Oxygen, carbon, and strontium isotope geochemistry of diamond-bearing carbonate rocks from Kumdy-Kol, Kokchetav Massif, Kazakhstan

M. Ohta, T. Mock, Yoshihide Ogasawara, D. Rumble

    Research output: Contribution to journalArticle

    13 Citations (Scopus)

    Abstract

    Diamond-bearing carbonate rocks from Kumdy-Kol, Kokchetav massif, Kazakhstan, were strongly altered by fluids flowing through fractures and infiltrating along grain boundaries during exhumation. Alteration includes retrogradation of high-grade silicate assemblages by hydrous minerals, replacement of diamond by graphite and of dolomite by calcite. Diamond-bearing carbonate rocks are among the most intensely altered isotopically with δ18OVSMOW values as low as + 9‰, δ13CVPDB = - 9‰, and 87Sr/86Sr as high as 0.8050. Evidence of isotopic equilibration between coexisting dolomite and high-Mg calcite during ultrahigh-pressure metamorphism (UHPM) is preserved only rarely in samples isolated from infiltrating fluids by distance from fractures. Isotopic heterogeneity and isotopic disequilibrium are widespread on a hand-specimen scale. Because of this lack of homogeneity, bulk analyses cannot provide definitive measurements of 13C/12C fractionation between coexisting diamond and carbonate. Our study adequately documents alteration on a scale commensurate with observed vein structures. But, testing the hypothesis of metamorphic origin of microdiamonds has not fully succeeded because our analytical spatial resolution, limited to 0.5 mm, is not small enough to measure individual dolomite inclusions or individual diamond crystals.

    Original languageEnglish
    Pages (from-to)77-90
    Number of pages14
    JournalLithos
    Volume70
    Issue number3-4
    DOIs
    Publication statusPublished - 2003 Oct

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    Keywords

    • Carbon isotopes
    • Continental collision
    • Diamond-eclogite facies
    • Exhumation
    • Oxygen isotopes
    • Strontium isotopes

    ASJC Scopus subject areas

    • Geochemistry and Petrology

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