Geology of the Rainier Mesa-Aqueduct Mesa Tunnel Areas-- U12n Tunnel
- US Geological Survey, Denver, CO (United States)
The U12n tunnel area is located beneath Rainier Mesa on the Nevada Test Site, Nye County, Nevada. Stratigraphic units in the U12n area include Precambrian and Cambrian quartzite, Ordovician to Devonian dolomite and limestone, Cretaceous quartz monzonite, 25 Miocene and Pliocene volcanic rock units, and Quaternary colluvium and alluvium. Volcanic rocks in drill holes are classified into two chemical groups, four depositional processes, and four alteration types. Alteration of the volcanic rocks to predominantly zeolites, clay minerals, or silica is related to both stratigraphy and structure. Pre-volcanic structures are the CP thrust fault, a right-lateral fault zone that can be projected into the U12n area, and the Gold Meadows stock; Tertiary structures are depositional folds and predominantly normal faults. The right-lateral fault zone may have provided pre-existing planes of weakness during Tertiary deformation that resulted in west-northwest to northwest normal faults in the U12n area in contrast to north-south to north-northeast faults north and south of the U12n area. Normal faults at tunnel level have displacements that range from less than 3 to 125 ft or more. The Tertiary volcanic rocks were deposited on a pre-Tertiary, steep-sided drainage system and formed depositional folds. The Rainier Mesa depositional syncline is the major structures in the U12n area in addition to the normal faults. Drill-hole data indicate that the axis of syncline in the volcanic rocks parallels the contact between quartzite in the upper plate and dolomite and limestone in the lower plate of the CP thrust fault.
- Research Organization:
- US Geological Survey, Denver, CO (United States)
- Sponsoring Organization:
- Defense Threat Reduction Agency (DTRA); USDOE; USGS
- DOE Contract Number:
- AI08-86NV10583
- OSTI ID:
- 5836355
- Report Number(s):
- USGS-OFR--90-623; ON: TI91010002
- Country of Publication:
- United States
- Language:
- English
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580000* -- Geosciences
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