Contrasting geothermal regimes of the Barbados Ridge Accretionary Complex

Abstract

Three E‐W transects of closely spaced heat flow measurements across the Barbados Accretionary Complex are reported. One transect, about 100 km in length at 14°20′N and a shorter 15‐km line at 14°35′N show that heat flow decreases arcward roughly in proportion to the thickening of the wedge over the actively accreting zone. This decrease is due to the combined thermal effects of the underthrusting oceanic lithosphere and thickening of sediments that have been ingested into the wedge. Except for anomalously high heat flow over a mud volcano on the eastern end of the 100‐km transect, fluid expulsion appears to have only a secondary effect on the seafloor heat flow in this region. An increase of heat flow is observed at the western end of the 100‐km transect where high‐angle arcward vergent thrusting is occurring. We attribute this increase primarily to a decrease in the arcward thickening of wedge material, and heat generated by friction on the décollement. In strong contrast a short line of stations at 15°30′N (the Deep Sea Drilling Project/Ocean Drilling Project (DSDP)/(ODP) drilling transect) found anomalously high heat flow (a 40% increase over the heat flux from the lithosphere) with large variability over the most recently accreted material and also in the adjacent basin. The thermal regime in the vicinity of the DSDP/ODP transect is dominated by a strong flow of pore fluids along the décollement and upward flow along fault planes in the toe of the wedge and adjacent basin sediments. Heat transport by pore fluids also appears to dominate the subseafloor thermal regime in a zone near 13°50′N. The thermal effects of dewatering of the sediments by upward diffusive flow were examined using a simple one‐dimensional model, which showed that the resulting effects are too small to produce detectable heat flow anomalies. Consequently, the flow of fluids must be channelized in subseafloor conduits to produce the observed anomalies in heat flow.