Reverse Faulting Within a Continental Plate Boundary Transform System

Contractional deformation is common along transform plate margins where motion oblique to the boundary. While faults that accommodate this are often inferred be subsidiary main boundary fault, we typically lack direct geometric or kinematic information. Here investigate timing of faulting relative changes in orientation North American-Pacific Coeval with development an segment (i.e., “Big Bend” San Andreas fault), active shortening have initiated at ?5 Ma Western Transverse Ranges (WTR). However, new low-temperature thermochronometric data yield Miocene Pleistocene apatite (U-Th-Sm)/He cooling ages and partially reset zircon (U-Th)/He ages. Inverse thermal modeling indicate reverse as early 10 Ma, several million years prior our current understanding Big Bend. Reverse WTR also propagate from west east, toward Fault, rather than outwards it. New existing thermochronometry delineate locus rapid post-Miocene exhumation, demonstrate similar exhumation not present broader region surrounding We posit localized because a weak underlying lithosphere predates more recent anomaly restraining bend margin.