На главную              К списку выставок

Физико-химические и петрофизические исследования в науках о Земле

Журнальные статьи

1.
Afonso J.C., Zlotnik S., Diez P. An efficient and general approach for implementing thermodynamic phase equilibria information in geophysical and geodynamic studies // Geochemistry Geophysics Geosystems. 2015. Vol. 16, № 10. P. 3767–3777.

We present a flexible, general, and efficient approach for implementing thermodynamic phase equilibria information (in the form of sets of physical parameters) into geophysical and geodynamic studies. The approach is based on Tensor Rank Decomposition methods, which transform the original multidimensional discrete information into a separated representation that contains significantly fewer terms, thus drastically reducing the amount of information to be stored in memory during a numerical simulation or geophysical inversion. Accordingly, the amount and resolution of the thermodynamic information that can be used in a simulation or inversion increases substantially. In addition, the method is independent of the actual software used to obtain the primary thermodynamic information, and therefore, it can be used in conjunction with any thermodynamic modeling program and/or database. Also, the errors associated with the decomposition procedure are readily controlled by the user, depending on her/his actual needs (e.g., preliminary runs versus full resolution runs). We illustrate the benefits, generality, and applicability of our approach with several examples of practical interest for both geodynamic modeling and geophysical inversion/modeling. Our results demonstrate that the proposed method is a competitive and attractive candidate for implementing thermodynamic constraints into a broad range of geophysical and geodynamic studies. MATLAB implementations of the method and examples are provided as supporting information and can be downloaded from the journal's website.

2.
Ashchepkov I.V. et al. Layering of the lithospheric mantle beneath the Siberian Craton: Modeling using thermobarometry of mantle xenolith and xenocrysts // Tectonophysics. 2014. Vol. 634. P. 55–75.

Single-grain thermobarometric studies of xenocrysts were used to compile local SCLM transects through the major regions of kimberlite magmatism in Siberia and longer transects through the subcontinental mantle lithosphere (SCLM) beneath the Siberian craton. The mantle structure was obtained using P-Fe#, Ca in garnets, oxygen fugacity values fO(2) and calculated temperatures T degrees C. The most detail transect obtained for the Daldyn field on the Udachnaya-Zarnitsa reveals layering showing an inclination of >35 degrees to Udachnaya. Mantle layering beneath the Alakit field determined from the Krasnopresnenskaya-Sytykanskaya transect shows a moderate inclination from N to S. The inflection near Yubileinaya-Aykhal is also supported by the extreme depletion in peridotites with low-Fe sub-Ca garnets. Beneath the Malo-Botuobinsky field the sharply layered mantle section starts from 5.5 GPa and reveals step-like P-Fe#OI trends for garnets and ilmenites. The deeper part of SCLM in this field was originally highly depleted but has been regenerated by percolation of protokimberlites and hybrid melts especially beneath Internationalnaya pipe. The three global transects reveal flat layering in granite-greenstone terranes and fluctuations in the granulite-orthogneiss Daldyn collision terranes. The mantle layering beneath the Daldyn - Alakite region may have been created by marginal accretion. Most of southern fields including the Malo-Botuobinsky field reveal flat layering. The primary subduction layering is smoothed beneath the Alakit field. Lower Jurassic kimberlites from the Kharamai-Anabar kimberlite fields reveal a small decrease of the thickness of the SCLM and heating of its base. The Jurassic Kuoyka field shows an uneven base of the SCLM inclined from west to east. SCLM sequences sampled at this time started mainly from depths of 130 km, but some pipes still showed mantle roots to 250 km. The garnet series demonstrates an inclined straight line pyroxenite P-Fe# trend due to interaction with superplume melts.

3.U10290
Auzende A.-L. et al. Deformation mechanisms of antigorite serpentinite at subduction zone conditions determined from experimentally and naturally deformed rocks // Earth and Planetary Science Letters. 2015. Vol. 411. P. 229–240.

We performed deformation-DIA experiments on antigorite serpentinite at pressures of 1-3.5 GPa and temperatures of between 400 and 650 degrees C, bracketing the stability of antigorite under subduction zone conditions. For each set of pressure-temperature (P-T) conditions, we conducted two runs at strain rates of 5 x 10(-5) and 1 x 10(-4) s(-1). We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400 degrees C (Chernak and Hirth, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Optical and transmission electron microscopies were used for microstructural characterization and determination of deformation mechanisms. Our observations on experimentally deformed antigorite prior to breakdown show that deformation is dominated by cataclastic flow with observable but minor contribution of plastic deformation (microkinking and (001) gliding mainly expressed by stacking disorder mainly). In contrast, in naturally deformed samples, plastic deformation structures are dominant (stacking disorder, kinking, pressure solution), with minor but also perceptible contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases and is coupled to local embrittlement that we attribute to antigorite dehydration. In dehydrating samples collected in the Alps, embrittlement is also observed suggesting that dehydration G22may contribute to intermediate-depth seismicity. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. However, the plastic deformation recorded by naturally deformed samples was likely acquired at low strain rates. We also document that the corrugated structure of antigorite controls the strain accommodation mechanisms under subduction conditions, with preferred inter- and intra-grain cracking along (001) and gliding along both a and b. We also show that antigorite rheology in subduction zones is partly controlled by the presence of fluids, which can percolate within the exhumation channel via deformation-induced interconnected porosity.

4.
Baltzell C. et al. A high-order numerical study of reactive dissolution in an upwelling heterogeneous mantle: 2. Effect of shear deformation // Geochemistry Geophysics Geosystems. 2015. Vol. 16, № 11. P. 3855–3869.

High-porosity dunite channels produced by orthopyroxene dissolution may provide pathways for orthopyroxene-undersaturated melt generated in the deep mantle to reach shallower depth without extensive chemical reequilibration with surrounding mantle. Previous studies have considered these highporosity channels and melt localization in the presence of a uniform upwelling mantle flow through the process of melt-rock reaction as well as shear deformation, but not both simultaneously. In this Part 2 of a numerical study of high-porosity melt and dunite channel formation during reactive dissolution, we considered the effect of shear deformation on channel distribution and channel geometry in an upwelling and viscously compacting mantle column. We formulated a high-order numerical experiment using conditions similar to those in Part 1, but with an additional prescribed horizontal shearing component in the solid matrix, as could be present in flowing mantle beneath spreading centers. Our focus was to examine orthopyroxene dissolution to determine the behavior of dunite formation and its interaction with melt flow field, by varying the upwelling and shear rate, orthopyroxene solubility gradient, and domain height. Introduction of shearing tilts the developing dunite, causing asymmetry in the orthopyroxene gradient between the dunite channels and the surrounding harzburgite. The downwind gradient is sharp, nearly discontinuous, whereas the upwind gradient is more gradual. For higher shear rates, a wave-like pattern of alternating high and low-porosity bands form on the downwind side of the channel. The band spacing increases with increasing shear rate, relative melt flow rate, and orthopyroxene solubility gradient, whereas the band angle is independent of solubility gradient and increases with increasing shear rate and decreasing relative melt flow rate. Such features could be observable in the field and provide evidence for mantle shearing. Standing wave-like patterns of melt fraction also develop on the downwind side with possible implications for the interpretation of seismic velocities in upwelling mantle.

5.
Burnard P., Reisberg L., Colin A. An observed link between lithophile compositions and degassing of volatiles (He, Ar, CO2) in MORBs with implications for Re volatility and the mantle C/Nb ratio // Earth and Planetary Science Letters. 2014. Vol. 395. P. 159–167.

There are systematic variations between relative noble gas abundances and lithophile tracers such as Sr-87/Sr-86, epsilon Nd and La/Sm in a suite of basaltic glasses from the South East Indian Ridge (SEIR). He-4/(40) Ar* (where Ar-40* is Ar-40 corrected for atmospheric contamination) correlates positively with Sr-87/Sr-86 and La/Sm but anticorrelates with epsilon Nd. The large range in He-4/(40) Ar* observed in the glasses is due to fractionation during magmatic degassing caused by the very different solubilities of He and Ar in silicate liquids, whereas Sr-87/Sr-86, epsilon Nd, La/Sm, etc. are insensitive to magmatic processes but rather reflect mantle heterogeneity. Thus, there is a curious situation in this suite of basalts where tracers of mantle heterogeneity (Sr-87/Sr-86, epsilon Nd, La/Sm, etc.) correlate with a tracer of magmatic volatile processes (He-4/Ar-40*). Here, we propose that "enriched" mantle (with high La/Sm and Sr-87/Sr-86, low eNd) also has a higher C concentration than "depleted" mantle. Magmas derived from enriched mantle will therefore have higher initial C concentrations, leading to a greater fraction of CO2 degassed and thus a higher He-4/Ar-40* ratio on eruption. Simple solubility-determined fractional degassing models show that the range in He-4/Ar-40* observed in SEIR basaltic glasses can be generated if the mantle C concentration varies by a factor of 2 over the length of the ridge, consistent with independent estimates of C concentration heterogeneity in the MORB mantle. The correlations between lithophile tracers and He-4/Ar-40* can be reproduced by mixing between a depleted endmember with Sr-87/Sr-86 = 0.70275, epsilon Nd = 8.2 and [C] = 12 ppm and an enriched endmember with Sr-87/Sr-86 = 0.70360, epsilon Nd = 5 and [C] = 24 ppm, followed by degassing. The proposed degassing model allows us to estimate the initial C concentration (i.e. prior to degassing) of each SEIR basalt (for which Sr or Nd isotopes are available); using independent Nb concentration data (Mahoney et al., 2002), we show that C/Nb ratios prior to degassing along the SEIR are relatively constant, probably with a C/Nb ratio of 200 +/- 100. However, although the constancy of C/Nb in these samples is a robust conclusion, the estimated C/Nb ratio itself is model dependent. We also use these data to evaluate volatility of Re during degassing of MORBs; Re is known to be moderately volatile during subaerial and shallow marine volcanism, although it is not known if this element is also volatile at conditions appropriate to MORB emplacement. Although there is a (poor) correlation between Re/Yb (Yb being a non-volatile element of similar apparent bulk compatibility to Re) and He-4/(40) Ar* in these samples, it is more likely that this correlation results from Re/Yb variation in the mantle source and is not due to loss of Re during magmatic degassing.

6.
Cherepanova Y., Artemieva I.M. Density heterogeneity of the cratonic lithosphere: A case study of the Siberian Craton // Gondwana Research. 2015. Vol. 28, № 4. P. 1344–1360.

Using free-board modeling, we examine a vertically-averaged mantle density beneath the Archean-Proterozoic Siberian Craton in the layer from the Moho down to base of the chemical boundary layer (CBL). Two models are tested: in Model 1 the base of the CBL coincides with the LAB, whereas in Model 2 the base of the CBL is at a 180 km depth. The uncertainty of density model is <0.02 t/m(3) or <0.6% with respect to primitive mantle. The results, calculated at in situ and at room temperature (SPT) conditions, indicate a heterogeneous density structure of the Siberian lithospheric mantle with a strong correlation between mantle density variations and the tectonic setting. Three types of cratonic mantle are recognized from mantle density anomalies. 'Pristine' cratonic regions not sampled by kimberlites have the strongest depletion with density deficit of 1.8-3.0% (and SFT density of 329-333 t/m(3) as compared 10 339 t/m(3) of primitive mantle). Cratonic mantle affected by magmatism (including the kimberlite provinces) has a typical density deficit of 1.0-1.5%, indicative of a metasomatic melt-enrichment. Intracratonic sedimentary basins have a high density mantle (3.38-3.40 t/m(3) at SPT) which suggests, at least partial, eclogitization. Moderate density anomalies beneath the Tunguska Basin imply that the source of the Siberian LIP lies outside of the Craton. In situ mantle density is used to test the isopycnic condition of the Siberian Craton. Both CBL thickness models indicate significant lateral variations in the isopycnic state, correlated with mantle depletion and best achieved for the Anabar Shield region and other intracratonic domains with a strongly depleted mantle. A comparison of synthetic Mg# for the bulk lithospheric mantle calculated from density with Mg# from petrological studies of peridotite xenoliths from the Siberian kimberlites suggests that melt migration may produce local patches of metasomatic material in the overall depleted mantle.

7.
Colin A. et al. Constraints on the noble gas composition of the deep mantle by bubble-by-bubble analysis of a volcanic glass sample from Iceland // Chemical Geology. 2015. Vol. 417. P. 173–183.

