NONPLANE EXTENSIONAL STRAIN DURING SLIP ON THE WASSUK RANGE FAULT ZONE, CENTRAL WALKER LANE, WEST-CENTRAL NEVADA

The Wassuk fault-system (WFS) in west-central Nevada records a late Neogene to Holocene history of nonplane strain produced by the interaction of a west-northwesterly directed displacement field and complex fault geometry. The WFS is ~100 km long and is localized along and the geometry strongly influenced by a late Mesozoic crustal boundary that controlled deformation kinematics of the region since inception. The WSF is composed of two sectors with different geometry and kinematics. In the north, the Wassuk Range is characterized by elongated, northwest-trending fault blocks whereas in the south the fault-block dimensions are more equant. The northern sector contains three blocks with cuspate east-facing range-front faults separated by right-lateral faults that branch from the eastern range-front and cross the mountains to the northwest. At their eastern terminations, the northwest-striking transcurrent faults merge with a system of northerly striking range-front faults dominated by dip- to right-oblique displacement and a concavity facing the adjacent basin along the eastern flank of the mountain chain. In the southern sector, the range-front fault system is markedly curvilinear with two, kilometer-scale convex undulations facing the basin to the east. At the ends of the convex cusps, the range-front faults are linked to east-northeast striking left-oblique faults that cross the mountain range to the southwest with moderate to subdued physiographic expression. In the southern sector, the range-front faults are characterized by dip-slip and left- and right-oblique-slip kinematics as the fault orientation changes along strike. For the entire Wassuk fault system, the azimuth of the extension direction determined from fault-slip inversion varies slightly from west-northwest to east-northeast and is consistent with the contemporary GNSS displacement field. In both sectors of the fault system, a secondary, north-northeast trending extension direction is developed and, based on superposition relations between fault-plane slickenlines, formed contemporaneously with the primary extension direct. The two directions of broadly contemporaneous extension on the faults records nonplane strain (flattening) imposed by the interaction of the displacement field and curved fault geometry.