Jurassic Salt Tectonics in the SW Sub-Alpine Fold-and-Thrust Belt

Evaporites play a major role in the evolution of an orogenic wedge, modifying the shape and the deformation kinematics inside the wedge. Salt tectonics can occur at various stages, but early salt activity can create a structural inheritance which compartmentalizes the building of the sedimentary succession and the mechanical architecture of the orogenic wedge. Sub-Alpine fold-and-thrust belts commonly show evidence of inherited salt-related structures, which were mostly described as having been initiated during the Liassic Tethyan rifting. However, even though a few authors tried to introduce salt tectonics as a major factor in the Alpine history, most of the interpretations underestimate the phenomenon. In this paper, we show that the Digne Nappe area presents many salt-controlled structures within both the Digne and the Authon-Valavoire thrust sheets. Salt activity began during the Hettangian and continued through the whole Jurassic. At a larger scale, our observations show alignments of salt-controlled structures following NW-SE and NNE-SSW directions, as well as preferential locations at tectonic unit boundaries. Distribution of salt structures seems to follow a well-defined pattern directly inherited from the rifting, and this strongly influences deformation of the sub-Alpine domain.