China's Chang'e-5 landing site: Geology, stratigraphy, and provenance of materials

Abstract

China's Chang'e-5 (CE-5) mission, the first lunar sample return mission since 1976, landed at 43.06°N, 51.92°W on Dec. 1, 2020, in Northern Oceanus Procellarum. CE-5 targeted a mare plain (Em4/P58) composed of distinctive young (∼1.6-1.7 Ga) moderate-Ti mare basalts, with elevated Th abundance (inherent or extraneous). Thus, the regolith and rock fragments sampled by CE-5 come from some of the youngest mare basalts on the Moon, near Rima Sharp, and from the center of the globally anomalous Procellarum KREEP Terrane (PKT), hypothesized to be responsible for the generation of the young volcanism. To provide context for the analysis and interpretation of the returned samples and in-situ measurements of the regolith substructure with penetrating radar, we constructed a detailed geologic map and stratigraphic assessment of the site. The stratigraphy consists of ancient highland materials (PKT crust and ejecta from Iridum and Imbrium basins), local silica-rich volcanism, overlain by a sequence of mare basalts, capped with Em4/P58. A ∼4-7 m thick regolith layer developed by post-mare bombardment overlies the Em4/P58 protolith and contains admixed impact ejecta from distant sources, mainly from Harpalus (∼6 wt.%), followed by Copernicus (∼2 wt.%) and Aristarchus (∼1 wt.%). New crater size-frequency measurements of Em4/P58 provide the necessary crater spatial density reference for calibration of the lunar cratering chronology with radiometric ages of the returned samples. The geological map and assessment of regolith provenance indicate that samples returned by CE-5 will address fundamental questions in lunar chronology, thermal evolution, basalt petrogenesis, and the nature of PKT, as well as provide key calibration for lunar and planetary chronologies and remote sensing data.