A shallow mantle source for the Chang'e 5 lavas reveals how top-down heating prolonged lunar magmatism

The 2-billion-year-old basalts collected by the Chang'e 5 mission are younger than any other sampled lunar igneous rock. These lavas provide critical insight into the evolution of the Moon at a time when magmatism was waning and represent a key data point for understanding how rocky bodies cool. Here, we present high-P-T experiments and phase equilibrium modeling performed on a Chang'e 5 basalt composition that show the parental magma formed in the shallow mantle, at ~75- to 130-kilometer depth. This shallow source and Sr-Nd isotopic evidence for the lack of the heat-producing KREEP reservoir in sources of the Chang'e 5 basalt and high-Ti basalts collected by Apollo demonstrate that KREEP was not carried into the deep mantle to generate prolonged melting. Rather, we show that a subcrustal KREEP layer conductively heating the nearside mantle from the top down is likely responsible for prolonged lunar magmatism.