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Всероссийский ежегодный семинар по экспериментальной минералогии, петрологии и геохимии

Журнальные статьи

Annen C. et al. Quantification of the Intrusive Magma Fluxes during Magma Chamber Growth at Soufriere Hills Volcano (Montserrat, Lesser Antilles) // J. Petrol. 2014. Vol. 55, № 3. P. 529–548.

Magma fluxes in the crust control the thermal viability and mechanical stability of magma chambers. We estimated the magma fluxes required to generate the negative seismic velocity anomaly observed below Soufriere Hills volcano, Montserrat. Growth of a magma body by accretion of andesitic sills was simulated numerically and the resulting temperatures and melt fractions were used to calculate a synthetic anomaly of seismic wave velocity, which was filtered to be comparable with the velocity anomaly obtained from a tomographic experiment. Petrology indicates that before it was reheated, remobilized and erupted, the temperature of the magma residing in the chamber was about 850 degrees C. We ran simulations where convection is assumed to be low and heat transfer is mostly by conduction and simulations where convection is assumed to be vigorous enough to rapidly cool the magma chamber to 850 degrees C. In both cases, magma chamber growth over the last 350 years results in tomography anomalies that are too strong, unless the magma was emplaced at an unlikely low melt fraction (< 0 center dot 5). Good fits between the modelled and the observed velocity anomaly were obtained with sills 2-5 km in radius emplaced over 6000-150 000 years, depending on the temperature and melt fraction of the emplaced magma. Because of a trade-off between intrusion dimensions and emplacement durations, the volumetric magma fluxes are restricted to 7 x 10(-4) and 5 x 10(-3) km(3) a(-1). The velocity anomaly can be reproduced with a chamber containing high melt-fraction magma or with a mush of crystals and melt. The range of magma ages in the modelled magma chamber is much wider than the crystal residence time of the erupted andesite. This suggests that the eruption taps small pockets of recently assembled magma and that the velocity anomaly is mostly due to a non-eruptible mush.

Bacik P. et al. Zoned Ree-Enriched Dravite from a Granitic Pegmatite in Forshammar, Bergslagen Province, Sweden: An Empa, Xrd and La-Icp-Ms Study // Can. Mineral. 2012. Vol. 50, № 4. P. 825–841.

Green to grayish green tourmaline crystals (up to 10 cm across), with distinct optical zoning, occurs with quartz, blocky albite and muscovite in the Forshammar granitic pegmatite, central Bergslagen province, Sweden. Tourmaline contains inclusions of zircon and xenotime-(Y), and it is cut by veinlets of muscovite and hydroxylbastnasite-(Ce). Microanalytical and structural data (from the rim) indicate that the tourmaline can be classified as a dravite with moderate Al-Mg disorder at the Y and Z sites. Tourmaline displays chemical zoning that reflects the distribution of Fe, Mg, Al, Ca and Na. The Mg/(Mg+Fe) value is high; it decreases from core (similar to 0.85) to intermediate zone (0.76-0.79), but increases in the rim and vein dravite (0.93). The core has the highest proportion of X-site vacancy and Al content, whereas the intermediate zone is the most enriched in Fe and Na. The rim is slightly depleted in Al and has the highest Na compared to inner zones. Tourmaline veins crosscut the pre-existing tourmaline and are relatively more enriched in Na and Ca. The main compositional variations are driven by Al-X square Mg-1Na-1 and AlOMg-1(OH)(-1) substitutions. The Forshammar dravite shows the highest known concentrations of REE from pegmatite tourmaline, <= 1200 ppm REE, <= 210 ppm La, <= 670 ppm Ce; the chondrite-normalized patterns reveal high La-N/Yb-N (32 to 464) values and strongly negative Eu anomalies (Eu/Eu* = 0.005 to 0.05). The contents of Ti, Mn, Y and REE generally increase at the boundary of the intermediate zone and rim, whereas the contents of Zn, Ga and Sn decrease from the core to the rim. The core is likely a product of an early magmatic process during the late Svecofennian pegmatite formation (similar to 1.8 Ga) as suggested by oscillatory zoning of trace elements. The intermediate zone, rim and tourmaline veins originated during the late magmatic to hydrothermal stage. Hydroxylbastnasite-(Ce) and muscovite are apparently the final products of the hydrothermal process.

Charlier B., Grove T.L. Experiments on liquid immiscibility along tholeiitic liquid lines of descent // Contrib. Mineral. Petrol. 2012. Vol. 164, № 1. P. 27–44.

Crystallization experiments have been conducted on compositions along tholeiitic liquid lines of descent to define the compositional space for the development of silicate liquid immiscibility. Starting materials have 46-56 wt% SiO2, 11.7-17.7 wt% FeOtot, and Mg-number between 0.29 and 0.36. These melts fall on the basaltic trends relevant for Mull, Iceland, Snake River Plain lavas and for the Sept Iles layered intrusion, where large-scale liquid immiscibility has been recognized. At one atmosphere under anhydrous conditions, immiscibility develops below 1,000-1,020A degrees C in all of these compositionally diverse lavas. Extreme iron enrichment is not necessary; immiscibility also develops during iron depletion and silica enrichment. Variations in melt composition control the development of silicate liquid immiscibility along the tholeiitic trend. Elevation of Na2O + K2O + P2O5 + TiO2 promotes the development of two immiscible liquids. Increasing melt CaO and Al2O3 stabilizes a single-liquid field. New data and published phase equilibria show that anhydrous, low-pressure fractional crystallization is the most favorable condition for unmixing during differentiation. Pressure inhibits immiscibility because it expands the stability field of high-Ca clinopyroxene, which reduces the proportion of plagioclase in the crystallizing assemblage, thus enhancing early iron depletion. Magma mixing between primitive basalt and Fe-Ti-P-rich ferrobasalts can serve to elevate phosphorous and alkali contents and thereby promote unmixing. Water might decrease the temperature and size of the two-liquid field, potentially shifting the binodal (solvus) below the liquidus, leading the system to evolve as a single-melt phase.

Cross J.K. et al. High level triggers for explosive mafic volcanism: Albano Maar, Italy // Lithos. 2014. Vol. 190. P. 137–153.

Colli Albani is a quiescent caldera complex located within the Roman Magmatic Province (RMP), Italy. The recent Via dei Laghi phreatomagmatic eruptions led to the formation of nested maars. Albano Maar is the largest and has erupted seven times between ca 69-33 ka. The highly explosive nature of the Albano Maar eruptions is at odds with the predominant relatively mafic (SiO2 = 48-52 wt.%) foiditic (K2O = 9 wt.%) composition of the magma. The deposits have been previously interpreted as phreatomagmatic, however they contain large amounts (up to 30%vol) of deep seated xenoliths, skarns and all pre-volcanic subsurface units. All of the xenoliths have been excavated from depths of up to 6 km, rather than being limited to the depth at which magma and water interaction is likely to have occurred, suggesting an alternative trigger for eruption. High precision geochemical glass and mineral data of fresh juvenile (magmatic) clasts from the small volume explosive deposits indicate that the magmas have evolved along one of two evolutionary paths towards foidite or phonolite. The foiditic melts record ca. 50% mixing between the most primitive magma and Ca-rich melt, late stage prior to eruption. A major result of our study is finding that the generation of Ca-rich melts via assimilation of limestone, may provide storage for significant amounts of CO2 that can be released during a mixing event with silicate magma. Differences in melt evolution are inferred as having been controlled by variations in storage conditions: residence time and magma volume. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

Cunningham H. et al. Rapid magmatic processes accompany arc-continent collision: the Western Bismarck arc, Papua New Guinea // Contrib. Mineral. Petrol. 2012. Vol. 164, № 5. P. 789–804.

New U-Th-Ra, major and trace element, and Sr-Nd-Pb isotope data are presented for young lavas from the New Britain and Western Bismarck arcs in Papua New Guinea. New Britain is an oceanic arc, whereas the latter is the site of an arc-continent collision. Building on a recent study of the Manus Basin, contrasts between the two arcs are used to evaluate the processes and timescales of magma generation accompanying arc-continent collision and possible slab detachment. All three suites share many attributes characteristic of arc lavas that can be ascribed to the addition of a regionally uniform subduction component derived from the subducting altered oceanic crust and sediment followed by dynamic melting of the modified mantle. However, the Western Bismarck arc lavas diverge from the Pb isotope mixing array formed by the New Britain and the Manus Basin lavas toward elevated Pb-208/Pb-204. We interpret this to reflect a second and subsequent addition of sediment melt at crustal depth during collision. U-238 and Ra-226 excesses are preserved in all of the lavas and are greatest in the Western Bismarck arc. High-Mg andesites with high Sr/Y ratios in the westernmost arc are attributed to recent shallow mantle flux melting at the slab edge. Data for two historical rhyolites are also presented. Although these rhyolites formed in quite different tectonic settings and display different geochemical and isotopic compositions, both formed from mafic parents within millennia.

Deering C.D. et al. Magmatic processes that generate chemically distinct silicic magmas in // Contrib. Mineral. Petrol. 2012. Vol. 163, № 2. P. 259–275.

