Hydrology of the Barbados Ridge complex, Lesser Antillies [sic] accretionary complex

The Barbados Ridge Complex is the easternmost portion of the Lesser Antillies Subduction Complex. At the deformation front forming its eastern boundary sediment is scraped off of the Atlantic Plate and accreted to the Caribbean Plate. Seismic profiles show that the sediments comprising the Barbados Ridge Complex are divided into an upper, deformed sequence and a lower, layered sequence seperated by a decollement. In attempts to penetrate the decollement DSDP Leg 78A and ODP Leg 110 encountered high pore fluid pressures, temperatures and methane concentrations. Pressures of up to 350 psi and 20.4°C were encountered at Sites 542 and 541, respectively. As the sediments are accreted to the overriding plate tectonic compression forces dewatering of the earliest accreted sediments. Due to the low permeability of the oceanic muds and clays, water is expelled along the decollement and thrust faults splaying from it. This water transmits heat from within the prism to the sediment-water interface. This expelled pore fluid concentrates thermogenic methane along these conduits, where oxidation of the methane within the sulfate reducing zone causes the precipitation of carbonates. As a byproduct hydrogen sulfide is produce, implying the possible existence of vent communities similar to those reported .off the Oregon coast.No embarg