Age and geochemistry of basement complexes in the south-central New Québec Orogen: Archean history, terrane correlations, and Paleoproterozoic reactivation

U–Pb geochronological, geochemical, and Sm–Nd isotopic data from metaplutonic rocks in the south-central New Québec Orogen (NQO) provide new insights into the long-term tectono-magmatic evolution of western Labrador. Basement units are divided into two complexes—the Snelgrove Lake Basement Complex (SLBC), exposed beneath sedimentary rocks of the Labrador Trough, and the Griffis Complex—separated from each other by a Hudsonian-aged ductile shear zone. The oldest rocks in both complexes are variably metamorphosed tonalite to granodiorite with whole-rock compositions similar to Archean tonalite–trondhjemite–granodiorite (TTG) suites (sensu lato), and εNd i = 1.69 to −4.83, indicating formation by medium- to high-pressure partial melting of meta-basalt with variable assimilation of older continental crust. Zircon U–Pb geochronological results indicate TTG magmatism at 2670.8 ± 4.6 and 2677 ± 12 Ma followed by broadly coeval metamorphism at 2620 ± 17 and 2594 ± 13 Ma, respectively, and support previous suggestions that NQO basement originated as part of the Superior craton. Proterozoic magmatism affected both domains but at different times. In the SLBC, the 2198.23 ± 0.89 Ma Snelgrove granite exhibits elevated REE contents, strong high-field-strength element enrichment, and negative εNd i (−4.64), suggesting formation by high-temperature, low-pressure crustal melting interpreted to represent an early phase of rifting in the Labrador Trough. Equivalent magmatism was not found in the Griffis Complex. Instead, deformed peraluminous leucogranite dykes, intruded at 1637.47 ± 1.1 and 1633.3 ± 5.8 Ma, and with εNd i = −12, reveal a previously unrecognized phase of crustal melting and deformation related to the Labradorian orogeny farther south. These data highlight a more complex history for the south-central NQO than established by previous reconnaissance-scale work and underscore the need for additional geoscience data to better constrain the tectonic evolution of the region.