This is a study of the thermal structure of continental crations. The investigations will comprise (i) the measurement of terrestrial heat flow in both cratonic and rifted areas of central and southern Africa, (ii) comparative studies of the heat flow in and around the cratonic regions of Africa, North Amierica, Australia, and India, and (iii) numerical model studies of the effect of cratonic structure on regional heat transfer. African heat flow measurement program, previously focussed in Botswana and Namibia, will be extended into Zimbabwe, Tanzania, and Zaire. These countries collectively comprise both stable Archean cratonic terrains and rifted Proterozoic mobile belts of the East African Rift system. The new measurements will provide additional observations with which to test the hypothesis that thick cratonic roots devert mantle heat away from Archean terrains into younger surrounding mobile belts. Heat flow data from the Archean terrains of North America, Australia, and India will also be examined in the context of the cratonic diversion model. numerical models of heat transfer beneath and within cratonic and surrounding terrains will examine (a) the range of parameters that yield conditions consistent with observations of surface heat flow and mantle temperatures determined from thermobarometry, (b) the effects of cratonic scale on the diversion mechanism, and (c) the comparison of present day conditions to those in the Archean when heat production was 2-3 time greater, but temperatures in the cratonic root were similar to present-day values.
