RADIOGENIC HEAT-PRODUCTION IN THE VARISCAN CRUST - NEW DETERMINATIONSAND DISTRIBUTION MODELS IN CORSICA (NORTHWESTERN MEDITERRANEAN)

New heat-production values of Variscan volcanic racks cropping out in the southern part of the Corsican batholith were determined in the lab oratory by analysing uranium, thorium and potassium concentrations wit h gamma-ray spectrometry. They vary from a minimum of 0.2 for basalts to a maximum of 4.2 mu W m(-3) for calc-alkaline granites. The Th/U ra tio 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 lithologi c composition was deduced from available P-wave velocity data, by taki ng into account the pressure and temperature effects. Depending on the rate of decrease with depth of the radiogenic heat, the crustal contr ibution in terms of heat flux ranges from 26 to 39 mW m(-2), and on av erage is 33 mW m(-2). The mean heat production of the crust is 1.0 mu W m(-3). Both average crustal heat source and crustal heat contributio n are quite similar to those estimated with the heat-production-seismi c velocity relationship. (C) 1998 Elsevier Science B.V. All rights res erved.