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Map of the Clear Creek Thrust, an east-verging thrust fault along the eastern flank of the Bighorn Mountains (from Ver Ploeg and Boyd, 2002). Red dashed line = Harzburgite body as indicated by Hoppin (1961), Ver Ploeg and Boyd (2002) and our mapping. Blue dashed line = additional mafic rocks of the Trailside complex of Luth (1960) and Lynds et al. (2014). The position of the major Laramide tear fault that is buried by White River Formation (Oligocene) gravels is indicated.
Source publication
A harzburgite intrusion, which is part of the trailside mafic complex) intrudes ~2900-2950 Ma gneisses in the hanging wall of the Laramide Bighorn uplift west of Buffalo, Wyoming. The harzburgite is composed of pristine orthopyroxene (bronzite), clinopyroxene, serpentine after olivine and accessory magnetite-serpentinite seams, and strike-slip stri...
Contexts in source publication
Context 1
... of small (~tens of meters of displacement) tear faults obliquely cut the Clear Creek thrust. The largest of these is a left-lateral tear fault with ~500 m of displacement that occurs along Mosier Gulch (Figure 3). This tear fault was the site of a major synorogenic alluvial system that transferred sediment and water from the Bighorn uplift to the adjacent Powder River Basin during and after the deposition of the early Eocene Moncrief alluvial fan conglomerate. ...
Context 2
... unique serpentinized harzburgite intrusion occurs along Highway 16 about 15 km west of Buffalo, Wyoming (Figure 3). This area is in the hanging wall of the Laramide Clear Creek thrust within the Bighorns Archean basement complex (Luth, 1960;Hopping, 1961;Ridgeway and Hoy, 1997;Ver Ploeg and Boyd, 2002;Lynds et al., 2014). ...
Context 3
... on the Clear Creek thrust is presumed to be from west to east bringing the Bighorn Archean core up and over the Powder River basin (Hoppin, 1961). Rotation of 90° of the hanging wall during thrusting is a new observation and there is no additional field evidence to support this in the Archean gneisses, but this portion of the Bighorn front is complexly deformed and east-striking tear faults are present (Figure 3) and there is evidence of thickening or attenuation of all the Paleozoic units along strike ( Lynds et al., 2014 16. Weighted mean and concordia plots determined with Isoplot (Ludwig, 2008). ...
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The focus of this project was the Early Proterozoic Kheis orogenic belt, situated in the Northern Cape Province, South Africa. A predominantly field-based study, it documents the evolution of the south-western margin of the Kaapvaal Craton, the sequence of geological events that led to deposition of the Olifantshoek Supergroup and subsequent deform...
Citations
... The Laramide structure of the Bighorn Mountains (e.g. Stone, 2003;Worthington et al., 2016;Wallenberg et al., 2020;Craddock et al., 2022;Tikoff et al., 2022) is well studied. Here the Laramide structure is dominated by the ~N-S trending reverse fault that verges to the west. ...
Here we present the results of detailed (1:24,000 scale) mapping of the Spanish Point 7.5 Minute Quadrangle, Wyoming, which occurs along the western flank of the Bighorn Mountains. The Quadrangle includes Archean crystalline rocks of the Wyoming Province Beartooth-Bighorn Magmatic Terrane, Paleozoic miogeoclinal clastic and carbonate strata (Flathead, Gros Ventre, Gallatin, Big Horn, Madison, and Amsden formations, and Quaternary (Pinedale Formation) glacial deposits. Isotopic age determinations (LA-ICPMS U-Pb on zircon) of the basement crystalline rocks, which occupy the higher elevations in the eastern part of the Quadrangle, were conducted at the University of Arizona Laserchron Center. Seven samples of grey foliated to massive granodiorite were analyzed, all yielding ages of about 2880-2885 Ma, which is correlative to the Lookout Mountain granodiorite to the north. The
dominant basement fabric orientation is ~N75W90. The Lookout Mountain Granodiorite was uplifted along the N-S striking, west verging Laramide Spanish Point Reverse fault, which dips steeply to the east. Paleozoic strata in
the footwall are steeply inclined to overturned. Displacement along the fault is as much as 150 m. To the west, the Paleozoic strata roll into a homocline that dips ~10 degrees to the west. The Pleistocene Pinedale Formation glacial deposits, which are as much as 50 m in thickness, occur as ground, end, and lateral moraines along the principal drainages.
... See Figures 1 and 6 for sample site locations, Table 3 for strain summary data, and Tables S1 and S2 (see text footnote 1) for sample details. Figure 9. Lower-hemisphere stereoplots of calcite strain data for the Beartooth-Rattlesnake structure (see Table 3; Tables S1 and S2 [see text footnote 1]). Strain axes (ε 1 -shortening; ε 2 -intermediate; ε 3 -extension axes) are plotted with contoured Turner (1953) (Wallenberg et al., 2020). The most remarkable finding is that none of the calcite twinning strain samples recorded any secondary strain overprint ( Fig. 14; Table 3), and, a few kilometers to the north, the Cambrian section has been removed entirely, with Archean gneisses in contact with vertical Bighorn Dolomite sediments (Fig. 12A). ...
