The thermal regime of South African continental margins

We present thermal data from 100 oil exploration boreholes on the continental margins of South Africa. Near surface temperature profiles are constrained with temperatures acquired during reservoir tests, corrected bottom-hole temperatures and seafloor temperatures. The thermal conductivity profiles are estimated from geophysical well logs using a neural network method. Available data allow us to determine 41 new heat flow values computed from depth ranges greater than 1000 m, located on the western and southern continental margins of South Africa. We believe that the variations in surface heat flow are not controlled by the contribution of the sediments or the basement, but rather by the mantle heat flow. An upper bound of ~ 30 mW m− 2 for the mantle heat flow on the interior of the continent can be inferred from the lowest available estimates, located near the coastline on the southern continental margin. On both continental margins, heat flow values reach a maximum of about 60 mW m− 2, 100 km away from the shore, and consistently decrease further away towards values typically encountered in old oceanic domains (~ 50 mW m− 2). This indicates that (1) the mantle heat flow increases over a short distance at the edge of the continent, which is consistent with studies on the effect of continents on mantle convection, and (2) it may increase to a value greater than heat flow on the adjacent ocean, as a possible consequence of the effect of the transition between thin oceanic lithosphere and thick and cold continental lithosphere on mantle convection.