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The Wopmay orogen is a Paleoproterozoic orogenic belt formed in part by the accretion of Hottah terrane, an east-facing continental magmatic arc, to the western margin of the Archean Slave craton at ca. 1.88 Ga. The arc-continent collision was responsible for the Calderian orogeny. Just prior to the collision, arc volcanism of the Hottah terrane had migrated trenchward and changed in composition from an aphyric calc-alkaline to a bimodal tholeiitic suite. The change in magmatism, along with subsidence and consequent high-temperature-low-pressure metamorphism of rocks on the upper plate, is attributed to extension and asthenospheric upwelling during rollback of the lower plate. The upwelling led to regional heating of the crust, melting, and generation of the metaluminous to peraluminous Hepburn intrusive suite within the arc just prior to accretion of Hottah terrane onto the Slave craton. During the collision, a 200-km-long, orogen-parallel swarm of mafi c sills was intruded into the lower plate and trench-fill sediments at the passive-margin shelf-slope break. The mafi c magmatism may have been induced by slab breakoff. The Calderian orogeny provides an excellent example of the magmatic history of an arc-continent collision.The Calderian orogeny was short-lived. Within a few million years, an east-dipping subduction zone formed outboard of the accreted terrane, creating volcanic rocks that were erupted atop the eroded Hottah-Slave collision zone. The short duration of the Calderian orogeny seems typical of arc-continent collisions, perhaps because the attenuated arc crust, coupled with the extended crust of the lower plate, never generates severely overthickened crust. Rise of asthenospheric mantle due to slab breakoff generates rapid uplift, erosion, and collapse of the mountains built during collision.

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Elevation of the Shaler Group to supergroup status and the following internal revisions are proposed in order to more properly reflect rock units of the Amundsen Basin. The names Escape Rapids, Mikkelsen Islands, Nelson Head and Aok are proposed to replace the lower clastic, cherty carbonate, upper clastic, and orange-weathering stromatolite members of the Glenelg Formation in Minto and Cape Lambton inliers, informal map units 19 to 21, 22, 23, and 24 in the Coppermine area and informal map units P1, P2, P3, and P4a in Brock Inlier, respectively. Collectively these are to be known as the Rae Group; the name Glenelg Formation is abandoned. The former Reynolds Point Formation is raised to group status and comprises the Grassy Bay, Boot Inlet, Fort Collinson and Jago Bay formations, which replace the lower clastic, lower carbonate, upper clastic and upper carbonate members in Minto Inlier and informal map units P4b, P4c, lower P4d and upper P4d in Brock Inlier, respectively.

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