Contamination of samples by air-derived noble gases is a well-known problem in noble gas geochemistry, and, as a result, determining the true neon and argon isotopic ratios of the mantle is not straightforward. Here, we directly target individual bubbles in an Icelandic volcanic glass, DICE 11, with a 193 nm excimer laser in order to reduce air-contamination, and analyze He and Ar isotopes, plus Ne-22 abundances, on a Helix SFT mass-spectrometer. The CO2 content of the bubbles was measured with a capacitance manometer. In addition, new He, Ne and Ar compositions obtained by crushing on similar samples (DICE 10 and DICE 11) are presented. Our analyses show that He-3/He-4 ratios are homogeneous in all the vesicles in this glass sample at 17.4 +/- 0.4 Ra and are consistent with analyses by crushing. Precise Ar-40/Ar-36 isotopic ratios were obtained on the largest vesicles only, due to high blank contributions to the smallest vesicles, and are 8600 +/- 700, i.e. the highest values measured so far in primitive basalts from Iceland. Considering that the Ar and He isotopic compositions obtained for individual vesicles (by laser ablation) are representative of the true mantle source values, not contaminated by air, we can precisely correct the Ne isotopic analyses obtained by crushing for air contamination; the corrected Ne-20/Ne-22 ratios are consistent with the presence of neon-B in the sub-Icelandic mantle, which is consistent with the hypothesis that neon in the OIB source region has an irradiated meteorite origin rather than purely solar. In contrast to He and Ar isotopic compositions (which are homogeneous), the relative He-Ne-Ar-CO2 abundances in the different bubbles are heterogeneous and show strong correlations which are compatible with equilibrium degassing of the magma. Because He and CO2 do not fractionate during this degassing, we can precisely constrain the CO2/He-3 ratio of the mantle source at 6.7 +/- 0.5 * 10(8), at the lower end of the MORB range. Therefore the deep mantle below Iceland is not enriched in carbon compared to the upper mantle (via recycling, for example).

8.
Criss R.E., Hofmeister A.M. Conductive cooling of spherical bodies with emphasis on the Earth // Terra Nova. 2016. Vol. 28, № 2. P. 101–109.

To explore planetary evolution, we provide conductive cooling profiles that account for planet size, phonon diffusivity and various internal heating scenarios. Our new analytical solution for simple cooling of spheres reveals that heat is removed from only Earth's outermost similar to 1000km over geological time. Numerical models with decaying heat production show that any upward concentration of radionuclides causeshigh temperatures at shallow depths, forcing interior temperatures to increase with time while producing a thermal gradient that forbids lower mantle convection. Hence, differentiation drives upper mantle magmatism and tectonics, leaving a quiescent but hot deep interior, while slowly melting the core.

9.
Dymshits A.M. et al. Thermal equation of state of majoritic knorringite and its significance for continental upper mantle // Journal of Geophysical Research-Solid Earth. 2014. Vol. 119, № 11. P. 8034–8046.

The P-V-T equation of state (EoS) for majoritic knorringite Mg3.19Cr1.60Si3.19O12 at pressures to 17GPa and temperatures to 1673K was obtained from in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus. Fitting of the room-temperature P-V data to a third-order Birch-Murnaghan EoS yielded an isothermal bulk modulus, K-0,K-300=154 (4) GPa, and a pressure derivative, K-0,K-300=5.4 (1.2). When fitting a high-temperature Birch-Murnaghan EoS using all of the P-V-T data at a fixed V-0=1549.08 angstrom(3), we find that K-0,K-300=157 (2) GPa, K-0,K-T=4.5 (6), (K-0,K-T/T)(P)=-0.019 (4) (GPaK(-1)), a=3.00 (14)x10(-5)K(-1), and b=0.65 (24)x10(-8)K(-2), where =a+bT is the volumetric thermal expansion coefficient. Fitting the Mie-Gruneisen-Debye EoS with the present data with a Debye temperature fixed at (0)=731K yielded a Gruneisen parameter, (0)=1.34 at q=1.0 (fixed). The thermoelastic parameters of pure knorringite were estimated and were compared with the previous data on other garnet compositions. The presence of Cr2O3 in pyrope garnets in the upper mantle decreases P- and S-velocities by 1.6% and the density increases by 1.7% (for 20mol.% knorringite end member) compared to pure pyrope. The results show the importance of accounting knorringite end-member for accurate estimation of mantle garnet acoustic velocities.

10.U10290
Ewing T.A., Rubatto D., Hermann J. Hafnium isotopes and Zr/Hf of rutile and zircon from lower crustal metapelites (Ivrea-Verbano Zone, Italy): Implications for chemical differentiation of the crust // Earth and Planetary Science Letters. 2014. Vol. 389. P. 106–118.

We have used granulite fades metapelites from the classic Ivrea-Verbano Zone (IVZ) lower crustal section, northern Italy, to investigate the behaviour of the hafnium (Hf) isotope system in rutile and zircon under conditions of high temperature (700-1050 degrees C) metamorphism and partial melting. The Hf isotope composition of rutile is shown to be robustly preserved from these conditions, and is also unaffected by retrogression, making it a powerful new tool for metamorphic petrology. Rutiles from our suite of IVZ metapelite samples have crustal Hf isotope signatures (81-wo = -6 +/- 1 to -13 +/- 1 at 288 Ma), with the most strongly crustal signature (epsilon(HF(i)) = -9.2 +/- 0.3 to -12.9 +/- 1.0) recorded by narrow slivers of metapelite incorporated within a gabbroic body. The Hf isotope composition of rutile from these metapelite slivers is the direct result of dissolution of ancient detrital zircon with strongly unradiogenic Hf-176/Hf-177 at ultra-high temperatures associated with the emplacement of the gabbro. Rutile is an important host of Zr and Hf in high temperature metapelites, containing up to 11 000 ppm Zr and 400 ppm Hf. It has subchondritic Zr/Hf (13-32) that is significantly lower than the Zr/Hf of both zircon (35-52) and the starting bulk rock composition (36-40). Dissolution of zircon into extracted melts is expected to lead to a lowering of bulk rock Zr/Hf towards that of rutile. In the IVZ samples this effect is balanced by the strongly superchondritic Zr/Hf of garnet (40-70). The IVZ case study demonstrates the strong control that dissolution of detrital or inherited zircon can exert on the available Hf isotope budget, whether in a metamorphic or magmatic setting. The link between dissolution of accessory phases into melt and changes in trace element and Hf isotope chemistry points to important differences between high- and ultra-high temperature metamorphism in terms of chemical and isotopic differentiation of the crust.

11.
Fitch P.J.R. et al. An integrated and quantitative approach to petrophysical heterogeneity // Marine and Petroleum Geology. 2015. Vol. 63. P. 82–96.

Exploration in anything but the simplest of reservoirs is commonly more challenging because of the intrinsic variability in rock properties and geological characteristics that occur at all scales of observation and measurement. This variability, which often leads to a degree of unpredictability, is commonly referred to as "heterogeneity", but rarely is this term defined. Although it is widely stated that heterogeneities are poorly understood, researchers have started to investigate the quantification of various heterogeneities and the concept of heterogeneity as a scale-dependent descriptor in reservoir characterization. Based on a comprehensive literature review we define "heterogeneity" as the variability of an individual or combination of properties within a specified space and/or time, and at a specified scale. When investigating variability, the type of heterogeneity should be defined in terms of grain pore components and the presence or absence of any dominant features (including sedimentological characteristics and fractures). Hierarchies of geologic heterogeneity can be used alongside an understanding of measurement principles and volumes of investigation to ensure we understand the variability in a dataset. Basic statistics can be used to characterise variability in a dataset, in terms of the amplitude and frequency of variations present. A better approach involves heterogeneity measures since these can provide a single value for quantifying the variability, and provide the ability to compare this variability between different datasets, tools/measurements, and reservoirs. We use synthetic and subsurface datasets to investigate the application of the Lorenz Coefficient, Dykstra-Parsons Coefficient and the coefficient of variation to petrophysical data - testing assumptions and refining classifications of heterogeneity based on these measures.

12.U01624
Georg R.B., Shahar A. The accretion and differentiation of Earth under oxidizing conditions // American Mineralogist. 2015. Vol. 100, № 11–12. P. 2739–2748.

We present a new approach to model planetary accretion and continuous core formation, and discuss the implications if Earth accreted under conditions initially more oxidized than the modem day mantle. The modified model uses the same partitioning data that were previously used to model accretion under reducing conditions, however, changing the partitioning between accreting metal and silicate mantle means that reducing conditions fail to meet expected core/mantle values. Instead, the model requires conditions more oxidized than the modern day mantle to converge and to yield expected elemental core/mantle distribution values for moderately siderophile elements. The initial oxygen fugacity required to provide the crucial level of oxidation is approximately Delta IW similar to -1.2 to -1.7 and thus is in the range of carbonaceous and ordinary chondrites. The range of peak pressures for metal silicate partitioning is 60-6 GPa and oxygen fugacity must decrease to meet modem FeO mantle contents as accretion continues. Core formation under oxidizing conditions bears some interesting consequences for the terrestrial Si budget. Although the presented partitioning model can produce a Si content in the core of 5.2 wt%, oxidizing accretion may limit this to a maximum of similar to 3.0 to 2.2 wt%, depending on the initial f(O2) in BSE, which places bulk earth Mg/Si ratio between 0.98-1.0. In addition, under oxidizing conditions, Si starts partitioning late during accretion, e.g., when model earth reached >60% of total mass. As a consequence, the high P-T regime reduces the accompanied isotope fractionation considerably, to 0.07 parts per thousand for 5.2 wt% Si in the core. The isotope fractionation is considerably less, when a maximum of 3.0 wt% in the core is applied. Under oxidizing conditions it becomes difficult to ascertain that the Si isotope composition of BSE is due to core-formation only. Bulk Earth's Si isotope composition is then not chondritic and may have been inherited from Earth's precursor material.

13.
Grant T.B., Harlov D.E., Rhede D. Experimental formation of pyroxenite veins by reactions between olivine and Si, Al, Ca, Na, and Cl-rich fluids at 800 degrees C and 800 MPa: Implications for fluid metasomatism in the mantle wedge // American Mineralogist. 2016. Vol. 101, № 3–4. P. 808–818.

Fluids buffered by a plagioclase matrix are experimentally reacted with olivine megacrysts at 800 degrees C and 800 MPa (piston-cylinder press, CaF2 assembly) to form secondary veins of orthopyroxene +/- clinopyroxene in the olivine. Fluids utilized were varied in both amount (0-2 wt%) and salinity (0-8 M NaCl). Assuming equilibrium with the plagioclase matrix, they are presumed enriched in Si, Al, Ca, Na, and Cl and are thereby similar in composition to slab-derived fluids. The experiments provide controlled, multi-component analogs of Si-metasomatism in the mantle wedge above subduction zones. The veins are dominated by orthopyroxene with minor clinopyroxene and form complex interconnected networks along fractures in the olivine. The reaction is rate limited by interfacial process of dissolution and precipitation. Porosity is developed throughout the veins and along sub-grain boundaries in the olivine megacrysts. These veins strongly resemble the textures observed in secondary metasomatic orthopyroxene veins widely reported in upper mantle xenoliths within arc magmas. A review of literature data on natural samples and experiments suggests that orthopyroxene +/- clinopyroxene veins primarily form between 750-950 degrees C and over a large pressure range from 0.8-3.4 GPa. The abundance and composition of these metasomatic veins may vary as a function of pressure, variances in the fluid-rock partition coefficients, and/or by modification of the metasomatic fluid during the reaction.

14.
Haggerty S.E. Spinel in planetary systems // American Mineralogist. 2016. Vol. 101, № 1–2. P. 5–6.

Spinel is ubiquitous as a rock-forming mineral in terrestrial, lunar, and planetary basalts and closely associated meteoritic equivalents. A major unknown is whether these rocks formed under similar conditions of partial melting of primary or modified mantle, whether redox environments played a role in evolutionary trends, and did mineral crystal chemistry have any influence on elemental partition between solids and liquids? In a novel approach by Papike et al. (2015), spinel is used as an informative, albeit complex indicator of oxygen fugacity, site occupancy of multiple valence elements, and spinel structural types. Planetary basalts may be reduced (IW-3), oxidized (Earth at FMQ), or of intermediate redox state (Mars). Taking an expansive view, the spinel approach holds enormous promise in understanding the magmatic differentiation of asteroids.

15.U07669
Hazen R.M. et al. Mineral Ecology: Chance and Necessity in the Mineral Diversity of Terrestrial Planets // Canadian Mineralogist. 2015. Vol. 53, № 2. P. 295–323.

