Anna Dymshits - Academia.edu (original) (raw)

Papers by Anna Dymshits

$Research paper thumbnail of Phase boundary between cubic B1 and rhombohedral structures in (Mg,Fe)O magnesiowüstite determined by in situ X-ray diffraction measurements$

Physics and Chemistry of Minerals, 2017

The phase relations and equation of state of (Mg0.08Fe0.92)O magnesiowüstite (Mw92) have been stu... more The phase relations and equation of state of (Mg0.08Fe0.92)O magnesiowüstite (Mw92) have been studied using the Kawai-type high-pressure apparatus coupled with synchrotron radiation. To determine the phase boundary between the NaCl-type cubic (B1) and rhombohedral (rB1) structures in Mw92, in situ X-ray observations were carried out at pressures of 0–35 GPa and temperatures of 300–1473 K. Au and MgO were used as the internal pressure markers and metallic Fe as oxygen fugacity buffer. The phase boundary between B1 and rB1 structures was described by a linear equation P (GPa) = 1.6 + 0.033 × T (K). The Clapeyron slope (dP/dT) determined in this study is close to that obtained at pressures above 70 GPa but steeper than that obtained for FeO. An addition of MgO to FeO structure expands the stability field of the rB1 phase to lower pressures and higher temperatures. Thus, the rB1 phase may be stabilized with respect to the B1 phase at a lower pressures. The pressure–volume–temperature equation of state of B1-Mw92 was determined up to 30 GPa and 1473 K. Fitting the hydrostatic compression data up to 30 GPa with the Birch–Murnaghan equation of state (EoS) yielded: unit cell volume (V0,T0), 79.23 ± 4 Å3; bulk modulus (K0,T0), 183 ± 4 GPa; its pressure derivative (K′T), 4.1 ± 0.4; (∂K0,T/∂T) = −0.029 ± 0.005 GPa K‒1; a = 3.70 ± 0.27 × 10−5 K−1 and b = 0.47 ± 0.49 × 10−8 K−2, where α0,T = a + bT is the volumetric thermal expansion coefficient. The obtained bulk modulus of Mw92 is very close to the value expected for stoichiometric iron-rich (Mg,Fe)O. This result confirms the idea that the bulk modulus of (Mg,Fe)O is greatly affected by the actual defect structure, caused by either Mg2+ or vacancies.

Journal of Raman Spectroscopy, 2021

Vestnik Otdelenia nauk o Zemle RAN, 2011

Geochemistry International, 2014

The CaO-MgO-Al 2 O 3 -SiO 2 -Na 2 O multicomponent system was experimentally studied at 7.0 and 8... more The CaO-MgO-Al 2 O 3 -SiO 2 -Na 2 O multicomponent system was experimentally studied at 7.0 and 8.5 GPa using an anvil with hole toroidal high pressure apparatus to examine two binary joins: pyropegrossular and grossular-Na majorite. These and literature data were employed to simulate the liquidus sur face of the pyrope-grossular-Na majorite system. The liquidus surface of garnet of predominantly pyrope composition is dominant in the diagram, and the garnet contains much of the Na 2 MgSi 5 O 12 end member. Melting was observed in this region at temperatures above 1900°C, and the solidus of the system occurs at temperatures below 1550°C. The pyrope-grossular system shows a miscibility gap at 50-65 mol % of the pyrope component and two series of garnet solid solutions. The dominant phase at grossular and Na majorite mixing is pyroxene, and garnet crystallizes within a fairly narrow field in the grossular rich region. All garnets synthesized in the systems have elevated Si and Na concentrations and belong to the majorite series, for which a uniform mechanism of isomorphism (Mg, Ca) + Al = Si + Na was proved.

Russian Geology and Geophysics

The equations of state of forsterite, wadsleyite, ringwoodite, MgSiO3-perovskite, akimotoite, and... more The equations of state of forsterite, wadsleyite, ringwoodite, MgSiO3-perovskite, akimotoite, and postperovskite are set up by joint analysis of experimentally measured isobaric heat capacity, bulk moduli, thermal expansion depending on temperature at ambient pressure, and volume at room and higher temperatures. Modified equations of state based on the Helmholtz free energy are used to construct a thermodynamic model. The derived equations of state permit calculation of all thermodynamic functions for the minerals depending on temperature and volume or temperature and pressure. A phase diagram of the system MgSiO3-MgO is constructed based on the Gibbs energy calibrated using the referred experimental points. The seismic boundaries at depths of 410 and 520 km and in the zone D" are interpreted on the basis of the phase transitions. The global upper/lower mantle discontinuity at a depth of 660 km remains debatable; it is in poor agreement with experimental and computational data ...

