RECENT GEOLOGIC MAPS
Geologic map of the Silver Zone Pass quadrangle, Elko County, Nevada
Author: David M. Miller and Linda L. Berg
Series: Map 192
Format: 1 sheet: 37 x 27 inches, cross sections, color; text: 8 pages, color
This 1:24,000-scale geologic map of the Silver Zone Pass quadrangle lies in the southern Toano Range in Elko County, Nevada. Metamorphic and sedimentary strata of the quadrangle range from Neoproterozoic to Permian in age. Important intrusions include the Late Jurassic (ca. 159 Ma) Silver Zone Pass pluton and Cretaceous Toano Spring pluton. In particular, the Silver Zone Pass pluton involves undeformed dikes that crosscut metamorphic foliations and the pluton is associated with pluton-margin anticlines. Interpretation of these characteristics suggests that the pluton was syn-kinematic with respect to metamorphism and strain, thus requiring a phase of Late Jurassic deformation. A Miocene rhyolite lava is of particular interest as one of the few topaz-bearing volcanic rocks in Nevada. A major detachment fault places non-metamorphosed Paleozoic rocks over low-grade Paleozoic and Proterozoic rocks. High-angle normal faults tilted the range in several blocks, and Miocene Humboldt Formation were deposited on, and faulted against, bedrock. Rocks of the Toano Range are bounded by broad valleys on the east and west, with the eastern basin being at much lower elevation than the western basin. Pleistocene lakes, which created distinctive beach deposits, occupied both basins, with Lake Bonneville on the east and Lake Waring on the west. Silver Zone Pass owes its low relief to the enhanced weathering and erosion of the rock within the pass, a granodiorite pluton. The weathering has created some unusual landforms such as tors.
Geologic map of the Silver Zone Pass quadrangle, Elko County, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the Soldier Peak quadrangle, Elko County, Nevada
Author: Arthur W. Snoke, Keith A. Howard, and Seth Dee
Series: Map 191
Format: 1 sheet: 31 x 35 inches, cross sections, color; text: 31 pages, color
The Soldier Peak quadrangle exposes evidence of a complex structural and metamorphic history involving a long stratigraphic record that ranges from the Neoproterozoic to the Holocene. The quadrangle exposes major elements of the architecture of the Ruby Mountains metamorphic core complex in the northern Ruby Mountains and East Humboldt Range. Mapped stratigraphic units ranging from Neoproterozoic to Upper Devonian are metamorphosed to amphibolite facies and intruded by myriad granitic to gabbroic bodies of Cretaceous to Oligocene age. The metamorphosed stratigraphic units trace out large recumbent folds in the infrastructure of the complex. An Oligocene to Miocene mylonitic shear zone, hundreds of meters thick, overprints the upper part of the complex. The Ruby Mountains–East Humboldt detachment-fault zone in turn is superposed on the mylonitic shear zone. The detachment-fault zone includes fault slices of the upper part of the stratigraphic sequence (Ordovician to Devonian), metamorphosed to greenschist facies and commonly brittlely faulted. A plexus of higher low-angle-fault slices of unmetamorphosed Upper Devonian to Permian formations defines the upper plate of the detachment fault and forms the upper tier of the core complex.
Pleistocene glacial moraine deposits are present in the mountains, and alluvial-fan and glacial-outwash deposits occur in Lamoille Valley west of the mountains. Vitric fallout ash originally correlated to the 2.1-Ma Huckleberry Ridge Tuff in the Yellowstone Plateau volcanic field occurs low in the exposed alluvial basin sequence. A new 40Ar/39Ar date on sanidine yielded an age of 2.35±0.07 Ma, somewhat older than the Huckleberry Ridge Tuff. Normal faults bounding the west side of the Ruby Mountains show offset as young as late Pleistocene and project toward seismically imaged subsurface listric faults.
