Âge Paléozoïque inférieur (U—Pb sur zircon) de métagranophyres de la nappe du Grand-Saint-Bernard (zona interna, vallée d'Aoste, Italie)

Early Paleozoic U—Pb age of zircons from metagranophyres of the Grand-Saint-Bernard Nappe (zona interna, Aosta Valley, Italy). The U—Pb age of a metagranophyre 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 subalkaline (monzonitic) magmatism, similar in age to orthogneisses known in other parts of the Variscan belt and generally interpreted as related to an extensional event.