[meteorite-list] Chondritic parent bodies

[Alan Rubin]

The general supposition is that all L chondrites come from one parent body, 
that H chondrites come from another, etc.  We don't know this to be strictly 
true, but there is evidence that it is broadly true.  For example, about 
two-thirds of all L chondrites (of different petrologic types) were shocked 
about 470 Ma ago or so, indicating that they were on the same parent body at 
that time.  Similarly, nearly half of all H chondrites (of different 
petrologic types) have a cosmic-ray exposure age of about 7.5 Ma indicating 
that they were all within about a kilometer of each other (or so) at that 
time.  The idea that the parent bodies were stratified with the type-6 
chondrites in the center and type-5s closer to the surface, etc. is known as 
the onion shell model.  There is some evidence for it and some against it. 
Hence, some researchers are strong advocates and others reject the model. 
As is clear, the situation is not yet resolved.
Alan Rubin

----- Original Message ----- 
From: "Dave Gheesling" <dave at fallingrocks.com>
To: "'Meteorite List'" <meteorite-list at meteoritecentral.com>
Sent: Tuesday, September 08, 2009 8:40 PM
Subject: [meteorite-list] Chondritic parent bodies


> All,
> Pete's question re: pallasites reminds me of one I've been meaning to 
> throw
> out to the group for a while.  I believe that, by definition, L6's come 
> from
> one parent body and L5's, say, come from another.  It's clear why breccias
> might simply be an association of the two.  But I've seen cross section
> illustrations of hypothetical asteroids more than once which indicate a
> transitional progression from L3 material at the exterior/crust through 
> L4,
> then L5, and eventually to L6 at the center/core.  Presumably this is due 
> to
> insulative properties and the like towards the interior which allow more
> heat from radioactivity to build up, etc, but this also seems to indicate 
> a
> single parent body.  I'm sure Sterling & Co. might have a field day with
> this one, and I'm looking forward to any responses out there...
> Thanks much,
> Dave
>
> Dave Gheesling
> IMCA #5967
> www.fallingrocks.com
>
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