[meteorite-list] Primitive Achondrite Question

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Tue, 6 Dec 2011 13:26:05 -0800
Message-ID: <53C2A861CCDB4203A253819DD7B3A516_at_igpp.ucla.edu>

    It seems that the primary classification of iron meteorites is best done
by compositon, i.e., comparing the Ga-Ge, Ir-Ni, Cu-As ratios etc. of
different irons on diagrams and look for relationships. This is what gives
rise to the IAB, IVA, IIIAB groups etc. Most groups are called "magmatic"
because their trends on such diagrams are consistent with fractional
crystallization inside a molten core. A few groups (IAB-IIICD and IIE) are
called "non-magmatic" because their trends are inconsistent with fractional
crystallization. Some researchers believe that all of these irons (magmatic
and non-magmatic alike) are derived from the cores of differentiated
asteroids or from large melt pods inside melted asteroids. Other
researchers (particularly John Wasson) think that the non-magmatic irons are
impact melts formed at the surfaces of chondritic bodies. I agree with
Wasson. Many of the non-magmatic irons have silicate inclusions that are
roughly chondritic in bulk composition and contain "planetary-type" rare
gases as do chondrites.
        In any case, the structures of irons (coarse octahedrite, ataxite,
hexahedrite) are secondary properties influenced by cooling rate and
nucleation; the primary properties are the bulk chemical and isotopic
compositions of the irons.
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: <cdtucson at cox.net>
To: <raremeteorites at yahoo.com>; "Alan Rubin" <aerubin at ucla.edu>;
<meteorite-list at meteoritecentral.com>
Sent: Tuesday, December 06, 2011 1:07 PM
Subject: Re: [meteorite-list] Primitive Achondrite Question


> Alan,
> I agree with Darryl. Very fascinating conversation.
> Speaking of tidy categories.
> How do you feel about the following suggested case for replacing the
> current obsolete metallurgy system for classifying Iron meteorites? see
> link;
>
> http://meteormetals.com/Case_for_New_Meteorite_Metallurgy.pdf
>
> Cheers,
> Carl
> meteoritemax
>
> ---- Alan Rubin <aerubin at ucla.edu> wrote:
>> Classifications are just a way of making sense of the world by putting
>> diverse objects into tidy categories. Even though real-world objects
>> don't
>> always fit (is light a wave or a particle?), good classifications last
>> longer than interpretations. For example, the Linnaeus classification
>> system was developed from a creationist perspective but is used today by
>> every evolutionary biologist. So, to answer your question,
>> classification
>> is an end in itself -- it certainly helps in understanding relationships
>> among diverse objects. But classification is not the only end --
>> understanding the origins of objects is also rather important, but
>> because
>> we have incomplete knowledge of objects, our interpretations are always
>> tentative, subject to revision when new data are acquired.
>> Classifications
>> should be longer-lasting.
>> As an aside, if you are interested in bad classification systems for
>> meteorites, look at George Merrill's "The Story of Meteorites" from 1929:
>> There are andrites, eukrites, shergottites, howardites, bustites,
>> chassignites, chladnites, amphoterites, howarditic chondrites, white
>> chondrites, intermediate chondrites, gray chondrites, black chondrites,
>> spherulitic chondrites, crystalline chondrites, carbonaceous chondrites,
>> orvinites, tadjerites, ureilites, lodranies, grahamite mesosiderites,
>> siderophyrs, and more. Some of the groups are still recogniable, others
>> less so. The problem was that the knowledge base at the time was
>> insufficient to distinguish essential from secondary properties. Similar
>> problems arose among classification schemes of living creatures and
>> especially fossils.
>>
>> 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 04:26:05 PM PST