Nano-scale impact shock features of diamond and graphite in ureilites

Investigating carbon in meteorites has the potential to provide vital clues about the origins and evolution of early planetesimals, filling in key gaps in our understanding of the carbon cycle in our Solar System. In particular, the nanoscale study of ureilitic carbon and its defects is crucial for determining the formation process of these phases and whether shock played a role. This study investigated ureilitic crystalline carbon and determined the characteristic shock deformation features in ureilites by closely examining diamond and graphite in five Frontier Mountain Antarctic ureilitic samples with increasing degrees of shock using Transmission Electron Microscopy. Our analysis of FRO 95028, FRO 01089, FRO 97013, FRO 01088, and FRO 01012 revealed a spectrum of features and shock-induced defects in graphite (e.g., modulation, sector zoning, and grain rotation) and diamond (e.g., stacking faults and nano-twin), as well as diaphite nanostructures. Each combination of defects is uniquely tied to specific shock levels, providing compelling evidence that definitively links diamond formation and graphite transformation in ureilites to shock events. This finding yields new and outstanding results to determine the effects of shock on carbon at the nanoscale and to shed light on the intricate world of shock-altered carbon within this enigmatic meteorite group.