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Abstract

Paleomagnetic studies in the Canadian Cordillera began in the late 1950s. During the past two decades efforts to determine displacements and rotations have concentrated largely on the terranes of the Intermontane and Insular belts, and, to a lesser extent, on Proterozoic and Cretaceous strata of the Foreland Belt.

Results obtained from Neogene rocks confirm the average dipolar nature of the ancient geomagnetic field and indicate that since the mid-Tertiary, except for the Queen Charlotte Islands, no paleomagnetically detectable tilting, rotations or horizontal motions relative to the craton haveoccurred throughout most of the Cordillera. Paleogene rocks commonly show significant rotations but no detectable latitudinal displacements.

Cretaceous paleopoles from the western Cordillera mostly are clustered in the North Atlantic whereas those from the craton occur northwest of Alaska. Many paleopoles have been determined from well-dated older rocks in the accreted terranes, all from overprints of probable mid- Cretaceous age. These data, when applied to Pacific plate motion reconstructions, suggest that the Intermontane and Insular superterranes may have been one coherent crustalfragment ("Baja British Columbia") by mid-Cretaceous time and located along the eastern edge of the Kula Plate some 2000 km south of its present position. Northward motion between mid-Cretaceous and Eocene time, together with clockwise rotation, terminated with the accretion of BajaBritish Columbia to ancestral North America when the Kula Plate ceased to exist as a separate plate and when the approximate position of the present Pacific-America plate boundary was established. Results from Cretaceous rocks of the Foreland

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