[meteorite-list] Primitive Achondrite Question

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Tue, 6 Dec 2011 10:05:34 -0800
Message-ID: <0AB249B2DBB249F99B1BE0A5DD14B5D5_at_igpp.ucla.edu>

I thought I would add my tuppance worth. I don't use the type-7
classification. If a chondrite shows no evidence of melting, I'll classify
it as type-6 no matter how recrystallized it may be -- whether there are
recognizable chondrules or not. If the rock does show evidence of melt,
there are invariably indications that the melt has been impact-generated and
I'll call the rock an impact-melt breccia. If the rock has been essentially
totally melted, I'll call it an impact-melt rock. Almost all of these rocks
can be assigned to a known chondrite group on the basis of olivine Fa, O
isotopes, bulk chemistry, etc. If a rock is a winonaite or acapulcoite, it
can be classified as such. But if we want to understand how these
"primitive achondrite" groups formed (not required for classification
purposes), there are basically two schools of thought. Most researchers
maintain that primitive achondrites are rocks that have been partly melted
by internal heating processes (ala Al-26) and the heating and fractionation
just did not proceed as far as in the case of true achondrites. A minority
of researchers (including me) believe it is more likely that primitive
achondrites are impact-melted chondrites and are thus not that different
than chondrite impact-melt breccias and chondrite impact-melt rocks. As I
said earlier, the origin of these meteorites is not important for their
proper classification, but it can lead to heated debates.
Alan



Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA 90095-1567
phone: 310-825-3202
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html


----- Original Message -----
From: "MexicoDoug" <mexicodoug at aim.com>
To: <raremeteorites at yahoo.com>; <meteorite-list at meteoritecentral.com>
Sent: Tuesday, December 06, 2011 9:31 AM
Subject: Re: [meteorite-list] Primitive Achondrite Question


> Adam wrote:
>
> "NWA 3133 is a CV Primitive Achondrite"
>
> Hi Adam, thanks ... The asteroid belt ought to be called the asteroid zoo!
>
> The question I have on this one, if CV is for certain, would be whether it
> is the result of a collision with a typical CV type, or is it certain that
> it is a fully baked CV (what happened to the possible CAI's - are there
> any, or is the CV possibly just impact regolith?), or, whether some
> innocent CV got hot all by itself.
>
>
> Kinest wishes
> Doug
>
> (Why does my wallet retract down my pocket every time ths stuff comes up!)
>
>
>
>
> -----Original Message-----
> From: Adam Hupe <raremeteorites at yahoo.com>
> To: Adam <meteorite-list at meteoritecentral.com>
> Sent: Tue, Dec 6, 2011 11:47 am
> Subject: Re: [meteorite-list] Primitive Achondrite Question
>
>
> Doug wrote: I can't wait until someone turns up a CV6+. Theoretically,
> there is
> no reason to
> bar the possibility,, or is there...
>
> NWA 3133 is a CV Primitive Achondrite
>
> All of these oxygen isotope compositions
> plot on the CV3 mixing line, suggesting that this achondritic meteorite
> has
> affinities with CV chondrites (Irving et al., 2004).
>
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Received on Tue 06 Dec 2011 01:05:34 PM PST