Cenozoic evolution of the Mojave block of southern California

Abstract

The recorded Cenozoic history of the Mojave Desert region of southern California began in the latest Oligocene, when intense volcanism and tectonism interrupted a long early Tertiary silence. Volcanism commenced across the region in an east-west band ca. 24-22 Ma. Northwest of Barstow, volcanism was accompanied by intense crustal extension and development of a metamorphic core complex. Outside of this relatively restricted area, extension was minor or absent. After extension ceased ca. 18 Ma, volcanism shifted to small-volume eruptions of basalt. Post-extensional deformation has largely been by strike-slip faulting along northwest-striking dextral faults and west-striking sinistral faults, and total dextral slip across the Mojave Desert region since the early Miocene is ϳ45-60 km. Strike-slip deformation has been overprinted locally by intense north-south contraction that is the dominant style of deformation in the western Mojave block.Paleomagnetic data indicate that parts of the Mojave block were rotated clockwise, although the magnitude and timing of this rotation are poorly determined. The best evidence for large (Ͼ45Њ) rotation comes from the area east of Barstow, where large clockwise declination anomalies and Mesozoic and Cenozoic dikes with anomalous strikes may reflect early Miocene clockwise deflection along the Mojave River fault.Volcanism and tectonism in the Mojave block resulted from interactions among the North American, Pacific, and various oceanic plates. Patterns of volcanism and tectonism do not correlate with growth of slab windows beneath the continent, but do correlate with the position of the subducted Mendocino fracture zone. Plate-circuit reconstructions suggest that the driving force for extension was divergence between the Pacific and North American plates along the transform margin that separated the two. This hypothesis accounts for the direction, magnitude, and rate of extension in the Mojave block.

Adaptive ambient noise tomography and its application to the Garlock Fault, southern California

“…These low anomalies are consistent with the sedimentary deposits indicated by the seismic reflection and borehole studies, which showed that the thickness of the sediments is around 9 km (Kilkenny 1951;Goodman & Malin 1992). The Western Mojave also shows low velocities, likely due to the disruption by the historical extension, strike-slip faulting (Glazner et al 2002) and sedimentary deposits.…”

On the formation of sand ramps: A case study from the Mojave Desert

“…Cady Fault and Manix/Afton Canyon Fault; Dokka and Travis, 1990). Hills of the Cady Range directly to the south and east of Soldier Mountain are mainly of similar lithology, interspersed with Tertiary volcanic and sedimentary sequences (Glazner et al, 2002). The sand ramp is located on the western side of Soldier Mountain approximately 0.5 km south of the current Mojave River channel which is assumed to be the single main source of aeolian derived material to the sand ramp.…”

Structural and stratigraphic evolution of the Calico Mountains: Implications for early Miocene extension and Neogene transpression in the central Mojave Desert, California

“…Dokka (1989) argued that regional extension occurred within an eastwest-trending belt across most of the Mojave Desert region. In contrast, Glazner et al (2002) suggested that extension was largely confi ned to an ~25-km-wide area centered around the central Mojave metamorphic core complex. Currently there is no strong consensus on the precise timing of extension in the central Mojave Desert.…”

“…Early Miocene detachment faulting and extensional basin development generally preceded transformdominated tectonics related to the Pacifi c-North American plate boundary, yet the timing, magnitude, and tectonic signifi cance of these disparate modes of deformation remain controversial (see Glazner et al, 2002, for a review).…”