Doklady Earth Sciences

The results of studies of the P-V-T equations of state (EOS) of Na-pyroxene using the multi-anvil... more The results of studies of the P-V-T equations of state (EOS) of Na-pyroxene using the multi-anvil technique and synchrotron radiation at pressures up to 15.3 GPa and temperatures up to 1673 K are presented. By fitting the Birch-Murnaghan EOS, the following parameters were determined: V 0 = 407.2 (5) Å3, the space group P2/n, K T0 = 103 (2) GPa, K T0 = 6.2 (7), ∂K T /∂T = −0.018 (7), α = 3.38(13) + 0.65(62)T. Thus, despite the small volume of the cell, Na-pyroxene has a sufficiently high bulk modulus. This can be caused by the appearance of antipathetic bonds in Na-polyhedron, Si-tetrahedra rotation, and the ordering of Mg and Si cations in the M1 position. Thus, it is substantiated that the phase transformations in the minerals accompanied by the presence of Si in octahedral coordination are characterized by a significant change in the physical characteristics, such as density (ρ) and bulk modulus (K T ). Such transformations occurring in the minerals and deep Earth can lead to sign...

American Mineralogist

In situ X-ray diffraction study of the pyroxene to majorite transition in Na 2 MgSi 5 O 12 was ca... more In situ X-ray diffraction study of the pyroxene to majorite transition in Na 2 MgSi 5 O 12 was carried out in Kawai-type high-pressure apparatus coupled with synchrotron radiation. The phase boundary between Na-pyroxene and Na-majorite was determined over the temperature interval of 1073-1973 K and was described by a linear equation P (GPa) = 12.39 + 0.0018×T (K). The Clapeyron slope (dP/ dT) determined in this study is similar to the one predicted by computer simulations (Vinograd et al. 2011) but smoother than the one obtained by quenched experiments . The presence of sodium in the system lowers the pressure of pyroxene-to-majorite transformation. For the first time Na-majorite was characterized using Raman spectroscopy. Raman peaks of Na-majorite are broader than pyrope due to the substitution of Mg 2+ for Na + at the X site. Both Si-O symmetric stretching (A 1g -n 1 ) and O-Si-O symmetric bending (A 1g -n 2 ) modes of Na-majorite are significantly shifted to higher frequencies relative to corresponding bands of pyrope. In contrast the A 1g -R (SiO 4 ) mode of Na-majorite (342 cm -1 ) displays a lower frequency than that of pyrope (365 cm -1 ). Our results enable further understanding of the mechanisms responsible for phase transformations in the Earth's transition zone and lower mantle.

American Mineralogist, 2015

Journal of Geophysical Research: Solid Earth, 2014

The P-V-T equation of state (EoS) for majoritic knorringite Mg 3.19 Cr 1.60 Si 3.19 O 12 at press... more The P-V-T equation of state (EoS) for majoritic knorringite Mg 3.19 Cr 1.60 Si 3.19 O 12 at pressures to 17 GPa and temperatures to 1673 K 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 0,300 = 154 (4) GPa, and a pressure derivative, K′ 0,300 = 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 Å 3 , we find that K 0,300 = 157 (2) GPa, K′ 0,T = 4.5 (6), (∂K 0,T /∂T) P = À0.019 (4) (GPa K À1 ), a = 3.00 (14) × 10 À5 K À1 , and b = 0.65 (24) × 10 À8 K À2 , where α = a + bT is the volumetric thermal expansion coefficient. Fitting the Mie-Grüneisen-Debye EoS with the present data with a Debye temperature fixed at θ 0 = 731 K yielded a Grüneisen parameter, γ 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 Cr 2 O 3 in pyrope garnets in the upper mantle decreases P-and S-velocities by 1.6% and the density increases by 1.7% (for 20 mol.% 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. (2014), Thermal equation of state of majoritic knorringite and its significance for continental upper mantle,

ABSTRACT Garnets, which are found as inclusions in diamonds, often have the excess of Na2O and Si... more ABSTRACT Garnets, which are found as inclusions in diamonds, often have the excess of Na2O and SiO2 [Stachel, 2001]. Experimental studies suggest that Na is incorporated in pyrope-rich garnet via the coupled substitution Mg+Al=Na+Si [Bobrov et al., 2008]. This study is concerned with the determination of the structure and the thermodynamic properties of NaGrt (Na2MgSi5O12), which is assumed to be the end-member of pyrope-rich garnets with the excess of Na2O and SiO2. Static lattice energy calculations were performed with the program GULP [Gale & Rohl, 2003] using the force-field model [Vinograd et al., 2007] for 200 structures of Na2MgSi5O12 composition. These structures were prepared from Ia3-d pyrope Mg3Al2Si3O12 by replacing all octahedral Al atoms with Si and 2/3 of Mg atoms with Na. The distribution of Mg and Na was varied randomly. The static energies of these structures were cluster expanded using 8 pairwise effective cluster interactions (ECI). The ECIs were used to constrain Monte Carlo simulations within a 4×4×4 supercell (NNN exchangeable sites). The annealing experiments have shown that the lowest energy structure has the space group I4

