Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27s.233h&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 233
Mathematics
Logic
Scientific paper
The ^187Re-^187Os isotopic pair can offer piercing chemical and chronological information for the early sequences of the solar system [1,2]. Its principal interest over the other chronometer stands not only in siderophilic nature, but also in highly refractory physicochemical characteristics of both Re and Os. Although the progress of Re-Os chronometer has been retarded by the difficulty in Os isotopic analysis, recent developments in a variety of mass spectrometry have enabled us to give easier access to the Os isotopic measurement with high sensitivity. We have analyzed Re and Os abundances in 12 iron meteorites of various groups and 5 stony iron meteorites by stable isotope dilution employing an enhanced sensitivity inductively coupled plasma mass spectrometry [3,4]. In Fig. 1 we show the Re vs. Os abundance plot for the iron and stony iron meteorites obtained. Present Re and Os abundance data indicate some important features that can contribute to the elucidation of the evolutional history of these metallic meteorites. 1. Re and Os abundances in iron and stony iron meteorites have a wide variation covering nearly four orders of magnitude. 2. In contrast, there is no significant change in abundance ratio of Re/Os. The relationship between the Re and Os abundances gives a correlation coefficient of 0.996. 3. The group with the highest Re and Os abundances are the iron meteorites of group IVB [5,6]. 4. Sikhote-Alin (IIB-Anom) has exceptionally low Re and Os abundance values compared with those for other iron meteorites, but fall on the regression line drawn by other meteorites. 5. The Re and Os abundances in pallasite stony iron meteorites (circles on Fig. 1) show extremely low values compared with those for most iron meteorites. 6. The Re and Os abundances in mesosiderite stony iron meteorites (squares on Fig. 1) show values comparable with those observed in most iron meteorites. Fig. 2 shows the abundance relationship between Ir and Os (Ir data were taken from [7]). A very high correlation is also observed for this pair of elements, giving a correlation coefficient of 0.985 and a slope of 0.930. It is worthwhile to note that the Re vs. Os relationship has a slightly higher slope and a better correlation coefficient compared with the Ir and Os relation. This is consistent with the better coherence between Re and Os than Ir and Os estimated from condensation temperature [8]. Furthermore, it should be noted that the Re/Os abundance ratio of the iron and stony iron meteorites show excellent agreement with that of ordinary and carbonaceous chondrites [2,9]. The highly coherent correlation of Re and Os in a variety of different meteorites may preclude a planetary differentiation and/or a chemical fractionation process for the formation of the iron meteorites. References: [1] Herr, W. et al. (1961) Z. Naturforsch. 16a. 1053-1058. [2] Luck, J.-M. and Allegre, C. J. (1983) Nature 302, 130-132. [3] Hirata, T. (1990) J. Anal. Atom. Sprctrom. 5, 589-591. [4] Masuda, A. and Hirata, T. (1991) Proc. Japan Acad. 67B, 72-77. [5] Wasson, J. T. (1967) Geochim. Cosmochim. Acta. 31, 161-180. [6] Kelly, W. R. and Larimer, J. W. (1977) Geochim. Cosmochim. Acta. 41, 93-111. [7] Wasson, J. T. (1974) Meteorites. Classification and Properties. Springer-Verlag, New York. 296 pp. [8] Grossman, L. and Larimer, J. W. (1974) Rev. Geophys. Space Phys. 12, 71-101. [9] Walker, R. J. and Morgan, J. W. (1989) Science 243, 519-522. Figure 1, which in the hard copy appears here, shows the correlation between Re and Os abundances in iron and stony iron meteorites. Figure 2, which in the hard copy appears here, shows the correlation between Ir and Os abundances in iron and stony iron meteorites. Abundance data for Ir are from reference [7].
Hirata Tomoyoshi
Masuda Akimasa
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