Chemistry and Structure of Grain and Phase Boundaries: Importance for Trace Element Storage and Transport in the Mantle

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This work seeks to answer the questions, "What is the storage capacity of grain and phase boundaries for incompatible elements in mantle rocks?" and "How does segregation to grain-grain interfaces affect intergranular diffusion in the mantle?" It was recently discovered that boundaries between grains of Mg-Fe olivine are enriched in elements such as Ca, Al, Cr, K and Ti. The concentrations vary systematically with the concentrations in the grain interiors, in some cases following classic thermodynamic models for elemental partitioning. This study involves systematic analytical and experimental investigation of these processes and the resultant effects on diffusive transport in Earth's mantle. The results will provide constraints on the geochemical evolution and behavior of Earth's deep interior. The broader impacts of this proposal emerge from education of undergraduates, professional development of a graduate student and a postdoctoral associate, and establishment of new experimental techniques. (1) The Department of Geology and Geophysics is an NSF-funded REU site for studies of Fluids in the Earth from Surface to Core. As such, undergraduates gain hands-on experience each summer carrying out experiments that are direct outgrowths of and intimately related to the research proposed in this document. (2) The research outlined in this proposal is a continuation of a project that was initiated as part of a recent doctoral fellowship project and will now be carried forward by a first-year graduate student and a young postdoctoral scientist, thus contributing to the professional development of both. (3) As part of the proposed research, new experimental techniques will be developed, which play an important part in building the research infrastructure in the solid-earth sciences.