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Всероссийский ежегодный семинар по экспериментальной минералогии, петрологии и геохимии

Журнальные статьи

1. U01624
Bai Z.-J. et al. Association of cumulus apatite with compositionally unusual olivine and plagioclase in the Taihe Fe-Ti oxide ore-bearing layered mafic-ultramafic intrusion: Petrogenetic significance and implications for ore genesis // Am. Miner. 2016. Vol. 101, № 9–10. P. 2168–2175.

In many large, layered, mafic-ultramafic intrusions worldwide cumulus apatite commonly occurs in the highly fractionated Fe-Ti oxide-rich lithological units at the top of the intrusions and the associated plagioclase and olivine, if present, have An content <50 mol% and Fo content <40 mol%. These are not true for several Fe-Ti oxide ore-bearing mafic-mafic intrusions in the Emeishan large igneous province, SW China. A good example is the Taihe intrusion, which is described in this paper. In this intrusion the associated olivine and plagioclase are significantly more primitive, containing 69 mol% Fo and 59 mol% An, respectively. MELTS simulation reveals that such unusual association is the result of previous cotectic crystallization of Fe-Ti oxides with silicate minerals during magma evolution under oxidizing condition close to that of nickel nickel oxide buffer. Supports for this new model include the observed upward decrease in plagioclase An contents coupled by lack of significant change in original olivine Fo contents in the Fe-Ti oxide ore-bearing sequence below the apatite-rich horizon, which is in turn supported by the facts that Fe-Ti oxide crystallization has a counter effect on MgO/FeO, but no effect on CaO/Na2O in the residual magma and that the addition of Fe-Ti oxides in the cumulus assemblage expedites the arrival of apatite on the liquidus. Our new findings support the interpretation that the oxide ores in the Taihe intrusion formed by gravitational accumulation of Fe-Ti oxides crystallizing from a basaltic magma, not a Fe-Ti-P-rich immiscible liquid segregated from such magma.


2. U01624
Barnes C.G., Memeti V., Coint N. Deciphering magmatic processes in calc-alkaline plutons using trace element zoning in hornblende // Am. Miner. 2016. Vol. 101, № 1–2. P. 328–342.

Hornblende in the Kuna Crest lobe (KCL) of the Tuolumne Intrusive Complex (TIC) and the upper zone of the Wooley Creek batholith (WCB) precipitated over a temperature range of 835 to 700 C, and thus has the potential to record magmatic processes. We measured trace element concentrations in hornblende from the WCB, from the KCL of the TIC, and from one sample from an adjacent interior unit of the TIC to compare and contrast magmatic processes in these two mid -crustal intrusions. In both systems the magmatic amphibole is magnesiohornblende in which Ti, Zr, Hf, Nb, Sr, Ba, and rare earth elements (REE) typically decrease from crystal interiors to rims, an indication of compatible behavior of these elements, and the size of the negative Eu anomaly decreases. In the Kuna Crest lobe, hornblende from individual mapped units differs in trace element abundances and zoning trends. Some samples contain at least two distinct hornblende populations, which is particularly evident in the shapes of REE patterns. In contrast, compositions of hornblende from all structural levels of the upper WCB and related dacitic roof -zone dikes form a single broad array and the REE patterns are essentially indistinguishable, regardless of rock type, from quartz diorite to granite. In the WCB, Zr/Hf ratios in hornblende are consistent with crystallization from a melt with chondritic Zr/Hf values. In contrast, most hornblende in the KCL has Zr/Hf values lower than expected from crystallization from a melt with chondritic values, suggesting that zircon fractionation occurred before and during crystallization of the hornblende. Simple fractional crystallization models indicate that REE, high field strength elements, Sr, and Ba were compatible in KCL and WCB magmas as hornblende grew; these trends require removal of hornblende + plagioclase + zircon ilmenite biotite. The uniform variations of trace element concentrations and patterns in the upper WCB and roof zone dikes indicates crystallization from a large magma body that was compositionally uniform; probably stirred by convection caused by influx of mafic magmas at the base of the zone (Coint et al. 2013a, 2013b; cf. Burgisser and Bergantz 2011). In contrast, in the KCL, each analyzed sample displays distinct hornblende compositions and zoning patterns, some of which are bimodal. These features indicate that each analyzed sample represents a distinct magma and that individual magmas were variably modified by fractionation and mixing. Hornblende trace element contents and zoning patterns prove to be powerful tools for identification of magma batches and for assessing magmatic processes, and thereby relating plutonic rocks to hypabyssal and volcanic equivalents.


3. S04675
Belhai D. et al. The fourth Arab Impact Cratering and Astrogeology Conference (AICAC IV), April 9-12, 2017, Algiers (Algeria) // Meteorit. Planet. Sci. 2017. Vol. 52, № 9. P. 2067–2071.

We present a report about the fourth Arab Impact Cratering and Astrogeology Conference (AICAC IV) that took place in Algiers at the USTHB (Universite des Sciences et Technologie Houari Boumedienne, Algiers, Algeria) in the presence of the presidents of the USTHB and Boumerdes Universities, the Director of CRAAG (Centre de Recherche en Astronomie, Astrophysique et Geophysique), and the General Director of the National Administration for Scientific Research (NASR/DGRSDT). This series of conferences aims to promote research interest for impact cratering in the Arab world and beyond, including for instance in African countries. In spite of persistently restraining travel measures to Algeria, the fourth edition held in Algiers was marked by continuous international participation, with participants from seven different countries. This conference focused on presentations of scientific results in the research fields related to planetology, meteorites, and impact craters. In particular, the Algerian impact structures were under the spotlights during both oral and poster sessions. During this conference, the presence of freshly graduated Ph.D. students and new Ph.D. projects related to impact cratering or meteoritic science was a positive sign for the consolidation of research groups in this domain in the Arab world and Africa. Therefore, international cooperation or external support and funding are still needed to ensure the development of this scientific discipline in this part of the world.


4. U47863
Boylan A.A. et al. Mechanisms of inorganic carbon-14 attenuation in contaminated groundwater: Effect of solution pH on isotopic exchange and carbonate precipitation reactions // Appl. Geochem. 2017. Vol. 85. P. 137–147.

Radioactive C-14 is a significant contaminant associated with nuclear fuels and wastes that is potentially highly mobile in the environment as dissolved inorganic carbonate species. This study investigated the mechanisms by which dissolved inorganic C-14 is retained in surface and groundwater environments via precipitation and isotopic exchange reactions. Precipitation of calcite in the presence and absence of nucleation sites is considered along with isotopic exchange with both atmospheric CO2 and solid carbonates. Precipitation occurs at calcite supersaturation values of SICAL > 1.5 in the absence of nucleation sites and SICAL > 0-0.5 in the presence of nucleation sites, suggesting that precipitation of C-14-bearing carbonates is much more likely in subsurface environments where nucleation sites are abundant. The maximum C-14 removal in solid isotopic exchange experiments occurred after approximately 2 weeks equilibration. In these experiments the amount of C-14 removed from solution was proportional to the amount of calcite surface area present, and removal from solution was equivalent to rapid equalisation of the isotope ratio in an 8-10 angstrom active surface layer. Although the reactivity of natural carbonates may be lower than the calcite samples used in this study, these results suggest isotopic exchange with solids will be an important C-14 retardation mechanism in subsurface environments containing only modest TIC concentrations. These results suggest that if inorganic C-14 is released into sub-surface environments, both precipitation and solid phase isotopic exchange can result in non-conservative C-14-DIC transport and C-14 contamination may persist in groundwater for decades following accidental releases. In contrast, in experiments open to atmosphere with pH values below 9.3, complete loss of dissolved inorganic C-14 was very rapid and occurred with timescales of 10's of hours. C-14 loss was due to a rapid exchange of dissolved C-14 species with (CO2)-C-12 (g) and the kinetics of C-14 removal increased as pH values were lowered (i.e. atmospheric isotopic exchange was first order with respect to the concentration of carbonic acid present). Thus these results suggest that release of inorganic C-14 to surface waters with pH values < 9.3 would result in rapid exchange with (CO2)-C-12 (g) and C-14 would not persist in the aqueous environment, whereas C-14-DIC released to saturated subsurface environments may persist close to the release site for decades due to precipitation and solid phase exchange reactions preventing/retarding transport with the groundwater. (C) 2016 The Authors. Published by Elsevier Ltd.


5. U59979
Canovas P.A., Hoehler T., Shock E.L. Geochemical bioenergetics during low-temperature serpentinization: An example from the Samail ophiolite, Sultanate of Oman // J. Geophys. Res.-Biogeosci. 2017. Vol. 122, № 7. P. 1821–1847.

