Petrography, geochemistry, and nd isotope systematics of metaconglomerates and matrix-rich metasedimentary rocks: Implications for the provenance and tectonic setting of the Labrador Trough, Canada

The New Quebec Orogen consists of a supracrustal belt that was reworked when the Superior Craton collided with the Core Zone terrane during the Paleoproterozoic Trans-Hudson Orogeny. Within the New Quebec Orogen, the Kaniapiskau Supergroup can be divided into four terrigenous lithotypes metamorphosed at low-grade: one set with greater compositional and textural sedimentary maturity classified as quartz arenites and subarkoses, and another set with lower textural maturity classified as feldspathic wackes and mudrocks. In contrast, the Laporte Group includes homogeneous lithotypes represented by feldspathic and lithic wackes with a range of matrix contents metamorphosed at low to medium grade. The Kaniapiskau Supergroup rocks have a wide range of SiO2 and Al2O3 contents (SiO2/Al2O3 = 3.7–51) compared to the restricted compositional range of the Laporte Group rocks (SiO2/Al2O3 = 4.4–6.8). In general, the geochemical variations in both formations of the Laporte Group are within the range of the main clast varieties from basal metaconglomerates, although the Deborah Formation (top unit) records higher TiO2, P2O5, MgO, and Ni contents and high Cr/Th, Co/Ba, Th/U, and Rb/Sr ratios indicating additional mafic sources. Our results support the hypothesis that the Kaniapiskau Supergroup was deposited along an intraplate continental margin with predominantly recycled (3Nd(1.87Ga) –12) Paleoarchean sources (TDM 3.2 Ga). In contrast, the Laporte Group marks the transition from a continental forearc (Grand Rosoy Fm.) with a typical juvenile source, including granitic clasts (3Nd(1.83Ga) –0.1 to +3.1), to a wedge-top depozone (Deborah Fm.) in the context of a collisional proforeland basin. This syncollisional sedimentary environment is characterized by the presence of old crustal components (3Nd(1.83Ga) –4.4 to –9.1).