Geologic map of the Soldier Peak quadrangle, Elko County, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the Nevada part of the Boulder Canyon quadrangle, Clark County, Nevada
Author: Michael H. Darin and Barbaros Demircan
Series: Open-File Report 2023-03
Version: first edition, March 2023; supersedes Open-File Report 2022-01
Format: map sheet: 30.5 x 41 inches, color; text: 10 pages, b/w
The Boulder Canyon 7.5-minute quadrangle is located east of Las Vegas, Nevada and almost entirely within the boundary of the Lake Mead National Recreation Area. The south half of the quadrangle overlaps the Nevada-Arizona state line along the north shore of Lake Mead and rugged topography at the northern end of the Black Mountains. The only access to this area is via Northshore Road (Nevada State Road 167), which intersects the north half of the quadrangle, or by boat. New detailed geologic mapping for this report was conducted by the authors between April 2021 and June 2022, and builds on various M.S. theses completed at Northern Arizona University (San Filippo, 2008; Winston, 2016; Demircan, 2019) and the University of Nevada, Las Vegas (Naumann, 1987; Eschner, 1989), as well as detailed geologic mapping in adjacent quadrangles (Anderson, 2003; Duebendorfer, 2003). This report and the accompanying geologic map provide useful insights into the geologic framework of the western Lake Mead structural domain, its complex deformation and magmatic evolution, and the potential for recent Quaternary faulting and seismic hazards proximal to the rapidly expanding Las Vegas urban area and within the Lake Mead National Recreation Area.
Geologic map of the Nevada part of the Boulder Canyon quadrangle, Clark County, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the Como quadrangle, Lyon County, Nevada
Author: Michael C. Say and Andrew V. Zuza
Series: Open-File Report 2022-09
Format: 1 sheet: 39.5 x 27.5 inches, cross section, color; text: 7 pages, color
This 1:24,000-scale geologic map of the Como 7.5-minute quadrangle covers part of the northern Pine Nut Mountains in Lyon County, Nevada. The northern Pine Nut Mountains consist of Mesozoic plutonic and sedimentary rocks unconformably overlain by west-tilted Oligocene tuff and a thick-package of Miocene volcanic and sedimentary strata. The range was tilted westward by Miocene east-dipping normal and left-oblique faulting along the middle and eastern flanks of the Pine Nut Mountains.
The map area consists mostly of parallel and conformable west-tilted Miocene volcanic and sedimentary rocks that are ~2 km thick. The volcanic sequence consists of mostly dacite to andesite, with some basaltic andesite. Some dacite-andesite dikes intrude the volcanic rocks. New 40Ar/39Ar dates bracket main volcanic sequence to 14.2–6.8 Ma, with most dates between 8.2 and 6.8 Ma. Miocene strata were deposited on sparse Oligocene ash-flow tuff and the Jurassic Gardnerville Formation. The Miocene sequence was tilted 30°–36° west by several north-striking east-dipping normal faults that must have initiated after ca. 6.8 Ma based on the parallel nature of the volcanic section. Restoration of the faulted strata suggests >14% extensional strain.
The Como mining district is located in the northern Pine Nut Mountains and hosts gold and silver mineralization. Active exploration projects are currently underway throughout the range including the Hercules project. Mineralization is thought to be a low-sulfidation volcanic-hosted epithermal gold and silver deposit. Abundant northeast-striking quartz veins are exposed throughout the Como, Hercules, and eastern flank areas. Large halos of hydrothermally altered volcanic rock envelope quartz veins. Alteration is not observed in the hanging wall of the main eastern fault block.
