The hot southern continent: heat flow and heat production in Australian Proterozoic terranes

Abstract

Available surface heat-flow measurements from Australian Proterozoic terranes (83 ± 18 mWm−2) are significantly higher than the global Proterozoic average of ∼50 mWm−2. Seismic evidence for the presence of relatively cool mantle together with the lack of evidence for neotectonic processes normally associated with thermal transients suggests that anomalous heat flow must reflect crustal radiogenic sources (U, Th and K). This is supported by a compilation of more than 6000 analyses from 455 individual granites, granitic gneisses and felsic volcanics which shows that the present-day average heat production of these rock types is 4.6 µWm−3 when normalised by area of outcrop (over more than 100 000 km2) ; roughly twice that of ‘average’ granite. At the time of this felsic magmatism (ca 1850–1500 Ma) heat production rates were some 25–30% greater than the present day such that the total complement of U, Th and K in many parts of the Australian Proterozoic crust may have contributed as much as 60–85 mWm−2 to the surface heat flow, or 2 to 3 times the present-day continental average. This extraordinary enrichment has played a key role in the tectonothermal evolution of the Australian Proterozoic crust, and has important implications for our understanding of the thermal budget of ancient continental crust.