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Физико-химические и петрофизические исследования в науках о Земле

Журнальные статьи

1. U01624
Davis F.A. et al. Revisiting the electron microprobe method of spinel-olivine-orthopyroxene oxybarometry applied to spinel peridotites // American Mineralogist. 2017. Vol. 102, № 2. P. 421–435.

Natural peridotite samples containing olivine, orthopyroxene, and spinel can be used to assess the oxygen fugacity fO2 of the upper mantle. The calculation requires accurate and precise quantification of spinel Fe3+/?Fe ratios. Wood and Virgo (1989) presented a correction procedure for electron microprobe (EPMA) measurements of spinel Fe3+/?Fe ratios that relies on a reported correlation between the difference in Fe3+/?Fe ratio by Mossbauer spectroscopy and by electron microprobe (?Fe3+/?FeMoss-EPMA) and the Cr# [Cr/(Al+Cr)] of spinel. This procedure has not been universally adopted, in part, because of debate as to the necessity and effectiveness of the correction. We have performed a series of replicate EPMA analyses of several spinels, previously characterized by Mossbauer spectroscopy, to test the accuracy and precision of the Wood and Virgo correction. While we do not consistently observe a correlation between Cr# and ?Fe3+/?FeMoss-EPMA in measurements of the correction standards, we nonetheless find that accuracy of Fe3+/?Fe ratios determined for spinel samples treated as unknowns improves when the correction is applied. Uncorrected measurements have a mean ?Fe3+/?FeMoss-EPMA = 0.031 and corrected measurements have a mean ?Fe3+/?FeMoss-EPMA = ?0.004. We explain how the reliance of the correction on a global correlation between Cr# and MgO concentration in peridotitic spinels improves the accuracy of Fe3+/?Fe ratios despite the absence of a correlation between ?Fe3+/?FeMoss-EPMA and Cr# in some analytical sessions. Precision of corrected Fe3+/?Fe ratios depends on the total concentration of Fe, and varies from ±0.012 to ±0.032 (1?) in the samples analyzed; precision of uncorrected analyses is poorer by approximately a factor of two. We also present an examination of the uncertainties in the calculation contributed by the other variables used to derive fO2 . Because there is a logarithmic relationship between the activity of magnetite and logfO2, the uncertainty in fO2 relative to the QFM buffer contributed by the electron microprobe analysis of spinel is asymmetrical and larger at low ferric Fe concentrations (+0.3/?0.4 log units, 1?, at Fe3+/?Fe = 0.10) than at higher ferric Fe concentrations (±0.1 log units, 1?, at Fe3+/?Fe = 0.40). Electron microprobe analysis of olivine and orthopyroxene together contribute another ±0.1 to ±0.2 log units of uncertainty (1?). Uncertainty in the temperature and pressure of equilibration introduce additional errors on the order of tenths of log units to the calculation of relative fO2. We also document and correct errors that appear in the literature when formulating fO2 that, combined, could yield errors in absolute fO2 of greater than 0.75 log units—even with perfectly accurate Fe3+/?Fe ratios. Finally, we propose a strategy for calculating the activity of magnetite in spinel that preserves information gained during analysis about the ferric iron content of the spinel. This study demonstrates the superior accuracy and precision of corrected EPMA measurements of spinel Fe3+/?Fe ratios compared to uncorrected measurements. It also provides an objective method for quantifying uncertainties in the calculation of fO2 from spinel peridotite mineral compositions.


2. Duncan Keppie J., Dostal J., Li J. Nd isotopic data indicating Oaxacan source of Ordovician granitoids in the Acatlan Complex, southern Mexico: Paleogeographic implications // Tectonophysics. 2018. Vol. 740–741. P. 1–9.

Ordovician megacrystic granitoids intrude the Neoproterozoic-Paleozoic Acatlan Complex of southern Mexico, which consists of rift-passive margin, clastic rocks and rift-related igneous rocks. Most of the Neoproterozoic-Ordovician rocks were folded at greenschist-amphibolite facies metamorphism, however some rocks underwent polyphase deformation, underthrusting under high-pressure metamorphism followed by extrusion during the Late Devonian-Carboniferous (365–330?Ma). Most of our new Nd isotopic data for Ordovician granitoids have ?Nd(T) ranging between ?4.5 and ?7.2 with TDM ages of 1.3–1.6?Ga that are similar to most published data from such Ordovician plutons: ?Nd(T) of ?0.2 to ?6.6 and TDM ages of 1.2–1.8?Ga. These values are comparable to the range shown by the Oaxacan Complex, which confirms the conclusion reached using zircon U-Pb isotopic data indicating an Oaxacan source. One exception is the Ordovician Teticic granitoid that has ?Nd(T) of ?4.8 to ?5.8 and TDM ages of 2162–2946?Ma. The combination of ca. 1.5 and 2–3?Ga TDM ages is also recorded in northwestern Amazonia, which is consistent with previous correlations of Oaxaquia with Amazonia. The transfer of Oaxaquia from Amazonia to southern Laurentia occurred during the amalgamation and breakup of Pangea, where the suture was roughly parallel to their relative motion: this resulted in dextral strike-slip faulting generally attributed to the Mojave-Sonora megashear.


