Tectono-stratigraphic evidence of salt tectonics during Jurassic extension in the Corbières nappe, Eastern Pyrenees, France

Tectono-stratigraphic evidence of salt tectonics during Jurassic extension in the Corbières nappe, Eastern Pyrenees, France

 Antoine Crémades¹, Mary Ford¹ et Julien Charreau¹

¹ CRPG, UMR 7358 CNRS, Université de Lorraine, Vandoeuvre‐lès‐Nancy, France

 

In this work, we investigate the tectono-stratigraphic architecture of a major transfer zone in the Mesozoic Pyrenean rift system and its subsequent alpine inversion. The NE-SW to NS-oriented Corbières transfert zone (70km long) lies between the EW-oriented Pyrenean (400km long) and Provençal (300km long) segments of the Pyrenean orogen. This salt-rich rift transfert zone was inverted during the Pyrenean orogenesis (late Santonian - Early Miocene). During the Oligo-Miocene, most of the transfert zone was further reactivated to form the northern margin of the Gulf of  Lion rift. Thus, only the lateral equivalent of the North Pyrenean Zone outcrops along the western French Mediterranean coast. Unlike the the North Pyrenean Zone, which is a narrow fold and thrust belt, this proximal part of the tranfert zone was previously interpreted as a large thrust sheet (the Corbières Nappe, 70km long) corresponding to Mesozoic cover decoupled from Variscan basement along a thick level of Upper Triassic evaporites (Keuper, 0m to 655m) and emplaced onto the Aquitaine retro-foreland basin during the Priabonian, at the end of Pyrenean orogenesis. 

Our detailed study of the tectono-stratigraphic architecture of the Corbières Nappe demonstrates for the first time the existence of major Jurassic extensional structures linked to strong halokinetic activity. These structures were previously interpreted as compressional and Pyrenean in origin: (1) The Treilles Fault is a N110 trending, shallowly S-SW dipping fault at least 12 km long, which roots on Triassic evaporites. This normal fault with 2.8 km of displacement cuts the Corbières Nappe into two distinct structural units. A 3D hangingwall dip fan associated with stratal thickening toward the fault demonstrates that this extensional fault was active during the full Jurassic and maybe during the early Cretaceous. (2) In the footwall of the Treilles Fault, the Valdria NE-SW trending fold pair was previously interpreted as a Pyrenean compressional fold. Detailed mapping of 3D thickness and geometry variations in the Jurassic series around these folds reveals NW verging syn-sedimentary folding during the Jurassic. We propose that this folding is linked to the growth of the Feuilla Keuper diapir that lies immediately to the south. The highlighting of these complex halokinetic and extensional structures of Early Jurassic to Early Cretaceous age have major implications for (1) the Pyrenean and Tethysian Mesozoic extensional systems in the eastern Pyrenees and (2) their impact as a major regional inheritance in later orogenic phases, in particular in the evolution of the Pyrenean Corbières Nappe.