Existence of Charnockites in Hellas Basin, Mars

Adnan Ahmad, Archana M Nair , Tomson Kallukalam, Amaldev J

Charnockite, an orthopyroxene-bearing granitic rock, is formed under high-temperature and high-pressure environments. Charnockite exhibits spectral characteristics similar to mafic rocks in the VNIR region and shows low emissivity at ~ 8.5 µm due to its high quartz content in the TIR region. The association of charnockite with the Anorthosite-Mangerite-Charnockite-Granite suite make it a suitable planetary analogue. Therefore, this study explores the occurrence of charnockite lithology by identifying coexisting locations of quartz and mafic minerals in the northern region of the Hellas basin of Mars. The study utilises DCS images from Thermal Emission Imaging System (THEMIS) and MAF browse products from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) datasets. Spectral characterisation of extracted spectra from both datasets shows the presence of quartz, feldspar, and pyroxene minerals, indicating the possibility of charnockite occurrence on Mars. Spectral mixture analysis using the Linear mixing and the Polynomial-Post nonlinear mixing models confirm the coexistence of quartz, high calcium pyroxene, low calcium pyroxene, and feldspar minerals, providing strong evidence for the presence of charnockitic rocks. The presence of charnockitic rocks indicates possible melting of the mafic crust during the Noachian-aged period. Partial melting of a mafic crust with low water content and high atmospheric carbon dioxide is a possible scenario for the occurrence of charnockite in Hellas Basin. These findings suggest that VNIR and TIR datasets can be combined for mapping charnockite type lithologies on Mars. This study provides valuable insights into the ancient magmatic processes and geologic history of the Martian surface.