Lattice preferred orientation of stishovite deformed at high pressure and high temperature

In the lower part of the mantle transition zone, seismic polarization anisotropies, which could be caused by the lattice preferred orientation (LPO) of elastically anisotropic minerals, were observed related with subducted materials. Stishovite, which is one of the dominant minerals in mid-ocean ridge basalt, continental crust and sediment layers, possesses significant anisotropic elasticity and has high potential to contribute to the observed seismic anisotropy. In this study, three types of deformation experiments (uniaxial compression, uniaxial tension and shear) on polycrystalline stishovite were conducted using either a D-DIA apparatus or a D-111 type apparatus with a Kawai-type cell assembly to investigate the LPO of stishovite developed during deformation at pressure of 12 GPa and temperatures of 1600 and 1800 °C. The obtained LPO patterns in all experiments are consistent each other and they suggested the dominant slip is in the [001] direction dispersed on the {110} and {100} planes with [001]{110} slightly more dominant, thus we concluded that the dominant slip system is [001]{hk0}. Based on the present results, the fast vertically and horizontally polarized shear wave anisotropy observed in the lower part of the mantle transition zone could be explained by the LPO of stishovite with vertical and horizontal flow, respectively, related with subducted materials.