Subducted mid-oceanic ridge basalt exists in the Earth's mantle as eclogite, a rock consisting mostly of the minerals garnet and clinopyroxene. Although both of these minerals are nominally anhydrous, a small amount of water or hydroxide has been identified in many eclogites brought to the Earth's surface by volcanic or tectonic processes. Water has major effects on the physical properties of minerals. Insight into the mechanisms of its occurrence will improve our understanding of the transport of water in the Earth's mantle, and cast light on the kinetics of mantle convection and the 'recycling' of the continental crust. This project will quantify the mechanisms for water substitution through an experimental program focused on excess SiO2 and OH contents, especially studying their correlation with cation vacancy concentrations in clinopyroxene at pressures of 4-12 GPa and temperatures of 900-1200oC. This work will extend and refine previous thermobarometric interpretations of eclogites and determine the upper limit of water solubility. The broader impacts of this work include education of graduate and undergraduate students in advanced analytical techniques.