Various classes of microbial and biomolecular evidence from global studies in marine and continental settings are used to identify a set of reactions that appear to support microbial metabolism during serpentinization of ultramafic rocks. Geochemical data from serpentinizing ecosystems in the Samail ophiolite of Oman are used to evaluate the extent of disequilibria that can support this set of microbial metabolisms and to provide a ranking of potential metabolic energy sources in hyperalkaline fluids that are direct products of serpentinization. Results are used to construct hypotheses for how microbial metabolism may be supported in the subsurface for two cases: ecosystems hosted in rocks that have already undergone significant serpentinization and those hosted by deeper, active serpentinization processes. Plain Language Summary Chemical energy that supports communities of microbes becomes available when water reacts with rock. A striking example occurs when water reacts with the type of rock normally found in the Earth's mantle. The resulting process called serpentinization releases energy that microbes can harvest to grow and reproduce. A classic example of serpentinization occurs in mantle rocks exposed in Oman. This work involved sampling of water from springs in Oman, geochemical analyses in the lab, and computer models to determine the energy supplies. Comparisons allow ranking among energy sources and predictions of how the reactions of water with rocks support different microbial communities both at the surface and deep below the surface. This work will help guide microbiological studies of serpentinization, which are ongoing in numerous locations around the world. In addition, serpentinization may supply energy to microbial communities on other planets, especially the icy worlds of the outer solar system, so the results form this study may also guide space exploration.


6. U10290
Capponi A., James M.R., Lane S.J. Gas slug ascent in a stratified magma: Implications of flow organisation and instability for Strombolian eruption dynamics // Earth Planet. Sci. Lett. 2016. Vol. 435. P. 159–170.

The canonical Strombolian paradigm of a gas slug ascending and bursting in a homogeneous low-viscosity magma cannot explain the complex details in eruptive dynamics recently revealed by field measurements and textural and geochemical analyses. Evidence points to the existence of high-viscosity magma at the top of the conduit of Strombolian-type volcanoes, acting as a plug. Here, new experiments detail the range of flow configurations that develop during the ascent and burst of a slug through rheologically stratified magma within a conduit. End-member scenarios of a tube fully filled with either high- or low-viscosity liquid bracket three main flow configurations: (1) a plug sufficiently large to fully accommodate an ascending gas slug; (2) A plug that can accommodate the intrusion of low-viscosity liquid driven by the gas expansion, but not all the slug volume, so the slug bursts with the nose in the plug whilst the base is still in the low-viscosity liquid; (3) Gas expansion is sufficient to drive the intrusion of low viscosity liquid through the plug, with the slug bursting in the low-viscosity layer emplaced dynamically above the plug. We show that the same flow configurations are viable at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results demonstrate that the key parameters controlling the transition between each configuration are gas volume, plug thickness and plug viscosity. The flow processes identified include effective dynamic narrowing and widening of the conduit, instabilities within the falling magma film, transient partial and complete blockage of the conduit, and slug disruption. These complexities influence eruption dynamics and vigour, promoting magma mingling and resulting in pulsatory release of gas.


7. U1045X
Childress T.M. et al. Iron and Oxygen Isotope Signatures of the Pea Ridge and Pilot Knob Magnetite-Apatite Deposits, Southeast Missouri, USA // Econ. Geol. 2016. Vol. 111, № 8. P. 2033–2044.

New O and Fe stable isotope ratios are reported for magnetite samples from high-grade massive magnetite of the Mesoproterozoic Pea Ridge and Pilot Knob magnetite-apatite ore deposits and these results are compared with data for other iron oxide-apatite deposits to shed light on the origin of the southeast Missouri deposits. The delta O-18 values of magnetite from Pea Ridge (n = 12) and Pilot Knob (n = 3) range from 1.0 to 7.0 and 3.3 to 6.7%, respectively. The delta Fe-56 values of magnetite from Pea Ridge (n = 10) and Pilot Knob (n = 6) are 0.03 to 0.35 and 0.06 to 0.27%, respectively. These delta O-18 and the delta Fe-56 values suggest that magnetite crystallized from a silicate melt (typical igneous delta Fe-56 ranges 0.06-0.49%) and grew in equilibrium with a magmatic-hydrothermal aqueous fluid. We propose that the delta O-18 and delta Fe-56 data for the Pea Ridge and Pilot Knob magnetite-apatite deposits are consistent with the flotation model recently proposed by Knipping et al. (2015a), which invokes flotation of a magmatic magnetite-fluid suspension and offers a plausible explanation for the igneous (i.e., up to similar to 15.9 wt % TiO2 in magnetite) and hydrothermal features of the deposits.


8. U18432
Churikova T.G. et al. Petrological and geochemical evolution of the Tolbachik volcanic massif, Kamchatka, Russia // J. Volcanol. Geotherm. Res. 2015. Vol. 307. P. 156–181.

Data on the geology, petrography, and geochemistry of Middle-Late-Pleistocene rocks from the Tolbachik volcanic massif (Kamchatka, Klyuchevskaya group of volcanoes) are presented and compared with rocks from the neighboring Mount Povorotnaya, Klyuchevskaya group basement, and Holocene-historical Tolbachik monogenetic cones. Two volcanic series of lavas, middle-K and high-K, are found in the Tolbachik massif. The results of our data analysis and computer modeling of crystallization at different P-T-H2O-fO(2) conditions allow us to reconstruct the geochemical history of the massif. The Tolbachik volcanic massif started to form earlier than 86 ka based on K-Ar dating. During the formation of the pedestal and the lower parts of the stratovolcanoes, the middle-K melts, depleted relative to NMORB, fractionated in water-rich conditions (about 3% of H2O). At the Late Pleistocene-Holocene boundary, a large fissure zone was initiated and the geodynamical regime changed. Upwelling associated with intra-arc rifting generated melting from the same mantle source that produced magmas more enriched in incompatible trace elements and subduction components; these magmas are high-K, not depleted relative to N-MORB melts with island arc signatures and rift-like characteristics. The fissure opening caused degassing during magma ascent, and the high-K melts fractionated at anhydrous conditions. These high-K rocks contributed to the formation of the upper parts of stratovolcanoes. At the beginning of Holocene, the high-K rocks became prevalent and formed cinder cones and associated lava fields along the fissure zone. However, some features, including 1975-1976 Northern Breakthrough, are represented by middle-K high-Mg rocks, suggesting that both middle-K and high-K melts still exist in the Tolbachik system. Our results show that fractional crystallization at different water conditions and a variably depleted upper mantle source are responsible for all observed variations in rocks within the Tolbachik volcanic massif. Sr-Nd isotopes are consistent with 2-4% crustal assimilation during formation of the pedestal and stratovolcanoes, while the young lava fields do not show evidence of crustal assimilation. Major and trace element data coupled with K-Ar dating provide strong evidence that Mount Povorotnaya, located in 8 km northeast of Plosky Tolbachik, is an old block of the Tolbachik massif pedestal and for the moment it is the oldest (306 ka) known object in Klyuchevskaya group of volcanoes.


9. U12309
Dartois E. et al. Interstellar and interplanetary carbonaceous solids in the laboratory // Geochem. J. 2014. Vol. 48, № 6. P. 511–518.

The interstellar medium (ISM) is a physico-chemical laboratory where extreme conditions are encountered and where particular environmental parameters (e.g., density, reactant nature, radiation, temperature, time scales) define the composition of matter. With present observational possibilities, the fundamental question regarding the possible link between ISM and solar system samples can be addressed by astrophysicists, planetologists, and cosmochemists. This article focuses on observations of diffuse ISM and dust components of molecular clouds, setting constraints on the composition of organic solids and large molecules associated with matter cycling in the Galaxy. This study aims at drawing some commonalities and differences between the materials found in the Solar System and those found in interstellar dust.


10. U10290
Gaillard F., Scaillet B. A theoretical framework for volcanic degassing chemistry in a comparative planetology perspective and implications for planetary atmospheres // Earth Planet. Sci. Lett. 2014. Vol. 403. P. 307–316.

Magmatic degassing is ubiquitous and enduring, yet its impact on both planetary surficial chemistry and how it may have varied among planetary systems remains imprecise. A large number of factors are likely to be involved in the control of magmatic gas compositions, leading roles being given to the redox state and volatile abundances in planetary interiors, and the fate of the latter during mantle melting. We however show that the pressure at which degassing occurs, that is the atmospheric pressure in most sensible cases, has a prime influence on the composition of subaerial volcanic gases on planets: high surface pressure produces N-2- and CO2-rich and dry volcanic gases, while low pressure promotes sulfur-rich gases. In-between, atmospheric pressures close to 1 bar trigger volcanic gases dominated by H2O. This simple pattern broadly mirrors the atmospheres of Venus-Earth-Mars-lo planetary suite and constitutes benchmarks for the prediction and interpretation of atmospheric features of extra-solar planets. Volatile abundances within the planetary body interiors also matter but they play a secondary role. Furthermore, our analysis shows that any difference in redox conditions prevailing during partial melting tends to disappear with the degassing process itself, converging toward a unique - planetary oxygen fugacity - at the venting pressure. A feedback relationship between volcanic gas compositions and atmospheric pressure implies a runaway drying during atmospheric growth; that is volcanic gases must become CO2 richer as the atmospheric mass increases. This may explain some features of the Venusian atmosphere. On Earth, impact ejection of the atmosphere and CO2-sink mechanisms, such as carbonate precipitation and plate tectonics, must have decreased atmospheric pressure allowing the reestablishment of water-rich volcanic gases.


