First-principles study of high-pressure elasticity of CF- and CT-structure MgAl2O4

Details First-principles study of high-pressure elasticity of CF- and CT-structure MgAl2O4 First-principles study of high-pressure elasticity of CF- and CT-structure MgAl2O4

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012georl..3902307y&link_type=abstract

Geophysical Research Letters, Volume 39, Issue 2, CiteID L02307

Physics

Geodesy And Gravity: Earth'S Interior: Composition And State (7207, 7208, 8105, 8124), Mineralogy And Petrology: Mineral And Crystal Chemistry (1042), Mineral Physics: Elasticity And Anelasticity, Mineral Physics: Equations Of State

Scientific paper

The high-pressure elastic properties of aluminous phases in the basaltic crust of subducted slabs are of interest since they may play important role in the cause of lower mantle seismic anomalies especially at the mid-mantle depth. The athermal elasticity of the Ca-Ferrite (CF) and Ca-Titanate (CT) structure MgAl2O4 which are believed to be constituents of the aluminous bearing phases in subducted basalt was performed by first-principles calculations in the framework of density functional theory. The full elastic constant tensors of the two orthorhombic phases were reported at pressures up to 80 GPa. It has been reported by experiment that a phase transition of CF to CT occurred around 40 GPa corresponding to a depth of about 1000 km. At the transition pressure, (1) the polycrystalline isotropic compressional (P) and shear (S) wave velocities of CT are about 0.7% and 1.6% faster than CF, respectively; (2) both phases show great elastic anisotropy and the fastest travelling direction of P-wave is along the shortest axis which is parallel to the triangle channels (i.e., [001] for CF and [100] for CT); (3) the largest velocity variation of two orthogonal S-waves at [001] of CT becomes 25% which is three times larger than that at the corresponding [100] direction of CF. The large velocity variation in S-waves implies the shear wave splitting observed in the mid-mantle depth of subducted zones is possible related to the elastic anisotropy of aluminous phases in subducted slabs.

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