Discovery of carbonaceous chondritic fragment in Chang'e-5 regolith samples

Abstract

Lunar regolith samples contain fragments of endogenic rocks and exogenous meteorites. We report the first discovery of a chondrule fragment preserved in Chang'e-5 (CE-5) regolith samples. Forsterite and enstatite phenocrysts have extremely high Mg# (> 99) and high Mn/Fe ratios in this chondrule fragment. Its glass mesostasis is heterogeneous and contains hydrogen and carbon, as indicated by Raman peaks. The mineral assemblage, chemical composition, and oxygen isotope anomaly of this fragment are similar to those of type-I chondrules from carbonaceous chondrites. This fragment and other chondritic relics with < 3.0 Ga impact ages exhibit compositional similarities to micrometeorites on Earth, but are different from ultramagnesian mafic fragments (UMMFs) discovered on the Moon with impact ages > 3.4 Ga. This contrast suggests that there may have been a change of impactors to the Earth–Moon system during the Imbrian period. Furthermore, this CE-5 chondrule fragment is a direct record of volatile addition to the Moon's surface from meteorites during the Eratosthenian period.