[meteorite-list] Could it be....

From: Razvan Andrei <asean-1_at_meteoritecentral.com>
Date: Wed, 24 Jan 2007 22:33:33 +0200
Message-ID: <008201c73ff7$125fd1d0$80db2454_at_asean1>

> Bernd Pauli wrote:

> The earliest email I have saved is from Thu, 20 Mar 1997 and it was
> written
> by no less a person than Frank ... Frank Stroik for those who still
> remember
> him.

Hi list,

My earliest mail saved is from Sun, May 11, 1997, also written by Frank
Stroik
on vesicles and vugs in chondrules. I guess I joined the list around that
date. The
header says 'archive/latest/331'.

The message is interesting and I will copy it here...

Best Regards,
Andrei


>From - Sun May 11 04:55:32 1997
Date: Sat, 10 May 1997 10:28:13 -0600 (MDT)
From: fes at UWYO.EDU
Subject: Re: Tying up some loose ends.
To: meteorite-list at meteoritecentral.com
Cc: meteorite-list at meteoritecentral.com
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X-Mailing-List: <meteorite-list at meteoritecentral.com> archive/latest/331
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 A few people on this list have asked me questions, and I
have yet not responded. Today, I will do my best to answer these
questions, as I will be out of town for three weeks, as of tommorow.
These are questions that the entire list may be interested in reading the
answer.
 I recieved a question a while back, about vesicles, and vugs in
chondrules. Bascily the gentleman wanted to know why I said " By
definition chondrules cannot have vugs/vesicles". Here now is my
expalnation, and I apologize to the person for the delay.
 My answer is derived from an article written for a book written
in 1983 entitled "Chondrules and Their Origins"(published by the Lunar
and Planetary Institiute, edited by Elbert A. King). Basicly the
definition of chondrule as of 1983, and 1988(a paper published by John
Wasson), is an object that has been melted, and cooled rapidly, thus
creating small and fine grained aggregates, and in some cases quenched
glass. These are spherical to subspherical, and may contain lithic
fragments.
 Now, anytime silicate material is cooled rapidly, the crystals
tend to be small, as well as the possible formation of "volcanic glass".
The mode of formation of chondrules precludes vesicles/vugs based on
this, as most gas was probobly removed due to volitization when the
material was initialy heated, thereby not allowing to be incorporated in
to the rapidly cooling silicates.
 Here on Earth, I am currently unaware of any igneous bodies, that
have been cooled rapidly(i.e. obsidian deposits) that contain any
appreciable gas bubbles. Pumice is in a sense volcanic glass that has
cooled rapidly, and contains gas in it, but in having this property, it
has little structural rigidity, and breaks down readily in relativly
short geologic time. So based on the above information, it seems that
that chondrules with vesicle/vugs are not likely to occur. However, I am
aware that there are still many debates on what exactly a chondrule is,
and how to define them. I choose the above definiton, because I am not a
chondrule expert, and prefer to follow what seems plausible as realistic
classification. I am positive, either right now, or sometime soon the
above idea may change, but I will use the above definition until I see
otherwise.
 One more quick comment. I have to upgrade my reference above, as
it is somewhat incomplete. The references I need have been checked out of
the Library here, and I can't properly site until they come back. I will
post the reference, with page numbers when I get back.
 I had a question on the E-chondrite Earth. I will attempt to
explain this paper in as much detail I can(M. Javoy, "The integral
enstatite chondrite model of the earth" Geophysical Research Letters,
Vol. 22, No. 16, Pages 2219-2222, August 15, 1995.) It should be kept in
mind that this is an alternative to the conventional earth model that says
ordinary chondritic material is what the earth formed from.
 The basic idea of the article is that E-chondrites match the
earth in stable isotope, and redox characteristics. Redox is term used
to denote a chemical reaction adding or taking away oxygen. By looking at
these properties, models can be made to explain the differentiation of
the earths mantle, meaning why the elements are found the way they are in
the mantle.
 The mantle is thought to be homogeneous based on elements found in
E,C, and Ordinary chondrites. Using simple chemistry, the depth at which
different elements would be found in the mantle is used to try and make a
picture of the mantle's makeup. The author of this paper
indicates this may be wrong, and the mantle is heterogoneous. The author
attempts to explain this by using e-chondrites as building blocks of
planet earth.
 EH- chondrites are the material that is used in the modeling,
because it appears to have the closest elemental, and isotopic
compositions of the earth. The author explains in some detail the various
effects of EH material in the earth, to show it to be feasible. The main
point to remember is that the mantle may not be as homgeneous as
previously thought, and that it may in fact hold two very different
elemental compositions. I should state that no one has sampled the mantle
directly, and there is alot of room for interpritation.
 Basicly this model helps to explain how metal migrated to the
core of the earth, and the compositional differences that are in the
mantle(this is based upon thermodynamic equations,and theory, and little
on actual specimen anaylisis). Also it gives a more rational explanation
for oxidize Fe. Instead of trying to use "ad-hoc" change in the type of
material being accumulated to explain this, the Fe in EH-chondrites are
close to this state, therefore the process is much simpler to explain, and
therfore better.
 I hope this enlighten a few of you. I could explain the article
in much greater detail, but that would require more writing, more than
most would like to do in this format. Please, if you have any questions,
let me know, and I will answer them when I get back.

Frank Stroik



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Received on Wed 24 Jan 2007 03:33:33 PM PST