Chronology, geochemistry, and tectonic controls of lunar farside mare basalts from multisource remote sensing data

Lunar farside mare basalts preserve important records of the Moon’s volcanic and thermal evolution, yet their spatial distribution, geochemical characteristics, and eruption chronology remain less systematically constrained than those of nearside basalts. In this study, we integrated multisource remote-sensing datasets, including Kaguya Terrain Camera (TC) imagery, Kaguya Multiband Imager (MI)-derived oxide abundance maps, Lunar Prospector Gamma-Ray Spectrometer (LP-GRS)-derived Th abundance data, and published geochemical constraints, to investigate the distribution, composition, and ages of lunar farside mare basalt units. Based on geomorphologic and compositional information, 201 discrete mare basalt units were identified across the lunar farside. Crater size-frequency distribution (CSFD) analysis was further applied to previously undated units, providing absolute model ages for 70 basaltic units. The results show that farside mare volcanism lasted from about 3.9 Ga to 1.58 Ga and can be broadly divided into two main eruptive episodes, with the major eruptive peak occurring around 3.5 Ga. The basalt units are dominated by very low-Ti and low-Ti compositions, while FeO, TiO 2 , Mg#, Th, Al 2 O 3 , CaO, and SiO 2 show measurable spatial heterogeneity among different basins and tectonic units. Age-composition relationships for TiO 2 , Mg#, and LP-GRS-derived Th abundance do not define a simple monotonic evolutionary sequence, suggesting that model age alone is insufficient to fully account for the geochemical variability of farside mare basalts. The contrasting compositional patterns among the Anorthosite Highland, Mare-Highland Transition, and South Pole-Aitken tectonic units further indicate that regional geological context, crustal substrate, basin modification, and magma ascent pathways influenced basalt composition and preservation. These results provide an updated remote sensing-based framework for the mapping, chronology, and compositional interpretation of lunar farside mare basalts, and offer new constraints on the volcanic history and crust–mantle evolution of the lunar farside.