Shock metamorphism and petrography of the Shergotty achondrite

Stöffler, D.; Ostertag, R.; Jammes, C; Pfannschmidt, G.; Gupta, P. R. Sen; Simon, S. B.; Papike, J. J.; Beauchamp, R. H.

doi:10.1016/0016-7037(86)90371-6

Cited by 213 publications

(194 citation statements)

References 33 publications

Supporting

Mentioning

180

Contrasting

Unclassified

Order By: Relevance

“…30 − 45 GPa for the shergottites, Stöffler et al, 1986). These signs include melt pockets, deformation features in the silicate minerals and the presence of maskelynite.…”

Section: High Temperature: Shock Remobilisation Andmentioning

confidence: 98%

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

Bridges

Catling

Saxton

et al. 2001

Space Sciences Series of ISSI

128

201

View full text Add to dashboard Cite

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...

show abstract

“…30 − 45 GPa for the shergottites, Stöffler et al, 1986). These signs include melt pockets, deformation features in the silicate minerals and the presence of maskelynite.…”

Section: High Temperature: Shock Remobilisation Andmentioning

confidence: 98%

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

Bridges

Catling

Saxton

et al. 2001

Space Sciences Series of ISSI

128

201

View full text Add to dashboard Cite

show abstract

“…Additionally, the lack of a remaining melt phase rules out melt-based fO 2 methods. Finally, the fact that many meteorites have experienced high shock pressures is an added complication (e.g., Stöffler et al 1986;Langenhorst et al 1991;Ikeda 1994).…”

Section: Introductionmentioning

confidence: 99%

Expanding the application of the Eu‐oxybarometer to the lherzolitic shergottites and nakhlites: Implications for the oxidation state heterogeneity of the Martian interior

McCanta¹,

Elkins-Tanton²,

Rutherford³

2009

Meteorit & Planetary Scien

View full text Add to dashboard Cite

“…In our work, of which this paper forms part, we focus on the basaltic shergottites. These are relatively fine-grained and consist predominantly of the clinopyroxenes pigeonite and augite, with lesser amounts of maskelynite (diaplectic glass produced from plagioclase during shock), titanomagnetite, ilmenite, whitlockite, and other accessory phases and mesostasis (Smith and Hervig 1979;Stolper and McSween 1979;Stˆffler et al 1986). Their petrogenesis began with the crystallization of homogeneous, Mg-rich pigeonite and augite grains followed by the alignment of the pyroxene grains and the crystallization of Fe-rich pyroxene rims onto the magnesian pigeonite and augite cores.…”

Section: Introductionmentioning

confidence: 99%

Martian xenon components in Shergotty mineral separates: Locations, sources, and trapping mechanisms

Ocker

Gilmour

2004

Meteorit & Planetary Scien

View full text Add to dashboard Cite

show abstract

Shock metamorphism and petrography of the Shergotty achondrite

Cited by 213 publications

References 33 publications

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

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

Expanding the application of the Eu‐oxybarometer to the lherzolitic shergottites and nakhlites: Implications for the oxidation state heterogeneity of the Martian interior

Martian xenon components in Shergotty mineral separates: Locations, sources, and trapping mechanisms

Contact Info

Product

Resources

About