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Физико-химические и петрофизические исследования в науках о Земле

Журнальные статьи

Acosta-Gongora P. et al. Trace Element Geochemistry of Magnetite and Its Relationship to Cu-Bi-Co-Au-Ag-U-W Mineralization in the Great Bear Magmatic Zone, NWT, Canada // Econ. Geol. 2014. Vol. 109, № 7. P. 1901–1928.

The Paleoproterozoic Great Bear magmatic zone is the focus of ongoing exploration for iron oxide copper-gold (IOCG) deposits and also hosts iron oxide-apatite occurrences. Examples of IOCG deposits in the Great Bear magmatic zone include Sue-Dianne.and NICO, and other smaller prospects, including Damp, Fab, and Nori/Ra. The past-producing Terra mine property hosts significant IOCG-like alteration that contains dome-shaped, iron oxide-apatite bodies. Petrographic study has identified multiple generations of magnetite at NICO, Fab, and Nori/Ra and, for the most part, a single generation of magnetite at Sue-Dianne, Damp, and Terra. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) documents important geochemical differences in V, Ni, Cr, and Co concentrations within the magnetite. Variations of trace elements in magnetite from the Great Bear magmatic zone could be a result of (1) host rock-fluid equilibration during regional metamorphism, (2) postmetamorphic hydrothermal metasomatism of Treasure Lake Group rnetasedimentary rocks, (3) preferential solubility of Co over Ni within the Fe-rich fluids, (4) changes in oxygen fugacity (f(O2)), and (5) partitioning of elements into coprecipitating sulfides. Regionally, the Cr/Co ratio is higher in barren and pre-ore magnetite compared to magnetite coprecipitated with ore minerals and/or present in ore-rich veins and breccias. Locally, at the Nori/Ra prospect, the V/Ni ratio in magnetite differentiates between barren and ore-related magnetite, and at Damp and Sue-Dianne the Co/Ni ratio is extremely high and clearly different from that of other Great Bear magmatic zone magnetite samples. These results provide the first database for geochemically characterized magnetite from different stages of IOCG alteration and illustrate the potential use of magnetite as an indicator mineral in the exploration for IOCG deposits.

Ali S., Ntaflos T., Upton B.G.J. Petrogenesis and mantle source characteristics of Quaternary alkaline mafic lavas in the western Carpathian-Pannonian Region, Styria, Austria // Chem. Geol. 2013. Vol. 337. P. 99–113.

In the Styrian Basin, i.e. the westernmost part of the Carpathian-Pannonian Region (CPR), the Pliocene to Quaternary post-extensional phase was accompanied by eruption of alkaline mafic magmas, some of which carry mantle xenoliths. The rocks range from nephelinites (Stradnerkogel and Waltrafelsen) to (predominant) basanites and ne-basanites (Kloch and Steinberg). They have high Ce/Pb, Nb/U and Nb/La ratios reflecting asthenospheric mantle source characteristics with negligible crustal contamination, differentiation en route to the surface and/or interaction with the lithospheric mantle. The calculated depths of magma generation are >100 km for the basanites and ne-basanites in comparison to 135 km or more for the nephelinites, implying an origin in the garnet stability field. The temperatures of mantle melting for the basanites and ne-basanites are from approximate to 1400 to 1500 degrees C Modeling calculation using the most primitive Styrian sample (a basanite) gives a mantle potential temperature (Tp) of 1466 degrees C similar to average Tp of upper mantle sources beneath MORB indicating that the Styrian magmas were generated from asthenospheric mantle sources at ambient temperatures that preclude plume activity beneath the study area. The nephelinites have elevated Zr/Hf (51-67) and La/Yb-N (29-31) ratios and negative K and Ti anomalies on the PM-normalized multi-element diagrams, similar to those of carbonatites. These characteristics suggest that their source had experienced enrichment by carbonatitic liquids; an inference supported by their estimated content of similar to 5% CO2. By contrast, the trace element signatures of the basanites and ne-basanites suggest that their asthenospheric source, which experienced higher degrees of melting than the nephelinites, was nearly unaffected by carbonatite metasomatism. From the overall similarity of the trace element distribution patterns and the narrow range of their Sr-Nd isotopic ratios, all the rocks can be related to a similar (OIB-like) asthenospheric mantle source, approximating the European Asthenospheric Reservoir (EAR-type).

Ariskin A.A. et al. Modeling Solubility of Fe-Ni Sulfides in Basaltic Magmas: The Effect of Nickel // Econ. Geol. 2013. Vol. 108, № 8. P. 1983–2003.

A new model of sulfur solubility in mafic and/or ultramafic silicate magmas, which accounts for the effects of pressure, temperature, oxygen fugacity, major element, and Ni contents in the silicate melt and the coexisting sulfide liquid, is presented in this paper. The model postulates the existence of positively charged Fe-Ni sulfide complexes in the melt of a general formula (FeyNi1-y)(z)S2(z-1)+, which are formed as a result of complexation reactions between the sulfide-forming ions (Fe2+, Ni2+, S2-) and (Fe,Ni)S species in the silicate liquid. The new model can explain both the anomalously high S solubility in iron-enriched silicate systems and the "parabola-like" dependence of S contents in silicate melts on their Fe content. The proposed mechanism of sulfide solubility was calibrated on a dataset of 213 anhydrous experimental glasses (both Ni free and Ni bearing) and 53 S-saturated MORB glasses, and incorporated into a new version of the COMAGMAT (v. 5) magma crystallization model. The COMAGMAT-5 model can estimate sulfur concentration at sulfide saturation (SCSS) in a wide range of experimental and natural compositions, including Fe/Ni variations in silicate melts and coexisting sulfides. Despite relatively low concentrations, nickel is shown to have a pronounced effect on S solubility, causing significant variations in the onset of sulfide immiscibility in melts with otherwise similar major element compositions. An application example of the new SCSS model to "B-1 magma" proposed as parent for the Lower and Lower Critical zones of the Rustenburg Layered Suite, Bushveld Complex, is discussed.

Baumgartner R.J. et al. Mineralogical and geochemical investigation of layered chromitites from the Bracco-Gabbro complex, Ligurian ophiolite, Italy // Contrib. Mineral. Petrol. 2013. Vol. 165, № 3. P. 477–493.

The Bracco-Gabbro Complex (Internal Liguride ophiolite), that intruded subcontinental mantle peridotite, contains layers of chromitite that are associated with ultramafic differentiates. The chromitites and disseminated chromites in the ultramafics have Al contents similar to the Al-rich podiform chromitites [0.40 < Cr# = Cr/(Cr + Al) < 0.55]. TiO2 contents of the chromitites are unusually high and range up to 0.82 wt%. The calculated Al2O3 and TiO2 content of the parental melt suggest that the melt was a MORB type. Geothermobarometrical calculations on few preserved silicate inclusions revealed formation temperatures between 970 and 820 A degrees C under a relatively high oxygen fugacity (Delta logfO(2) at +2.0-2.4). Chromitites were altered during the post-magmatic tectono-metamorphic uplift and the final exposure at the seafloor, as evidenced by the formation of ferrian chromite. The PGE contents of the chromitites and associated ultramafics are unusually low (PGEmax 83 ppb). The chondrite-normalized PGE spidergrams show positive PGE patterns and to some extent similarities with the typical trend of stratiform chromitites. No specific PGM have been found but low concentrations of PPGE (Rh, Pt, and Pd) have been detected in the sulphides that occur interstitially to or enclosed in chromite. Recently, it has been shown that the Internal Liguride gabbroic intrusions have formed by relatively low degrees of partial melting of the asthenospheric mantle. We conclude that the low degree of partial melting might be the main factor to control the unusual low PGE contents and the rather unique PGE distribution in the Bracco chromitites.

Baxter E.F., Caddick M.J. Garnet growth as a proxy for progressive subduction zone dehydration // Geology. 2013. Vol. 41, № 6. P. 643–646.

The release of volatiles from subducting lithologies is a crucial triggering process for arc magmatism, seismicity, the growth and maturation of continents, and the global geological water-CO2 cycle. While models exist to predict slab volatile release from hydrous phases, it is challenging to reconstruct and test these fluid fluxes in nature. Here we show that the growth of garnet may be used as a proxy for devolatilization at blueschist to lower eclogite facies conditions in subduction zones. Using thermodynamic analysis including the effects of garnet fractionation and fluid removal, we show the proportional relationship between garnet and water production in two end-member crustal lithologies (pelitic sediment and hydrated mid-oceanic-ridge basalt [MORB]) in three representative subduction geotherms. Dehydrating minerals such as lawsonite, chlorite, amphibole, and epidote contribute to garnet growth, especially between similar to 1.4 and 3.0 GPa where geophysical models and observations predict dehydration. The average production ratio for altered MORB compositions is 0.52 (wt% water as fluid per vol% garnet) in cooler geotherms (Honshu [Japan] and Nicaragua) and 0.27 in hotter geotherms (Cascadia [North America]), whereas for pelite the production ratios are about half (0.24 and 0.13, respectively). Garnet growth correlates with production of 3.3-5.9 wt% water in hydrated MORB and 1.8-3.1 wt% water in pelite, representing 42%-100% of the water lost between 0.5 and 6.5 GPa from a fully saturated starting material. Garnet abundance, its pressure-temperature growth span, and its growth chronology may be used to recognize, reconstruct, and test models for progressive subduction zone dehydration.

Bell A.S. et al. XANES measurements of Cr valence in olivine and their applications to planetary basalts // Am. Miner. 2014. Vol. 99, № 7. P. 1404–1412.

and Cr valence ratio in olivine grown from a basaltic liquid. These experiments are specifically targeted for an olivine-rich martian basalt composition that was modeled after the bulk chemistry of the meteorite Yamato 980459 (i.e., Y-98). The chromium valence ratio in the olivine crystals was measured with X-ray absorption near edge spectroscopy (XANES) at the Advanced Photon Source, Argonne National Laboratory. Results from the XANES measurements indicate that the ratio of divalent to trivalent Cr in the olivine is not only systematically correlated with f(O2), but is also reflective of the molar Cr3+/Cr2+ in the silicate liquid from which it grew. In this way, measurements of Cr valence in olivine phenocrysts can yield important information about the oxygen fugacity and molar Cr3+/Cr2+ of its parental liquid in the absence of a quenched melt phase. Although the results from the experiments presented in this work specifically apply to the Y-98 parental melt, the concepts and XANES analytical techniques discussed within the text present a novel, generalized methodology that may be applicable to any olivine-bearing basalt. Furthermore, the XANES-based measurements are made on a micrometer-scale, thus potential changes of the Cr3+/Cr2+ in the melt during crystallization could be examined with a great deal of spatial detail.

Berry A.J. et al. Quantitative mapping of the oxidative effects of mantle metasomatism // Geology. 2013. Vol. 41, № 6. P. 683–686.

The oxidation state of Fe in garnets in a garnet peridotite xenolith from the Wesselton kimberlite (South Africa) was quantitatively mapped using X-ray absorption near edge structure (XANES) spectroscopy. Maps of Fe3+/Sigma Fe were produced by recording the fluorescence intensity at discrete energies rather than recording the full spectrum at each point. The intensity at each point in the map was quantitatively converted to Fe3+/Sigma Fe with reference to a linear calibration derived from garnet standards for which Fe3+/Sigma Fe had been determined previously by Mossbauer spectroscopy. The resolution of these maps approaches that of elemental maps obtained using an electron microprobe. The maps reveal zoning in Fe3+/Sigma Fe between the core (0.075) and rim (0.125) that correlates with zoning of other elements. The rims record an oxidizing metasomatic event in the lithospheric mantle. The oxygen fugacity (f(O2)) of this metasomatism is considerably higher than expected from studies of homogeneous garnets that exhibit metasomatic signatures; such garnets may represent a re-equilibrated average of the original (core) and metasomatic (rim) f(O2) values. Metasomatism of the lithospheric mantle may thus have a greater impact on diamond stability than previously thought.

Botcharnikov R.E. et al. Behavior of gold in a magma at sulfide-sulfate transition: Revisited // Am. Miner. 2013. Vol. 98, № 8-9. P. 1459–1464.

We have investigated experimentally the partitioning of Au between solid and liquid sulfide phases and basaltic melts at 200 MPa, at redox conditions close to the sulfide-sulfate transition, over temperatures between 1050 and 1200 degrees C, which span the monosulfide solid solution (MSS) - sulfide liquid (SuL) solidus. The measured MSS/basalt partition coefficient of Au (D-Au(MSS-sil)) is about 100-200, whereas the partition coefficient of sulfide liquid/basalt (D-Au(SuL-sil)) is approximately 10 times larger at 2200. Although we find that temperature, pressure, and oxygen fugacity (f(O2)) exert relatively weak controls on Au partitioning, they exert major indirect influences on Au behavior by controlling the identity of the condensed sulfide phase and by affecting S solubility. These observations have important implications for the behavior of Au in the processes of partial melting in the mantle and magma crystallization in the crust. The occurrence of natural magmas with elevated concentrations of Au and presumably other highly siderophile and chalcophile elements requires predominance of MSS over SuL in the source or/and oxidizing conditions close to or above the sulfide-sulfate transition in the magma.

Bouhifd M.A. et al. Superchondritic Sm/Nd ratio of the Earth: Impact of Earth’s core formation // Earth Planet. Sci. Lett. 2015. Vol. 413. P. 158–166.

This study investigates the impact of Earth's core formation on the metal-silicate partitioning of Sm and Nd, two rare-earth elements assumed to be strictly lithophile although they are widely carried by the sulphide phases in reducing material (e.g. enstatite chondrites). The partition coefficients of Sm and Nd (D-Sm and D-Nd) between molten CI and EH chondrites model compositions and various Fe-rich alloys (in the Fe-Ni-C-Si-S system) have been determined in a multi-anvil between 3 and 26 GPa at various temperatures between 2073 and 2440 K, and at an oxygen fugacity ranging from 1 to 5 log units below the iron-wustite (IW) buffer. The chemical compositions of the run products and trace concentrations in Sm and Nd elements were determined using electron microprobe and laser ablation inductively coupled plasma-mass spectrometry. Our results demonstrate the non-fractionation of Sm and Nd during the segregation of the metallic phases: the initial Sm/Nd ratio of about 1 in the starting materials yields precisely the same ratio in the recovered silicate phases after the equilibration with the metal phases at all conditions investigated in this study. In addition, D-Sm and D-Nd values range between 10(-3) and 10(-5) representing a low solubility in the metal. An increase of the partition coefficients is observed with decreasing the oxygen fugacity, or with an increase of S content of the metallic phase at constant oxygen fugacity. Thus, based on the actual Sm and Nd concentrations in the bulk Earth, the core should contain less than 0.4 ppb for Sm and less than 1 ppb for Nd. These estimates are three orders of magnitude lower than what would be required to explain the reported Nd-142 excess in terrestrial samples relative to the mean chondritic value, using the core as a Sm-Nd complementary reservoir. In other words, the core formation processes cannot be responsible for the increase of the Sm/Nd ratio in the mantle early in Earth history.

