Structural evolution of the superimposed Provencal and Subalpine fold-thrust belts (SE France)

Highlighting how crustal shortening is accommodated in space and time in fold-thrust belts is a major issue for understanding the long-term tectonic evolution of orogenic systems. In this study, we combine surface and subsurface data to build a 150 km-long sequentially restored balanced cross-section across two superimposed foreland fold-thrust belts in southeastern France: the upper Cretaceous-Eocene Provencal belt and Oligocene Neogene Subalpine belt. These belts are composed of inverted Paleozoic-Mesozoic basins with Mesozoic halokinetic structures, basement thrusts, and cover thrusts-nappes detached in the Triassic evaporites. The multiphase growth of the Provencal and Subalpine belts has been constrained along the studied cross-section by synorogenic deposits and kinematic indicators of thrusting. The pre-orogenic palinspastic reconstruction of the cross-section to Late Santonian shows a large uplift zone in the center of the section (Durance and Valensole highs), which led to the separation of the Beausset basin (South Provence basin) to the south from the BarlesDigne basin (Vocontian basin) to the north. The Provencal shortening propagated-NNE-ward from the Beausset basin up to folds in the Barles area during the Latest Santonian to Eocene times. Shortening value reaches 38 km and has been mainly accommodated by the inversion of the South Provence basin-Durance high. The Sub alpine shortening propagated-SW-ward from the Barles-Digne basin up to the Mediterranean coast during the Oligocene-Miocene to Quaternary times. It reaches 35 km and has been mainly consumed by the inversion of the thick Digne basin. The Provencal thrust wedge is characterized by distributed basement thrusts reworking numerous structures inherited from the Variscan belt and Permian-Mesozoic rifts. This structural style might have favored the development of confined foreland basins, as the Arc and Rians basins. In contrast, the vertical stacking of the thick Digne Nappe and Barles basement triangle zone in the Subalpine thrust wedge might have controlled the large flexure of the Valensole foreland basin. The lack of Triassic evaporites in the Valensole high probably explains that shortening was not transferred into the cover of this domain. Consequently, the Provencal then the Subalpine shortenings might have been transferred more deeply to induce the reactivation of basement faults into the external zones. The Mesozoic halokinetic structures also strongly influenced the location of contractional deformation. This study highlights that the crustal structural inheritances influenced the structural styles and development of extensional basins and subsequent Provencal and Subalpine belts.