11. Gregory M.J., Mathur R. Understanding Copper Isotope Behavior in the High Temperature Magmatic-Hydrothermal Porphyry Environment // Geochem. Geophys. Geosyst. 2017. Vol. 18, № 11. P. 4000–4015.

Copper stable isotope geochemistry has the potential to constrain aspects of ore deposit formation once variations in the isotopic data can be related to the physiochemical conditions during metal deposition. This study presents Cu isotope ratios for samples from the Pebble porphyry Cu-Au-Mo deposit in Alaska. The Cu-65 values for hypogene copper sulfides range from -2.09 to 1.11 and show linear correlations with the O-18 isotope ratios calculated for the fluid in equilibrium with the hydrothermal alteration minerals in each sample. Samples with sodic-potassic, potassic, and illite alteration display a negative linear correlation between the Cu and O isotope results. This suggests that fractionation of Cu isotopes between the fluid and precipitating chalcopyrite is positive as the hydrothermal fluid is evolving from magmatic to mixed magmatic-meteoric compositions. Samples with advanced argillic alteration display a weak positive linear correlation between Cu and O isotope results consistent with small negative fluid-chalcopyrite Cu isotope fractionation during fluid evolution. The hydrothermal fluids that formed sodic-potassic, potassic, and illite alteration likely transported Cu as CuHS0. Hydrothermal fluids that resulted in advanced argillic alteration likely transport Cu as CuCl2-. The pH conditions also control Cu isotope fractionation, consistent with previous experimental work. Larger fractionation factors were found between fluids and chalcopyrite precipitating under neutral conditions contrasting with small fractionation factors calculated between fluids and chalcopyrite precipitating under acidic conditions. Therefore, this study proposes that hydrothermal fluid compositions and pH conditions are related to Cu isotope variations in high temperature magmatic-hydrothermal deposits.


12. S13710
Helling C. et al. Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond // Surv. Geophys. 2016. Vol. 37, № 4. P. 705–756.

Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) brown dwarfs which are amongst the oldest objects in the Universe. Despite this diversity, solar system planets, extrasolar planets and brown dwarfs have broadly similar global temperatures between 300 and 2500 K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emissions. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emissions that potentially originate from accelerated electrons on brown dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation.


13. U20470
Hensler A.-S. et al. Using oxygen isotope chemistry to track hydrothermal processes and fluid sources in itabirite-hosted iron ore deposits in the Quadrilatero Ferrifero, Minas Gerais, Brazil // Miner. Depos. 2014. Vol. 49, № 3. P. 293–311.

The Quadrilatero Ferrifero, Brazil, is presently the largest accumulation of single itabirite-hosted iron ore bodies worldwide. Detailed petrography of selected hypogene high-grade iron ore bodies at, e.g. the Aguas Claras, Concei double dagger o, Pau Branco and Pico deposits revealed different iron oxide generations, from oldest to youngest: magnetite -> martite (hematite pseudomorph after magnetite) -> granoblastic (recrystallised) -> microplaty (fine-grained, < 100 mu m) -> specular (coarse-grained, > 100 mu m) hematite. Laser-fluorination oxygen isotope analyses of selected iron ore species showed that the delta O-18 composition of ore-hosted martite ranges between -4.4 and 0.9 aEuro degrees and is up to 11 aEuro degrees depleted in O-18 relative to hematite of the host itabirite. During the modification of iron ore and the formation of new iron oxide generations (e.g. microplaty and specular hematite), an increase of up to 8 aEuro degrees in delta O-18 values is recorded. Calculated delta O-18 values of hydrothermal fluids in equilibrium with the iron oxide species indicate: (1) the involvement of isotopically light fluids (e.g. meteoric water or brines) during the upgrade from itabirite-hosted hematite to high-grade iron ore-hosted martite and (2) a minor positive shift in delta O-18(fluid) values from martite to specular hematite as result of modified meteoric water or brines with slightly elevated delta O-18 values and/or the infiltration of small volumes of isotopically heavy (metamorphic and/or magmatic) fluids into the iron ore system. The circulation of large fluid volumes that cause the systematic decrease of O-18/O-16 ratios from itabirite to high-grade iron ore requires the presence of, e.g. extensive faults and/or large-scale folds.


14. U01624
Herzberg C., Vidito C., Starkey N.A. Nickel-cobalt contents of olivine record origins of mantle peridotite and related rocks // Am. Miner. 2016. Vol. 101, № 9–10. P. 1952–1966.

Olivine is distinguished from all other minerals in providing a remarkable chemical narrative about magmatic processes that occurred in Earth's crust, mantle, and core over the entire age of Earth history. Olivines in mantle peridotite have Ni contents and Mg numbers that were largely produced by equilibrium crystallization in an early turbulently convecting magma ocean; subsequent stages of partial melting operated to slightly elevate Ni and Mg number in residual olivines. Olivines from Archean komatiites from the Abitibi greenstone belt have Ni contents and Mg numbers that are consistent with an extensively melted peridotite source at great depths in the mantle. Olivines from basaltic oceanic crust, the Icelandic mantle plume and other Phanerozoic occurrences have compositions that record magma chamber crystallization, recharge, mixing, and partial melting. Olivines from the present-day Icelandic mantle plume have compositions that are consistent the melting of a peridotite source; unlike Hawaii, the melting of recycled crust as a distinct pyroxenite lithology is not evident in the olivine chemistry of Iceland. Paleocene picrites from Baffin Island and West Greenland from the ancient Icelandic plume have olivines with Ni contents that are consistent with either Ni-rich peridotite that formed by core-mantle interaction or by low-pressure crystallization of hot and deep magmas. In general, hot magma oceans, mantle plumes, and ambient mantle magmatism form in ways that are captured by the compositions of the olivine crystals that they contain.


15. U12332
Holmkvist L. et al. Sulfidization of lacustrine glacial clay upon Holocene marine transgression (Arkona Basin, Baltic Sea) // Geochim. Cosmochim. Acta. 2014. Vol. 142. P. 75–94.

Towards the end of the last deglaciation more than 13,500 years ago the southern Baltic Sea was a freshwater lake, the Baltic Ice Lake, for several thousand years during which iron-rich, organic-poor clay was deposited. The modern brackish-marine stage started about 8600 years ago with the deposition of organic-rich mud, which is today characterized by high rates of sulfate reduction and high concentrations of free sulfide. We studied the iron-sulfur diagenesis in gravity cores from the Arkona Basin, SW Baltic Sea, to track the progressing sulfidization front in the buried Ice Lake sediment. The geochemical zonation was unusual as the sulfate concentration dropped steeply by two thirds below which it increased again due to a deep sulfate reservoir. The reservoir had been established during the early Holocene marine period as sulfate and other seawater ions diffused down into the lake sediment for several thousand years. Sulfur isotope analyses confirmed its origin as seawater sulfate, while its oxygen isotope composition indicated a microbially catalyzed equilibration with ambient interstitial water, decoupled from net sulfate reduction. Today, hydrogen sulfide diffuses from the marine mud down into the lake sediment where a black band with high magnetic susceptibility and high iron monosulfide, greigite and elemental sulfur content shows progressing sulfidization of the large pool of solid-phase reactive iron. Dissolved iron from the deep Ice Lake sediment diffuses up to the sulfide front and provides a small supplement to the solid Fe(III) pool as a sulfide sink. Pyrite formation at the sulfidization front may involve surface-bound zero-valent sulfur while, above the front, polysulfides are in equilibrium with the system hydrogen sulfide - polysulfide - rhombic sulfur and may not be important for further pyrite formation. The Holocene iron-sulfur diagenesis observed in the Arkona Basin represents an important transitional state for post-glacial transgressions with organic-rich marine sediment overlying lacustrine clay, such as in other areas of the Baltic Sea or in the Black Sea.


16. S13710
Khan A. On Earth’s Mantle Constitution and Structure from Joint Analysis of Geophysical and Laboratory-Based Data: An Example // Surv. Geophys. 2016. Vol. 37, № 1. P. 149–189.

