EVIDENCE FOR CONTINUOUS SHORTENING WITHIN THE MOJAVE DESERT, CALIFORNIA: CASE STUDY OF THE NORTHERN RODMAN MOUNTAINS

The Mojave portion of the Eastern California Shear Zone (ECSZ) is best characterized by modern dextral shear occurring along primarily northwest-southeast striking right-lateral faults. In addition to dextral motion, numerous locations within the Mojave ECSZ show evidence for older north-south contraction through folds and unconformities developed in Miocene strata; which have since been truncated by strike-slip faulting. However, questions remain regarding whether north-south contraction still plays a major role in modern deformation of the Mojave ECSZ, and if active thrust faults may be a previously un-recognized earthquake source within the Mojave block. In this case study, I evaluate the relationship between dextral faulting and north-south shortening along the Calico Fault in the northern Rodman Mountains by combining previous studies with new field data and cross-sectional interpretations. Unconformities in Miocene rocks, progressive folding in Plio-Quaternary growth strata, and vertically displaced late Quaternary alluvial fans indicate that shortening has been an on-going phenomena and not isolated to before the onset of dextral shear. Estimates for total north-south shortening along partially blind thrusts range from 1.3- 1.8 km with modern slip rates at 0.1- 0.2 mm/yr. Though late Quaternary thrust slip rates are an order of magnitude less than dextral rates in the region, these rates suggest recognition of blind thrusts as potential earthquake sources in the Mojave Desert.