Published in 'Science' on Nov. 15, their findings highlight the unique opportunity these samples provide to study the Moon's dichotomy. "The samples returned by Chang'e-6 provide a best opportunity to investigate the lunar global dichotomy," said Professor XU.
The surface of the Moon has been shaped by volcanic activity, with mare basalts - volcanic rocks - more prevalent on the near side, where they cover approximately 30% of the terrain compared to just 2% on the far side. To fully explore the lunar dichotomy, it is crucial to study samples from both hemispheres.
Chang'e-6 soil samples revealed two distinct types of mare basalts: low-Ti and very low-Ti (VLT). The low-Ti basalt likely represents the local unit around the landing site, while the VLT basalt appears to have originated from a region east of the site.
High-precision dating methods, including Pb-Pb dating of Zr-bearing minerals and Rb-Sr dating of plagioclase and mesostasis in the low-Ti basalt, determined an age of 2.83 billion years. "Young magmatism also exits on the lunar far side," the study states.
When compared to samples from the Apollo and Chang'e-5 missions, the Chang'e-6 low-Ti basalt exhibited a lower u value, lower 87Sr/86Sr ratio, and higher eNd value, indicating a depleted mantle source.
Traditionally, variations in crustal thickness have been considered a primary factor in explaining the disparity in volcanic activity between the Moon's near and far sides. However, this assumption has faced challenges, particularly due to the SPA basin's unusually thin crust, which remains largely unfilled by volcanic material.
XU's team proposed that the mantle composition beneath the SPA basin plays a significant role in limiting volcanic activity. "Although the SPA basin has a thin crust, the depleted and refractory mantle source beneath the SPA basin hinders partial melting to a large degree," noted XU.
Their research also provides a calibration point at 2.83 billion years for lunar crater chronology, supporting a steady impact flux since that time. This refined chronology model enhances the use of crater statistics for age estimation on both the Moon and other rocky planets, contributing to the understanding of lunar impactor evolution and potential early planetary migrations in the Solar System.
This study received funding from the Chinese Academy of Sciences and GIGCAS's lunar research program.
Research Report:A sample of the Moon's far side retrieved by Chang'e-6 contains 2.83-billion-year-old basalt
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Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
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