Paleomagnetism of the Roskruge and Gringo Gulch Volcanics, southeast Arizona

Paleomagnetic data were obtained from nine cooling units of the Late Cretaceous (∼72 Ma) Roskruge Volcanics and from 25 flows in the lower Paleocene Gringo Gulch Volcanics, both from southeastern Arizona. Alternating field demagnetization successfully erased the infrequent secondary components of magnetization. The paleomagnetic pole position obtained from the Roskruge Volcanics is at 73.6°N, 176.0°E with dp = 6.2° and dm = 8.8°. The Gringo Gulch Volcanics pole position is at 77.0°N, 201.0°E with dp = 1.2° and dm = 1.7°. In conjunction with other recently published Paleocene and Eocene paleomagnetic poles, these data provide details of North American apparent polar wander during the Laramide orogeny (∼80 to ∼40 Ma). An episode of rapid apparent polar wander from the Cretaceous pole position in the Bering Strait to the Eocene pole position near the present rotation axis occurred during that interval of time. The initiation of this episode of apparent polar wander appears to be coincident with the major plate reorganizations which occurred at the onset of the Laramide orogeny