Twenty-two new determinations of heat flow and radiogenic heat production in the Superior and Grenville provinces of the Canadian Shield are presented. The new data and previously published measurements strongly constrain the thermal structure of the eastern Canadian Shield. In the Abitibi greenstone belt, heat flow gradually increases from 29 mW m -2 near the Grenville Front to 44 mW m -2 east of the Kapuskasing uplift. This heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1.1 m -3. This interpretation, based on estimated heat production of major rock types in the region, is consistent with crustal models derived from recent seismic reflection and refraction studies. It also leads to an estimate of about 12 mW m-2 for the mantle heat flow beneath the area. The average heat flow in the Grenville Province, 41 +-10 mW m -2, is the same as that of the Superior Province. This similarity and the lack of significant variation of heat flow across the Grenville Front indicate that the crust on both sides of the front has similar heat production and thus composition. In the western part of the Grenville Province, heat flow reaches high values in the vicinity of the boundary between the Allochtonous Polycyclic and Monocyclic belts where enriched granitic plutons are found. In the crystalline terranes in the central part of the Grenville Province, heat flow and heat production are related to each other. The parameters of the linear •eat flow-heat production relationship (Qr = 30 +_ 2 mW m -2 and D = 7.1 +_ 1.7 km) are close to those of the much younger Appalachian Province,implying that the higher Appalachian heat flow is due solely to higher heat production in the upper crust. The data provide no evidence for variation of mantle heat flow between the Superior, Grenville, and Appalachian provinces, whose tectonic ages range between 2700 and 400 Ma. The small value of the mantle heat flow, about 12 mW m -2, implies that the depth to the 450øC isotherm, which controls the effective elastic thickness of the lithosphere, is very sensitive to crustal heat production.

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The present geology of southern Scandinavia offers the unique opportunity to sample deep and intermediate levels from the same crustal section for both heat flow and heat production. In the central part of southern Norway, amphibolite facies terranes appear to lie on top of the same deeper crustal formations which crop out on their western and eastern margins. An extensive data set on the geochemistry of all types of rocks in the region culled from the literature is used to derive values for radiogenic heat production for each kind of crustal facies. Using constraints from heat flow data in the same area allows a reliable model of the distribution of crustal heat production. The average heat production of granulite facies terranes is 0.4 µW/m³, similar to values in other parts of the world. For amphibolite facies rocks, the value is 1.6 µW/m³. The present shield also includes heat producing element enriched granites formed in later events and the average heat production of presently exposed crust is 2.7 µ/m³. Using heat flow and radioactivity data from ten stations, the reduced heat flow in the area is 22 ± 2 mW/m². This corresponds to the heat flow at the top of 28 km of deep crustal facies, implying that the mantle heat flow is probably as low as 10 mW/m². Over the whole crustal thickness, the average amount of radiogenic heat is 31 mW/m².

New heat flow density (HFD) measurements were performed at 10 sites in Quebec. For five of the sites located in the Superior Province, the heat flow density varies between 24 and 35 mW/m2 (26 and 37 mW/m2 after adjustment for Pleistocene climatic variations). In the Grenville Province, the values obtained range between 25 and 28 mW/m2 (29 and 31 mW/m2 after adjustment). For two nearby sites in the Gaspé region (Appalachians), the heat flow density is 47 mW/m2 (48 mW/m2 after adjustment). Radiogenic heat production was also measured. At the sites located in the meta-volcano-sedimentary sequences of the Superior Province, the heat production is low (0.1–0.6 μW/m3) and it does not always correlate with the surface heat flow. In the Grenville Province, the HFD is close to (slightly higher than) the reduced heat flow of the Superior. The higher HFD in the Appalachians is partly explained by the higher crustal heat production, and partly by higher deep heat flow.