High-Pressure Study of Some Large Ions in Mantle Minerals

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9903203Harlow The proposed research is an experimental investigation at high pressure and temperature of potassium- andfluorine-rich minerals/phases that may be stable in variably hydrous environments of Earth's upper mantle. The study will start with a pair of compounds that have been demonstrated to be stable at such Earth conditions but are otherwise inadequately understood; these phases include K-cymrite (KAlSi3O8onH2O), the hydrous analog of K-feldspar, and KMgF3, a perovskite-structure phase used as an analog for silicate perovskites. The research will 1) determine the upper range of pressure and temperature stability of these phases in mineral(fluid assemblages appropriate to known mantle rocks and to crustal rocks that are candidates for subduction into the mantle, 2) characterize the phases with respect to composition, OH content, and structural state, and 3) determine the inter-phase partitioning of constituent elements. Other phases to be included in experiments will be fluorphlogopite, phengitic mica, fluor-K-richterite, and K-feldspar, and results from this study knowledge will improve the knowledge of their stability conditions as well. Experiments will be carried out in Walker-type multianvil apparati, and products will be analyzed by a combination of electron microprobe, scanning-electron microscopic and cathodoluminescence imaging, x-ray diffraction, and FT-IR spectroscopy. Results from the research will be used to improve predictions of the storage of potassium and fluorine in reservoirs in the mantle as compared to the elements' partitioning into fluids and melts.