Four factors contribute to the roles played by chance and necessity in determining mineral distribution and diversity at or near the surfaces of terrestrial planets: (1) crystal chemical characteristics; (2) mineral stability ranges; (3) the probability of occurrence for rare minerals; and (4) stellar and planetary stoichiometries in extrasolar systems. The most abundant elements generally have the largest numbers of mineral species, as modeled by relationships for Earth's upper continental crust (E) and the Moon (M), respectively: Log (N-E) = 0: 22 Log (C-E) + 1.70 (R-2 = 0.34)(4861 minerals, 72 elements) Log (N-M) = 0.19 Log (C-M) + 0.23 (R-2 = 0.68) (63 minerals, 24 elements) where C is an element's abundance in ppm and N is the number of mineral species in which that element is essential. Several elements that plot significantly below the trend for Earth's upper continental crust (e.g., Ga, Hf, and Rb) mimic other more abundant elements and thus are less likely to form their own species. Other elements (e.g., Ag, As, Cu, Pb, S, and U) plot significantly above the trend, which we attribute to their unique crystal chemical affinities, multiple coordination and oxidation states, their extreme concentration in some ore-forming fluids, and/or frequent occurrence with a variety of other rare elements-all factors that increase the diversity of mineral species incorporating these elements. The corresponding diagram for the Moon shows a tighter fit, most likely because none of these elements, except Cu and S, are essential constituents in lunar minerals. Given the similar slopes for Earth and the Moon, we suggest that the increase in mineral diversity with element abundance is a deterministic aspect of planetary mineral diversity. Though based on a limited number of collecting sites, the Moon's observed mineralogical diversity could be close to the minimum for a rocky planet or moon comparable in size-a baseline against which diversity of other terrestrial planets and moons having radii in the same range as Earth and its Moon can be measured. Mineral-forming processes on the Moon are limited to igneous activity, meteor impacts, and the solar wind-processes that could affect any planet or moon. By contrast, other terrestrial planets and moons have been subjected to more varied physical, chemical, and (in the case of Earth) biological processes that can increase mineral diversity in both deterministic and stochastic ways. Total mineral diversity for different elements is not appreciably influenced by the relative stabilities of individual phases, e.g., the broad pressure-temperature-composition stability ranges of cinnabar (HgS) and zircon (ZrSiO4) do not significantly diminish the diversity of Hg or Zr minerals. Moreover, the significant expansion of near-surface redox conditions on Earth through the evolution of microbial oxygenic photosynthesis tripled the available composition space of Earth's near-surface environment, and resulted in a corresponding tripling of mineral diversity subsequent to atmospheric oxidation. Of 4933 approved mineral species, 34% are known from only one or two localities, and more than half are known from five or fewer localities. Statistical analysis of this frequency distribution suggests that thousands of other plausible rare mineral species await discovery or could have occurred at some point in Earth's history, only to be subsequently lost by burial, erosion, or subduction-i.e., much of Earth's mineral diversity associated with rare species results from stochastic processes. Measurements of stellar stoichiometry reveal that stars can differ significantly from the Sun in relative abundances of rock-forming elements, which implies that bulk compositions of some extrasolar Earth-like planets likely differ significantly from those of Earth, particularly if the fractionation processes in evolving stellar nebulas and planetary differentiation are factored in. Comparison of Earth's upper continental crust an

16.
Hurlimann N. et al. Primary Magmas in Continental Arcs and their Differentiated Products: Petrology of a Post-plutonic Dyke Suite in the Tertiary Adamello Batholith (Alps) // Journal of Petrology. 2016. Vol. 57, № 3. P. 495–533.

Determining the primary compositions of arc magmas is fundamental in retracing the chemical differentiation processes responsible for the formation of juvenile arc crust and the thermal structure of the mantle wedge. We have investigated a series of post-plutonic dykes that intruded the gabbroic to tonalitic southern part of the Tertiary Adamello Batholith in the Alps. The dyke rocks range in composition from primary, hydrous high-Mg basalts to basalts, basaltic andesites, andesites and dacites. Field relationships and high-precision U-Pb dating of titanite and zircon show that the dyke suite ranges in age from 41.67 +/- 0.06 Ma for the high-Mg basalt to 38.62 +/- 0.12 Ma for the youngest dacitic dykes, closely associated with plutonic activity from 42.5 to 39.0 Ma. Andesites and dacites have primitive Sr-87/(86)Sri (0.7032-0.7038) and Nd-143/Nd-144(i) (epsilon Nd-CHUR +3.5-3.2) isotopic signatures strongly limiting the extent of crustal assimilation, whereas some of the high-Mg basalts have selectively assimilated pelitic metasedimentary rocks as shown by high Cs/Rb, Rb/Sr and Rb/Zr ratios, and isotopically more enriched compositions (Sr-87/(86)Sri 0.7039-0.7046; epsilon Nd-CHUR +1.6-0.0). Primitive high-Mg basaltic dykes that escaped assimilation processes are primary mantle partial melts that were extracted from their source at pressures of 2.7 +/- 0.2 GPa and temperatures of 1390 +/- 30 degrees C, conditions corresponding to the spinel-garnet transition in mantle peridotite. Major element modelling constrains the degree of melting to 20 +/- 2% leaving a harzburgite residue, consistent with the trace element chemistry of the high-Mg basalts, which have moderate [Gd/Yb](N) ratios of 1-1.2. Differentiated basaltic andesites and dacites follow experimentally constrained liquid lines of descent for fractional crystallization at mid-to deep crustal levels. The trace element chemistry of amphiboles from basaltic andesite and andesite dykes reveals the coexistence of amphibole with primitive melts, indicating elevated pressures and H2O contents in their parental magmas. Thermobarometric constraints for amphibole phenocrysts result in pressures from 0.65 to 0.78 GPa and temperatures ranging from 930 to >1000 degrees C. The absence of any significant Eu-anomaly in the rare earth element patterns in these amphiboles indicates the late appearance of plagioclase in the crystallization sequence. The crystallization of amphibole drives the differentiated magmas to slightly peraluminous, corundum-normative compositions that are common for tonalites building the major part of the Adamello Batholith. Fractionation models at mid-to lower crustal conditions result in the cumulative crystallization of 17% olivine, 2% Cr-rich spinel, 18% clinopyroxene, 41% amphibole, 4% plagioclase and 0.1% magnetite to obtain an andesitic composition from a primary, hydrous high-Mg continental arc basalt. Cumulates formed during fractional crystallization at mid- to deep crustal levels are dunites and wehrlites followed by hornblendites and hornblendegabbros. The trace element signatures of basaltic andesites and dacites display low Rb/Zr and Rb/Sr, and are consistent with fractionation-dominated processes within the crust in an active continental margin. Significant crustal assimilation is not required to obtain the trace element signatures of the evolved andesitic magmas.

17.
Jamtveit B., Austrheim H., Putnis A. Disequilibrium metamorphism of stressed lithosphere // Earth-Science Reviews. 2016. Vol. 154. P. 1–13.

Most changes in mineralogy, density, and rheology of the Earth's lithosphere take place by metamorphism, whereby rocks evolve through interactions between minerals and fluids. These changes are coupled with geodynamic processes and have first order effects on the global geochemical cycles of a large number of elements. In the presence of fluids, metamorphic reactions are fast compared to tectonically induced changes in pressure and temperature. Hence, rocks evolve through near-equilibrium states during fluid-producing metamorphism. However, much of the Earth's lower crust, and a significant fraction of the upper mantle do not contain free fluids. These parts of the lithosphere exist in a metastable state and are mechanically strong. When subject to changing temperature and pressure conditions at plate boundaries or elsewhere, these rocks do not react until exposed to externally derived fluids. Metamorphism of such rocks consumes fluids, and takes place far from equilibrium through a complex coupling between fluid migration, chemical reactions, and deformation processes. This disequilibrium metamorphism is characterized by fast reaction rates, dissipation of large amounts of energy as heat and work, and the generation of a range of emergent pore structures and fracture patterns that often control transport properties and thus further reaction progress. Fluid-consuming metamorphism leads to mechanical weakening due to grain size reduction, the formation of sheet silicates, and local heat production. Strain localization in the lower crust and upper mantle is therefore likely to be controlled by the availability of fluids. Fault controlled migration of meteoric fluids from the brittle crust to the underlying ductile region in areas of compressive stress may provide a spatial and temporal link between localized strain and seismic activity in the upper crust and shear zone controlled deformation below. In a similar way, channelized fluid migration from areas undergoing prograde metamorphism in the lower plate of a subduction zone, may control the distribution of retrograde metamorphism and strain localization in the lower parts of the upper plate.

18.
Kaban M.K. et al. Density, temperature, and composition of the North American lithosphere-New insights from a joint analysis of seismic, gravity, and mineral physics data: 1. Density structure of the crust and upper mantle // Geochemistry Geophysics Geosystems. 2014. Vol. 15, № 12. P. 4781–4807.

We introduce a new method to construct integrated 3-D models of density, temperature, and compositional variations of the crust and upper mantle based on a combined analysis of gravity, seismic, and tomography data with mineral physics constraints. The new technique is applied to North America. In the first stage, we remove the effect of the crust from the observed gravity field and topography, using a new crustal model (NACr2014). In the second step, the residual mantle gravity field and residual topography are inverted to obtain a 3-D density model of the upper mantle. The inversion technique accounts for the notion that these fields are controlled by the same factors but in a different way, e.g., depending on depth and horizontal dimension. This enables us to locate the position of principal density anomalies in the upper mantle. Afterward, we estimate the thermal contribution to the density structure by inverting two tomography models for temperature (NA07 and SL2013sv), assuming a laterally and vertically uniform fertile mantle composition. Both models show the cold internal part and the hot western margin of the continent, while in some Proterozoic regions (e.g., Grenville province) NA07 at a depth of 100 km is >200 degrees C colder than SL2013sv. After removing this effect from the total mantle anomalies, the residual compositional fields are obtained. Some features of the composition density distribution, which are invisible in the seismic tomography data, are detected for the first time in the upper mantle. These results serve as a basis for the second part of the study, in which we improve the thermal and compositional models by applying an iterative approach to account for the effect of composition on the thermal model.

19.U07669
Kaminsky F.V., Wirth R., Schreiber A. A Microinclusion of Lower-Mantle Rock and Other Minerals and Nitrogen Lower-Mantle Inclusions in a Diamond // Canadian Mineralogist. 2015. Vol. 53, № 1. P. 83–104.

A microcrystalline polymineral aggregate was identified as an inclusion in a diamond from the Rio Soriso area, Mato Grosso State, Brazil. It is composed of iron carbides, Fe-rich periclase (with exsolved magnesioferrite), and two orthorhombic, postspinel phases-Mg-Cr-Fe and Ca-Cr oxides, which are new mineral phases. This association was formed during several stages and may be considered as a rock microfragment from the lower mantle. In addition to the carbide-oxide fragment, other phases were identified as inclusions in the diamond, such as parascandolaite KMgF3 (that is stable at pressures of up to 50 GPa) in association with orthorhombic MgO, and porous dolomite occurring together with nanoinclusions of calcite, apatite, spinel, Fe-sulfide, and an assemblage of periclase plus wustite. These minerals belong to the carbonatitic association and, along with syngenetic nanoinclusions of fluid nitrogen, represent the media of diamond formation. The assemblage of periclase and wstite within the carbonatitic matrix points to the origin of diamond from a carbonatitic environment within the lower mantle under pressure conditions of >= 85-86 GPa (similar to 1,900 km depth).

20.U07669
Kaminsky F.V., Wirth R., Schreiber A. Carbonatitic Inclusions in Deep Mantle Diamond from Juina, Brazil: New Minerals in the Carbonate-Halide Association // Canadian Mineralogist. 2013. Vol. 51, № 5. P. 669–688.

Eleven new minerals were identified in deep mantle primary carbonatitic association as inclusions in diamond from the Juina area, Mato Grosso, Brazil. Specifically, two carbonates [magnesite and eitelite Na2Mg(CO3)(2)], two phosphates [mixed-anion phosphate Na4Mg3(PO4)(2)(P2O7), Fe-diphosphate Fe2Fe5(P2O7)(4)], two fluorides [oskarssonite AlF3 and Ba-rich fluoride (Ba,Sr)AlF5], three sulfides [pentlandite (Fe,Ni)(9)S-8, violarite FeNi2S4, and millerite NiS], hematite, and metallic Ni-iron were detected; the two phosphates and Ba-rich fluoride are observed in the natural environment for the first time. The mineral compositions of the analyzed inclusions are variable, even at a nanometer scale, which indicates variability in the source media during the formation of diamond. Volatiles, represented in the form of porosity, played a significant role in this process. Most mineral phases contain volatile elements, as well. Carbonatitic inclusions most likely originated from high-density fluid (HDF) microinclusions encapsulated in diamond during its growth. During the ascent of diamond, HDF inclusions underwent disintegration in composition and crystallized as polymineralic inclusions. Formation of diamond in the studied case took place in a carbonatitic, carbonate-halide-phosphate-fluoride medium, which was enriched in volatiles and acted as an open system during diamond formation.

21.
Kempl J. et al. Silicon stable isotope fractionation between metal and silicate at high-pressure, high-temperature conditions as a tracer of planetary core formation // Netherlands Journal of Geosciences-Geologie En Mijnbouw. 2016. Vol. 95, № 2. P. 113–129.

The largest differentiation event in Earth and other terrestrial planets was the high-pressure, high-temperature process of metal core segregation from a silicate mantle. The abundant element silicon (Si) can be partially sequestered into the metallic core during metal-silicate differentiation, depending on pressure, temperature and planetary oxidation state. Knowledge of the Si content of a planet's core can constrain the conditions of core formation, but in the absence of direct samples from planetary cores, quantifying core Si content is challenging. One relatively new tool to study core formation in terrestrial planets is based on combining measurements of the Si stable isotopic composition of planetary crust and mantle samples with measurements of the Si stable isotope fractionation between metal and silicate at high-temperature and high-pressure conditions. In this study we present the results of a small set of high-pressure, high-temperature (HPT) experiments and combine these with a review of literature data to investigate how the Si isotope fractionation behaviour between metal and silicate varies as a function specifically of experimental run time and temperature. We show that although there is no debate about the sign of fractionation, absolute values for Si isotope fractionation between metal and silicate are difficult to constrain because the experimental database remains incomplete, and because Si isotopic measurements of metals in particular suffer from the absence of a true inter-laboratory comparison. We conclude that in order to derive accurate quantitative estimates of the Si content of the core of the Earth or other planets a wide range of additional experiments will be required.

22.
Khan A. On Earth’s Mantle Constitution and Structure from Joint Analysis of Geophysical and Laboratory-Based Data: An Example // Surveys in Geophysics. 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.

23.
Kuskov O.L. et al. Thermo-chemical structure of the lithospheric mantle underneath the Siberian craton inferred from long-range seismic profiles // Tectonophysics. 2014. Vol. 615. P. 154–166.

