Silica‐Bearing Mounds and Strata in the Southwest Melas Basin, Valles Marineris, Mars: Evidence for a Hydrothermal Origin

• Published in: Journal of geophysical research. Planets 2023-11, Vol.128 (11), p.n/a
• Main Authors: Rogers, Emma R., Qualizza, Briar R., Heidenreich, Joseph R., Dawson, Henry G., Horgan, Briony H. N.
• Format: Article
• Language: English
• Subjects: Absorption bands; Absorption spectra; Canyons; Digital imaging; Earth; geological processes; Image resolution; Imaging spectrometers; Infrared reflection; Infrared spectra; Lake basins; Lake levels; Lakes; Mars; Mars surface; Mineralogy; Minerals; Morphology; Mounds; Opal; Paleolakes; Questions; Reconnaissance; Reflectance; Sediment deposits; Silica; Silicon dioxide; Spectral absorption; Spectral signatures; spectroscopy; Strata; Stratigraphy; surface; Terrain models
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2023JE007881

A small basin on the Southwest (SW) margin of Melas Chasma in Valles Marineris, Mars, hosts a variety of previously identified sedimentary fans and layered strata hypothesized to have been formed by one or more paleolakes. This basin also contains light‐toned layered mounds that have distinct spectral absorption bands consistent with amorphous hydrated silica (e.g., opal). While the general morphology and mineralogy of these features and the basin itself have been previously characterized, the formation mechanism of the hydrated silica features and their temporal relationships with the proposed paleolake remain to be determined. We use Compact Reconnaissance Imaging Spectrometer for Mars visible through short‐wave infrared reflectance spectra (0.35–2.65 μm) and High Resolution Imaging Science Experiment digital terrain models and images to analyze the stratigraphic location and morphology of the opaline silica‐bearing features in the SW Melas basin. We find that the basin hosts fourteen high‐relief “mounds,” eight low‐relief “patches,” and two extended layers within the sedimentary strata that are light‐toned, fractured, and often exhibit hydrated silica‐like spectral signatures. We hypothesize that the mounds are spring deposits formed by sub‐aerial hydrothermal activity, while the patches and layers correspond to sub‐lacustrine hydrothermal activity. The varied elevations of the mounds and patches indicate at least one fluctuation of lake level in the basin during its history. The combination of contemporaneous hydrothermal and lacustrine activity to form silica‐cemented sedimentary deposits in a nutrient‐rich subaqueous environment would have been conducive to forming and preserving biosignatures in the SW Melas basin. Plain Language Summary A small basin within Valles Marineris, the largest canyon system on Mars, is thought to have contained one or more lakes in its ancient past. This lake basin also contains signs of opal and other minerals that suggest the interaction of water with the rocks present in the basin. While the different features and minerals of the study site have been previously described, there are still many outstanding questions on how these features were formed and how they relate to the lake activity also seen in the basin. We use various orbital instruments on the Mars Reconnaissance Orbiter to answer these questions. We find that there are two different opal‐bearing features, which we separate into “mounds” and “patches,” as well