3. U09363
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.


4. S13759
Gong H. et al. Geology and Lead–Sulphur Isotope Compositions of the Tongyu Volcanic-Hosted Massive Sulphide Copper Deposit in the Western Part of the North Qinling Orogen, China // Acta Geologica Sinica - English Edition. 2017. Vol. 91, № 5. P. 1767–1777.

The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide (VHMS) deposits with industrial value and is also a typical example of mineralization related to the subduction and metallogenesis during the Caledonian orogeny. We conducted systematic lead–sulphur isotope geochemical analyses of the Tongyu deposit to understand the possible ore-forming material sources and tectonic settings. Twenty-six sulphide samples yielded clustered ?34SCDT values of 1.13‰–3.36‰, average 2.22‰, and show a tower-type distribution, implying that the sulphur of the Tongyu copper deposit mainly originated from a mantle source. The Pb isotope compositions of sulphides (206Pb/204Pb = 17.59225–18.56354, average 18.32020; 207Pb/204Pb = 15.51770–15.69381, average 15.66217; 208Pb/204Pb = 37.99969–39.06953, average 38.52722) are close to the values of the volcanic host rocks (206Pb/204Pb = 18.10678–18.26293, average 18.21158; 207Pb/204Pb = 15.63196–15.68188, average 15.65345; 208Pb/204Pb = 38.43676–38.56360, average 38.49171), thus consistent with the Pb in ores and volcanic host rocks having been derived from a common source that was island-arc Pb related to oceanic crust subduction. The northward subduction of the Palaeo–Qinling oceanic crust triggered dehydration of the slab, which generated a large amount of high-oxygen-fugacity aqueous hydrothermal fluid. The fluid rose into the mantle wedge, activated and extracted metallogenic material and promoted partial melting of the mantle wedge. The magma and ore-forming fluid welled up and precipitated, finally forming the Tongyu VHMS copper deposit.


5. U10290
Kennedy B.M. et al. Surface tension driven processes densify and retain permeability in magma and lava // Earth and Planetary Science Letters. 2016. Vol. 433. P. 116–124.

We offer new insights into how an explosive eruption can transition into an effusive eruption. Magma containing >0.2 wt% dissolved water has the potential to vesiculate to a porosity in excess of 80 vol.% at atmospheric pressure. Thus all magmas contain volatiles at depth sufficient to form foams and explosively fragment. Yet gas is often lost passively and effusive eruptions ensue. Magmatic foams are permeable and understanding permeability in magma is crucial for models that predict eruptive style. Permeability also governs magma compaction models. Those models generally imply that a reduction in magma porosity and permeability generates an increased propensity for explosivity. Here, our experimental results show that surface tension stresses drive densification without creating an impermeable ‘plug’, offering an additional explanation of why dense magmas can avoid explosive eruption. In both an open furnace and a closed autoclave, we subject pumice samples with initial porosity of ?70 vol.% to a range of isostatic pressures (0.1–11 MPa) and temperatures (350–950?°C) relevant to shallow volcanic environments. Our experimental data and models constrain the viscosity, permeability, timescales, and length scales over which densification by pore-scale surface tension stresses competes with density-driven compaction. Where surface tension dominates the dynamics, densification halts at a plateau connected porosity of ?25 vol.% for our samples. SEM, pycnometry and micro-tomography show that in this process (1) microporous networks are destroyed, (2) the relative pore network surface area decreases, and (3) a remaining crystal framework enhances the longevity of macro-pore connectivity and permeability critical for sustained outgassing. We propose that these observations are a consequence of a surface tension-driven retraction of viscous pore walls at areas of high bubble curvature (micro-vesicular network terminations), and that this process drives bulk densification and permits continued outgassing. We propose a regime diagram of the relative dominance of surface tension and gravitational compaction that illustrates the interplay between viscosity, permeability, lengthscale and timescale. We contend that surface tension-driven magma densification is an as-yet overlooked phenomenon that extends our volcanological, geothermal and hydrothermal knowledge of how gas can escape densifying volcanic plugs and why dense lavas remain permeable.


6. U01624
Konecke B.A. et al. Co-variability of S6+, S4+, and S2? in apatite as a function of oxidation state: Implications for a new oxybarometer // American Mineralogist. 2017. Vol. 102, № 3. P. 548–557.

