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(a) Map of folds and thrust faults of the Sevier hinterland in central Nevada (location shown on Figure 1) (compiled from Colgan et al., 2010; Di Fiori et al., 2020; Long, 2012; Long & Walker, 2015; Taylor et al., 2000; Thorman et al., 1991). Structures that have timing constraints that narrow their motion timing as either Jurassic or younger or Cretaceous or older are highlighted in black (all structures without precise timing constraints are shown in gray). Numbers correspond to supporting studies that are compiled on Table 1. The central Nevada thrust belt is shaded gray, and the Sevier fold‐thrust belt in southern Nevada is shaded blue. (b) Graph of deformation timing constraints for Sevier hinterland structures (green, gray, red, and blue‐green boxes), the Luning‐Fencemaker thrust belt (orange box), the East Sierran thrust belt (yellow box), and the Sevier fold‐thrust belt (dark and light blue polygons) versus latitude (same latitude scale as A). Numbers correspond to supporting studies compiled on Table 1. Timing constraints for the East Sierran thrust belt (from Walker et al., 1995; Dunne & Walker, 1993; 2004), Luning‐Fencemaker thrust belt (summarized in Wyld, 2002), and the western and eastern thrust systems of the Sevier fold‐thrust belt are shown (from DeCelles & Coogan, 2006; Giallorenzo et al., 2018; Pujols et al., 2020; Yonkee et al., 2019); see text for discussion.
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Documenting the spatio‐temporal progression of deformation within fold‐thrust belts is critical for understanding orogen dynamics. In the North American Cordillera, the geometry, magnitude, and timing of contractional deformation across a broad region of Nevada known as the “Sevier hinterland” has been difficult to characterize due to minimal expos...
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The study of the Devonian to Cretaceous sequence in central and northem East Greenland was continued in 1987. Field work was carried out from early July to mid August covering the region between Ymer Ø and Hochstetter Forland (fig. 1). This was the second year of a two-year field work programme (Marcussen et al., 1987) which forms part of a regiona...
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... The Cordilleran hinterland broadly records Middle Jurassic to Cretaceous plutonism, metamorphism, and distributed lowmagnitude shortening 19,31-35 , which was followed by a widespread phase of Late Cretaceous to Early Cenozoic (ca. 90-60 Ma) regional metamorphism, crustal anatexis with peraluminous plutonism originating from partial melting of pelites and orthogneisses, synconvergent extension, and negligible contractional deformation 15,32,33,[36][37][38][39][40][41] . ...
The Late Cretaceous to Paleogene Laramide orogen in the North American Cordillera involved deformation >1,000 km from the plate margin that has been attributed to either plate-boundary end loading or basal traction exerted on the upper plate from the subducted Farallon flat slab. Prevailing tectonic models fail to explain the relative absence of Laramide-aged (ca. 90–60 Ma) contractional deformation within the Cordillera hinterland. Based on Raman spectroscopy of carbonaceous material thermometry and literature data from the restored upper 15–20 km of the Cordilleran crust we reconstruct the Late Cretaceous thermal architecture of the hinterland. Interpolation of compiled temperature data (n = 200) through a vertical crustal column reveals that the hinterland experienced a continuous but regionally elevated, upper-crustal geothermal gradient of >40 °C/km during Laramide orogenesis, consistent with peak metamorphic conditions and synchronous peraluminous granitic plutonism. The hot and partially melted hinterland promoted lower crust mobility and crust-mantle decoupling during flat-slab traction.
... Two samples collected near the base of Knc1 yielded weighted mean ages of 118.8 ± 2.5 Ma from the southern part of the exposure (n = 8) (defined by the youngest population of zircons that overlap within error) and 119.0 ± 1.8 Ma from the northern part of the exposure (n = 11). A sample collected near the top of Knc5 yielded a weighted mean age of 110.4 ± 2.2 Ma (n = 24) (Di Fiori et al., 2021). Because these three samples were collected from minimally reworked waterlain tuffs, we interpret these weighted mean ages to represent actual ages of deposition. ...
