Crustal evolution and age of thermotectonic reworking in the western hinterland of the Trans-Hudson Orogen, northern Saskatchewan

The Hearne province in northern Saskatchewan forms the western hinterland of the Trans-Hudson Orogen. It is a fault-bounded terrane, lying structurally and geographically between the Rae province to its west and the Wathaman batholith and orogenic internides of the Trans-Hudson Orogen to its east. Hearne province is comprised primarily of Archean high-grade metamorphic rocks, structurally overlain by Archean or Proterozoic metasedimentary rocks and intruded by Proterozoic granites, whereas the Rae province to the west is comprised primarily of higher-grade Archean rocks. The calc-alkaline Wathaman batholith was intruded at ca. 1.85 Ga, and the orogenic internides to the east of it include low-grade mafic and intermediate, and possibly volcanic rocks that crystallized between 1.92 and 1.86 Ga. Terminal collision in the internides has been constrained to be between 1.82 Ga and 1.78 Ga.;Mineral U/Pb data from the Black Birch Lake area presented here unequivocally demonstrate that high-grade metamorphism and large-volume anatexis across the southern Hearne province were approximately synchronous with terminal collision and high-grade metamorphism across the Trans-Hudson Orogen. Zircon data for most samples are complex, but unequivocally demonstrate a high-grade overprint at 1810-1805 Ma. Zircons typically show inherited components of Archean age, suggesting the presence of extremely old rocks in the Hearne province and a potential connection with the Rae province in the Archean. The proposed Archean connection between Hearne and Rae provinces and the great antiquity of Hearne crust is further supported by Sm-Nd data, with ca. 3500 Ma model ages for similar parageneses in both terranes. Sm/Nd results also elucidate the similarity of the ca. 1.80 Ga anatectic granites of the Hearne province to the Junction granite, which intruded the Virgin River shear zone, thereby constraining the timing of final motion on that structure. Monazite ;Standard thermobarometric analysis of mineral assemblages in gneisses from the Black Birch Lake area constrain metamorphic conditions to have been greater than 700...