Magmatic dikes in the Chang'e-6 sampling area

Abstract

Volcanic deposits on the Moon are mainly distributed at the nearside but are rarer at the farside, and most farside mare are concentrated in the prominent South Pole-Aitken (SPA) basin. The asymmetric distribution of volcanic deposits is related to the fundamental characteristics of the Moon. The Chang'e-6 mission recently returned farside mare deposits from the Apollo basin in the SPA, which contain a wealth of information about the volcanic eruption mechanisms, magmatic processes, and mantle compositions of lunar farside. To assist ongoing sample analysis, we investigated magmatic dikes in the Apollo basin using the GRAIL gravity model. We detected 14 magmatic dikes that have a total length of ∼2200 km. The dikes exhibit circumferential distribution around the basin walls, some of which are spatially correlated with volcanic deposits and shallow intrusions visible at the surface, indicating that magma may have ascended along weakness planes formed by the Apollo basin. Volcanic deposits and shallow intrusive structures are not visible on the surface of most detected dikes, thus the ascending magma may have cooled as plutonic rocks. Root depths of the detected dikes are ∼37–49 km, which are not strictly correlated with their local crustal thicknesses, indicating that other factors in addition to lithostatic pressures affected magma ascending. The dikes beneath the Chang'e-6 landing mare have root depths of over 39 km, suggesting that partial melting occurred at greater depths that have pressures of excess ∼161 MPa. The estimated volume of plutonic rocks in these dikes is about 1.2 × 10⁴ km³, which is 15 times larger than that of the basaltic deposits in the landing mare.