U-Pb SHRIMP data on the crystallization age of the Gran Paradiso augengneiss, Italian Western Alps: Further evidence for Permian magmatic activity in the Alps during break-up of Pangea

Abstract

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.