Ages and origins of lunar light plains

Light plains are widespread, smooth, and horizontal deposits distributed across the lunar surface. Despite their morphological similarities with mare basalts, which led to their early interpretation as volcanic deposits, samples returned from the Apollo 16 mission were found to instead be mostly impact breccias. Consequently, light plains have been re-interpreted as being formed by the ballistic emplacement of primary basin ejecta and mixing of local crater materials. In this paper, we present 1) a mid-latitude absolute model age (AMA) study of light plains, including 60 previously undated light plains deposits to better constrain their range of surface ages, and 2) we revisit the formation age of the Orientale impact as a potential source for many light plains. We find a) the Orientale impact event to be ~3.7 Ga old, consistent with past work and with the surface ages of most light plains deposits we investigated in this study, b) deposits younger than the Orientale impact are likely related to local cratering processes, and c) deposits located north of mare Frigoris and at the Imbrium Sculpture date to ~3.8 Ga, consistent with the Imbrium event and/or the Schrödinger basin as possible sources. Thus, light plains formation from a single basin event is unlikely. Instead, this work supports an origin of light plains via the ballistic emplacement of ejecta from multiple primary basin(s) and large crater(s) ejecta across the lunar surface. • The age of the Orientale basin impact event as seen in our CSFD measurements is 3.77 Ga • Most LP deposits date to ~3.7 Ga old consistent with our measurements of Orientale basin • Older LPs show AMAs of ~3.8 Ga old potentially of Imbrium origin and/or other events such as the Schrödinger basin • Deposits younger than Orientale might be related to local process • The range of ages exhibited by the LPs in our study support a LP origin via the deposition of material from multiple basin and crater events