Early Paleozoic U-Pb age of zircons from meta-granophyres f the Grand-Saint-Bernard nappe (zona interna, Aosta Valley, Italy)

The U-Pb age of a meta-granophyre from the Val de Rhemes (Brianconnais basement of the Aosta valley) of 511±9 Ma suggests that the micaschists which dominate the pre-alpine basement of the Grand-Saint-Bernard Nappe are, in part, of Early Paleozoic age. The Brianconnais domain is characterized by a Cambrian to Ordovician alkaline to sub-alkaline (monzonitic) magmatism, similar in age to orthogneisses known in other parts of the Variscan belt and generally interpreted as related to an extensional event. (authors)