Paper No. 3
Presentation Time: 9:30 AM


CHINN, Logan Daniel, Earth & Space Sciences, University of Washington, Earth and Space Sciences | University of Washington, Johnson Hall, box 351310, Seattle, WA 98105,

New apatite (U-Th)/He and fission-track cooling ages from the eastern terminus of the Garlock fault zone establish exhumation rates and indicate that blind contractional structures are responsible for the whole exhumation of this region since ~10 Ma. The left-lateral Garlock fault zone, a principal strike-slip fault zone of California, terminates to the east in the Avawatz Mountains. A thermochronometric study spanning the Mule Spring branch of the Garlock fault zone, previously thought to have exhumed the Avawatz Mountains with reverse dip-slip motion, reveals late Miocene and Pliocene cooling ages within error in hanging wall and footwall samples from comparable elevations. Thus, there is no evidence of vertical motion on this fault since at least late Miocene time. Instead, cooling ages as young as 6 Ma from Avawatz Peak may relate to an unidentified blind structure (or structures) at depth beneath the mountain front and/or the adjacent bajada. New data indicate regional exhumation rates vary between 0.3-0.6 km/Myr for apatite fission-track closure temperatures between 90-120°C, and between 0.4-1.3 km/Myr for apatite (U-Th)/He closure temperatures between 55-80°C, assuming a geothermal gradient between 20-30°C/km. These data indicate that exhumation occurred at moderate to high and constant rates since at least the late Miocene to present, as field observations indicate recent deformation within the footwall of the Mule Spring fault. An uplifted unconformity capped by stranded and folded alluvial fans is thought to relate to a blind structure beneath the bajada, which may be responsible for the exhumation of the eastern Garlock fault zone since the late Miocene. This study is important because it establishes a previously non-existent exhumational history of the eastern Garlock fault zone, and contributes to our regional understanding of the complex fault interactions of the southern Death Valley area by offering an explanation as to how some of the strain from the clockwise rotation of the Mojave tectonic block can be accommodated by partitioning left-lateral displacement of the Garlock fault zone into the vertical exhumation of the Avawatz Mountains.