Tectonic significance of the McCoy Mountains Formation, southeastern California and southwestern Arizona

Poorly preserved fossil wood collected throughout the terrane had been the basis of a Cretaceous age assignment. New age constraints come from paleomagnetic data which fail the fold test at both regional and local levels. These data indicate that the paleomagnetism was produced by a post-folding metamorphic event. The resulting paleomagnetic pole at 58.9°N, 114.6°E falls on the North American apparent polar wander path very near a pole from the Callovian Summerville Formation. These data imply that Callovian is a minimum age for the metamorphism and that the proto1ith is older.