Determining Earth's structure is a fundamental goal of Earth science, and geophysical methods play a prominent role in investigating Earth's interior. Geochemical, cosmochemical, and petrological analyses of terrestrial samples and meteoritic material provide equally important insights. Complementary information comes from high-pressure mineral physics and chemistry, i.e., use of sophisticated experimental techniques and numerical methods that are capable of attaining or simulating physical properties at very high pressures and temperatures, thereby allowing recovered samples from Earth's crust and mantle to be analyzed in the laboratory or simulated computationally at the conditions that prevail in Earth's mantle and core. This is particularly important given that the vast bulk of Earth's interior is geochemically unsampled. This paper describes a quantitative approach that combines data and results from mineral physics, petrological analyses of mantle minerals, and geophysical inverse calculations, in order to map geophysical data directly for mantle composition (major element chemistry and water content) and thermal state. We illustrate the methodology by inverting a set of long-period electromagnetic response functions beneath six geomagnetic stations that cover a range of geological settings for major element chemistry, water content, and thermal state of the mantle. The results indicate that interior structure and constitution of the mantle can be well-retrieved given a specific set of measurements describing (1) the conductivity of mantle minerals, (2) the partitioning behavior of water between major upper mantle and transition-zone minerals, and (3) the ability of nominally anhydrous minerals to store water in their crystal structures. Specifically, upper mantle water contents determined here bracket the ranges obtained from analyses of natural samples, whereas transition-zone water concentration is an order-of-magnitude greater than that of the upper mantle and appears to vary laterally underneath the investigated locations.


17. U01624
Kirkpatrick R.J. et al. NMR and computational molecular modeling studies of mineral surfaces and interlayer galleries: A review // Am. Miner. 2015. Vol. 100, № 7. P. 1341–1354.

This paper reviews experimental nuclear magnetic resonance (NMR) and computational molecular dynamics (MD) investigations of the structural and dynamical behavior of cations, anions, H2O, and CO2 on the surfaces and in the interlayer galleries of layer-structure minerals and their composites with polymers and natural organic matter (NOM). The interaction among mineral surfaces, charge-balancing cations or anions, H2O, CO2, and NOM are dominated by Coulombic, H-bond, and van der Waals interactions leading to statically and dynamically disordered systems and molecular-scale processes with characteristic room-temperature frequencies varying from at least as small as 10(2) to >10(12) Hz. NMR spectroscopy provides local structural information about such systems through the chemical shift and quadrupolar interactions and dynamical information at frequencies from the sub-kilohertz to gigahertz ranges through the T-1 and T-2 relaxation rates and line shape analysis. It is often difficult to associate a specific structure or dynamical process to a given NMR observation, however, and computational molecular modeling is often effective in providing a much more detailed picture in this regard. The examples discussed here illustrate these capabilities of combining experimental NMR and computational modeling in mineralogically and geochemically important systems, including clay minerals and layered double hydroxides.


18. U1045X
Large R.R. et al. Ocean and Atmosphere Geochemical Proxies Derived from Trace Elements in Marine Pyrite: Implications for Ore Genesis in Sedimentary Basins // Econ. Geol. 2017. Vol. 112, № 2. P. 423–450.

Trace element concentrations in marine pyrite, measured by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), have the potential to open a new window into deep-time ocean chemistry, atmosphere oxygenation, and genesis of basin-hosted ore deposits. Only early-formed syngenetic and early diagenetic marine pyrite preserves the trace element chemistry of the past oceans, as late diagenetic and metamorphic recrystallization of pyrite changes the trace element budget. A database of over 5,000 marine pyrite trace element analyses by LA-ICP-MS has enabled the development of deep-time proxies for nutrient supply, productivity, ocean pH, and atmosphere oxygenation. These proxies suggest that the Archean ocean was enriched in Fe, Ni, Co, As, Au, and Hg compared with modern oceans, probably related to composition of erosive flux from the continents and active seafloor hydrothermal activity. This was also a time for major iron, gold, and nickel ore formation in sedimentary and greenstone settings. In the Paleoproterozoic, there was a decrease in Ni, Co, As, and Au, replaced by increasing Cu, Zn, and SO42- in the oceans and O-2 in the atmosphere. The first appearance of red beds and evaporites is a response to the rise in O-2 and SO42-, and provided the conditions necessary for sediment-hosted Cu and stratiform Pb-Zn-Ag sedimentary exhalative (SEDEX) deposits. Through 1700 to 1500 Ma, phosphorous, gold, and most other nutrient trace elements dropped to a minimum in the ocean, possibly related to tectonic stasis and changes in atmosphere O-2 and/or ocean pH. Sediment-hosted Au, orogenic Au, and volcanic-hosted massive sulfide (VHMS) deposits are virtually absent from this period, whereas mineral systems that required relatively oxidized ore fluids, such as SEDEX Zn-Pb, iron oxide copper-gold (IOCG), and unconformity uranium became more abundant, due to these changed conditions. All redox-sensitive and nutrient trace elements rose dramatically in concentration at the Proterozoic-Phanerozoic boundary and peaked in the mid- to Late Cambrian oceans, accompanied by black shale deposition enriched in Mo, Se, Ni, Ag +/- Au, and platinum group elements. Cyclic variation in nutrient trace elements increased in frequency through the Phanerozoic on a wavelength of 50 to 100 m.y., compared with 500 to 1,000 m.y. in the Proterozoic. The more frequent Phanerozoic cycles relate to repeated episodes of continent collision, mountain building, and increased erosive flux of trace elements into the oceans. Ore deposit cycles in the Phanerozoic of SEDEX Zn-Pb, orogenic sediment-hosted Au, and VHMS have a time frame similar to the tectonic and seawater chemistry cycles.


19. U01624
Ma C., Krot A.N., Nagashima K. Addibischoffite, Ca2Al6Al6O20, a new calcium aluminate mineral from the Acfer 214 CH carbonaceous chondrite: A new refractory phase from the solar nebula // Am. Miner. 2017. Vol. 102, № 7. P. 1556–1560.

Addibischoffite (IMA 2015-006), Ca2Al6Al6O20, is a new calcium aluminate mineral that occurs with hibonite, perovskite, kushiroite, Ti-kushiroite, spinel, melilite, anorthite, and FeNi-metal in the core of a Ca-Al-rich inclusion (CAI) in the Acfer 214 CH3 carbonaceous chondrite. The mean chemical composition of type addibischoffite measured by electron probe microanalysis is (wt%) Al2O3 44.63, CaO 15.36, SiO2 14.62, V2O3 10.64, MgO 9.13, Ti2O3 4.70, FeO 0.46, total 99.55, giving rise to an empirical formula of (Ca-2.00)(Al2.55Mg1.73V1.083+Ti0.503+Ca0.09Fe0.052+)(Sigma 6.01)(Al4.14Si1.86)O-20. The general formula is Ca-2(Al, Mg,V,Ti)(6)(Al, Si)(6)O-20. The end-member formula is Ca2Al6Al6O20. Addibischoffite has the P (1) over bar aenigmatite structure with a = 10.367 angstrom, b = 10.756 angstrom, c = 8.895 angstrom, alpha = 106.0 degrees, beta = 96.0 degrees, gamma = 124.7 degrees, V = 739.7 angstrom(3), and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.41 g/cm(3). Addibischoffite is a new member of the warkite (Ca2Sc6Al6O20) group and a new refractory phase formed in the solar nebula, most likely as a result of crystallization from an O-16-rich Ca, Al-rich melt under high-temperature (similar to 1575 degrees C) and low-pressure (similar to 10(-4) to 10(-5) bar) conditions in the CAI-forming region near the protosun, providing a new puzzle piece toward understanding the details of nebular processes. The name is in honor of Addi Bischoff, cosmochemist at University of Munster, Germany, for his many contributions to research on mineralogy of carbonaceous chondrites, including CAIs in CH chondrites.


20. U12332
Mathur R. et al. Fractionation of silver isotopes in native silver explained by redox reactions // Geochim. Cosmochim. Acta. 2018. Vol. 224. P. 313–326.

Scant data exist on the silver isotope composition of native silver specimens because of the relative newness of the technique. This study increases the published dataset by an order of magnitude and presents 80 silver new isotope analyses from native silver originating from a diverse set of worldwide deposits (8 deposit types, 33 mining districts in five continents). The measured isotopic range (defined as delta Ag-109/Ag-107 in per mil units compared to NIST 978 Ag isotope standard) is +2.1 to -0.86 parts per thousand(2 sigma errors less than 0.015); with no apparent systematic correlations to date with deposit type or even within districts. Importantly, the data centering on 0 parts per thousand all come from high temperature hypogene/primary deposits whereas flanking and overlapping data represent secondary supergene deposits. To investigate the causes for the more fractionated values, several laboratory experiments involving oxidation of silver from natural specimens of Ag-rich sulfides and precipitation and adsorption of silver onto reagent grade MnO2 and FeOOH were conducted. Simple leach experiments demonstrate little Ag isotope fractionation occurred through oxidation of Ag from native Ag (Delta Ag-109(solution-native) = 0.12 parts per thousand). In contrast, significant fractionation occurred through precipitation of native Ag onto MnO2 (up to Delta Ag-109(solution-MnO2) = 0.68 parts per thousand, or 0.3amu). Adsorption of silver onto the MnO2 and FeOOH did not produce as large fractionation as precipitation (mean value of Delta Ag-109(solution-MnO2) = 0.10 parts per thousand). The most likely cause for the isotopic variations seen relates to redox effects such as the reduction of silver from Ag (I) to Ag degrees that occurs during precipitation onto the mineral surface. Since many Ag deposits have halos dominated by MnO2 and FeOOH phases, potential may exist for the silver isotope composition of ores and surrounding geochemical haloes to be used to better understand ore genesis and potential exploration applications. Aside from the Mn oxides, surface fluid silver isotope compositions might provide information about geochemical reactions relevant to both environmental and hydrometallurgical applications.


