Cross-propagation of the western Alpine orogen from early to late deformation stages: Evidence from the Internal Zones and implications for restoration

The internal zones of the Western Alps arc are derived from an oceanic and continental subduction wedge developed beneath Adria plate during its paleogene northward drift. Exhumation proceded early Oligocene onwards due to westward extrusion plate. prominent fold-and-thrust structures which follow shape, either forward or backward verging, postdate initial nappe stacking overprint differently oriented older deformations relevant proper retoration this arcuate orogen minimise overlap problems. We document phase through outcrop-scale structural analysis at 55 sites between Maurienne Ubaye valleys, along with larger-scale examples structures. They consistently show N- NW tectonic transport, whose kinematic indicators overprinted by (W- SW-directed) (E- NE-directed) deformation associated post-nappe transport Penninic thrust. Accordingly, restoring Briançonnais fold/thrust system must incorporate reconstruction stack top N-NW direction orogenic propagation, careful consideration their paleogeographic origin towards S-SE. This was built Eocene Adria-Iberia collision, overthrust Subbriançonnais-Valaisan trough before involving Dauphiné-Helvetic foreland. It includes different types Paleozoic units, Permo-Carboniferous sediments base, polymetamorphic basement above, can be explained inversion a late Variscan basin southern shoulder, whereas uppermost Prepiedmont units result Tethyan margin toe. Mixed breccia, locally preserved close contact latter overlying "Schistes Lustrés" nappes, interpreted as olistostromes fed both in very collision stage. 39Ar/40Ar dating suggests that these shallow tectono-sedimentary formations were involved Eocene, younger (late Eocene) equivalent mark propagation over external (Dauphiné/Helvetic) rapidly exhumed indentation radial spreading, markedly context driven around Adriatic upper mantle indenter, controlled development relation Ligurian sea opening.