Silicon self-diffusion of MgSiO3 perovskite by molecular dynamics and its implication for lower mantle rheology

Abstract

The pressure effect of silicon self-diffusion of MgSiO3 perovskite was investigated by molecular dynamics (MD). The viscosity variation of MgSiO3 perovskite in the lower mantle was derived by the Nabarro-Herring (Herring-Nabarro) model. For the MD calculation, the spontaneous jumping of atoms by self-diffusion was reproduced without using artificial forces, and the consistency of migration enthalpy (Hm*) with experimental data was improved. The results showed that migration enthalpy increases monotonically with increasing pressure. The viscosity of MgSiO 3 perovskite in the lower mantle increases monotonically with increasing depth. The obtained depth profile is distinguishable from that of MgO periclase and can be utilized to determine which mineral dominates the lower mantle rheology. Depending upon the assumed shape of the depth profile for lower mantle viscosity, we considered the dominant mineral as (1) MgSiO3 perovskite for the monotonic shape case or (2) MgO periclase for the hill shape case that has the highest-viscosity zone in the middle of the lower mantle. Copyright 2010 by the American Geophysical Union.