21. U01624
Mikhail S., Howell D. A petrological assessment of diamond as a recorder of the mantle nitrogen cycle // Am. Miner. 2016. Vol. 101, № 3–4. P. 780–787.

Nitrogen is fundamental to the evolution of Earth and the life it supports, but for reasons poorly understood, it is cosmochemically the most depleted of the volatile elements. The largest reservoir in the bulk silicate Earth is the mantle, and knowledge of its nitrogen geochemistry is biased, because >= 90% of the mantle nitrogen database comes from diamonds. However, it is not clear to what extent diamonds record the nitrogen characteristics of the fluids/melts from which they precipitate. There is ongoing debate regarding the fundamental concept of nitrogen compatibility in diamond, and empirical global data sets reveal trends indicative of nitrogen being both compatible (fibrous diamonds) and incompatible (non-fibrous monocrystalline diamonds). A more significant and widely overlooked aspect of this assessment is that nitrogen is initially incorporated into the diamond lattice as single nitrogen atoms. However, this form of nitrogen is highly unstable in the mantle, where nitrogen occurs as molecular forms like N-2 or NH4+ both of which are incompatible in the diamond lattice. A review of the available data shows that in classic terms, nitrogen is the most common substitutional impurity found in natural diamonds because it is of very similar atomic size and charge to carbon. However, the speciation of nitrogen, and how these different species disassociate during diamond formation to create transient monatomic nitrogen, are the factors governing nitrogen abundance in diamonds. This suggests the counter-intuitive notion that a nitrogen-free (Type II) diamond could grow from a N-rich media that is simply not undergoing reactions that liberate monatomic N. In contrast, a nitrogen-bearing (Type I) diamond could grow from a fluid with a lower N abundance, in which reactions are occurring to generate (unstable) N atoms during diamond formation. This implies that diamond's relevance to nitrogen abundance in the mantle is far more complicated than currently understood. Therefore, further petrological investigations are required to enable accurate interpretations of what nitrogen data from mantle diamonds can tell us about the deep nitrogen budget and cycle.


22. U01624
Neave D.A., Putirka K.D. A new clinopyroxene-liquid barometer, and implications for magma storage pressures under Icelandic rift zones // Am. Miner. 2017. Vol. 102, № 4. P. 777–794.

Pressure is one of the key variables that controls magmatic phase equilibria. However, estimating magma storage pressures from erupted products can be challenging. Various barometers have been developed over the past two decades that exploit the pressure-sensitive incorporation of jadeite (Jd) into clinopyroxene. These Jd-in-clinopyroxene barometers have been applied to rift zone magmas from Iceland, where published estimates of magma storage depths span the full thickness of the crust, and extend into the mantle. However, tests performed on commonly used clinopyroxene-liquid barometers with data from experiments on H2O-poor tholeiites in the 1 atm to 10 kbar range reveal substantial pressure-dependent inaccuracies, with some models overestimating pressures of experimental products equilibrated at 1 atm by up to 3 kbar. The pressures of closed-capsule experiments in the 1-5 kbar range are also overestimated, and such errors cannot be attributed to Na loss, as is the case in open furnace experiments. The following barometer was calibrated from experimental data in the 1 atm to 20 kbar range to improve the accuracy of Jd-in-clinopyroxene barometry at pressures relevant to magma storage in the crust: P(kbar) = -26.27 + 39.16 T(K)/10(4) ln [X-Id(Cpx)/X-NaO0.5(liq) X-AlO1.5(liq) (X-SiO2(liq))(2)] - 4.22ln(X-DiHd(Cpx)) + 78.43X(AlO1.5)(liq) + 393.81(X-NaO0.5(liq) X-KO0.5(liq))(2) This new barometer accurately reproduces its calibration data with a standard error of estimate (SEE) of +/- 1.4 kbar, and is suitable for use on hydrous and anhydrous samples that are ultramafic to intermediate in composition, but should be used with caution below 1100 degrees C and at oxygen fugacities greater than one log unit above the QFM buffer. Tests performed using with data from experiments on H2O-poor tholeiites reveal that 1 atm runs were overestimated by less than the model precision (1.2 kbar); the new calibration is significantly more accurate than previous formulations. Many current estimates of magma storage pressures may therefore need to be reassessed. To this end, the new barometer was applied to numerous published clinopyroxene analyses from Icelandic rift zone tholeiites that were filtered to exclude compositions affected by poor analytical precision or collected from disequilibrium sector zones. Pressures and temperatures were then calculated using the new barometer in concert with Equation 33 from Putirka (2008). Putative equilibrium liquids were selected from a large database of Icelandic glass and whole-rock compositions using an iterative scheme because most clinopyroxene analyses were too primitive to be in equilibrium with their host glasses. High-Mg# clinopyroxenes from the highly primitive Borgarhraun eruption in north Iceland record a mean storage pressure in the lower crust (5.7 kbar). All other eruptions considered record mean pressures in the mid-crust, with primitive clinopyroxene populations recording slightly higher pressures (3.1-3.6 kbar) than evolved populations (2.6-2.8 kbar). Thus, while some magma processing takes place in the shallow crust immediately beneath Iceland's central volcanoes, magma evolution under the island's neovolcanic rift zones is dominated by mid-crustal processes.


23. U10290
Ozawa H. et al. High-pressure melting experiments on Fe-Si alloys and implications for silicon as a light element in the core // Earth Planet. Sci. Lett. 2016. Vol. 456. P. 47–54.

We carried out melting experiments on Fe-Si alloys to 127 GPa in a laser-heated diamond-anvil cell (DAC). On the basis of textural and chemical characterizations of samples recovered from a DAC, a change in eutectic liquid composition in the Fe-FeSi binary system was examined with increasing pressure. The chemical compositions of coexisting liquid and solid phases were quantitatively determined with field emission-type electron microprobes. The results demonstrate that silicon content in the eutectic liquid decreases with increasing pressure to less than 1.5 +/- 0.1 wt.% Si at 127 GPa. If silicon is a single light element in the core, 4.5 to 12 wt.% Si is required in the outer core in order to account for its density deficit from pure iron. However, such a liquid core, whose composition is on the Si-rich side of the eutectic point, crystallizes less dense solid, CsCl (B2)-type phase at the inner core boundary (ICB). Our data also show that the difference in silicon concentration between coexisting solid and liquid is too small to account for the observed density contrast across the ICB. These indicate that silicon cannot be the sole light element in the core. Previous geochemical and cosmochemical arguments, however, strongly require similar to 6 wt.% Si in the core. It is possible that the Earth's core originally included similar to 6 wt.% Si but then became depleted in silicon by crystallizing SiO2 or MgSiO3.


24. Pham-Ngoc C. et al. Characteristic Features of REE and Pb-Zn-Ag Mineralizations in the Na Son Deposit, Northeastern Vietnam // Resour. Geol. 2016. Vol. 66, № 4. P. 404–418.

The Na Son deposit is a small-scale Pb-ZnPb-Zn-Ag deposit in northeast Vietnam and consists of biotite-chlorite schist, reddish altered rocks, quartz veins and syenite. The biotite-chlorite schist is intruded by syenite. Reddish altered rocks occur as an alteration halo between the biotite-allanite-bearing quartz veins and the biotite-chlorite schist. Allanite occurs in the biotite-allanite-bearing quartz veins and in the proximal reddish altered rocks. Rare earth element (REE) fluorocarbonate minerals occur along fractures or at rim of allanite crystals. The later horizontal aggregates of sulfide veins and veinlets cut the earlier reddish altered rocks. The earlier Pb-Zn veins consist of a large amount of galena and lesser amounts of sphalerite, pyrite and molybdenite. The later Cu veins cutting the Pb-Zn veins include chalcopyrite and lesser amounts of tetrahedrite and pyrite. The occurrences of two-phase H2O-CO2 fluid inclusions in quartz from biotite-allanite-bearing quartz veins and REE-bearing fluorocarbonate minerals in allanite suggest the presence of CO2 and F in the hydrothermal fluid. The oxygen isotopic ratios of the reddish altered rocks, biotite-chlorite schist, and syenite range from +13.9 to +14.9, +11.5 to +13.3 parts per thousand, and +10.1 to +11.6 parts per thousand, respectively. Assuming an isotopic equilibrium between quartz (+14.6 to +15.8 parts per thousand) and biotite (+8.6 parts per thousand) in the biotite-allanite-bearing quartz vein, formation temperature was estimated to be 400 degrees C. At 400 degrees C, O-18 values of the hydrothermal fluid in equilibrium with quartz and biotite range from +10.5 to +11.7 parts per thousand. These O-18 values are consistent with fluid that is derived from metamorphism. Assuming an isotopic equilibrium between galena (+1.5 to +1.7 parts per thousand) and chalcopyrite (+3.4 parts per thousand), the formation temperature was estimated to be approximately 300 degrees C. The formation temperature of the Na Son deposit decreased with the progress of mineralization. Based on the geological data, occurrence of REE-bearing minerals and oxygen isotopic ratios, the REE mineralization is thought to result from interaction between biotite-chlorite schist and REE-, CO2- and F-bearing metamorphic fluid at 400 degrees C under a rock-dominant condition.


