Fluid Flow within the Barbados Ridge Complex, Part I: Dewatering within the Toe of the Prism

Abstract

Sediment compaction at convergent margins expels pore fluids, which in turn influence many aspects of subduction zone geology. Drilling in the Barbados Ridge complex during ODP Leg 110 and DSDP Leg 78A provided information about sediment types, porosities, and the geometry of the complex. In this paper, we use these observations to estimate the rates of sediment porosity loss and accompanying fluid expulsion from the prism, the decollement, and the underthrust sediments. Rates of porosity loss depend on how rapidly the sediments move arcward through the complex. We compute rates of sediment movement in the prism and decollement as a function of distance from the deformation front. This calculation assumes that the rates of sediment movement decrease arcward as the result of porosity loss in the prism and decollement and thickening of the prism. According to computed rates of sediment movement for the prism, sediment deceleration is greatest within the first 3 to 5 km arcward from the deformation front. Similarly, most dewatering of the prism sediments takes place in this region. Beyond 5 km, rates of sediment dewatering become great­ est in the underthrust sediments, assuming these sediments are carried downward at a uniform rate with the oceanic plate.