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Re: Tatahouine
Varricchio, Louis wrote:
>
> Also on the subject of meteorite info--
>
> Can anyone please supply me with technical details about the Tautouine
> (sp.?) diogenite and Toluca iron? Thanks!
>
> Lou Varricchio
Tatahouine Meteorite
Basic Information
Location : Foum Tatahouine, Tunisia, Latitude 32 degrees 56 minutes
North, Longitude 10 degrees 27 minutes East.
Composition Type : Achondrite, Ca - poor, Diogenite -- ADIO.
Time of Fall : 1931, June 27, 1931, at 01:30 hours
1. Introduction : the story of the fireball and meteorite.
Early in the morning of June 27, 1931 a fireball exploded about 2 1/2
mi. NE of the village of Foum Tatahouine, Tunisia spraying small
fragments over a 500 meter area. Most of the fragments recovered
weighed less than 10 grams each. Explosion prior to hitting ground
resulted in only small fragments of this rare Diogenite. Most of the 12
kg found reside in the museums in Paris, Chicago and India. Diogenites
are extremely rare This is a very rare and unique meteorite.The visual
appearance of this Diogenite variety of Achondrite is: light olive green
color, translucent-opaque, criss-crossed by small black veinlets, and/or
spotted with inclusions displaying a green cristaline structure.
2. Igneous Fractionation and Subsolidus Equilibration of Diogenite
Meteorites
Diogenites are coarse-grained orthopyroxenite breccias of remarkably
uniform major element composition. Most diogenites contain homogeneous
pyroxene fragments up to 5 cm across of Wo(sub)2En(sub)74Fs(sub)24
composition. Common minor constituents are chromite, olivine, troilite,
and metal, while silica, plagioclase, merrillite, and diopside are trace
phases. Diogenites are
generally believed to be cumulates from the eucrite parent body,
although their relationship with eucrites remains obscure. It has been
suggested that some diogenites are residues after partial melting. I
have performed EMPA and INAA for major, minor, and trace elements on
most diogenites, concentrating on coarse-grained mineral and lithic
clasts in order to elucidate their igneous formation and subsequent
metamorphic history.
Eucrite, howardite, and diogenite members of the achondrites are
considered, by many, to be genetically related. Therefore, each provide
a piece of the puzzle for reconstructing magmatic processes on the
eucrite parent body (EPB). The relationship between eucrites and
diogenites can be viewed within the context of two distinctly different
models: (1) fractional crystallization and (2) partial melting. In
fractional crystallization models, eucrites and diogenites represent a
complementary continuum of planetary fractional crystallization products
in which the diogenites represent crystal accumulations during the
crystallization of eucritic magmas at shallow to deep levels in the EPB.
Alternatively, experimental studies may be interpreted as indicating
eucrites represent peritectic partial melts of a primitive, chondritic
EPB mantle. Within this type of model, the diogenites are also generally
considered to be cumulates; however, their petrogenetic relationship to
the eucrites is less clear. Sack et al. proposed that the olivine
diogenites represent residua from the partial melting events that
produced eucritic liquids. Initial trace element studies of
orthopyroxene (OPX) are consistent with this model. However, this trace
element modeling of the olivine diogenites is nonunique. As a further
test of these models, we (1) analyzed OPX from cumulate diogenites to
compare with the olivine diogenite data, (2) improved ion microprobe
analytical techniques for the analysis of elements critical to our
interpretations, and (3) selected more relevant Kds for opx-eucritic
melt.
3. Petrologic Constraints on the Surface Processes on Asteroid 4 Vesta
and on Excavation Depths of Diogenite Fragments
The eucrite-howardite-diogenite meteorite groups are thought to be
related by magmatic processes. Asteroid 4 Vesta has been proposed as the
parent body for the these basaltic achondrite meteorites. The similarity
of the planetesimal's surface composition to eucrite and diogenite
meteorites and the large size of the asteroid (r = 250 km) make it an
attractive source, but its position in the asteroid belt far from the
known resonances from which meteorites originate make a relation between
Vesta and eucrite-howardite-diogenite group problematic. It has been
proposed that diogenites are low-Ca pyroxene-rich cumulates that
crystallized from a magnesian parent (identified in howardite breccias),
and this crystallization process led to evolved eucrite derivative
magmas. This eucrite-diogenite genetic relationship places constraints
on the physical conditions under which crystallization occurred.
Elevated pressure melting experiments on magnesian eucrite parent
compositions show that the minimum pressure at which pyroxene
crystallization could lead to the observed compositions of main series
eucrites is 500 bars, equivalent to a depth of 135 km in a 4 Vesta-sized
eucrite parent body. Therefore, the observation of diogenite on the
surface of 4 Vesta requires a postcrystallization process that excavates
diogenite cumulate from depth. The discovery of diogenite steroidal
fragments is consistent with an impact event on 4 Vesta that penetrated
the deep interior of this planetesimal.
4. Remanent Magnetism of HED Meteorites--Implications for Their
Evolution and Ancient Magnetic Fields
The magnetic properties of extraterrestrial materials, in particular
natural remanent magnetization (NRM) is a potentially useful study for
detecting ancient Solar System magnetic fields and for elucidating
meteorite evolutionary processes. Results reported here are for
howardites Kapoeta, Petersburg, Le Teilleul and EET87503, eucrites Sioux
County and Millbillillie, and diogenites Shalka and Johnstown.
Significant features of their magnetism are within-sample inhomogeneity
of NRM directions in several of the meteorites and within - sample
uniformity of axes of anisotropy of magnetic susceptibility. Both these
phenomena bear on the meteorites' evolution and the timing of the
magnetisation process.
References: