Abstract

Seismic reflection data from the Interior Platform in the Arctic of northwestern Canada image upper crustal structures to about 15 km depth that are almost certainly part of a thin-skinned foreland thrust and fold belt in Proterozoic rocks. Thrust faults are identified on the basis of reflection discontinuities and apparent structural repetition of layered strata. The faults are listric and merge at depth into a décollement surface above a basement which regional considerations suggest is Early Proterozoic, associated with the development of the Hudsonian (2.1-1.8 Ga) Wopmay orogen some 400 km to the east. The structures of the thrust and fold belt are unconformably overlain by nearly horizontal layers of Paleozoic (Lower Cambrian to Middle Devonian) and perhaps upper Proterozoic (Mackenzie Mountains Supergroup?) sediments. The age of the thrusting is thus likely to be older than the Mackenzie Mountains Supergroup (0.77-0.88 b.y.) and younger than the Hudsonian orogeny; it may therefore be associated with that of the incompletely defined Racklan orogeny (about 1.1 b.y.) of the northern Cordillera. Some reactivation of the thrust structures probably took place during the Laramide compression that formed the Colville Hills. The thrust belt is of unknown extent but may be present over a large area, although hidden in most places by younger sediment layers. As the thin-skinned geometry of this thrust belt is similar to that of many Phanerozoic thrust belts, the lithospheric processes that formed these structures were probably similar to those acting today.

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