Physics of the Earth and Planetary Interiors, 2013

Pressure-volume-temperature relations have been measured to 33 GPa and 1673 K for natural siderit... more Pressure-volume-temperature relations have been measured to 33 GPa and 1673 K for natural siderite (Fe 0.95 Mn 0.05 CO 3 ) using synchrotron X-ray diffraction with a multianvil apparatus at the 'SPring-8' facility. A least-squares fit of the room-temperature compression data to a third-order Birch-Murnaghan equation of state (EOS) yielded K 0 = 120 ± 1 GPa and K 0 = 3.57 ± 0.09, with fixed V 0 = 293.4 ± 0.1 Å 3 . Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (@ K T /@T) P = À0.015 ± 0.001 GPa/K and zero-pressure thermal expansion a = a 0 + a 1 T with a 0 -= 3.57(9) Â 10 À5 K À1 and a 1 = 0.06(14) Â 10 À8 K À2 . The analysis of axial compressibility indicates that the c-axis is more compressible (K Tc = 59 ± 1 GPa at K 0 = 2.7 ± 0.1) than the a-axis (K Ta = 166 ± 2 GPa at K 0 = 14.0 ± 0.8). The present thermal EOS enables accurate calculation the density and thermodynamic properties of siderite to the deep mantle conditions.

Lithos, 2014

Trace and rare-earth elements Garnet/melt partitioning coefficients High-pressure experiment Eclo... more Trace and rare-earth elements Garnet/melt partitioning coefficients High-pressure experiment Eclogite New experimental data on trace element partitioning between Na-bearing majoritic garnet and melt at P = 8.5 GPa and T = 1500-1900°C applicable to partial melting of Na-rich eclogite are presented. We have found that Na-bearing garnet is a liquidus phase of the system at 1850-1650°C being accompanied by enstatitic pyroxene at lower temperatures. With decreasing temperature, Na concentration in garnet increases up to N 1 wt.% Na 2 O due to progressive incorporation of a Na majorite component (Na 2 MgSi 5 O 12 ). Most of the studied trace elements are incompatible, except for Er, Tm, Yb (in some runs), Lu, and Sc (in all runs), which are distributed into garnet. The main characteristic of the trace-element partitioning in our experiments is a different behaviour of the LREE (La, Ce, Pr) in comparison with MREE and HREE (Nd, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, and Lu). In particular, a significant increase of D values for LREE with the increase of Na 2 O concentration in garnet is observed. As predicted from lattice strain, partitioning coefficients for REEs entering the X site of garnet exhibit a near-parabolic dependence on ionic radius. The results of the study are applied to the formation of inclusions of Na-bearing majoritic garnets in diamonds, and equilibrium melts significantly enriched in LREEs.

Geochimica et Cosmochimica Acta, 2013

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.

Geochemistry International, 2009

Results of experimental study at 7.0-8.5 GPa and 1300-1900@C of the systems pyrope Mg 3 Al 2 Si 3... more Results of experimental study at 7.0-8.5 GPa and 1300-1900@C of the systems pyrope Mg 3 Al 2 Si 3 O 12 ( Prp )-Na 2 MgSi 5 O 12 ( Na Grt modeling solid solutions of Na-bearing garnets, Prp -jadeite NaAlSi 2 O 6 ( Jd ) in a simplified mode demonstrating melting relations of Na-rich eclogite, and Prp -Na 2 CO 3 are presented. Prp -Na 2 MgSi 5 O 12 join is a pseudobinary that results from the decomposition of Na Grt on to coesite and Na-pyroxene. Synthesized garnets are characterized by Na admixture (>0.32 wt % Na 2 O). Maximal Na 2 O concentrations (1.5 wt % Na 2 O) are reached on the solidus of the system at 8.5 GPa. Clear correlation between Na and Si was established in synthesized garnets; this provides evidence for heterovalent isomorphism of the Mg + Al Na + Si type with the appearance of Na 2 MgSi 5 O 12 component as a mechanism of such garnet formation. The Prp -Jd join is also pseudobinary that results from the formation of two series of solid solutions:

Doklady Earth Sciences, 2011

Doklady Earth Sciences, 2010

The solubility of alkalis in the structures of highpressure minerals, as well as their abundance ... more The solubility of alkalis in the structures of highpressure minerals, as well as their abundance under the conditions of the upper mantle and transition zone, attracts considerable interest from experimentalists and mineralogists. Sodium admixture in garnets was originally discovered by Sobolev and Lavrent'ev [1] in the study of a representative collection of this mineral from inclusions in diamonds, xenoliths of diamondiferous eclogites, and high-pressure metamorphic complexes. By now garnets with significant sodium concentrations (>1 wt % Na 2 O) have been found in many diamond provinces of the world including South Africa, Brazil, Guinea, and Yakutia (see, for example, review [2]). Excessive (relatively to 3 f.u.) silicon concentration is a characteristic feature of these garnets that allows us to attribute them to Na-bearing majoritic garnets.

Doklady Earth Sciences, 2009