KINEMATIC, STRATIGRAPHIC, AND SEDIMENTOLOGIC EVIDENCE FOR MID-MIOCENE-EARLY PLEISTOCENE TRANSTENSION AND TRANSPRESSION, EAST OF THE EASTERN CALIFORNIA SHEAR ZONE (ECSZ), NE MOJAVE

East of the ECSZ, a 0.5-1km thick sequence of Cenozoic coarse clastic strata (Tc) consisting of polymict conglomerates, breccias, and block glides has not been studied in detail due to poor exposures and Quaternary cover. Minor interbedded volcanic rocks, suggest coarse clastics are mostly mid-late Miocene in age. In the Old Dad Mtn., Seventeenmile Point, and Indian Spring 7.5 Quads, Quaternary downcutting has exposed 5-30 m stratigraphic sections and the contact with basement rocks over a distance of ≈20 km. Tc can be divided into 7 unconformity bounded sequences, Tc1-7, based on composition, flow direction, stratal dip, and stratigraphic position. Tc1-5 and Tc7 are faulted against Proterozoic-Mesozoic basement rocks along the range-bounding Eastern Old Dad shear zone (EODSZ), a 17km long, NW trending, 0.75 km wide zone of high-angle faults consisting of anastomosing 0.1-5m wide zones of breccia and gouge. Kinematic indicators mostly show dextral strike-slip, with local reverse and normal motion. In the south, we interpret a left bend in the EODSZ to have formed a NE-vergent transpressive flower structure in a SW-dipping <100m thick sequence of Tc1-3 and volcanic rocks. In the north, Tc3-5 are 100-300m thick, dip moderately NW, thicken and coarsen upward and westward towards the EODSZ, contain a high percentage of breccias and glide blocks, and are cut by numerous NE-trending normal and sinistral faults. We interpret Tc3-5 to have been deposited in <100sqkm transtensional or extensional basins related to movement on the EODSZ. Tc6, overlies older units with angular unconformity, dips E, and thickens to the SE away from the EODSZ. Within the EODSZ, weakly consolidated Pliocene?-early Pleistocene? conglomerates (Tc7), similar in composition and flow direction to modern drainages, are broadly folded, cut by numerous NE trending fractures, and, locally, dip steeply E. Tc7 is overlain by deeply incised but flat-lying alluvial terraces. Geometry, conglomerate sources, and offset basement units, including a previously unrecognized, mostly pre-Miocene, top-to-the-NE, brittle extensional fault system, the Old Dad Detachment (ODD) that provided basinward dipping slip surfaces for block glides and breccias, suggest 6km of mid-Miocene or younger right lateral offset on the EODSZ.