An Extended Semianalytical Approach for Thermoelasticity of Monoclinic Crystals: Application to Diopside

Here we extend a semianalytical method to compute thermoelastic properties of materials (Wu & Wentzcovitch, ) to monoclinic systems and apply it to diopside (MgCaSi2O6), a mineral with monoclinic symmetry and an end-member of clinopyroxene. Using ab initio results for structural and vibrational properties, we obtain the density, the elastic tensor, single crystal elastic anisotropies, and seismic wave velocities of diopside over a wide pressure and temperature range. Our results agree well with previous available experimental results. Compared with other minerals in the upper mantle, clinopyroxene has the lowest P wave velocity (V-P) and S wave velocity (V-S) at depths greater than 240km. Combining our results with elastic properties of other major upper-mantle minerals obtained by previous studies, we estimate the density and wave velocity profiles of a pyrolitic mantle in the depth range of 220-400km, where pyroxene is gradually dissolved into garnet. The obtained profiles agree well with seismic models (PREM and AK135) supporting the notion of a pyrolitic upper mantle.