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 mWrrr 2 ) are significantly higher than the global Proterozoic average of -50 mWnrr 2 . Seismic evidence for the presence of relatively cool mantle together with the lack of evidence for neotectonlc 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 felslc volcanlcs which shows that the present-day average heat production of these rock types is 4.6 uWrrr 3 when normalised by area of outcrop (over more than 100 000 km 2 ); 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 mWrrr 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.

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

“…Four of the clasts give high values between 4.0 and 7.5 µW m −3 , which are similar to global occurrences of crust characterized by high heat production (Mareschal and Jaupart, 2013;Jaupart et al, 2016) and exemplified by the Central Australian Heat Flow Province (Neumann et al, 2000;Sandiford and McLaren, 2002;McLaren et al, 2003). Nonetheless, all but two of the samples in this suite have heat production less than the mean for the CAHFP (4.6 µW m −3 ).…”

“…As a group they are distinctly different from the regional pattern shown by anomalously warm Proterozoic crust in central Australia with average q o = 80 mW m −2 (McLaren et al, 2003), which has been suggested to extend across the Wilkes Land margin of Antarctica based on Gondwana supercontinent reconstructions (Carson et al, 2014;Aitken et al, 2014). Despite general age similarities among some of the clast population with parts of the Gawler Craton, and basement age correlations that indicate continuity of Mawson-type crust into the Wilkes sector of East Antarctica (Goodge and Fanning, 2016), the proxy heat production determinations and heat flow estimates provided here suggest that central portions of the East Antarctic ice sheet are underlain by stable continental crust with quite normal thermal properties represented by average values of heat production of about 2.5 µW m −3 and heat flow of about 50 mW m −2 .…”

“…Their model results thus show variable heat flow governed to first order by the age and type of crust represented and punctuated by heat production spikes contributed from Th-rich granitoids. Although much of the area underlying the Rauer Islands and Vestfold Hills has low heat flow (< 50 mW m −2 ) typical of Proterozoic and Archean crust, Carson et al (2014) emphasized that some early Paleozoic granites with anomalously high heat production can cause local elevation of heat flow (> 80 mW m −2 ), as observed in the Central Australian Heat Flow Province (CAHFP; McLaren et al, 2003). Thus, spatially coarse models of heat flow based on geophysical data across East Antarctica indicate relatively typical continental values ranging from about 35 to 60 mW m −2 , yet there are (Fretwell et al, 2013).…”

Helium in the Australian liquefied natural gas economy

“…Amadeus and McArthur basins; Figs 6 and 7). In addition, in central Australia the crustal contribution to heat flow is about twice that expected of the global-average continental crust (McLaren et al 2003). This is a direct result of a higher than average concentrations of crustal radiogenic elements U and Th (McLaren et al 2003), leading to 4 He.…”

“…In addition, in central Australia the crustal contribution to heat flow is about twice that expected of the global-average continental crust (McLaren et al 2003). This is a direct result of a higher than average concentrations of crustal radiogenic elements U and Th (McLaren et al 2003), leading to 4 He. More restricted areas with high surface heat flow are outboard of the Browse and Perth basins (Cull and Conley 1983); interestingly, the first-order heat flow is relatively low and fairly constant throughout the North West Shelf (Cull and Conley 1983).…”