AW: [meteorite-list] Re: Mercury Meteorite Puzzle

From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:49 2004
Message-ID: <20020517013316.79994.qmail_at_web10402.mail.yahoo.com>

Actually Norbert,

I'm on your side.
And I was going to mention the "low shock"
descriptions but, then, I came across this statement
in the Yamaguchi et al, Science article:
"Because the enrichments of siderophile elements
cannot be explained in terms of igneous processes, we
suggest that NWA 011 was contaminated by projectile
materials, being consistent with the textural evidence
for impact brecciation of NWA 011." !?

So, I didn't pursue it, because I didn't know that you
could have it both ways - low shock and impact brecc.

And you were right about the oxygen isotope ratios.
The following web site graph shows NWA 011 as being
well below the "terrestrial fractionation line" !?
<http://www.sciencemag.org/cgi/content/full/296/5566/334/F3>

And here is the REE distribution that you asked about:
<http://www.sciencemag.org/cgi/content/full/296/5566/334/F2>

But you'll have to read "Yamaguchi et al," in order to
see how they attempt to explain away the "fractionated
REE pattern" yet still propose a "Vesta-like asteroid"
parent body for NWA 011.

Bob V.


--- Norbert Classen <trifid_at_timewarp.de> wrote:
> Hello Rob, hello Mercury enthusiasts,
>
> It's not okay! I think the statement that "NWA 011
> has an
> oxygen isotope ratio that indicates it came from a
> body
> larger than a big asteroid" is quite nonsensical.
> What's the
> connection between oxygen isotope ratios and the
> size of
> a planet or an asteroid? If that would be true the
> aubrites
> would qualify as planetary meteorites, too, since
> they
> share the Earth's O-isotopic ratio...
>
> Okay, I'm no planetary scientist, but what I've
> learned
> from my private studies on planetary meteorites is
> that the
> person who wrote this article mixed up some things.
> The facts
> suggesting NWA 011's origin from a larger body are
> most
> probably the unusually high FeO/MnO ratios similar
> to lunar
> values, although they are slightly lower for
> pyroxenes in
> NWA 011.
>
> However, do the other data on NWA 011 suggest a
> planetary
> or Mercurian origin of this peculiar achondrite? I
> don't
> think so. Look at the data, NWA 011 has been
> described as
> "virtually unshocked", a fact making it hard to
> believe that
> this rock has been blasted off a planet. None of its
> plagioclase has been converted to maskelynite - the
> rims of
> the plagioclase crystals in NWA 011 aren't even
> slightly
> distorted. From what we know about lunar and Martian
> meteorites it seems quite improbable that this
> strange
> rock is of planetary origin at all. Don't get me
> wrong,
> I would be glad if we finally had the first
> Mercurian rock,
> and I would be willing to pay dearly for even a
> small piece.
>
> Please correct me if I'm wrong. As stated above, I'm
> no
> planetary scientist, but from what I know I must
> conclude
> that the "Mercurian origin" of NWA 011 is nothing
> but a
> wild guess. Has anyone seen data on the REE
> distribution
> in NWA 011 so far? Why don't they show as a nice
> "S"??
> Now, that would be something...
>
> Best regards,
> Norbert Classen
>
> --------Rob Verish wrote-------
> >
> > "NWA 011 has an oxygen isotope ratio that
> indicates it
> > came from a body larger than a big asteroid."
> >
> > Okay. This article explains to me why this
> meteorite
> > came from a body larger than an asteroid. But it
> > doesn't explain how the other "planet-sized
> bodies" in
> > our solar system are being ruled-out in favor of
> > Mercury.
> >
> > Is there an upper limit for the suspect
> "planet-sized"
> > parent body, that would exclude Mars, Venus, or
> Earth!
> > (The 81Kr-Kr age for NWA011 is 39 ± 5 Ma, which
> can be
> > interpreted as an upper limit of the cosmic-ray
> > exposure age, which would exclude the
> proto-versions
> > of these inner planets)?
> >
> > Same-sized planetary bodies? We know enough about
> the
> > Moon to rule out a Lunar-origin, but do we know
> enough
> > about the Galilean moons of Jupiter to rule them
> out?
> >
> > It would be interesting to see a matrix showing
> > suspect parent bodies vs. NWA 011 data, and to see
> > which evidence favors which "planet-sized body".
> >
> > Here's what we already know:
> >
> > April12th issue of Science, Akira Yamaguchi
> (National
> > Institute of Polar Research, Tokyo)
> >
>
<http://www.sciencemag.org/cgi/content/short/296/5566/334>
> >
> > Meteoritical Bulletin 84, Table 9
> >
> > ----------------------------------
> > [meteorite-list] MAPS and Mercury
> >
> > Bernd Pauli HD
> bernd.pauli_at_lehrer1.rz.uni-karlsruhe.de
> >
> > Sun, 14 Apr 2002 15:20:10 +0200
> >
> > LOVE S.G. et al. (1995) Recognizing mercurian
> > meteorites (MAPS 30-3, 1995, 269-278).
> >
> > ROBINSON M.S. et al. (2001) Ferrous oxide in
> Mercury's
> > crust and mantle (MAPS 36-6, 2001, pp. 841-847).
> >
> > Best regs,
> >
> > Bernd
> > -------------------------------------------
=== message truncated ===


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Received on Thu 16 May 2002 09:33:16 PM PDT