Abstract: U-Pb geochronology and the evolution of the Grenville Province of western Labrador

The Grenville Province of western Labrador comprises the Lac Joseph Terrane (UT) (dominated by two leucosome migmatites intruded by granite and gabbro), structurally underlain to the northwest by the Molson Lake Terrane (ML T) comprising only metaigneous rocks. Monazite from both melt generations within UT migmatites formed during leucosome crystallization between 1640-1600 Ma (Labradorian Orogeny); most zircon fractions from these melts show premetamorphic inheritance. However, zircons from shear zones within the migmatites are concordant around 1630 Ma, implying that shearing and the synkinematic mineral assemblage sillimanite-biotite-garnet within these shear zones, and by extension the same assemblage ubiquitous throughout the UT migmatites outside the shear zones, must be of Labradorian age. Granites and gabbros within the UT are also ofLabradorian age. Although no U-Pb evidence was found to suggest that the UT