Flow Features among Orientale Light Plains: Implications for Basin-Scale Melt Transport

Recently, light plains within 4 basin radii of the Orientale basin were interpreted as primarily the result of the basin-forming impact, though the exact mechanism of formation and relationship to Orientale's continuous ejecta remain unclear. Among the recently mapped light plains associated with Orientale, we identify flow features consisting primarily of lobes with no observable headscarp as well as straight-edged deposits, remnant channels, and ridges in Kaguya Terrain Camera images ( 10 m/pixel) and both Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera images ( 100 m/pixel) and Narrow Angle Camera (NAC) images ( 50 cm/pixel). The flow lobes display a range of morphologies, suggesting a change in the physical properties of the emplaced materials. Flows nearest the Orientale basin are the largest (10s of km across, >200 m thick) and display the most blocks in LROC NAC images and Diviner Rock Abundance maps. Smaller flows, occurring > 2 basin radii from the rim, are on average a few kilometers across and 10s of meters thick. Some small flows are more heavily cratered than the terrain they embay. Near-basin flows > 100 m in thickness also exhibit blocky superposed impacts and margins, indicating a more coherent layer of material beneath the regolith. The slopes of the blocky margins exceed 30° in some locations, measured from LROC NAC DTMs, but the flows themselves occur on slopes of <10°. There is no compositional distinction (e.g., FeO, TiO₂) between the flows and the highland terrain in which they are found. Nearside flows are found within light plains that display high CPR in Arecibo P-band data, indicating a coherent layer previously interpreted as melt-rich ejecta from Orientale within 10s of meters of the surface. As such, we interpret these flow features as melt-rich materials, with decreasing melt content with increasing distance from the Orientale basin causing the observed changes in morphology. This work suggests that significant quantities of impact melt were emplaced well beyond the continuous ejecta of the basin, which has important implications for the basin formation process in terms of melt production and transport.