Crustal evolution of the Archean Rae Province (northern Canada) from oxygen and hafnium isotopes in zircon

The isotope characteristics of the continental crust are fundamental to understanding its formation and evolution. We present zircon O and Hf isotope data for 115 Archean magmatic rocks (>2.58 Ga) from the Rae Province (northern Canada), providing constraints that have been missing from the global Archean archive thus far. Zircon from >2.65 Ga, dominantly tonalite−trondhjemite−granodiorite samples, show mantle-like δ18O, while εHfinitial and two-stage depleted mantle model ages (TDM) are variable and define four broad isotope domains. Two domains comprise relatively juvenile crust (TDM < 3.0 Ga) that define a central spine of the Rae Province. These are flanked to the west and east by two separate domains of more evolved crust with Meso- to Eoarchean histories (TDM > 3.0 Ga). A decrease in εHfinitial with age within each isotope domain is most consistent with infracrustal reworking of local crust. Relative to pre−2.65 Ga crust, zircon from 2.65−2.58 Ga potassic granitoids show a greater range in δ18O, whereas their εHfinitial are more homogenized. Zircon yielding δ18O >6.5‰ are dominant in the northern Rae Province, where sedimentary sequences are most abundant and likely reflect widespread erosion and sediment/crustal recycling following the emergence of >2.65 Ga crust. The relatively homogeneous εHfinitial is most consistent with an infracrustal origin and mixing with local sediment. The zircon isotope data are used to evaluate and refine boundaries of crustal blocks, and to interrogate models for the construction of the Rae Province. The isotope signatures of the Rae Province are consistent with the global Archean archive for the emergence of the depleted mantle and cratonization.