The Variscan tectonic inheritance of the Upper Rhine Graben: evidence of reactivations in the Lias, Late Eocene–Oligocene up to the recent

Abstract

Processing of gravity and magnetic maps shows that the basement of the Upper Rhine Graben area is characterized by a series of NE-SW trending discontinuities and elongated structures, identified in outcrops in the Vosges, Black Forest, and the Odenwald Mountains. They form a 40 km wide, N30-40°s triking, sinistral wrench-zone that, in the Visean, shifted the Variscan and pre-Variscan structures by at least 43 km to the NE. Wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340-325 Ma. The subvertical, NE-SW trending discontinuities in the basement acted as zones of weakness, susceptible to reactivation by subsequent tectonism. The first reactivation, marked by mineralizations and palaeomagnetic overprinting along NE-SW faults of the Vosges Mountains, results from the Liassic NW-SE extension contemporaneous with the break-up of Pangea. The major reactivation occurred during the Late Eocene N-S compression and the Early-Middle Oligocene E-W extension. The NE-SW striking basement discontinuities were successively reactivated as sinistral strike-slip faults, and as oblique normal faults. Elongated depocenters appear to form in association with reactivated Variscan wrench faults. Some of the recent earthquakes are located on NE-SW striking Variscan fault zones, and show sinistral strikeslip focal mechanisms with the same direction, suggesting also present reactivation.

New stratigraphic interpretation of the Soultz-sous-Forêts 30-year-old geothermal wells calibrated on the recent one from Rittershoffen (Upper Rhine Graben, France)

“…The URG is part of a series of rifts in the "West European Palaeogene Rift System", which extends over 1000 km from Spain to the north of Holland into the North Sea (Illies 1967;Bergerat 1985;Brun and Wenzel 1991;Schumacher 2002;Ziegler and Dèzes 2005;Rotstein et al 2005;Edel et al 2007;Bauer et al 2015). The URG is located in north-eastern France (Fig.…”

Relationships between magmatism and extension along the Autun–La Serre fault system in the Variscan Belt of the eastern French Massif Central

“…These Variscan faults were locally reactivated by the Late Eocene-Oligocene extension in the Upper Rhine graben or by the Pliocene shortening during formation of the Jura fold-and-thrust belt (Giamboni et al 2004). The gentle curvature of the Autun-La Serre Fault System, from an E-W trend, to the west, to an ENE-WSW trend, to the east, could be related to local block rotations either due to Late Variscan adjustments as suggested by Edel and Schulmann (2007) or by Oligocene extension in the Bresse graben, or due to Pliocene tectonics of the Jura Mountains.…”

Structure and nature of the Palaeozoic basement based on magnetic, gravimetric and seismic investigations in the central Upper Rhinegraben

“…6,7,8,9). The most important faults belong to the Upper-Rhine-Shear-Zone (URSZ), which shifts the Lalaye-Lubine fault zone by approximately 40 km northeastward, where it is relayed by the Baden-Baden fault zone Edel et al 2007). The sinistral URSZ that extends from the southeastern Vosges to the Mid-German Crystalline Rise was conjugated with the large-scale dextral faults of Bray and northern Bavaria (Edel and Weber 1995).…”

“…9, inset). Reactivation of the Variscan NE-SW sinistral strike-slip faults of the URSZ led to the formation of N-S oriented pull-apart basins (Villemin and Bergerat 1987;Schumacher 2002;Edel et al 2007). The major activity of the Eschau fault zone is due to the E-W extension responsible for the Rhine-Rhone rifting that lasted during the whole Rupelian.…”

“…b Location of the investigated area in the upper Rhinegraben. CF: Champ du Feu; URSZ: Upper-Rhine Shear Zone (Edel et al 2007). The dashed line in a locates the temperature section of Fig.…”