Abstract
Angrite meteorites are thought to represent ancient basaltic igneous rocks that formed inward of Jupiter’s orbit on the basis of their isotopic parameters such as ε50Ti, ε54Cr and Δ17O in addition to Fe/Mn ratios of pyroxene. New bulk oxygen isotope measurements of nine angrites, and of olivine ‘xenocrysts’ and groundmass fractions from three quenched angrites, however, reveal clear isotopic disequilibrium, implying an impact melt origin. Groundmass fractions from Asuka 12209, Asuka 881371 and Northwest Africa 12320 quenched angrites demonstrate an average Δ17O value of −0.003 ± 0.020‰. Here, excluding the bulk value and all groundmass fractions of Northwest Africa 12320, which is contaminated by an impactor, we determine a new well constrained average Δ17O value for the angrite parent body (−0.066 ± 0.016‰). Microstructural investigations of Northwest Africa 12320 reveal the presence of both fully recrystallized and undeformed olivine xenocrysts, indicating that some xenocrysts underwent high-temperature processes. These results suggest that angrites bear signatures of impact-driven isotopic mixing, possibly in response to early giant planet migration. The evidence for impact mixing raises doubts about the utility of quenched angrites as a suitable Pb–Pb isotopic anchor, which in turn has consequences for accurately defining the timeline of other Solar System events.
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Data availability
All data generated or analysed during this study are included in either the article or its supplementary information.
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Acknowledgements
K. Green and M. Higgins are thanked for their help in sample preparation. G. Degli-Alessandrini is thanked for her assistance with scanning electron microscopy and EBSD analyses. J. Malley is thanked for assisting with laser-fluorination work. G. Ensor is thanked for his help in procuring the NWA angrites. B.G.R.-S. was supported by an STFC studentship. M.A. and I.A.F. acknowledge support from STFC grant ST/T000228/1. Acquisition and analysis of A 12209 and A 881371 were supported by JSPS KAKENHI (JP19H01959 to A.Y., JP19H00726 and JP21K1845 to T.M.) and NIPR (research project KP307 to A.Y.), in collaboration with the Belgian Science Policy (Belspo) project BELAM for A 12209. V.D., S.G. and P.C. acknowledge the FWO-FNRS Excellence of Science (EOS) programme ET-HoME. V.D., L.P., S.G. and P.C. also acknowledge the Belspo project BELAM for past funding. V.D. thanks FRS-FNRS for support. S.G. and P.C. acknowledge the support of the VUB Strategic Programme.
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R.C.G., M.A. and I.A.F. devised the project. M.A. acquired the NWA samples while A samples were provided by A.Y. B.G.R.-S. and R.C.G. led the data acquisition and processing, supported by other authors. B.G.R.-S. produced the first draft of the paper. All authors participated in data interpretation and contributed during various stages of paper revision.
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Rider-Stokes, B.G., Greenwood, R.C., Anand, M. et al. Impact mixing among rocky planetesimals in the early Solar System from angrite oxygen isotopes. Nat Astron (2023). https://doi.org/10.1038/s41550-023-01968-0
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DOI: https://doi.org/10.1038/s41550-023-01968-0