Fluid flow along a decollement layer: A Model applied to the 16°N section of the Barbados Accretionary Wedge

Abstract

A seismic section across the whole Barbados accretionary complex at 16°N recently published by Westbrook et al. (1988) shows that the reflection marking the decollement fades between 40 and 60 km arcward of the deformation front but is present again further inland. This interruption appears to be related to a thrust cutting through the wedge. One‐dimensional steady state models of water flow along the decollement suggest a mechanism responsible for decollement disruption: a local increase of the slope either of the wedge, or of the decollement, causes the subducted layer to compact, and locally increases the friction along the decollement. If the thrust is used as a conduit for fluids to escape from the decollement, the friction along the decollement toeward of the thrust is further increased. The model also shows that the permeability of the decollement should be of the order of 10−14 m2, but may be higher near the deformation front for short periods if fluid expulsion mainly occurs in transient bursts associated with hydraulic fracturing. As a consequence of the non‐linearity of the compaction equation, pore pressure at depth in the decollement depends on the water flux, on the lithostatic pressure gradient along the decollement and on the parameters from which the physical properties of the sediment are calculated. However, it is almost independent on the pore pressure below the toe.