[meteorite-list] Osmium and the size of parent bodies

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Sun, 22 Apr 2007 02:33:20 -0700 (PDT)
Message-ID: <190466.22150.qm_at_web36906.mail.mud.yahoo.com>

Hi Sterling, list -

What I am interested in, Sterling, may broadly be
described as the "accretion" problem.

One aspect of the "accretion" problem, and this is
only one of many, may be broadly called the
"precipitation" problem. That's where the high osmium
ratios in some irons comes in.

Thanks for the links, but I'm afraid I'll have to wait
until they figure it out, and are able to "explain"
the ratios they are observing.


--- "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>

> Hi, Ed, List,
> "More" work? More than who, what, when?
> Are you referring to the indications of an early
> cooling of the cores of irons, demonstrated by
> their 187Rhenium/187Osmium ratios? As shown
> in this:
> "Some iron meteorites (the so called "magmatic"
> irons) likely are pieces of asteroidal cores. As
> such
> their study can provide valuable insights to
> planetary
> core formation and crystallization processes. The
> highly siderophile elements (HSE: "iron-loving",
> including Re, Os, Ir, Ru, Pt and Pd) are useful in
> elucidating crystallization sequence, so these
> elements
> have been the focus of much of our work on irons.
> We recently completed a 187Re-187Os and 190Pt-186Os
> isotopic and elemental study of the two largest
> magmatic
> iron meteorite groups, IIAB and IIIAB (Cook et al.,
> 2004).
> That study revealed that the cores these meteorites
> sample
> crystallized very early in solar system history
> (approximately
> 4.5 billion years ago)... However, complex trace
> element
> behavior for Re, Pt and Os in these groups,
> particularly
> group IIIAB proved difficult to explain. During the
> past
> several years we have extended our study to the
> magmatic
> groups IVA and IVB (each of the groups presumably
> sample the cores of different asteroids)."
> More by the same researcher:
> Crystallization age is "when it cooled" and that
> is related to the size of the body but also the time
> of
> formation. Some irons are "younger" than most:
> Kodaikanal (a IIE iron) has a crystallization age of
> only 3.8 billion years, something that's really hard
> to explain.
> Anyway, it's a long piece with lots of details
> and a substantial bibliography on osmium and its
> siderophile buddies in iron meteorites.
> Osmium plays a role in this:
> Headline reads: Tiny Traces of a Big Asteroid
> Breakup!
> Fossil meteorites and chromite grains record a
> hundred-fold
> increase in the number of meteorites that fell 480
> million years
> ago compared to the meteorite influx today.
> They used chromite instead of osmium for their
> analysis
> because there was more of it, but the pattern was
> the same.
> (I threw this in, E.P., because you're always
> interested in
> Big Asteroid Breakups, right?)
> Sterling K. Webb
> ----- Original Message -----
> From: "E.P. Grondine" <epgrondine at yahoo.com>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Saturday, April 21, 2007 3:53 AM
> Subject: [meteorite-list] Osmium and the size of
> parent bodies
> Hello list -
> I wonder if any more work has been done on the
> osmium
> ratios in irons?
> good hunting all,
> Ed

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Received on Sun 22 Apr 2007 05:33:20 AM PDT

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