[meteorite-list] NWA 2736 - Aubrite or not??

From: David Weir <dgweir_at_meteoritecentral.com>
Date: Sat Feb 25 14:46:18 2006
Message-ID: <4400B406.3000702_at_earthlink.net>

Hey Adam,

If different types of material from a single PB forms a metamorphic
continuum as has been published recently, what are the exact parameters
for these different groupings; e.g., chondrite, metachondrite, primitive
achondrite, achondrite, stony-iron, iron. I have not yet seen the
particulars for where one stops and the other begins, but a continuum is
not given to such deterministic lines in the true nature of things.

An aubrite by most definitions would be associated with the achondrite
(igneously derived) portion of this continuum, but a primitive
achondrite and even a metachondrite could be close enough that it would
take in-depth analyses to distinguish between them, and some labs don't
even recognize all of these metamorphic divisions to begin with. At
least one aubrite is classified as a stony-iron (Mt. Egerton), and one
enstatite achondrite is more like an iron (Horse Creek).

I suppose the classification of NWA 2736 as an aubrite may be acceptable
given the fact that an aubrite is not a term referring to any one
particular PB; e.g. Shallowater is from a unique aubritic PB, and there
are several other ungrouped enstatite-related meteorites such as Itqiy,
Zaklodzie, NWA 1235, and NWA 1839 just to name a few. I think O-isotopic
composition data is needed for all of these enstatite-related rocks, and
of course more samples of such meteorites will hopefully be found in
order to answer some of these PB source questions and to better
distinguish their petrologic history for an accurate classification
assignment.

David
Received on Sat 25 Feb 2006 02:46:14 PM PST