SIMS measurements on oxygen-isotopic compositions of chondrules and matrix in the Yamato 691 EH3 chondrite

Introduction: Whole rocks, chondrules and matrix from the same chondrite group typically have the same or very similar oxygen-isotopic compositions [e.g., 1]. Among the three major clans of chondrites, enstatite chondrites (ECs) have the most uniform oxygen isotopic compositions (Fig. 1). In order to study oxygen-isotopic heterogeneity of ECs in microscale, we carried out SIMS measurements on chondrules and matrix of the EH3 chondrite,Yamato 691 (hereafter Y691). We chose Y691 because it is the one of the most primitive ECs [2] and contains fine-grained matrix material [3, 4]. Bulk oxygen-isotopic compositions of Y691 were reported in [5]. SIMS measurements on pyroxenes and olivine in EH3 Sahara 97159 EH3 chondrite have also been reported [6].