AW: [meteorite-list] Tafassasset classification

From: Norbert Classen <trifid_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:54 2004
Message-ID: <NCBBKMGDKLMGIBALJOFCAEMICOAA.trifid_at_timewarp.de>

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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Received on Wed 02 Oct 2002 02:30:26 PM PDT