[meteorite-list] NEW Plutonic Angrite - NWA 4590 "Tamassint"

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Thu, 12 Apr 2007 09:58:49 -0700 (PDT)
Message-ID: <765910.66145.qm_at_web50901.mail.re2.yahoo.com>

Greg,

In light of recent comments about new rocks getting
scant discussion, I will make some input on this one.

I have to spend some time to pore/paw? over the Lunar
and Planetary Science stuff in detail but it it seems
interesting at a glance through. The great diversity
of minerals in this rock and the fact that there are
seemingly angrites of many different types and form
make this new rock a great discovery.

I used to think they were simply melted CVs but the
structure of this seems to throw this into question.
Probably wrong but it's very interesting. Can't wait
until the messenger probe finally does it's stuff and
starts sending back answers on Mercury. How
embarrasing that here we are 46 years to the day since
Gagarin's flight and we still know very little about
one of our nearest neighbours.

I somehow doubt that Mercury is the APB. Even with the
bizaar theories of how mercury formed, these rocks
should match the FeO characteristics we have for
Mercury, surely? They are unlikely to have spent 4
billion years finding their way to earth.

Amazing stuff, non-the-less. I'd love to be wrong. I
can't help think they have an inkling of suspicion
when they even have a name for them. Hermean
meteorites? How interesting. I've never heard the term
used before...but it has a certain ring to it.

Rob McC

--- Greg Hupe <gmhupe at tampabay.rr.com> wrote:

