[meteorite-list] Tafassasset classification

From: John Divelbiss <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:54 2004
Message-ID: <000501c26a70$a6740d20$19155a0c_at_0m824>

Hello All,

Primitive is primitive! Help me to understand the differences please.

Is the argument about where the line(s) should be drawn between a chondrite
(that is "really" differentiated...like a 7) versus a primitive achondrite
(that is not quite differentiated enough to be called a achondrite)?

Is there really a 7 category and why?

Are primitive achondrites now considered differentiated enough to be
distinguished from a highly changed chondrite? small versus coarse grains in
matrix?

How is this line drawn? mineral makeup, level of glass, age, grain
size/changes, etc. ?

Lots of questions with this story.

Alain would have something to say about all this. Ann Black, is there a
position written from his corner?


John

----- Original Message -----
From: "Norbert Classen" <trifid_at_timewarp.de>
To: "Bernd Pauli HD" <bernd.pauli_at_lehrer.uni-karlsruhe.de>; "Svend Buhl"
<svendbuhl_at_web.de>
Cc: <meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, October 02, 2002 2:30 PM
Subject: AW: [meteorite-list] Tafassasset classification


> Hello Bernd, Svend, Anne, and List,
>
> I discussed this subject several times with my old friend Dr. Otto,
> the German researcher who did the original analysis on Tafassasset
> (Freiburg), a stone that was originally submitted to the NomCom.
> as Tenere 001, a new ungrouped primitive achondrite similar to
> Divnoe, and the brachinites. He was more than suprised that the
> paired Tafassasset (Paris) has been submitted as an equilibrated
> CR chondrite.
>
> He gave me several reasons for his original classification of Taf-
> Frei as a primitive achondrite, but I can't remember them all right
> now (you know, I don't have a degree in mineralogy, petrology, and/
> or cosmochemistry). But I remember his central argument: primitive
> achondrites show a more or less completely recrystallized matrix
> that looks entirely different from even highly equilibrated chondrites.
> He showed me several thin sections of various PACs, and equilibrated
> chondrites, and in fact, Tafassasset closely resembles other primitive
> achondrites, such as Divnoe, Reid 027, and Zag (b). No equilibrated
> chondrite has such a coarse grained matrix, which is a typical sign
> for recrystallization (if I got Dr. Otto right).
>
> There were other points in Dr. Otto's argumentation that convinced
> me of his point of view, and his view is obviously backed up by the
> research that Dr. Zipfel et al performed on Tafassasset, more recently.
> Obviously, there is some resistance to accept the fact that this nice
> meteorite is no extraordinary CR - something that has to do with
> the self importance of certain scientists that made extraordinary
> claims, but failed to provide extraordinary proofs.
>
> Just my two Tafs,
> Norbert
>
>
> > -----Original Message-----
> >
> > Svend wrote:
> >
> > > J. Zipfel from the MPI in Mainz says that refractory lithophiles
> > > fractionated compared to a typical CR composition is leading to
> > > a possible classification as primitive achondrite. Does anybody
> > > know about a final classification yet?
> >
> >
> > Hello Anne, Svend and List,
> >
> > In the Abstract issue of MAPS (vol. 37-7, July 2002, p. A155),
> > Jutta Zipfel et al. published an abstract re: Tafassasset. In the
> > discussion part, the authors state:
> >
> > The figure illustrates that both samples have compositions clearly
> > fractionated from CI and other chondrite groups. Tafassasset has AI/Mg
> > and Mn/Mg ratios similar to other primitve achondrites, indicating
> > incipient partial melting involving mobilization of SiO2 (+/- A1203,
> > CaO, etc.) -, P205- and S-rich melts. Although the bulk compositions
> > are heterogeneous, characteristic element signatures (e.g., low Zn,
> > Mn/Mg,depletion in refractory lithophile elements) e x c l u d e
> > a relationship to CR chondrites and support pairing of Taf-Pa and
> > Taf-Frei*.
> >
> > * Taf-Pa is the Paris material - Taf-Frei the Freiburg material
> >
> >
> > Cheers,
> >
> > Bernd
> >
> > ______________________________________________
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> >
>
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Received on Wed 02 Oct 2002 08:05:55 PM PDT