... Forms ledges and cliffs and erodes as blocks. U-Pb zircon geochronology from a waterlain tuff horizon indicates a depositional age of 110.4 ± 2.2 Ma (Di Fiori et al., 2021). Thickness ~50 m. ...
... The basal contact with Jfc is sharp and is an unconformity with <5-10° of difference in dip. U-Pb zircon geochronology from a minimally reworked, waterlain tuff indicates depositional ages of 118.8 ± 2.5 Ma and 119.0 ± 1.8 Ma (Di Fiori et al., 2021). ~35 m. ...
1:20k scale geologic map of the eastern flank of the northern Cortez Mountains, Nevada.
... The depositional age of NCF is not precisely known, but the lower mudstone has yielded dinosaur bones that indicate deposition in the Late Jurassic or Cretaceous (Perry and Dixon, 1993). In a related study that focuses on the structural geometry and geologic history of the map area (Di Fiori et al., 2021), we dated detrital zircons separated from the basal mudstone and obtained a maximum depositional age (defined by the youngest 5 zircon grains that overlap within error) of 129.2 ± 2.6 Ma, defining the base of the section as Albian or younger. This geochronology, combined with the age range of the dinosaur fossils, defines a permissible depositional age range between ~129 Ma and ~66 Ma (Early to Late Cretaceous). ...
... We mapped the NCF in one isolated exposure in the center of the map (similar to the mapping of Perry and Dixon, 1993) and documented that it consists of a conformable stratigraphic sequence defined by a basal mudstone, a middle carbonate-clast conglomerate, and a capping, algal mound-bearing sandstone horizon. This stratigraphic package is broadly similar to other NCF exposures that we have examined to the north and northwest in the Fish Creek Range, Diamond Mountains, and Cortez Mountains (Di Fiori et al., 2020, 2021. Our mapping shows that the NCF dips gently to the east, and projects northward ~1.3 km to ~45° west-dipping Permian rocks within the eastern limb of the McClure Spring syncline. ...
... Dinosaur bones bracketed between Late Jurassic and Cretaceous in age have been described from the basal mudstone (Jack Horner pers. comm. in Perry and Dixon, 1993), and the youngest five detrital zircons that overlap within error yield a ~129 Ma maximum depositional age for the basal mudstone (Di Fiori et al., 2021). The cumulative thickness unit Knc (NCF) is ~30 m. ...
1:24k scale geologic map of the McClure Spring syncline of the central Pancake Range, Nevada.
... 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. STRATIGRAPHY Bedrock units exposed in the map area consist of Late Devonian to Mississippian carbonate and clastic rocks, Early Cretaceous fluvio-lacustrine clastic sedimentary rocks of the NCF, late Eocene to early Oligocene alluvial sediments of the Sheep Pass Formation, and late Eocene and early Oligocene felsic volcanic rocks. ...
... Finally, U-Pb detrital zircon ages (Di Fiori et al., 2021) yielded a maximum deposition age (as defined by the weighted mean age of the five youngest grains that overlap within error) of 130.6 ± 2.6 Ma for the basal member of the NCF in the map area (Knc1), indicating that the NCF in the southern Fish Creek Range was deposited no earlier than the Hauterivian stage. In summary, available geochronologic data and fossil assemblages indicate that deposition of the NCF in the southern Fish Creek Range can be bracketed between the Hauterivian (~133 Ma) and the Albian (~100 Ma) (Fouch et al., 1979;Carpenter et al., 1993;Bonde et al., 2015;Di Fiori et al., 2021). ...
