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 of Labrador occurred during the Labradorian orogeny (1710-1620 Ma) prior 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 corroborate previous evidence that calc-alkaline plutonism occurred ca. 1672 Ma and was followed closely by Labradorian metamorphism ca. 1659 Ma. Dates from strongly deformed rocks at the base of the Mealy Mountains Terrane have yielded ca. 1712, 1754, and 1775 Ma maximum upper intercept ages of plutonic and (or) metamorphic origin. These apparent ages represent the oldest component of the Labradorian crust that has been recognized to date and appear to be a distinctive feature of Mealy Mountains Terrane. The initial Pb isotope signature of these rocks, however, precludes the presence of significantly earlier (pre-1.8 Ga) crust. New U-Pb ages also support previous models for episodic Grenvillian metamorphism and indicate metamorphic pulses ca. 1035, 1010, 990, and 970 Ma, which probably represent the metamorphic response to progressive overthrusting by Mealy Mountains Terrane. Overthrusting of this terrane occurred along the Grand Lake thrust system, which is highlighted as a fundamental structure of the eastern Grenville Province and one that may have developed by reactivation of a Labradorian terrane boundary.