Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples.

Spinels represent a small fraction of lunar surface materials but provide important insights into the petrological evolution of the lunar crust and mantle. Previous remote sensing analyses of highlands spinel‐bearing lithologies have focused on pure Mg‐Al spinels, which are rare in the lunar sample collection. Using Moon Mineralogy Mapper data, we develop and test an approach for detecting spectral signatures of spinel across a wider range of Mg, Al, Fe, Cr, Ti‐bearing compositions than have been addressed in previous studies, including within mafic‐bearing assemblages. This approach is validated through integration with laboratory‐measured spinel spectra and petrographic observations of samples returned by the Luna 20 mission from the Hilly and Furrowed Terrain surrounding the Crisium Basin. Applying this approach to data from the Crisium region, small abundances of spinel (<∼5 vol%) with a range of Mg, Al, Fe, Cr, and Ti content and petrologic origin (inferred from Luna 20 samples) were found to be widespread within highlands soils across the Crisium region. This result diverges from previous remote sensing analyses, which only reported small, isolated exposures of pure Mg‐Al spinel (as well as a possible detection of Fe, Cr‐bearing spinels localized within pyroclastic materials at Sinus Aestuum). Geologic associations of candidate spinel detections across this region are consistent with a shallow crustal origin rather than excavation from depth during the Crisium‐forming impact. These spinels are detectible in near‐infrared spectroscopic data, particularly in areas of low optical maturity and may influence the spectral continuum of highlands soils. Plain Language Summary: Spinels are minerals that make up only a few percent of lunar surface rocks, but are interesting to lunar scientists because they reveal important details on how those rocks formed. Spinel minerals have a wide range of compositions, but previous satellite observations only focused on a few specific types of spinel. Recent measurements of spinels returned by the robotic Luna 20 mission helped us develop new tools to search for spinels in spacecraft images. Our new approach can detect a wider range of spinel compositions, and we observe that detectable spinel signatures are widespread across the lunar highlands surrounding the Crisium Basin. Key Points: Moon Mineralogy Mapper data can detect spinel signatures within lunar highlands soils including diverse spinel compositions and assemblagesThis approach was developed and validated through integration with laboratory spectra and petrographic studies of spinels in Luna 20 samplesDiverse spinel‐bearing assemblages are distributed across the lunar highlands, consistent with a shallow origin indicated by sample analyses [ABSTRACT FROM AUTHOR]