Early evolution of the solar accretion disk inferred from Cr-Ti-O isotopes in individual chondrulesOPEN ACCESS 

Jonas M. Schneider, Christoph Burkhardt, Yves Marrocchi, Gregory A. Brennecka, Thorsten Kleine

Submitted to EPSL on Jan 29 2020, accepted in revised form Sep. 12 2020

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Update (23 September 2020):

Earth and Planetary Science Letters
Volume 551, 1 December 2020, 116585

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“Highlights

• First combined Cr, Ti, O isotope data for individual chondrules.
• Isotopic compositions of NC chondrules distinct from CC chondrules.
• Isotopic variability not due to chondrule transport, but precursor heterogeneity.
• Incomplete mixing of NC-like and CAI-like nebular components in the disk at all scales.”

“Isotopic anomalies in chondrules hold important clues about the dynamics of mixing and transport processes in the solar accretion disk. The meaning of these anomalies is debated and they have been interpreted to indicate either disk-wide transport of chondrules or local heterogeneities of chondrule precursors. However, all previous studies relied on isotopic data for a single element (either Cr, Ti, or O), which does not allow distinguishing between source and precursor signatures as the cause of the chondrules’ isotope anomalies. To overcome this problem, we obtained the first combined O, Ti, and Cr isotope data for individual chondrules from enstatite, ordinary, and carbonaceous chondrites. We find that chondrules from non-carbonaceous (NC) chondrites have relatively homogeneous ∆17O, ε50Ti, and ε54Cr, which are similar to the compositions of their host chondrites. By contrast, chondrules from carbonaceous chondrites (CC) have more variable compositions, some of which differ from the host chondrite compositions. Although the compositions of the analyzed CC and NC chondrules may overlap for either ε50Ti, ε54Cr, or ∆17O, in multi-isotope space none of the CC chondrules plot in the compositional field of NC chondrites, and no NC chondrule plots within the field of CC chondrites. As such, our data reveal a fundamental isotopic difference between NC and CC chondrules, which is inconsistent with a disk-wide transport of chondrules across and between the NC and CC reservoirs. Instead, the isotopic variations among CC chondrules reflect local precursor heterogeneities, which most likely result from mixing between NC-like dust and a chemically diverse dust component that was isotopically similar to CAIs and AOAs. The same mixing processes, but on a larger, disk-wide scale, were likely responsible for establishing the distinct isotopic compositions of the NC and CC reservoirs, which represent in inner and outer disk, respectively.”