U-PB GEOCHRONOLOGY OF DEFORMATION AND METAMORPHISM ACROSS A CENTRAL TRANSECT OF THE EARLY PROTEROZOIC TORNGAT OROGEN, NORTH-RIVER MAP AREA,LABRADOR

The Early Proterozoic Torngat Orogen resulted from the oblique collisi on of the Archean Nain and southeastern Rae provinces and evolved in f our stages: (0) deposition of platformal supracrustal assemblages foll owed by subduction-related arc magmatism in the margin of the Rae Prov ince; (I) crustal thickening and nappe tectonics; (II) sinistral trans pression and formation of the Abloviak shear zone; (III) uplift on ste eply dipping, east-verging mylonites along the eastern orogenic front. U-Pb geochronology on zircon and monazite from major rock units and s yntectonic intrusions indicates that arc magmatism at ca. 1880 Ma was followed by 40 Ma. of deformation and high-grade metamorphism from ca. 1860 to 1820. Subsequent uplift and final cooling occurred ca. 1795 - 1770 Ma. Several ages of mineral growth that correspond to distinct s tructural and metamorphic events have been recognized: (1) 1858 - 1853 Ma zircon and monazite dates are interpreted as the minimum age of st age I and peak metamorphic conditions; (2) 1844 Ma zircons from anatec tic granitoids in the Tasiuyak gneiss complex (TGC), syntectonic with stage II deformation, are interpreted to date the formation of the Abl oviak shear zone; (3) 1837 Ma magmatic zircons from an intrusive grani te vein deformed along the western contact of the TGC represent a disc rete intrusive event: (4) 1825 - 1822 Ma metamorphic overgrowths and n ewly grown zircons in granitic veins from the western portion of the o rogen (Lac Lomier complex) represent a period of renewed transpression al deformation; (5) 1806 Ma magmatic zircons from a post-stage II gran ite emplaced along the eastern edge of the Abloviak shear zone defines the transition between stage II and stage III events: (6) 1794 - 1773 Ma zircons from leucogranites and pegmatites that are associated with uplift of the orogen (stage III). 1780 - 1740 Ma dates for monazite a nd a Ar-40/Ar-39 hornblende age correspond to the latest stages of upl ift and cooling of the orogen.