Diagenesis and clay mineral formation at Gale Crater, Mars

Abstract

The Mars Science Laboratory rover Curiosity found host rocks of basaltic composition and alteration assemblages containing clay minerals at Yellowknife Bay, Gale Crater. On the basis of the observed host rock and alteration minerals, we present results of equilibrium thermochemical modeling of the Sheepbed mudstones of Yellowknife Bay in order to constrain the formation conditions of its secondary mineral assemblage. Building on conclusions from sedimentary observations by the Mars Science Laboratory team, we assume diagenetic, in situ alteration. The modeling shows that the mineral assemblage formed by the reaction of a CO2-poor and oxidizing, dilute aqueous solution (Gale Portage Water) in an open system with the Fe-rich basaltic-composition sedimentary rocks at 10–50°C and water/rock ratio (mass of rock reacted with the starting fluid) of 100–1000, pH of ∽7.5–12. Model alteration assemblages predominantly contain phyllosilicates (Fe-smectite, chlorite), the bulk composition of a mixture of which is close to that of saponite inferred from Chemistry and Mineralogy data and to that of saponite observed in the nakhlite Martian meteorites and terrestrial analogues. To match the observed clay mineral chemistry, inhomogeneous dissolution dominated by the amorphous phase and olivine is required. We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component.

Experimental hydrothermal alteration of basaltic glass with relevance to Mars

“…This is also inferred by formation of phyllosilicates in the Gale crater where essential elements were sourced from olivine and glass phases resulting in a phyllosilicate of similar composition as observed in the current experiment (Bridges et al. ). But, due to differences in dissolution rates of crystalline phases and glass, the rate of formation may not be comparable (Gudbrandsson et al.…”

Phase Equilibria Modeling of Low‐Grade Metamorphic Martian Rocks

“…The presence of hydrous phases indicates multiple diverse aqueous environments and episodes of activity. Most of these hydrous minerals are associated with surface weathering processes, evaporation, diagenesis, and impact-generated hydrothermal systems, as also predicted by thermochemical models (Bridges et al, 2015;Bridges & Schwenzer, 2012;Filiberto & Schwenzer, 2013;Griffith & Shock, 1997;Schwenzer et al, 2016;Schwenzer & Kring, 2013). The occurrence of prehnite, epidote, serpentine, and zeolites, however, is an indication for low-grade metamorphic reactions at deeper levels of Mars' crust.…”

Diagenetic silica enrichment and late‐stage groundwater activity in Gale crater, Mars

“…Notably, monoclinic tridymite, a SiO 2 polymorph, constitutes ~34 wt % of the crystalline mineralogy, while amorphous silica dominates the amorphous component (~77 wt % SiO 2 ). As Morris et al [] interpret the tridymite as detrital in origin, the Buckskin sample is consistent with previous analyses that show no evidence of high‐temperature (>80°C) diagenesis in Gale [ Vaniman et al , ; Bridges et al , ; Rapin et al , ].…”