Evolution of the lithosphere in the area of the Rhine Rift System

Abstract

The Rhine Rift System (RRS) forms part of the European Cenozoic Rift System (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and lithospheric thicknesses range in the RRS area between 24-36 km and 50-120 km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan lithosphere into an end-Mesozoic stabilised cratonic lithosphere, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45-60 km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted lithospheric slabs, asthenospheric upwelling and thermal thinning of the mantlelithosphere. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, lithospheric thicknesses ranged between 40 km and 80 km, whilst the thickness of the crust was reduced to 28-35 km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the lithosphere-asthenosphere system governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, lithospheric thicknesses had increased to 100-120 km. Paleocene mantle plumes caused renewed thermal weakening of the lithosphere. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive rifting under a collision-related north-directed compressional stress field. Following endOligocene consolidation of the Pyrenees, west-and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional strain across ECRIS amounts to some 7 km. Plume-related thermal thinning of the lithosphere underlies uplift of the Rhenish Massif and Massif Central. Lithospheric folding controlled uplift of the VosgesBlack Forest Arch.

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.…”

Subcontinental lithospheric mantle beneath Central Europe

“…The lithospheric mantle of Lower Silesia and adjoining part of Upper Lusatia exhibits "Saxothuringian" seismic characteristics , suggesting that it is a coherent fragment of mantle root of one of the terranes accreted to the Variscan orogen. Geological models of the evolution of the Variscan orogen assume significant post-orogenic delamination and upwelling of asthenospheric material (Ziegler and Dèzes 2005;Massone 2006). Therefore, at the end of Variscan time, the subcontinental lithospheric mantle (SCLM) of the peneplained orogen probably consisted of mantle roots of the accreted terranes, which in places have been replaced by lithospherised upwelled asthenosphere.…”

Separation of rifting and lithospheric folding signatures in the NW-Alpine foreland

“…The question of whether and how the Alpine orogeny and the opening of the ECRIS are related to each other are still debated (e.g. Ziegler 1994;Merle and Michon 2001;Michon andMerle 2001, 2005;Dèzes et al 2004Dèzes et al , 2005Ziegler and Dèzes 2005). However, these events were responsible for two superimposed, partly coeval modes of deformation in the European plate.…”

“…The location, geometry, timing and mechanism of folding are poorly known however. Amongst the currently proposed processes are foreland flexural bending (Gutscher 1995;Burkhard and Sommaruga 1998;Bourgeois et al 2001;Leseur et al 2005), far-field intraplate buckling Agarwal 1996, 2002;Guillocheau et al 2000;Michon andMerle 2001, 2005;Michon et al 2003;Bourgeois et al 2004;Dèzes et al 2004Dèzes et al , 2005Ziegler and Dèzes 2005) or dynamic support by asthenospheric flow . Thermal erosion of the lithosphere by up-welling asthenospheric thermal anomalies may also have played a role in the long-wavelength deformation of the European lithosphere Ziegler and Dèzes 2005).…”

“…Although the ECRIS has been studied for several decades, its origin is controversial because the timing, the orientation and the magnitude of tectonic motions during its formation are still debated. A variety of hypotheses for its origin have been proposed, involving processes such as plume-related active rifting (Neugebauer 1978), foreland splitting in response to the Alpine orogeny (Sengör 1976;Tapponnier 1977;Sengör et al 1978;Bergerat and Geyssant 1980;Dewey and Windley 1988;Regenauer-Lieb and Petit 1997;Dèzes et al 2004Dèzes et al , 2005Ziegler and Dèzes 2005), back-arc rifting (Jowett 1991) or slab-pull (Stampfli et al 1998; Dèzes et al 2004, modified). BF Black Forest, EG Eger (Ore) Graben, FP Franconian Platform, HG Hessian grabens, LG Limagne Graben, LRG Lower Rhine (Roer Valley) Graben, LRhG Lower Rhône Merle and Michon 2001;Michon et al 2003;Michon and Merle 2005).…”