The Lower Paleozoic to Permian evolution of the Dora-Maira Massif basement (Western Alps) revealed by zircon geochronology

Abstract The Dora-Maira Massif offers a unique window into the pre-Alpine and Alpine tectonic history of continental crust involved in the collision that formed the Western Alps. Whereas high-pressure Alpine metamorphism has strongly affected the rocks, zircon crystals still retain age domains from earlier magmatic events, offering a reliable tool for reconstructing the evolution of the continental basement. Combining new U–Pb LA-ICP-MS zircon geochronology with whole-rock geochemistry, this study unveils a more complex magmatic and tectonic evolution than previously recognized. New findings reveal that the Dora-Maira basement preserves three distinct magmatic cycles: Ediacaran–Early Cambrian ( c . 550–530 Ma), Ordovician–Silurian ( c . 460–440 Ma) and Permian ( c . 280–260 Ma). These results challenge the overestimated presence of Permian intrusions in the Massif, instead highlighting a significant Lower Paleozoic magmatic component that was previously overlooked. We document the oldest magmatic suite recognized to date in the area (540.0 ± 5.4 and 548.0 ± 5.5 Ma), which sheds light on the Cambrian-to-Precambrian tectonic history of the northern margin of Gondwana. This contribution refines the geodynamic framework of the Dora-Maira Massif. It demonstrates that its polycyclic basement was assembled through successive crust-forming events during the Ediacaran–Early Paleozoic and subsequently reworked during the Variscan and Alpine orogenies. This underlines the key role of Lower Paleozoic tectono-magmatic processes in shaping the continental crust of the Western Alps.