25. U22974
Puckett E.G. et al. New numerical approaches for modeling thermochemical convection in a compositionally stratified fluid // Phys. Earth Planet. Inter. 2018. Vol. 276. P. 10–35.

Geochemical observations of mantle-derived rocks favor a nearly homogeneous upper mantle, the source of mid ocean ridge basalts (MORE), and heterogeneous lower mantle regions. Plumes that generate ocean island basalts are thought to sample the lower mantle regions and exhibit more heterogeneity than MORB. These regions have been associated with lower mantle structures known as large low shear velocity provinces (LLSVPS) below Africa and the South Pacific. The isolation of these regions is attributed to compositional differences and density stratification that, consequently, have been the subject of computational and laboratory modeling designed to determine the parameter regime in which layering is stable and understanding how layering evolves. Mathematical models of persistent compositional interfaces in the Earth's mantle may be inherently unstable, at least in some regions of the parameter space relevant to the mantle. Computing approximations to solutions of such problems presents severe challenges, even to state-of-the-art numerical methods. Some numerical algorithms for modeling the interface between distinct compositions smear the interface at the boundary between compositions, such as methods that add numerical diffusion or 'artificial viscosity' in order to stabilize the algorithm. We present two new algorithms for maintaining high-resolution and sharp computational boundaries in computations of these types of problems: a discontinuous Galerkin method with a bound preserving limiter and a Volume-of-Fluid interface tracking algorithm. We compare these new methods with two approaches widely used for modeling the advection of two distinct thermally driven compositional fields in mantle convection computations: a high-order accurate finite element advection algorithm with entropy viscosity and a particle method that carries a scalar quantity representing the location of each compositional field. All four algorithms are implemented in the open source finite element code ASPECT, which we use to compute the velocity, pressure, and temperature associated with the underlying flow field. We compare the performance of these four algorithms on three problems, including computing an approximation to the solution of an initially compositionally stratified fluid at Ra = 10(5) with buoyancy numbers B that vary from no stratification at B = 0 to stratified flow at large B.


26. U01624
Putirka K. Amphibole thermometers and barometers for igneous systems and implications for eruption mechanisms of felsic magmas at arc volcanoes // Am. Miner. 2016. Vol. 101, № 3–4. P. 841–858.

Calcic, igneous amphiboles are of special interest as their compositional diversity and common occurrence provide ample potential to investigate magmatic processes. But not all amphibole-based barometers lead to geologically useful information: recent and new tests reaffirm prior studies (e.g., Erdman et al. 2014), indicating that amphibole barometers are generally unable to distinguish between experiments conducted at 1 atm and at higher pressures, except under highly restrictive conditions. And the fault might not lie with experimental failure. Instead, the problem may relate to an intrinsic sensitivity of amphiboles to temperature (7) and liquid composition, rather than pressure. The exceptional conditions are those identified by Anderson and Smith (1995): current amphibole barometers are more likely to be useful when T < 800 degrees C and Fe#(Amp) = Fe-AmP/(Fe-AmP+Mg-AmP) < 0.65. Experimentally grown and natural calcic amphiboles are here used to investigate amphibole solid solution behavior, and to calibrate new thermometers and tentative amphibole barometers that should be applicable to igneous systems generally. Such analysis reveals that amphiboles are vastly less complex than may be inferred from published catalogs of end-member components. Most amphiboles, for example, consist largely of just three components: pargasite [NaCa2(Fm4Al)Si6Al2O22(OH)(2)], kaersutite [NaCa2(Fm4Ti)Si6Al2O23(OH)], and tremolite + ferro-actinolite [Ca2Fm5Si8O22(OH)(2), where Fm = Fe+Mn+Mg]. And nearly all remaining compositional variation can be described with just four others: alumino-tschermakite [Ca-2(Fm3Al2)Si6Al2O22(OH)(2)], a Na-K-gedrite-like component [(Na,K)Fm6AlSi6Al2O22(OH)(2)], a ferri-ferrotschermakite-like component [Ca-2(Fm3Fe)Si6Al2O22(OH)(2)], and an as yet unrecoDrii7ed component with 3 to 4Al atoms per formula unit (apfu), 1 apfu each of Na and Ca, and <6 Si apfu, here termed aluminous kaersutite: NaCaFm4Ti(Fe3+,Al) Si5Al3O23(OH). None of these components, however, are significantly pressure (P) sensitive, leaving the Al-in-amphibole approach, with all its challenges, the best existing hope for an amphibole barometer. A new empirical barometer based on D-Al successfully differentiates experimental amphiboles crystallized at 1 to 8 kbar, at least when multiple P estimates, from multiple amphibole compositions, are averaged. Without such averaging however, amphibole barometry is a less certain proposition, providing 2 kbar precision on individual estimates for calibration data, and +/- 4 kbar at best for test data; independent checks on P are thus needed. Amphibole compositions, however, provide for very effective thermometers, here based on D-Ti, D-Na, and amphibole compositions alone, with precisions of 30 degrees C. These new models, and tests for equilibrium, are collectively applied to Augustine volcano and the 2010 eruption at Merapi. Both localities reveal a significant cooling and crystallization interval (>190-270 degrees C) at pressures of 0.75 to 2.2 kbar atAugustine and Merapi, respectively, perhaps the likely depths from which pre-eruption magmas are stored. Such considerable intervals of cooling at shallow depths indicate that mafic magma recharge is not a proximal cause of eruption. Rather, eruption triggering is perhaps best explained by the classic "second boiling" concept, where post-recharge cooling and crystallization drive a magmatic system toward vapor saturation and positive buoyancy.


27. Smith D.J. et al. Hydrothermal alteration and fluid pH in alkaline-hosted epithermal systems // Ore Geol. Rev. 2017. Vol. 89. P. 772–779.

Epithermal gold mineralisation is found in a wide compositional range of host lithologies, but despite the diversity the alteration mineral assemblages are often similar between deposits. Notable exceptions are those gold deposits hosted in alkaline host rocks. Alkaline-hosted epithermal deposits are rare, but important, as they include some of the world's largest known epithermal deposits by contained metal (e.g. Ladolam, Cripple Creek, Porgera). As well as the exceptional gold contents, the alkaline -hosted systems tend to exhibit different alteration mineral assemblages, with less quartz and widespread silicification than sub-alkaline -hosted equivalents, and greaterenrichments in tellurium, and a scarcity of acid alteration (advanced argillic) types. In this study, geochemical modelling is used to demonstrate that 300 degrees C hydrothermal fluids in equilibrium with alkali, silica-undersaturated host rocks at low water/rock ratios reach significantly higher pH than equivalents in sub-alkaline lithologies. A maximum, near neutral pH (5.5-6) is buffered by reactions involving quartz in silica-saturated alkaline and calcalkaline lithologies. In silica-undersaturated, alkaline host rocks, quartz is exhausted by progressive water-rock interaction, and pH increases to 7 and above. Both tellurium and gold solubility are favoured by neutral to high fluid pH, and thus there is a clear mechanism within these hydrothermal systems that can lead to effective transport and concentration to produce gold telluride ore deposits in alkaline igneous hosts. This modelling demonstrates that alkaline rocks can still be altered to advanced argillic assemblages; the paucity of this alteration type in alkaline hosts instead points to NaCl >> HCl in magmatic volatile phases at the initiation of hydrothermal alteration.


28. U10290
von Strandmann P.A.E.P. et al. Chemical weathering processes in the Great Artesian Basin: Evidence from lithium and silicon isotopes // Earth Planet. Sci. Lett. 2014. Vol. 406. P. 24–36.

