Shergottite

Greenwood JP, Riciputi LR, McSween HY (1997) Sulfide isotopic compositions in shergottites and ALH 84001, and possible implications for life on Mars. Geochim Cosmochim Acta 61 4449 453... 

Martian meteorites ( SNC for shergottite, nakhlite, chassignite) comprise a diverse suite of igneous rocks (McSween, 2004). With only one exception, they are geologically young. Presently, 34 of these meteorites are recognized, most recovered from Antarctica and North African deserts. 

Martian meteorites, viewed in plane polarized light with FOV = 5.4 mm. (a) Zagami basaltic shergottite, composed of pyroxene and plagiodase (white), which has been converted to maskelynite by shock, (b) Lafayette nakhlite, composed mostly of high-calcium pyroxene, (a) from Lauretta and Killgore (2005), with permission. 

Ma (Fig. 9.16). The 40Ar-jyAr ages appear to be considerably older, but are compromised by the presence of trapped 40Ar from the Martian atmosphere and possibly inherited radio-genic Ar as well. In contrast to the mineral (internal) isochrons, whole-rock Rb- Sr and Pb-Pb isochrons for shergottites suggest a much older age of-4.1 Ga (Bouvier et al., 2008). Most workers interpret this age to reflect planetary differentiation that established mantle... 

Borg and Drake (2005) have determined the timing of aqueous alteration events in Martian meteorites from the ages of secondary minerals. Carbonates in ALH 84001 formed at 3.9 Ga, iddingsite in nakhlites formed -630 Myr ago, and salts in shergottites formed sometime after the crystallization of these rocks, 170 Myr ago. 

Ejection ages (sum of cosmic-ray exposure age + terrestrial age) for Martian meteorites. The ages cluster by meteorite type, suggesting that each cluster represents a distinct impact (ejection) event. The only outliers are the EETA 79001 and Dhofar 019 shergottites and ALHA84001. Modified from McSween (2008). 

Ma, and five of six olivine-phyric shergottites were sent on their way to Earth by an impact at 1.2-0.1 Ma. 

Bouvier, A., Blichert-Toft, J., Vervoort, J. D., Gillet, P. and Albarede, F. (2008) The case for old basaltic shergottites. Earth and Planetary Science Letters, 266, 105-124. 

Source Lodders (1998) Shergotty and QUE94201 are basaltic shergottites, ALH 77005 is a lherzolitic shergottite, ALH 84001 is an orthopyroxenite, Nakhla is a nakhlite, and Chassigny is a chassignite. Analytical uncertainties are Is deviations for multiple analyses. 

Although the rocks in Meridiani Planum analyzed by the Opportunity rover are fascinating (see below), they are unusual. Therefore, we will focus on the rocks and soils in Gusev crater analyzed by the Spirit rover, which are spectrally similar to the bulk of the Martian crust. We will compare these compositions with those of Martian meteorites and Bounce Rock in Meridiani, which is similar to shergottites. We will also consider orbital geochemical data obtained by GRS. 

Lodders, K. (1998) A survey of shergottite, nakhlite and chassigny meteorites whole-rock compositions. Meteoritics and Planetary Science, 33, A183-A190. 

Treiman, A. H., Jones, J. H. and Drake, M. J. (1987) Core formation in the shergottite parent body and comparison with the Earth. Journal of Geophysical Research, 92, E627-E632. 

Wiens, R. C., Pepin, R. O. (1988) Laboratory shock emplacement of noble gases, nitrogen, and carbon dioxide into basalt, and implications for trapped gases in shergottite EETA 79001. Geochim. Cosmochim. Acta, 52, 295-307. 

Sheroottites. The shergottite meteorites are a rare class of meteorites which consist essentially of pyroxene and maskelynite. Their composition, petrography, age and gases trapped within the fabric of the meteorite have led to a widespread idea that these meteorites, and the related nakhlites and Chassigny meteorites, were ejected from Mars,... 

Figure 18. Glow curves for two Shergottite meteorites with an explanation for the differences in glow curve shape based on two components whose relative abundance depends on maximum temperature and cooling rates. (Reprinted with permission from Ref. 30. Copyright 1986 Pergamon Press.)...

Gooding, J. L. Muenow, D. W. (1986) Martian volatiles in shergottite EETA 79001 New evidence from oxidized sulfur and sulfur-rich aluminosilicates. Geochim. Cosmochim. Acta, 50, 1049-59. 

McFadden, L. A. (1989) Remote sensing and the Shergottite-Nakhlite-Chassignite meteorite parent body. Bull. Amer. Astronom. Soc., 21, 967. 

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