NEOGENE CLOCKWISE TECTONIC ROTATION OF THE EASTERN TRANSVERSE RANGES, CALIFORNIA, SUGGESTED BY PALEOMAGNETIC VECTORS.

Results from a paleomagnetic study of Neogene volcanic rocks situated within and around the Pinto basin region of the eastern Transverse Ranges suggest that the ranges have undergone a clockwise tectonic rotation of 41. 4 degree plus or minus 7. 7 degree since late Miocene time. Both normal and reversed polarities are observed, and inclination data indicate no significant flattening. The rotation was accompanied by progressive sinistral slip on the several east-west-trending faults which bound and transect the eastern Transverse Ranges. A computation indicates that approx. 35 degree of clockwise rotation is required, which roughly agrees with the paleomagnetic data. Removal of the eastern Transverse Ranges rotation in a reconstruction shows that the distributed dextral shear across the Mojave Desert region to the north must have been on the order of 100 km since late Miocene time. From the results of this study, we infer that crustal rotation of the eastern Transverse Ranges began later and is of less magnitude than that of the western Transverse Ranges.