Calcium–aluminum-rich inclusions in non-carbonaceous chondrites: Abundances, sizes, and mineralogy

Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13975]
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California 90025,USA
2Department of Earth and Planetary Science, University of California, Santa Cruz, Santa Cruz, California 95064, USA
3Harvard-MIT Science Research Mentoring Program, Boston, Massachusetts 02142, USA
4Lawrence Livermore National Laboratory, Livermore, California 94550, USA
Published by arrangement wit John Wiley & Sons

As the Sun was forming, calcium–aluminum-rich inclusions (CAIs) were the firstrocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceouschondrites (CCs) contain abundant CAIs but are thought to have accreted in the outerSolar System, requiring that CAIs must have been transported outward. Curiously, CAIsare rare in ordinary, enstatite, rumuruti, and kakangari chondrites, non-carbonaceouschondrites (NCs), that likely formed in the inner Solar System. Thus, CAI abundances andcharacteristics can provide constraints on the early dynamical evolution of the disk. In thiswork, we address whether the hypothesis of an early-formed proto-Jupiter “opening a gap”in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NCchondrites. We searched 76 NC meteorite sections to find 232 CAIs which have an averageapparent diameter of 46μm and comprise 0.01 area%, about half the size of and~200 timesless abundant than CC CAIs on average. Unlike CC CAIs, only 4% of the NC CAIscontain melilite and most contain alteration features suggesting that NC CAIs underwentpervasive fluid-assisted thermal metamorphism on asteroidal parent bodies. However, basedon NC CAI populations correlating with meteorite metamorphic grade, we argue that diskdynamics is likely the primary reason behind the existence of small (<100μm) and rare NCCAIs. Our data support astrophysical models which suggest that, after outward transport ofCAIs, formation of a gap in the disk trapped CAIs in the outer Solar System.


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