[meteorite-list] Tafassasset classification

From: John Divelbiss <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:54 2004
Message-ID: <001701c26a8b$b48049e0$61145a0c_at_0m824>

Frank,

I understand the description of the primitive achondrite...including the
types you mention.

>From that statement in Nortons book, they are still chondrites...just
overdone a bit. What line did they cross to be called achondrites? And how
does it relate to Tafassasset being also called a CR7?

John

----- Original Message -----
From: "fcressy" <fcressy_at_prodigy.net>
To: "John Divelbiss" <j.divelbiss_at_worldnet.att.net>; "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 10:55 PM
Subject: Re: [meteorite-list] Tafassasset classification


> 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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Received on Wed 02 Oct 2002 11:19:33 PM PDT