Radiogenic heat production of Variscan granites from the Western Bohemian Massif, Germany

[摘要] Much of the Mid-European basement has been consolidated during the Variscan Orogeny and includes large volumesof granitic intrusions. Gamma radiation spectroscopic measurements in three study areas along the western margin ofthe Bohemian Massif give a record of radiogenic element concentrations in the Variscan granites. Most intrusions of theFichtelgebirge (except for the Tin Granite) and intrusive complexes in the Bavarian Forest show Th/U ratios exceedingunity, most likely related to abundance of monazite. In contrast, some of the Oberpfalz granites located near the Saxothuringian–Moldanubian boundary (Flossenbürg, Steinwald and Friedenfels types) are characterized by higher uraniumconcentrations and thus Th/U < 1. The low Th/U ratios here are in agreement with a possible U mobilisation along theSaxothuringian–Moldanubian contact zone observed in previous studies. Heat production rates of granites in the threestudy areas vary between 3.9 and 8.9 µW/m3, with a mean of 4.9 µW/m3. This classifies the intrusions as moderate- tohigh-heat-producing granites. Considering the huge volume of granitic bodies in the Variscan crust of the BohemianMassif, the contribution of in situ radiogenic heat production had to have a major impact and should be considered infurther thermal modeling.

[学科分类] 自动化工程

[关键词] Variscan granites;gamma spectrometry;heat production;Uranium;Thorium;Bohemian Massif