Variations in lithium and silicon isotope ratios in groundwaters of the Great Artesian Basin in Australia, and the causes of these variations, have been explored. The chemistries of Li and Si in groundwater are influenced by the dissolution of primary phases, the formation of secondary minerals, and the reaction of solid phases with dissolved constituents, while isotopic variations are generated by uptake into clays, which preferentially incorporate the light isotopes. The lithium isotopic composition (expressed as delta Li-7) of the groundwaters ranges from +9 to +16 parts per thousand, and clearly reflects changes in aquifer conditions. Reaction-transport modelling indicates that changes in Li concentrations are principally controlled by the ratio of the weathering rate of primary minerals to the precipitation rate of secondary minerals, whereas delta Li-7 is affected by the extent of isotope fractionation during secondary mineral formation (which is dependent on mineralogy). The patterns of groundwater Si concentrations and delta Si-30 values versus flow distance suggest that Si is at steady state in the aquifer. The delta Si-30 value of most of the groundwater samples is close to -1 parts per thousand, which is significantly lower than the delta Si-30 value of the reservoir rocks (similar to 0 parts per thousand). Since precipitation of clays preferentially removes the light Si isotopes from solution, the most plausible explanation for these low groundwater delta Si-30 values is addition of Si by dissolution of isotopically light secondary minerals. These data, together with model calculations, show that Li isotopes are extremely sensitive to changes in the chemical and physical conditions in the aquifer, whereas Si is not. Importantly, the model suggests that even in large aquifers with long fluid residence times, where steady-state would be expected to be reached, the concentrations and isotopic fractionation of trace elements are not controlled by Li adsorption. The model developed here provides a basis for using Li isotopes measured in groundwaters and surface waters to constrain weathering processes.


29. U01624
Yuan X. et al. Determination of pressure in aqueo-carbonic fluid inclusions at high temperatures from measured Raman frequency shifts of CO2 // Am. Miner. 2017. Vol. 102, № 1–2. P. 404–411.

Due to the presence of additional volatiles and/or electrolytes in CO2-H2O fluids, the total pressure of many natural aqueo-carbonic fluid inclusions at high temperatures as determined using microther-mometry is usually made with considerable uncertainty. In this paper, we present the results of our high P-T in situ Raman scattering study of high-density aqueo-carbonic fluids, with and without a small amount of CH4 and NaCl, whose objective is to derive a new method for pressure determination in aqueo-carbonic fluid inclusions at high temperatures. The measurement of the Fermi dyad bands at temperatures up to 400 degrees C and pressures up to 1200 MPa is described. The manner in which the frequency shifts and intensity of Raman bands are governed by pressure, temperature, presence of CH4 in carbonic and NaCl in aqueous fluids is discussed. From the monotonic dependence of the frequency shifts of the lower Fermi dyad band nu_ and the Fermi resonant splitting D (D = nu(+) - nu_) with pressure and temperature, the pressure (in MPa) in aqueo-carbonic fluid inclusions at elevated temperatures can be determined directly by using the following two polynomial equations: P (MPa) = -16 + 1.232x T -53.72x(Delta v_) 1.83 x 10(-3)x T-2 + 24.46x(Delta v_)(2) -0.292x Tx(Delta v_), P (MPa) = 26 + 1.501xT+ 193.24x(Delta D) 1.61 x 10(-3)xT(2)+ 5.436x(Delta D)(2) + 0.158xTx(Delta D), where T is in degrees C, Delta v_ and Delta D represent frequency shifts (in cm(-1)) of the lower band and the resonant splitting relative to the reference values measured at 23 degrees C and 6 MPa, respectively. Based on the attainable accuracy of the fitted peak positions and the results from fitting of Raman frequency shifts' dependence with pressure and temperature, the uncertainty in pressure determination is about 50 MPa for pressures determined from nu_ and 40 MPa from that determined from D.


30. 001408
Акинфиев Н.Н., Тагиров Б.Р. Цинк в гидротермальных системах: термодинамическое описание гидроксо-, хлоридных и гидросульфидных комплексов // Геохимия. 2014. № 3. С. 214-232.

Выполнен критический анализ литературных данных по константам устойчивости частиц водного раствора в системе Zn O H S-II Cl. Для уточнения состава и устойчивости хлоридных комплексов Zn поставлены дополнительные опыты по растворимости сфалерита (ZnSкр) в хлоридно-сульфидных растворах при 175°С и давлении насыщенного пара раствора. В результате получен набор значений термодинамических свойств для 25°С, 1 бар и параметров уравнения модели НКF (Хелгесон-Киркхэм-Флауэрс) для гидроксо-, хлоридных и гидросульфидных комплексов Zn. Константы реакций растворения сфалерита с образованием гидросульфидных и особенно хлоридных комплексов увеличиваются по мере роста температуры. В высокотемпературных (>250°С) хлоридно-сульфидных гидротермальных растворах основной формой переноса цинка являются хлоридные комплексы при преобладающей роли ZnCl . По мере снижения температуры увеличивается доля комплексов с меньшим числом лигандов Cl-. В области от слабокислых до щелочных рН доминируют гидросульфидные комплексы Zn, однако их концентрация в равновесии со сфалеритом невысока (первые ppm при 400°C и концентрации серы <0.1 моль кг-1) и убывает при снижении температуры. В области доминирования хлоридных комплексов концентрация растворенного цинка может составлять десятые доли процента в области близнейтральных рН при 400°C и m(NaCl) = 1.0, увеличиваясь при подкислении флюида. Важнейшим фактором, контролирующим концентрацию растворенного цинка, является температура: охлаждение приводит к эффективному отложению сфалерита, особенно в области преобладания хлоридных комплексов. Термодинамические свойства твердых фаз и параметры модели HKF для частиц водного раствора в системе Zn O-H S-II Cl представлены в on-line версии базы данных FreeGC (http://www-b.ga.gov.au/minerals/research/methodology/geofluids/thermo/calculator/search.jsp), позволяющей рассчитывать значения энергии Гиббса компонентов системы и константы реакций с их участием в области PT-параметров до 600°С и 3 кбар.


31. 044066
Бочкарев В.С. Причина появления рудоносных химических элементов на планете Земля. Металлогения и планетология // Горные Ведомости. 2015. № 12 (139). С. 6–21.

В статье рассматривается авторская модель геодинамики Земли от двойной звезды к взрывному формированию планет, которая позволила вскрыть и объяснить особенности структуры Солнечной системы. Гипотетическая вторая звезда двойной системы (Елена Прекрасная) после первого взрыва и формирования планет-гигантов в последовательности Нептун, Юпитер, Сатурн и Уран испытала коллапс, обязанный появлению тяжелых элементов от железа до урана. Второй взрыв привел к созданию плотных планет от Марса до Меркурия.


32. 001408
Воропаев С.А. и др. Спектральные и структурные свойства наночастиц углерода, синтезируемых в природных и искусственных процессах // Геохимия. 2016. № 10. С. 909–918.

Рассмотрены особенности формирования углеродных наночастиц в космосе и при извержениях вулканов определенного типа, проведено сравнение с существующими методами синтеза в нанотехнологиях. С помощью методов электронной дифракции и рамановской спектроскопии исследованы образцы наноалмазов, синтезируемых при гидродинамической кавитации в различных углеводородных жидкостях. Выделены такие наноформы углерода как сложные фуллерены, наноалмазы и ГЦК-углерод. Проведено легирование синтезируемых наноалмазов кремнием, проанализированы спектры фотолюминесценции и рассмотрены приложения результатов для гео- и космохимии.


33. 001573
Ковалев С.Г. и др. Условия образования магматических пород при плюмовом процессе (на примере западного склона Южного Урала) // Доклады Академии Наук. 2017. Т. 475. № 2. С. 171–175.

Приведены новые данные об условиях формирования магматических пород западного склона Южного Урала и прилегающей части Восточно-Европейской платформы. На основе расчётов Р-Т-параметров плавления мантийного субстрата показано, что при реализации плюмового процесса образуются однотипные породы (пикриты, пикродолериты), генезис которых различен. Первый тип?- результат кристаллизации недифференцированного мантийного расплава в верхних горизонтах коры, второй?- образуется в результате внутрикамерной дифференциации в крупных внутрикоровых магматических камерах/очагах.


34. 001408
Костицын Ю.А. и др. Современные проблемы геохимических и U–Pb геохронологических исследований циркона в океанических породах // Геохимия. 2015. № 9. С. 771-800.

