Mesozoic tectonic inheritance of the European crystalline basement (SE France) revealed by thermochronology

The Alpine orogenic belt in SE France is the result of the collision between the European, Adriatic and Iberian plates. The accreted Variscan continental crust, which now forms the external crystalline massifs (ECMs), recorded a complex Mesozoic thermal and tectonic evolution, that is not fully understood. In the Maures-Tanneron massif (MTM), the basement has undergone periods of subsidence and uplift, the latter indicated by stratigraphic gaps from the Albian and Upper Turonian to the Maastrichian. In the Ecrins-Pelvoux massif (EPM), differential subsidence is documented during Lower Jurassic by lateral variation from marine to continental environment, but most of the Cretaceous and Paleogene periods correspond to a stratigraphic hiatus that ends with the deposition of upper Eocene sediments. The link between these stratigraphic gaps and inheritance associated with the rifting, opening of the Alpine Tethys, and early convergence between Europe, Iberia and Adria is still not resolved. The goal of this study is to elucidate the thermal evolution of the European basement in SE France (EPM and MTM) during the Mesozoic using apatite and zircon fission track low-temperature thermochronology (AFT and ZFT). ZFT data from the southern EPM indicates a complex thermal history with central ages ranging from 158 to 45 Ma, thus revealing significant Jurassic to Eocene resetting and cooling. These ages are interpreted as resulting from several tectonic stages related to (1) Jurassic rifting (2) Mesozoic shortening and erosion and/or (3) incomplete Alpine reset during the main phase of underthrusting below the Penninic Frontal Thrust during the Oligocene. In contrast, the MTM shows several thermal events, comprising a major cooling stage at ca. 200 Ma coincident with the CAMP event preserved in the northern part of the massif. A final cooling event between 30 and 25 Ma, that is mostly represented to the South of the massif, is related to the opening of the Ligurian sea. Intermediate AFT ages between these two events are also identified, likely reflecting cooling events during the Mesozoic that can be resolved using thermal modelling. Finally, the long-term thermal evolution reported from SE France ECMs allows refining the geodynamics of this region from Pangea fragmentation to the onset of Alpine orogeny.