, Sáo Tiago, Maio and Sáo Vicente) and Canary (Fuerteventura) Islands. Carbonatites show pronounced enrichment in Ba, Th, REE, Sr and Pb in comparison to most silicate volcanic rocks and relative depletion in Ti, Zr, Hf, K and Rb. Calcio (calcitic)-carbonatites have primary (mantle-like) stable isotopic compositions and radiogenic isotopic compositions similar to HIMU-type ocean island basalts. Cape Verde carbonatites, however, have more radiogenic Pb isotope ratios (e.g. 206Pb/204Pb=19.3-20.4) than reported for silicate volcanic rocks from these islands (18.7-19.9 Gerlach et al. 1988; Kokfelt 1998). We interpret calcio-carbonatites to be derived from the melting of recycled carbonated oceanic crust (eclogite) with a recycling age of 1.6 Ga. Because of the degree of recrystallization, replacement of calcite by secondary dolomite and elevated ∂13C and ∂18O, the major and trace element compositions of the magnesio (dolomitic)-carbonatites are likely to reflect secondary processes. Compared with Cape Verde calcio-carbonatites, the less radiogenic Nd and Pb isotopic ratios and the negative Δ7/4 of the magnesio-carbonatites (also observed in silicate volcanic rocks from the Canary and Cape Verde Islands) cannot be explained through secondary processes or through the assimilation of Cape Verde crust. These isotopic characteristics require the involvement of a mantle component that has thus far only been found in the Smoky Butte lamproites from Montana, which are believed to be derived from subcontinental lithospheric sources. Continental carbonatites show much greater variation in radiogenic isotopic composition than oceanic carbonatites, requiring a HIMU-like component similar to that observed in the oceanic carbonatites and enriched components. We interpret the enriched components to be Phanerozoic through Proterozoic marine carbonate (e.g. limestone) recycled through shallow, subcontinental-lithospheric-mantle and deep, lower-mantle sources.

Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

NASA Astrophysics Data System (ADS)

Hoernle, Kaj; Tilton, George; Le Bas, Mike; Duggen, Svend; Garbe-Schönberg, Dieter

2001-11-01

Major and trace element and Sr-Nd-Pb-O-C isotopic compositions are presented for carbonatites from the Cape Verde (Brava, Fogo, Sáo Tiago, Maio and Sáo Vicente) and Canary (Fuerteventura) Islands. Carbonatites show pronounced enrichment in Ba, Th, REE, Sr and Pb in comparison to most silicate volcanic rocks and relative depletion in Ti, Zr, Hf, K and Rb. Calcio (calcitic)-carbonatites have primary (mantle-like) stable isotopic compositions and radiogenic isotopic compositions similar to HIMU-type ocean island basalts. Cape Verde carbonatites, however, have more radiogenic Pb isotope ratios (e.g. 206Pb/204Pb=19.3-20.4) than reported for silicate volcanic rocks from these islands (18.7-19.9 Gerlach et al. 1988; Kokfelt 1998). We interpret calcio-carbonatites to be derived from the melting of recycled carbonated oceanic crust (eclogite) with a recycling age of 1.6 Ga. Because of the degree of recrystallization, replacement of calcite by secondary dolomite and elevated ∂13C and ∂18O, the major and trace element compositions of the magnesio (dolomitic)-carbonatites are likely to reflect secondary processes. Compared with Cape Verde calcio-carbonatites, the less radiogenic Nd and Pb isotopic ratios and the negative Δ7/4 of the magnesio-carbonatites (also observed in silicate volcanic rocks from the Canary and Cape Verde Islands) cannot be explained through secondary processes or through the assimilation of Cape Verde crust. These isotopic characteristics require the involvement of a mantle component that has thus far only been found in the Smoky Butte lamproites from Montana, which are believed to be derived from subcontinental lithospheric sources. Continental carbonatites show much greater variation in radiogenic isotopic composition than oceanic carbonatites, requiring a HIMU-like component similar to that observed in the oceanic carbonatites and enriched components. We interpret the enriched components to be Phanerozoic through Proterozoic marine carbonate (e.g. limestone) recycled through shallow, subcontinental-lithospheric-mantle and deep, lower-mantle sources.

Dynamic observations of vesiculation reveal the role of silicate crystals in bubble nucleation and growth in andesitic magmas

NASA Astrophysics Data System (ADS)

Pleše, P.; Higgins, M. D.; Mancini, L.; Lanzafame, G.; Brun, F.; Fife, J. L.; Casselman, J.; Baker, D. R.

2018-01-01

Bubble nucleation and growth control the explosivity of volcanic eruptions, and the kinetics of these processes are generally determined from examinations of natural samples and quenched experimental run products. These samples, however, only provide a view of the final state, from which the initial conditions of a time-evolving magmatic system are then inferred. The interpretations that follow are inexact due to the inability of determining the exact conditions of nucleation and the potential detachment of bubbles from their nucleation sites, an uncertainty that can obscure their nucleation location - either homogeneously within the melt or heterogeneously at the interface between crystals and melts. We present results of a series of dynamic, real-time 4D X-ray tomographic microscopy experiments where we observed the development of bubbles in crystal bearing silicate magmas. Experimentally synthesized andesitic glasses with 0.25-0.5 wt% H2O and seed silicate crystals were heated at 1 atm to induce bubble nucleation and track bubble growth and movement. In contrast to previous studies on natural and experimentally produced samples, we found that bubbles readily nucleated on plagioclase and clinopyroxene crystals, that their contact angle changes during growth and that they can grow to sizes many times that of the silicate on whose surface they originated. The rapid heterogeneous nucleation of bubbles at low degrees of supersaturation in the presence of silicate crystals demonstrates that silicates can affect when vesiculation ensues, influencing subsequent permeability development and effusive vs. explosive transition in volcanic eruptions.

Melting of the Primitive Mercurian Mantle, Insights into the Origin of Its Surface Composition

NASA Technical Reports Server (NTRS)

Boujibar, A.; Righter, K.; Rapp, J. F.; Ross, D. K.; Pando, K. M.; Danielson, L. R.; Fontaine, E.

2016-01-01

Recent findings of the MESSENGER mission on Mercury have brought new evidence for its reducing nature, widespread volcanism and surface compositional heteregeneity. MESSENGER also provided major elemental ratios of its surface that can be used to infer large-scale differentiation processes and the thermal history of the planet. Mercury is known as being very reduced, with very low Fe-content and high S and alkali contents on its surface. Its bulk composition is therefore likely close to EH enstatite chondrites. In order to elucidate the origin of the chemical diversity of Mercury's surface, we determined the melting properties of EH enstatite chondrites, at pressures between 1 bar and 3 GPa and oxygen fugacity of IW-3 to IW-5, using piston-cylinder experiments, combined with a previous study on EH4 melting at 1 bar. We found that the presence of Ca-rich sulfide melts induces significant decrease of Ca-content in silicate melts at low pressure and low degree of melting (F). Also at pressures lower than 3 GPa, the SiO2-content decreases with F, while it increases at 3 GPa. This is likely due to the chemical composition of the bulk silicate which has a (Mg+Fe+Ca)/Si ratio very close to 1 and to the change from incongruent to congruent melting of enstatite. We then tested whether the various chemical compositions of Mercury's surface can result from mixing between two melting products of EH chondrites. We found that the majority of the geochemical provinces of Mercury's surface can be explained by mixing of two melts, with the exception of the High-Al plains that require an Al-rich source. Our findings indicate that Mercury's surface could have been produced by polybaric melting of a relatively primitive mantle.

Insights into Silicate and Oxide Melt Structure from Amorphous, Non-Glass-Forming Materials

NASA Astrophysics Data System (ADS)

Stebbins, J. F.

2015-12-01

Many silicate and oxide liquids of interest in the Earth sciences and in technology cannot readily be quenched to glasses, either because of low silica contents (and hence low viscosity at the melting point and accompanying liquid 'fragility') or because of liquid-liquid unmixing at high temperature. Although in-situ, high temperature structural tools have been in use for decades and are rapidly developing, many methods are still most informative for glass samples quenched to ambient pressure and temperature, e.g. high-resolution solid-state NMR. Amorphous oxides, including alumina and silicate compositions, have widespread technological applications. These are generally deposited by a variety of high-energy sputtering methods, as films of thicknesses of 10's to 100's of nm. Using Al-27, Si-29, and O-17 NMR, we have recently shown that for such films, very similar short-range structure is seen in materials made by very different kinetic pathways, such as sol-gel synthesis vs. ion-beam sputtering. This path-independent structure suggests that these materials pass through transient equilibrium states during their formation, probably that of deeply supercooled liquids just above glass transition temperatures. In the HfO2-SiO2 and ZrO2-SiO2 systems, for example, samples have well-resolved O-17 NMR spectra, allowing quantitation of O sites with only Hf(Zr) neighbors (so-called "free" oxide ions), with mixed Hf(Zr) and Si neighbors, and Si only. The observed oxygen speciation agrees well with a simple thermodynamic model of one of the most fundamental equilibria in silicate systems, namely the reaction of bridging (Si-O-Si) and "free" (e.g. OHf3 and OHf4) oxide ions to produce "non-bridging" oxygens (e.g. Si-OHf2). This new approach to sampling such structural equilibria in compositions far outside the range of normal glass-forming liquids may provide new insights into more geological compositions as well, as well as in more general models of silicate melt chemistry.

Some physical aspects of fluid-fluxed melting

NASA Astrophysics Data System (ADS)

Patiño Douce, A.

2012-04-01

Fluid-fluxed melting is thought to play a crucial role in the origin of many terrestrial magmas. We can visualize the fundamental physics of the process as follows. An infinitesimal amount of fluid infiltrates dry rock at the temperature of its dry solidus. In order to restore equilibrium the temperature must drop, so that enthalpy is released and immediately reabsorbed as enthalpy of melting. The amount of melt produced must be such that the energy balance and thermodynamic equilibrium conditions are simultaneously satisfied. We wish to understand how an initially dry rock melts in response to progressive fluid infiltration, under both batch and fractional melting constraints. The simplest physical model for this process is a binary system in which one of the components makes up a pure solid phase and the other component a pure fluid phase, and in which a binary melt phase exists over certain temperature range. Melting point depression is calculated under the assumption of ideal mixing. The equations of energy balance and thermodynamic equilibrium are solved simultaneously for temperature and melt fraction, using an iterative procedure that allows addition of fluid in infinitesimal increments. Batch melting and fractional melting are simulated by allowing successive melt increments to remain in the system (batch) or not (fractional). Despite their simplified nature, these calculations reveal some important aspects of fluid-fluxed melting. The model confirms that, if the solubility of the fluid in the melt is sufficiently high, fluid fluxed melting is an efficient mechanism of magma generation. One might expect that the temperature of the infiltrating fluid would have a significant effect on melt productivity, but the results of the calculations show this not to be the case, because a relatively small mass of low molecular weight fluid has a strong effect on the melting point of minerals with much higher molecular weights. The calculations reveal the somewhat surprising result that fluid infiltration produces more melt during fractional melting than during batch melting. This behavior, which is opposite to that of decompression melting of a dry solid, arises because the melting point depression effect of the added fluid is greater during fractional melting than during batch melting, which results in a greater release of enthalpy and, therefore, greater melt production for fractional melting than for batch melting, for the same total amount of fluid added. The difference may be considerable. As an example, suppose that 0.1 mols of H2O infiltrate 1 mol or silicate rock. Depending on the rock composition this may corresponds to ˜ 1 wt% H2O. For a given choice of model parameters (initial temperature, heat capacity and entropy of fusion), about 28% of the rock melts during fractional melting, versus some 23 % during batch melting. Fluid fluxing is a robust process of melt generation, without which magmatism at Earth's convergent plate margins would be impossible.

Oxygen and iron production by electrolytic smelting of lunar soil

NASA Technical Reports Server (NTRS)

Colson, R. O.; Haskin, L. A.

1992-01-01

Work during the past year involved two aspects: (1) electrolysis experiments on a larger scale than done before, and (2) collaboration with Carbotek Inc. on design for a lunar magma electrolysis cell. It was demonstrated previously that oxygen can be produced by direct electrolysis of silicate melts. Previous experiments using 50-100 mg of melt have succeeded in measuring melt resistivities, oxygen production efficiencies, and have identified the character of metal products. A series of experiments using 1-8 grams of silicate melt, done in alumina and spinel containers sufficiently large that surface tension effects between the melt and the wall are expected to have minor effect on the behavior of the melt in the region of the electrodes were completed. The purpose of these experiments was to demonstrate the durability of the electrode and container materials, demonstrate the energy efficiency of the electrolysis process, further characterize the nature of the expected metal and spinel products, measure the efficiency of oxygen production and compare to that predicted on the basis of the smaller-scale experiments, and identify any unexpected benefits or problems of the process. Four experimental designs were employed. Detailed results of these experiments are given in the appendix ('Summary of scaling-up experiments'); a general report of the results is given in terms of implications of the experiments on container materials, cathode materials, anode materials, bubble formation and frothing of the melt, cell potential, anode-cathode distance, oxygen efficiency, and energy efficiency.

Metal/Silicate Partitioning of W, Ge, Ga and Ni: Dependence on Silicate Melt Composition

NASA Astrophysics Data System (ADS)

Singletary, S.; Drake, M. J.

2004-12-01

Metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle (Drake and Righter, 2002; Jones and Drake, 1986; Righter et al. 1997). The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. In this work, we investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid. Experiments were performed in the Experimental Geochemistry Laboratory at the University of Arizona utilizing a non-end loaded piston cylinder apparatus with a barium carbonate pressure medium. Starting materials were created by combining the mafic and silicic compositions of Jaeger and Drake (2000) with Fe powder (~25 wt% of the total mixture) to achieve metal saturation. Small amounts of W, Ge, Ga2O3 and NiO powder (less than 2 wt% each) were also added to the starting compositions. The experiments were contained in a graphite capsule and performed with temperature and pressure fixed at 1400ºC and 1.5 GPa. Experimental run products were analyzed with the University of Arizona Cameca SX50 electron microprobe with four wavelength dispersive spectrometers and a PAP ZAF correction program. All experiments in our set are saturated with metal and silicate liquid, indicating that oxygen fugacity is below IW. Several of the runs also contain a gallium-rich spinel as an additional saturating phase. Quench phases are also present in the silicate liquid in all runs. The experimentally produced liquids have nbo/t values (calculated using the method of Mills, 1993) that range from 1.10 to 2.97. These values are higher than those calculated for the liquids in the Jaeger and Drake (2000) study. The higher nbo/t values are due to uptake of Fe by the melt. The initial silicate composition contained no FeO, however the experimentally produced silicate liquids contained from 15 to 26 wt % FeO. We find that W is incompatible over the range of compositions used in this study. However, W compatibility increases as melts become more silicic, with D(W) = 0.0005 at nbo/t = 2.97 and D(W) = 0.09 at nbo/t = 1.1. The slope of the best fit line for the W data when plotted in nbo/t vs Log D space is -1.22 and close to the value of -1.34 found by Jaeger and Drake (2000). Ge is compatible at all compositions and follows a similar pattern to that of W becoming more compatible with decreasing nbo/t (D(Ge)= 14 at nbo/t = 2.97 and D(Ge) = 100 at nbo/t = 1.1). Ni and Ga display essentially flat slopes within the error of our analysis, with D(Ni) = 395 at nbo/t = 2.97 and D(Ni) = 870 at nbo/t 1.10 and D(Ga) = 0.08 at nbo/t = 2.97 and D(Ga) = 0.02 at nbo/t = 1.1. A second series of experiments is in progress to verify these data and extend the study to lower values of nbo/t. References: Drake, M.J. and Righter, K. (2002) Nature, v. 416, 39-44; Jones, J.H. and Drake, M.J. (1986) Nature, v. 323, 470-471; Righter, K., et al. (1997) Physics Earth and Planet. Int., v. 100, 115-134; Jaeger, W.L. and Drake, M.J. (2000) Geo. Cosmo. Acta, v. 64, 3887-3895; Mills, K.C. (1993) ISIJ International, v. 33, 148-155.

Thermal and mass implications of magmatic evolution in the Lassen volcanic region, California, and minimum constraints on basalt influx to the lower crust

USGS Publications Warehouse

Guffanti, M.; Clynne, M.A.; Muffler, L.J.P.

1996-01-01

We have analyzed the heat and mass demands of a petrologic model of basaltdriven magmatic evolution in which variously fractionated mafic magmas mix with silicic partial melts of the lower crust. We have formulated steady state heat budgets for two volcanically distinct areas in the Lassen region: the large, late Quaternary, intermediate to silicic Lassen volcanic center and the nearby, coeval, less evolved Caribou volcanic field. At Caribou volcanic field, heat provided by cooling and fractional crystallization of 52 km3 of basalt is more than sufficient to produce 10 km3 of rhyolitic melt by partial melting of lower crust. Net heat added by basalt intrusion at Caribou volcanic field is equivalent to an increase in lower crustal heat flow of ???7 mW m-2, indicating that the field is not a major crustal thermal anomaly. Addition of cumulates from fractionation is offset by removal of erupted partial melts. A minimum basalt influx of 0.3 km3 (km2 Ma)-1 is needed to supply Caribou volcanic field. Our methodology does not fully account for an influx of basalt that remains in the crust as derivative intrusives. On the basis of comparison to deep heat flow, the input of basalt could be ???3 to 7 times the amount we calculate. At Lassen volcanic center, at least 203 km3 of mantle-derived basalt is needed to produce 141 km3 of partial melt and drive the volcanic system. Partial melting mobilizes lower crustal material, augmenting the magmatic volume available for eruption at Lassen volcanic center; thus the erupted volume of 215 km3 exceeds the calculated basalt input of 203 km3. The minimum basalt input of 1.6 km3 (km2 Ma)-1 is >5 times the minimum influx to the Caribou volcanic field. Basalt influx high enough to sustain considerable partial melting, coupled with locally high extension rate, is a crucial factor in development of Lassen volcanic center; in contrast. Caribou volcanic field has failed to develop into a large silicic center primarily because basalt supply there has been insufficient.

Interior Volatile Reservoirs in Mercury

NASA Astrophysics Data System (ADS)

Anzures, B. A.; Parman, S. W.; Milliken, R. E.; Head, J. W.

2018-05-01

More measurements of 1) surface volatiles, and 2) pyroclastic deposits paired with experimental volatile analyses in silicate minerals can constrain conditions of melting and subsequent eruption on Mercury.

The nature and origin of ureilites

NASA Technical Reports Server (NTRS)

Berkley, J. L.; Taylor, G. J.; Keil, K.; Harlow, G. E.; Prinz, M.

1980-01-01

A theory of the origin of ureilites is presented based on mineralogical and petrological investigation of eight species including Kenna, Novo Urei, and Goalpara. The theory suggests that ureilites are primarily olivine-pigeonite cumulates crystallized from a silicate liquid which also contained suspended solid carbon phases. The carbon induced reduction of the melt and affected the ureilite mineral compositions. Petrofabric analyses show that mafic silicates are oriented in lineated and foliated patterns similar to cumulate rocks; strain rate of silicates suggests that ureilites were deformed after lithification by a mild tectonic stress and a moderate to severe shock.

An experimental study of ^{{{{Fe}}^{2 + } {-}{{Mg}}}} K_{{D}} between orthopyroxene and rhyolite: a strong dependence on H2O in the melt

NASA Astrophysics Data System (ADS)

Waters, Laura E.; Lange, Rebecca A.

2017-06-01

The effect of temperature, pressure, and dissolved H2O in the melt on the Fe2+-Mg exchange coefficient between orthopyroxene and rhyolite melt was investigated with a series of H2O fluid-saturated phase-equilibrium experiments. Experiments were conducted in a rapid-quench cold-seal pressure vessel over a temperature and pressure range of 785-850 °C and 80-185 MPa, respectively. Oxygen fugacity was buffered with the solid Ni-NiO assemblage in a double-capsule assembly. These experiments, when combined with H2O-undersaturated experiments in the literature, show that ^{{{{Fe}}^{2 + } {-}{{Mg}}}} K_{{D}} between orthopyroxene and rhyolite liquid increases strongly (from 0.23 to 0.54) as a function of dissolved water in the melt (from 2.7 to 5.6 wt%). There is no detectable effect of temperature or pressure over an interval of 65 °C and 100 MPa, respectively, on the Fe2+-Mg exchange coefficient values. The data show that Fe-rich orthopyroxene is favored at high water contents, whereas Mg-rich orthopyroxene crystallizes at low water contents. It is proposed that the effect of dissolved water in the melt on the composition of orthopyroxene is analogous to its effect on the composition of plagioclase. In the latter case, dissolved hydroxyl groups preferentially complex with Na+ relative to Ca2+, which reduces the activity of the albite component, leading to a more anorthite-rich (calcic) plagioclase. Similarly, it is proposed that dissolved hydroxyl groups preferentially complex with Mg2+ relative to Fe2+, thus lowering the activity of the enstatite component, leading to a more Fe-rich orthopyroxene at high water contents in the melt. The experimental results presented in this study show that reversely zoned pyroxene (i.e., Mg-rich rims) in silicic magmas may be a result of H2O degassing and not necessarily the result of mixing with a more mafic magma.

Melt densities in the CaO-FeO-Fe 2O 3-SiO 2 system and the compositional dependence of the partial molar volume of ferric iron in silicate melts

NASA Astrophysics Data System (ADS)

Dingwell, Donald B.; Brearley, Mark

1988-12-01

The densities of 10 melts in the CaO-FeO-Fe 2O 3-SiO 2 system were determined in equilibrium with air, in the temperature range of 1200 to 1550°C, using the double-bob Archimedean technique. Melt compositions range from 6 to 58 wt% SiO 2, 14 to 76 wt% Fe 2O 3 and 10 to 46 wt% CaO. The ferric-ferrous ratios of glasses drop-quenched from loop fusion equilibration experiments were determined by 57Fe Mössbauer spectroscopy. Melt densities range from 2.689 to 3.618 gm/cm 3 with a mean standard deviation from replicate experiments of 0.15%. Least-squares regressions of molar volume versus molar composition have been performed and the root mean squared deviation shows that a linear combination of partial molar volumes for the oxide components (CaO, FeO, Fe 2O 3 and SiO 2) cannot describe the data set within experimental error. Instead, the inclusion of excess terms in CaFe 3+ and CaSi (product terms using the oxides) is required to yield a fit that describes the experimental data within error. The nonlinear compositional-dependence of the molar volumes of melts in this system can be explained by structural considerations of the roles of Ca and Fe 3+. The volume behavior of melts in this system is significantly different from that in the Na 2O-FeO-Fe 2O 3-SiO 2 system, consistent with the proposal that a proportion of Fe 3+ in melts in the CaO-FeO-Fe 2O 3-SiO 2 system is not tetrahedrally-coordinated by oxygen, which is supported by differences in 57Fe Mössbauer spectra of glasses. Specifically, this study confirms that the 57Fe Mössbauer spectra exhibit an area asymmetry and higher values of isomer shift of the ferric doublet that vary systematically with composition and temperature (this study; Dingwell and Virgo, 1987, 1988). These observations are consistent with a number of other lines of evidence ( e.g., homogeneous redox equilibria, Dickenson and Hess, 1986; viscosity, Dingwell and Virgo, 1987,1988). Two species of ferric iron, varying in proportions with temperature, composition and redox state, are sufficient to describe the above observations. The presence of more than one coordination geometry for Fe 3+ in low pressure silicate melts has several implications for igneous petrogenesis. The possible effects on compressibility, the pressure dependence of the redox ratio, and redox enthalpy are briefly noted.

Electrolysis of lunar soil to produce oxygen and metals

NASA Technical Reports Server (NTRS)

Colson, Russell O.; Haskin, Larry A.; Keller, R.

1991-01-01

The discussion of melt electrolysis consists of three sections. The implications of the chemistry and physics of fluxed and raw melts on melt electrolysis are discussed first. This includes discussion of the factor that influence melt resistivity, melt viscosity, oxygen production efficiency, and the theoretical energy required to produce oxygen. Second, the implications of phase equilibria and solubilities in silicate melts on the selection of materials for container and electrodes are discussed. The implications of proposed container and electrode materials on melt composition and how this effects expected resistivities, viscosities, as outlined in the first section are discussed. Finally, a general discussion of the basic features of both the fluxed and unfluxed melt electrolysis is given, including their advantages and disadvantages and how they compare with alternative processes.

Experimental Studies of Phase Equilibria of Meteorites and Planetary Bodies

NASA Technical Reports Server (NTRS)

Stolper, Edward M.

2005-01-01

The primary theme of this project was the application of experimental petrology and geochemistry to a variety of problems in meteoritics and planetary geology. The studies were designed to help develop constraints on the histories of primitive meteorites and their components, the environments in which they formed and evolved, and to understand quantitatively the processes involved in the evolution of igneous rocks on the earth and other planetary bodies. We undertook several projects relating to the origin of CAIs and chondrules. Systematics in the thermodynamic properties of CAI-like liquids were investigated and used to elucidate speciation of multi-valent cations and sulfide capacity of silicate melts and to constrain redox conditions and the vapor pressures of volatile species over molten chondrules. We experimentally determined vanadium speciation in meteoritic pyroxenes and in pyroxenes crystallized from CAI-like melts under very reducing conditions. We also found that bulk oxygen isotope compositions of chondrules in the moderately unequilibrated LL chondrites are related to the relative timing of plagioclase crystallization. We completed an experimental study on the vaporization of beta-SiC and SiO2 (glass or cristobalite) in reducing gases and established the conditions under which these presolar grains could have survived in the solar nebula. We expanded our technique for determining the thermodynamic properties of minerals and liquids to iron-bearing systems. We determined activity-composition relationships in Pt-Fe, Pt-Cr and Pt-Fe-Cr alloys. Results were used to determine the thermodynamic properties of chromite-picrochromite spinels including the free energy of formation of end-member FeCr2O4. We also established a new approach for evaluating Pt-Fe saturation experiments. We calculated the T-fO2 relationships in equilibrated ordinary chondrites and thereby constrained the conditions of metamorphism in their parent bodies.

Self diffusion of alkaline-Earth in Ca-Mg-aluminosilicate melts: Experimental improvements on the determination of the self-diffusion coefficients

NASA Technical Reports Server (NTRS)

Paillat, O.; Wasserburg, G. J.

1993-01-01

Experimental studies of self-diffusion isotopes in silicate melts often have quite large uncertainties when comparing one study to another. We designed an experiment in order to improve the precision of the results by simultaneously studying several elements (Mg, Ca, Sr, Ba) during the same experiment thereby greatly reducing the relative experimental uncertainties. Results show that the uncertainties on the diffusion coefficients can be reduced to 10 percent, allowing a more reliable comparison of differences of self-diffusion coefficients of the elements. This type of experiment permits us to study precisely and simultaneously several elements with no restriction on any element. We also designed an experiment to investigate the possible effects of multicomponent diffusion during Mg self-diffusion experiments by comparing cases where the concentrations of the elements and the isotopic compositions are different. The results suggest that there are differences between the effective means of transport. This approach should allow us to investigate the importance of multicomponent diffusion in silicate melts.

Predicting major element mineral/melt equilibria - A statistical approach

NASA Technical Reports Server (NTRS)

Hostetler, C. J.; Drake, M. J.

1980-01-01

Empirical equations have been developed for calculating the mole fractions of NaO0.5, MgO, AlO1.5, SiO2, KO0.5, CaO, TiO2, and FeO in a solid phase of initially unknown identity given only the composition of the coexisting silicate melt. The approach involves a linear multivariate regression analysis in which solid composition is expressed as a Taylor series expansion of the liquid compositions. An internally consistent precision of approximately 0.94 is obtained, that is, the nature of the liquidus phase in the input data set can be correctly predicted for approximately 94% of the entries. The composition of the liquidus phase may be calculated to better than 5 mol % absolute. An important feature of this 'generalized solid' model is its reversibility; that is, the dependent and independent variables in the linear multivariate regression may be inverted to permit prediction of the composition of a silicate liquid produced by equilibrium partial melting of a polymineralic source assemblage.

Effects of crustal thickness on magmatic differentiation in subduction zone volcanism: A global study

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Variations in mid-ocean ridge magmatism and carbon emissions driven by glacial cycles

NASA Astrophysics Data System (ADS)

Katz, R. F.; Burley, J. M.; Huybers, P. J.; Langmuir, C. H.; Crowley, J. W.; Park, S. H.; Carbotte, S. M.; Ferguson, D.; Proistosescu, C.; Boulahanis, B.

2015-12-01

Glacial cycles transfer ˜5×10^19 kg of water between the oceans and ice sheets, causing pressure changes in the upper mantle with consequences for the melting of Earth's interior. Forced with Plio-Pleistocene sea-level variations, theoretical models of mid-ocean ridge magma/mantle dynamics predict temporal variations up to 10% in melt supply to the base of the crust. Moreover, a transport model for a perfectly incompatible element suggests that CO2 emissions from mid-ocean ridges could vary by a similar proportion, though with a longer time-lag.Bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills record the magmatic response to changes in sea level. The mechanism by which variations in the rate of melt supply are expressed in the bathymetry is not understood.The same pressure variations that modulate the melting rate could also modulate the depth of the onset of silicate melting. As ice sheets grow and sea level drops, this onset deepens, causing melting at the base of the silicate melting regime. Excess highly incompatible elements like CO2 enter the melt and begin their journey to the ridge axis. Tens of thousands of years later, this additional CO2 flux is emitted into the climate system. Because of its delay with respect to sea-level change, the predicted variation in CO2 emissions could represent a restoring force on climate (and sea-level) excursions. This mechanism has a response time determined by the time scale of melt transport; it potentially introduces a resonant frequency into the climate system.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

Magma plays a vital role in the break-up of continental lithosphere. However, significant uncertainty remains about how magma-crust interactions and melt evolution vary during the development of a rift system. Ethiopia captures the transition from continental rifting to incipient sea-floor spreading and has witnessed the eruption of large volumes of silicic volcanic rocks across the region over ∼45 Ma. The petrogenesis of these silicic rocks sheds light on the role of magmatism in rift development, by providing information on crustal interactions, melt fluxes and magmatic differentiation. We report new trace element and Sr-Nd-O isotopic data for volcanic rocks, glasses and minerals along and across active segments of the Main Ethiopian (MER) and Afar Rifts. Most δ18 O data for mineral and glass separates from these active rift zones fall within the bounds of modelled fractional crystallization trajectories from basaltic parent magmas (i.e., 5.5-6.5‰) with scant evidence for assimilation of Pan-African Precambrian crustal material (δ18 O of 7-18‰). Radiogenic isotopes (εNd = 0.92- 6.52; 87Sr/86Sr = 0.7037-0.7072) and incompatible trace element ratios (Rb/Nb <1.5) are consistent with δ18 O data and emphasize limited interaction with Pan-African crust. However, there are important regional variations in melt evolution revealed by incompatible elements (e.g., Th and Zr) and peralkalinity (molar Na2 O +K2 O /Al2O3). The most chemically-evolved peralkaline compositions are associated with the MER volcanoes (Aluto, Gedemsa and Kone) and an off-axis volcano of the Afar Rift (Badi). On-axis silicic volcanoes of the Afar Rift (e.g., Dabbahu) generate less-evolved melts. While at Erta Ale, the most mature rift setting, peralkaline magmas are rare. We find that melt evolution is enhanced in less mature continental rifts (where parental magmas are of transitional rather than tholeiitic composition) and regions of low magma flux (due to reduced mantle melt productivity or where crustal structure inhibits magma ascent). This has important implications for understanding the geotectonic settings that promote extreme melt evolution and, potentially, genesis of economically-valuable mineral deposits in ancient rift-settings. The limited isotopic evidence for assimilation of Pan-African crustal material in Ethiopia suggests that the pre-rift crust beneath the magmatic segments has been substantially modified by rift-related magmatism over the past ∼45 Ma; consistent with geophysical observations. We argue that considerable volumes of crystal cumulate are stored beneath silicic volcanic systems (>100 km3), and estimate that crystal cumulates fill at least 16-30% of the volume generated by crustal extension under the axial volcanoes of the MER and Manda Hararo Rift Segment (MHRS) of Afar. At Erta Ale only ∼1% of the volume generated due to rift extension is filled by cumulates, supporting previous seismic evidence for a greater role of plate stretching in mature rifts at the onset of sea-floor spreading. We infer that ∼45 Ma of magmatism has left little fusible Pan-African material to be assimilated beneath the magmatic segments and the active segments are predominantly composed of magmatic cumulates with δ18 O indistinguishable from mantle-derived melts. We predict that the δ18 O of silicic magmas should converge to mantle values as the rift continues to evolve. Although current data are limited, a comparison with ∼30 Ma ignimbrites (with δ18 O up to 8.9‰) supports this inference, evidencing greater crustal assimilation during initial stages of rifting and at times of heightened magmatic flux.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pleše, P.; Higgins, M. D.; Mancini, L.

