Quantifying Dextral Shear on the Bristol-Granite Mountains Fault Zone: Successful Geologic Prediction from Kinematic Compatibility of the Eastern California Shear Zone

摘要

For regional kinematic compatibility to be a valid boundary condition for continental tectonic reconstructions, there must be tests that validate or invalidate kinematic model predictions. In several reconstructions of western North America, the displacement history of the Mojave block continues to be unresolved. The magnitude of displacement along the Bristol-Granite mountains fault zone (BGMFZ), which is the eastern margin of the Eastern California Shear Zone (ECSZ) in the Mojave block, is a key example of a long-standing kinematic prediction that has defied a positive field test until now. The ECSZ is a network of late Neogene and Quaternary right-lateral strike-slip faults that extend from the Gulf of California north through the Mojave Desert, linking Pacific-North America plate motion with Basin and Range extension. This network of faults accounts for similar to 15% of post-16-Ma plate transform motion. Geologic estimates of net dextral offset along the Mojave portion of the ECSZ (53 +/- 6 km) are approximately half that measured to the north in the Owens Valley-Death Valley region (similar to 100 +/- 10 km). Previous geological estimates of BGMFZ slip range from 0 to 15 km. Models of right-lateral displacement that are based on kinematic compatibility suggest 21-27 km of BGMFZ displacement. We map and describe a tuff- and gravel-filled paleovalley offset by the BGMFZ. The orientation of the Lost Marble paleovalley is constrained by the position of gravel outcrops, provenance, and tuff anisotropy of magnetic susceptibility. Reconstruction of the paleovalley indicates at least 24 km of post-18.5-Ma dextral offset, confirming a significant, previously undocumented component of dextral slip in the Mojave portion of the ECSZ.