Stable Isotope Investigation of a Fossil Hydrothermal System in Oceanic Crust Formed at a Superfast Spreading Rate (ODP/IODP Hole 1256D)

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Intellectual Merit: This research investigates hydrothermally altered rocks in a drill core collected by NSF's Ocean Drilling Program (IODP Hole 1256D), which penetrates a complete 1 km thick section of ocean crust from pillow lavas to underlying gabbroic rocks. Trace elements as well as stable isotopes of O, H, S, and C in secondary minerals from veins and bulk rocks from the section will be analyzed and examined in terms of hydrothermal signatures and reactions with seawater. Objectives will be to examine whether anhydrite records reactions with seawater discharge, determine at what temperatures fluids penetrate and alter sheeted dike margins and gabbros, at what temperatures silicate alternation minerals form, and what types of fluids form them. Isotope analyses of mineral pairs will be used as geothermometers. Analysis of the S contents and isotope compositions of representative bulk rocks will enable determination of the sulfur budget. Broader Impacts: This work will provide support for a female post-doctoral researcher and support the institutional infrastructure for the stable isotope laboratory at the University of Michigan. Results of the work will be incorporated into undergraduate courses in Marine Geology.