Lunar mare basalt flow units: Thicknesses determined from crater size-frequency distributions.

Abstract

Accurate lava flow unit thicknesses estimates are necessary to place constraints on volcanic flux estimates. We refine the technique of using the shape of crater size-frequency distribution (CSFD) curves to estimate the thickness of individual lunar mare flow units. We find that a characteristic knee often observed in CSFD curves is reasonably interpreted to represent the presence of two lava flow units separated in time, and that the diameter at which this knee occurs is related to the thickness of the overlying flow unit. Examination of 58 curves with this characteristic knee in several lunar nearside basins (Oceanus Procellarum, Imbrium, Tranquillitatis, Humorum, Cognitum, Nubium, and Insularum) allowed us to identify flow units that have not been detected in low-sun images. We found that the range of flow unit thickness is ~20-220 m and the average is ~30-60 m. This technique expands considerably the ability to assess lava flow unit thicknesses and volumes on the Moon and planets.