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

TL;DR

This study uses Fe and Mg isotope analyses to reveal that the youngest lunar mare basalts from Chang'E 5 originate from a hybrid mantle source combining early and late lunar magma ocean cumulates, shedding light on lunar mantle evolution.

Contribution

It provides the first combined Fe and Mg isotope evidence supporting a hybrid mantle source for young lunar basalts, challenging previous models of lunar mantle composition.

Findings

CE-5 basalts have intermediate isotope compositions.

Hybrid mantle source includes both early and late-stage LMO cumulates.

Late LMO cumulate played a key role in recent lunar volcanism.

Abstract

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 basalt, 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# (~29) and show similar Mg isotope compositions with 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 which 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 REE 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.