Early Pleistocene initiation of the San Felipe fault zone, SW Salton Trough, during reorganization of the San Andreas fault system

摘要: Structural and stratigraphic analyses along the western margin of Salton Trough show that San Andreas fault system was reorganized in early Pleistocene time from a dominated by two zones (the West detachment fault) to network dextral faults include at least four southwest. The Felipe zone, one these faults, has ~5.8 ± 2.8 km right separation consists three principal Peninsular Ranges. These are WNW, Sunset middle, Fish Creek Mountains ESE. They form left-stepping array bound domains which Conglomerate, older fault, Cretaceous mylonitic rocks below folded about WNW-trending folds. A complex flower structure within left-stepovers probably produced this fault-parallel folding. Because all stepovers Pleistocene, deformed folds record broadly similar shortening strains, we infer Quaternary age deformation. Parts zone cut latest Holocene surficial deposits, is likely active. Evidence for initiation preserved conglomerate NE fault. Poorly sorted angular boulder pebbly sandstone Conglomerate ~600 m thick lie unconformity on Pliocene Palm Spring Group. coarsens upward toward plutonic clasts derived SW it. beds contain up 10% recycled basin fill accumulated proximal medial alluvial fans were shed uplifted then-active Based lithologic, stratigraphic, structural, compositional similarities, correlate Ocotillo Formation. Clasts erosion detachment-related predates once covered Vallecito mountains. crystalline-cored mountain ranges first emerged beneath during slip above nascent ca. 1.1–1.3 Ma. Later, upward, folded, across, deactivated ~9-km-wide contractional bend pair left-steps. Areas sediment step-over between 1.1 0.6 Ma currently being inverted folded. Initiation significant event reorganization southern system. broadened plate boundary south-westward roughly 25 (during coeval 50–70 km, mark change dominant structural style transtension distributed faulting south Big Bend.