Carboniferous tectonics of the Variscan basement collage in eastern Bavaria and western Bohemia

Abstract

 The tectonometamorphic units in the Variscan basement of eastern Bavaria and western Bohemia have a long and complex record of large-scale continental deformation, metamorphism, and syn- and posttectonic magmatism. Although there is a large database describing each of the above-mentioned phenomena, an integrated tectonic synthesis is hard to achieve. In this paper we review some of the prominent effects in the Carboniferous tectonic evolution, which is accountable for much of the deformation, regionally extensive low-pressure/high-temperature metamorphism, and abnormally intense partial anatexis and plutonism. Deformation was multistage and its kinematics were dominated by lateral compression, transpression, and strike-slip shearing. Tectonic units were mostly deformed “en masse”, without operation of large, discrete shear zones. An exception were the boundary zones of those units that had already cooled to sub-greenschist-facies temperatures before the onset of Carboniferous deformation. These boundaries were operated as normal or transtensive faults. The large present vertical thickness of the Zone of Erbendorf-Vohenstrauss at the KTB drill site is most probably due to a combination of Carboniferous block tilting related to the intrusion of the Falkenberg granite, and Cretaceous distributed reverse faulting and imbrication. Late-orogenic plutonism in the Bohemian massif led to the emplacement of at least 176 000 km³ of granitoids. Melt flux through the Moldanubian unit may have been as high as 0.2 km/m.y., allowing the estimated volume of granitoids to be segregated by partial anatexis of the continental crust within a time span of approximately 8.8 million years.