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  • 1
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    Application of U-Th-Pb Phosphate Geochronology to Young Orogenic Gold Deposits: New Age Constraints on the Formation of the Grass Valley Gold District, Sierra Nevada Foothills Province, California (2015)
    Society of Economic Geologists (SEG)
    Details
    Publication Date: 2015-05-23
    Description: The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping E-W veins located along lithologic contacts in accreted ca. 300 and 200 Ma oceanic rocks and shallowly dipping N-S veins hosted by the Grass Valley granodiorite; the latter have yielded about 70% of the 13 million ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170 to 140 Ma and 120 to 80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. Uranium-lead isotope dating of hydrothermal xenotime yielded the first absolute age of 162 ± 5 Ma for the economically more significant N-S veins. The vein-hosted xenotime, as well as associated monazite, are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of an Eu anomaly, and low U and Th concentrations. Furthermore, the crack-seal texture of the veins, with abundant wall-rock slivers, suggests their formation as a result of episodic fluid flow possibly related to reoccurring seismic events, rather than a period of fluid exsolution from an evolving magma. The N-S veins are temporally distinct from a younger 153 to 151 Ma gold event that was previously reported for the E-W veins. Overlapping U-Pb zircon (159.9 ± 2.2 Ma) and 40 Ar/ 39 Ar biotite and hornblende (159.7 ± 0.6–161.9 ± 1.4 Ma) ages and geothermobarometric calculations indicate that the Grass Valley granodiorite was emplaced at ca. 160 Ma at elevated temperatures (~800°C) within approximately 3 km of the paleosurface and rapidly cooled to the ambient temperature of the surrounding country rocks (〈300°C). The age of the granodiorite is indistinguishable from that of the N-S veins, as recorded by the U-Pb age of xenotime in those veins. Consequently, the N-S veins must have formed between 162 and 157 Ma, the maximum permissive age of magma emplacement and the youngest permissive xenotime U-Pb age, respectively, during an E- to ENE-directed compressional regime. The geochemistry of the Grass Valley granodiorite is consistent with it being the product of arc magmatism. It served as a receptive host for mineralization, but it is has no direct genetic relationship to gold mineralization. Initial uplift of the intrusive mass correlates with the initial voluminous fluid flow event and vein formation at depths of no greater than 3 km. The E-W gold-bearing veins hosted within greenschist-facies country rocks adjacent to the intrusion formed during a second hydrothermal event 5 to 10 million years later than the magmatism and were contemporaneous with a shift to transtensional deformation denoted by sinistral strike-slip faulting.
    Print ISSN: 0361-0128
    Topics: Geosciences
    Published by Society of Economic Geologists (SEG)
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  • 2
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    Microstructural Controls on Elastic Anisotropy of Finely Laminated Mancos Shale (2018)
    Oxford University Press
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Summary〈/div〉Shales commonly exhibit anisotropy in their elastic wave velocity, which directly impacts the accuracy of seismic imaging and their geomechanical response to drilling and completions. Anisotropy is often caused by mineralogical layering, fractures, and rock fabric (i.e. oriented grains and intrinsic anisotropy of clay sediments). However, the relative impact of each of these features on macroscopic shale properties is not well understood. We combined scanning electron microscopy (SEM) and X-ray micro-computed tomography (CT) to image the mineralogical and structural heterogeneity of Mancos Shale and converted the acquired CT and SEM images into heterogeneous 2D elastic models. We used wave propagation numerical simulations to understand the effects that layering and fractures have on elastic wave velocity anisotropy. Consistent 〈span〉Vp〈/span〉/〈span〉Vs〈/span〉 ratios around 1.46 for modeled and measured velocities validates SEM observations of a quartz-dominated shale lithology. CT-derived models containing layering and fractures exhibit 28.6 per cent and 58.8 per cent of the 〈span〉Vp〈/span〉 and 〈span〉Vs〈/span〉 anisotropy observed in the laboratory, whereas SEM derived models exhibit 74.5 per cent and 73.2 per cent of the anisotropy, respectively. The increased anisotropy of SEM-derived elastic models is a result of the ability of the SEM to discern individual mineral grains and microstructural features, whereas the CT models require the use of an effective medium theory to model variations of lithology. Overall, modeled wave propagation perpendicular to bedding more closely captures the experimental velocities than parallel to bedding. Therefore, sub-resolution rock fabric anisotropy likely accounts for the relatively larger velocity mismatch in the parallel direction, and is likely responsible for the decreased anisotropy in coarse rock models. Future modeling would require higher resolution images to structurally constrain these features and/or anisotropic elements to account for fabric anisotropy. Despite some limitations, our study provides a reliable procedure to estimate anisotropy of dynamic mechanical properties of laminated shales using SEM and CT imaging combined with numerical simulation of wave propagation.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
