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Showing 1 to 20 of 72 for “"zircons"”.
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Microtechniques in Pb-U dating of Moroccan zircons.
Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences.
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Archean detrital zircons in the Proterozoic Vishnu Schist of the Grand Canyon, Arizona : implications for crustal architecture and Nuna reconstructions
U-Pb dating of 1035 detrital zircons from twelve spatially-distributed samples of the Paleoproterozoic Vishnu Schist reveals a bimodal 207Pb/ 206Pb age probability diagram with peaks at 1.8 Ga and 2.5 Ga. Surprisingly, only 13% of detrital zircon ages overlap with the published depositional age …
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U-Pb geochronology of the Acasta Gneiss Complex in Northwest Canada
… 4.03-3.6 Ga, as determined by U-Pb dating of zircons (Bowring and Williams 1999). U-Pb dating of xenocrystic cores in these zircons indicates a cryptic record of continental crust older than 4.0 Ga. In this study, zircons were selected and characterized from thirteen samples of Acasta …
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Zircon Geochronology of Ash Beds in the Marcellus Shale of the Appalachian Basin
… Ma to 403.8+/-4 Ma (Frasnian to Emsian). Zircons containing inherited cores reflect ages of greater than 1.1 Ga and are interpreted to originate from the regional basement. In some cases, zircons on the same ash horizon produced ages ranging from 390 to 400 Ma. With no evidence of Pb loss, …
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The Dynamics of the Late Neogene Antarctic Ice Sheets in the Central Ross Sea using a Multianalytical Approach
… a suite of three analyses. A total of 3,869 zircons, between 250-63 microns in size, from sixteen different cores were measured for U-Pb isotopes via LA-ICP-MS. Zircon data was compared to neodymium isotope and clast lithology datasets from collaborators. Site U1522 shows three distinct …
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Tracking multistage deformation within an ultrahigh-pressure terrane: zircon and monazite microstructures and petrochronology from shear zones of the Western Gneiss Region, Norway
… Ti-in-zirconthermometry, and EBSD data from zircons and monazites to investigate the timing ofUHP metamorphism, exhumation, and deformation during these events. Samples werecollected from eclogites, orthogneisses, and paragneisses within five tens-of-meters scaleshear zones exposed in …
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Detrital zircon geochronology of the Upper Miocene Boleo Formation in the Santa Rosalia, Baja California Sur, Mexico
… zircon separation methods yielding roughly 1,000 zircons per sample. We analyzed 315 zircons per sample by LA-ICPMS. Detrital zircon U-Pb ages from the Boleo Formation range dominantly from Late Miocene through Early Cretaceous, with minor Paleozoic and Precambrian ages. Only 5 to 22 grains per …
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Isotopic systematics and mass transfer in amphibolite-grade mylonites
… function of the degree of metamictization of the zircons, the chemistry and mineralogy of the enclosing rock, the P-T conditions of metamorphism and the presence and composition of metamorphic fluids. The possible effects of dynamic metamorphism on the isotopic ages obtained from zircons range …
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Paleogeography of Western North America: Insights from Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry
… and Hf isotope geochemistry of detrital zircons, as well as, geologic mapping and paleocurrent analysis. The Neoproterozoic through Pennsylvanian Yukon-Tanana terrane (YTTs) in the Coast Mountains of southeastern Alaska, the Cretaceous through Eocene strata in the San Juan basin of …
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Detrital Zircon Analysis of Permian Victoria Group Sandstones, Transantarctic Mountains, Antarctica
… the sedimentary provenance further, detrital zircons have been examined from both flanks of the basin. At Clarkson Peak, samples were collected from the lower (quartzose) and upper (volcaniclastic) Buckley Formation. At Mt. Bowers the complete Permian section, from pre-glacial to upper Buckley …
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Miocene core complex development and coeval supradetachment basin evolution of Paros, Greece
… and improbable results in the footwall suite of zircons are examined using laser ablation depth-profiling to address the inherent assumption of homogeneous parent nuclide distribution in the zircon (U-Th)/He technique. Results from footwall zircon (U-Th)/He analyses indicate rapid cooling in …
