Evidence of decoupled deformation during Jurassic rifting and Cenozoic inversion phases in the salt-rich Corbières-Languedoc Transfer Zone (Pyreneo-Provençal orogen, France)

Abstract

A detailed field study of Jurassic tectono-stratigraphic architecture of the southwestern part of the Corbières-Languedoc Transfer Zone (CLTZ, NE-SW oriented), between the Pyrenean and Provençal orogenic segments (N110 oriented) in SE France, document for the first time variations in thickness and stratigraphic geometries in relation to oblique extensional cover structures (NE-SW and N110 oriented). These structures (low-dip normal faults, salt rollers, rollovers, forced folds) formed during a Jurassic extension phase with strong decoupling between basement and cover on the Keuper pre-rift salt (Carnian-Norian evaporites). Some of these structures such as the Treilles Fault, the Valdria and the Terres Noires fold pairs, were previously interpreted as compressional and Pyrenean in origin (Late Santonian-Bartonian). Our study instead shows that these are Jurassic extensional and salt related structures, which were later affected by Pyrenean compression and Oligo-Miocene extension. Evidence of Jurassic extension is still observable in the field despite later rectivations, making these good field analogs for gently inverted extensional salt structures. During the Jurassic the interference between oblique structures above Keuper, leads to the formation of three dimensional growth strata observable at kilometric scale. Despite the mechanical decoupling effect of Keuper, we infer that their formation was linked to a strong interaction between oblique basement structures (NE-SW and N110) as the area lies during the Jurassic at the intersection between the eastern part of the Pyrenean E-W trending rift system and the NE-SW trending European margin of the Alpine Tethys rift. The decoupled deformation and the strong segmentation above and below Keuper detachement are here identified as Jurassic structural inheritence for later tectonic events, notably for the Nappe des Corbières Orientales emplaced at the end of Pyrenean orogenesis. Associated to previous works, this study highlights that the CLTZ is a key area to better understand Pyreneo-Provençal system evolution along its whole Wilson cycle and to better understand the processes that govern the formation of a salt-rich transfer zone in a strongly pre-structured crust, its multiple reactivations and the decoupling role of salt.