Dy, Er, and Yb isotope compositions of meteorites and their components: Constraints on presolar carriers of the rare earth elements

Abstract

One way to study the original building blocks of the Solar System is to investigate primitive meteorites and their components. Specifically, isolating these meteorites' individual components via sequential acid leaching can reveal isotopically diverse material present in the early Solar System, which can provide new insights into the mixing and transport processes that eventually led to planet formation. Such isotopic differences in the components are likely to be found in heavy rare earth elements, such as dysprosium (Dy), erbium (Er), and ytterbium (Yb), because their isotopes have different nucleosynthetic production pathways and the elements have significant differences in volatility; however, these specific elements have yet to be thoroughly investigated in the field of cosmochemistry. As such, we present the first combined Dy, Er, and Yb isotope compositions of sequential acid leachates from the Murchison meteorite, along with multiple bulk meteorites from different taxonomic classes. This work also presents a new method to separate, purify, and accurately measure Dy isotopes. Here we show that resolved Dy, Er, and Yb isotope variations in most bulk meteorites are due to neutron capture processes. However, Dy and Er isotopic compositions of bulk Murchison and Murchison leachates stem from the additions or depletions of a nucleosynthetic component formed by the s-process, most likely mainstream silicon carbide (SiC) grains. In contrast, the Yb isotope compositions of bulk Murchison and Murchison leachates display either unresolved or relatively small isotope anomalies. The disparate isotopic behavior between Dy-Er and Yb likely reflects their differing volatilities, with Dy and Er condensing/incorporating into the mainstream SiC grains, whereas the less refractory Yb remains in the gas phase during SiC formation. This work suggests that Yb is hosted in a non-SiC presolar carrier phase and, furthermore, that mainstream SiC grains may be the primary source of isotopic variation in bulk meteorites.