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R. Ernest Anderson

Publications and source records attributed to R. Ernest Anderson.

At least 19 recordsLinked to original sources
USGS2013

Analysis of Neogene deformation between Beaver, Utah and Barstow, California: Suggestions for altering the extensional paradigm

For more than two decades, the paradigm of large-magnitude (~250 km), northwest-directed (~N70°W) Neogene extensional lengthening between the Colorado Plateau and Sierra Nevada at the approximate latitude of Las Vegas has remained largely unchallenged, as has the notion that the strain integrates with coeval strains in adjacent regions and with plate-boundary strain. The paradigm depends on poorly constrained interconnectedness of extreme-case lengthening estimated at scattered localities within the region. Here we evaluate the soundness of the inferred strain interconnectedness over an area reaching 600 km southwest from Beaver, Utah, to Barstow, California, and conclude that lengthening is overestimated in most areas and, even if the estimates are valid, lengthening is not interconnected in a way that allows for published versions of province-wide summations. We summarize Neogene strike slip in 13 areas distributed from central Utah to Lake Mead. In general, left-sense shear and associated structures define a broad zone of translation approximately parallel to the eastern boundary of the Basin and Range against the Colorado Plateau, a zone we refer to as the Hingeline shear zone. Areas of steep-axis rotation (ranging to 2500 km 2 ) record N-S shortening rather than unevenly distributed lengthening. In most cases, the rotational shortening and extension-parallel folds and thrusts are coupled to, or absorb, strike slip, thus providing valuable insight into how the discontinuous strike-slip faults are simply parts of a broad zone of continuous strain. The discontinuous nature of strike slip and the complex mixture of extensional, contractional, and steep-axis rotational structures in the Hingeline shear zone are similar to those in the Walker Lane belt in the west part of the Basin and Range, and, together, the two record southward displacement of the central and northern Basin and Range relative to the adjacent Colorado Plateau. Understanding this province-scale coupling is critical to understanding major NS shortening and westerly tectonic escape in the Lake Mead area. One north-elongate uplift in the Hingeline shear zone is a positive flower structure along a strike-slip fault, and we postulate that most other large uplifts are diapiric, resulting from extension-normal inflow of ductile substrate, rather than second-order isostatic responses to tectonic unloading. We also postulate that large steep-axis rotations, and some small ones as well, result from basal tractions imparted by gradients in southerly directed subjacent ductile flow rather than by shear coupling imparted by laterally variable elongation strains. The shortening strain recorded in the rotations and related structures probably matches or exceeds the magnitude of lengthening, even for the Lake Mead area where we do not question local large (~65 km) west-directed lengthening. We assess the results of extensive recent earth-science research in the Lake Mead area and conclude that previously published models of N-S convergence, westerly tectonic rafting, and N-S occlusion are valid and record unique tectonic escape accommodation for south-directed displacement of the Great Basin sector of the Basin and Range. Genetic ties between the south-directed displacement and plate-interaction forces are elusive, and we suggest the displacement results from body forces inherent in the Basin and Range.

Arizona, California, Nevada, Utah↗
USGS2010

Geology of the Lake Mead region: An overview

The Lake Mead region contains major Miocene disruptions of structures formed during Mesozoic tectonic shortening. Erosion by the Colorado River and its tributaries has produced exceptional exposures of diverse structures and basin deposits recording the disruptions. Here we provide an overview of the results of studies of these features that started in earnest in 1934 when Chester Longwell began assessing the geology of the reservoir floor prior to impoundment of Lake Mead. The analysis was reinvigorated in the 1970s and early 1980s with geological mapping and structural and stratigraphic studies by Ernie Anderson and Bob Bohannon, as well as geochemical and volcanological studies by Gene Smith and his students, and has culminated in numerous subsequent studies.

