Rotation of the Colorado Plateau: An analysis of paleomagnetic data

Abstract

Hamilton (1981) has proposed that the Colorado Plateau has rotated clockwise relative to cratonic North America by a total of 5°–7° since mid‐Cretaceous time. A rotation this small is unresolvable by most paleomagnetic studies. In this paper we present a new method for simultaneously comparing all of the available paleomagnetic data from on and off the plateau in order to estimate rotation of the Colorado Plateau. Our new method examines the effect of various hypothetical plateau rotations on the dispersion of data fit to a smooth model of apparent polar wander. A maximum likelihood criterion is used to estimate the amount of rotation. Confidence limits are found using an F ratio test. Assuming the plateau‐craton Euler pole to be located at 37°N, 103°W, we applied this method to North American paleomagnetic data of Carboniferous to Cretaceous age. The best paleomagnetic estimate of the rotation is 3.9° clockwise (with a 95% confidence interval of 1.4°–6.6° clockwise), in good agreement with geologic estimates of rotation. Because of the dependence of published North American apparent polar wander paths on data from the Colorado Plateau, the existence of such a rotation requires a minor revision in the apparent polar wander path, the largest change being a 3.9° eastward shift of the cusp connecting the Carboniferous‐Permian‐Triassic and Jurassic‐Cretaceous tracks.