Geochemistry of rock units at the potential repository level,Yucca Mountain,Nevada |
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| Institution: | 1. Laboratoire Magmas et Volcans, Université Blaise Pascal-CNRS, Campus Universitaire des Cézeaux, 63178 Aubière, France;2. Dept. of Petrology and Geochemistry, Complutense University of Madrid, 12 Jose Antonio Novais, 28040 Madrid, Spain;3. NordVulk, Institute of Earth Sciences, University of Iceland, 101 Reykjavik, Iceland;1. Departamento de Química, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil;2. Instituto Nacional de Ciência e Tecnologia do CNPq, INCT de Energia e Ambiente, Universidade Federal da Bahia, 40170-115 Salvador, BA, Brazil;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Key Laboratory of Ocean and Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Institutions of Earth Science, Chinese Academy of Sciences, China;4. Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA;5. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB30ET, UK;6. College of Oceanography, Hohai University, Nanjing 210098, China;1. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;2. School of Earth sciences, Yangtze University, Wuhan 430100, China |
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| Abstract: | The compositional variability of the phenocryst-poor member of the 12.8 Ma Topopah Spring Tuff at the potential repository level was assessed by duplicate analysis of 20 core samples from the cross drift at Yucca Mountain, Nevada. Previous analyses of outcrop and core samples of the Topopah Spring Tuff showed that the phenocryst-poor rhyolite, which includes both lithophysal and nonlithophysal zones, is relatively uniform in composition. Analyses of rock samples from the cross drift, the first from the actual potential repository block, also indicate the chemical homogeneity of this unit excluding localized deposits of vapor-phase minerals and low-temperature calcite and opal in fractures, cavities, and faults. The possible influence of vapor-phase minerals and calcite and opal coatings on rock composition at a scale sufficiently large to incorporate these heterogeneously distributed deposits was evaluated and is considered to be relatively minor. Therefore, the composition of the phenocryst-poor member of the Topopah Spring Tuff is considered to be adequately represented by the analyses of samples from the cross drift. The mean composition as represented by the 10 most abundant oxides in wt.% or g/100 g is: SiO2, 76.29; Al2O3, 12.55; FeO, 0.14; Fe2O3, 0.97; MgO, 0.13; CaO, 0.50; Na2O, 3.52; K2O, 4.83; TiO2, 0.11; and MnO, 0.07. |
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