Slip systems and plastic shear anisotropy in Mg2SiO4 ringwoodite: insights from numerical modelling

Knowledge on the deformation mechanisms of Mg2SiO4 ringwoodite is important for the understanding of flow and seismic anisotropy in the Earth’s mantle transition zone. We report here the first numerical modelling of dislocation structures in ringwoodite. The dislocation properties are calculated through the Peierls-Nabarro model using the generalized stacking fault (GSF) results as a starting model. The GSF are determined from first-principle calculations using the code VASP. They enable us to determine the relative ease of slip for dislocation glide systems in ringwoodite. The dislocation properties such as core spreading and Peierls stresses were determined for the easy dislocation glide systems. Our results show that 1⁄2 ‹ 110 8 {110} and 1⁄2 ‹ 110 8 {111} are the easiest slip systems in ringwoodite at 20 GPa and 0 K. These results are used as input of a viscoplastic model to predict the deformation of a ringwoodite rich aggregate. Calculated crystal preferred orientation (CPO) accounts satisfactorily for experimental data available from either diamond anvil cell or D-DIA experiments. Key-words: ringwoodite, deformation mechanisms, dislocations, slip systems, first-principle calculations, Peierls-Nabarro model, seismic anisotropy, Earth mantle transition zone.