Pre-Variscan (Lower Devonian) deformation of the Silurian magmatic arc of the East Odenwald (Mid-German Crystalline Zone, Variscides)

The Böllstein Odenwald is forming a large anticline of mainly pre-Devonian rock in the Mid-German Crystalline Zone (MCGZ). The contact between core and schist envelope of the anticline is well exposed at Weichberg quarry. Metasedimentary rocks of the schist envelope are intruded by granodioritic sills of a Silurian magmatic arc, showing at least two folding phases: Recumbent tight isoclinal folds are overprinted by upright gentle folds. A pegmatite dike, intruding at 411 ±2 Ma (U-Pb analyses on zircon) into the schist envelope rocks, crosscuts perpendicular to the main foliation. It shows only a weak schistosity related to the isoclinal folding, which therefore must have been active in Lower Devonian (>411 ±2 Ma; Lochkovian/Pragian) after the Silurian intrusion of the granodiorite sills (U-Pb on zircon ca. 423 Ma, Dörr et al. in press). The Lower Devonian deformation of the East Odenwald probably results from the collision of the MGCZ with the NW boundary of the Saxothuringian Zone.

The core is represented by a (meta)granite intruding into the schist envelope at 404 ±2 Ma (U-Pb method on zircon). A deformed fold directly at the contact between metagranite and metasediments and dikes terminated at the contact point to eastward directed tectonic movements between core and schist envelope after 404 ±2 Ma, probably at 375 Ma (U-Pb on zircon, Todt et al. 1995). These results are compared to other units occupying a similar position in the European Variscides and help to clarify the position of the East Odenwald during Variscan orogeny.