P-V-T equation of state of MgSiO3 perovskite and MgO periclase:: Implication for lower mantle composition

The P-V-T equation of state (EOS) for magnesium silicate perovskite (MaSiO(3)) and periclase (MgO) was obtained by fitting measured P, V, T data. The EOS of MaSiO(3) perovskite was determined by applying the Mie-Grdneisen-Debye approach, based on three alternative bulk modulus values (Kn = 240, 250 and 261 GPa), yielding substantially different values for high-order thermoelastic parameters such as the Gruneisen parameter (gamma) and the temperature derivative of bulk modulus ((aK(T)/aT)(P)). Combined with the EOS of magnesiowustite, we calculated the density (rho), bulk modulus (K-S) and seismic parameter (phi) for simplified pyrolitic lower mantle along a plausible adiabat (temperature at 670 km, T-a = 1900 K), and compared these values to those of a seismological model (PREM). The results based on K,10 of 261 GPa, which has been commonly used, showed good agreement with PREM, within 0.5% for rho, and 2-3% for K-S and phi, throughout the lower mantle. The EOS obtained using the recent K-T0 data (240-250GPa), substantially overestimated K-S and phi by 5-10%, requiring a progressive enrichment in (Mg,Fe)O with increasing depth. In addition, a more realistic vibrational density of states (VDOS) model (Kieffer-type model) was applied to calculate the EOS. The effect of VDOS on thermoelastic parameters was not large enough to modify those conclusions. (c) 2005 Elsevier B.V. All rights reserved.