The compositions of the lunar crust and upper mantle: Spectral analysis of the inner rings of lunar impact basins

• Published in: Planetary and space science Vol. 165; pp. 230 - 243
• Main Authors: Lemelin, Myriam, Lucey, Paul G., Miljković, Katarina, Gaddis, Lisa R., Hare, Trent, Ohtake, Makiko
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2019
• Subjects: Impact processes; Mineralogy; Moon; Radiative transfer; Impact processes; Radiative transfer; Moon; Mineralogy
• ISSN: 0032-0633; 1873-5088
• DOI: 10.1016/j.pss.2018.10.003

The innermost ring in impact basins exposes material originating from various depths, and can be used to study the composition of the lunar crust with depth. In this study, we conduct quantitative mineralogical analyses of the innermost ring in 13 lunar impact basins using reflectance data from the Kaguya Multiband Imager and radiative transfer modeling. We use results from recent hydrocode modeling to calculate the depth of origin of the material exposed by the innermost rings. We find that the most abundant rock type on the innermost ring of most basins is anorthosite. The mafic assemblages are dominated by olivine in some cases, but most often by pyroxene. The impact modeling suggests that the innermost ring material was excavated from a wide range of depths. Here we focus on two mean depths: a crustal component and a mantle component. The crustal component largely dominates the innermost ring material, and the mantle component is present on the innermost ring of 9 of the basins we studied. On these 9 rings, the abundance of low-calcium pyroxene decreases with the proportion of crustal component, suggesting a dominantly mantle origin. However, as we do not detect exposures of ultramafic material, such mantle material is possibly present at the sub-pixel scale (<62 m). This quantitative study reassesses the composition of the lunar crust and upper mantle, which is of great importance for understanding the formation of the Moon. •We conduct a quantitative mineral analysis of the inner ring of 13 impact basins.•We use radiative transfer modeling and near-infrared images at 60 m resolution.•Hydrocode impact modeling is used to link detected compositions to depths of origin.•The most abundant rock type on the innermost ring of most basins is anorthosite.•A small portion of the inner ring material of 9 basins may originate from the mantle.