Regional geochemistry and continental heat flow: implications for the origin of the South Australian heat flow anomaly

Existing measurements from South Australia define a broad ( > 250 km wide) zone of anomalously high surface heat flow (92 +/- 10 mW m(-2)). This zone is centred on the western margin of the Adelaide Fold Belt (Neoproterozoic to early Phanerozoic cover floored by Palaeoproterozoic to Mesoproterozoic basement), where it borders the eastern Gawler Craton and Stuart Shelf (Pal aeoproterozoic-Mesoproterozoic). To the west, in the western Gawler Craton (Archaean to Palaeoproterozoic), heat flow averages similar to 54 mW m(-2) while to the east in the Willyama Inliers (Palaeoproterozoic) heat flow ave rages similar to 75 mW m(-2). We use a regional geochemical dataset compris ing > 2500 analyses to show that the anomalous heat flow zone correlates wi th exceptional surface heat production values, mainly hosted in Palaeoprote rozoic to Mesoproterozoic granites. The median heat production of Precambri an 'basement' rocks increases from < 3 <mu>W m(-3) west of the anomalous zo ne to similar to 6 muW m(-3) within the anomalous zone. In the highest know n part of the heat flow anomaly, Mesoproterozoic gneisses and granites of t he Mount Painter Province in the northern Adelaide Fold Belt yield an area- integrated mean heat production of 9.9 muW m(-3). These data suggest that t he anomalous heat flow reflects an unusual enrichment in U and Th in this p art of the Proterozoic crust, with the total complement of these elements s ome 2-3 times greater than would be expected for Proterozoic crust on the b asis of the global heat flow database. This extraordinary enrichment has pl ayed an important role in modulating the thermal regime of the crust in thi s region, and particularly its response to tectonic activity. (C) 2000 Else vier Science B.V. All rights reserved.