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Journal articles on the topic "Metamorphic rocks Nevada"
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Ririe, G. Todd. "A comparison of alteration assemblages associated with Archean gold deposits in Western Australia and Paleozoic gold deposits in the southeast United States." Canadian Journal of Earth Sciences 27, no. 12 (December 1, 1990): 1560–76. http://dx.doi.org/10.1139/e90-168.
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A comparison of high-alumina mineral assemblages spatially associated with the Haile and Brewer gold deposits in the Paleozoic Carolina slate belt (CSB) of the southeast United States and the Sons of Gwalia and Mount Celia gold deposits in the Archean Norseman–Wiluna greenstone belt (NWGB) in Western Australia suggests a similar hydrothermal origin and subsequent metamorphic and deformational history. A common hydrothermal origin is supported by the striking similarity in whole-rock chemistry, even though there were probably significant variations in original unaltered protoliths. An analysis of rocks from each of the deposits that contain high-alumina minerals demonstrates that the protoliths were leached of alkalis with respect to aluminum and have a ratio of Al2O3/Na2O + CaO + K2O greater than three. Although the rocks contain abundant high-alumina minerals, the aluminum content in these rocks is not unusually high, and it does not appear that there has been any significant transport of aluminum either into or out of the rocks that were altered.The most common high-alumina minerals found in rocks affected by the feldspar destructive alteration event include andalusite, kyanite, pyrophyllite, kaolinite, and sericite. Other minerals present in variable amounts include diaspore, chloritoid, alunite, natroalunite, paragonite, and topaz. It is possible that some of these minerals formed during the early hydrothermal alteration event and were recrystallized during metamorphism. Regardless of when the high-alumina minerals formed, textural relations suggest that the rocks had been hydrothermally altered by the time the metamorphic minerals formed. A comparison of alteration from the deposits studied in the CSB and the NWGB suggests there are many similarities to acid-sulfate alteration associated with geothermal areas, such as Yellowstone Park, Wyoming, and with acid-sulfate gold deposits, such as Goldfield, Nevada. Thus, it is possible that the protolith of the metamorphosed rocks in the CSB and NWGB contained an alteration assemblage that included alunite, pyrophyllite, and kaolinite.A generalized paragenetic sequence determined from petrographic and field observations, beginning with regional metamorphism, follows: (i) formation of andalusite, kyanite, chloritoid, and topaz during prograde metamorphism, depending on whole rock chemistry, (ii) formation of pyrophyllite and quartz-rich pods during silicification of aluminosilicate-bearing rocks, (iii) bedding parallel schistosity and fracturing produced by a deformational event, (iv) fractures filled by quartz, sericite, pyrophyllite, or calcite, (v) folding of early layering in the rocks to form a crenulation cleavage accompanied by introduction of quartz veins at high angles to foliation; and (vi) retrograde metamorphism of andalusite–kyanite-pyrophyllite to produce an assemblage of kaolinite ± diaspore.The spatial association of the acid-sulfate alteration with gold mineralization, together with comparison of analogous alteration associated with younger unmetamorphosed acid-sulfate gold deposits, suggests that at least some of the gold was introduced during the early premetamorphic alteration event. The present location of gold in each deposit is a result of local changes brought about by later metamorphic and deformational events.
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Blackford, Nolan R., Sean P. Long, Austin Stout, David W. Rodgers, C. M. Cooper, Kimberly Kramer, Russell V. Di Fiori, and Emmanuel Soignard. "Late Cretaceous upper-crustal thermal structure of the Sevier hinterland: Implications for the geodynamics of the Nevadaplano." Geosphere 18, no. 1 (November 22, 2021): 183–210. http://dx.doi.org/10.1130/ges02386.1.
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Abstract Crustal temperature conditions can strongly influence the evolution of deformation during orogenesis. The Sevier hinterland plateau in Nevada and western Utah (“Nevadaplano”) experienced a Late Cretaceous episode of shallow-crustal metamorphism and granitic magmatism. Here, we investigate the thermal history of the Nevadaplano by measuring peak thermal field gradients attained in the upper 10–20 km of the crust along an east-west transect through nine ranges in eastern Nevada and western Utah, by integrating Raman spectroscopy of carbonaceous material thermometry and published conodont alteration indices with reconstructed cross sections. Thermal field gradients of 29 ± 3 °C/km were obtained in the House and Confusion Ranges in westernmost Utah. The Deep Creek, Schell Creek, and Egan Ranges in easternmost Nevada yielded elevated gradients of 49 ± 7 °C/km, 36 ± 3 °C/km, and 32 ± 6 °C/km, respectively. Moving westward, the White Pine, Butte, Pancake, and Fish Creek Ranges exhibit gradients typically between ~20–30 °C/km. The elevated thermal gradients in easternmost Nevada are interpreted to have been attained during ca. 70–90 Ma granitic magmatism and metamorphism and imply possible partial melting at ~18 km depths. Our data are compatible with published interpretations of Late Cretaceous lithospheric mantle delamination under the Sevier hinterland, which triggered lower-crustal anatexis and the resulting rise of granitic melts. The lack of evidence for structures that could have accommodated deep burial of rocks in the nearby Northern Snake Range metamorphic core complex, combined with thermal gradients from adjacent ranges that are ~1.5–3 times higher than those implied by thermobarometry in the Northern Snake Range, further highlights the debate over possible tectonic overpressure in Cordilleran core complexes. Cross-section retro-deformation defines 73.4 ± 4.6 km (76 ± 8%) of extension across eastern Nevada and 15 km of shortening in the Eastern Nevada fold belt.
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Long, Sean P., and Matthew J. Kohn. "Distributed ductile thinning during thrust emplacement: A commonly overlooked exhumation mechanism." Geology 48, no. 4 (January 31, 2020): 368–73. http://dx.doi.org/10.1130/g47022.1.