... Though field relationships between the Vanadium thrust and Mesozoic rock units are not exposed, we consider it likely that the thrust is genetically related to thrust faults of the central Nevada thrust belt (CNTB), which are exposed in the surrounding region. This interpretation is supported by observations of several other north-striking, east-vergent thrust faults along-strike to the north in the Fish Creek Range and Diamond Mountains, to the west in the Antelope Range, and to the east in the Pancake Range, which have been interpreted to be part of the Cordilleran (i.e., late Mesozoic) CNTB (e.g., Hose, 1983;McDonald, 1989;Carpenter et al., 1993;Nolan et al., 1974;Taylor et al., 1993Taylor et al., , 2000Long, 2012Long, , 2015Long et al., 2014a;Di Fiori et al., 2020, 2021. Approximately ~35 km along-strike to the north in the Diamond Mountains, field relationships between the Early Cretaceous NCF and several thrust faults and folds demonstrate that the NCF was deposited and deformed during CNTB deformation (Long et al., 2014a;Di Fiori et al., 2020). ...
1:15k scale geologic map of the southern Fish Creek Range, Nevada.
... 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. (1962Nolan et al. ( , 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, 2012Long, , 2015Long 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). ...
1:24k scale geologic map of the southern Diamond Mountains, Nevada.
... This brings into question the dominant thickening processes that drove construction of such a broad hinterland plateau. This high-elevation region of eastern Nevada and western Utah experienced minimal uppercrustal shortening (∼35 km total at 39°N) and thickening (e.g., Gans and Miller, 1983;Long, 2012;Di Fiori et al., 2021;Blackford et al., 2022). As much as ∼10-20 km of localized Jurassic-Cretaceous thrust-related thickening has been interpreted in the vicinity of metamorphic core complexes on the basis of thermobarometry (e.g., McGrew et al., 2000;Lewis et al., 1999). ...
Quantification of the crustal thickening processes that construct orogenic plateaus is essential for interpreting their genesis. In the North American Cordillera, a 2.75−3.5-km-elevation, 200−250-km-wide plateau was constructed to the west of the Cretaceous−Paleogene Sevier fold-and-thrust belt (SFTB). The SFTB deformed a Mesoproterozoic to Mesozoic sedimentary package that thickened westward from a 2−3-km-thick platform section that was deposited above the ∼40-km-thick craton to a 15−25-km-thick continental margin section that was deposited above middle to lower crust that had been significantly thinned during Neoproterozoic rifting. Shortening in the SFTB translated this thick sedimentary package as much as 265 km eastward, which resulted in the relative westward underthrusting of an equivalent length of thick cratonic basement beneath the hinterland region. Measurement of components of thickening with respect to the initial and final crustal thickness above and below the basal thrust décollement demonstrates that thickening accommodated by underthrusting outweighed thickening in the overlying SFTB by a factor of 1.5−3 and was likely the dominant thickening mechanism that constructed the broad hinterland plateau. In eastern Nevada, the reconstructed western edge of the underthrusted craton underlies the western limit of 2.75−3.5 km paleoelevations, which supports this interpretation. This analysis provides an important case study for underthrusting as a first-order thickening process in fold-and-thrust systems that deform sedimentary packages with a high pre-orogenic taper.
... The white box indicates the area of the map shown in (b) Regional tectonic map adapted from Di Fiori et al. (2020); Long, Henry, Muntean, Edmondo, and Cassel (2014), and Long, Henry, Muntean, Edmondo, and Thomas (2014). Gray shading shows the approximate spatial extents of Jurassic-Cretaceous deformational provinces of the North American Cordilleran mountain belt in western United States, while pink shading marks the Sierra Nevada magmatic arc (from Van Buer et al., 2009 Fiori et al., 2021;Long, Henry, Muntean, Edmondo, & Cassel, 2014;Long, Henry, Muntean, Edmondo, & Thomas, 2014;Nolan & Hunt, 1962;Nolan et al., 1974Nolan et al., , 1956. Sedimentation in the NCF type section basin is attributed to erosion of the eastern flank of the Eureka Culmination, a structural high of the Central Nevada Thrust belt (Figure 1), based on clast and cross-bedding orientations from the NCF type section that indicate an east-flowing fluvial system Fetrow et al., 2020;Long, 2012Long, , 2015Long, Henry, Muntean, Edmondo, & Cassel, 2014;Long, Henry, Muntean, Edmondo, & Thomas, 2014;Long et al., 2015;Vandervoort & Schmitt, 1990). ...