Geologic map of the Como quadrangle, Lyon County, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the eastern flank of the northern Cortez Mountains, Eureka County, Nevada
Author: Russell V. Di Fiori and Sean P. Long
Series: Open-File Report 2022-06
Format: sheet: 24 x 27.5 inches, color; text: 7 pages, color
The Cortez Mountains are located in north-central Nevada, southwest of Carlin (fig. 1). Previous geologic mapping in this region (Smith and Ketner, 1978) and previous stratigraphic studies (e.g., Smith and Ketner, 1976; Suydam, 1988) have defined an extensive exposure of the Early Cretaceous Newark Canyon Formation (NCF) on the eastern flank of the northern Cortez Mountains. In this region of Nevada, there have been differing interpretations of the timing and style of contractional deformation associated with construction of the Cordilleran mountain belt, as well as the potential relationship of the NCF to this deformation. Smith and Ketner (1977) did not observe evidence for contractional deformation in the NCF, and interpreted that regional Mesozoic contractional deformation must have taken place prior to NCF deposition.
Alternatively, Vandervoort (1987) and Suydam (1988) interpreted that the NCF was deposited in isolated basins that formed in response to regional tectonism along the ‘Eureka thrust belt’ (also known as the Central Nevada thrust belt of Taylor et al. [1993, 2000]). The goal of this study is to present map data that illustrate field relations between the NCF and surrounding rock units. We present a new 1:20,000-scale geologic map of the eastern flank of the northern Cortez Mountains that covers ~42 km2 (a ~13 km north–south by ~4 km east–west distance), which covers the extent of exposure of the NCF (fig. 1). To illustrate the deformation geometry of the NCF relative to underlying and overlying rock units, we also present two retro-deformable cross sections. This report is meant to accompany Di Fiori et al. (2021), which characterizes the stratigraphic architecture, deposition timing, and deformation history of three NCF exposures in central Nevada, including the Cortez Mountains exposure. The following report provides descriptions of all rock and surficial units in the map area, with a focus on intraformational members of the NCF that we defined in our mapping, as well as the structural framework and geologic history of the map area and surrounding region.
Geologic map of the eastern flank of the northern Cortez Mountains, Eureka County, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the southern Fish Creek Range, Eureka and Nye counties, Nevada
Author: Russell V. Di Fiori and Sean P. Long
Series: Open-File Report 2022-05
Format: sheet: 33 x 22 inches, cross sections, color; text: 9 pages, color
The southern part of the Fish Creek Range is located in central Nevada, ~40 km south of the town of Eureka (fig. 1). Previous studies in the Fish Creek Range (e.g., Merriam, 1967; Hose, 1983; Sans, 1986) have presented differing interpretations of the tectonic significance of Paleozoic, Mesozoic, and Cenozoic rock units exposed in the southern part of the range, including using different naming schemes for Paleozoic sedimentary rock units (e.g., Hose, 1983; Poole et al., 1983) and varying interpretations of the depositional age range and nature (i.e., stratigraphic versus structural) of the upper and lower contacts of the Cretaceous Newark Canyon Formation (NCF) and Paleogene Sheep Pass Formation (e.g., Hose, 1983; Sans, 1986). These Cretaceous and Paleogene sedimentary units are only sparsely exposed in eastern Nevada, and therefore the southern Fish Creek Range is an important field locality that offers a rare opportunity to bracket the timing of Mesozoic and early Cenozoic depositional events. In addition, the southern Fish Creek Range also has been interpreted to lie within the central Nevada thrust belt (CNTB), a system of north-striking, east-vergent thrust faults and folds that branch northward off the Sevier thrust in southern Nevada (fig. 1; e.g., Taylor et al., 1993, 2000). However, to date there have been vastly differing interpretations presented for the geometry, timing, and tectonic significance of contractional structures in the southern Fish Creek Range (e.g., Hose, 1983; Sans, 1986).
The purpose of this study is to present an updated structural and stratigraphic interpretation of rock units in the southern Fish Creek Range. Here, we present a new 1:15,000-scale geologic map, which covers an area of ~21.5 km2 and focuses on the outcrop extent of the NCF and Sheep Pass Formation. This technical report, which is meant to accompany the geologic map, presents revisions to the Paleozoic stratigraphy as mapped by Hose (1983), divides the NCF into four mappable members, and presents an updated view of the structural framework of the range, including documenting a previously unmapped thrust fault. In addition, new U-Pb zircon geochronology presented in Di Fiori et al. (2021) provides additional depositional age constraints on both the NCF and the Sheep Pass Formation.
