Structural Cross-Section and Tectonic Model of the Southeastern Canadian Cordillera

Abstract

Recent models for the structural evolution of the southern Canadian Rocky Mountains have emphasized 'thin-skinned' tectonics whereby thrust sheets piled up from west to east above a décollement on a passive crystalline basement. The concept implies that the more westernly Omineca Crystalline Belt, including granitoid gneiss believed to be basement more than 800 m.y. old, is allochthonous and has moved eastward by at least the amount of shortening in the thrust-faulted zone.Mildly deformed and metamorphosed stratified rocks in the northern Columbia Mountains (central Omineca Crystalline Belt) and adjacent Rocky Mountains permit construction of well-controlled structural and restored stratigraphic cross-sections, which show that the Crystalline Belt and Main Ranges were relatively uniformly uplifted by about 35 000 ft (11 km) whereas flanking regions experienced minor uplifts. Combined with other evidence this indicates that 'thick-skinned' tectonics with vertical movements of the entire crust affected the Omineca Crystalline Belt and the Main Ranges; major horizontal movements seem unnecessary. The Omineca Crystalline Belt is regarded as an autochthon in which the basement was extensively deformed and it is suggested that basement is deformed beneath the Main Ranges. The zone of thrusting and décollement above the basement is restricted to the Front Ranges and Foothills and may result from westward underthrusting of the craton.