Northwestern Costa Rica is built upon an oceanic plateau that has developed chemical and geophysical characteristics of the upper continental crust. A major factor in converting the oceanic plateau to continental crust is the production, evolution, and emplacement of silicic magmas. In Costa Rica, the Caribbean Large Igneous Province (CLIP) forms the overriding plate in the subduction of the Cocos Plate-a process that has occurred for at least the last 25 my. Igneous rocks in Costa Rica older than about 8 Ma have chemical compositions typical of ocean island basalts and intra-oceanic arcs. In contrast, younger igneous deposits contain abundant silicic rocks, which are significantly enriched in SiO2, alkalis, and light rare-earth elements and are geochemically similar to the average upper continental crust. Geophysical evidence (high Vp seismic velocities) also indicates a relatively thick (similar to 40 km), addition of evolved igneous rocks to the CLIP. The silicic deposits of NW Costa Rica occur in two major compositional groups: a high-Ti and a low-Ti group with no overlap between the two. The major and trace element characteristics of these groups are consistent with these magmas being derived from liquids that were extracted from crystal mushes-either produced by crystallization or by partial melting of plutons near their solidi. In relative terms, the high-Ti silicic liquids were extracted from a hot, dry crystal mush with low oxygen fugacity, where plagioclase and pyroxene were the dominant phases crystallizing, along with lesser amounts of hornblende. In contrast, the low-Ti silicic liquids were extracted from a cool, wet crystal mush with high oxygen fugacity, where plagioclase and amphibole were the dominant phases crystallizing. The hot-dry-reducing magmas dominate the older sequence, but the youngest sequence contains only magmas from the cold-wet-oxidized group. Silicic volcanic deposits from other oceanic arcs (e.g., Izu-Bonin, Marianas) have chemical characteristics distinctly different from continental crust, whereas the NW Costa Rican silicic deposits have chemical characteristics nearly identical to the upper continental crust. The transition in NW Costa Rica from mafic oceanic arc and intra-oceanic magma to felsic, upper continental crust-type magma is governed by a combination of several important factors that may be absent in other arc settings: (1) thermal maturation of the thick Caribbean plateau, (2) regional or local crustal extension, and (3) establishment of an upper crustal reservoir.

Devineau K. et al. Incorporation of Zn in the destabilization products of muscovite at 1175 degrees C under disequilibrium conditions, and implications for heavy metal sequestration // Am. Miner. 2013. Vol. 98, № 5-6. P. 932–945.

This work reports on the thermal decomposition of muscovite within a granite powder doped with 8.5 wt% ZnO and heated during 10 min to 68 h at 1175 degrees C, and the implications for the sequestration of Zn, and other heavy metalts in such decomposition products. Samples were characterized using analytical scanning and transmission electron microscopy. After 10 min, muscovite is completely pseudomorphosed by Si-rich glass, spinel structure phases, and minor mullite. Spinel phases incorporate Zn, but their compositions depend on their position within the muscovite pseudomorphs. Al-rich oxides crystallize at the core of the pseudomorphs while Zn-Al spinels are located at the rims. The most Al-rich spinels have compositions close to gamma-Al2O3, a metastable transition alumina, with up to 5 wt% MgO, 2 wt% Fe2O3, 4 wt% ZnO, and 9 wt% SiO2. The most Zn-rich spinels show compositions intermediate between Al2O3 and gahnite (ZnAl2O4), with up to 31 wt% ZnO and significant contents of MgO (3 wt%), Fe2O3 (5 wt%), and SiO2 (10 wt%). After 68 h, stable spinels are gahnite close to the end-member composition with MgO and Fe2O3 contents below ca. 5 wt%, and SiO2 contents ca. 1 wt%. These results support the existence of a metastable solid solution between gamma-Al2O3 and gahnite. This experimental work shows that Zn can be incorporated in spinel structures after heating at 1175 C during short durations and Zn is preferentially incorporated in the muscovite pseudomorphs as opposed to the Qtz-Fds glass. Consequently, the thermal breakdown of phyllosilicates can be a viable process to immobilize heavy metals such as Zn.

Enggist A., Chu L., Luth R.W. Phase relations of phlogopite with magnesite from 4 to 8 GPa // Contrib. Mineral. Petrol. 2012. Vol. 163, № 3. P. 467–481.

To evaluate the stability of phlogopite in the presence of carbonate in the Earth's mantle, we conducted a series of experiments in the KMAS-H2O-CO2 system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl(90)-mag(10); wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550A degrees C. We bracketed the solidus between 1,200 and 1,250A degrees C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200A degrees C at a pressure of 7 GPa. Below the solidus, phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite and olivine appear. Phlogopite melts over a temperature range of similar to 150A degrees C. The amount of garnet increases above solidus from similar to 10 to similar to 30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures a parts per thousand yen5 GPa. Relative to CO2-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of similar to 7.5 GPa. In a cold (40 mWm(-2)) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate at a depth of 180-200 km.

Erdmann S. et al. Zircon textures and composition: refractory recorders of magmatic volatile evolution? // Contrib. Mineral. Petrol. 2013. Vol. 165, № 1. P. 45–71.

Zircon textures and composition have been used to infer magmatic processes including closed-system fractional crystallization, magma mixing or replenishment, and country-rock assimilation. Here, we propose that zircon textures and composition may also be refractory recorders of magmatic volatile evolution. We present field, whole-rock chemical, textural, mineral chemical, and U-Pb age data from evolved, fine-to-coarse-grained granite intrusions on Melville Peninsula, Nunavut, Canada. Zircon forms two main populations in these granites, Type-1 and Type-2 zircon. Type-1 zircon is present in all samples, but predominant in fine-grained granite. Crystals are euhedral and inclusion-rich and show periodic, fine-scale oscillatory zoning, comparatively low concentrations of U (< 2,200 ppm) and Hf (< 1.6 wt%), high Zr/Hf (similar to 40-62), and pervasive alteration. Type-2 zircon is predominant in coarse-grained granite. Crystals form overgrowths on Type-1 zircon and individual crystals. They are subhedral and inclusion-poor and show weak, irregular, large-scale oscillatory zoning, high U (up to similar to 7,250 ppm) and Hf (1.5-2.0 wt%), low Zr/Hf (similar to 37-44), and only local alteration. Compatible trace-element concentrations and Zr/Hf change sharply across the boundary of Type-1 to Type-2 zircon; Pb-207/Pb-206 ages preclude a significant hiatus between crystallization of the two types. We argue against magmatic versus hydrothermal crystallization, country-rock assimilation, or magma mixing as causes for the crystallization of Type-1 and Type-2 zircon. We propose instead that Type-1 zircon formed from volatile-undersaturated magmas and that Type-2 zircon formed from volatile-saturated magmas. Magmas fractionated by volatile-driven filter pressing into crystal-rich mush and crystal-poor magma. Crystal-rich mush with abundant Type-1 zircon crystallized to fine-grained granite. Volatile-rich magma crystallized to Type-2 zircon and coarse-grained granite. While Type-1 zircon was pervasively altered by exsolving magmatic volatiles, Type-2 zircon was only locally affected by subsolidus hydrothermal alteration.

Etschmann B. et al. Grain boundaries as microreactors during reactive fluid flow: experimental dolomitization of a calcite marble // Contrib. Mineral. Petrol. 2014. Vol. 168, № 2. P. 1045.

Limestone dolomitization is an example of a fluid-induced mineralogical transformation that commonly affects extensive rock volumes. To understand the mechanisms enabling these efficient replacement reactions, we investigated experimentally the dolomitization of a fractured calcite marble under flow-through conditions at mild hydrothermal conditions. Contrary to most earlier studies of coupled dissolution reprecipitation reactions that were conducted using small, individual grains, in this study, the integrity of the rock was preserved, so that the experiment explored the links between flow in a fracture and fluid-rock interaction. In these experiments, grain boundaries acted as microreactors, in which a Mg-poor 'protodolomite' formed initially, and then transformed into dolomite. The difficulty in nucleating dolomite played a key role in controlling the evolution of the porosity, by allowing for (1) initial dissolution along grain boundaries, and (2) formation of coarse porosity at the reaction interface. This porosity evolution not only enabled the reaction to progress efficiently, but also controlled the mineralogy of the system, as shown by brucite replacing calcite near the fracture once the fluid along calcite grain boundaries became sufficiently connected to the fluid flowing through the fracture. This study illustrates the role of grain boundaries, porosity evolution and nucleation in controlling reaction progress as well as the nature and textures of the products in pervasive mineralogical transformations.

Funk S.P., Luth R.W. An experimental study of a minette from the Milk River area, southern Alberta, Canada // Contrib. Mineral. Petrol. 2012. Vol. 164, № 6. P. 999–1009.

Buhlmann et al. (Can J Earth Sci 37: 1629-1650, 2000) studied the minettes and xenoliths from the Milk River area of southern Alberta, Canada. Based on previous work, they hypothesized that the minettes were derived from a source containing phlogopite + clinopyroxene +/- A olivine, at pressures a parts per thousand yen1.7 GPa. To test this hypothesis, liquidus experiments were performed on a primitive minette between 1.33 and 2.21 GPa and between 1,300 and 1,400 A degrees C to constrain the mineralogy of its source region. We found a multiple saturation point along the liquidus at 1.77 GPa and 1,350 A degrees C, where the liquid coexists with orthopyroxene and olivine. Neither phlogopite nor clinopyroxene were found to be liquidus phases, which is inconsistent with Buhlmann et al.'s hypothesis. We suggest that our minette is not primary, but had re-equilibrated with harzburgitic mantle subsequent to formation. In such a scenario, partial melting of a veined source containing mica and clinopyroxene occurred at or near the base of the Wyoming craton (similar to 200 km). Minimal heating or the introduction of hydrous fluids into the source would be required to induce partial melting. Rapid ascent rates, coupled with slow cooling rates, of the "primary minette magma" would preserve the high temperature observed in our experiments. At similar to 58 km, our "primary minette magma" likely stalled and re-equilibrated with the harzburgite surroundings.

Garcia-Arias M., Guillermo Corretge L., Castro A. Trace element behavior during partial melting of Iberian orthogneisses: An experimental study // Chem. Geol. 2012. Vol. 292. P. 1–17.

The determination of the exact protolith from which every leucogranite is derived may be a hard task. The trace element composition of both the leucogranite and their likely source rock can be a way to establish this relationship. This hypothesis is checked in an experimental study on the partial melting of two Iberian orthogneisses, the Ollo de Sapo and the Tormes Dome Gneisses. Several runs between 700 and 900 degrees C at 0.6 and 1.0 GPa, with added water ranging from 2% wt. to 10% wt. have been carried out in piston-cylinder devices. Their results show that two gneisses of virtually the same major and trace element composition yield partial melts of closely similar major element composition but extremely different trace element composition, above all REE. These differences are produced because of several factors, mainly the ASI value of melts (which in turn depends on minor differences in the composition in the main oxides of the gneisses) and the phosphorus hosted in the feldspars of the gneisses. The consequence of these minor changes is that the dissolution of the trace-element-bearing accessories, mainly apatite, can be delayed until higher temperatures are achieved, so melts formed under these circumstances are depleted in REE, Th and Y. Gneisses of relatively low aluminosity and phosphorus-rich feldspars will produce REE-poor melts saturated in P2O5 at low temperatures because neither apatite nor other phosphates dissolve. In contrast, gneisses of relatively high aluminosity and phosphorus-poor feldspars will produce REE-rich melts subsaturated in P2O5 at low temperatures. For this reason, using the trace element composition of peraluminous granites as the only way to establish their protoliths is not recommended. (C) 2011 Elsevier B.V. All rights reserved.

