Water in SNC Meteorites: Evidence for a Martian Hydrosphere

Karlsson, Haraldur R.; Clayton, Robert N.; Gibson, E. K.; Mayeda, T. K.

doi:10.1126/science.11537889

Cited by 156 publications

(82 citation statements)

References 22 publications

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“…Martian silicate itself has 17 O = +0.3‰ compared to the terrestrial fractionation line (Franchi et al, 1999). The data of Farquhar and Thiemens is similar to that of Karlsson et al (1992) who showed that water in the SNC meteorites had 17 O greater than that of the anhydrous silicates by values up to 17 O = +0.6‰ (Nakhla) although Shergotty and EETA 79001 showed no 17 O excesses over their whole rock values.…”

Section: Oxygensupporting

confidence: 67%

“…In this model, the water has the same 17 O as the silicate. However, the discovery that water and secondary minerals in ALH84001, Nakhla and Lafayette have 17 O in excess of the host rock (Karlsson et al, 1992; implies that not only the carbonates, but also the waters from which they formed were not equilibrated with the parent rocks. Saxton et al (1998) considered several models for the formation of the ALH84001 carbonates.…”

Section: Oxygenmentioning

confidence: 99%

“…Previously, the presence of 17 O excesses was attributed to the influx of cometary material (Karlsson et al, 1992) but as no chondritic material with suitably high 17 O has been identified this idea remains unsubstantiated.…”

Section: Mass-independent Fractionation Processesmentioning

confidence: 99%

“…Other SNCs have lower proportions of secondary minerals. Bulk meteorite water contents, associated with the secondary minerals range from 0.04 wt% in the shergottites to 0.4 wt% in the clay-rich nakhlites (Karlsson et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Saxton

et al. 2001

Space Science Reviews

219

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Abstract. The SNC (Shergotty-Nakhla-Chassigny) meteorites have recorded interactions between martian crustal fluids and the parent igneous rocks. The resultant secondary minerals -which comprise up to ~ 1 vol.% of the meteorites -provide information about the timing and nature of hydrous activity and atmospheric processes on Mars. We suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature (25-150 o C) brines. This is consistent with the simple mineralogy of these assemblages -Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays -and the chemical fractionation of Ca-to Mg-rich carbonate in ALH84001 'rosettes'. Longer-lived, and higher temperature, hydrothermal systems would have caused more silicate alteration than is seen and probably more complex mineral assemblages. Experimental and phase equilibria data on carbonate compositions similar to those present in the SNCs imply low temperatures of formation with cooling taking place over a short period of time (e.g. days). The ALH84001 carbonate also probably shows the effects of partial vapourisation and dehydration related to an impact event postdating the initial precipitation. This shock event may have led to the formation of sulphide and some magnetite in the Fe-rich outer parts of the rosettes.Radiometric dating (K-Ar, Rb-Sr) of the secondary mineral assemblages in one of the nakhlites (Lafayette) suggests that they formed between 0 and 670 Ma, and certainly long after the crystallisation of the host igneous rocks. Crystallisation of ALH84001 carbonate took place 0.5 Ga after the parent rock. These age ranges and the other research on these assemblages suggest that environmental conditions conducive to near-surface liquid water have been present on Mars periodically over the last ~1 Ga. This fluid activity cannot have been continuous over geological time because in that case much more silicate alteration would have taken place in the meteorite parent rocks and the soluble salts would probably not have been preserved.The secondary minerals could have been precipitated from brines with seawater-like composition, high bicarbonate contents and a weakly acidic nature. The co-existence of siderite (Fe-carbonate) and clays in the nakhlites suggests that the pCO 2 level in equilibrium with the parent brine may have been 50 mbar or more. The brines could have originated as flood waters which percolated through the top few hundred metres of the crust, releasing cations from the surrounding parent rocks. There is no spectroscopic or photographic evidence for extensive evaporite deposits on the current martian surface but some salt precipitation through solute concentration must have occurred as floodwaters associated with many of the martian channels ponded in low-lying areas. The high sulphur and chlorine concentrations of the martian soil have most likely resulted from aeolian redistribution of such aqueously-deposited salts and from reaction of the martian surface with volcanic acid volatiles. However, the SNC...

