Heat flow and heat generation in the Churchill Province of the Canadian Shield, and their palaeotectonic significance

Abstract

Six new heat flow determinations are presented for Proterozoic mobile belts of the Churchill Province of the Canadian Shield, an area that was affected by several stages of the Hudsonian orogenic sequence (1.9-1.6 Ga ago). With other, previously published, values the mean of eight determinations considered reliable and representative and corrected for the effects of Pleistocene glaciation is 44 ± 7 mW m −2. Heat generation measurements have also been made; values range from 0.1–1.04 μW m −3. A linear relation between heat flow and heat production is apparent. The heat flow axis intercept is 37 mW m −2, and the scale depth is 11 km, compared with 28 mW m −2 and 13.6 km for the Archaean Superior Province. Approximately 20% of the Churchill heat flow appears to be derived from radioactive decay in the upper crust, compared with 30% for the Superior Province and shields as a whole. The observations imply that the heat flow-heat production relation for the Churchill Province should be written as Q = Q c + Q e + A 0 b where Q c is equivalent to the reduced heat flow for the Archaean terrain, b is similar for the two, and Q e is an additional component of heat flow in the Proterozoic mobile belts of the Churchill Province. A speculative tectonic model is presented. It is suggested that rifting along two axes of an original craton, which had lateral variations in near surface radiogenic element concentration, followed by erosion of the radiogenic layer and subsequent reconvergence of the cratonic segments, led to widespread redistribution of radioactive elements into the reactivated inter-rift crustal block. One result would be that crustal temperatures are higher in that part of the Churchill Province than in the Superior.