Abstract

The western part of the North American Cordillera has been divided into numerous suspect terranes. Some of these terranes have traveled hundreds to thousands of kilometres between the time of their formation and their final incorporation into the accretionary belt of the Cordillera. Most of the terranes appear to be relics of island arcs, oceanic plateaus and islands, continental margin fragments, and complex accretionary terranes, the latter including melange belts, ophiolite fragments, and thrust-faulted forearc provinces. Because the terranes have complex histories and diverse stratigraphies, it has been difficult to envisage an actualistic setting for the Mesozoic Cordillera. Here we propose an analogy with the tectonic setting of the Indo-Pacific region, from the Tonga trench on the east to eastern Indonesia on the west. This region comprises several distinct island arcs, several large oceanic plateaus, numerous accretionary terranes, melange zones, ophiolite fragments, and a variety of continental fragments, all moving toward the central collision zone. Like the Cordillera, this part of the Indo-Pacific region is undergoing oblique convergence, driven by relatively high rates of movement between the oceanic plates and the collision zone. Also analogous to the Cordillera is the formation of a foreland fold and thrust belt, developing between the collision zone and the Australian continent, and a zone of basement-rooted foreland folds, suggestive of an early Laramide style of deformation.

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