Deciphering shallow paleomagnetic inclinations: 1. Implications from correlation of Albian volcanic rocks along the Insular/Intermontane Superterrane boundary in the southern Canadian Cordillera

Abstract

Geologic and paleomagnetic data lead to two contradictory hypotheses regarding the paleoposition of the Insular and Intermontane Superterranes that presently constitute the western Canadian Cordillera. Paleomagnetic data from the Insular and Intermontane superterranes suggest a southerly origin coinciding with the latitude of Mexico and the northwest United States, respectively, during the mid‐Cretaceous. Geologic evidence points to a northerly origin for these same tectonic entities during this period; both models cannot be correct. Geologic and paleomagnetic data from the Empire Valley–Churn Creek area in south central British Columbia (51.5°N, 122.5°W) are critical to resolving these contradictory hypotheses. Late Cretaceous rocks correlated to the Insular Superterrane with large paleomagnetic displacements unconformably overlie mid‐Cretaceous rocks correlative to the Spences Bridge Group of the Intermontane Superterrane. We provide paleomagnetic evidence of this correlation based on similar magnetic properties, opaque mineral assemblages, demagnetization behavior, fold test results, mean inclinations, clockwise vertical axes rotations, and statistically indistinguishable paleomagnetic poles and displacement estimates. This correlation and the observed geologic relationships in the Empire Valley–Churn Creek area indicate that the Insular and Intermontane Superterranes were linked by the mid‐Cretaceous. Sites from the two previous Spences Bridge Group studies are combined with their correlatives in the Empire Valley–Churn Creek area to give 81 sites that yield a paleomagnetic pole of 60.5°N, 304.5°E, dp = 3.7°, dm = 5.5° which corresponds to 1050 ± 450 km of displacement from the south. This new displacement estimate suggests that the Spences Bridge arc formed at the latitude of southern Oregon during the mid‐Cretaceous.