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Abstract Quantifying the processes that control exhumation is essential for understanding the evolution of mountain belts. In the Cordilleran orogen in Nevada (western United States), rocks exhumed in the Ruby–East Humboldt metamorphic core complex underwent 4 ± 2 kbar of decompression between 85 and 60 Ma, which has been interpreted as a consequence of synorogenic extension. However, evidence for significant normal faulting in this region prior to 45 Ma is lacking. Here, we present an alternative interpretation: that this decompression can be attributed to distributed ductile thinning (DDT) of mid-crustal metamorphic rocks above the basal Cordilleran décollement during eastward translation. Such a process has been documented within the Himalayan Main Central thrust sheet, which locally accommodated up to 15 km of DDT during Miocene translation. Other examples of DDT have been documented in the Alpine and Caledonian orogens (Europe), and the Sanbagawa belt (Japan). DDT may represent a widespread exhumation process that can account for a significant portion of the decompression path of deeply exhumed rocks. As a condition of strain compatibility, thrust-parallel stretching accompanying DDT is expected to enhance displacement magnitude in the transport direction, and is therefore an important component of the deformation field that must be considered for accurate assessment of mass balance in thrust systems.
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Friedman, G. M., and D. J. Schultz. "Precipitation of vaterite (CaCO3) during oil field drilling." Mineralogical Magazine 58, no. 392 (September 1994): 401–8. http://dx.doi.org/10.1180/minmag.1994.058.392.05.
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AbstractVaterite, a CaCO3 polymorph, is a rare mineral that is said to be metastable under all known conditions. According to the literature, vaterite precipitated from carbonate solution recrystallizes spontaneously to calcite or aragonite. Yet vaterite has been identified in hard tissues of organisms, in gallstones, in contact metamorphic aureoles, in zones of thermal metamorphism, in a meteorite, and in cone-in-cone concretions. Newly precipitated vaterite has formed at the expense of carbonate rock in drilling fluids in wells of New York, Michigan, Nevada, Texas, and New Zealand. Petrographic examination reveals a light brown core of Ca3SiO5 surrounded by a colourless rim of vaterite. The δ18OPDB of New York vaterite is −12.4‰ and that of the Michigan vaterite is −17.6‰, which reflect the oxygen isotopic composition of meteoric freshwater used in drilling. The δ13CPDB value of −19.2‰ for New York vaterite and that of −17.6‰ for Michigan vaterite suggest that natural gas dissolved original carbonate in the subsurface. Drilling records from both wells indicate that natural gas was released into the drilling muds from the formations exposed at the time vaterite was encountered. Crossplots of the oxygen and carbon isotopic ratios overlap those of spurrite rocks in thermal metamorphic zones in Israel. A C-14 radiocarbon analysis of the Michigan vaterite gave an age of 953±39 yr. BP. 88.8±0.6% is modern carbon and 11.2% is dead carbon. Hence this carbon, and therefore the vaterite, is essentially modern. A sample of the New York vaterite yielded a modern age.
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Cooper, Frances J., John P. Platt, and Whitney M. Behr. "Rheological transitions in the middle crust: insights from Cordilleran metamorphic core complexes." Solid Earth 8, no. 1 (February 21, 2017): 199–215. http://dx.doi.org/10.5194/se-8-199-2017.
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Abstract. High-strain mylonitic rocks in Cordilleran metamorphic core complexes reflect ductile deformation in the middle crust, but in many examples it is unclear how these mylonites relate to the brittle detachments that overlie them. Field observations, microstructural analyses, and thermobarometric data from the footwalls of three metamorphic core complexes in the Basin and Range Province, USA (the Whipple Mountains, California; the northern Snake Range, Nevada; and Ruby Mountains–East Humboldt Range, Nevada), suggest the presence of two distinct rheological transitions in the middle crust: (1) the brittle–ductile transition (BDT), which depends on thermal gradient and tectonic regime, and marks the switch from discrete brittle faulting and cataclasis to continuous, but still localized, ductile shear, and (2) the localized–distributed transition, or LDT, a deeper, dominantly temperature-dependent transition, which marks the switch from localized ductile shear to distributed ductile flow. In this model, brittle normal faults in the upper crust persist as ductile shear zones below the BDT in the middle crust, and sole into the subhorizontal LDT at greater depths.In metamorphic core complexes, the presence of these two distinct rheological transitions results in the development of two zones of ductile deformation: a relatively narrow zone of high-stress mylonite that is spatially and genetically related to the brittle detachment, underlain by a broader zone of high-strain, relatively low-stress rock that formed in the middle crust below the LDT, and in some cases before the detachment was initiated. The two zones show distinct microstructural assemblages, reflecting different conditions of temperature and stress during deformation, and contain superposed sequences of microstructures reflecting progressive exhumation, cooling, and strain localization. The LDT is not always exhumed, or it may be obscured by later deformation, but in the Whipple Mountains, it can be directly observed where high-strain mylonites captured from the middle crust depart from the brittle detachment along a mylonitic front.
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Affinati, Suzanne Craddock, Thomas D. Hoisch, Michael L. Wells, and Jeffrey D. Vervoort. "Pressure-temperature-time paths from the Funeral Mountains, California, reveal Jurassic retroarc underthrusting during early Sevier orogenesis." GSA Bulletin 132, no. 5-6 (September 17, 2019): 1047–65. http://dx.doi.org/10.1130/b35095.1.
