[meteorite-list] Primitive Achondrite Question

From: Ted Bunch <tbear1_at_meteoritecentral.com>
Date: Mon, 05 Dec 2011 20:00:42 -0700
Message-ID: <CB02D36A.1A59C%tbear1_at_cableone.net>

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 10:00:42 PM PST