On dislocation glide in MgSiO3 bridgmanite at high-pressure and high- temperature
A Kraych and P Carrez and P Cordier, EARTH AND PLANETARY SCIENCE LETTERS, 452, 60-68 (2016).
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 tau(p), and the formation enthalpy of a single kink H-k. 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. (C) 2016 The Authors. Published by Elsevier B.V.
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