Geological insights into lunar floor-fractured crater Atlas

Abstract

The mineralogy and morphology of class-1 type lunar floor-fractured crater (FFC) (i.e., the lunar FFCs having central peak complexes, radial and/or concentric fractures, extended wall terraces and crescent-shaped mare patches over the crater floor) Atlas has been investigated thoroughly in this study using high-resolution data from recent lunar missions. Spectral data from the Moon Mineralogy Mapper (M3) interestingly reveal a mafic-rich central peak complex (CPC) for crater Atlas unlike other class-1 FFCs. The mafic–rich CPC suggests the possible tapping of a mafic pluton emplaced at a shallow subsurface level. The crater floor hosts two localized late-stage, Vulcanian-type pyroclastic deposits exhibiting varied TiO2 concentrations. We further report two categories of hydration features in crater Atlas: (1) Endogenic - associated with nominally anhydrous minerals (NAMs), namely, olivine, pyroxenes and Mg-spinel, in the CPC and on the southern crater wall, and with the pyroclastic deposits; (2) Exogenic - related to solar wind implantation in matured soils in the crater floor. In the present study, a detailed quantitative analysis of the hydration features has been presented. The hydration features associated with NAMs imply a hydrous nature of the mantle-sourced magma that formed the mafic pluton. Overall, the varied water contents associated with the NAMs and the two pyroclastic patches indicate heterogeneity in the hydrous enrichment of the lunar mantle underneath the studied site. The high-resolution morphological study unravels a partially uplifted crater floor, and several features like radial, elongated and concentric fractures, which suggest that the floor had suffered numerous brittle and ductile deformations. The radial and concentric fracture systems have different dimensions, indicating spatial variation in stresses suffered when the floor uplift. The localized pyroclastic deposits and the warped crater floor suggest multiple events of late stage magmatic activity.