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Tephrostratigraphy, petrography, geochemistry, age and fossil record of the Ganigobis Shale Member and associated glaciomarine deposits of the Dwyka Group, Late Carboniferous, southern Africa
… new radiometric age data from their juvenile zircons. Carboniferous-Permian Karoo deposits in the Aranos Basin of southern Namibia include the glacially dominated, Carboniferous Dwyka Group and the shelf sediments of the overlying Permian Ecca Group. The Dwyka Group can be subdivided into four …
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The Global Detrital Zircon Database: Quantifying the Timing and Rate of Crustal Growth
… model ages suggest that the majority of detrital zircons U-Pb ages reflect crustal recycling events that generated granitic magmatism, as most grains exhibited Hf isotope ages that are much older than the corresponding U-Pb age. The Triassic Dry Fork Formation was sampled from a site in southern …
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Tertiary Sediments of the Big Hole Valley and Pioneer Mountains, Southwestern Montana: Age, Provenance, and Tectonic Implications
… fluvial deposits. U-Pb geochronology of detrital zircons and air-fall tuffs indicates the presence of Oligocene to Middle Miocene sedimentary rocks outcropping at the surface. Though the presence of detrital muscovite in several outcrops indicates derivation from the nearby 2-mica Chief Joseph …
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Tertiary Sediments of the Big Hole Valley and Pioneer Mountains, Southwestern Montana: Age, Provenance, and Tectonic Implications
… fluvial deposits. U-Pb geochronology of detrital zircons and air-fall tuffs indicates the presence of Oligocene to Middle Miocene sedimentary rocks outcropping at the surface. Though the presence of detrital muscovite in several outcrops indicates derivation from the nearby 2-mica Chief Joseph …
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The Box Ankle and Ocmulgee shear zones of central Georgia: a study of geochemical response to Southern Appalachian deformation events
… east of the Pine Mountain window. U-Pb ages of zircons constrain the timing of deformation along the Box Ankle and Ocmulgee faults at 304 ± 144 and 335 ± 7 Ma respectively. A contrast in zircon response to high grade deformation from both fault zones is observed. The response of zircon U-Pb …
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RECONSTRUCTING PAST ANTARCTIC ICE FLOW PATHS IN THE ROSS EMBAYMENT, ANTARCTICA USING SAND PETROGRAPHY, PARTICLE SIZE AND DETRITAL ZIRCON PROVENANCE
… Particle size, sand petrography, and detrital zircons were used to provide new information on the subglacial geology of Antarctica, as well as assisting in the reconstruction of Last Glacial Maximum (LGM) ice flow paths. Statistical analyses using the Kolmogorov-Smirnov (K-S test) reveal that …
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Geochemical and Geochronological Constraints on the Origin and Evolution of Rocks in the Active Woodlark Rift of Papua New Guinea
… of this chapter was simply to use U-Pb dating of zircons from felsic and intermediate gneisses in the Woodlark Rift to understand the history of rocks from (U)HP terranes that don't preserve the (U)HP metamorphic paragenesis. It was soon realized that the types of U-Pb zircon analyses typically …
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Zircon U-PB and LU-HF isotopic data from some peri-gondwana variscan terranes (Sardinia-Corsica block and calabropeloritan arc): new insights on the cenozoic geodynamic evolution of the central mediterranean basin
… the geochemical data from magmatic and detrital zircons of the basement rocks highlight analogies or differences between the tectono-sedimentary sectors of the Sardinian Variscides (nappe and foreland zones) and between them and the Calabria Variscides. The geochemical whole rocks analyses and …
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Sediment incorporation into continental arc systems and paleogeography of the western North American Cordillera: Insights from the North Cascades, Washington
… Mesozoic peaks, unradiogenic Late Cretaceous zircons, distinct peaks ca. 1.38 and 1.8-1.6 Ga, and unradiogenic Nd-isotope compositions. These results indicate that the tectonic setting evolved from basins associated with oceanic arcs that were isolated from the continent, to a mid-Cretaceous, …
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