Petrology, geochemistry, and geochronology of some Precambrian rocks of the north-western Melville Peninsula, Northwest Territories

Abstract

<p> The northwestern Melville Peninsula in the area of 69°34'N/84°50'W consists of Precambrian Shield rocks that have suffered multiple metamorphic events, including a high grade metamorphic event in the late Archean, ranging from upper amphibolite to granulite grade locally. The oldest unit present is a tonalite-granodiorite-granite suite showing both foliation and lineation and a somewhat migmatic texture. This biotite-hornblende orthogneiss has produced a Rb-Sr whole rock age date of 2.55 +/- 0.2 Ga. Field relationships indicate that this is a metamorphically induced age rather than an emplacement age. A coarse grained granitic pegmatite associated with the orthogneiss has produced a Rb-Sr isochron indicating an age of 1.83 +/- 0.06 Ga. Petrographic and field evidence indicate that this represents the emplacement age of the pegmatite. </p>