269-1 Demystifying the Early Moon: A Case Study Through Mapping of the Humorum Basin

Session: Planetary Geologic Mapping Across the Solar System (Posters)

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Abstract:

Advancing the science of the early Moon requires accurate interpretation of lunar basin deposits. Basin-generated impact melt, massifs, and ejecta deposits hold a record of both the earliest compositions and timing of impacts on the Moon. Yet, geologic mapping of lunar basins can be challenging given their large areal extent and extensive post-basin modification. In this work, we employ a best-effort approach to applying USGS standards and best-practices [Skinner et al., 2022, Planetary Geologic Mapping Protocol- 2022, USGS TM 11-B13, 28 p.] to create a geologic map of Humorum basin. The need for this map was inspired by a preliminary sketch map of the area revealing clues about the basin's deposits [Parry et al., 2025, LPSC Abs #2138]. The new map is georeferenced to the standard projected Lunar Reconnaissance Orbiter Wide Angle Camera Morphology basemap. To identify units, we are employing a variety of orbital data sets, including available topography, gravity, composition, and radar. Humorum basin, while being one of the younger basins, has experienced extensive post-basin modification. Nonetheless, the basin ejecta is distinguishable from nearby younger Orientale ejecta, as well as extensive younger mafic volcanic deposits. Portions of the basin ejecta exhibit a “knobby” texture that is similar to parts of the Montes Rook Formation (Orientale), as well as additional areas occurring around several other basins. Interior to the inferred Humorum basin rings, maria obscure much of the original basin materials except for massifs and a possible melt deposit of non-mafic composition. Using our new mapping efforts, in combination with previously developed maps of other lunar basins [e.g., listed in Stopar et al. 2025, LPSC Abs #2406], we find that highland massifs and basin rims offer ample locations for basin melt to be preserved for study, even after significant subsequent geological events. In addition, we make comparisons of compositions derived from the orbital data to those of other basins with mapped ejecta and melt deposits. The compositions of the basin deposits have the potential to provide insights into early crustal compositions, including broad-scale heterogeneities, potentially more mafic crustal components and magmatism, and perhaps even the earliest mare eruptions.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8285

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