Diffusion in Lower Mantle Minerals

Case Western Reserve University, Cleveland OH

Investigators

Abstract

Van Orman 0337125 Diffusion plays a critical role in many important mantle processes, including chemical exchange, solid-state creep, seismic attenuation and electrical conduction. This study will provide experimental data on cation and oxygen diffusion rates in the two most abundant lower mantle minerals, perovskite (MgSiO3) and periclase (MgO). High-pressure, high-temperature experiments on both minerals will be performed under well-defined thermochemical conditions, with point defect concentrations controlled by the addition of aliovalent cations. In periclase, diffusion coefficients for oxygen and a broad range of monovalent, divalent and trivalent cations will be determined at pressures between 1 atm and 25 GPa and temperatures of 1200-2300 K. An important goal of these experiments is to determine quantitative relationships between diffusivity and ionic parameters such as radius, charge and polarizability. Experiments on perovskite will focus on Mg and O self-diffusion at 25 GPa and 1700-2300 K. The study is designed to gain a fundamental understanding of the mechanisms for ionic transport in perovskite and periclase, and the influence of temperature, pressure and composition on diffusivity. The work proposed will provide data that crosses disciplinary boundaries between geochemistry and geophysics. The project will also help support the research infrastructure at Case Western Reserve University and allow the integration of research and education of graduate and undergraduate students in this institution.