Precambrian geology of the Indin Lake map area, District of Mackenzie, Northwest Territories

Abstract

Indin Lake map area straddles the boundary between the Slave Structural Province on the southeast and the south-central zones of the Wopmay Orogen on the northwest. Within the Slave, supracrustal rocks form irregular, generally north trending belts made up of metamorphosed basaltic volcanic rocks, and turbiditic greywackes, and mudstones of 2.67 Ga age. Intervening areas are made up of hybrid rocks derived from both basement granitoid (about 2.99 Ga) and supracrustal rocks as well as plutonic rocks of mainly granodiorite or granite composition. An orogeny analogous to the Kenoran (about 2.6 Ga) modified existing structures, metamorphosed rocks to the upper amphibolite facies, and re-equilibrated some isotopic systems. The boundary between the Slave Structural Province and the Wopmay Orogen in the map area is a normal fault over most of its length. Evidence of penetrative deformation during the Proterozoic Calderian Orogeny is most abundant in the supracrustal rocks of the Coronation Supergroup, but evidence of minor penetrative and brittle deformation is present in Archean rocks as much as 40 km into the Slave craton. The west margin of the Slave Province has been thickened by westward subduction of the Bear plate, which caused regional uplifts of areas underlain by buoyant granitoid rock and downwarps of areas underlain by denser rock. Within the Wopmay Orogen, Archean cratonic rocks are unconformably overlain by the Proterozoic Coronation Supergroup, which is deformed into tight upright- to eastward-verging folds adjacent to the Slave Province. The style and complexity of deformation and regional metamorphism increase westward, changing from a single set of folding and one recognized phase of greenschist metamorphism to three sets of deformation and regional metamorphism up to the granulite facies. Plutons of megacrystic, rapakivi-textured granite, correlated with the Hepburn intrusive Suite, intruded metamorphosed and deformed rocks of the Coronation Supergroup. Older rocks of the Wopmay Orogen show isotopic reequilibration at about 2.3 Ga and again with Proterozoic rocks at about 1.9 Ga.