Based on a self-consistent thermodynamic-geophysical approach and xenolith-based constraints, we map the 2-D seismic, thermal and density structure of the mantle beneath the Siberian craton along the long-range profiles (Craton, Kimberlite, Rift and Meteorite) carried out in Russia with peaceful nuclear explosions. Structural peculiarities of the cratonic mantle are manifested by changes in seismic velocities, the degree and nature of layering and the relief of seismic boundaries. The results predict appreciable lateral temperature variations within the root to a depth of about 200 km, which are the main cause of seismic velocity variations. We find that the cratonic mantle is 300-400 degrees C colder than the tectonically younger surrounding mantle in this depth range. At greater depths, lateral changes in temperatures have little effect implying that thermal heterogeneity rapidly decreases. The present-day geotherms pass close to the 32.5-35 mW m(-2) conductive models and suggest low mantle heat flow. Within the model resolution, the thickness of the thermal boundary layer, TBL (defined as the depth of the 1300 degrees C adiabat) beneath Siberia does not depend significantly on the composition and can be estimated as 300 +/- 30 km; temperature at the base of the TBL is close to the 1450 +/- 100 degrees C isotherm. Changes in the composition from depleted to fertile material reveal a negligible effect on seismic velocities, which are practically unresolved by seismic methods, but remain the most important factor for the density increase of the cratonic root Density variations in the lower part of the root due to the chemical composition are greater than those caused by temperature. We find that both compositional and thermal anomalies are required to explain the Siberian mantle by a keel model consisting of depleted garnet peridotite at depths of 100 to 180 km and more fertile material at greater depths.

24.
Kuwatani T. et al. Markov random field modeling for mapping geofluid distributions from seismic velocity structures // Earth Planets and Space. 2014. Vol. 66. Art. 5 (9pp.)

We applied the Markov random field model, which is a kind of a Bayesian probabilistic method, to the spatial inversion of the porosity and pore shape in rocks from an observed seismic structure. Gaussian Markov chains were used to incorporate the spatial continuity of the porosity and the aspect ratio of the pore shape. Synthetic inversion tests were able to show the effectiveness and validity of the proposed model by appropriately reducing the statistical noise from the observations. The proposed model was also applied to natural data sets of the seismic velocity structures in the mantle wedge beneath northeastern Japan, under the assumptions that the fluid was melted and the temperature and petrologic structures were uniformly distributed. The result shows a significant difference between the volcanic front and the forearc regions, at a depth of 40 km. Although the parameters and material properties will need to be determined more precisely, the Markov random field model presented here can serve as a basic inversion framework for mapping geofluids.

25.
Labidi J. et al. Experimentally determined sulfur isotope fractionation between metal and silicate and implications for planetary differentiation // Geochimica Et Cosmochimica Acta. 2016. Vol. 175. P. 181–194.

The Earth's mantle displays a subchondritic S-34/S-32 ratio. Sulfur is a moderately siderophile element (i.e. iron-loving), and its partitioning into the Earth's core may have left such a distinctive isotope composition on the terrestrial mantle. In order to constrain the sulfur isotope fractionation occurring during core-mantle differentiation, high-pressure and temperature experiments were conducted with synthetic mixtures of metal and silicate melts. With the purpose to identify the mechanism(s) responsible for the S isotope fractionations, we performed our experiments in different capsules - namely, graphite and boron nitride capsules - and thus at different fO(2), with varying major element chemistry of the silicate and metal fractions. The S isotope fractionations Delta S-34(metal-silicate) of equilibrated metal alloys versus silicate melts is + 0.2 perpendicular to 0.1% in a boron-free and aluminum-poor system quenched at 1-1.5 GPa and 1650 degrees C. The isotope fractionation increases linearly with increasing boron and aluminum content, up to +1.4 + 0.2%, and is observed to be independent of the silicon abundance as well as of the fO(2) over similar to 3.5 log units of variations explored here. The isotope fractionations are also independent of the graphite or nitride saturation of the metal. Only the melt structural changes associated with aluminum and boron concentration in silicate melts have been observed to affect the strength of sulfur bonding. These results establish that the structure of silicate melts has a direct influence on the S2- average bonding strengths. These results can be interpreted in the context of planetary differentiation. Indeed, the structural environments of silicate evolve strongly with pressure. For example, the aluminum, iron or silicon coordination numbers increase under the effect of pressure. Consequently, based on our observations, the sulfur-bonding environment is likely to be affected. In this scheme, we tentatively hypothesize that S isotope fractionations between the silicate mantle and metallic core of terrestrial planetary bodies would depend on the average pressure at which their core-mantle differentiation occurred.

26.
Liu J. et al. Computational challenges in the analyses of petrophysics using microtomography and upscaling: A review // Computers & Geosciences. 2016. Vol. 89. P. 107–117.

Microtomography provides detailed 3D internal structures of materials in micro- to tens of nano-meter resolution and is quickly turning into a new technology for studying petrophysical properties of rocks. An important step is the upscaling of these properties as micron or sub-micron resolution can only be achieved on the sample-scale of millimeters or even less than a millimeter. We have developed a computational workflow for the analysis of microstructures including the upscaling of material properties. Computations of properties are first performed using conventional material science simulations at micro to nano-scale. The subsequent upscaling of these properties is done by a novel renormalization procedure based on percolation theory. In this paper we discuss the computational challenges arising from the workflow, which include: 1) characterization of microtomography for extremely large data sets; 2) computational fluid dynamics simulations at pore-scale for permeability estimation; 3) solid mechanical computations at pore-scale for estimating elasto-plastic properties; 4) Extracting critical exponents from derivative models for scaling laws. We conclude that significant progress in each of these challenges is necessary to transform microtomography from the current research problem into a robust computational big data tool for multi-scale scientific and engineering problems.

27.
Maas C., Hansen U. Effects of Earth’s rotation on the early differentiation of a terrestrial magma ocean // Journal of Geophysical Research-Solid Earth. 2015. Vol. 120, № 11. P. 7508–7525.

Similar to other terrestrial planets like Moon and Mars, Earth experienced a magma ocean period about 4.5 billion years ago. On Earth differentiation processes in the magma ocean set the initial conditions for core formation and mantle evolution. During the magma ocean period Earth was rotating significantly faster than today. Further, the viscosity of the magma was low, thus that planetary rotation potentially played an important role for differentiation. However, nearly all previous studies neglect rotational effects. All in all, our results suggest that planetary rotation plays an important role for magma ocean crystallization. We employ a 3-D numerical model to study crystal settling in a rotating and vigorously convecting early magma ocean. We show that crystal settling in a terrestrial magma ocean is crucially affected by latitude as well as by rotational strength and crystal density. Due to rotation an inhomogeneous accumulation of crystals during magma ocean solidification with a distinct crystal settling between pole and equator could occur. One could speculate that this may have potentially strong effects on the magma ocean solidification time and the early mantle composition. It could support the development of a basal magma ocean and the formation of anomalies at the core-mantle boundary in the equatorial region, reaching back to the time of magma ocean solidification.

28.
Malavergne V. et al. The formation of nuggets of highly siderophile elements in quenched silicate melts at high temperatures: Before or during the silicate quench? // Earth and Planetary Science Letters. 2016. Vol. 434. P. 197–207.

The Highly Siderophile Elements (HSE) are powerful tracers of planetary differentiation. Despite the importance of their partitioning between silicate and metal for the understanding of planetary core formation, especially for the Earth and Mars, there is still a huge discrepancy between conclusions based on different high temperature (HT) experimental studies. These disagreements may be due to the presence of HSE micro and nanonuggets in HT experiments. The formation of these nuggets is still interpreted in different ways. One hypothesis is that these HSE nuggets formed during the quench of the silicate melt, while another hypothesis supposes that these nuggets formed before the quench and represented artefacts of HT experiments. The goal of this work is to clarify whether the presence of HSE nuggets in silicate melts is linked to a quench effect or not. Understanding the formation of these HSE nuggets represents thus a necessary step towards the resolution of the Earth's core formation scenarios. We performed new HT experiments (1275-2000 degrees C) at different oxygen fugacities (fO(2)), between ambient air up to similar to 5 log units below the Iron-Wustite buffer [IW-5], for two different silicate compositions (synthetic martian and terrestrial basalts) mixed with a metallic mixture of Pt-Au-Pd-Ru. Our 1275-1600 degrees C experiments were contained in either olivine, diopside or graphite crucible; experiments at 2000 degrees C were performed using a levitation method, so no capsule was necessary. Our samples contained quenched silicate melts, minerals (olivine, pyroxene, spinel depending on the run), a two-phase metallic bead and nano and micro-nuggets of HSE. Our samples underwent fine textural, structural and analytical characterizations. The distribution of the nuggets was not homogeneous throughout the quenched silicate melt. HSE nuggets were present within crystals. Dendritic textures from the quenched silicate melt formed around HSE nuggets, which could be crystallized, showing that the nuggets acted as nucleation sites during the quench. Thus they predated the quench. Finally, these nuggets also had strong heterogeneities suggesting at least a two-stage formation process under reducing conditions. Consequently, our observations clearly show that these HSE nuggets formed before the quench in the silicate melt. Our results agreed with previous studies, which concluded that HSE abundances in the Earth's mantle require the late accretion of chondritic material subsequent to core formation. However, the effects of metallic Si, O, H, or the effect of pressure on the HSE partitioning are still not fully understood. Further work to constrain these effects is to be encouraged to understand the Earth's core formation.

29.
Malvoisin B., Podladchikov Y.Y., Vrijmoed J.C. Coupling changes in densities and porosity to fluid pressure variations in reactive porous fluid flow: Local thermodynamic equilibrium // Geochemistry Geophysics Geosystems. 2015. Vol. 16, № 12. P. 4362–4387.

Mineralogical reactions which generate or consume fluids play a key role during fluid flow in porous media. Such reactions are linked to changes in density, porosity, permeability, and fluid pressure which influence fluid flow and rock deformation. To understand such a coupled system, equations were derived from mass conservation and local thermodynamic equilibrium. The presented mass conservative modeling approach describes the relationships among evolving fluid pressure, porosity, fluid and solid density, and devolatilization reactions in multicomponent systems with solid solutions. This first step serves as a framework for future models including aqueous speciation and transport. The complexity of univariant and multivariant reactions is treated by calculating lookup tables from thermodynamic equilibrium calculations. Simplified cases were also investigated to understand previously studied formulations. For nondeforming systems or systems divided into phases of constant density, the equations can be reduced to porosity wave equations with addition of a reactive term taking the volume change of reaction into account. For closed systems, an expression for the volume change of reaction and the associated pressure increase can be obtained. The key equations were solved numerically for the case of devolatilization of three different rock types that may enter a subduction zone. Reactions with positive Clapeyron slope lead to an increase in porosity and permeability with decreasing fluid pressure resulting in sharp fluid pressure gradients around a negative pressure anomaly. The opposite trend is obtained for reactions having a negative Clapeyron slope during which sharp fluid pressure gradients were only generated around a positive pressure anomaly. Coupling of reaction with elastic deformation induces a more efficient fluid flow for reactions with negative Clapeyron slope than for reactions with positive Clapeyron slope.

30.U12510
McGee L.E. et al. Mantle heterogeneity controls on small-volume basaltic volcanism // Geology. 2015. Vol. 43, № 6. P. 551–554.

Eruptions of basaltic material in small-scale volcanic fields located in intraplate settings display a very diverse range in physical and chemical characteristics. Despite its relevance to the understanding of volcanic hazards, the relationship between physical properties of eruptions (explosivity, volume, location) and chemical composition of erupted products has, to date, not been investigated. Here we present a relationship between mantle heterogeneity and extents of partial melting, and both erupted volumes and eruptive style from the Auckland Volcanic Field (New Zealand), and we suggest that this provides a general model for small-scale "monogenetic" magmatic systems globally. Small volcanic centers consistently take the form of nephelinitic tuff rings and scoria cones, whereas larger centers are produced from effusive eruptions of less alkalic magmas. Nephelinitic melts are generated by melting of a deep, carbonated source, whereas less alkalic melts are the products of melting of a shallower, noncarbonated source. U-Th-Ra isotope data from eruptions closely paired in space and time show that mixing between magmas is extremely limited as a consequence of different ascent mechanisms due to differential segregation of melts from varying sources (early, carbonated melts ascending by higher porosity channels, and later, uncarbonated melts by a more diffusive regime). This suggests that extraction of melt is nearly instantaneous in these environments. Our results stress the importance of melting and magma dynamics in determining the size and style of eruptions in small volcanic fields, and suggest that mantle controls should be an important consideration in volcanic hazard assessment.

31.U01624
Mysen B.O. et al. Speciation of and D/H partitioning between fluids and melts in silicate-D-O-H-C-N systems determined in-situ at upper mantle temperatures, pressures, and redox conditions // American Mineralogist. 2014. Vol. 99, № 4. P. 578–588.

