2.5-1.9 GA TECTONIC EVOLUTION OF THE WESTERN CHURCHILL PROVINCE: A DANCE IN FOUR PARTS

Owing to its remarkable sojourn in an upper plate setting between 2.5 and 1.7 Ga, the western Churchill Province experienced multiple tectonic events during this formative phase of Earth’s evolution. New targeted stratigraphic and tectonometamorphic studies are radically changing our perspective on the northern and southern components (Rae and Hearne domains, respectively) of this largest, but most-poorly known part of the Canadian Shield.

At 2.55-2.5 Ga, mafic-felsic magmatism, moderate pressure metamorphism and crustal thickening localized in the Rae and NW Hearne domains, is thought to represent a phase of crustal amalgamation. In contrast, rocks of the central Hearne domain underwent 2.5-2.45 Ga extension, as reflected by Kaminak dyke intrusion and local deposition of the rift-related Spi Group.

A second crustal thickening event in the western and northern Rae at ca. 2.35 Ga is ascribed to collisional orogenesis following continental arc magmatism on its western margin. Syn-collisional felsic magmatism and local sedimentation occur to the southwest at this time. Limited U-Pb data suggest a similar thermomagmatic event in the southernmost Hearne. The central Hearne experienced a period of broad thermal subsidence, with deposition of the lower Hurwitz group in a shallow epicontinental sea.

Widespread extension of the Rae and Hearne domains characterize a third tectonic phase at ca. 2.2-2.1 Ga. Major mafic dyke swarms of 2.19 to 2.11 Ga indicate a protracted period of extension–related magmatism. Development of intracratonic basins containing local continental flood basalts across more than 1000 km of the Rae highlights the broad extent of the extensional regime. Whether extension ultimately led to continental break-up is unclear, as is the link between the Rae Proterozoic supracrustal sequences and those of the southern Hearne.

At ca. 1. 9 Ga, continental clastic and marine carbonate rocks of the upper Hurwitz and Amer-Ketyet groups were deposited across both the Rae and Hearne. Deposition of these strata was broadly coeval with regional-scale folding and thrusting in the NW Hearne, and moderate to high pressure metamorphism and mafic magmatism in the lower crust of the Rae. Accretion of microcontinental blocks, (e.g. central Hearne domain), may have been the driving force for this phase of orogenesis.