Nine new heat flow and heat production measurements are presented for the Trans-Hudson Orogen, an Early Proterozoic Province between the Archean Superior and Hearne Provinces of the Canadian Shield. Seventeen heat flow values now available in this region range between 23 and 81 mW m-2. The highest value is anomalous and is due to heat refraction effects in and around highly conducting quartzite formations. When refraction effects are accounted for, the Flin Flon and Thompson belts appear as distinct crustal blocks with different mean heat flow values of 42¿3(s.d.) mW.m-2 and 54¿8(s.d.) mW.m-2. Such differences can be accounted for by variations in the amount of felsic rocks in the uppermost 15 km of the crust. Comparison between heat flow and elastic thickness studies show that variations in elastic thickness of the lithosphere are not thermally induced. ¿ American Geophysical Union 1996