Abstract

Reflection seismic data from the Colville Hills and Anderson Plain document an intracratonic compressional event, herein named the Forward orogeny, which affected strata considered equivalent to the >1663 Ma Hornby Bay Group outcropping on Coppermine Homocline. Forward orogeny structures were peneplaned and unconformably overlain by strata considered equivalent to the >1267 Ma Dismal Lakes Group. A comparable tectonic history is recorded in the exposed rocks of Coppermine Homocline to the east. Structural orientations indicate a general northwest–southeast direction of maximum compression during an early phase and a more west–east direction in a later phase. Regional sequence A of G.M. Young and co-workers is subdivided into preorogenic sequence A1 (Hornby Bay and equivalents), and postorogenic sequences A2 (Dismal Lakes and equivalents) and A3 (Coppermine River group and equivalents). The Forward orogeny, dated as approximately 1663 Ma (the age of the syntectonic Kaertok Formation on Coppermine Homocline), is not related to the 1.84–1.9 Ga Wopmay Orogen. Relationships between the Forward orogeny and the Racklan orogeny, in the Wernecke and Ogilvie mountains, remain unresolved because the age of the Racklan is uncertain.

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