Cordilleria Revisited, with a Three-Dimensional Model for Cretaceous Tectonics in British Columbia

Abstract

The Cordilleria microcontinent theory for the tectonics of British Columbia in the Cretaceous and Early Tertiary and for the origin of the Canadian Rocky Mountains and related features is reviewed. New isotopic, geological, and paleomagnetic data support the hypothesis that the amalgamated superterranes of British Columbia and Alaska were not attached to the mainland of North America in the early Cretaceous and were probably well south of their present relative position. Consideration of that evidence, together with sedimentological evidence from the Albian, leads to a slightly earlier best estimate (115 Ma) for the time of initial collision in the Yukon. New geophysical data for southeastern British Columbia and Idaho lead to a comparison with the Iapetus Suture in northern England: it is suggested that the Cordilleria Suture dips west from the present Purcell Thrust and related structures and should cut the Moho. A new model for regional deformation in SE British Columbia is proposed, involving a flake structure based on regional thrusts, which originally dipped northwest. These were contemporaneous with the first phases of thrusting to the east in the cover above the A-type subduction zone of the Rockies, from which they were separated by a major zone of weakness at the surface of the subduction zone.