Gardner J.E. et al. Experimental constraints on rhyolite-MELTS and the Late Bishop Tuff magma body // Contrib. Mineral. Petrol. 2014. Vol. 168, № 2. P. 1051.

Thermodynamic models are vital tools to evaluate magma crystallization and storage conditions. Before their results can be used independently, however, they must be verified with controlled experimental data. Here, we use a set of hydrothermal experiments on the Late-erupted Bishop Tuff (LBT) magma to evaluate the rhyolite-MELTS thermodynamic model, a modified calibration of the original MELTS model optimized for crystallization of silicic magmas. Experimental results that are well captured by rhyolite-MELTS include a relatively narrow temperature range separating the crystallization of the first felsic mineral and the onset of the ternary minimum (quartz plus two feldspars), and extensive crystallization over a narrow temperature range once the ternary minimum is reached. The model overestimates temperatures by similar to 40 degrees C, a known limitation of rhyolite-MELTS. At pressures below 110 MPa, model and experiments differ in the first felsic phase, suggesting that caution should be exercised when applying the model to very low pressures. Our results indicate that for quartz, sanidine, plagioclase, magnetite, and ilmenite to crystallize in equilibrium from LBT magma, magma must have been stored at <= 740 degrees C, even when a substantial amount of CO2 occurs in the coexisting fluid. Such temperatures are in conflict with the hotter temperatures retrieved from magnetite-ilmenite compositions (similar to 785 degrees C for the sample used in the experiments). Consistent with other recent studies, we suggest that the Fe-Ti oxide phases in the Late Bishop Tuff magma body are not in equilibrium with the other minerals and thus the retrieved temperature and oxygen fugacity do not reflect pre-eruptive storage conditions.

14. U18998
Gozzi F. et al. Primary magmatic calcite reveals origin from crustal carbonate // Lithos. 2014. Vol. 190. P. 191–203.

We have investigated lava flows representative of the whole eruptive history of the Colli Albani ultrapotassic volcanic district (Central Italy). One of the most intriguing features concerning some of these lava flows is the occurrence of primary, magmatic calcite in the groundmass. The primary, magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i) interstitially, associated with clinopyroxene, nepheline and phlogopite, ii) in spherical ocelli, associated with nepheline, fluorite and tangentially arranged clinopyroxene, and iii) in corona-like reaction zones around K-feldspar xenocrysts. These microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass, implying that the temperature of the system was above the solidus of the hosted lava flow (>850 degrees C). Geochemical features of calcite crystals (i.e., stable isotope values and trace element patterns) corroborate their primary nature and give insights into the origin of the parental carbonate melt. The trace element patterns testify to a high-temperature crystallization process (not hydrothermal) involving a carbonate melt coexisting with a silicate melt. The high delta C-18 (around 27 parts per thousand SMOW) and wide delta C-13 (-18 to + 5 parts per thousand PDB) values measured in the calcites preclude a mantle origin, but are consistent with an origin in the crust. In this framework, the crystallization of calcite can be linked to the interaction between magmas and carbonate-bearing wall rocks and, in particular, to the entrapment of solid and/or molten carbonate in the silicate magma. The stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented, high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn-eruptive time scales. (C) 2013 Elsevier B.V. All rights reserved.

Harvey J.-P. et al. Global Minimization of the Gibbs Energy of Multicomponent Systems Involving the Presence of Order/Disorder Phase Transitions // Am. J. Sci. 2013. Vol. 313, № 3. P. 199–241.

We present in this paper a robust strategy to determine the equilibrium state, in the isobaric-isothermal (NPT) ensemble, of complex multicomponent systems in which solid solutions presenting order/disorder transitions are stable. The algorithm specifically designed to construct the first estimate of the phase assemblage describing the equilibrium state of the system is presented in detail in this work and tested on different binary and ternary systems in which solid solutions are modeled using i) the cluster site approximation or the cluster variation method in the tetrahedron approximation for both the face-centered and body-centered cubic solutions. The performance of the sequential quadratic strategy using an exact Newton method and a linesearch method, implemented in this work for the specific resolution of Gibbs free energy minimization problems, is compared to the one of other large-scale optimization software packages: SNOPT, IPOPT, and KNITRO. Key subroutines implemented in the strategy to locate local minima, and specifically implemented to improve the convergence toward targeted local minima, are also presented in this work and highlight the robustness of our approach.

Honma U. Hydrous and anhydrous melting experiments of an alkali basalt and a transitional tholeiite from the Oginosen volcano, Southwest Japan: The possible influence of melt depolymerization on Ca-Na partitioning between plagioclase and the melt // J. Mineral. Petrol. Sci. 2012. Vol. 107, № 1. P. 8–32.

It has been well established that the exchange partition coefficient for the exchange of Ca and Na between plagioclase and silicate melts [Kd = (Ca/Na)(pl)/(Ca/Na)(melt)] increases with increasing water content in the melt, but its atomistic interpretation is not well developed. This work presents new experimental data on the partition coefficient in an alkali basalt and a transitional tholeiite from the Oginosen volcano, southwest Japan and discusses the possible role of melt polymerization in the variations of the partition coefficient. The experiments were conducted at 0.1 MPa, and hydrous 100 MPa and 200 MPa conditions. The partition coefficient at 0.1 MPa increases from 0.8-1.4 to 1.5-1.8 over a temperature increase from 1090 degrees C to 1190 degrees C in the transitional tholeiite, and from 1.2 to 1.7 for 1090 degrees C to 1150 degrees C in the alkali basalt. The partition coefficient increases up to 4.1-4.2 in the presence of 3.4-3.5 wt% water in the melt in both basalts. The variations of the Ca-Na partition coefficient between the plagioclase and the melt is interpreted in terms of the degree of polymerization of the melt. The degree of polymerization of the melt decreases with the increase of temperature and water content, both of which increase the Ca-Na partition coefficient. The anorthite content of the core of natural plagioclase phenocrysts in the alkali basalt is 63-66 mol%, suggesting crystallization under water-undersaturated conditions. In the transitional tholeiite, some of the cores of the plagioclase phenocrysts have An(81-85), which is formed in a water-supersaturated run at 100 MPa and 1085 degrees C; however, the significance of the presence of Ar81-85 is unknown and must be investigated further.

Jakobsson S. Oxygen fugacity control in piston-cylinder experiments // Contrib. Mineral. Petrol. 2012. Vol. 164, № 3. P. 397–406.

The main goal of this study was to develop and test a capsule assembly for use in piston-cylinder experiments where oxygen fugacity could be controlled in the vicinity of the QFM buffer without H2O loss or carbon contamination of the sample material. The assembly consists of an outer Pt-capsule containing a solid buffer (Ni-NiO or Co-CoO) plus H2O and an inner AuPd-capsule, containing the sample, H2O and a Pt-wire. No H2O loss is observed from the sample, even after 48 h, but a slight increase in H2O content is found in longer runs due to oxygen and hydrogen diffusion into the AuPd-capsule. Oxygen fugacity of runs in equilibrium with the Ni-NiO (NNO) and Co-CoO (CoCO) buffers was measured by analyzing Fe dissolved in the Pt-wire and in the AuPd-capsule. The second method gives values that are in good agreement with established buffer values, whereas results from the first method are one half to one log units higher than the established values.

Johnson E.A., Rossman G.R. The diffusion behavior of hydrogen in plagioclase feldspar at 800-1000 degrees C: Implications for re-equilibration of hydroxyl in volcanic phenocrysts // Am. Miner. 2013. Vol. 98, № 10. P. 1779–1787.

To use structural hydroxyl (OH) concentrations preserved in volcanic phenocrysts to constrain magmatic water contents prior to eruption, it is first necessary to understand the diffusive behavior of hydrogen in plagioclase. In this study, diffusion coefficients for a natural OH-bearing plagioclase feldspar (Ab(66)An(31)Or(3)) are determined from a series of integrated loss heating experiments performed at 800-1000 degrees C and 1 atm under air, nitrogen gas, and a CO2-H-2 mixture at the FMQ oxygen buffer. Hydrogen diffusion is found to be isotropic within analytical error. Using a one-dimensional diffusive loss model for an infinite slab, the diffusion behavior for hydrogen in plagioclase is described by the diffusion parameters log D-0 = -1.62 +/- 0.31 (m(2)/s) and E-a = 266 +/- 77 kJ/mol, and log D-0 = -0.97 +/- 0.35 (m2/s) and Ea = 278 90 kJ/mol for experiments only conducted under nitrogen gas. Nearly complete (83-97%) loss of OH from the andesine was achieved in 900 and 1000 degrees C heating series, except for the 900 degrees C FMQ buffer experiment in which only 64% of the total OH was lost after 21.6 days of cumulative heating. The diffusion rates of hydrogen in the plagioclase after 800-1000 C are similar to interpolated diffusion rates for sodium diffusion in An(30) feldspar, implying that Na+ and H+ both diffuse via Frenkel defects involving the large cation sites and interstitial ions. The diffusion coefficient (D) values for hydrogen in plagioclase are lower than most reported diffusion data for hydrogen in nominally anhydrous minerals, and are most similar to D reported for pure forsterite, unaffected by iron redox reactions. Based on the hydrogen diffusion parameters in this study, a 1 mm spherical plagioclase phenocryst experiencing dehydration under lowered water activity during ascent and eruption at 800 degrees C retains 50% of its initial OH concentration after 34 days. At 900 and 1000 degrees C, a 1 mm phenocryst retains 50% of its initial OH concentration after only 1.3 days and 0.25 day, respectively. OH concentrations in plagioclase are therefore most indicative of magmatic water contents during the latest stages of ascent and eruption.

