Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.440s&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 440
Other
1
Scientific paper
We have compiled our instrumental neutron activation data of CI chondrites and performed several new analyses. We find a surprisingly good agreement of our results with the CI data of Kallemeyn and Wasson [1]. In Table 1, which appears in the hard copy, averages of CI analyses done in Mainz and at UCLA [1] are listed. The standard deviations are, in most cases, calculated from variations of analytical results of individual analyses. Since both sets of data are completely independent we believe that the agreement justifies a high degree of confidence in the accuracy of the data. We therefore suggest that the mean of the two datasets represents the best available estimate for solar system abundances of the elements listed in Table 1, except for the REE. For the elements Mg, Al, and Ca there are more accurate analytical procedures than INAA. However, the INAA-results are in good agreement with wet chemical data and XRF analyses. A very small internal spread in both datasets is obvious for Sc, Cr, Mn, Fe, and Co. In addition, the agreement between the two datasets is better than +- 3% (except Mn, with -3.1%). The average solar system ratios among these five elements are known to within at least 2%. The Anders and Grevesse [2] compilation has within a 3% limit the same abundances for these elements except for Fe, which is 4.4% higher for average CI chondrites, but comes closer to the INAA data when only Orgueil is considered. More serious differences between INAA data and the A&G compilation are found for Se (12.7%), Au (7.9%), and Ir (4.7%). The internal spread in Se data from Mainz and UCLA is very small and the agreement is better than 1%. Recent data on S and Se on the same samples in chondrites have shown a constant S/Se weight ratio of 2518 (+-6%) in CI and CM chondrites [3] and an average CI content of 5.41% S in Orgeuil and Ivuna, in agreement with older Orgueil data of 5.25%. The very constant S/Se ratio in all chondrites and the CI content of 21.3 ppm Se lead to CI sulfur content of 5.36%, which is considerably below the A&G CI average of 6.25%. A very special case is Hg, which can be easily determined by INAA at the expected abundance level in CI chondrites. All our Orgueil samples appear to be more or less contaminated with Hg. A single Ivuna analysis gave a value of 0.31 ppm. This is basically in agreement with s-process calculations, which predict for 198Hg an abundance of 0.38 ppm [4]. The good agreement of solar and meteoritic abundances justifies a more sophisticated treatment of CI abundances. Small differences in element ratios between CI and other chondrite groups may require different nebular processing of these components and thus provide information on early solar nebula conditions. The INAA data on CI also demonstrate the basic homogeneity of CI chondrites for compatible elements. References: [1] Kallemeyn G. W. and Wasson J. T. (1981) GCA, 45, 1217-1230. [2] Anders E. and Grevesse N. (1989) GCA, 53, 197-214. [3] Dreibus G. et al. (1993), this volume. [4] Palme H. and Beer H. (1993) Landolt B"rnstein, in press.
Dreibus Gerlind
Palme Herbert
Spettel Bernhard
Wanke Heinrich
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