Chadwick J.P. et al. Petrology and geochemistry of igneous inclusions in recent Merapi deposits: a window into the sub-volcanic plumbing system // Contrib. Mineral. Petrol. 2013. Vol. 165, № 2. P. 259–282.

Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography, geochemistry and geobarometric calculations. The inclusions may be classified into four main suites: (1) highly crystalline basaltic-andesite inclusions, (2) co-magmatic enclaves, (3) plutonic crystalline inclusions and (4) amphibole megacrysts. Highly crystalline basaltic-andesite inclusions and co-magmatic enclaves typically display liquid-liquid relationships with their host rocks, indicating mixing and mingling of distinct magmas. Co-magmatic enclaves are basaltic in composition and occasionally display chilled margins, whereas highly crystalline basaltic-andesite inclusions usually lack chilling. Plutonic inclusions have variable grain sizes and occasionally possess crystal layering with a spectrum of compositions spanning from gabbro to diorite. Plagioclase, pyroxene and amphibole are the dominant phases present in both the inclusions and the host lavas. Mineral compositions of the inclusions largely overlap with compositions of minerals in recent and historic basaltic-andesites and the enclaves they contain, indicating a cognate or 'antelithic' nature for most of the plutonic inclusions. Many of the plutonic inclusions plot together with the host basaltic-andesites along fractional crystallisation trends from parental basalt to andesite compositions. Results for mineral geobarometry on the inclusions suggest a crystallisation history for the plutonic inclusions and the recent and historic Merapi magmas that spans the full depth of the crust, indicating a multi-chamber magma system with high amounts of semi-molten crystalline mush. There, crystallisation, crystal accumulation, magma mixing and mafic recharge take place. Comparison of the barometric results with whole rock Sr, Nd, and Pb isotope data for the inclusions suggests input of crustal material as magma ascends from depth, with a significant late addition of sedimentary material from the uppermost crust. The type of multi-chamber plumbing system envisaged contains large portions of crystal mush and provides ample opportunity to recycle the magmatic crystalline roots as well as interact with the surrounding host lithologies.

Cicconi M.R. et al. Competition between two redox states in silicate melts: An in-situ experiment at the Fe K-edge and Eu L-3-edge // Am. Miner. 2015. Vol. 100, № 4. P. 1013–1016.

The understanding of redox equilibria as well as the knowledge of the elemental distribution in magmatic melts are of fundamental importance to constrain the genesis of magmas. In particular, the partitioning of trace elements (e.g., Eu) has demonstrated to be a useful tool for estimating the redox conditions in Earth and planetary materials. However, for a more complete comprehension of Eu in silicate melts, information regarding the effects of temperature (7), redox conditions, compositions, and the possible interference of other multivalent elements is still lacking. Here we provide new data on the oxidation states of two commonly coexistent multivalent elements (Eu and Fe) in melts, acquired by "in situ" dispersive X-ray absorption spectroscopy experiments at high temperatures and at different oxygen fugacity conditions. This work, for the first time, shows the possibility to monitor in real-time the behavior and valence variations of two elements under varying environmental conditions (like T and redox state).

Cortes J.A. et al. Intrinsic conditions of magma genesis at the Lunar Crater Volcanic Field (Nevada), and implications for internal plumbing and magma ascent // Am. Miner. 2015. Vol. 100, № 2-3. P. 396–413.

The northern part of the Lunar Crater Volcanic Field (central Nevada, U.S.A.) contains more than 100 Quaternary basaltic cones and maars and related eruptive products. We focused on four informal units of different ages and locations in the field to test the compositional variability and magma ascent processes within the time span of an individual eruption and the variability between very closely spaced volcanoes with different ages. Based in whole-rock chemistry, mineral chemistry and the calculation of intrinsic properties (pressure, temperature, and oxygen fugacity) we found that individual magma batches were generated in the asthenospheric mantle from a heterogeneous garnet lherzolite/olivine websterite source by similar to 3-5% partial melting. Each magma batch and temporary deep reservoir was a separate entity rather than part of a continuous long-lived reservoir. Magmas ascended relatively fast, stalled and crystallized in the uppermost several kilometers of the mantle near the base of the crust and some also stalled at mid-crustal levels with minor or no geochemical interaction with surrounding rocks. Our data also suggest that volcanoes erupting within certain time windows had similar source characteristics and ascent processes whether they were located within a few hundred meters of each other or were separated by many kilometers.

Dai L. et al. Electrical conductivity of gabbro: the effects of temperature, pressure and oxygen fugacity // Eur. J. Mineral. 2015. Vol. 27, № 2. P. 215–224.

The electrical conductivity of gabbro was investigated at 623-1173 K, 0.5-2.0 GPa and oxygen fugacities controlled by three solid buffers (Cu + CuO, Ni + NiO and Mo + MoO2) using a YJ-3000t multianvil press and Solartron-1260 impedance spectroscopy analyzer within the frequency range 10(-1)-10(6) Hz. The measured electrical conductivity shows an Arrhenius increase with temperature and increases with increasing pressure. The activation energy and activation volume of charge carriers have been determined as 0.72 +/- 0.01 eV and -6.8 +/- 0.69 cm(3)/mol, respectively. The hydrogen-assisted electrical conductivity in gabbro decreases with increasing oxygen fugacity. Furthermore, it is inferred that some hydrogen-related defects with minor concentration (e.g., H'(M) or H-center dot) are the main charge carriers in the sample and provide reasonable explanations for the behavior of electrical conductivity of gabbro at high pressure.

Dalou C., Mysen B.O. The effect of H2O on F and Cl solubility and solution mechanisms of in aluminosilicate melts at high pressure and high temperature // Am. Miner. 2015. Vol. 100, № 2-3. P. 633–643.

Effects of H2O on the solution behavior of fluorine and chlorine in peralkaline sodium aluminosilicate glasses quenched from melts at high temperature (1400 degrees C) and pressure (1.5 GPa) were studied by combining solubility measurements and Raman spectroscopy. With increasing H2O content from 0 to similar to 10 wt%, the fluorine solubility increases from 3.3 to 4.4 mol% in Al-free glasses and from 6.3 to 9.3 mol% in Al-rich glasses (10 mol% Al2O3). In contrast, in the same H2O concentration range the chlorine solubility decreases from 5.7 to 3.4 mol% in Al-free glasses and from 3.6 to 1.7 mol% in Al-rich glasses. In Al-free glasses, interaction between H2O and the silicate to depolymerize the network is Q(4) + H2O <-> Q(2)(H) and Q(3) + H2O <-> Q(2)(H). The effect of water on silicate melt structure is different in halogen-bearing melts because in hydrous melt systems both F and Cl can act to depolymerize the melt further. For fluorine, this is accomplished via formation of Si-F, Al-F, and Na-F bonding in addition to Si-OH, whereas in chlorine-bearing hydrous melts, there is no interaction between Si4+ and Cl-. The halogen solubility in the magmatic liquid influences mineral/melt partition coefficients of chlorine and fluorine and implies partition coefficients different from unity. Moreover because of the contrasting effects of H2O on fluorine and chlorine solubility, the Cl/F ratio in magmas formed in water-rich environments such as subduction zones can be a sensitive indicator of H2O content during arc magmas genesis. Transport properties of melts, such as diffusion and viscosity, also vary differently in halogen-bearing hydrous melts compared with halogen-free systems. Moreover, those effects on melt properties are the strongest in F-bearing systems.

Dasgupta R. et al. Carbon solution and partitioning between metallic and silicate melts in a shallow magma ocean: Implications for the origin and distribution of terrestrial carbon // Geochim. Cosmochim. Acta. 2013. Vol. 102. P. 191–212.

The origin of bulk silicate Earth carbon inventory is unknown and the fate of carbon during the early Earth differentiation and core formation is a missing link in the evolution of the terrestrial carbon cycle. Here we present high pressure (P)-temperature (T) experiments that offer new constraints upon the partitioning of carbon between metallic and silicate melt in a shallow magma ocean. Experiments were performed at 1-5 GPa, 1600-2100 degrees C on mixtures of synthetic or natural silicates (tholeiitic basalt/alkali basalt/komatiite/fertile peridotite) and Fe-Ni-C +/- Co +/- S contained in graphite or MgO capsules. All the experiments produced immiscible Fe-rich metallic and silicate melts at oxygen fugacity (fO(2)) between similar to IW-1.5 and IW-1.9. Carbon and hydrogen concentrations of basaltic glasses and non-glassy quenched silicate melts were determined using secondary ionization mass spectrometry (SIMS) and speciation of dissolved C-O-H volatiles in silicate glasses was studied using Raman spectroscopy. Carbon contents of metallic melts were determined using both electron microprobe and SIMS. Our experiments indicate that at core-forming, reduced conditions, carbon in deep mafic-ultramafic magmas may dissolve primarily as various hydrogenated species but the total carbon storage capacity, although is significantly higher than solubility of CO2 under similar conditions, remains low (<500 ppm). The total carbon content in our reduced melts at graphite saturation increases with increasing melt depolymerization (NBO/T), consistent with recent spectroscopic studies, and modestly with increasing hydration. Carbon behaves as a metal-loving element during core-mantle separation and our experimental D-C(metal/silicate) varies between similar to 4750 and >= 150 and increases with increasing pressure and decreases with increasing temperature and melt NBO/T. Our data suggest that if only a trace amount of carbon (similar to 730 ppm C) was available during early Earth differentiation, most of it was partitioned to the core (with 0.20-0.25 wt.% C) and no more than similar to 10-30% of the present-day mantle carbon budget (50-200 ppm CO2) could be derived from a magma ocean residual to core formation. With equilibrium core formation removing most of the carbon initially retained in the terrestrial magma ocean, explanation of the modern bulk silicate Earth carbon inventory requires a later replenishment mechanism. Partial entrapment of metal melt in solid silicate matrix, carbon ingassing by magma ocean-atmosphere interaction, and carbon outgassing from the core aided by reaction of core metal and deeply subducted water are some of the viable mechanisms. (C) 2012 Elsevier Ltd. All rights reserved.

Davis F.A. et al. Experimentally determined mineral/melt partitioning of first-row transition elements (FRTE) during partial melting of peridotite at 3 GPa // Geochim. Cosmochim. Acta. 2013. Vol. 104. P. 232–260.

Ratios of first-row transition elements (FRTE), such as Fe/Mn and Zn/Fe, may be fractionated differently by partial melting of peridotite than by partial melting of recycled lithologies like eclogite, and therefore may be useful as indicators of the source lithologies of mantle- derived basalts. Interpretation of basalt source lithologies from FRTE ratios requires accurate assessment of FRTE partitioning behavior between peridotitic minerals and coexisting melts. We present experimental determinations of partition coefficients for several of the FRTE (Sc, Ti, V, Cr, Mn, Fe, Co, Zn) and Ga and Ge between basaltic melt and olivine, garnet, pyroxenes, and spinel at 3 GPa. Because mineral/melt partitioning is sensitive to phase compositions, a key feature of these experiments is that the melts and minerals are known from previous experiments to be in equilibrium at the solidus of garnet peridotite at 3 GPa. Therefore, these partition coefficients are directly applicable to near-solidus partial melting of the mantle at 3 GPa. We use these partition coefficients to calculate compositions of model partial melts of peridotite and compare these to natural OIB. Model partial melts of peridotite have lower Fe/Mn (<62) and higher Co/Fe (>7 * 10(-4)) than many primitive OIB, which implies that some other source lithology participates in the formation of many OIB. Alternatively, these ratios may potentially be produced by garnet peridotite if the source contains similar to 0.3% Fe2O3, consistent with observations from continental xenoliths. Zn/Fe is a less sensitive indicator of non-peridotite source lithology than either Fe/Mn or Co/Fe, as Zn/Fe in partial melts of peridotite overlaps with >75% of primitive OIB. Ga and Sc are fractionated significantly by residual garnet, and high Ga/Sc may indicate the presence of garnet in basalt source regions. When taking into account several FRTE ratios simultaneously, few OIB appear to be consistent with derivation solely from a reduced peridotitic source. The source either must have a modest non-peridotitic component, be Fe-enriched, or be slightly oxidized.

de Vries D.F.W. et al. Micron-scale coupled carbon isotope and nitrogen abundance variations in diamonds: Evidence for episodic diamond formation beneath the Siberian Craton // Geochim. Cosmochim. Acta. 2013. Vol. 100. P. 176–199.

The internal structure and growth history of six macro-diamonds from kimberlite pipes in Yakutia (Russia) were investigated with cathodoluminescence imaging and coupled carbon isotope and nitrogen abundance analyses along detailed core to rim traverses. The diamonds are characterised by octahedral zonation with layer-by-layer growth. High spatial resolution SIMS profiles establish that there is no exchange of the carbon isotope composition across growth boundaries at the mu m scale and that isotopic variations observed between (sub) zones within the diamonds are primary. The macro-diamonds have delta C-13 values that vary within 2 parts per thousand of -5.3 parts per thousand and their nitrogen contents range between 0-1334 at. ppm. There are markedly different nitrogen aggregation states between major growth zones within individual diamonds that demonstrate Yakutian diamonds grew in multiple growth events. Growth intervals were punctuated by stages of dissolution now associated with <10 mu m wide zones of nitrogen absent type II diamond. Across these resorption interfaces carbon isotope ratios and nitrogen contents record shifts between 0.5-2.3 parts per thousand and up to 407 at. ppm, respectively. Co-variation in delta C-13 value-nitrogen content suggests that parts of individual diamonds precipitated in a Rayleigh process from either oxidised or reduced fluids/melts, with two single diamonds showing evidence of both fluid types. Modelling the co-variation establishes that nitrogen is a compatible element in diamond relative to its growth medium and that the nitrogen partition coefficient is different between oxidised (3-4.1) and reduced (3) sources. The reduced sources have delta C-13 values between -7.3 parts per thousand and -4.6 parts per thousand, while the oxidised sources have higher delta C-13 values between -5.8 parts per thousand and -1.8 parts per thousand (if grown from carbonatitic media) or between -3.8 parts per thousand and +0.2 parts per thousand (if grown from CO2-rich media). It is therefore concluded that individual Yakutian diamonds originate from distinct fluids/melts of variable compositions. The diamond-forming fluids within the cratonic mantle beneath the Siberian Craton record significant variations in composition and volume and include both oxidised and reduced sources. These observations suggest that dating diamond inclusions using an isochron approach will best provide geologically meaningful ages if inclusions can be shown to be genetically (spatially) related.

