Magmatic Evolution of the Marius Hills, Rümker Hills, and Gardner Volcanic Complexes on the Moon: Constraints From Topography and Gravity

Marius Hills, Rümker Hills, and Gardner are three prominent volcanic complexes on the lunar nearside characterized by well-preserved elevated topography, highly concentrated domes/cones, and positive gravity anomalies. Here, we perform a comparative study of the geology and geophysics of these three volcanic complexes using multi-source remote-sensing data to better understand the volcanism diversity and magmatic evolution of the lunar nearside. Uniform and precise feature extraction methods are used to explore the morphological and geochemical characteristics of the volcanic complexes and their quasi-circular small shields (domes/cones). A new generalized approach based on three-dimensional (3D) gravity forward modeling is utilized to estimate the subsurface magma intrusion volumes. The results are about 2.63–6.65 × 10⁴, 1.48–3.86 × 10⁴, and 2.75–4.22 × 10⁴ km³ for the Marius Hills, Rümker Hills, and Gardner, respectively. Together with their extrusion volumes, Marius Hills has the largest magnitude of magmatic activity and the lowest ratio of intrusive versus extrusive volumes. Taking into account their geological and geophysical diversities, we propose three magma intrusion and extrusion schematic models and suggest that potassium, rare earth elements, and phosphorus (KREEP) may serve as an important driving force for the long-term and large-magnitude volcanism in Marius Hills, while the relatively short-lived and small-scale volcanism in Rümker Hills and Gardner may not be related to KREEP. Future geochemical studies of basalt samples from the Marius Hills region may provide additional clues to the role of KREEP in lunar nearside volcanism and thermal evolution.