Heterogenous 48Ca isotopic anomalies in a diverse suite of refractory inclusions, insights into the primordial Solar System

Thermal ionization mass spectrometry measurements of non-mass-dependent calcium isotope effects in calcium-aluminum-rich refractory inclusions show resolvable anomalies, both 48 Ca isotope excesses and deficits, when compared to measured reference materials used to define the normal terrestrial planet composition (ε 48 Ca = 0 ± 3.52SD ε-unit, part in 10,000, for the 48 Ca/ 44 Ca ratio). For two of the studied inclusions resolvable intra ε 48 Ca heterogeneity also exists. The measured range and heterogeneity of calcium isotope effects represent a vestige of presolar stellar nucleosynthetically distinct carriers contributed to the Solar protoplanetary disk at the time refractory inclusions were forming, representing the earliest record of infall events since molecular cloud collapse. When directly compared to mass-dependent calcium isotope fractionation effects, as well as mass-dependent and non-mass-dependent titanium isotope effects, and moderately refractory element isotopic signatures, a more complete view of how inclusions, and through their compositions, the early Solar System formed. Additionally, the long-debated nature of several common inclusion types, e.g., melilite-mantled coarse-grained Type B’s, can be more clearly understood when evidence from both refractory elements, for a primordial record, and the moderately refractory elements, for late nebular formation events are considered. Collectively, cosmochemical and chronological records contained in refractory inclusions are important because they formed during the early period of Solar System evolution in which the protoplanetary disk began to dissect into distinct radial reservoirs, likely caused by the formation of giant gaseous planets, directly recording reservoirs, processes, and timescales from which building blocks of terrestrial planets emerged.