School of Earth Sciences - Theses
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ItemThe origin of the South Australian Heat Flow Anomaly( 2007)The South Australian Heat Flow Anomaly is a zone of high surface heat flow (averaging 92 ± 10 mW m-2); one of several central Australian Proterozoic terranes rich in heat producing elements (HPEs). Its bulk crustal average heat production is between two and three times the global average, indicating an enormous regional enrichment of uranium, thorium and potassium. Until now the distribution of HPEs in the crust has been calculated based on surface heat production; here, a method that uses the temperature at the Moho (as calculated by seismic inversion models) is introduced and found to have good agreement with models that assume a single enriched layer in the upper crust. This layer is found to be between 15-20km. The onset of recycling of uranium through the crust and mantle at the end of the Archaean has been proposed to have produced a peak in uranium available to crust-building, at least partially contributing to the creation of a long-lived geochemical anomaly in Central Australia. However analysis of lead isotopes of K-feldspars from the SAHFA indicates that at the time that crust was first extracted from the mantle, thorium was enriched relative to uranium (not vice versa). In order to investigate more recent effects of such high heat flow, the Tertiary cooling history of the Mt. Painter Inlier is investigated using (U-Th-Sm)/He thermochronology, which has a closure temperature of ~70°C. The most recent ages recorded are ~38 ± 5 Ma, and are argued to record burial of 1400 ± 200m under basement and Cretaceous sediment.