Chassigny and the nakhlites: Carbon-bearing components and their relationship to martian environmental conditions

Wright, I. P.; Grady, M. M.; Pillinger, C. T.

doi:10.1016/0016-7037(92)90100-w

Cited by 89 publications

(77 citation statements)

References 40 publications

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“…Finally, the possibility exists that the magmatic CO 2 on Mars is substantially enriched in 13 C compared to the Earth. However, this is not supported by measurements from martian meteorites which in fact suggest that the carbon isotopic content of magmatic carbon on Mars is depleted in 13 C compared to the Earth (Wright et al 1992). No other mechanisms have been proposed that might explain an enrichment in δ 13 C of >50 h for the magmatic CO 2 contained within the planet, and given the available evidence, it is most likely that the δ 13 C of the martian atmosphere has changed substantially through martian history as a result of atmospheric loss, carbonate formation, and volcanic degassing.…”

Section: Formation Environments and Insight Into Martian Climate Historymentioning

confidence: 74%

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

Niles¹,

Catling²,

Berger³

et al. 2012

Quantifying the Martian Geochemical Reservoirs

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Ongoing research on martian meteorites and a new set of observations of carbonate minerals provided by an unprecedented series of robotic missions to Mars in the past 15 years help define new constraints on the history of martian climate with important cross- cutting themes including: the CO 2 budget of Mars, the role of Mg-, Fe-rich fluids on Mars, and the interplay between carbonate formation and acidity.Carbonate minerals have now been identified in a wide range of localities on Mars as well as in several martian meteorites. The martian meteorites contain carbonates in low abundances (<1 vol.%) and with a wide range of chemistries. Carbonates have also been identified by remote sensing instruments on orbiting spacecraft in several surface locations as well as in low concentrations (2-5 wt.%) in the martian dust. The Spirit rover also identified an outcrop with 16 to 34 wt.% carbonate material in the Columbia Hills of Gusev Crater that strongly resembled the composition of carbonate found in martian meteorite ALH 84001. Finally, the Phoenix lander identified concentrations of 3-6 wt.% carbonate in the soils of the northern plains.The carbonates discovered to date do not clearly indicate the past presence of a dense Noachian atmosphere, but instead suggest localized hydrothermal aqueous environments with limited water availability that existed primarily in the early to mid-Noachian followed by low levels of carbonate formation from thin films of transient water from the late Noachian to the present. The prevalence of carbonate along with evidence for active carbonate precipitation suggests that a global acidic chemistry is unlikely and a more complex relationship between acidity and carbonate formation is present.

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Section: Formation Environments and Insight Into Martian Climate Historymentioning

confidence: 74%

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

Niles¹,

Catling²,

Berger³

et al. 2012

Quantifying the Martian Geochemical Reservoirs

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“…A summary of the carbon data for the coarse and fine samples plus the glass and pigeonite separates is given in [Wright et al, , 1992a), a component which has previously been interpreted as mostly from organic contaminants. Low-temperature carbon in the bulk samples has a/5•3C of-29%o to-23%o, values typical of terrestrial organic contaminants, and accounts for most of the carbon in Zagami (Table 1).…”

Section: Resultsmentioning

confidence: 99%

A carbon and nitrogen isotope study of Zagami

Grady¹,

Wright²,

Pillinger³

1997

J. Geophys. Res.

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“…A common starting point for consideration of carbonate oxygen isotope data (Clayton and Mayeda, 1988;Wright et al, 1992;Romanek et al, 1994;Saxton et al, 1998Saxton et al, , 2000b) has been to consider water (or a water-CO 2 mixture) equi-378 BRIDGES ET AL. librated with the silicate at high temperature (at which isotopic fractionation is small), and then cooled.…”

Section: Oxygenmentioning

confidence: 99%

“…Carbonate concentrations are generally low with between 30 − 60 ppm for the nakhlites (Grady et al, 1997). Carbon isotope results fall into two groups: ALH84001 and the nakhlites all contain 13 C-enriched carbonates, with δ 13 C ranging from +10‰ to +55‰ (Carr et al, 1985;Wright et al, 1992;Romanek et al, 1994;Jull et al, 1995), whereas Chassigny and the shergottites have acid-extractable carbon, presumably from the carbonate anion, with δ 13 C ranging from 0‰ to −30‰. The most extensive study has been undertaken on ALH84001.…”

Section: Carbon Hydrogen and Sulphurmentioning

confidence: 99%

“…The two clear isotopic groups of carbonate are interpreted to represent formation of the minerals in two different environments: the lighter δ 13 C values are from carbonate formed at depth within the martian crust by interaction of primary magmatic fluids with host rock, whereas carbonates in ALH84001 and the nakhlites formed either at, or close to Mars' surface, where fluid exchanged with martian atmospheric CO 2 (Carr et al, 1985;Wright et al, 1992;Romanek et al, 1994). The carbon isotopic composition of martian atmospheric CO 2 is known to be 13 C-enriched, but a precise measurement of its δ 13 C is still awaited.…”

Section: Carbon Hydrogen and Sulphurmentioning

confidence: 99%

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Bridges

Catling

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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Chassigny and the nakhlites: Carbon-bearing components and their relationship to martian environmental conditions

Cited by 89 publications

References 40 publications

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

A carbon and nitrogen isotope study of Zagami

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