Experimental Study of Mineral Solubility in Fluids of the Deep Crust and Upper Mantle

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Fluids in Earth's deep crust and upper mantle play an important role in a wide range of geological processes. They change rock compositions, participate in crustal and mantle melting, and mediate how rocks deform. Their ability to change rock composition figures prominently in Earth?s long term compositional evolution that resulted in formation of the continental crust on which we live. The action of fluids in deep environments is a fundamental aspect of melting that leads to large volcanoes whose volatile content governs explosivity and therefore the hazards they pose. By controlling how rocks deform, fluids in deep settings also play a poorly understood role in deep, slow-slip earthquakes whose generation we are only now beginning to understand.This project aims to experimentally characterize the basic physical chemistry of how water interacts with and dissolves minerals in the deep crust and upper mantle. It is proposed to conduct experiments in three areas. The first will provide robust thermodynamic constraints on the speciation of aqueous silica, the most abundant neutral species at most crustal conditions. A second component of the work focuses on dissolved Si at alkaline conditions. This is because models suggest that the pH crustal and mantle fluids is alkaline over a wide range of P and T. Finally. the team will extend previous experiments on quartz and feldspar solubility in H2O-salt solutions to include CaCl2 and anorthite, which have not previously been studied but which are key ingredients to any understanding of deep fluids. All experiments will involve hydrothermal piston-cylinder methods which provide precise and accurate solubility constraints at the requisite conditions. The work will provide constraints that will help improve new models of the chemistry of fluid-rock interaction at high pressure and temperature.