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Moore J C Mascle A et al 1990 Proceedings of the Ocean Drilling Program Scientific Results Vol 110 2 1 F L U I D F L O W W I T H I N T H E B A R B A D O S R I D G E C O M P L E X P A R T I D E W A T E R I N G W I T H I N T H E TOE OF T H E PRISM1 Elizabeth J Screaton 2 3 Dennis R Wuthrich 2 4 and Shirley J Dreiss 2 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 Leg110and 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 INTRODUCTION At sediment rich subduction zones highly porous sediments are deformed by tectonic and gravitational stresses as they are either accreted or underthrust Fluids expelled from the com pacting sediments influence many aspects of subduction zone geology including heat transport Langseth and Hobart 1984 diagenesis and metamorphism Etheridge et al 1983 and ben thic biology Kulm et al 1986 In addition the

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