Abstract

The Stateline fault system is a 200-km-long zone of active right-lateral shear along the California-Nevada border, United States. Recent identification of 30 ± 4 km of dextral offset since 13.1 Ma on the southern segment of the fault requires significant displacement to extend farther south than has been commonly considered in the past. However, major structures exposed where the fault projects to the south reveal predominantly dip-slip extensional faulting, suggesting that displacement is transferred into substantial northwest-oriented extension in eastern Ivanpah Valley. New (U-Th)/He apatite data from Proterozoic orthogneiss in the southern McCullough Range and northern New York Mountains support this model by recording dates as young as 5 ± 1 Ma in the structurally deepest parts of the footwalls to the range-bounding normal faults. This age is distinctly younger than both the ages of regional extension in surrounding areas and the youngest (U-Th)/He apatite dates reported from the immediately adjacent Colorado River extensional corridor. Late Miocene–Pliocene extension in Ivanpah Valley, contemporaneous with that elsewhere in the Eastern California shear zone, provides an independent line of support that the eastern margin of the Eastern California shear zone extends to the California-Nevada border. If this age marks the onset of deformation on the State-line system, then long-term slip rates on the southern segment may be as high as 5 mm/yr, significantly higher than the present-day estimate of 0.9 mm/yr derived from geodetic observations across the northern segment of this fault system.

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