HR: 15:10h
AN: MR33B-07 INVITED     [Abstracts]
TI: High-pressure elasticity of perovskite and post-perovskite (Mg,Fe,Al)(Al,Si)O3
AU: * Caracas, R
EM: r.caracas@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, DC 20015 United States
AU: Cohen, R E
EM: r.cohen@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, DC 20015 United States
AB: We determine the effect of chemistry on the elasticity and seismic wave velocities of perovskite and post-perovskite using first-principles calculations. The elastic constants tensor in perovskite is more isotropic than in post-perovskite. The pure shear elastic constants are comparable between perovskite and post-perovskite; for post-perovskite, MgSiO₃ has the largest values, and both Al₂O₃ and FeSiO₃ show elastic instability at low pressures. The shear modulus of post-perovskite is larger than of perovskite at high pressures in all three cases. The difference in bulk modulus between the perovskite and post-perovskite structures, for MgSiO₃ and FeSiO₃ is on the order of about 15-20 GPa. The post-perovskite phase of Al₂O₃ shows the smallest bulk modulus at high pressures. The V_p values for FeSiO₃ and Al₂O₃ post-perovskite are respectively about 2.0 and 1.6 km/s below the values for MgSiO₃ post-perovskite. V_s shows similar trends for all the three compositions: at low pressures post-perovskite is softer than perovskite and has lower V_s values, while at higher pressure post-perovskite has larger values than perovskite. At 120 GPa MgSiO₃ post-perovskite has V_s higher than FeSiO₃ post-perovskite by about 1.7 km/s and higher than Al₂O₃ by about 0.9 km/s. For a pyrolitic mantle the effect of chemistry is relatively small, decreases on the order of up to 2% for V_p and up to 1.5% for V_s. Due to the perovskite to post-perovskite transition in Fe- and Al- bearing MgSiO₃, V_p increases by 0.7% (about 0.1 km/s) and Vs by 2.5% (about 0.2 km/s) at 120 GPa.
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005