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 crystallization of the lunar magma ocean 2 and the duration of lunar volcanism 2 . The Chang’e-5 mission returned some of the youngest mare basalt samples reported so far, dated at 2.0 billion years ago (Ga) 3 , from the northwestern Procellarum KREEP Terrane, 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 the Chang’e-5 basalts. We derive a maximum water abundance of 283 ± 22 μg g −1 and a deuterium/hydrogen ratio of (1.06 ± 0.25) × 10 – 4 for the parent magma. Accounting for low-degree partial melting of the depleted mantle followed by extensive magma fractional crystallization 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 a modest water content for the Chang’e-5 basalt mantle source region is at the low end of the range estimated from mare basalts that erupted from around 4.0 Ga to 2.8 Ga (refs. 5 , 6 ), suggesting that the mantle source of the Chang’e-5 basalts had become dehydrated by 2.0 Ga through previous melt extraction from the Procellarum KREEP Terrane mantle during prolonged volcanic activity. Water abundance and hydrogen isotope compositions of two-billion-year-old basalt samples returned from the Moon by the Chang’e-5 mission suggest that the samples came from a relatively dry mantle source.