Dilles J.H. et al. Zircon Compositional Evidence for Sulfur-Degassing from Ore-Forming Arc Magmas // Econ. Geol. 2015. Vol. 110. № 1. P. 241–251.

Porphyry Cu (+/- Mo +/- Au) and epithermal Au-Ag deposits are major sources of mined metals and are commonly formed by magmatic-hydrothermal fluids derived from hydrous magmas in Phanerozoic convergent margin settings. The igneous rock assemblages associated with porphyry mineral deposits are common in modern convergent margin settings, but while many have produced acidic magmatic fluids, very few, past or present, have produced sufficient metal, chlorine, and sulfur enrichments necessary to engender an ore deposit. The reasons for this remain uncertain. We report SHRIMP-RG ion microprobe analyses of hafnium, titanium and rare earth element (REE) abundances in zircon, a nearly ubiquitous and robust trace mineral in crustal magmas. Comparison of the compositions of zircons in ore-forming and barren granitic plutons indicate that ore-forming granites crystallized at relatively low temperature and have relatively small negative europium anomalies (mostly Eu-N/Eu-N degrees >= 0.4). We interpret these small zircon europium anomalies to indicate oxidizing magmatic conditions and hypothesize that in many cases this reflects oxidation due to SO2 degassing from magmas with a relatively low Fe/S ratio. Oxidation of europium and iron in the melt is produced by reduction of magmatic sulfate (S6+) to SO2 (S4+) upon degassing. This interpretation reinforces the important role of oxidized sulfur-rich fluids in porphyry and epithermal mineral deposit formation. Zircon compositions thus may be used to identify ancient magmas that released significant amounts of SO2-rich gases, and regional surveys of zircon composition are potentially a valuable tool for mineral exploration.

Elardo S.M. et al. Petrogenesis of primitive and evolved basalts in a cooling Moon: Experimental constraints from the youngest known lunar magmas // Earth Planet. Sci. Lett. 2015. Vol. 422. P. 126–137.

We have conducted high-temperature experiments over a range of pressures to constrain the petrogenesis of the youngest sampled lunar magmas, which have contrasting primitive and evolved compositions. Our results indicate that at similar to 3 Ga, melting still occurred within the same mantle depth range that produced crystalline mare basalts for the previous similar to 1 Ga, although our data cannot support or confirm that the shallowest extents of melting moved deeper into the mantle by similar to 3 Ga, as is predicted by most thermal evolution models. Furthermore, melting still occurred in regions with low abundances of heat-producing elements. Basaltic lunar meteorite NEA 003A has some of the lowest abundances of incompatible trace elements among all mare basalts and no negative Eu anomaly. Our experiments show that NEA 003A is multiply saturated with olivine and low-Ca pyroxene on its liquidus at similar to 1.1 GPa (similar to 215 km) and similar to 1330 degrees C. If the primitive NEA 003A liquid composition is a minimally-modified melt, the relatively low Mg# of its source region (73-75), its lack of a Eu anomaly, and its chondritic initial Nd isotopic composition indicate its source region likely escaped mixing during mantle overturn with later-stage magma ocean cumulates that formed after plagioclase saturation. This condition would require the sources of the ultramafic glasses to have experienced cumulate mixing, or for assimilation of later-stage magma ocean cumulates by the ultramafic glass parental magmas before eruption in order to account for their higher Mg4t's and deeper negative Eu anomalies. Alternatively, NEA 003A may have undergone some fractional crystallization, in which case its more primitive source region would be deeper than 215 km and may approach the depth range of the ultramafic glass source regions. Iron- and incompatible trace element-rich basaltic lunar meteorites LAP 02205, NWA 032/479, and NWA 4734 have nearly identical bulk compositions and have a multiple saturation point on their high pressure liquidus at <0.6 GPa (<105 km) and 1150-1200 degrees C. The P-T conditions of this multiple saturation point are inconsistent with the expectation from thermal modeling of a thick, cold lunar elastic lithosphere at 3 Ga, and likely indicate these melts underwent fractional crystallization before eruption, thus increasing their abundances of incompatible trace elements. However, these LREE-enriched basalts possess a very deep negative Eu-anomaly but do not show other chemical fingerprints of KREEP, indicating that a component of Fe-rich, low-Ti late-stage magma ocean cumulates are required in their hybridized source region.

Ferriss E. et al. The whole-block approach to measuring hydrogen diffusivity in nominally anhydrous minerals // Am. Miner. 2015. Vol. 100, № 4. P. 837–851.

A method is developed for determining the diffusivity of infrared-active species by transmission Fourier transform infrared spectroscopy (FTIR) in samples prepared as rectangular prisms without cutting the sample. The primary application of this "whole-block" or "3D-WB" method is in measuring the diffusion of hydrogen (colloquially referred to as "water") in nominally anhydrous minerals, but the approach is applicable to any IR-active species. The whole-block method requires developing a three-dimensional model that includes the integration of the beam signal through the sample, from rim to core to opposite rim. The analysis is carried out using both forward and tomographic inverse modeling techniques. Measurements collected from central slices cut from the whole block are simpler to interpret than whole-block measurements, but slicing requires destructive sample analysis. Because the whole-block method is nondestructive, this approach allows a time-series of diffusion experiments on the same sample. The potential pitfalls of evaluating whole-block measurements without correcting for path integration effects are explored using simulations. The simulations demonstrate that diffusivities determined from whole-block measurements without considering path-averaging may be up to half an order of magnitude too fast. The largest errors are in fast and/or short directions, in which the diffusion profiles are best developed. A key characteristic of whole-block measurements is that the central values in whole-block traverses always change before the concentration of the IR-active species changes in the block's center because of signal integration that includes concentrations in the sample rims. The resulting plateau in the measurements is difficult to fit correctly without considering path integration effects, ideally by using 3D whole-block models. However, for early stages of diffusion with <50% progress, diffusivities can be accurately determined within 0.5 log units using a ID approximation and the whole-block central plateau values because diffusivities are more dependent on profile shape than absolute concentrations. To test the whole-block method, a dehydration experiment was performed on an oriented piece of diopside from the Kunlun Mts with minimal zoning, cracks, or inclusions. The experiment was performed in a gas mixing furnace for 3 days at a temperature of 1000 degrees C and oxygen fugacity of 10-(11.1) bar (QFM). First, whole-block analysis was performed by taking FTIR traverses in three orthogonal directions. Then, a slice was cut from the center of the sample, and hydrogen profiles were measured by FTIR and secondary ion mass spectrometry (SIMS). The results of FTIR and SIMS measurements on the slice are in good agreement both with each other and with diffusion profiles calculated based on the results of forward and inverse models of the whole-block FTIR measurements. Finally, the new method is applied to previous whole-block measurements of hydrogen diffusion in San Carlos olivine using both the forward and inverse approaches.

Fraley K.J., Frank M.R. Gold Solubilities in Bornite, Intermediate Solid Solution, and Pyrrhotite at 500 degrees to 700 degrees C and 100 MPa // Econ. Geol. 2014. Vol. 109, № 2. P. 407–418.

Experiments were conducted at 100 MPa with an oxygen fugacity buffered by Ni-NiO, and at temperatures of 500 degrees, 600 degrees, and 700 degrees C, to determine the solubility of Au within bornite, high-temperature chalcopyrite (intermediate solid solution [ISS]), and pyrrhotite over a range of sulfur activities likely to be found in the porphyry environment. The activity of sulfur in the system, a(S2)(sys) was buffered by ISS (Cu = Fe), ISS + bornite, or ISS + pyrrhotite mineral assemblages, which induced a log a(S2)(sys) between -11 +/- 1 and 0.4 +/- 0.8 (1 sigma). The solubility of Au in bornite increased from 1,000 mu g/g at 500 degrees C to 1,800 mu g/g at 700 degrees C and with an increase in the log a(S2)(sys) of -11 to -6.0. The solubility of Au in ISS was evaluated as both a function of temperature and the a(S2)(sys) and increased from 300 mu g/g at 500 degrees C and low a(S2)(sys) to 4,000 mu g/g at 700 degrees C and high a(S2)(sys) . The a(S2)(sys) was found to exert a control on Au solubility as, at 700 degrees C, Au solubility in ISS increased from 1,100 to 4,000 mu g/g as the log a(S2)(sys) increased from -6.0 +/- 0.1 to 0.4 +/- 0.8 (1 sigma). The solubility of Au in ISS at 600 degrees C increased from 800 to 1,800 mu g/g as the log a(S2)(sys) increased from -8.3 +/- 0.7 to -2 +/- 1 (1 sigma). Gold in pyrrhotite ranged from 300-500 mu g/g and did not vary appreciably over the entire range of temperature and a(S2)(sys) studied. Nernst-style partition coefficients for gold between ISS and pyrrhotite, D-Au(ISS/Po), were calculated at 600 degrees C to be 3.6 +/- 1.9 (1 sigma) for a log a(S2)(sys) of -2 +/- 1 (1 sigma) and at 700 degrees C to be 7.3 +/- 4.7, 7.8 +/- 2.9, and 10 +/- 4 (1 sigma) at log a(S2)(sys) of -0.2 +/- 0.4, 0.3 +/- 0.4, and 0.4 +/- 0.8 (1 sigma), respectively. Partition coefficients for gold between bornite and ISS, D-Au(Bn/ISS), were calculated to be 2.5 +/- 1.8, 1.9 +/- 0.7, and 1.6 +/- 0.7 (1 sigma) for 500 degrees, 600 degrees, and 700 degrees C at log a(S2)(sys) of -11 +/- 1, -8.3 +/- 0.7, and -6.0 +/- 0.1 (1 sigma), respectively. In summary, the solubility of Au in bornite and ISS was found to increase with increasing temperature and the a(S2)(sys) , whereas Au in pyrrhotite did not vary over the range of temperature and a(S2)(sys) studied. Further, Au will partition preferentially into ISS relative to pyrrhotite in porphyry systems with an ISS + pyrrhotite assemblage and into bornite for the bornite + ISS assemblage. These data illustrate the importance of temperature and the a(S2)(sys) in controlling the solubility of Au in sulfide minerals and provide important constraints for exploration.

Fu R.R., Elkins-Tanton L.T. The fate of magmas in planetesimals and the retention of primitive chondritic crusts // Earth Planet. Sci. Lett. 2014. Vol. 390. P. 128–137.

High abundances of short-lived radiogenic isotopes in the early solar system led to interior melting and differentiation on many of the first planetesimals. Petrologic, isotopic, and paleomagnetic evidence suggests that some differentiated planetesimals retained primitive chondritic material. The preservation of a cold chondritic lid depends on whether deep melts are able to ascend and breach the chondritic crust. We evaluate the likelihood of melt ascent on a range of chondritic parent bodies. We find that, due to the efficient ascent of free volatiles in the gas and supercritical fluid phases at temperatures still below the solidus for silicates and metals, mobile silicate melts on planetesimals were likely volatile-depleted. By calculating the densities of such melts, we show that silicate melts likely breached crusts of enstatite chondrite compositions but did not ascend in the CV and CM parent bodies. Ordinary chondrite melts represent an intermediate case. These predictions are consistent with paleomagnetic results from CV and CM chondrites as well as spectral observations of large E-type asteroids.

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.

Ghiorso M.S., Gualda G.A.R. A method for estimating the activity of titania in magmatic liquids from the compositions of coexisting rhombohedral and cubic iron-titanium oxides // Contrib. Mineral. Petrol. 2013. Vol. 165, № 1. P. 73–81.

A method is described for estimating the activity of titania (TiO2) in a magmatic liquid from the compositions of coexisting cubic oxide (spinel) and rhombohedral oxide (ilmenite). These estimates are derived from the thermodynamic models of Ghiorso and Evans (Am J Sci 308:957-1039, 2008; see also Sack and Ghiorso in Contrib Mineral Petrol 106:474-505, 1991a; Am Mineral 76:827-847, 1991b) and may be computed self consistently along with temperature and oxygen fugacity for an assumed pressure. The method is applied to a collection of 729 naturally occurring oxide pairs from rhyolites and dacites. For this suite of oxides, values of titania activity relative to rutile saturation range from 0.3 to 0.9. Genetically related groups of oxide pairs display activity-temperature trends with negative slopes at higher activities (0.6-0.9) or positive slopes at lower activities (0.3-0.7). Thermodynamic analysis supports the assumption of two-oxide, liquid equilibrium for the former group, but suggests that such an interpretation for oxide sequences with positive activity-temperature trends may be problematic. Application of the estimation method to oxide pairs from the Shiveluch Volcano and the Bishop Tuff reveals that the former are consistent with having equilibrated with known matrix glass compositions, whereas the latter pairs are inconsistent with equilibration with pre-eruptive liquids trapped in quartz inclusions.

Giehl C., Marks M., Nowak M. Phase relations and liquid lines of descent of an iron-rich peralkaline phonolitic melt: an experimental study // Contrib. Mineral. Petrol. 2013. Vol. 165, № 2. P. 283–304.

