Late Quaternary offset along the sinistral Cady fault within the greater dextral Eastern California Shear Zone, southern California
Abstract
We investigated offsets along the E-W-striking sinistral Cady fault to address the mismatch between geodetically and geologically determined strain rates in the Mojave block of the eastern California shear zone (ECSZ). Although the ECSZ is dominated by NW-striking dextral faults, E-W-striking sinistral faults may act as block boundaries that accommodate some of the inter-shear zone strain and account for why geologically determined strain rates for the broader ECSZ are lower than those geodetically determined. Aeromagnetic data and field mapping of Quaternary deposits indicate that the Cady fault does indeed form a significant structural boundary separating NW-striking faults to the south, such as the dextral Rodman, Pisgah, and Lavic Lake faults, from ENE-striking faults to the north, such as the Manix fault. Both these methods indicate that strands of the Cady fault truncate NW-striking dextral faults and hence sinistral offset in this region is likely younger in age and more dominant kinematically. Oblique sinistral offset rates estimated from field mapping of displaced Quaternary alluvial fan deposits and regional dating through luminescence techniques decrease with older deposit age. Rates estimated from offset late Pleistocene/Holocene deposits are 0.8 mm/yr, whereas minimum rates for middle to early Pleistocene deposits are as low as 0.002 mm/yr assuming the time-averaged fault offset ensued immediately following deposit formation. In contrast, published geodetic rates for collective dextral slip across the entire ECSZ range between 7-14 mm/yr. The observable surface trace of the Cady fault, primarily south-side up, extends for roughly 23 km and is concealed at its western end by young and active eolian deposits south of the Mojave River. Maps derived from aeromagnetic data support the interpretation that the Cady fault extends westward in the subsurface under unfaulted young eolian-dominated deposits for a total estimated length of 32 km, but that its orientation changes to a more WNW strike and may connect with the ENE-striking Manix fault east of the Calico fault. We estimate a total sinistral offset of about 5 km along the Cady fault based upon reconstruction of displaced magnetic anomalies. The aeromagnetic data and field mapping document a larger number and greater length of Cady fault strands than previously recognized and provide offset estimates spanning different timescales ranging from Miocene to late Pleistocene/Holocene aged units.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.G33B0652S
- Keywords:
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- 0925 EXPLORATION GEOPHYSICS / Magnetic and electrical methods;
- 1517 GEOMAGNETISM AND PALEOMAGNETISM / Magnetic anomalies: modeling and interpretation;
- 8107 TECTONOPHYSICS / Continental neotectonics;
- 8175 TECTONOPHYSICS / Tectonics and landscape evolution