Hydrogen isotope compositions in carbonado diamond: constraints on terrestrial formation

Demény, Attila and Nagy, Géza and Bajnóczi, Bernadett and Németh, Tibor and Garai, József and Drozd, Vadym and Hegner, Ernst (2011) Hydrogen isotope compositions in carbonado diamond: constraints on terrestrial formation. Central European Geology, 54 (1-2). pp. 51-74. ISSN 1788-2281

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Abstract

Abstract In this study we report the first hydrogen isotope composition analyses on carbonado diamond along with cathodoluminescence and scanning electron microscopic imaging, electron microprobe analyses, and stable (H and C) and radiogenic (Sr) isotope measurements. The hydrogen of bulk carbonado (consisting diamond and pore-filling minerals) yielded ∼ −4‰, consistent with usual crustal or mantle-derived fluids. The diamond-related hydrogen component is about 70 ± 30 ppm and shows a D-depletion down to −200‰. Determined H isotope values — together with C isotope compositions — overlap the ranges for mantle-derived hydrocarbons. Textural characteristics and Sr isotope ratios of pore-filling florencite indicate that the carbonado was formed in a fluid-rich environment, underwent a significant high-temperature influence and finally suffered thorough alteration. Based on these observations, a terrestrial formation during interaction of mantle rocks/melts or subducted crustal materials and reduced C-H fluids seems to be more plausible than an extraterrestrial origin.

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