Delivery of carbonaceous materials to the Moon

Asteroidal impacts play an important role in creating new lithology, shaping the morphology, and transporting water to the inner Solar System planets. Massive impact records have been preserved on the Moon; however, exogenous impactors have not been adequately identified in lunar samples. Here we carried out petrological and geochemical investigations on the newly lunar samples returned by Chang'e-6 (CE6) to estimate the source of impactors to the Moon. One spinel-bearing troctolite-like clast was identified in the CE6 soils. This clast displays porphyritic texture and is mainly composed of olivine (32 %), plagioclase (31 %), and mesostasis (34 %) with minor troilite (2 %) and spinel (1 %), and rare Fe-Ni metal, in area%. The sample olivines have a forsterite variation range of 75–85 and a Fe/Mn atomic ratio of 55–80. The trace element concentrations of Co (113–223 μg.g⁻¹), Ni (121–938 μg.g⁻¹), Cr (1191–4832 μg.g⁻¹), and P (827–1645 μg.g⁻¹) in olivines are notable higher than the typical lunar samples. Furthermore, these olivines exhibit notable ¹⁶O depletion features (δ¹⁸O: +10.7 ‰ to +16.7 ‰ and δ¹⁷O: +5.9 ‰ to +9.5 ‰). The investigated clast has a bulk Ir content of 51 ng.g⁻¹, significantly higher than local lunar materials. The unusual texture, mineral chemistry, trace element concentrations, and oxygen isotopic compositions suggest this clast was likely derived from an impact event created by a CI- or CY-like carbonaceous chondrite. Such chemical and isotopic features are correlated with textures, indicating that some olivine have relict cores originated from the impactor. Such an impact event could have produced a new lithology of spinel-bearing troctolite on the Moon. Meanwhile, the carbonaceous chondritic impactor would have delivered a great amount of water and volatiles to the Moon.