Extensive Intrusive Magmatism in the Lunar Farside Apollo and South Pole–Aitken Basins, Chang’e-6 Landing Site

Abstract

Lunar igneous activities, including intrusive magmatism and extrusive volcanism, and their products contain significant information about the lunar interior and its thermal state. Their distribution is asymmetrical on the nearside and farside, reflecting the global dichotomy. Samples from the South Pole–Aitken (SPA) basin on the farside hold the key to disclosing the dichotomy conundrum and rebalancing the asymmetrical understandings of the Moon, in addition to previously returned nearside samples (Apollo, Luna, Chang’e-5). For the first time, the Chang’e-6 mission obtained ∼1935.5 g of lunar soils from the farside in the southern Apollo basin, northeast of SPA, opening a window to solve this long-standing question. However, compared with the well-known mare/cryptomare volcanism in SPA, intrusive activity has a much more obscure presence and origin, due to its unclear surface expression, thus impeding the ongoing Chang’e-6 sample analysis, which is therefore emphasized here. We found evidence that intrusive magmatism is extensive across SPA, including Mg-suite intrusions, floor-modified craters, and linear/ring dikes, consistent with its intermediate crustal thickness, where dike intrusion is favored. Intrusive magmatism is abundant in the Apollo basin, where Chang’e-6 landed. Two obscure craters were discovered (Apollo X and Q) with evidence for subsurface intrusions, strongly suggesting the intensive intrusion in the region. Plutonic materials are very likely to be obtained by Chang’e-6, especially the Mg-suite from the western peak ring of the Apollo basin that delivered and mixed in the soils by the Chaffee S crater, whose components might provide critical new insights into their petrogenesis, early lunar evolution, and the origin of dichotomy.