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All pre-Miocene rocks in the Canadian Cordillera have been regionally metamorphosed. The highest grade rocks, reflecting deep burial and high temperatures, form core zones in the Coast and Omineca belts whereas lower grade rocks, suggestive of burial metamorphism, characterize most of the Insular, Intermontane, and Foreland belts. Regional metamorphism reached its peak in the Omineca Belt in Middle Jurassic time and in the Coast Belt in Late Cretaceous time. Both episodes correlate with periods of intense crustal contraction and thickening and were followed by great and rapid uplift.

Except for metamorphic culminations in the Deserters Range east of the Northern Rocky Mountain Trench and a local area east of the Southern Rocky Mountain Trench most of the regional metamorphism in the Foreland Belt is of low-grade burial type. Precambrian rocks are commonly in greenschist facies, Paleozoic and some Mesozoic strata are mainly in prehnite-pumpellyite facies, and most Mesozoic strata are in zeolite facies. Although there is a general westward increase in coal rank with increasing stratigraphic burial, several east- to northeasttrending belts of anomalous organic maturation parallel present geothermal gradients. These belts may be related to faults in the Precambrian basement.

Rocks in the Omineca Belt received their main metamorphic imprint in Middle Jurassic time, presumably as a result of collision between ancestral North America and the Intermontane Superterrane. Locally, there is evidence for Precambrian metamorphism in the Monashee Complex, pre-Late Mississippian metamorphism in the Kootenay Arc, Late Permian(?) high-pressure and lowtemperature metamorphism in accreted terranes in the southern

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