Rare earth and some other elements in acid-residues of unequilibrated ordinary chondrites

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Some major, minor and trace elements including rare earth elements (REEs) were determined in bulk and acid (hydrochloric or nitric acid)-residual samples of unequilibrated ordinary chondrites (UOC's), Allan Hills (ALH-) 77299,ALH-78084,Yamato-74191,ALH-77011,ALH-78038,ALH-77252 and ALH-77278. REEs were analyzed by radiochemical neutron activation analysis (NAA), other elements by instrumental NAA. The content of REEs was found to be higher and more variable in acid-residues of UOC's than in acid-residues of equilibrated ordinary chondrites (EOC's). Clnormalized REE abundance patterns of acid-residues of UOC's show a gradual increase from La to Lu but their slopes are less steep than for EOC's. Both ALH-78038 and ALH-77011 show a weak negative Eu anomaly in the REE abundance patterns of acid-residues, which is again in sharp contrast to the large positive Eu anomaly in EOC's. Among the UOC's studies, paired meteorites, ALH-77011 and ALH-78038,are the most primitive UOC's. The amount of REE and the Cl-normalized REE pattern for acid-residues of ALH-77252 are different from those of other UOC's and are essentially the same as those for EOC's, suggesting that this meteorite (or at least the specimen used in this work) is related to EOC's rather than UOC's.
国立極地研究所の論文