Chemical components of the Martian soil: Melt degassing, hydrothermal alteration, and chondritic debris

• Published in: Journal of Geophysical Research, Washington, DC Washington, DC, 1997-08, Vol.102 (E8), p.19345-19355
• Main Authors: Newsom, Horton E., Hagerty, Justin J.
• Format: Article
• Language: English
• Subjects: Cosmochemistry. Extraterrestrial geology; Earth sciences; Earth, ocean, space; Exact sciences and technology; Extraterrestrial geology
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/97JE01687

On the basis of measurements by the Viking and Soviet Phobos missions the fine grained surficial drift material on Mars is enriched in moderately volatile and mobile elements such as S, Cl, K, and Br. The compounds of these elements may amount to as much as 16 wt% of the soil, while the bulk of the soil appears to consist primarily of crustal material whose composition is similar to that of the basaltic Mars meteorites (Clark, 1993). Three possible geochemical sources (melt degassing, hydrothermal alteration, and accretion of chondritic material) may have contributed to the enrichments. We have evaluated possible chemical signatures for these sources by examining the relative abundances of chemical elements in the different components to the measured K abundance in the Mars soil and have identified characteristic elements for each component. The relative abundances of mobile elements in the different components are much less variable than their absolute abundances, which strongly depend on conditions such as temperature and water composition. The volatility controlled elemental signature of the melt degassing process includes enrichments of Zn, Mo, Cd, Ba, and W, relative to the elemental abundances in the other components and Martian meteorites. Hydrothermal alteration of minerals and glass, controlled by low‐temperature solubility, makes up a second component with a characteristic lithium enrichment signature. A chondritic component is enriched in siderophile and chalcophile elements including Ni, compared to material derived from the Martian mantle, which was depleted in siderophile elements due to core formation. Unfortunately, the existing data for the Mars soil do not include any of these key signature elements, and the uncertainties for the Viking analyses could allow large amounts of each of these elements. The Mars Pathfinder inorganic analysis experiment and the 2001 orbital gamma ray experiment have the potential to determine some of these characteristic elements and to reveal the possible contributions to the soil. The enriched components of the soil, especially Cd and Pb, could also be a potential hazard for future Martian explorers who will be exposed to the dust carried into their habitats on their space suits.