Mesozoic deformation in the Nevada Test Site and vicinity: Implications for the structural framework of the Cordilleran Fold and thrust belt and tertiary extension north of Las Vegas Valley

Abstract

Detailed studies in the CP Hills and Mine Mountain area of the Nevada Test Site (NTS), together with analysis of published maps and cross sections and a reconnaissance of regional structural relations, indicate that the CP thrust of Barnes and Poole [ 1968] actually comprises two separate, oppositely verging Mesozoic thrust systems: (1) the west vergent CP thrust, which is well exposed in the CP Hills and at Mine Mountain, and (2) the east vergent Belted Range thrust located northwest of Yucca Flat. Regional structural relations indicate that the CP thrust forms part of a narrow sigmoidal belt of west vergent folding and thrusting traceable for over 180 km along strike. The Belted Range thrust represents earlier Mesozoic deformation that was probably related to the Last Chance thrust system in southeastern California, as suggested by earlier workers. A reconstruction of the pre-Tertiary geometry of the Cordilleran fold and thrust belt in the region between the NTS and the Las Vegas Range bears a close resemblance to other regions of the Cordillera and suggests that west vergent deformation developed in the hinterland of a part of the Sevier fold and thrust belt characterized by substantial structural relief. Reconstruction of the fold and thrust belt also suggests that previous estimates of upper crustal Tertiary extension north of the Las Vegas Valley shear zone (e.g., 80% [Guth, 1981]) are 2 or 3 times too large. INTRODUCTION The Nevada Test Site (NTS) (Figure 1) of the southern Great Basin lies within the dominantly east vergent Mesozoic Cordilleran thrust belt near one of the thickest known parts of the Paleozoic Cordilleran miogeocline. In this region, Barnes and Poole [1968] and Hinrichs [ 1968] interpreted several thrust faults that place upper Precambrian and lower Paleozoic rocks over upper Paleozoic rocks as remnants of a single, regional, east to southeast vergent thrust system. They named this thrust system the CP thrust Paper number 92TC00456, 027 8-7407/92/92TC-00456510.00 for exposures in the CP Hills, south of Yucca Flat (Figure 1). Subsequent work on the Mesozoic structure in the region has been hampered by the general inaccessibility of the NTS and surrounding regions. Later discussions of the regional structural setting of the NTS and vicinity [e.g. Cart, 1984; Wemicke et al., 1988a,b] have therefore relied on these earlier interpretations. Our derailed studies in the CP Hills and Mine Mountain area (Figure 1), together with published maps and cross sections by Orkild [ 1968] and McKeown et al. [ 1976] and a reconnaissance of regional structural relations, indicate that the CP thrust of Barnes and Poole [1968] actually comprises parts of two separate, oppositely verging thrust systems:(1) the west vergent CP thrust, which is well exposed in the CP Hills and at Mine Mountain (Figures 1 and 4), and (2) the southeast vergent Belted Range thrust, located northwest of Yucca Flat (Figure 1). Herein, we redefine the CP thrust of Barnes and Poole [ 1968](1968) and suggest a revision of nomenclature for...

Nevada Test Site Environmental Report 2005, Attachment A - Site Description

“…In several places along the western and southern portions of Yucca Flat, east-vergent structures related to the Belted Range thrust were deformed by younger west-vergent structural activity (Cole and Cashman, 1999). This west-vergent deformation is related to the CP thrust fault which also placed Cambrian and Ordovician rocks over Mississippian and Pennsylvanian-age rocks beneath western Yucca Flat (Caskey and Schweickert, 1992).…”

A Hydrostratigraphic Model and Alternatives for the Groundwater Flow and Contaminant Transport Model of Corrective Action Unit 97: Yucca Flat-Climax Mine, Lincoln and Nye Counties, Nevada

“…The Paleozoic rocks show contractional deformation most likely related to both east-and west-directed thrusting during the Mesozoic (e.g., Belted Range and CP thrust faults). However, contractional deformation has been overprinted by extensive extensional deformation related to basin-and-range extension during the late Cenozoic (Caskey and Schweickert, 1992;. During the middle Late Cretaceous, granitic bodies (including the Climax stock in northern Yucca Flat) intruded these deformed rocks (Maldonado, 1977;Houser and Poole, 1960).…”

Natural Resources Assessment

“…Identification of these sites requires a paleogeologic interpretation to filter structural noise of subsequent tectonism. The work of Trexler, J.H., Jr. et al (1996, p. 1756, Caskey andSchwieckert (1992, p. 1318), and Snow (1992, Figure 1 l), shows that source rocks of the Eleana Formation could have been buried in this manner by the Belted Range Thrust fault in an arcuate belt fkom the area of the Eleana Range south and west through the Yucca Mountain natural resources site study area to the vicinity of Bare Mountain. Some of the petroleum generated during this episode would have migrated into structural traps in the upper plate of the thrust fault that evolved during emplacement.…”

“…The Paleozoic strata of the Yucca Mountain natural resources site study area also have been deformed by late Paleozoic to Mesozoic tectonism (Caskey andSchweickert 1992, p. 1314). Most of the compressional structure is associated with the Sevier orogeny, but some thrust faults and folds are older and may be products of Permian-Triassic compression (Snow 1992, pp.…”