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Abstract New metamorphic pressure-temperature (P-T) paths and Lu-Hf garnet ages reveal a temporal correlation between Middle to Late Jurassic retroarc underthrusting and arc magmatism in southwestern North America. P-T paths were determined for 12 garnet porphyroblasts from six samples from the Chloride Cliff area of the Funeral Mountains in southeastern California. The composite path shows a pressure increase from 4.2 to 6.5 kbar as temperature increased from 550 to 575 °C, followed by a pressure decrease to 5.1 kbar during a further increase in temperature to 590 °C. Lu-Hf garnet ages from a pelitic schist (167.3 ± 0.7 Ma) and a garnet amphibolite (165.1 ± 9.2 Ma) place these P-T paths in the Middle Jurassic. We interpret the near-isothermal pressure increase portion of the P-T path to have developed during thrust-related burial, similar to lower grade rocks at Indian Pass, 8 km to the southeast, where garnet P-T paths show a pressure increase dated by the Lu-Hf method at 158.2 ± 2.6 Ma. We interpret the pressure decrease portion of the composite P-T path from the Chloride Cliff area to reflect exhumation contemporaneous with cooling in the Indian Pass area documented from muscovite 40Ar/39Ar step-heating ages of 152.6 ± 1.4 and 146 ± 1.1 Ma. The conditions and timing of metamorphism determined for the Indian Pass and Chloride Cliff areas, and isogradic surfaces that cut across stratigraphy, support the interpretation that the strata were dipping moderately NW during metamorphism, parallel to the thrust ramp that buried the rocks. Burial likely resulted from top-SE motion along the Funeral thrust, which was later reactivated as a low-angle normal fault with opposite motion to become the currently exposed Boundary Canyon detachment that was responsible for Miocene and possibly older exhumation. The part of the burial history captured by garnet growth occurred ∼6 m.y. before the 161 Ma peak of high-flux magmatism in the arc. Burial was contemporaneous with metamorphic ages from the western Sierra Nevada metamorphic belt, with the possible timing of accretion of arc terranes in northern California, and with the initiation of Franciscan subduction. Burial ages are also similar in timing with generally E-W crustal shortening in the retroarc that produced the East Sierra thrust system, the Luning-Fencemaker fold and thrust belt, the possible early history of the Central Nevada thrust belt, and the western thrusts of the southern Sevier belt. The timing of tectonic burial documented in this study and of high-flux magmatism in the arc supports the interpretation that the development of a coherent arc-trench system in the Early Jurassic resulted in the underthrusting of melt-fertile material beneath the arc along west- to northwest-dipping faults such as the Funeral thrust in the Jurassic, which penetrated the basement to the west as well as the roots of the magmatic arc, leading to increased magmatism.
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MILLER, DAVID M., WENDY C. HILLHOUSE, ROBERT E. ZARTMAN, and MARVIN A. LANPHERE. "Geochronology of intrusive and metamorphic rocks in the Pilot Range, Utah and Nevada, and comparison with regional patterns." Geological Society of America Bulletin 99, no. 6 (1987): 866. http://dx.doi.org/10.1130/0016-7606(1987)99<866:goiamr>2.0.co;2.
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Zuza, Andrew V., Christopher D. Henry, Seth Dee, Charles H. Thorman, and Matthew T. Heizler. "Jurassic–Cenozoic tectonics of the Pequop Mountains, NE Nevada, in the North American Cordillera hinterland." Geosphere 17, no. 6 (October 27, 2021): 2078–122. http://dx.doi.org/10.1130/ges02307.1.
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Abstract The Ruby Mountains–East Humboldt Range–Wood Hills–Pequop Mountains (REWP) metamorphic core complex, northeast Nevada, exposes a record of Mesozoic contraction and Cenozoic extension in the hinterland of the North American Cordillera. The timing, magnitude, and style of crustal thickening and succeeding crustal thinning have long been debated. The Pequop Mountains, comprising Neoproterozoic through Triassic strata, are the least deformed part of this composite metamorphic core complex, compared to the migmatitic and mylonitized ranges to the west, and provide the clearest field relationships for the Mesozoic–Cenozoic tectonic evolution. New field, structural, geochronologic, and thermochronological observations based on 1:24,000-scale geologic mapping of the northern Pequop Mountains provide insights into the multi-stage tectonic history of the REWP. Polyphase cooling and reheating of the middle-upper crust was tracked over the range of <100 °C to 450 °C via novel 40Ar/39Ar multi-diffusion domain modeling of muscovite and K-feldspar and apatite fission-track dating. Important new observations and interpretations include: (1) crosscutting field relationships show that most of the contractional deformation in this region occurred just prior to, or during, the Middle-Late Jurassic Elko orogeny (ca. 170–157 Ma), with negligible Cretaceous shortening; (2) temperature-depth data rule out deep burial of Paleozoic stratigraphy, thus refuting models that incorporate large cryptic overthrust sheets; (3) Jurassic, Cretaceous, and Eocene intrusions and associated thermal pulses metamorphosed the lower Paleozoic–Proterozoic rocks, and various thermochronometers record conductive cooling near original stratigraphic depths; (4) east-draining paleovalleys with ∼1–1.5 km relief incised the region before ca. 41 Ma and were filled by 41–39.5 Ma volcanic rocks; and (5) low-angle normal faulting initiated after the Eocene, possibly as early as the late Oligocene, although basin-generating extension from high-angle normal faulting began in the middle Miocene. Observed Jurassic shortening is coeval with structures in the Luning-Fencemaker thrust belt to the west, and other strain documented across central-east Nevada and Utah, suggesting ∼100 km Middle-Late Jurassic shortening across the Sierra Nevada retroarc. This phase of deformation correlates with terrane accretion in the Sierran forearc, increased North American–Farallon convergence rates, and enhanced Jurassic Sierran arc magmatism. Although spatially variable, the Cordilleran hinterland and the high plateau that developed across it (i.e., the hypothesized Nevadaplano) involved a dynamic pulsed evolution with significant phases of both Middle-Late Jurassic and Late Cretaceous contractional deformation. Collapse long postdated all of this contraction. This complex geologic history set the stage for the Carlin-type gold deposit at Long Canyon, located along the eastern flank of the Pequop Mountains, and may provide important clues for future exploration.
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Gabet, Emmanuel J. "Lithological and structural controls on river profiles and networks in the northern Sierra Nevada (California, USA)." GSA Bulletin 132, no. 3-4 (July 15, 2019): 655–67. http://dx.doi.org/10.1130/b35128.1.
