High pore pressure generation in sediments in front of the Barbados Ridge Complex

Abstract

DSDP data for the Barbados Ridge complex show the existence of high pore pressures in sediments both oceanward and arcward of oceanic trenches. We model the evolution of pore pressure by using a finite element procedure. Three consecutive stages are recognized: (1) In the oceanic basin, sedimentation rate is low; there is little excess pore pressure. (2) Approaching the trench but before being incorporated into the accretionary prism, sediments are subjected to increasing tectonic compression as well as greater sediment overburden. Thus, high pore pressure can be created. An important result is that the lowest effective stress occurs within the sedimentary layer instead of at its base and a decollement may develop along this weakened zone. (3) Arcward of the trench, sediments above the decollement are offscraped while those beneath it are subducted. Fast sedimentation combined with tectonic compression can create pore pressures so high as to cause porosity to increase with depth. This facilitates the formation of mud volcanoes, even oceanward of the deformation front.