HR: 0800h
AN: G11A-0773    [Abstracts]
TI: Cosmogenic Be-10 ages of Angel Lake and Lamoille moraines and late Pleistocene slip rate of the rangefront normal fault, Ruby Mountains, Basin and Range, Nevada
AU: * Briggs, R W
EM: briggs@seismo.unr.edu
AF: Center for Neotectonic Studies, University of Nevada, Reno, MS 169, Reno, NV 89557 United States
AU: Wesnousky, S G
EM: stevew@seismo.unr.edu
AF: Center for Neotectonic Studies, University of Nevada, Reno, MS 169, Reno, NV 89557 United States
AU: Ryerson, F J
EM: ryerson1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550
AU: Finkel, R C
EM: finkel@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550
AU: Meriaux, A
EM: meriaux@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550
AB: We use Be-10 cosmogenic radionuclide (CRN) exposure dating to quantify the timing of late Pleistocene glacial advances and to estimate the rangefront normal fault slip rate along the Ruby Mountains in the Basin and Range, Nevada. Ten Be-10 CRN exposure ages from the Angel Lake terminal moraine in Hennen Canyon limit deposition to between 15.4-23.1 ka (average = 18.2 ka; SD = 2.5 ka), an interval that overlaps with the Tioga glacial advances in the Sierra Nevada and Pinedale advances in the Rocky Mountains during MIS-2. The termination of the Angel Lake glaciation at ~15.4 ka is nearly synchronous with the final highstand and subsequent rapid desiccation of Lake Lahontan. Previous relative age dating studies in the Ruby Mountains have inferred deposition of Lamoille moraines during MIS-4 (~59-74 ka) or MIS-6 (~130-190 ka). However, fifteen Be-10 CRN exposure dates obtained from a Lamoille lateral moraine in Hennen Canyon (average = 30.7 ka; SD = 11.5; range = 19.3-66.5 ka) do not support these assignments and instead suggest that the moraine may have been deposited during MIS-3. Assuming the average Be-10 model age from the Lamoille surface represents a minimum age constraint, we obtain a maximum fault slip rate of 0.40-0.60 mm/year for a $60\deg$ dipping fault and 11-16 m of vertical separation across faulted Lamoille moraines. Accommodation of 0.4-0.6 mm/year of slip by the Ruby Mountains fault zone implies an average 0.2-0.3 mm/year of horizontal strain accumulation across the fault during the last ~31 ka, and thus characterization of the central Basin and Range as a geodetic microplate may be at odds with late Pleistocene horizontal displacement rates along the Ruby Mountains fault zone. If correct, the observed disparity between the CRN exposure dates and geologic correlations underscores the importance of quantitative age constraints for climate reconstruction, landscape evolution, and tectonic geomorphology.
DE: 8199 General or miscellaneous
DE: 8107 Continental neotectonics
DE: 8109 Continental tectonics--extensional (0905)
DE: 1208 Crustal movements--intraplate (8110)
DE: 1299 General or miscellaneous
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting