ALVIN Diving on the East Pacific Rise, 9-10 Degrees North: Hydrothermal, Volcanological, and Geochemical Studies in Support of ODP Bare Rock Drilling

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A new view of sea-floor spreading center processes is emerging from integration of detailed bathymetric, geophysical, and petrological data sets. Variations in the supply of magma along the ridge axis appears to play a fundamental role in controlling morphologic, tectonic, seismic and geochemical "segmentation" of spreading centers. Such magmatic segmentation has profound implications for hydrothermal processes which are controlled by the thermal and permeability characteristics of the newly formed crust. The present project will support a detailed examination of hydrothermal processes along the East Pacific Rise south of the Clipperton Transform Fault. This section of ridge has been extensively studied using standard geologic and geophysical techniques. Only data on the chemistry and nature of vent fluids to be gathered by this project is lacking for this ridge segment. Additionally, future drilling is planned which will provide a depth perspective on volcanic and hydrothermal processes. These additional data will provide the first complete three dimensional characterization of a ridge crest spreading segment. Additional work to be accomplished during Alvin dives in this study includes: structural mapping, basalt sampling, and evaluation of specific sites for future drilling.