We experimentally investigated the phase relations of a peralkaline phonolitic dyke rock associated with the Ilimaussaq plutonic complex (South Greenland). The extremely evolved and iron-rich composition (magnesium number = 2, alkalinity index = 1.44, FeO* = 12 wt%) may represent the parental magma of the Ilimaussaq complex. This dyke rock is therefore perfectly suited for performing phase-equilibrium experiments, since in contrast to the plutonic rocks of the complex, no major cumulate formation processes complicate defining a reasonable starting composition. Experiments were carried out in hydrothermal rapid-quench cold-seal pressure vessels at P = 100 MPa and T = 950-750 A degrees C. H2O contents ranging from anhydrous to H2O saturated (similar to 5 wt% H2O) and varying fO(2) (similar to Delta logFMQ -3 to +1; where FMQ represents the fayalite-magnetite-quartz oxygen buffer) were applied. Reduced and dry conditions lead to substantial crystallization of alkali feldspar, nepheline, hedenbergite-rich clinopyroxene, fayalite-rich olivine and minor amounts of ulvospinel-rich magnetite, which represent the phenocryst assemblage of the natural dyke rock. Oxidized and H2O-rich conditions, however, suppress the crystallization of olivine in favor of magnetite and clinopyroxene with less or no alkali feldspar and nepheline formation. Accordingly, combined low fO(2) and aH(2)O force the evolution of the residual melt toward decreasing SiO2, increasing FeO* and alkalinity index (up to 3.55). On the contrary, high fO(2) and aH(2)O produce residual melts with relatively low FeO*, high SiO2 and a relatively constant alkalinity index. We show that variations of aH(2)O and fO(2) lead to contrasting trends regarding the liquid lines of descent of iron-rich silica-undersaturated peralkaline compositions. Moreover, the increase in FeO* and alkalinity index (reduced and dry conditions) in the residual melt is an important prerequisite to stabilize late-magmatic minerals of the dyke rock, for example, aenigmatite (Na2Fe5TiSi6O20), coexisting with the most evolved melts at 750 A degrees C. Contrary to what might be expected, experiments with high aH(2)O and interlinked high fO(2) exhibit higher liquidus T's compared with experiments performed at low aH(2)O and fO(2) for experiments where magnetite is liquidus phase. This is because ulvospinel-poor magnetite crystallizes at higher fO(2) and has a higher melting point than ulvospinel-rich magnetite, which is favored at lower fO(2).

Hin R.C. et al. Experimental determination of the Si isotope fractionation factor between liquid metal and liquid silicate // Earth Planet. Sci. Lett. 2014. Vol. 387. P. 55–66.

The conditions of core formation and the abundances of the light elements in Earth's core remain debated. Silicon isotope fractionation provides a tool contributing to this subject. We present experimentally determined Si isotope fractionation factors between liquid metal and liquid silicate at 1450 degrees C and 1750 degrees C, which allow calibrating the temperature dependence of Si isotope fractionation. Experiments were performed in a centrifuging piston cylinder at 1 GPa, employing both graphite and MgO capsules. Tin was used to lower the melting temperature of the metal alloys for experiments performed at 1450 degrees C. Tests reveal that neither Sn nor C significantly affects Si isotope fractionation. An alkaline fusion technique was employed to dissolve silicate as well as metal phases prior to ion exchange chemistry and mass spectrometric analysis. The results show that metal is consistently enriched in light isotopes relative to the silicate, yielding average metal-silicate fractionation factors of -1.48 +/- 0.08 parts per thousand and -1.11 +/- 0.14 parts per thousand at 1450 degrees C and 1750 degrees C, respectively. The temperature dependence of equilibrium Si isotope fractionation between metal and silicate can thus be described as Delta Si-30(Metal-Silicate) = -4.42(+/- 0.05) x 10(6)/T-2. The Si isotope equilibrium fractionation is thus about 1.7 times smaller than previously proposed on the basis of experiments. A consequence of this smaller fractionation is that the calculated difference between the Si isotope composition of the bulk Earth and that of the bulk silicate Earth generated by core formation is smaller than previously thought. It is therefore increasingly difficult to match the Si isotope composition of the bulk silicate Earth with that of chondrites for metal-silicate equilibration temperatures above similar to 2500 K. This suggests that Si isotopes were more sensitive to the early stages of core formation when low oxygen fugacities allowed significant incorporation of Si into metal.

Huang R., Keppler H. Anhydrite stability and the effect of Ca on the behavior of sulfur in felsic magmas // Am. Miner. 2015. Vol. 100, № 1. P. 257–266.

The distribution of sulfur in the system Na2O-K2O-CaO-Al2O3-SiO2-H2O-S was investigated at 2 kbar, 750-950 degrees C, and oxygen fugacities ranging from the Co-CoO to the Re-ReO2, buffer. Anhydrite (CaSO4) crystallized in all the experiments conducted at oxidizing conditions (Ni-NiO + 0.5 to 1 and above). Under otherwise equal conditions, an inverse relationship between sulfur and CaO concentration was observed in melts coexisting with anhydrite, with the solubility product K = [CaO][SO3] being constant, where [CaO] and [SO3] are the molar fraction of CaO and SO3 in the quenched glasses. This suggests that anhydrite dissociates upon dissolution in the melt according to CaSO4anhydrite = Ca-melt(2+) + SO4melt2-. The solubility product strongly depends on temperature, with lnK = -(28 573 +/- 917)/T+ (11.26 +/- 0.80). This corresponds to an enthalpy of dissolution of Delta H-R = 237.5 +/- 7.6 kJ/mol. Under reducing conditions (Co-CoO and Ni-NiO buffer), CaO has no effect on the fluid/melt partition coefficient of sulfur D-s(fluid/melt). At 850 degrees C, 2 kbar partition coefficients were 519 +/- 30 at the Ni-NiO buffer and 516 +/- 11 at the Co-CoO buffer, for CaO contents in the melt up to 1 wt%. These data are virtually identical to those measured in the CaO-free haplogranite system under reducing conditions. However, under more oxidizing conditions, the fluid/melt partition coefficient of sulfur appeared to have increased somewhat in the presence of CaO. This increase may, however, also be related to the fact that the final melt compositions in these runs were distinctly peraluminous. Our data show that calcium has no effect on the degassing of sulfur at reducing conditions, but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite.

Jian W. et al. Mineralogy, Fluid Characteristics, and Re-Os Age of the Late Triassic Dahu Au-Mo Deposit, Xiaoqinling Region, Central China: Evidence for a Magmatic-Hydrothermal Origin // Econ. Geol. 2015. Vol. 110, № 1. P. 119–145.

The Dahu Au-Mo deposit is located in the Xiaoqinling region and belongs to the Qinling-Dabie orogen of central China. The quartz vein-style Dahu Au-Mo deposit (31 t Au, average grade: 4.7 g/t; 30,000 t Mo, average grade: 0.13 %) formed in four stages, i.e., an early quartz-K-feldspar stage (I), a pyrite-molybdenite stage (II), a sulfide-telluride-sulfosalt-gold stage (III), and a late carbonate-barite stage (IV). Abundant tellurides and sulfosalts occur in stage III: altaite, tellurobismuthite, buckhornite, hessite, petzite, calaverite, aikinite, kupcikite, lindstromite, salzburgite, wittichenite, and tetradymite. The system is characterized by carbono-aqueous fluids of low to moderate salinity and high oxygen fugacity. Total homogenization temperatures of the H2O-CO2 fluid inclusions in stage I and stage III quartz range from 230 degrees to 440 degrees C and 198 to 320 degrees C, respectively. The variation in CO2/H2O ratios and microthermometric data of the H2O-CO2 fluid inclusions results from a combination of fluid unmixing and sequential trapping of fluid inclusions, but also from postentrapment reequilibration. Abundant minerals are present as solid phases in H2O-CO2 fluid inclusions in stage I quartz: Cu1.6.5S, covellite, chalcopyrite, bornite, molybdenite, pyrite, colusite, anhydrite, and celestine. delta O-18(qartz) values of stage I quartz range from 10.2 to 12.0 parts per thousand, with calculated delta O-18(fluid) values ranging from 5.6 to 7.4 parts per thousand. The delta D values of fluid inclusion waters (thermal decrepitation) in stage I quartz range from -117 to -54 parts per thousand. The low and scattered delta D values reflect a mixture of ore-forming fluids trapped by the H2O-CO2 fluid inclusions at deep crustal levels and postmineralization fluids, possibly meteoric waters, trapped by secondary aqueous fluid inclusions at higher crustal levels during uplift of the Xiaoqinling core complex. Four molybdenite samples yield an Re-Os isochron age of 206.4 +/- 3.9 Ma (MSWD = 0.88), suggesting ore formation in the Late Triassic. Metal signature, mineral association, fluid characteristics, and isotope data of the Dahu deposit, together with the tectonomagmatic setting, imply that the ore-forming fluids were derived from an unexposed and oxidized Magmatic system, which likely stems from partial melting of enriched lithospheric mantle beneath the North China craton in a postcollisional extensional setting.

Jian W. et al. Mineralogy, Fluid Characteristics, and Re-Os Age of the Late Triassic Dahu Au-Mo Deposit, Xiaoqinling Region, Central China: Evidence for a Magmatic-Hydrothermal Origin // Econ. Geol. 2015. Vol. 110, № 1. P. 119–145.

The Dahu Au-Mo deposit is located in the Xiaoqinling region and belongs to the Qinling-Dabie orogen of central China. The quartz vein-style Dahu Au-Mo deposit (31 t Au, average grade: 4.7 g/t; 30,000 t Mo, average grade: 0.13 %) formed in four stages, i.e., an early quartz-K-feldspar stage (I), a pyrite-molybdenite stage (II), a sulfide-telluride-sulfosalt-gold stage (III), and a late carbonate-barite stage (IV). Abundant tellurides and sulfosalts occur in stage III: altaite, tellurobismuthite, buckhornite, hessite, petzite, calaverite, aikinite, kupcikite, lindstromite, salzburgite, wittichenite, and tetradymite. The system is characterized by carbono-aqueous fluids of low to moderate salinity and high oxygen fugacity. Total homogenization temperatures of the H2O-CO2 fluid inclusions in stage I and stage III quartz range from 230 degrees to 440 degrees C and 198 to 320 degrees C, respectively. The variation in CO2/H2O ratios and microthermometric data of the H2O-CO2 fluid inclusions results from a combination of fluid unmixing and sequential trapping of fluid inclusions, but also from postentrapment reequilibration. Abundant minerals are present as solid phases in H2O-CO2 fluid inclusions in stage I quartz: Cu1.6.5S, covellite, chalcopyrite, bornite, molybdenite, pyrite, colusite, anhydrite, and celestine. delta O-18(qartz) values of stage I quartz range from 10.2 to 12.0 parts per thousand, with calculated delta O-18(fluid) values ranging from 5.6 to 7.4 parts per thousand. The delta D values of fluid inclusion waters (thermal decrepitation) in stage I quartz range from -117 to -54 parts per thousand. The low and scattered delta D values reflect a mixture of ore-forming fluids trapped by the H2O-CO2 fluid inclusions at deep crustal levels and postmineralization fluids, possibly meteoric waters, trapped by secondary aqueous fluid inclusions at higher crustal levels during uplift of the Xiaoqinling core complex. Four molybdenite samples yield an Re-Os isochron age of 206.4 +/- 3.9 Ma (MSWD = 0.88), suggesting ore formation in the Late Triassic. Metal signature, mineral association, fluid characteristics, and isotope data of the Dahu deposit, together with the tectonomagmatic setting, imply that the ore-forming fluids were derived from an unexposed and oxidized Magmatic system, which likely stems from partial melting of enriched lithospheric mantle beneath the North China craton in a postcollisional extensional setting.

Kamenetsky V.S. et al. Noble metals potential of sulfide-saturated melts from the subcontinental lithosphere // Geology. 2013. Vol. 41, № 5. P. 575–578

The origin of vast accumulations of nickel and platinum in some continental magmatic rocks is still enigmatic, but ultimately linked to silicate-sulfide liquid immiscibility. The exact composition of pristine sulfide melts has proved extremely difficult to document and understand, largely because of the ephemeral, reactive qualities and small quantities of such melts. Here we report the discovery of Fe-Ni sulfide melt globules highly enriched in noble metals (Pt, Pd, Au; 120 ppm total platinum group elements [PGE]) within an unusual high-Mg andesitic glass (8.2 wt% MgO, 57.3 wt% SiO2) dredged from the southern Mid-Atlantic Ridge, near the Bouvet triple junction. The composition of this glass indicates derivation of its parental silicate melt from a garnet pyroxenite mantle source with pronounced "continental" isotopic (Pb, Sr, Nd, Hf, Os, O) signatures. We infer that the chemical properties of this high-temperature (1250 degrees C) melt, notably high SiO2 and Ni (310 ppm) contents, promoted sulfide saturation at low pressures in a purely oceanic setting, and propose that this unique example, with its likely origin in the continental lithospheric mantle, may be a useful analogue for incipient Ni-PGE-sulfide melt generation and magmatic PGE enrichment.

Keith M. et al. Effects of temperature, sulfur, and oxygen fugacity on the composition of sphalerite from submarine hydrothermal vents // Geology. 2014. Vol. 42, № 8. P. 699–702.

Experimental studies have shown that temperature, pressure, sulfur fugacity (f(S2)), and oxygen fugacity (f(O2)) influence the Fe content of sphalerite. We present compositional in situ data on sphalerite from submarine volcanic-hosted massive sulfide (VHMS) ores of hydrothermal vents from different plate tectonic settings and with variable host-rock compositions. Sphalerite from sediment-hosted vents has systematically higher S contents and Fe/Zn ratios than those of the sediment-starved vents, reflecting an influence of f(S2) and f(O2) on Fe partitioning between fluid and sphalerite. The Fe/Zn ratios of sphalerite from sediment-starved vent systems apparently increase systematically with the fluid temperatures of the corresponding vents. We conclude that the composition of sphalerite can be used to (1) distinguish between sediment-hosted and sediment-starved hydrothermal processes, and (2) estimate minimum fluid temperatures of sphalerite precipitation from inactive sediment-starved hydrothermal vent sites and fossil VHMS deposits.

Kerr M. et al. Preliminary Evaluation of Trace Hydrocarbon Speciation and Abundance as an Exploration Tool for Footwall-Style Sulfide Ores Associated with the Sudbury Igneous Complex, Ontario, Canada // Econ. Geol. 2015. Vol. 110, № 2. P. 531–556.

