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    Petrology of a non-indigenous microgranitic clast in polymict ureilite EET 87720: evidence for formation of evolved melt on an unknown parent body

    Beard, Andrew D and Downes, Hilary and Chaussidon, M. (2015) Petrology of a non-indigenous microgranitic clast in polymict ureilite EET 87720: evidence for formation of evolved melt on an unknown parent body. Meteoritics & Planetary Science 50 (9), pp. 1613-1623. ISSN 1086-9379.

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    Abstract

    EET 87720 is a polymict ureilite breccia known to contain numerous non-indigenous fragments. We have discovered a microgranitic clast in an interior chip of EET 87720. The clast consists of a granophyre-like intergrowth of a pure SiO2 phase (tridymite) and albite, mantling a zoned oligoclase phenocryst. In the intergrowth, the tridymite occurs as thin elongate vermicular blebs within larger albite crystals. The granophyre-like intergrowth and the oligoclase phenocryst share a common margin, suggesting that the clast was originally part of a larger fragment. An estimate of its bulk composition is equivalent to that of granite (77 wt.% SiO2). Patches of high-Si K-bearing glass occur interstitially within the clast; they have high concentrations of SO3 (11-12 wt.%) and contain Cl (0.6 wt.%), suggesting that the clast formed on a volatile-rich parent body perhaps resembling early Mars. The mean oxygen isotope composition of the feldspar and tridymite in the clast is very different from the oxygen isotope compositions of ureilites, and is similar to those of silicate inclusions in IIE and IVA irons. Thus the clast is not indigenous to the ureilite parent body, but it provides evidence for the formation of evolved melts on an unknown parent body in the early solar system.

    Metadata

    Item Type: Article
    Additional Information: This is the peer reviewed version of the article, which has been published in final form at the cited link. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
    Keyword(s) / Subject(s): ureilite, granitic, oxygen isotopes
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Andy Beard
    Date Deposited: 01 Oct 2015 09:01
    Last Modified: 02 Jul 2020 20:01
    URI: http://eprints.bbk.ac.uk/id/eprint/12989

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