Potential Primary Xenon Components in Nanodiamond-Enriched Fractions of Meteorites: Characteristics of Isolated Components During Oxidation

Abstract

To achieve a detailed picture of the isolated potential primary xenon components during stepwise oxidation of nanodiamond-enriched fractions (NDEF) of meteorites, a new isotopically anomalous component Xe-pr3 has been introduced. The peculiarity of this component is a lower value of the ratio ¹³⁴Xe/¹³⁶Xe compared to that component used in (Fisenko et al., 2024b) Xe-pr2n (0.529 versus 0.591, respectively). As a result, the modeling interval of possible values of the ratio ¹³⁴Xe/¹³⁶Xe has increased in anomalous isotopic compositions of isolated xenon. This has led to the possibility of obtaining a complete and detailed picture of the isolated putative xenon components based on the analysis of high-precision data for xenon isolated during stepwise oxidation of LD1 NDEF of the Murchison meteorite (CM2) (Lewis, 1994). Comparative analysis of isolated xenon components using calculated cosmogenic neon contents (²¹Ne_c) showed the following. The relatively low-temperature, nearly isotopically normal Xe-P3 component in NDEF meteorites, identified in (Huss, Lewis, 1994), is contained in an individual carrier phase with low thermal-oxidative stability. This component, according to the authors’ concept, represents a mixture of Xe-P3n with Xe-S in a ratio of 1 : 0.013. The carrier phase of this component is likely to be diamond-like rims. Their surface localization is indicated by the simultaneous release of radiogenic ¹²⁹Xe. The release of isotopically anomalous Xe-pr1n corresponds to the layer-by-layer oxidation of diamond grains. When using SiC-X grains as the carrier phase, the components Xe-pr3 (Fisenko et al., 2024a) its unusual (“explosive”) release (about 70% at one oxidation stage) is explained by us by the formation of surface amorphous films of silicon dioxide on these grains. The assumption about SiC-X grains as a carrier phase of the isotopically anomalous component Xe-pr3 is confirmed by the revealed connection between this component and cosmogenic neon ²¹Ne_c. It is also shown that the “normal” primary component of neon in terms of isotopic composition (designated by us as Ne-P3n) corresponds to the isotopic composition of neon isolated at the high-temperature oxidation stage of LD1 NDEF. Therefore, the isotopic composition of the Ne-P3 component is the result of mixing the primary composition with an additional portion of the isotope ²²Ne (Ne-E) in a ratio of 1 : 0.05. This mixing probably occurred early in the evolution of the protoplanetary cloud of the Solar system. Successful modeling of the isotopic compositions of xenon isolated at almost all stages of the temperature range of oxidation of LD1 NDEF of the Murchison meteorite using a new(?) potentially primary component of xenon in combination with the rest allows us to consider them real and possible when analyzing xenon in NDEF of other meteorites.