Bubble nucleation and growth control the explosivity of volcanic eruptions, and the kinetics of these processes are generally determined from examinations of natural samples and quenched experimental run products. These samples, however, only provide a view of the final state, from which the initial conditions of a time-evolving magmatic system are then inferred. The interpretations that follow are inexact due to the inability of determining the exact conditions of nucleation and the potential detachment of bubbles from their nucleation sites, an uncertainty that can obscure their nucleation location – either homogeneously within the melt or heterogeneously at the interface betweenmore » crystals and melts. We present results of a series of dynamic, real-time 4D X-ray tomographic microscopy experiments where we observed the development of bubbles in crystal bearing silicate magmas. Experimentally synthesized andesitic glasses with 0.25–0.5 wt% H2O and seed silicate crystals were heated at 1 atm to induce bubble nucleation and track bubble growth and movement. In contrast to previous studies on natural and experimentally produced samples, we found that bubbles readily nucleated on plagioclase and clinopyroxene crystals, that their contact angle changes during growth and that they can grow to sizes many times that of the silicate on whose surface they originated. The rapid heterogeneous nucleation of bubbles at low degrees of supersaturation in the presence of silicate crystals demonstrates that silicates can affect when vesiculation ensues, influencing subsequent permeability development and effusive vs. explosive transition in volcanic eruptions.« less

Element Abundances in Meteorites and the Earth: Implication for the Accretion of Planetary Bodies

NASA Astrophysics Data System (ADS)

Mezger, K.; Vollstaedt, H.; Maltese, A.

2017-12-01

Essentially all known inner solar system materials show near chondritic relative abundances of refractory elements and depletion in volatile elements. To a first approximation volatile element depletion correlates with the respective condensation temperature (TC) of the elements. Possible mechanisms for this depletion are incomplete condensation and partial loss by evaporation caused by heating prior to or during the planetesimal accretion. The stable isotope compositions of almost all moderately volatile elements in different meteorite classes show only minor, or no evidence for a Rayleigh-type fractionation that could be attributed to partial condensation or evaporation. The different classes of meteorites also show that the degree of depletion in their parent bodies (i.e. mostly planetesimals) is quite variable, but nevertheless systematic. For primitive and least disturbed carbonaceous chondrites the element depletion pattern is a smooth function of TC. The accessible silicate Earth also shows this general depletion pattern, but in detail it is highly complex and requires differentiation processes that are not solely controlled by TC. If only highly lithophile elements are considered the depletion pattern of the silicate Earth reveals a step function that shows that moderately volatile lithophile elements have abundances that are ca. 0.1 times the chondritic value, irrespective of their TC. This element pattern observed for bulk silicate Earth can be modelled as a mixture of two distinct components: ca. 90% of a strongly reduced planetary body that is depleted in highly volatile elements and ca. 10% of a more volatile element rich and oxidized component. This mixture can account for the apparent Pb- paradox observed in melts derived from the silicate Earth and provides a time constraint for the mixing event, which is ca. 70 My after the beginning of the solar system. This event corresponds to the giant impact that also formed the Moon.

Petrogenesis of Silicic Magmas in the Afro-Arabian Flood Volcanic Province in Yemen: A Melt Inclusion Study

NASA Astrophysics Data System (ADS)

Falkena, L. B.; Peate, D.; Ukstins Peate, I.

2009-05-01

The Oligocene (˜26-30 Ma) Afro-Arabian Flood Volcanic Province in Yemen and Ethiopia contains significant silicic material primarily deposited as large volume (>1,000 km 3 ) ignimbrites. These deposits have been correlated to tephra layers in ODP cores ˜2700 km SE of Yemen in the Indian Ocean. We are using melt inclusions (MI) in 4 ignimbrite units to model the petrogenesis and pre-eruptive volatile contents of the ignimbrites. Although quartz is a better MI host in silicic systems, these units only contain plagioclase that has the potential for degassing and leakage in cleavage planes. Through a series of experiments to investigate the rehomogenization temperature of the MI, we found inclusions were glassy at 1075 ° C after 24 hours. We also have compositional data from shorter duration runs (˜20 min.) at 1050 ° C. Reconnaissance MI data show a wide compositional variation compared to whole rock samples of the ignimbrites, and they provide a better estimate of true magmatic compositions compared to the heterogeneous whole rock samples. The inclusions are generally lower in Si (˜59-85 wt.%), yet significantly higher in Na and Al, which both decrease with increasing Si. We are currently modeling these variations to determine the petrogenesis of these silicic magmas. In terms of pre-eruptive volatiles, sulfur in the long duration experiments appears degassed (<5 ppm) yet is retained in the shorter duration runs (up to 500 ppm). Cl appears robust in the MI at ˜340 ppm and is consistent with modeled high halogen contents in such peralkaline melts. We will present estimates for the total S and Cl released during these large ignimbrite eruptions.

The geologic classification of the meteorites

USGS Publications Warehouse

Elston, Donald Parker

1968-01-01

The meteorite classes of Prior and Mason are assigned to three proposed genetic groups on the basis of a combination of compositional, mineralogical, and elemental characteristics: l) the calcium-poor, volatile-rich carbonaceous chondrites and achondrites; 2) the calcium-poor, volatile-poor chondrites (enstatite, bronzite, hypersthene, and pigeonite), achondrites (enstatite, hypersthene, and pigeonite), stonyirons (pallasites, siderophyre), and irons; and, 3) the calcium-rich (basaltic) achondrites. Chondrites are correlated with calcium-poor achondrites and the silicate phase of the pallasitic meteorites on Fe contents of olivine and pyroxene; and with metal of the stony-irons and irons on the basis of trace elements (Ga and Ge). Transitions in structure and texture between the chondrites and achondrites are recognized. The Van Schmus-Wood chemical-petrologic classification of the chondrites has been modified and expanded to a mineralogic-petrologic classification of the chondrites and calcium-poor achondrites. Chondrites apparently are the first rocks of the solar system. Paragenetic and textural relations in the Murray carbonaceous chondrite shed new light on the manner of accretion, and on the character of dispersed solid materials ('dust', and chondrules and metal) that existed in the solar system before accretion. Two pre-accretionary mineral assemblages (components) are recognized in the carbonaceous chondrites and in the unequilibrated volatile-poor chondrites. They are: 1) a 'low temperature' water-, rare gas-, and carbon-bearing component; and, 2) a high temperature anhydrous silicate and metal component. Paragenetic relations indicate that component 2 materials predate chondrite formation. An accretionary assemblage (component 3) also is recognized in the carbonaceous chondrites and in the unequilibrated volatile-poor chondrites. Component 3 consists of very fine grains of olivine and pyroxene, which occur as pervasive disseminations, as small irregular aggregates of grains, and as large subround to round, finely granular accretional chondrules. Evidence in Murray indicates that component 3 silicates precipitated abruptly and at low pressures, possibly from a high temperature gas, in an environment that contained dispersed component 1 and 2 materials. All component 3 aggregates in Murray contain component 1 material, most commonly as flakes, and locally as tiny granules and larger spherules, some of which are hollow and some of which were broken prior to their mechanical incorporation in accretionary chondrules. Accretion may have occurred as ices associated with dispersed water-bearing component 1 materials temporarily melted during the precipitation of component 3 silicates, and then abruptly refroze to form an icy cementing material. Group 1 materials may be cometary, and group 2 materials may be asteroidal. Schematic models are proposed. Evidence is reviewed for the lunar origin of the pyroxeneplagioclase achondrites. On the basis of natural remanent magnetism, it is suggested that the very scarce diopside-olivine achondrites may be samples from Mars. A classification of the meteorite breccias, including the calcium-poor and calcium-rich mesosiderites, and irons that contain silicate fragments, is proposed. A fragmentation history of the meteorites is outlined on the basis of evidence in the polymict breccias, and from gas retention ages in stones and exposure ages in irons. Cometal impacts appear to have caused the initial fragmentation, stud possibly the perturbation of orbits, of two inferred asteroidal bodies (enstatite and bronzite), one and possibly both events occurring before 2000 m.y. ago. Several impacts apparently occurred on the inferred hypersthene body in the interval 1000 to 2000 m.y. ago. Major breakups of the three bodies apparently occurred as the result of interasteroidal collisions at about 900 m.y. ago, and 600 to 700 m.y. ago. The breakups were followed by a number of fr

Mechanism of Phase Formation in the Batch Mixtures for Slag-Bearing Glass Ceramics - 12207

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stefanovsky, Sergey V.; Stefanovsky, Olga I.; Malinina, Galina A.

2012-07-01

Slag surrogate was produced from chemicals by heating to 900 deg. C and keeping at this temperature for 1 hr. The product obtained was intermixed with either sodium di-silicate (75 wt.% waste loading) or borax (85 wt.% slag loading). The mixtures were heat-treated within a temperature range of 25 to 1300 deg. C. The products were examined by X-ray diffraction and infrared spectroscopy. The products prepared at temperatures of up to 1000 deg. C contained both phase typical of the source slag and intermediate phases as well as phases typical of the materials melted at 1350 deg. C such asmore » nepheline, britholite, magnetite and matrix vitreous phase. Vitrification process in batch mixtures consisting of slag surrogate and either sodium di-silicate or sodium tetraborate runs through formation of intermediate phases mainly silico-phosphates capable to incorporate Sm as trivalent actinides surrogate. Reactions in the batch mixtures are in the whole completed by ∼1000 deg. C but higher temperatures are required to homogenize the products. If in the borate-based system the mechanism is close to simple dissolution of slag constituents in the low viscous borate melt, then in the silicate-based system the mechanism was found to be much complicated and includes re-crystallization during melting with segregation of newly-formed nepheline type phase. (authors)« less

Intraplate mantle oxidation by volatile-rich silicic magmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, Audrey M.; Médard, Etienne; Righter, Kevin

The upper subcontinental lithospheric mantle below the French Massif Central is more oxidized than the average continental lithosphere, although the origin of this anomaly remains unknown. Using iron oxidation analysis in clinopyroxene, oxybarometry, and melt inclusions in mantle xenoliths, we show that widespread infiltration of volatile (HCSO)-rich silicic melts played a major role in this oxidation. We propose the first comprehensive model of magmatism and mantle oxidation at an intraplate setting. Two oxidizing events occurred: (1) a 365–286 Ma old magmatic episode that produced alkaline vaugnerites, potassic lamprophyres, and K-rich calc-alkaline granitoids, related to the N–S Rhenohercynian subduction, and (2)more » < 30 Ma old magmatism related to W–E extension, producing carbonatites and hydrous potassic trachytes. These melts were capable of locally increasing the subcontinental lithospheric mantle fO2 to FMQ + 2.4. Both events originate from the melting of a metasomatized lithosphere containing carbonate + phlogopite ± amphibole. The persistence of this volatile-rich lithospheric source implies the potential for new episodes of volatile-rich magmatism. Similarities with worldwide magmatism also show that the importance of volatiles and the oxidation of the mantle in intraplate regions is underestimated.« less

Intraplate mantle oxidation by volatile-rich silicic magmas

NASA Astrophysics Data System (ADS)

Martin, Audrey M.; Médard, Etienne; Righter, Kevin; Lanzirotti, Antonio

2017-11-01

The upper subcontinental lithospheric mantle below the French Massif Central is more oxidized than the average continental lithosphere, although the origin of this anomaly remains unknown. Using iron oxidation analysis in clinopyroxene, oxybarometry, and melt inclusions in mantle xenoliths, we show that widespread infiltration of volatile (HCSO)-rich silicic melts played a major role in this oxidation. We propose the first comprehensive model of magmatism and mantle oxidation at an intraplate setting. Two oxidizing events occurred: (1) a 365-286 Ma old magmatic episode that produced alkaline vaugnerites, potassic lamprophyres, and K-rich calc-alkaline granitoids, related to the N-S Rhenohercynian subduction, and (2) < 30 Ma old magmatism related to W-E extension, producing carbonatites and hydrous potassic trachytes. These melts were capable of locally increasing the subcontinental lithospheric mantle fO2 to FMQ + 2.4. Both events originate from the melting of a metasomatized lithosphere containing carbonate + phlogopite ± amphibole. The persistence of this volatile-rich lithospheric source implies the potential for new episodes of volatile-rich magmatism. Similarities with worldwide magmatism also show that the importance of volatiles and the oxidation of the mantle in intraplate regions is underestimated.

A Structural Molar Volume Model for Oxide Melts Part I: Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-Al2O3-SiO2 Melts—Binary Systems

NASA Astrophysics Data System (ADS)

Thibodeau, Eric; Gheribi, Aimen E.; Jung, In-Ho

2016-04-01

A structural molar volume model was developed to accurately reproduce the molar volume of molten oxides. As the non-linearity of molar volume is related to the change in structure of molten oxides, the silicate tetrahedral Q-species, calculated from the modified quasichemical model with an optimized thermodynamic database, were used as basic structural units in the present model. Experimental molar volume data for unary and binary melts in the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-Al2O3-SiO2 system were critically evaluated. The molar volumes of unary oxide components and binary Q-species, which are model parameters of the present structural model, were determined to accurately reproduce the experimental data across the entire binary composition in a wide range of temperatures. The non-linear behavior of molar volume and thermal expansivity of binary melt depending on SiO2 content are well reproduced by the present model.

Space Weathering Effects in Lunar Soils: The Roles of Surface Exposure Time and Bulk Chemical Composition

NASA Technical Reports Server (NTRS)

Zhang, Shouliang; Keller, Lindsay P.

2011-01-01

Space weathering effects on lunar soil grains result from both radiation-damaged and deposited layers on grain surfaces. Typically, solar wind irradiation forms an amorphous layer on regolith silicate grains, and induces the formation of surficial metallic Fe in Fe-bearing minerals [1,2]. Impacts into the lunar regolith generate high temperature melts and vapor. The vapor component is largely deposited on the surfaces of lunar soil grains [3] as is a fraction of the melt [4, this work]. Both the vapor-deposits and the deposited melt typically contain nanophase Fe metal particles (npFe0) as abundant inclusions. The development of these rims and the abundance of the npFe0 in lunar regolith, and thus the optical properties, vary with the soil mineralogy and the length of time the soil grains have been exposed to space weathering effects [5]. In this study, we used the density of solar flare particle tracks in soil grains to estimate exposure times for individual grains and then perform nanometer-scale characterization of the rims using transmission electron microscopy (TEM). The work involved study of lunar soil samples with different mineralogy (mare vs. highland) and different exposure times (mature vs. immature).

Clinopyroxene-melt element partitioning during interaction between trachybasaltic magma and siliceous crust: Clues from quartzite enclaves at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Mollo, S.; Blundy, J. D.; Giacomoni, P.; Nazzari, M.; Scarlato, P.; Coltorti, M.; Langone, A.; Andronico, D.

2017-07-01

A peculiar characteristic of the paroxysmal sequence that occurred on March 16, 2013 at the New South East Crater of Mt. Etna volcano (eastern Sicily, Italy) was the eruption of siliceous crustal xenoliths representative of the sedimentary basement beneath the volcanic edifice. These xenoliths are quartzites that occur as subspherical bombs enclosed in a thin trachybasaltic lava envelope. At the quartzite-magma interface a reaction corona develops due to the interaction between the Etnean trachybasaltic magma and the partially melted quartzite. Three distinct domains are observed: (i) the trachybasaltic lava itself (Zone 1), including Al-rich clinopyroxene phenocrysts dispersed in a matrix glass, (ii) the hybrid melt (Zone 2), developing at the quartzite-magma interface and feeding the growth of newly-formed Al-poor clinopyroxenes, and (iii) the partially melted quartzite (Zone 3), producing abundant siliceous melt. These features makes it possible to quantify the effect of magma contamination by siliceous crust in terms of clinopyroxene-melt element partitioning. Major and trace element partition coefficients have been calculated using the compositions of clinopyroxene rims and glasses next to the crystal surface. Zone 1 and Zone 2 partition coefficients correspond to, respectively, the chemical analyses of Al-rich phenocrysts and matrix glasses, and the chemical analyses of newly-formed Al-poor crystals and hybrid glasses. For clinopyroxenes from both the hybrid layer and the lava flow expected relationships are observed between the partition coefficient, the valence of the element, and the ionic radius. However, with respect to Zone 1 partition coefficients, values of Zone 2 partition coefficients show a net decrease for transition metals (TE), high-field strength elements (HFSE) and rare earth elements including yttrium (REE + Y), and an increase for large ion lithophile elements (LILE). This variation is associated with coupled substitutions on the M1, M2 and T sites of the type M1(Al, Fe3 +) + TAl = M2(Mg, Fe2 +) + TSi. The different incorporation of trace elements into clinopyroxenes of hybrid origin is controlled by cation substitution reactions reflecting local charge-balance requirements. According to the lattice strain theory, simultaneous cation exchanges across the M1, M2, and T sites have profound effects on REE + Y and HFSE partitioning. Conversely, both temperature and melt composition have only a minor effect when the thermal path of magma is restricted to 70 °C and the value of non-bridging oxygens per tetrahedral cations (NBO/T) shifts moderately from 0.31 to 0.43. As a consequence, Zone 2 partition coefficients for REE + Y and HFSE diverge significantly from those derived for Zone 1, accounting for limited cation incorporation into the newly-formed clinopyroxenes at the quartzite-magma interface.

Evidence for a sulfur-undersaturated lunar interior from the solubility of sulfur in lunar melts and sulfide-silicate partitioning of siderophile elements

NASA Astrophysics Data System (ADS)

Steenstra, E. S.; Seegers, A. X.; Eising, J.; Tomassen, B. G. J.; Webers, F. P. F.; Berndt, J.; Klemme, S.; Matveev, S.; van Westrenen, W.

2018-06-01

Sulfur concentrations at sulfide saturation (SCSS) were determined for a range of low- to high-Ti lunar melt compositions (synthetic equivalents of Apollo 14 black and yellow glass, Apollo 15 green glass, Apollo 17 orange glass and a late-stage lunar magma ocean melt, containing between 0.2 and 25 wt.% TiO2) as a function of pressure (1-2.5 GPa) and temperature (1683-1883 K). For the same experiments, sulfide-silicate partition coefficients were derived for elements V, Cr, Mn, Co, Cu, Zn, Ga, Ge, As, Se, Mo, Sn, Sb, Te, W and Pb. The SCSS is a strong function of silicate melt composition, most notably FeO content. An increase in temperature increases the SCSS and an increase in pressure decreases the SCSS, both in agreement with previous work on terrestrial, lunar and martian compositions. Previously reported SCSS values for high-FeO melts were combined with the experimental data reported here to obtain a new predictive equation to calculate the SCSS for high-FeO lunar melt compositions. Calculated SCSS values, combined with previously estimated S contents of lunar low-Ti basalts and primitive pyroclastic glasses, suggest their source regions were not sulfide saturated. Even when correcting for the currently inferred maximum extent of S degassing during or after eruption, sample S abundances are still > 700 ppm lower than the calculated SCSS values for these compositions. To achieve sulfide saturation in the source regions of low-Ti basalts and lunar pyroclastic glasses, the extent of degassing of S in lunar magma would have to be orders of magnitude higher than currently thought, inconsistent with S isotopic and core-to-rim S diffusion profile data. The only lunar samples that could have experienced sulfide saturation are some of the more evolved A17 high-Ti basalts, if sulfides are Ni- and/or Cu rich. Sulfide saturation in the source regions of lunar melts is also inconsistent with the sulfide-silicate partitioning systematics of Ni, Co and Cu. Segregation of significant quantities of (non)-stoichiometric sulfides during fractional crystallization would result in far larger depletions of Ni, Co and Cu than observed, whereas trends in their abundances are more likely explained by olivine fractionation. The sulfide exhaustion of the lunar magma source regions agrees with previously proposed low S abundances in the lunar core and mantle, and by extension with relatively minor degassing of S during the Moon-forming event. Our results support the hypothesis that refractory chalcophile and highly siderophile element systematics of low-Ti basalts and pyroclastic glasses reflect the geochemical characteristics of their source regions, instead of indicating the presence of residual sulfides in the lunar interior.

Development of high purity large forgings for nuclear power plants

NASA Astrophysics Data System (ADS)

Tanaka, Yasuhiko; Sato, Ikuo

2011-10-01

The recent increase in the size of energy plants has been supported by the development of manufacturing technology for high purity large forgings for the key components of the plant. To assure the reliability and performance of the large forgings, refining technology to make high purity steels, casting technology for gigantic ingots, forging technology to homogenize the material and consolidate porosity are essential, together with the required heat treatment and machining technologies. To meet these needs, the double degassing method to reduce impurities, multi-pouring methods to cast the gigantic ingots, vacuum carbon deoxidization, the warm forging process and related technologies have been developed and further improved. Furthermore, melting facilities including vacuum induction melting and electro slag re-melting furnaces have been installed. By using these technologies and equipment, large forgings have been manufactured and shipped to customers. These technologies have also been applied to the manufacture of austenitic steel vessel components of the fast breeder reactors and components for fusion experiments.

Abundances of Ag and Cu in mantle peridotites and the implications for the behavior of chalcophile elements in the mantle

NASA Astrophysics Data System (ADS)

Wang, Zaicong; Becker, Harry

2015-07-01

Silver abundances in mantle peridotites and the behavior of Ag during high temperature mantle processes have received little attention and, as a consequence, the abundance of Ag in the bulk silicate Earth (BSE) has been poorly constrained. In order to better understand the processes that fractionate Ag and other chalcophile elements in the mantle, abundances of Ag and Cu in mantle peridotites from different geological settings (n = 68) have been obtained by isotope dilution ICP-MS methods. In peridotite tectonites and in a few suites of peridotite xenoliths which display evidence for variable extents of melt depletion and refertilization by silicate melts, Ag and Cu abundances show positive correlations with moderately incompatible elements such as S, Se, Te and Au. The mean Cu/Ag in fertile peridotites (3500 ± 1200, 1s, n = 38) is indistinguishable from the mean Cu/Ag of mid ocean ridge basalts (MORB, 3600 ± 400, 1s, n = 338) and MORB sulfide droplets. The constant mean Cu/Ag ratios indicate similar behavior of Ag and Cu during partial melting of the mantle, refertilization and magmatic fractionation, and thus should be representative of the Earth's upper mantle. The systematic fractionation of Cu, Ag, Au, S, Se and Te in peridotites and basalts is consistent with sulfide melt-silicate melt partitioning with apparent partition coefficients of platinum group elements (PGE) > Au ⩾ Te > Cu ≈ Ag > Se ⩾ S. Because of the effects of secondary processes, the abundances of chalcophile elements, notably S, Se, but also Cu and the PGE in many peridotite xenoliths are variable and lower than in peridotite massifs. Refertilization of peridotite may change abundances of chalcophile and lithophile elements in peridotite massifs, however, this seems to mostly occur in a systematic way. Correlations with lithophile and chalcophile elements and the overlapping mean Cu/Ag ratios of peridotites and ocean ridge basalts are used to constrain abundances of Ag and Cu in the BSE at 9 ± 3 (1s) ng/g and 30 ± 6 μg/g (1s), respectively. The very different extent of depletion of Ag and Cu in the BSE cannot be explained by low pressure-temperature core formation if currently available metal-silicate partitioning data are applied.

An Overview of the Origin of A-type Silicic Magmatism Along the Snake River Plain-Yellowstone Hotspot Track

NASA Astrophysics Data System (ADS)

Christiansen, E. H.; Bindeman, I. N.; Leishman, J. R.

2015-12-01

Disparate models have been proposed for the origin of A-type rhyolites--a volumetrically minor part of modern terrestrial magmatism. But understanding the origin of A-type granites and rhyolites has significance for understanding the formation of the Earth's first silicic crust and for planetary magmatism--small volumes of such granitic materials have been found in lunar rocks, martian and asteroidal meteorites, and have been speculated to have formed on Venus. On other planets, vertical tectonics and plume-like mantle convection dominate, not the recycling of wet, oxidized plates of lithosphere as on Earth. Thus, understanding the origins of A-type silicic magma is important on multiple levels. Voluminous A-type rhyolite were produced on the Snake River Plain-Yellowstone hotspot track and provide the opportunity to better understand these important silicic magmas. Detailed petrologic studies suggest that most Snake River Plain rhyolites ultimately formed by partially melting of previously emplaced basaltic intrusions rather than by fractional crystallization of basalt or melting of Archean crust. This hypothesis is favored because of the bimodal association of rhyolite and basalt without linking intermediate compositions. In addition, incompatible element ratios (e.g., La/Nb, Pb/Ce), a lack of old zircon antecrysts, low-U inherited zircon, high ɛNd and ɛHf values, high eruption temperatures (1050°C to 850°C), low fO2 (near QFM), and H2O (as low as 1.5%), link the rhyolites to a plume-derived basaltic parent through partial melting with lesser incorporation of the Archean to Mesozoic crust that underlies the plain. Moreover, the contrast with wetter, lower temperature rhyolites that must have formed by direct crustal melting (e.g., Arbon Valley Tuff) strengthens this interpretation. Many of the rhyolites also have low δ18O values that must be produced in two stages: first by partial melting of already hydrothermally altered basalt, and subsequently in single volcanic centers, by progressive cannibalism of hydrothermally altered intracaldera rhyolites like those identified in many calderas and the Kimberly drill core. The oxygen and Hf isotopic diversity of zircon found in most units is one of the principle evidences for this pervasive recycling.

Lightning in the Protoplanetary Nebula?

NASA Technical Reports Server (NTRS)

Love, Stanley G.

1997-01-01

Lightning in the protoplanetary nebula has been proposed as a mechanism for creating meteoritic chondrules: enigmatic mm-sized silicate spheres formed in the nebula by the brief melting of cold precursors.

Formation of wadsleyite in a shock experiment - implications for the duration of shock events in meteorite parent bodies

NASA Astrophysics Data System (ADS)

Tschauner, O.; Asimow, P. D.; Ahrens, T. J.; Kostandova, N.; Sinogeikin, S.

2007-12-01

We report the first observation of the high-pressure silicate phase wadsleyite in the recovery products of a shock experiment. Wadsleyite was detected by micro-X ray diffraction and EBSD. Wadsleyite grew from melt which formed by chemical reaction of periclase and silica during shock. Our findings show that the growth rate of high pressure silicate phases in shock-generated melts can be of the order of m/s and is probably not diffusion controlled. Our finding has important implications for the time scale of shock events recorded by meteorites and indicates that the presence of high pressure silicates found in shocked meteorites does not necessarily imply large impactor sizes. This work was supported by the NNSA Cooperative Agreement DOE-FC88-01NV14049 and NASA/Goddard grants under awards NNG04GP57G and NNG04GI07G. Use of the HPCAT facility was supported by DOE-BES, DOE-NNSA, NSF, DOD -TACOM, and the W.M. Keck Foundation. APS is supported by DOE-BES under Contract No. W-31-109-Eng-38.

Eutectic propeties of primitive Earth's magma ocean

NASA Astrophysics Data System (ADS)

Lo Nigro, G.; Andrault, D.; Bolfan-Casanova, N.; Perillat, J.-P.

2009-04-01

It is widely accepted that the early Earth was partially molten (if not completely) due to the high energy dissipated by terrestrial accretion [1]. After core formation, subsequent cooling of the magma ocean has led to fractional crystallization of the primitive mantle. The residual liquid corresponds to what is now called the fertile mantle or pyrolite. Melting relations of silicates have been extensively investigated using the multi-anvil press, for pressures between 3 and 25 GPa [2,3]. Using the quench technique, it has been shown that the pressure affects significantly the solidus and liquidus curves, and most probably the composition of the eutectic liquid. At higher pressures, up to 65 GPa, melting studies were performed on pyrolite starting material using the laser-heated diamond anvil cell (LH-DAC) technique [4]. However, the quench technique is not ideal to define melting criteria, and furthermore these studies were limited in pressure range of investigation. Finally, the use of pyrolite may not be relevant to study the melting eutectic temperature. At the core-mantle boundary conditions, melting temperature is documented by a single data point on (Mg,Fe)2SiO4 olivine, provided by shock wave experiments at around 130-140 GPa [5]. These previous results present large uncertainties of ~1000 K. The aim of this study is to determine the eutectic melting temperature in the chemically simplified system composed of the two major lower mantle phases, the MgSiO3 perovskite and MgO periclase. We investigated melting in-situ using the laser-heated diamond anvil cell coupled with angle dispersive X-ray diffraction at the ID27 beamline of the ESRF [6]. Melting relations were investigated in an extended P-T range comparable to those found in the Earth's lower mantle, i.e. from 25 to 120 GPa and up to more than 5000 K. Melting was evidenced from (a) disappearance of one of the two phases in the diffraction pattern, (b) drastic changes of the diffraction image itself, and/or (c) appearance of a broad band of diffuse X-ray scattering associated to the presence of silicate liquid. The pressure evolution of the eutectic temperature is found below the melting curve of pure MgSiO3 perovskite [7] for more than 500 K and also below the solidus curve of pyrolite [4] for 100-200 K at 60 GPa. References [1] B. T. Tonks, H. J. Melosh, Journal of Geophysical Research 98 5319 (1993). [2] Litasov, K., and Ohtani, E. Physics of The Earth and Planetary Interiors, 134(1-2), 105-127, (2002). [3] E. Ito, A. Kubo, T. Katsura et al., Phys. Earth Planet. Inter. 143-144 397 (2004). [4] A. Zerr, R. Boehler, Nature 506-508 (1994). [5] J. A. Akins, S. N. Luo, P. D. Asimov et al., Geophys. Res. Lett. 31 doi:10.1029/2004GL020237 (2004). [6] Schultz et al. International Journal of High Pressure Research. 25, 1, 71-83 (2005). [7] Zerr, A. and Boehler, R. Science, 262, 553-555 (1993).

Melt-processing of small molecule organic photovoltaics via bulk heterojunction compatibilization.

PubMed

Rahmanudin, Aiman; Yao, Liang; Jeanbourquin, Xavier A; Liu, Yongpeng; Sekar, Arvindh; Ripaud, Emilie; Sivula, Kevin

2018-05-21

Melt-processing of organic semiconductors (OSCs) is a promising environmentally-friendly technique that can alleviate dependence on toxic chlorinated solvents. While melt-processed single-component OSC devices ( e.g. field-effect-transistors) have been demonstrated, multi-component bulk heterojunctions (BHJs) for organic photovoltaics (OPVs) remain a challenge. Herein, we demonstrate a strategy that affords tunable BHJ phase segregation and domain sizes from a single-phase homogeneous melt by employing strongly-crystalline small-molecule OSCs together with a customized molecular compatibilizing (MCP) additive. An optimized photoactive BHJ with 50 wt% MCP achieved a device power conversion efficiency of ca. 1% after melting the active layer at 240 °C (15 min, followed by slow cooling) before deposition of the top electrode. BHJ morphology characterization using atomic force and Kelvin probe microscopy, X-ray diffraction, and photo-luminescence measurements further demonstrate the trade-off between free charge generation and transport with respect to MCP loading in the BHJ. In addition, a functional OPV was also obtained from the melt-processing of dispersed micron-sized solid BHJ particles into a smooth and homogeneous thin-film by using the MCP approach. These results demonstrate that molecular compatibilization is a key prerequisite for further developments towards true solvent-free melt-processed BHJ OPV systems.

Brillouin-scattering studies of K2Si4O9 glass and melt up to 1000 °C

NASA Astrophysics Data System (ADS)

Xu, Ji-An; Manghnani, Murli H.; Richet, Pascal

1992-10-01

The Brillouin-scattering technique has been used with glass plate samples and with glass sandwich assemblies to measure the acoustic velocities of K2Si4O9 glass as a function of temperature up to 1000 °C. Results differ from those of the sodium silicate glass reported earlier in that the turning points of the velocity versus temperature curves for the potassium silicate glass are found not only at the strain point (466 °C) but also at the softening point (720 °C). Combined with the results of the 90° platelet- and 180° back-scattering geometry measurements, the refractive index n and equation of state of the glass and melt as a function of temperature were also determined.

Evidence for a Meteoritic Component in Impact Melt Rock from the Chicxulub Structure

NASA Technical Reports Server (NTRS)

Koeberl, Christian; Sharpton, Virgil L.; Schuraytz, Benjamin C.; Shirey, Steven B.; Blum, Joel D.; Marin, Luis E.