Geologic map of the southern Fish Creek Range, Eureka and Nye counties, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the southern Diamond Mountains, Eureka and White Pine counties, Nevada
Author: Russell V. Di Fiori and Sean P. Long
Series: Open-File Report 2022-04
Format: sheet: 58.5 x 38.5 inches, color, cross sections; text: 10 pages, color
The Diamond Mountains are located in east-central Nevada, east and northeast of the town of Eureka (fig. 1). Early geologic mapping in the surrounding region by Nolan et al. (1962, 1971) revealed exposures of several thrust faults and folds, which have since been interpreted as part of the central Nevada thrust belt (CNTB), a system of N-striking contractional structures that branch northward off of the Sevier fold-thrust belt in southern Nevada (e.g., Taylor et al., 2000; Long, 2012, 2015; Long et al., 2014; Di Fiori et al., 2021). The southern part of the Diamond Mountains have been important for this interpretation, as they contain exposures of the Cretaceous Newark Canyon Formation (NCF), which has long been hypothesized to have been deposited during regional contractional deformation (e.g., Nolan et al., 1956; Vandervoort and Schmitt, 1990; Long et al., 2014; Long, 2015). However, there have been significant variations in interpretations of the style, timing, and magnitude of contractional deformation in the southern Diamond Mountains across multiple generations of studies (e.g., Nolan, 1962; Nolan et al., 1971; Druschke et al., 2011; Long et al., 2014). In addition, several generations of Late Cretaceous to Cenozoic normal faults have extensionally dismembered the region (Long et al., 2015), which further complicates the regional structural architecture.
In this study, our goal is to present an updated view of the structural geometry and deformational and depositional history of this complex region of central Nevada, by presenting a new 1:24,000-scale geologic map of the southern Diamond Mountains that covers an area of ~235 km2, including the exposed extent of the NCF (fig. 1). Our field work consisted of new geologic mapping focused on two main exposures of the Newark Canyon Formation, accompanied by compilation and field-checking of key localities on the 1:31,680-scale geologic map of the Eureka 15′ quadrangle (Nolan et al., 1971) and the 1:12,000-scale map of the Eureka mining district (Nolan, 1962). We also present three retro-deformable cross sections, which illustrate the deformation geometry both above and below the modern erosion surface. This map and technical report are meant to accompany Di Fiori et al. (2020), which presents details on the stratigraphy, deposition timing, and deformational history of the NCF in the southern Diamond Mountains. This report presents detailed descriptions of members of the NCF that we defined in our mapping, as well as descriptions of Paleozoic sedimentary rock units, and explains revisions to the older structural interpretations that we have performed in our new work.
Geologic map of the southern Diamond Mountains, Eureka and White Pine counties, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the McClure Spring syncline, central Pancake Range, Nye County, Nevada
Author: Russell V. Di Fiori and Sean P. Long
Series: Open-File Report 2022-03
Format: map: 29.5 x 29 inches, color, two cross sections; text: 9 pages (one page in color)
Documenting the style, geometry, and timing of contractional deformation is critical to understanding how orogenic systems evolve. In the Jurassic-Paleogene Cordilleran orogenic belt, many questions remain regarding the timing and geometry of crustal shortening, particularly within the hinterland region of the Sevier fold-thrust belt in Nevada, where Cenozoic extension has complexly overprinted Cordilleran contractional deformation (e.g., Gans and Miller, 1983; Taylor et al., 1993; 2000; Colgan and Henry, 2009; Long, 2012, 2015, 2019). In particular, the geometry and timing of deformation in the central Nevada thrust belt (CNTB), a system of east-vergent thrust faults and folds that branches northward off of the Sevier thrust belt in southern Nevada (fig. 1), have yet to be resolved along much of the along-strike length of this province (e.g., Bartley and Gleason, 1990; Vandervoort and Schmitt, 1990; Taylor et al., 1993, 2000; Long, 2012, 2015; Long et al., 2014). Near Eureka, Nevada (fig. 1), deformation in the CNTB has been interpreted to be coeval with deposition and folding of the Early Cretaceous Newark Canyon Formation, a sparsely preserved fluvio-lacustrine rock unit (Long et al., 2014; Di Fiori et al., 2020). However, south of Eureka, the timing of motion of the CNTB structures can, in most places, only be bracketed between the Pennsylvanian and Oligocene (Taylor et al., 2000).
