Great Bear magmatic zone

Great Bear Magmatic Zone
Volcanic arc
Geological map of north-western Canada. Wopmay orogen is D; Great Bear Magmatic Zone is the red area stretching from the northern tip of Great Slave Lake to the eastern shore of Great Bear Lake.
Country	Canada
Regions	Northwest Territories
Period	Proterozoic

The Great Bear Magmatic Zone (GBMZ) is a Paleoproterozoic (1.875-1.86 Ga) multi-collisional orogenic belt of which 100 km × 400 km (62 mi × 249 mi) is exposed in the northwestern Canadian Shield east of Great Bear Lake, Northwest Territories.

Covering 40,000 km² (15,000 sq mi), the GBMZ forms part of the Wopmay orogen together with the Coronation Margin and Hottah terrane and overlies these two tectonic elements. The GBMZ, in turn, is covered by Paleozoic and Proterozoic sediments and, as indicated by a long aeromagnetic line, the sub-aerial part of the GMBZ is probably 800 km (500 mi) long. Volcanics of the GBMZ range from basalt to rhyolite and geologic studies show it is part of an early Proterozoic continental volcanic arc.

The GBMZ formed following a flip in subduction polarity from east to west dipping when the Hottah terrane collided with the Slave Craton 1.875–1.855 Ga.

The GBMZ is a magmatic arc on the western margin of the Wopmay orogen which developed 1.875–1.840 Ga on older Proterozoic basement rocks. The medial or internal zone of the orogen form the eastern margin of the GBMZ and is marked by the complex Wopmay fault zone which the GBMZ partly covers in the north.

The early history of the GBMZ (1.870–1.865 Ga) was dominated by volcanism and intrusions that produced a stratum of volcanic rocks 10 km (6.2 mi) thick in the north to 5 km (3.1 mi) in the south. The volcanic layers in the north are folded and have been intruded by quartz monzonite plutons. Large granite batholiths were emplaced during late stages of volcanism (1.865–1.840 Ga). The GBMZ at this stage is thought to be the result of eastward-directed subduction of oceanic lithosphere.