Calcium and titanium isotope fractionation in refractory inclusions: Tracers of condensation and inheritance in the early solar protoplanetary disk

• Published in: Earth and planetary science letters 2017-08, Vol.472, p.277-288
• Main Authors: Simon, J.I., Jordan, M.K., Tappa, M.J., Schauble, E.A., Kohl, I.E., Young, E.D.
• Format: Article
• Language: English
• Subjects: 50Ti isotopic anomalies; Ca and Ti isotope fractionation; Ca-, Al-rich inclusions; condensation; protoplanetary disk; solar nebula
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2017.05.002

Measured and modeled Ca and Ti isotopic fractionation effects in a diverse suite of refractory inclusions are used to understand processes of condensation in the solar protoplanetary disk where they and their precursor materials formed. This coordinated approach reveals largely decoupled isotopic signatures and implies that few, if any, of the studied inclusions can be considered primary condensates. All studied inclusions are enriched in light Ca isotopes (∼−0.2 to −2.8‰/amu), but only two show correspondingly light Ti isotopes. Studied inclusions exhibit both heavy and light Ti isotope enrichments (∼0.3 to −0.4‰/amu). These refractory element isotopic signatures, therefore, suggest admixture and reprocessing of earlier formed materials with distinct condensation histories. Along with coordinated measurements of 50Ti isotopic anomalies, which span a range from ∼0 to ∼40 epsilon-unit excesses, the comparison of measured and modeled fractionation of Ca and Ti isotopes provides a powerful approach to understanding primitive nebular processes and environments in the protoplanetary disk. Remarkable evidence for Ca isotopic zoning within a typical Type B1 inclusion exemplifies the potential record of the earliest solar nebula that is likely lost and/or overprinted in the isotopic compositions of more volatile elements (e.g., Mg, Si, and O) by later modification processes. •A report of measured and modeled mass dependent Ca and Ti isotopes in CAIs.•A discovery of Ca isotopic zoning within an individual refractory inclusion.•Theoretical condensation models show decoupling of Ca and Ti isotope records in CAIs.•With 50Ti anomalies, results used to probe processes and environments in the nebula.•Results exemplify complicated condensation and later subsolidus histories of CAIs.