Comprehensive Analysis of the Alteration of Tyrrhena Terra: Implications for Source-to-Sink Processes on Mars

Tyrrhena Terra, a region located in the cratered highlands between Hellas and Isidis Planitia on Mars, is distinguished by its extensive presence of hydrated minerals. Using 542 hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars, we detected 252 exposures of hydrated minerals. This region is characterized by a widespread distribution of Fe/Mg-smectites/vermiculites and chlorite, with additional detections of Al-phyllosilicates, zeolites, prehnite, hydrated silica, and carbonates. We classified the mineralogical detections in classes of impact crater diameters, locations in craters, and for those $>$20 km, their relative degradation stages. We found that craters 10 km display a lower mineral diversity than larger ones. In contrast, craters $>$20 km display a high mineral diversity, especially in central peaks, suggesting a strong influence of hydrothermal processes and deep excavation. Among this diameter range, fresh, young craters exhibit a much higher mineral diversity than degraded, old craters. Fe/Mg-phyllosilicates are dominant in the latter, as well as in sedimentary units of topographically low areas. These results indicate a long-term alteration cycle in the most ancient period, where the initial, diverse hydrated minerals—formed through exhumation and/or hydrothermal circulation within large impacts—were subsequently transformed by surface weathering and/or buried, dissolved, or eroded away by other post-impact processes, then transported and deposited in lowlands by fluvial erosion. Although Tyrrhena Terra is dominated by impact-related hydrated mineral detections, our study shows that the overprint of Noachian age weathering is visible within these detections.