Baja British Columbia hypothesis

The Baja British Columbia (Baja B.C.) hypothesis derives primarily from observed discordant paleomagnetic directions of Insular and Intermontane terranes interpreted to indicate post-mid-Cretaceous northward transport by up to 4000 km with respect to the continental interior. Recent paleomagnetic results from near Prince Rupert, British Columbia, document that discordant directions in plutonic rocks of this area are primarily due to local deformation rather than transport from a Cretaceous location along the southwest margin of North America. Expanded paleomagnetic studies of Cretaceous rocks at Duke Island and MacColl Ridge, Alaska, have led to much smaller estimates of latitudinal motion for Insular terranes than previously concluded. Recognition of likely chemical remagnetization of Cretaceous sequences in the Tyaughton and Methow basins, along with effects of compaction shallowing on marine sediments of the Nanaimo Group, indicate that paleomagnetic data from these rocks may not require the magnitude of northward transport suggested by the Baja B.C. paleogeography. Instead, the paleomagnetic observations are consistent with a Cretaceous paleogeography that limits post-mid-Cretaceous northward motion to ∼ 1000 km. The resulting paleogeography has the appealing feature of an Andean-like, continuous subduction-related magmatic arc along the Cordilleran margin during Cretaceous time.