The moon’s volcanic eruption 2 billion years ago was still strong

Tian Hengci, associate researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences, and his collaborators studied the scale of volcanic eruptions in the Chang’e-5 basalt and found that there were still large-scale magma eruptions in the late lunar period about 2 billion years ago. By comparing and analyzing the scale of early magmatic eruptions on the moon, the results show that although the volcanic activity of the moon has gradually weakened over time, the intensity of its eruptions shows intermittent bulges, which is helpful to further understand the thermal evolution history of the moon. The study was recently published in Nature Communications.

Flowing magma Photo courtesy of interviewee

At the end of 2020, the Chang’e-5 mission returned the youngest lunar basalt to date, and Chinese scientists proved through lunar soil samples that the moon still erupted hot magma about 2 billion years ago, extending the known lunar geological life by 800 million to 900 million years. “Our study further answers the question of how much magma erupted from the late Moon.” Tian Hengci, the first and corresponding author of the paper, told China Science News.

How to determine the size of a lunar magma eruption from trace rock samples? Tian explained that understanding the age of basalt formation, geochemical characteristics and the cooling rate behind it is critical.

Based on the previous work, the researchers found that the Chang’e-5 basalt is likely to be the product of the same volcanic eruption, and the source is relatively single, which provides an excellent opportunity to restore the thickness of the basalt lava flow and the scale of its eruption.

“It’s like eating a soup dumpling, the skin of the bun on the top is already cold, but the soup inside is still very hot. The magma surface cools the fastest, and gradually inward, its cooling rate decreases. Tian Hengci explained that by analyzing the changes of certain characteristic elements in rock minerals to infer the cooling time of magma and the cooling rate, the thickness of the lava flow can be inferred according to the cooling rate, and then the eruption scale can be determined.

Their analysis of 21 olivine grains showed that most of the olivine grains had a short cooling time, less than one year; On this basis, with the help of thermodynamic models, they estimated that the thickness of basalt eruptions was about 10~30 meters, which was consistent with the results obtained by remote sensing detection methods.

The research team also compared the results of the study on the scale of volcanic eruptions on the moon’s 4.5 billion years as a whole, and found that although the intensity of volcanic activity on the moon gradually weakened from early to late stages, its eruption scale showed intermittent bulges, and volcanic eruptions were still relatively strong in the late stage, which provided key parameters for constraining the thermal evolution history of the moon.

For a long time, scientists have mainly used the impact crater excavation depth method, lunar surface ground penetrating radar, gravity field and seismic wave methods to quantify the thickness of lunar sea basalt and the volume of volcanic activity with time. “This study is a direct study of the sample, and more importantly, the combination of diffusion chronology with thermodynamic models to obtain lava flow thickness is a very novel research idea.” An international reviewer commented.

However, the researchers said that the specific reasons for the large-scale volcanic eruptions found in the late lunar period are still unclear. The next step is to work with other teams to build a thermal evolution model of the landing area to answer this question as much as possible. (Source: China Science News Feng Lifei)

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