Приводятся результаты исследования методом лазерной абляции (LA-ICP-MS) зерен циркона, выделенного из магматических пород впадины Маркова и гидротермального поля Ашадзе (Срединно-Атлантический хребет). Изучены U-Pb и Lu-Hf изотопные системы индивидуальных зерен циркона и их микроэлементный состав. Также исследованы Sm-Nd и Rb-Sr изотопные системы пород, содержащих циркон. U-Pb система зерен циркона трех образцов габбро-норитов впадины Маркова показала значения возраста от 0.90 ± 0.02 до 2.00 ± 0.05 млн лет, причем более молодой возраст оказался у образцов, драгированных с большей глубины. Циркон из четырех образцов габбро и трондьемитов поля Ашадзе оказался одновозрастным - от 1.04 ± 0.07 до 1.12 ± 0.09 млн лет. В образце I-1069/19 плагиоклазового троктолита впадины Маркова были обнаружены экзотические зерна циркона с возрастом от 90 млн лет до 3.2 млрд лет, что не согласуется с возрастом пород в Срединно-Атлантическом хребте. В статье обсуждаются гипотезы происхождения подобных экзотических зерен, в частности, их образование в мантийных глубинах, попадание туда с субдуцированным материалом и др. Эксперименты по растворимости циркония показывают, что основные и ультраосновные расплавы могут стать пересыщенными относительно циркония только при нереально высоких его содержаниях, которых в соответствующих породах обычно не встречаются. Инородный, захваченный циркон в расплавах основного и ультраосновного состава должен растворяться и его находки в этих породах, скорее всего, указывают на отсутствие равновесия. Циркон может формироваться в интрузивных породах основного состава в условиях фракционной кристаллизации на заключительных ее стадиях, поэтому в габброидах нередко присутствует собственный циркон.


35. 001200
Петрова В.И. и др. Молекулярная геохимия органического вещества триасовых пород Северо-Восточной части Баренцева моря - влияние тектонических и магматических процессов // Геология и геофизика. 2017. Т. 58. № 3–4. С. 398–409.

По результатам хромато-масс-спектрометрического изучения состава и распределения углеводородных молекулярных маркеров (алканов, изопреноидов, цикланов, аренов) охарактеризованы генезис, фациальные условия осадконакопления и уровень катагенеза рассеянного органического вещества триасовых отложений северо-восточной части Баренцевоморского осадочного бассейна, вскрытых опорно-параметрическим бурением на Адмиралтейском поднятии, архипелаге Земля Франца-Иосифа и Ферсмановской структуре. Показано, что позднемезозойско-кайнозойский аплифт региона и последующая интенсивная магматическая деятельность оказали существенное влияние на историю их термального развития. Наиболее ярко данная тенденция проявлена в осадочном разрезе архипелага Земля Франца-Иосифа, где аддитивное воздействие указанных факторов привело к радикальному увеличению трансформации рассеянного органического вещества вплоть до градации АК1.


36. 035245
Холоднов В.В. и др. Рифейский магматизм и рудообразование, предшествующие раскрытию Уральского палеоокеана (западный склон Южного Урала) // Литосфера. 2017. № 2. С. 5–26.

Проведен анализ состава и рудоносности магматических пород нижнего и среднего рифея в рифтогенных структурах Башкирского мегантиклинория (БМА) с привлечением данных по ряду соседних сегментов западного склона Ю. Урала. Установлена эволюция составов во времени - от пород c геохимическими параметрами типа OIB (трахибазальты месторождения Сибирка) и пород, близких E-MORB (вулканиты машакской свиты, базиты и гранитоиды кусинско-копанского комплекса, силлово-дайковые рои и др.), - в направлении к N-MORB (назямские амфиболиты). Этот факт корелирует с изменением изотопно-геохимических параметров. Первичные отношения изотопов Nd в магматических породах и связанных с ними рудно-метасоматических образованиях меняются от отрицательных значений, характерных для производных зрелой континентальной коры, до положительных величин ?Nd = +4...+5, отражая увеличение степени деплетирования рифейско-вендской литосферной мантии и эволюцию магматических и флюидных источников во времени. Указанные закономерности для возрастного диапазона 1750-1200 млн лет, а также данные по изотопии Nd и Sr для магматитов последующих этапов формирования континентальной коры Уральского орогена свидетельствуют о возможном раскрытии океанического бассейна к востоку от Восточно-Европейской платформы, начиная еще со второй половины среднего рифея. В границах БМА этому предшествовало формирование рифтовых структур типа Красного моря. Одна из таких структур (Кувашско-Назямский рифт-грабен) на территории БМА была относительно короткоживущей и закрылась в течение интервала 1250-1150 млн лет.


37. 001408
Цехоня Т.И. Хроника всероссийского ежегодного семинара по экспериментальной минералогии, петрологии и геохимии 2015 года // Геохимия. 2015. № 12. С. 1132-1141.

21-22 апреля 2015 года в Москве прошел очередной Всероссийский ежегодный семинар по экспериментальной минералогии, петрологии и геохимии, организованный Институтом геохимии и аналитической химии им. В.И. Вернадского и Институтом экспериментальной минералогии РАН при поддержке Российского фонда фундаментальных исследований (грант 15-05-20159г). На семинаре рассмотрены новейшие экспериментальные исследования по различным геохимическим проблемам: фазовые равновесия при высоких Т-Р параметрах, образование и дифференциация магм, влияние летучих на процесс магмообразования, гидротермальный процесс и рудообразование, синтез минералов и изучение их термодинамических параметров, планетологические и космохимические исследования, изучение физических свойств геоматериалов, проблемы биогеохимии и геоэкологии. Семинар открыл председатель семинара профессор А.А. Кадик. Он отметил, что семинар продолжает пользоваться большой популярностью, на что указывает количество представленных докладов, а также с удовлетворением проинформировал, что среди участников немало молодых ученых.


38. 035245
Чащин В.В., Кульчицкая А.А., Елизарова И.Р. Флюидный режим формирования малосульфидного платинометалльного месторождения Лойпишнюн, Мончетундровский базитовый массив (Кольский полуостров, Россия) // Литосфера. 2017. Т. 17. № 6. С. 91–109.

Методом пиролитической газовой хроматографии исследованы особенности распределения летучих компонентов (H2O, H2, CO2, CO, H2S, SO2, CH4 и N2) в безрудных и рудоносных породах малосульфидного платинометалльного месторождения Лойпишнюн базального структурного типа, локализованного в пределах Мончетундровского базитового массива Кольского региона. Установлено, что платинометалльные руды отличаются от безрудных пород более высокой общей флюидонасыщенностью, повышенным содержанием H2O и, особенно, H2S и SO2. В безрудных породах в отличие от оруденелых выявлена более высокая концентрация CO, H2 и N2. Основную роль в процессе платинометалльного рудообразования играют H2S и SO2. На начальном этапе платинометалльного рудообразования вклад этих компонентов равноценен, о чем свидетельствуют близкие величины положительных корреляционных связей этих летучих компонентов с платиноидами и рудными элементами. При дальнейшем снижении температуры доминирующую роль в рудогенезе играет сероводород, который имеет высокую положительную корреляцию в основном с медью и платиноидами. Полученные результаты позволяют предполагать, что процесс платинометалльного рудообразования протекал в широком диапазоне температур от 1050 до 450°С. Он начинался на позднемагматической, посткумулусной стадии (1050-850°С) при переменных окислительно-восстановительных условиях и продолжался в процессе постепенного снижения температуры до 450°С в условиях уменьшения концентрации серы.


39. 042658
Шилобреева С.Н. Масс-спектрометрия вторичных ионов в гео- и космохимии: определение и распределение водорода и углерода в силикатных образцах // Масс-Спектрометрия. 2017. Т. 14. № 1. С. 40–54.

Представлен обзор отечественной и зарубежной литературы последних лет, посвященный использованию метода масс-спектрометрии вторичных ионов (МСВИ) для определения углерода и водорода при решении задач геохимии и космохимии. Особое внимание уделено проблемам, возникающим при градуировке для количественного определения углерода и водорода методом МСВИ. Описаны приборы, используемые в масс-спектрометрии вторичных ионов. Рассмотрен метод масс-спектрометрической визуализации (имиджинг) с использованием математической обработки результатов регистрации вторичного ионного тока углерода и водорода для визуализации 3D распределения углерода и водорода.


40. 001573
Широносова Г.П. и др. Термодинамическое моделирование поведения РЗЭ в высококонцентрированных по сульфатной сере окисленных гидротермальных флюидах // Доклады Академии Наук. 2016. Т. 469. № 5. С. 611–615.

Проведены термодинамические расчеты минеральных равновесий с участием РЗЭ во фторидно-сульфидно-хлоридно-карбонатно-сульфатной системе в присутствии Na, Ca, P с флюидами различной кислотности–щелочности с использованием программного комплекса HCh [11]. Полученные термодинамические характеристики тенардита позволили провести расчеты с его участием в сложных гидротермальных условиях, имитирующих присутствие окисленных флюидов при 500–100°С, 2000–125 бар. Из других возможных твердых фаз наблюдали образование РЗЭ-флюорита, монацита, РЗЭ-F-апатита в виде идеальных твердых растворов: (CaF2–(Ln,Y)F3), LnPO4, (Ca5(PO4)3F–(Ln,Y)3(PO4)3) соответственно, где Ln – La, Ce, Pr, Nd, Sm, Eu, Gd, ксенотима, ангидрита, элементарной S, кальцита.


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