Fig. 17

Tectonic evolution of the former Briançonnais passive margin around our study area during Alpine orogeny. During stage (a), the External Briançonnais margin (affected by late extension during the Late Cretaceous–Paleocene) is not affected yet by the orogenic deformation, which is limited to the eastern part of the lower plate (Piemonte-Liguria oceanic crust and distal Briançonnais margin). Conversely, stages (b) and (c) correspond to the tectonic phases D1–D2 and D3 described in this work, respectively. a Middle–Late Eocene (45–40 Ma). The External Briançonnais domain is approaching the subduction interface; in continuation of the Late Cretaceous–Paleocene extension, syn-sedimentary extension possibly related to crossing of the forebulge takes place (modified and adapted after Bonnet et al. (2022), Michard and Martinotti (2002), Michard et al. (2022). Note that deposition of “Flysch noir” above the more distal Briançonnais units is uncertain). b In the Late Eocene (c. 35 Ma), the Briançonnais units are decoupled and stacked in the subduction channel and in the trench domain (D1–D2 in this study). The overlying accretionary wedge consists of Helminthoid Flysch in its upper/external part and of metamorphic Schistes Lustrés units in its deepest/internal parts (modified after Michard et al., 2004). c In the Latest Eocene to Early Oligocene (c. 35–30 Ma) backfolding and backthrusting affected the Briançonnais units (D3 in this study) in the internal part of the wedge (modified after Michard et al., 2004). This internal-ward deformation is nearly coeval with the fore thrusting along the Penninic Front (PF) and with extension in the uppermost part of the wedge (see Bucher et al., 2004, Simon-Labric et al., 2009, Schmid et al., 2017 and Michard et al., 2022). The Helminthoid Flysch nappes, in the footwall of the Penninic Front, are emplaced onto the “Grès d’Annot” basin, dragging slivers of Subbriançonnais and Briançonnais units at their base (Kerckhove, 1969). The Sérenne-Guillestre unit represents that part of the Helminthoid Flysch nappes that remained in the hanging-wall of Penninic Front