Rapid exhumation of young granites in an extensional domain: the example of the Giglio Island pluton (Tuscany)

Abstract

Abstract The presence of recently intruded granites at Earth’s surface suggests that their exhumation may have occurred rapidly. The Neogene granites of the Tuscan Magmatic Province (Italy) were emplaced during a period of extensional tectonics and are ideal for determining and quantifying the exhumation process. The peraluminous monzogranite of Giglio Island in the northern Tyrrhenian Sea is characterized by the presence of roof pendants, xenoliths and miarolitic cavities. The petrologic study of metamorphic xenoliths and new zircon U–Pb ages show that the granite was emplaced at 6.4–10 km depth at 5.7 ± 0.4 Ma. Exhumation, constrained by apatite (U–Th)/He ages, was essentially complete in 0.9 Myr at a minimum rate of 6 mm/year. This requires rapid tectonic unroofing, isostatic rebound and thermal softening activity, weakening the upper crust and favouring exhumation at a previously undocumented rate.