Koeberl C. et al. Geochemistry of Impactites // Elements. 2012. Vol. 8, № 1. P. 37–42.

Geochemical analysis is an essential tool for the confirmation and study of impact structures and the characterization of the various rock types involved (target rocks, impact breccias, melt rocks, etc.). Concentrations and interelement ratios of the platinum-group elements, as well as the osmium and chromium isotope systems, allow quantification of extraterrestrial components and the identification of impactor types in impact deposits. In addition, chemolithostratigraphy can reveal the possible role of impacts In environmental change throughout the geologic record. This article deals predominantly with terrestrial impact structures.

Krawczynski M.J., Grove T.L., Behrens H. Amphibole stability in primitive arc magmas: effects of temperature, H2O content, and oxygen fugacity // Contrib. Mineral. Petrol. 2012. Vol. 164, № 2. P. 317–339.

The water-saturated phase relations have been determined for a primitive magnesian andesite (57 wt% SiO2, 9 wt% MgO) from the Mt. Shasta, CA region over the pressure range 200-800 MPa, temperature range of 915-1,070 A degrees C, and oxygen fugacities varying from the nickel-nickel oxide (NNO) buffer to three log units above NNO (NNO+3). The phase diagram of a primitive basaltic andesite (52 wt% SiO2, 10.5 wt% MgO) also from the Mt. Shasta region (Grove et al. in Contrib Miner Petrol 145:515-533; 2003) has been supplemented with additional experimental data at 500 MPa. Hydrous phase relations for these compositions allow a comparison of the dramatic effects of dissolved H2O on the crystallization sequence. Liquidus mineral phase stability and appearance temperatures vary sensitively in response to variation in pressure and H2O content, and this information is used to calibrate magmatic barometers-hygrometers for primitive arc magmas. H2O-saturated experiments on both compositions reveal the strong dependence of amphibole stability on the partial pressure of H2O. A narrow stability field is identified where olivine and amphibole are coexisting phases in the primitive andesite composition above 500 MPa and at least until 800 MPa, between 975-1,025 A degrees C. With increasing H2O pressure (), the temperature difference between the liquidus and amphibole appearance decreases, causing a change in chemical composition of the first amphibole to crystallize. An empirical calibration is proposed for an amphibole first appearance barometer-hygrometer that uses Mg# of the amphibole and This barometer gives a minimum recorded by the first appearance of amphibole in primitive arc basaltic andesite and andesite. We apply this barometer to amphibole antecrysts erupted in mixed andesite and dacite lavas from the Mt. Shasta, CA stratocone. Both high H2O pressures (500-900 MPa) and high pre-eruptive magmatic H2O contents (10-14 wt% H2O) are indicated for the primitive end members of magma mixing that are preserved in the Shasta lavas. We also use these new experimental data to explore and evaluate the empirical hornblende barometer of Larocque and Canil (2010).

Krenn E. et al. LREE-redistribution among fluorapatite, monazite, and allanite at high pressures and temperatures // Am. Miner. 2012. Vol. 97, № 11-12. P. 1881–1890.

The REE enrichment process in fluorapatite and the REE redistribution among fluorapatite, monazite, and allanite were studied in a series of three sets of experimental runs at P-T conditions of 0.5 to 4 GPa and 650 to 900 degrees C. The first two sets of experimental runs utilized fluorapatite as a P-source, synthetic monazite or allanite as the REE sources, albite, quartz, and NaF-H2O or NaCl-H2O. The third set of runs was carried out with powdered Ca-3(PO4)(2), allanite, quartz, (+/- Al2O3), and a NaF-H2O solution. In all runs REE-bearing fluorapatite with up to 28 wt% Sigma REE2O3 formed at the expense of monazite or allanite; either as narrow zones at the margin of synthetic fluorapatite in runs 1 and 2 or as discrete grains in run 3. The REE-enrichment of fluorapatite in melt-bearing runs is explained in terms of the high solubility of monazite in the presence of alkali-rich melts together with the high partitioning values for REEs among fluorapatite and alkali-rich melts. The formation of REE-enriched fluorapatite in melt-absent runs implies that the solubility of monazite and the REE-uptake of fluorapatite are similarly high in both alkali-rich melts and fluids and depends foremost on the activity of alkalis in fluids or melts. The results from this study show the importance of fluorapatite as a REE-carrier in rocks whose petrogenesis involved alkali-bearing fluids/melts. In metamorphic rocks, alkali-enriched fluids or melts will likely form under higher-grade conditions, explaining the preferential occurrence of REE-enriched fluorapatite in granulite and eclogite-facies rocks.

Lambart S., Laporte D., Schiano P. Markers of the pyroxenite contribution in the major-element compositions of oceanic basalts: Review of the experimental constraints // Lithos. 2013. Vol. 160. P. 14–36.

Based on previous and new results on partial melting experiments of pyroxenites at high pressure, we attempt to identify the major element signature of pyroxenite partial melts and to evaluate to what extent this signature can be transmitted to the basalts erupted at oceanic islands and mid-ocean ridges. Although peridotite is the dominant source lithology in the Earth's upper mantle, the ubiquity of pyroxenites in mantle xenoliths and in ultramafic massifs, and the isotopic and trace elements variability of oceanic basalts suggest that these lithologies could significantly contribute to the generation of basaltic magmas. The question is how and to what degree the melting of pyroxenites can impact the major-element composition of oceanic basalts. The review of experimental phase equilibria of pyroxenites shows that the thermal divide, defined by the aluminous pyroxene plane, separates silica-excess pyroxenites (SE pyroxenites) on the right side and silica-deficient pyroxenites (SD pyroxenites) on the left side. It therefore controls the melting phase relations of pyroxenites at high pressure but, the pressure at which the thermal divide becomes effective, depends on the bulk composition; partial melt compositions of pyroxenites are strongly influenced by non-CMAS elements (especially FeO, TiO2, Na2O and K2O) and show a progressive transition from the liquids derived from the most silica-deficient compositions to those derived from the most silica-excess compositions. Another important aspect for the identification of source lithology is that, at identical pressure and temperature conditions, many pyroxenites produce melts that are quite similar to peridotite-derived melts, making the determination of the presence of pyroxenite in the source regions of oceanic basalts difficult; only pyroxenites able to produce melts with low SiO2 and high FeO contents can be identified on the basis of the major-element compositions of basalts. In the case of oceanic island basalts, high CaO/Al2O3 ratios can also reveal the presence of pyroxenite in the source-regions. Experimental and thermodynamical observations also suggest that the interactions between pyroxenite-derived melts and host peridotites play a crucial role in the genesis of oceanic basalts by generating a wide range of pyroxenites in the upper mantle: partial melting of such secondary pyroxenites is able to reproduce the features of primitive basalts, especially their high MgO contents, and to impart, at least in some cases, the major-element signature of the original pyroxenite melt to the oceanic basalts. Finally, we highlight that the fact the very silica depleted compositions (SiO2<42 wt.) and high TiO2 contents of some ocean island basalts seem to require the contribution of fluids (CO2 or H2O) through melting of either carbonated lithologies (peridotite or pyroxenite) or amphibole-rich veins. (C) 2012 Elsevier B.V. All rights reserved.

23. U01624
Liebscher A. et al. Ca-Sr fractionation between zoisite, lawsonite, and aqueous fluids: An experimental study at 2.0 and 4.0 GPa/400 to 800 degrees C // Am. Miner. 2013. Vol. 98, № 5-6. P. 955–965.

The Ca-Sr fractionation between zoisite and, respectively, lawsonite and an aqueous fluid has been determined by synthesis experiments in the presence of a 1 M (Ca,Sr)Cl-2 aqueous fluid at 2.0 GPa/550, 600, and 700 degrees C and 4.0 GPa/800 degrees C for zoisite and 2.0 GPa/400 degrees C and 4.0 GPa/600 degrees C for lawsonite. Solid run products were characterized by EMP, SEM, and XRD with Rietveld refinement and fluids were analyzed by ICP-OES. Zoisite exhibits notable intracrystalline Ca-Sr fractionation between the A1 and A2 sites and calculated intracrystalline exchange coefficients K-D(Sr-Ca)(A1-A2) = 1.5 to 26 show strong preference of Sr over Ca for the slightly larger A2 site. Calculated individual site-dependent zoisite/aqueous fluid (af, in superscripts)-exchange coefficients for the studied 1 M (Ca,Sr)Cl-2 aqueous fluids are K-(Sr-Ca)(zo al-af)(Oat = 3.38 to 41.08 for the A1 site and K-(Sr-Ca)(zoA2-af) = 0.45 to 6.51 for the A2 site. Assuming gamma(af)(Ca)= ye and a symmetric mixing model, the thermodynamic evaluation of the site-dependent exchange reactions Ca2+(af) Sr-Al(M2+)(A2) Al-3[Si3O11(O/OH) and Ca2+(af)+ (M2+)Sr-A1(A2)[Si3O11(O/OH)] = Sr2+(af)+(M2+)Al3Ca(A2)Al(3)[Si3O11(O/OH)] yields mu(0) = 29 kJ/mol and W-Sr-Ca(ZO Al) = 5.5 kJ/mol for the Al site and AA = 1.1 kJ/mol and W-Sr-Ca(ZO A2) = 0 kJ/mol for the A2 site at P and T of the experiments. The data indicates ideal Ca-Sr substitution on the A2 site. Lawsonite formed in both the orthorhombic Cmcm and the monoclinic P2(1)/m form. Calculated lawsonite-aqueous fluid-exchange coefficients indicate overall preference of Ca over Sr in the solid and are K (law Cmcm-af)(D(Sr-Ca)) to 11.32 for orthorhombic and K-D(Sr-Ca)(law P21m-af) = 1.67 to 4.34 for monoclinic lawsonite. Thermodynamic evaluation of the exchange reaction Ca2+af + SrAl2Si2O7(OH)(2).H2O = Sr2+af + CaAl2Si2O7(OH)(2).H2O assuming gamma(af)(Ca) = gamma(af)(Sr) and a symmetric mixing model yields similar values of Delta mu(0) = 9 kJ/mol and In% (cmcm) = 10 kJ/mol for orthorhombic and 49 = 10 kJ/mol and WSr-Ca (lawP21/m)= 11 kJ/mol for monoclinic lawsonite. Calculated Nernst distribution coefficients for the studied 1 M (Ca,Sr)Cl2 aqueous fluids are D-Sr(Zo-af):= 2.8 0.7 for zoisite at 2 GPa/600 C and Dr C-Sr(law-af) = 0.6 +/- 0.2 for orthorhombic lawsonite at 4 GPa/600 C and show Sr to be compatible in zoisite but incompatible in lawsonite. This opposite mineral-aqueous fluid-fractionation behavior of Sr with respect to zoisite and lawsonite on the one hand and the ideal Ca-Sr substitution on the zoisite A2 site in combination with the strong intracrystalline Ca-Sr fractionation in zoisite on the other hand, make Sr a potential tracer for fluid-rock interactions in zoisite- and lawsonite-bearing rocks. For low Sr-concentrations, x(Sr)(Zo), directly reflects xi (af)(Sr) and allows us to calculate Sr-concentrations in a metamorphic aqueous fluid. During high-pressure aqueous fluid-rock interactions in subduction zone settings the opposite mineral-aqueous fluid-fractionation behavior of Sr results in different aqueous fluid characteristics for lawsonite- vs. zoisite-bearing rocks. Ultimately, subduction zone magmas may trace these different aqueous fluid characteristics and allow distinguishing between cold, lawsonite-bearing vs. warm, zoisite-bearing thermal regimes of the underlying subduction zone.

