Abstract

The plutonic evolution of the Canadian Cordillera was continuous from Late Triassic to Miocene time, with periods of climactic plutonism during Middle Jurassic, Upper Cretaceous, and Eocene times. Although plutonism has been recurrent along extensive tracts of the Cordillera, the focus progressively migrated ocean-ward from the Intermontane belt during Late Triassic time to the Insular belt during late Tertiary time. The composition of the plutonic rocks is strongly associated with geologic age. Moore and others' (1963) quartz diorite line reflects predominantly granodioritic plutonism along the central Cordillera during the Jurassic and Cretaceous Periods and reflects quartz dioritic plutonism along the Coast Mountains belt during early Tertiary time. Rb, Sr, Rb/Sr, K/Rb, and initial Sr87/Sr86 values of intrusions suggest origins related to different magmatic sources. Batholiths along the oceanic belts have initial Sr87/Sr86 values similar to continental basalt, chondritic K/Rb and Rb/Sr values, and low Ca/Sr values. Intrusions along epicontinental belts have high initial Sr87/Sr86, Rb/Sr, and low K/Rb values. It is suggested that intrusions along oceanic (eugeosynclinal) belts were generated in a marginal arc-trench framework, whereas those along the epicontinental (miogeosynclinal) belts were generated by anatexis of older continental crust.

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