[meteorite-list] Primitive Achondrite Question

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Tue, 6 Dec 2011 13:30:13 -0500 (EST)
Message-ID: <8CE825C3A25C7DC-1CE0-13CC9_at_webmail-m043.sysops.aol.com>

Dr. Rubin wrote:

"the origin of these meteorites is not important for their proper
classification, but it can lead to heated debates."

*Heated debates* - Pun intended or was it an unintended bonus?!

Thanks for your perspective on classification. I think you are kindly
answering this question but holding back on the philosophical question
- Is it the classification that is the end in itself; or does the
classification exist mainly to make sense out of the origin of these
species? Dynamical/Population vs. 'Geo'logical?

Kindest wishes
Doug
(in a perpetual minority myself)



-----Original Message-----
From: Alan Rubin <aerubin at ucla.edu>
To: raremeteorites <raremeteorites at yahoo.com>; meteorite-list
<meteorite-list at meteoritecentral.com>
Sent: Tue, Dec 6, 2011 1:05 pm
Subject: Re: [meteorite-list] Primitive Achondrite Question


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 01:30:13 PM PST