Fluid Flow within the Barbados Ridge Complex, Part II: Permeability Estimates and Numerical Simulations of Flow Velocities and Pore Pressures

Abstract

Measurements of sediment physical properties and pore-water chemistry gathered during ODP Leg 110 and DSDP Leg 78A suggest that (1) fluid flow in the decollement is predominantly updip, and (2) near-lithostatic pore pressures may exist just above the decollement at Site 542. We use these observations to constrain a numerical model of fluid flow in the toe of the complex. Gravitational and tectonic forces drive flow within the complex and are incorporated in the numerical model by esti­ mating the rate and distribution of fluid generation from sediment compaction. Modeling results reveal that near-litho­ static fluid pressures could form at Site 542 if the equivalent prism permeability is between I0 -18 and I0 -19 m2 (hydrau­ lic conductivity of I0 -9 to I0 -10 cm/s). Predominantly horizontal flow in the decollement can occur if the decollement permeability exceeds the equivalent prism permeability by three to four orders of magnitude. Under these conditions, average linear fluid velocities in the decollement range between 3 and 10 cm/yr (1.5 to 5 times the convergence rate). Fluid velocities in the prism are about 1000 times slower. Depending on the permeability contrast between the decolle­ ment and the underthrust sediments, between 65% and 90% of the fluids expelled beneath the accretionary prism flow out of the complex through the decollement.