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Structural geology of the proposed site area for a high-level radioactive waste repository, Yucca Mountain, Nevada

Christopher J. Potter, Warren C. Day, Donald S. Sweetkind and Robert P. Dickerson
Structural geology of the proposed site area for a high-level radioactive waste repository, Yucca Mountain, Nevada
Geological Society of America Bulletin (August 2004) 116 (7-8): 858-879

Abstract

Geologic mapping and fracture studies have documented the fundamental patterns of joints and faults in the thick sequence of rhyolite tuffs at Yucca Mountain, Nevada, the proposed site of an underground repository for high-level radioactive waste. The largest structures are north-striking, block-bounding normal faults (with a subordinate left-lateral component) that divide the mountain into numerous 1-4-km-wide panels of gently east-dipping strata. Block-bounding faults, which underwent Quaternary movement as well as earlier Neogene movement, are linked by dominantly northwest-striking relay faults, especially in the more extended southern part of Yucca Mountain. Intrablock faults are commonly short and discontinuous, except those on the more intensely deformed margins of the blocks. Lithologic properties of the local tuff stratigraphy strongly control the mesoscale fracture network, and locally the fracture network has a strong influence on the nature of intrablock faulting. The least faulted part of Yucca Mountain is the north-central part, the site of the proposed repository. Although bounded by complex normal-fault systems, the 4-km-wide central block contains only sparse intrablock faults. Locally intense jointing appears to be strata-bound. The complexity of deformation and the magnitude of extension increase in all directions away from the proposed repository volume, especially in the southern part of the mountain where the intensity of deformation and the amount of vertical-axis rotation increase markedly. Block-bounding faults were active at Yucca Mountain during and after eruption of the 12.8-12.7 Ma Paintbrush Group, and significant motion on these faults postdated the 11.6 Ma Rainier Mesa Tuff. Diminished fault activity continued into Quaternary time. Roughly half of the stratal tilting in the site area occurred after 11.6 Ma, probably synchronous with the main pulse of vertical-axis rotation, which occurred between 11.6 and 11.45 Ma. Studies of sequential formation of tectonic joints, in the context of regional paleo-stress studies, indicate that north- and northwest-striking joint sets formed coevally with the main faulting episode during regional east-northeast-west-southwest extension and that a prominent northeast-striking joint set formed later, probably after 9 Ma. These structural analyses contribute to the understanding of several important issues at Yucca Mountain, including potential hydrologic pathways, seismic hazards, and fault-displacement hazards.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 116
Serial Issue: 7-8
Title: Structural geology of the proposed site area for a high-level radioactive waste repository, Yucca Mountain, Nevada
Affiliation: U. S. Geological Survey, Denver, CO, United States
Pages: 858-879
Published: 200408
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 72
Accession Number: 2004-057844
Categories: Environmental geologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. block diag., sects., 1 table, geol. sketch map
N36°43'60" - N37°00'00", W116°34'60" - W116°25'00"
Secondary Affiliation: S. M. Stoller Corporation, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200417
Program Name: USGSOPNon-USGS publications with USGS authors
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