1,2Jingdong Zhang, 1Yuzheng Zhang, 1Jian Chen, 3,2Luyuan Xu, 1,2Le Qiao
Icarus, (in Press), 117372 Link to Article [DOI: 10.1016/j.icarus.2026.117372]
1Shandong Key Laboratory of Space Environment and Exploration Technology, School of Space Science and Technology, Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209, China
2State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
3International Institute for Interdisciplinary and Frontiers, Beihang University, Beijing 100191, China
Copyright Elsevier
Investigations of the ages and compositions of lunar volcanic deposits
provide insights into the geologic and thermal evolution of the Moon. Among the 22
recognized lunar maria, the majority have been chronologically studied, and Maria
Undarum and Spumans remain the two major maria that lack reliable age constraints.
In this work, 66 undated mare basalt units were delineated in the two maria and adjacent
regions. Our analysis reveals that the absolute model ages (AMAs) of these 66 basalt
units range from 2.9 to 3.8 Ga. Additionally, noticeable heterogeneity in surface
composition is observed among these mare units. Combining characteristics of regional
volcanic flux and mare composition, we suggest a gradual decline in volcanic activity
after the main phase of volcanism, with older units (3.8–3.5 Ga) generally exhibiting
greater exposed basalt volumes than younger units (3.4–2.9 Ga). The AMAs of these
maria show weak negative correlations with their surface FeO and TiO2 abundances,
although neither relationship is statistically significant. Younger basalts are dominated
by relatively lower titanium contents and have a narrower variety in iron contents than
older basalts. Furthermore, we constrain the lower limit of the basalt thickness in this
region, ranging from ~41 m to 207 m. Systematic investigation of the age, composition,
basalt thickness, and volumetric flux of the Maria Undarum and Spumans region
demonstrates that small-scale volcanic eruptions outside major impact basins are
generally very ancient (>3.5 Ga), and are characterized by short durations, irregular
mare outlines, small eruptive volumes, and emplacement in depressions in highland
terrains.
