Barbados Accretionary Prism Hydrogeologic Characteristics: Submersible-Based Tests at ODP Sealed Boreholes

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Carson 9415924 This program, led by Dr. Bobb Carson of Lehigh University, involves researchers from Indiana University, from Scripps Institution of Oceanography at the University of California, San Diego, and from the French marine research laboratory IFREMER. The study follows Ocean Drilling Program Leg 156, whose primary goal was to assess the hydrogeologic conditions along the decollement (a fluid pathway deeply buried in the sedimentary wedge) of the Barbados accretionary prism. During that drilling program on JOIDES Resolution, sealed boreholes ("CORKs") with temperature and chemical sampling systems were emplaced at two drill sites to isolate the section across the decollement, allowing future study of this horizon along which pore waters are hypothesized to migrate. The present project will carry out hydrogeologic studies and pore water sampling for geochemical study in the summer of 1995, approximately one year after drilling, at one of the two borehole sites; French researchers will conduct similar experiments during the same field program at the second site. The field program will be carried out on the French research submersible Nautile. The research program seeks to determine in situ hydrogeologic characteristics and conditions that will provide realistic parameters to the next generation of fluid flow models for accretionary prisms. The overall objective of this research, as well as that of the ocean drilling leg which emplaced the casings and sampled the sediments, is to understand the nature of the processes by which sediments are transformed in the process of subduction, and how the transport of fluids affects the chemistry of the sediments and the ocean. The Barbados region is one of the best studied accretionary prisms in the world, and it provides a natural laboratory for the investigation of subduction, deformation and lithification of sediments in the context of plate tectonics. Understanding the processes involved in plate subduction is a high priority of the Oce an Drilling Program. ***