THE LATE NEOGENE DEFORMATION HISTORY OF THE SOUTH BRISTOL MOUNTAINS FAULT ZONE

The Southern Bristol mountains lie near the eastern border of the Mojave block and eastern California shear zone. The rock units composing the range are dissected by at least two generations of faults: early Miocene normal faults associated with early Miocene volcanism and sedimentation, and high angle northwest striking faults of the South Bristol Mountains fault (SBMF), including fault splays that cut Quaternary units. Total offset on the SBMF is estimated to be at least 6 km based on correlation of plutonic rocks across the fault zone. The range is composed of remnants of Proterozoic plutons, metamorphosed Paleozoic passive margin rocks, Jurassic hypabyssal and plutonic rocks, and. Neogene volcanic and sedimentary sequences.The onset of early Miocene volcanism and sedimentation in the Southern Bristol mountains predates a newly dated ash with a U-Pb zircon age of 23.8 ± 0.4 Ma (1 sigma) overlying rhythmic fluvial to lacustrine volcaniclastic beds. The early Miocene lake bed sequence and subsequent volcanic and sedimentary sequences have been dismembered by Neogene and Quaternary faulting. Detailed mapping of the Neogene sedimentary and volcanic rocks should allow us to produce a more detailed total slip budget for the Quaternary strike slip faulting.