Rotation Of the Colorado Plateau: An updated analysis of paleomagnetic poles

Abstract

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.

Paleomagnetism of the Chinle and Kayenta Formations, New Mexico and Arizona

“…In addition, deformational structures north, northeast, and east of the Colorado Plateau suggest that the plateau may have rotated clockwise by 3 O during the Laramide Orogeny and an additional 2' during Rio Grande rifting [Hamilton, 1981;Cordell, 19821. Comparisons of paleomagnetic poles provide further evidence of a small clockwise rotation of the Colorado Plateau since the Late Triassic [Bryan a n d Gordon, 1990;Steiner, 19881. We return to this point in the discussion.…”

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

“…The main advantage of the method is that it finds a best-fit Euler pole and its confidence limit from the weighted misfit of many paleomagnetic poles. Unlike the paleomagnetic Euler pole (PEP) analysis of Bryan and Gordon [ 1990], this method makes no assumption about the shape of the APW path. Similar to PEP analysis, biases in the rotation estimate caused by age differences between on-and oil-plateau poles are less likely because many poles are being used.…”

“…Independent support for the hypothesis of modest and perhaps statistically indeterminate CP clockwise rotation is provided by small westward displacement of paleomagnetic pole positions from strata on the plateau with respect to those obtained from coeval strata on the craton [Steiner, 1988;Bazard and Butler, 1991;Molina Garza et al, 1995;Bryan and Gordon, 1990; Kent and Witte, 1993]. Using a method that simultaneously compares all available paleomagnetic poles from on and off the plateau, but assuming that apparent polar wander (APW) can be fitted by a smooth curve as well as a fixed Euler pole of rotation, Bryan and Gordon [1990] estimated the angle of rotation of the plateau at 5.0 ø (+/-2.3 ø ) in a clockwise sense.…”

“…Using a method that simultaneously compares all available paleomagnetic poles from on and off the plateau, but assuming that apparent polar wander (APW) can be fitted by a smooth curve as well as a fixed Euler pole of rotation, Bryan and Gordon [1990] estimated the angle of rotation of the plateau at 5.0 ø (+/-2.3 ø ) in a clockwise sense. In contrast, direct comparison of coeval poles from on and off the plateau have yielded both larger [Steiner, 1988;Kent and Witte, 1993] and smaller estimates [Bazard and Butler, 1991;Molina Garza et al, 1995].…”

“…In contrast, direct comparison of coeval poles from on and off the plateau have yielded both larger [Steiner, 1988;Kent and Witte, 1993] and smaller estimates [Bazard and Butler, 1991;Molina Garza et al, 1995]. As discussed by Bryan and Gordon [1990], direct pole comparisons may suffer from several difficulties. Uncertainties in the age of the rocks compared and the timing of remanence acquisition are large enough that even slight differences (e.g., 2 m.y.…”