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

[M come Meteorite Meteorites]

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 ===


M come Meteorite - Matteo Chinellato
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