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Diagenesis and clay mineral formation at Gale Crater, Mars.

Bridges JC, Schwenzer SP, Leveille R, Westall F, Wiens RC, Mangold N, Bristow T, Edwards P, Berger G - J Geophys Res Planets (2015)

Bottom Line: 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.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.We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component.

View Article: PubMed Central - PubMed

Affiliation: Space Research Centre, Department of Physics and Astronomy, University of Leicester Leicester, UK.

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.

No MeSH data available.


Related in: MedlinePlus

Portage soil reacted with GPW and 0.62 mol of H2CO3 added. Other parameters are 10°C, 1 bar, and 10% Fe as Fe3+. All models include apatite and trace phases (below 3%) are not plotted either. W/R is the ratio of incoming fluid with reacted rock.
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fig07: Portage soil reacted with GPW and 0.62 mol of H2CO3 added. Other parameters are 10°C, 1 bar, and 10% Fe as Fe3+. All models include apatite and trace phases (below 3%) are not plotted either. W/R is the ratio of incoming fluid with reacted rock.

Mentions: The main differences between the systems with and without CO2 are observed at high W/R (Figure 7). At the highest W/R, carbonate (effectively siderite; Figure 7b) is the second most abundant phase, while the most abundant phase is an SiO2-phase (between W/R of 10,000 and 2000, then stilbite between W/R 2000 and 750, after which chlorite becomes the most abundant phase). In contrast to the CO2-poor case (composition in Figure 3a), chlorite formation is not possible, while CO2 concentrations are high and ion concentrations from the silicate are low, and kaolinite forms at the highest W/R (>1700). Nontronite formation, too, is not possible during the peak siderite formation (Figure 7). At intermediate W/R, more ions from the silicate dissolution become available, facilitating nontronite formation (W/R of <300). The carbonate is initially siderite (Figure 7b), between W/R of 1000 and 500 siderite-ankerite assemblage, pure ankerite in a very short interval (W/R of 500–450), then calcite-ankerite (W/R 450–330) after which the carbonate is calcite until carbonate formation ceases at W/R of 13. This example demonstrates that high HCO3− activity would favor carbonate formation over clay [Catalano, 2013[, especially those that take up Fe, Mg, and Ca. Since SAM analyses allow the possibility of only minor carbonate amounts [Ming et al., 2014[, and CheMin found up to 22% clay, this points toward a carbonate-poor alteration scenario, within the subsurface and not able to exchange with the atmosphere, especially not a potentially thicker CO2-atmosphere that is generally envisaged for early Mars.


Diagenesis and clay mineral formation at Gale Crater, Mars.

Bridges JC, Schwenzer SP, Leveille R, Westall F, Wiens RC, Mangold N, Bristow T, Edwards P, Berger G - J Geophys Res Planets (2015)

Portage soil reacted with GPW and 0.62 mol of H2CO3 added. Other parameters are 10°C, 1 bar, and 10% Fe as Fe3+. All models include apatite and trace phases (below 3%) are not plotted either. W/R is the ratio of incoming fluid with reacted rock.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508961&req=5

fig07: Portage soil reacted with GPW and 0.62 mol of H2CO3 added. Other parameters are 10°C, 1 bar, and 10% Fe as Fe3+. All models include apatite and trace phases (below 3%) are not plotted either. W/R is the ratio of incoming fluid with reacted rock.
Mentions: The main differences between the systems with and without CO2 are observed at high W/R (Figure 7). At the highest W/R, carbonate (effectively siderite; Figure 7b) is the second most abundant phase, while the most abundant phase is an SiO2-phase (between W/R of 10,000 and 2000, then stilbite between W/R 2000 and 750, after which chlorite becomes the most abundant phase). In contrast to the CO2-poor case (composition in Figure 3a), chlorite formation is not possible, while CO2 concentrations are high and ion concentrations from the silicate are low, and kaolinite forms at the highest W/R (>1700). Nontronite formation, too, is not possible during the peak siderite formation (Figure 7). At intermediate W/R, more ions from the silicate dissolution become available, facilitating nontronite formation (W/R of <300). The carbonate is initially siderite (Figure 7b), between W/R of 1000 and 500 siderite-ankerite assemblage, pure ankerite in a very short interval (W/R of 500–450), then calcite-ankerite (W/R 450–330) after which the carbonate is calcite until carbonate formation ceases at W/R of 13. This example demonstrates that high HCO3− activity would favor carbonate formation over clay [Catalano, 2013[, especially those that take up Fe, Mg, and Ca. Since SAM analyses allow the possibility of only minor carbonate amounts [Ming et al., 2014[, and CheMin found up to 22% clay, this points toward a carbonate-poor alteration scenario, within the subsurface and not able to exchange with the atmosphere, especially not a potentially thicker CO2-atmosphere that is generally envisaged for early Mars.

Bottom Line: 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.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.We therefore deduce a dissolving composition of approximately 70% amorphous material, with 20% olivine, and 10% whole rock component.

View Article: PubMed Central - PubMed

Affiliation: Space Research Centre, Department of Physics and Astronomy, University of Leicester Leicester, UK.

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.

No MeSH data available.


Related in: MedlinePlus