Noble gases in oxidized residue prepared from the Saratov L4 chondrite and Raman spectroscopic study of residues to characterize phase Q

Abstract

We analyzed noble gases in an oxidized residue prepared from a HF‐HCl residue of the Saratov L4 chondrite. The Ar, Kr, and Xe concentrations in the oxidized residue are two orders of magnitude lower than those in the HF‐HCl residue, and they are close to concentrations in the bulk. The He and Ne concentrations are similar in the three samples. The Ne isotopic ratios are almost purely cosmogenic, indicating absence of presolar diamonds (the carrier of the HL component). Thus, Saratov contains phase Q without presolar diamond. A study of the Raman spectroscopic parameters for the HF‐HCl residue and the oxidized residue shows large changes due to oxidation. The directions of these changes are the same as observed in Allende, except oxidation increased the ID/IG (intensity ratio of the D band to the G band) in Saratov but decreased in Allende. This difference may be attributed to the different crystalline stages of carbon in both meteorites. The shifts in the Raman parameters to a discrete and/or more expanded region suggest that (1) oxidation changes the crystalline condition of graphitic carbon, (2) phase Q is not a dissolved site, and (3) the release of Q‐gas is simply related to the rearrangement of the carbon structure during oxidation.

On the carrier phase of the “planetary” noble gases: TEM, Raman, and stepped combustion data for acid‐resistant residues from the Saratov (L4) meteorite

“…The Raman spectra of the fractions studied here differ considerably from the ARR sample of the Saratov meteorite studied by Matsuda et al. () in relative widths of the D band and, more importantly, in the ratio I(D)/I(G). Used with caution, this ratio serves as a proxy for the size of the ordered graphitic domains.…”

“…A similar behavior of He relative to Ar and Xe is also observed upon etching of the AC fraction by Cr 2 O 7 −2 (Matsuda et al. ). Note that the 4 He/ 36 Ar ratio in the gas released from the SU‐BA fraction after the H 2 O 2 treatment is 0.6, i.e., less than the value for the Q‐phase (5.2 ± 1.1; Busemann et al.…”

“…Carbonaceous material from the sample studied by Matsuda et al. () are characterized by a noticeably higher I(D)/I(G) ratio (~1–1.5) than the fractions studied by us (~1), indicating either higher densities of point defects for the former sample or more disordered “amorphous” carbon. The closest spectral analogues to our results were reported by Wopenka et al.…”

“…Solid lines—this work, dotted—Matsuda et al. (). (Color figure can be viewed at wileyonlinelibrary.com.…”

“…The study of the ARR fraction of the Saratov (L4) using Raman spectroscopy suggests that the release of the Q‐gases is related to structural rearrangements of a carbonaceous matter (Matsuda et al. , ). Transmission electron microscopy (TEM) data indicate that the Q‐gases probably reside between layers of few‐layer graphenes (Bernatowicz et al.…”