Speciation of D-O-H-C-N volatiles in alkali aluminosilicate melts and of silicate in D-O-H-C-N fluid has been determined in situ to 800 degrees C and >2 GPa under reducing and oxidizing conditions by using an externally heated hydrothermal diamond-anvil cell with Raman spectroscopy as the structural probe. Reducing conditions were near those of the IW oxygen buffer, whereas oxidizing conditions were obtained by conducting the experiments with oxidized components only and with Pt as a catalyst. Raman bands assigned to C-H stretching in CHxDy isotopologues and CH4 groups (including CH3) were employed to determine the CH4/CHxDy ratio in fluids and melts. This ratio decreases from 1.5-2 at 500 degrees C to between 1.2 and 1 with 800 degrees C with Delta H-values of 13.6 +/- 2.1 and 5.5 +/- 1.1 kJ/mol for melt and fluid, respectively. The CHx/CHxDy fluid/melt partition coefficient ranges between similar to 16 and similar to 3 with Delta H= 33 +/- 6 kJ/mol assuming no pressure effect. This behavior of deuterated and protonated complexes is ascribed to speciation of volatile and silicate components in fluids and melts in a manner that is conceptually similar to D/H partitioning among complexes and phases in brines and hydrous silicate systems. Molecular N-2 is the N-bearing species in fluids and melts under oxidizing conditions. Under reducing conditions, the dominant species are molecular NH3 and ammine groups, NH2-. The NH3/NH2 ratio varies between 0.15 and 0.75 in the 425-800 degrees C temperature range.

32.
Padron-Navarta J.A. et al. On topotaxy and compaction during antigorite and chlorite dehydration: an experimental and natural study // Contributions to Mineralogy and Petrology. 2015. Vol. 169, № 4. Art. 35. (20pp.)

Dehydration reactions result in minerals' replacement and a transient fluid-filled porosity. These reactions involve interface-coupled dissolution-precipitation and might therefore lead to fixed crystallographic orientation relations between reactant (protolith) and product phases (i.e. topotaxy). We investigate these two phenomena in the dehydration of a foliated antigorite (atg) serpentinite by comparing the crystallographic preferred orientation (CPO) developed by olivine (ol), orthopyroxene (opx) and chlorite (chl) during high-pressure antigorite and chlorite dehydration in piston-cylinder experiments and in natural samples recording the dehydration of antigorite (Cerro del Almirez, Betic Cordillera, Spain). Experiments were performed under undrained conditions resulting in fluid-filled porosity and in strong CPO of the prograde minerals, controlled by the pre-existing antigorite CPO in the reactant foliated serpentinite. The orientation of a(ol,opx) and c(chl)* is parallel to c(atg)* from the protolith. The Cerro del Almirez samples show similar, locally well-developed topotactic relations between orthopyroxene, chlorite and antigorite, but the product CPOs are weaker and more complex at the thin section scale. In contrast to the experiments, olivine from natural samples shows a weak correlation between b(ol) and the former c(atg)*. We relate the strengthening of local topotactic relations and the weakening of the inherited CPO at a larger scale in natural samples to compaction and associated fluid migration. Microstructural features that might be related to compaction in the natural samples include: (1) smooth bending of the former foliation, (2) gradual crystallographic misorientation (up to 16 degrees) of prismatic orthopyroxene due to buckling by dislocation creep, (3) inversion of enstatite to low clinoenstatite (P2(1)/c) along lamellae and (4) brittle fracturing of prismatic orthopyroxene enclosed by plastically deformed chlorite. The coexistence of orthopyroxene buckling and clinoenstatite lamellae enables estimating the local strain rates and shear stresses generated during compaction. An lower bound for the strain rates in the order of 10(-12) to 10(-13) s(-1) and shear stresses of 60-70 MPa are estimated based on creep data. Lower shear stresses (20-40 MPa) are retrieved using a theoretical approach. These data point to slow compaction (and fluid extraction) in nature if the system is not perturbed by external forces, with rates only marginally higher than the viscoplastic deformation of the solid matrix.

33.U01624
Papike J.J. et al. Normal to inverse transition in martian spinet: Understanding the interplay between chromium, vanadium, and iron valence state partitioning through a crystal-chemical lens // American Mineralogist. 2015. Vol. 100, № 10. P. 2018–2025.

Spinel is a very important rock-forming mineral that is found in basalts from Earth, Mars, the Earth's Moon, and basaltic meteorites. Spinel can be used as a sensitive indicator of petrologic and geochemical processes that occur in its host rock. This paper highlights the role of increasing fo(2) (from IW-1 to FMQ+2) in converting a >90% normal spinel to an similar to 25% magnetite (inverse) spinel the trajectory of D-V(spincel/melt) as it relates to the ratio of V3+/V4+ in the melt, and the crystal chemical attributes of the spinel that control the intrinsic compatibility of both V3+ and V4+. This work examines the nuances of the V partitioning and provides a crystal chemical basis for understanding Fe3+, Cr, and V substitution into the octahedral sites of spinel. Understanding this interplay is critical for using spinels as both indicators of planetary parentage and reconstructing the redox history of magmatic systems on the terrestrial planets. Three potential examples for this use are provided. In addition, this work helps explain the ubiquitous miscibility gap between spinels with changing tilvospinel contents.

34.
Piccardo G.B., Padovano M., Guamieri L. The Ligurian Tethys: Mantle processes and geodynamics // Earth-Science Reviews. 2014. Vol. 138. P. 409–434.

Ophiolite massifs (i.e., Lanzo, Voltri, Ligurides, Corsica) of the Alpine-Apennine system represent lithosphere remnants of the Jurassic Ligurian Tethys oceanic basin, which separated the Europe and Adria continental margins. Ophiolitic mantle peridotites record structural and compositional features induced by tectonic and magmatic processes in the sub-continental lithosphere by passive rifting leading to continental breakup and sea-floor spreading in the Jurassic Ligurian Tethys. Field, structural, petrologic and geochemical studies of the lithospheric peridotites provide important tools to unravel the processes that drove extension and rifting of the continental Europe-Adria lithosphere towards breakup and oceanic spreading. Extension in the pre-Triassic Europe-Adria continental domain was a classic example of passive rifting, driven by far field tectonic forces. The early stage of rifting was a-magmatic (a-magmatic passive rifting). The far-field tectonic forces induced lithosphere stretching and thinning by means of melt-free extensional shear zones, that allowed passive upwelling of the asthenosphere until it reached melting conditions on decompression. Silica-undersaturated, isolated single melt increments, strongly depleted in trace elements, were formed by fractional melting. They infiltrated unmixed through the extending mantle lithosphere under spinel-facies conditions by diffuse and focused porous flow (magmatic passive rifting) and induced significant melt/peridotite interactions during upward percolation (i.e., thermo-chemical and mechanical erosion, asthenospherization and rejuvenation of the mantle lithosphere). The percolating liquids became silica-saturated by melt/peridotite interaction (pyroxene dissolution/olivine precipitation) and migrated to shallow lithospheric levels (i.e., plagioclase-peridotite facies conditions). There, increasing heat loss by conduction induced their stagnation, storage and progressive crystallization, that impregnated and refertilized the host peridotite (the hidden, non-extrusive magmatism). Melt thermal advection through the extending lithosphere, above the melting asthenosphere, strongly modified the compositional and theological characteristics of the percolated mantle lithosphere. A wedge-shaped, softened and weakened zone was formed along the axial mantle lithosphere of the extensional system, between the future continental margins. This axial wedge represented a preferential zone where the underlying hotter and deeper asthenosphere upwelled and "intruded" the extending colder sub-continental mantle lithosphere. Further extension led to continental break-up and splitting, to formation of the extended Europe and Adria margins and to sea-floor exposure of the sub-continental lithospheric mantle. The hot upwelling asthenosphere column was characterized by higher degrees of partial melting on decompression, complete aggregation of the single fractional melt increments, and deepening of the melting sources (i.e., onset of partial melting under garnet-peridotite facies conditions). This partial melting event formed the aggregated MORE liquids (the oceanic magmatism) which migrated from the asthenosphere within high porosity dunite channels through the melt-reacted sub-continental peridotites, without significant interaction with the host peridotites. These aggregated MORBs formed olivine gabbro intrusions in the shallow mantle lithosphere and MOR pillow basalt flows and edifices, above the tectonically denudated and sea-floor exposed, lithospheric mantle peridotites. In this scenario, the divergent forces induced by the active upwelling asthenosphere may compete with far-field tectonic forces and even drive the system causing a change from passive rifting to active rifting and the installation of a ridge-type system.

35.
Plechov P. et al. Petrology and volatile content of magmas erupted from Tolbachik Volcano, Kamchatka, 2012-13 // Journal of Volcanology and Geothermal Research. 2015. Vol. 307. P. 182–199.

We report petrography, and bulk rock, mineral and glass analyses of eruptive products of the 2012-13 eruption of Tolbachik volcano, Central Kamchatka Depression, Russia. Magmas are shoshonitic in composition, with phenocrysts of olivine and plagioclase; clinopyroxene phenocrysts are scarce. Samples collected as bombs from the active vent, from liquid lava at the active lava front, and as naturally solidified "toothpaste" lava allow us to quantify changes in porosity and crystallinity that took place during 525 km of lava flow and during solidification. Olivine-hosted melt inclusions from rapidly-cooled, mm-size tephra have near-constant H2O contents (1.19 +/- 0.1 wt%) over a wide range of CO2 contents (<900 ppm), consistent with degassing. The groundmass glasses from tephras lie at the shallow end of this degassing trend with 0.3 wt% H2O and 50 ppm CO2. The presence of small saturation, rather than shrinkage, bubbles testifies to volatile saturation at the time of entrapment. Calculated saturation pressures are 0.3 to 1.7 kbar, in agreement with the depths of earthquake swarms during November 2012 (0.6 to 7.5 km below the volcano). Melt inclusions from slowly-cooled and hot-collected lavas have H2O contents that are lower by an order of magnitude than tephras, despite comparable CO2 contents. We ascribe this to diffusive H2O loss through olivine host crystals during cooling. The absence of shrinkage bubbles in the inclusions accounts for the lack of reduction in dissolved CO2 (and S and Cl). Melt inclusions from tephras experienced <3 wt% post-entrapment crystallisation. Melt inclusion entrapment temperatures are around 1080 degrees C. Compared to magmas erupted elsewhere in the Kluchevskoy Group, the 2012-13 Tolbachik magmas appear to derive from an unusually H2O-poor and K2O-rich basaltic parent.

36.
Putirka K. Rates and styles of planetary cooling on Earth, Moon, Mars, and Vesta, using new models for oxygen fugacity, ferric-ferrous ratios, olivine-liquid Fe-Mg exchange, and mantle potential temperature // American Mineralogist. 2016. Vol. 101, № 3–4. P. 819–840.

Mantle potential temperatures (T-p) provide insights into mantle circulation and tests of whether Earth is the only planet to exhibit thermally bi-modal volcanism-a distinctive signature of modem plate tectonics. Planets that have a stagnant lid, for example, should exhibit volcanism that is uni-modal with T-p, since mantle plumes would have a monopoly on the genesis of volcanism. But new studies of magmatic ferric ferrous ratios (x(Fe2O3)(liq)/x(Feo)(liq)) (Cottrell and Kelley 2011) and the olivine-liquid Fe-Mg exchange coefficient, K-D(Fe-Mg)(Ol-liq) (or K-D) (Matzen et al. 2011) indicate that re-evaluations of T-p are needed. New tests and calibrations are thus presented for oxygen fugacity (fo(2)), x(Fe2O3)(liq)/x(Feo)(liq), potential temperature (T-p), melt fraction (F), K-D, and peridotite enthalpies of fusion (Delta H-fus) and heat capacities (C-p). The new models for x(Fe2O3)(liq)/x(Feo)(liq) and fo(2) reduce error by 25-30%, and residual error for all models appears random; this last observation supports the common, but mostly untested, assumption that equilibrium is the most probable of states obtained by experiment, and perhaps in nature as well. Aggregate la error on T-p is as high as similar to +/- 77 degrees C, and estimates of F, and mantle olivine composition, are the greatest sources of error. Pressure and Delta H-fus account for smaller, but systematic uncertainties (a constant Delta H-fus, can under-predict T-excess = T-p(plume)-T-p(ambient) assumptions of 1 atm can under-predict T-p). However, assumptions about whether parental magmas are incremental, accumulated, or isobaric batch melts induces no additional systematic error. The new models show that maximum T-p estimates on the oldest samples from Earth, Mars, Moon, and Vesta, decrease as planet size decreases. This may be expected since T-p should scale with accretion energy and reflect the Clausius-Clapeyron slope for the melting of silicates and Fe-Ni alloys. This outcome, however, occurs only if shergottites (from Mars) are 4.3 Ga (e.g., Bouvier et al. 2009; Werner et al. 2014), and the highest MgO komatiites from Earth's Archean era (27-30% MgO; Green et al. 1975) are used to estimate T-p. With these assumptions, Earth and Mars exhibit monotonic cooling, and support for Stevenson's (2003) idea that smaller planets cool at similar rates (similar to 90-135 degrees C/Ga), but at lower absolute temperatures. Tp estimates for Mars and Earth are also important in two other ways: Mars exhibits non-linear cooling, with rates as high as 275-550 degrees C/Ga in its first 0.5 Ga, and Archean volcanism on Earth was thermally bi-modal. Several hundred Archean volcanic compositions are in equilibrium with Fo92-94 olivine, and yield Tp modes at 1940 and 1720 degrees C, possibly representing plume and ambient mantle, respectively. These estimates compare to modem T, values of 1560-1670 degrees C at Mauna Loa (plume) and 1330-1450 degrees C at MORB (ambient). We conclude that plate tectonics was active in some manner in the Archean, and that assertions of an Archean "thermal catastrophe" are exaggerated. Our new models also show that the modem Hawaiian source, when compared at the same T, has a lower fo(2), compared to MORB, which would discount a Hawaiian source rich in recycled pyroxenite.

