Carboniferous through Jurassic paleomagnetic data and their bearing on rotation of the Colorado plateau

Abstract

Small, yet systematic, differences between paleomagnetic poles derived from strata on the Colorado plateau and paleopoles determined from rocks on the North America craton have been interpreted to support the hypothesis of modest post‐Late Cretaceous clockwise rotation of the plateau, as a quasi‐rigid body, with respect to the craton. Using an iterative search for the best fit Euler pole and rotation angle, comparison of the best quality Late Carboniferous through Late Jurassic paleomagnetic poles from the Colorado plateau and the North America craton gives a cumulative rotation estimate (based on a rotation pole at 34°N, 105°W) of 7.4°±3.8° (95% confidence limits). A similar comparison using subsets of the cratonic database from localities in (1) northeast North America and (2) the craton platform interior give larger (8.8°±3.6°) and smaller (5.1°±3.8°) estimates, respectively, reflecting the fact that poles from localities in northeast North America, in particular those from Triassic rift basins, indicate a larger rotation (as concluded in direct pole to pole comparisons). The Euler pole, as determined by the paleomagnetic data only, can lie anywhere within a relatively large area that encompasses locations in the western United States previously proposed from geological observations. Paleomagnetic data and geologic observations, together or independently, do not support the hypothesis of a large Colorado plateau rotation (of 11° to 15°). If geologically reasonable, previous estimates of significant (>∼20 km) dextral slip along the eastern margin of the plateau require a position for the Euler pole east of the 105°W meridian.