In this study, we use micro-X-ray absorption near-edge structures (?-XANES) spectroscopy at the S K-edge to investigate the oxidation state of S in natural magmatic-hydrothermal apatite (Durango, Mexico, and Mina Carmen, Chile) and experimental apatites crystallized from volatile-saturated lamproitic melts at 1000 °C and 300 MPa over a broad range of oxygen fugacities [( log(fO2)=FMQ, FMQ+1.2, FMQ+3; FMQ = fayalite-magnetite-quartz solid buffer]. The data are used to test the hypothesis that S oxidation states other than S6+ may substitute into the apatite structure. Peak energies corresponding to sulfate S6+ (~2482 eV), sulfite S4+ (~2478 eV), and sulfide S2? (~2470 eV) were observed in apatite, and the integrated areas of the different sulfur peaks correspond to changes in fO2 and bulk S content. Here, multiple tests confirmed that the S oxidation state in apatite remains constant when exposed to the synchrotron beam, at least for up to 1 h exposure (i.e., no irradiation damages). To our knowledge, this observation makes apatite the first mineral to incorporate reduced (S2?), intermediate (S4+), and oxidized (S6+) S in variable proportions as a function of the prevailing fO2 of the system. Apatites crystallized under oxidizing conditions (FMQ+1.2 and FMQ+3), where the S6+/STotal peak area ratio in the coexisting glass (i.e., quenched melt) is ~1, are dominated by S6+ with a small contribution of S4+, whereas apatites crystallizing at reduced conditions (FMQ) contain predominantly S2?, lesser amounts of S6+, and possibly traces of S4+. A sulfur oxidation state vs. S concentration analytical line transect across hydrothermally altered apatite from the Mina Carmen iron oxide-apatite (IOA) deposit (Chile) demonstrates that apatite can become enriched in S4+ relative to S6+, indicating metasomatic overprinting via a SO2-bearing fluid or vapor phase. This XANES study demonstrates that as the fO2 increases from FQM to FMQ+1.2 to FMQ+3 the oxidation state of S in igneous apatite changes from S2? dominant to S6+ > S4+ to S6+ >> S4+. Furthermore, these results suggest that spectroscopic studies of igneous apatite have potential to trace the oxidation state of S in magmas. The presence of three S oxidations states in apatite may in part explain the non-Henrian partitioning of S between apatite and melt. Our study reveals the potential to use the S signature of apatite to elucidate both oxygen and sulfur fugacity in magmatic and hydrothermal systems. GeoRef Subject orthosilicates silicates apatite Chile Mexico Durango Mexico olivine group phosphates South America nesosilicates silica minerals crystal chemistry quartz framework silicates sulfur fayalite


7. U10290
Lee C.-T.A., Morton D.M. High silica granites: Terminal porosity and crystal settling in shallow magma chambers // Earth and Planetary Science Letters. 2015. Vol. 409. P. 23–31.

High silica (>70 wt.% SiO2) granites (HSGs) are important carriers of highly incompatible elements, thus, understanding their origin is relevant to understanding how the composition of the continental crust evolves. We examined a large-scale geochemical study of plutons in the Peninsular Ranges Batholith in southern California (USA) to better understand the petrogenetic relationships between HSGs and the batholith. Using highly incompatible and compatible elements, we show that HSGs represent residual liquids within a felsic (69–72 wt.% SiO2) magmatic crystal mush at crystal fractions of 50–60% and residual liquid fractions of 40–50%. Trace element systematics show that separation of the HSG liquid from the crystal mush is inefficient, such that no more than 70–80% of the HSG is fully extracted and the remaining greater than 20–30% remains trapped in cumulate mush. We find little evidence of more efficient liquid–crystal segregation, which suggests that compaction-induced segregation may be too slow to be important on a large scale. Instead, the terminal porosity of 20–30% coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension (?0.74), which may indicate that crystal settling – perhaps in the form of hindered settling – drives segregation of viscous silicic melts and crystals. Unlike compaction, settling operates on timescales of 1–10 ky, fast enough to generate large volumes of HSG and complementary cumulates with trapped melt before magma chambers freeze. Many felsic plutons may thus be cumulates, but because of trapped melt, they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent. The approach here, using a combination of highly incompatible and compatible elements, provides a way of identifying and quantifying trapped melt fractions. Finally, we show that HSGs appear to form only in the shallow crust (<10 km) and rarely in the middle to lower crust. Where HSGs are common, mafic magmas are common too, suggesting a genetic relationship between the two. If HSGs derive by crystal fractionation of basaltic parents, they represent at most 5% of the original mass of parental magma, but because they form almost exclusively at low pressures, they may be over-represented in shallowly exhumed batholiths. Why HSGs form primarily in the upper crust is unclear.


8. U01624
Li Y. Temperature and pressure effects on the partitioning of V and Sc between clinopyroxene and silicate melt: Implications for mantle oxygen fugacity // American Mineralogist. 2018. Vol. 103, № 5. P. 819–823.

