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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 has been reacted with dilute Adapted Water AW at 50°C. The fluid was extracted from the original reaction at W/R (ratio of reacted rock with incoming fluid) of 100 and subsequently cooled to form Gale Portage water GPW, which we use in our model runs for the Yellowknife Bay diagenesis assemblage. (a) Plot of temperature (T in °C) versus ion concentration in 1 kg of water (in mol) of the fluid in equilibrium with the precipitate at different temperatures. Cooling causes precipitation—most noticeably of SiO2, Fe, Al and S. (b) Minerals precipitated upon cooling. Main precipitates are quartz (or another SiO2 phase, depending on reaction kinetics), pyrite, stilbite, and apatite.
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fig02: Portage soil has been reacted with dilute Adapted Water AW at 50°C. The fluid was extracted from the original reaction at W/R (ratio of reacted rock with incoming fluid) of 100 and subsequently cooled to form Gale Portage water GPW, which we use in our model runs for the Yellowknife Bay diagenesis assemblage. (a) Plot of temperature (T in °C) versus ion concentration in 1 kg of water (in mol) of the fluid in equilibrium with the precipitate at different temperatures. Cooling causes precipitation—most noticeably of SiO2, Fe, Al and S. (b) Minerals precipitated upon cooling. Main precipitates are quartz (or another SiO2 phase, depending on reaction kinetics), pyrite, stilbite, and apatite.

Mentions: Next, solid of Portage soil composition (Table 1) was titrated into this fluid at 50°C and 1 bar to account for a reaction of buried sediment (potentially at a higher geothermal gradient post impact) with the country rock. Portage soil from the Rocknest sand shadow is taken to be representative of average crustal compositions in the vicinity of Gale Crater. The resulting fluid composition at W/R of 100 was separated from the clay precipitate and cooled to 1°C (Figure 2), during which it produced a quartz (or amorphous SiO2, depending on kinetics) dominated precipitate (Figure 2). This is a common feature of cooling alteration fluids, and there is evidence for silica-rich deposits on Mars, probably forming under a variety of temperatures and other conditions [e.g., McAdam et al., 2008; Squyres et al., 2008[. The Gale fluid was again separated from the precipitate, and the ions left in the fluid were considered to be GPW. CO2—as a proxy for C-bearing species—is added as 1.68E-4 mol HCO3−, a concentration that precludes carbonate formation, consistent with MSL results, and used in our previous work [e.g., Schwenzer and Kring, 2009[. All S species in GPW are summarized as SO4−. Species with concentrations below 10−10 mol were not considered in this starting fluid composition.


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 has been reacted with dilute Adapted Water AW at 50°C. The fluid was extracted from the original reaction at W/R (ratio of reacted rock with incoming fluid) of 100 and subsequently cooled to form Gale Portage water GPW, which we use in our model runs for the Yellowknife Bay diagenesis assemblage. (a) Plot of temperature (T in °C) versus ion concentration in 1 kg of water (in mol) of the fluid in equilibrium with the precipitate at different temperatures. Cooling causes precipitation—most noticeably of SiO2, Fe, Al and S. (b) Minerals precipitated upon cooling. Main precipitates are quartz (or another SiO2 phase, depending on reaction kinetics), pyrite, stilbite, and apatite.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig02: Portage soil has been reacted with dilute Adapted Water AW at 50°C. The fluid was extracted from the original reaction at W/R (ratio of reacted rock with incoming fluid) of 100 and subsequently cooled to form Gale Portage water GPW, which we use in our model runs for the Yellowknife Bay diagenesis assemblage. (a) Plot of temperature (T in °C) versus ion concentration in 1 kg of water (in mol) of the fluid in equilibrium with the precipitate at different temperatures. Cooling causes precipitation—most noticeably of SiO2, Fe, Al and S. (b) Minerals precipitated upon cooling. Main precipitates are quartz (or another SiO2 phase, depending on reaction kinetics), pyrite, stilbite, and apatite.
Mentions: Next, solid of Portage soil composition (Table 1) was titrated into this fluid at 50°C and 1 bar to account for a reaction of buried sediment (potentially at a higher geothermal gradient post impact) with the country rock. Portage soil from the Rocknest sand shadow is taken to be representative of average crustal compositions in the vicinity of Gale Crater. The resulting fluid composition at W/R of 100 was separated from the clay precipitate and cooled to 1°C (Figure 2), during which it produced a quartz (or amorphous SiO2, depending on kinetics) dominated precipitate (Figure 2). This is a common feature of cooling alteration fluids, and there is evidence for silica-rich deposits on Mars, probably forming under a variety of temperatures and other conditions [e.g., McAdam et al., 2008; Squyres et al., 2008[. The Gale fluid was again separated from the precipitate, and the ions left in the fluid were considered to be GPW. CO2—as a proxy for C-bearing species—is added as 1.68E-4 mol HCO3−, a concentration that precludes carbonate formation, consistent with MSL results, and used in our previous work [e.g., Schwenzer and Kring, 2009[. All S species in GPW are summarized as SO4−. Species with concentrations below 10−10 mol were not considered in this starting fluid composition.

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