Search Results - (Author, Cooperation:W. D. Sharp)

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  1. 1
    Staff View
    Publication Date:
    2014-06-21
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Animals ; Brain/anatomy & histology ; Extinction, Biological ; *Fossils ; Genetic Drift ; Humans ; Neanderthals/*anatomy & histology/*genetics ; Organ Size ; Reproductive Isolation ; Skull/*anatomy & histology ; Spain
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2

    Harlow, etc. : Periodicals Archive Online (PAO) Published 1920
    Staff View
    ISSN:
    0013-8266
    Topics:
    History
    URL:
    http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:0027-1920-035-00-000020

    Articles: DFG German National Licenses
  3. 3
    Deino, A. L., Behrensmeyer, A. K., Brooks, A. S., Yellen, J. E., Sharp, W. D., Potts, R.
    American Association for the Advancement of Science (AAAS)
    Published 2018
    Staff View
    Publication Date:
    2018-04-06
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Geosciences
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Anthropology, Geochemistry, Geophysics
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  4. 4
    Sharp, W. D., Paces, J. B.
    American Association for the Advancement of Science (AAAS)
    Published 2018
    Staff View
    Publication Date:
    2018-10-26
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Geosciences
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Anthropology
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  5. 5
    Ross, J. A. ; Sharp, W. D.
    Springer
    Published 1988
    Staff View
    ISSN:
    1432-0967
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Geosciences
    Notes:
    Abstract The effects of sub-blocking temperature metamorphism on the K/Ar system in hornblende, as revealed by 40Ar/39Ar release spectra, have been studied in a polymetamorphic “knocker” from the Franciscan Complex (FC), California. A primary amphibolite assemblage of horn-blende +rutile+epidote+apatite±garnet±sphene is variably overprinted by a blueschist facies assemblage of blue amphibole +lawsonite+chlorite+white mica+pumpellyite±sphene. The secondary assemblage formed at a temperature of ≤370° C, below that at which rapid Ar diffusion is expected in hornblende. Hornblendes from three, variably-altered samples of garnet amphibolite yield total gas ages of 147 to 161 Ma, but the corresponding plateau ages of 163.0±2.8, 160.6±2.2, and 161.8±2.2 Ma are identical within error. Hornblende separates with lower total gas ages come from more highly overprinted rocks, have “excess” K compared to that expected on the basis of electron probe analyses, and exhibit anomalously high K/Ca ratios in the low-temperature fractions of their incremental heating spectra. The reduced total gas ages result from the presence of thin (∼2 μm) sheets of younger white mica in hornblendes from the moderately and highly altered amphibolites. The secondary micas are difficult to detect because of their small size and low abundance (≤2%), but because their K content is 50 to 100 times that of the host hornblende, they contribute significantly to the K and Ar budgets of the sample. The mica intergrowths are not removed by normal sample preparation, but because the mica inclusions degas at lower temperatures than hornblende during vacuum extraction, incremental heating analyses can provide precise cooling ages for the hornblendes as well as useful estimates of the age of the mica inclusions. The hornblende separate from the most altered sample contained 20±10% younger blue amphibole replacing hornblende, but its plateau age was not significantly affected. This is consistent with a replacement process in which K and Ar loss from the hornblende are coupled, leaving the K/Ar system undisturbed in relict primary grains. The K and Ar budgets of the sample are not strongly affected by the blue amphibole because of its very low K content. Because partial replacement of primary amphibole by high-K phyllosilicates occurs in many geological environments, effects like those described here could be widespread.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00373587

    Articles: DFG German National Licenses