The partition coefficients of V and Sc between clinopyroxene and silicate melt (DVCpx/SM and DScCpx/SM) have been determined experimentally at 1200–1400 °C and 0.8–2.3 GPa, using a hornblende- and clinopyroxene-rich mantle rock in graphite-lined Pt95Rh05 capsules. The results show that the DVCpx/SM and DScCpx/SM values decrease from 3.8 to 2.3 and from 2.6 to 1.1, respectively, as the experimental temperature and pressure vary from 1200 °C and 0.8 GPa to 1400 °C and 2.3 GPa. The presence of water in silicate melts may also reduce DVCpx/SM and DScCpx/SM. These results imply that the effects of temperature, pressure, and melt water content on DVCpx/SM should be considered when using V systematics in cratonic mantle peridotites to constrain cratonic mantle oxygen fugacity (fO2). However, although the dominant V in the present silicate melt is mixed V3+ and V4+, the DVCpx/SM/DScCpx/SM together with literature data obtained at similar fO2 shows a nearly constant value of 1.68 ± 0.26, regardless of temperature, pressure, melt composition, and melt water content, indicating that these factors cannot cause fractionation of Sc3+ from mixed V3+ and V4+ in mantle melts through clinopyroxene/silicate melt partitioning. Therefore, in combination with V/Sc systematics in primitive MORBs and arc basalts, using DVCpx/SM and DScCpx/SM obtained at 1 bar and dry conditions should be valid to constrain mantle fO2, except for the case that the DCpx/SM for Sc3+ can be demonstrated to be fractionated from the DCpx/SM for mixed V4+ and V5+, which are present in oxidized basalts.


9. U01624
Neave D.A., Putirka K.D. A new clinopyroxene-liquid barometer, and implications for magma storage pressures under Icelandic rift zones // American Mineralogist. 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+39.16T(K)104ln[XCpxJdXliqNaO0.5XliqAlO1.5(XliqSiO2)2]?4.22ln(XCpxDiHd)+78.43XliqAlO1.5+393.81(XliqNaO0.5XliqKO0.5)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 °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."


10. U01624
Papike J.J. et al. Chromium, vanadium, and titanium valence systematics in Solar System pyroxene as a recorder of oxygen fugacity, planetary provenance, and processes // American Mineralogist. 2016. Vol. 101, № 4. P. 907–918.

Pyroxene is arguably the most powerful, single-phase geochemical and petrologic recorder of Solar System processes, from nebular condensation through planetary evolution, over a wide range of temperatures, pressures, and fo2. It is an important mineral phase in the crusts and mantles of evolved planets, in undifferentiated and differentiated asteroids, and in refractory inclusions—the earliest Solar System materials. Here, we review the valence state partitioning behavior of Cr (Cr2+, Cr3+), Ti (Ti3+, Ti4+), and V (V2+, V3+, V4+, V5+) among crystallographic sites in pyroxene over a range of fo2 from approximately fayalite-magnetite-quartz (FMQ) to ~7 log units below iron-wustite (IW-7), and decipher how pyroxene can be used as a recorder of conditions of planetary and nebular environments and planetary parentage. The most important crystallographic site in pyroxene with respect to its influence on mineral/melt partitioning is M2; its Ca content has a huge effect on partitioning behavior, because the large Ca cation expands the structure. As a result, distribution coefficients (Ds) for Cr and V increase with increasing Ca content from orthopyroxene to pigeonite to augite. In addition, it is noted that V3+ is favored over V4+ in olivine and pyroxene. In pyroxene in refractory inclusions, Ti3+ is favored over Ti4+ and incorporation of Ti is facilitated by the high availability of Al for coupled substitution. The most important results from analysis of pyroxene in martian meteorites (e.g., QUE 94201) are the oxygen fugacity estimates of IW+0.2 and IW+0.9 derived from partitioning and valence data for Cr and V, respectively, obtained from experiments using appropriate temperatures and melt compositions. In angrites, changes in V valence state may translate to changes in fo2, from IW-0.7 during early pyroxene crystallization, to IW+0.5 during later episodes of pyroxene crystallization. In addition to fo2, the partitioning behavior of Cr, V, and Ti between pyroxene and melt is also dependent upon availability of other cations, especially Al, for charge-balancing coupled substitutions.


11. U01624
Pu X., Lange R.A., Moore G. A comparison of olivine-melt thermometers based on DMg and DNi: The effects of melt composition, temperature, and pressure with applications to MORBs and hydrous arc basalts // American Mineralogist. 2017. Vol. 102, № 4. P. 750–765.

