Chondrules and Ca-Al-rich inclusions (CAIs) are high-temperature components of meteorites that formed during transient heating events in the early Solar System. A major unresolved issue is the relative timing of CAI and chondrule formation1,2,3,4. From the presence of chondrule fragments in an igneous CAI, it was concluded that some chondrules formed before CAIs (ref. 5). This conclusion is contrary to the presence of relict CAIs inside chondrules6,7,8,9,10, as well as to the higher abundance of 26Al in CAIs11; both observations indicate that CAIs pre-date chondrules by 1–3 million years (Myr). Here we report that relict chondrule material in the Allende meteorite, composed of olivine and low-calcium pyroxene, occurs in the outer portions of two CAIs and is 16O-poor (Δ17O ≈ - 1‰ to -5‰). Spinel and diopside in the CAI cores are 16O-rich (Δ17O up to -20‰), whereas diopside in their outer zones, as well as melilite and anorthite, are 16O-depleted (Δ17O = -8‰ to 2‰). Both chondrule-bearing CAIs are 26Al-poor with initial 26Al/27Al ratios of (4.7 ± 1.4) × 10-6 and <1.2 × 10-6. We conclude that these CAIs had chondrule material added to them during a re-melting episode ∼2 Myr after formation of CAIs with the canonical 26Al/27Al ratio of 5 × 10-5.
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Financial support for this project was provided by NASA (A.N.K., I.D.H., G.J.M.) and Monkasho (H.Y.). We thank R. H. Hewins for comments and suggestions.
The authors declare that they have no competing financial interests.
Oxide wt% vs. distance (µm) for compositional profiles AB and CD. (JPG 441 kb)
Optical micrograph in transmitted light and combined X-ray elemental map of the CAI TS26. (JPG 867 kb)
Bulk compositions of the chondrule-bearing Type C CAIs ABC plotted on a triangular diagram. (JPG 197 kb)
Legends to accompany the above Supplementary Figures. (DOC 20 kb)
Representative electron microprobe analyses of primary minerals in the chondrule-bearing CAIs ABC and TS26 from the CV carbonaceous chondrite Allende. (DOC 75 kb)
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Krot, A., Yurimoto, H., Hutcheon, I. et al. Chronology of the early Solar System from chondrule-bearing calcium-aluminium-rich inclusions. Nature 434, 998–1001 (2005). https://doi.org/10.1038/nature03470
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