HR: 08:45h
AN: U31A-02    [Abstracts]
TI: Effects of chemistry on the properties and transformation of perovskite to the post-perovskite phases with implications for the lowermost mantle
AU: * Caracas, R
EM: r.caracas@gl.ciw.edu
AF: Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Road, N.W., Washington, DC 20015 United States
AU: Cohen, R E
EM: r.cohen@gl.ciw.edu
AF: Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Road, N.W., Washington, DC 20015 United States
AB: We perform 0K static first-principles calculations on the perovskite (pv) and post-perovskite (ppv) phases in the MgSiO₃ - FeSiO₃ - Al₂O₃ system up to lower mantle pressures. We determine the relative stability and the elastic properties of the pure and some intermediate terms and discuss some implications for the Earth's lower mantle. We show that the addition of Fe²⁺ in MgSiO₃ considerably decreases the pv-ppv transition pressure. The ppv phase of FeSiO₃ is stable at all pressures with respect to the pv phase. FeSiO₃ ppv is metallic, in antiferromagnetic configuration, and stable with respect to oxides (FeO and SiO₂) above 115-120 GPa. The addition of Fe also increases the bulk modulus and decreases the shear modulus of MgSiO₃. The addition of Al₂O₃ in MgSiO₃ slightly increases the pv-ppv transition. The pv phase of Al₂O₃ is unstable at all pressures with respect to corundum, Rh₂O₃(II) and ppv structures. Both the bulk and the shear modulus of MgSiO₃ pv and ppv decrease with the increase of Al content. Both Fe and Al decrease the seismic wave velocities of MgSiO₃ pv and ppv. Our calculations suggest that the lower mantle might be locally enriched in Fe, forming low and ultra-low velocity zones that ensure the electromagnetic coupling between the mantle and the outer core.
DE: 3620 Crystal chemistry
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
SC: Union [U]
MN: 2005 Joint Assembly