Mathematics – Logic
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.336c&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 336
Mathematics
Logic
Atlanta, Enstatite Chondrites, Hvittis, Pillistfer, Qingzhen, St. Marks, Sulfide Mineral, Trace Elements
Scientific paper
Oldhamite, being the carrier of REE in enstatite chondrites, may provide unique clues to the origin and history of the enstatite chondrites. We have previously reported that oldhamite grains from Qingzhen (EH3) contain 80% of the REE in the bulk rock [1], and this phase is highly enriched in several other refractory elements such as Sc, Th, and Hf. Perhaps surprisely, oldhamite are also enriched in the volatile chalcophile elements Se, Br, and Zn. This suggests interactions at low temperature [2]. Here we report INAA data for the REE, Sc, Se, Br, and Zn in CaS extracted from five enstatite chondrites (Qingzhen EH3, St. Marks EH5, Atlanta EL6, Hvittis EL6, and Pillistfer EL6) using a diamond drill attached to a standard microscope. Nine CaS grains from Qingzhen were analyzed, two from St. Marks and one from each of remaining meteorites. We found that the REE abundances in CaS from higher petrologic types are much lower than from unequilibrated enstatite chondrite, Qingzhen (Table 1). Similarly, the abundances of Sc, Se, Br, and Zn in the CaS from Qingzhen are higher than that in CaS grains from equilibrated chondrites. Since both refractory and volatile element abundances decrease with petrologic type, the high abundances of these elements must reflect primary (i.e. pre-metamorphic) process. We conclude first, the CaS grains from enstatite chondrites are not simply residues of an evaporative process, as suggested by thermodynamic models for the REE patterns observed in the CaS [1,3-7], since such material would be depleted in volatiles. Secondly, metamorphism has caused considerable redistribution of the trace elements among the minerals in most enstatite chondrites. References: [1] Chen et al. (1992) Chinese J. Space Sci., 12, 129-138. [2] Chen et al. (1989) Meteoritics, 24, 258. [3] Larimer J. W. and Ganapathy R. (1987) EPSL, 84, 123-134. [4] Lundberg L. L. and Crozaz G. (1988) Meteoritics, 23, 285-286. [5] Lundberg L. L. et al. (1989) Meteoritics, 24, 296. [6] Lundberg L. L. et al., (1991) LPSC, XXII, 835-836. [7] Lodders K. and Fegley B. (1993) EPSL (in press). Table 1, which appears here in the hard copy, shows CI-normalized element abundances in CaS extracted from enstatite chondrites.
Chen Yafeng
Pernicka Ernst
Sears Derek W. G.
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