Presentation #302.01 in the session “Moon and Mercury 1”.
Chang’e-5, China’s first lunar sample return mission, is targeted to land in Northern Oceanus Procellarum (OP), a region selected based on 1) its location outside the Apollo-Luna sample return region, 2) occurrence in the anomalous Procellarum-KREEP Terrain (PKT), 3) containing one of the youngest lunar mare basalts (Em4), and 4) its association with Rima Sharp, the longest lunar sinuous rille. OP is also a non-mascon mare, shows a diversity of smaller gravity anomalies attributed to lava-filled buried craters, is the site of the thinnest regional crust (typically <30 km), displays three major volcanic complexes (Marius Hills, Aristarchus Plateau, Rümker Hills), has the highest concentration of silica-rich red spots (e.g., Gruithuisen and Mairan domes), has the highest abundance, longest and largest sinuous rilles, is the region of two of the youngest impact basins (Imbrium, Iridium) and may have been the site of an extremely large, very ancient impact basin. In order to provide context for returned sample analyses, we conducted a comprehensive study of the geomorphology, composition, mineralogy, and chronology of the Em4 mare basalts. The unit is superposed on Imbrian-aged low-Ti basalts, covers 37,000 km2 and is composed of Eratosthenian-aged (~1.46 Ga), high-Ti basalts with a mean thickness of ~51 m and a volume between ~1450 and 2350 km3. Thorium content is high (~6.7 wt%), typical of PKT mare basalt regolith. We document minor variations in TiO2 and FeO abundance and we found no specific source vents (e.g., fissures, cones, domes) within the unit. Detailed analysis of sinuous rilles, however, revealed that it was composed of two major rilles whose source vents, located outside the Em4 unit, enter and merge in its eastern part, suggesting that they may be the Em4 sources. The small source vent sizes and lack of significantly associated pyroclastic deposits suggest that erupting lavas had low volatile content. Regolith is thin, consistent with the young age of the unit and there is abundant evidence for vertical/lateral mixing. Returned samples will thus provide significant new insights into lunar geochronology, inner solar system impact fluxes, the age of extremely young mare basalts, the role of the PKT in the generation of mare basalts, the role of sinuous rilles in lava flow emplacement, and the thermal evolution of the Moon.