Raman characterization of carbonaceous matter in CONCORDIA Antarctic micrometeorites

Abstract– We report a multi‐wavelength Raman spectroscopy study of carbonaceous matter in 38 Antarctic micrometeorites (AMMs) from the 2006 CONCORDIA collection. The particles were selected as a function of their degree of thermal alteration developed during the deceleration in the atmosphere. These samples range from unmelted (fine‐grained—Fg; ultracarbonaceous—UCAMMs) to partially melted AMMs (scorias—Sc) and completely melted particles (cosmic spherules—CS). More than half of the analyzed AMMs contain a substantial amount of polyaromatic carbonaceous matter with a high degree of disorder. The proportion of particles where carbon is not detected increase from the Fg to the Fg‐Sc and to the Sc‐AMMs, and no carbon is detected in CS. In addition, the spectral characteristics of the G and D bands of the carbonaceous matter in Sc‐AMMs plot apart from the trend formed by the data from Fg‐AMMs and UCAMMs. These results suggest that oxidation processes occurred during the deceleration of the particles in the atmosphere. In Fg‐AMMs and UCAMMs, the spectral characteristics of the G and D bands reveal the high degree of disorder of the carbonaceous matter, precluding a long duration thermal metamorphism on the parent body and suggesting that AMMs have a connection with C1–C2 chondrites. The Raman parameters of the deuterium‐rich carbonaceous matter of UCAMMs do not differ from that of Fg‐AMMs. Using a 244 nm excitation, we detected the cyanide (–CN) functional group for the first time in a UCAMM, reinforcing the likely cometary origin of this type of micrometeorites.