Contrasting Regional Soil Alteration Across the Topographic Dichotomy of Mars

Abstract

Landscapes on either side of the martian topographic dichotomy bear distinct soil chemistry, but the processes associated with this distinction remain poorly understood. Here, correlation of soil chemistry at global to regional scales is examined with multivariate analysis of Gamma-Ray Spectrometer chemical maps and the Thermal Emission Spectrometer-derived Dust Cover Index (DCI). In the analysis, the northern lowlands show a strong S-Cl correlation, contrasting with the southern highlands, which show a stronger S-H 2 O correlation. These observations suggest aqueous interaction with soils throughout the southern highlands, preferentially dissolving Cl compounds and weakening S-Cl correlation. Strong S-Cl correlations in the northern lowlands suggest less interaction with aqueous H 2 O. Additionally, regional analyses demonstrate that DCI does not correlate with volatile chemistry at smaller scales and that Ca may be an important component of volatile-bearing material. These results provide new evidence for widespread aqueous interaction and possibly alteration of soil in the southern highlands.Plain Language Summary Mars can be divided into two large regions: the northern lowlands and southern highlands, separated by a planet-circling change in elevation known as the topographic dichotomy. The soils that cover the landscape in these two areas appear distinct from one another, although it is unclear what processes cause this distinction. This investigation examines the chemistry of soils on either side of the dichotomy based on Gamma-Ray Spectrometer data, to elucidate changes in soils. The identified changes in correlation of three soil components, sulfur, chlorine, and H 2 O, suggest that much of the southern highlands soils have interacted with water, but fluid interaction occurred far less in the northern lowlands. These findings show that the processes by which water interacts with soils were likely active over larger areas in the southern highlands than previously realized, but such processes were not active after the northern lowlands soils were deposited.

Compositional Enhancement of Crustal Magnetization on Mars

“…The Mars Odyssey Gamma Ray Spectrometer (GRS) derived chemical maps were derived from the spectral data archived on the PDS by applying the spectra-to-chemistry modeling methods described by Boynton et al (2007), Evans et al (2006), and Karunatillake et al (2007). The derived chemical maps have also been described and analyzed in the works by Hood et al (2019) and Ojha et al (2019), among others.…”

Amagmatic hydrothermal systems on Mars from radiogenic heat

“…The Mars Odyssey Gamma Ray Spectrometer (GRS) derived chemical maps were derived from the spectral data archived at the PDS ( https://pds-geosciences.wustl.edu/missions/odyssey/grs.html ) by applying the spectra-to-chemistry modeling methods described in previous work 58 , 65 , 118 . The derived chemical maps have also been described and analyzed in other recent works 59 , 119 . The gravity model of Mars is available through the gravity model page of PDS node ( https://pds-geosciences.wustl.edu/dataserv/gravity_models.htm ).…”

Mars in multi-dimensions: a global geological survey

“…Despite this increase in model performance, the highest VIP summary parameters in the Cl model are not dust-related (ISLOPE 1, D2300, BD19002) though, R770 does have a VIP>1 (Figure 5.6). This may indicate a correlation of Cl with dusty areas that it is not strictly related to the dust, and is instead caused by mineralogical connections with the other volatile elements, as suggested in Hood et al [46].…”

“…Several data-integration attempts are performed using different infrared orbital instruments, such as TES [87], OMEGA [84], and CRISM [105], but although they might explain locally the variation of element concentration the global variation remains uncertain. Also, new modeling attempts resulted in new global element maps for Al, Ca, and S which are made available [46] for this study. These maps are interpreted here globally for the first time.…”

“…The gamma-ray data are often discussed in relation to the dustcoverage, often referred as dust mantling in literature [58,98,46]. With the PLS modelling we evaluate the effect of the dust by studying the models with and without the dust-covered pixels, and by studying the VIP values for the dust covered summary products for each model.…”