Terrestrial heat flow in Botswana and Namibia

Abstract

We report terrestrial heat flow measurements from 25 new sites in Botswana and Namibia. Twelve sites from the Archean Kaapvaal‐Zimbabwe Craton and the Limpopo Belt have a mean of 47 ± 4 mW m−2 (standard error of the mean) but show a trend of increasing heat flow from less than 40 mW m−2 within the cratonic nucleus to about 60 mW m−2 at its edge. Thirteen sites in the Proterozoic and Pan African mobile belts that surround the craton have a mean of 66 ± 3 mW m−2, increasing from about 60 mW m−2 at the cratonic margin to more than 70 mW m−2 several hundred kilometers away. Radiogenic heat production in near‐surface basement rocks was measured for four sites on the craton and seven sites in the mobile belts. The limited heat flow‐heat production data from the craton are insufficient to establish a correlation. Heat flow and heat production data from the mobile belts, when combined with published data from six sites in Zambia, exhibit a linear trend with an intercept of 50 ± 3 mW m−2 and a slope of 5.5 ± 1.1 km. Some but not all of the observed difference in surface heat flow between the mobile belts and the cratonic nucleus may be due to differences in crustal heat production. That part of the regional variation in surface heat flow which originates at greater depths implies a fundamental difference in thermal structure of the lithosphere between the craton and the mobile belts in southern Africa.