Pb isotope constraints on fluid flow and mineralization processes in SW Germany

摘要

Southwest Germany hosts a variety of Permian to Cenozoic hydrothermal mineralizations of different types. Veins are most abundant, but also Mississippi-Valley type and other stratabound mineralizations are present. This contribution presents a set of Pb isotope data for ore minerals from these mineralizations as well as isotope data of possible source rocks for the Pb. We show that lead isotope ratios of the mineralizations depend on the source rocks, the age of a given mineralization and its tectonic setting. For example, Pb isotope ratios of Jurassic mineralizations show a trend to higher isotope ratios towards the south. The reason for this might be the higher exhumation rate in the southern Schwarzwald that exposes deeper crustal levels. There, the influence of radiogenic lead derived from the basement is higher during mineralization and thus, the isotope ratios rise towards the south. Interestingly, Pb isotopes of mineralizations from the Central Schwarzwald Gneiss Complex and the Southern Schwarzwald Gneiss Complex, two different crustal blocks with a large oceanic suture in between, have significantly different Pb isotope systematics. This fact is explained by the different ages and tectonic origin of the protoliths of the two blocks.