LABRADORIAN AND GRENVILLIAN CRUSTAL EVOLUTION OF THE GOOSE BAY-REGION, LABRADOR - NEW U-PB GEOCHRONOLOGICAL CONSTRAINTS

Major initial crust formation in the northeastern Grenville Province o f Labrador occurred during the Labradorian orogeny (1710-1620 Ma) prio r to re-deformation in the Grenvillian orogeny between 1050 and 950 Ma . The Goose Bay region includes several types of juvenile Labradorian crust, including calc-alkaline (arc-related?) terranes and the granite -anorthosite massif of the Mealy Mountains Terrane. New U-Pb dates cor roborate previous evidence that calc-alkaline plutonism occurred ca. 1 672 Ma and was followed closely by Labradorian metamorphism ca. 1659 M a. Dates from strongly deformed rocks at the base of the Mealy Mountai ns Terrane have yielded ca. 1712, 1754, and 1775 Ma maximum upper inte rcept ages of plutonic and (or) metamorphic origin. These apparent age s represent the oldest component of the Labradorian crust that has bee n recognized to date and appear to be a distinctive feature of Mealy M ountains Terrane. The initial Pb isotope signature of these rocks, how ever, precludes the presence of significantly earlier (pre-1.8 Ga) cru st. New U-Pb ages also support previous models for episodic Grenvillia n metamorphism and indicate metamorphic pulses ca. 1035, 1010, 990, an d 970 Ma, which probably represent the metamorphic response to progres sive overthrusting by Mealy Mountains Terrane. Overthrusting of this t errane occurred along the Grand Lake thrust system, which is highlight ed as a fundamental structure of the eastern Grenville Province and on e that may have developed by reactivation of a Labradorian terrane bou ndary.