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Abstract In this study, the strong lithological heterogeneity of the northern Sierra Nevada (California, USA) is exploited to elucidate the role of lithology on river profiles and patterns at the mountain-range scale. The analyses indicate that plutonic, metavolcanic, and quartzite bedrock generally host the steepest river reaches, whereas gentle reaches flow across non-quartzite metasedimentary rocks and fault zones. In addition, the largest immobile boulders are often in the steepest reaches, suggesting that wide joint spacing plays a role in creating steep channels, and a positive relationship between boulder size and hillslope angle highlights the coupling of the hillslope and fluvial systems. With respect to river network configurations, dendritic patterns dominate in the plutonic bedrock, with channels aligned down the slope of the range; in contrast, river reaches in the metamorphic belts are mainly longitudinal and parallel to the structural grain. River profiles and patterns in the northern Sierra Nevada, therefore, bear a strong lithological imprint related to differential erosion. These observations indicate that attempts to infer uplift and tilting of the range based on the gradients and orientations of paleochannel remnants should first account for the effect of bedrock erodibility. Indeed, the differences in gradients of Tertiary paleochannel remnants used to argue for late Cenozoic uplift of the range can be wholly explained by differences in lithology.
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Percival, John A. "Orthopyroxene–poikilitic tonalites of the Desliens igneous suite, Ashuanipi granulite complex, Labrador–Quebec, Canada." Canadian Journal of Earth Sciences 28, no. 5 (May 1, 1991): 743–53. http://dx.doi.org/10.1139/e91-064.
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The Ashuanipi complex of the Archean Superior Province consists of an older sequence of sedimentary rocks cut by sills and goblet-shaped intrusions of the Desliens igneous suite (DIS). The complex was regionally metamorphosed to granulite facies and subsequently intruded by peraluminous granodiorite batholiths. Tonalites of the DIS contain characteristic < 2 cm inclusion-filled orthopyroxene crystals of probable igneous origin, variably recrystallized and overgrown by garnet, biotite and blocky orthopyroxene that suggest metamorphic P–T conditions of 0.5–0.62 GPa and 750–850 °C. Andesine in tonalite contains abundant drop-like quartz inclusions. Inclusion-filled pyroxene and plagioclase are both inferred to have nucleated on partly resorbed quartz and plagioclase grains within a melt. Similar poikilitic textures characterize subordinate leucotonalite, diorite, gabbro, and pyroxenite, which together with tonalite make up the DIS. Some of the petrological characteristics of the suite are unusual, but known from other regions: (i) some felsic magmatic rocks in the southern Sierra Nevada and Barrington Tops (Australia) batholiths contain primary orthopyroxene; (ii) goblet-shaped plutons are common in orogenic belts, and tonalites with this geometry occur within a sedimentary succession in the Trinity Alps of California; (iii) orthopyroxene oikocrysts characterize parts of the Bjerkreim–Sokndal lopolith of southwestern Norway.
Dissertations / Theses on the topic "Metamorphic rocks Nevada"
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Plummer, Kelly. "Contact metamorphism of calc-silicate rocks in the Belmont Contact aureole, central Nevada." 2006. http://etd.utk.edu/2006/PlummerKelly.pdf.
Full textBooks on the topic "Metamorphic rocks Nevada"
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Ross, Donald Clarence. Metamorphic framework rocks of the southern Sierra Nevada, California. Menlo Park, Calif: U.S. Dept. of the Interior, Geological Survey, 1987.
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Ross, Donald Clarence. The metamorphic and plutonic rocks of the southernmost Sierra Nevada, California, and their tectonic framework. Washington: U.S. G.P.O., 1989.
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Ross, Donald Clarence. The metamorphic and plutonic rocks of the southernmost Sierra Nevada, California, and their tectonic framework. [Reston, Va.?]: Dept. of the Interior, U.S. Geological Survey, 1989.
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Garside, Larry J. Mesozoic metavolcanic and metasedimentary rocks of the Reno-Carson City area, Nevada and adjacent California. Reno: MacKay School of Mines, University of Nevada, 1998.
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M, Miller David. K-Ar ages of Jurassic to Tertiary plutonic and metamorphic rocks, northwestern Utah and northeastern Nevada. Washington, D.C: U.S. G.P.O., 1990.
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1921-, Ketner Keith Brindley, and United States Geological Survey, eds. An outline of tectonic, igneous, and metamorphic events in the Goshute-Toano range between Silver Zone Pass and White Horse Pass, Elko County, Nevada: A history of superposed contractional and extensional deformation. Washington: U.S. G.P.O., 1998.
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Jiang, Ganqing, and Carol Dehler, eds. Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting. Geological Society of America, 2022. http://dx.doi.org/10.1130/fld063.
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Prepared in conjunction with the 2022 GSA Cordilleran/Rocky Mountain Sections Joint Meeting, this Field Guide showcases trips to geologically interesting areas in Arizona, Nevada, and California. Enjoy a three-day trip to the Buckskin-Rawhide and northern Plomosa Mountains metamorphic core complexes in Arizona. In Nevada, learn about the geology of Frenchman Mountain and Rainbow Gardens and landslide deposits and mechanisms in the eastern Spring Mountains. Or learn about microbialites in Miocene and modern lakes near Las Vegas. When weather permits, unravel the geological history of southern Death Valley, and explore vertebrate paleontology and Cenozoic depositional environments in Death Valley, California.
Book chapters on the topic "Metamorphic rocks Nevada"
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Hoiland, C., J. Hourigan, and E. Miller. "Evidence for large departures from lithostatic pressure during Late Cretaceous metamorphism in the northern Snake Range metamorphic core complex, Nevada." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2555(07).
