Exhumation of the Western Alpine collisional wedge: New thermochronological data

Collisional shortening in the external Western Alps was first accommodated by internal (distributed) deformation External Crystalline Massifs (ECM) and then on frontal crustal ramps (localized deformation). However, timing of transition between these two periods is still under-constrained, mainly because available dataset incomplete Alps. We here provide new zircon apatite fission-track (ZFT AFT) (U-Th-Sm)/He (ZHe) data that constrain early stages cooling hence exhumation Alpine wedge, as well Raman Spectroscopy Carbonaceous Material (RSCM) from Belledonne massif. ZFT ages range 15 20 Ma, ZHe 5 12 AFT 2 10 Ma. Those are integrated within inverse forward thermal history modelling (HeFTy) along with literature to late Oligocene-Miocene suggest Pelvoux massifs may have started ca. 27 This rather slow (~ 50 m.Myrs?1 ± m.Myrs?1) date distributed localized mode shortening, i.e., initiation below massifs. Further north, Mont Blanc Aiguilles Rouges massifs, active around 18 possibly earlier, 20–25 From this time (18 Ma), rates increased all 500 40 m.Myrs?1, both North South). age most likely corresponds end period localisation rapid associated exhumation, hangingwall (even considering start a few Myrs later than if isoterms advected). notably molasse mega-sequences foreland basin (Lower Marine/Freshwater Molasse Upper Molasse).