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Search for isotopic anomalies in oldhamite (CaS) from unequilibrated (E3) enstatite chondrites
Author(s) -
Lundberg Laura L.,
Zinner Ernst,
Crozaz Ghislaine
Publication year - 1994
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1994.tb00602.x
Subject(s) - chondrite , enstatite , troilite , meteorite , chondrule , geology , fractionation , kamacite , mineralogy , isotope , chemistry , isotope fractionation , geochemistry , astrobiology , physics , organic chemistry , quantum mechanics
— The Ca isotopic compositions of 32 oldhamite (CaS) grains from the Qingzhen (EH3), MAC88136 (EL3), and Indarch (EH4) enstatite chondrites were determined by ion microprobe mass spectrometry. Also measured were the S isotopic compositions of eight oldhamite, two niningerite (MgS), and seven troilite (FeS) grains. The S isotopic compositions of all minerals are normal, but oldhamite grains of the first two meteorites exhibit apparent small 48 Ca excesses and deficits that are correlated with isotopic mass fractionation as determined from the 40 Ca‐ 44 Ca pair. The interpretation of these results is complicated by the fact that none of the established mass fractionation laws can account for the data in the Norton County oldhamite standard. The method of analysis is carefully scrutinized for experimental artifacts. Neither interferences nor any known mass fractionation effect can satisfactorily explain the observed small deviations from normal isotopic composition. If these are truly isotopic anomalies, they are much smaller than those observed in hibonite. The nucleosynthetic origin of Ca isotopes is discussed.