[meteorite-list] NWA 5400 two research papers, great read up on this new meteorite find!

From: Shawn Alan <photophlow_at_meteoritecentral.com>
Date: Thu, 10 Jun 2010 22:16:39 -0700 (PDT)
Message-ID: <421592.76487.qm_at_web35402.mail.mud.yahoo.com>

Hello Greg and Listers,

First off, congrats Greg on the NWA 5400 meteorite. It will be exciting to here about?the new research that is being done on this unique find. So far I was able to find two research papers on NWA 5400.
?
Up first is:

ULTRAMAFIC ACHONDRITE NORTHWEST AFRICA 5400: A UNIQUE BRACHINITE-LIKE
METEORITE WITH TERRESTRIAL OXYGEN ISOTOPIC COMPOSITION.

A. J. Irving1, D. Rumble, III2,S. M. Kuehner1, M. Gellissen3 and G. M. Hup? 1Dept. of Earth & Space Sciences, University of Washington, Seattle,WA 98195 (irving at ess.washington.edu), 2Geophysical Laboratory, Carnegie Institution, Washington, DC 20015,3Inst. f?r Geologie, Mineralogie und Geophysik, Ruhr-Universit?t Bochum, Germany.
?
Published in
40th Lunar and Planetary Science Conference (2009)

Abtracts taken from the research paper:

A metal-bearing ultramafic achondrite with
petrological similarities to brachinites has been found
to have an oxygen isotopic composition on the Terrestrial
Fractionation Line (TFL). The only other types of
meteorites with this characteristic are the majority of
lunar meteorites and the various enstatite-rich meteorites
(both chondrites and achondrites)....

Petrography:

Northwest Africa 5400 is a single
dense, dark brown, rounded stone (4818 grams) about
half covered with weathered fusion crust and exhibiting
several narrow fractures...

Formation Age and Radiogenic Isotopic Studies:
We have no specific data constraining the formation
age of NWA 5400, but its strong textural and mineralogical
similarities to brachinites suggest that it may be
very ancient....

Discussion:

The provenance of NWA 5400 is difficult
to establish with certainty. We exclude the possibility
of any relationship to aubrites and other enstatite
achondrites based upon the very different mineralogy,
and the inference that NWA 5400 formed under
more oxidizing conditions than aubrites....

Thus we are left with the possibility that NWA
5400 could be an ancient terrene meteorite, or else a
sample from a different, differentiated Earth-like body.
The well-known overlap in oxygen isotopic compositions
for lunar and terrestrial samples provides strong
support for the giant impact hypothesis for the origin of
the Moon [4]...

Here is the link to the whole research paper:
http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2332.pdf

Here is the second research paper I found which this one was published in 2010.

CONSTRAINTS ON THE FORMATION AGE, HIGHLY SIDEROPHILE ELEMENT BUDGET AND NOBLE GAS ISOTOPE COMPOSITIONS OF NORTHWEST AFRICA 5400: AN ULTRAMAFIC ACHONDRITE WITH TERRESTRIAL ISOTOPIC CHARACTERISTICS.

A. Shukolyukov1, G. Lugmair1, J. M. D. Day2, R. J. Walker2, D. Rumble, III3, D. Nakashima4, K. Nagao5 and A. J. Irving6 1Scripps Inst. of Ocean-ography, University of California, San Diego, La Jolla, CA 92093 (AShukolyukov at ucsd.edu), 2Dept. of Geology, University of Maryland, College Park, MD 20742 3Carnegie Institution, Washington, DC 20015, 4Dept. of Geology & Geophysics, University of Wisconsin, Madison, WI 53706, 5Lab. for Earthquake Chemistry, University of To-kyo, Japan, 6Dept. of Earth & Space Sciences, University of Washington, Seattle, WA 98195.

Published in
41st Lunar and Planetary Science Conference (2010)

Abstracts from the research paper:

Introduction:

Northwest Africa 5400 is a brachinite-like achondrite meteorite that is remarkable for having an oxygen isotopic composition indistin-guishable from that of the Earth and Moon [1]....

Discussion: Although the chromium isotope results do not provide more than a maximum formation age for NWA 5400, they do show that this specimen is significantly younger than brachinites like Brachina [10]. Discrimination from brachinites is also clear on the basis of oxygen isotopic composition [11]. This, together with the presence of abundant radiogenic 129Xe, leaves us with the conclusion at this stage of our studies that NWA 5400 appears to be a moderately ancient ultramafic achondrite with terrestrial oxygen and 54Cr isotopic compositions. These observations provide permissible evidence consistent with NWA 5400 representing a terrene-related meteorite [1].

However, the elevated abundances of highly sidero-phile elements imply limited metal-silicate fractionation, which might not be expected in a parent body that had already undergone significant core formation. The necessity for storage over the last 4.5 Ga, and more recent re-capture, also may pose difficulties for a proto-terrestrial origin, as does the high 53Cr/52Cr ratio. Alternatively, NWA 5400 may represent the ultramafic portion of an asteroidal parent body that witnessed similar processing to brachinites, but that evolved more slowly (larger?) and originated from a compositionally distinct reservoir, yet one with similarities to the planetary feeding zones of the Earth-Moon system. Further chemical and multi-isotopic analyses are in progress to elucidate the origin and significance of NWA 5400.

Here is a link to the full research paper:
http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1492.pdf

I am very intrested to see what the new research will tell about NWA 5400 and its role in meteorotic science and links to differentiated Earth-like bodies.

Shawn Alan
IMCA 1633
eBaystore
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Received on Fri 11 Jun 2010 01:16:39 AM PDT