Arizona, Nevada, Utah↗
USGS2010

Geometry and kinematics of the eastern Lake Mead fault system in the Virgin Mountains, Nevada and Arizona

The Lake Mead fault system is a northeast-striking, 130-km-long zone of left-slip in the southeast Great Basin, active from before 16 Ma to Quaternary time. The northeast end of the Lake Mead fault system in the Virgin Mountains of southeast Nevada and northwest Arizona forms a partitioned strain field comprising kinematically linked northeast-striking left-lateral faults, north-striking normal faults, and northwest-striking right-lateral faults. Major faults bound large structural blocks whose internal strain reflects their position within a left step-over of the left-lateral faults. Two north-striking large-displacement normal faults, the Lakeside Mine segment of the South Virgin–White Hills detachment fault and the Piedmont fault, intersect the left step-over from the southwest and northeast, respectively. The left step-over in the Lake Mead fault system therefore corresponds to a right-step in the regional normal fault system. Within the left step-over, displacement transfer between the left-lateral faults and linked normal faults occurs near their junctions, where the left-lateral faults become oblique and normal fault displacement decreases away from the junction. Southward from the center of the step-over in the Virgin Mountains, down-to-the-west normal faults splay northward from left-lateral faults, whereas north and east of the center, down-to-the-east normal faults splay southward from left-lateral faults. Minimum slip is thus in the central part of the left step-over, between east-directed slip to the north and west-directed slip to the south. Attenuation faults parallel or subparallel to bedding cut Lower Paleozoic rocks and are inferred to be early structures that accommodated footwall uplift during the initial stages of extension. Fault-slip data indicate oblique extensional strain within the left step-over in the South Virgin Mountains, manifested as east-west extension; shortening is partitioned between vertical for extension-dominated structural blocks and south-directed for strike-slip faults. Strike-slip faults are oblique to the extension direction due to structural inheritance from NE-striking fabrics in Proterozoic crystalline basement rocks. We hypothesize that (1) during early phases of deformation oblique extension was partitioned to form east-west–extended domains bounded by left-lateral faults of the Lake Mead fault system, from ca. 16 to 14 Ma. (2) Beginning ca. 13 Ma, increased south-directed shortening impinged on the Virgin Mountains and forced uplift, faulting, and overturning along the north and west side of the Virgin Mountains. (3) By ca. 10 Ma, initiation of the younger Hen Spring to Hamblin Bay fault segment of the Lake Mead fault system accommodated westward tectonic escape, and the focus of south-directed shortening transferred to the western Lake Mead region. The shift from early partitioned oblique extension to south-directed shortening may have resulted from initiation of right-lateral shear of the eastern Walker Lane to the west coupled with left-lateral shear along the eastern margin of the Great Basin.

Arizona, Nevada↗
USGS2010

Integration of tectonic, sedimentary, and geohydrologic processes leading to a small-scale extension model for the Mormon Mountains area north of Lake Mead, Lincoln County, Nevada

Scattered remnants of highly diverse stratigraphic sections of Tertiary lacustrine limestone, andesite flows, and 23.8–18.2 Ma regional ash-flow tuffs on the north flank of the Mormon Mountains record previously unrecognized deformation, which we interpret as pre–17 Ma uplift and possibly weak extension on the north flank of a growing dome. Directly to the north of the Mormon dome, 17–14 Ma ash-flow tuffs and rhyolite are interstratified with landslides, debris avalanches, debris flows, and alluvial-fan deposits that accumulated to a thickness of more than 2 km in an extension-parallel basin. The source for the landslides and debris avalanche deposits is unknown, but it was probably an adjacent scarp along a transverse fault bounding an early part of the Mormon dome. An average 45° of easterly tilt of the entire Tertiary basin-fill succession represents the major post–14 Ma deformation event in the region. We question the basis for the published estimate of 22 km of westerly displacement on the Mormon Peak detachment fault and, on the basis of landslides in the upper plate having a probable source in the adjacent Mormon dome, constrain the heave to ~4 km. We interpret the dome and basin as coupled strains similar to others in the region and suggest that these strains reflect a waveform pattern of extension-normal lateral midcrustal ductile flow. Previously, doming was interpreted as an isostatic response to tectonic unloading by large-displacement detachment faults or as pseudo-structural highs stranded by removal of middle crust from adjacent areas. Moreover, we argue that the strong thinning of upper-plate rock successions throughout the Mormon Mountains and Tule Springs Hills resulted from a loss of rock volume by protracted fluid flow, dissolution, and collapse, seriously limiting the usefulness of upper-plate strain in evaluating extension magnitude. We present a geohydrologic model that couples uplift driven by ductile inflow with dissolution driven by fluid infiltration, possibly augmented by mantle-derived CO 2 -rich fluids. Karsting in the uplands led to carbonate sedimentation in adjacent lowlands. Whether or not our downward revision of extension in the Mormon Mountains is valid, extension at that latitude is isolated from extension in the Lake Mead area by a low-strain corridor between the two areas. Recognition of the isolated and potentially diminished strain impacts estimates of maximum finite elongation of the Basin and Range Province because one of three vector paths used in those estimates passes through the Mormon Mountains.

