U–Pb Dating of Cambrian Magmatism in the Pinerolo‐Sanfront Unit, Dora‐Maira Massif (Western Alps)

ABSTRACT The Pinerolo‐Sanfront Unit (PSU), the structurally lowest tectonic unit of the Dora‐Maira Massif (Western Alps), has been regarded as a monocyclic unit composed of Permo‐Carboniferous sediments and Permian granitoids that were metamorphosed during the Alpine orogeny. We present new geochemical data and U–Pb zircon dating of an amphibolite boudin and a meta‐aplitic dyke, which yield Early Cambrian protolith intrusion ages of 532 ± 11 Ma and 530 ± 11 Ma, respectively. The occurrence of Early Cambrian magmatic rocks emplaced within the surrounding micaschist requires the presence of a (pre‐)Early Cambrian host rock, providing direct evidence for an older basement within the PSU than previously constrained. The presence of a previously unrecognised (pre‐)Early Cambrian basement requires a revision of the pre‐Alpine architecture and early geological evolution of the PSU along the Gondwana margin.