A finite-strain study in the central and northern Gran Paradiso massif of the Italian Western Alps has been carried out to elucidate whether ductile strain shows a relationship to nappe contacts and to shed light on the nature of the subhorizontal foliation typical of the gneiss nappes in the Alps. The R _f /φ and Fry methods were used on feldspar porphyroclasts from 98 samples of the Gran Paradiso unit (upper tectonic unit of the Gran Paradiso massif) and 12 samples from the underlying Erfaulet unit (lower unit of the Gran Paradiso massif). Microstructures and thermobarometric data show that feldspar ductility at temperatures higher than c . 450 °C occurred only during high-pressure metamorphism, when the rocks were underplated beneath the overriding Adriatic plate. Therefore, the finite-strain data can be related to high-pressure metamorphism in the Alpine subduction zone. The augen gneiss was heterogeneously deformed and axial ratios of the strain ellipse in xz sections range from 2.1 to 69.8. The long axes of the finite-strain ellipsoids trend west–WNW and the short axes are subvertical, associated with a subhorizontal foliation. The strain magnitudes do not increase towards the nappe contacts. The data indicate flattening strain type in the Gran Paradiso unit and constrictional strain type in the Erfaulet unit and prove deviations from simple shear. We conclude that nappe stacking occurred early during subduction probably by brittle imbrication and that ductile strain was superimposed on and modified the nappe structure during high-pressure underplating in the Alpine subduction zone. The accumulation of ductile strain during underplating was not by simple shear and involved a component of vertical shortening, which caused the subhorizontal foliation in the Gran Paradiso massif.

New U-Pb Sensitive High Resolution Ion MicroProbe (SHRIMP) ages from two augengneiss samples of the Gran Paradiso Massif in the Italian Western Alps yielded well-defined Late Permian crystallization ages of 269.0±6.5 Ma and 270.2±5.0 Ma. The ages provide further evidence that the Gran Paradiso augengneiss is not Variscan basement but reflects post-Variscan magmatic activity related to the break-up of Pangea after the Variscan orogeny eventually leading to the formation of Neo-Tethys. The Gran Paradiso Massif belongs to the so-called internal massifs, which are marked by extension-related bimodal magmatism during the Permian and Mesozoic. Furthermore, the Late Permian ages suggest that the Gran Paradiso Massif did not belong to the same pre- Alpine tectonic domain as the External massifs (as part of the European plate margin), which are characterized by Variscan basement.