Geochemical and mineralogical interpretation of the Viking inorganic chemical results

Abstract

The elemental analyses whose basis is described in the preceding two papers represent the composition of samples of Martian fines; the only undetermined major constituents thought to be present are H2O, CO2, Na2O, and possibly NOx. The samples are principally silicate particles, with some admixture of oxide and probably carbonate minerals; the fines appear to have been indurated to a variable degree by a sulfate‐rich intergranular cement. The overall elemental composition is dissimilar to any single known mineral or rock type and apparently represents a mixture of materials. Close chemical similarity among samples at each site, and between the two sites, indicates effective homogenization of the fines, presumably by planetary windstorms, and further suggests that the samples analyzed represent the fine, mobilizable materials over a large part of the planet's surface. Low trace element, alkali, and alumina contents suggest that the great preponderance of the materials in the mixture is of mafic derivation; highly differentiated, salic igneous rocks or their weathering products are insignificant components of the samples. Normative calculations, comparisons with reference libraries of analytical data, and mathematical mixture modeling have led to a qualitative mineralogical model in which the fines consist largely of iron‐rich smectites (or their degradation products), carbonates, iron oxides, probably in part maghemite, and sulfate minerals concentrated in a surface duricrust. The original smectites may have formed by interaction of mafic magma and subsurface ice, and the sulfates (and carbonates?) may have been concentrated in the surface crust by subsurface leaching, upward transport, and evaporation of intergranular moisture films. Testing and refinement of this and competing models will accompany continuing acquisition of samples and data and refinement of the analyses, particularly with respect to the critical light elements Mg, Al, and Si.

Ceramic ChemCam Calibration Targets on Mars Science Laboratory

“…For these reasons, calibration targets were created with (1) a clay mineral component that has been processed in a manner (heating to 1000°C) that prevents hydration/dehydration cycling yet preserves the anhydrous chemical composition and (2) a relatively stable sulfate component. Past missions have shown that sediments on Mars incorporate a significant amount of basaltic detritus (e.g., Toulmin et al 1977;); therefore we have included a basaltic component in these targets. The clay samples chosen were Fe-rich smectite (nontronite) and an aluminous clay mineral (kaolinite).…”

A stringent upper limit to SO2in the Martian atmosphere

“…The surface chemistry experiments of the Viking landers detected sulfates in the soil with abundances of 5 to 10 wt% (Toulmin et al 1977). More recently, the Spirit and Opportunity rover experiments reported the detection of sulfates (in particular ferric sulfates and magnesium sulfates) at the Gusev and Meridiani sites (Squyres et al 2004;Rieder et al 2004;Johnson et al 2007).…”

A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology

“…The palagonitization of basaltic glass is considered to be a viable process on Mars (Toulmin et al, 1977;Allen et al, 1981;Gooding, 1992). Allen et al (1981) specifically suggested that hydrothermal palagonitization could take place down to depths of about 150 m, and that after the initial quenching of magma with ground ice, further low-temperature alteration could continue for some time afterward through the interaction of subsurface waters with cooling volcanic material.…”