Résumé
The D" layer, located right above the core-mantle boundary (CMB), represents a very complex region with significant seismic anisotropy both at the global and local scale. Being a part of inaccessible deep Earth interior, characterized by extreme P-T conditions in excess of 120 GPa and 2000 K, this region is extremely challenging for interpretation relying only on the direct geophysical observations and high-pressure experiments, leading often to contradictory results. Thus, the reasons of the pronounced anisotropy in D" are still debated (e.g. crystal preferred orientation (CPO), oriented inclusions, thermo-chemical heterogeneities etc.). Among them, contribution of CPO in anisotropic silicate post-perovskite (ppv) phase is commonly considered as substantial. Furthermore, the D" layer is a thermal boundary layer located at the interface between liquid iron alloy, constituting the outer core, and solid although viscous silicates of the lowermost mantle. As such, its physical properties are critical for our understanding of the heat transfer from the core, driving mantle convection. The latter is governed by plastic flow, which, in turn, is controlled by the motion of defects in crystals. For high pressure phases, numerical modelling represents a powerful tool able to provide the intrinsic properties and the elementary deformation mechanisms, not available for direct observations during high-pressure experiments. Here we demonstrate how atomic-scale modeling of dislocation processes can be used to address the anisotropic plasticity in MgSiO (sub 3) ppv and further deduce an essential information on such important geophysical implications as viscosity, CPO development, anisotropy and attenuation of seismic waves.