[meteorite-list] Abstract: EL3 Chondrite (not Aubrite) NorthwestAfrica 2828

From: M come Meteorite Meteorites <mcomemeteorite2004_at_meteoritecentral.com>
Date: Thu, 29 Mar 2007 17:04:20 +0200 (CEST)
Message-ID: <328076.47260.qm_at_web26210.mail.ukl.yahoo.com>

unfortunately all analysis say this material I have
here is not a EL but a Aubrite...is not possible have
all from the world, dear USA people

Matteo

--- "E.P. Grondine" <epgrondine at yahoo.com> ha scritto:

> Hello Sterling -
>
> The "present ice age" is not going to return. The
> currents of the Pacific Ocean were altered by a
> massive impact at the end of the last ice age, and
> most likely that impact was what ended it.
>
> The important point here is how long NWA meteorites
> have been accumulating, and as you point out it has
> been a relatively short period.
>
> Ed
> E.P. Grondine
> Man and Impact in the Americas
> $34.95 at amazon, or contact me off list
>
> --- "Sterling K. Webb" <sterling_k_webb at sb7
> cglobal.net> wrote:
>
> > Hi, All,
> >
> > > an ancient fluvial and/or acidic lacustrine
> > environment...
> >
> > Most people think of the Sahara as an ancient,
> > primordial environment. It's a relatively new
> > feature.
> >
> > The Sahara was a well-watered mixed forest and
> > glassland temperate environment, with lakes and
> > many rivers (whose ancient courses are still
> visible
> > in many places) 14,000 years ago and more.
> >
> > There was plentiful game and a large human
> > population.
> > The NE Sahara seems to have desertified first,
> > driving
> > humans into the Nile Valley. By 8 to 10 thousand
> > years ago, it was a dry grassland and the lakes
> and
> > rivers were vanishing rapidly. The Sahara "grows"
> > from its center, where the bulk of the sand is
> > generated
> > that flows out to make the Great Sand Sea. The
> > process
> > is on-going and the remains of vast Roman
> > "plantations"
> > can be found 100 miles or more into the Sand that
> > were
> > thriving and productive 1600 years ago! North
> Africa
> > was the Breadbasket of the Roman Empire, green
> > and growing.
> >
> > Like so many deserts, it is unlikely to revert to
> a
> > paradise again when the present Ice Age resumes
> > after
> > this interglacial, because of the smothering
> effect
> > of
> > the Sand. The Amazon Rain Forest, another
> temporary
> > Interglacial abnormality, will likely recover from
> > the
> > damage done by its runaway forestation and revert
> to
> > the vast rolling Sea of Grass it was 12 to 16
> > thousand
> > years ago, when things get back to normal.
> >
> > Any meteorite in the Sahara need not be highly
> > ancient to be completely weathered out. One sees
> > statements that completely weathered NWA's "must"
> > have terrestrial ages of 40 to 50 thousand years.
> > They would IF the Sahara had always been as dry
> > as it is, but it hasn't been. They need only be
> old
> > enough to have been exposed during the "wet"
> times.
> >
> > This one seems to have sat in the lake bottom for
> > a long time, though, for all those changes. Still,
> I
> > doubt it's more than 20,000 years old, tops, and
> > it could be much younger. Chondrites don't last
> > that long in water!
> >
> >
> > Sterling K. Webb
> >
>
-------------------------------------------------------------
> > ----- Original Message -----
> > From: "Jeff Kuyken" <info at meteorites.com.au>
> > To: "Meteorite List"
> > <meteorite-list at meteoritecentral.com>
> > Sent: Sunday, March 25, 2007 1:39 AM
> > Subject: [meteorite-list] Abstract: EL3 Chondrite
> > (not Aubrite)
> > NorthwestAfrica 2828
> >
> >
> > Hi all,
> >
> > Thought some may find this abstract that I just
> > found interesting.
> >
> >
>
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006AGUFM.P51E1247K
> >
> > Cheers,
> >
> > Jeff
> >
> >
>
------------------------------------------------------
> >
> > Title:
> > EL3 Chondrite (not Aubrite) Northwest Africa 2828:
> > An Unusual
> > Paleo-meteorite Occurring as Cobbles in a
> > Terrestrial Conglomerate
> >
> > Authors:
> > Kuehner, S. M.; Irving, A. J.; Bunch, T. E.;
> Wittke,
> > J. H.
> >
> > Publication:
> > American Geophysical Union, Fall Meeting 2006,
> > abstract #P51E-1247
> >
> > Publication Date:
> > 12/2006
> >
> > Abstract:
> > Although we recently classified NWA 2828 as an
> > aubrite [1], our examination
> > of new material (now comprising over 120 stones
> > totaling >27 kg) requires
> > revision of that classification. New information
> on
> > the find site in Algeria
> > indicates that these stones were excavated from a
> > subsurface deposit, and we
> > have found terrestrial rhyolite pebbles and sandy
> > matrix attached to several
> > NWA 2828 stones (see images at
> > http://www.ess.washington.edu/meteoritics).
> > Thus this is a rare example of a paleo-meteorite
> or
> > 'fossil' meteorite. Some
> > stones contain sparse (<5 vol.%) but very distinct
> > round, radial pyroxene
> > chondrules (up to 3 mm across), as well as
> rounded,
> > fine-grained aggregates
> > (up to 6 mm across) rich in either enstatite or
> > sodic plagioclase. Remnant
> > Na-Al-Si-rich glass is present within cavities in
> > chondrules, both between
> > enstatite blades and in annular zones. The matrix
> > contains pervasive 0.2-0.5
> > mm cavities with coatings of calcite and minor
> > halite and gypsum. Iron
> > sulfate (after troilite), jarosite, an
> inhomogeneous
> > (possibly amorphous)
> > phase rich in Fe, Cr, Si, Ca, Ti, P, S and Cl,
> minor
> > native sulfur and
> > silica also are present, and brown Fe-rich rinds
> on
> > one stone contain up to
> > 6.5 wt.% Ni. These secondary minerals signify
> > terrestrial alteration of
> > primary metal, sulfides, phosphides, nitrides and
> > glass in an ancient
> > fluvial and/or acidic lacustrine environment. The
> > dominant primary phase in
> > NWA 2828 is enstatite (En98.4Wo1.4), which forms
> > stubby prismatic grains
> > (lacking polysynthetic twinning indicative of
> > inverted clinoenstatite [cf.,
> > 1]). Our original classification was based on a
> very
> > small specimen of an
> > apparently igneous-textured rock, but the
> discovery
> > of chondrules and the
> > absence of twinned enstatite now suggests that it
> is
> > instead an
> > unequilibrated enstatite chondrite. Additional
> > primary phases noted
> > previously [1] are sodic plagioclase (An14-
> > 15Or3-4), troilite, graphite,
> > daubreelite, alabandite, oldhamite, schreibersite,
> > glass and very rare
> > kamacite. The well-formed, round chondrules
>
=== message truncated ===


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Received on Thu 29 Mar 2007 11:04:20 AM PDT