[meteorite-list] Tafassasset classification

From: fcressy <fcressy_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:54 2004
Message-ID: <001901c26a88$6cc45d60$84119e40_at_pavilion>

Hello John and all,
Regarding your primative achondrite question, Norton's "Encyclopedia of
Meteorites" has a page dedicated to the subject (P. 165). He states that
"primative achondrites have achondrite textures but still retain something
of their chondritic composition." and that they "are transitional between"
chondrites and achondrites. As examples of primative achondrites, he uses
acapulcoites, lodranites and winonaites.
Hope this helps.
Frank




----- Original Message -----
From: John Divelbiss <j.divelbiss_at_worldnet.att.net>
To: Norbert Classen <trifid_at_timewarp.de>; Bernd Pauli HD
<bernd.pauli_at_lehrer.uni-karlsruhe.de>; Svend Buhl <svendbuhl@web.de>
Cc: <meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, October 02, 2002 5:05 PM
Subject: Re: [meteorite-list] Tafassasset classification


> 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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>
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Received on Wed 02 Oct 2002 10:55:57 PM PDT