1994-01-01

The Chicxulub structure in Yucatan, Mexico, has recently been recognized as a greater then 200-km-diameter multi-ring impact crater of K-T boundary age. Crystalline impact melt rocks and breccias from within the crater, which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects, have been studied for trace element and Re-Os isotope compositions. Re-Os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact-derived rocks. A melt rock sample shows elevated iridium concentrations, an osmium concentration of 25 ppb, and a low Os-187/Os-188 ratio of 0.113, which are incompatible with derivation from the continental crust. Even though the Os-187/Os-188 ratio is slightly lower than the range so far measured in meteorites, a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material. The data support the hypothesis of a heterogeneously distributed meteoritic component in the Chicxulub melt rock. A sample of impact glass from the Haitian K-T boundary at Beloc yielded about 0.1 ppb osmium and an Os-187/0s-188 ratio of 0.251, indicating the presence of a small meteoritic component in the impact ejecta as well.

Carbonatitic and granitic melts produced under conditions of primary immiscibility during anatexis in the lower crust

NASA Astrophysics Data System (ADS)

Ferrero, Silvio; Wunder, Bernd; Ziemann, Martin A.; Wälle, Markus; O'Brien, Patrick J.

2016-11-01

Carbonatites are peculiar magmatic rocks with mantle-related genesis, commonly interpreted as the products of melting of CO2-bearing peridotites, or resulting from the chemical evolution of mantle-derived magmas, either through extreme differentiation or secondary immiscibility. Here we report the first finding of anatectic carbonatites of crustal origin, preserved as calcite-rich polycrystalline inclusions in garnet from low-to-medium pressure migmatites of the Oberpfalz area, SW Bohemian Massif (Central Europe). These inclusions originally trapped a melt of calciocarbonatitic composition with a characteristic enrichment in Ba, Sr and LREE. This interpretation is supported by the results of a detailed microstructural and microchemical investigation, as well as re-melting experiments using a piston cylinder apparatus. Carbonatitic inclusions coexist in the same cluster with crystallized silicate melt inclusions (nanogranites) and COH fluid inclusions, suggesting conditions of primary immiscibility between two melts and a fluid during anatexis. The production of both carbonatitic and granitic melts during the same anatectic event requires a suitable heterogeneous protolith. This may be represented by a sedimentary sequence containing marble lenses of limited extension, similar to the one still visible in the adjacent central Moldanubian Zone. The presence of CO2-rich fluid inclusions suggests furthermore that high CO2 activity during anatexis may be required to stabilize a carbonate-rich melt in a silica-dominated system. This natural occurrence displays a remarkable similarity with experiments on carbonate-silicate melt immiscibility, where CO2 saturation is a condition commonly imposed. In conclusion, this study shows how the investigation of partial melting through melt inclusion studies may unveil unexpected processes whose evidence, while preserved in stiff minerals such as garnet, is completely obliterated in the rest of the rock due to metamorphic re-equilibration. Our results thus provide invaluable new insights into the processes which shape the geochemical evolution of our planet, such as the redistribution of carbon and strategic metals during orogenesis.

Simulating the behavior of volatiles belonging to the C-O-H-S system in silicate melts under magmatic conditions with the software D-Compress

NASA Astrophysics Data System (ADS)

Burgisser, Alain; Alletti, Marina; Scaillet, Bruno

2015-06-01

Modeling magmatic degassing, or how the volatile distribution between gas and melt changes at pressure varies, is a complex task that involves a large number of thermodynamical relationships and that requires dedicated software. This article presents the software D-Compress, which computes the gas and melt volatile composition of five element sets in magmatic systems (O-H, S-O-H, C-S-O-H, C-S-O-H-Fe, and C-O-H). It has been calibrated so as to simulate the volatiles coexisting with three common types of silicate melts (basalt, phonolite, and rhyolite). Operational temperatures depend on melt composition and range from 790 to 1400 °C. A specificity of D-Compress is the calculation of volatile composition as pressure varies along a (de)compression path between atmospheric and 3000 bars. This software was prepared so as to maximize versatility by proposing different sets of input parameters. In particular, whenever new solubility laws on specific melt compositions are available, the model parameters can be easily tuned to run the code on that composition. Parameter gaps were minimized by including sets of chemical species for which calibration data were available over a wide range of pressure, temperature, and melt composition. A brief description of the model rationale is followed by the presentation of the software capabilities. Examples of use are then presented with outputs comparisons between D-Compress and other currently available thermodynamical models. The compiled software and the source code are available as electronic supplementary materials.

Petrogenesis of Miller Range 07273, a new type of anomalous melt breccia: Implications for impact effects on the H chondrite asteroid

NASA Astrophysics Data System (ADS)

Ruzicka, Alex M.; Hutson, Melinda; Friedrich, Jon M.; Rivers, Mark L.; Weisberg, Michael K.; Ebel, Denton S.; Ziegler, Karen; Rumble, Douglas; Dolan, Alyssa A.

2017-09-01

Miller Range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine-grained (<5 μm), largely crystalline, igneous matrix. Data indicate that MIL was derived from the H chondrite parent asteroid, although it has an oxygen isotope composition that approaches but falls outside of the established H group. MIL also is distinctive in having low porosity, cone-like shapes for coarse metal grains, unusual internal textures and compositions for coarse metal, a matrix composed chiefly of clinoenstatite and omphacitic pigeonite, and troilite veining most common in coarse olivine and orthopyroxene. These features can be explained by a model involving impact into a porous target that produced brief but intense heating at high pressure, a sudden pressure drop, and a slower drop in temperature. Olivine and orthopyroxene in chondrule clasts were the least melted and the most deformed, whereas matrix and troilite melted completely and crystallized to nearly strain-free minerals. Coarse metal was largely but incompletely liquefied, and matrix silicates formed by the breakdown during melting of albitic feldspar and some olivine to form pyroxene at high pressure (>3 GPa, possibly to 15-19 GPa) and temperature (>1350 °C, possibly to ≥2000 °C). The higher pressures and temperatures would have involved back-reaction of high-pressure polymorphs to pyroxene and olivine upon cooling. Silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration.

Solidus of carbonated fertile peridotite under fluid-saturated conditions

NASA Astrophysics Data System (ADS)

Falloon, Trevor J.; Green, David H.

1990-03-01

The solidus for a fertile peridotite composition ("Hawaiian pyrolite") in the presence of a CO2-H2O fluid phase has been determined from 10 to 35 kbar. The intersection of the decarbonation reaction (olivine + diopside + CO2 ←→ orthopyroxene + dolomite) with the pyrolite solidus defines the point Q‧, located at 22 kbar and 940 °C. At pressures less than Q‧, the solidus passes through a temperature maximum at 14 kbar, 1060 °C. The solidus is coincident with amphibole breakdown at pressures less than 16 kbar. At pressures above Q‧, the solidus is defined by the dissolution of crystalline carbonate into a sodic, dolomitic carbonatite melt. The solidus is at a temperature of 925 °C at ˜28 kbar. The solidus temperature above the point Q‧ is similar to the solidus determined for Hawaiian pyrolite-H2O-CO2 for small contents of H2O (<0.3 wt%) and CO2 (<5 wt%), thus indicating that the primary sodic dolomitic carbonatite melt at both solidi has a very low and limited H2O solubility. The new data clarify the roles of carbonatite melt, carbonated silicate melt, and H2O-rich fluid in mantle conditions that are relatively oxidized (fO2 ˜ MW to FMQ). In particular, a carbonatite melt + garnet lherzolite region is intersected by continental shield geothermal gradients, but such geotherms only intersect regions with carbonated silicate melt if perturbed to higher temperatures ("kinked geotherm").

Shock, Post-Shock Annealing, and Post-Annealing Shock in Ureilites

NASA Technical Reports Server (NTRS)

Rubin, Alan E.

2006-01-01

The thermal and shock histories of ureilites can be divided into four periods: 1) formation, 2) initial shock, 3) post-shock annealing, and 4) post-annealing shock. Period 1 occurred approx.4.55 Ga ago when ureilites formed by melting chondritic material. Impact events during period 2 caused silicate darkening, undulose to mosaic extinction in olivines, and the formation of diamond, lonsdaleite, and chaoite from indigenous carbonaceous material. Alkali-rich fine-grained silicates may have been introduced by impact injection into ureilites during this period. About 57% of the ureilites were unchanged after period 2. During period 3 events, impact-induced annealing caused previously mosaicized olivine grains to become aggregates of small unstrained crystals. Some ureilites experienced reduction as FeO at the edges of olivine grains reacted with C from the matrix. Annealing may also be responsible for coarsening of graphite in a few ureilites, forming euhedral-appearing, idioblastic crystals. Orthopyroxene in Meteorite Hills (MET) 78008 may have formed from pigeonite by annealing during this period. The Rb-Sr internal isochron age of approx.4.0 Ga for MET 78008 probably dates the annealing event. At this late date, impacts are the only viable heat source. About 36% of ureilites experienced period 3 events, but remained unchanged afterwards. During period 4, approx.7% of the ureilites were shocked again, as is evident in the polymict breccia, Elephant Moraine (EET) 83309. This rock contains annealed mosaicized olivine aggregates composed of small individual olivine crystals that exhibit undulose extinction. Ureilites may have formed by impact-melting chondritic material on a primitive body with heterogeneous O isotopes. Plagioclase was preferentially lost from the system due to its low impedance to shock compression. Brief melting and rapid burial minimized the escape of planetary-type noble gases from the ureilitic melts. Incomplete separation of metal from silicates during impact melting left ureilites with relatively high concentrations of trace siderophile elements.

Solubility of tungsten in a haplobasaltic melt as a function of temperature and oxygen fugacity

NASA Astrophysics Data System (ADS)

Ertel, W.; O'Neill, H. St. C.; Dingwell, D. B.; Spettel, B.

1996-04-01

The solubility of tungsten (W) in a haplobasaltic melt has been determined as a function of oxygen fugacity in the temperature range 1300-1500°C using the mechanically assisted equilibrium technique of Dingwell et al. (1994), and at 1600-1700°C by the wire loop method. Quenched samples were analysed for W by using ICP-AES as well as INAA, and sample major element compositions were checked by electron microprobe. W concentrations ranged from 20 ppm to 17 wt%, and the solution of WO 2 in the melt may be described by Henry's Law up to remarkably high concentrations (e.g., 14 wt% at 1500°C). W dissolves in the melt with a quadrivalent (4+) formal oxidation state over the entire range of oxygen fugacity and temperature investigated. The solubility of W decreases strongly with increasing temperature at constant oxygen fugacity. The solubility data have been used to calculate trace distribution coefficients for W between Fe-rich metal and silicate melt, using literature values for the activity coefficient of W in liquid Fe. Comparison of our data with the distribution coefficients for Mo calculated from the analogous Mo solubility data of Holzheid et al. (1994) shows that the ratio of the metal-silicate distribution coefficient DMomet/sil/ DWmet/sil remains very high (~10 3) at all T-fO 2 conditions. However, in the Earth's mantle, Mo is relatively more depleted than W only by a factor of three. The relative abundances of W and Mo in the Earth's mantle cannot, therefore, be explained by core formation from a homogeneously accreted Earth whatever the temperature at which metal/silicate equilibrium may have ocurred might have been. Their abundances may be quantitatively accounted for by a heterogeneous accretion model such as that of O'Neill (1991).

An effective utilization of the slag from acid leaching of coal-waste: preparation of water glass with a low-temperature co-melting reaction.

PubMed

Fang, Li; Duan, Xiaofang; Chen, Rongming; Cheng, Fangqin

2014-08-01

This paper presents an effective utilization of slag from acid leaching of coal-waste with a novel approach, namely low-temperature co-melting method, for preparation of sodium silicate (Na2O x nSiO2) using slag from acid leaching of coal-waste as feedstock. It is very interesting that the co-melting reaction temperature of the mixture of Na2CO3 and the feedstock (50-100 microm) was as low as 850 degrees C, which was significantly lower than the temperature used in traditional sodium silicate production (1400 degrees C). The optimum SiO2/Na2O ratio was identified as 7:3 according to the results of thermogravimetry-differential scanning calorimetry (TGA-DSC), ICP-AES, and X-ray diffraction (XRD) analyses. In this condition, the main product was sodium disilicate (Na2O x 2SiO2), with water solubility of 85.0%. More importantly, the impurities such as aluminum in the feedstock, which had adverse effect on subsequent treatment, were concentrated almost completely in the filter residue as insoluble sodium alumunosilicates, i.e., Na(Si2Al)O6 x H2O. The lower co-melting temperature of this process demonstrates a significant energy-saving opportunity and thus a promising approach for highly effective utilization of coal-waste. Implications: Recently, alumina extraction from coal-waste has been extensively investigated and industrial applied in China. However, the slag-containing silica generated from the acid leaching process of coal-waste led to a secondary pollution, which hindered large-scale production. The proposed low-temperature co-melting method for preparation of sodium silicate (Na2O x nSiO2) using slag from acid leaching of coal-waste as feedstock indicated that it is an efficient approach for the recovery of silica from the acid-leached slag of coal-waste with minimal environmental impact.

Paleomagnetism and Mineralogy of Unusual Silicate Glasses and Baked Soils on the Surface of the Atacama Desert of Northern Chile: A Major Airburst Impact ~12ka ago?.

NASA Astrophysics Data System (ADS)

Roperch, P. J.; Blanco, N.; Valenzuela, M.; Gattacceca, J.; Devouard, B.; Lorand, J. P.; Tomlinson, A. J.; Arriagada, C.; Rochette, P.

2015-12-01

Unusual silicate glasses were found in northern Chile in one of the driest place on earth, the Atacama Desert. The scoria-type melted rocks are littered on the ground at several localities distributed along a longitudinal band of about 50km. The silicate glasses have a stable natural remanent magnetization carried by fine-grained magnetite and acquired during cooling. At one locality, fine-grained overbank sediments were heated to form a 10 to 20 cm-thick layer of brick-type samples. Magnetic experiments on oriented samples demonstrate that the baked clays record a thermoremanent magnetization acquired in situ above 600°C down to more than 10cm depth and cooled under a normal polarity geomagnetic field with a paleointensity of 40μT. In some samples of the silicate glass, large grains of iron sulphides (troilite) are found in the glass matrix with numerous droplets of native iron, iron sulphides and iron phosphides indicating high temperature and strong redox conditions during melting. The paleomagnetic record of the baked clays and the unusual mineralogy of the silicate glasses indicate a formation mainly by in situ high temperature radiation. Paleomagnetic experiments and chemical analyses indicate that the silicate glasses are not fulgurite type rocks due to lightning events, nor volcanic glasses or even metallurgical slags related to mining activity. The existence of a well-developped baked clay layer indicates that the silicate glasses are not impact-related ejectas. The field, paleomagnetic and mineralogical observations support evidence for a thermal event likely related to a major airburst. The youngest calibrated 14C age on a charcoal sample closely associated with the glass indicates that the thermal event occurred around 12 to 13 ka BP. The good conservation of the surface effects of this thermal event in the Atacama Desert could provide a good opportunity to further estimate the threats posed by large asteroid airbursts.

H2O-CO2-S-Cl partitioning and mixing in rhyolitic melts and fluid - Implications on closed-system degassing in rhyolite

NASA Astrophysics Data System (ADS)

Ding, S.; Webster, J. D.

2017-12-01

Magmatic degassing involving multiple volatile components (C, O, H, S, Cl, etc.) is one of the key factors influencing the timing and nature of volcanic eruptions, and the chemistry of volcanic gases released to the surface. In particular, exsolution of these volatiles from silicic magma during ascent could trigger explosive volcanic eruptions, which can exert strong impacts on surface temperature, ecology and human health. However, quantitative evaluation of this process in silicic magma remains ambiguous due to the lack of experiments in such chemically complex systems. Rhyolite-fluid(s) equilibria experiments were conducted in an IHPVat 100-300 MPa and 800 ° C to determine the solubilities, fluid-melt partitioning, and mixing properties of H2O, CO2, S, and Cl in the oxygen fugacity (fO2) range of FMQ to FMQ+3. The integrated bulk fluids contain up to 94 mol% H2O, 32 mol% CO2, 1 mol% S and 1mol% Cl. Rhyolite melt dissolved 20- 770 ppm CO2 and 4-7 wt.% H2O, varying with pressure, fluid composition, and fO2. Concentrations of H2O and CO2 in melt from C-O-H-S-Cl- bearing experiments at 100 and 200 MPa, and from C-O-H only experiments are generally consistent with the predictions of existing CO2-H2O solubility models based on the C-O-H only system [1-4], while the solubilities of H2O and CO2 in melt with addition of S±Cl at 300 MPa are less than those of the C-O-H- only system. This reduction in H2O and CO2 solubilities exceeds the effects of simple dilution of the coexisting fluid owing to addition of other volatiles, and rather, reflects complex mixing relations. Rhyolite melt also dissolved 20-150 ppm S and 850-2000 ppm Cl, varying with pressure. At 300 MPa, S concentrations in the melt change with fO2. The partitioning of CO2 and S between fluid and melt varies as a function of fluid composition and fO2. Solubilities and complex mixing relationships of CO2, H2O, S and Cl revealed in our experiments can be applied to massive rhyolitic eruptions like those of the Bishop tuff, Toba tuff and Pinatubo to better understand the degassing process, to estimate fluid compositions, and thus, to evaluate the potential environmental impacts of these super eruptions. [1] Ghiorso amd Gualda, 2015, CMP; [2] Liu et al., 2005, J. Volcanol. Geotherm. Res.; [3] Newman and Lowenstern, 2002, Comput. Geosci.; [3] Tamic et al., 2001, Chem. Geol..

Origin and evolution of rare amphibole-bearing mantle peridotites from Wilcza Góra (SW Poland), Central Europe

NASA Astrophysics Data System (ADS)

Matusiak-Małek, Magdalena; Puziewicz, Jacek; Ntaflos, Theodoros; Grégoire, Michel; Kukuła, Anna; Wojtulek, Piotr Marian

2017-08-01

Mantle xenoliths in the 20 Ma Wilcza Góra basanite (Lower Silesia, NE Bohemian Massif) are mostly harzburgites, some with amphibole which is exceptional in the region. Forsterite content in olivine defines two Groups of peridotites: Group A (Fo89.1-91.5) and Group B (Fo84.2-89.2). Hornblende-clinopyroxenite, websterite and one composite xenolith consisting of dunite, olivine-hornblendite and pyroxene-hornblende-peridotite contain olivine with Fo77.3-82.5 and are classified as Group C. Group A xenoliths contain Al-poor orthopyroxene and some contain LREE-enriched clinopyroxene with negative Ti, Zr-Hf and Nb-Ta anomalies. Spinel (Cr# 0.57-0.68) is scarce in Group A, and Cr-rich pargasite occurs in only two xenoliths. Group B xenoliths contain less magnesian orthopyroxene and clinopyroxene. The REE patterns of Group B clinopyroxene are convex downward, less enriched in LREE and have smaller negative Ti, Zr-Hf and Nb-Ta anomalies than those in Group A. The Cr# in Group B spinel is 0.26-0.56, while pargasite is Ti-rich and Cr-poor. Clinopyroxene from Group C is low magnesian, slightly enriched in LREE and has no negative Ti, Zr-Hf and Nb-Ta anomalies. Group C pargasite is rich in Ti and poor in Cr. Equilibration temperatures recorded in all groups vary within the range of 905-970 °C. Xenoliths from Wilcza Góra record a polyphase lithospheric mantle evolution, starting with melting which extracted ca. 30% melt from the protolith and left a harzburgite residuum depleted in Al, lacking clinopyroxene and containing rare Cr-rich spinel. This residuum was later overprinted by chromatographic metasomatism by carbonated hydrous silicate melt related to Cenozoic volcanism. The metasomatic agent was locally hydrous enough to enable amphibole to crystallize. The Group C pyroxenites formed directly from the metasomatic melt or during peridotite-melt reactions at high melt-rock ratio. The melt is inferred to have percolated through the wall-rock peridotite, decreasing its amount and changing composition (and that of the crystallizing clinopyroxene and amphibole) as it differentiated chromatographically from Groups B to A. Enrichment in carbonatite component occurred in the further parts of a chromatographic column. Group B peridotites closest to the source of the metasomatic agent were percolated by an iron-rich melt. The latter, aside from crystallizing clinopyroxene and amphibole, caused Fe-enrichment in the host harzburgite. Such a metasomatic history is typical for the lithospheric mantle located beneath the northern margin of the Bohemian Massif, but Wilcza Góra is the only locality, where activity of a hydrous metasomatic agent is recorded. Thus, the lithospheric mantle in this area was affected by mafic silicate metasomatic agents of variable compositions.

Tungsten Abundances in Hawaiian Picrites: Implications for the Mantle Sources of Hawaiian Volcanoes

NASA Astrophysics Data System (ADS)

Ireland, T. J.; Arevalo, R. D.; Walker, R. J.; McDonough, W. F.

2008-12-01

Tungsten abundances have been measured in a suite of Hawaiian picrites (MgO >13 wt.%) from nine Hawaiian shield volcanoes (Mauna Kea, Mauna Loa, Hualalai, Loihi, Koolau, Kilauea, Kohala, Lanai and Molokai). Tungsten concentrations in the parental melts for these volcanoes have been estimated via the intersection of linear W-MgO trends with the putative MgO content of the parental melt (~16 wt.%). Tungsten behaves as a highly incompatible trace element in mafic to ultramafic systems; thus, given an independent assessment of the degree of partial melting for each volcanic center, the W abundances in their mantle sources can be determined. The mantle sources for Hualalai, Kilauea, Kohala and Loihi have non- uniform estimated W abundances of 11, 13, 16 and 27 ng/g, respectively, giving an average source abundance of 17±5 ng/g. This average source abundance is nearly six times more enriched than Depleted MORB Mantle (DMM: 3.0±2.3 ng/g) and slightly elevated relative to the Bulk Silicate Earth (BSE: 13±10 ng/g). The relatively high abundances of W in the Hawaiian sources relative to the DMM can potentially be explained as a consequence of crustal recycling. For example, incorporation of 30% oceanic crust (30 ng/g W), including 3% sediment (1500 ng/g W), into a DMM source could create the W enrichment observed in the Loihi source, consistent with estimates from earlier models based on other trace elements and isotope systems. The Hualalai source, however, has also been suggested to contain a substantial recycled component, as implied by similarly radiogenic 187Os/188Os, yet this source has the lowest estimated W abundance among the volcanic centers studied. The conflict between these results may: 1) reflect chemical differences among recycled components, 2) indicate a more complex history for Hualalai samples, e.g. involvement of a melt percolation component, or 3) implicate other sources of W.

Formation of Apollo 16 impactites and the composition of late accreted material: Constraints from Os isotopes, highly siderophile elements and sulfur abundances

NASA Astrophysics Data System (ADS)

Gleißner, Philipp; Becker, Harry

2017-03-01

Fe-Ni metal-schreibersite-troilite intergrowths in Apollo 16 impact melt rocks and new highly siderophile element (HSE) and S abundance data indicate that millimeter-scale closed-system fractional crystallization processes during cooling of impactor-derived metal melt droplets in impact-melts are the main reason for compositional variations and strong differences in abundances and ratios of HSE in multiple aliquots from Apollo 16 impact melt rocks. Element ratios obtained from linear regression of such data are therefore prone to error, but weighted averages take into account full element budgets in the samples and thus represent a more accurate estimate of their impactor contributions. Modeling of solid metal-liquid metal partitioning in the Fe-Ni-S-P system and HSE patterns in impactites from different landing sites suggest that bulk compositions of ancient lunar impactites should be representative of impact melt compositions and that large-scale fractionation of the HSE by in situ segregation of solid metal or sulfide liquid in impact melt sheets most likely did not occur. The compositional record of lunar impactites indicates accretion of variable amounts of chondritic and non-chondritic impactor material and the mixing of these components during remelting of earlier ejecta deposits. The non-chondritic composition appears most prominently in some Apollo 16 impactites and is characterized by suprachondritic HSE/Ir ratios which increase from refractory to moderately volatile HSE and exhibit a characteristic enrichment of Ru relative to Pt. Large-scale fractional crystallization of solid metal from sulfur and phosphorous rich metallic melt with high P/S in planetesimal or embryo cores is currently the most likely process that may have produced these compositions. Similar materials or processes may have contributed to the HSE signature of the bulk silicate Earth (BSE).

Influence of valence state of copper ions on structural and spectroscopic properties of multi-component PbO-Al2O3-TeO2-GeO2-SiO2 glass ceramic system- a possible material for memory switching devices

NASA Astrophysics Data System (ADS)

Tirupataiah, Ch.; Narendrudu, T.; Suresh, S.; Srinivasa Rao, P.; Vinaya Teja, P. M.; Sambasiva Rao, M. V.; Chinna Ram, G.; Krishna Rao, D.

2017-11-01

Multi-component glass ceramics with composition 29PbO-5Al2O3-1TeO2 -10GeO2- (55-x) SiO2 doped with different concentrations of CuO (0 ≤ x ≤ 1.0 mol %) were synthesized by melt quenching technique and subsequent heat treatment. These glass ceramics were characterized by X-ray diffraction, scanning electron microscope, differential thermal analysis, optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman studies. The absorption spectra of these glass ceramics exhibited a broad absorption band in the range 650-950 nm which is ascribed to 2B1g → 2B2g octahedral transition of Cu2+ ions. A feeble band around 364 nm is also identified in the samples doped with CuO up to 0.6 mol% as being due to charge transfer between the two oxidation states Cu2+ and Cu+ of copper ions. The EPR spectrum recorded at room temperature exhibited a strong resonance signal at g⊥ = 2.072 and a shallow quadruplet at about gǁ = 2.401. FTIR and Raman spectra of the titled samples provide significant information about various structural units viz., silicate, germanate, PbO4, PbO6, AlO6, TeO4 and TeO3 that are present in these ceramic matrix. Analysis of the spectroscopic investigations reveals that with an increase in the concentration of CuO up to 0.6 mol% copper ions do exist in Cu2+ and Cu+ states and they act as modifiers and net work formers respectively. Therefore, glass ceramic sample contains 0.6 mol% of CuO is favorable for memory switching action.

Sulfides in the Garnet Pyroxenite xenoliths from Oahu, Hawaii

NASA Astrophysics Data System (ADS)

Sen, I. S.; Sen, G.; Bizimis, M.

2007-12-01

Oahu is known for its garnet bearing xenoliths that occur in the Honolulu Volcanics. Clinopyroxene is the dominant minerals of these rocks, and modes of other silicate minerals - orthopyroxene, olivine, garnet, amphibole, and phlogopite vary considerably. Ilmenite and Spinels of diverse variety also occur (Keshav et al. 2007, J. Petrol.). In this report we present new electron microprobe and LA-ICPMS data on the sulfides that are always present in these xenoliths although they make up only trace amounts. In terms of morphology and mode of occurrence the sulfides can be divided fundamentally into two types - Type I occurs as poikilitic inclusions in the silicate phases mostly in clinopyroxene and Type II occurs in the interstitial spaces between the silicates, along grain boundaries and along cracks within individual silicate grains. Sizes of both types vary considerably. Type I sulfides are generally globular and appear to have formed from immiscible sulfide melts that got enclosed by the silicate minerals that grew from the main body of silicate melt. Keshav et al. (2007) estimate the average solidus temperatures of garnet pyroxenites from Oahu to range from 1215 to 1600°C (average 1325°C) at 3-5 GPa. Therefore, the Type I sulfides are high temperature sulfides that formed above the silicate solidus. Type II sulfides take various forms - from vein-like to dendritic. Compositionally, both types include Ni rich pyrrhotites (Ni content varies from 3-5 wt%) and monosulfide solid solutions(MSS). The MSS are divided into Ni rich MSS containing as much as 20 wt% of Ni, the average is 15 wt% while the Ni poor MSS has 5-9 wt% of Ni in it. We have limited data on PGE so far but the Type II sulfides have a very low PGE content. Two recent papers have noted that Hawaiian plume-derived shield tholeiites are too rich in Ni for a given SiO2% to be produced by partial melting of a peridotite and called for an unusual Ni-rich pyroxenite source in which the large Ni content is locked in clinopyroxene. The many experiments that have been conducted on pyroxenites have not been able to generate such high Ni clinopyroxenes. We propose that the Ni actually comes from the high Ni monosulfide solid solutions similar to those in the pyroxenites studied. However, we do not think that these pyroxenites are the source of Hawaiian shield lavas because their isotopic composition is distinct from shield lavas.

Advances in Constraining Solubilities of H-O-C-S-Cl-bearing Fluids in Silicate Melts

NASA Astrophysics Data System (ADS)

Webster, J. D.

2009-12-01

Magmatic-hydrothermal fluids that are variably enriched in the volatile components H2O, CO2/CH4, H2S/SO2, Cl, F, ± B alter rock; dissolve, transport, and deposit ore metals, and drive volcanism. The efficacy of these processes varies directly with the compositions and quantities, and in particular, with the molar volumes of the fluids involved. Although natural hydrothermal fluids are geochemically diverse, experimental constraints on volatile solubilities in silicate melts are largely limited to two volatiles. Recent experimental research, however, has begun to address mutual solubility relationships of three and four volatiles in felsic to intermediate aluminosilicate melts at shallow crustal pressures. Following well-established correlations demonstrating that as little as a few hundred to thousand ppm CO2 or Cl reduce H2O solubility in melts, and hence enhance the tendency for magma to exsolve one or two fluid phases, recent work shows fundamentally important solubility relationships involving H2O, S, and Cl. Research on rhyodacitic (Botcharnikov et al., 2004) and phonolitic melts at 200 MPa reveals that hundreds to thousands of ppm S will reduce Cl solubility in these melts. Thus, S reduces Cl solubility, which in turn reduces H2O solubility in melts. Other investigations have determined that CaSO4 solubility in oxidizing hydrothermal fluids varies directly with the concentrations of NaCl ± KCl in these fluids (Newton and Manning, 2005; Webster et al., 2009). The CaSO4 contents in the most alkali chloride-enriched fluids exceed 60 wt.%. It follows that some mineralizing saline magmatic fluids are strongly enriched in Ca, Na, K, Cl, SO4, and reduced S species. Research on H2O-, CO2-, and Cl-bearing melts at 200 MPa also highlights critical reciprocal volatile solubility behavior. Work at 1200°C on andesitic melts saturated in two fluids determines that the presence of CO2 enlarges the immiscibility gap for vapor plus brine and increases the activities of H2O and Cl (Botcharnikov et al. 2007). Conversely, other work involving Cl-enriched phonolitic melts plus two fluids at 900°C observes that the presence of Cl strongly reduces CO2 solubility in the melt. In fact, for runs containing as much as 80 mole percent CO2 in the fluid, the CO2/CO3 contents of the melts were reduced to values below the limit of detection for FTIR (< ca. 30-40 ppm). Thus, Cl works to reduce CO2 solubility, which in turn reduces H2O solubility in phonolitic melts. Current work on the solubility of H-O-C-S in haplogranitic melts at 200 MPa demonstrates that the addition of C reduces the (fluid/melt) partition coefficient for S. In addition, these experimentally determined partition coefficients decrease in the order CO2 > S > H2O, and their ranges are virtually identical to and thus confirm modeled values computed (Scaillet and Pichavant, 2003) for pre-eruptive magmatic fluids based on volatile fugacities of volcanic gases of arc-related magmas. Botcharnikov R et al (2004) Chem. Geol. 213, 207-225. Botcharnikov R, Holtz F, Behrens H (2007) Eur. J. Mineral. 19, 671-680. Newton R, Manning C (2005) J. Petrol. 46, 701-716. Scaillet B, Pichavant M (2003) Volcanic Degassing, Geol. Soc. Spec. Pub. 213, 23-52. Webster J, Sintoni M, De Vivo B (2009) Chem. Geol. 263, 19-36.

Experimental Melting Study of Basalt-Peridotite Hybrid Source: Constrains on Chemistry of Recycled Component

NASA Astrophysics Data System (ADS)

Gao, S.; Takahashi, E.; Matsukage, K. N.; Suzuki, T.; Kimura, J. I.