The North American Newark Canyon Formation (NCF; ∼113–98 Ma) presents an opportunity to examine how terrestrial carbonate facies reflect different aspects of paleoclimate during one of the hottest periods of Earth's history. The lower NCF type section preserves heterogeneous palustrine facies and the upper NCF preserves lacustrine deposits. We combined carbonate facies analysis with δ¹³C, δ¹⁸O, and Δ47 data sets to assess which carbonate facies preserve stable isotope signals that are most representative of climatic conditions. Palustrine facies record the heterogeneity of the original wetland environment in which they formed. Using the pelmicrite facies that formed in deeper wetlands, we interpret a lower temperature zone (35–40°C) to reflect warm season water temperatures. In contrast, a mottled micrite facies which formed in shallower wetlands records hotter temperatures (36–68°C). These hotter temperatures reflect radiatively heated “bare‐skin” temperatures that occurred in a shallow depositional setting. The lower lacustrine unit has been secondarily altered by hydrothermal fluids while the upper lacustrine unit likely preserves primary temperatures and δ¹⁸Owater of catchment‐integrated precipitation. Resultantly, the palustrine pelmicrite and lacustrine micrite are the facies most likely to reflect ambient climate conditions, and therefore, are the best facies to use for paleoclimate interpretations. Average warm season water temperatures of 41.1 ± 3.6°C and 37.8 ± 2.5°C are preserved by the palustrine pelmicrite (∼113–112 Ma) and lacustrine micrite (∼112–103 Ma), respectively. These data support previous interpretations of the mid‐Cretaceous as a hothouse climate and demonstrate the importance of characterizing facies for identifying the data most representative of past climates.
... In contrast, the Eureka district is located east of the Roberts Mountain thrust front within the foreland region of the Antler orogeny (Figure 1; Giles and Dickinson, 1995;Poole and Sandberg, 2015). Thrust faults and large-scale folds in the Eureka district are interpreted to be younger than the late Paleozoic Antler orogeny and instead, related to Jurassic to Early Cretaceous shortening (Long, 2012;Long et al., 2014a) in the central Nevada thrust belt (Taylor et al., 1993;Taylor et al., 2000;Di Fiori et al., 2021) located in the hinterland of the Sevier fold and thrust belt (e.g., Yonkee and Weil, 2015;Long, 2015). In the Eureka district, the fold-belt structures are offset by a younger set of normal faults which tend to strike N-S in addition to subsidiary NE-SW and NW-SE fault strands (e.g., Di Fiori, 2014;Hoge et al., 2015). ...
