Mesozoic-Cenozoic deformation in the Canadian Cordillera: The record of a 'Continental Bulldozer'?

A possible Mesozoic-Cenozoic trajectory for the North American craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path, and from westward movement of the craton based on the assumption that Africa has been the least mobile continent geographically since the latest Paleozoic. During each of five time intervals that span 220 million years, the craton trajectory had a different vector. Each vector appears to be reflected in the Canadian Cordillera by the dominant style and orientation of structures formed during that interval. For much of the past ~ 220 million years, the ~meridionally-oriented western margin of the Pangea-Laurasia-North America Plate has been the site of arc magmatism where weak arc/back arc lithosphere, sandwiched between strong ocean-floor and craton lithospheres at times coupled across convergent or transform plate boundaries, focused and recorded strain. When the craton apparently moved due westward, between ~180–160 Ma and ~120–60 Ma, the dominant structures formed then record orogen-normal compression and were accompanied by orogeny. Structures formed during the earlier episode are mainly in the eastern and interior Cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin. In the later episode, compressional structures span the entire Cordillera, which emerged as a tectonic and physiographic entity. Before and between these intervals, when the craton apparently moved mostly northwestward, mainly geological and paleomagnetic considerations indicate some terranes moved southward (sinistrally) relative to the craton. After ~60 Ma, southwestward movement of the craton was concurrent with large northward (dextral) strike-slip faults that disrupted the newly-established ancestral Cordillera. The coincidence between the age of structures that record dominant orogen-normal compression at times when the craton apparently moved due westward, and orogen-parallel displacements when the craton had either northward or southward components of motion, suggests the craton, acting as a “Continental Bulldozer”, was the primary driver of Cordilleran deformation and orogenesis.