Effect of Redox and pH on the Reaction Kinetics of Anhydrite in a Coupled Chemical System: An Experimental Study with Implications for Modeling Vent Fluid Evolution at EPR 9-10 N

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ABSTRACTOCE-0813861Intellectual Merit: The objective of the proposed experimental study entails acquisition of kinetic and thermodynamic data to enhance the development and application of geochemical models needed to constrain the temporal and spatial evolution of the expanding database for hydrothermal vent fluids at EPR 9-10°N and at other R2K IS Sites. Existing vent fluid data suggest that anhydrite coexisting with plagioclase, magnetite and calcic-bearing aluminosilicates may provide redox buffering in response to the addition of seawater derived sulfate into portions of subseafloor reaction zones at mid-ocean ridges. The redox buffer capacity unique to this chemical system, however, is a function of reaction rates between anhydrite and dissolved H2 and ferrous iron, the principle reducing agents derived from hydrolysis of primary and secondary minerals in basalt. At present little is known about the kinetics and thermodyamics of this system. The research project will obtain the requisite kinetic/thermodynamic data, and will apply these to geochemical models that will be used to constrain the temporal/spatial evolution of hydrothermal vent fluids at the East Pacific Rise 9N Ridge2000 Integrated Study Site, with applicability to the other Ridge2000 ISS as well. The project will make use of a newly-developed hydrothermal flow reactor with monitored pH and redox conditions. Broader Impacts: The project will provide essential data required for Ridge2000 integration and synthesis efforts, including the baseline data required for subsequent development of reaction-transport models. The acquisition of kinetic and thermodynamic data under hydrothermal conditions will help to develop reaction-transport models designed to couple physical and chemical processes in subseafloor reaction zones at mid-ocean ridges. This takes on added significance considering the potential role of anhydrite on crustal permeability at mid-ocean ridges. The proposed research will benefit from the participation of undergraduate summer interns in connection with the NSF/REU program in the Department of Geology and Geophysics at the UM entitled ?Fluids in the Earth?, while also enhancing graduate student training and mentoring. Moreover, the further development of the Ti-flow reactor in the course of the proposed study enhances the research infrastructure available to scientists involved in research and training in geology, biology and chemistry, as well as in a broad range of engineering disciplines.