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ABSTRACT The highest-grade Barrovian-type metamorphic rocks of the North American Cordillera exposed today are Late Cretaceous in age and found within an orogen-parallel belt of metamorphic core complexes for which the tectonic histories remain controversial. Thermobarometric studies indicate that many of these Late Cretaceous metamorphic assemblages formed at pressures of >8 kbar, conventionally interpreted as >30 km depth by assuming lithostatic conditions. However, in the northern Basin and Range Province, detailed structural reconstructions and a growing body of contradictory geologic data in and around the metamorphic core complexes indicate these metamorphic rocks are unlikely to have ever been buried any deeper than ~15 km depth (~4 kbar, lithostatic). Recent models controversially interpret this discrepancy as the result of “tectonic overpressure,” whereby the high-grade mineral assemblages were formed under superlithostatic conditions without significant tectonic burial. We performed several detailed studies within the Snake Range metamorphic core complex to test the possibility that cryptic structures responsible for additional burial and exhumation might exist, which would refute such a model. Instead, our data highlight the continued discordance between paleodepth and paleopressure and suggest the latter may have reached nearly twice the lithostatic pressure in the Late Cretaceous. First, new detrital zircon U-Pb geochronology combined with finite-strain estimates show that prestrain thicknesses of the lower-plate units that host the high-pressure mineral assemblages correspond closely to the thicknesses of equivalent-age units in adjacent ranges rather than to those of the inferred, structurally overridden (para) autochthon, inconsistent with cross sections and interpretations that assume a lower plate with a deeper origin for these rocks. Second, new Raman spectroscopy of carbonaceous material of upper- and lower-plate units identified an ~200 °C difference in peak metamorphic temperatures across the northern Snake Range detachment but did not identify any intraplate discontinuities, thereby limiting the amount of structural excision to motion on the northern Snake Range detachment itself, and locally, to no more than 7–11 km. Third, mapped geology and field relationships indicate that a pre-Cenozoic fold truncated by the northern Snake Range detachment could have produced ~3–9 km of structural overburden above Precambrian units, on the order of that potentially excised by the northern Snake Range detachment but still far short of expected overburden based on lithostatic assumptions. Fourth, finite-strain measurements indicate a shortening (constrictional) strain regime favorable to superlithostatic conditions. Together, these observations suggest that pressures during peak metamorphism may have locally reached ~150%–200% lithostatic pressure. Such departures from lithostatic conditions are expected to have been most pronounced above regions of high heat flow and partial melting, and/or at the base of regional thrust-bounded allochthons, as is characteristic of the spatial distribution of Cordilleran metamorphic core complexes during the Late Cretaceous Sevier orogeny.
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Muntean, John L. "Chapter 36: Carlin-Type Gold Deposits in Nevada: Geologic Characteristics, Critical Processes, and Exploration." In Geology of the World’s Major Gold Deposits and Provinces, 775–95. Society of Economic Geologists, 2020. http://dx.doi.org/10.5382/sp.23.36.
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Abstract Carlin-type gold deposits in Nevada account for ~5% of worldwide annual gold production, typically about ~135 metric tons (t) (~4.5 Moz) per year. They are hydrothermal epigenetic replacement bodies hosted predominantly in carbonate-bearing sedimentary rocks. They are known for their “invisible” gold that occurs in the crystal structure of pyrite. Over 95% of the production from these deposits is from four clusters of deposits, which include the Carlin trend and the Cortez, Getchell, and Jerritt Canyon camps. Despite differences in the local geologic settings, the characteristics of the deposits are very similar in the four clusters. Shared characteristics include: (1) alteration characterized by carbonate dissolution, silicate argillization, and silicification; (2) ore formation characterized by auriferous arsensian pyrite, typically as rims on preore pyrite, followed by late open-space deposition of orpiment, realgar, stibnite, and other minerals; (3) Ag/Au ratios of <1 in ore; (4) an As-Hg-Sb-Tl geochemical signature; (5) low temperatures (~160°–240°C) and salinities of ore fluids (~1–6 wt % NaCl equiv) and fairly shallow depths of formation (<~2–3 km); and (6) lack of mineral and elemental zoning around ore. The four clusters share regional geologic controls related to formation as follows: (1) along the rifted margin of a craton, (2) within the slope facies of a passive margin sequence dominated by carbonates, (3) in the lower plate of a regional thrust fault, and (4) during a narrow time interval in the late Eocene (~42–34 Ma). The geometries and ore controls of the deposits in the four clusters are also very similar. At the deposit scale, ore and hydrothermal alteration are commonly associated with high-angle faults and preore low-angle contractional structures, including thrust faults and folds. The high-angle faults acted as fluid pathways for upwelling ore fluids, which were then diverted into lower angle favorable strata and contractional structures, where fluid-rock interaction led to replacement of carbonate and formation of ore. Rheologic contrasts between lithologies were also critical in diverting fluids into wall rocks. Common rheologic contrasts include contacts between thin- and thick-bedded lithologic units and the margins of contact metamorphic aureoles associated with Mesozoic intrusions. The similarities suggest common processes. Four critical processes are apparent: (1) development of source(s) for gold and other critical components of the ore fluids, (2) formation of fluid pathways, (3) water-rock interaction and gold deposition, and (4) a tectonic trigger, which was renewal of magmatism and a change from contraction to extension in the late Eocene. Consensus exists on these processes, except for the source of gold and other components of the ore fluid, with most models calling upon either a magmatic-hydrothermal source or a crustal source, where metals were scavenged by either meteoric or metamorphic fluids. Future research should focus on Carlin-style deposits in Nevada that exhibit epithermal characteristics and deposits that appear to have a clear genetic association with magmatic-hydrothermal systems associated with upper crustal intrusions. Rather than discrete types of ore deposits, there may be continua between Carlin-type gold deposits, epithermal deposits, and distal disseminated deposits, with the four large camps representing an end member.
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Craddock Affinati, Suzanne, Thomas D. Hoisch, Michael L. Wells, and Samuel Wright. "Retroarc Jurassic burial and exhumation of Barrovian metamorphic rocks dated by monazite petrochronology, Funeral Mountains, California." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2555(01).
