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1.
Kronrod E. V. Kronrod V. A. Kuskov O. L. Nefedyev Yu. A. 《Doklady Earth Sciences》2018,483(1):1475-1479
Doklady Earth Sciences - The bulk composition of the silicate Moon (crust + mantle, BSM) is determined on the basis of inversion of gravitational and seismic data. It is shown that the mantle... 相似文献
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Calculations of thermal effects of oxidation-reduction reactions in the open systems for the undifferentiated earth have been carried out up to 2000 kbar. It is shown that a change in the sign of the thermal effect occurs with increase of pressure in these open systems: endothermal reactions which occur at pressures Ps < Pc become exothermal at pressures Ps > Pc and vice versa. At a certain critical pressure Ps = Pc the enthalpy of reaction is equal to zero.The results of calculations show that the central part of the earth and the deep interior could become warm due to reduction processes (for example reduction of ferromagnesian silicates and oxides, and stishovite) during core formation. Reducing conditions in the undifferentiated earth during core formation imply that a large fraction of the total heat of chemical reactions was released in the deep interior and was absorbed in the upper parts of the planet. 相似文献
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Based on the simultaneous inversion of unique ultralong-range seismic profiles Craton, Kimberlite, Meteorite, and Rift, sourced by peaceful nuclear and chemical explosions, and petrological and geochemical data on the composition of xenoliths of garnet peridotite and fertile primitive mantle material, the first reconstruction was obtained for the thermal state and density of the lithospheric mantle of the Siberian craton at depths of 100–300 km accounting for the effects of phase transformation, anharmonicity, and anelasticity. The upper mantle beneath Siberia is characterized by significant variations in seismic velocities, relief of seismic boundaries, degree of layering, and distribution of temperature and density. The mapping of the present-day lateral and vertical variations in the thermal state of the mantle showed that temperatures in the central part of the craton at depths of 100–200 km are somewhat lower than those at the periphery and 300–400°C lower than the mean temperature of tectonically younger mantle surrounding the craton. The temperature profiles derived from the seismic models lie between the 32.5 and 35 mW/m2 conductive geotherms, and the mantle heat flow was estimated as 11–17 mW/m2. The depth of the base of the cratonic thermal lithosphere (thermal boundary layer) is close to the 1450 ± 100°C isotherm at 300 ± 30 km, which is consistent with published heat flow, thermobarometry, and seismic tomography data. It was shown that the density distribution in the Siberian cratonic mantle cannot be described by a single homogeneous composition, either depleted or enriched. In addition to thermal anomalies, the mantle density heterogeneities must be related to variations in chemical composition with depth. This implies significant fertilization at depths greater than 180–200 km and is compatible with the existence of chemical stratification in the lithospheric mantle of the craton. In the asthenosphere-lithosphere transition zone, the craton root material is not very different in chemical composition, thermal regime, and density from the underlying asthenosphere. It was shown that minor variations in the chemical composition of the cratonic mantle and position of chemical (petrological) boundaries and the lithosphere-asthenosphere boundary cannot be reliably determined from the interpretation of seismic velocity models only. 相似文献
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Models of the internal structure of completely differentiated Europa and partially differentiated Callisto have been constructed on the basis of Galileo gravity measurements, geochemical constraints on composition of ordinary and carbonaceous chondrites, and thermodynamic data on the equations of state of water, high-pressure ices, and meteoritic material. We assume thermal and mechanical equilibrium for the interiors of the satellites. A geophysically and geochemically permissible thickness of Europa's outer water-ice shell lies between 105 and 160 km (6.2-9.2% of total mass). Our results show that the bulk composition of the rock-iron core of Europa may be described by material approaching the L/LL-type chondrites in composition, but cannot be correlated either with the material of CI chondrites or H chondrites. For Europa's L/LL-chondritic models, core radii are estimated to be 470-640 km (5.3-12.5% of total mass). The allowed thickness of Europa's H2O layer ranges from 115±10 km for a differentiated L/LL-type chondritic mantle with a crust to 135±10 km for an undifferentiated mantle. We show