Ab initio study of the elastic behavior of MgSiO³ ilmenite at high pressure

We investigate the athermal high pressure behavior of the elastic properties of MgSiO³ ilmenite up to 30 GPa using the ab initio pseudopotential method. Our results at zero pressure are in good agreement with single-crystal elasticity measurements. The elastic anisotropy is shown to decrease slightly under compression and hence to remain substantial (25 to 20% shear wave anisotropy and 16 to 10% longitudinal wave anisotropy) over the pressure regime studied. The directions of fastest and slowest wave propagation are found to change slightly with pressure as determined by the pressure dependence of c₁₄ and c₂₅. Comparisons with the elastic behavior of other deep transition zone phases such as ringwoodite and garnet show that ilmenite is likely to be the fastest and most anisotropic mineral in this region. Large contrasts (~ 10%) in velocities and densities between ilmenite and garnet are suggested to be significant for the interpretation of lateral structure in the transition zone.