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Showing 1 to 20 of 98 for “"Archean"”.
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Temperature-dependent thermal transport properties of major Archean rock types and implications for the thermal evolution of Archean terranes
… vertical tectonics may have operated during the Archean, leading to formation of dome-and-keel terranes. Early continental crust was comprised of rock associations such granite-greenstone (GG) belts and intrusions of high heat-producing tonalite-trondhjemite-granodiorite (TTG), and the burial of …
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Archean metamorphism in northwestern Ontario and southeastern Manitoba
… studies. A non subduction model assumes that Archean plates were too thin and hot to be subducted (Fig. 43-47). The plate tectonics model includes subducting plates and is based on the work of Langford and Morin (1976) (Fig. 49). </p>
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Archean continental crust formation and the rise of atmospheric oxygen
… pathways and the oxygenation history of the late Archean atmosphere using combined sulfur and iron isotope signals as recorded in distinct morphologies of pyrite. This work represents a critical step in deconstructing the pathways of S-MIF production, transfer and preservation in the sedimentary …
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The Geology And Geochemistry Of The Archean Flavrian Pluton, Noranda, Quebec
The composite Flavrian pluton is the west part of an intrusive complex which is emplaced in and is partially coeval with Blake River Group volcanic rocks in Noranda. The pluton's intrusive sequence is summarized as follows: an extensive diorite sill, volumetrically minor porphyritic rhyolite, the …
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Paleomagnetism conglomerate test on Archean conglomerate rock from Jack Hills, Australia
… study known as a conglomerate test was run on an Archean sandstone conglomerate rock to determine if the sample contained a remnant magnetization from the time of its formation. Twenty-nine clasts from a thin section of the sample were thermally demagnetized up to a temperature of 395°C. The …
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Geology of an Archean Greenstone Belt at Point Lake, Northwest Territories, Canada
<p>Several well-preserved circa 2.6 Ga Archean granite-greenstone belts are exposed in the Slave Province of Northwest Territories, Canada. At Point Lake, a "supracrustal sequence" comprised mainly of mafic volcanic and metasedimentary rocks lies over and east of a granitoid gneissic terrane. Field …
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Uranium-lead isotopic investigation of the Archean Imataca complex, Guayana shield, Venezuela.
Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences.
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Volcanic framework and geochemical evolution of the Archean Hope Bay Greenstone Belt, Nunavut, Canada
… framework the belt. Three recently discovered Archean lode gold deposits in the Hope Bay Greenstone belt have associations with major structures and specific lithologies (Fe-Ti enriched basalts). The Flake Lake and the Clover Transects are in the southern part of the belt and the Wolverine and …
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Dependence of tropical cirrus clouds on sea surface temperature and consequences for the Archean climate
… thin upper level clouds, in the climate of the Archean using a simple radiative-convective model that includes the effect of the variations in the area of thin cirrus clouds. First, we look at the variation in area of upper level clouds using TRMM VIRS (Tropical Rainfall Measuring Mission, …
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Geologic evolution of the Archean Buhwa Greenstone Belt and surrounding granite-gneiss terrane, southcentral Zimbabwe
The Archean (~3.0 Ga) Buhwa Greenstone Belt, and surrounding granite-gneiss terrane, is the least understood major greenstone belt in the Archean Zimbabwe Craton, despite occupying a critical position between an early Archean continental nucleus and the Limpopo Belt. The cover succession in the …
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The Archean origin of assimilatory sulfate metabolisms provides novel insight into redox conditions of early Earth environments
… These results suggest sulfate cycling in Paleoarchean environments, despite extensive evidence of low marine sulfate concentrations (Crowe & Canfield et al., 2014). Archean sulfate biogeochemical cycling could result from microbial sulfur oxidation and sources could include abiotic oxidation of …
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Contributions and New Methods in Paleontology: Geochemical, Ultrastructural, and Microstructural Characterization of Archean, Proterozoic, and Phanerozoic Fossils
… from microfossils to macrofossils and from the Archean (beginning at 3800 Ma) to the Cenozoic (ending at the recent). These techniques, predominantly used for geochemical, morphological, and ultra-/micro-structural analyses, have unlocked an incredible amount of detail contributing to our …
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Trace Element Geochemistry of Volcanogenic Massive Sulfide Deposits in Archean Greenstone Belts: Implications for Metal Endowment and Geodynamic Settings
The Neoarchean greenstone belts of the Canadian Superior Province host world-class Au and base metal (Cu-Zn-Pb) massive sulfide deposits with distinct geological features, including a wide range of different host rocks and crustal settings. The range of settings is reflected in the trace metal …
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Exploring the contributions of liquid-phase sulfur chemistry to the mass-independent sulfur fractionation of the Archean rock record
Archean sulfur mass-independent fractionation (S-MIF) has been widely recognized as one of the strongest indicators for the rise of atmospheric oxygen in the Early Proterozoic. A decade after its discovery, the wide-ranging implications of Archean sulfur MIF have been discussed extensively and …
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Facies, paleogeography, and the carbonate precipitation on the archean (2520 Ma) Campbellrand-Malmani carbonate platform, Transvaal supergroup, South Africa
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.
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Archean detrital zircons in the Proterozoic Vishnu Schist of the Grand Canyon, Arizona : implications for crustal architecture and Nuna reconstructions
… rather than in a juvenile 1.75 Ga arc setting. Archean grains of 3.8–2.5 Ga comprise 30% of all grains. A comparison of the > 2.2 Ga ages from the Vishnu Schist (495 grains) with compilations of zircon ages from other cratons does not support provenances in the Wyoming, South China, or Siberian …
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A detailed petrographic and oxygen isotope study of metamorphic rocks and archean basement complex Gneisses from the Vredefort dome, South Africa
Metamorphism observed in the Vredefort structure increases in grade on a regional scale from lower greenschist facies in the outer perimeter of the Potchefstroom syncline, throughupper greenschist and amphibolite grades within rocks of the Witwatersrand Supergroupand Dominion Group in the collar of …
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How Hot, How Deep, How Long: Constraints on the Tectono-Metamorphic Evolution of Granulite Terranes
… crust. Granulites are ubiquitous in exhumed Archean cratons and are thought to comprise much of Earth's stable lower crust. Understanding the mechanisms responsible for crustal heating in Archean terranes is thus paramount to understanding the stabilisation of early continental crust, and …
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Evolution of an Archean greenstone belt in the Stormy Lake - Kawashegamuk Lake area (stratigraphy, structure and geochemistry) - Western Wabigoon Subprovince, Northwest Ontario /
330 km 2 of the easter-n part of the Archean Manitou Lakes - Stormy Lake metavolcanic - metasedimentary belt have been mapped and sampled. A large number of rocks ~.vere analyzed for the major and trace constituents including the rare-earth elements (REE). The Stormy Lake - Kawashegamuk Lake area …
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