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Timing and rates of Holocene normal faulting along the Black Mountains fault zone, Death Valley, USA

Alluvial fans displaced by normal faults of the Black Mountains fault zone at Badwater and Mormon Point in Death Valley were mapped, surveyed, and dated using optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) methods. Applying TCN methods to Holocene geomorphic surfaces in Death Valley is challenging because sediment flux is slow and complex. However, OSL dating produces consistent surface ages, yielding ages for a regionally recognized surface (Qg3a) of 4.5 ± 1.2 ka at Badwater and 7.0 ± 1.0 ka at Mormon Point. Holocene faults offsetting Qg3a yield horizontal slip rates directed toward 323° of 0.8 +0.3/–0.2 mm/yr and 1.0 ± 0.2 mm/yr for Badwater and Mormon Point, respectively. These slip rates are slower than the ~2 mm/yr dextral slip rate of the southern end of the northern Death Valley fault zone and are half as fast as NNW-oriented horizontal rates documented for the Panamint Valley fault zone. This indicates that additional strain is transferred southwestward from northern Death Valley and Black Mountains fault zones onto the oblique-normal dextral faults of the Panamint Valley fault zone, which is consistent with published geodetic modeling showing that current opening rates of central Death Valley along the Black Mountains fault zone are about three times slower than for Panamint Valley. This suggests that less than half of the geodetically determined ~9–12 mm/yr of right-lateral shear across the region at the latitude of central Death Valley is accommodated by slip on well-defined faultsand that distributed deformational processes take up the remainder of this slip transferred between the major faults north of the Garlock fault.

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