The evolution of the South Hunsrück and Taunus Borderzone

Abstract

The main fabric development of the South Hunsrück and Taunus Borderzone (HTB) occurred during Late Variscan homoaxial backfolding of an Early Variscan stack of thrust sheets in a narrow WSW-ENE trending zone, several hundred kilometres long. Rotation and uplift of the southern Rhenohercynian Zone was accompanied by the subsidence of the southward adjacent, northernmost parts of the Saxothuringian Zone, and the development of the Saar-Nahe Basin.During the latest Carboniferous changing stress conditions gave rise to the development of normal faults along the HTB and an extensive tholeiitic and rhyolitic volcanism. Contemporaneous uplift of the Hunsrück is reflected by coarse elastics in the Saar-Nahe Basin. Subsequently the HTB became covered by latest Carboniferous, Early Permian and Mesozoic sediments. Cretaceous uplift of the Rhenish Shield caused their erosion.The faultzone separating the Rhenohercynian Hunsrück and Taunus from the Permo-Carboniferous Saar-Nahe Basin is characterised by reverse and normal faults. Conjugate shear, indicated by slickensides on steep oblique fracture planes, as well as slight folding and small scale thrusting in post-Variscan sediments, may be attributed to compressional foreland deformation, reactivating Variscan joint fabrics and fault systems. Timing of these deformations is ambiguous and could partly be related to dextral shear during the Cenozoic subsidence of the Rhine Graben.Cenozoic sediments of the Upper Rhine graben overstep the northeastern parts of the HTB. Seismic investigations indicate that the HTB is associated with a system of southeast hading listric planes, extending beneath the Moho. Occasional dip-slip earthquakes occur along these fractures.