Isotope composition of oxygen in the high-melting inclusions of carbonaceous chondrites

To investigate the nature of the oxygen-isotope anomaly in the Ca- and Al-rich high-melting inclusions of carbonaceous chondrites, the values of the O-17/O-18 ratio were determined in several individual refractory inclusions of Efremovka (C3V) and Groznaia (C3V) carbonaceous chondrites. While the Efremovka inclusions do not show traces of secondary transformations, the Groznaia inclusions bear evidence of metasomatic substitutions to a degree even higher than that of the high-melting inclusions of the Allende chondrite. Differences found between the oxygen isotope compositions of the chondrules and the refractory inclusions in the individual chondrites indicates that chondrules and the inclusions are two independent types of matter and must have been generated during different phases of the solid-matter formation process. Comparisons between data on the Efremovka, Groznaia, and Allende inclusions indicated that the primary oxygen isotope composition was not influenced by the subsequent metasomatic transformations.