Post-collisional granite generation and HT-LP metamorphism by radiogenic heating: the Variscan South Bohemian Batholith

The Palaeozoic Variscan Orogen of Europe is a well-documented example of a collision zone characterized by widespread late-orogenic high-temperature m etamorphism and associated crustal magmatism. However, the heat source is s till under debate. Based on the Bohemian Massif in the internal zone of the Variscides as case study, we present geological, geochemical, petrological and geochronological data arguing against a substantial mantle involvement in metamorphism and magma genesis in the area of the South Bohemian Bathol ith. In order to provide an alternative explanation consistent with heat tr ansfer mechanism, we apply a two-dimensional thermal-kinematic modelling ap proach. The model calculates the transient lithospheric temperature field d uring crustal thickening and subsequent thinning by erosion from material p arameters and boundary conditions specific to the study area. Model results show that the increased contribution of radiogenic heat in the thickened c rust can indeed cause a substantial temperature increase in the middle and lower crust. Model predictions are in good agreement with observations, e.g . the P-T-t evolution of the country rocks, the formation of syn-kinematic migmatites, the large volumes of peraluminous granites derived from dehydra tion melting of metasediments and the small volumes of lamprophyric melts f rom the mantle lithosphere. The results of this study emphasize the importa nce of radiogenic heat as the source for high-temperature metamorphism and granite petrogenesis in the Bohemian Massif and potentially in other areas of the Variscan Orogen.