Effect of Water on Fe-Mg Interdiffusion in Mantle Minerals: Implications for Geodynamical Processes

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9805419KohlstedtOur laboratory study will quantify the dependence of the rate of diffusion of Fe-Mg on water concentration in olivine and magnesiowstite, two important mantle minerals. One goal of our experiments is to develop relationships between cation diffusivity and water/hydroxyl concentration under well-defined thermochemical conditions. For many nominally anhydrous minerals, a small amount of water significantly enhances diffusion-dependent properties. However, these observations are only qualitative: Does the presence of water result in an enhancement in the kinetics of a specific process ... yes or no? Quantitative relationships between diffusivity and water/hydroxyl content have not been determined for either olivine or magnesiowstite. The results will be used in the context of point defect thermodynamics to gain a fundamental understanding of the mechanism(s) by which water influences transport properties such as ionic diffusion and electrical conductivity. The resulting theoretical framework is essential for reliably extrapolating laboratory results to mantle environments and for utilizing experimental observations to developmodels of the dynamic behavior and geochemical evolution of Earth s interior.