[meteorite-list] Chondrule formation mechanism (Info Please)

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Wed Oct 25 11:52:30 2006
Message-ID: <BAY104-F36F0CCDE65CA0834A19C88F8060_at_phx.gbl>

Hi, all,

This discussion about chondrules is fascinating!

Hoping not to digress off this topic too much, but a question I have is
about the metal flecks (not the later-formed iron meteorites) in any of the
stonies.

Have they ever been given an estimated age?

If the heavy elements, such as nickel and iron, are created by a supernova,
and the chondrules are in theory formed much later during the future
dynamics of our solar system's nebula, would it be fair to say that the
metal flecks would be billions and billions (apologies, Carl) of years OLDER
than chondrules?

And that they came from a distance much further than our solar system's
vicinity?

Considering that the supernova is exploding outward and the new elements'
density is thinning out very quickly, wouldn't it be more likely that these
iron and nickel flecks that eventually found a new home in our solar nebula
and meteorites have come from more than one, probably a lot more, supernova?

If so, why don't we see any remnants of any supernova explosion in our
relative proximity? The Helix Nebula is the closest to us, at 450
light-years!
http://images.google.ca/images?q=helix+nebula&hl=en&lr=&sa=X&oi=images&ct=title

Not even a wisp left...
Are tiny, but very dense, nebulas even possible? I can't imagine dust-bunny
nebulae.

If not, would it be unreasonable to expect that our planetary nebula could
have extended out to Centauri, where our closest star neighbours are?
When I dwell on the "Pillars of Creation" photos
(Orion stellar-formation nebula,
http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/44/image/a)

that describes a small point being comparable to the breadth of our solar
system, ~4.3 light-years to Centauri isn't that far...

Maybe the seldom-discussed/appreciated metal flecks are the real gems in the
meteorites?

Or, is the nebula in my head too dense that am I just missing something
obvious?
How is my logic flawed?

Cheers,
Pete




From: Warin Roger <warinroger_at_yahoo.fr>
To: "Sterling K. Webb"
<sterling_k_webb_at_sbcglobal.net>,meteorite-list@meteoritecentral.com
CC: "E.P. Grondine" <epgrondine_at_yahoo.com>
Subject: Re : [meteorite-list] Chondrule formation mechanism (Info Please)
Date: Tue, 24 Oct 2006 16:15:53 +0000 (GMT)

Hi, all,

I am surprised that nobody evoked the theory following which chondrules were
formed in relatively very few privileged zones of space. They would then
form through one or more impacts of relatively large asteroids, onto the
parent body covered with regoliths (and even with megaregoliths).
The excellent book of Derek Sears, entitled “The origin of chondrules and
chondrites” (Cambridge Planetary Science, 2004) supports this hypothesis. In
corollary, ordinary chondrites (85% on Earth) would be quite rare in cosmos,
and only few parent bodies would produce chondrites.

Glad to hear some comments on the above assumptions.

Thanks,

Roger Warin



----- Message d'origine ----
De : Sterling K. Webb <sterling_k_webb_at_sbcglobal.net>
À : meteorite-list_at_meteoritecentral.com
Cc : E.P. Grondine <epgrondine_at_yahoo.com>
Envoyé le : Dimanche, 22 Octobre 2006, 20h38mn 55s
Objet : Re: [meteorite-list] Chondrule formation mechanism (Info Please)


Hi, Ed, Rob,

     This scenario (Ed's) would require that we would
find a chondrule with a formation age of 3.9 Gya, I
think. As far as I know, that has never happened.

     All chondrites (so called because they contain
chondrules) are the same age: "about" 4.555 Gya.
Chondrules are the same age (2 to 5 million years
variation among chondrules) as the chondrites they
occur in. The "about" is because the dating methods
have a limit to how precisely they can resolve
small age differences.

     Dating by lead isotopes says the solar system
is 4.560 +/- 0.005 Gya old. Other systems of isotope
measurements (like 147Sm/143Nd) give 4.553 +/- 0.003,
and so forth. Within the limits of measurement, all
chondrites are the same age, a hair younger than the
solar system itself, the Class of Zero, and so are their
chondrules.

     Meteorites that do not (never did) contain chondrules
have varying ages. Lunaites are the age of that portion
of the lunar crust they came from, generally quite old
compared to Martians which have the "formation age"
of the basalt flow they were chipped off of for the long
haul to Earth. Irons, which formed inside a differentiating
body, have younger ages; some very much younger if
the differentiation took a long time (Weekeroo Station IIe
is 4.340 Gya, Kodaikanal IIe 3.800 Gya, many IAB irons
the same).

     I'm thinking that before you need to develop a theory
to explain a 3.9 Gya chondrule, you'd have to actually
have a 3.9 Gya chondrule. As far as I know, none with
discordant ages have ever been found. In certain solar
circles it would be Big News.

     Oddly, if you Google for "oldest chondrule," you get
the oldest chondrules, and if you Google for "youngest
chondrule," you get the oldest chondrules... on the grounds
that it is "young" as the solar system. If you Google for
"discordant chondrule age," you get arguments over 2 or 3
million years in the age of something 4-1/2 billion years old.


Sterling K. Webb
--------------------------------------------------------------------
----- Original Message -----
From: "E.P. Grondine" <epgrondine_at_yahoo.com>
To: <meteorite-list_at_meteoritecentral.com>
Sent: Sunday, October 22, 2006 10:24 AM
Subject: Re: [meteorite-list] Chondrule formation mechanism (Info Please)


> Hi Rob -
>
> You noticed the contradiction in cooling periods as
> well.
>
> What I am thinking is that there was at least one
> larger parent body which was "disrupted" about 3.9 Gya
> (at time of LPBE). When this larger parent body was
> disrupted, then the "effervescent" "foaming" that led
> to some chondrules occured - sudden cooling, as
> gravitation pressure had been released, and much lower
> local gravity. Local processes suddenly take over - a
> sharp gravitational and pressure transition, and a
> sudden cooling. Gross processes - perhaps sufficiently
> gross to overwhelm other small forces.
>
> Through collisions of the resulting fragments, we see
> some of the meteorite types we see today.
>
> good hunting,
> Ed
>


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Received on Wed 25 Oct 2006 11:52:23 AM PDT