Mineralization and paleofluids in the vicinity of the Upper Rhine Graben

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The Variscan massifs of the Vosges Mountains in France and the Schwarzwald (Black Forest) in Germany are separated by and have been uplifted during the formation of the Upper Rhinegraben (URG) in the Middle Paleogene. This tectonic movement brought gneissic and granitic basement rocks into contact with various strata of Mesozoic and Paleogene sediments and especially, it brought basement and various sedimentary aquifers into contact, which had been separated by impermeable layers before. The mixing of these distinct types of fluids led to and is monitored by various types of hydrothermal veins occurring along the margins of the URG. Six principle types of mineralization can be distinguished based on preliminary observations at 31 localities. These comprise variable amounts of carbonates, barite, quartz, galena, fahlore and rarer ore minerals. It is suggested here, that these distinct mineralizations record mixing processes of specific aquifers during the Paleogene evolution of the URG. Fluid inclusion, mineralogical and geochemical investigations in these veins will be coupled to thermodynamic models of fluid-rock interaction resulting in reconstructed paleo-fluid compositions, which will be compared to modern fluids known from deep drillholes and thermal waters (e. g., NAGRA drillholes in Nothern Switzerland, Soultz-sous-Forêt, Bruchsal, Bühl, Baden-Baden and others) and to compositions of modern formation waters to unravel the details of fluid migration and reaction in response to the major tectonic movement.