Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..343d&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 343
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2
Acfer 086, Acfer 094, Acfer 097, Acfer 202, Acfer 217, Acfer 270, Alais, Allende, Arch, Bali, Cochabamba, Cold Bokkeveld, Colony, Efremovka, Esna, Ivuna, Maralinga, Mulga West, Murchison, Nogoya, Orgueil, Ornans, Tonk, Warrenton
Scientific paper
Selenium is the only truly chalcophile element in chondritic meteorites. It has no other host phases except sulfides. Since Se-volatility is similar to S-volatility one may expect constant S/Se ratios. To test this hypothesis chondritic meteorites were analyzed for Se and S. To avoid problems from inhomogeneous distribution of sulfides the same samples that had been analyzed for Se by INAA were analyzed for S (see Table 1) using a Leybold Heraeus Carbon and Sulfur Analyser (CSA 2002). Solar System Abundances of S and Se: The average S-content of CI- meteorites is with 5.41% in agreement with an earlier average of 5.25% for Orgueil [1], but not with higher S-contents for Ivuna, Alais, and Tonk. Inclusion of these data led to an average CI- content of 6.25% in the Anders and Grevesse compilation [2]. The essentially constant average S/Se ratio in all groups of carbonaceous chondrites of 2563 +- 190 suggests that our Orgueil S-content provides a reliable estimate for the average solar system. The new solar S/Se ratio and the CI-value of Se of 21.3 ppm [3] yield an atomic S/Se ratio of 6200 +- 170, 24% below that calculated from [2]. Weathering Effects: Some of the carbonaceous chondrite finds have similar S/Se ratios as falls (see Table 1). However the badly- weathered Arch (CVR) and Colony (CO) and the two C4-chondrites Mulga West and Maralinga have much lower S and somewhat lower Se contents compared to unweathered meteorites. Their S/Se ratios of 1000-230 indicate higher losses of S--probably by oxidation--as of Se. The low Na-contents in Arch and Colony rel. to CV3 and CO3 may also reflect weathering. Low S/Se ratios in the Sahara meteorites are also indicative of weathering processes. The depletion factors for the CV3- chondrite Acfer086 are, relative to average CV, 10 (S), 5 (Se), 6 (Na), and 4 (Ni). Lower absolute depletions, but the same depletion sequence are found for the CO-meteorite Acfer 202. In the CO/CM Acfer 094 only S and Na are depleted. The influence of weathering in the two CR-types Acfer 097 and Acfer 270 is less obvious. Although Se does not appear to be depleted in these meteorites [4] the lower S/Se ratios of 1660 res. 1970 rel. to CI and the low Na-contents indicate weathering related losses of S and Na. Losses of Ni by weathering are more pronounced in meteorites containing Ni-rich sulfides, whereas metallic Ni is apparently less affected (CR-meteorites). A high depletion of S and Ni but none for Se and Na is found in the Carlisle Lake-type, Acfer 217. In summary, weathering effects in the carbonaceous chondrites result in losses of S, Se, Na, and Ni. Sulfur is in all cases significantly more affected by weathering than Se resulting in low S/Se ratio rel. to CI. References: [1] Mason B. (1962) Space Sci. Rev., 1, 621-646. [2] Anders E. and Grevesse N. (1989) GCA, 53, 197-214. [3] Spettel B. et al. (1993) this volume. [4] Bischoff A. et al. (1993) GCA, 57, in press.
Dreibus Gerlind
Palme Herbert
Spettel Bernhard
Wanke Heinrich
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