Progressive Strain Reorganization in Late Neogene Structural Stepovers, Central Walker Lane, Western Great Basin

Late Neogene deformation within the northern Eastern California Shear Zone (ECSZ) and central Walker Lane (WL) records a major geometric and kinematic reorganization in the mid-Pliocene. East of the central Sierra Nevada, the ECSZ and WL are misaligned and since mid-Miocene (ca. 12-8 Ma) were linked by extensional stepovers. Mid-Miocene to mid-Pliocene displacement transfer was accommodated by the Silver Peak – Lone Mountain (SPLM) extensional complex that passed motion from the NNW-trending Furnace Creek fault system of the ECSZ to NW-trending transcurrent faults of the central WL. The SPLM was underlain by a NW-dipping detachment bound on the west and east by transcurrent structures. The southern margin of the SPLM exposes a NW-dipping breakaway fault and to the north, an EW trending belt of extensional basins that separated the extensional complex from structurally coherent tectonic blocks in the central WL. Paleomagnetic data from Cenozoic volcanic rocks and Mesozoic intrusions exposed in the upper plate of the extensional complex and sets of Miocene mafic dikes in the lower plate show uniform clockwise vertical-axis rotation of 20-30° not found elsewhere in the central WL (e.g., Excelsior Mountains and farther north). Large-magnitude extension and vertical-axis rotation was localized within the stepover during vertical thinning and horizontal components of simple- and pure-shear extension along a NW axis. This nonplane stain continued until the SPLM was abandoned at ~3 Ma and was followed by the development of a broadened stepover, the Mina deflection (MD), showing transtensional kinematics of the contemporary deformation field. The MD exposes an array of ENE faults with left-oblique slip that cross-cut the SPLM. Geodetic velocities, focal mechanisms, and fault kinematic data reflect active transtensional deformation that is heterogeneously distributed, with the western and eastern parts of the boundary zone experiencing wrench-dominated and extension-dominated transtension, respectively.