Modeling Creep in the Lower Mantle: Insights from the Atomic Scale

Abstract:

Convection and plastic deformation in the Earth's lower mantle are expected to occur by processes at various scales, including grain boundary sliding, diffusion, and dislocation creep. Although the composition of the Earth's lower mantle is dominated by the (Mg,Fe,Al)(Si,Al)O₃ perovskite, the mechanical properties of this phase, its microstructure, and the relative importance of the mechanisms cited above for its plastic deformation, are still a matter of debate. Given the thermodynamic conditions, both dislocation glide and climb are expected to contribute significantly to the plastic flow, however the activation energies and rates of these mechanisms are still to be determined.

In this study we utilize numerical simulations at the atomic scale in MgSiO₃ perovskite to investigate the climb of dislocations, at pressure relevant to Earth's lower mantle. The interaction of vacancies with dislocations, as elementary mechanism for dislocation climb, is explicitly computed. It is shown to be dominated by electrostatic effects due to the ionic character of this material, and allow to give scenarios for climb mechanisms. These results give insight into the importance of dislocation creep in the rheology of the mantle.

This work was supported by funding from the European Research Council under the Seventh Framework Program (FP7), ERC grant N.290424 – RheoMan.