A new olivine-melt thermometer based on the partitioning of Ni (DOl/liqNi), with a form similar to the Beattie (1993),DOl/liqMg thermometer, is presented in this study. It is calibrated on a data set of 123 olivine-melt equilibrium experiments from 16 studies in the literature that pass the following five filters: (1) 1 bar only, (2) analyzed totals between 99.0–101.0 wt% for olivine and 98.5–101.0 wt% for quenched glasses, (3) olivine is the only silicate phase in equilibrium with the melt, (4) the NiO concentration is ?0.1 wt% in olivine and ?0.01 wt% in quenched glass, and (5) no metallic phase is present other than the capsule. The final data set spans a wide range of temperatures (1170–1650 °C), liquid compositions (37–66 wt% SiO2; 4–40 wt% MgO; 107–11 087 ppm Ni), and olivine compositions (Fo36–100; 0.10–15.7 wt% NiO). The Ni-thermometer recovers the 123 experimental temperatures within ±29 °C (1?), with an average residual of 0 °C. A re-fitted version of the Mg-thermometer of Beattie (1993), calibrated on the same 123 experiments as for the Ni-thermometer, results in an average residual of 1 ± 26 °C (1?). When both thermometers are applied to the same 123 experiments, the average ?T (TMg ? TNi) is 1 ± 29 °C (1?), which confirms that the Mg- and Ni-thermometers perform equally well over a wide range of anhydrous melt composition and temperature at 1 bar. The pressure dependence of the Ni-thermometer under crustal conditions (?1 GPa) is shown to be negligible through comparison with experimental results from Matzen et al. (2013), whereas the pressure dependence of the Mg-thermometer is up to 52 °C at ?1 GPa (Herzberg and O’Hara 2002). Therefore, neglecting the effect of pressure when applying both thermometers to basalts that crystallized olivine at crustal depths (?1 GPa) is expected to lead to negative ?T (TMg ? TNi) values (? ?52 °C). Application of the two thermometers to nine mid-ocean ridge basalts results in an average ?T of ?3°, consistent with shallow crystallization of olivine under nearly anhydrous conditions. In contrast, application of the two thermometers to 18 subduction-zone basalts leads to an average ?T of +112°; this large positive ?T value cannot be explained by the effect of pressure, temperature or anhydrous melt composition. It is well documented in the literature that DOl/liqMg is affected by dissolved water in the melt and that Mg-thermometers overestimate the temperature of hydrous basalts if an H2O correction is not applied (e.g., Putirka et al. 2007). Therefore, the reason why hydrous arc basalts have higher ?T (TMg ? TNi) values than MORBs may be because DOl/liqNi is less sensitivite to water in the melt, which is supported by new Ni-partitioning results on three olivine-melt equilibrium experiments on a basaltic andesite with up to 5 wt% H2O. More hydrous experiments are needed to confirm that the Ni-thermometer can be applied to hydrous melts without a correction for H2O in the melt.


12. Vavrycuk V., Hrubcova P. Seismological evidence of fault weakening due to erosion by fluids from observations of intraplate earthquake swarms // Journal of Geophysical Research: Solid Earth. 2017. Vol. 122, № 5. P. 3701–3718.

The occurrence and specific properties of earthquake swarms in geothermal areas are usually attributed to a highly fractured rock and/or heterogeneous stress within the rock mass being triggered by magmatic or hydrothermal fluid intrusion. The increase of fluid pressure destabilizes fractures and causes their opening and subsequent shear-tensile rupture. The spreading and evolution of the seismic activity are controlled by fluid flow due to diffusion in a permeable rock (fluid-diffusion model) and/or by redistribution of Coulomb stress (intrusion model). These models, however, are not valid universally. We provide evidence that none of these models is consistent with observations of swarm earthquakes in West Bohemia, Czech Republic. Full seismic moment tensors of microearthquakes in the 2008 swarm in West Bohemia indicate that fracturing at the starting phase of the swarm was not associated with fault openings caused by pressurized fluids but rather with fault compactions. This can physically be explained by a fault-weakening model, when the essential role in the swarm triggering is attributed to degradation of fault strength due to long-lasting chemical and hydrothermal fluid-rock interactions in the focal zone. Since the rock is exposed to circulating hydrothermal, CO2-saturated fluids, the walls of fractures are weakened by dissolving and altering various minerals. The porosity of the fault gauge increases, and the fault weakens. If fault strength lowers to a critical value, the seismicity is triggered. The fractures are compacted during failure, the fault strength recovers, and a new cycle begins.


13. U08182
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.


14. U01624
Watenphul A. et al. Influence of the octahedral cationic-site occupancies on the framework vibrations of Li-free tourmalines, with implications for estimating temperature and oxygen fugacity in host rocks // American Mineralogist. 2016. Vol. 101, № 11. P. 2554–2563.

