[meteorite-list] new terminology for Vestan meteorites

From: Impactika at aol.com <Impactika_at_meteoritecentral.com>
Date: Thu, 7 Apr 2011 14:57:59 EDT
Message-ID: <4f700.2930958b.3acf6337_at_aol.com>

On behalf of Dr. Tony Irving who occasionally reads the MetList archives:
Anne M. Black
_http://www.impactika.com/_ (http://www.impactika.com/)
_IMPACTIKA at aol.com_ (mailto:IMPACTIKA at aol.com)
President, I.M.C.A. Inc.
_http://www.imca.cc/_ (http://www.imca.cc/)
 
 
In a message dated 4/7/2011 8:23:40 AM Mountain Daylight Time,
irving at ess.washington.edu writes:

I noticed the interest on the list about the wider variety of rock types
among HED meteorites. In fact a new terminology proposed in a paper
last year has been adopted by the NomCom, wherein all of the rocks
previously called olivine diogenites as well as the Vestan dunites are
called diogenites. Under this base name there is a wide range in the
relative amounts of orthopyroxene and olivine (from zero olivine to over
90% olivine). By adopting established names for terrestrial peridotites
as qualifying adjectives, the new names are as follows:

"Regular" diogenite (with up to 10 volume% olivine) = orthopyroxenitic
diogenite

"Olivine diogenite" (with >40 volume% olivine) = harzburgitic diogenite

Olivine-rich Vestan rocks (with >90 volume% olivine) = dunitic diogenite

By analogy with established terrestrial nomenclature, there also should be
a category for specimens containing between 10 and 40 volume% olivine (so
far only one is known), and that would be olivine-orthopyroxenitic
diogenite.

I realize that these names are a bit cumbersome, but they do make sense.
In addition, diogenites with <90 volume% olivine can contain up to 10
vol.% plagioclase, and still be called diogenites.

Another effect of this nomenclature is that the acronym HEDOD (which we
have used) is unnecessary, and so we can go back to calling the suite of
(evidently) Vestan rocks by the traditional HED acronym.

Actually there are at least three other dunitic diogenites: MIL 03443, NWA
5784 and NWA 5968. The first that Ted Bunch and I knew about the new
terminology was when we submitted the classifications for NWA 5784 and NWA
5968, and were told (to our inital amazement) that they would be approved
as diogenites. We presented our work on these specimens last summer at
the MetSoc meeting in NYC:
http://www.lpi.usra.edu/meetings/metsoc2010/pdf/5315.pdf

I am not a list member but I do check the archives periodically. Please
feel free to share any of this with both IMCA and List members.

Best regards,

Tony
Received on Thu 07 Apr 2011 02:57:59 PM PDT