2015-12-01

It is believed that magma genesis of OIB is largely influenced by recycled oceanic crust component involved in the mantle plume (e.g., Hauri et al., 1996; Takahashi & Nakajima., 2002; Sobolev et al., 2007). Mallik & Dasgupta (2012) reported that the wall-rock reaction in MORB-eclogite and peridotite layered experiments produced a spectrum of tholeiitic to alkalic melts. However, the proper eclogite source composition is still under dispute. In order to figure out the geochemistry of recycled component as well as their melting process, we conducted a series of high-P, high-T experiments. Melting experiments (1~10hrs) were performed under 2.9GPa with Boyd-England type piston-cylinder (1460~1540°C for dry experiments, 1400~1500°C for hydrous experiments) and 5GPa with Kawai-type multi-anvil (1550~1650°C for dry experiments, 1350~1550°C for hydrous experiments), at the Magma Factory, Tokyo Tech. Spinel lherzolite KLB-1 (Takahashi 1986) was employed as peridotite component. Two basalts were used as recycled component: Fe-enriched Columbia River basalt (CRB72-180, Takahashi et al., 1998) and N-type MORB (NAM-7, Yasuda et al., 1994). In dry experiments below peridotite dry solidus, melt compositions ranged from basaltic andesite to tholeiite. Opx reaction band generated between basalt and peridotite layer hindered chemical reaction. On the other hand, alkali basalt was formed in hydrous run products because H2O promoted melting process in both layers. Compared with melts formed by N-MORB-peridotite runs, those layered experiments with CRB are enriched in FeO, TiO2, K2O and light REE at given MgO. In other words, melts produced by CRB-peridotite layered experiments are close to alkali basalts in OIB and tholeiite in Hawaii, while those by layered experiments with N-MORB are poor in above elements. Thus we propose that Fe-rich Archean or Proterozoic tholeiite (BVSP 1980) would be a possible candidate for recycled component in OIB source.

Hydrogen-alkali exchange between silicate melts and two-phase aqueous mixtures: an experimental investigation

NASA Astrophysics Data System (ADS)

Williams, Thomas J.; Candela, Philip A.; Piccoli, Philip M.

Experiments were performed in the three-phase system high-silica rhyolite melt + low-salinity aqueous vapor + hydrosaline brine, to investigate the exchange equilibria for hydrogen, potassium, and sodium in magmatic-hydrothermal systems at 800 °C and 100 MPa, and 850 °C and 50 MPa. The Kaqm/meltH,Na and Kaqm/meltH,K for hydrogen-sodium exchange between a vapor + brine mixture and a silicate melt are inversely proportional to the total chloride concentration (ΣCl) in the vapor + brine mixture indicating that HCl/NaCl and HCl/KCl are higher in the low-salinity aqueous vapor relative to high-salinity brine. The equilibrium constants for vapor/melt and brine/melt exchange were extracted from regressions of Kaqm/meltH,Na and Kaqm/meltH,K versus the proportion of aqueous vapor relative to brine in the aqueous mixture (Faqv) at P and T, expressed as a function of ΣCl. No significant pressure effect on the empirically determined exchange constants was observed for the range of pressures investigated. Model equilibrium constants are: Kaqv/meltH,Na(vapor/melt)=26(+/-1.3) at 100 MPa (800 °C), and 19( +/- 7.0) at 50 MPa (850 °C) Kaqv/meltH,K=14(+/-1.1) at 100 MPa (800 °C), and 24(+/-12) at 50 MPa (850 °C) Kaqb/meltH,b(brine/melt)= 1.6(+/-0.7) at 100 MPa (800 °C), and 3.9(+/-2.3) at 50 MPa (850 °C) and Kaqb/meltH,K=2.7(+/-1.2) at 100 MPa (800 °C) and 3.8(+/-2.3) at 50 MPa (850 °C). Values for Kaqv/meltH,K and Kaqb/meltH,K were used to calculate KCl/HCl in the aqueous vapor and brine as a function of melt aluminum saturation index (ASI: molar Al2O3/(K2O+Na2O+CaO) and pressure. The model log KCl/HCl values show that a change in melt ASI from peraluminous (ASI = 1.04) to moderately metaluminous (ASI = 1.01) shifts the cooling pathway (in temperature-log KCl/HCl space) of the aqueous vapor toward the andalusite+muscovite+K-feldspar reaction point.

The solvation radius of silicate melts based on the solubility of noble gases and scaled particle theory.

PubMed

Ottonello, Giulio; Richet, Pascal

2014-01-28

The existing solubility data on noble gases in high-temperature silicate melts have been analyzed in terms of Scaling Particle Theory coupled with an ab initio assessment of the electronic, dispersive, and repulsive energy terms based on the Polarized Continuum Model (PCM). After a preliminary analysis of the role of the contracted Gaussian basis sets and theory level in reproducing appropriate static dipole polarizabilities in a vacuum, we have shown that the procedure returns Henry's law constants consistent with the values experimentally observed in water and benzene at T = 25 °C and P = 1 bar for the first four elements of the series. The static dielectric constant (ɛ) of the investigated silicate melts and its optical counterpart (ɛ(∞)) were then resolved through the application of a modified form of the Clausius-Mossotti relation. Argon has been adopted as a probe to depict its high-T solubility in melts through an appropriate choice of the solvent diameter σs, along the guidelines already used in the past for simple media such as water or benzene. The σs obtained was consistent with a simple functional form based on the molecular volume of the solvent. The solubility calculations were then extended to He, Ne, and Kr, whose dispersive and repulsive coefficients are available from theory and we have shown that their ab initio Henry's constants at high T reproduce the observed increase with the static polarizability of the series element with reasonable accuracy. At room temperature (T = 25 °C) the calculated Henry's constants of He, Ne, Ar, and Kr in the various silicate media predict higher solubilities than simple extrapolations (i.e., Arrhenius plots) based on high-T experiments and give rise to smooth trends not appreciably affected by the static polarizabilities of the solutes. The present investigation opens new perspectives on a wider application of PCM theory which can be extended to materials of great industrial interest at the core of metallurgical processes, ceramurgy, and the glass industry.

Refertilization of the Subcontinental Lithospheric Mantle and its link to the formation of Metallogenic Provinces

NASA Astrophysics Data System (ADS)

Tassara, C. S.; González-Jiménez, J. M.; Reich, M.; Morata, D.; Barra, F.; Gregoire, M.; Saunders, J. E.; Cannatelli, C.

2017-12-01

Refertilisation of the subcontinental lithospheric mantle is a key process controlling the noble metal budget of the mantle, and recent views point to anomalously enriched mantle sources as a critical factor in the formation of noble metal (e.g., Au) provinces at a lithospheric scale. Here we test this hypothesis by studying peridotite xenoliths from the mantle beneath the Deseado Massif auriferous province in southern Patagonia, Argentina. Extensive Neogene back-arc plateau magmatism composed of alkaline basalts ( 3.5 Ma) has brought to the surface deep-seated mantle xenoliths from beneath the crust that host the Au mineralization. In the studied xenolith samples we found gold particles enclosed within primary olivine and pyroxene, and embedded in a highly alkaline interstitial glass or sulphides. Detailed inspection of the sulphide hosts using FESEM reveals abundant native Au nanoparticles, which are consistent with the high Au (up to 6 ppm) obtained by LA-ICP-MS analysis of these sulphides. It is relevant to note that these sulphides also contain significant amounts of Ag (up to 163 ppm). Different generations of sulphides were identified on the basis of their chondrite-normalized PGE patterns, and they can be systematically associated with different events of melt depletion and metasomatism in the mantle. Noticeably, Cu-Pd-Pt-Au rich sulfides are associated with clinopyroxene showing typical carbonatite markers (i.e., large LREE/HREE, Zr and Hf negative anomalies) and accessory minerals such as carbonates and apatite. Still, clinopyroxene commonly has high Ti contents suggesting that a "basaltic" component was also present during the metasomatism. These results suggest that overprinting of events of melt depletion and metasomatism lead to the formation of several generations of sulfides. We propose that the Cu-Pd-Pt-Au rich sulfides may be associated with carbonated silicate melts in the mantle. Our results point to 1) a link between an enriched source of gold (and silver) in the mantle and the formation of the Deseado Massif auriferous province; and 2) carbonated silicate melt metasomatism as an important factor in the PPGE + Au refertilisation of the mantle.

Effect of Organo-Modified Nanoclay on the Thermal and Bulk Structural Properties of Poly(3-hydroxybutyrate)-Epoxidized Natural Rubber Blends: Formation of Multi-Components Biobased Nanohybrids.

PubMed

Salehabadi, Ali; Bakar, Mohamad Abu; Bakar, Noor Hana Hanif Abu

2014-06-13

Multi-component nanohybrids comprising of organo-modified montmorillonite (MMT) and immiscible biopolymer blends of poly(3-hydroxybutyrate) (PHB) and epoxidized natural rubber (ENR-50) were prepared by solvent casting technique. The one and three dimensional morphology of PHB/ENR-50/MMT systems were studied using Polarizing Optical Microscopy (POM) and Scanning Electron Microscopy (SEM). Differential scanning calorimetry (DSC) technique was used to evaluate the thermal properties of the nanohybrids. The melting temperature ( T m ) and enthalpy of melting (Δ H m ) of PHB decrease with respect to the increase in ENR-50 as well as MMT content. The non-isothermal decomposition of the nanohybrids was studied using thermogravimetric (TG-DTG) analysis. FTIR-ATR spectra supported ring opening of the epoxide group via reaction with carboxyl group of PHB and amines of organic modifier. The reaction mechanism towards the formation of the nanohybrids is proposed.

Amphibole and felsic veins from the gabbroic oceanic core complex of Atlantis Bank (Southwest Indian Ridge, IODP Hole U1473A): when the fluids meets the melts

NASA Astrophysics Data System (ADS)

Sanfilippo, A.; Tribuzio, R.; Antonicelli, M.; Zanetti, A.

2017-12-01

We present a petrological/geochemical investigation of brown amphibole and felsic veins drilled during IODP 360 expedition at Atlantis Bank, a gabbroic oceanic core complex from Southwest Indian Ridge. The main purpose of this study is to unravel the role of seawater and magmatic components in the origin of these veins. Brown amphibole veins were collected at 90-170 mbsf. These veins typically include minor modal amounts of plagioclase and are associated with alteration halos made up of brown amphibole and whitish milky plagioclase in host gabbros. Two sets of late magmatic felsic veins, which mostly consist of plagioclase and minor brown amphibole, were selected. Amphibole-plagioclase geothermometry (Holland and Blundy, 1994) documents that crystallization of brown amphibole and felsic veins occurred in the 850-700 °C interval. In the brown amphibole veins, amphibole and plagioclase have relatively low concentrations of incompatible trace elements and significant Cl (0.2-0.3 wt%). The development of these veins at near surface levels is therefore attributed to seawater-derived fluids migrating downward through cracks developing in the exhuming gabbro. To explain the high temperature estimates for the development of these shallow veins, however, the seawater-derived fluids must have interacted not only with the gabbros, but also with a high temperature magmatic component. This petrogenetic hypothesis is consistent with oxygen and hydrogen isotopic compositions of amphiboles from shallow veins in adjacent Hole 735B gabbros (Alt and Bach, 2006). Trace element compositions of amphibole and plagioclase from the felsic veins show formation by silicate melts rich in incompatible elements. In addition, Cl concentrations in amphibole from the felsic veins are low, thereby indicating that the melts feeding these veins had low or no seawater component. We cautiously propose that: (i) the felsic veins were generated by SiO2-rich melts residual after crystallization of Fe-Ti-oxide phases, and (ii) the brown amphibole veins were generated by interaction of seawater-derived fluids with the late-stage residual melts rising through the gabbroic sequence.

Vitrification of organics-containing wastes

DOEpatents

Bickford, D.F.

1995-01-01

A process for stabilizing organics-containing waste materials and recovery metals therefrom, and a waste glass product made according to the process are described. Vitrification of wastes such as organic ion exchange resins, electronic components and the like can be accomplished by mixing at least one transition metal oxide with the wastes, and, if needed, glass formers to compensate for a shortage of silicates or other glass formers in the wastes. The transition metal oxide increases the rate of oxidation of organic materials in the wastes to improve the composition of the glass-forming mixture: at low temperatures, the oxide catalyzes oxidation of a portion of the organics in the waste; at higher temperatures, the oxide dissolves and the resulting oxygen ions oxidize more of the organics; and at vitrification temperatures, the metal ions conduct oxygen into the melt to oxidize the remaining organics. In addition, the transition metal oxide buffers the redox potential of the glass melt so that metals such as Au, Pt, Ag, and Cu separate form the melt in the metallic state and can be recovered. After the metals are recovered, the remainder of the melt is allowed to cool and may subsequently be disposed of. The product has good leaching resistance and can be disposed of in an ordinary landfill, or, alternatively, used as a filler in materials such as concrete, asphalt, brick and tile.

Vitrification of organics-containing wastes

DOEpatents

Bickford, Dennis F.

1997-01-01

A process for stabilizing organics-containing waste materials and recovering metals therefrom, and a waste glass product made according to the process. Vitrification of wastes such as organic ion exchange resins, electronic components and the like can be accomplished by mixing at least one transition metal oxide with the wastes, and, if needed, glass formers to compensate for a shortage of silicates or other glass formers in the wastes. The transition metal oxide increases the rate of oxidation of organic materials in the wastes to improve the composition of the glass-forming mixture: at low temperatures, the oxide catalyzes oxidation of a portion of the organics in the waste; at higher temperatures, the oxide dissolves and the resulting oxygen ions oxidize more of the organics; and at vitrification temperatures, the metal ions conduct oxygen into the melt to oxidize the remaining organics. In addition, the transition metal oxide buffers the redox potential of the glass melt so that metals such as Au, Pt, Ag, and Cu separate from the melt in the metallic state and can be recovered. After the metals are recovered, the remainder of the melt is allowed to cool and may subsequently be disposed of. The product has good leaching resistance and can be disposed of in an ordinary landfill, or, alternatively, used as a filler in materials such as concrete, asphalt, brick and tile.

Vitrification of organics-containing wastes

DOEpatents

Bickford, D.F.

1997-09-02

A process is described for stabilizing organics-containing waste materials and recovering metals therefrom, and a waste glass product made according to the process is also disclosed. Vitrification of wastes such as organic ion exchange resins, electronic components and the like can be accomplished by mixing at least one transition metal oxide with the wastes, and, if needed, glass formers to compensate for a shortage of silicates or other glass formers in the wastes. The transition metal oxide increases the rate of oxidation of organic materials in the wastes to improve the composition of the glass-forming mixture: at low temperatures, the oxide catalyzes oxidation of a portion of the organics in the waste; at higher temperatures, the oxide dissolves and the resulting oxygen ions oxidize more of the organics; and at vitrification temperatures, the metal ions conduct oxygen into the melt to oxidize the remaining organics. In addition, the transition metal oxide buffers the redox potential of the glass melt so that metals such as Au, Pt, Ag, and Cu separate from the melt in the metallic state and can be recovered. After the metals are recovered, the remainder of the melt is allowed to cool and may subsequently be disposed of. The product has good leaching resistance and can be disposed of in an ordinary landfill, or, alternatively, used as a filler in materials such as concrete, asphalt, brick and tile. 1 fig.

What Petit-Spot Volcanoes Tell us about the Lithosphere-Asthenosphere Boundary?

NASA Astrophysics Data System (ADS)

Pilet, S.; Abe, N.; Rochat, L.; Kaczmarek, M. A.; Bessat, A.; Duretz, T.; Muntener, O.

2015-12-01

The top of the low seismic velocity zone (LVZ) is frequently used to localize the lithosphere -asthenosphere boundary (LAB) which separates rigid oceanic plates from the underlying ductile asthenosphere. The seismic and electric properties of the LVZ are generally explained by the presence of low degree melts located at the base of the lithosphere, but the composition of these melts (silicate or carbonated melts) is still in debate. If most models for the LAB are based on geophysical or experimental studies, the discovery of petit-spot volcanoes on the top of the down-going Pacific plate (1) provides unique opportunities to obtain direct information on the LAB. Petit-spot volcanoes are interpreted as small-scale seamounts formed by the extraction of low-degree melts from the base of the lithosphere in response of plate flexure and/or crack propagation (2). The petrology of petit-spot lavas from Japan and Costa Rica demonstrates, first, that melts from the LVZ correspond to volatiles rich low degree silicate melts rather then to carbonatitic melts. Second, the discovery of lithospheric metasomatized mantle xenoliths and xenocrysts in the petit-spot lavas suggest that plate bending in front of subduction zones does not only produce petit-spot lavas at the surface, but allowed low degree melts from the LVZ to percolate and differentiate across the base of the oceanic lithosphere. This observation has important implication for the LAB because it demonstrates that deformed LAB does not represent a impermeable barrier for melt percolation as communally assumed, but deformation allows melts from the asthenosphere to percolate through peridotite matrix for significant distance (~10-20 km) modifying the rheology and the seismic properties of the base of the lithospheric mantle. This aspect needs to be taking into account in any model trying to simulate lithosphere asthenosphere deformation. (1) Hirano et al., 2006, Science 313, 1426-1428; (2) Valentine & Hirano, 2010, Geology 38, 55-58.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, Cressie E.; Pfeiler, William A.

1996-01-01

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material. The multi-piece crucible is contained in a thermal can assembly of a high temperature induction furnace during a high temperature melt-casting operation. One embodiment of the multi-piece crucible comprises a tubular member having a vertical slot filled with a ceramic sealing material to provide expansion of the tubular member without cracking during the high temperature melt-casting operation.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, C.E.; Pfeiler, W.A.

1996-01-09

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material. The multi-piece crucible is contained in a thermal can assembly of a high temperature induction furnace during a high temperature melt-casting operation. One embodiment of the multi-piece crucible comprises a tubular member having a vertical slot filled with a ceramic sealing material to provide expansion of the tubular member without cracking during the high temperature melt-casting operation. 9 figs.

Conductimetric determination of decomposition of silicate melts

NASA Technical Reports Server (NTRS)

Kroeger, C.; Lieck, K.

1986-01-01

A description of a procedure is given to detect decomposition of silicate systems in the liquid state by conductivity measurements. Onset of decomposition can be determined from the temperature curves of resistances measured on two pairs of electrodes, one above the other. Degree of decomposition can be estimated from temperature and concentration dependency of conductivity of phase boundaries. This procedure was tested with systems PbO-B2O3 and PbO-B2O3-SiO2.

Partial reactive crystallization of variable CO2-bearing siliceous MORB-eclogite-derived melt in fertile peridotite and genesis of alkalic basalts with signatures of crustal recycling

NASA Astrophysics Data System (ADS)

Mallik, A.; Dasgupta, R.

2013-12-01

The presence of heterogeneity in the form of recycled altered oceanic crust (MORB-eclogite) has been proposed in the source of HIMU ocean island basalts (OIBs) [1]. Partial melts of recycled oceanic crust, however, are siliceous and Mg-poor and thus do not resemble the major element compositions of alkalic OIBs that are silica-poor and Mg-rich. In an upwelling heterogenous mantle, MORB-eclogite undergoes melting deeper than volatile-free peridotite, hence, andesitic partial melt derived from eclogite will react with subsolidus peridotite. We have examined the effect of such a melt-rock reaction under volatile-free conditions at 1375 °C, 3 GPa by varying the melt-rock ratio from 8 to 50 wt.% [2]. We concluded that the reacted melts reproduce certain major element characteristics of oceanic basanites, but not nephelinites. Also, the melt-rock reaction produces olivine and garnet-bearing websteritic residue. Because presence of CO2 has been invoked in the source of many HIMU ocean islands, the effect of CO2 on such a melt-rock reaction needs to be evaluated. Accordingly, we performed reaction experiments on mixtures of 25% and 33% CO2-bearing andesitic partial melt and peridotite at 1375 °C, 3 GPa by varying the dissolved CO2 content of the reacting melts from 1 to 5 wt.% (bulk CO2 from 0.25 to 1.6 wt.%) [3, this study]. Owing to melt-rock reaction, with increasing CO2 in the bulk mixture, (a) modes of olivine and cpx decrease while melt, opx and garnet increase, (b) reacted melts evolve to greater degree of Si-undersaturation (from andesite through basanite to nephelinite), (c) enhanced crystallization of garnet take place with higher CO2 in the melt, reducing alumina content of the reacted melts, and (d) CaO and MgO content of the reacted melts increase, without affecting FeO* and Na2O contents (indicating greater propensity of Ca2+ and Mg2+ over Fe2+ and Na+ to enter silicate melt as carbonate). For a given melt-MgO, the CO2-bearing reacted melts are a better match for alkalic basalts in terms of SiO2, Al2O3, CaO and CaO/Al2O3 than the CO2-free ones [3]. Using the experimental data, we have further developed an empirical model to predict mineral modes in residue and reacted melt compositions for olivine-opx saturated lithologies as a function of melt:rock ratio and bulk CO2 content. For example, in case of 5 wt.% eclogite melt infiltrating in fertile peridotite, with bulk CO2 from 0 to 2 wt.%, the derivative melts show an increase in CaO and MgO from 11 to 16 wt.%, 15 to 24 wt.%, respectively and decrease in SiO2 and Al2O3 from 45 to 39 wt.% and 14 to 5 wt.%, respectively. From this model, we have created a major element composition space of MORB-eclogite-derived reactive melt mass vs. bulk CO2 and we predict that primary HIMU-type magmas require <5 to 10 wt.% of MORB-eclogite melt input and up to 0.8 wt.% bulk CO2 in their source. Our model also allows determining the residual lithology at the source of alkalic basalts, produced owing to eclogite melt-peridotite reaction with or without CO2. [1] Jackson & Dasgupta (2008) EPSL 276, 175-186. [2] Mallik & Dasgupta (2012) EPSL 329-330, 97-108. [3] Mallik & Dasgupta (in press) JPetrol.

Isotopic and trace element characteristics of an unusual refractory inclusion from Essebi

NASA Technical Reports Server (NTRS)

Deloule, E.; Kennedy, A. K.; Hutcheon, I. D.; Elgoresy, A.

1993-01-01

The isotopic and chemical properties of Ca-Al-rich inclusions (CAI) provide important clues to the early solar nebula environment. While the abundances of refractory major and trace elements are similar to those expected for high temperature condensates, the variety of textural, chemical, and isotopic signatures indicate most CAI experienced complex, multi-stage histories involving repeated episodes of condensation, evaporation, and metamorphism. Evidence of multiple processes is especially apparent in an unusual refractory inclusion from Essebi (URIE) described by El Goresy et al. The melilite (mel)-rich core of URIE contains polygonal framboids of spinel (sp) and hibonite (hb) or sp and fassaite (fas) and is surrounded by a rim sequence consisting of five layers. In contrast to rims on Allende, the mineralogy of the URIE rim layers becomes increasingly refractory from the core outwards, ending in a layer of spinel-Al2O3 solid solution + Sc-rich fassaite. The chemical and mineralogical features of URIE are inconsistent with crystallization from a homogeneous melt, and El Goresy et al. proposed a multi-step history involving condensation of sp + hb and aggregation into framboids, capture of framboids by a refractory silicate melt droplet, condensation of rim layers, and alteration of mel to calcite and feldspathoid. The PANURGE ion probe was used to investigate the isotopic and trace element characteristics of URIE to develop a more complete picture of the multiple processes leading to formation and metamorphism.

Modes of planetary-scale Fe isotope fractionation

NASA Astrophysics Data System (ADS)

Schoenberg, Ronny; von Blanckenburg, Friedhelm

2006-12-01

A comprehensive set of high-precision Fe isotope data for the principle meteorite types and silicate reservoirs of the Earth is used to investigate iron isotope fractionation at inter- and intra-planetary scales. 14 chondrite analyses yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of - 0.015 ± 0.020‰ (2 SE) relative to the international iron standard IRMM-014. Eight non-cumulate and polymict eucrite meteorites that sample the silicate portion of the HED (howardite-eucrite-diogenite) parent body yield an average δ56Fe/ 54Fe value of - 0.001 ± 0.017‰, indistinguishable to the chondritic Fe isotope composition. Fe isotope ratios that are indistinguishable to the chondritic value have also been published for SNC meteorites. This inner-solar system homogeneity in Fe isotopes suggests that planetary accretion itself did not significantly fractionate iron. Nine mantle xenoliths yield a 2 σ envelope of - 0.13‰ to + 0.09‰ in δ56Fe/ 54Fe. Using this range as proxy for the bulk silicate Earth in a mass balance model places the Fe isotope composition of the outer liquid core that contains ca. 83% of Earth's total iron to within ± 0.020‰ of the chondritic δ56Fe/ 54Fe value. These calculations allow to interprete magmatic iron meteorites ( δ56Fe/ 54Fe = + 0.047 ± 0.016‰; N = 8) to be representative for the Earth's inner metallic core. Eight terrestrial basalt samples yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of + 0.072 ± 0.016‰. The observation that terrestrial basalts appear to be slightly heavier than mantle xenoliths and that thus partial mantle melting preferentially transfers heavy iron into the melt [S. Weyer, A.D. Anbar, G.P. Brey, C. Munker, K. Mezger and A.B. Woodland, Iron isotope fractionation during planetary differentiation, Earth and Planetary Science Letters 240(2), 251-264, 2005.] is intriguing, but also raises some important questions: first it is questionable whether the Fe isotope composition of lithospheric mantle xenoliths are representative for an undisturbed melt source, and second, HED and SNC meteorites, representing melting products of 4Vesta and Mars silicate mantles would be expected to show a similar fractionation towards heavy isotope compositions. This is not observed. Four international granitoid standards with SiO 2 contents between 60 and 70 wt.% yield δ56Fe/ 54Fe values between 0.118‰ and 0.132‰. An investigation of the alpine Bergell igneous rock suite revealed a positive correlation between Fe isotope compositions and SiO 2 contents — from gabbros and tonalites ( δ56Fe/ 54Fe ≈ 0.03 to 0.09‰) to granodiorites and silicic dykes ( δ56Fe/ 54Fe ≈ 0.14 to 0.23‰). Although in this suite δ56Fe/ 54Fe correlates with δ18O values and radiogenic isotopes, open-system behavior to explain the heavy iron is not undisputed. This is because an obvious assimilant with the required heavy Fe isotope composition has so far not been identified. Alternatively, the relatively heavy granite compositions might be obtained by fractional crystallisation of the melt. Ultimately, further detailed studies on natural rocks and the experimental determination of mineral/melt fractionation factors at magmatic conditions are required to unravel whether or not iron isotope fractionation takes place during partial mantle melting and crystal fractionation.

Synthesis of a single phase of high-entropy Laves intermetallics in the Ti-Zr-V-Cr-Ni equiatomic alloy

NASA Astrophysics Data System (ADS)

Yadav, T. P.; Mukhopadhyay, Semanti; Mishra, S. S.; Mukhopadhyay, N. K.; Srivastava, O. N.

2017-12-01

The high-entropy Ti-Zr-V-Cr-Ni (20 at% each) alloy consisting of all five hydride-forming elements was successfully synthesised by the conventional melting and casting as well as by the melt-spinning technique. The as-cast alloy consists entirely of the micron size hexagonal Laves Phase of C14 type; whereas, the melt-spun ribbon exhibits the evolution of nanocrystalline Laves phase. There was no evidence of any amorphous or any other metastable phases in the present processing condition. This is the first report of synthesising a single phase of high-entropy complex intermetallic compound in the equiatomic quinary alloy system. The detailed characterisation by X-ray diffraction, scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the existence of a single-phase multi-component hexagonal C14-type Laves phase in all the as-cast, melt-spun and annealed alloys. The lattice parameter a = 5.08 Å and c = 8.41 Å was determined from the annealed material (annealing at 1173 K). The thermodynamic calculations following the Miedema's approach support the stability of the high-entropy multi-component Laves phase compared to that of the solid solution or glassy phases. The high hardness value (8.92 GPa at 25 g load) has been observed in nanocrystalline high-entropy alloy ribbon without any cracking. It implies that high-yield strength ( 3.00 GPa) and the reasonable fracture toughness can be achieved in this high-entropy material.

Universal calibration of Raman spectroscopy for the analysis of volatiles in glasses of variable composition

NASA Astrophysics Data System (ADS)

Schiavi, Federica; Bolfan-Casanova, Nathalie

2017-04-01

The amount and distribution of volatiles (water, carbon dioxide …) in magmas represent key parameters for the understanding of magma processes and dynamics within volcanic plumbing systems. Micro-Raman spectroscopy is an excellent technique for accurate determination of volatile contents in magmas, as it combines several advantages. The technique is non-destructive and requires minimal sample preparation before the analysis. Its high lateral and in-depth spatial resolution is crucial for the study of small objects and samples that are chemically and texturally heterogeneous at the small scale (microns). Moreover, the high confocality allows analysis of sample regions not exposed to the surface and 3D mapping. We present a universal calibration of Raman spectroscopy for quantification of volatiles in silicate glasses. The proposed method is based on internal calibration, i.e., on the correlation between the glass water content and the ratio between the areas of the water and silicate Raman bands. Synthetic glasses with variable major element compositions (basaltic, andesitic, rhyolitic, dacitic ..) bearing different H2O (up to 7 wt%) and CO2 contents are used as standard glasses. Natural silicate glasses, mainly in the form of melt inclusions, are used to test the goodness of the proposed method. In addition to quantification of volatiles in glass, in bubble-bearing melt inclusions we perform micro-Raman spectroscopy investigation of gas-bearing bubbles for accurate determination of total volatile contents in melt inclusions.

Iron K-edge X-ray absorption near-edge structure spectroscopy of aerodynamically levitated silicate melts and glasses

DOE PAGES

Alderman, O. L. G.; Wilding, M. C.; Tamalonis, A.; ...

2017-01-26

Here, the local structure about Fe(II) and Fe(III) in silicate melts was investigated in-situ using iron K-edge X-ray absorption near-edge structure (XANES) spectroscopy. An aerodynamic levitation and laser heating system was used to allow access to high temperatures without contamination, and was combined with a chamber and gas mixing system to allow the iron oxidation state, Fe 3+/ΣFe, to be varied by systematic control of the atmospheric oxygen fugacity. Eleven alkali-free, mostly iron-rich and depolymerized base compositions were chosen for the experiments, including pure oxide FeO, olivines (Fe,Mg) 2SiO 4, pyroxenes (Fe,Mg)SiO 3, calcic FeO-CaSiO 3, and a calcium aluminosilicatemore » composition, where total iron content is denoted by FeO for convenience. Melt temperatures varied between 1410 and 2160 K and oxygen fugacities between FMQ – 2.3(3) to FMQ + 9.1(3) log units (uncertainties in parentheses) relative to the fayalite-magnetite-β-quartz (FMQ) buffer.« less

Lead recovery from waste CRT funnel glass by high-temperature melting process.

PubMed

Hu, Biao; Hui, Wenlong

2018-02-05

In this research, a novel and effective process for waste CRT funnel glass treatment was developed. The key to this process is removal of lead from the CRT funnel glass by high-temperature melting process. Sodium carbonate powder was used as a fusion agent, sodium sulfide serves as a catalytic agent and carbon powder acts as reducing agent. Experimental results showed that lead recovery rate increased with an increase in the amount of added sodium carbonate, sodium sulfide, carbonate, temperature and holding time initially, and then reached a stable value. The maximum lead recovery rate was approximately 94%, when the optimum adding amount of sodium carbonate, sodium sulfide, carbonate, temperature and holding time were 25%, 8%, 3.6%, 1200°C and 120min, respectively. In the high-temperature melting process, lead silicate in the funnel glass was firstly reduced, and then removed. The glass slag can be made into sodium and potassium silicate by hydrolysis process. This study proposed a practical and economical process for recovery of lead and utilization of waste glass slag. Copyright © 2017 Elsevier B.V. All rights reserved.

Chondrule-like objects and brown glasses in howardites

NASA Technical Reports Server (NTRS)

Olsen, Edward J.; Fredriksson, Kurt; Rajan, Sundar; Noonan, Albert

1990-01-01

Chondrulelike objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses, the chondrulelike objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (greater than 400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. It is concluded that at least two parent bodies are likely sources for the basaltic achondrites.

Evaluation of the Lithospheric Contribution to Southern Rio Grande Rift Mafic Melts

NASA Astrophysics Data System (ADS)

Konter, J. G.; Crocker, L.; Anaya, L. M.; Rooney, T. O.

