K-Ar dating of episodic Mesozoic fluid migrations along the fault system of Gernsbach between the Moldanubian and Saxothuringian (Northern Black Forest, Germany)
Along the SW-NE trending fault zone of Gernsbach (northern Black Forest), over a distance of about 45 km between Baden-Baden and Pforzheim, basal series of the sedimentary cover are extensively altered by hydrothermal solutions. The fluids were conveyed in the fault zone and because of favourable permeabilities they spread out along the unconformity between the basement and sedimentary cover. K-Ar dates on authigenic white micas (illites) and hydrothermally altered detrital micas point to the occurrence of two major episodes of fluid migration. The extensive alteration along the entire fault system occurred about 150 Ma ago during the Jurassic. In relation to these hydrothermal activities, the epigenetic strata-bound uranium deposit of Müllenbach originated in Upper Carboniferous sediments near the fault and the fluorite-quartz vein-type mineralization of Käfersteige was formed along the fault about 100 Ma ago during the Cretaceous. The results indicate various geological processes of the fault system of Gernsbach, which is located between the Saxothuringian and Moldanubian zone. The mobilization of the fluids and the formation of the ore deposits were probably caused by and connected with tectonic activities in mid-Europe.