All available Jurassic, Triassic, and late Paleozoic paleomagnetic poles from the Colorado Plateau and stable North America are used to estimate the rotation of the Colorado Plateau relative to stable North America since Jurassic time. The paleomagnetic poles differ from those of our prior study [Bryan and Gordon, 1986] through the addition of seven recently published poles, the deletion of one pole, and the replacement of two others. We also improve on our prior analysis by omitting Cretaceous poles. From the systematic offset between plateau poles and stable North American poles we estimate rotation of the Colorado Plateau to be (95% confidence limits) clockwise, ∼1° larger than we found before. The null hypothesis of no systematic difference between plateau poles and stable North American poles can be rejected with a formally high level of confidence (99.99%). The hypothesis that the systematic differences between plateau and off‐plateau poles is as large as 10°, as proposed by several workers using fewer poles, can be rejected at an equally high level of confidence.

Hamilton (1981) has proposed that the Colorado Plateau has rotated clockwise relative to eratonic North America by a total of 5o-7 ø 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 37øN, 103øW, we applied this method to North American paleomagnetic data of Carboniferous to Cretaceous age. The best paleomagnetic estimate of the rotation is 3.9 ø clockwise (with a 95% confidence interval of 1.4ø-6.6 ø 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 ø eastward shift of the cusp connecting the Carboniferous-Permian-Triassic and Jurassic-Cretaceous tracks.

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In prior studies paleomagnetic data have been used to determine ancient minimum velocities of the continents. The greatest minimum velocities, ∼50 km/m.y., exceed the present‐day absolute velocities of the major continents. This result is important because the observation that present‐day oceanic plates move faster than present‐day continental plates can be treated as a major constraint on plate dynamics. However, these prior studies are limited because they ignore known errors in the paleomagnetic data. In this paper we present a technique for incorporating these errors and using them to estimate 95% confidence limits on the minimum velocities. This new technique was applied to Pennsylvanian to Cretaceous paleomagnetic data from North America and to the ancient geometry of Laurasia. When errors are considered, minimum velocities are 10 to 50 km/m.y. lower than when errors are ignored. Additional uncertainties owing to a hypothesized clockwise rotation of the Colorado Plateau, a source of many of the data, are considered and found to alter the minimum velocities only negligibly. Allowing for uncertainties in the pole positions, uncertainties in ages, and the uncertainty due to possible rotation of the Colorado plateau, we estimate that Laurasia moved at least 48 km/m.y. from Early Jurassic to Early Cretaceous time, and at least 43 km/m.y. from Pennsylvanian through Late Triassic time. There is only a 5% risk that the true minimum velocities are lower than these lower bounds. These velocities are less than the peak velocities over short intervals found in prior analyses, but exceed the average velocities previously found for Triassic and Jurassic time. These newly estimated velocities are still much higher than the present velocities of the continents and, as in the prior studies, imply that the slow motion characteristic of major continents at present is not a fundamental attribute of plate motions.