Abstract
The gradual buildup of rare isotopes from interactions between cosmic rays and atoms in an exposed rock provides a new method of directly determining the exposure age of rock surfaces. The cosmogenic nuclide method can also provide constraints on erosion rates and the length of time surface exposure was interrupted by burial. Numerous successful applications of the technique have been imperative to the complete surface geologic characterization of Yucca Mountain, Nevada, a potential high level nuclear waste repository. The 10Be exposure age of Black Cone lava, within a ten mile radius of the proposed repository site, is 840 ±210 kyr (in agreement with previous K/Ar dates of 1.0 ± 0.1 Ma). Rates of erosion of the tuff bedrock (< 0.4 cm/kyr from 7 10Be measurements) and of hillslope colluvium (~ 0.5 cm/kyr from 10Be dates on boulder deposits) preclude denudation of the mountain as a concern. Neotectonic concerns (rate of slip and timing of last significant movement along faults) are also being addressed with in situ 14C and 10Be measurements on scarp surfaces and on fault-dissected landforms where no surficial expression of the fault is preserved.
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Acknowledgments
The studies providing the reported data were sponsored by the Department of Energy’s Yucca Mountain Project In Las Vegas, Nevada. Field work has continued since 1984. We thank A. Murphy, J. Klein, T. Jull, N. Lifton, B. Phillips, P. Sharma, and S. Vogt for analyses or discussions.
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Gosse, J.C., Harrington, C.D. & Whitney, J.W. Applications of in Situ Cosmogenic Nuclides in the Geologic Site Characterization of Yucca Mountain, Nevada. MRS Online Proceedings Library 412, 799–806 (1995). https://doi.org/10.1557/PROC-412-799
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DOI: https://doi.org/10.1557/PROC-412-799