The central Pancake Range, located ~50 km southeast of Eureka, lies near the eastern limit of the CNTB (fig. 1). 1:250,000-scale reconnaissance geologic mapping in this range by Kleinhampl and Ziony (1985) revealed the presence of a broad-scale (~10 km minimum north-south length, ~3 km minimum east-west width), N-trending, overturned fold: the McClure Spring syncline. An aerially restricted exposure, the Cretaceous Newark Canyon Formation has been mapped within its hinge zone; however, there is disagreement over whether the Newark Canyon Formation is folded or whether it overlaps the fold (Perry and Dixon, 1993). The existing 1:250,000-scale mapping does not permit evaluation of this important field relationship, which warrants investigation at a more detailed scale. To address this issue, we performed 1:24,000-scale geologic mapping of the full extent of exposed Paleozoic bedrock that defines the McClure Spring syncline (fig. 1). Our map encompasses a north-south extent of ~16 km and an east-west extent of ~5.5 km.
Geologic map of the McClure Spring syncline, central Pancake Range, Nye County, Nevada [MAP AND TEXT] (unr.edu)
Geologic map of the Parran quadrangle, Churchill County, Nevada
Author: James E. Faulds, Richard D. Koehler, Nolan P. Dellerman, and Heather L. Green
Series: Open-File Report 2022-02
Format: 1 sheet: 38.5 x 28 inches, cross sections, color; text: 6 pages, b/w
NBMG geologists James Faulds, Richard Koehler, Nolan Dellerman, and Heather Green completed a detailed geologic map of the Parran 7.5ꞌ quadrangle. The quadrangle is located in the eastern Hot Springs Mountains of Churchill County, Nevada about 80 km northeast of Reno. This area contains the Desert Queen geothermal system, which is a hidden geothermal system (no surface expressions such as hot springs) with temperatures >140°C at depths as shallow as ~150 m. The map area includes the western part of a large composite basin, the Desert Queen basin, and adjacent parts of the Hot Springs Mountains. The detailed mapping has revealed the stratigraphic and structural framework of the area, which is critical to developing a conceptual model for the geothermal system.
In the Desert Queen area, Tertiary volcanic and sedimentary strata rest nonconformably on Mesozoic metasedimentary-metavolcanic and plutonic basement. Quaternary sediments onlap the bedrock units. The Mesozoic basement is exposed directly west of the quadrangle in the footwall of the east-dipping Desert Queen fault zone. An erosional surface of moderate relief (i.e., hundreds of meters) is developed on the Mesozoic rocks, above which rests the Tertiary section. The Tertiary section is a heterogeneous mix of volcanic and sedimentary rocks, with a total of thickness of ~2–3 km. Only middle to late Miocene rocks are exposed in the quadrangle, but Oligocene units have been observed in deep wells in the area and altered sedimentary rocks of probable Eocene age crop out directly west of the map area. Although significant lateral variations exist, the Tertiary section exposed within the quadrangle can be grouped into several discrete packages.
Geologic map of the Parran quadrangle, Churchill County, Nevada [MAP AND TEXT] (unr.edu)