Structure of Oceanic Crust Formed at 200 mm/yr. Spreading Rate

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Collaborative Project OCE 98-11948 Wilson OCE 98-12612 Harding The recommended project involves funds for an extensive geophysical survey of oceanic crust in the south-central Cocos Plate region, in support of ODP Proposal 522-Pre. This area of the ocean crust was formed by the fastest spreading rate ever documented by marine magnetic anomalies, with a spreading rate of about 200 mm/yr at the southern end of the Cocos-Pacific Plate boundary from 13-17 Ma. The survey will measure the basic properties of oceanic crust formed at this extraordinary spreading rate. Extrapolating observed and theoretical variations with spreading rate suggests that seismic layer 3 and the dike-gabbro transition may occur at a depth shallower than 1km. Using multi-channel seismic reflection and ocean-bottom hydrophone siesmic refraction, the structure of the upper oceanic crust will be mapped at very high resolution. Four specific areas will be targeted for detailed mapping as potential sites for future drilling by the Ocean Drilling Program. ***