Deposits of Cu-Ni-platinum group elements (PGE) rich sulfides occur along the North Range footwall of the Sudbury Igneous Complex, Ontario, Canada. The deposits have been modified chemically, mineralogically, and texturally by multiple syn- to postmagmatic hydrothermal events and are hosted mainly within Sudbury breccia, a contact metamorphosed and hydrothermally altered impact breccia. The composition of C1 to C6 unsaturated and saturated hydrocarbons in bulk fluid inclusion volatiles in the matrix of the Sudbury breccia was investigated using in-line rock-crushing gas chromatography (GC) in order to compare the hydrocarbon composition of this rock type in breccia zones containing economic footwall sulfide deposits at the Morrison deposit (Levack mine, North Range, Sudbury, Ontario) with barren breccia zones. Trace hydrocarbons, possibly abiogenic in origin, occur throughout the Sudbury Igneous Complex footwall and country rocks investigated. However, there are differences in the composition and abundance of bulk hydrocarbons released from mineralized and barren Sudbury breccia when fluid inclusions are opened. Volatiles released from samples of Sudbury breccia from sulfide-mineralized and sulfide-barren environments showed the following: (1) higher average abundances of light saturated hydrocarbons (C1-C4) and an approximately 2 X higher total abundance of hydrocarbons (mol/g of rock basis) associated with samples from the mineralized study area, and (2) comparable average unsaturated hydrocarbon abundances in both settings, but a larger range in unsaturated hydrocarbon abundances in the mineralized study area. Differences in bulk hydrocarbon abundance and composition reflect differences in the abundance and hydrocarbon content of fluid inclusions trapped in the barren and mineralized Sudbury breccia zones. In addition, the compositional modification of circulating fluids by processes and conditions unique to the mineralized Sudbury breccia environment may have occurred prior to inclusion entrapment (e.g., modification by mineral catalysts, differences in temperature and oxygen fugacity). Preliminary spatial analysis of the hydrocarbon distribution within and surrounding the Morrison deposit shows that the total hydrocarbon abundance in the Sudbury breccia does not change with orebody proximity within a single host breccia zone. However, volatiles trapped in the Sudbury breccia matrix near the top of the footwall deposit, where it is physically connected to contact-style (Ni-Cu-PGE) ores, have elevated unsaturated hydrocarbon abundances (e.g., propene) compared to other parts of the same breccia zone distal to this zone of physical connection. Samples of the PGE-enriched Sudbury breccia and mineralized veins containing alteration assemblages characteristic of the footwall ore styles have higher unsaturated hydrocarbon abundances and unsaturated/saturated ratios compared to Sudbury breccia and vein samples that are PGE poor. Localized enrichments in unsaturated hydrocarbons in Sudbury breccia zones may be the result of specific ore minerals and metal complexes (involving the PGE and group VIII metals) that acted as catalytic agents, modifying the composition of initially light saturated hydrocarbon species prior to entrapment in fluid inclusions. To apply the analysis of hydrocarbon compositions in trapped fluid inclusions to discriminating mineralized from barren zones of Sudbury breccia, samples from targeted areas were compared to samples of barren Sudbury breccia ("background"). Although a large data set is presented here to establish these compositional fields, analysis of smaller sample subsets from each environment yields a statistically significant separation between the two environments. Total hydrocarbon abundance, C3/C1 ratios, and unsaturated/saturated hydrocarbon ratios are useful indicators of sulfide ore proximity and may help delineate regions enriched in PGE.

Liang X., Clarke D.R. Relation between thermolectric properties and phase equilibria in the ZnO-In2O3 binary system // Acta Mater. 2014. Vol. 63. P. 191–201.

The electrical conductivities, Seebeck coefficients and thermal conductivities across the ZnO-In2O3 binary system are reported and related to the phase compositions and microstructures present at 1150 and 1250 degrees C. The ZnO- In2O3 binary system is of particular interest as it contains a variety of different types of phases, superlattice (modular) phases, solid solutions, two-phase regions and crystallographic features. Throughout much of the phase diagram, the thermal conductivities are less than 2 W m(-1) K-1, being limited by both solid solution disorder and thermal resistance due to the presence of InO/ZnO interfaces. Across the phase diagram, irrespective of the actual phases, the materials behave at high temperatures (800 degrees C) as free-electron conductors with the Seebeck coefficient and electron conductivity satisfying the Jonker's relationship. In the two-phase regions of the phase diagram, the values of the power factor and figure of merit (ZT) are consistent with a simple law of mixtures, weighted according to the volume fractions of the two phases. Although the largest values of electrical conductivity and Seebeck coefficient occur over a range of composition centered at 40 m/o InO1.5, the maximum ZT and power factors are observed at k = 4 (33 m/o InO1.5). In contrast to the other modular phases at 1250 degrees C and below, this phase is hexagonal rather than rhombohedral.

Makino T. et al. CO2 absorption properties, densities, viscosities, and electrical conductivities of ethylimidazolium and 1-ethyl-3-methylimidazolium ionic liquids // Fluid Phase Equilib. 2014. Vol. 362. P. 300–306.

We have focused on a protic ionic liquid, ethylimidazolium bis(trifluoromethanesulfonyl)amide ([eimH][Tf2N]), and the analogous aprotic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([emim][Tf2N]). Densities, viscosities, and electrical conductivities of the two ionic liquids have been measured over the temperature range T=(273.15-363.15) K at atmospheric pressure. The densities of [eimH][Tf2N] and [emim][Tf2N] decrease with increasing temperature. The protic ionic liquid has the higher density (the smaller molar volume) than the aprotic one. The transport properties of the two ionic liquids show ordinary temperature dependencies. [eimH][Tf2N] has the higher viscosities (smaller electrical conductivities) than [emim][Tf2N]. Empirical Walden products indicate that [eimH]ITf2N] shows smaller conductivities than [emini][Tf2N] at certain viscosities. To investigate CO2 absorption properties of the ionic liquids, binary phase equilibria in CO2 + ionic liquid systems have been investigated under high pressures up to 6 MPa at T= (298.15, 313.15, 333.15)K. The solubilities of CO2 in [eimH][Tf2N] and [emim][Tf2N] show typical pressure dependencies in both mole fraction and molarity scales as physical absorbents. The mole fraction of CO2 in [eimH]ITf2N] is slightly smaller than that in [emim][Tf2N] under the conditions investigated, while the molarity of CO2 in [eimH][Tf2N] is comparable to that in [emim][Tf2N]. The molar volumes in ionic liquid phase almost linearly decrease with the mole fraction of CO2 in the present systems. The partial molar volume of CO2 in [eimH][Tf2N] at infinite dilution is almost same as that in [emim][Tf2N].

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.

Neill O.K. et al. Pre-eruptive magma mixing and crystal transfer revealed by phenocryst and microlite compositions in basaltic andesite from the 2008 eruption of Kasatochi Island volcano // Am. Miner. 2015. Vol. 100, № 4. P. 722–737.

populations of plagioclase phenocrysts. The first, volumetrically dominant population consists of oscillatory-zoned phenocrysts with an overall normal zonation trend toward comparatively sodic rims (An(55-65)), interrupted by dissolution features and spikes in calcium content (up to similar to An(85)). The second population consists of phenocrysts with highly calcic compositions (similar to An(90)). These phenocrysts contain sharp decreases in calcium content close to their rims (reaching as low as similar to An(60)), but are otherwise texturally and compositionally homogeneous. Groundmass plagioclase microlites are generally much more calcic than rims of the first phenocryst population, with more than 50% of measured microlites containing >An(80). Major, minor, and trace element concentrations of plagioclase microlites and phenocrysts indicate that oscillatory-zoned phenocrysts derived from cooler (800-950 degrees C), more silicic mixing magma, while unzoned, calcic phenocrysts were associated with hotter (900-1050 degrees C), mafic magma. The mixing of these magmas just prior to eruption, followed by decompression during the eruption itself created high effective undercoolings in the mafic end-member, and lead to the nucleation of high-An microlites. MgO and FeO concentrations of plagioclase microlites and high-An phenocryst rims (up to similar to 0.4 and similar to 1.3 wt%, respectively) provide further evidence for high mixing- and eruption-induced effective undercoolings.

Ripley E.M., Li C. Sulfide Saturation in Mafic Magmas: Is External Sulfur Required for Magmatic Ni-Cu-(PGE) Ore Genesis? // Econ. Geol. 2013. Vol. 108, № 1. P. 45–58.

The importance of externally derived sulfur in the genesis of sulfide-rich, magmatic Ni-Cu-(platinum group element [PGE]) deposits remains a key, yet unresolved, issue. Calculations utilizing a variety of mafic magma types indicate that, in general, sulfide saturation by fractional crystallization occurs after Ni has been depleted due to olivine crystallization. Cu- and PGE-rich layers. may form during relatively later stages of closed-system crystallization, but unless the collection of the cotectic proportion of immiscible sulfide is extremely efficient, the mass of sulfide is too small to produce an economic deposit. We show that there are numerous processes that may lead to early sulfide saturation in mafic/ultramafic magmas. Contamination of mantle-derived magmas by siliceous country rocks or their partial melts will lower the sulfur content needed to induce sulfide liquid saturation, typically by amounts ranging from 200 to 700 ppm. The mixing of magmas, particularly if the result is to lower the liquidus temperature of the mixed magma, may also lower the sulfur content needed to attain sulfide saturation by similar amounts. An increase in magma fo(2) related to the addition of volatiles such as H2O and CO2 is less effective in decreasing the sulfur concentration needed to achieve sulfide liquid saturation. Contamination processes that lead to an increase in the activity of SiO2 in the melt, and hence may promote orthopyroxene rather than olivine crystallization, aid in generating relative Ni enrichment in remaining liquid as a result of the lower D-Ni (mineral-melt) value of orthopyroxene relative to olivine. Although contamination and magma mixing may produce early sulfide saturation without the addition of externally derived sulfur, Ni-rich sulfide deposits can form in such cases only from large-volume, open systems, where the efficiency of sulfide collection is high. No matter what the liquidus minerals may be, without the addition of country rock-derived sulfur, the mass of sulfide necessary to generate economic Ni-Cu-(PGE) concentrations requires efficient sulfide collection from large, but not necessarily unrealistic, volumes of magma. Small deposits (4-30 Mt of sulfide) may form from the collection of cotectic proportions of sulfide from less than 50 km(3) of magma. Larger deposits such as those at Noril'sk could involve more than 200 km(3) of magma; this volume of magma is not unreasonable, particularly in rift/plume-related settings. Despite such possibilities, sulfur isotope data clearly indicate that externally derived sulfur has been involved in the formation of many large deposits, and that collection of mantle-derived sulfide in sufficient quantities to produce orebodies is a rare process. We propose that magmatic Ni-Cu-(PGE) sulfide ore formation normally requires significant sulfide supersaturation, and that the addition of sulfur derived from xenoliths is the most viable mechanism for producing sulfide well above the cotectic proportion in mafic/ultramafic magmas.

Roda-Robles E. et al. Tourmaline as a petrogenetic monitor of the origin and evolution of the Berry-Havey pegmatite (Maine, USA) // Am. Miner. 2015. Vol. 100, № 1. P. 95–109.

The Berry-Havey pegmatite (Oxford pegmatite field, Androscoggin County, Maine, U.S.A.), enriched in Li, F, B, Be, and P, is intruded in hornblende-rich amphibolite, with minor biotite or diopside. The pegmatite has a complex internal structure, with four texturally and compositionally different zones that show an increasing degree of evolution inward: wall zone, intermediate zone, core margin, and core zone. The main minerals are quartz, feldspars, Al-micas, tourmaline, with minor Fe-micas, garnet, beryl, amblygonite-montebrasite, Fe-Mn phosphates, and apatite. Tourmaline is present in all zones of the pegmatite, showing different textures: black anhedral crystals in the wall and intermediate zones; black prisms of up to 40 cm in length in the intermediate zone; black tapered prisms, surrounded by a pseudo-graphic intergrowth of quartz or albite with black +/- green/bluish tourmaline, and constituting a continuous layer under the core zone; multicolored and "watermelon" zoned crystals in the core zone; and gemmy deep green and color-zoned "watermelon" tourmaline prisms, up to 15 cm length, inside the pockets. A complete chemical evolution from Mg-rich schorl in the wall zone to elbaite with an important deprotonation in the pockets inside the core zone is observed. The most plausible exchange vectors for this chemical evolution are FeMg-1, (AlO)-Al-Y-O-W[R-Y(2+W)(OH)](-1) and Al[X](X)(R2+Na)(-1) (where R2+ = Fe2++Mg2++Mn2++Zn2+), for the tourmalines from the wall and intermediate zones. In the core margin, tourmaline composition evolves from schorl toward Li-rich species through the substitution ((Y)AL(Y)Li(Y)R(-2)(2+)). Later, during the crystallization of the core zone, this exchange vector combined with the substitution ([X] (Al0.5Na-1Li-0.5)-Al-Y-Na-X-Li-Y). Finally, the gemmy tourmalines from the pockets show a deprotonation related to the exchange vector (Y)AL(W)O(2)(Y)L(i-1)W(OH)(-2) and may be classified as darrellhenryite. These substitutions may reflect an increase in oxygen fugacity and a decrease in Li and F related to the crystallization of lepidolite and amblygonite-montebrasite in the core zone adjacent to or within the pockets. The crystallization of these minerals would reduce the availability of Li and F for the very latest tourmaline crystals, growing inside the pockets, where the deprotonation becomes important. Chemical and textural variation in tourmaline is consistent with a fractional crystallization process for the internal evolution of the Berry-Havey pegmatite. Crystallization of the tourmaline layer under the core zone may be related to the exsolution of the fluid phase implied in the formation of pockets.

Satake W., Mikouchi T., Miyamoto M. Redox states of thirteen shergottites as inferred from iron micro X-ray absorption near edge structure of maskelynite // Geochem. J. 2014. Vol. 48, № 1. P. 85–98.

We used synchrotron radiation Fe micro-XANES (X-ray Absorption Near Edge Structure) analysis to determine the iron valence of maskelynite (shocked-plagioclase glass) in thirteen shergottites, and we compared the Fe3+-Fe2+ peak-intensity ratios for maskelynite in the shergottites in order to compare the redox states of the shergottites and discuss the evolution of the Martian crust and mantle. We analyzed two geochemically depleted (Dar al Gani 476 and Dhofar 019), four geochemically intermediate (EETA 79001 lithology A, ALH 77005, LEW 88516, and NWA 5029), and seven geochemically enriched (NWA 856, Zagami, Shergotty, RBT 04262, NWA 4468, NWA 1068, and LAR 06319) shergottite samples. The Fe3+-Fe2+ peak-intensity ratios for maskelynite in the depleted, intermediate, and enriched shergottites were 0.39-0.49, 0.13-0.66, and 0.40-0.81, respectively. LAR 06319, NWA 856, NWA 1068, Zagami, and Shergotty, whose log fO(2)s were higher than QFM-2.0. RBT 04262 showed the highest Fe3+-Fe2+ peak-intensity ratios for maskelynite in the enriched shergottites; therefore, RBT 04262 might have crystallized under a more oxidized environment than the other enriched shergottites. Similarly, NWA 4468 was estimated to have crystallized at log fO(2) higher than QFM-2.3. This is the first report showing that RBT 04262 and NWA 4468 are oxidized samples because no oxybarometer measurements had previously been performed on these samples. We showed that XANES analysis can be applied to any maskelynite-bearing samples in order to discuss the difference between the redox states of Martian meteorites. We also revealed that the Fe3+-Fe2+ peak-intensity ratios for maskelynite in the intermediate shergottites show a very wide range (0.13-0.66), exceeding the ratios obtained for maskelynite in the depleted and enriched shergottites. When previously reported geochemical characteristics such as the epsilon Nd and crystallization ages are included, the wide range of the Fe3+-Fe2+ peak-intensity ratios obtained for maskelynite in the intermediate shergottites does not support the model that proposes that two distinct mantle reservoirs mix during melting. The results of this study reveal that the redox state of the source of the enriched shergottites is heterogeneous.

