LATE MIOCENE STRAIN TRANSFER AND CORE-COMPLEX FORMATION IN THE SILVER PEAK-LONE MOUNTAIN EXTENSIONAL COMPLEX IN THE CENTRAL WALKER LANE, NEVADA

In the late Miocene and early Pliocene, strike-slip displacement in the northern part of the Eastern California Shear Zone (ECSZ) was concentrated on the Furnace Creek fault system and was coeval with displacement on northwest-trending transcurrent faults in the Central Walker Lane (CWL). Displacement transfer from the ECSZ to the CWL was localized within the Silver Peak-Lone Mountain (SPLM) extensional complex. The extensional complex stretches 85 km northeast from the northern end of the Furnace Creek fault and has a northwest-southeast extent of ~100 km, stretching from the Sylvania and Palmetto Ranges in the south to the southern flank of the Excelsior Mountains in the north. The central SPLM consists of a series of northwest-trending turtleback structures exposing lower-plate amphibolite-facies metamorphic tectonites that are separated from structurally overlying low-grade and non-metamorphic upper plate rocks by a folded detachment fault in the Silver Peak Range, Weepah Hills, and Lone Mountain. Upper- and lower-plate assemblages share a common deformation history during the late Cenozoic and contain penetrative structures associated with detachment displacement. Systematic apatite and zircon (U-Th)/He thermochronometry was undertaken to investigate the timing of onset and slip rates along these detachment faults. Samples were collected from the lower-plate of the SPLM along horizontal transects sub-parallel to slip direction in the Silver Peak Range, Weepah Hills, and Lone Mountain. These new zircon and apatite (U-Th)/He age data generally decrease in slip direction and indicate an onset of rapid fault slip and footwall exhumation at ~7-8 Ma. The timing of deformation in the SPLM transfer zone appears to be in good agreement with the initiation of motion along the Furnace Creek fault and the notion that deformation in parts of the central Walker Lane changed from east-west extension to right-lateral strike-slip displacement at ~8 Ma; at a time corresponding to a change in relative motion between the Pacific and North American plates.