Geology of the Archean Nain Province and Paleoproterozoic Torngat Orogen in a trasect of the North River-Nutak map areas, Newfoundland (Labrador) and Quebec

Abstract

The report, based on 1:100 000 scale bedrock mapping, describes the lithology, structure, metamorphism, geochronology, economic geology, and some geophysical characteristics of the Archean Nain Province in the east and the adjacent, early Proterozoic Torngat orogen of Churchill (Rae) Province in the west. Nain Province is underlain by mainly granulite/amphibolite facies, migmatitic orthogneisses, and minor remnants of supracrustal and basic igneous rocks up to 3.6 Ga old. The province formed by the amalgamation of at least two terranes, after 2.7 Ga, resulting in widespread crustal reactivation at ca. 2.56 Ga. Discrete events in the early Proterozoic, granulite facies Torngat orogen include collision with Nain Province and crustal thickening (ca. 1860 Ma), strike-slip shear /transpression (ca. 1845-1822 Ma), and reactivation and uplift (ca. 1790-1780 Ma). The precollisional configuration of units in the orogen immediately west of Nain Province includes the protoliths of the Tasiuyak gneiss on the margin of Churchill (Rae) Province, probably as an east-facing accretionary prism intruded by calc-alkaline plutonic rocks of a magmatic arc ca. 1880 Ma. The orogeny transgressed eastward into Nain Province, reworking Archean gneisses and deforming the supracrustal Paleoproterozoic Ramah Group in an amphibolite facies foreland. The effects of orogeny extend 70 km east of this foreland, to the coastal reaches of Nain Province, mainly in the form of a metamorphic waning to lower greenschist facies, affecting early Paleoproterozoic tholeiitic diabase dykes and the volcanic and sedimentary rocks of the Mugford Group.