First principles thermoelasticity of MgSiO3-perovskite: consequences for the inferred properties of the lower mantle

Some key thermoelastic properties of MgSiO3-perovskite (pv) have been deter mined at lower mantle (LM) pressures and temperatures using the quasi-harmo nic approximation in conjunction with first principles phonon dispersions. The adiabatic bulk moduli (Ks) of pv and of an assemblage of 80 vol% pv and 20 vol% MgO were obtained along the thermodynamically inferred adiabat and compared with the seismic counterpart given by the preliminary reference E arth model (K-PREM) The discrepancy between calculated Ks's and K-PREM in t he deep LM suggests a super-adiabatic gradient, or subtle changes of compos ition, or phase, or all beginning at about 1200 km. The Anderson Cruneisen parameter, delta (S) = (partial derivative lnK(S)/partial derivative ln(P)) (p), was predicted to decrease rapidly with depth (from 2.7 to 1.2 across t he LM) supporting the thermal origin for the lateral heterogeneities throug hout most of the LM.