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Abstract

The geological architecture of the Cordilleran Orogen in Canada is the product of a long-lived evolution through a variety of tectonic processes acting upon and adjacent to the ancient continental margin. From its rift inception during the Middle Proterozoic until the present, the continental margin discontinuously moved oceanward through sediment progradation and as a result of convergence and transform-related processes involving the accretion of island arc and oceanic assemblages of distant and disparate origin. Throughout much of this time (1.44 Ga), the miogeocline of ancestral western North America evolved in a passive margin setting. One or more Precambrian folding events, accompanied by low-grade regional metamorphism, occurred in the northern and southern parts of the Cordillera but their timing and extent are poorly documented. Following Late Proterozoic to Early Cambrian rifting, broad carbonate platforms developed on a westerly sloping shelf, the edge of which was irregularly indented by numerous embayments and basins which received terrigenous clastics from the craton and intra-platform ridges and shoals. Local, episodic volcanism and graben development reflect rifting in the outer part of the miogeocline in early Paleozoic time. The northern part of the Cordillera was flooded by an Upper Devonian and Mississippian westerly derived clastic wedge succeeded by Mississippian and Pennsylvanian clastics whose source lay to the north, presumably in the Innuitian Orogen. Since the Middle Jurassic Epoch, as a consequence of collision and incorporation of the large exotic superterranes, intense metamorphism, plutonism and uplift took place in the Omineca Belt, and the miogeocline was

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