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    National Tsing Hua University Institutional Repository > 歷任校長 > 沈君山 (1994-1997) > 期刊論文 >  Precise Re-Os determinations and systematics of iron meteorites


    Please use this identifier to cite or link to this item: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/80860


    Title: Precise Re-Os determinations and systematics of iron meteorites
    Authors: J.J. Shen;D.A. Papanastassiou;G.J. Wasserburg
    教師: 沈君山
    Date: 1996
    Publisher: Meteoritical Society
    Relation: GEOCHIMICA ET COSMOCHIMICA ACTA, Meteoritical Society, Volume 60, Issue 15, AUG 1996, Pages 2887-2900
    Keywords: IONIZATION MASS-SPECTROMETRY
    ISOTOPE RATIO DETERMINATIONS
    RE-187-OS-187 SYSTEMATICS
    GROUPS IAB
    GROUP-IIAB
    RHENIUM
    OSMIUM
    ORIGIN
    SULFUR
    CLASSIFICATION
    Abstract: The Re-Os system for samples of FeNi, sulphide, and phosphide from iron meteorites was investigated. Techniques were developed which yield reproducible analyses for Re/Os at the 2 parts per thousand level and which permit complete isotopic exchange between sample and tracer, as is necessary for concentration measurements of Re and Os by isotope dilution. High precision osmium and rhenium isotope data have been obtained using negative ion thermal ionization, with ionization efficiencies of up to 10% for Os and 20% for Re, both for normals and for Re and Os extracted from the samples, Replicate analyses of Re/Os are in good agreement, within +/-2.5 parts per thousand. The results show a well defined correlation line on a Re-187-Os-187 evolution diagram for iron meteorites from groups IAB, IIAB, IIIAB, IVA, and IVB, all taken together. This correlation line yields a slope of 0.07863 +/- 0.00031 (2 sigma) and initial Os-187/Os-188 = 0.09560 -/+ 0.00018 (2 sigma). If the individual groups of iron meteorites for which there is sufficient dispersion in Re/Os are considered, data on the IIAB and on the IVA irons appear to indicate a difference in age of 60 +/- 45 Ma, with the IVA group being older-This age difference is qualitatively the same as obtained for Pd-Ag data but is larger. Sulphides from two IAB iron meteorites show extremely low concentrations of Re and Os and indicate that Re and Os are not partitioned into this phase during planetary differentiation. There is evidence for recent element remobilization or contamination, corresponding to relative enrichment of Re or loss of Os in the sulphides. Schreibersites contain small but significant amounts of Re and Os, with high Re/Os relative to the metal phases and with Os-187/Os-188 much more radiogenic than in the metal. Model ages for the schreibersites are relatively young (4.3-3.5 AE) and indicate that the schreibersites were open-systems for Re-Os at least 0.5-1 AE after the original formation of the iron meteorites, It now appears possible to use metal-schreibersite pairs to determine internal isochrons. Based on the schreibersite model ages, the cooling rates for the two IAB meteorites are estimated to be similar to 1 degrees C/Ma, more than an order of magnitude lower than the most recently determined metallographic cooling rates for IAB irons (Herpfer et al., 1994).
    Relation Link: http://www.meteoriticalsociety.org/
    URI: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/80860
    Appears in Collections:[沈君山 (1994-1997)] 期刊論文
    [物理系] 期刊論文

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