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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

(a) NavCam image of the John Klein outcrop (sol 197). S, sulfate veins; R, raised ridges. The 849 arrow points toward the John Klein drill holes. (b) MastCam image of sulfate veins and nodules 850 within the Sheepbed mudstone outcrop (sol 170). Scale bar of 10 cm. (c) McGrath diagenetic Mg-rich raised ridges within Sheepbed mudstone (sol 234) ChemCam Remote MicroImager. Scale bar of 4 mm.
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fig01: (a) NavCam image of the John Klein outcrop (sol 197). S, sulfate veins; R, raised ridges. The 849 arrow points toward the John Klein drill holes. (b) MastCam image of sulfate veins and nodules 850 within the Sheepbed mudstone outcrop (sol 170). Scale bar of 10 cm. (c) McGrath diagenetic Mg-rich raised ridges within Sheepbed mudstone (sol 234) ChemCam Remote MicroImager. Scale bar of 4 mm.

Mentions: The 4.5 m thick Yellowknife Bay formation is subdivided into different members with the lowest one, Sheepbed, being an at least 1.5 m thick mudstone, but its lower contact is not visible; its upper contact to the overlying Gillespie member is sharp. The Sheepbed member is a mudstone of overall basaltic chemical composition with ∽15% smectite, ∽50% igneous minerals, and ∽35% X-ray amorphous material [Grotzinger et al., 2014[. The observed magnetite is considered to be of authigenic origin [Grotzinger et al., 2014[. The unit contains abundant nodules, hollow nodules, voids, raised ridges, and sulfate-filled cracks (Figure 1), all of which are associated with the late stages of the diagenesis [Grotzinger et al., 2014; McLennan et al., 2014[. Chemistry and Camera (ChemCam) analyses also showed that the raised ridges have a Mg-rich composition (1.2–1.7 times) relative to the surrounding mudstone [Leveille et al. 2014[. Key textural observations are that the raised ridges postdate the sedimentary layering and sulfate veins postdate the raised ridges. The notably pure Ca-sulfate composition of the late veins was initially established by ChemCam (Laser Induced Breakdown Spectroscopy) and was confirmed by Alpha Proton X-ray Spectrometer (APXS) [McLennan et al., 2014[. Both drilled samples—named John Klein and Cumberland—are within the Sheepbed member [Vaniman et al., 2014[.


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)

(a) NavCam image of the John Klein outcrop (sol 197). S, sulfate veins; R, raised ridges. The 849 arrow points toward the John Klein drill holes. (b) MastCam image of sulfate veins and nodules 850 within the Sheepbed mudstone outcrop (sol 170). Scale bar of 10 cm. (c) McGrath diagenetic Mg-rich raised ridges within Sheepbed mudstone (sol 234) ChemCam Remote MicroImager. Scale bar of 4 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig01: (a) NavCam image of the John Klein outcrop (sol 197). S, sulfate veins; R, raised ridges. The 849 arrow points toward the John Klein drill holes. (b) MastCam image of sulfate veins and nodules 850 within the Sheepbed mudstone outcrop (sol 170). Scale bar of 10 cm. (c) McGrath diagenetic Mg-rich raised ridges within Sheepbed mudstone (sol 234) ChemCam Remote MicroImager. Scale bar of 4 mm.
Mentions: The 4.5 m thick Yellowknife Bay formation is subdivided into different members with the lowest one, Sheepbed, being an at least 1.5 m thick mudstone, but its lower contact is not visible; its upper contact to the overlying Gillespie member is sharp. The Sheepbed member is a mudstone of overall basaltic chemical composition with ∽15% smectite, ∽50% igneous minerals, and ∽35% X-ray amorphous material [Grotzinger et al., 2014[. The observed magnetite is considered to be of authigenic origin [Grotzinger et al., 2014[. The unit contains abundant nodules, hollow nodules, voids, raised ridges, and sulfate-filled cracks (Figure 1), all of which are associated with the late stages of the diagenesis [Grotzinger et al., 2014; McLennan et al., 2014[. Chemistry and Camera (ChemCam) analyses also showed that the raised ridges have a Mg-rich composition (1.2–1.7 times) relative to the surrounding mudstone [Leveille et al. 2014[. Key textural observations are that the raised ridges postdate the sedimentary layering and sulfate veins postdate the raised ridges. The notably pure Ca-sulfate composition of the late veins was initially established by ChemCam (Laser Induced Breakdown Spectroscopy) and was confirmed by Alpha Proton X-ray Spectrometer (APXS) [McLennan et al., 2014[. Both drilled samples—named John Klein and Cumberland—are within the Sheepbed member [Vaniman et al., 2014[.

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