High-temperature equation of state of CaSiO 3 perovskite and its implications for the lower mantle

Abstract

A method for calculating thermal equation of state (EOS) of solids is presented and is applied to CaSiO 3 perovskite. The input parameters are the volume, V 0, the bulk modulus, K 0, its pressure derivative, K′ 0, and the Debye temperature, Θ 0, all in the static lattice at zero pressure. These were determined from experimental data at room temperature. The present values of V 0, K 0 and K′ 0 agree well with recent theoretical values by Wentzcovitch et al. The present EOS is in good 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 and Richet. The calculated density and thermal expansivity of CaSiO 3 perovskite under lower mantle conditions are in agreement, respectively, with PREM (Preliminary Reference Earth Model) within −1.2 −1.2% and with thermal expansivity of the lower mantle estimated by O.L. Anderson within 6.8 to −3.1% over the depth from 670 km to 2891 km. A method of calculating Lamé constants, λ S and μ S , for an isotropic medium is also presented and is applied to CaSiO 3 perovskite under lower mantle conditions. The calculated sound velocities, ν p and ν s, agree with PREM within 1.3–2.7% and −1.2 to −4.5%, respectively. The present results suggest that CaSiO 3 perovskite behaves as an invisible component in the lower mantle.