A dry lunar mantle reservoir for young mare basalts of Chang\u2019e-5

Sen Hu,Ruiying Li,Jialong Hao,Jianglong Ji,Hejiu Hui,Yangting Lin,Yihong Yan,Lixin Gu,Romain Tartèse,Huicun He,Huaiyu He,Mahesh Anand,Qian Guo,Ziyuan Ouyang

doi:10.1038/s41586-021-04107-9

Abstract

The distribution of water in the Moon’s interior carries implications for the origin of the Moon1, the crystallization of the lunar magma ocean2 and the duration of lunar volcanism2. 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 crystallization4, 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.

Highlights

Key Laboratory of the Earth and Planetary Physics, Chinese Academy of Sciences, Beijing, State Key Laboratory for Mineral Deposits Research& Lunar and Planetary Science Institute, School of the Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China
208‰, 1 ) ( D = 1000 × ([D/Hsample]/[D/Hstandard]-1), using Vienna standard mean ocean water as the standard) (Fig. 2 and Extended Data Table 2), which overlap with apatite water abundances and D values measured in Apollo high-Ti and low-Ti basalts[11, 15,16,17, 28, 29, 32,33,34,35]
Region with ~2-6 g.g-1 water experienced a low degree (2-3%) of partial melting followed by a moderate-to-high degree (43-78%) of fractional crystallisation[4], generating a basaltic magma with ~370 g.g-1 water and a D of ~-300‰. This maximum water abundance, yielding our best estimate for the hydrogen isotopic composition of water in the parent magma, was recorded in the melt inclusions captured by the earliest-formed ilmenite analysed here

Summary

Introduction

Key Laboratory of the Earth and Planetary Physics, Chinese Academy of Sciences, Beijing, State Key Laboratory for Mineral Deposits Research& Lunar and Planetary Science Institute, School of the Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China. We report the water abundance and hydrogen isotope composition of apatite and ilmenite-hosted melt inclusions from CE5 basalts, from which we derived a maximum water abundance of 370 ± Advances in in situ analytical techniques over the past decade have allowed analysis of water abundances at micro-scale in various lunar samples, including in olivine- and pyroxene-hosted melt inclusions in mare basalts

Results

Conclusion