Metamorphic zircon, trace elements and Neoarchean metamorphism in the ca. 3.75 Ga Nuvvuagittuq supracrustal belt, Québec (Canada)

The Nuvvuagittuq supracrustal belt (NSB) in northwestern Québec ranks as one of the oldest granitoid gneiss complexes thus far discovered. Emplacement ages for intrusive trondhjemitic dikes that transect amphibolites and quartz–magnetite schists at the Porpoise Cove outcrops of the NSB cluster at 3.75 Ga. As with all other pre-3.7 Ga terranes thus far documented, the NSB has been metamorphosed and multiply deformed. In a combined approach to explore the thermal history of the NSB, conventional garnet–biotite and plagioclase–hornblende geothermometry was coupled with zircon U–Th–Pb depth profiles, REE partitioning and Ti-in-zircon thermometry to show that Neoarchean metamorphism in the belt reached upper amphibolite facies conditions (~ 640 °C). This metamorphism resulted in some cases in thick zircon overgrowths on older cores and likely corresponds to the amalgamation of terranes in the Northeast Superior Province and the initiation of widespread igneous activity in the vicinity of the NSB. An earlier (resolvable) metamorphic episode from a zircon depth-profile, recorded at 3.62 Ga, probably corresponds to the intrusion of the granitoids which envelope the NSB.