Nevada↗
USGS2010

Fluid flow, solution collapse, and massive dissolution at detachment faults, Mormon Mountains, Nevada

Dissolution has removed large volumes of rock at low-angle normal faults, i.e., detachment faults, in the Mormon Mountains and the Tule Springs Hills in the eastern Basin and Range Province, southeastern Nevada. Evidence for major dissolution includes widespread solution-collapse breccias, meter-scale stylolite structures, and high-angle accommodation faults that terminate at or merge with dissolution seams. Chemically reactive fluids moving along the fault zones led to a strong depletion of 18 O in the detachment fault breccias (e.g., a δ 18 O decrease of 8‰ relative to the unaltered rocks). These strong chemical shifts, demonstrated by (1) negative oxygen isotope values and (2) steep compositional gradients marked by metal enrichment in elements such as Au, Ag, Ti, Pb, Zn, and Cu, are generally restricted to the narrow (<1 m to 8 m) microbreccia zones. Extensional faulting and fracturing, accompanying regional uplift, opened conduits for the influx of meteoric waters from above and hydrothermal fluids from below. As the largest, most permeable structures that formed during uplift, detachment faults focused the fluid flow. In this deformation and hydrogeologic model, dissolution-caused stratal thinning is a major complement to detachment faulting and is an important process that resolves void space issues in the reconstruction of cross section.

Nevada↗
USGS2003

Geologic map of the Callville Bay Quadrangle, Clark County, Nevada, and Mohave County, Arizona

Report : 139 Map Scale: 1:24,000 Map Type: colored geologic map A 1:24,000-scale, full-color geologic map and four cross sections of the Callville Bay 7-minute quadrangle in Clark County , Nevada and Mohave County , Arizona . An accompanying text describes 21 stratigraphic units of Paleozoic and Mesozoic sedimentary rocks and 40 units of Cenozoic sedimentary, volcanic, and intrusive rocks. It also discusses the structural setting, framework, and history of the quadrangle and presents a model for its tectonic development.

Report↗
USGS1999

Yucca Mountain as a Radioactive-Waste Repository

Yucca Mountain straddles the west boundary of the Nevada Test Site in an arid, remote, and thinly populated region of southwestern Nevada. It is the potential site of a monitored geologic repository for the Nation’s commercial and military spent nuclear fuel, high-level radioactive waste derived from reprocessing of uranium and plutonium, surplus plutonium, and other nuclear-weapons materials. (Collectively, these radioactive materials are known as high-level waste [HLW] and are to be distinguished from the low-level radioactive waste to be stored at the recently opened Waste Isolation Pilot Plant in southeastern New Mexico.) Tens of thousands of metric tons of HLW is presently stored at more than a hundred sites in 40 States (fig. 1). The fundamental rationale for a geologic repository for radioactive materials is to securely isolate them from the environment and its occupants to the greatest extent possible.