Lofgren G. New data on lunar magmatic processes // Am. Miner. 2014. Vol. 99, № 4. P. 561–561.

New data based on a detailed analysis of pyroxene zoning strongly suggests that convection is an important process in lunar magmas. Elardo and Shearer (2014) carefully document irregular oscillatory zoning that is best explained by movement of pyroxene crystals in a convecting magma. Lunar samples that contain such data are rare, but this study should inspire more extensive efforts to further document magmatic processes.

Louvel M. et al. Constraints on the mobilization of Zr in magmatic-hydrothermal processes in subduction zones from in situ fluid-melt partitioning experiments // Am. Miner. 2014. Vol. 99, № 8-9. P. 1616–1625.

The partitioning of Zr between high P-T aqueous fluids and melts has been investigated in situ in the haplogranite-H2O and haplogranite-(F)-H2O systems to assess the mobilization of high field strength elements (HFSE) in magmatic-hydrothermal processes in subduction zones. The partition coefficients D-Zr(f/m) were determined from Zr concentrations measured in situ by synchrotron X-ray fluorescence (SXRF) in both aqueous fluids and F-free or F-bearing hydrous haplogranite melts equilibrated in diamond-anvil cells at 575 to 800 degrees C and 0.3 to 2.4 GPa. This experimental approach eliminates the need for internal or external calibrations of the SXRF signal and/or post-mortem analysis of the melt phase, hence decreasing the total uncertainties on D-Zr(f/m) below 16%. Above 0.6 GPa, Zr partitions favorably into the hydrous silicate melt in both F-free and F-bearing systems, with D-Zr(f/m) that range between 0.19 +/- 0.02 and 0.38 +/- 0.03. However, the relatively high D-Zr(f/m) values indicate that alkali-silica rich aqueous fluids generated by metamorphic devolatilization may contribute significantly to the recycling of HFSE in subduction zones. The efficient uptake of Zr (and likely other HFSE) by subduction zone fluids, regardless of their nature (aqueous fluid, hydrous melt, or supercritical fluid), supports the idea that the typical HFSE depletion recorded in arc magmas does not result from their incompatibility in water-rich slab-derived fluids but most probably originates from complex fluid-melt-rock interactions occurring at the slab interface and within the mantle wedge. At shallow crustal pressure conditions (800 degrees C and 0.3 GPa), Zr partitions reversely into the aqueous fluid in the presence of fluorine (D-Zr(f/m) = 1.40 +/- 0.10) as observed for Nb at similar conditions by Webster et al. (1989). The enrichment of the aqueous phase in HFSE (Zr, Nb) at shallow crustal conditions is likely related to the enhanced peralkalinity of low pressure, F-bearing aqueous fluid with temperature, that provides the favorable conditions for their mobilization via the formation of HFSE-O-Si/Na clusters. This mechanism may control the enrichment in HFSE (and plausibly other rare metals such as REE) in early magmatic fluids exsolved from granitic melts, leading to the formation of HFSE-enriched aggregates in shallow magmatic-hydrothermal environments (e.g., Strange Lake and Thor Lake Nechalacho deposit, Canada; Galineiro complex, Spain).

Lukanin O.A., Tsekhonya T.I. Annual seminar on experimental mineralogy, petrology, and geochemistry of 2011 // Geochem. Int. 2012. Vol. 50, № 2. P. 193–204.

Marks M.A.W. et al. The volatile inventory (F, Cl, Br, S, C) of magmatic apatite: An integrated analytical approach // Chem. Geol. 2012. Vol. 291. P. 241–255.

Apatite is ubiquitous in a wide range of magmatic rocks and its F-Cl-Br-S systematics can be used to decipher e.g., mixing processes within a magmatic complex and may give insights into fluid un-mixing and degassing processes during the emplacement and cooling of plutonic rocks. In this study, we analyzed a F-apatite (Durango, Mexico), a Cl-apatite (Odegarden, Norway) and apatites from five plutonic samples from the alkaline Mt. Saint Hilaire Complex (Canada) by means of Electron Microprobe Analysis (EPMA), Laser Ablation ICP-MS (LA-ICP-MS), Secondary Ion Mass Spectrometry (SIMS), pyrohydrolysis combined with ion chromatography, Fourier Transformed Infrared Spectroscopy (FTIR), Instrumental Neutron Activation Analysis (INAA) and Total Reflection X-ray Fluorescence Analysis (TXRF). The special focus of our study is Br, since the analytical possibilities for this element are especially in the low-to sub-mu g/g range restricted and thus, reliable concentration data for Br in rock-forming minerals are scarce. We demonstrate here that TXRF, which is barely used in geosciences so far, is suitable for analyzing the bulk content of Br and Cl as well as of a range of important trace metals (e.g., Sr, Ce, Fe, Mn, As) in apatite simultaneously. The TXRF method combines the advantages of low to very low detection limits (mu g/g- to sub-mu g/g range), small sample amounts needed (mg range) and a relatively fast and inexpensive analytical procedure. Depending on the As content of apatite, reliable concentration data for Br can be produced with detection limits as low as 0.2 mu g/g. Using the Durango apatite as an internal reference material, SIMS analyses give consistent results with EPMA, INAA and TXRF and allow for detailed insights into the F-Cl-Br-S systematics of apatites. The presented data set reveals significant heterogeneities within and between different apatite grains from a single sample.

Martin A.M., Righter K., Treiman A.H. Experimental constraints on the destabilization of basalt plus calcite plus anhydrite at high pressure-high temperature and implications for meteoroid impact modeling // Earth Planet. Sci. Lett. 2012. Vol. 331. P. 291–304.

Calcite CaCO3 and anhydrite CaSO4 are two sedimentary components or alteration products of basalts on the Earth, Venus, and Mars. The fate of anhydrite-, calcite-bearing crust during a meteoroid impact must be addressed in order to evaluate: (1) the potential S- and C-gas release to the atmosphere, (2) the formation of S- and C-rich melts, and (3) the crystallization of S- and C-rich minerals which may be recognized by spectral analyses of planetary surfaces. We performed piston-cylinder experiments at 1 GPa, between 1200 and 1750 degrees C, on a mixture of 70 wt.% tholeiitic basalt + 15 wt.% anhydrite + 15 wt.% calcite. Up to similar to 1440 degrees C, an ultracalcic (CaO > 19.8 wt.%; CaO/Al2O3 > 1 wt.%) picrobasaltic (SiO2 similar to 39-43 wt.%; Na2O + K2O < 2 wt.%) melt containing up to 5.7 wt.% SO3 and up to 5.1 wt.% CO2 + H2O (calculated by difference) is present in equilibrium with fassaitic clinopyroxene, anhydrite, scapolite, chromian spinel and a gas composed mainly of CO and, occasionally, aliphatic thiols like CH3(CH2)(3)SH. Hydrogen was incorporated either by contact between the starting material and air or by diffusion through the capsule during the experiments. Above similar to 1440 degrees C, a CaO-rich (similar to 35 wt.%) sulfate-carbonate (SC) melt which contains 41-47 wt.% SO3, 7-12 wt.% CO2 + H2O and a few percent of Na2O, forms in equilibrium with the picrobasaltic melt. This study shows that a meteoroid impact onto an anhydrite- and calcite-bearing basaltic crust is likely to release CO gas to the atmosphere, while S is trapped in solid or liquid phases. Under hydrous conditions, however, the S/C in the gas may increase. The importance of the temperature parameter on the impact phase relations is also demonstrated. In particular, SC melt may form by meteoroid impact, and flow rapidly on a planetary surface. Physical modeling must therefore be combined with high P-high T phase diagrams of complex assemblages similar to planetary lithologies in order to evaluate the effects of a meteoroid impact. Published by Elsevier B.V.

Mollo S. et al. The control of cooling rate on titanomagnetite composition: implications for a geospeedometry model applicable to alkaline rocks from Mt. Etna volcano // Contrib. Mineral. Petrol. 2013. Vol. 165, № 3. P. 457–475.

