H and Cl isotope characteristics of indigenous and late hydrothermal fluids on the differentiated asteroidal parent body of Grave Nunataks 06128

Romain Tartese, Mahesh Anand, Ian A. Franchi

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The paired achondrites Graves Nunataks (GRA) 06128 and 06129
    are samples of an asteroid that underwent partial melting within a few
    million years after the start of Solar System formation. In order to
    better constrain the origin and processing of volatiles in the early
    Solar System, we have investigated the abundance of H, F and Cl and the
    isotopic composition of H and Cl in phosphates in GRA 06128 using
    secondary ion mass spectrometry. Indigenous H in GRA 06128, as recorded
    in magmatic merrillite, is characterised by an average dD of ca. -152 ±
    330‰, which is broadly similar to estimates of the H isotope composition
    of indigenous H in other differentiated asteroidal and planetary bodies
    such as Mars, the Moon and the angrite and eucrite meteorite parent
    bodies. The merrillite data thus suggest that early accretion of locallyderived
    volatiles was widespread for the bodies currently populating the
    asteroid belt. Apatite formed at the expense of merrillite around 100
    million years after the differentiation of the GRA 06128/9 parent body,
    during hydrothermal alteration, which was probably triggered by an impact
    event. Apatite in GRA 06128 contains 5.4-5.7 wt.% Cl, 0.6-0.8 wt.% F, and
    ~20 to 60 ppm H2O, which is similar to the H2O abundance in merrillite
    from which apatite formed. The apatite dD values range between around
    +100‰ and +2000‰ and are inversely correlated with apatite H2O contents.
    The Cl isotope composition of apatite appears to be homogeneous across
    various grains, with an average d37Cl value of 3.2 ± 0.7‰. A possible
    scenario to account for the apatite chemical and isotopic characteristics
    involves interaction of GRA 06128/9 with fumarole-like fluids derived
    from D- and HCl-rich ices delivered to the GRA 06128/9 parent-body by an
    ice-rich impactor.
    Original languageEnglish
    JournalGeochimica et Cosmochimica Acta
    Early online date25 Jan 2019
    DOIs
    Publication statusPublished - 2019

    Keywords

    • Apatite
    • Merrillite
    • Asteroids
    • H isotopes
    • Cl isotopes
    • Secondary Ion Mass Spectrometry

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