On dislocation glide in MgSiO3 bridgmanite at high-pressure and high-temperature

- Dislocations are modeled in MgSiO3 bridgmanite at the atomic scale.
- The thermally activated mobility of dislocations is determined at mantle pressures from a kink-pair model.
- The model can reproduce previous deformation experiments in Bridgmanite.
- The model gives access to the deformation of bridgmanite generated by dislocation glide at mantle strain rates.

Dislocation glide in MgSiO3 bridgmanite with Pbnm perovskite structure is modeled at 30 and 60 GPa for the [100](010) and [010](100) slip systems. The velocity of screw dislocations is calculated in the thermally activated regime based on the kink-pair mechanism. We show that the dislocation velocity determination can rely on the atomic scale calculations of a limited amount of parameters: the Peierls stress τp, and the formation enthalpy of a single kink Hk. From the dislocation velocities, the evolution of stress as a function of temperature can be derived from the Orowan equation at any strain rate. Calculations performed at laboratory strain-rates of 10−5 s−1 reproduce well the high stress levels found experimentally. This demonstrates the influence of lattice friction in the mechanical properties of bridgmanite. The same calculations are performed at mantle strain-rate (10−16 s−1). They demonstrate that in the lower mantle, bridgmanite would always be in the thermally activated regime and that stresses close to 1 GPa are still necessary to move dislocations in bridgmanite. In the uppermost lower mantle, dislocation glide is inhibited and other deformation mechanisms, involving diffusion, are needed.