SM-ND ISOTOPIC AND GEOCHEMICAL CHARACTERIZATION OF THE PALEOPROTEROZOIC TORNGAT OROGEN, LABRADOR, CANADA

The Torngat orogen is a Paleoproterozoic, granulite-facies belt that w elds the Archean components of the Nain and Rae provinces in eastern L abrador. Sm-Nd isotopic and supporting bulk rock major, trace and rare earth element data help elucidate the sources of the main Paleoproter ozoic lithologies that comprise the orogen. In the foreland, Paleoprot erozoic Ramah Group metasediments intercalated with reworked Nain Prov ince gneiss show variable trace element and epsilon(Nd)(1.9 Ga) from - 2.9 to -12.0, ranging between Nain Province crust and Paleoproterozoic Mugford Group basalts compositions. The Ramah Group data suggest deri vation of Ramah detritus from Archean Nain Province gneisses and from the Mugford Group. In the Lac Lomier complex (Rae Province hinterland) , metasediments with variable trace element distribution patterns akin to Rae Province crust, and epsilon(Nd)(1.9 Ga) from -2.9 to -10.5 sug gest derivation from Rae Province crust and from an unspecified juveni le component. In the core of the orogen, pelitic and psammitic protoli ths of the Tasiuyak gneiss (epsilon(Nd)(1.9 Ga) from -1.9 to -2.6) wer e derived from crustal sources unknown in both Nain and Rae provinces, and may have been deposited in a trench environment starved of adjace nt cratonic debris. Dioritic to granitic eastern and western metapluto nic suites intruding the Tasiuyak gneiss and the Lac Lomier complex di splay contrasting geochemical and Sm-Nd isotopic compositions. The eas tern metaplutonic suite has a tendency toward lower SiO2, total alkali s, less fractionated REE and higher MgO, CaO and TiO2 relative to the western metaplutonic suite. The eastern suite yields epsilon(Nd)(1.9 G a) from +3.8 to -6.7 and negative f(Sm/Nd) suggesting igneous precurso rs from Rae crust and a LREE-enriched juvenile component. The western suite yields epsilon(Nd)(1.9 Ga) from -1.5 to -8.5, suggesting an impo rtant contribution from Rae crustal sources in the petrogenesis of the igneous protoliths. The presence of Rae Province Nd isotopic composit ions, and the absence of Nain Province signatures in these intrusions favors the eastern Rae Province as the active margin during Nain-Rae c onvergence.