A Moderate Translation Alternative to the Baja British Columbia Hypothesis

The Baja British Columbia (Baja B.C.) hypothesis derives primarily fro m observed discordant paleomagnetic d i rections of Insular and Interm o n t a n e terranes interpreted to indicate p o s t -m i d -C retaceous northward transport by up to 4000 km with re s p e c t to the continental interior.Recent paleomagnetic results from near Prince Rupert, British Columbia, document that discordant directions in plutonic ro c k s of this area are primarily due to local d e f o rmation rather than transport from a C retaceous location along the southwest m a rgin of North America.Expanded paleomagnetic studies of Cre t a c e o u s rocks at Duke Island and MacColl Ridge, Alaska, have led to much smaller estimates of latitudinal motion for Insular terranes than pre v i o u s l y concluded.Recognition of likely chemical remagnetization of Cre t a c e o u s sequences in the Tyaughton and Methow basins, along with effects of compaction shallowing on marine sediments of the Nanaimo Gro u p , indicate that paleomagnetic data fro m these rocks may not re q u i re the magnitude of northward transport suggested by the Baja B.C. paleogeography.Instead, the paleomagnetic observations are consistent with a Cre t a c e o u s paleogeography that limits post-mid-C retaceous northward motion to ~1000 km.The resulting paleogeography has the appealing feature of an Andean-like, continuous subduction-related magmatic a rc along the Cordilleran margin during C retaceous time.