Abstract

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° ± 7.7° 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 using the observed amount of cumulative left slip on the east-west–trending faults of the eastern Transverse Ranges (∼50 km) and the spacing between the Pinto Mountain and Salton Creek faults which bound the region (∼70 km) indicates that ∼35° 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.

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