Abstract

Three time–space profiles have been constructed using geologic data from British Columbia between 49° N and 56° N. They illustrate variations across the Cordillera, (1) in the stratigraphic and tectonic setting of volcanism, (2) in the age and modal type of granitoids, and (3) in the distribution and types of copper and lead deposits related to volcanic and plutonic rocks. These profiles provide the basis for a plate tectonic synthesis of the Mesozoic–Cenozoic geology, illustrated by six true-scale cross sections.The preferred model has, in the Triassic, two eastward-dipping subduction zones, giving rise to the copper-rich Karmutsen and Nicola–Takla volcanics respectively. After collision of the two volcanic belts by the Early Jurassic, a single eastward-dipping subduction zone remained active until the Eocene. Magmas produced by partial melting and fractionation of subducted lithosphere occurred across the western 300 km of the Cordillera, leading to thickening of the crust, and eventually to anatectic melting to generate large batholiths now containing pendants of volcanics. Jurassic and later geologic and metallogenic events across the eastern 500 km of the Cordillera are the results of an increased heat flux through inhomogeneous crust of varying thickness, comprised of relict ocean floor, continental margin sediments, older volcanics, and ancient cratonic basement. This results in patterns of metamorphism, volcanism, and plutonism which have no simple spatial relationship to the subduction zone.

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