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ABSTRACT In this study, we determined the timing of burial and subsequent exhumation of Barrovian metamorphic rocks from the Chloride Cliff area of the Funeral Mountains in southeastern California by constraining the ages of different portions of a pressure-temperature (P-T) path. Using a split-stream laser-ablation inductively coupled plasma–mass spectrometry (ICP-MS) system, we analyzed 192 domains from 35 grains of monazite within five samples with a spot size of 8 µm to determine U-Pb ages and trace-element abundances from the same samples (same polished sections) that were analyzed to produce the P-T paths. Changes that took place within individual monazite grains reflect localized equilibrium and captured the changes in heavy rare earth element (HREE) abundances in the matrix reservoir that occurred as garnet grew, resorbed, and then regrew, thus constraining ages on different portions of the P-T path. The results show that garnet began growing ca. 168 Ma, began resorbing ca. 160 Ma, began retrograde regrowth ca. 157 Ma, and continued to regrow at least through ca. 143 Ma. The early garnet growth corresponds to a period of pressure increase along the P-T path. The subsequent partial resorption corresponds to the prograde crossing of a garnet-consuming reaction during decompression, and the retrograde garnet regrowth occurred when this same reaction was recrossed in the retrograde sense during further decompression. These results are consistent with previously determined ages, which include a Lu-Hf garnet age of 167.3 ± 0.72 Ma for the early pressure-increase portion of the P-T path, and 40Ar/39Ar muscovite cooling ages of 153 and 146 Ma in the lower-grade Indian Pass area 10 km southeast of Chloride Cliff. The 40Ar/39Ar muscovite ages document cooling at the same time as retrograde garnet regrowth was taking place at Chloride Cliff. The oldest monazite age obtained in this study, 176 ± 5 Ma, suggests that southeast-directed thrusting within the Jurassic retroarc was ongoing by this time along the California portion of the western North American plate margin, as a consequence of east-dipping subduction and/or arc collision. The Funeral Mountains were likely located on the east side of the northern Sierra Nevada range in the Jurassic, taking into account dextral strike-slip displacement along the Cretaceous Mojave–Snow Lake fault. The Late Jurassic timing of burial in the Funeral Mountains and its Jurassic location suggest burial was associated with the East Sierran thrust system. The timing of prograde garnet resorption during exhumation (160–157 Ma) corresponds to a change from regional dextral transpression to sinistral transtension along the Jurassic plate margin inferred to have occurred ca. 157 Ma. The recorded exhumation was concurrent with intrusion of the 148 Ma Independence dike swarm in the eastern Sierra Nevada and Mojave regions, which developed within a regime of northeast-southwest extension.
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Singleton*, John S., Nikki M. Seymour, and Evan D. Strickland. "The Buckskin-Rawhide and northern Plomosa Mountains metamorphic core complexes, west-central Arizona, USA." In Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting, 85–107. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.0063(05).
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ABSTRACT The Buckskin-Rawhide and northern Plomosa Mountains in west-central Arizona are metamorphic core complexes that record NE-directed, large-magnitude extension in the early to middle Miocene. Both core complexes consist of mylonites exposed in the footwall of corrugated, low-angle detachment faults. The Late Cretaceous Orocopia Schist and early Miocene intrusions dominate the mylonitic footwall of the northern Plomosa Mountains. The Orocopia Schist was emplaced during low-angle subduction of the Farallon plate and exhibits the hallmarks of the underplated Laramide subduction complexes, including blocks of metasomatized peridotite encased in quartzofeldspathic schist. In the Buckskin-Rawhide Mountains, carbonate-rich metasedimentary rocks that were buried to midcrustal depths by Mesozoic thrust faults preferentially absorbed Miocene footwall strain and localized the Buckskin detachment fault. A correlation between distinct granodiorite in the footwall of the Buckskin detachment fault in the eastern Bouse Hills and a hanging-wall conglomerate sourced from this granodiorite provides constraints on middle Miocene displacement across the detachment fault and indicates that displacement increased northeastward in the slip direction. The termination of slip on the Buckskin detachment fault also younged northeastward, largely ending by ca. 19 Ma in the western Bouse Hills and ca. 17 Ma in the westernmost Buckskin Mountains, but continuing to <16 Ma in the southern Buckskin Mountains and to ca. 12 Ma in the eastern Buckskin Mountains. Late stages of slip on the detachment fault record minor NW-SE shortening during amplification of corrugation folds. Postdetachment faulting across the region was dominated by dextral and oblique-dextral slip on NW-striking faults influenced by the Pacific–North America plate boundary. Locations visited on this three-day field trip highlight the structural evolution of these metamorphic core complexes.
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Bradley, Mark A., L. Page Anderson, Nathan Eck, and Kevin D. Creel. "Chapter 16: Giant Carlin-Type Gold Deposits of the Cortez District, Lander and Eureka Counties, Nevada." In Geology of the World’s Major Gold Deposits and Provinces, 335–53. Society of Economic Geologists, 2020. http://dx.doi.org/10.5382/sp.23.16.