Nevada↗
USGS1983

Cenozoic structural history of selected areas in the eastern Great Basin, Nevada-Utah

The Confusion Range structural trough (CRST) of west-central Utah predates the Oligocene rocks that are exposed along it. The northern part of the axial region of the CRST is complicated by structures that include reverse faults and associated folds, a large-amplitude mushroom fold, and belts of sharply flexed to overturned strata some of which are fault bounded. These structures, which also predate the Oligocene rocks, formed in a compressional regime that has been interpreted as resulting from thin-skinned gravitational gliding toward the axis of the CRST. Study of the sparse Tertiary rocks that are scattered along the axial region of the CRST reveals abundant evidence of Oligocene and younger deformation. The chief evidence includes (1) widespread Oligocene and Miocene coarse clastic rocks, many of which are conglomerates, that attest to local and distant tectonism, (2) faults that range from high-angle structures generally with less than 100 m of normal displacement to low-angle attenuation faults some of which may have large displacements, and (3) open asymmetric folds. Together with the distribution of sheet-form bodies of ash-flow tuffs, the Oligocene stratigraphic record allows for paleogeographic reconstruction of a lacustrine basin across what is now the northern Confusion Range and one or more basins in the southern part of the CRST. The basins are inferred to have been fault controlled by reactivation of previously formed faults or steep fold flanks. They may have been localized by differential vertical movements similar to those that produced the older systems of folds and faults. Parts of early formed basins were cannibalized as local syndepositional deformation took place in the axial region of the CRST. Both limbs of the CRST have been modified by folds that involve Oligocene rocks. Some of these folds appear to be genetically related to displacements on faults that bound them. They may record thin-skinned Neogene tectonic displacements toward the axis of the CRST. The most intensely faulted and tilted rocks along the axis of the CRST are located in the Tunnel Spring Mountains where Miocene(?) extension on closely spaced listric faults produced as much as 70 percent extension locally. Three episodes of Oligocene-Miocene deformation, all interpreted to have formed in an extensional environment, are recognized in the Tunnel Spring Mountains. The nearby Burbank Hills area may have been involved in the same deformational episodes, though there the relationships are not as clear-cut nor does evidence occur of extreme extension. Tight asymmetric folds in the Burbank Hills are interpreted as drape structures formed over buried normal faults. Other structures along the southern CRST have fold-like forms, but they result from cross-strike alternations in fault-related tilt directions, and they formed in an extensional stress regime. Least-principal stress directions inferred from orientations of extensional structures vary from ENE-WSW in the southern Tunnel Spring Mountains to approximately E-W in the Disappointment Hills and NW-SE in selected areas east of the axis of the CRST. The size, geographic distribution, and new data on the age of areas of major extensional faulting preclude previously published interpretations that the extension is related to major east-directed overthrusting of the Sevier orogeny in areas east of the hinterland of west-central Utah.

Nevada, Utah↗
USGS1978

Chemistry of Tertiary volcanic rocks in the Eldorado Mountains, Clark County, Nevada, and comparisons with rocks from some nearby areas

Chemical variations of 27 rocks that erupted from in and near the Eldorado Mountains, southern Nevada, show (1) fair to good correlation suggestive of a cogenetic suite, (2) a range of uncorrected silica values from about 48 to 74 weight percent with no strong tendency toward bimodality, (3) a calc-alkaline characteristic, and (4) a shift from early eruptions having an anomalously low level of iron enrichment to later eruptions having a more normal level of iron enrichment. Analyses of rocks not known to have been erupted from the Eldorado Mountains (for example, five analyses of the tuff of Bridge Spring and two analyses of the Fortification Basalt Member of the Muddy Creek Formation) are not anomalous when compared with the other rocks, except that iron concentration in the Fortification Basalt Member may be higher than normal. Extensive K-Ar age data provide a clear time framework for the chemical changes as well as for the structural history of the area. The inception of intense extensional tectonism about 15 million years ago was marked by an abrupt shift to more iron-rich and more typically calc-alkalic volcanic products (Mount Davis Volcanics) than those erupted earlier (Patsy Mine Volcanics), but no corresponding shift in K 2 O or total alkali contents or ratios is recognized nor is there any obvious shift toward bimodality in rocks younger than 15 million years. These data, together with data from the Oatman district of Arizona, 100 kilometers to the south-southeast, indicate that the northern part of the lower Colorado River area does not fit into the published Cenozoic patterns of volcanic and tectonic evolution of the western United States. A brief review of nearby areas indicates that they may not fit well either.

Nevada↗