Chang'e-6 samples reveal ancient volcanic history of lunar farside
by Simon Mansfield
Sydney, Australia (SPX) Nov 16, 2024

Basalt samples collected by China's Chang'e-6 mission have shed light on volcanic activity on the Moon's farside, revealing eruptions occurring 2.8 billion years ago (Ga) and 4.2 Ga. This significant finding was made by Prof. LI Qiuli's lab at the Institute of Geology and Geophysics, Chinese Academy of Sciences, and recently published in 'Nature'.

"Unraveling the volcanic history of the lunar farside is crucial for understanding the hemispheric dichotomy of the Moon," stated Prof. LI.

The Moon's nearside and farside display notable asymmetries, including variations in basalt presence, surface features, crustal thickness, and thorium (Th) content. The Chang'e-6 mission has provided a rare opportunity to study these differences by returning 1,935.3 g of lunar soil from the farside, the first such sample in history.

Prof. LI and postdoctoral researcher ZHANG Qian performed detailed radioisotope analysis on 108 basalt fragments from the sample. Of these, 107 were determined to have an age of 2807 +/- 3 million years (Ma), marking the eruption period at the Chang'e-6 landing site. This 2.8 Ga volcanic episode is unique to the farside, as no comparable age has been found in nearside samples.

One exceptional fragment, identified as high-aluminum basalt, was dated at 4203 +/- 4 Ma and likely originated from a cryptomare south of the landing site. This piece is the oldest precisely dated basaltic sample returned to Earth.

The data indicates that volcanic activity on the lunar farside spanned at least 1.4 billion years, from 4.2 Ga to 2.8 Ga. Lead isotope analysis points to separate mantle sources: the older, 4.2 Ga basalt came from a KREEP-rich source rich in potassium (K), rare earth elements (REE), and phosphorous (P), while the 2.8 Ga basalt came from a KREEP-poor source.

The correlation between the 2.8 Ga basalt age and existing crater-counting models supports the applicability of nearside-derived cratering chronology to the lunar farside. The precise dating of Chang'e-6 basalts offers a vital calibration point for refining these models and improving their accuracy, as noted by Prof. LI.

Research Report:Lunar farside volcanism 2.8 billion years ago from Chang'e-6 basalts

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Institute of Geology and Geophysics, Chinese Academy of Sciences
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