Constraints on Lower Mantle Viscosity from Diffusion Experiments on MgSiO3 Perovskite and MgO Periclase

Van Orman, James A, West Somerville MA

Investigators

Abstract

0074189 Van Orman This is a project to investigate diffusional mass transport in MgSiO3 perovskite and MgO periclase under high pressure (>23 Gpa). The study is aimed at placing rigorous experimental constraints on the plastic rheologies of these important high-pressure phases under temperature and pressure conditions of the lower mantle. Perovskite and periclase are generally agreed to be the most abundant minerals in the lower mantle, and their plastic flow properties are thus expected to control the viscosity of the mantle below 670 km. It will be possible using the results of this experimental investigation to directly estimate the viscosity of a perovskite-periclase lower mantle deforming by diffusion creep, as well as the dependence of the viscosity on temperature, pressure, and grain size. The study will thus provide a much-needed constraint on geophysical models of viscosity stratification in the mantle, and in doing so is expected to significantly improve our understanding of the dynamics of the Earth's deep interior.