A dry lunar mantle reservoir for young mare basalts of Chang’E-5

The distribution of water in the Moon’s interior carries implications for the origin of the Moon ¹, the crystallisation of the lunar magma ocean ², and the duration of lunar volcanism ². The Chang’E-5 (CE5) mission returned the youngest mare basalt samples, dated at 2.0 billion years ago (Ga) ³, from the northwestern Procellarum KREEP Terrane (PKT), providing a probe into the spatiotemporal evolution of lunar water. Here we report the water abundances and hydrogen isotope compositions of apatite and ilmenite-hosted melt inclusions from CE5 basalts. We derive a maximum water abundance of 283 ± 22 μg.g ^-1 and a δD value of -330 ± 190‰ for the parent magma. Accounting for a low degree partial melting of the depleted mantle followed by extensive magma fractional crystallisation ⁴, we estimate a maximum mantle water abundance of 1-5 μg.g ^-1, suggesting that the Moon’s youngest volcanism was not driven by abundant water in its mantle source. Such modest water contents for the CE5 basalt mantle source region is at the low end of the range estimated from mare basalts that erupted from ca. 4.0-2.8 Ga ^5,6, suggesting that the mantle source of CE5 basalts had become dehydrated by 2.0 Ga through previous melt extraction from the PKT mantle during prolonged volcanic activity.