[meteorite-list] Fred's TAN 057 a CK or a CV Chondrite?

From: Meteoriteshow <meteoriteshow_at_meteoritecentral.com>
Date: Wed Nov 2 05:02:27 2005
Message-ID: <00a001c5df94$84059780$0400a8c0_at_IBM>

Dear Bernd and All,

Many thanks for your help in trying to understand what Tnz057 really is and providing many information about studies that have been
carried out already about CVs and CKs.
I will try my best in order to get more information about this meteorite, from labs that are willing to work on it and of course
will share the results (when available!) with the Meteorite List.
Any other comments & clues are welcome of course, my goal being to find out what we have recovered from the Tanezrouft: a CV4? a
CK4? a CK5?... or anything else??? One of the main interests is to me that it may bring some new information about the
classification of CVs and CKs, causing Scientitsts to face new questions. Isn't it exciting?
I agree that it does not fit completely to the criterias of classification as a CK (the most obvious points to me are the huge CAIs
and sharply defined chondrules that are present in this meteorite...) but it does not fit to the criterias of classification as a CV
as well. O isotopes have not been searched so far, maybe one day?
For all those reasons I really believe that before we get more information about the CK and CV groups, the classification reached by
Bertrand Devouard, Brigitte Zanda and Michele Denise is what had to be provided in the present knowledge that we have. The new
question is also about its metamorphism since UCLA concluded to a CK5... but once again this meteorite is quite heterogeneous (John
Wasson has seen the complete meteorite and various sections) and the partslices that have been used for the study on CK and R
chondrites is quite small and maybe not fully representative... I don't know as I'm not a scientist myself and I simply wonder,
taking the different results the way they come! And once again the fact that quite different conclusions are obtained is very
interesting, for a meteorite that is "anomalous" from its "head down to its toes"! (to mention Bernd's expression).

"May the Force be with Tnz057"!!!
Best regards,

Frederic

----- Original Message -----
From: <bernd.pauli_at_paulinet.de>
To: <Meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, November 02, 2005 12:00 AM
Subject: [meteorite-list] Fred's TAN 057 a CK or a CV Chondrite?


> David Weir kindly wrote:
>
> "The CK-CV group designation has been the subject of some debate, as can
> be seen in the paper by Greenwood et al. (2003):'Are CK Chondrites Really
> a Distinct Group or Just Equilibrated CVs?' "
>
> http://www.lpi.usra.edu/meetings/metsoc2003/pdf/5179.pdf
>
> Hello List,
>
> Just in case you did not download this abstract or did not read it in full:
> It contains three important passages (plus one typo ;-)
>
> 1. Chondrule abundance, or perhaps more correctly, apparent
> chondrule abundance, will also decrease with increasing grade.
>
> I think there are too many chondrules in Fred's TAN 057 to classify it as
> a CK5 - especially the "5" is disturbing... "4" ... OK, ...maybe but "5" ??
>
> 2. The main classification criteria used to define the [CK] group are:
>
> 1) low chondrule to matrix ratio; (-)
> 2) chondrule size intermediate between the CO and CV groups; (+)
> 3) absence of coarse-grained rims around chondrules; (-)
> 4) low abundance of refractory inclusions compared to CO and CV groups; (?)
> 5) low C content; (?)
> 6) refractory lithophile abundances intermediate between CO and CV groups (?)
> 7) O-isotope compositions overlapping those of the CO and CV groups (?)
>
> The "+" says I agree, the "-" says I don't agree, and "?" indicates I don't know with
> regard to Fred's TAN 057 and its classification as a CK chondrite, but who am I to
> disagree with renowned meteoriticists ?!
>
> Anyway, this leads us to:
>
> 3. The authors conclude:
>
> The distinction between CK and CV3 (oxidized subgroup) chondrites may be more
> apparent than real and may reflect varying metamorphic conditions rather than
> more fundamental compositional differences.
>
> Where have we heard that before? Yeah, right! Look here:
>
> NORTON O.R. (1998) RFSII, pp. 196-197: CK Carbonaceous Chondrites
>
> Meteorites that were earlier labeled CV4-5 are now a new class, the CK
> carbonaceous chondrites. There are only thirteen known, most found in
> Antarctica. The only observed fall of a CK chondrite occurred in 1930 in
> Karoonda, South Australia. It is the type specimen for all CK meteorites.
> A large mass, the only CK chondrite available to the collector, was found
> in Maralinga, Australia, in 1974.
>
> All CK chondrite meteorites show various degrees of metamorphism, displaying
> petrologic types 3-6 and some showing shock veins, suggesting an impact history.
> The cut surfaces of these meteorites appear blackened with a sooty substance so
> that the structure is difficult to distinguish*. The blackening agent is fine part-
> icles of magnetite and dark sulfides dispersed in the silicates of the groundmass
> and chondrules(+). Like most other carbonaceous chondrites, CK chondrites are highly
> oxidized, show no metal grains, and have iron-rich olivine and pyroxene. This group
> is similar to CV and CO chondrites but differs in bulk chemistry.
>
> * Is the structure in Fred's TAN 057 so difficult to distinguish ???
> (+) Does anyone see any traces of this black, sooty substance in TAN 057?
> Well, after all, don't forget it is "anomalous" from its "head down to
> its toes"!
>
>
> Cheers and good night,
>
> Bernd
>
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Received on Wed 02 Nov 2005 05:02:20 AM PST