The effect of hot spots on the oceanic age‐depth relation

Abstract

Hot spots located both midplate and on midocean ridges can bias the empirical age‐depth relation. Ocean floor bathymetry for seafloor greater than 80 m.y. B.P. in age has been previously used to determine if the oceanic lithosphere behaves as a cooling half space or as a cooling plate. However, large areas of the ocean basins do not fit a simple age‐depth relation. Anomalously shallow swells, approximately 1000 km wide and 1 km high surround hot spots such as Iceland, the Azores, and the Cape Verde Islands. By sorting seafloor depth data by distance to the nearest hot spot track, we show that the along‐isochron variation in depth in the North Atlantic correlates with distance from a hot spot track. Due to the absence in the North Atlantic of seafloor both old and far from hot spots, we compare depth versus age at constant distance and do not observe flattening of the age‐depth relation in any distance range. The age‐depth relation, depth (meters) = 2700 + 295 t(m.y.)1/2, derived for seafloor 1200 to 1800 km from a hot spot track represents our best estimate of the age‐depth relation appropriate to seafloor unaffected by a hot spot track. In the North Atlantic the previously inferred flattening of the age‐depth relation appears to be caused by the inclusion of hot spot swells. This implies that hot spots may be the primary means of heat transfer from the deeper mantle to the base of the lithosphere.