37.U01624
Ruzicka A. et al. Shock-induced mobilization of metal and sulfide in planetesimals: Evidence from the Buck Mountains 005 (L6 S4) dike-bearing chondrite // American Mineralogist. 2015. Vol. 100, № 11–12. P. 2725–2738.

The conditions under which metal cores formed in silicate-metal planetary bodies in the early Solar System are poorly known. We studied the Buck Mountains 005 (L6) chondrite with serial sectioning, X-ray computed microtomography, and optical and electron microscopy to better understand how metal and troilite were redistributed as a result of a moderately strong (shock stage S4) shock event, as an example of how collisional processes could have contributed to differentiation. The chondrite was recovered on Earth in multiple small pieces, some of which have a prominent, 1.5-3 mm wide holocrystalline shock melt dike that forms a jointed, sheet-like structure, as well as an associated shock vein network. The data suggest that metal and troilite within the dike were melted, sheared, and transported as small parcels of melt, with metal moving out of the dike and along branching veins to become deposited as coarser nodules and veins within largely unmelted host. Troilite also mobilized but partly separated from metal to become embedded as finer-grained particles, vein networks, and emulsions intimately intergrown with silicates. Rock textures and metal compositions imply that shock melts cooled rapidly against relatively cool parent body materials, but that low-temperature annealing occurred by deep burial within the parent body. Our results demonstrate the ability of shock processes to create larger metal accumulations in substantially unmelted meteorite parent bodies, and they have implications for the formation of iron meteorites and for core formation within colliding planetesimals.

38.
Schoenberg R. et al. The stable Cr isotopic compositions of chondrites and silicate planetary reservoirs // Geochimica Et Cosmochimica Acta. 2016. Vol. 183. P. 14–30.

The depletion of chromium in Earth's mantle (similar to 2700 ppm) in comparison to chondrites (similar to 4400 ppm) indicates significant incorporation of chromium into the core during our planet's metal-silicate differentiation, assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of Earth. Stable Cr isotope compositions - expressed as the parts per thousand-difference in Cr-53/Cr-52 from the terrestrial reference material SRM979 (delta Cr-53/52(SRM979) values) - of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites. The stable Cr isotopic compositions of 7 carbonaceous chondrites, 11 ordinary chondrites, 5 HED achondrites and 2 martian meteorites determined by a double spike MC-ICP-MS method are within uncertainties indistinguishable from each other and from the previously determined delta Cr-53/52(SRM979) value of -0.124 +/- 0.101 parts per thousand for the igneous silicate Earth. Extensive quality tests support the accuracy of the stable Cr isotope determinations of various meteorites and terrestrial silicates reported here. The uniformity in stable Cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal-silicate differentiation of Earth, Mars and the HED parent body did not cause measurable stable Cr isotope fractionation between these two reservoirs. Our results also imply that the accretionary disc, at least in the inner solar system, was homogeneous in its stable Cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation. Small but reproducible variations in delta Cr-53/52(SRM979) values of terrestrial magmatic rocks point to natural stable Cr isotope variations within Earth's silicate reservoirs. Further and more detailed studies are required to investigate whether silicate differentiation processes, such as partial mantle melting and crystal fractionation, can cause stable Cr isotopic fractionation on Earth and other planetary bodies.

39.U01624
Shearer C.K. et al. Origin of the lunar highlands Mg-suite: An integrated petrology, geochemistry, chronology, and remote sensing perspective // American Mineralogist. 2015. Vol. 100, № 1. P. 294–325.

The Mg-suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation. This review examines the mineralogy, geochemistry, petrology, chronology, and the planetary-scale distribution of this suite of highlands plutonic rocks, presents models for their origin, examines petrogenetic relationships to other highlands rocks, and explores the link between this style of magmatism and early stages of lunar differentiation. Of the models considered for the origin of the parent magmas for the Mg-suite, the data best fit a process in which hot (solidus temperature at >= 2 GPa = 1600 to 1800 degrees C) and less dense (rho similar to 3100 kg/m(3)) early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn. Some decompressional melting would occur, but placing a hot cumulate horizon adjacent to the plagioclase-rich primordial crust and KREEP-rich lithologies (at temperatures of <1300 degrees C) would result in the hybridization of these divergent primordial lithologies, producing Mg-suite parent magmas. As urKREEP (primeval KREEP) is not the "petrologic driver" of this style of magmatism, outside of the Procellarum KREEP Terrane (PKT), Mg-suite magmas are not required to have a KREEP signature. Evaluation of the chronology of this episode of highlands evolution indicates that Mg-suite magmatism was initiated soon after primordial differentiation (<10 m.y.). Alternatively, the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust. Petrogenetic relationships between the Mg-suite and other highlands suites (e.g., alkali-suite and magnesian anorthositic granulites) are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources.

40.
Tirupathi S. et al. Multilevel and local time-stepping discontinuous Galerkin methods for magma dynamics // Computational Geosciences. 2015. Vol. 19, № 4. P. 965–978.

Discontinuous Galerkin (DG) method is presented for numerical modeling of melt migration in a chemically reactive and viscously deforming upwelling mantle column at local chemical equilibrium. DG methods for both advection and elliptic equations provide a robust and efficient solution to the problems of melt migration in the asthenospheric upper mantle. Assembling and solving the elliptic equation is the major bottleneck in these computations. To address this issue, adaptive mesh refinement and local time-stepping methods have been proposed to improve the computational wall time. The robustness of DG methods is demonstrated through two benchmark problems by modeling detailed structure of high-porosity dissolution channels and compaction dissolution waves.

41.
Vervoort J.D., Kemp A.I.S. Clarifying the zircon Hf isotope record of crust-mantle evolution // Chemical Geology. 2016. Vol. 425. P. 65–75.

Zircon has played a critically important role in our understanding of the growth and evolution of the Earth. The U-Pb isotope system as preserved in zircon, more than any other mineral or method, has provided the most precise geochronological constraints for timing of geological events and processes on the Earth. More recently, technological advances have allowed for the precise determination of the Hf isotope composition of zircon, a geo-chemical tracer that has provided important details on the Earth's chemical evolution, in particular the evolution of the crust-mantle system. When combined, U-Pb ages and Hf isotopes in zircons hold the promise of providing unprecedented resolution in the timing and processes of planetary differentiation. Nowhere is this more true than for the early history of the Earth, where younger tectonothermal processes have compromised the isotope information in bulk rock samples. With the promise of this integrated technique, however, lies numerous potential pitfalls in the acquisition and interpretation of these data. In this paper we review several important issues related to unraveling the complexities of integrated U-Pb age and Hf isotope datasets, especially with respect to understanding crust-mantle evolution. In particular, we address the potential difficulty of assigning accurate initial Hf isotope compositions as well as some of the inherent problems associated with so-called "depleted-mantle model ages". Finally, we make some suggestions regarding the optimum analytical approach and presentation of the Hf (and Nd) isotope data to obtain the clearest record of Earth's chemical evolution.

42.
Veveakis E., Regenauer-Lieb K., Weinberg R.F. Ductile compaction of partially molten rocks: the effect of non-linear viscous rheology on instability and segregation // Geophysical Journal International. 2015. Vol. 200, № 1. P. 519–523.

The segregation of melt from a linear viscous matrix is traditionally described by McKenzie's compaction theory. This classical solution overlooks instabilities that arise when non-linear solid matrix behaviour is considered. Here we report a closed form 1-D solution obtained by extending McKenzie's theory to non-linear matrix behaviours. The new solution provides periodic stress singularities, acting as high porosity melt channels, to be the fundamental response of the compacted matrix. The characteristic length controlling the periodicity is still McKenzie's compaction length (delta) over bar (c), adjusted for non-linear rheologies.

43.
Wilson C.R. et al. Fluid flow in subduction zones: The role of solid rheology and compaction pressure // Earth and Planetary Science Letters. 2014. Vol. 401. P. 261–274.

Arc volcanoes tend to occur at locations where the slab is at approximately 100 km depth but most models of fluid production from the downgoing slab suggest fluids are released over a wide range of depths. Reconciling the models with the observations suggests that focusing of slab-produced fluids is necessary if flux-melting is a primary mechanism for the production of arc magmas. This paper investigates one possible mechanism for inducing focusing of fluid flow toward the sub-arc mantle. Through a series of simplified models we explore the role of compaction pressure gradients in modifying fluid flow. These gradients are produced by variations in fluid flux interacting with the permeability and viscosity structure of the solid mantle. When these gradients are neglected, high-permeability systems are dominated by buoyancy and fluid flow is primarily vertical. However, when included, compaction pressure terms have three principal effects: (i) enhancement of upslope flow within high-permeability layers in the slab produced by local dehydration reactions, (ii) deflection of fluids along the sloping rheologically strengthening region in the upper thermal boundary layer, and (iii) production of non-linear porosity waves that locally modulate the flow of fluids and can allow significant transient accumulation of fluids. We demonstrate significant localization of fluid flux toward the sub-arc region due to the permeability and solid viscosity structure. We also estimate the amount of melting expected among the different models and show that models with compaction pressure could produce similar to 10% flux melting, whereas distributed fluid flow produces less than or similar to 1% in most cases.

44.U10290
Wu L. et al. Pressure-induced elastic and structural changes in hydrous basalt glasses: The effect of H2O on the gravitational stability of basalt melts at the base of the upper mantle // Earth and Planetary Science Letters. 2014. Vol. 406. P. 165–173.

To understand the effect of hydration on the elastic properties of silicate melts, we conducted in situ high-pressure Brillouin scattering measurements on two hydrous basalt glasses with different water contents in diamond anvil cells. Second-order phase transitions were observed in the hydrous basalt glasses and are due to the topological rearrangement of the silicate network to a high [Si,Al]-O coordination. Up to a pressure of 10 GPa at 300 K, the extra 2.23 wt% H2O lowers the elastic moduli of FX-2 basalt glass (2.69 wt% H2O) by 10%-18%, but does not affect the pressure derivatives of the elastic moduli, compared with FX-1 (0.46 wt% H2O) basalt glass. The phase transition takes place at a higher pressure in FX-2 compared with FX-1, possibly because of the depolymerization of water to silicate glass. Water interacts with network-forming cations and creates Si-OH and Al-OH groups, and prohibits nonbridging oxygen ions from being connected to other nearby framework cations (i.e., ([5.6])(Si,Al)), resulting in the hysteresis of the second-order phase transition. The density contrasts of our hydrous basalt melts with previous mid-ocean ridge basalt and preliminary reference Earth model data indicate that basalt melts may need very low water content (<0.46 wt% H2O) to maintain gravitational stability at the base of the upper mantle. Our results show that the elastic properties of hydrous silicate melts may have important implications for the dynamic evolution and chemical differentiation of the mantle.

45.U12510
Yamamoto J. et al. Melt-rich lithosphere-asthenosphere boundary inferred from petit-spot volcanoes // Geology. 2014. Vol. 42, № 11. P. 967–970.

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

46.
Yang X., Yang Y., Chen J. Pressure dependence of density, porosity, compressional wave velocity of fault rocks from the ruptures of the 2008 Wenchuan earthquake, China // Tectonophysics. 2014. Vol. 619. P. 133–142.

The uniaxial compressibility (beta), density (p), porosity (psi) and P-wave velocity (Vi,) of fault rocks from the rupture zone of the 2008 wWenchuan earthquake, China, were systematically measured at pressures ranging from 10 MPa to 600 MPa on oedometer at room temperature. This paper provides a new approach to measure total pores as the function of pressure. The total pores can be divided into two portions, compliant pores and framework ones. The former is fully closed at the pressure P-cp - "closure pressure of compliant pore" and the latter can survive in specimens even when the pressure reaches 600 MPa. The observations demonstrate that p and V-p nonlinearly rise with pressurization at low pressure regime followed by a linearly upward tendency at pressure beyond FP, and P. However, the beta-values, pressure derivatives of density (D-p) and of velocity (D-v) are at least one order of magnitude higher than the counterparts of crystallized rocks, which are attributed to the persistence of framework pores at pressure beyond P-cp. Hence, we conclude that a linear rise in elastic wave velocity with pressurization should not be regarded as the criterion for the judgment of pore-free materials. Furthermore, the experimental results provide a reliable constraint on the porosity of fault rocks as the function of depth.

47.
Yarushina V.M., Podladchikov Y.Y., Connolly J.A.D. (De)compaction of porous viscoelastoplastic media: Solitary porosity waves // Journal of Geophysical Research-Solid Earth. 2015. Vol. 120, № 7. P. 4843–4862.

Buoyancy-driven flow in deformable porous media is important for understanding sedimentary compaction as well as magmatic and metamorphic differentiation processes. Here mathematical analysis of the viscoplastic compaction equations is used to develop an understanding of the porosity wave instability and its sensitivity to the choice of rheological model. The conditions of propagation, size, speed, and shape of the porosity waves depend strongly on the properties of the solid rock frame. Whereas most of the previous studies on porosity waves were focused on viscous or viscoelastic mode, here we consider the ability of a solid matrix to undergo simultaneous plastic (rate-independent) and viscous (rate-dependent) deformation in parallel. Plastic yielding is identified as a cause of compaction-decompaction asymmetry in porous mediathis is known to lead to a strong focusing of porous flow. Speed and amplitude of a porosity wave are given as functions of material parameters and a volume of a source region. Formulation is applicable to fluid flow in sedimentary rocks where viscous deformation is due to pressure solution as well as in deep crustal or upper mantle rocks deforming in a semibrittle regime.

