Rare gas isotopic compositions in diamonds

Abstract

RARE gas isotopic compositions such as ⁴⁰Ar/³⁶Ar, ³He/⁴He and ¹²⁹Xe/¹³²Xe in the Earth have provided a powerful tool for understanding the origin and evolution of the terrestrial atmosphere^1–4. The isotopic information may be obtained from rare gases trapped in some mantle-derived materials such as volcanic rocks, volcanic xenoliths or volcanic gases. Among these mantle-derived materials, diamond seems to be unique due to its almost complete inertness to any known chemical and to its enormous stability against high temperature. Although the presence of O₂, H₂, CH₄, H₂O, CO, N₂, Ar and CO₂ in diamonds has been reported^5,6. No previous measurement has been made either on elemental compositions or on isotopic ratios of rare gases in diamonds. Here we report on rare gas elemental composition and isotopic ratios in diamond. We found that ³He/⁴He ratio is more than an order of magnitude larger than the atmospheric value and also ⁴⁰Ar/³⁶Ar ratio is significantly higher.