Systematic measurements have been carried out in the Canadian Shield by researchers at GEOTOP and the Institut de Physique du Globe, in Paris. These measurements have shown that most the variations in heat flux are due to variations in crustal heat production and that heat flux at the base of the lithosphere is small and does not vary much.

Heat flux measurements have thus been used to trace variations in crustal composition. Heat flux measurements also provide the only direct constraint on the thermal regime and thickness of the lithosphere. Because heat flux determinations require temperature measurements in drill holes, most of the data come from the southernmost part of the Canadian Shield, where many holes have been drilled for mining exploration. Trends suggest that heat flow is low and the lithosphere thick in the Hudson Bay region, but few heat flux data are available.

Following a recent surge in mining exploration in the James Bay lowlands of Ontario, many holes have been drilled, in particular in the so called “Ring of fire”. Jean-Claude Mareschal and Catherine Phaneuf from GEOTOP, accompanied by Claude Jaupart and Hélène Bouquerel from IPGP went to make heat flux measurements in early September at the Esker camp of Noront Resources, some 300km north of Geraldton, Ontario. These measurements will provide some of the crucial data needed to understand the thermal structure beneath the central part of the Canadian Shield.