48.U60656
Yi C., Bin S., Shun G. The Dabie-Sulu orogenic peridotites: Progress and key issues // Science China-Earth Sciences. 2015. Vol. 58, № 10. P. 1679–1699.

Orogenic peridotites in the Dabie-Sulu orogenic belt are commonly subdivided into 'crustal' type and 'mantle' type. They exhibit distinct mineral textures, metamorphic evolution, and whole-rock and mineral compositions. Most 'mantle' type peridotites originated from the subcontinental lithospheric mantle (SCLM) of the North China Craton and thus provide direct evidence of crust-mantle interactions in the continental subduction channel. In garnet peridotites, both garnet and Cr-spinel can be equilibrated at peak pressure conditions. Their stabilities are mainly controlled by the refertilized degree of whole-rock; therefore, spinel composition cannot be used to discriminate the partial melting degree of orogenic peridotites. Refractory mantle-derived dunites contain the textures of low Mg and high Ca olivine veins that crosscut orthopyroxene porphyroblasts, which is considered as evidence for silica-undersaturated melt-rock reactions. Such reactions occurring before subduction may potentially affect Re-Os isotopic compositions. Rutile, Ti-clinohumite and zircon in mantle-derived peridotites or pyroxenites provide direct mineralogical evidence for the transport of high field strength elements (HFSEs) from the subducted crust into the mantle wedge. Based on detailed in situ element and isotope analyses, we can constrain the source of metasomatic agents, the metasomatic time and the process of mass transfer. The mantle wedge above continental subduction zones has a wide range of oxygen fugacity values (FMQ=-5.50-1.75), showing a roughly negative correlation with the subducted depths. However, the calculated results of oxygen fugacity are significantly affected by mineral assemblages, P-T conditions and dehydrogenation-oxidation of nominally anhydrous mantle olivine during exhumation. Although significant progress has been made in the study of orogenic peridotites in the Dabie-Sulu orogenic belt, many critical questions remain. With new approaches and advanced technologic applications, additional knowledge of the phase relation in the peridotite-pyroxenite complex system, the mantle geodynamic process before continental subduction, the effects of crustal metasomatism on chemical composition, the oxygen fugacity, and the physical properties of the mantle wedge is anticipated.

49.U01624
Yoshioka T. et al. The speciation of carbon monoxide in silicate melts and glasses // American Mineralogist. 2015. Vol. 100, № 7. P. 1641–1644.

We have studied the speciation of carbon monoxide in both Fe-bearing and Fe-free basaltic glasses using Raman, FTIR, and Mossbauer spectroscopy. We show that a band at 2110 cm(-1) in the Raman spectrum and another band at 2210 cm(-1) in the FTIR spectrum occur both in the Fe-bearing and Fe-free samples, implying that they cannot be due to any Fe-bearing species. This observation is consistent with Fe-57 Mossbauer spectra, which do not show any evidence for Fe species with zero isomer shift, as expected for carbonyls. Thermodynamic calculations show that iron carbonyl in basaltic melts under crustal and upper mantle conditions may only be a trace species. Rather than being due to distinct chemical species, the range of vibrational frequencies observed for carbon monoxide in silicate glasses appears to be due to rather subtle interactions of the CO molecule with the matrix. Similar effects are known from the extensive literature on carbon monoxide adsorption on oxides and other surfaces. In the melt at high temperature, there is likely little interaction of the CO molecule with the silicate matrix and solubility may be largely controlled by pressure, temperature, and the overall polymerization or ionic porosity of the melt.

50.U10290
Zha Y. et al. Seismological imaging of ridge-arc interaction beneath the Eastern Lau Spreading Center from OBS ambient noise tomography // Earth and Planetary Science Letters. 2014. Vol. 408. P. 194–206.

The Lau Basin displays large along-strike variations in ridge characters with the changing proximity of the adjacent subduction zone. The mechanism governing these changes is not well understood but one hypotheses relates them to interaction between the arc and back-arc magmatic systems. We present a 3D seismic velocity model of the shallow mantle beneath the Eastern Lau back-arc Spreading Center (ELSC) and the adjacent Tofua volcanic arc obtained from ambient noise tomography of ocean bottom seismograph data. Our seismic images reveal an asymmetric upper mantle low velocity zone (LVZ) beneath the ELSC. Two major trends are present as the ridge-to-arc distance increases: (1) the LVZ becomes increasingly offset from the ridge to the north, where crust is thinner and the ridge less magmatically active; (2) the LVZ becomes increasingly connected to a sub-arc low velocity zone to the south. The separation of the ridge and arc low velocity zones is spatially coincident with the abrupt transition in crustal composition and ridge morphology. Our results present the first mantle imaging confirmation of a direct connection between crustal properties and uppermost mantle processes at ELSC, and support the prediction that as ELSC migrates away from the arc, a changing mantle wedge flow pattern leads to the separation of the arc and ridge melting regions. Slab-derived water is cutoff from the ridge, resulting in abrupt changes in crustal lava composition and crustal porosity. The larger offset between mantle melt supply and the ridge along the northern ELSC may reduce melt extraction efficiency along the ridge, further decreasing the melt budget and leading to the observed flat and faulted ridge morphology, thinner crust and the lack of an axial melt lens.

51.U18998
Zheng Y. et al. Petrogenesis of Cretaceous adakite-like intrusions of the Gangdese Plutonic Belt, southern Tibet: Implications for mid-ocean ridge subduction and crustal growth // Lithos. 2014. Vol. 190. P. 240–263.

We have conducted a whole-rock geochemical, U-Pb zircon geochronological, and in situ zircon Hf-O isotopic compositional study of rocks in southern Tibet from the Langxian igneous suite (including a lamprophyre dyke, mafic enclaves, a granodiorite, and a two-mica granite) and the Nuri igneous suite (a quartz-diorite). U-Pb zircon dating indicates that the timing of crystallization of the mafic enclaves and host granodiorite of the Langxian suite are ca. 105 Ma and 102 Ma, respectively, that the Langxian lamprophyre dyke and the two-mica granite were emplaced at ca. 96 Ma and 80-76 Ma, respectively, and that the Nuri quartz-diorite was emplaced at ca. 95 Ma. With the exception of the lamprophyre dyke and mafic enclaves in the Langxian area, felsic rocks from the Langxian and Nuri igneous suites all show signs of a geochemical affinity with adakite-like rocks. The high Mg-numbers, high abundance of compatible elements, high epsilon(Nd(t)) (2.7 and 2.8) and delta O-18 (8.9 and 9.2%.) values, elevated zircon epsilon(Hf(t)) (11.0-17.0) values, and low Sr-87/Sr-86((i)) ratios (0.7040), collectively indicate that the Nuri adakite-like quartz-diorite was derived from partial melting of the low temperature altered Neo-Tethyan oceanic crust, and that these dioritic magmas subsequently interacted with peridotite as they rose upwards through the overlying mantle wedge. The observation of identical differentiation trends, similar whole-rock Sr-Nd and zircon Hf isotopic compositions, and consistently low (Dy/Yb)(N) ratios among the Langxian igneous suite rocks, indicates that the adakite-like granodiorite was produced by low-pressure fractional crystallization of precursor magmas now represented by the (relict) mafic enclaves. However, relatively high Al2O3 contents, low MgO, Cr and Ni contents, and low (La/Yb)(N) and (Dy/Yb)(N) values indicate that the two-mica granite was derived from partial melting of the southern Tibetan mafic lower crust in the absence of garnet, while isotopic data suggest that at least 70% of the magma source region was juvenile materials. Combined with the presence of HT (high temperature) charnockitic magmatism, HT granulite facies metamorphism, and large volumes of Late Cretaceous batholiths, the oceanic-slab-derived Nuri adakitic rocks indicate a substantial high heat flux in the Gangdese batholith belt during the Late Cretaceous, which may have been related to subduction of a Neo-Tethyan mid-ocean ridge system. According to this model, hot asthenosphere would rise up through the corresponding slab window, and come into direct contact with both the oceanic slab and the base of the overlying plate. This would cause melting of both the oceanic slab and the overlying plate by the addition of heat that was ultimately linked with peak magmatism and the significant growth and chemical differentiation of juvenile crust in southern Tibet during the late Cretaceous (105-76 Ma). In addition, the petrogenesis of the Langxian adakite-like two-mica granite indicates that the southern Tibetan crust was still of normal thickness prior to the emplacement of these intrusions at ca. 76 Ma. This probably means that large parts of southern Tibet were not very highly elevated prior to the Indian-Asian collision.

52.
Zhong R. et al. Contrasting regimes of Cu, Zn and Pb transport in ore-forming hydrothermal fluids // Chemical Geology. 2015. Vol. 395. P. 154–164.

Sulfur and chlorine are the two most important ligands accounting for metal transport in the upper crust. In this study, four metal- and sulfur-saturated model fluids with varying salinities and redox states were simulated in the Fe-Cu-Pb-Zn-Au-S-C-H-O system, over a wide pressure-temperature (P-T) range (50-650 degrees C, 0.8-5.0 kbar), in order to compare the roles of chloride and bisulfide complexing for metal transport at the light of the latest available thermodynamic properties. The range in simulated Zn and Pb concentrations of the model fluids compares well with those of natural hydrothermal fluids, suggesting that the model can be used to evaluate hydrothermal ore-forming processes in Nature. The modeling reveals two different modes of Cu, Pb and Zn complexing in sulfur-saturated hydrothermal solutions. At lower temperature, chloride complexes are the predominant Cu, Pb and Zn species in sulfide-saturated systems, as expected from previous studies. However, hydrosulfide Cu, Pb and Zn complexes predominate at higher temperature. The predominance of bisulfide complexing for base metals at high temperature in sulfur-saturated systems is related to the prograde dissolution of pyrite and/or pyrrhotite, which results in a rapid increase in sulfur solubility. Metals transport as chloride or bisulfide complexes determines the modes of metal enrichment. In chloride-complexing dominated systems (e.g., Mississipi Valley Type deposits), low sulfide solubilities mean that the ore fluids cannot carry both reduced sulfur and metals, and ore precipitation is triggered when the ore fluid encounters reduced sulfur, e.g., via fluid mixing or via sulfate reduction. In contrast, in fluids where bisulfide complexing is predominant, cooling and desulfidation reactions are efficient mechanisms for base metal sulfide precipitation. Since both Au and base metals (Cu, Pb and Zn) are predicted to be transported as hydrosulfide complexes in high-temperature primary magmatic fluids in equilibrium with sulfide minerals, high-salinity is not a necessity for magmatic hydrothermal deposits such as porphyry- and skarn-style deposits.

53.001573
Балицкий В.С., Пентелей С.В. и др. Фазовые состояния водно-углеводородных флюидов при повышенных и высоких температурах и давлениях в связи с выяснением форм и максимальных глубин нахождения нефти в земных недрах // Доклады Академии наук. 2016. Т. 466. № 4. С. 454-458.

На основе синтетических флюидных включений в кварце, выращенном при 240-490°С и 7-150 МПа в водно-нефтяных растворах, изучены поведение, состав и фазовые состояния жидких, газовых, твердых углеводородов. Исследования проводили с использованием обычной и флуоресцентной микроскопии, микротермометрии, локальной обычной и высокотемпературной ИК-Фурье-спектроскопии, КР-спектроскопии, хроматографии, рентгенометрии, зондового микроанализа. Анализ полученных данных позволил выяснить влияние термобарических условий и объемных соотношений нефтяной, водной, газовой фаз на состав, фазовое состояние, поведение водно-углеводородных флюидов, а также оценить формы и возможные максимальные глубины нахождения залежей нефти в земных недрах.

54.002294
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. 87-94.

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.

55.
Бутвина В.Г. Экспериментальное изучение эклогитовой системы (гранат-омфацит) при 4.0-7.0 ГПА: моделирование условий формирования алмазоносных эклогитов // Научно-исследовательские публикации. 2013. № 4. С. 68-89

При давлениях 4.0 – 7.0 ГПа экспериментально изучены фазовые равновесия в многокомпонентной эклогитовой системе гранат-омфацит и некоторых ее сечениях. Экспериментальное исследование псевдотройной системы омфацит – пироп (+32 мол.% гроссуляра) - альмандин (+32 мол.% гроссуляра) в ее политермическом сечении омфацит-пироп 15альмандин 53 гроссуляр 32при давлении 7.0 ГПа показало, что плавление гранат-омфацитовой ассоциации является котектическим, а температура ее солидуса в данном сечении составляет около 1450 0С. Это значение выше, чем расчетные температуры образования эклогитов в нодулях кимберлитовых трубок, что может свидетельствовать о флюидной природе эклогитовых магматических систем мантии. Построенные фазовые диаграммы позволяют интерпретировать физико-химические условия образования и эволюции природных эклогитовых парагенезисов, в частности по особенностям кристаллизации главного минерала эклогитов – граната.