2011-12-01

As continental rifting proceeds, the accommodation of lithospheric thinning by mechanical extension and magmatic intrusion represents an important but poorly constrained tectonic process. Insight into role of the magmatic component may come from the composition of volcanic products, which can record magma-lithosphere interactions. The volcanic activity in continental rift environments is frequently characterized by bimodal associations of mafic and silicic volcanism with heterogenous lithospheric contributions. We present a new integrated data set from several mafic volcanic fields in the Rio Grande Rift, consisting of major and trace element compositions, as well as isotopes. This data set provides insight into asthenospheric melting processes and interactions with the overlying lithosphere. The melting processes and the related extensional volcanism is the result of foundering of the Farallon slab. Large volume silicic eruptions such as those in the Sierra Madre Occidental originate from a large contribution of lithospheric melting, with a subordinate asthenospheric contribution. In contrast, Late Tertiary and Quaternary basaltic volcanic fields in the Rio Grande Rift were likely sourced in the asthenosphere and did not reside in the lithosphere for substantial periods. As a result the region is the ideal natural laboratory to investigate the interaction of asthenospheric melts with the lithosphere. In particular the wide array of volcanic fields contain multiple xenolith localities, such as Kilbourne Hole, providing direct samples of lithosphere and crust. Although previous studies have focused on correlations between amount of extension related to Farallon slab foundering, volcanic compositions, and their mantle sources, we present data that suggest that some compositional signatures may pre-date current tectonic processes. Radiogenic isotope data from several volcanic fields in New Mexico show a converging pattern in Pb isotope compositions, focusing on the unradiogenic Pb isotope composition of lower crustal xenoliths from Kilbourne Hole. The opposite ends of the converging trends are more radiogenic for some volcanic fields than the (lithospheric) mantle xenoliths of the Potrillo, San Carlos and Geranimo volcanic fields. Combined Pb-Sr isotope compositions for these fields are consistent with a trend from lower crustal xenoliths to mantle xenoliths, but show more variability. This variability may be explained by a small upper crustal contribution, in agreement with the Pb isotope systematics. Therefore, a common unradiogenic lower crustal composition likely contributed to the asthenospheric melts, followed by upper crustal contamination. The unradiogenic character of the lower crust implies an ancient event created the required low U/Pb ratios that generated the present-day Pb isotope compositions.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, C.E.; Pfeiler, W.A.

1994-08-02

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material. 6 figs.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, Cressie E.; Pfeiler, William A.

1994-01-01

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material.

Muscovite-Dehydration Melting: A Textural Study of a Key Reaction in Transforming Continental Margin Strata Into a Migmatitic Orogenic Core

NASA Astrophysics Data System (ADS)

Dyck, B. J.; St Onge, M. R.; Waters, D. J.; Searle, M. P.

2015-12-01

Metamorphosed continental margin sedimentary sequences, which comprise the dominant tectonostratigraphic assemblage exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. This study explores the textural effect of anatexis in amphibolite-grade conditions and documents the mineral growth mechanisms that control nucleation and growth of K-feldspar, sillimanite and silicate melt. The constrained textural evolution follows four stages: 1) Nucleation - K-feldspar is documented to nucleate epitaxially on isomorphic plagioclase in quartzofeldspathic (psammitic) domains, whereas sillimanite nucleates in the Al-rich (pelitic) domain, initially on [001] mica planes. The first melt forms at the site of muscovite breakdown. 2) Chemically driven growth - In the quartzofeldspathic domain, K-feldspar progressively replaces plagioclase by a K+ - Na+ cation transfer reaction, driven by the freeing of muscovite-bound K+ during breakdown of the mica. Sillimanite forms intergrowths with the remaining hydrous melt components, contained initially in ovoid clots. 3) Merge and coarsening - With an increase in pressure, melt and sillimanite migrate away from clots along grain boundaries. A melt threshold is reached once the grain-boundary network is wetted by melt, increasing the length-scale of diffusion, resulting in grain boundary migration and grain-size coarsening. The melt threshold denotes the transition to an open-system on the lithology scale, where melt is a transient phase. 4) Residual melt crystallization - Residual melt crystallizes preferentially on existing peritectic grains as anatectic quartz, plagioclase, and K-feldspar. As the system cools and closes, grain growth forces melt into the intersections of grain-boundaries, recognized as irregular shaped melt films, or as intergrowths of the volatile-rich phases (i.e. Tur-Ms-Ap). In the Himalayan metamorphic core these processes result in the formation of: pelitic K-feldspar augen gneiss, stockwork leucogranites, and an effective strengthening of the hinterland, as evidenced by a switch in tectonic deformation style, from thin-skinned cover sequence thrust imbrication and folding to out-of-sequence basement-involved thick-skinned thrusting and folding.

Petrologic Applications of Tourmaline

NASA Astrophysics Data System (ADS)

London, D.; Morgan, G. B., VI; Wolf, M. B.; Guttery, B. M.

2011-12-01

Compositions of tourmaline reflect its chemical environment of formation. Schorl-dravite is an accessory in metapelites and persists up to the onset of anatexis. Amphibolites and marbles contain uvite, and magnesiofoitite-povandraite is distinctive of base-metal porphyries. In granitic pegmatites, schorl-dravite at the contacts evolves toward foitite and olenite (aluminous) components as Fe is depleted from the melt. Fractionation may bring residual melts to saturation in elbaite, an Li-rich component of tourmaline. Common tourmaline (schorl-dravite-olenite-foitite solid solution) possesses a wide P-T field of stability. Synthesis experiments put the upper thermal limit of common tourmaline at ~ 750°-850°C from 50 MPa to 10 GPa, and dravite has been synthesized as low as 350°C. The boron content of granitic melt or aqueous fluid in equilibrium with common tourmaline alone and with equivalent silicate mineral assemblages varies sharply with temperature according to a relationship of CB2O3melt,vapor ~ 0.0032e0.0087T(C). Common tourmaline is stable over an aSiO2 at and below saturation in Qtz; besides FeMg, its stability hinges principally on the solubility product [aAl2O3]3*[aB2O3]1.5 in vapor or melt. Surprisingly, increasing activities of H2O or fluoride components (both are present in tourmaline) destabilize common tourmaline in granitic melt, as both components form complexes with Al that reduce aAl2O3 in the melt. As a result, common tourmaline may survive anatexis when the aH2O attending melting is low. In contrast to common tourmaline, most attempts to synthesize elbaite have failed. Aluminous tourmaline containing 37 mol% Elb component has been synthesized recently, which is significant for understanding occurrences in pegmatites as well as for the potential appearance of synthetic elbaite on the gem market. Experimental calibration of δ11B between aqueous fluid and dravite at 50-500 MPa and 350°-750°C varies by only 6.1 % over this range of conditions (tourmaline is isotopically light with respect to the fluid), but it is pressure-dependent at least up to 200 MPa. This isotopic range is narrow in relation to vast tourmaline-producing magmatic-hydrothermal systems, such as the granites of Cornwall, UK. Preliminary experiments by Hervig et. al. (2002) report a large variation of Δ11B between aqueous fluid and granitic melt over small ranges of T, such that the isotopic composition of tourmaline should shift dramatically to higher (vapor) or lower (melt) values when crystallization occurs from a two-phase fluid system. Existing studies of consanguineous granite-pegmatite systems show nearly no variation of δ11B from common tourmaline in source granites to elbaite in the most fractionated pegmatites; the values correspond to those of tourmaline-melt, with little evidence for crystallization from vapor. Tourmaline may prove useful as a geothermometer in the same way as other AFM minerals, but the complexities of coupled substitutions in relation to the multitude of site occupancies in tourmaline will make experimental calibration a difficult, if not futile effort. Elemental fractionation between the polar ends of tourmaline, and its tendency for unidirectional growth, further complicate any quantitative treatment of its chemical composition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Düchs, Dominik; Delaney, Kris T., E-mail: kdelaney@mrl.ucsb.edu; Fredrickson, Glenn H., E-mail: ghf@mrl.ucsb.edu

Field-theoretic models have been used extensively to study the phase behavior of inhomogeneous polymer melts and solutions, both in self-consistent mean-field calculations and in numerical simulations of the full theory capturing composition fluctuations. The models commonly used can be grouped into two categories, namely, species models and exchange models. Species models involve integrations of functionals that explicitly depend on fields originating both from species density operators and their conjugate chemical potential fields. In contrast, exchange models retain only linear combinations of the chemical potential fields. In the two-component case, development of exchange models has been instrumental in enabling stable complexmore » Langevin (CL) simulations of the full complex-valued theory. No comparable stable CL approach has yet been established for field theories of the species type. Here, we introduce an extension of the exchange model to an arbitrary number of components, namely, the multi-species exchange (MSE) model, which greatly expands the classes of soft material systems that can be accessed by the complex Langevin simulation technique. We demonstrate the stability and accuracy of the MSE-CL sampling approach using numerical simulations of triblock and tetrablock terpolymer melts, and tetrablock quaterpolymer melts. This method should enable studies of a wide range of fluctuation phenomena in multiblock/multi-species polymer blends and composites.« less

Key new pieces of the HIMU puzzle from olivines and diamond inclusions.

PubMed

Weiss, Yaakov; Class, Cornelia; Goldstein, Steven L; Hanyu, Takeshi

2016-09-29

Mantle melting, which leads to the formation of oceanic and continental crust, together with crust recycling through plate tectonics, are the primary processes that drive the chemical differentiation of the silicate Earth. The present-day mantle, as sampled by oceanic basalts, shows large chemical and isotopic variability bounded by a few end-member compositions. Among these, the HIMU end-member (having a high U/Pb ratio, μ) has been generally considered to represent subducted/recycled basaltic oceanic crust. However, this concept has been challenged by recent studies of the mantle source of HIMU magmas. For example, analyses of olivine phenocrysts in HIMU lavas indicate derivation from the partial melting of peridotite, rather than from the pyroxenitic remnants of recycled oceanic basalt. Here we report data that elucidate the source of these lavas: high-precision trace-element analyses of olivine phenocrysts point to peridotite that has been metasomatized by carbonatite fluids. Moreover, similarities in the trace-element patterns of carbonatitic melt inclusions in diamonds and HIMU lavas indicate that the metasomatism occurred in the subcontinental lithospheric mantle, fused to the base of the continental crust and isolated from mantle convection. Taking into account evidence from sulfur isotope data for Archean to early Proterozoic surface material in the deep HIMU mantle source, a multi-stage evolution is revealed for the HIMU end-member, spanning more than half of Earth's history. Before entrainment in the convecting mantle, storage in a boundary layer, upwelling as a mantle plume and partial melting to become ocean island basalt, the HIMU source formed as Archean-early Proterozoic subduction-related carbonatite-metasomatized subcontinental lithospheric mantle.

Unravelling the effects of melt depletion and secondary infiltration on mantle Re-Os isotopes beneath the French Massif Central

NASA Astrophysics Data System (ADS)

Harvey, J.; Gannoun, A.; Burton, K. W.; Schiano, P.; Rogers, N. W.; Alard, O.

2010-01-01

Spinel lherzolite xenoliths from Mont Briançon, French Massif Central, retain evidence for multiple episodes of melt depletion and melt/fluid infiltration (metasomatism). Evidence for primary melt depletion is still preserved in the co-variation of bulk-rock major elements (MgO 38.7-46.1 wt.%; CaO 0.9-3.6 wt.%), and many samples yield unradiogenic bulk-rock Os isotope ratios ( 187Os/ 188Os = 0.11541-0.12626). However, many individual xenoliths contain interstitial glasses and melt inclusions that are not in equilibrium with the major primary minerals. Incompatible trace element mass balance calculations demonstrate that metasomatic components comprise a significant proportion of the bulk-rock budget for these elements in some rocks, ranging to as much as 25% of Nd and 40% of Sr Critically, for Re-Os geochronology, melt/fluid infiltration is accompanied by the mobilisation of sulfide. Consequently, bulk-rock isotope measurements, whether using lithophile (e.g. Rb-Sr, Sm-Nd) or siderophile (Re-Os) based isotope systems, may only yield a perturbed and/or homogenised average of these multiple events. Osmium mass balance calculations demonstrate that bulk-rock Os in peridotite is dominated by contributions from two populations of sulfide grain: (i) interstitial, metasomatic sulfide with low [Os] and radiogenic 187Os/ 188Os, and (ii) primary sulfides with high [Os] and unradiogenic 187Os/ 188Os, which have been preserved within host silicate grains and shielded from interaction with transient melts and fluid. The latter can account for >97% of bulk-rock Os and preserve geochronological information of the melt from which they originally precipitated as an immiscible liquid. The Re-depletion model ages of individual primary sulfide grains preserve evidence for melt depletion beneath the Massif Central from at least 1.8 Gyr ago despite the more recent metasomatic event(s).

Geochemical and Isotopic Data from Micron to Across-Arc Scales in the Andean Central Volcanic Zone: Applications for Resolving Crustal Magmatic Differentiation and Modification Processes

NASA Astrophysics Data System (ADS)

Michelfelder, G.; Wilder, A.; Feeley, T.

2014-12-01

Plagioclase crystals from silicic (andesitic to dacitic) lavas and domes at Volcán Uturuncu, a potentially active volcano in the back-arc of the Andean CVZ (22.3°S, 67.2°W), exhibit large variations in An contents, textures, and core to rim 87Sr/86Sr ratios. Many of the isotopic variations can not have existed at magmatic temperatures for more than a few thousand years. The crystals likely derived from different locations in the crustal magmatic system and mixed just prior to eruption. Uturuncu magmas initially assimilated crustal rocks with high 87Sr/86Sr ratios. The magmas were subsequently modified by frequent recharge of more mafic magmas with lower 87Sr/86Sr ratios. A typical Uturuncu silicic magma therefore only attains its final composition just prior to or during eruption. In the Lazufre region of active surface uplift (~25˚14'S; Volcán Lastarria and Cordon del Azufre) closed system differentiation processes are not the only factors influencing silicic magma compositions. 87Sr/86Sr (0.70651-0.70715) and 206Pb/204Pb ratios (18.83-18.88) are highly elevated and143Nd/144Nd ratios (0.512364 -0.512493) are low relative to similar composition rocks from the "southern Cordillera domain." These data, along with major and trace element trends, reflect a multitude of differentiation processes and magma sources including crystallization-differentiation of more mafic magmas, melting and assimilation of older crustal rocks, and magma mixing and mingling. On an arc-wide scale silicic lavas erupted from three well-characterized composite volcanoes between 21oS and 22oS (Aucanquilcha, Ollagüe, and Uturuncu) display systematically higher K2O, LILE, REE and HFSE contents and 87Sr/86Sr ratios with increasing distance from the arc-front. In contrast, the lavas have systematically lower Na2O, Sr, and Ba contents; LILE/HFSE ratios; 143Nd/144Nd ratios; and more negative Eu anomalies. Silicic magmas along the arc-front apparently reflect melting of relatively young, mafic composition amphibolitic source rocks with the continental crust becoming increasingly older with a more felsic bulk composition toward the east. We suggest this results from progressively smaller degrees of mantle partial melting, primary melt generation, and crustal hybridization with distance from the arc-front.

Bursting the bubble of melt inclusions

USGS Publications Warehouse

Lowenstern, Jacob B.

2015-01-01

Most silicate melt inclusions (MI) contain bubbles, whose significance has been alternately calculated, pondered, and ignored, but rarely if ever directly explored. Moore et al. (2015) analyze the bubbles, as well as their host glasses, and conclude that they often hold the preponderance of CO2 in the MI. Their findings entreat future researchers to account for the presence of bubbles in MI when calculating volatile budgets, saturation pressures, and eruptive flux.

Residual Hydrochloride - Silicate Melt Associated With the Platinum-bearing Alaskan-type Galmoenan Intrusion (Koryak Highland, Russia)

NASA Astrophysics Data System (ADS)

Batanova, V.; Kamenetsky, D.; Pertsev, A.; Sobolev, A.

2005-12-01

Alaskan-type mafic-ultramafic complexes formed in subduction-related environments are considered to be a major source of platinum placer deposits [1]. A specific feature of these deposits is the dominant occurrence of Pt-Fe alloys (mainly isoferroplatinum) among PGE-bearing minerals [e.g. 2]. The PGE mineralization can be related to the high activity of chlorine in the parental magmas of Alaskan-type intrusions [3] and the potential of saline fluids to dissolve and transport Pt [4,5,6]. Fluxing of a refractory mantle wedge in a supra-subduction zone by chlorine-rich aqueous fluids was considered primarily responsible for the formation of PGE-enriched parental magmas [3]. Potential role of the saline magmatic fluids is further tackled by this study of melt/fluid inclusions in olivine from the Galmoenan pluton belonging to the Alaskan-type intrusive complex in the Kamchatka-Koryak province [7] and spatially associated with one of the most significant platinum placer deposits in Russia [8]. High-magnesian olivine (Fo 90.8) from the Galmoenan dunites hosts abundant hydrosaline chloride and hydrosaline chloride-silicate melt inclusions (5-30mkm). Inclusions trail fractures confined to individual olivine grains, and thus formed before re-crystallization completed. Heating stage experiments at 1 atm showed early melting within the inclusions at ~350C, however complete melting and homogenization was hampered by decrepitation at 650-750C. This suggests elevated pressures of trapping, at least 3-4 kb. The study of phase and chemical compositions of these inclusions by an electron probe, laser ablation ICP-MS and SIMS ion probe showed chlorides of Na, K, Ca, Fe and Ba, Fe-Cu-Ni sulfides and diopside among daughter phases; 2) high H2O abundances; 3) high abundances of alkali and alkali-earth elements (Na, K, Rb, Sr, Ba, Ca) and metals (Fe, Mn, Pb, Ni, Cu, Zn). Such compositions confirm the presence of metal-enriched hydrosaline melt at the latest stages of formation of the Pt-bearing Alaskan-type intrusion. We envisage that the hydrosaline melt owed its origin to prolonged fractionation of the parental ultramafic K- and Cl-rich melt [9,3], followed by saturation in the chloride components [10]. Our melt inclusion evidence suggests that the Galmoenan dunite was soaked in the residual chloride melt/fluid. The bearing of this melt/fluid on Pt mineralization is likely, but is yet to be established. [1] Taylor and Noble, Rep.21 IGC, pt 13, Copenhagen, 175-187, 1960; [2] Slansky et al, Miner.Petrol. 43, 161-180, 1991; [3] Batanova et al, JP. 46, 1345-1366, 2005; [4] Ballhaus and Stumpfl, CMP 94, 193-204, 1986; [5] Sassani and Shock, GCA 62, 2643-2671, 1998; [6] Hanley et al, GCA 69, 2593-2611, 2005; [7] Batanova and Astrakhantsev, Proc. 29 IGC, pt D, VSP, 129-143, 1994; [8] Tolstykh et al, Can.Miner.42, 619-630, 2004; [9] Kamenetsky et al, JP 37, 637-662, 1995; [10] Webster, Chem.Geol 210, 33-48, 2004

Multi-material composites prepared by additive manufacturing and melt casting

NASA Astrophysics Data System (ADS)

Murialdo, Maxwell; Sullivan, Kyle; White, Bradley; LLNL MSD Collaboration

2017-06-01

Recent advances in additive manufacturing have disrupted not only means of production, but also have enabled a new parameter space of multiscale materials designs. Understanding the role of architecture to control material response is being investigated for a wide range of applications, from light-weight structural components to energetic materials. In this work, we combine 3D printing of scaffold structures with a subsequent melt-infiltration step to render an architected multi-material composite article. Both the scaffold architecture and material type were investigated. The processing challenges of filling such scaffolds using a melt-infiltration step will be discussed, along with our progress in this area. Using the combined method of printing and casting, we will discuss our path forward for testing the mechanical properties and the high-strain response of our composite architected parts. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release: LLNL-ABS-725497-DRAFT.

Silicate Crystal Formation in the Disk of an Erupting Star Artist Concept

NASA Image and Video Library

2009-05-13

This artist's concept illustrates how silicate crystals like those found in comets can be created by an outburst from a growing star. The image shows a young sun-like star encircled by its planet-forming disk of gas and dust. The silicate that makes up most of the dust would have begun as non-crystallized, amorphous particles. Streams of material are seen spiraling from the disk onto the star increasing its mass and causing the star to brighten and heat up dramatically. The outburst causes temperatures to rise in the star's surrounding disk. The animation (figure 1) zooms into the disk to show close-ups of silicate particles. When the disk warms from the star's outburst, the amorphous particles of silicate melt. As they cool off, they transform into forsterite (figure 2), a type of silicate crystal often found in comets in our solar system. In April 2008, NASA's Spitzer Space Telescope detected evidence of this process taking place on the disk of a young sun-like star called EX Lupi. http://photojournal.jpl.nasa.gov/catalog/PIA12008

Perspectives on Magmatic Differentiation of Mercury

NASA Astrophysics Data System (ADS)

Charlier, B.; Namur, O.; Cartier, C.

2018-05-01

Silicate/metal liquid immiscibility, crystallization of a magma ocean, partial melting of mantle rocks, and surface crystallization have shaped Mercury as we know it today. We review these processes based on high-T experiments at reducing conditions.

High Pressure and Temperature Core Formation as an Alternative to the "Late Veneer" Hypothesis

NASA Technical Reports Server (NTRS)

Righter, Kevin; Pando, K.; Humayun, M.; Danielson, L.

2011-01-01

The highly siderophile elements (HSE; Re, Au and the Platinum Group Elements - Pd Pt, Rh, Ru, Ir, Os) are commonly utilized to constrain accretion processes in terrestrial differentiated bodies due to their affinity for FeNi metal [1]. These eight elements exhibit highly siderophile behavior, but nonetheless have highly diverse metal-silicate partition coefficients [2]. Therefore the near chondritic relative concentrations of HSEs in the terrestrial and lunar mantles, as well as some other bodies, are attributed to late accretion rather than core formation [1]. Evaluation of competing theories, such as high pressure metal-silicate partitioning or magma ocean hypotheses has been hindered by a lack of relevant partitioning data for this group of eight elements. In particular, systematic studies isolating the effect of one variable (e.g. temperature or melt compositions) are lacking. Here we undertake new experiments on all eight elements, using Fe metal and FeO-bearing silicate melts at fixed pressure, but variable temperatures. These experiments, as well as some additional planned experiments should allow partition coefficients to be more accurately calculated or estimated at the PT conditions and compositions at which core formation is thought to have occurred.

Temperature Effects on Aluminoborosilicate Glass and Melt Structure

NASA Astrophysics Data System (ADS)

Wu, J.; Stebbins, J. F.

2008-12-01

Quantitative determination of the atomic-scale structure of multi-component oxide melts, and the effects of temperature on them, is a complex problem. Ca- and Na- aluminoborosilicates are especially interesting, not only because of their major role in widespread technical applications (flat-panel computer displays, fiber composites, etc.), but because the coordination environments of two of their main network cations (Al3+ and B3+) change markedly with composition and temperature is ways that may in part be analogous to processes in silicate melts at high pressures in the Earth. Here we examine a series of such glasses with different cooling rates, chosen to evaluate the role modifier cation field strength (Ca2+ vs. Na+) and of non-bridging oxygen (NBO) content. To explore the effects of fictive temperature, fast quenched and annealed samples were compared. We have used B-11 and Al-27 MAS NMR to measure the different B and Al coordinations and calculated the contents of non-bridging oxygens (NBO). Lower cooling rates increase the fraction of [4]B species in all compositions. The conversion of [3]B to [4]B is also expected to convert NBO to bridging oxygens, which should affect thermodynamic properties such as configurational entropy and configurational heat capacity. For four compositions with widely varying compositions and initial NBO contents, analysis of the speciation changes with the same, simple reaction [3]B = [4]B + NBO yields similar enthalpy values of 25±7 kJ/mol. B-11 triple quantum MAS NMR allows as well the proportions of [3]B boroxol ring and non-ring sites to be determined, and reveals more [3]B boroxol ring structures present in annealed (lower temperature) glasses. In situ, high-temperature MAS NMR spectra have been collected on one of the Na-aluminoborosilicate and on a sodium borate glass at 14.1 T. The exchange of boron between the 3- and 4-coordinated sites is clearly observed well above the glass transition temperatures, confirming the importance of such local structural dynamics in controlling the bulk viscosity.

Uranium in granitic magmas: Part 2. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H 2O-NaX (X = Cl, F) system at 770°C, 2 kbar

NASA Astrophysics Data System (ADS)

Peiffert, Chantal; nguyen-Trung, Chinh; Cuney, Michel

1996-05-01

The solubility of uranium oxide was investigated in both aqueous halide (Cl, F) fluid and granitic melt in equilibrium in the system uranium oxide-haplogranite-H 2O-NaCl (0.1-5.0 molal), NaF (0.1-0.5 molal) at 770°C, 2 kbar, and fO 2 conditions controlled by Ni-NiO, Fe 3O 4-Fe 2O 3, and Cu 2O- CuO buffers. Three distinct uranium oxides UO (2+ x) with x = 0.01 ± 0.01; 0.12 ± 0.02; and 0.28 ± 0.02, respec- tively, were obtained in both chloride and fluoride systems, under the three fO 2 conditions cited above. Changes in the composition of aqueous solutions and silicate melt were observed after the runs. These changes were more pronounced for the fluoride-bearing experiments. Quench pH decreased from 5.9 to 2.1 with increasing chloride molality from 0.085-4.38 molal. For fluoride solutions, the decrease of pH from 5.4 to 3.4 corresponded to the increase of fluoride molality from 0.02-0.23 molal. The U solubility in chloride solutions was in the range 10-967 ppm. For the same molality, fluoride solutions appeared to dissolve up to twenty times more uranium than chloride solutions. The increase of halide molality and oxidation led to increase the U solubility. The U solubility in silicate glasses was in the range 10-1.8 × 10 4 ppm and increased with increasing oxidation and halide concentration. In addition, increasing agpaicity also increased U solubility in the chloride system. This effect was not observed in the fluoride system. The chloride concentration in the silicate melt increased from 100-790 ppm with increasing initial aqueous chloride concentration from 0.1-5.0 m. The fluoride concentration in the silicate melt increased from 2.8 × 10 3 to 1.1 × 10 4 ppm with increasing initial fluoride concentra- tion from 0.1-0.5 m. In the chloride system, the partition coefficient of U (log D)(U) fluid/melt) increased from -1.2-0 with increasing agpaicity from 0.92-1.36, for increasing chloride concentration from 0.085-4.38 molal and for increasing fO 2 from 10 -15 to 10 -4 bar. In the fluoride system, a linear correlation was established between the partition coefficient of U and the log fO 2. In F-rich system, D(U) fluid/melt values was in the range 2.4 × 10 -2-4.2 × 10 -2 for increasing fluoride concentration from 0.02-0.22 molal and for the same increasing of fO 2. In the chloride system, the partition coefficients of Na ( D (Na) fluid/melt) and K ( D) (K) fluid/melt) are in good agreement up to 1.0 m NaCl with the two linear equations established by Holland (1972) : D (Na) fluid/melt = 0.46 × (Cl)(m) (1) and D(Na) fluid/melt = 0.34 × (Cl)(m) (2). However, in initial 5.0 m NaCl, slopes of Eqns. 1 and 2 decreased to 0.41 and 0.16, respectively. Data obtained in the present study provide useful information for the understanding of the behaviour of U in the fractionation processes of halide rich magmas. Fluid/melt partition coefficients higher than one, favorable for the genesis of magmatic U mineralization, can be reached for peraluminous leucogran- ites in equilibrium with chloride-rich solutions.

Harmonically mode-locked erbium-doped waveguide laser

NASA Astrophysics Data System (ADS)

Fanto, Michael L.; Malowicki, John E.; Bussjager, Rebecca J.; Johns, Steven T.; Vettese, Elizabeth K.; Hayduk, Michael J.

2004-08-01

The generation of ultrastable picosecond pulses in the 1550 nm range is required for numerous applications that include photonic analog-to-digital converter systems and high-bit rate optical communication systems. Mode-locked erbium-doped fiber ring lasers (EDFLs) are typically used to generate pulses at this wavelength. In addition to timing stability and output power, the physical size of the laser cavity is of primary importance to the Air Force. The length of the erbium (Er)-doped fiber used as the gain medium may be on the order of meters or even tens of meters which adds complexity to packaging. However, with the recent advancements in the production of multi-component glasses, higher doping concentrations can be achieved as compared to silicate glasses. Even more recent is the introduction of Er-doped multi-component glass waveguides, thus allowing the overall footprint of the gain medium to be reduced. We have constructed a novel harmonically mode-locked fiber ring laser using the Er-doped multi-component glass waveguide as the gain medium. The performance characteristics of this Er-doped waveguide laser (EDWL) including pulse width, spectral width, harmonic suppression, optical output power, laser stability and single sideband residual phase noise will be discussed in this paper.

Melt inclusions: Chapter 6

USGS Publications Warehouse

,; Lowenstern, J. B.

2014-01-01

Melt inclusions are small droplets of silicate melt that are trapped in minerals during their growth in a magma. Once formed, they commonly retain much of their initial composition (with some exceptions) unless they are re-opened at some later stage. Melt inclusions thus offer several key advantages over whole rock samples: (i) they record pristine concentrations of volatiles and metals that are usually lost during magma solidification and degassing, (ii) they are snapshots in time whereas whole rocks are the time-integrated end products, thus allowing a more detailed, time-resolved view into magmatic processes (iii) they are largely unaffected by subsolidus alteration. Due to these characteristics, melt inclusions are an ideal tool to study the evolution of mineralized magma systems. This chapter first discusses general aspects of melt inclusions formation and methods for their investigation, before reviewing studies performed on mineralized magma systems.

The effects of small amounts of H2O on partial melting of model spinel lherzolite in the system CMAS

NASA Astrophysics Data System (ADS)

Liu, X.; St. C. Oneill, H.

2003-04-01

Water (H_2O) is so effective at lowering the solidus temperatures of silicate systems that even small amounts of H_2O are suspected to be important in the genesis of basaltic magmas. The realization that petrologically significant amounts of H_2O can be stored in nominally anhydrous mantle minerals (olivine and pyroxenes) has fundamental implications for the understanding of partial melting in the mantle, for it implies that the role that H_2O plays in mantle melting may not be appropriately described by models in which the melting is controlled by hydrous phases such as amphibole. Although the effect of water in suppressing the liquidus during crystallization is quite well understood, such observations do not provide direct quantitative information on the solidus. This is because liquidus crystallization occurs at constant major-element composition of the system, but at unbuffered component activities (high thermodynamic variance). By contrast, for partial melting at the solidus the major-element component activities are buffered by the coexisting crystalline phases (low variance), but the major-element composition of the melt can change as a function of added H_2O. Accordingly we have determined both the solidus temperature and the melt composition in the system CMAS with small additions of H_2O, to 4 wt%, in equilibrium with the four-phase lherzolite assemblage of fo+opx+cpx+sp. Experiments were conducted at 1.1 GPa and temperatures from 1473 K to the dry solidus at 1593 K in a piston-cylinder apparatus. Starting materials were pre-synthesised assemblage of fo+opx+cpx+sp, plus an oxide/hydroxide mix of approximately the anticipated melt composition. H_2O was added as either Mg(OH)_2 or Al(OH)_3. The crystalline assemblage and melt starting mix were added as separate layers inside sealed Pt capsules, to ensure large volumes of crystal-free melt. After the run doubly polished sections were prepared in order to analyse the quenched melt by FTIR spectroscopy, to quantify the amounts of H_2O. This is necessary, as Pt capsules are to some extent open to H_2 diffusion. All melts were found to contain CO_2 (<0.7 wt%), which appears to come mainly from the hydroxide starting materials but also by C diffusion through the Pt capsule. Since CO_2 is experimentally correlated with H_2O, its presence significantly effects the interpretation of the results. Ignoring this complication, we find that 1 wt% H_2O decreases the solidus by ˜40 K; melt compositions do not change greatly, the main effect being a small decrease in MgO.

In situ Raman spectroscopic investigation of the structure of subduction-zone fluids

USGS Publications Warehouse

Mibe, Kenji; Chou, I.-Ming; Bassett, William A.

2008-01-01

In situ Raman spectra of synthetic subduction-zone fluids (KAlSi3O8-H2O system) were measured to 900?? and 2.3 GPa using a hydrothermal diamond-anvil cell. The structures of aqueous fluid and hydrous melt become closer when conditions approach the second critical endpoint. Almost no three-dimensional network was observed in the supercritical fluid above 2 GPa although a large amount of silicate component is dissolved, suggesting that the physical and chemical properties of these phases change drastically at around the second critical endpoint. Our experimental results indicate that the fluids released from a subducting slab change from aqueous fluid to supercritical fluid with increasing depth under the volcanic arcs. Copyright 2008 by the American Geophysical Union.

Cosmic setting for chondrule formation

NASA Technical Reports Server (NTRS)

Taylor, G. J.; Scott, E. R. D.; Keil, K.

1983-01-01

Chondrules are igneous-textured, millimeter-sized, spherical to irregularly-shaped silicate objects which constitute the major component of most chondrites. There is agreement that chondrules were once molten. Models for chondrule origin can be divided into two categories. One involves a 'planetary' setting, which envisages chondrules forming on the surfaces of parent bodies. Melting mechanisms include impact and volcanism. The other category is concerned with a cosmic setting in the solar nebula, prior to nebula formation. Aspects regarding the impact on planetary surfaces are considered, taking into account chondrule abundances, the abundancy of agglutinates on the moon, comminution, hypervelocity impact pits, questions of age, and chondrule compositions. Attention is also given to collisions during accretion, collisions between molten planetesimals, volcanism, and virtues of a nebular setting.

