U–Pb geochronology of the Nain craton on the eastern margin of the Torngat Orogen, Labrador

Abstract

New U–Pb geochronological results provide insight into the geological evolution of the northernmost Nain craton. A tonalitic orthogneiss, retrogressed from granulite to amphibolite facies, is interpreted to have crystallized at 2832 ± 3 Ma; zircon overgrowths, dated at 2769 ± 5 Ma, are interpreted as metamorphic in origin, whereas metamorphic monazite crystallized at 2692 ± 2 Ma. The crystallization age of this sample suggests it may be correlative with similar rocks of the Kanairiktok Plutonic Suite of the Hopedale block, whereas the age of the zircon overgrowths is synchronous with metamorphism in the Saglek block and may indicate a link at this time. A foliated tonalité crystallized at 2802 ± 2 Ma; titanite in this sample records deformation at 1745 ± 4 Ma; the emplacement age suggests a link with Hopedale block, whereas the titanite growth is clearly related to Torngat orogeny. Two foliated granites crystallized at 2587 ± 3 and 2564 ± 2 Ma, respectively, synchronous with late magmatic events recognized in the southern Nain craton. An Avayalik mafic dyke was emplaced at [Formula: see text] Ma, and subsequently metamorphosed at [Formula: see text] Ma. An intraboudin granitic pegmatite crystallized at 1780 ± 2 Ma, and titanite in a diorite formed at 1735 ± 3 Ma, recording the effects of deformation in the Komaktorvik shear zone during Torngat orogeny.