[meteorite-list] Tirhert is official - Met Bulletin Update

From: Galactic Stone & Ironworks <meteoritemike_at_meteoritecentral.com>
Date: Fri, 15 Aug 2014 00:12:57 -0400
Message-ID: <CAKBPJW87-MSfz1FJhijPiniSsKut5uU-KJaTckQy-XusmLpgNA_at_mail.gmail.com>

Hi Bulletin Watchers,

The recent Tirhert eucrite fall is officially approved.

Link : http://www.lpi.usra.edu/meteor/metbull.php?code=60285

Write-up :

Tirhert 28.935?N, 8.905?W
Guelmim-Es-Semara, Morocco
Fell: 2014 Jul 9
Classification: HED achondrite (Eucrite, unbrecciated)

History: (H. Chennaoui Aoudjehane, A. Aaronson, M. Aoudjehane, A.
Bouferra, A. Bouragaa) On Wednesday, 9 July 2014 around 9:30 pm,
residents of Tirhert, Foum El Hisn, Douar Imougadir and nearby
villages in southern Morocco, witnessed an intense fireball moving
horizontally in a NW to SE direction and lasting about 4 s, shortly
followed by multiple sonic booms. The fireball was seen by people from
cities and villages more than 220 km around the fall site near
Tirhert. Immediately following the fireball event the mayor and the
authorities of the area organized a field search with police to check
for possible security problems. The first meteorites were recovered
the following day close to the road between Foum El Hisn and Assa.
Thousands of people moved to the site from surrounding cities and
villages to search, but many soon left because of the difficulties of
searching during the hot 50?C daytime temperatures. The positions of
many of the pieces were recorded from eyewitness testimonials, forming
a roughly 6 ? 3 km strewnfield trending NW to SE. The largest recorded
mass around 1300 g was collected close to Tirhert at the coordinates
listed for this entry. Recovered pieces weighed from 1 to 1300 g, with
an estimated total mass of 8 to 10 kg. Most pieces are covered by a
very shiny, black fusion crust.

Physical characteristics: Glassy black fusion crust with translucent
patches revealing plagioclase grains beneath. Broken surface shows
mm-size white plagioclase and honey brown pyroxene grains, also some
scattered mm-size opaque grains. Friable.

Petrography: (C. Agee and N. Muttik, UNM) Microprobe examination of a
polished mount shows texturally equilibrated pyroxene and plagioclase,
granoblastic to poikilitic with many triple junctions. Pyroxenes show
exsolution lamellae. Plagioclase and pyroxene grain size up to ~1-2
mm. Silica, ilmenite, chromite, troilite, and Fe-metal (low Ni)
present. Fusion crust ~50-100 ?m thick, vesicles up to 20 ?m present,
glassy with compositional gradients and swirls. (A. Irving, UWS)
Optical petrographic examination of a thin section of a different
specimen shows that it is composed of subequal amounts of pyroxene and
twinned plagioclase with accessory opaque oxides and minor troilite.
The overall texture is equigranular, but plagioclase occurs as
aggregates of multiple subgrains, and some plagioclase contains
clusters of tiny pyroxene inclusions. Magnetic susceptibility: Log ? =
2.53

Geochemistry: (C. Agee and N. Muttik, UNM) Low-Ca pyroxene
Fs53.6?4.8Wo9.3?5.9, Fe/Mn=32?1, n=29; augite Fs30.3?1.3Wo39.2?1.0,
Fe/Mn=33?2, n=15; plagioclase An89.9?0.9Ab9.6?0.9Or0.4?0.1, n=7.
Fusion crust, proxy for bulk composition (mean value from EMPA with 20
?m beam) SiO2=48.25?0.99, TiO2=0.54?0.17, Al2O3=12.15?3.48,
Cr2O3=0.22?0.04, FeO=19.32?2.82, MnO=0.58?0.09, MgO=7.72?1.21,
CaO=10.09?1.14, Na2O=0.44?0.12 (all wt%), Mg#=41.6?0.5, n=23. Oxygen
isotopes (Karen Ziegler, UNM): six acid-washed aliquots of bulk sample
(1.3, 1.3, 2.4, 1.6, 1.7, 1.4 mg) analyzed by laser fluorination gave,
respectively, ?17O = 1.524, 1.474, 1.106, 1.451, 1.286, 1.314, ?18O =
3.415, 3.233, 2.588, 3.268, 2.866, 2.961, ?17O = -0.279, -0.233,
-0.260, -0.275, -0.227, -0.249 (linearized, all permil).

Classification: Achondrite (unbrecciated gabbroic eucrite). Highly
equilibrated with clear compositional separation of the low and high
calcium pyroxenes consistent with type 6 eucrites (Takeda and Graham,
1991).

Specimens: 14 g at FSAC (0.6 g provided by A. Bouferra, 13.4 g
provided by Aaronson); 41.4 g including a probe mount at UNM; 9 g
including one polished thin section at UWB; 64.4 g in total for type
specimens, and 72 g at ASU. Main masses are held by Aaronson and
various private collectors. A. Habibi provided 25 g to UNM.

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Received on Fri 15 Aug 2014 12:12:57 AM PDT