[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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