Fe and Mg Isotope Compositions Indicate a Hybrid Mantle Source for Young Chang'E 5 Mare Basalts

The Chang'E 5 (CE-5) samples represent the youngest mare basalt ever known and provide an access into the late lunar evolution. Recent studies have revealed that CE-5 basalts are the most evolved lunar basalts, yet controversy remains over the nature of their mantle sources. Here we combine Fe and Mg isotope analyses with a comprehensive study of petrology and mineralogy on two CE-5 basalt clasts. These two clasts have a very low Mg# (similar to 29) and show similar Mg isotope compositions to Apollo low-Ti mare basalts as well as intermediate TiO2 and Fe isotope compositions between low-Ti and high-Ti mare basalts. Fractional crystallization or evaporation during impact cannot produce such geochemical signatures that otherwise indicate a hybrid mantle source that incorporates both early- and late-stage lunar magma ocean (LMO) cumulates. Such a hybrid mantle source would be also compatible with the KREEP-like Rare Earth Elements pattern of CE-5 basalts. Overall, our new Fe-Mg isotope data highlight the role of late LMO cumulate for the generation of young lunar volcanism.

Automated summary

The CE-5 samples from the Chang'E 5 mission are the youngest lunar basalts discovered so far and offer insights into the late lunar evolution. A study combining Fe and Mg isotope analyses with petrology and mineralogy of two CE-5 basalt clasts reveals a hybrid mantle source that incorporates early- and late-stage lunar magma ocean cumulates. This finding challenges previous theories and highlights the role of late lunar magma ocean cumulates in the generation of young lunar volcanism.