Multi-Phase Evolution and Composition Variations of Volcanic Activities on the Lunar Farside Revealed by Chang'e-4 Lunar Penetrating Radar

Abstract

Volcanism is the primary endogenic geological process on the Moon, with mare basalts being the critical indicators of such activity. The abundance of titanium in these mare basalts reflects different lunar mantle sources, magma origins, and thermal evolution processes. The Chang'e-4 mission, which landed in the Von Kármán crater within the South Pole-Aitken Basin on the farside of the Moon, employed a lunar penetrating radar with a low-frequency channel to reveal the subsurface structures and abundance of FeO and TiO₂ of these structures down to approximately 300 m. The dielectric properties and iron-titanium content are crucial for interpreting basalt units. This study utilizes radar wave-impedance inversion to derive the permittivity from the low-frequency lunar penetrating data collected during the first 62 lunar days. The frequency shift method was used to calculate the loss tangent and estimate the abundance of FeO and TiO₂ in the subsurface materials at the landing area. Based on permittivity, variations in abundance of FeO and TiO₂, and impact crater statistics near the landing site, we infer at least four distinct periods of magma with varying FeO and TiO₂ beneath the Chang'e-4 landing site, spanning from the Nectarian to the Eratosthenian periods. High titanium and medium titanium basalts were found in the Nectarian and Imbrian periods. This study reveals the evolutionary process of multi-phase volcanic eruptions on the farside of the Moon, indicating not only temporal but also compositional variations in volcanic activities, thereby highlighting the complexity of volcanic processes on the lunar farside.