Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: Implications for biogenic mineralization

Bradley, J. P.; McSween, H. Y.; Harvey, R. P.

doi:10.1111/j.1945-5100.1998.tb01682.x

Cited by 54 publications

(45 citation statements)

References 34 publications

(43 reference statements)

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“…The current balance of evidence does not strongly support the biogenic theory of origin for ALH84001 carbonates (Scott, 1999;Steele et al, 2000;Kathie et al, 2000;Bradley et al, 1998;. The best argument for a biological origin rests with the morphology of some of the magnetite grains.…”

Section: Suggested Relic Biological Activity In Alh84001mentioning

confidence: 83%

“…Brearley suggested that the phlogopite was derived through the breakdown of pre-existing clay during shock heating at <500 • C. Treiman (1998a) documented fracturing episodes within ALH84001 and proposed that the carbonate had experienced 4 discrete deformation events. Bradley et al (1998) also carefully documented the magnetite structures around the carbonate rosettes and suggested that whisker-shaped grains they found were most consistent with precipitation at high temperatures (500 − 800 • C) from a vapour. This was taken by Scott (1999) to be a result of the shock remobilisation of pre-existing carbonates and resultant break down of Fe-carbonate to a magnetite-bearing assemblage.…”

Section: High Temperature: Shock Remobilisation Andmentioning

confidence: 99%

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Bridges

Catling

Saxton

et al. 2001

Space Science Reviews

215

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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: Suggested Relic Biological Activity In Alh84001mentioning

confidence: 83%

Section: High Temperature: Shock Remobilisation Andmentioning

confidence: 99%

Untitled

Bridges

Catling

Saxton

et al. 2001

Space Science Reviews

215

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“…Bradley et al (1998) also carefully documented the magnetite structures around the carbonate rosettes and suggested that whisker-shaped grains they found were most consistent with precipitation at high temperatures (500 − 800…”

Section: High Temperature: Shock Remobilisation Andmentioning

confidence: 99%

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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“…Although magnetite forms predominantly diamond-shape octahedrons {111} in the cubic crystal classes, it also crystallizes in several other forms (e.g., dodecahedral and cubic). Unusual, elongated forms known as whiskers have also been reported to form from a vapor phase at high temperatures (3). Magnetite crystals formed by magnetotactic bacteria (magnetosomes) also have a variety of distinct morphologies.…”

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confidence: 99%

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15

Vali

Weiss

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

103

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Distinct morphological characteristics of magnetite formed intracellularly by magnetic bacteria (magnetosome) are invoked as compelling evidence for biological activity on Earth and possibly on Mars. Crystals of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15, thermophilic bacteria, and psychrotolerant bacteria are, however, traditionally not thought to have nearly as distinct morphologies. The size and shape of extracellular magnetite depend on the culture conditions and type of bacteria. Under typical CO2-rich culture conditions, GS-15 is known to produce superparamagnetic magnetite (crystal diameters of approximately <30 nm). In the current study, we were able to produce a unique form of tabular, single-domain magnetite under nontraditional (low-CO 2) culture conditions. This magnetite has a distinct crystal habit and magnetic properties. This magnetite could be used as a biosignature to recognize ancient biological activities in terrestrial and extraterrestrial environments and also may be a major carrier of the magnetization in natural sediments.

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Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: Implications for biogenic mineralization

Cited by 54 publications

References 34 publications

Untitled

Untitled

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

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15

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