Tourmalines, XY3Z6T6O18(BO3)3V3W, are excellent petrogenetic indicators as they capture the signature of the host-rock bulk composition. Raman spectra of tourmalines can be used as fingerprints for species identification and crystal-chemical analysis. While Li-bearing species are directly distinguishable by the shape of the OH-stretching vibrations, the discrimination of Mg- and Fe-dominant species can be hindered by the coexistence of at least two types of octahedrally coordinated Rn+ cations. Thirty Li-free tourmaline samples comprising 14 different species were studied by Raman spectroscopy and electron microprobe. All nine Fe3+-bearing samples were also analyzed by single-crystal X-ray diffraction and Mossbauer spectroscopy. The Raman scattering analysis shows that Mg-dominant species can be immediately distinguished from Fe-dominant species by the shape of the vibrational modes at ~200–240 cm?1 arising from the YO6 vibrations. Trivalent Fe can be observed and quantified by shifts of the framework vibrations toward lower wavenumbers. The position of the main ZO6 vibrational mode (275–375 cm?1) can be used to determine the ZFe3+ content, while the YFe3+ content can be inferred from the position of the peak at ~315 cm?1. Fits to the data points indicate that the homovalent substitution of Fe3+ for Al3+ leads to a considerably larger downward shift of the ZO6 vibrational mode than the heterovalent substitution Mg2+ for Al3+. The intensity ratio of the two major YO6 vibrational modes (200–240 cm?1) of the fully characterized Fe3+-bearing samples reflects the amount of Y-site Mg and thus can be used to deduce the site-occupancy disorder of Mg over the Y and Z site for tourmaline species with Mg ?2 apfu. By combining the information from framework and OH-stretching vibrations, Raman spectroscopy alone can be used as a micrometer-scale sensitive non-destructive method for the analysis of tourmaline crystal chemistry including trivalent Fe, which is the major tracer for oxygen fugacity and central for intersite geothermometry.


15. Yoshino T., Katsura T. Electrical Conductivity of Mantle Minerals: Role of Water in Conductivity Anomalies // Annu. Rev. Earth Planet. Sci. 2013. Vol. 41, № 1. P. 605–628.

The electrical conductivity of Earth's mantle has recently become an interesting topic across diverse Earth science communities. Many electrical conductivity data of mantle phases have been accumulated through the development of high-pressure experiments. These data will provide information on valence states, water concentration, Fe concentration, oxygen fugacity, and the connectivity of the conductive phase in geological materials such as minerals, melts, and rocks. Although several groups have measured the electrical conductivity of mantle materials at high pressure, they have provided inconsistent results, especially with regard to the effect of water. Thus, it is timely to review the problems underlying experimental techniques. We discuss the current understanding of the effect of water on the electrical conductivity of nominally anhydrous mantle minerals, with some speculation on the form of volatile components in Earth's interior. Finally, we consider the role of water in major conductivity anomalies observed in the upper mantle and transition zone.


16. U10290
Yu X., Lee C.-T.A. Critical porosity of melt segregation during crustal melting: Constraints from zonation of peritectic garnets in a dacite volcano // Earth and Planetary Science Letters. 2016. Vol. 449. P. 127–134.

The presence of leucogranitic dikes in orogenic belts suggests that partial melting may be an important process in the lower crust of active orogenies. Low seismic velocity and low electrical resistivity zones have been observed in the lower crust of active mountain belts and have been argued to reflect the presence of partial melt in the deep crust, but volcanoes are rare or absent above many of these inferred melt zones. Understanding whether these low velocity zones are melt-bearing, and if so, why they do not commonly erupt, is essential for understanding the thermal and rheologic structure of the crust and its dynamic evolution. Central to this problem is an understanding of how much melt can be stored before it can escape from the crust via compaction and eventually erupt. Experimental and theoretical studies predict trapped melt fractions anywhere from <5% to >30%. Here, we examine Mn growth-zoning in peritectic garnets in a Miocene dacite volcano from the ongoing Betic–Rif orogeny in southern Spain to estimate the melt fraction at the time of large-scale melt extraction that subsequently led to eruption. We show that the melt fraction at segregation, corresponding approximately to the critical melt porosity, was ?30%, implying significant amounts of melt can be stored in the lower crust without draining or erupting. However, seismic velocities in the lower crust beneath active orogenic belts (southern Spain and Tibet) as well as beneath active magmatic zones (e.g., Yellowstone hotspot) correspond to average melt porosities of <10%, suggesting that melt porosities approaching critical values are short-lived or that high melt porosity regions are localized into heterogeneously distributed sills or dikes, which individually cannot be resolved by seismic studies.


17. U09363
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).


18. 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.


19. 002294
Баталев В.Ю., Баталева Е.А. Состояние литосферы зоны сочленения Тарима и Тянь-Шаня по результатам петрологической интерпретации магнитотеллурических данных // Физика Земли. 2013. № 3. С. 87.

