Die Variszischen Massive am Oberrhein, Bindeglied zwischen Mitteldeutschland und dem Zentralmassiv
published: Dec 1, 2005
ArtNo. ESP171015604013, Price: 29.00 €
At first, this paper deals with the geological circumstances of the Variscan massifs on both sides of the Upper Rhein valley (Vosges and Black Forest), referring especially to their southern parts. There exist clear indications of an orogenic Middle Devonian event. It contradicts a continuous Silurian-Carboniferous evolution, which is accepted until now. So the Upper Devonian and Lower Carboniferous deposits indicate still a second orogenic evolution, initiated by a northward directed subduction. Then, this paper takes into account a subdivision of the rock assemblage in facies areas. Side by side, there are to recognize deeper turbiditic basins, and (at least partially) shallow marine island-arc domains with >90 % effusive and intrusive rocks and volcano-sedimentary deposits. Then, the tectonic structures and the geological evolution are discussed. Contrary to the southern Vosges and the Zone of Badenweiler-Lenzkirch (including parts of the external massifs of the Alps), none of the gneiss areas on both sides of the Upper Rhine valley show any signatures of a Middle Devonian orogenic event. So, from the position of the gneisses in the southern Black Forest between the Zone of Badenweiler-Lenzkirch and the external massifs of the Alps, it can be deduced, that the Zone of Badenweiler has been thrusted antithetically to the north. This will be supported by several northward thrusts of some importance in the southern Vosges. The reigning opinion of an exclusive southward vergency does not coincide with the documented facts. The axial planes of folds and the dip of big rock sequences show a bi-vergency. Remarkable are almost vertical faults of different directions, dividing the rock-assemblage in a real mosaic. About E–W directed dextral and N–S directed sinistral strike slip faults are dominating. They are almost of the same age and the sinistral ones, reaching into the southern Vosges, steps up to 30 km. Further on, there will be shown tight geological relations between the southern Vosges and the southern Black Forest to the NE (Tepla Barrandium) and to the SW (Beaujolais-Lyon up to the southern Brittany).