Abstract

A plate-tectonic model relates the genesis of Upper Cretaceous-to-Tertiary porphyry-type deposits to the evolution of the western and central Canadian Cordillera. Existence of two Benioff zones is assumed from definition of two distinct younging trends of intrusive centers. The first Benioff zone, initiated west of the Queen Charlotte Islands near the Middle Triassic, continued activity until the early Tertiary, when 50 m.y.-old granitic rocks and associated porphyry deposits near the eastern boundary of the Coast Crystalline Belt were formed. The second Benioff zone, initiated near the earliest Cretaceous, extended under the western margin of the North America plate and produced intrusive stocks and associated porphyry deposits that become younger from west to east across the Intermontane Belt. Intrusive activity associated with both Benioff zones ceased at about the same time, 50 m.y. ago, implying that the Benioff zones became imbricated. As a result, the North America plate overrode the Insular plate. Doubling of these plates is reflected in the late Mesozoic and Tertiary uplift and erosion of the Coast Crystalline Belt.

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