In this study, we have investigated the control of cooling rate on the composition of titanomagnetite formed from a trachybasaltic melt. Results show that disequilibrium growth conditions exert a primary control on the abundance, texture, and composition of the crystals. As the degree of cooling is increased, titanomagnetites show immature textures and are progressively enriched in Al + Mg and depleted in Ti. Thus, early-formed titanomagnetite nuclei do not re-equilibrate with the melt over faster cooling rates; instead, their compositions are far from equilibrium. On the basis of the different intra-crystal redistribution rates for Ti, Al, and Mg, we have calibrated a geospeedometer that represents the first quantitative description of the effect of cooling rate on titanomagnetite composition. This model was tested using the compositions of titanomagnetites in lava and dike samples from Mt. Etna volcano whose crystallization conditions resemble those of our experiments. Cooling rates calculated for lava samples are comparable with those measured in several volcanic complexes. At Mt. Etna, compositional variations of titanomagnetite grains from the innermost to the outermost part of a dike testify to progressively higher degrees of cooling, in agreement with numerical simulations of thermal gradients in and around magmatic intrusions.

Mollo S. et al. The role of cooling rate in the origin of high temperature phases at the chilled margin of magmatic intrusions // Chem. Geol. 2012. Vol. 322. P. 28–46.

Both large (i.e. from hundreds to thousands of metres thick) and small (i.e. from centimetres to a few metres thick) magmatic intrusions are characterized by mineral compositional variations proceeding from the outermost to the innermost part of the intrusive body. However, in the case of large intrusions, mineral compositions become progressively more primitive (e.g. An-rich plagioclases and En-rich pyroxenes) from the chilled margin towards the interior; whereas, the opposite occurs for small intrusive bodies. Since it is unclear to what extent variable cooling rate conditions may alter the phase compositions, we have performed isothermal and dynamic experiments within a temperature interval of 1250-1100 degrees C using four different cooling rates of 150, 50, 10 and 2.5 degrees C/h. Numerical simulations of thermal regimes in and around small and large magmatic intrusions have also been performed and compared with phase compositional variations observed in our laboratory experiments. Results indicate that, over rapid cooling rate conditions, the crystal compositions faithfully reproduce those of high-temperature formations, i.e. An-rich plagioclases, En-rich pyroxenes and Usp-poor spinels. However, such a process is limited to a maximum distance of 2-3 m from the margin of the intrusion. Moreover, in active volcanic systems, heat fluxes are released from the main regions of magma storage into host rocks; therefore, only magmas solidifying at the contact of cold wall rocks may develop chilled margins with features related to rapid cooling rate conditions. In the presence of hot host rocks, thermal gradients are significantly reduced and the role played by cooling dynamics on textural and compositional variations of minerals is practically negligible. (C) 2012 Elsevier B.V. All rights reserved.

Mysen B. Hydrogen isotope fractionation between coexisting hydrous melt and silicate-saturated aqueous fluid: An experimental study in situ at high pressure and temperature // Am. Miner. 2013. Vol. 98, № 2-3. P. 376–386.

Hydrogen isotope fractionation between water-saturated silicate melt and silicate-saturated aqueous fluid has been determined experimentally by using vibrational spectroscopy as the analytical tool. The measurements were conducted in situ with samples at the high temperature and pressure of interest in an externally heated diamond cell in the 450-800 degrees C and 101-1567 MPa temperature and pressure range, respectively. The starting materials were glass of Na-silicate with Na/Si = 0.5 (NS4), an aluminosilicate composition with 10 mol% Al2O3 and Na/(Al+Si) = 0.5 (NA10), and a 50:50 (by volume) H2O:D2O fluid mixture. Platinum metal was used to enhance equilibration rate. Isotopic equilibrium was ascertained by using variable experimental duration at given temperature and pressure. In the Al-free NS4 system, the enthalpy of the D/H equilibrium of fluid is 3.1 +/- 0.7 kJ/mol, whereas that of coexisting melt equals 0 within error. For NA10 fluids the Delta H = 5.2 +/- 0.9 kJ/mol, whereas for coexisting NA10 melt, Delta H is near 0 within error. For the exchange equilibrium between melt and coexisting fluid, H2O(melt)+D2O(fluid) = H2O(fluid)+D2O(melt) the Delta H = 4.6 +/- 0.7 and 6.5 +/- 0.7 kJ/mol for NS4 and NA10 compositions, respectively. The D/H fractionation between melt and fluid is affected significantly by the positive temperature- and pressure-dependence of silicate solubility and silicate structure in silicate-saturated aqueous fluids. Water in melts is much less important than silicate in aqueous fluid because even at the lowest temperature and pressure conditions studied (450 degrees C/101 MPa), the water content in the melt is so high (>4 wt%) that further increase in total water by increasing temperature and pressure does not affect the silicate melt structure significantly. This is because most of the water in this concentration range is dissolved in molecular form.

Nishimura K. A mathematical model of trace element and isotopic behavior during simultaneous assimilation and imperfect fractional crystallization // Contrib. Mineral. Petrol. 2012. Vol. 164, № 3. P. 427–440.

The process of coupled assimilation and fractional crystallization (AFC) is one of the most popular petrogenetic concepts that explains magmatic differentiation. Conventional geochemical models for this process assume that crystals are removed instantaneously from the magma body as they are produced; however, recent advances in isotopic microanalysis have clarified that the crystals are suspended within the magma body for a certain period, affecting the whole-rock composition in response to the intra-grain isotopic zoning. This study develops a mass balance model for simultaneous assimilation and imperfect fractional crystallization (AIFC) to describe the effects of suspended crystals on the path of magma evolution. The mass balance differential equations for the liquid and suspended crystals are solved simultaneously. The analytical solution of the AIFC equations gives a quantitative account of the evolution paths of trace elements and isotopes within bulk crystals, liquid, and magma (crystals plus liquid). The chemical path of the magma differs markedly from that predicted by the conventional AFC model.

Palinkas S.S. et al. The role of magmatic and hydrothermal processes in the evolution of Be-bearing pegmatites: Evidence from beryl and its breakdown products // Am. Miner. 2014. Vol. 99, № 2-3. P. 424–432.

Beryl and euclase crystals from the Mina do Santino and the Jacu pegmatites in the Borborema Pegmatite Province in northeastern Brazil contain several generations of melt and fluid inclusions, which allow interpretation of P-T-X conditions responsible for beryl crystallization and for alteration of a primary pegmatitic mineral assemblage to a mixture of hydrothermal minerals (euclase, bertrandite, kaolinite, and quartz). Primary melt and fluid inclusions hosted by beryl were trapped simultaneously. However, their homogenization temperatures are significantly higher (870-900 degrees C) than the values previously reported for pegmatitic systems (<712 degrees C) and should be treated with caution. An isobaric drop of temperature resulted in the exsolution of a fluid. A low-salinity CO2-enriched phase and a saline water-rich phase were trapped in pseudosecondary inclusions in beryl at a pressure of 2.1-2.7 kbar and temperature of 390-480 degrees C. Cooling of the country rocks below 400 degrees C caused a ductile-to-brittle transition and allowed infiltration of cold groundwater, which further decreased the temperature in the system to 190-240 degrees C. At the same time, the pressure dropped from a lithostatic (2.1-2.7 kbar) to a hydrostatic value (0.57-0.73 kbar). Consequently, minerals deposited under magmatic conditions (feldspars and beryl) became unstable and a newly formed hydrothermal mineral paragenesis (euclase, bertrandite, kaolinite, and quartz) overprinted the earlier one. The hydrothermal fluids responsible for the alteration differ from the earlier-exsolved fluids in having a lower salinity, lower homogenization temperature, the absence of CO2, and the presence of CH4.

Pritchard C.J., Larson P.B. Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling // Contrib. Mineral. Petrol. 2012. Vol. 164, № 2. P. 205–228.

An array of samples from the eastern Upper Basin Member of the Plateau Rhyolite (EUBM) in the Yellowstone Plateau, Wyoming, were collected and analyzed to evaluate styles of deposition, geochemical variation, and plausible sources for low delta O-18 rhyolites. Similar depositional styles and geochemistry suggest that the Tuff of Sulphur Creek and Tuff of Uncle Tom's Trail were both deposited from pyroclastic density currents and are most likely part of the same unit. The middle unit of the EUBM, the Canyon flow, may be composed of multiple flows based on a wide range of Pb isotopic ratios (e.g., Pb-206/Pb-204 ranges from 17.54 to 17.86). The youngest EUBM, the Dunraven Road flow, appears to be a ring fracture dome and contains isotopic ratios and sparse phenocrysts that are similar to extra-caldera rhyolites of the younger Roaring Mountain Member. Petrologic textures, more radiogenic Sr-87/Sr-86 in plagioclase phenocrysts (0.7134-0.7185) than groundmass and whole-rock ratios (0.7099-0.7161), and delta O-18 depletions on the order of 5aEuro degrees found in the Tuff of Sulphur Creek and Canyon flow indicate at least a two-stage petrogenesis involving an initial source rock formed by assimilation and fractional crystallization processes, which cooled and was hydrothermally altered. The source rock was then lowered to melting depth by caldera collapse and remelted and erupted. The presence of a low delta O-18 extra-caldera rhyolite indicates that country rock may have been hydrothermally altered at depth and then assimilated to form the Dunraven Road flow.

Qiang L., Yao W. Dehydration melting of UHP eclogite and paragneiss in the Dabie orogen: Evidence from laboratory experiment to natural observation // Chin. Sci. Bull. 2013. Vol. 58, № 35. P. 4390–4396.