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Abstract The Cortez district is in one of the four major Carlin-type gold deposit trends in the Great Basin province of Nevada and contains three giant (>10 Moz) gold orebodies: Pipeline, Cortez Hills, and Goldrush, including the recently discovered Fourmile extension of the Goldrush deposit. The district has produced >21 Moz (653 t) of gold and contains an additional 26 Moz (809 t) in reserves and resources. The Carlin-type deposits occur in two large structural windows (Gold Acres and Cortez) of Ordovician through Devonian shelf- and slope-facies carbonate rocks exposed through deformed, time-equivalent lower Paleozoic siliciclastic rocks of the overlying Roberts Mountains thrust plate. Juxtaposition of these contrasting Paleozoic strata occurred during the late Paleozoic Antler orogeny along the Roberts Mountains thrust. Both upper and lower plate sequences were further deformed by Mesozoic compressional events. Regional extension, commencing in the Eocene, opened high- and low-angle structural conduits for mineralizing solutions and resulted in gold deposition in reactive carbonate units in structural traps, including antiforms and fault-propagated folds. The Pipeline and Cortez Hills deposits are located adjacent to the Cretaceous Gold Acres and Jurassic Mill Canyon granodioritic stocks, respectively; although these stocks are genetically unrelated to the later Carlin-type mineralization event, their thermal metamorphic aureoles may have influenced ground preparation for later gold deposition. Widespread decarbonatization, argillization, and silicification of the carbonate host rocks accompanied gold mineralization, with gold precipitated within As-rich rims on fine-grained pyrite. Pipeline and Cortez Hills also display deep supergene oxidation of the hypogene sulfide mineralization. Carlin-type mineralization in the district is believed to have been initiated in the late Eocene (>35 Ma) based on the age of late- to postmineral rhyolite dikes at Cortez Hills. The Carlin-type gold deposits in the district share common structural, stratigraphic, alteration, and ore mineralogic characteristics that reflect common modes of orebody formation. Ore-forming fluids were channeled along both low-angle structures (Pipeline, Goldrush/Fourmile) and high-angle features (Cortez Hills), and gold mineralization was deposited in Late Ordovician through Devonian limestone, limy mudstone, and calcareous siltstone. The Carlin-type gold fluids are interpreted to be low-salinity (2–3 wt % NaCl equiv), low-temperature (220°–270°C), and weakly acidic, analogous to those in other Carlin-type gold deposits in the Great Basin. The observed characteristics of the Cortez Carlin-type gold deposits are consistent with the recently proposed deep magmatic genetic model. Although the deposits occur over a wide geographic area in the district, it is possible that they initially formed in greater proximity to each other and were then spatially separated during Miocene and post-Miocene regional extension.
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Francis, Robert D., Gregory J. Holk, Tor B. Lacy, and Charles T. Walker. "Coalescing upper-crust detachment faults as a major structural style in the Great Basin: Evidence from the White Pine and Horse Ranges, east-central Nevada, USA." In Plate Tectonics, Ophiolites, and Societal Significance of Geology: A Celebration of the Career of Eldridge Moores. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.2552(05).
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ABSTRACT Determining the origin and evolution of basin-and-range geomorphology and structure in the western United States is a fundamental problem with global implications for continental tectonics. Has the extensional tectonic development of the Great Basin been dominated by steeply dipping (horst and graben) faulting or detachment faulting? The purpose of this paper is to provide evidence that attenuation due to multiple coalescing detachment faults has been a significant or dominant upper-crustal process in at least some areas of the Great Basin. We present mapping at a scale of 1:3000 and seismic refraction profiling of an area at the discontinuity between the White Pine and Horse Ranges, east-central Nevada, USA, which indicate the existence of a detachment rooted in an argillaceous ductile unit. This fault, which we call the Currant Gap detachment, coalesces with the previously mapped regional White Pine detachment. Our data suggest that the Currant Summit strike-slip fault at the surface, previously proposed to explain a nearly 2500 m east-west surface offset between the two ranges, likely does not exist. If a discontinuity exists at depth, it could be manifested at the surface by the undulating topography of the two coalescing detachments. On the other hand, offset domal uplifts in the two ranges would obviate the need for any lateral discontinuity at depth to explain the observed surface features. Our previous mapping of the White Pine detachment showed that it extends over the White Pine, Horse, and Grant Ranges and into Railroad Valley (total of 3000 km2). Accordingly, we propose a model of stacked, coalescing detachments above the metamorphic infrastructure; these detachments are regional and thus account for most of the basin-range relief and upper-crust extension in this area. An essential feature of our model is that these detachments are rooted in ductile units. Detachments that have been observed in brittle units could have initiated at a time when elevated temperatures or fluid flow enhanced the ductility of the rocks. The Currant Gap and White Pine detachments exhibit distinctive types of fluid-genetic silicified rocks. Study of such rocks in fault contacts could provide insights into the initiation and early history of detachment faulting as well as the migration of fluids, including petroleum.
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Fleming*, Zachariah, Terry Pavlis*, and Ghislain Trullenque*. "Unraveling the multi-phase history of southern Death Valley geology." In Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting, 67–83. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.0063(04).
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ABSTRACT This field trip is designed to highlight recent findings in regard to the tectonic history of the southern Death Valley region. During the first day, stops will take place in the Ibex Hills and adjacent Ibex Pass area. These stops were chosen to emphasize recent work that supports multiple phases of extension in the region, and is recorded by the interactions of complexly overprinted normal faults. Mapping of the Ibex Hills revealed an older set of normal faults that have a down-to-the-SW sense of movement and are cross-cut by down-to-the-NW style normal faults. Additionally, the Ibex Pass basin poses a number of questions regarding its stratigraphy and how it relates to the timing and kinematics of the region. Multiple stops within the basin will show the variation of volcanic and sedimentary units across Ibex Pass. The second day of the field trip is focused more so on the more recent transtensional and strike-slip history of southern Death Valley. In particular, recent mapping has correlated features in the Avawatz and Owlshead Mountains that indicate ~40k m of offset along the Southern Death Valley Fault Zone (SDVFZ). Stops will take place along traces of the SDVFZ in the Avawatz Mountains and the Noble Hills. The final stop of the trip is in the Mormon Point turtleback, where the implications of the SDVFZ offset are discussed, alongside the metamorphic rocks at the stop, suggesting the restoration of the Panamint Range partially atop the Black Mountains.
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Nevle, Richard J., Steven Nightingale, and Mattias Lanas. "Roof Pendants." In The Paradise Notebooks, 19–22. Cornell University Press, 2022. http://dx.doi.org/10.7591/cornell/9781501762697.003.0005.