Experimental mineral/liquid partition coefficients of the rare earth elements /REE/, Sc and Sr for perovskite, spinel and melilite

NASA Technical Reports Server (NTRS)

Nagasawa, H.; Schreiber, H. D.; Morris, R. V.

1980-01-01

Experimental determinations of the mineral/liquid partition coefficients of REE (La, Sm, Eu, Gd, Tb, Yb and Lu), Sc and Sr are reported for the minerals perovskite, spinel and melilite in synthetic systems. Perovskite concentrates light REE with respect to the residual liquid but shows no preference for heavy REE. Spinel greatly discriminates against the incorporation of REE, especially light REE, into its crystal structure. The partition of REE into melilite from a silicate liquid is quite dependent upon both the bulk melt and melilite solid-solution (gehlenite and akermanite components) compositions. As such, melilite can be enriched in REE or will reject REE with corresponding strong negative or strong positive Eu anomalies, respectively.

Miocene silicic volcanism in southwestern Idaho: Geochronology, geochemistry, and evolution of the central Snake River Plain

USGS Publications Warehouse

Bonnichsen, B.; Leeman, W.P.; Honjo, N.; McIntosh, W.C.; Godchaux, M.M.

2008-01-01

New 40Ar-39Ar geochronology, bulk rock geochemical data, and physical characteristics for representative stratigraphic sections of rhyolite ignimbrites and lavas from the west-central Snake River Plain (SRP) are combined to develop a coherent stratigraphic framework for Miocene silicic magmatism in this part of the Yellowstone 'hotspot track'. The magmatic record differs from that in areas to the west and east with regard to its unusually large extrusive volume, broad lateral scale, and extended duration. We infer that the magmatic systems developed in response to large-scale and repeated injections of basaltic magma into the crust, resulting in significant reconstitution of large volumes of the crust, wide distribution of crustal melt zones, and complex feeder systems for individual eruptive events. Some eruptive episodes or 'events' appear to be contemporaneous with major normal faulting, and perhaps catastrophic crustal foundering, that may have triggered concurrent evacuations of separate silicic magma reservoirs. This behavior and cumulative time-composition relations are difficult to relate to simple caldera-style single-source feeder systems and imply complex temporal-spatial development of the silicic magma systems. Inferred volumes and timing of mafic magma inputs, as the driving energy source, require a significant component of lithospheric extension on NNW-trending Basin and Range style faults (i.e., roughly parallel to the SW-NE orientation of the eastern SRP). This is needed to accommodate basaltic inputs at crustal levels, and is likely to play a role in generation of those magmas. Anomalously high magma production in the SRP compared to that in adjacent areas (e.g., northern Basin and Range Province) may require additional sub-lithospheric processes. ?? Springer-Verlag 2007.

Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts

NASA Technical Reports Server (NTRS)

Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK

1987-01-01

The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.

Melt inclusions in veins: linking magmas and porphyry Cu deposits.

PubMed

Harris, Anthony C; Kamenetsky, Vadim S; White, Noel C; van Achterbergh, Esmé; Ryan, Chris G

2003-12-19

At a porphyry copper-gold deposit in Bajo de la Alumbrera, Argentina, silicate-melt inclusions coexist with hypersaline liquid- and vapor-rich inclusions in the earliest magmatic-hydrothermal quartz veins. Copper concentrations of the hypersaline liquid and vapor inclusions reached maxima of 10.0 weight % (wt %) and 4.5 wt %, respectively. These unusually copper-rich inclusions are considered to be the most primitive ore fluid found thus far. Their preservation with coexisting melt allows for the direct quantification of important oreforming processes, including determination of bulk partition coefficients of metals from magma into ore-forming magmatic volatile phases.

Structural environments of incompatible elements in silicate glass/melt systems: I. Zirconium at trace levels

NASA Astrophysics Data System (ADS)

Farges, Franã§Ois; Ponader, Carl W.; Brown, Gordon E., Jr.

1991-06-01

The structural environments of trace levels (2˜000 ppm) of Zr 4+ in several silicate glasses were examined as a function of melt composition and polymerization using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Glass compositions investigated were albite (NaAlSi 3O 8: AB) and a peralkaline composition (Na 3.3AlSi 7O 17: PR)- Zirconium was added to the oxide-carbonate mix prior to melting in the form of ZrO 2 (baddeleyite). A second set of Zr-silicate glasses containing 2000 ppm Zr and 1.0 to 2.4 wt% halogens (F as NaF and Cl as NaCl) was also synthesized. These included the Zr-AB and Zr-PR base-glass compositions as well as Zr-sodium trisilicate composition (Na2Si 3O 7: TS). In all glasses studied, Zr is mainly 6-coordinated by oxygen atoms ( d[Zr-O] ˜2.07 ± 0.01 Å). In the most polymerized glass (AB), a small but significant amount of Zr was also found to occur in 8-coordinated sites ( d[Zr-O] ˜2.22 Å). No clear evidence for F or Cl complexes of Zr was observed in any of the halogen-containing glasses. The regularity of the Zr site increases in the series AB < TS ˜PR. We attribute this change to an increase in the number of non-bridging oxygens in the first-coordination sphere of Zr related to the depolymerizing effects of halogens and/or sodium. Minor but significant interactions of Zr with the tetrahedral network were observed ( d[Zr-{Si, Al}] ˜3.65-3.71 Å ± 0.03 Å), which are consistent with Zr-O-{Si, Al} angles close to 160-170°, as in catapleiite (Na 2ZrSi 3O 9 · 2H 2O). Intermediaterange order, as reflected by the presence and number of second-neighbor {Si, Al} around Zr, increases significantly with increasing melt polymerization. The local environment around Zr is more strongly influenced by bonding requirements than by the network topology of the melt. Stabilization of zirconium in 6-coordinated sites in relatively depolymerized melts should act to decrease the crystal-melt partition coefficients of Zr and may explain the normally incompatible character of Zr during magmatic differentiation. The presence of Zr in sites of higher coordination (ZrO 8) in highly polymerized melts could be a precursor to the crystallization of zircon from such melts and thus may explain why Zr becomes a more compatible element, especially in the latest stages of magmatic differentiation.

Multiple Olivine Phase Transitions in the Shocked Martian Meteorite Tissint

NASA Astrophysics Data System (ADS)

Sharp, T. G.; Hu, J.; Walton, E. L.

2013-09-01

In some melt regions of Tissint olivine dissociated into silicate perovskite + magnesiowüstite while in others it transformed into ringwoodite. These different reactions and reaction mechanisms can be explained by local temperature variations.

The effect of oxygen fugacity on the partitioning of nickel and cobalt between olivine, silicate melt, and metal

NASA Technical Reports Server (NTRS)

Ehlers, Karin; Grove, Timothy L.; Sisson, Thomas W.; Recca, Steven I.; Zervas, Deborah A.

1992-01-01

The effect of oxygen fugacity, f(O2), on the partitioning behavior of Ni and Co between olivine, silicate melt, and metal was investigated in the CaO-MgO-Al2O3-SiO2-FeO-Na2O system, an analogue of a chondrule composition from an ordinary chondrite. The conditions were 1350 C and 1 atm, with values of f(O2) varying between 10 exp -5.5 and 10 exp -12.6 atm (i.e., the f(O2) range relevant for crystal/liquid processes in terrestrial planets and meteorite parent bodies). Results of chemical analysis showed that the values of the Ni and Co partitioning coefficients begin to decrease at values of f(O2) that are about 3.9 log units below the nickel-nickel oxide and cobalt-cobalt oxide buffers, respectively, near the metal saturation for the chondrule analogue composition.

Calcium isotopic fractionation in mantle peridotites by melting and metasomatism and Ca isotope composition of the Bulk Silicate Earth

NASA Astrophysics Data System (ADS)

Kang, Jin-Ting; Ionov, Dmitri A.; Liu, Fang; Zhang, Chen-Lei; Golovin, Alexander V.; Qin, Li-Ping; Zhang, Zhao-Feng; Huang, Fang

2017-09-01

To better constrain the Ca isotopic composition of the Bulk Silicate Earth (BSE) and explore the Ca isotope fractionation in the mantle, we determined the Ca isotopic composition of 28 peridotite xenoliths from Mongolia, southern Siberia and the Siberian craton. The samples are divided in three chemical groups: (1) fertile, unmetasomatized lherzolites (3.7-4.7 wt.% Al2O3); (2) moderately melt-depleted peridotites (1.3-3.0 wt.% Al2O3) with no or very limited metasomatism (LREE-depleted cpx); (3) strongly metasomatized peridotites (LREE-enriched cpx and bulk rock) further divided in subgroups 3a (harzburgites, 0.1-1.0% Al2O3) and 3b (fertile lherzolites, 3.9-4.3% Al2O3). In Group 1, δ44/40Ca of fertile spinel and garnet peridotites, which experienced little or no melting and metasomatism, show a limited variation from 0.90 to 0.99‰ (relative to SRM 915a) and an average of 0.94 ± 0.05‰ (2SD, n = 14), which defines the Ca isotopic composition of the BSE. In Group 2, the δ44/40Ca is the highest for three rocks with the lowest Al2O3, i.e. the greatest melt extraction degrees (average 1.06 ± 0.04 ‰, i.e. ∼0.1‰ heavier than the BSE estimate). Simple modeling of modal melting shows that partial melting of the BSE with 103 ln ⁡αperidotite-melt ranging from 0.10 to 0.25 can explain the Group 2 data. By contrast, δ44/40Ca in eight out of nine metasomatized Group 3 peridotites are lower than the BSE estimate. The Group 3a harzburgites show the greatest δ44/40Ca variation range (0.25-0.96‰), with δ44/40Ca positively correlated with CaO and negatively correlated with Ce/Eu. Chemical evidence suggests that the residual, melt-depleted, low-Ca protoliths of the Group 3a harzburgites were metasomatized, likely by carbonate-rich melts/fluids. We argue that such fluids may have low (≤0.25‰) δ44/40Ca either because they contain recycled crustal components or because Ca isotopes, similar to trace elements and their ratios, may be fractionated by kinetic and/or chromatographic effects of melt percolation in the mantle. The δ44/40Ca in Group 3b lherzolites (0.83-0.89‰) are lower than in the BSE as well, but the effects of metasomatism on δ44/40Ca are smaller, possibly because of the high Ca contents in their protoliths and/or smaller δ44/40Ca differences between the protoliths and metasomatic agents. The BSE estimates based on fertile peridotites in this study fall in the δ44/40Ca ranges for oceanic and continental basalts, various meteorites (achondrites; carbonaceous, ordinary and enstatite chondrites), Mars, and the Moon. These results provide benchmarks for the application of Ca isotopes to planet formation, mantle evolution, and crustal recycling.

Experimental Compressibility of Molten Hedenbergite at High Pressure

NASA Astrophysics Data System (ADS)

Agee, C. B.; Barnett, R. G.; Guo, X.; Lange, R. A.; Waller, C.; Asimow, P. D.

2010-12-01

Experiments using the sink/float method have bracketed the density of molten hedenbergite (CaFeSi2O6) at high pressures and temperatures. The experiments are the first of their kind to determine the compressibility of molten hedenbergite at high pressure and are part of a collaborative effort to establish a new database for an array of silicate melt compositions, which will contribute to the development of an empirically based predictive model that will allow calculation of silicate liquid density and compressibility over a wide range of P-T-X conditions where melting could occur in the Earth. Each melt composition will be measured using: (i) double-bob Archimedean method for melt density and thermal expansion at ambient pressure, (ii) sound speed measurements on liquids to constrain melt compressibility at ambient pressure, (iii) sink/float technique to measure melt density to 15 GPa, and (iv) shock wave measurements of P-V-E equation of state and temperature between 10 and 150 GPa. Companion abstracts on molten fayalite (Waller et al., 2010) and liquid mixes of hedenbergite-diopside and anorthite-hedenbergite-diopside (Guo and Lange, 2010) are also presented at this meeting. In the present study, the hedenbergite starting material was synthesized at the Experimental Petrology Lab, University of Michigan, where melt density, thermal expansion, and sound speed measurements were also carried out. The starting material has also been loaded into targets at the Caltech Shockwave Lab, and experiments there are currently underway. We report here preliminary results from static compression measurement performed at the Department of Petrology, Vrije Universiteit, Amsterdam, and the High Pressure Lab, Institute of Meteoritics, University of New Mexico. Experiments were carried out in Quick Press piston-cylinder devices and a Walker-style multi-anvil device. Sink/float marker spheres implemented were gem quality synthetic forsterite (Fo100), San Carlos olivine (Fo90), and natural pyropic garnet(Pyr74 Alm13.5 Gro12.5). We bracketed the density of molten hedenbergite with Fo100 to be 3.09 g cm-3 at 1.1 GPa and 1450°C, and with Fo90 to be 3.27 g cm-3 at 3.0 GPa and 1450-1550°C. These sink-float values represent an increase in isothermal density from reference ambient pressure of 6% and 12% respectively, or linear compressions of 0.16 and 0.12 g cm-3 GPa-1. The density-with-pressure increases in our static compression experiments are in good agreement with the Michigan ambient pressure sound speed measurements that yield an isentropic bulk modulus of KS=18.77 GPa. Currently we are performing higher pressure sink/float experiments in the range 7-8 GPa with pyrope garnet marker spheres to better constrain values for the isothermal bulk modulus (KT) and its pressure derivative K'. As a by-product of our sink/float experiments we are also determining the melting curve of hedenbergite well beyond the published pressure extent of approximately 1.5 GPa (Lindsley, 1967). Our early data show the hedenbergite liquidus to be 1450°C at 3 GPa and approximately 1750°C at 7 GPa.

Uranium in granitic magmas: Part 1. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H 2O-Na 2CO 3 system at 720-770°C, 2 kbar

NASA Astrophysics Data System (ADS)

Peiffert, Chantal; Cuney, Michel; Nguyen-Trung, Chinh

1994-06-01

The solubility of uranium was investigated in both carbonated aqueous fluid and granitic melt in equilibrium in the system haplogranite-uranium oxide-H 2O-Na 2CO 3 (0.5-1 molal) at 720-770°C, 2 kbar, andƒo 2 fixed by Ni-NiO, Fe 3O 4-Fe 2O 3, and Cu 2O-CuO buffers. As complete solid solution exists between UO 2.00 and UO 2.25 (i.e., 75 mol% UO 2 + 25 mol% UO 3), three distinct uranium oxides: UO (2.01 ± 0.01), UO (2.1.0 ± 0.02), and UO (2.25 ± 0.02) were, respectively, obtained at equilibrium, under the three ƒo 2 conditions cited above. Thus, the percentage of U (VI) in uranium oxide increased with increasing log ƒo 2. The thermal decomposition of Na 2CO 3 to CO 2 and Na 2O led to the decrease of the sodium carbonate concentration from 0.5-1 molal to ~10 -2 molal in all aqueous fluids and to the dissolution of Na in the silicate melts. Crystal-free silicate glasses with four agpaitic coefficients, α = ( (Na+K)/Al) = 1.1, 1.3, 1.5, and 1.7 were obtained. The uranium solubility in 10 -2 m aqueous carbonated fluid ((8.1 ± 0.1) ≤ quench pH ≤ (8.9 ± 0.1)) was in the range 1-17 ppm and increased linearly with increasing ƒo 2 according to the expression: log (U) (ppm) = 0.09 ·log ƒo 2 (bar) + 1.47 . This equation is valid for the temperature range 720-770°C and 2 kbar. U(IV) carbonate possibly were major species in aqueous solutions under reducing conditions (Ni-NiO buffer) whereas U(VI) carbonate complexes dominated under higher oxidation conditions (Fe 3O 4-Fe 2O 3, Cu 2O-CuO buffers). The uranium content in silicate glasses varied in a large range (10 2-2 × 10 5 ppm) and log (U) (ppm) increases linearly with both ƒo 2, and α in the range 1.1-1.5 according to the equation log (U) (ppm) = 0.04 log ƒo 2 (bar) + 3.80α -1.34 . This equation is valid for (1)ƒ o 2 ranging from Ni-NiO to Cu 2O-CuO, and (2) the temperature range 720-770°C at 2 kbar. The effect of ƒo 2 on the uranium solubility in silicate melt slightly decreased with increasing α from 1.1 to 1.5. For α in the range 1.5-1.7, the effect of both ƒo 2 and agpaicity index on the uranium solubility was considerably reduced. The temperature variation in the range 720-770°C had no significant effect on the uranium solubility in either aqueous fluid or silicate melt. The partition coefficient (D fluid/melt) of uranium was in the range 10 -4.0-10 -1.5 and depended on both ƒo 2 and α according to the equation log D fluid/melt = 0.05 log ƒo 2 (bar) - 3.78α + 2.84 . The validity conditions of this equation are similar to those of the preceding one. Results obtained in the present study could be used to predict the geochemical behaviour of uranium during magma fractionation and to further understanding of the formation of uranium ore deposits related to partial melting or fractional crystallization of felsic magmas. The genesis of the Kvanefjeld (Ilimaussaq, Greenland) uranium deposit is discussed.

Dissipation in the deep interiors of Ganymede and Europa

NASA Astrophysics Data System (ADS)

Hussmann, Hauke; Shoji, Daigo; Steinbruegge, Gregor; Stark, Alexander; Sohl, Frank

2017-04-01

Jupiter's satellites are subject to strong tidal forces which result in variations of the gravitational potential and deformations of the satellites' surfaces on the diurnal tidal cycle. Tidal flexing in the deep interiors can be a significant heat source for the satellites' thermal-orbital evolution. Whereas typical structure models of Europa consist of a core, a silicate mantle, an ocean and an outer ice-I shell [1], pressures inside Ganymede are sufficient for high-pressure ice phases to occur between the silicate mantle and the ocean [2]. With current data it is unknown whether the deep interiors (i.e., Europa's silicate shell and Ganymede's silicate mantle and/or high-pressure ice layer) are dissipative. Other possibilities would be that the dissipation rates are in general very low (unlikely at least for Europa due to recent observations) or that dissipative processes are mainly occurring in the ice-I shell and/or ocean. Thus, for evaluations of the heating state of these satellites, it is important to measure the magnitude of the interior dissipation. However, observation of the interior layers such as high-pressure ice layers is more challenging than that of the surface ice-I layer. Here we suggest a method to constrain the dissipation states of the deep interiors of Ganymede and Europa by altimetry and gravity measurements from an orbiting or multi-flyby spacecraft. Tidal variations are generally described by the Love numbers k2 and h2 for the tide-induced potential variation due to internal mass redistribution and the radial surface displacement, respectively. The phase-lags of these complex numbers contain information about the rheological and dissipative states of the satellites. For the satellites we assume a decoupling of the outer ice-shell from the deep interior by a liquid subsurface water ocean. We show that, in this case, the phase-lag difference between the lags of k2 and h2 can provide information on the rheological and thermal state of the deep interiors if the viscosities of the deeper layers are small (the phase-lag difference is almost independent of the dissipation in the surface layer). In case of Ganymede, phase-lag differences can reach values of a few degrees for high-pressure ice viscosities of 1e13-1e14 Pa s (around the lower boundary at its melting temperature) and would indicate a highly dissipative state of the deep interior. In this case, in contrast to the phase lags itself, the phase-lag difference is dominated by dissipation in the high-pressure ice layer rather than dissipation within the ice-I shell. These phase lags would be detectable from spacecraft in orbit around the satellite [3]. For Europa the phase-lag difference could reach values exceeding 20 deg if the silicate mantle contains melt and phase-lag measurements could help distinguish between (1) a hot dissipative (melt-containing) silicate mantle which would in thermal equilibrium correspond to a very thin outer ice-I shell and (2) a cold deep interior implying that dissipation would mainly occur in a thick (several tens of km) outer ice-I shell. These measurements are highly relevant for ESA's Jupiter Icy Moons Explorer (JUICE) and NASA's Europa Multiple Flyby Mission, both targeted for the Jupiter system. References: [1] Schubert, G., F. Sohl and H. Hussmann 2009. Interior of Europa. In: Europa, (R.T. Pappalardo, W.B. McKinnon, K. Khurana, Eds.), University of Arizona Press, pp. 353 - 368. [2] Schubert G., J. D. Anderson, T. Spohn, and W. B. McKinnon 2004. Interior composition, structure, and dynamics of the Galilean satellites. In: F. Bagenal, T. E. Dowling, and W. B. McKinnon (eds.) Jupiter. The Planet, Satellites, and Magnetosphere, pp. 281-306. Cambridge University Press. [3] Hussmann, H., D. Shoji, G. Steinbrügge, A. Stark, F. Sohl 2016. Constraints on dissipation in the deep interiors of Ganymede and Europa from tidal phase-lags. Cel. Mech. Dyn. Astr. 126, 131 - 144.

Mutual interactions of redox couples via electron exchange in silicate melts - Models for geochemical melt systems

NASA Technical Reports Server (NTRS)

Schreiber, Henry D.; Merkel, Robert C., Jr.; Schreiber, V. Lea; Balazs, G. Bryan

1987-01-01

The mutual interactions via electron exchange of redox couples in glass-forming melts were investigated both theoretically and experimentally. A thermodynamic approach for considering the mutual interactions leads to conclusion that the degree of mutual interaction in the melt should be proportional in part to the difference in relative reduction potentials of the interacting redox couples. Experimental studies verify this conclusion for numerous redox couples in several composition/temperature/oxygen fugacity regimes. Geochemical systems simultaneously possess many potentially multivalent elements; the stabilized redox states in the resulting magmas can be explained in part by mutual interactions and by redox buffering through the central Fe(III)- Fe(II) couples in the melts. The significance of these results for basaltic magmas of the earth, moon, and meteorites is addressed.

P- T phase relations of silicic, alkaline, aluminous liquids: new results and applications to mantle melting and metasomatism

NASA Astrophysics Data System (ADS)

Draper, David S.; Green, Trevor H.

1999-07-01

We report new experimental results obtained under nominally anhydrous conditions at 1.0-1.5 GPa on a synthetic melt whose composition is typical of extreme-composition xenolith glasses. These results demonstrate that part of this extreme compositional range is in equilibrium with a lherzolitic assemblage (olivine, orthopyroxene, and clinopyroxene on the liquidus), extending our earlier findings [D.S. Draper, T.H. Green P- T phase relations of silicic, alkaline, aluminous mantle-xenolith glasses under anhydrous and C-O-H fluid-saturated conditions, J. Petrol. 38 (1997) 1187-1224] showing saturation with harzburgite minerals (olivine and orthopyroxene on the liquidus). The new results strengthen the view that such liquids can readily coexist with upper mantle rocks. Our results also bear on the current debate regarding the nature of low-degree mantle melts between proponents of the diamond-aggregate technique [who argue for comparatively silica- and alkali-rich low-degree melts; e.g., M.B. Baker, M.M. Hirschmann, M.S. Ghiorso, E.M. Stolper, Compositions of near-solidus peridotite melts from experiments and thermodynamic calculations, Nature 375 (1995) 308-311; M.B. Baker, M.M. Hirschmann, L.E. Wasylenki, E.M. Stolper, M.S. Ghiorso, Quest for low-degree mantle melts, Nature 381 (1996) 286] and those favoring the sandwich technique [who question the value of the diamond-aggregate work and argue that near-solidus melts must be nepheline- and olivine-normative; T.J. Falloon, D.H. Green, H.St.C. O'Neill, C.G. Ballhaus, Quest for low-degree mantle melts, Nature 381 (1996) 285; T.J. Falloon, D.H. Green, H.St.C. O'Neill, W.O. Hibberson, Experimental tests of low degree peridotite partial melt compositions: implications for the nature of anhydrous near-solidus peridotite melts at 1 GPa, Earth Planet. Sci. Lett. 152 (1997) 149-162]. Our results support aspects of both views. The sandwich-technique view is supported, for example, because all our liquids coexisting with mantle minerals are nepheline- and olivine-normative; and our olivine-liquid Fe-Mg exchange KD values fall on a trend similar to that supported by those workers. The diamond-aggregate view is supported, for example, because we find equilibrium between highly silicic, alkaline liquids and mantle minerals, showing the effect of high alkali contents to allow high silica contents at silica activities buffered by magnesian olivine and orthopyroxene at low pressure [M.M. Hirschmann, M.B. Baker, E.M. Stolper, The effect of alkalis on the silica content of mantle-derived melts, Geochim. Cosmochim. Acta 62 (1998) 883-902]. Additionally, the melting trends put forward by the sandwich-technique workers include revised low-degree melt compositions, as reported by Hirschmann et al., and our compositions fall on extensions of these trends. These new analyses also yield an olivine-liquid KD that more closely follows the trend of KD vs. melt alkali contents. The views of both sides of this controversy appear to permit, under certain conditions, the existence of small amounts of melt in the upper mantle with compositions similar to the extreme-composition xenolith glasses that are the focus of our work. On the basis of our new results, we conclude that extreme-composition xenolith glasses can act as agents of cryptic metasomatism in the upper mantle.

Abrupt shift in δ18O values at Medicine Lake volcano (California, USA)

USGS Publications Warehouse

Donnelly-Nolan, J. M.

1998-01-01

 Oxygen-isotope analyses of lavas from Medicine Lake volcano (MLV), in the southern Cascade Range, indicate a significant change in δ18O in Holocene time. In the Pleistocene, basaltic lavas with <52% SiO2 averaged +5.9‰, intermediate lavas averaged +5.7‰, and silicic lavas (≥63.0%SiO2) averaged +5.6‰. No analyzed Pleistocene rhyolites or dacites have values greater than +6.3‰. In post-glacial time, basalts were similar at +5.7‰ to those erupted in the Pleistocene, but intermediate lavas average +6.8‰ and silicic lavas +7.4‰ with some values as high as +8.5‰. The results indicate a change in the magmatic system supplying the volcano. During the Pleistocene, silicic lavas resulted either from melting of low-18O crust or from fractionation combined with assimilation of very-low-18O crustal material such as hydrothermally altered rocks similar to those found in drill holes under the center of the volcano. By contrast, Holocene silicic lavas were produced by assimilation and/or wholesale melting of high-18O crustal material such as that represented by inclusions of granite in lavas on the upper flanks of MLV. This sudden shift in assimilant indicates a fundamental change in the magmatic system. Magmas are apparently ponding in the crust at a very different level than in Pleistocene time.

Late-stage magmatic to deuteric/metasomatic accessory minerals from the Cerro Boggiani agpaitic complex (Alto Paraguay Alkaline Province)

NASA Astrophysics Data System (ADS)

Comin-Chiaramonti, Piero; Renzulli, Alberto; Ridolfi, Filippo; Enrich, Gaston E. R.; Gomes, Celso B.; De Min, Angelo; Azzone, Rogério G.; Ruberti, Excelso

2016-11-01

This work describes rare accessory minerals in volcanic and subvolcanic silica-undersaturated peralkaline and agpaitic rocks from the Permo-Triassic Cerro Boggiani complex (Eastern Paraguay) in the Alto Paraguay Alkaline Province. These accessory phases consist of various minerals including Th-U oxides/silicates, Nb-oxide, REE-Sr-Ba bearing carbonates-fluorcarbonates-phosphates-silicates and Zr-Na rich silicates. They form a late-stage magmatic to deuteric/metasomatic assemblage in agpaitic nepheline syenites and phonolite dykes/lava flows made of sodalite, analcime, albite, fluorite, calcite, ilmenite-pyrophanite, titanite and zircon. It is inferred that carbonatitic fluids rich in F, Na and REE percolated into the subvolcanic system and metasomatically interacted with the Cerro Boggiani peralkaline and agpaitic silicate melts at the thermal boundary layers of the magma chamber, during and shortly after their late-stage magmatic crystallization and hydrothermal deuteric alteration.

About the Influence of the initial Atmosphere on the Earth's Temperature Distribution during it's Accumulation

NASA Astrophysics Data System (ADS)

Khachay, Y.; Anfilogov, V.; Antipin, A.

2012-04-01

We suggested a new model for accumulation of planets of the Earth's group [1], which is based on the contemporary results of geochemical analyses, which allow to obtain the concentrations of short living radioactive isotopes of 26Al in the matter of the pre planet cloud [2]. With use of that data new estimations of temperature distribution into the growing planetary pre planetary bodies into the Earth's nebular zone had been obtained. For the further Earth's temperature evolution, as it had been showed by the results of numerical modeling, the main role belongs to the temperature distribution in the forming Earth's core and the existence of a dense and transparent atmosphere. The shadow influence of the initial atmosphere had been researched in the paper [3]. We shall give the main consideration to these problems in that paper. It had been shown in [1], that on the earliest accumulation stage the heat release by the decay of 26Al it is sufficient for forming a central melted area and solid relatively thin mainly silicate upper envelope in the pre planetary body, with dimensions, larger than (50-100) km. The impact velocities on that stage are yet not large, therefore by the bodies impact with these or near dimensions liquid and mainly iron their parts merge, but the masses of the pre planetary bodies are not sufficient to gravitational keeping of silicate parts of the cold solid envelope. On that stage they remain into the nebular zone of the proto planet and the mechanism of matter differentiation for the future core and mantle reservoirs realizes. The process takes place yet in small bodies and is in time to finish during less than 10 million years. The next forming of the core and mantle structure continues according to all known estimations about 100 million years. Because of the merging of inner liquid parts of impacting bodies occur due to inelastic impact, the main part of potential energy transforms into heat. That continues up to that time when the iron core mass increases to the main part of the contemporary mass. The silicate particles of different dimensions remain in the proto planet cloud and in the initial atmosphere, reducing it's transparency and release of the heat radiation. On the finishing stage of the core growing the mass of the pre planetary body is sufficient for keeping of the rising part of the silicate envelope of falling bodies. The matter of the growing planet enriches more and more with a touch of silicates. The impact process of accumulated bodies gradually converts to the mechanism of elastic impact, by which only a small part of kinetic energy transforms into the merging by the pre planet body heat. The atmosphere losses the silicate particles and it's transparency exceeds. It is forming either a non melted mantle, or a mantle with a rising melted layer. That results show that the existence of a dense, nontransparent atmosphere leads to temperature growing in the inner areas of the planet during it's accumulation process. 1.Anfilogov V.N., Khachay Yu.V. A possible variant of matter differentiation on the initial stage of Earth's forming. // DAN. 2005, V. 403, N. 6, 803-806. 2.Merk R.,Breuer D., Spohn T., 2002. Numerical modeling of 26Al - Induced radioactive melting of asteroids concerning accretion, Icarus, 159, 183-191. 3.Hayashi C., Nakazawa K., Mizuno H. Earth's melting due to the blanketing effect of primordial dense atmosphere. // Earth and Plenetary Science Letters. (1979). v. 43, 22-28

Sulfide in the core and the composition of the silicate Earth

NASA Astrophysics Data System (ADS)

Burton, K. W.

2015-12-01

The chemical composition of the Earth is traditionally explained in terms of evolution from a solar-like composition, similar to that found in primitive 'chondritic' meteorites. It now appears, however, that the silicate Earth is not 'chondritic', but depleted in incompatible elements, including refractory lithophile and heat-producing elements. Either Earth lost material during planet-building due to collisional erosion or else internal differentiation processes produced a hidden reservoir deep in the early Earth. Sulfide in the core may provide a reservoir capable of balancing the composition of the silicate Earth. Recent experimental work suggests that the core contains a significant proportion of sulfide, added during the final stages of accretion and new data suggests that at high pressures sulfide can incorporate a substantial amount of refractory lithophile and heat-producing elements [1]. Pioneering work using the short-lived 146Sm-142Nd system strongly suggests that Earth's silicate mantle is non-chondritic [e.g. 2]. The drawback of such radiogenic isotope systems is that it is not possible to distinguish the fractionation of Sm/Nd that occurs during silicate melting from that occurring during the segregation of a sulfide-melt to form the core. Neodymium stable isotopes have the potential to provide just such a tracer of sulfide segregation, because there is a significant contrast in bonding environment between sulfide and silicate, where heavy isotopes should be preferentially incorporated into high force-constant bonds involving REE3+ (i.e. the silicate mantle). Preliminary data indicate that mantle rocks do indeed possess heavier 146Nd/144Nd values than chondritic meteorites, consistent with the removal of light Nd into sulfide in the core, driving the residual mantle to heavy values. Overall, our isotope and elemental data indicate that the rare earths and other incompatible elements are substantially incorporated into sulfide. While Nd Stable isotope data for chondritic meteorites and mantle rocks, are consistent with the segregation of sulfide to the core. [1] Wohlers &Wood, Nature 520, 337 (2015) [2] Boyet & Carlson, Science 309, 576 (2005)

Magmatic controls on the genesis of porphyry Cu-Mo-Au deposits: The Bingham Canyon example

NASA Astrophysics Data System (ADS)

Grondahl, Carter; Zajacz, Zoltán

2017-12-01

Bingham Canyon is one of the world's largest porphyry Cu-Mo-Au deposits and was previously used as an example to emphasize the role of magma mixing and magmatic sulphide saturation in the enhancement of ore fertility of magmatic systems. We analyzed whole rocks, minerals, and silicate melt inclusions (SMI) from the co-genetic, ore-contemporaneous volcanic package (∼38 Ma). As opposed to previous propositions, whole-rock trace element signatures preclude shoshonite-latite genesis via mixing of melanephelinite and trachyte or rhyolite, whereas core to rim compositional profiles of large clinopyroxene phenocrysts suggests the amalgamation of the ore-related magma reservoir by episodic recharge of shoshonitic to latitic magmas with various degrees of differentiation. Major and trace element and Sr and Nd isotopic signatures indicate that the ore-related shoshonite-latite series were generated by low-degree partial melting of an ancient metasomatized mantle source yielding volatile and ore metal rich magmas. Latite and SMI compositions can be reproduced by MELTS modeling assuming 2-step lower and upper crustal fractionation of a primary shoshonite with minimal country rock assimilation. High oxygen fugacities (≈ NNO + 1) are prevalent as evidenced by olivine-spinel oxybarometry, high SO3 in apatite, and anhydrite saturation. The magma could therefore carry significantly more S than would have been possible at more reducing conditions, and the extent of ore metal sequestration by magmatic sulphide saturation was minimal. The SMI data show that the latites were Cu rich, with Cu concentrations in the silicate melt reaching up to 300-400 ppm at about 60 wt% SiO2. The Au and Ag concentrations are also high (1.5-4 and 50-200 ppb, respectively), but show less variation with SiO2. A sudden drop in Cu and S concentrations in the silicate melt at around 65 wt% SiO2 in the presence of high Cl, Mo, Ag, and Au shows that the onset of effective metal extraction by fluid exsolution occurred at a relatively late stage of magma evolution. Overall, our results show that fluid exsolution during simple magmatic differentiation of oxidized alkaline magmas is capable of producing giant porphyry Cu deposits.

