Absolute model age of lunar Finsen crater and geologic implications

As the primary source of materials measured inside of Von Kármán crater by the Chang'e-4 rover, the absolute model age (AMA) of Finsen crater is derived by the crater size-frequency distribution (CSFD) measurements. Both cumulative and differential fits reveal an AMA of ~3.5 Ga, indicating Finsen crater is Imbrium-aged. Based on thickness estimation of the Finsen crater ejecta-sourced fine-grained regolith at Chang'e-4 landing site (~12 m) (Lai et al., 2019; Li et al., 2020), the average regolith growth rate at the landing site is estimated to be about 3.4 m/Gyr. The current depths of 25 largest craters on the floor of Finsen crater are calculated by the profile-average-depth method, and their original depths are estimated under the assumption that the initial depth-to-diameter (d/D) ratio is 0.2. Depth differences between current and estimated original depths, together with the AMA of Finsen crater, derive the average crater degradation/infilling rate within Finsen crater is about 21 ± 3 m/Gyr.