9302907 Gieskes This award will support a study of fluid flow through accreted sediments of the Costa Rica margin, the southern extension of the Middle America Trench. Fluid flow along other accretionary margins has been shown to be extremely important in controlling mechanical and chemical characteristics of such margins. The Costa Rica margin differs from other trench environments in having a low input of pelagic sediment on the underthrusting ocean plate and a low input of continental derived sediments. Underthrusting of the oceanic plate is high relative to other trenches and it therefore represents an endmember of trench environments. The objectives of the project are to locate sites of fluid venting, to sample the fluids and relate them to structural features of the margin, and to determine the heat-flow along the margin and its relation to fluid flow. In addition to examining the basic fluid low system on this margin, data from this project will be used for siting future drill holes in the region. The project is a cooperative study between scientists at the University of California at Santa Cruz, the University of California at San Diego, and Columbia University. The field program will be undertaken from the research submersible Alvin. ***
