Thin-skinned tectonics in the northern Rhenish Massif, Germany

Abstract

A network of profiles in the Hercynian mountain system (Geo-traverse Rhenoherzynikum) is needed to determine details of the geological structure and find the reasons for tectonic movements. Outstanding features within the mountain system such as the large fault zone along the southern boundary of the Hunsruck1 and the left flank of the Rhinegraben have already been investigated by reflection seismology2,3 We describe here a new reflection–refraction experiment carried out in 1978 in the most northern part of the Rhenish Massif, across the Stavelot–Venn Massif near Aachen (Fig. 1). While layers in the lower crust dip to the NNW, a strong upper reflector at 3–4 km depth shows a slight dip to the SSE and indicates a prominent fault zone near Aachen, known in Belgium as the Faille du Midi. Here, a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile. We interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the Variscan orogeny.