Shiryaev A.A., Gaillard F. Local redox buffering by carbon at low pressures and the formation of moissanite - natural SiC // Eur. J. Mineral. 2014. Vol. 26, № 1. P. 53–59.

Grains of natural SiC, moissanite, are encountered in various geological settings. According to thermodynamic calculations and high-pressure experiments, SiC formation requires very reducing conditions, approx. 6-10 orders of magnitude in fO(2) more reducing than the present-day mantle redox state. SiC occurrences have motivated several studies but the required extremely reducing conditions remain a major inconsistency that has not been solved. It is shown here that such reducing conditions can be achieved during the ultimate steps of ascent of carbon-saturated melts, when pressure is lower than 100 bars. At these conditions, the redox buffering by carbon can impose fO(2) similar to IW-6. Conditions favorable to SiC growth can therefore be reached around carbonaceous grains during the shallow emplacement of silicate melts or kimberlites and do not necessarily imply extremely localized oxygen-depleted regions in the mantle. Such reduced conditions can also explain the presence of elemental Si and ironcarbide inclusions in association with moissanite grains.

Sigmarsson O. et al. Formation of U-depleted rhyolite from a basanite at El Hierro, Canary Islands // Contrib. Mineral. Petrol. 2013. Vol. 165, № 3. P. 601–622.

Phonolite and trachyte are the felsic magmas of the alkaline magma suites, which characterize the Canary Islands. The October 2011 submarine eruption off El Hierro, the westernmost island, nevertheless, produced a small volume of rhyolitic magma. The rhyolite occurred as highly vesicular, white coloured pumices enveloped in and mingled with darker coloured basanitic pumice. The basanitic pumice is relatively crystal poor with a few euhedral olivines (mostly Fo(77-79)), clinopyroxenes and Fe-rich spinels, whereas very rare olivine of same composition is found together with equally rare Fe-sulphide and FeTi-rich oxides in the rhyolite. The Fe-Mg exchange equilibrium in the oxides permits to calculate an equilibrium temperature of 970-890 A degrees C for the rhyolite, in agreement with quartz-melt equilibrium at ca. 930 A degrees C. A striking mineralogical feature of the rhyolite is the presence of rounded to contorted grains of milky quartz, which are xenocrysts incorporated and partly dissolved into the magma. Analyses of residual volatile concentrations in the glasses show that the rhyolite melt was highly degassed, whereas the basanitic glass still has important halogen concentrations. Trace element patterns of the mafic glasses and their elevated incompatible element concentrations are typical of the western Canary Island basanites. In contrast, the trace element composition of the rhyolite shows surprisingly low concentrations for all elements except the most incompatible ones (e.g. Rb, Ba, K and Th). All other measured LILE, HFSE and REE have significantly lower concentration than the basanitic counterpart that can be explained by fractionation of accessory phases (1 % apatite, 1 % sphene and 0.1 % zircon). Surprisingly, low U concentration is presumably related to elevated oxygen fugacity in the rhyolite, causing U to be in a hexavalent state, and fluxing of F-rich gas leading to volatilization of UF6, known to emanate at low temperature. The results suggest that a gas-rich basanitic melt remobilized a small volume of stagnant rhyolitic melt formed by incorporation of approximately 10 % quartz-rich sediment into a late differentiate of trachytic composition. Sediments at the interface of an old oceanic crust adjacent to a continental shield and younger volcanic island are likely to act as magma traps were sediment assimilation may alter the mantle-derived magma composition. Quartz assimilation thus explains the production of rhyolite magma in a volcanic island characterized by an alkaline magma series from primitive basanites to trachytes.

Wade J., Wood B.J., Norris C.A. The oxidation state of tungsten in silicate melt at high pressures and temperatures // Chem. Geol. 2013. Vol. 335. P. 189–193.

Although at 1 atm pressure the oxidation state of W in silicate melts is 6 + at oxygen fugacities from air down to several logf(O2) units below Fe-FeO (IW) equilibrium, Cottrell et al. (2009) suggested that, at pressures above 6 GPa, W becomes predominantly 4 + in this oxygen fugacity range. Wade and Wood (2005), using a similar, but expanded metal-silicate partitioning dataset found, however, no evidence for an oxidation state change. In order to resolve the issue we collected tungsten L-3 edge XANES spectra of a series of synthetic tungsten- bearing glass standards and of silicates from a range of high-pressure (1.5 to 25 GPa) metal/silicate partitioning experiments. Glass standards were made at 1 atm pressure and equilibrated at oxygen fugacities spanning a range from approximately 5.5 log units below the Fe-FeO buffer (IW-5.5) to Air. Metal-silicate partitioning experiments were performed at oxygen fugacities between IW-6.2 and IW-1 and at pressures between 1.5 and 25 GPa. At low pressures and oxygen fugacities above IW-3.5, W exists in the silicate melt almost exclusively as W6+ (identical L-3-edge energy to WO3) with the progressive reduction to W4+ completed by about IW-6. The XANES spectra of W from experiments at 6, 7 and 25 GPa are completely consistent with those from 1 atm and 1.5 GPa experiments and with that of WO3. We conclude that there is no change of oxidation state with increasing pressure to 25 GPa and that modelling of the oxygen-fugacity dependence of core formation requires use of a + 6 oxidation state of W.

Wallace P.J., Kamenetsky V.S., Cervantes P. Melt inclusion CO2 contents, pressures of olivine crystallization, and the problem of shrinkage bubbles // Am. Miner. 2015. Vol. 100, № 4. P. 787–794.

Wang R. et al. Increasing Magmatic Oxidation State from Paleocene to Miocene in the Eastern Gangdese Belt, Tibet: Implication for Collision-Related Porphyry Cu-Mo +/- Au Mineralization // Econ. Geol. 2014. Vol. 109, № 7. P. 1943–1965.

In the Gangdese belt of southern Tibet, Paleocene-Eocene magmas record the final stage of Neo-Tethyan subduction and are associated with few economic porphyry deposits. In contrast, magmas formed during later stages of the India-Asia collision in the Oligo-Miocene are associated with several large porphyry Cu-Mo +/- Au deposits, especially in the eastern part of the belt (similar to 89 degrees E-93 degrees E). In a previous study, we showed that these Oligocene-Miocene magmas were more hydrous than the earlier Paleocene-Eocene magmas. In this study, we show that the later magmas were also more oxidized. Paleocene-Eocene rocks from the eastern Gangdese belt are characterized by low zircon Ce4+/Ce3+ ratios (mostly <50; 6.0-66.8; average = 25.7 +/- 18.4, n = 26) and low to moderate Delta FMQ values (-1.2 to +0.8, average = 0.2 +/- 0.8, n = 5; estimated from ilmenite-magnetite mineral pairs). In comparison, Miocene igneous rocks from the eastern Gangdese belt show higher zircon Ce4+/Ce3+ ratios (mostly >50; 32.3-141.9, average = 74.3 +/- 30.1, n = 33) and higher f(O2) values (Delta FMQ 0.8-2.9, average = 1.8 +/- 0.8, n = 6; estimated from magnetite-ilmenite pairs). Estimates of magmatic oxidation state from amphibole compositions also show an increase from Delta FMQ 1.2 to 2.1 (average = 1.6 +/- 0.2, n = 40) in the Paleocene-Eocene to 2.0 to 2.8 (average = 2.5 +/- 0.2, n = 58) in the Miocene. Sparse whole-rock Fe3+/Fe2+ ratios show the same general trend. The amphibole results are systematically shifted to higher Delta FMQ compared to data from magnetite-ilmenite pairs, but their trend is internally consistent. The higher oxidation states (and water contents) of Miocene igneous rocks from the eastern Gangdese belt may explain their unique association with large porphyry deposits in Tibet, because it has been shown from other studies that the potential for hydrous calc-alkaline magmas to transport Au is maximized near Delta FMQ 1.0, and Cu at higher f(O2) (Delta FMQ > 1.0). In comparison, the somewhat less oxidized and less hydrous Paleocene-Eocene magmas would have been less fertile for the formation of such deposits. We suggest that these differences reflect the tectonomagmatic evolution of the Cenozoic Gangdese collisional orogen, from early collision-related magmatism in the Paleocene-Eocene to late collisional magmatism in the Miocene. Asthenospheric upwelling following slab breakoff in the Miocene caused interaction between mantle-derived magmas and previously subduction modified Tibetan lithosphere. The resultant evolved magmas had high oxidation states and water contents, which are favorable properties for the subsequent formation of magmatic-hydrothermal porphyry Cu-Mo +/- Au deposits.

Xiaohu H. et al. Enrichment of Platinum-group Elements (PGE) and Re-Os Isotopic Tracing for Porphyry Copper (Gold) Deposits // Acta Geol. Sin.-Engl. Ed. 2014. Vol. 88, № 4. P. 1288–1309.

Platinum-group elements (PGE) in PGE-rich porphyry copper (gold) deposits are mainly Pt and Pd, whereas the concentrations of other PGE (Ru, Rh, Os, Ir) are significantly low. Moreover, Pt and Pd mainly exist in sulfides in the forms of crystal lattice or tiny platinum-group mineral (PGM) inclusions. The present data show that there is a positive relationship between Pt and Pd concentrations and Cu (Au) in porphyry copper (gold) deposits. The comparison of chondrite-normalized PGE distribution patterns between the ore-bearing porphyry intrusions and ore-barren porphyry intrusions in arc setting, 187Os/188Os, 87Sr/86Sr and S isotopes for porphyry copper (gold) deposits shows that PGEs were mainly derived from the mantle, and fluids from subduction zones devoted trivial PGE to the magma. The porphyry copper (gold) deposits associated with subducted events are most probably enriched in PGE, whereas those related to crustal thickening, lithospheric delamination or underplating rarely concentrate PGE. The osmium isotopic compositions in porphyry copper (gold) deposits reveal that (187Os/188Os)i values are highly variable and not lower than those of primitive upper mantle (PUM) and mantle peridotite, however, osmium concentrations are commonly lower than mantle peridotite, suggesting that parental magmas of some porphyry intrusions had experienced crustal contamination during magma evolution. Experimental investigations have proved that PGE exist in the forms of Cl- and HS- complexes during transportation and migration of the ore-forming fluids. This paper summarizes previous studies including crucial controlling factors and mechanisms for PGE enrichment, and points out that the mantle-derived magmas parental to porphyry intrusions are the prerequisite for PGE enrichment in porphyry copper (gold) deposits. Favorable physical and chemical conditions (including salinity, temperature, pressure, pH, and oxygen fugacity) in hydrothermal fluids crucially control the PGE enrichment, and sulfur concentrations of melts play important roles in this process as well.

Xu S., Shim S.-H., Morgan D. Origin of Fe3+ in Fe-containing, Al-free mantle silicate perovskite // Earth Planet. Sci. Lett. 2015. Vol. 409. P. 319–328.

We have studied the ferrous (Fe2+) and ferric (Fe3+) iron concentrations in Al-free Fe containing Mg-silicate perovskite (Mg-Pv) at pressure (P), temperature (T), and oxygen fugacity (fO(2)) conditions related to the lower mantle using a thermodynamic model based on ab initio calculations. We consider the oxidation reaction and the charge disproportionation reaction, both of which can produce Fe3+ in Mg-Pv. The model shows qualitatively good agreement with available experimental data on Fe3+/Sigma Fe (Sigma Fe = total Fe in system), spin transitions, and equations of state. We predict that under lower-mantle conditions Fe3+/Sigma Fe determined by the charge disproportionation is estimated to be 0.01-0.07 in Al-free Mg-Pv, suggesting that low Al Mg-Pv in the uppermost pyrolitic mantle (where majoritic garnet contains most of the Al) and in the harzburgitic heterogeneities throughout the lower mantle contains very little Fe3+. We find that the volume reduction by the spin transition of the B-site Fe3+ leads to a minimum Fe3+/Sigma Fe in Mg-Pv at mid-mantle pressures. The model shows that configurational entropy is a key driving force to create Fe3+ and therefore Fe3+ content is highly temperature sensitive. The temperature sensitivity may lead to a maximum Fe3+/Sigma Fe in Mg-Pv in warm regions at the core-mantle boundary region, such as Large Low Shear Velocity Provinces (LLSVPs), potentially altering the physical (e.g., bulk modulus) and transport (e.g., thermal and electrical conductivities) properties of the heterogeneities.

Yamamoto J. et al. Melt-rich lithosphere-asthenosphere boundary inferred from petit-spot volcanoes // Geology. 2014. Vol. 42, № 11. P. 967–970.

Young basaltic knolls have been discovered on the old oceanic lithosphere, namely petit-spot volcanoes. Based on their geochemical signatures, they have presumably originated from partial melts in the asthenosphere. However, there is no direct information on the depth provenance of petit-spot formation. Here we report new geothermobarometric data of rare mantle xenoliths discovered from petit-spot lavas exhibiting a geotherm much hotter than expected for the ca. 140 Ma seafloor on which petit-spots were formed. Such an anomalously hot geotherm indicates that melt porosity around the lithosphere-asthenosphere boundary (LAB) must be as high as a few percent. Such high melt porosity would be possible by continuous melt replenishment. Excess pressure induced by the outer-rise topography enables horizontal melt migration along the LAB and sustains a continuous melt supply to petit-spot magmatism. Given the general age-depth relationship of ocean basins, a melt-rich boundary region could also be a global feature.

Yoo B.C., White N.C. Mineralogy, fluid inclusion and stable isotope constraints on the genesis of the Namseong Au-Ag deposit, Republic of Korea // Geochem. J. 2013. Vol. 47, № 3. P. 285–307.