We report the results of 167 calcite twinning strain analyses (131 limestones and 36 calcite veins, n = 7368 twin measurements) from the Teton-Gros Ventre (west; n = 21), Wind River (n = 43), Beartooth (n = 32), Bighorn (n = 32), and Black Hills (east; n = 11) Laramide uplifts. Country rock limestones record only a layer-parallel shortening (LPS) strain fabric in many orientations across the region. Synorogenic veins record both vein-parallel shortening (VPS) and vein-normal shortening (VNS) fabrics in many orientations. Twinning strain overprints were not observed in the limestone or vein samples in the supracrustal sedimentary veneer (i.e., drape folds), thereby suggesting that the deformation and uplift of Archean crystalline rocks that form Laramide structures were dominated by offset on faults in the Archean crystalline basement and associated shortening in the midcrust. The twinning strains in the pre-Sevier Jurassic Sundance Formation, in the frontal Prospect thrust of the Sevier belt, and in the distal (eastern) foreland preserve an LPS oriented approximately E-W. This LPS fabric is rotated in unique orientations in Laramide uplifts, suggesting that all but the Bighorn Mountains were uplifted by oblique-slip faults. Detailed field and twinning strain studies of drape folds identified second-order complexities , including: layer-parallel slip through the fold axis (Clarks Fork anticline), attenuation of the sedimentary section and fold axis rotation (Rattlesnake Mountain), rotation of the fold axis and LPS fabric (Derby Dome), and vertical rotations of the
Here we present the results of detailed (1:24,000 scale) mapping of the Spanish Point 7.5 Minute Quadrangle, Wyoming, which occurs along the western flank of the Bighorn Mountains. The Quadrangle includes Archean crystalline rocks of the Wyoming Province Beartooth-Bighorn Magmatic Terrane, Paleozoic miogeoclinal clastic and carbonate strata (Flathead, Gros Ventre, Gallatin, Big Horn, Madison, and Amsden formations, and Quaternary (Pinedale Formation) glacial deposits. Isotopic age determinations (LA-ICPMS U-Pb on zircon) of the basement crystalline rocks, which occupy the higher elevations in the eastern part of the Quadrangle, were conducted at the University of Arizona Laserchron Center. Seven samples of grey foliated to
massive granodiorite were analyzed, all yielding ages of about 2880-2885 Ma, which is correlative to the Lookout Mountain granodiorite to the north. The
dominate basement fabric orientation is ~N75W90. The Lookout Mountain Granodiorite was uplifted along the N-S trending, west verging Laramide Spanish Point Reverse fault, which dips steeply to the east. Paleozoic strata in the footwall are steeply inclined to overturned. Displacement along the fault is as much as 150 m. To the west, the Paleozoic strata roll into a homocline that dips ~10 degrees to the west. Pinedale Formation glacial deposits,
which are as much as 50 m in thickness, occur as ground, end, and lateral moraines along the principal drainages.
Here we present the results of detailed (1:24,000 scale) mapping of the Woodrock 7.5 Minute Quadrangle Wyoming, which mainly consists of Archean basement rocks of the Laramide Bighorn uplift. Our focus was on the Archean geology of the Laramide age Bighorn uplift. Isotopic age determinations (U-Pb on zircon) were conducted at the University of Arizona LaserChron Center. Our work revealed the presence of four different components of the batholith. The oldest unit is a ~2880 Ma foliated Lookout Mountain Granodiorite that occurs in the southern part of the quadrangle in the vicinity of Bruce and Lookout Mountains. The ~2775 Black Mountain Tonalite
occurs in the northeastern part of the quadrangle. The age of the Black Mountain Tonalite and Lookout Mountain Granodiorite overlap but the units are distinct in terms of structure and lithology so they were mapped separately. The central part of the quadrangle is underlain by the massive, ~2860 Ma Taylor Mine Granite. This unit is poorly exposed and variable in texture. The youngest unit is the ~2850 Ma Owen Creek Alkali Feldspar Granite, which occurs in the western part of the quadrangle. Mafic dikes of variable geometry, texture and age cross-cut the quartzofeldspathic rocks. Less than 25 m of poorly exposed Cambrian Flathead Sandstone occurs along the extreme western margin of the quadrangle. We discovered as much as 30 m of Oligocene White River Formation strata occur as terrace deposits along the western side of the Tongue River in the central part of the quadrangle. The White River strata are poorly exposed and consist of thin bedded tuffaceous sandstone and massive conglomerate that are light colored and include as clasts Paleozoic carbonate and Archean basement rocks. Less than 50 m of Pinedale-age glacial tills occur along the upper Tongue River in the southern part of the Quadrangle, forming hummocky, poorly-drained topography. Quaternary alluvium occurs along some of the larger streams.
This project involved the construction of a detailed geologic map of the Park Reservoir, Wyoming 7.5-Minute
Quadrangle (Scale 1:24,000). The Quadrangle occurs entirely in the Bighorn National Forest, which is a popular
recreation site for thousands of people each year. This research advances the scientific understanding of the geology of the Bighorn Mountains and the Archean geology of the Wyoming Province. Traditional geologic mapping
techniques were used in concert with isotopic age determinations. Our goal was to further subdivide the various
phases of the 2.8–3.0 Ga Archean rocks based on their rock types, age, and structural features.
This research supports the broader efforts of the Wyoming State Geological Survey to complete 1:24,000 scale
geologic maps of the state. The northern part of the Bighorn Mountains is composed of the Bighorn batholith, a
composite complex of intrusive bodies that were emplaced between 2.96–2.87 Ga. Our mapping of the Park Reservoir Quadrangle has revealed the presence of five different Archean quartzofeldspathic units, two sets of amphibolite and diabase dikes, a small occurrence of the Cambrian Flathead Sandstone, two Quaternary tills, and Quaternary alluvium. The Archean rock units range in age from ca. 2.96–2.75 Ga, the oldest of which are the most
ancient rocks yet reported in the Bighorn batholith.
All the Archean rocks have subtle but apparent planar fabric elements, which are variable in orientation and
are interpreted to represent magmatic flow during emplacement. The Granite Ridge tear fault, which is the northern boundary of the Piney Creek thrust block, is mapped into the Archean core as a mylonite zone. This relationship indicates that the bounding faults of the Piney Creek thrust block were controlled by weak zones within the
Precambrian basement rocks.
