A γ-ray spectrometer has been used to measure the concentrations of uranium, thorium, and potassium in plutonic rocks from three areas of the Cordillera in British Columbia. Samples of crystalline rock from southeastern British Columbia, including the Nelson batholith, and samples from the Jennings River area of northern British Columbia, including the Cassiar batholith, have similar heat productions, the average being 2.5 μWm−3 (6.1 hgu). Samples of the less potassic southern Coast Range Crystalline Complex between 50° and 51 °N have a significantly lower heat production: the average value for quartz diorites is 0.50 μWm−3 (1.2 hgu), for granodiorites, 1.0 μWm−3 (2.4 hgu), and for quartz monzonites, 1.3 μWm−3 (3.1 hgu). For this part of the Coast Range the average heat generation, 0.79 μWm−3, and the average ratio of thorium to uranium content, 2.1, are low for crystalline rocks.These results for the Coast Range support the hypothesis that this material is primitive, and was originally part of the oceanic crust, or a mixture of oceanic and continental crust. These heat production values are needed along with surface heat flux to construct thermal models of the crust and upper mantle.

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