Crustal heat production in the Superior Province, Canadian Shield, and in North America inferred from heat flow data

Abstract

Measurements of heat flow and U, Th, K concentrations are used to determine the amount of heat generated in various belts of the Superior Province, the largest Archean craton on Earth. These data allow estimates of the average crustal heat production and indicate compositional differences between upper and lower crustal assemblages. The bulk average heat production of the Superior Province crust is 0.64 μW m−3and is almost the same in different belts of slightly different ages, illustrating the remarkable uniformity of crust‐building mechanisms. In the wider context of the North American continent, the bulk crustal heat production decreases from 1.0 μW m−3in the oldest Slave Province to a minimum of 0.55 μW m−3in the Paleo‐Proterozoic Trans‐Hudson Orogen. It increases in younger provinces, culminating with a high value of 1.05 μW m−3in the Phanerozoic Appalachian Province. In all provinces, U and Th enrichment is systematically associated with sedimentary accumulations. A crustal differentiation index is obtained by calculating the ratio between the average values of heat production at the surface and in the bulk crust. The differentiation index is correlated with the bulk average heat production, which suggests that crustal differentiation processes are largely driven by internal radiogenic heat.