9405845 Hirth This project involves experimental research on the solubility of water in nominally anhydrous mantel minerals (olivine and selected pyroxenes) and on the role of water in ionic diffusion in olivine. The research involves three aspects: (1) determining the speciation of water in olivine, using experimental data on the solubility of water in olivine obtained at pressures of , 0.3 GPa to ~ 12 GPa and over a wide range of water fugacity and proton activity, (2) constraining the upper limit for water content of the upper mantle, using measured solubilities of water in high- Ca pyroxene as a function of water fugacity and proton activity, and (3) determining the mechanism by which water affects diffusion-dependent properties in nominally anhydrous minerals, using dependence of Fe-Mg interdiffusion and O tracer diffusion on water fugacity and proton activity. The results of these laboratory experiments will provide fundamental constraints on the extent to which nominally anhydrous minerals can be reservoirs for water in the mantle and also on the magnitude of the effect of water on diffusion-dependent properties such as creep and electrical conductivity of mantle rocks.
