Volcanism on the lunar far side spanned 1.4 billion years

Nov. 15 () –

Basalt samples recovered by the Chang’e-6 mission have revealed volcanic events on the far side of the Moon 2.8 billion years ago and 4.2 billion years ago.

The asymmetry between the near and far sides of the Moon, encompassing differences in basalt distribution, topography, crustal thickness, and thorium (Th) concentration, has long been a mystery. However, China’s Chang’e-6 mission, the first to recover samples from the far side of the Moon, has created a unique opportunity to explore volcanic activity in this hemisphere. with the 1,935.3 gram lunar soil sample he recovered.

Led by Professor LI Qiuli at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, postdoctoral researcher ZHANG Qian performed systematic radioisotope dating of 108 basalt fragments from this sample. Of these, 107 fragments revealed a constant formation age of 2807 +/- 3 million years, indicating the eruption age of local basalts at the Chang’e-6 landing site. Notably, this 2.8 billion-year-old volcanic episode has not been observed in samples from the near side.

The remaining fragment, of high-aluminium basalt dating back 4.203 million years, is believed to have originated in a cryptotidal region south of the landing site. It is the oldest sample of lunar basalt recovered so far whose age has been precisely determined.

AT LEAST 1,400 MILLION YEARS

These data indicate that volcanic activity on the far side of the Moon persisted for at least 1.4 billion years, from 4.2 billion years ago to 2.8 billion years ago. Initial lead isotope analysis suggests that these basalts are derived from distinct mantle sources: the 4.2 billion-year-old basalt came from a KREEP-rich source, that is, one with abundant potassium (K), rare earth elements ( REE) and phosphorus (P), while the 2.8 billion year old basalt came from a poor source in KREEP.

The close alignment between the basalt age of 2.8 billion years and the crater count estimates suggests that the crater chronology model, established based on near-side observations, is also applicable to the far side of the Moon. The radioisotope ages of the Chang’e-6 basalts provide an essential calibration point to refine the chronology of the lunar crater count, thus improving its precision, according to Professor LI.

This work was recently published in Nature.