[meteorite-list] Shergotty a eucrite ... not: Then and Now

[Gerald Flaherty]

Bernd and List, # 5 is definitely a NEW item and well worth a bonus point. 
Thanks for the update Bernd.
Jerry Flaherty
----- Original Message ----- 
From: <bernd.pauli at paulinet.de>
To: <Meteorite-list at meteoritecentral.com>
Sent: Friday, June 01, 2007 2:25 PM
Subject: [meteorite-list] Shergotty a eucrite ... not: Then and Now


> Hello List,
>
> We all know that the acronym SNC stands for the three "typical" samples of 
> the group:
> Shergotty, Nakhla, and Chassigny. But 135 years ago, G. Tschermak was 
> still unaware
> of the exotic nature of these meteorites and grouped them with the 
> eucrites. In 1872,
> he wrote: "Shergotty, which I described several years ago, should also be 
> included with
> the eucrites. It is a conspicuously granular rock consisting essentially 
> of dull yellow-gray
> grains and prisms, which were found to be augite, and water-clear glassy 
> grains and laths.
> The latter resemble no known mineral; I named this material maskelynite."
>
> The SNC's must have come from a different parent body - different from 
> Earth, from our Moon,
> and from the parent body or bodies of the HED suite. This is reflected in 
> the displacement of
> their oxygen isotopes when plotted in a diagram (see O.R. Norton's 
> Encyclopedia of Meteorites,
> p. 157, Fig. 8,15). Another telling feature of the SNC group is their 
> young crystallization ages
> - in other words they must have come from a celestial neighbor where 
> volcanic activity was an
> ongoing process not too long ago.
>
> According to Susanne Schwenzer et al., the following observations are
> considered highly indicative of a Martian origin of the SNC meteorites:
>
> 1. SNC meteorites belong to one group, as proven by many chemical and 
> isotopic
> investigations, pointing to a common parent body.
>
> 2. All SNC meteorites are differentiated magmatic rocks, with some of them 
> showing
> volcanic textures.
>
> 3. The young crystallization ages of 1.3 Gyr, requiring a parent body that 
> still shows
> igneous activity at such a late time in solar system history.
>
> 4. Direct evidence from Viking 1, when the concentrations and compositions 
> of noble gases
> in the Martian atmosphere were measured and compared to those found in SNC 
> meteorites
> in our collections.
>
> 5. The rovers Spirit and Opportunity found rocks on Mars with chemical 
> signatures identical
> to those of some of the Martian meteorites in our collections (Bounce 
> Rock, for example, has
> geochemical characteristics, such as the Fe/Mg ratio, consistent with that 
> of shergottites).
>
> Reference:
>
> Schwenzer S. et al. (2007) Noble gases in mineral separates from three 
> shergottites:
> Shergotty, Zagami, and EETA79001 (MAPS 42-3, pp. 387-412, Introduction).
> --------------------
>
> Best wishes,
>
> Bernd
>
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