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Abstract

The geomorphic development of the Canadian Cordillera is here considered as starting from Middle or Late Jurassic time when ancestral North America collided with the Intermontane Superterrane along its western margin. This, and a similar event later in the Mesozoic, produced two metamorphic and plutonic complexes, each of which are loci of high-grade metamorphism, rapid uplift, and vigorous erosion. These complexes, the Omineca Belt in the east and the Coast Belt to the west, constitute two of the five morphogeological belts in the Cordillera.

Development of the Foreland Belt was an additional outcome of plate collision. With the growth of this belt in mid-Mesozoic to earliest Cenozoic time, a trellis drainage pattern developed, simulating that in the present Cordillera. Individual river courses of that time, however, bear little or no relationship to present drainage. The early erosion-products, together with material from the Omineca Belt to the west, contributed to an almost continuous apron of alluvial fans and associated deltaic deposits in the foredeep, east of the rising orogen.

Widespread Early Cretaceous pediplanation, recorded by pre-Hauterivian to Albian erosion surfaces, coincided with a lull in magmatic activity throughout the Cordillera. Contemporaneous uplift and volcanism in the western Cordillera provided sources for rapid degradation and alluvial sedimentation in and adjacent to contemporaneous narrow seaways.

Although transcurrent faulting and arc (Andean?) magmatism prevailed in part of the western Cordillera erosional and depositional activity west of the Foreland Belt subsided in Late Cretaceous and Paleocene time only to become vigorously rejuvenated in Early

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