56.001408
Зайцев В.А., Когарко Л.Н., Сенин В.Г. Фазовые равновесия в системе лампрофиллит-нефелин // Геохимия. 2013. № 11. С. 987-994.

Экспериментально исследована диаграмма плавкости ламрофиллит-нефелин, изучен состав кристаллизующихся в этой системе фаз. Показано, что лампрофиллит инконгруэнтно плавится с образованием расплава и оксидов титана. Предельная температура сосуществования нефелина и ламрофиллита оценена как 833 ± 6°С.

57.033165
Когарко Л.Н., Рябчиков И.Д. Алмазоносность и окислительный потенциал карбонатитов // Петрология. 2013. Т. 21. № 4. С. 350-371.

Проведена оценка физико-химических условий формирования графита и алмаза в богатых карбонатами магматических средах. Получен большой объем аналитического материала по составам сосуществующих минералов в изученных объектах (Черниговский массив, Украина и Чагатайский карбонатитовый комплекс, Узбекистан). Измерен изотопный состав углерода в сосуществующих карбонатах и графите из этих карбонатитов. Предложены новые методы термодинамической оценки потенциала кислорода, применимые к карбонатитам с графитом или с алмазом. Фугитивность кислорода в графитсодержащих карбонатитах несколько ниже уровня буфера кварц-фаялит-магнетит. Доказывается, что процесс алмазообразования происходит в ходе восстановления карбонатных компонентов, приносимых из плюмового материала в нижнюю субконтинентальную литосферу, а не в результате частичного окисления метановых флюидов. Ограниченная роль метана в глубинной мантии определяется низкой активностью воды, что следует из изучения оливинов и других номинально безводных минералов в кимберлитах. Метан может появляться в мантии в особых условиях, кoгда фугитивность кислорода очень низка (например, в основании континентальной литосферы), а активность воды повышается, например в ходе кристаллизационной дифференциации глубинных очагов кимберлитовой или протокимберлитовой магмы.

58.033165
Кусков О.Л., Кронрод В.А., Прокофьев А.А., Павленкова Н.И. Петролого-геофизические модели внутреннего строения литосферной мантии Сибирского кратона // Петрология. 2014. Т. 22. № 1. С. 21-49.

На основании совместной инверсии уникальных сверхдлинных профилей Кратон, Кимберлит, Метеорит и Рифт, отpаботанных c мирными ядеpными и химическими взpывами, и петролого-геохимических данных по составу ксенолитов гранатовых перидотитов и фертильного вещества примитивной мантии впервые проведена реконструкция термального состояния и плотности литосферной мантии Сибирского кратона на глубинах 100 - 300 км с учетом эффектов фазовых превращений, ангармонизма и неупругости. Для веpxней мантии Cибиpи xаpактеpны cущеcтвенные неодноpодноcти cейcмичеcкиx cкоpоcтей, pельефа cейcмичеcкиx гpаниц, cтепени pаccлоенноcти, распределения температуры и плотности. Картирование современного термального состояния мантии по латерали и вертикали показывает, что на глубинах 100 - 200 км температура в центральной части кратона несколько ниже, чем на его периферии, и на 300-400°C ниже средней температуры окружающей кратон более молодой в тектоническом отношении мантии. Выведенные из сейсмических моделей температурные профили лежат между кондуктивными геотермами 32.5-35 мВт/м2; мантийный тепловой поток равен 11-17 мВт/м2. Глубина залегания термической литосферы (термального погранслоя) кратона близка к изотерме 1450 ± 100°С и составляет 300 ± 30 км, что согласуется с имеющимися в литературе данными по тепловым потокам, термобарометрии и сейсмотомографии. Показано, что распределение плотности в мантии Сибирского кратона невозможно описать каким-либо одним однородным составом как обедненным, так и обогащенным. Плотностные неоднородности мантии должны быть связаны не только с тепловыми аномалиями, но также и с изменением химического состава по глубине. Это подразумевает заметную фертилизацию вещества на глубинах ниже 180-200 км и допускает стратификацию литосферной мантии кратона по химическому составу. В зоне перехода от литосферы к астеносфере вещество корня кратона по химическому составу, тепловому режиму и плотности мало отличается от подстилающей астеносферы. Показано, что выявление тонких различий в химическом составе мантии кратона так же, как и локализация химической (петрологической) границы и границы литосфера-астеносфера, только лишь на основе интеpпpетации сейсмических скоростных моделей не представляется возможным.

59.002294
Лебедев Е.Б., Рыженко Б.Н. 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.

60.J01801
Манштейн А.К., Нестерова Г.В. и др. Об оценке величины сейсмоэлектрического эффекта первого рода // Технологии сейсморазведки. 2013. № 4. С. 81-88.

Анализ полевых электроразведочных данных и физического моделирования показывает существенное уменьшение удельного электрического сопротивления проводящих горизонтов, связанное с последействием сейсмических источников. В статье предложена математическая модель и выполнены расчеты возможного изменения удельного сопротивления горных пород в результате трансформации порового пространства. Кроме того, рассмотрена модель изменения удельного сопротивления в результате разрушения двойного электрического слоя в порах различного размера после сейсмического воздействия. Показано, что при этом могут наблюдаться как эффекты уменьшения удельного электрического сопротивления (УЭС), связанного с возникновением дополнительной электропроводности флюида за счет появления дополнительных подвижных ионов в поровом пространстве, так и эффекты вызванной поляризации.

61.000960
Мороз Ю.Ф., Карпов Г.А. и др. Геоэлектрическая модель кальдеры Узон на Камчатке // Вулканология и сейсмология. 2014. № 5. С. 38-51.

Рассмотрены результаты магнитотеллурических и магнитовариационных исследований кальдеры Узон. На основе анализа магнитотеллурических параметров определена методика интерпретации. Инверсия кривых МТЗ выполнена в рамках двумерной модели с помощью программы REBOCC. Построены геоэлектрические разрезы кальдеры по двум ортогональным профилям. Выявлены аномалии повышенной электропроводности в осадочном чехле и фундаменте, которые приурочены к выходам геотермальных источников. Повышенная проводимость аномалий связывается с наличием высокоминерализованных гидротермальных растворов. По удельному электрическому сопротивлению пород выполнена приближенная оценка пористости пород осадочного чехла и фундамента. На глубинах 1.5-3.5 км в кальдере выделена субвертикальная зона повышенной пористости, связываемая с каналом, по которому флюиды поднимаются вверх в осадочный чехол. Предполагается, что здесь высокоминерализованные растворы разбавляются вадозными водами и по трещинам поступают на дневную поверхность в виде горячих источников. По комплексу полученных данных предложена концептуальная модель, характеризующая основные особенности формирования гидротермальных источников в кальдере Узон.

62.002294
Мороз Ю.Ф., Мороз Т.А. и др. Изменение электропроводности литосферы в районе очага сильнейшего Олюторского землетрясения в Корякском нагорье // Физика Земли. 2016. № 1. С. 31-46.

Рассмотрены результаты магнитотеллурического зондирования до и после землетрясения. В основу интерпретации положены кривые МТЗ по направлениям, отвечающим простиранию и вкрест простирания основных тектонических элементов. Кривые МТЗ подвержены влиянию -эффекта и берегового эффекта. Оценка влияния берегового эффекта выполнена с помощью пробной трехмерной модели. Установлено, что на периодах до 1000 с влияние берегового эффекта невелико, и им можно пренебречь. Детально исследован эффект расхождения продольной и поперечной кривых МТЗ, отражающий наличие глубинных разломов. Инверсия кривых МТЗ выполнена с помощью программы численного двумерного моделирования REBOCC. В ней использованы процедуры погашения эффекта и совместной инверсии продольной и поперечной кривых МТЗ. Полученные геоэлектрические разрезы дают представление о структуре электропроводности литосферы до и после землетрясения. Изменения электропроводности в большей мере проявились в зоне глубинных разломов. Они связываются с изменением пористости и степени насыщенности пород высокоминерализованными растворами.

63.003795
Мурцовкин В.А. Электропроводность пористых сред с двухфазным насыщением // Коллоидный журнал. 2013. Т. 75. № 1. С. 109-117.

Получены соотношения для расчета электропроводности пористых сред с двухфазным насыщением. В основе рассматриваемых расчетов лежит капиллярно-решеточная модель пористой среды, состоящая из нескольких разномасштабных трехмерных кубических решеток капилляров. Каждая решетка может быть представлена в виде большого количества одинаковых кубических ячеек с одинаковой структурой порового пространства и с заданным распределением размеров пор по ячейкам. Исходными данными для расчета всех параметров модели является распределение пористости по размерам пор. Количество решеток и их масштаб определяются особенностями этого распределения. Показаны возможности практического использования рассматриваемой модели на примере экспериментальных данных, полученных для образцов пористых горных пород. Это, в частности, указывает на возможность применения модели для решения задач прикладной геофизики, связанных с определением насыщенности горных пород водой и углеводородами.

64.001408
Рябчиков И.Д., Когарко Л.Н. Физико-химические параметры кристаллизационной дифференциации и формирования Fe-Ti руд в магматической системе массива Елеть-Озеро (Северная Карелия) // Геохимия. 2016. № 3. С. 233-255.

Породы интрузии Елеть-Озеро характеризуются относительной обогащенностью наиболее несовместимыми элементами-примесями (La/Lu)N варьирует от 2.1 до 36.6). Oтмечается отчетливая положительная бариевая аномалия, выражающаяся в том числе в появлении минералов бария еще на стадии формирования мафических пород. Возможно, аномальная обогащенность барием связана с крупномасштабным флюидным массопереносом, сопровождавшим субдукционное погружение литосферной плиты; он происходил в пределах Карельского кратона синхронно с образованием магмы, давшей начало плутону Елеть-Озеро. Присутствие в габброидах среди первичных магматических минералов высокоглиноземистой шпинели свидетельствует об относительно высоких давлениях (порядка 0.5 ГПа, т.е. глубины порядка 15 км). Фугитивность кислорода менялась в ходе эволюции магматической системы, достигая максимума (примерно на 1.5 логарифмических единицы выше буфера кварц–фаялит–магнетит) на стадии интенсивной кристаллизации Fe–Тi окислов. Высокие значения рассчитанных фугитивностей кислорода, обогащенность сильно несовместимыми элементами (включая титан) основных пород могут рассматриваться как признаки потенциальной рудоносности базитовых интрузий.

65.
Рябчиков И.Д., Когарко Л.Н. Физико-химические параметры материала глубинных мантийных плюмов // Геология и геофизика. 2016. Т. 57. № 5. С. 874-888.

Термодинамический анализ базы экспериментальных данных показал, что активность FеО в силикатных расплавах, идентичных по составу природным магмам, может быть описана моделью регулярных растворов, учитывающей взаимодействия всех катионов с кремнием, а также взаимодействие кальция с алюминием. Использование этой модели позволило предложить геооксометр для пары шпинель + магма, применимый к природным системам. Новый геооксометр, в отличие от предложенных ранее методов оценки потенциала кислорода, позволяет работать в области, близкой к ликвидусу магматического процесса. Новый вариант геооксометра применен к оценкам потенциала кислорода для ряда магм плюмовой обстановки, включая сибирские меймечиты, пикриты Гавайских островов, крупной интрузивной провинции (LIP) Эмейшан и Гренландии. Показано, что в большинстве случаев магмы, связанные с деятельностью глубинных мантийных плюмов, характеризуются более высоким относительным потенциалом кислорода по сравнению с магматизмом срединных океанических хребтов. Термодинамические расчеты полей устойчивости различных углеродсодержащих фаз при Р - Т параметрах нижней мантии также показали, что материал восходящих мантийных плюмов характеризуется относительно повышенными значениями фугитивности кислорода. В частности, выяснилось, что для формирования в нижней мантии алмаза требуются более окислительные условия, чем это предполагается для преобладающей части этой геосферы, в которой ожидается присутствие железоникелевого металлического сплава. Выдвинута гипотеза, что главной причиной повышения фугитивности кислорода в отдельных участках нижней мантии является смещение окислительно-восстановительных равновесий с ростом температуры в сторону уменьшения количества, а затем исчезновения Fе-Ni сплава.

66.006651
Тойкка А.М., Самаров А.А., Тойкка М.А. Фазовое и химическое равновесие в многокомпонентных флюидных системах с химической реакцией // Успехи химии. 2015. Т. 84. № 4. С. 378-392.

Исследование фазовых и химических равновесий в системах с химическим взаимодействием компонентов включает широкий круг проблем, связанных как с экспериментальным определением физико-химических свойств, так и с различными аспектами термодинамического анализа фазовых и химических процессов. Целью обзора является систематизация и анализ известных экспериментальных данных о равновесиях жидкость-пар и жидкость-жидкость в многокомпонентных системах с химическими реакциями. Рассматриваются преимущественно работы последних лет, включающие достаточно подробные данные о физико-химических свойствах, фазовых переходах и химических процессах во флюидных системах, существенные для термодинамического анализа. Обсуждаются существующие подходы к термодинамическому исследованию гетерогенных систем с химическими реакциями. Особое внимание уделяется работам, в которых рассматривается одновременное фазовое и химическое равновесие. Результаты могут быть полезны как для фундаментальных исследований гетерогенных реакционных систем, так и для практических задач, связанных с организацией совмещенных реакционно-массообменных процессов.

На главную              К списку выставок