STRUCTURE AND KINEMATIC HISTORY OF THE PALMETTO MOUNTAIN FAULT ZONE, SOUTHWEST NEVADA

The Palmetto Mountain fault zone is part of an active displacement transfer system linking the north-northwest striking, right-oblique Fish Lake Valley fault system in southwest Nevada to right-lateral transcurrent faults in the central Walker Lane. The Palmetto Mountain fault stretches east from the Fish Lake Valley fault for about 60 km and consists of left-oblique, west-northwest striking fault strands that form a belt of structures 2 to 5 km wide. The Palmetto Mountain fault has a cumulative left-lateral displacement of 8 to12 km based on the lateral offset of mid-Paleozoic thrust-faults and Mesozoic granitoids. Displacement on the Palmetto Mountain fault decreases from west to east and is successively transferred northeast via a system of north-northeast striking faults. The north-northeast faults emanate from the eastern half of the Palmetto Mountain fault system and are linked to the west-northwest striking Palmetto Mountain fault zone through curvilinear fault segments. The north-northeast faults are dominated by extensional displacement and control basins filled with late Miocene to Holocene volcanic and sedimentary rocks. A 30 km long segment of the Palmetto Mountain fault exposed along the northern flank of the Palmetto Mountains localized deposition of thick assemblage of mid- to late Miocene andesite and younger tuffaceous sediments and ashflow tuffs. This segment of the fault system records two directions of extension determined by fault-slip inversion. An early history of north-south extension was followed by northwest extension, with the sequential development of extension directions determined by superposed slip-lineations found on both west-northwest and north-northeast striking faults. The timing of the extension-direction reorganization is estimated by the restricted development of north-south slip-directions to volcanic and sedimentary rocks older than 6.0 to 4.0 Ma. Slip-directions associated with northwest extension are found in rocks of all ages and are consistent with contemporary displacements recorded by earthquake focal mechanisms and geodetic velocities.