A new study, led by the Planetary Science Group at Shandong University, provides insights into the oldest volcanic eruptions of our Moon. This research, entitled “Mare domes in Mare Tranquillitatis: Identification, characterization, and implications for their origin” is recently published online in the Journal of Geophysical Research: Planets (Qiao et al., 2021). This is an international cooperation accomplishment by scientists from Shandong University (China), Brown University (USA), and Lancaster University (UK).

Volcanic eruptions are the violent releases of energy and materials from the interior of the Earth to its surface. It serves as an important window for peering into the composition, thermal status of the Earth’s deep interior and its evolution histories. The same is true for extraterrestrial bodies, such as the Moon and Mars. Investigation of the spatial distribution and characteristics of the resultant volcanic deposits can provide fundamental evidence for constraining eruption processes and enhancing our understanding of the geological and thermal evolutions of these bodies.

In this study, the international research group led by Dr. Qiao Le , focused on Mare Tranquillitatis on the lunar Earth side. They firstly reviewed the ages and compositional characteristics of volcanic eruption products (lunar mare basalts) in Mare Tranquillitatis. These characteristics are then compared with mare basalts elsewhere on the global Moon, which revealed that the volcanic basalts in Mare Tranquillitatis have titanium content up to 12 wt.% (TiO₂). This makes Mare Tranquillitatis one of the most titanium-rich areas on the Moon and shows its great potential for In-Situ Resource Utilization (ISRU). Moreover, most of the Mare Tranquillitatis basalts erupted over 3.5 billion years ago, among the oldest volcanic deposits on the Moon (Figure 1). Mare basalts in Mare Tranquillitatis represent the earliest major phase of exposed mare volcanism, and investigation of their detailed characteristics should provide fundamental insights into the early geologic and thermal evolution of the Moon.

Figure 1. Global map of ages of mare basalts on the Moon: Mare Tranquillitatis is the oldest mare on the global Moon.

The research team employed the latest high-resolution altimetric and other remote sensing data sets obtained by lunar orbiters to identify and characterize volcanic domes in Mare Tranquillitatis (Figure 2). They found over 283 volcanic domes and showed that Mare Tranquillitatis contains one of the highest densities of mare domes among the entire lunar maria (Figure 3). On the basis of spatial distribution and geological characteristic analyses, these dome features are interpreted as small shield volcanoes that were built from individual low-volume, low volatile content, short duration, cooling-limited eruptions that built the shields and supplied lava flows to the immediate surroundings. These observations are obviously different from the late-stage volcanic eruptions in the Mare Imbrium region of the Moon (near the landing site of China’s Chang’e-3 mission), where very extensive fields of long lava flows are seen. This contrast indicates that shield-building eruptions may be a prevalent volcanic eruption style in the earliest stage of lunar volcanism, providing a potentially important constraint into the relation of mare volcanism and lunar thermal evolution history.

Figure 2. Examples of volcanic domes in Mare Tranquillitatis. The dome in the lower panel is a new dome identified in this study.

Figure 3. Spatial distribution of mare domes in Mare Tranquillitatis.

In recent years, the Planetary Science Group at Shandong University focuses on the national strategic needs of deep space exploration and has achieved a series of research results in lunar geology, meteoritics and cosmochemistry, planetary remote sensing and spectroscopy. This study was jointly sponsored by the National Key R&D Program of China, the Pre-research Project on Civil Aerospace Technologies of CNSA, the National Natural Science Foundation of China, and the China Postdoctoral Science Foundation.

Citation: Qiao, L., Head, J. W., Wilson, L., Chen, J., Ling, Z., 2021. Mare domes in Mare Tranquillitatis: Identification, characterization, and implications for their origin. Journal of Geophysical Research: Planets, 126, e2021JE006888

Link to the study: https://doi.org/10.1029/2021JE006888