В работе сочетаются геолого-геофизические и петролого-геохимические методы исследования земной коры и верхней мантии с целью определения состояния литосферы в зоне сочленения Тарима и Тянь-Шаня. Результаты лабораторных измерений электропроводности образцов верхнемантийных и нижнекоровых пород в сопоставлении с геоэлектрической и тепловой моделями позволили выделить в глубинном разрезе зоны сочленения Тарима и Тянь-Шаня массивы лерцолитов, гранулитов и эклогитов. На основе результатов экспериментальных исследований предполагается, что мощность земной коры Южного Тянь-Шаня около 70 млн. лет назад составляла 35-40 км.


20. 001200
Васильев Ю.Р., Гора М.П., Кузьмин Д.В. Петрология фоидитового и меймечитового вулканизма Маймеча-Котуйской провинции (Полярная Сибирь) // Геология и геофизика. 2017. Т. 58. № 6. С. 817–833.

Сравнительный анализ ультраосновных меймечитов маймечинской свиты и щелочных вулканитов арыджангской свиты (фоидитов: нефелинитов, анальцимитов, лимбургитов и др., а также мелилититов) показал их генетическую близость, свидетельствующую о связи с единой магматической системой, пульсационно продуцирующей крупные объемы щелочно-ультраосновных расплавов. Изучались петрогеохимические и минералогические составы пород, а также расплавные включения в оливинах из этих пород. Существенное различие между составами пород арыджангской и маймечинской свит установлено по содержанию MgO, что хорошо объяснимо аккумуляцией оливина. Составы включений из оливинов меймечитов и пород арыджангской свиты соответствуют фоидитам. Характер распределения редких и редкоземельных элементов в фоидитах и в меймечитах однотипен как в породах, так и в расплавных включениях - наблюдаются минимумы для Rb и K и максимумы для Nb и Ta. Отношения индикаторных элементов (Nb/Ta, Ba/La, Ta/La и др.) для пород маймечинской и арыджангской свит имеют постоянные значения и практически не зависят от изменения их магнезиальности. Отношение La/Yb в фоидитах значительно выше, чем в меймечитах и расплавных включениях из оливинов меймечитов, что также свидетельствует о том, что породы арыджангской свиты являются результатом фракционирования исходного высокомагнезиального щелочного пикритоидного расплава.


21. 035245
Дьяконова А.Г. и др. Геоэлектрическое строение земной коры и верхней мантии Среднего Зауралья // Литосфера. 2014. № 1. С. 3–12.

При изучении электропроводности земных недр по четырем геотраверсам Среднего Зауралья общей протяженностью ~1000 км, получен новый экспериментальный материал, демонстрирующий возможности геоэлектрики на современном уровне развития аппаратурно-методического обеспечения. По исследуемым геотраверсам построены геоэлектрические разрезы (модели) в диапазоне глубин от первых метров до 300 км. Представлена карта суммарной продольной проводимости литосферы рассматриваемой территории. Получены новые данные о расслоенности коры и верхней мантии по электрическим параметрам, позволяющие дополнить, а в ряде случаях уточнить имеющуюся геолого-геофизическую информацию о строении литосферы приуральской части Западно-Сибирской платформы.


22. 001408
Жаркова Е.В. Хроника Всероссийского ежегодного семинара по экспериментальной минералогии, петрологии и геохимии 2017 года // Геохимия. 2018. № 1. С. 86–94.


23. 046767
Иванов О.К. Неравновесная магматическая петрология - новая парадигма петрологии // Уральский геологический журнал. 2017. № 4 (118). С. 27–42.

Представления о равновесной кристаллизации магматических пород, подкрепленные экспериментальными диаграммами плавления-кристаллизации, не подтверждаются геологическими материалами. Анализ влияния условий кристаллизации по 27 параметрам (структурным, минералогическим, химическим и геологическим) вулканических и плутонических пород показал их резкие различия, что позволяет говорить о существенно неравновесной кристаллизации. При этом, практически все диаграммы плавкости-кристаллизации силикатных и алюмосиликатных систем также получены в резконеравновесных условиях, что ограничивает их применение в петрологии только некоторыми вулканитами. Приводится ранжирование магматических пород по степени их неравновесной кристаллизации и закон кристаллизации природных расплавов. Делается вывод о необходимости смены равновесной, точнее псевдоравновесной, парадигмы Боуэна на новую неравновесную парадигму кристаллизации.


24. 002294
Лебедев Е.Б. и др. 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.


25. Мороз Ю.Ф., Логинов В.А., Улыбышев И.С. Глубинный геоэлектрический разрез области сочленения срединного Камчатского массива, Ганальского выступа и Центрально-Камчатского прогиба // Вестник Камчатской Региональной Организации Учебно-научный центр. Серия: Науки о Земле. 2016. № 1 (29). С. 17–34.

