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Understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the Cordilleran margin of North America is prevented by conflicts in paleogeographic models for major terranes, oceanic plates, and the North American margin. We present new paleomagnetic data suggesting that the Blue Mountains superterrane, located at an inboard portion of the Cordilleran margin, has undergone substantial northward translation and clockwise rotation relative to North America since mid-Cretaceous time. Positive baked-contact, conglomerate, and fold tests, provide evidence that the magnetization of these rocks dates from their deposition. These results yield a mean direction of D = 10.8°, I = 58.5°, k = 127, α95 = 4.1°, and N = 11. Comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error. A paleolatitude of 39.2° +4.8°/−4.3°N is obtained, indicating a paleolatitude anomaly of 15.9° ± 4.1° (northward translation of 1760 ± 460 km) and CW rotation of 37° ± 7.3° with respect to North America since circa 93 Ma. Application of an ad hoc 5° inclination error yields translation of 1200 ± 460 km. Through comparison with other units in the western Cordillera we infer that the Mitchell Inlier was located adjacent to the Sierra Nevada arc during mid-Cretaceous time and that the Blue Mountains province may correlate with the Intermontane superterrane in British Columbia. Other interpretations, such as large inclination errors or an independent displacement history for the Mitchell Inlier, are possible but unlikely. More work is needed to fully test these hypotheses and resolve major questions of Cordilleran tectonics.

Publication Title

Journal of Geophysical Research-Solid Earth





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© 2005, American Geophysical Union. View original article at Journal of Geophysical Research-Solid Earth, DOI: 10.1029/2004JB003458.





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