The Lookout Mountain deposit is a Carlin-type gold deposit located in the Fish Creek Range of central Nevada. Historic mining at the Lookout Mountain pit produced approximately 17,700 ounces of gold averaging 4.11 grams per tonne (g/t). This study presents an updated description and interpretation of the major structural and stratigraphic features of the Lookout Mountain deposit and nearby exploration targets based on ongoing exploration by Timberline Resources Corporation. We integrate new geological, drillhole, and geophysical data to better resolve the structural style of faulting and the architecture of the offset Paleozoic strata to define new prospective zones for Carlin-type gold mineralization beyond the known gold resource in the vicinity of the Lookout Mountain pit. Five first-order structural and geologic elements of the Lookout Mountain and adjacent area are described from west to east. The first is the north-south striking, west-dipping Lookout Mountain fault, a high-angle normal fault with an apparent stratigraphic separation of at least ~1500 m which juxtaposes upper Cambrian strata in its eastern footwall against Silurian-Devonian strata in its western hanging wall. The second major structure is the east-dipping Highwall fault, observed along the western highwall of the Lookout Mountain pit where it juxtaposes altered dolomite against a shale-rich and sulfide mineralized stratigraphic section. The third element is an alluvial and sediment covered 'pediment area' with sporadic and receded outcrops of upper Cambrian strata and Eocene volcanic rocks. The geology of this pediment area is largely understood from geophysical and drillhole data, which reveal the presence of a gold-bearing carbonaceous breccia unit in the lowermost Dunderberg Shale and a previously unrecognized buried fault overlain by volcanic rocks. The fourth structural element is the Eastern Boundary fault, which juxtaposes Cambrian against Ordovician strata in its eastern hanging wall and defines the eastern boundary of the pediment area. The Eastern Boundary fault generally strikes north-south but is characterized by a northwest bend in its fault trace, interpreted as part of a relay zone that merges with the Lookout Mountain fault to the north. Ordovician strata are in turn juxtaposed against lower Cambrian strata across the fifth structural element, a north-south 2 striking, west-dipping normal fault known as the Dugout Tunnel fault, which has an apparent stratigraphic separation of at least ~1600-1700 m. Newly acquired geophysical data reveal subsurface relationships not apparent from the surface geology. For example, new induced polarization data reveal a significant volume of chargeable rock beneath the eastern section of the pediment area. Core data from the chargeability anomaly indicate the presence of fine-grained aplitic intrusive rocks containing disseminated pyrite. The age of this intrusion is unknown, but it may be related to a district-wide magmatic event during the mid-Cretaceous.
The multiple origins proposed for the Kanarra anticline in southwestern Utah as a drag-fold along the Hurricane fault, a Laramide monocline, a Sevier fault-propagation fold, or a combination of these processes, serve to muddy its tectonic significance. This in part reflects the structural complexity of the exposed eastern half of the fold. The fold evolved from open and up-right to overturned and tight, is cross-cut by multiple faults, and was subsequently dismembered by the Hurricane fault. The western half of the fold is obscured because of burial, along with the hanging wall of the Hurricane fault, beneath Neogene and younger sediments and volcanics. We present the results of detailed bedrock geologic mapping, and geologic cross sections restored to Late Cretaceous time (prior to Basin and Range extension), to demonstrate the Kanarra anticline is a compound anticline-syncline pair inextricably linked with concomitant thrust faulting that formed during the Sevier orogeny. We propose the name Kanarra fold-thrust structure to unambiguously identify the close spatial and temporal association of folding and thrusting in formation of this prominent geologic feature. We identify a previously unrecognized thrust, the Red Rock Trail thrust, as a forelimb shear thrust that was in a favorable orientation and position to have been soft-linked, and locally hard-linked, with the thrust ramp of the basal detachment to form a break thrust. The east verging Red Rock Trail thrust is recognized by a distinctive cataclasite in the Lower Jurassic Navajo Sandstone. The hanging wall of the Red Rock Trail thrust is displaced eastward over the Middle Jurassic Carmel Formation and Upper Cretaceous formations and can be traced for at least 27 km and possibly farther. We contend the Kanarra fold-thrust structure unambiguously defines the leading edge of the Sevier fold-thrust beltin southwestern Utah. Stratigraphic relationships in the southern and northern part of the Kanarra fold-thrust structure constrain its development between the early and late Campanian (about 84 to 71 Ma) but possibly younger. In southwestern Utah, initial movement along the Iron Springs thrust at about 100 Ma (Quick and others, 2020) and subsequent eastward advancement of the Sevier deformation front to the Red Rock Trail thrust at about 84 to 71 Ma coincided with well-documented magmatic flare ups in the Cordilleran arc in the hinterland of the Sevier fold-thrust belt. This temporal relationship between magmatic flare ups and thrusting is consistent with a close correspondence between arc-related processes and episodic foreland deformation.
