期刊
PHYSICS OF THE EARTH AND PLANETARY INTERIORS
卷 240, 期 -, 页码 125-131出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.pepi.2014.10.005
关键词
Pyrope; Phase stability; Elasticity; Ab inito calculations; Density functional calculations
资金
- KAKENHI [23540560, 23224012, 24840020, 26257212]
- Grants-in-Aid for Scientific Research [26287137, 23540560, 13F03023, 24840020, 26257212] Funding Source: KAKEN
We study the high-pressure stability and elastic properties of Mg3Al2Si3O12 Pyrope garnet using the density functional first principles computation method. Pyrope garnet is found to dissociate into an assemblage of MgSiO3 Mg-perovskite (Pv) and Al2O3 corundum (Cor) solid solutions at similar to 19.7 GPa at static conditions. Then, this assemblage undergoes a phase transition to pyropic (Al-bearing) Pv at similar to 65 GPa. The enthalpy of an assemblage of MgAl2O4 calcium ferrite (CF), MgPv, and stishovite (St) is less stable than that of MgPv plus Cor. A continuous reaction in the MgSiO3-Al2O3 system suggested by this study is consistent with previous experimental and computational studies but not with a recently modeled phase diagram. This implies that the formation of pyropic Pv could not cause any seismic scatterers in the mid-lower mantle. The investigated anisotropy of elastic velocities further indicates that pyrope garnet is a very isotropic mineral. Our results suggest that seismological anisotropy inferred in the upper mantle could not be due to garnet. (C) 2014 Elsevier B.V. All rights reserved.
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