The Namseong gold and silver deposit is located in the Seolcheon metallogenic province, one of the most important gold production areas in the Republic of Korea. It consists of three gold and silver-bearing quartz veins that fill fractures oriented NW along fault zones in Triassic porphyritic granite. The gold and silver-bearing quartz veins are simple and consist of only one mineralization stage on basis of vein mineralogy and paragenesis. Coarse-grained quartz is found in mainly comb, and partially cockade and cavity-filling textures throughout most of the veins. Wall-rock alteration minerals include sericite, minor pyrite and chlorite. Ore minerals deposited along with electrum include pyrite, sphalerite, chalcopyrite, galena, pyrargyrite, argentite and native silver. Its mineralization age (78.2 +/- 1.7 Ma) determined on sericite from wall-rock alteration indicates that the gold and silver mineralization was synchronous with Cretaceous igneous activity. Petrographic examination of textural relationships among sulfides, fluid inclusions, and quartz from one stage shows the genetic relationships between Au-Ag deposition and fluid entrapment. Early wall-rock alteration in one stage was produced and sulfides were deposited from H2O-NaCl-CO2 fluids (260-1,700 bar, average 1,000 bar) with Th-total values of 250 degrees C to 380 degrees C and salinities less than about 4 wt.% NaCl. The late sulfides and electrum in one stage were deposited from H2O-NaCl fluids (100 bar) with Th-total values of 195 degrees C to 331 degrees C and salinities less than about 7 wt.% NaCl. The H2O-NaCl fluids either evolved through unmixing of H2O-NaCl-CO2 fluids or through mixing with circulating meteoric waters as a result of uplift or unloading during mineralization, or both. The deposition of electrum and silver minerals was caused by a decrease in sulfur fugacity/aH(2)S/aCl, oxygen fugacity and temperature during wallrock alteration, cooling and dilution produced by mixing of the saline aqueous fluids with meteoric water. The calculated sulfur isotope compositions of hydrothermal fluids from the Namseong deposit (delta S-34(H2S) = 3.7 parts per thousand to 7.2 parts per thousand) indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks. The calculated and measured oxygen and hydrogen isotope compositions of the ore-forming fluids (delta O-18(H2O) = -2.2 parts per thousand to 1.6 parts per thousand, delta D = -83 parts per thousand to -64 parts per thousand) indicate that the fluids were derived from meteoric water and evolved by mixing with local meteoric water and by limited water-rock exchange during mineralization in uplift zones.

Zhukova I. et al. The effect of silica activity on the diffusion of Ni and Co in olivine // Contrib. Mineral. Petrol. 2014. Vol. 168, № 2. P. 1029.

The diffusion of Ni and Co was measured at atmospheric pressure in synthetic monocrystalline forsterite (Mg2SiO4) from 1,200 to 1,500 degrees C at the oxygen fugacity of air, along [ 100], with the activities of SiO2 and MgO defined by either forsterite + periclase (fo + per buffer) or forsterite + protoenstatite (fo + en buffer). Diffusion profiles were measured by three methods: laserablation inductively-coupled-plasma mass-spectrometry, nano-scale secondary ion mass spectrometry and electron microprobe, with good agreement between the methods. For both Ni and Co, the diffusion rates in protoenstatite-buffered experiments are an order of magnitude faster than in the periclase-buffered experiments at a given temperature. The diffusion coefficients D-M (M = Ni or Co) for the combined data set can be fitted to the equation: log D-M in m(2) s(-1) = -6.77(+/- 0.33) + Delta E-a(M)/RT + 2/3 log a(SiO2) with E-a(Ni) = -284.3 kJ mol(-1) and E-a(Co) = -275.9 kJ mol(-1), with an uncertainty of +/- 10.2 kJ mol(-1). This equation fits the data (24 experiments) to +/- 0.1 in log D-M. The dependence of diffusion on a(SiO2) is in agreement with a point-defect model in which Mg-site vacancies are charge-balanced by Si interstitials. Comparative experiments with San Carlos olivine of composition Mg1.8Fe0.2SiO4 at 1,300 degrees C give a slightly small dependence on aSiO(2), with D proportional to (a(SiO2)(0.5)), presumably because the Mg-site vacancies increase with incorporation of Fe3+ in the Fe-bearing olivines. However, the dependence on fO(2) is small, with D proportional to (fO(2))(0.12 +/- 0.12). These results show the necessity of constraining the chemical potentials of all the stoichiometric components of a phase when designing diffusion experiments. Similarly, the chemical potentials of the major-element components must be taken into account when applying experimental data to natural minerals to constrain the rates of geological processes. For example, the diffusion of divalent elements in olivine from low SiO2 magmas, such as kimberlites or carbonatites, will be an order of magnitude slower than in olivine from high SiO2 magmas, such as tholeiitic basalts, at equal temperatures and fO(2).

Авдонина И.С., Прибавкин С.В. Магматический ангидрит и апатит в эпидотсодержащих порфирах Среднего Урала // Литосфера. 2013. № 4. С. 62-72.

Аптикаева О.И. Миграция очагов слабых землетрясений Гармского района и вариации скорости вращения Земли // Вопросы инженерной сейсмологии. 2013. Т. 40. № 3. С. 54-63.

Рассматриваются пространственно-временные вариации локализации очагов землетрясений с H ? 14 км на территории Гармского района. Неравномерность распределения таких землетрясений связывается с блоковым строением: в ослабленных зонах их больше, чем в блоках. Выделены три ослабленные зоны, характеризующиеся повышенной активностью заглубленной сейсмичности, которая варьирует во времени, увеличиваясь перед землетрясениями. Характер временных вариаций распределения очагов землетрясений с глубиной позволяет высказать предположение о существовании связи между скоростью вращения Земли и активностью заглубленной сейсмичности.

Арутюнян А.В. Геофлюиды, нефть, вода, кимберлиты и алмаз: генезис, миграция и аккумуляция в земной коре (на примере Малого Кавказа) // Глубинная нефть. 2013. Т. 1. № 3. С. 317-327.

На предложенной модели состава, строения и эволюции земной коры Малого Кавказа, рассмотрены следующие взаимосвязанные проблематичные вопросы: 1. Вследствие закрытия океанической коры Тетис происходило погружение всего комплекса пород, в том числе серпентинизированных ультрабазитов и серпентинитов третьего слоя коры. Вследствие повышения давления и температуры на различных глубинах коры происходила дегидратация серпентинитов и серпентинизированных ультрабазитов. Происходило отделение флюидов различного состава, в том числе водородосодержащих компонентов, которые в этих условиях встречаются с углеродосодержащими компонентами. Химические реакции между этими приводит к образованию неорганических углеводородов, которые вместе с флюидами, в смешанном состоянии, по глубинным разломам мигрируют в верхние горизонты коры и накапливаются как в разломных зонах, так и в трещиноватых породах фундамента и в примыкающих к разломам слоях, обладающими коллекторскими свойствами. Вследствие растворения солей на различных глубинах, в верхних горизонтах коры появляются соленые воды. При миграции, на различных глубинах, постепенно происходит гравитационная дифференциация и формирование пластов соляных вод и нефтегазоносных структур. 2. Из предложенной модели эволюции земной коры следует, что вследствие погружения осадочного комплекса океанической коры, происходила их метаморфизация, выжимание связанных вод и формирование углеводородов из органического материала, содержащегося в осадочном комплексе. 3. Таким образом, согласно предложенной концепции вода и нефть имеют единый источник образования и единый путь миграции, и дифференциации. Так как в природе нефть и вода являются самыми распространенными и употребляемыми человеком, предлагается считать их сестрами близнецами. 4. Согласно опытным данным при высоких термобарических параметрах, процесс дегидратации сопровождается одновременным плавлением пород (следовательно, в коре формируются магматические очаги in situ). Этим можно объяснить наличие углеводородов в изверженных продуктах вулканов и в порах, трещинах магматических пород. 5. Опыты показывают, что процесс дегидратации сопровождается скачкообразными изменениями объемов, доходящими иногда до 30%, которые естественно должны привести к сейсмическим явлениям различной интенсивности. 6. Имеются данные о существовании в земной коре платформ слоев, характеризующиеся низкими скоростями, повышенной электропроводностью и высокой намагниченностью. Серпентинизированные ультрабазиты, как породы, слагающие средний слой коры платформ, удовлетворяют сейсмической, электрической и магнитной моделям. Следовательно, можно полагать, что вышеуказанные все процессы (генезис УВ, наличие магматических очагов под месторождениями УВ, слабые сейсмические явления) обусловлены с дегидратацией серпентинизированных пород. 7. Реликты океанической коры в континентальной коре могут находиться на различных глубинах. При дегидратации реликтов на небольшой глубине, взрывы вместе с остальными компонентами могут образовать алмазоносные кимберлитовые трубки.

Голубкова А.Б., Носова А.А., Ларионова Ю.О. Мегакристы Mg-ильменита из кимберлитов Архангельской провинции (Россия): генезис и взаимодействие с кимберлитовым расплавом и посткимберлитовым флюидом // Геохимия. 2013. № 5. С. 396-427.

Были изучены мегакристы Mg-ильменита из кимберлитов Кепинского поля (трубка Котуга и силл 748д) и мантийных ксенолитов из трубки им. В.П. Гриба Архангельской алмазоносной провинции (ААП). Свидетельством генетической близости мегакристов Mg-ильменита и кимберлитов служат данные о RbSr возрасте флогопита из ксенолита ильменитового клинопироксенита (384 млн. лет), который близок к возрасту вмещающих кимберлитов тр. Гриба (372 ± 8 млн. лет, RbSr, Шевченко и др., 2004). На то же указывает и полученная нами оценка возраста кимберлитов трубки Котуга (378 ± 25 млн. лет). Микроэлементный и изотопный (Sr, Nd, O) состав мегакристов также свидетельствует об их генетической связи с кимберлитами. Соответствие изотопного состава Sr и Nd мегакристов (Mg-ильмениты из кимберлитов имеют 87Sr/86Sr(t) = 0.70500.7063, Nd(384) = +1.7, +1.8, из ксенолита ильменит-гранатового клинопироксенита имеет 87Sr/86St(t) = 0.7049, ? Nd(384) = +3.5) изотопному составу вмещающих кимберлитов рассматривается как довод в пользу генетического родства мегакристов Mg-ильменита и кимберлитового расплава. Изотопные составы кислорода в ильменитах ( ?18O = 3.84.5), с учетом изотопного фракционирования ильменит-расплав, также свидетельствуют об их происхождении из расплава.

Гусейнов А.А. Взаимосвязь химического состава с ионной электропроводностью монтмориллонитов // Труды Института геологии Дагестанского научного центра РАН. 2014. № 63. С. 284-288.

"Статье в плане комплексного подхода к изучению глинистых минералов, входящих в состав почв сухого климата, исследована зависимость между удельной электропроводностью и содержанием главных петрогенных элементов Si, Al, Fe, Mg, K, Na, Ti в монтмориллонитах. Дано объяснение физической природе стимулирующей электропроводность этих минералов роли атомов железа, калия, натрия, титана и уменьшающей электропроводность роли атомов алюминия, кремния и магния. "

Калмыков Г.А., Балушкина Н.С., Белохин В.С., Билибин С.И., Дьяконова Т.Ф., Исакова Т.Г. Пустотное пространство пород баженовской свиты и насыщающие его флюиды // Недропользование XXI век. 2015. № 1 (51). С. 64-71.

Февраль 2015 63 Проведенные авторами анализы выявили, что емкостное пространство пород баженовской свиты определяется несколькими типами пустот. В пустотном пространстве баженовской свиты и в нижней переходной зоне присутствуют подвижные и физически связанные углеводороды. Пористость пород баженовской свиты можно оценивать по комплексу геофизических исследований скважин с предварительной петрофизической настройкой

Каракин А.В., Покаташкин П.А. Автоколебательный режим процесса седиментации частично расплавленных пород // Физика Земли. 2015. № 4. С. 31-37.

"Рассматривается явление седиментации частично расплавленных пород в интрузиях. В процессе седиментации суспензии возникает стратифицированная структура, состоящая из зон с различной степенью уплотнения твердой фазы. Высшая степень уплотнения соответствует поровязкой среде. Над ней при критическом значении пористости на границе располагается тонкий промежуточный слой. Закритические значения пористости соответствуют нарушению связности скелета. В указанном тонком слое скелет поровязкой среды, в целом, сохраняет свои свойства, хотя и в сильно ослабленном виде. Связанные сильной гидродинамической связью зерна образуют структуры, которые отличаются неустойчивостью. В процессе седиментации они периодически разрушаются и восстанавливаются и на макроуровне воспринимаются как периодические автоколебания. Автоколебательный режим седиментации приводит к тому, что в кумулятах возникает периодическая слоистая структура, которая может быть обнаружена через много миллионов лет после застывания интрузивной камеры. В данной работе приводится исследование указанного процесса. "

Каргин А.В., Носова А.А., Ларионова Ю.О. и др. Мезопротерозойские оранжеиты (кимберлиты II) Западной Карелии: минералогические, геохимические и ND-SR изотопно-геохимические особенности // Петрология. 2014. Т. 22. № 2. С.171-207