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This chapter focuses on the Sierra Nevada roof pendants. Gazing out across the roof of the Sierra Nevada, one might spy thin black and rust-orange fins of frost-heaved metamorphic rock riding atop bright granite. These fins, known as roof pendants, were travelers once, geologic migrants from the sea. The distinctive chemical compositions of these geologic travelers give rise to thin scrapes of distinctive soils. Such soils, in the austere climatic conditions of high elevation, nurture gardens with delicate wildflowers. Into these Sierra flower gardens wander bees and butterflies and hummingbirds. The chapter then considers the nature of beauty. In most cultures, in every century, beauty is bound up with unity.
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Bevins, Richard E., and Douglas Robinson. "Regional low-grade polygenetic metamorphism and inversion in the northern part of the Eastern Belt, Northern Sierra Nevada, California." In Low-Grade Metamorphism of Mafic Rocks, 29–50. Geological Society of America, 1995. http://dx.doi.org/10.1130/spe296-p29.
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Gottlieb, Eric S., Elizabeth L. Miller, John W. Valley, Christopher M. Fisher, Jeffrey D. Vervoort, and Kouki Kitajima. "Zircon petrochronology of Cretaceous Cordilleran interior granites of the Snake Range and Kern Mountains, Nevada, USA." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2555(02).
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ABSTRACT We addressed fundamental questions about the lithology, age, structure, and thermal evolution of the deep crust of the retroarc hinterland of the North American Cordilleran orogen through systematic investigation of zircons from Cretaceous plutons in the Snake Range and Kern Mountains of east-central Nevada. Geochronological (U-Pb) and geochemical (trace element, O and Hf isotopes) characterization of pre- and synmagmatic growth domains of zircons, coupled with traditional petrologic methods (petrography, field relationships, and whole-rock major-element, trace-element, and Sr-Nd and Pb isotope geochemistry), fingerprinted temporal variations in crustal contributions to magmatism. The samples are typical felsic, peraluminous Cordilleran interior granitoids that formed between 102 ± 2 Ma and 71 ± 1 Ma (95% confidence). Over the entire time span of magmatism, 87Sr/86Srinitial, εNd(t), 208Pb/204Pb, and εHf(t) exhibit incrementally more “crustal” ratios. The oldest and youngest samples, respectively, predate and postdate all published timing constraints of Cretaceous peak metamorphism in the region and exhibit the least and most radiogenic whole-rock isotopic results in the study (87Sr/86Srinitial = 0.7071 vs. 0.7222; εNd(t) = −3.4 vs. −18.8; 208Pb/204Pb = 38.8 vs. 40.1). Accordingly, the least intrasample variability of εHf(t), δ18OZrc, and trace-element ratios in magmatic zircon domains is also observed in these oldest and youngest samples, whereas greater intrasample variability is observed in intermediate-age samples that intruded during peak metamorphism. The geochemistry of zircon growth in the intermediate-age samples suggests assimilation of partially molten metasedimentary crust led to increased heterogeneity in their magma chemistry. Interaction of magmas with distinctive crust types is indicated by contrasts between four categories of inherited zircon observed in the studied intrusions: (1) detrital zircon with typical magmatic trace-element ratios; (2) zircon derived from high-grade 1.8–1.6 Ga basement; (3) zircon with anomalously low δ18O of uncertain origin, derived from 1.7/2.45 Ga basement (or detritus derived thereof); and (4) zircon from variably evolved Jurassic–Early Cretaceous deep-seated intrusions. The progression of zircon inheritance patterns, correlated with evolving geochemical signatures, in Late Cretaceous granitic plutons is best explained by early, relatively primitive intrusions and their penecontemporaneously metamorphosed country rock having been tectonically transported cratonward and superposed on older basement, from which the later, more-evolved Tungstonia pluton was generated. This juxtaposition consequentially implies tectonic transport of synorogenic plutonic rocks occurred in the Cordilleran hinterland during the Sevier orogeny as a result of the interplay of retroarc magmatism and convergent margin tectonism.
Conference papers on the topic "Metamorphic rocks Nevada"
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Claypoole, Micah N., and Michael W. Ressel. "GOLD BEARING QUARTZ VEINS IN METAMORPHIC ROCK AT MINERAL RIDGE, ESMERALDA COUNTY, NEVADA." In 68th Annual Rocky Mountain GSA Section Meeting. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016rm-276046.
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Long, Sean P., and Emmanuel Soignard. "SHALLOW-CRUSTAL METAMORPHISM DURING LATE CRETACEOUS ANATEXIS IN THE NEVADAPLANO: INSIGHTS FROM A METAMORPHIC FIELD GRADIENT THROUGH THE UPPER CRUST, GRANT RANGE, EASTERN NEVADA, U.S.A." In 68th Annual Rocky Mountain GSA Section Meeting. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016rm-276038.
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Claypoole, Micah N., and Michael W. Ressel. "SHEAR-RELATED GOLD BEARING QUARTZ VEINS IN METAMORPHIC ROCK AT MINERAL RIDGE, ESMERALDA COUNTY, NEVADA." In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-287651.
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Lee, Jeff, Terrence J. Blackburn, and Scott M. Johnston. "EVOLUTION OF THE NORTHERN SNAKE RANGE METAMORPHIC CORE COMPLEX, NEVADA: INTEGRATING FIELD, STRUCTURE, GEOCHRONOLOGIC, AND THERMOCHRONOLOGIC DATA SETS." In Joint 70th Annual Rocky Mountain GSA Section / 114th Annual Cordilleran GSA Section Meeting - 2018. Geological Society of America, 2018. http://dx.doi.org/10.1130/abs/2018rm-314173.
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Thorman, Charles H. "WERE CORE COMPLEX COVER ROCKS IN NE NEVADA BURIED TO GREAT DEPTH DURING METAMORPHISM? – I DON’T THINK SO!!" In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-286239.
Full textReports on the topic "Metamorphic rocks Nevada"
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K-Ar ages of Jurassic to Tertiary plutonic and metamorphic rocks, northwestern Utah and northeastern Nevada. US Geological Survey, 1990. http://dx.doi.org/10.3133/b1906.
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