Carbon isotope heterogeneity in metamorphic diamond from the Kokchetav UHP dolomite marble, northern Kazakhstan

Kyoko Imamura, Yoshihide Ogasawara, Hisayoshi Yurimoto, Minoru Kusakabe

    Research output: Contribution to journalArticle

    7 Citations (Scopus)

    Abstract

    We analysed isotopic compositions of metamorphic microdiamond secondary ion mass spectrometry. Typical microdiamonds in this dolomite marble show star-shaped morphologies (S-type) consisting of single-crystal cores and polycrystalline rims. Four S-type microdiamonds and two R-type microdiamonds (single crystals with rugged surfaces) were analysed using a 5 μm diameter ion beam. S-type microdiamonds have heterogeneous carbon isotopic compositions even in a single grain. Analysis of a typical S-type microdiamond (no. xx01-1-13) revealed clear difference in δ13C between core and rim. The rim shows lighter isotopic compositions ranging from -17.2% to -26.9%, whereas the core is much heavier, with δ13C ranging from -9.3% to -13.0%. The δ13C values of R-type microdiamonds fall into narrow ranges from -8.3% to -14.9% for no. xx01-1-10 and from -8.3% to -15.3% for no. xx01-1-16. These δ13C values are similar to those of the S-type microdiamond cores. The R-type probably formed at the same stage as the core of the S-type, whereas rim growth at a second stage did not occur or occurred very weakly in R-type microdiamonds. These carbon isotopic data support the two-stage growth of microdiamonds in the Kokchetav ultrahigh-pressure host rock. To explain the second stage growth of S-type microdiamonds, we postulate a simple fluid infiltration of light carbon from neighbouring gneisses into the dolomite marble.

    Original languageEnglish
    Pages (from-to)453-467
    Number of pages15
    JournalInternational Geology Review
    Volume55
    Issue number4
    DOIs
    Publication statusPublished - 2013 Mar 1

    Keywords

    • carbon isotopes
    • dolomite marble
    • microdiamond
    • SIMS
    • UHP metamorphism

    ASJC Scopus subject areas

    • Geology

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