We present ab initio (LDA + U sc ) studies of high-temperature and high-pressure elastic properties of pure as well as iron-bearing (ferrous, Fe 2+ , and ferric, Fe 3+ ) and aluminum-bearing MgSiO 3 postperovskite, the likely dominant phase in the deep lower mantle of the Earth. Thermal effects are addressed within the quasiharmonic approximation by combining vibrational density of states and static elastic coefficients. Aggregate elastic moduli and sound velocities for the Mg end members are successfully compared with scarce experimental data available. Effects of iron (Fe) and aluminum (Al) substitutions on elastic properties and their pressure and temperature dependence have been thoroughly investigated. At the observed perovskite to postperovskite transition (P = 125 GPa and T = 2,500 K), compressional and shear velocities increase by 0–1% and 1.5–3.75%, respectively. This observation is consistent with some seismic studies of the D ′′ discontinuity beneath the Caribbean, which suggests that our robust estimates of elastic properties of the postperovskite phase will be very helpful to understand lateral velocity variations in the deep lower mantle region and to constrain its composition and thermal structure.
Bibliographical noteFunding Information:
This work was supported primarily by NSF Grant NSF-EAR-1348066. Computations were performed on TACC's stampede2 systems under the XSEDE allocation Grant TG-DMR180081, and Blue Waters system at NCSA. The authors also gratefully acknowledge Juan Valencia-Cardona for helpful discussions. Results produced in this study are available in the supporting information (Tables S2?S6).
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