Heat flow and heat production in Zambia: Evidence for lithospheric thinning in central Africa

Abstract

Heat-flow results from eleven widely spaced sites in central and western regions of the Republic of Zambia range between 54 and 76 mW m-2. Ten of the sites are located in late Precambrian (Katangan) metasediments or Kibaran age basement, while one site is located in Karroo age sandstone. Compared to the global mean of 39 +/- 7 (sd) mW m-2 for Precambrian provinces elsewhere, these heat-flow results are anomalously high by some 25 mW m-2. Heat-production measurements on borehole core samples indicate that enhanced radioactivity of an enriched surface zone can account for only half of the observed anomaly. The remaining anomalous heat flow must have a deeper source, and can be interpreted as a flux from the asthenosphere, providing the overlying lithosphere has been thinned to less than 60 km. Such an interpretation supports the existence of an incipient arm of the East African rift system trending southwest from Lake Tanganyika into the central African plateau.