Dehydration melting of subducted continental crust is significant during exhumation, and its study from both experimental and petrological observations is of great importance to our understanding of continental geodynamics. Dehydration melting experiments were carried out on ultrahigh-pressure (UHP) eclogite from Bixiling in the Dabie orogen using a piston cylinder at 1.5-3.0 GPa and 800-950A degrees C to investigate partial melting of eclogite induced by phengite breakdown. The phengite-bearing eclogite started to melt at Ta (c) 1/2800-850A degrees C and P=1.5-2.0 GPa and produced about 3% granitic melt. The products of dehydration melting vary with temperature and pressure. Such results provide valuable constraints on the micro-texture related to partial melting of UHP rocks in the Dabie-Sulu orogenic belt. Three types of polyphase inclusions were identified in garnet from the Shuanghe UHP eclogite. K-feldspar and quartz inclusions are interpreted to represent the products of segregation and crystallization of minor amounts of melt that formed during dehydration melting of phengite by the inferred reaction Phengite+Omphacite +/- Quartz -> Amphibole +/- Garnet+Melt (K-feldspar+Quartz +/- Plagioclase). Polyphase inclusions of phengite and K-feldspar+Quartz inclusions were also found in zoisite/clinozoisite and garnet from the Shuanghe garnet-bearing paragneiss. These polyphase inclusions provide evidence for a continuous process from sub-solidus dehydration to partial melting within the UHP gneissic rocks. The compositional variation of garnets demonstrates that breakdown of epidote-group minerals may have played a crucial role during dehydration melting reaction of phengite. The Ti-in-zircon thermometry and Si content of phengite in zircon suggest that partial melting would occur at 783-839A degrees C and 2.0-2.5 GPa. Therefore, both experimental results and petrological observations indicate that dehydration melting and fluid activity within the Dabie UHP rocks at micro-scale are controlled by the breakdown of phengite.

Roulleau E. et al. N, Ar and Pb isotopic co-variations in magmatic minerals: Discriminating fractionation processes from magmatic sources in Monteregian Hills, Quebec, Canada // Chem. Geol. 2012. Vol. 326. P. 123–131.

Nitrogen, argon and helium isotopic compositions were measured by vacuum crushing in pyroxenes and amphiboles from mafic rocks belonging to the Monteregian Hills (Quebec, Canada). For comparison, lead isotopic compositions were measured in plagioclase in the same samples. The goal of this study was to constrain the mantle sources of this igneous province, resolving a controversial issue that has persisted for more than 30 years. The measured He and Ar show solubility-controlled elemental fractionation while N is affected by kinetic isotopic fractionation during melt degassing. In contrast, the Ar-40/Ar-36 ratio seems not to be affected by kinetic fractionation, but likely reflects mantle sources. The Ar-40/Ar-36 and Pb-208/Pb-206 ratios are meaningfully correlated, suggesting the mixing between a plume source showing high (208)pb/Pb-206 (<= 2.06) and low Ar-40/Ar-36 ratios (similar to 1200) and a recycled source such as HIMU showing low Pb-208/Pb-206 (<= 1.95) and near-atmospheric Ar-40/Ar-36 ratios (similar to 300). The N-2/Ar-36 and Pb-206/Pb-204 ratios are inversely correlated. Although the N-2/Ar-36 ratios are diluted by an atmospheric-like component, this relationship can be interpreted as the mixing between a recycled component (HIMU) and a mantle source that ambiguously could be either a plume source or the depleted mantle. The samples showing less radiogenic Pb-206/Pb-204 ratios show delta N-15 values of -7.6 to -7.4 parts per thousand, which points to a MORB-type mantle source (delta N-15=-5 +/- 2 parts per thousand) rather than a plume source (delta N-15=+3 parts per thousand). Thus, there is contrasting evidence arguing for either a plume or a depleted mantle component. This ambiguity could be resolved by assuming that the plume source provided heat to melt a sub-continental mantle source. Thus, part of the volatile budget might be issued from this distinct mantle source. This study demonstrates the great potential of coupling radiogenic isotopes together with Ar and N isotopes. Nitrogen and argon are efficiently recycled in the mantle and thus can be helpful in tracing the crustal sources that affect the Sr-Nd-Pb isotopic systems in oceanic and continental volcanism.

Saunders K. et al. TOF-SIMS and electron microprobe investigations of zoned magmatic orthopyroxenes: First results of trace and minor element analysis with implications for diffusion modeling // Am. Miner. 2012. Vol. 97, № 4. P. 532–542.

Zoned phenocrysts in volcanic rocks potentially provide an archive of magmatic processes. As a crystal grows and comes into contact with different melt batches, the chemical and textural signature of this journey is recorded within its crystal lattice. The timescale of some magmatic processes can be investigated through the relaxation of chemical gradients across crystal growth zones through the application of diffusion modeling techniques. One of the current limitations to diffusion modeling is the spatial and analytical resolution of the chemical profile that conventional techniques such as electron probe microanalyzer (EPMA), dynamic secondary ion mass spectrometry (SIMS), and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) can achieve. Here, for the first time, we present time-of-flight (TOF) SIMS (TOF-SIMS) data for zoning of orthopyroxene crystals from the May 1982 eruption of Mount St. Helens volcano, U.S.A., and cross-calibrate these data between backscattered electron images and EPMA. TOF-SLMS has the advantage of being able to achieve micrometer to nanoscale spatial resolution of major elements as well as analyses of light elements, such as Li, and trace and minor elements (Na, K, and Ni) at concentrations that cannot be achieved by EPMA, provided that convolution (overlap) effects and polyatomic mass inferences are carefully considered. With TOF-SIMS analyses we identified zoning of Li on a spatial scale (ca. 5-10 mu m) that would be inaccessible to most other conventional analytical techniques. Preliminary results indicate that Li, a fast-diffusing element, may be introduced to the crystals in the minutes, hours, or days prior to eruption and may provide insights into pre-eruptive magmatic processes. Thus, TOF-SIMS has the potential to be a powerful tool for obtaining minor and trace element profiles across compositional interfaces within crystals at high-spatial resolution.

Scordari F. et al. Fluorophlogopite from Piano delle Concazze (Mt. Etna, Italy): Crystal chemistry and implications for the crystallization conditions // Am. Miner. 2013. Vol. 98, № 5-6. P. 1017–1025.

Fluorine is an important proxy for magmatic differentiation processes in the shallow parts of volcanic plumbing systems. Fluorphlogopite is one of the more important fluorine carriers in magmatic rocks. In the present study, a full crystal chemical investigation of fluorophlogopite 1M from Piano delle Concazze, Mt. Etna volcano, Italy, is carried out. The fluorophlogopite occurs in a benmoreitic lava from prehistoric volcanic activity at Mt. Etna (post-caldera forming phase of the "Ellittico" eruptive center; similar to 15 ka BP). It is primarily associated with fluorapatite covered with amorphous SiO2 and crystallized during syn/post-eruption pneumatolytic stages. The mica sample studied here is among the most Fe- and Ti-rich fluorophlogopite found in nature. EPMA data yielded the following mean chemical formula for this mineral (K0.83Na0.13)(Fe0.442+Fe0.093+Mg2.18Al0.05Ti0.23Mn0.01)(Al0.92Si3.08)O-10.64(Cl-0.01 F-1.35). Structure refinements on four fluorophlogopite crystals, performed in space group C2/m, converged at R = 0.03-0.04, with cell parameters in the ranges a = 5.323-5.324, b = 9.219-9.222, c = 10.116- 10.119 angstrom, beta = 100.1-100.3 degrees. Major substitutions are OH- double left right arrow F-,M3+-oxy (v1M(2+)+OH-double left right arrow VIm(3+)+O2-) and Ti-oxy substitution: v1M2++2(OH)- Ti-vI(4+)+2O(2-). The fluorophlogopite from Piano delle Concazze exhibits the shortest c-parameter with respect to other fluorophlogopites found in nature. The short c parameter is essentially due to the absence of the hydroxyl group in favor of F- and especially of O2- and to the thus increased attractive interaction between the interlayer cation and the anion content (F-, 021 located at the 04 site. A comparison with other natural fluorophlogopites (namely from Biancavilla, Etna and Presidente Olegario, Brazil) show intermediate crystal-chemical features for the Piano delle Concazze fluorophlogopite. Particularly at Etna, differences in the chemical composition of the crystallized fluorophlogopites could be related to the various extent of enrichments by transfer of a gas phase achieved in specific parts of the volcanic plumbing system.

Stanley B.D., Schaub D.R., Hirschmann M.M. CO2 solubility in primitive martian basalts similar to Yamato 980459, the effect of composition on CO2 solubility of basalts, and the evolution of the martian atmosphere // Am. Miner. 2012. Vol. 97, № 11-12. P. 1841–1848.

To determine the influence of basalt composition on the CO2 solubility in martian lavas, we investigated experimentally a synthetic melt based on the martian meteorite Yamato 980459 (Y 980459), an olivine-phyric shergottite and a picritic rock (19 wt% MgO) thought to be a near-primary liquid derived from high-temperature (>1540 degrees C) partial melting of the martian mantle. Experiments were performed in a piston-cylinder apparatus at 1-2 GPa and 1600-1650 degrees C. CO2 contents in quenched glasses were determined using Fourier transform infrared spectroscopy (FTIR) and range from 0.45-1.26 wt%. Despite large differences in FeO* and MgO contents, the CO2 solubilities in Y 980459 are similar to that in a less primitive synthetic martian basalt based on the Humphrey rock and to a Hawaiian tholeiite. the lack of enhanced solubility in Fe2+- and Mg2+-rich melts is likely owing to the complex structural role of these cations in silicate melts, acting partly as network formers, rather than network modifiers. The small sensitivity of CO2 solubility to compositional variations among martian and tholeiitic basalts means that the experimentally determined solubilities may be applicable to a wide spectrum of martian magmatic products. Using experimentally determined CO2 solubilities of Y 980459 and Humphrey allows the calibration of the thermodynamic parameters governing dissolution of CO2 vapor as carbonate in martian basalts. This relation facilitates calculation of the CO2 dissolved in magmas derived from graphite-saturated martian basalt source regions as a function of P, T, and f(o2) The hot conditions in the source of Y 980459, 1540 +/- 10 degrees C, and 1.2 +/- 0.5 GPa, are plausible for plume-related magmas forming the giant Tharsis volcanic complex, which accounts for 50% of martian igneous activity since stabilization of the primordial crust. If oxygen fugacity in the sources of hot Tharsis magmatism were equivalent to that at the iron-wustite buffer (IW) or 1 log unit above (IW+1), respectively, then the entire Tharsis event would outgas 30-300 mbars of CO2 to the martian atmosphere, which is far from the 2 bars required to stabilize an equable climate in the late Noachian and early Hesperian epochs. This mismatch could be reconciled if significant martian igneous activity derived from comparatively oxidized mantle sources (i.e., IW+2) similar to those responsible for the nokhlite meteorites.