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    Structural disorder of monomeric alpha-synuclein persists in mammalian cells (2016)
    Nature Publishing Group (NPG)
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    Publication Date: 2016-01-26
    Description: Intracellular aggregation of the human amyloid protein alpha-synuclein is causally linked to Parkinson's disease. While the isolated protein is intrinsically disordered, its native structure in mammalian cells is not known. Here we use nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy to derive atomic-resolution insights into the structure and dynamics of alpha-synuclein in different mammalian cell types. We show that the disordered nature of monomeric alpha-synuclein is stably preserved in non-neuronal and neuronal cells. Under physiological cell conditions, alpha-synuclein is amino-terminally acetylated and adopts conformations that are more compact than when in buffer, with residues of the aggregation-prone non-amyloid-beta component (NAC) region shielded from exposure to the cytoplasm, which presumably counteracts spontaneous aggregation. These results establish that different types of crowded intracellular environments do not inherently promote alpha-synuclein oligomerization and, more generally, that intrinsic structural disorder is sustainable in mammalian cells.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Theillet, Francois-Xavier -- Binolfi, Andres -- Bekei, Beata -- Martorana, Andrea -- Rose, Honor May -- Stuiver, Marchel -- Verzini, Silvia -- Lorenz, Dorothea -- van Rossum, Marleen -- Goldfarb, Daniella -- Selenko, Philipp -- England -- Nature. 2016 Feb 4;530(7588):45-50. doi: 10.1038/nature16531. Epub 2016 Jan 25.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉In-Cell NMR Laboratory, Department of NMR-supported Structural Biology, Leibniz Institute of Molecular Pharmacology (FMP Berlin), Robert-Rossle Strasse 10, 13125 Berlin, Germany. ; Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel. ; Department of Molecular Physiology and Cell Biology, Leibniz Institute of Molecular Pharmacology (FMP Berlin), Robert-Rossle Strasse 10, 13125 Berlin, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26808899" target="_blank"〉PubMed〈/a〉
    Keywords: Acetylation ; Cell Line ; Cytoplasm/chemistry/metabolism ; Electron Spin Resonance Spectroscopy ; HeLa Cells ; Humans ; Intracellular Space/*chemistry/*metabolism ; Neurons/cytology/metabolism ; Nuclear Magnetic Resonance, Biomolecular ; Protein Conformation ; alpha-Synuclein/*chemistry/*metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    Goldfarb's Thanks (1986)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1986-11-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Goldfarb, D -- New York, N.Y. -- Science. 1986 Nov 14;234(4778):801.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17758085" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
    Electronic Resource
    Electronic Resource
    The Coordination of VO2+ to Hydroxamate Binders as Studied by Orientation Selective ESEEM Spectroscopy (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 383-391 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00106a043
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  • 6
    Electronic Resource
    Electronic Resource
    Coordination of Cu(II) to Lipophilic Bis-hydroxamate Binders As Studied by One- and Two-Dimensional Electron Spin Echo Spectroscopy (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 12771-12778 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00156a014
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  • 7
    Electronic Resource
    Electronic Resource
    Chemical and Heisenberg Exchange in Ion-Pair Solutions Revisited by Two-Dimensional EPR Spectroscopy (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 5805-5813 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00092a035
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of Iron in Zeolites by X-band and Q-Band ESR, Pulsed ESR, and UV-Visible Spectroscopies (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 6344-6353 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00093a039
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  • 9
    Electronic Resource
    Electronic Resource
    Evidence for Water Binding to the Fe Center in Cytochrome P450cam Obtained by 17O Electron Spin-Echo Envelope Modulation Spectroscopy (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 8243-8251 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00136a023
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  • 10
    Electronic Resource
    Electronic Resource
    Deuterium and carbon-13 NMR of the solid polymorphism of benzenehexoyl hexa-n-hexanoate (1987)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 109 (1987), S. 7280-7286 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00258a006
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