Shock-Induced Phase Transitions in the Martian Meteorite Tissint: Mechanisms and Constraints on Shock Pressure

NASA Astrophysics Data System (ADS)

Sharp, T. G.; Hu, J.; Walton, E. L.

2013-12-01

Martian meteorites are important samples for understanding the origin and age of the Martian crust. All of these samples have been shocked to some degree during their ejection from Mars or earlier. Tissint, a picritic shergottite, has many high-pressure phases that have been used to constrain shock conditions and suggest a deep crustal origin [1] and to argue for multiple impact events [2]. Here we investigate the products and mechanisms of various olivine transformation reactions. Olivine in and adjacent to shock-melt veins and pockets is transformed into high-pressure minerals. In the hottest parts of the sample, olivine dissociated into 50-nm crystals of magnesiowüstite intergrown with either a pyroxene-composition glass or with low-Ca clinopyroxene. In both cases, the olivine is inferred to have transformed to silicate perovskite + magnesiowüstite during shock with subsequent breakdown of the perovskite after pressure release. Olivine along the margins of shock veins transformed into ringwoodite. Polycrystalline ringwoodite formed at the olivine-melt interface wheras coherent ringwoodite lamellae formed farther from the melt. These ringwoodite lamellae have the same topotaxial relationship to olivine as seen in static high-pressure experiments [3] and shocked meteorites [4]: (100)Ol || {111}Rw and [011]Ol || <110>Rw. The various olivine reactions can be explained by a single shock to above 24 GPa where only the highest temperatures allowed the dissociation of olivine to silicate-perovskite plus magnesiowüstite. The silicate perovskite in the melt pocket transformed to pyroxene because the melt pocket remained very hot after pressure release. At lower temperatures, the kinetically easier polymorphic transformation of olivine to metastable ringwoodite occurred. At the lowest temperatures, this reaction was facilitated by nucleation of ringwoodite lamellae on stacking faults in olivine. The variation in assemblages that we see are consistent with a single shock and a relatively short shock pulse. References: [1] Baziotis1, I. P. et. al 2013 Nature Communications 4:1404, [2] El Goresey, A. et. al 2013 #1037. 44th LPSC. [3] Kerschhofer, L. et. al 1996 Science 274, 79-81. [4] Miyahara et. al, 2010 EPSL. 295, 321-327.

Modelling the gravity and magnetic field anomalies of the Chicxulub crater

NASA Technical Reports Server (NTRS)

Aleman, C. Ortiz; Pilkington, M.; Hildebrand, A. R.; Roest, W. R.; Grieve, R. A. F.; Keating, P.

1993-01-01

The approximately 180-km-diameter Chicxulub crater lies buried by approximately 1 km of sediment on the northwestern corner of the Yucatan Peninsula, Mexico. Geophysical, stratigraphic and petrologic evidence support an impact origin for the structure and biostratigraphy suggests that a K/T age is possible for the impact. The crater's location is in agreement with constraints derived from proximal K/T impact-wave and ejecta deposits and its melt-rock is similar in composition to the K/T tektites. Radiometric dating of the melt rock reveals an age identical to that of the K/T tektites. The impact which produced the Chicxulub crater probably produced the K/T extinctions and understanding the now-buried crater will provide constraints on the impact's lethal effects. The outstanding preservation of the crater, the availability of detailed gravity and magnetic data sets, and the two-component target of carbonate/evaporites overlying silicate basement allow application of geophysical modeling techniques to explore the crater under most favorable circumstances. We have found that the main features of the gravity and magnetic field anomalies may be produced by the crater lithologies.

Diffusion coefficients of Mg isotopes in MgSiO3 and Mg2SiO4 melts calculated by first-principles molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Liu, Xiaohui; Qi, Yuhan; Zheng, Daye; Zhou, Chen; He, Lixin; Huang, Fang

2018-02-01

The mass dependence of diffusion coefficient (D) can be described in the form of Di/Dj = (mj/mi)β, where m denotes masses of isotope i and j, and β is an empirical parameter as used to quantify the diffusive transport of isotopes. Recent advances in computation techniques allow theoretically calculation of β values. Here, we apply first-principles Born-Oppenheimer molecular dynamics (MD) and pseudo-isotope method (taking mj/mi = 1/24, 6/24, 48/24, 120/24) to estimate β for MgSiO3 and Mg2SiO4 melts. Our calculation shows that β values for Mg calculated with 24Mg and different pseudo Mg isotopes are identical, indicating the reliability of the pseudo-isotope method. For MgSiO3 melt, β is 0.272 ± 0.005 at 4000 K and 0 GPa, higher than the value calculated using classical MD simulations (0.135). For Mg2SiO4 melt, β is 0.184 ± 0.006 at 2300 K, 0.245 ± 0.007 at 3000 K, and 0.257 ± 0.012 at 4000 K. Notably, β values of MgSiO3 and Mg2SiO4 melts are significantly higher than the value in basalt-rhyolite melts determined by chemical diffusion experiments (0.05). Our results suggest that β values are not sensitive to the temperature if it is well above the liquidus, but can be significantly smaller when the temperature is close to the liquidus. The small difference of β between silicate liquids with simple compositions of MgSiO3 and Mg2SiO4 suggests that the β value may depend on the chemical composition of the melts. This study shows that first-principles MD provide a promising tool to estimate β of silicate melts.

Possible terrestrial analogs of Valhalla and other ripple-ring basins

NASA Technical Reports Server (NTRS)

Wood, C. A.

1981-01-01

The most remarkable feature on Callisto is Valhalla, a 3000 km wide structure comprised of dozens of concentric ridges and scarps surrounding a central smooth zone. Conventionally, Valhalla is interpreted as a multi-ring impact basin (similar to those on the terrestrial planets) whose morphology has been strongly effected by a thin and weak icy lithosphere in which it formed. Alternatively, Valhalla may have been formed by some non-impact related processes. In particular, ice cauldrons formed in Iceland by subsidence of glacier ice into voids created by geothermal melting are grossly similar to Valhalla in that both formed in ice and have multiple rings. Theoretical support for a similar subsidence mode of origin for Valhalla is provided by models of the thermal evolution of ice-silicate planets that result in diapiric sinking of lithospheric material into a water mantle (e.g., Paramentier and Head, 1979).

Fractional ultrabasic-basic evolution of upper-mantle magmatism: Evidence from xenoliths in kimberlites, inclusions in diamonds and experiments

NASA Astrophysics Data System (ADS)

Litvin, Yuriy; Kuzyura, Anastasia

2017-04-01

Ultrabasic peridotites and pyroxenites together with basic eclogites are the upper-mantle in situ rocks among xenoliths in kimberlites. Occasionally their diamond-bearing varieties have revealed within the xenoliths. Therewith the compositions of rock-forming minerals demonstrate features characteristic for primary diamond-included minerals of peridotite and eclogite parageneses (the elevated contents of Cr-component in peridotitic garnets and Na-jadeitic component in eclogitic clinopyroxenes). High-pressure experimental study of melting equilibria on the multicomponent peridotie-pyroxenite system olivine Ol - orthopyroxene Opx - clinopyroxene Cpx - garnet Grt showed that Opx disappeared in the peritectic reaction Opx+L→Cpx (Litvin, 1991). As a result, the invariant peritectic equilibrium Ol+Opx+Cpx+Grt+L of the ultrabasic system was found to transform into the univariant cotectic assemblage Ol+Cpx+Grt+L. Further experimental investigation showed that olivine reacts with jadeitic component (Jd) with formation of garnet at higher 4.5 GPa (Gasparik, Litvin, 1997). Study of melting relations in the multicomponent system Ol - Cpx - Jd permits to discover the peritectic point Ol+Omph+Grt+L (where Omph - omphacitic clinopyroxene) at concentration 3-4 wt.% Jd-component in the system. The reactionary loss of Opx and Ol makes it possible to transform the 4-phase garnet lherzolite ultrabasic association into the bimineral eclogite assemblage. The regime of fractional Ol, Cpx and Grt crystallization must be accompanied by increasing content of jadeitic component in residual melts that causes the complete "garnetization of olivine". In the subsequent evolution, the melts would have to fractionate for basic SiO2-saturated compositions responsible for petrogenesis of eclogite varieties marked with accessory corundum Crn, kyanite Ky and coesite Coe. Both the peritectic mechanisms occur in regime of fractional crystallization. The sequence of the upper-mantle fractional ultrabasic-basic magmatic evolution and petrogenesis may be controlled by the following melting relations: from Ol, Opx, L field to cotectic curve Ol, Opx, Cpx, L, peritectic point Ol, Opx, Cpx, Grt, L (loss of Opx), cotectic curve Ol, (Cpx+Jd), Grt, L, peritectic point Ol, (Cpx→Omph), Grt, L (loss of Ol), divariant field Omph,Grt,L, cotectic curve Ky, Omph, Grt, L, eutectic point Ky,Coe,Omph, Grt,L, subsolidus assemblage Ky,Coe,Omph, Grt. The fractional ultrabasic-basic evolution of the upper-mantle silicate-carbonate-carbon melts-solutions, which are responsible for genesis of diamond-and-inclusions associations and diamond-bearing peridotites and eclogites, follows the similar physico-chemical mechanisms (Litvin et al., 2016). This is illustrated by fractional syngenesis diagram for diamonds and associated minerals which construction is based on evidence from high pressure experiments. References Gasparik T., Litvin Yu.A (1997). Stability of Na2Mg2Si2O7 and melting relations on the forsterite - jadeite join at pressures up to 22 GPa. Eur, J. Mineral. 9(2), 311-326. Litvin Yu.A. (1991). Physico-Chemical Study of Melting of Materials from the Deep Earth. Moscow: Nauka. 312 p. Litvin Yu.A., Spivak A.V., Kuzyura A.V. (2016). Fundamentals of the mantle-carbonatite concept of diamond genesis, Geochemistry Internat. 34(10), 839-857.

Pulse energy dependence of refractive index change in lithium niobium silicate glass during femtosecond laser direct writing.

PubMed

Cao, Jing; Poumellec, Bertrand; Brisset, François; Lancry, Matthieu

2018-03-19

Femtosecond laser-induced refractive index changes in lithium niobium silicate glass were explored at high repetition rate (300 fs, 500 kHz) by polarized light microscopy, full-wave retardation plate, quantitative birefringence microscopy, and digital holographic microscopy. We found three regimes on energy increase. The first one corresponds to isotropic negative refractive index change (for pulse energy ranging 0.4-0.8 μJ/pulse, 0.6 NA, 5μm/s, 650μm focusing depth in the glass). The second one (0.8-1.2 μJ/pulse) corresponds to birefringence with well-defined slow axis orientation. The third one (above 1.2 μJ/pulse) is related to birefringence direction fluctuation. Interestingly, these regimes are consistent with crystallization ones. In addition, an asymmetric orientational writing effect has been detected on birefringence. These topics extend the possibility of controlling refractive index change in multi-component glasses.

Influence of HMW tail chains on the structural evolution of HDPE induced by second melt penetration.

PubMed

Zhu, Chun-Xia; Xia, Xiao-Chao; Huang, Yan-Hao; Xie, Dan-Dan; Chen, Rui; Yang, Ming-Bo

2017-07-21

It is widely accepted that the role of the high molecular weight (HMW) component is cooperative in shear-induced crystallization, owing to entanglements among long chains. However, this paper demonstrates that the HMW component has a novel effect on structural evolution during the process of multi-melt multi-injection molding (M 3 IM), organized as follows. First, the appropriate HDPE system with an incremental concentration of HMW tails was established. Second, the crystalline morphologies and orientation behaviors of the M 3 IM samples were characterized using a combination of scanning electron microscopy (SEM) and two-dimensional small angle X-ray scattering (2D-SAXS), and these suggested that the amount of shish-kebabs was not monotonically promoted with an increasing content of HMW tails but tended to reduce at a certain value. Third, in order to explain this phenomenon, the special temperature and shear profiles of M 3 IM were depicted subsequently, and finally the mechanism of hierarchical structure formation with the influence of various amounts of HMW tail chains was discussed, based on the classical rheological viewpoint.

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

NASA Astrophysics Data System (ADS)

Huber, Christian; Parmigiani, Andrea

2018-04-01

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

A snapshot of mantle metasomatism: Trace element analysis of coexisting fluid (LA-ICP-MS) and silicate (SIMS) inclusions in fibrous diamonds

NASA Astrophysics Data System (ADS)

Tomlinson, E. L.; Müller, W.; EIMF

2009-03-01

We have determined the trace element compositions of coexisting fluid (carbonate-K-chloride-H 2O) and single-phase mineral inclusions in peridotitic (Cr-diopside) and eclogitic (omphacite, garnet) inclusions in fibrous diamonds from the Panda kimberlite (Slave craton, Canada). These diamonds provide a unique insight into the nature of the metasomatic agent, the metasomatised minerals and the pre-metasomatic protolith. The fluid component is strongly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE). Co-existing peridotitic minerals record a melt extraction event (high Cr and Ni) in the protolith prior to the influx of the trapped metasomatic fluid. The silicate minerals are also strongly enriched in LREE. Calculated partition coefficients agree with experimentally determined values in the literature, despite the complex composition of the natural fluid. This indicates that the minerals have re-equilibrated with the metasomatic fluid. The trace element compositions of the mineral inclusions are comparable to many equivalent phases in monocrystalline diamonds. This suggests that the metasomatic fluid and the process recorded in these samples may also be responsible for the growth of some types of monocrystalline diamonds.

Reaction rim growth on olivine in silicic melts: Implications for magma mixing

USGS Publications Warehouse

Coombs, Michelle L.; Gardner, James E.

2004-01-01

Finely crystalline amphibole or pyroxene rims that form during reaction between silicic host melt and cognate olivine xenocrysts, newly introduced during magma mixing events, can provide information about the timing between mixing and volcanic eruptions. We investigated rim growth experimentally by placing forsteritic olivine in rhyolitic and rhyodacitic melts for times between 25 and 622 h at 50 and 150 MPa, H2O-saturated, at the Ni-NiO buffer. Rims of orthopyroxene microlites formed from high-silica rhyolite and rhyodacite melts at 885°C and 50 MPa, and in the rhyolite at 150 MPa and 885°C. Rims of amphibole with lesser orthopyroxene formed in the rhyolite at 150 MPa and 800°C and in the rhyodacite at 150 MPa and 885°C. Irregular, convolute olivine edges and mass balance between olivine, melt, and rim phases show that olivine partly dissolved at all conditions. Iron-rich zones at the exteriors of olivines, which increased in width parabolically with time, show that Fe-Mg interdiffusion occurring in olivines was not outpaced by olivine dissolution. Linear increases of the square of rim widths with time suggest that diffusion within the melt is the rate-controlling process for olivine dissolution and rim growth. Rims grew one-half to one order-of-magnitude faster when melt water contents were doubled, unless conditions were far above the liquidus. Rim growth rate in rhyolite increases from 0.055 ± 0.01 µm2/h at 885°C and 50 MPa to 0.64 ± 0.13 µm2/h at 800°C and 150 MPa. Melt composition has a lesser effect on rim growth rates, with growth rate increasing as melt SiO2 content decreases. Pyroxene rims on olivines in andesite erupted from Arenal volcano (Costa Rica) grew at a rate of 3.0 ± 0.2 µm2/h over an eleven-year period. This rate is faster than those of the experiments due to lower melt viscosity and higher temperatures, and suggests that a magma mixing event preceded the start of the eruption by days.

Chronology and Petrology of Silicates From IIE Iron Meteorites: Evidence of a Complex Parent Body Evolution

NASA Technical Reports Server (NTRS)

Bogard, Donald D.; Garrison, Daniel H.; McCoy, Timothy J.

1999-01-01

IIE iron meteorites contain silicate inclusions whose characteristics suggest a parent body similar to that of H-chondrites. However, these silicates show a wide range of alteration, ranging from Netschadvo and Techado, whose inclusions are little altered. to highly differentiated silicates like-those in Kodaikanal, Weekeroo Station and Colomera, which have lost metal and sulfur and are enriched in feldspar. We find these inclusions to show varying degrees of shock alteration. Because only a limited amount of data on - isotopic ages of HE silicates were available, we made Ar-39 - Ar-40 age determinations of Watson, Techado, miles Colomera, and Sombrerete. Watson has an Ar-Ar age of 3.653 +/- 0.012 Gyr, similar to previously reported ages for Kodaikanal and Netschadvo. We suggest that the various determined radiometric ages of these three meteorites were probably reset by a common impact event. The space exposure ages for these three meteorites are also similar to each other and are considerably younger than exposure ages of other IIEs. Ar-39 - Ar-40 ages inferred for the other four meteorites analyzed are considerably older than Watson and are: Techado =4.49 +/- 0.01 Gyr, Miles =4.412 +/- 0.016 Gyr, Colomera =4.469 +/- 0.012 Gyr, and Sombrerete =4.535 +/- 0.005 Gyr. These ages are in fair agreement with previously reported Rb-Sr isochron ages for Colomera and Weekeroo Station. Although several mechanisms to form HE meteorites previously were suggested, it is not obvious that a single mechanism could produce a suite of meteorites with very different degrees of silicate differentiation and with isotopic ages that differ by >0.8 Gyr. We suggest that those IIEs with older isotopic ages are a product of partial melting and differentiation within the parent body, followed by mixing of silicate and metal while both were relatively hot. Netschadvo and Watson may have formed by this same process or by impact mixing about 4.5 Gyr ago, but their isotopic ages were subsequently reset by shock heating. Kodaikanal apparently is required to have formed more recently, in which case impact melting and differentiation seems the only viable process. We see no compelling reasons to believe that IIE silicate and metal derived from different parent bodies or that the parent body of IIEs was the same as that of H-chondrites.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Fe3+ partitioning during basalt differentiation on Mars: insights into the oxygen fugacity of the shergottite mantle source(s).

NASA Astrophysics Data System (ADS)

Medard, E.; Martin, A. M.; Collinet, M.; Righter, K.; Grove, T. L.; Newville, M.; Lanzirotti, A.

2014-12-01

The partitioning of Fe3+ between silicate melts and minerals is a key parameter to understand magmatic processes, as it is directly linked to oxygen fugacity (fO2). fO2 is, a priori, not a constant during magmatic processes, and its evolution depends on the compatibility of Fe3+. We have experimentally determined the partition coefficients of Fe3+ between augite, pigeonite, and silicate melt, and use them to constrain the fO2of the martian mantle and of differentiated martian basalts. A series of experiments on various martian basaltic compositions were performed under controlled fO2 in one-atmosphere gas-mixing furnaces. Fe3+/Fetotal ratios in silicate melts and pyroxenes were determined using synchrotron Fe K-edge XANES on the 13 IDE beamline at APS (Argonne). Fe3+ mineral/melt partition coefficients (DFe3+) for augite and pigeonite were obtained with a relative uncertainty of 10-15 %. Both are constant over a wide range of oxygen fugacity (FMQ-2.5 to FMQ+2.0). DFe3+ for augite and pigeonite are broadly consistent with previous data by [1], but DFe3+ for augite is significantly higher (by a factor of 2) than the indirect determinations of [2]. Since augites in [2] are extremely poor in iron compared to ours (0.18 wt% vs 13 wt% FeO), this strongly suggests that DFe3+ varies with Mg#, indicating that Fe3+is more compatible than previously thought in terrestrial mantle pyroxenes (3 wt% FeO) as well. Crystallization paths for shergottite parental melts have been calculated using the MELTS software, combined with our partition coefficients. fO2 in the residual melts is calculated from the models of [3] and [4]. It stays relatively constant at high temperatures, but increases very strongly during the latest stages of crystallization. These results explain the large range of fO2 determined in enriched shergottites. In order to estimate the fO2 of the martian mantle, only the highest temperature phases in the most primitive martian samples should be used. The most primitive shergottites record a mantle fO2 around FMQ-2.5, consistent with the lowest fO2estimated for surface basalts [5]. [1] McCanta et al. (2004) Am Min 89:1685-1693; [2] Mallmann and O'Neill (2009) J Petrol 50:1765-1794; [3] Righter et al. (2013) Am Min 98:616-628; [4] Kress and Carmichael (1991) CMP 108:82-92; [5] Schmidt ME et al. (2014) EPSL 384:198-208.

Rapid assembly and rejuvenation of a large silicic magmatic system: Insights from mineral diffusive profiles in the Kidnappers and Rocky Hill deposits, New Zealand

NASA Astrophysics Data System (ADS)

Cooper, George F.; Morgan, Daniel J.; Wilson, Colin J. N.

2017-09-01

The timescales over which magmas in large silicic systems are reactivated, assembled and stored remains a fundamental question in volcanology. To address this question, we study timescales from Fe-Mg interdiffusion in orthopyroxenes and Ti diffusion in quartz from the caldera-forming 1200 km3 Kidnappers and 200 km3 Rocky Hill eruptions from the Mangakino volcanic centre (Taupo Volcanic Zone, New Zealand). The two eruptions came from the same source area, have indistinguishable 40Ar/39Ar ages (∼1.0 Ma) and zircon U-Pb age spectra, but their respective deposits are separated by a short period of erosion. Compositions of pumice, glass and mineral species in the collective eruption deposits define multiple melt dominant bodies but indicate that these shared a common magmatic mush zone. Diffusion timescales from both eruptions are used to build on chemical and textural crystal signatures and interpret both the crystal growth histories and the timing of magma accumulation. Fe-Mg interdiffusion profiles in orthopyroxenes imply that the three melt-dominant bodies, established through extraction of melt and crystals from the common source, were generated within 600 years and with peak accumulation rates within 100 years of each eruption. In addition, a less-evolved melt interacted with the Kidnappers magma, beginning ∼30 years prior to and peaking within 3 years of the eruption. This interaction did not directly trigger the eruption, but may have primed the magmatic system. Orthopyroxene crystals with the same zoning patterns from the Kidnappers and Rocky Hill pumices yield consistently different diffusion timescales, suggesting a time break between the eruptions of ∼20 years (from core-rim zones) to ∼10 years (outer rim zones). Diffusion of Ti in quartz reveals similarly short timescales and magmatic residence times of <30 years, suggesting quartz is only recording the last period of crystallization within the final eruptible melt. Accumulation of the eruptible magma for these two, closely successive eruptions was accomplished over centuries to decades, in contrast to the gestation time of the magmatic system of ∼200 kyr, as indicated by zircon age patterns. The magmatic system was able to recover after the Kidnappers eruption in only ∼10-20 years to accumulate enough eruptible melt and crystals for a second ∼ 200 km3 eruption. Our data support concepts of large silicic systems being stored as long-lived crystal mushes, with eruptible melts generated over extraordinarily short timescales prior to eruption.

Constraints on Nubular Electromagnetic Pulses

NASA Astrophysics Data System (ADS)

Eisenhour, D. D.; Buseck, P. R.

1993-07-01

Chondritic meteorites contain an abundance of silicate minerals with opaque inclusions of oxides, sulfides, and metals. These host silicates interact differently from their enclosed opaques to electromagnetic (EM) radiation; specifically, silicates are inefficient at absorbing EM energy in the visible and near infrared while metals, sulfides, and Fe oxides absorb strongly in this frequency range. In the presence of a strong electromagnetic pulse (EMP), this preferential absorption leads to the selective heating of the opaque inclusions and can produce unique textures ("dirty snowballs": intimate, ~spherical intergrowths of silicate and opaque minerals with radii of < 1 to 10 micrometers) that record the passage of the EMP. Many chondrules, CAIs, and isolated silicate grains within chondritic meteorites exhibit these unique features, suggesting that strong EMPs were common in the early solar nebula [1]. Here we discuss new constraints on nebular EMPs obtained from both experimental simulations and calculations of radiative heat transport. To test the feasibility of producing "dirty snowball" textures by EMP heating, olivines and pyroxenes containing metal and sulfide inclusions were heated with a 10 watt, argon-ion, CW laser operated at 514 nm. Comparisons between meteoritic "dirty snowball" textures and experimentally produced textures confirm the ability to produce the meteoritic textures by EMP heating and suggest heating times and fluxes of 0.25 to 10 seconds and 10^9 to 10^10 ergs cm^-2 sec^-1. Fluxes less than 10^9 ergs cm^-2 sec^-1 were insufficient to melt metal and sulfide inclusions, while fluxes greater than 10^10 ergs cm^-2 sec^-1 resulted in complete melting of metal, sulfide, and silicates. The experimentally determined heating time scales suggest that radiative equilibrium was reached in the "dirty snowball" formation process, indicating that the range of observed textures is controlled by cooling rates. Calculations of radiative absorption and emission allow further constraints to be placed on the EMPs responsible for "dirty snowball" formation. The absorption and emission efficiencies of grains in a blackbody radiation field were determined by calculating Planck mean cross sections for olivine, pyroxene, and iron as a function of grain size [2,3]. This information was combined with conductive heat flow calculations to determine the behavior of olivine and pyroxene grains with small inclusions of metal. Results indicate that "dirty snowball" formation results only over a narrow flux range for a given multiphase assemblage, with higher fluxes required for smaller, more transparent, or more refractory grains. For a 100-mm olivine chondrule containing a 10-micrometer "dirty snowball," the required flux is ~9 +- 1 x 10^8 ergs cm^-2 sec^-1, with a minimum pulse duration of 4 seconds (assuming an initial grain temperature of 500 K prior to heating). These values are in good agreement with experimentally determined values. The results show that pulses energetic enough to create "dirty snowballs" are also capable of producing the total melting required for chondrule formation with only slight increases in flux, or with only marginally different grain properties (e.g., more opaque inclusions, lower melting points, higher absorption cross sections). Because of the temperature and grain size dependence of the Planck mean cross sections of silicates, an EMP of the type described above will selectively melt larger aggregates and individual grains (>100 micrometer) while leaving smaller aggregates and grains unmelted. Therefore, natural products of EMP heating are: 1) the formation of chondrules in a sustained dusty environment, 2) a paucity of small chondrules, and 3) residual grains relatively unaffected by the EMPs. References: [1] Eisenhour D. D. and Buseck P. R. (1993) LPSC XXIV, 435-436. [2] Falk S. W. and Scalo J. M. (1975) Ap. J., 202, 690-695. [3] Gilman R. C. (1974) Ap. J. Supp., 268, 28, 397-403.

Constraints on Enceladus' Interior from Cassini Observations - Requirements for Future Geophysical Investigations

NASA Astrophysics Data System (ADS)

Castillo-Rogez, J. C.; Matson, D. L.; Johnson, T. V.; Lunine, J. I.

2006-12-01

We review the constraints on Enceladus' interior inferred from multi-instrument observations by the Cassini Orbiter. Available surface temperature mapping, shape data and geological imaging indicate that the body presents large lateral variations in internal viscoelastic properties, which makes it greatly non-hydrostatic. We will present geophysical evidence that the satellite is differentiated and that there cannot be a global ocean inside Enceladus, but that most probably liquid is located under young surfaces only. Temperature measurements and geyser modeling indicate that the water ice melting point could be reached a few tens meters under the South pole surface (Spencer et al. 2006; Porco et al. 2006). However, this is not enough to conclude that there is a liquid layer immediately below the surface. Water ice could be at the melting point. Different models in development show that a hotspot localized under the South pole, at a temperature close to the water ice melting point may be able to explain the power radiated from the "South pole area" (e.g., Tobie and Cadek, Europlanet Conference 2006; Castillo et al., submitted) and why this exceptional region is located at the South pole (Nimmo and Pappalardo, Nature 441, 614, 2006). The models provide a basis for specifying measurements needed for further investigation of Enceladus' interior from an orbiter and/or a lander. Gravity measurements from Doppler tracking and ranging are necessary to provide information on the distribution of density. The degree-two component J¬2 ranges from 5.2x10e-3 to 7.8x10e-3 as a function of the degree of differentiation and the silicate density, assuming the satellite is in hydrostatic equilibrium. The dynamical term of the degree-two gravity component (function of the potential tidal Love number k2) is ~10e-7. If Enceladus' shape deviates from hydrostatic equilibrium by 1 or 2 km, it is going to make gravity observations difficult to interpret. Assuming that the South pole is relaxed (because its mechanical lithosphere is expected to be thin) it would be the best place to fly over in order to get information on the deep interior from gravity measurements. Coupled gravity and altimetric measurements with a high spatial resolution are then necessary to better constrain the internal dynamics of the satellite. Full surface temperature coverage, especially during nighttime, is crucial to better assess the distribution of heat sources total heat flow. This work was carried out at the Jet Propulsion Laboratory-California Institute of Technology, under contract to NASA.

Tracking the source of the enriched martian meteorites in olivine-hosted melt inclusions of two depleted shergottites, Yamato 980459 and Tissint

NASA Astrophysics Data System (ADS)

Peters, T. J.; Simon, J. I.; Jones, J. H.; Usui, T.; Moriwaki, R.; Economos, R. C.; Schmitt, A. K.; McKeegan, K. D.

2015-05-01

The apparent lack of plate tectonics on all terrestrial planets other than Earth has been used to support the notion that for most planets, once a primitive crust forms, the crust and mantle evolve geochemically-independent through time. This view has had a particularly large impact on models for the evolution of Mars and its silicate interior. Recent data indicating a greater potential that there may have been exchange between the martian crust and mantle has led to a search for additional geochemical evidence to support the alternative hypothesis, that some mechanism of crustal recycling may have operated early in the history of Mars. In order to study the most juvenile melts available to investigate martian mantle source(s) and melting processes, the trace element compositions of olivine-hosted melt inclusions for two incompatible-element-depleted olivine-phyric shergottites, Yamato 980459 (Y98) and Tissint, and the interstitial glass of Y98, have been measured by Secondary Ionization Mass Spectrometry (SIMS). Chondrite-normalized Rare Earth Element (REE) patterns for both Y98 and Tissint melt inclusions, and the Y98 interstitial glass, are characteristically light-REE depleted and parallel those of their host rock. For Y98, a clear flattening and upward inflection of La and Ce, relative to predictions based on middle and heavier REE, provides evidence for involvement of an enriched component early in their magmatic history; either inherited from a metasomatized mantle or crustal source, early on and prior to extensive host crystallization. Comparing these melt inclusion and interstitial glass analyses to existing melt inclusion and whole-rock data sets for the shergottite meteorite suite, defines mixing relationships between depleted and enriched end members, analogous to mixing relationships between whole rock Sr and Nd isotopic measurements. When considered in light of their petrologic context, the origin of these trace element enriched and isotopically evolved signatures represents either (1) crustal assimilation during the final few km of melt ascent towards the martian surface, or (2) assimilation soon after melt segregation, through melt-rock interaction with a portion of the martian crust recycled back into the mantle.

