The thermal evolution of Corsica as recorded by zircon fission-tracks

Abstract

New zircon fission-track (ZFT) ages from Corsica record multiple thermal events that can be tied to the structural evolution of the western Mediterranean region. The Corsican zircons have a wide scatter of ZFT grain ages (243–14 Ma), which together define several age domains. Western Corsica consists largely of stable Hercynian basement characterized by ZFT ages in the range 161–114 Ma. We interpret these ages (Late Jurassic–Early Cretaceous) as the product of a long-lived Tethyan thermal event related to continental rifting and subsequent drifting during the separation of the European and African plates and the formation of the Liguro–Piemontese ocean basin. In contrast to Hercynian Corsica, Alpine Corsica (northeast Corsica) experienced widespread deformation and metamorphism in Late Cretaceous(?)–Tertiary time. Dated samples from Alpine Corsica range in age from 112 to 19 Ma and all are reset or partially reset by one or more Alpine thermal events. The youngest ZFT grain ages are from the northernmost Alpine Corsica and define an age population at ∼ 24 Ma that indicates cooling after Tertiary thermal events associated with the Alpine metamorphism and the opening of the Liguro–Provençal basin. A less well-defined ZFT age population at ∼ 72 Ma is present in both Alpine Corsica and Hercynian basement rocks. The thermal history of these rocks is not clear. One interpretation is that the ZFT population at ∼ 72 Ma reflects resetting during a Late Cretaceous event broadly synchronous with the early Alpine metamorphism. Another interpretation is that this peak is related to variable fission-track annealing and partial resetting during the Tertiary Alpine metamorphic event across central to north-eastern Corsica. This partial age resetting supports the presence of a fossil ZFT partial annealing zone and limits the peak temperature in this area below 300 °C, for both the affected pre-Alpine and Alpine units.