LIDAR BASED GEOLOGIC MAPPING AND TERRESTRIAL COSMOGENIC NUCLIDE EXPOSURE DATING TO CHARACTERIZE FAULT SLIP RATES AND THE AGE OF GLACIATION IN THE RUBY MOUNTAINS - EAST HUMBOLDT RANGE, NEVADA

The Ruby Mountains - East Humboldt range in NE Nevada is bound to the west by an 80 km long frontal fault zone expressed as continuous scarps in Quaternary sediments. Many catchments in the range were glaciated during the last two Pleistocene glaciations, known in the Great Basin as the Lamoille (penultimate) and Angel Lake (last) glaciations. Lidar based geologic mapping and ¹⁰Be cosmogenic nuclide exposure dating were used to document the timing of late-Pleistocene glaciation in the range and re-evaluate the late Quaternary slip rate of the fault system. Two distinctly aged glacial outwash surfaces, Qgo1 (younger) and Qgo2 (older), are faulted by the range front fault system with scarps up to 7 m high in Qgo1 and 30 m high in Qgo2. Boulders exposed on the relatively low gradient and well-preserved glacial outwash surfaces are suitable for cosmogenic ¹⁰Be exposure dating. Three faulted surfaces were sampled for exposure dating, two in Qgo2 and one in Qgo1. At the Qgo1 surface a grouping of three exposure ages at ~22-25 ka are thought to represent deposition during the Angel Lake glaciation (LGM). Boulders from the Qgo2 surfaces range from ~24-181 ka; with a preferred grouping of six ages between ~135-181 ka. The preferred grouping suggests that the Lamoille glaciation and associated outwash deposition occurred within Marine Isotope Stage (MIS) 6 time (~190–130 ka). This finding is in line with recently completed exposure ages from boulders in terminal moraines to the south at Lamoille Canyon which also yielded MIS 6 exposure ages. Lidar derived topographic profiles of fault scarps at each of the dated outwash surfaces were used to calculate mean vertical separation values. An average of 5.2 m of vertical separation was measured on scarps in the Qgo1 surface. The two dated Qgo2 surfaces had average vertical separation values of 17.3 m and 23.1 m. Preliminary vertical separation rates, calculated using the preferred ages of the surfaces, range from 0.1 - 0.2 mm/ yr.