Geology of the Western Part of Los Alamos National Laboratory (TA-3 to TA-16), Rio Grande Rift, New Mexico

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We present data that elucidate the stratigraphy, geomorphology, and structure in the western part of Los Alamos National Laboratory between Technical Areas 3 and 16 (TA-3 and TA-16). Data include those gathered by geologic mapping of surficial, post-Bandelier Tuff strata, conventional and high-precision geologic mapping and geochemical analysis of cooling units within the Bandelier Tuff, logging of boreholes and a gas pipeline trench, and structural analysis using profiles, cross sections, structure contour maps, and stereographic projections. This work contributes to an improved understanding of the paleoseismic and geomorphic history of the area, which will aid in future seismic hazard evaluations ... continued below

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108 pages

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C.J.Lewis; A.Lavine; S.L.Reneau; J.N.Gardner; R.Channell & C.W.Criswell December 1, 2002.

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Description

We present data that elucidate the stratigraphy, geomorphology, and structure in the western part of Los Alamos National Laboratory between Technical Areas 3 and 16 (TA-3 and TA-16). Data include those gathered by geologic mapping of surficial, post-Bandelier Tuff strata, conventional and high-precision geologic mapping and geochemical analysis of cooling units within the Bandelier Tuff, logging of boreholes and a gas pipeline trench, and structural analysis using profiles, cross sections, structure contour maps, and stereographic projections. This work contributes to an improved understanding of the paleoseismic and geomorphic history of the area, which will aid in future seismic hazard evaluations and other investigations. The study area lies at the base of the main, 120-m (400-ft) high escarpment formed by the Pajarito fault, an active fault of the Rio Grande rift that bounds Los Alamos National Laboratory on the west. Subsidiary fracturing, faulting, and folding associated with the Pajarito fault zone extends at least 1,500 m (5,000 ft) to the east of the main Pajarito fault escarpment. Stratigraphic units in the study area include upper units of the Tshirege Member of the early Pleistocene Bandelier Tuff, early Pleistocene alluvial fan deposits that predate incision of canyons on this part of the Pajarito Plateau, and younger Pleistocene and Holocene alluvium and colluvium that postdate drainage incision. We discriminate four sets of structures in the area between TA-3 and TA-16: (a) north-striking faults and folds that mark the main zone of deformation, including a graben in the central part of the study area; (b) north-northwest-striking fractures and rare faults that bound the eastern side of the principal zone of deformation and may be the surface expression of deep-seated faulting; (c) rare northeast-striking structures near the northern limit of the area associated with the southern end of the Rendija Canyon fault; and (d) several small east-west-striking faults. We consider all structures to be Quaternary in that they postdate the Tshirege Member (1.22 million years old) of the Bandelier Tuff. Older mesa-top alluvial deposits (Qoal), which may have a large age range but are probably in part about 1.13 million years old, are clearly faulted or deformed by many structures. At two localities, younger alluvial units (Qfo and Qfi) appear to be truncated by faults, but field relations are obscure, and we cannot confirm the presence of fault contacts. The youngest known faulting in the study area occurred in Holocene time on a down-to-the-west fault, recently trenched at the site of a new LANL Emergency Operations Center (Reneau et al. 2002).

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108 pages

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OSTI as DE00809576

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  • Other Information: PBD: 1 Dec 2002

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  • Report No.: LA-13960-MS
  • Grant Number: W-7405-ENG-36
  • DOI: 10.2172/809576 | External Link
  • Office of Scientific & Technical Information Report Number: 809576
  • Archival Resource Key: ark:/67531/metadc734407

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  • December 1, 2002

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  • Oct. 18, 2015, 6:40 p.m.

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  • March 21, 2016, 7:12 p.m.

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C.J.Lewis; A.Lavine; S.L.Reneau; J.N.Gardner; R.Channell & C.W.Criswell. Geology of the Western Part of Los Alamos National Laboratory (TA-3 to TA-16), Rio Grande Rift, New Mexico, report, December 1, 2002; New Mexico. (digital.library.unt.edu/ark:/67531/metadc734407/: accessed September 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.