HIGH-TEMPERATURE EQUATION OF STATE OF CASIO3 PEROVSKITE AND ITS IMPLICATIONS FOR THE LOWER MANTLE

A method for calculating thermal equation of state (EOS) of solids is presented and is applied to CaSiO3 perovskite. The input parameters ar e the volume, V-0, the bulk modulus, K-0, its pressure derivative, K-0 ', and the Debye temperature, Theta(0), all in the static lattice at z ero pressure. These were determined from experimental data at room tem perature. The present values of V-0, K-0 and K-0' agree well with rece nt theoretical values by Wentzcovitch et al. The present EOS is in goo d agreement with the high-temperature data to 1600 K and to 13 GPa by Wang et al. as well as the room-temperature data to 134 GPa by Mao et al., those to 112 GPa by Yagi et al. and those to 90 GPa by Tarrida an d Richet. The calculated density and thermal expansivity of CaSiO2 per ovskite under lower mantle conditions are in agreement, respectively, with PREM (Preliminary Reference Earth Model) within -1.2-1.2% and wit h thermal expansivity of the lower mantle estimated by O.L. Anderson w ithin 6.8 to -3.1% over the depth from 670 km to 2891 km. A method of calculating Lame constants, lambda(S) and mu(S), for an isotropic medi um is also presented and is applied to CaSiO3 perovskite under lower m antle conditions. The calculated sound velocities, upsilon(p) and upsi lon(s), agree with PREM within 1.3-2.7% and -1.2 to -4.5%, respectivel y. The present results suggest that CaSiO3 perovskite behaves as an in visible component in the lower mantle. (C) 1998 Elsevier Science B.V.