The metamorphic internal zone of Wopmay Orogen (Early Proterozoic), Canada: 30 km of structural relief in a composite section based on plunge projection

Abstract

In Wopmay Orogen, an early Proterozoic volcano‐sedimentary marginal prism and its underlying Archean structural basement, deformed together during the 1885 Ma Calderian orogeny, are exposed in oblique view as a result of regional cross folding. A composite cross section displaying over 30 km of structural relief provides a framework in which to examine the geologic relationships in the metamorphic‐internal zone of the orogen. A sole thrust separates Archean basement and a thin mantle of autochthonous, early Proterozoic strata from the eastward transported Calderian allochthon. The allochthon is characterized by a transition from external thrust‐fold belt geometries in the east to polyphase, isoclinal recumbent folds and thrusts in the west. The center of the zone contains the Hepburn Batholith which has been been transported, along with the deforming, hot allochthon, over the exposed basement. Both basement and allochthon are deformed by late, large‐scale, upright folds. The metamorphic‐internal zone is interpreted to record the closing of a rift basin during which the basin fill was shortened, thickened (to over 30 km), metamorphosed and thrust eastward while still hot over the relatively cool Archean craton. The basement presently exposed beneath the sole thrust remained relatively nondeformed during thrusting but underwent large‐scale folding due to continued compression during uplift of the internal zone.