> Dear List Members,
>
> Yesterday I announced my new NomCom Approved Angrite
> which has a different
> lithology than the other known angrites. It is NWA
> 4590 "Tamassint" and is a
> Plutonic Angrite. For those who do not want to go to
> eBay to look up the
> complete information, here is the approved
> classification and a link to an
> abstract. This new angrite is gorgeous!!
>
> Link to Lunar and Planetary Science Conference
> abstract on NWA 4590:
>
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1522.pdf
>
> Here is the NomCom Approved classification submitted
> to the Meteoritical
> Bulletin:
>
>
==================================================================================
>
> Northwest Africa 4590
> Morocco/Algeria
>
> Find: June 2006
>
> Achondrite (angrite)
>
>
>
> History: Scattered fragments from a small stone
> which appears to have
> shattered upon landing recently were found covering
> an area of ~40 m2 in the
> Morocco-Algeria border zone, 21 km SSW of Tamassint
> oasis and 18 km S of
> Agoult, Morocco. Greg Hup? purchased all the
> recovered material in June
> 2006 from a Moroccan dealer in Tagounite. He then
> traveled to Morocco and
> was shown the location by the original finder, and
> measured GPS coordinates.
> Physical characteristics: Fragments totaling 212.8 g
> of a very friable
> specimen composed of coarse yellow-green, black and
> white grains; very fresh
> with preserved shiny, black fusion crust on some
> pieces, and minor pale
> orange terrestrial weathering coatings on some
> broken surfaces.
>
> Petrography: (A. Irving and S. Kuehner, UWS) Coarse
> grained (mostly 0.6-1.6
> mm, but some olivine grains up to 12 mm) with a
> plutonic igneous (cumulate)
> texture, and composed of clinopyroxene (33%, with
> rare pigeonite exsolution
> lamellae), pure anorthite (28%), olivine (14 %, with
> prominent subparallel
> exsolution lamellae (10-50 microns wide) of
> kirschsteinite), kirschsteinite
> (5%, with thin exsolution lamellae of olivine),
> ulv?spinel (18%), and
> accessory glass, troilite merrillite, Ca
> silicophosphate and metal
> (kamacite). Some anorthite occurs as subhedral
> grains partially enclosed
> within large ulv?spinel grains, but most occurs as
> intercumulus aggregates.
> Clinopyroxene is strongly zoned with paler colored,
> corroded cores
> surrounded by darker purple-brown mantles and
> distinct rims. Thin (5-50
> microns wide) discontinuous, curvilinear zones of
> glass are present on some
> grain boundaries (notably those between anorthite
> and ulv?spinel, but also
> around and cutting across troilite grains), and are
> associated with
> secondary clinopyroxene, kirschsteinite, olivine,
> anorthite and troilite
> grains; these films of glass+daughter minerals
> truncate kirschteinite
> exsolution lamellae in adjacent olivine. This
> angrite is unlike other known
> specimens, having neither a fine grained quench or
> ophitic/intesertal
> basaltic texture nor a coarse metamorphic texture
> (Irving et al., 2006;
> Kuehner et al., 2007).
>
> Geochemistry: Clinopyroxene (Fs20.8-33.3Wo53-54.9,
> FeO/MnO = 85-278),
> olivine host (Fa72.6-74.7Ln3.5-3.6, FeO/MnO =
> 70-87), kirschsteinite
> lamellae (Fa44.7-45.4Ln46-47.2, FeO/MnO = 73-82),
> kirschsteinite host
> (Fa46.6-47.5Ln43.6-45.5, FeO/MnO = 63-68), olivine
> lamellae
> (Fa75-76.7Ln2.7-2.8, FeO/MnO = 71-74). Oxygen
> Isotopes (D. Rumble, CIW):
> analyses of two aliquots of acid-washed mineral
> fragments by laser
> fluorination gave, respectively, d18O = 3.845,
> 3.881; d17O = 1.927, 1.967;
> D17O = 0.0956, 0.0745 per mil.
>
> Classification: Achondrite (angrite).
>
> Specimens: A total of 20.01 g of sample, two
> polished thin sections and two
> polished mounts are on deposit at UWS, and 4 g at
> Harper. Mr. G. M. Hup?
> holds the main mass.
>
>
>
> Irving, A. J., Kuehner, S. M., Rumble, D. and Hup?,
> G. M. (2006) A fresh
> plutonic igneous angrite containing grain boundary
> glass from Tamassint,
> Northwest Africa. EOS, Trans. Amer. Geophys. Union
> 87, Fall Meet. Suppl.,
> Abstract P51E-1245.
>
>
>
> Kuehner, S. M. and Irving, A. J. (2007) Grain
> boundary glasses in the
> Tamassint plutonic angrite: Evidence for rapid
> decompressive partial melting
> and cooling on Mercury? Lunar Planet. Sci. XXXVIII,
> Abstract #1522.
>
>
==================================================================================
>
>
>
> Here are some links to photographs of NWA 4590
> "Tamassint":
>
> Group image of NWA 4590 "Tamassint":
>
> http://www.lunarrock.com/nwa4590/nwa4590group.jpg
>
>
>
> Microscopic image of matrix at 12x magnification::
>
> http://www.lunarrock.com/nwa4590/nwa4590micro.jpg
>
>
>
> Close-up image of fusion crust at 10x magnification:
>
> http://www.lunarrock.com/nwa4590/nwa4590crust.jpg
>
>
>
> Optical thin section image in cross-polarized light
> showing kirschsteinite
> and olivine (blue to green), clinopyroxene
> (yellow-brown to dark grey),
> intercumulus anorthite (white to pale grey) and
> ulv?spinel (black). Width of
> field is 2cm:
>
> http://www.lunarrock.com/nwa4590/nwa4590xpl.jpg
>
>
>
> Thank you for looking and enjoy!
>
>
>
> Best regards,
> Greg
>
>
> ====================
> Greg Hupe
> The Hupe Collection
> NaturesVault (eBay)
> gmhupe at tampabay.rr.com
> www.LunarRock.com
> IMCA 3163
> ====================
>
>
>
> ______________________________________________
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> Meteorite-list at meteoritecentral.com
>
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>



       
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Received on Thu 12 Apr 2007 12:58:49 PM PDT