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Section: Oxygensupporting

confidence: 67%

Section: Oxygenmentioning

confidence: 99%

Section: Mass-independent Fractionation Processesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Untitled

Bridges

Catling

Saxton

et al. 2001

Space Science Reviews

219

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“…Martian silicate itself has 17 O = +0.3‰ compared to the terrestrial fractionation line (Franchi et al, 1999). The data of Farquhar and Thiemens is similar to that of Karlsson et al (1992) Temperature and isotopic fractionation constraints from oxygen: Carbonate equilibrated with silicate at 500−700…”

Section: Oxygensupporting

confidence: 65%

Alteration Assemblages in Martian Meteorites: Implications for Near-Surface Processes

Bridges

Catling

Saxton

et al. 2001

Space Sciences Series of ISSI

128

201

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Abstract. The SNC (Shergotty-Nakhla-Chassigny) meteorites have recorded interactions between martian crustal fluids and the parent igneous rocks. The resultant secondary minerals -which comprise up to ~ 1 vol.% of the meteorites -provide information about the timing and nature of hydrous activity and atmospheric processes on Mars. We suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature o C) brines. This is consistent with the simple mineralogy of these assemblages -Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays -and the chemical fractionation of Ca-to Mg-rich carbonate in ALH84001 'rosettes'. Longer-lived, and higher temperature, hydrothermal systems would have caused more silicate alteration than is seen and probably more complex mineral assemblages. Experimental and phase equilibria data on carbonate compositions similar to those present in the SNCs imply low temperatures of formation with cooling taking place over a short period of time (e.g. days). The ALH84001 carbonate also probably shows the effects of partial vapourisation and dehydration related to an impact event postdating the initial precipitation. This shock event may have led to the formation of sulphide and some magnetite in the Fe-rich outer parts of the rosettes.Radiometric dating (K-Ar, Rb-Sr) of the secondary mineral assemblages in one of the nakhlites (Lafayette) suggests that they formed between 0 and 670 Ma, and certainly long after the crystallisation of the host igneous rocks. Crystallisation of ALH84001 carbonate took place 0.5 Ga after the parent rock. These age ranges and the other research on these assemblages suggest that environmental conditions conducive to near-surface liquid water have been present on Mars periodically over the last ~1 Ga. This fluid activity cannot have been continuous over geological time because in that case much more silicate alteration would have taken place in the meteorite parent rocks and the soluble salts would probably not have been preserved.The secondary minerals could have been precipitated from brines with seawater-like composition, high bicarbonate contents and a weakly acidic nature. The co-existence of siderite (Fe-carbonate) and clays in the nakhlites suggests that the pCO 2 level in equilibrium with the parent brine may have been 50 mbar or more. The brines could have originated as flood waters which percolated through the top few hundred metres of the crust, releasing cations from the surrounding parent rocks. There is no spectroscopic or photographic evidence for extensive evaporite deposits on the current martian surface but some salt precipitation through solute concentration must have occurred as floodwaters associated with many of the martian channels ponded in low-lying areas. The high sulphur and chlorine concentrations of the martian soil have most likely resulted from aeolian redistribution of such aqueously-deposited salts and from reaction of the martian surface with volcanic acid volatiles. However, the SNC salt a...

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Meteoroids and Meteorites

2005

Van Nostrand's Scientific Encyclopedia

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Water in SNC Meteorites: Evidence for a Martian Hydrosphere

Cited by 156 publications

References 22 publications

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Alteration Assemblages in Martian Meteorites: Implications for Near-Surface Processes

Meteoroids and Meteorites

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