Radiogenic heat production in the Variscan crust: new determinations and distribution models in Corsica (northwestern Mediterranean)

Abstract

New heat-production values of Variscan volcanic rocks cropping out in the southern part of the Corsican batholith were determined in the laboratory by analysing uranium, thorium and potassium concentrations with gamma-ray spectrometry. They vary from a minimum of 0.2 for basalts to a maximum of 4.2 μW m −3 for calc-alkaline granites. The Th/U ratio in Variscan granitoids is slightly higher than normal. Generally, our measurements yield values higher than those previously determined. These data, together with those available for the Variscan massifs of the northwestern Mediterranean, were used for constructing models of distribution of radiogenic heat production of the crust. The lithologic composition was deduced from available P-wave velocity data, by taking into account the pressure and temperature effects. Depending on the rate of decrease with depth of the radiogenic heat, the crustal contribution in terms of heat flux ranges from 26 to 39 mW m −2, and on average is 33 mW m −2. The mean heat production of the crust is 1.0 μW m −3. Both average crustal heat source and crustal heat contribution are quite similar to those estimated with the heat-production-seismic velocity relationship.