C, N and SI Isotopes from the EL Djouf 001 (CR) Meteorite: Comparison with Murchison SiC

Details C, N and SI Isotopes from the EL Djouf 001 (CR) Meteorite: Comparison with Murchison SiC C, N and SI Isotopes from the EL Djouf 001 (CR) Meteorite: Comparison with Murchison SiC

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.598w&link_type=abstract

Meteoritics, vol. 30, no. 5, page 598

Other

Anomalies, Isotopic, Carbon, Chondrites, Carbonaceous, El Djouf 001, Murchison, Probes, Ion

Scientific paper

We have isolated 39 single SiC grains from the El Djouf (CR) meteorite and analyzed them for the isotopic compositions of C, N and Si in order to compare with results from Murchison ([1] and own data).The average size of the analyzed grains was about 5 micrometers, but there were also three very large grains of more than 20 micrometers size.The analyses were performed using a modified CAMECA Ion-microprobe IMS 3f and a negative O primary beam. Carbon and nitrogen isotopic compositions were measured as negative secondary ions (CN) --, silicon as positive secondary ions Si+. Our results for carbon and nitrogen in Murchison and El Djouf 001 are plotted in Fig.1, the silicon data in Fig. 2. In both cases the Murchison literature data for the 'mainstream' (about 95 %) grains are represented by shaded areas [1].Our results for Murchison show the same trend as former measurements [1]. El Djouf 001 Results: For El Djouf 001 the carbon isotopic signature for the majority of the grains is close to terrestrial, but there are some outliers on the high side. The nitrogen ratios fall in an interval of 250 < 14N / 15N < 400, much narrower than for Murchison, but we also found four grains with low carbon- and low nitrogen-ratios. In addition there isone grain (12C/ 13C = 216 + 4, 14N / 15N = 300 + 6) which has the signature of a 'Y-Grain', and another with a 12C/13C ratio of 698 + 15, but 'normal' nitrogen (272 + 5). In the case of silicon isotopic ratios El Djouf 001 and Murchison are distinct. The data for Murchison are concentrated in the first quadrant, whereas El Djouf 001 data plot (with one exception) in the third quadrant .Almost all of our grains from Murchison fall near the 1.34-slope line, where the 'mainstream' SiC-grains are located [1]. In contrast to this only two grains from El Djouf 001 fall on this line. Most El Djouf 001 data points scatter around a value delta 29Si about -70 per mil and delta 30Si about -120 per mil. This is compatible both with a position on the extension of the slope 0.35 line found for 'Y-Grains' [1] or on a mass fractionation slope 0.5 line through the origin. Since, with one exception, the C-, N-data do not show evidence for 'Y-Grains', it may be more likely that El Djouf 001 SiC grains contain Si that is mass-fractionated although the fractination would be surprisingly large. References: [1] Hoppe P. et al. (1994) Astrophys. J., 430, 870-890.

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