Significant rotations related to cover–substratum decoupling: Example of the Dôme de Barrôt (Southwestern Alps, France)

The Barrôt area presents an important contrast of deformation between a foliated, faulted and non-rotated Permian substratum and a folded and strongly rotated Meso-Cenozoic sedimentary cover. The Permian substratum and the sedimentary cover are separated by a décollement level of Triassic gypsum. While numerous studies have been done on the Dôme de Barrôt (i.e., the Permian substratum), we focused our work on the deformed Meso-Cenozoic sedimentary cover around the Dôme de Barrôt where we measured and analyzed both the magnetic susceptibility fabrics and the paleomagnetic directions. Our results highlight an arcuate pattern of the directions of shortening trajectories revealed by type II–III fabrics of anisotropy of magnetic susceptibility (which predates the folding) and a later syn- or post-folding anticlockwise rotation of large amplitude (64±14°) for the sedimentary cover. The arcuate pattern of the directions of shortening and the different rotations between the Permian substratum and the sedimentary cover can be partly explained after restoring the paleogeographic location of the sedimentary cover before the Oligocene Alpine compression event. We tend to interpret the remaining 30° anticlockwise rotation as a result of the high efficiency of the Triassic gypsum décollement surface, a nearby regional left-lateral shear zone (RDFZ), and a possible near-field gravitational sliding near the later exhumed Dôme de Barrôt. •The substratum and the cover show similar arcuate magnetic lineation trends.•The cover recorded a 64° anticlockwise rotation whereas the substratum does not.•The bent trajectory of shortening of the substratum explains half of the rotation.•The efficiency of the gypsum décollement could explain the other half of the rotation.