Multiple Arc Development in the Paleoproterozoic Wopmay Orogen, Northwest Canada

Abstract

The Wopmay Orogen formed between about 1.88 and 1.84 Ga as island arcs (Hottah arc and Nahanni/Fort Simpson arc) converged with the western (today’s coordinates) Coronation margin of the Archean Slave craton. Convergence produced virtually all of the regional geological and geophysical hallmarks that are commonly observed in Phanerozoic plate margin orogens today. These include (1) a north–south arrangement of margin-parallel belts, within which geological features are consistent along strike; (2) an east-to-west transition from undeformed foreland, to (3) the Asiak foreland thrust and fold belt, then to (4) allochthonous metamorphic and plutonic rocks in the Turmoil klippe, (5) volcanic, plutonic and sedimentary rocks of the Great Bear magmatic zone, and finally, (6) rocks that were exotic to the Coronation margin of the Slave craton prior to the formation of the Great Bear arc (Hottah and Nahanni/Fort Simpson terranes). The orogen thus exhibits two types of magmatic arcs: subduction-related accreted arc terranes (Hottah and Fort Simpson arc terranes) and a post-collisional arc (e.g., Great Bear magmatic zone and Bishop suite). Moreover, in addition to the surface characteristics, geophysical studies have produced some of the clearest images anywhere of sub-Moho lithospheric structures. In Wopmay Orogen, these data outline remnants of the subduction processes that indicate subduction flipped following the collision of the Hottah arc with the Slave craton, that Slave craton crust was tectonically wedged into the Hottah terrane and the Hottah terrane was wedged into the Nahanni/Fort Simpson terrane, and support the notion that recycling of crustal and upper mantle material is an important process during arc–continent collisions.