Chinese scientists offer new insights into the thermal and chemical evolution of the Moon, with a study of China’s Chang’E-5 lunar sample return mission.
These samples of volcanic rock, which is a type of basalt, are the youngest directly dated lunar samples, around 2 billion years old. Analysis of these basalts reveals how the Moon’s composition and water content have changed over time, which can help us understand the Moon’s geological and geochemical evolution.
Their results are presented in three Nature papers October 19.
On December 17, 2020, the Chang’E-5 mission returned approximately 1.73 kg of lunar material to Earth, more than 40 years since the previous samples were recovered by the US Apollo and Soviet Luna missions. The Chang’E mission landing site was selected to be one of the youngest units of sea basalt, formed by volcanic eruptions. These volcanic rocks serve as a record of the thermal and chemical evolution of the Moon.
Earlier radioisotope dating of lunar samples suggests that most lunar volcanic activity ceased around 2.9 to 2.8 billion years ago. The Chronology of Crater Counting, an alternative method for calculating the age of planetary surfaces, predicts that there may be volcanic flows 3 to 1 billion years old, suggesting that volcanism may have persisted for a longer period of time. long. This latter dating method presents great uncertainties due to the lack of samples returned for calibration.
However, analysis of the new samples by LI Xianhua and colleagues shows that they are 2.03 billion years old, extending the reported duration of lunar volcanic activity to around 800 to 900 million years and reveals that the interior of the Moon was still evolving at around 2 billion. years ago.
The dates of the basalts estimated by LI and his colleagues are estimated to be high precision, and are older than recently reported analyzes of samples from the same region.
“This discovery advances the time when the interior of the Moon was still evolving from about 4 billion years to 2 billion years ago,” said LI of the Institute of Geology and Geophysics (IGG ) of the Chinese Academy of Sciences. The new age of lunar basalts is also being used to better calibrate time series crater counting models, to date planetary surface ages elsewhere in the solar system.
In the second study, HU Sen and his colleagues at IGG analyze the water composition of basalt samples. The distribution of water inside the Moon can give clues about the processes that led to mantle formation and volcanic activity, as well as the duration of volcanic activity.
The researchers show that the parent magma of the 2 billion year old basalts sampled by the Chang’E-5 mission contained less water than samples from regions of older volcanism (basalts that erupted 4.0 at 2.8 billion years).
They suggest that the source of the younger basalts dehydrated during prolonged volcanic activity, consistent with the idea that volcanic activity continued until at least 2 billion years ago.
LI and HU colleague YANG Wei and his team show in their study that the source of the younger basalts appears to have contained lower levels of heat-producing elements than expected.
This finding indicates that the Moon may have cooled more slowly than previously thought, which would affect mantle dynamics. The results of YANG and his colleagues could provide a basis for exploring new models of thermal evolution of the Moon.
“Non-KREEP origin for Chang’E-5 basalts in Procellarum KREEP terrane” by Heng-Ci Tian, Hao Wang, Yi Chen, Wei Yang, Qin Zhou, Chi Zhang, Hong-Lei Lin, Chao Huang, Shi -Tou Wu, Li-Hui Jia, Lei Xu, Di Zhang, Xiao-Guang Li, Rui Chang, Yue-Heng Yang, Lie-Wen Xie, Dan-Ping Zhang, Guang-Liang Zhang, Sai-Hong Yang and Fu- Yuan Wu, October 19, 2021, Nature.
DOI: 10.1038 / s41586-021-04119-5
“A two billion year old volcanism on the Moon from the basalts of Chang’E-5” by Qiu-Li Li, Qin Zhou, Yu Liu, Zhiyong Xiao, Yangting Lin, Jin-Hua Li, Hong-Xia Ma , Guo-Qiang Tang, Shun Guo, Xu Tang, Jiang-Yan Yuan, Jiao Li, Fu-Yuan Wu, Ziyuan Ouyang, Chunlai Li and Xian-Hua Li, October 19, 2021, Nature.
DOI: 10.1038 / s41586-021-04100-2
“A dry lunar mantle reservoir for basalts of young Chang’E-5 ′ mares” by Sen Hu, Huicun He, Jianglong Ji, Yangting Lin, Hejiu Hui, Mahesh Anand, Romain Tartèse, Yihong Yan, Jialong Hao, Ruiying Li, Lixin Gu, Qian Guo, Huaiyu He and Ziyuan Ouyang, October 19, 2021, Nature.
DOI: 10.1038 / s41586-021-04107-9