Paleomagnetism of Jurassic and Cretaceous plutonic rocks in the Sierra Nevada, California, and its significance for polar wandering and continental drift

Directions of natural remanent magnetization (NRM) have been determined at thirteen sites in two intrusive igneous bodies in the western Sierra Nevada, California. Late Jurassic to Early Cretaceous potassium-argon ages of these rocks are: Guadalupe Mountains igneous complex, 136 m.y., and diorite of the Bucks batholith, 142 to 129 m.y. Normal and reversed NRM directions are found in both plutons. The mean paleomagnetic pole position corresponding to mean NRM directions at all sites after ac demagnetization is at 54°N 174°W, and the radius of the 95% confidence circle is 9.5°. This pole position is not significantly different from five previously published poles from widely separated North American rocks that range in age from 124 to 84 m.y. Such concordance strongly favors the geocentric dipolar configuration of the earth's magnetic field and further indicates that from about 138 to about 84 m.y ago polar wandering relative to North America did not occur. Comparison with similar paleomagnetic data from Australia and Africa suggests that apparent polar wandering during Mesozoic time was entirely due to continental drift and not to true polar wandering as an independent process.