The Subalpine chains of Haute Provence have been studied for over 100 years. Upper Triassic evaporites are known to be the basal detachment surface for thin-skinned Alpine compression and diapirs have been also identified. However, the importance of salt tectonics during Tethyan rifting and the passive margin subsidence which followed it, and the influence of precursor salt structures in the evolution of the Alpine fold and thrust belt have been underestimated. This work describes pre-Alpine salt structures in the Subalpine chains in more detail and discusses in depth the effects of salt tectonics in the evolution of the fold and thrust belt.
The initiation of salt tectonics was triggered by the Early-Middle Jurassic Tethyan rifting. First generation salt structures developed north of the Provençal platform in the slope and basin palaeogeographical domains. Passive diapirism dominated during the subsequent passive margin phase leading to the formation of a polygonal primary minibasin and salt-ridge system.
Salt tectonic activity culminated in the extrusion of evaporites onto the seafloor during the Albian-Cenomanian and coincided with the deposition of black shales. Allochthonous salt sheets were emplaced from mature diapirs, and extrusive sheets coalesced to form a salt canopy which covered large areas of the primary minibasin and salt-ridge system and the Tethyan margin. A second generation of salt structures developed above the canopy, and they bounded elongated secondary minibasins.
From the Late Cretaceous onwards, Alpine compression led to the squeezing of the first-generation salt structures and depletion of the canopy. Secondary minibasins were carried as piggyback basins in the actively deforming fold and thrust belt and the interaction of salt tectonics and thrusting resulted in the formation of asymmetric hybrid basins.
The geometry of the pre-Alpine salt structures and adjacent minibasins strongly influenced the structural style of the fold and thrust belt.