Deformation history of a subducted continental crust (Gran Paradiso, Western Alps): continuing crustal shortening during exhumation

Eclogite-facies continental basement in the Western Alps outcrops as tectonic windows below the oceanic units. In the Gran Paradiso massif, eclogite-facies assemblages in mafic rocks display a N–S stretching lineation (DA1). The main-phase foliation formed under epidote amphibolite-facies conditions (DA2) and defines a regional dome structure for the whole Gran Paradiso massif. Structural data, including new detailed mapping, microstructural analyses and metamorphic studies in the northern part of the Gran Paradiso (Cogne valley) reveal the occurrence of major thrusts in this continental basement associated with the DA2 deformation. E–W-trending stretching lineations and fold axes are associated with this second and main deformation. Nappe stacking of the different units was achieved by top-to-the-west shearing during exhumation of the eclogite-facies basement. The antiformal doming of the Gran Paradiso basement is thus produced by the nappe stacking during exhumation, under epidote amphibolite facies.