Проведено изучение минералогических и петролого-геохимических особенностей мезопротерозойских (1.23-1.20 млрд лет) щелочно-ультраосновных пород Западной Карелии, распространенных в районах Костомукши-Таловейса (Россия) и Лентиира-Кухмо (Финляндия). По минеральным и геохимическим особенностям эти породы более близки к кимберлитам группы II Южной Африки (оранжеитам), чем к оливиновым лампроитам или ультрамафитовым лампрофирам. По составу фенокристов среди изученных оранжеитов нами выделено три минералогических типа: Cpx-Phl-Ol, Phl-Ol и Phl-Carb оранжеиты. Оранжеиты Cpx-Phl-Ol типа из Костомукши заметно отличаются от оранжеитов того же Cpx-Phl-Ol типа из Лентиира. Вещественные характеристики оранжеитов Phl-Ol типа свидетельствуют об интенсивной фракционной кристаллизации расплавов; оранжеиты Cpx-Phl-Ol типа из Костомукши несут признаки интенсивной ассимиляции литосферного материала. Оранжеиты Phl-Carb типа из Таловейса и Cpx-Phl-Ol типа из Лентиира наиболее близки к первичным расплавам. Для оранжеитов Костомукши характерны низко- и умеренно-радиогенные значения отношений (87Sr/86Sr)1220, варьирующие от 0.7038 до 0.7067. Оранжеиты Phl-Carb типа Таловейса отличаются менее радиогенным изотопным составом Nd ( ?Nd от -11 до -12) по сравнению с Cpx-Phl-Ol и Phl-Ol оранжеитами Костомукши ( ?Nd от -6.9 до -9.4). В оранжеитах Cpx-Phl-Ol типа из Лентиира был обнаружен свежий оливин. По морфологии и составу оливины можно разделить на три генерации: 1) крупные кристаллы с округлыми контурами, обычно зональные, состав ядра Fo92, содержание NiO 0.33-0.37 мас. % и СаО 0.03-0.04 мас. %; это могут быть ксенокристы из деплетированных перидотитов; 2) оливины средних размеров неправильной формы с округлыми контурами, зонального строения, состав ядра Fo82-83, содержание СаО 0.03-0.05 мас. %, NiO 0.12-0.17 мас. % и MnO до 0.40 мас. %; эти оливины также были захвачены оранжеитовым расплавом, и, скорее всего, представляют кумулаты базитовых расплавов либо происходят из метасоматизированных перидотитов; 3) мелкие идиоморфные оливины и идентичные им по составу каймы ксенокристов, отвечающие Fo88-89, имеют содержание СаО 0.10-0.42 мас. %, NiO 0.14-0.35 мас. % и MnO до 0.07-0.21 мас. %; их происхождение с наибольшей вероятностью связано с кристаллизацией из кимберлитового расплава. С помощью Nb-Fe-перовскитового оксибарометра оценено значение fO2 кимберлитового расплава при кристаллизации перовскитов: перовскиты из Cpx-Phl-Ol оранжеитов Костомукши кристаллизовались при фугитивности кислорода, соответствующей ?NNO от -3.3 до -1.1, а перовскиты оранжеитов Лентиира при похожих условиях, ?NNO от -3.3 до -0.9. На основе изучения Sm-Nd и Rb-Sr изотопных систем получены свидетельства участия древнего обогащенного источника в петрогенезисе оранжеитов и предложена двухэтапная последовательность образования их мантийного источника: 1) метасоматическая проработка ранее деплетированного литосферного источника в основании Карельского кратона в ходе палеопротерозойских орогенных событий 2.1-2.0 млрд лет назад; 2) генерация оранжеитовых расплавов, инициированная процессами растяжения 1.27-1.20 млрд лет назад.

Короновский Н.В., Демина Л.И., Промыслова М.Ю., Мышенкова М.С. Признаки глубинных взрывов флюидов в продуктах самостоятельного центра извержения Битюк-Тюбе (Западное Приэльбрусье) // Вестник Московского университета. Серия 4: Геология. 2013. № 2. С. 7-15.

В наиболее ранних продуктах извержения (флюидолитах) центра Битюк-Тюбе в Западном Приэльбрусье обнаружены четыре резко различающихся по кремнекислотности и соотношениям K 2O/Na 2O стекла, а также два стекла, близких к мономинеральным плагиоклазовому и кварцевому. Такой набор исходных расплавов — следствие глубинных взрывов флюидов. Показано, что глубинные взрывы флюидов инициируют, с одной стороны, плавление субстрата, а с другой — подготавливают и разрабатывают каналы, по которым впоследствии извергается магматический материал.

Кривдик C.Г. Геохимические особенности ильменитов из щелочных комплексов украинского щита (по данным LA-ICP MS) // Геохимия. 2014. № 4. С. 319-328.

"Методом LA-ICP MS проанализированы ильмениты из различных пород щелочных комплексов Украинского щита (Черниговский карбонатитовый, Октябрьский, Малотерсянский и Южно-Кальчикский габбро-сиенитовый массивы). Ильмениты из пород ранних интрузивных фаз (щелочных пироксенитов, габброидов, ультрамафитов) имеют повышенное содержание Cr, Co, Ni и V, а в более поздних щелочных и нефелиновых сиенитах, монцосиенитах и карбонатитах ильмениты значительно обогащены Nb и Ta, что обусловлено изменением щелочности среды минералообразования. Поведение Zr более сложное; его обычно больше в ильмените из основных и ультраосновных пород, чем в ильмените из нефелиновых сиенитов и карбонатитов. Это обусловлено главным образом температурными условиями формирования дифференцированных щелочных массивов. В карбонатитах выявлены магнезиальные ильмениты (до 22 мол. % MgTiO3). Изменение состава ильменитов сопряжено (по содержанию MgO) с магнезиальностью фемических минералов и зависит также от окисленности железа (количества магнетита) в карбонатитах. В щелочных массивах Украинского щита ильмениты чаще всего имеют невысокое содержание (37 мол. %) гематитового минала. Ильменит является чутким минералом-индикатором, состав которого отражают температура, фугитивность кислорода и щелочность среды минералообразования при кристаллизации. "

Кузин А.М. О флюидной составляющей процесса образования зон трещиноватости и разрывных нарушений // Геология, геофизика и разработка нефтяных и газовых месторождений. 2014. № 5. С. 43-50.

В статье рассмотрены некоторые механизмы образования зон трещиноватости и разрывных нарушений, в которых флюиды оказывают существенное влияние на параметры залегания. Обоснована гипотеза флюидного происхождения листрических разломов в консолидированной коре и верхней мантии.

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Лаптев Ю.В. Сульфатно-хлоридные высокотемпературные флюиды с участием золота и редких элементов (экспериментальные данные) // Геология и минерально-сырьевые ресурсы Сибири. 2014. № 3с-1. С. 86-88.

Опыты проведены в рамках модели магматогенных процессов при формировании месторождений с участием флюидов сульфатно-сульфидно-хлоридного типа. Экспериментально определены удельные объемы (, см3/г) флюидов состава 2 m Na2SO4-H2O и 2 m Na2SO4 -0,5 m NaCl-H2O в интервале 300-450 °С, 100-700 бар с измерением их параметров гомогенизации (Tгом, Pгом). В этих флюидах исследовано влияние давления на изменение растворимости золота Au(мет) и синтезированных сульфидов Fe, Cu, Mo при Р = 230-550 бар и температуре 376 °С. Впервые установлены эффекты явного уменьшения растворимости сульфидов и, наоборот, повышения растворимости Au(мет) с повышением давления от 230 до 550 бар.

Лебедев Е.Б., Рыженко Б.Н., Буркхардт Г., Жариков А.В., Рощина И.А., Кононкова Н.Н., Зебрин С.Р. Влияние состава флюидов на упругие свойства пород (песчаника, кварцита) при высоких температурах и давлениях (в приложении к проблеме коровых волноводов) // Физика Земли. 2014. № 3. С. 65-76.

"Геофизические исследования последних лет обнаружили существование в средней части земной коры зоны с аномально низкими сейсмическими скоростями и повышенной электропроводностью. Имеются предположения, что они могут быть связаны с изменениями пористости и проницаемости пород, а также с присутствием флюидов и могут объяснять существование коровых волноводов. Для проверки этой модели было проведено экспериментальное исследование. Среди изучаемых метаморфических процессов кислый метасоматизм наиболее полно объясняет процесс окварцевания пород. В работе рассмотрены физико-химические причины переотложения кварца из растворов, влияние рН растворов на массоперенос и отложение кварца при окварцевании и изменение физических свойств породы. С процессом окварцевания связано цементация породы, изменение микроструктуры и увеличение плотности. С окварцеванием пород также связано изменение сейсмических скоростей в земной коре. "

Лиманцева О.А. Установление иерархии процессов преобразования порового пространства водовмещающих пород с использованием термодинамического моделирования // Геохимия. 2014. № 11. С. 1043-1056.

Выполнена серия термодинамических расчетов при различных физико-химических параметрах в рамках единого модельного эксперимента краевой части артезианского бассейна. Выявлено, что температурный фактор сказывается интенсивней на степень преобразования порового пространства, нежели начальная пористость пород. Степень термодинамической открытости-закрытости системы вода-породы играет второстепенную роль в преобразовании пористости, косвенно определяя условия выщелачивания для карбонатных пород. Скорость фильтрации незначительно влияет на насыщенность подземных вод в конкретной точке водоносного горизонта при фиксированных Р-Т параметрах. При рассмотрении этого критерия на первый план выступает минеральный состав водовмещающих пород.

Люль А.Ю., Колесов Г.М., Лаврентьева З.А. Элементный состав и история металла энстатитовых ахондритов Песьяное и Norton County // Геохимия. 2013. № 10. C. 866-882.

Обсуждаются результаты нейтронно-активационного анализа Fe,Ni-фазы энстатитовых ахондритов (обритов) Norton County и Песьяное. Показано, что тренды фракционирования элементов в металле обритов отличны от ожидаемых в рамках чисто конденсационной или магматической моделей образования обритов. Нодули металла обритов с распространенностью элементов, подобной таковой для металла энстатитовых хондритов, являются реликтами первичных конденсатов протопланетного облака. Металл матрицы, обедненный труднолетучим иридием относительно умеренно летучих элементов, прошел стадию магматической дифференциации. Наличие общих для металла обрита Norton County положительных корреляций Ni?Au, Ni?As, Au?As и отрицательных корреляций Ir?Ni(Au) для металла матрицы и нодулей с низким содержанием Ir свидетельствует о генетической связи между этими фракциями металла. Металл матрицы является продуктом частичного плавления нодулей ? первичного металла родительской планетезимали ?тела состава энстатитовых хондритов, в результате плавления и дифференциации которого образовалось вещество обритов. Особенности состава Fe,Ni-фазы обритов согласуются с двухстадийной моделью образования энстатитовых ахондритов, включающей ударное разрушение родительской планетезимали на ранней стадии эволюции Солнечной системы с последующей гравитационной агломерацией выброшенных с разной глубины фрагментов в тело астероидных размеров.

Магомедов Р.А. Тектоника, современная геодинамика и сейсмичность области Дагестанского клина Восточного Кавказа // Вестник Дагестанского научного центра РАН. 2013. № 49. С. 27-34.

"Проведен анализ опубликованного и фондового материалов, а также результатов собственных исследований и полевых наблюдений с целью представления современной картины геодинамической ситуации, сейсмотектонических условий и современной сейсмичности области Дагестанского клина. Уточнено пространственное расположение разломов области Дагестанского клина и на этой основе составлена схема дизъюнктивной тектоники. По результатам исследований выполнено прогнозирование зон возможных очагов землетрясений (ВОЗ) в области Дагестанского клина. "

Петров В.А., Андреева О.В., Полуэктов В.В. Влияние петрофизических свойств и деформаций пород на вертикальную зональность метасоматитов в ураноносных вулканических структурах (на примере Стрельцовской кальдеры, Забайкалье) // Геология рудных месторождений. 2014. Т. 56. № 2. С. 95-117.

На примере Стрельцовской кальдеры мезозойского возраста, вмещающей крупнейшее в России Стрельцовское урановорудное поле, рассмотрены причины и механизмы развития вертикальной зональности околорудных метасоматических изменений вмещающих пород. В пределах рудного поля широко распространены метасоматические породы с участием разнообразных слоистых силикатов, а также карбонатов, альбита, цеолитов. В восточном блоке кальдеры, где сосредоточены самые крупные месторождения урана, распространены гидрослюдистые метасоматиты, которые с глубиной сменяются березитами. Аргиллизиты типичны для западного блока, где они сменяются гидрослюдизитами и березитами только на значительных глубинах. При этом в нижней части разреза проявлены пострудные аргиллизиты, которые наложены на березитизированные породы. Показано, что формирование двух мотивов вертикальной метасоматической зональности обусловлено разным характером деформационных преобразований пород в западной и восточной частях кальдеры. Исследованы вариации важнейших петрофизических параметров вмещающих пород, включая плотность, эффективную пористость, скорости продольных и поперечных волн, значения динамических модулей Юнга и коэффициента Пуассона по данным ультразвукового прозвучивания образцов с различных глубин. Предполагается, что фактором, вызывающим фациальное разнообразие метасоматитов, могла послужить миграция границы перехода от упруго-хрупкого к упруго-пластичному поведению вещества на более глубокие горизонты в результате проявления новой фазы тектонотермального воздействия, сопровождавшегося увеличением скорости деформаций пород и/или внедрением новой порции разогретых флюидов. Временное опускание этой границы обусловливает увеличение глубины гидродинамически открытой зоны, связанной с поверхностью, что приводит к ускоренному проникновению на большие глубины холодных метеорных вод. Это вызывает понижение температур гидротерм и, как следствие, развитие более протяженных по вертикали ореолов аргиллизации, а также концентрирование богатой урановой минерализации глубже, чем в других участках кальдеры.

Реутский В.Н., Пальянов Ю.Н., Борздов Ю.М., Сокол А.Г. Изотопное фракционирование углерода при кристаллизации алмаза в модельных системах // Геология и геофизика. 2015. Т. 56. № 1-2. С. 308-315.

Рябчиков И.Д., Каминский Ф.В. Физико-химические параметры материала мантийных плюмов по данным термодинамического анализа минеральных включений в сублитосферных алмазах // Геохимия. 2014. № 11.C. 963-971.

Проведен термодинамический анализ равновесий с участием породообразущих минералов нижней мантии пиролитового состава и кристаллических соединений углерода. Показано, что диапазон фугитивностей кислорода, при которых может происходить образование алмаза, отделен от области формирования богатого железом металлического сплава полем устойчивости карбидов железа. Отсюда вытекает, что для формирования в нижней мантии алмаза требуются более окислительные условия, чем это предполагается для преобладающей части этой геосферы. Отсутствие металлической фазы среди минералов нижнемантийного алмазсодержащего парагенезиса согласуется с высокими (около 1%) содержаниями Ni в ферропериклазах, включенных в алмазы (богатый железом металлический сплав будет интенсивно экстрагировать Ni). Повышенный редокс-потенциал подтверждается находками карбонатных фаз среди минеральных включений в нижнемантийных алмазах. В качестве главной причины повышения фугитивности кислорода в отдельных участках нижней мантии представляется смещение окислительно-восстановительных равновесий с ростом температуры в сторону уменьшения количества, а затем исчезновения FeNi сплава. Важную роль в формировании алмазов может играть зарождение, миграция и взаимодействие с боковыми породами карбонатно-фосфатных и силикатных расплавов, возникающих в высокотемпературных зонах. Связь сублитосферного алмазообразования с высокотемпературными условиями подтверждает приуроченность этих процессов, а также формирование кимберлитовых магм, к деятельности мантийных плюмов.

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