1. Hawai'i Institute of Geophysics & Planetology, School of Ocean & Earth Science & Technology, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA
2. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
3. Institute of Geophysics & Planetary Physics and G.T. Seaborg Institute, Lawrence Livermore National Laboratory, Livermore, California 94451, USA
4. Smithsonian Institution, Department of Mineral Sciences, NHB 119, Washington DC 20560, USA

Correspondence to: Alexander N. Krot¹ Correspondence and requests for materials should be addressed to A.N.K. (Email: sasha@higp.hawaii.edu).

Abstract

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 formation^{1, 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 chondrules^{6, 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 (¹⁷O - 1 to -5). Spinel and diopside in the CAI cores are ¹⁶O-rich (¹⁷O up to -20), whereas diopside in their outer zones, as well as melilite and anorthite, are ¹⁶O-depleted (¹⁷O = -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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