Cycling of H2O between the mantle and the Earth's surface and between different reservoirs in the mantle are critical processes governing Earth's geodynamical and geochemical evolution, influencing everything from plate tectonics to habitability and climate. However, the distribution and inventory of H2O in the mantle remains uncertain, the mechanisms of transport between principal mantle reservoirs are not fully known, and the microscopic mechanisms by which H2O influences the properties of key Earth materials remain controversial. This project represents a multidisciplinary effort combining theoretical mineral physics, experimental petrology, and experimental rock physics to address some of the key outstanding questions regarding the distribution and behavior of H2O in the mantle.
The current proposal will pursue several broad problems that arise from previous CSEDI funding to this group: 1) To investigate the conditions required to incite hydrous melting in the asthenosphere or in the deep upper mantle above 410 km, we will conduct experimental, theoretical and spectroscopic studies to determine the mechanism and limits of H substitution in peridotite-saturated nominally anhydrous minerals, with a focus on garnet and pyroxene, and evaluate the conditions for hydrous melting of the asthenosphere and the upper mantle atop the 410 km discontinuity. 2) To resolve seeming contradictions in our understanding of how H substitutes in olivine and how it influences key properties such as mantle creep strength, we will combine experiments, first-principle calculations and infrared spectroscopy to resolve critical uncertainties regarding the connection between structure, chemical environment, and minor element substitution on the mechanisms of incorporation of OH in olivine, garnets, and pyroxene and on the influence of H on diffusivity and creep strength. 3) We will continue our efforts to use ERDA (Elastic Recoil Detection Analysis) to improve the accuracy of FTIR and SIMS determinations of H in nominally anhydrous minerals.
The broader impacts of this project includes continuation of a significant inter-departmental multidisciplinary effort integrating state-of-the-art materials theory with expertise in petrology and rock physics. The effort includes involving three faculty, two post-doctoral researchers, and one graduate student and is facilitated by regular group meetings to ensure that our focus remains on multidisciplinary approaches and to promote interdisciplinary learning of all of the participants. For Hirschmann, Kohlstedt, and Withers, the proposed research dovetails well with the Earth sciences REU undergraduate intern site (Fluids in the Earth, from the Surface to the Core. Wentzcovitch and Umemoto communicate results and methods to the broader scientific community through the Quantum ESPRESSO project and related workshops and tutorials and in the training of undergraduates through summer internships.
