Wide-angle seismic measurements made along an east-west profile across the basement high sampled during Legs 149 and 173 at Sites 900, 1067 and 1068 and the region immediately landward, ~8 km north of the sites, indicate crust of continental affinity that is ~2-3 km thick above a serpentinized upper mantle (Chian et al., 1999). Given such a reduced crustal thickness and the values of radiogenic heat production reported here and at Site 900, only ~2-3 mW/m2 (15%) of the increased heat flow can be attributed to enhanced radiogenic heating if the averages from the tonalite samples are representative of this crust, with the amount decreasing if the crust is a mixture of tonalite and metagabbro.