Enigma of lamprohyres

NASA Astrophysics Data System (ADS)

Vasyukova, Elena

2013-04-01

Till now lamprophyres are 'the camera obscure' in petrology. There is no the complete agreement about the origin, classification, genetic links and their role in the ore formation processes yet. Traditionally ca-alkaline lamprophyres associated with the diorites, syenites and granitoids. But modern studies show the geochronological, geochemical and isotopic evidences of the genetic links between lamprophyres and carbonatites (Woodard, 2010;.Coulson et al., 2003) and as a consequence the formation of REE-ore deposits. These authors explain the origin of lamprophyres and carbonatites by the different melting degrees of the metasomatised mantle. In this work we found another mechanism of their generation - the liquation of carbonate-silica melt. Within the area of Chuya complex (South-East Altai-North-West Mongolia) the lamphrophyric dykes are distributed irregularly and create the belts or series of bodies located next to the faults of different order. We studied about 30 dykes from three different areas (South Chuya, Yustyd, Aktash) and related rocks from the Tarakhata intrusion. Very similar rock and mineral composition, close time-space characteristics allow us to suggest their comagmatic nature. In the lamprophyres of South-Chuya area there are strong petrography evidences of liquation of carbonate-silicate melt during their evolution. The ocellar structures with the ocelli composed by the silicate mineral and inter globule material represented by carbonates with ore and other nonmetallic minerals. One of them is Ba-celestine which compiles the intergranular space, veinlets and pseudomorphoses after the silicates. It associates with the apatites, quartz, chlorite, carbonates (calcite and dolomite) and oxides (magnetite, goethite, chromite etc). The multi-element and rare-earth diagrams of all investigated rocks are equal in the form, at the position of HFSE minima, high La/Yb and Gd/Yb relations, except the Ba and Sr anomalies. In the graphs of the south-chuya area rocks, where Ba-celestine was found, marked Ba and Sr minima. Accordingly this fact Ba and Sr couldn't be brought into the system. And Ba-celestine is the residual sign of the segregated liquid, enriched in Ba, Sr, Ca ? P. 1. Rock, N. M. S., 1991. Lamprophyres. Blackie and Son Ltd, Glasgow and London, 285 pp. 2. J. Woodard Genesis and Emplacement of Carbonatites and Lamprophyres in the Svecophennian Domain, Academic Dissertation, University of Turku, Finland, 50 p., 2010 3. I.M.Coulson, K.M. Goodenough, N.J.G. Pearce, M.J. Leng Carbonatites and lamprophyres of the Gardar Province - a "window" to the sub-Gardar mantle? // Mineralogical Magazine, October 2003, Vol. 67(5), pp. 855-872. 4. McDonough, W.F. and Sun, S.-S. (1995). Composition of the Earth. Chemical Geology 120: 223-253. doi: 10.1016/0009-2541(94)00140-4.

Hf-W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26Al in the solar nebula

NASA Astrophysics Data System (ADS)

Budde, Gerrit; Kruijer, Thomas S.; Kleine, Thorsten

2018-02-01

Renazzo-type carbonaceous (CR) chondrites are distinct from most other chondrites in having younger chondrule 26Al-26Mg ages, but the significance of these ages and whether they reflect true formation times or spatial variations of the 26Al/27Al ratio within the solar protoplanetary disk are a matter of debate. To address these issues and to determine the timescales of metal-silicate fractionation and chondrule formation in CR chondrites, we applied the short-lived 182Hf-182W chronometer to metal, silicate, and chondrule separates from four CR chondrites. We also obtained Mo isotope data for the same samples to assess potential genetic links among the components of CR chondrites, and between these components and bulk chondrites. All investigated samples plot on a single Hf-W isochron and constrain the time of metal-silicate fractionation in CR chondrites to 3.6 ± 0.6 million years (Ma) after the formation of Ca-Al-rich inclusions (CAIs). This age is indistinguishable from a ∼3.7 Ma Al-Mg age for CR chondrules, suggesting not only that metal-silicate fractionation and chondrule formation were coeval, but also that these two processes were linked to each other. The good agreement of the Hf-W and Al-Mg ages, combined with concordant Hf-W and Al-Mg ages for angrites and CV chondrules, provides strong evidence for a disk-wide, homogeneous distribution of 26Al in the early solar system. As such, the young Al-Mg ages for CR chondrules do not reflect spatial 26Al/27Al heterogeneities but indicate that CR chondrules formed ∼1-2 Ma later than chondrules from most other chondrite groups. Metal and silicate in CR chondrites exhibit distinct nucleosynthetic Mo and W isotope anomalies, which are caused by the heterogeneous distribution of the same presolar s-process carrier. These data suggest that the major components of CR chondrites are genetically linked and therefore formed from a single reservoir of nebular dust, most likely by localized melting events within the solar protoplanetary disk. Taken together, the chemical, isotopic, and chronological data for components of CR chondrites imply a close temporal link between chondrule formation and chondrite accretion, indicating that the CR chondrite parent body is one of the youngest meteorite parent bodies. The relatively late accretion of the CR parent body is consistent with its isotopic composition (for instance the elevated 15N/14N) that suggests a formation at a larger heliocentric distance, probably beyond the orbit of Jupiter. As such, the accretion age of the CR chondrite parent body of ∼3.6 Ma after CAI formation provides the earliest possible time at which Jupiter's growth could have led to scattering of carbonaceous meteorite parent bodies from beyond its orbit into the inner solar system.

Microscopic, Macroscopic, and Megascopic Melts: a simple model to synthesize simulation, spectroscopy, shock, and sink/float constraints on silicate melts and magma oceans

NASA Astrophysics Data System (ADS)

Asimow, P. D.; Thomas, C.; Wolf, A. S.

2012-12-01

Silicate melts are the essential agents of planetary differentiation and evolution. Their phase relations, element partitioning preferences, density, and transport properties determine the fates of heat and mass flow in the high-temperature interior of active planets. In the early Earth and in extrasolar super-Earth-mass terrestrial planets it is these properties at very high pressure (> 100 GPa) that control the evolution from possible magma oceans to solid-state convecting mantles. Yet these melts are complex, dynamic materials that present many challenges to experimental, theoretical, and computational understanding or prediction of their properties. There has been encouraging convergence among various approaches to understanding the structure and dynamics of silicate melts at multiple scales: nearest- and next-nearest neighbor structural information is derived from spectroscopic techniques such as high-resolution multinuclear NMR; first-principles molecular dynamics probe structure and dynamics at scales up to hundreds of atoms; Archimedean, ultrasonic, sink/float, and shock wave methods probe macroscopic properties (and occasionally dynamics); and deformation and diffusion experiments probe dynamics at macroscopic scale and various time scales. One challenge that remains to integrating all this information is a predictive model of silicate liquid structure that agrees with experiments and simulation both at microscopic and macroscopic scale. In addition to our efforts to collect macroscopic equation of state data using shock wave methods across ever-wider ranges of temperature, pressure, and composition space, we have introduced a simple model of coordination statistics around cations that can form the basis of a conceptual and predictive link across scales and methods. This idea is explored in this presentation specifically with regard to the temperature dependence of sound speed in ultramafic liquids. This is a highly uncertain quantity and yet it is key, in many models, to extrapolating the equation of state up or down temperature to geophysically relevant conditions. Ultrasonic data on felsic to basaltic melts, across a fairly narrow temperature range from their liquidi to ≤1650 °C, suggest either no temperature dependence or sound speeds that increase with temperature. Simulations, conducted at much higher temperature to obtain relaxation, suggest a strong decrease in sound speed with temperature. Our shock wave data on Mg2SiO4 liquid at 2000 °C yield a sound speed significantly lower than that predicted from data on less mafic liquids collected at lower temperatures where Mg2SiO4 liquid is not stable. The same shock method applied to melt compositions that are stable at 1300-1550 °C, however, yields sound speeds comparable to the ultrasonic results. Although each of these methods has its shortcomings, we show that considerable insight can be obtained in the context of a predictive model of Mg2+ and Si4+ coordination statistics as functions of temperature and pressure. We suggest that this can explain the difference between results obtained at ordinary upper mantle magmatic temperatures and those expected for magma oceans.

Zinc isotope fractionation during mantle melting and constraints on the Zn isotope composition of Earth's upper mantle

NASA Astrophysics Data System (ADS)

Wang, Ze-Zhou; Liu, Sheng-Ao; Liu, Jingao; Huang, Jian; Xiao, Yan; Chu, Zhu-Yin; Zhao, Xin-Miao; Tang, Limei

2017-02-01

The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an initial approach, the terrestrial mantle, and by inference, the bulk silicate Earth (BSE), have previously been suggested to have an average δ66Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during mantle melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites (n = 47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ66Zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31 ± 0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ66Zn range of -0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66Zn value of +0.18 ± 0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during mantle partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ66ZnSpl-Ol = +0.12 ± 0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11-88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high Zn concentrations and heavy Zn isotopic compositions of MORB. Therefore, preferential melting of spinel in the peridotites may account for the Zn isotopic difference between spinel peridotites and basalts. By contrast, the absence of Zn isotope fractionation between silicate minerals suggests that Zn isotopes are not significantly fractionated during partial melting of spinel-free garnet-facies mantle. If the studied non-metasomatized peridotites represent the refractory upper mantle, mass balance calculation shows that the depleted MORB mantle (DMM) has a δ66Zn value of +0.20 ± 0.05‰ (2SD), which is lighter than the primitive upper mantle (PUM) estimated in previous studies (+0.28 ± 0.05‰, 2SD, Chen et al., 2013b; +0.30 ± 0.07‰, 2SD, Doucet et al., 2016). This indicates that the Earth's upper mantle has a heterogeneous Zn isotopic composition vertically, which is probably due to shallow mantle melting processes.

The effects of pressure, temperature and composition on olivine-liquid exchange coefficients

NASA Astrophysics Data System (ADS)

Matzen, A. K.; Wood, B. J.

2017-12-01

It has recently been observed that there is a correlation between trace element (Ni and Mn) concentrations in olivine (ol) phenocrysts and thickness of the lithosphere on which they were erupted [1]. There are a number of potential explanations for this observation: the mantle may have interacted with the Ni-rich core; the trace element concentrations reflect presence of recycled crust in the mantle; or it arises from melting of peridotite at different temperatures (T) and pressures (P). Discriminating between these hypotheses requires accurate models of olivine-silicate liquid (liq) partitioning. The three variables that control the observed variations in experimentally-derived ol-liq partition coefficients are T, P, and the composition of the silicate liquid (and to a lesser extent the olivine composition). However, experiments cannot unambiguously disentangle the effects of these variables. For olivine-saturated liquids at constant P, any change in T results in the crystallization or dissolution of olivine and thus a change in liquid composition, resulting in a correlation between T and silicate liquid composition (note that changing the bulk composition such that olivine saturation occurs at a different T also results in a correlation with composition and T). Alternatively, P and T can be varied in concert such that liquid and olivine compositions remain approximately constant [e.g., 2], resulting in a correlation between T and P. In an attempt to resolve the conflation of T, P and compositional effects we turned to metal (met)-liq partitioning studies. Experiments show that, unlike most other elements, P has a strong effect on the partitioning of Ni between Fe-rich metal and silicate melt. Assuming that the pressure dependence of K_{D, Ni-Fe}^{met-liq} (0-25 GPa) [3] is driven primarily by the changing activities in the silicate melt, we can approximate the effect that pressure will have on K_{D, Ni-Fe}^{ol-liq} as measured by [2], using Kress and Carmichael [4] to calculate Fe3+/Fe2+. We find that the pressure effect should be a significant contributor to the observed systematics of K_{D, Ni-Fe}^{ol-liq} between 1 atm and 3 GPa [2]. [1] Sobolev et al (2007) Science, 316, 412-417, [2] Matzen et al (2017) CMP 172:3, [3] Kegler et al (2008) EPSL 268, 28-40, [4] Kress & Carmichael (1991) CMP 108, 82-92.

Contrasting Effects of Carbon and Sulfur on Fe-Isotope Fractionation between Metal and Silicate Melt during Planetary Core Formation

NASA Astrophysics Data System (ADS)

Elardo, S. M.; Shahar, A.

2015-12-01

There are numerous studies that show well-resolved Fe isotope fractionations in igneous materials from different planetary bodies. Potential explanations for these fractionations include a non-chondritic bulk planetary Fe isotopic composition, and equilibrium fractionation between Fe-alloys or minerals and silicate melts during planetary differentiation, mantle melting, or fractional crystallization. This is further complicated by the fact that these processes are not mutually exclusive, making the interpretation of Fe isotope data a complex task. Here we present new experimental results investigating the effect of C on Fe isotope fractionation between molten peridotite and an Fe-alloy. Experiments were conducted at 1 GPa and 1850° C for 0.5 - 3 hours on a mixture of an 54Fe-spiked peridotite and Fe-metal with and without Ni metal in an end-loaded piston cylinder at the Geophysical Laboratory. Carbon saturation was achieved with a graphite capsule, and resulted in C contents of the Fe-alloy in our experiments ranging from 3.8 - 4.9 wt. %. The metal and silicate phases from half of each experiment were separated manually and dissolved in concentrated acids. Iron was separated from matrix elements by anion exchange chromatagraphy. Iron-isotopic compositions were determined with the Nu Plasma II MC-ICP-MS at GL. The other half of each experiment was used for quantitative microbeam analysis. Equilibrium was assessed with a time series and the three-isotope exchange method. The Ni-free experiments resulted in no resolvable Fe isotope fractionation between the Fe-C-alloy and molten silicate. This is in contrast to the results of Shahar et al. (2015) which showed a fractionation for Δ57Fe of ~0.18 ‰ between a peridotite and an Fe-alloy with a similar S abundance to C in these experiments. The one experiment thus far that contained Ni (~4 wt. % in the alloy) showed a resolvable fractionation between the Fe-Ni-C alloy and silicate of ~0.10 ‰. Shahar et al. found a similar magnitude fractionation to our Ni bearing experiment in experiments with no C or S. The difference in temperature (1650° C in Shahar et al. vs. 1850° C here) may be partially responsible for these discrepancies. Ongoing experiments will further investigate the effects of C and other light elements on Fe isotope fractionation during core segregation.

Mineralogy, Petrology, Chemistry, and Ar-39 - Ar-40 and Ages of the Caddo County IAB Iron: Evidence for Early Partial Melt Segregation of a Gabbro Area Rich in Plagioclase-Diopside

NASA Technical Reports Server (NTRS)

Takeda, Hiroshi; Bogard, Donald D.; Mittlefehldt, David W.; Garrison, Daniel H.

2000-01-01

We found coarse-grained gabbroic material rich in plagioclase and diopside in the Caddo County IAB iron meteorite. The polished thin sections studied were made from areas rich in Al and Ca detected by a micro-focus X-ray fluorescence (XRF) mapping technique. The gabbro is not a clast within a breccia, but rather this area is located mainly at silicate-metal boundaries only a few cm away from an area with fine-grained, ultramafic silicate similar to winonaites. Medium-grained orthopyroxene and olivine are found in transitional areas showing no disturbance of their crystalline textures. A vein-like region, starting at the area rich in fine-grained mafic silicate, extends towards the gabbroic area with a gradual increase in abundance of plagioclase and diopside. This texture and our accumulated knowledge of the formation mechanism of IAB/winonaltes meteorites, suggest that the gabbroic materials were formed by inhomogeneous segregation of partial melts of chondritic source materials. Compositional data on two mineralogically distinct samples of the gabbro-rich portion of the inclusion were obtained by INAA. Compared to an average of LAB silicate inclusions or winonaites, the Caddo County gabbro is enriched in the incompatible lithophile elements Na, Ca, Sc, REE and Hf, which is consistent with a melt origin for the gabbro. The cosmogenic space exposure age of Caddo County (511 Ma) is significantly younger than exposure ages of some other IAB meteorites, An 39Ar-40Ar age determination of the gabbroic material indicates a series of upward steps in age from 4.516 Ga to 4.523 Ga, with a few high temperature ages up to 4.54 Ga. The older age could approximate the primary recrystallization age of silicates. The stepped Ar age spectrum may indicate differences in Ar closure temperatures during slow cooling of -2-20'C/Myr in the parent body. Alternatively, the younger Ar-Ar ages may date a shock event which occurred while Caddo County was hot and which also created textures such as a linear metal vein with rounded zigzag walls in a diopside crystal and slightly miss-oriented rounded plagioclase domain.

Effect of H2O on metal-silicate partitioning of Ni, Co, V, Cr, Mn and Fe: Implications for the oxidation state of the Earth and Mars

NASA Astrophysics Data System (ADS)

Clesi, V.; Bouhifd, M. A.; Bolfan-Casanova, N.; Manthilake, G.; Fabbrizio, A.; Andrault, D.

2016-11-01

This study investigates the metal-silicate partitioning of Ni, Co, V, Cr, Mn and Fe during core mantle differentiation of terrestrial planets under hydrous conditions. For this, we equilibrated a molten hydrous CI chondrite model composition with various Fe-rich alloys in the system Fe-C-Ni-Co-Si-S in a multi-anvil over a range of P, T, fO2 and water content (5-20 GPa, 2073-2500 K, from 1 to 5 log units below the iron-wüstite (IW) buffer and for XH2O varying from 500 ppm to 1.5 wt%). By comparing the present experiments with the available data sets on dry systems, we observes that the effect of water on the partition coefficients of moderately siderophile elements is only moderate. For example, for iron we observed a decrease in the partition coefficient of Fe (Dmet/silFe) from 9.5 to 4.3, with increasing water content of the silicate melt, from 0 to 1.44 wt%, respectively. The evolution of metal-silicate partition coefficients of Ni, Co, V, Cr, Mn and Fe are modelled based on sets of empirical parameters. These empirical models are then used to refine the process of core segregation during accretion of Mars and the Earth. It appears that the likely presence of 3.5 wt% water on Mars during the core-mantle segregation could account for ∼74% of the FeO content of the Martian mantle. In contrast, water does not play such an important role for the Earth; only 4-6% of the FeO content of its mantle could be due to the water-induced Fe-oxidation, for a likely initial water concentration of 1.8 wt%. Thus, in order to reproduce the present-day FeO content of 8 wt% in the mantle, the Earth could initially have been accreted from a large fraction (between 85% and 90%) of reducing bodies (similar to EH chondrites), with 10-15% of the Earth's mass likely made of more oxidized components that introduced the major part of water and FeO to the Earth. This high proportion of enstatite chondrites in the original constitution of the Earth is consistent with the 17O,48Ca,50Ti,62Ni and 90Mo isotopic study by Dauphas et al. (2014). If we assume that the CI-chondrite was oxidized during accretion, its intrinsically high water content suggests a maximum initial water concentration in the range of 1.2-1.8 wt% for the Earth, and 2.5-3.5 wt% for Mars.

The effect of CO2 on the water-saturated solidus of K-poor peridotite between 4 and 6 GPa

NASA Astrophysics Data System (ADS)

Dvir, Omri; Kessel, Ronit

2017-06-01

The effect of various amounts of CO2 on the solidus of H2O-CO2-bearing peridotite was examined by determining the composition of H2O-CO2-bearing fluids and melts in equilibrium with garnet peridotite at 4-6 GPa and 900-1100 °C. Two capsules were placed in a rocking multi-anvil apparatus in each experiment. Both capsules contained a fertile peridotite with 10 wt% H2O, one with 1 (CLZ1) and the other with 5 wt% CO2 (CLZ5). In both capsules a diamond trap was placed on one end of the capsule as a fluid/melt trap. The H2O and CO2 content in the fluid or melt trapped in between the diamonds were measured using the quartz-tube-system technique by releasing the volatiles through infrared gas analyzer. The total dissolved solids in these phases were determined using the cryogenic laser-ablation - inductive couple plasma - mass spectrometry technique. The residual lherzolite consists of olivine, orthopyroxene, ±clinopyroxene, garnet, and ±magnesite as carbonate phase. The solidus of CLZ1 peridotite was located between 900 and 1000 °C at 4 GPa and between 1000 and 1100 °C at 5 and 6 GPa. CLZ5 peridotite melts below 900 °C at 4 GPa and between 900 and 1000 °C at 5 and 6 GPa. The results demonstrate a decrease in melting temperature of hydrous peridotite at pressures between 4 and 6 GPa with increasing amount of CO2. The H2O-CO2-bearing fluids found in this study at 900-1000 °C are similar in composition to low-Mg carbonatitic to silicic high-density fluids found in fluid inclusions in diamonds. With increasing temperature, the melts approach type II kimberlites. We propose that H2O-CO2-induced partial melting of metasomatized garnet lherzolite at 4-6 GPa is a possible origin for group II kimberlites.

Behaviour of niobium during early Earth’s differentiation: insights from its local structure and oxidation state in silicate melts at high pressure

NASA Astrophysics Data System (ADS)

Sanloup, C.; Cochain, B.; de Grouchy, C.; Glazyrin, K.; Konôpkova, Z.; Liermann, H.-P.; Kantor, I.; Torchio, R.; Mathon, O.; Irifune, T.

2018-02-01

Niobium (Nb) is one of the key trace elements used to understand Earth’s formation and differentiation, and is remarkable for its deficiency relative to tantalum in terrestrial rocks compared to the building chondritic blocks. In this context, the local environment of Nb in silica-rich melts and glasses is studied by in situ x-ray absorption spectroscopy (XAS) at high pressure (P) up to 9.3 GPa and 1350 K using resistive-heating diamond-anvil cells. Nb is slightly less oxidized in the melt (intermediate valence between  +4 and  +5) than in the glass (+5), an effect evidenced from the shift of the Nb-edge towards lower energies. Changes in the pre-edge features are also observed between melt and glass states, consistently with the observed changes in oxidation state although likely enhanced by temperature (T) effects. The oxidation state of Nb is not affected by pressure neither in the molten nor glassy states, and remains constant in the investigated P-range. The Nb-O coordination number is constant and equal to 6.3+/-0.4 below 5 GPa, and only progressively increases up to 7.1+/-0.4 at 9.3 GPa, the maximum P investigated. If these findings were to similarly apply to basaltic melts, that would rule out the hypothesis of Nb/Ta fractionation during early silicate Earth’s differentiation, thus reinforcing the alternative hypothesis of fractionation during core formation on reduced pre-planetary bodies.

Aubrite basalt vitrophyres: High sulfur silicate melts and a snapshot of aubrite formation. [Abstract only

NASA Technical Reports Server (NTRS)

Fogel, R. A.

1994-01-01

Two aubrite basalt vitrophyre clasts have been found within AMNH thin sections from the Parsa EH3 chondrite and the Khor Temiki aubrite. Polished sections of the Parsa Aubrite Inclusion (PAI) and the Khor Temiki Inclusion (KTI) were studied by optical, electron probe microanalysis (EPMA), and scanning electron microscopy (SEM) techniques with broad-beam and low absorbed EPMA currents used to minimize glass volatile loss. Some data have previously been reported for PAI and KTI may possibly correlate to a previously reported inclusion in Khor Tiimiki. In polished sections, PAI and KTI are approximately equal 4 mm in diameter and contain a large volume of glass. The clasts have similar textural characteristics and are akin to lunar vitrophyre textures. The glasses have high alkali rhyodacitic compositions Al-though PAI is peraluminous, KTI is significantly peralkaline. Additionally, the glasses have elevated sulfur concentrations that are extremely high by geochemical standards. SEM examination for beam overlap of microscopic CaS, FeS, and (Mg, Mn, Fe) S inclusions showed no such contamination. Furthermore, homogeneity of glass S content and low FeO contents help rule out contamination. Materials research data show that under reducing conditions alumino-silicate melts can dissolve up to several weight percent sulfur in the absence of Fe. The high S and alkali contents, the lack of associated high shock features, and the rationalized phase equilibria suggest that PAI and KTI are igneous melting products of an E-chondrite-like source material. Although large-scale impact melting cannot totally be ruled out, the above observations eliminate the possibility of in-situ shock melting.

Environmental barrier coating

DOEpatents

Pujari, Vimal K.; Vartabedian, Ara; Collins, William T.; Woolley, David; Bateman, Charles

2012-12-18

The present invention relates generally to a multi-layered article suitable for service in severe environments. The article may be formed of a substrate, such as silicon carbide and/or silicon nitride. The substrate may have a first layer of a mixture of a rare earth silicate and Cordierite. The substrate may also have a second layer of a rare earth silicate or a mixture of a rare earth silicate and cordierite.

Multi-platform observations on melt pond in Arctic summer 2010

NASA Astrophysics Data System (ADS)

Wang, Y.; Huang, W.; Lu, P.; Li, Z.

2011-12-01

Melt ponds play an important role in sea ice surface albedo and further affect the heat budget between ice-air interface. The overall reductions of Arctic sea ice extend and thickness especially in recent years is considered to be enhanced partly by the melt ponds, and understanding of melt ponds on how they change the heat and mass balance of sea ice through the ice surface albedo decrease is urgently required. Although satellite remote sensing is a general tool to observe sea ice surface features on a large scale, the small scale information with higher spatial and temporal resolution is more helpful to understand the physical mechanism in the evolution of melt ponds. Arctic summer in 2010 is special because of an obvious trans-polar melting, during which the multi-year ice in the central Arctic was seriously melted, and formed a trans-polar zone with ice concentration less than 80% stretching from the Chukchi Sea to the Greenland Sea. It provided a fantastic opportunity to observe melt ponds especially at the high latitude. The Fourth Chinese National Arctic Research Expedition in 2010 (CHINARE-2010) was carried out from July 1 to September 20, 2010. As R/V Xuelong sailing in the ice-infested seas, a multi-platform observation was conducted to investigate the evolution of melt ponds on Arctic sea ice. Among which, aerial photography provided a downward-looking snapshot of the ice surface by using the camera installed on a helicopter, and melt pond information on a 100-meter scale can be obtained. Shipboard photography gave an inclined inspection on the ice conditions beside the ship using the camera installed on the vessel, and melt pond information on a 10-meter scale can be determined. Ground-based photography was similar to the shipboard photography, but the camera with tilt angle was installed on the top of a vertical lifting device fixed on the ice, and melt pond information on a 1-meter scale can be observed. Over 10,000 sea ice images from different platforms were collected during the cruise, and the survey area covered the regions 140°W-180°W, 70°N-88°N. An image processing technique based on difference in colors of the surface features was used to divide each image into three components: snow-covered ice floes, melt ponds and leads. And then geometric features of melt ponds, such as area, perimeter, and roundness, could be extracted from the aerial images. These data can enrich our knowledge on the distribution of melt pond on different spatial scale, especially those in the high latitude regions where summer melting was never so serious in previous years.

Characterization of layered silicate-reinforced blends of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate).

PubMed

Lendvai, László; Apostolov, Anton; Karger-Kocsis, József

2017-10-01

A two-step melt blending procedure was used to produce binary systems composed of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT). To improve the properties of the blends, two different layered silicates, viz. bentonite (BT) and organically modified montmorillonite (oMMT) were incorporated. First, TPS and its layered silicate nanocomposites were prepared via extrusion compounding during which starch was plasticized with glycerol and water. In the second step, PBAT was added to TPS/layered silicate to produce blends in a batch-type mixer. Mechanical and thermal properties were determined. The blends showed acceptable ductility over 50wt.% PBAT content, although at the cost of strength and stiffness. By contrast to oMMT the BT became intercalated in TPS and TPS/PBAT blends. The reinforcing effect of BT and oMMT was most prominent for the glassy states of both TPS and TPS/PBAT blends. Thermal, and thermooxidative properties were not significantly affected by the presence of layered silicates. Copyright © 2017 Elsevier Ltd. All rights reserved.

Melting and Its Influence on the Long-term Evolution of the Lower Mantle Heterogeneities (LLSVP and ULVZ)

NASA Astrophysics Data System (ADS)

Fomin, I.; Tackley, P. J.

2017-12-01

Recent investigations have shown mantle solidus close to the range of proposed core-mantle boundary (CMB) temperatures (e.g. [Andrault et al., 2011, 2014], [de Koker et al., 2013]). Certain fraction of distinct rocks may reduce the effective melting temperature to values below the CMB temperature. It is especially true for iron enriched materials such as MORB [Nomura et al., 2011], BIF [Kato et al., 2016], iron-rich periclase [Boukare et al., 2015] and other rock species used to explain observed seismic anomalies. Computer simulations allow to study evolution and stability for chemically distinct piles proposed from geophysical data. Previous researches (e.g. [Mulyukova et al., 2015]) found those piles stirring in several hundreds of Ma. Our investigation adds influence of melting and following chemical differentiation on preservation of such structures.We present StagYY code [Tackley et al., 2008] with extended set of routines to model melting, melt redistribution and melt-dependent rheology in addition to solid-state mantle convection to reveal fate of chemically distinct piles in long-term (millions of years) perspective. A new point of our approach is usage of chemically independent oxides to describe rock composition and physical properties. Thin layers homogenize in few tens of millions of years despite whether melting happens or not. Thick structures (like periclase piles proposed for ULVZ [Wicks et al., 2010] or MORB-bearing domes for LLSVP [Ohta et al., 2008]) undergo partial melting if CMB temperature is above 3700K. Melt migration results in extraction of fusible components and therefore segregation of iron-enriched material. However, we weren't able to obtain any stabilized layer of iron-rich partially molten material at the CMB, because ongoing interaction and reequilibration of melt and solid results in buoyant liquids spreading to the adjacent mantle. Rheological influence of melt on bulk rock properties reduces time pile can exist.Our modeling puts severe constraints on the presence and fate of chemical heterogeneities in the lowermost mantle. Melting enhances stirring of such heterogeneities and generally no silicate melt can be stabilized at CMB for long time. Only low CMB temperatures (generally lower than 3700 K) allow anomalies to exist for geological periods of time (hundreds of Ma).

A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems

USGS Publications Warehouse

Duffield, W.A.; Ruiz, J.

1998-01-01

Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.

Temperature and pressure dependences of kimberlite melts viscosity (experimental-theoretical study)

NASA Astrophysics Data System (ADS)

Persikov, Eduard; Bykhtiyarov, Pavel; Cokol, Alexsander

2016-04-01

Experimental data on temperature and pressure dependences of viscosity of model kimberlite melts (silicate 82 + carbonate 18, wt. %, 100NBO/T = 313) have been obtained for the first time at 100 MPa of CO2 pressure and at the lithostatic pressures up to 7.5 GPa in the temperature range 1350 oC - 1950 oC using radiation high gas pressure apparatus and press free split-sphere multi - anvil apparatus (BARS). Experimental data obtained on temperature and pressure dependences of viscosity of model kimberlite melts at moderate and high pressures is compared with predicted data on these dependences of viscosity of basaltic melts (100NBO/T = 58) in the same T, P - range. Dependences of the viscosity of model kimberlite and basaltic melts on temperature are consistent to the exponential Arrenian equation in the T, P - range of experimental study. The correct values of activation energies of viscous flow of kimberlite melts have been obtained for the first time. The activation energies of viscous flow of model kimberlite melts exponentially increase with increasing pressure and are equal: E = 130 ± 1.3 kJ/mole at moderate pressure (P = 100 MPa) and E = 160 ± 1.6 kJ/mole at high pressure (P = 5.5 GPa). It has been established too that the viscosity of model kimberlite melts exponentially increases on about half order of magnitude with increasing pressures from 100 MPa to 7.5 GPa at the isothermal condition (1800 oC). It has been established that viscosity of model kimberlite melts at the moderate pressure (100 MPa) is lover on about one order of magnitude to compare with the viscosity of basaltic melts, but at high pressure range (5.5 - 7.5 GPa), on the contrary, is higher on about half order of magnitude at the same values of the temperatures. Here we use both a new experimental data on viscosity of kimberlite melts and our structural chemical model for calculation and prediction the viscosity of magmatic melts [1] to determine the fundamental features of viscosity of kimberlite and basaltic magmas at the T, P - parameters of the Earth's crust and upper mantle. The Russian Foundation for Basic Research (project 15-05-01318) and the Russian Science Foundation (project 14-27-00054) are acknowledged for the financial support. [1] Persikov, E.S. & Bukhtiyarov, P.G. (2009) Russian Geology & Geophysics, 50, No 12, 1079-1090.

Electrolytic production of oxygen from lunar resources

NASA Technical Reports Server (NTRS)

Keller, Rudolf

1991-01-01

Some of the most promising approaches to extract oxygen from lunar resources involve electrochemical oxygen generation. In a concept called magma electrolysis, suitable oxides (silicates) which are molten at 1300 to 1500 C are then electrolyzed. Residual melt can be discarded after partial electrolysis. Alternatively, lunar soil may be dissolved in a molten salt and electrolyzed. In this approach, temperatures are lower and melt conductances higher, but electrolyte constituents need to be preserved. In a different approach ilmenite is reduced by hydrogen and the resulting water is electrolyzed.