that Callisto must only be partially differentiated into an outer ice-I layer, a water ocean, a rock-ice mantle, and a rock-iron core (mixture of anhydrous silicates and/or hydrous silicates + FeFeS alloy). We accept that the composition of the rock-iron material of Callisto is similar to the bulk composition of L/LL-type chondritic material containing up to 10-15% of iron and iron sulfide. Assuming conductive heat transfer through the ice-I crust [Ruiz, 2001. The stability against freezing of an internal liquid-water ocean on Gallisto. Nature, 412, 409-411], heat flows were estimated and the possibility of the existence of a water ocean in Callisto was evaluated. The liquid phase is stable (not freezing) beneath the ice crust, if the heat flow is between 3.3 and 3.7 mW m−2, which corresponds to the heat flow from radiogenic sources. The thickness of the ice-I crust is 135-150 km, and that of the underlying water layer, 120-180 km. The results of modeling support the hypothesis that Callisto may have an internal liquid-water ocean. The allowed total (maximum) thickness of the outer water-ice shell is up to 270-315 km. Rock-iron core radii, depending on the presence or absence of hydrous silicates, do not exceed 500-700 km, the thickness of an intermediate ice-rock mantle is not less than 1400 km, and its density is in the range of 1960-2500 kg m−3. The surface temperature of Callisto is expected to be 100-112 K. The total amount of H2O in Callisto is found to be 49-55 wt%. The correspondence between the density and moment of inertia values for bulk ice-free Io, rock-iron core of ice-poor Europa, and rock-iron cores of Ganymede and Callisto shows that their bulk compositions may be, in general, similar and may be described by the composition close to a material of the L/LL-type chondrites with the (Fetot/Si) weight ratios ranging from 0.9 to 1.3. Planetesimals composed of these types of ordinary chondrites could be considered as analogues of building material for the rock-iron cores of the Galilean satellites. Similarity of bulk composition of the rock-iron cores of the inner and outer satellites implies the absence of iron-silicon fractionation in the protojovian nebula. 相似文献
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V. M. Gurevich O. L. Kuskov N. N. Smirnova K. S. Gavrichev A. V. Markin 《Geochemistry International》2009,47(12):1170-1179
The heat capacity of eskolaite Cr2O3(c) was determined by adiabatic vacuum calorimetry at 11.99–355.83 K and by differential calorimetry at 320–480 K. Experimental
data of the authors and data compiled from the literature were applied to calculate the heat capacity, entropy, and the enthalpy
change of Cr2O3 within the temperature range of 0–1800 K. These functions have the following values at 298.15 K: C
p
0 (298.15) = 121.5 ± 0.2 J K−1mol−1, S
0(298.15) = 80.95 ± 0.14 J K−1mol−1, and H
0(298.15)-H
0(0) = 15.30±0.02 kJ mol−1. Data were obtained on the transitions from the antiferromagnetic to paramagnetic states at 228–457 K; it was determined
that this transition has the following parameters: Neel temperature T
N
= 307 K, Δ
tr
S = 6.11 ± 0.12 J K−1mol−1 and δ
tr
H = 1.87 ± 0.04 kJ mol−1. 相似文献
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The VPREMOON seismic reference Moon model (Garcia et al., 2011) has been tested with respect to the thermal regime and chemical composition of the mantle. Based on a self-consistent thermodynamic approach and petrological models of the lunar mantle covering a wide range of concentrations of CaO, Al2O3, and FeO, we convert the P- and S-wave velocity profiles to the temperature–depth profiles. The solution procedure relies on the method of the Gibbs free energy minimization and the equations of state for the mantle material which take into account the effects of phase transformations, anharmonicity, and anelasticity. We find that regardless of the chemical composition, the positive P- and S-wave velocity gradient in the lunar mantle leads to a negative temperature gradient, which has no physical basis. For adequate mantle temperatures, the P- and S-wave velocities should remain almost constant or slightly decrease with depth (especially VS) as a result of the effects of the temperature, which grows faster than pressure. These findings underscore the importance of the relationship of the thermodynamics and physics of minerals with seismology. 相似文献
