Asimow (0550216) Existing data and theory show that small amounts of water significantly affect the interpretation of basalt composition data in terms of mantle temperature and source composition. This research uses these constraints, coupled with water-saturated multi-anvil experiments in the range 3-15 GPa at ~1100degreesC on a variety of natural orthopyroxenes with 0 to 6 weight percent Al2O3 to improve our understanding of trace water in the mantle source regions of basalts. Work is focused on three main issues. First, determining the water storage capacity of the abundant mantle mineral, orthopyroxene, as a function of pressure and composition. Second, how partition coefficients for water between mantle minerals and melts behave, especially in the compositional realm relevant to the melting of slightly hydrous peridotite on the geotherm below mid-ocean ridges. Experimental run products from the first and second parts of the research will be determined by Fourier transmission infrared spectroscopy (FTIR) and continued development of this method to analyze in situ mineral water contents will be carried out. The third part of the study focuses on determining silicate liquid compositions formed by the equilibrium partial melting of hydrous peridotite at high pressure below the dry solidus temperature. Experiments will use an iterated sandwich technique that is being applied for the first time to hydrous melts. Results of the project should help to directly answer questions about the deep, low degree melting region beneath mid-ocean ridges and provide key constraints for the calibration of hydrous melting in future thermodynamic models that may be applied to subduction zone volcanism, transition zone melting, and other processes. Broader impacts of this work include support and training of a PhD student and undergraduates, as well as acquisition of key experimental data needed to develop the geochemical/ petrological modeling tools that widely used by the Earth and Ocean Science communities.
