In a new paper published in Geochimica et Cosmochimica Acta, PhD Candidate Zack Torrano and co-authors investigate whether the isotope compositions of previously analyzed calcium-aluminum-rich inclusions (CAIs) are representative of CAIs from other chondrites and chondrite groups and, by extension, the broader CAI-forming region in the solar nebula.
CAIs are the oldest dated solids formed in our Solar System and therefore can provide us with important information about the initial isotopic composition of the Solar protoplanetary disk. However, most previous isotopic studies of CAIs have been limited to inclusions from the Allende CV chondrite and a few CAIs from other CV, CO, CM, and ordinary chondrites.
In this study, the authors analyze the mass-independant Ti isotopic compositions of 23 CAIs of different petrologic and geochemical types, including 11 CAIs from the Allende CV meteorite as well as 12 CAIs from 7 different CV and CK chondrites. These include the first reported measurements of the Ti isotope compositions of CAIs from CK chondrites.
The authors found that the mass-independent Ti isotopic compositions of CAIs from CV and CK chondrites define a single population (consistent with previously reported Ti isotope data for CAIs from other CV, CO, CM, and ordinary chondrites), indicative of a common CAI-forming region in the early Solar System. They further observed resolvable variation within this population, which indicates that some isotopic variability was present in the CAI-forming region.
This data, when taken in the context of previous studies, suggest that the isotopic reservoir from which CAIs formed was in the final stages of isotopic homogenization.
Torrano Z. A., Brennecka G. A., Williams C. D., Romaniello S. J., Rai V. K., Hines R. R., and Wadhwa M. (2019) Titanium isotope signatures of calcium-aluminum-rich inclusions from CV and CK chondrites: Implications for early Solar System reservoirs and mixing. Geochimica et Cosmochimica Acta 263: 13-30.