[meteorite-list] Primitive Achondrite Question

From: John Lutzon <jl_at_meteoritecentral.com>
Date: Mon, 5 Dec 2011 22:45:30 -0500
Message-ID: <523CB73911D14D14ACD6756675A9C719_at_Home>

Thank you Jeff,

Believe it or not, you enlightened my small small knowledge about this.

Further sales of "metachondrite" terminology is hereby suspended until Ted's
posterier heals.

Sorry, just had to, John.

----- Original Message -----
From: "Ted Bunch" <tbear1 at cableone.net>
To: "Jeff Grossman" <jngrossman at gmail.com>;
<meteorite-list at meteoritecentral.com>
Sent: Monday, December 05, 2011 10:00 PM
Subject: Re: [meteorite-list] Primitive Achondrite Question


> Well stated Jeff and I agree! Thank you. There is the thing about
> "metachondrite" terminology, but we shall leave this "dead horse" alone
> for
> the time being.
>
> Two of these unremitting classification issues in 3 days is much too much
> for me in one week, especially when my butt is tied to both of them.
>
> Ted
>
>
> On 12/5/11 7:02 PM, "Jeff Grossman" <jngrossman at gmail.com> wrote:
>
>> Type 7 is considered by most of those who use it to represent the
>> highest degree of thermal metamorphism that a chondrite can experience
>> without melting. As implied in that first sentence, some petrologists
>> don't distinguish these from type 6. The term "primitive achondrite" is
>> widely taken to be the next stage: you make them when a chondrite
>> partially melts, and the process of crystal-melt separation begins. The
>> "primitive" part says that the bulk composition is still fairly close to
>> chondritic. But these definitions are not used by everybody, and you
>> will get arguments about them.
>>
>> Clearly, the "LL" part of an LL7 classification for NWA 3100 is
>> unlikely. O isotopes are below the terrestrial fractionation line,
>> which basically rules it out. So it is not an LL7. Bunch has shown
>> that the O isotopes are closer to CR chondrites.
>>
>> The hard part is the type 7 vs. primitive achondrite distinction. Bunch
>> et al.'s 2005 and 2008 LPSC abstracts do not report anything in NWA 3100
>> that I take as evidence of melting or differentiation. So I don't see
>> any reason to call these primitive achondrites, at least not based on
>> these findings. I think the Bunch et al.'s conclusion that NWA 3100 is
>> a CR6 is the best we have right now, but I think you still have to think
>> of this as preliminary. Ted can correct me, but I think it was actually
>> the nomcom that pushed for calling this a PAC, amid controversy on the
>> committee.
>>
>> Jeff
>>
>>
>> On 12/5/2011 8:23 PM, Ruben Garcia wrote:
>>> Hi all,
>>>
>>> I just bought a smallish collection and several of the slices that
>>> came with are NWA 3100. Mike Farmer's card was included and lists NWA
>>> 3100 as an LL7. The Met-Bul calls NWA 3100 a Primitive achondrite -
>>> not an LL7.
>>>
>>> My question is this,
>>>
>>> Does LL7 denote a particular Primitive achondrite? If so which one? If
>>> not then what type is this?
>>>
>>> BTW - I think Ted Bunch did the classification
>>>
>>
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Received on Mon 05 Dec 2011 10:45:30 PM PST