MESOZOIC STRUCTURAL LOCALIZATION AND LATE NEOGENE AND HOLOCENE SLIP ALONG THE LOW-ANGLE WASSUK RANGE FRONT FAULT, CENTRAL WALKER LANE, WESTERN-CENTRAL NEVADA

The NNW-trending Wassuk Range of west-central Nevada forms a prominent physiographic boundary separating the NW-striking transcurrent faults of the central Walker Lane from NNW-striking extensional faults that underlie the region stretching west to the eastern Sierra Nevada. The Wassuk Range is bounded to the east by a major range-front fault system over 100 km long that was localized along a Mesozoic transcurrent fault system that separated contractional structures of the Luning-Fencemaker thrust belt from the Sierran arc and western margin of the backarc basin. This ancient crustal boundary localized and controlled subsequent deformation in the region and is reflected in the abrupt termination of large-magnitude Miocene extension and west-side down crustal tilt that the Wassuk Range experienced as part of the Yerington extensional complex. In the Wassuk Range, paleomagnetic analysis of Mesozoic plutonic rocks and mapping of overlying mid- to late Tertiary volcanic and sedimentary deposits indicate that the entire range was tilted up to 70°. In contrast, basement rocks in the Gillis Range, Garfield Hills, and Excelsior Range to the east are not tilted and Mesozoic plutons yield paleomagnetic directions that are similar to expected North America directions. West tilt of the Wassuk Range occurred between 12-4 Ma with the contemporary kinematic regime initiating at ~3 Ma. Today, active scarps with displacements of tens of meters in alluvium mark the eastern range-front fault system. Where dissected by deep canyons, particularly in the northern part of the range, the range-front fault dips to the east at less than 25° and exposes an upper plate of steeply (up to 50°) west-dipping Quaternary gravel cut by east-dipping normal faults that sole into the underlying detachment. Gravity profiles across the active range-front fault system with station spacing of 50 m were made using Scintrex CG5 gravimeters and dual frequency Leica GNSS receivers providing positioning with a vertical resolution of 2.0 cm or better. The gravity data were inverted for depth using GMSYS software and show that faults with Holocene displacement do not off-set the subsurface projection of the detachment. The implication is that the low-angle normal fault system along the Wassuk range front is active.