Lunar Geochemical Characterisation with Multiwavelength Spectroscopy

Abstract

This study conducts a thorough exploration of the mineralogical composition of a surveyed geochemical anomaly pinpointed within the Mare Tranquillitatis territory of the Moon. Employing a multidisciplinary methodology, it harnesses data from the Moon Mineralogy Mapper (M3) on Chandrayaan-1, the Imaging Infra-Red Spectrometer (IIRS), and Chandrayaan 2's Low Area Soft X-Ray Spectrometer (CLASS) onboard Chandrayaan-2. The principal aim of this research is to unravel the intricate mineralogical tapestry underlying this lunar anomaly. To achieve this, colour composite images were meticulously crafted utilising integrated band depth parameters and mineral indices, serving as a visual representation of the mineralogical variations within the study area. Subsequently, the unique spectral signatures corresponding to these composite colours, as discerned from the M3 dataset, were scrutinised in detail. Furthermore, the Modified Gaussian Model (MGM) deconvolution technique was applied to these spectra, enhancing the precision of mineral identification. A parallel methodology was implemented to analyse the IIRS dataset, culminating in a correlation with an abundance file derived from the CLASS data. The outcomes of this extensive spectral analysis unveil a landscape characterised by heterogeneous lithologies. Predominantly, the study region comprises anorthosite, complemented by the presence of pyroxene-bearing and olivine-bearing basaltic lithologies. Notably, significant topographic disparities are observed between the eastern and western regions of the Mare Tranquillitatis. These differences manifest not only in topography but also in the spatial dispersal of spectral units and compositional trends. The western Mare area exhibits a higher prevalence of olivine-bearing material within the olivine-pyroxene mixture, while the eastern Mare prominently exhibits pyroxene-bearing material. The correlation of spectral findings with lunar morphology yields intriguing insights. Pyroxene-rich compositions are notably associated with fresh craters and their ejecta, indicative of their geological origins. In contrast, olivine is found to be pervasive across the lunar surface, dispersed widely, and often distributed along the ejecta blankets of large impact craters. This association suggests that the pyroxene-hosted layer likely resides beneath the olivine-bearing layer. The noticed mineral assemblages are hypothesized to have arisen through physical blending processes during the impact cratering episodes that have shaped the lunar landscape.