Chromium isotopic composition of some chondritic meteorites

概要

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The Cr isotopic composition of primitive meteorites (acid-residue fractions) was studied. Five chondrites were analyzed in this work [Allende (CV3), Murchison (CM2), Nuevo Mercurio (H5), La Criolla (L6), Qingzhen (EH3)]. Although in most samples, no isotopic anomalies beyond the experimental errors could be detected, an elevated ^<54>Cr/^<52>Cr ratio was found in the acid-soluble fraction from Qingzhen. Moreover, ε^<53>Cr and ε^<54>Cr show an inverse correlation among the meteorites analyzed in this study, and the acid residues have larger ε^<54>Cr and smaller ε^<53>Cr values than do the acid-soluble fractions in Allende and Murchison. The enrichment of ^<54>Cr in the Qingzhen sample suggests that the ^<54>Cr heterogeneity due to stellar nucleosynthesis has remained in enstatite chondrite as well as carbonaceous chondrite. In addition, the inverse correlation of ε^<53>Cr and ε^<54>Cr detected in acid residue samples indicates that the high-temperature condensate contained more exotic ^<54>Cr. It is also suggested that the homogenization of Cr isotopes proceeded with time, and terminated within a relatively short time scale of less than 2-3 Ma.
国立極地研究所の論文