Meteoritic Nanodiamonds: Alternative Composition of Xenon Components

For the first time, abundances of the main xenon components (Xe-P3, Xe-P3(fr), Xe-P6 and Xe-pr instead Xe-HL) in the nanodiamonds of Orgueil (CI), Tieschitz (H3.6) and Indarch (EH3-4) meteorites have been calculated. The Xe-pr component is the excess fraction of xenon isotopes in the Xe-HL component relative to Xe-P3 (fr) and mainly consists of the 124, 126, 134, 136Хе isotopes formed in p- and r-processes of nucleosynthesis in a type II supernova explosion. Analysis of the data has shown the following. (1) The main nanodiamond component of Xe is Xe-P3 (fr), and its maximum during pyrolysis, like Xe-pr and Xe-P6, is high-temperature (>1000°C), irrespectively of the petrological type of meteorites. (2) The relative abundance of the Xe-pr component in the nanodiamonds of Indarch meteorite, which is most enriched in anomalous xenon components, is about 15% of the total xenon abundance in the diamond of this meteorite, which is significantly lower than the abundance of the Xe-HL component – about 87%. (3) The xenon components are contained in the individual populations of the diamond grains with different thermo-oxidative stability. The data we obtained and in (Huss, Lewis, 1994b) on the abundances and the yield kinetics of xenon components in meteoritic nanodiamonds, based on the Xe-pr and Xe-HL isotope compositions, respectively, most likely show their limiting values. Тhe real properties of xenon components are assumed to be similar to those obtained when using Xe-pr component for calculations, taking into account the data on the carbon isotope composition in the nanodiamond grains of the Allende meteorite (Lewis et al., 2019).