Vogt K., Gerya T.V., Castro A. Crustal growth at active continental margins: Numerical modeling // Phys. Earth Planet. Inter. 2012. Vol. 192. P. 1–20.

The dynamics and melt sources for crustal growth at active continental margins are analyzed by using a 2D coupled petrological-thermomechanical numerical model of an oceanic-continental subduction zone. This model includes spontaneous slab retreat and bending, dehydration of subducted crust, aqueous fluid transport, partial melting, melt extraction and melt emplacement in form of extrusive volcanics and intrusive plutons. We could identify the following three geodynamic regimes of crustal growth: (i) stable arcs, (ii) compressional arcs with plume development, and (iii) extensional arcs. Crustal growth in a stable subduction setting results in the emplacement of flattened intrusions in the lower crust. At first dacitic melts, extracted from partially molten rocks located atop the slab (gabbros and basalts), intrude into the lower crust followed by mantle-derived (wet peridotite) basaltic melts from the mantle wedge. Thus extending plutons form in the lower crust, characterized by a successively increasing mantle component and low magmatic addition rates (10 km(3)/km/Myrs). Compressional arcs are accomplished by the formation and emplacement of hybrid plumes. In the course of subduction localization and partial melting of basalts and sediments along the slab induces Rayleigh Taylor instabilities. Hence, buoyant plumes are formed, composed of partially molten sediments and basalts of the oceanic crust:. Subsequently. these plumes ascend, crosscutting the lithosphere before they finally crystallize within the upper crust in form of silicic intrusions. Additionally, intrusions are formed in the lower crust derived by partial melting of rocks located atop the slab (basalts, gabbros, wet peridotite) and inside the plume (basalts, sediments). Magmatic addition rates are somewhat higher compared to stable arcs (40-70 km(3)/km/Myrs). Subduction in an extensional arc setting results in decompression melting of dry peridotite. The backward motion of the subduction zone relative to the motion of the plate leads to thinning of the overriding plate. Thus, hot and dry asthenosphere rises into the neck as the slab retreats, triggering decompression melting of dry peridotite. Consequently large volumes of mafic (oceanic) crust are formed in the backarc region with total magmatic addition rates being as high as 90-170 km(3)/km/Myrs. (C) 2012 Elsevier B.V. All rights reserved.

Walker B.A. et al. Crystal reaming during the assembly, maturation, and waning of an eleven-million-year crustal magma cycle: thermobarometry of the Aucanquilcha Volcanic Cluster // Contrib. Mineral. Petrol. 2013. Vol. 165, № 4. P. 663–682.

Phenocryst assemblages of lavas from the long-lived Aucanquilcha Volcanic Cluster (AVC) have been probed to assess pressure and temperature conditions of pre-eruptive arc magmas. Andesite to dacite lavas of the AVC erupted throughout an 11-million-year, arc magmatic cycle in the central Andes in northern Chile. Phases targeted for thermobarometry include amphibole, plagioclase, pyroxenes, and Fe-Ti oxides. Overall, crystallization is documented over 1-7.5 kbar (similar to 25 km) of pressure and similar to 680-1,110 A degrees C of temperature. Pressure estimates range from similar to 1 to 5 kbar for amphiboles and from similar to 3 to 7.5 kbar for pyroxenes. Pyroxene temperatures are tightly clustered from similar to 1,000-1,100 A degrees C, Fe-Ti oxide temperatures range from similar to 750-1,000 A degrees C, and amphibole temperatures range from similar to 780-1,050 A degrees C. Although slightly higher, these temperatures correspond well with previously published zircon temperatures ranging from similar to 670-900 A degrees C. Two different Fe-Ti oxide thermometers (Andersen and Lindsley 1985; Ghiorso and Evans 2008) are compared and agree well. We also compare amphibole and amphibole-plagioclase thermobarometers (Ridolfi et al. 2010; Holland and Blundy 1994; Anderson and Smith 1995), the solutions from which do not agree well. In samples where we employ multiple thermometers, pyroxene temperature estimates are always highest, zircon temperature estimates are lowest, and Fe-Ti oxide and amphibole temperature estimates fall in between. Maximum Fe-Ti oxide and zircon temperatures are observed during the middle stage of AVC activity (similar to 5-3 Ma), a time associated with increased eruption rates. Amphibole temperatures during this time are relatively restricted (similar to 850-1,000 A degrees C). The crystal record presented here offers a time-transgressive view of an evolving, multi-tiered subvolcanic reservoir. Some crystals in AVC lavas are likely to be true phenocrysts, but the diversity of crystallization temperatures and pressures recorded by phases in individual AVC lavas suggests erupting magma extensively reams and accumulates crystals from disparate levels of the middle to upper crust.

Wetzel D.T. et al. Degassing of reduced carbon from planetary basalts // Proc. Natl. Acad. Sci. U. S. A. 2013. Vol. 110, № 20. P. 8010–8013.

Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO(2))] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO(2) higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO(2), we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO(2) less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO(2) controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential.

White, L. T.; Ireland, T. R. This record has been added to your Marked List., // Chemical Geology (NLD). 2012 г., т. 306-307, cnh.78-91

A correlation has previously been noted between extremely high-uranium concentrations in zircon and apparent U/Pb age as measured in ion microprobe analysis. Here we present data from two zircon populations with extremely high-uranium concentrations in an attempt to quantify effects related to the nature of the samples and/or instrumentally induced fractionation (instrument, analytical setup, and/or matrix effect). The high-uranium matrix effect is apparent in zircons from the 180 Ma Tasmanian Dolerite, which typically shows an increase in Pb/U age of around 3% per thousand wig of uranium when measured on SHRIMP RG. One session on SHRIMP RG shows a correlation with 8% per thousand mu g/g of uranium. Data from SHRIMP II show a weak correlation and no correlation is evident in data collected on SHRIMP I. High-uranium zircons from the 98 Ma Mt Dromedary monzonite show little to no correlation between uranium concentration and U/Pb age. Analyses of younger (similar to 20-50 Ma) high-uranium zircons show a correlation between uranium concentration and an increase in apparent age, but this is less pronounced than the results obtained from the older Tasmanian Dolerite. Raman spectroscopy of the Tasmanian Dolerite zircons shows that these zircons are metamict. The link between uranium concentration and apparent age appears to be related to the degradation of the zircon matrix from radiation damage. The change in matrix enhances the emission of Pb+ relative to U and U oxide species. As this effect is associated with matrix and machine parameters, an external correction cannot be made assuming a constant correction value. With a secondary high-uranium standard, it might be possible to quantify the effect, but the matrix of this standard needs to be closely matched in age (radiation damage) and chemistry (U concentration): this solution is impractical. We instead propose that workers be aware of this matrix effect in SHRIMP analyses of zircon and to use Raman spectroscopy before or after SHRIMP analyses to ensure that the zircon is crystalline. These findings have important consequences for the use of SHRIMP data for zircon geochronology.

Yang S.-Y., Jiang S.-Y. Chemical and boron isotopic composition of tourmaline in the Xiangshan volcanic-intrusive complex, Southeast China: Evidence for boron mobilization and infiltration during magmatic-hydrothermal processes // Chem. Geol. 2012. Vol. 312. P. 177–189.

Three types of tourmaline occurrences have been distinguished in the Xiangshan volcanic-intrusive complex, SE China: (1) tourmaline-quartz nodules (NT type) in the porphyroclastic rhyolitic lava, (2) tourmalinite or tourmaline-rich quartzite (TT type) as xenoliths in the porphyroclastic rhyolitic lava; and (3) tourmaline-rich biotite schist (BT type) which also occurs as xenoliths in the porphyroclastic rhyolitic lava. Detailed petrographic study suggests that all three types of tourmaline are of magmatic-hydrothermal origin. The occurrence of tourmaline in the latter two types (TT and BT) reflects strong boron mobilization and infiltration from the magma into the meta-sedimentary xenoliths during interaction between the magmatic-hydrothermal fluids and the xenoliths. This interpretation is supported by the similar chemical compositions of tourmaline in all three types, although small differences exist between the BT and NT type tourmalines, i.e., the BT type tourmaline is slightly enriched in Ca and Mg, while the NT type tourmaline is slightly enriched in Na and Fe. The boron isotope analyses of tourmaline by both bulk TIMS and in-situ LA-MC-ICP-MS methods reveal that all three tourmaline types show similar delta B-11 values, with a narrow range between -14 and -11 parts per thousand, indicating a single boron source. The formation of NT type tourmaline was most likely triggered by liquid immiscibility during highly evolved magmatic differentiation, and tourmaline crystallization typically occurred during the magmatic stage transitional from latter solidus to early subsolidus crystallization.

Yoshimura S., Nakamura M. Flux of volcanic CO2 emission estimated from melt inclusions and fluid transport modelling // Earth Planet. Sci. Lett. 2013. Vol. 361. P. 497–503.

Volcanic CO2 degassing is considered the primary process that controls the global carbon cycle over geological timescales. However, fluxes of CO2 from individual volcanoes, in particular those in past activities, have been poorly constrained. One way to estimate the flux is by using the H2O-CO2 systematics of melt inclusions, which, according to petrological studies, records fluxing of a deep-derived CO2-rich fluid in the deep to shallow-level crustal magmatic systems. Assuming that this fluid fluxing is the process of volcanic CO2 emission, we quantified the fluxes of CO2 by combining a fluid transport model with melt inclusion data. We formulated CO2 fluxing as an advective fluid flow in a basaltic magma column with exchanging volatiles, and applied it to the melt inclusion data from Mount Etna, the type locality of a CO2-emitting volcano. The flux of CO2 was calculated to be 2.4-6.0 kt/day, which is consistent with the observed volcanic CO2 emission rate of 1-10 kt/day. We propose that this method potentially provides a means to quantify CO2 emission rates in past volcanic activities. Because CO2 fluxing is an open-system process, the estimated CO2 emission over geological timescales evaluated with this method should give much higher values than evaluations based simply on the volume of the erupted magmas. (C) 2012 Elsevier B.V. All rights reserved.

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