Latest Pliocene to recent thick-skinned tectonics at the Upper Rhine Graben – Jura Mountains junction

Abstract

The southernmost Upper Rhine Graben and adjacent Jura experienced basement-rooted shortening that occurred after the deposition of the Pliocene fluvial "Sundgau gravels". Folds affecting the base of these gravels systematically trend NE to ENE. Combined evidence from reflection seismic lines and contour maps of the base-Tertiary and base-Pliocene levels indicates that these folds probably formed by thick-skinned reactivation of both NNE-SSW and WSW-ENE-striking faults. This thick-skinned shortening is NW-SE oriented, i.e. parallel to the maximum horizontal stresses inferred from seismotectonics. NNE-SSW-striking faults (paralleling the Upper Rhine Graben) have been reactivated in sinistral strike-slip mode. However, dextrally transpressive reactivation of the WSW-ENE-trending faults that belong to the Rhine-Bresse Transfer Zone is interpreted to predominate.Deflections of recent river courses around the crests of en-échelon-aligned surface anticlines suggest that the deformation is ongoing at present.Retro-deformation of the folds affecting the base of the Sundgau gravels indicates horizontal displacement rates of about 0.05 mm/a. This corresponds to a minimum strain rate in the order of 2·10 -16 s -1 , given the maximum time span of 2.9 Ma for this deformation, i.e. the biostratigraphically determined minimum age of the gravels. A change from thin-skinned tectonics, that prevailed during the main phase of Jura folding, to very probably still ongoing thick-skinned tectonics is inferred to have occurred in the Late Pliocene. We speculate that this change might be linked to the incipient inversion of Permo-Carboniferous troughs within the Alpine foreland in general. This inversion in dextrally transpressive or purely compressive mode along a WNW-ESE-trending basement fault, that is part of the Rhine-Bresse Transfer Zone, which in turn was prestructured during the formation of the Permo-Carboniferous troughs, could have triggered the 1356 Basel earthquake.

The probabilistic seismic hazard assessment of Germany—version 2016, considering the range of epistemic uncertainties and aleatory variability

“…Elevated blocks west and east of the URG are separated as LASZ in this model, forming in the west the block of the Vosges (B28), and in the east the block of the Black Forest in a broader sense (B26, 30) with the elongated area (B27) where a kind of book shelf tectonics seems to occur (Bankwitz et al 2003). It can be seen as a northeasterly extension of the BresseRhine transitional zone (BRTZ, B35), as already indicated in Illies (1972Illies ( , 1981 and even better constrained in Ustaszewski et al (2005) or Ustaszewski and Schmid (2007). The assembly of tectonic fractures of Fig.…”

Erosion-driven uplift of the modern Central Alps

“…Also at the same time, deformation and exhumation became focused in the core of the Central Alps and particularly in the region surrounding the Aar massif . Note, that Pliocene to modern deformation continued in the Jura Mountains at, however, very low horizontal displacement rates of approximately 0.05 mm/yr (Ustaszewski & Schmid, 2007). These slow rates of deformation are in agreement with the results of GPS surveys revealing relative movements between the Jura Mountains and the Eurasian Plate that are hardly different from zero (Walpersdorf et al, 2006).…”

“…However, there is no geologic or geophysical evidence for subsidence. Rather, a series of Quaternary cut-terraces north of the Jura Mountains (Nivière and Winter, 2000), as well as very slow compressional neotectonic movements in this area (Ustaszewski & Schmid, 2007) suggest a small relative surface uplift. Therefore, the geodetic base level of Aarburg is very likely experiencing a positive vertical motion with respect to the undeformed reference lithosphere.…”

Feedback between erosion and active deformation: geomorphic constraints from the frontal Jura fold-and-thrust belt (eastern France)

“…Nevertheless, the area is prone to seismic hazard as evidenced by the M L 4.8 Rigney earthquake of 23 February 2004 (Baer et al 2005), one of the strongest recent seismic events in the wider area. Moreover, the famous 1356 Basel earthquake, which represents one of the strongest historically recorded seismic events throughout central Western Europe (Mayer-Rosa and Cadiot 1979), was possibly triggered by motions along an ENE-WSW striking basement fault of the Late Paleozoic Burgundy Trough System that underlies the Cenozoic Rhine-Bresse Transfer Zone (Meyer et al 1994;Ustaszewski and Schmid 2007).…”

“…A first marker is provided by the paleo-topographic reconstruction of the Middle Pliocene Sundgau-Forêt de Chaux gravel surface. These gravels were deposited by a braided river that formed part of the Aare-Doubs drainage system (Liniger 1967;Bonvalot 1974;Petit et al 1996;Ziegler and Fraefel 2009) and presumably post-date the formation of the thin-skinned Jura fold-and-thrust belt (Becker 2000;Ustaszewski and Schmid 2007). Plio-Pleistocene terraces along the valleys of the Ognon and Doubs rivers provide a second set of geomorphic markers.…”