Classification and provenance of exotic impact glasses in Chang’e-5 lunar soil

Lunar impact glasses have been identified as crucial indicators of geochemical information regarding their source regions. Impact glasses can be categorized as either local or exotic. Those preserving geochemical signatures matching local lithologies (e.g., mare basalts or their single-minerals) or regolith bulk soil compositions are classified as ‘local’. Otherwise, they could be defined as ‘exotic’. The analysis of exotic glasses provides the opportunity to explore previously unsampled lunar areas. This study focuses on the identification of exotic glasses within the CE-5 soil sample by analyzing the trace elements of 29 impact glasses with distinct major element compositions in comparison to the CE-5 bulk soil. However, the results indicate that 18 of the analyzed glasses exhibit trace element compositions comparable to those of the local CE-5 materials, particularly some of them could match the local single-mineral component in major and trace elements, suggesting a local origin. Therefore, it is recommended that the investigation be expanded from using major elements to including non-volatile trace elements, with a view to enhancing our understanding on provenance of lunar impact glasses. In order to achieve a more accurate identification of exotic glasses within the CE-5 soil sample, a novel classification plot of Mg# versus La is proposed. The remaining 11 glasses, which exhibited diverse trace element variations were identified as exotic. A comparative analysis of their chemical characteristics with remote sensing data indicates that they may have originated from the Aristarchus, Mairan, Sharp or Pythagoras craters. This study elucidates the classification and possible provenance of exotic materials within the CE-5 soil sample, thereby providing constraints for the enhanced identification of local and exotic components at the CE-5 landing site.