Chapter 10 Cordilleran Sedimentary Basins of Western Canada Record 180 Million Years of Terrane Accretion

Abstract

Abstract The North American Cordillera is a collage of disparate and commonly far-traveled lithospheric blocks and slivers (terranes). Beginning in the early part of the Jurassic, terranes accreted to the western margin of the North American craton such that the margin has grown several hundred kilometres westward to its present position. Terrane accretion continues today. Jurassic to Recent foreland, forearc, backarc, wrench, and remnant-ocean basins in the Canadian Cordillera, west of the Foreland Belt, record complex relationships between terrane accretion to ancestral North America, and the crust-lithosphere responses (subsidence, uplift, denudation) associated with collision, subduction, rifting, and wrench tectonics. Basin subsidence, driven for example by tectonic loading during terrane collision, may be terminated by accretion of successive terranes and terrane-amalgams (superterranes). The significance of successive accretion events for basin evolution is well illustrated in Bowser Basin where subsidence and sedimentation were associated with the interaction among Stikinia, Quesnellia, and Cache Creek terrane (components of the Intermontane superterrane) and ancestral North America, beginning in the early Middle Jurassic. Crustal shortening across Bowser Basin beginning in the Early Cretaceous, was likely driven by the docking farther west of Insular superterrane. Indeed, it is likely that tectonic loading and accumulation of major clastic wedges in the Western Canada foreland basin in Alberta and British Columbia also were mechanically linked to Intermontane and Insular superterrane accretion. It is generally accepted that most Cordilleran terranes traveled some distance prior to accretion. Some, like Stikinia, essentially traveled alone; others, like the Insular superterrane contained lithospheric blocks that were amalgamated before docking with North America. However, vigorous debate continues concerning the distances and paleolatitudes traversed by each terrane, and to some extent the timing of terrane accretion to the North American plate margin.