Рассмотрена методика и результаты магнитотеллурического зондирования (МТЗ) по профилю, расположенному в районе сложнейшего тектонического узла Южной Камчатки. По данным анализа магнитотеллурических параметров геоэлектрическая среда близка к двумерно-неоднородной. Выполнен анализ возможных искажающих эффектов кривых МТЗ с привлечением пробных моделей, изученных с помощью численного моделирования магнитотеллурического поля. В качестве основных для количественной интерпретации приняты продольные кривые МТЗ, которые являются поперечными для Ганальского выступа и структур, осложняющих Срединный Камчатский массив и Центрально-Камчатский прогиб. В результате инверсии кривых в рамках ТМ-моды с использованием численного моделирования получен геоэлектрический разрез, который сопоставлен с данными гравиметрии, магнитометрии и сейсмотомографии. В геоэлектрическом разрезе земной коры и верхней мантии выделены субвертикальные, изометричные и субгоризонтальные аномалии как повышенной, так и пониженной электропроводности. По данным электропроводности и сейсмической скорости выполнена оценка пористости пород в районе коровой аномалии Ганальского выступа. Природа коровой аномалии связывается с гидротермальными растворами и магматическими расплавами.


26. 009414
Старостенко В.И., Бурахович Т.К. Возможная природа сейсмической активности недр Преддобруджского прогиба и Северной Добруджи // Геофизический журнал. 2013. Т. 35. № 1. С. 61–74.

Преддобрудзький прогиб и смежные структуры относятся к части мантии под Восточноевропейской платформой, определенной изменениями нулевой изолинии невязок скорости с глубиной в пределах верхней мантии и ее переходной зоны по данным 3D Р-скоростной модели. Мантийной пограничного зоне соответствует система наклонных слоев. Особенности скоростной строения мантии под Переддобрудзьким прогибом и смежными структурами позволяют выделить мантийные предпосылки сейсмичности этой области, связанные с проявлением мантийного плюма в нижней и средней мантии. Трехмерная глубинная геоэлектрических модель, построенная по результатам современных исследований методами МТЗ и МВП, отражает неоднородное распределение удельного электрического сопротивления в недрах региона. Вытянутые на сотни километров проводники приурочены к глубинным ведущих разломов разного ранга и их пересечений. В пределах южного борта Переддобрудзького прогиба выделено высокопроводящего слой сложной конфигурации, который залегает на глубинах, соответствующих нижней коре и верхам верхней мантии. Очаги землетрясений, как и аномалии высокой электропроводности, в основном соответствуют размещению активных глубинных тектонических разломов и зон сочленения разновозрастных геологических структур. В интервале 28-30 ° в. д. - 45-46 ° с. ш. пространственное размещение аномалий электропроводности соотносится с зоной проявления глубинных мантийных флюидов, соответствующие мантийном плюма.


27. 033165
Федоров П.И., Богомолов Е.С. Ультракалиевый вулканизм Валагинского хребта, Камчатка // Петрология. 2018. Т. 26. № 1. С. 72–91.

Изучен изотопно-геохимический состав поздний мел-палеоценовых ультракалиевых вулканических пород щелочно-ультраосновного комплекса Валагинского хребта Восточной Камчатки. Высокое содержание магния, низкие кальция и алюминия при высоких K/Na отношениях обуславливают сходство рассматриваемых пород с лампроитами и ультракалиевыми породами средиземноморского типа. Низкие концентрации высокозарядных (HFSE) и тяжелых редкоземельных (HREE) элементов относительно состава MORB, низкие изотопные отношения Sr и высокие Nd свидетельствуют о формировании первичных расплавов из источника обедненной мантии. Обогащение ультракалиевых пород крупноионными литофильными элементами (LILE) может объясняться ролью флюидов, привнесенных в расплавы в ходе плавления субдуцированной океанической коры.


28. 001200
Шайдуров Г.Я. О наблюдении сейсмоэлектрического эффекта на газоконденсатном месторождении в естественных электромагнитных и сейсмических шумах земли в диапазоне 0.1-20.0 Гц // Геология и геофизика. 2018. Т. 59. № 5. С. 703–708.

На двух площадях Минусинского газоконденсатного месторождения (Хакассия) в 2014 и 2015 гг., с использованием разработанного в СФУ двухканального геофизического прибора ВПЕМПЗ-М1 (Шум-6), были поставлены первые опытные работы по измерению функции взаимной корреляции (ФВК) сейсмических и электрических шумов Земли, снимаемых одновременно с электрического диполя и сейсмоприемника в диапазоне частот 0.1-20.0 Гц. Продуктивная залежь на глубинах 1800-2000 м была в обоих случаях отмечена максимумом ВКФ, в 5-7 раз превышающим нормальный фон, что указывает на проявление сейсмоэлектрического эффекта в пассивных полях.


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