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Unraveling the context of unique basin-related alteration on early Mars

Presentation #300.06 in the session Martian Ice, Climate, and Habitability (Oral Presentation)

Published onOct 23, 2023
Unraveling the context of unique basin-related alteration on early Mars

The presence of clay minerals on Mars can be categorized into three geological settings: i) clay-bearing units formed through in situ alteration, ii) impact craters’ central peaks, walls, and ejecta, and iii) clay mineral-containing units in sedimentary basins. Alteration and an unknown hydroxylated phase have recently been observed in uplifted massifs on the rim of Hellas basin. The characteristics of these massifs, resulting from the massive Hellas impact basin, offer a unique environment to investigate the alteration of Mars’ oldest, pre-Noachian crust. We aim to explore whether hydrothermal alteration and fracturing of the ancient crust can account for the formation of these alteration phases. If confirmed, this basin setting could represent a unique near-surface environment where Mars may have sustained habitability in the past, with the potential for accessible preservation of biosignatures.

In this study, we combine spectral and morphologic analyses in the northern Hellas region to understand the processes leading to the formation of both altered and primary compositions. Analysis of CRISM targeted observations provides compositional detections, while HiRISE/CTX provides geological context for alteration phases in these massifs. Analysis of CRISM reveals the following composition results: 1) primary lithologies include “feldspathic” material, olivine, and low-Ca pyroxene (consistent with previous and ongoing investigations; Phillips et al. 2022), 2) secondary lithologies are predominantly kaolinite (often associated with plagioclase), hydrated Fe/Mg-smectite, and an unknown Mg-OH phase (see Viviano et al. 2021). Massifs exhibit various compositions of primary lithologies throughout their exposure. Although the Mg-OH phase resembles laboratory talc spectra, slight differences in the position of a weak 2.25-µm band make identification less certain. Both the Fe/Mg-smectite and Mg-OH phase in this region display the 2.25-µm band, unlike regions north of the Hellas rim. Further analysis will focus on recently acquired HiRISE observations to enhance the understanding of the morphological context of plagioclase-bearing massifs.


Phillips, M. S., et al. (2022), Geology; 50 (10): 1182–1186.

Viviano, C. E., et al. (2021), 52nd LPSC, Abs. #1675.

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