CRUSTAL EXHUMATION IN A TRANSPRESSIONAL SETTING, THE SAN EMIGDIO MOUNTAINS, CALIFORNIA
The (U-Th)/He ages indicate an exhumation rate of ~0.4 mm/yr for the late Miocene and early Pliocene, with continued uplift after ~4 Ma. The proximity of this exhumed section to the San Andreas fault is consistent with previous observations of crustal exhumation along steeply dipping strike-slip faults, including other portions of the San Andreas system (Spotila et al. 1998) and along the San Gregorio-Hosgri fault system (House et al., 2000), but is significantly greater in scale. Apatite (U-Th)/He ages from the Mt. Pinos region, on the opposite side of the San Andreas from the San Emigdio Mountains, yield early to mid-Miocene ages, and thus no evidence of significant crustal exhumation. Rheologic heterogeneities and pre-existing structural fabrics are two potential causes for the localization of such extreme crustal exhumation in this transpressional system.