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Internally consistent thermodynamic computation of equilibria in the FeO-MgO-SiO2 system up to 300 kbar is carried out and phase diagrams and profiles of the elastic properties and density are constructed at the depths of 300–800 km. Comparisons of calculated thermodynamic properties for different petrological models with seismic velocity profiles have been used to constrain the mineralogy of the mantle discontinuities. The 400-km discontinuity may represent the univariant or divariant transition in the olivine component of pyrolite as well as a chemical boundary. For the pyrolite composition at the depth of 650 km there are two different spinel + perovskite + stishovite (640 km) and magnesiowustite + spinel + perovskite (650 km) divariant loops (1–2 km wide) separated by a Invariant zone spinel + perovskite (4–6 km wide). The results indicate that phase changes in pyrolite do not explain the 650-km discontinuity. It is also shown that it is impossible to match the seismic properties observed at the depths of 600–800 km and through the discontinuity with any isochemical petrological model considered in the FMS system. However, increasing the iron content or silica and iron contents across the 650-km discontinuity can produce thermodynamic properties in the lower mantle that are more consistent with those inferred from seismic observations. Constraints on the SiO2 and iron contents in the mantle are inferred from the comparison of thermodynamic and seismological data. 相似文献
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A new model is proposed for the structure of the Kaapvaal craton lithosphere. Based on chemical thermodynamics methods, profiles of the chemical composition, temperature, density, and S wave velocities are constructed for depths of 100–300 km. A solid-state zone of lower velocities is discovered on the S velocity profile in the depth interval 150–260 km. The temperature profiles are obtained from absolute values of P and S velocities, taking into account phase transformations, anharmonicity, and anelastic effects. The examination of the sensitivity of seismic models to the chemical composition showed that relatively small variations in the composition of South African xenoliths result in lateral temperature variations of ～200°C. Inversion of some seismic profiles (including IASP91) with a fixed bulk composition of garnet peridotites (the primitive mantle material) leads to a temperature inversion at depths of 200–250 km, which is physically meaningless. It is supposed that the temperature inversion can be removed by gradual fertilization of the mantle with depth. In this case, the craton lithosphere should be stratified in chemical composition. The depleted lithosphere composed by garnet peridotites exists to depths of 175–200 km. The lithospheric material at depths of 200–250 km is enriched in basaltoid components (FeO, Al2O3, and CaO) as compared with the material of garnet peridotites but is depleted in the same components as compared with the fertile substance of the underlying primitive mantle. The material composing the craton root at a depth of ～275 km does not differ in its physical and chemical characteristics from the composition of the normal mantle, and this allows one to estimate the thickness of the lithosphere at 275 km. The results of this work are compared with data of seismology, thermal investigations, and thermobarometry. 相似文献
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Models for the composition and structure of the Galilean satellites of Jupiter (Io, Europa, and Ganymede) were constructed using geophysical data provided by the Galileo mission on the mass, average density, and moment of inertia, as well as thermodynamic data on the equation of the state of water, high-pressure ices, and meteoritic materials. The distribution of density, pressure, temperature, and gravity acceleration in the interiors of the satellites was determined. A simulation of the internal structure of the satellites showed the possibility of identical bulk compositions for water-free Io and the rock-iron cores of Europa and Ganymede (i.e., satellites without their outer ice-water shells). The sizes of the satellites’ cores (Fe with 10 wt % S) and the thicknesses of the ice-water shells of Europa (120 km) and Ganymede (900 km) were also estimated. These satellites contain 7 and 47% H2O, respectively. The radii of Fe-10% S cores are 737 km for Io, 695 km for Ganymede, and 576 km for Europa. The ratios of the radii and masses of the Fe-S scores and rock-iron cores of Io, Ganymede, and Europa are almost identical and equal R(Fe-10%S core)/R Cor = 0.4 and M(Fe-10% S core)/M Cor = 10.55 ± 0.3 wt %. It was shown that the geochemical parameters of the rock-iron constituent of the satellites are similar to the material of L/LL chondrites. The silicate fraction of the satellites contains about 16 wt % FeO and shows an Fe/Si mass ratio of 0.53. The total iron to silicon mass ratio is also identical in the three satellites: (Fetot/Si)Cor = 0.99 ± 0.02. This value is different from that in the bulk compositions of the most oxidized carbonaceous chondrites and the most reduced H chondrites. Io, Europa, and Ganymede could be formed in the accretion disk of Jupiter from a material similar to L/LL chondrites under relatively low temperatures, not higher than the evaporation temperature of Fe and Fe-Mg silicates. 相似文献