Paleomagnetism of three upper Jurassic ash-flow sheets in southeastern Arizona: Implications for regional deformation

A sequence of three petrologically distinct Upper Jurassic ash-flow tuffs has been sampled for paleomagnetic analysis in the Huachuca Mountains, Canelo Hills, and Mustang Mountains of southeastern Arizona. Site-mean paleomagnetic directions for these units indicate significant vertical-axis rotations between sampling localities (≃15°–40°), and a comparison of these and previously published data with reference directions from the Colorado Plateau implies that the Jurassic rocks in southeastern Arizona have been rotated in a clockwise sense with respect to stable North America. These new data are consistent with paleomagnetic results showing clockwise rotation of Upper Cretaceous rocks in south central Arizona, and further indicate that studies of North American apparent polar wander based on rocks from southern Arizona could be subject to error. The clockwise rotations in southern Arizona are likely related to Late Cretaceous and early Tertiary strike-slip movement on northwest-trending high-angle faults in the region, and this movement may be linked to an increase in oblique Farallon-North American plate convergence at that time.