There are some porous chondrites but as far as I know there is no reason to
believe that they are from separate bodies. They may have suffered more (or
less) impact-induced compaction than the majority of rocks. But one should
check their cosmic-ray exposure ages, shock ages, etc. to see if they share
some of these characteristics with their colleagues.
Alan Rubin
----- Original Message -----
From: "Meteorite-Recon.com" <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 09, 2009 6:21 AM
Subject: Re: [meteorite-list] Chondritic parent bodies
Hi Jeff, others,
certainly true as far as the majority of L-chondritic material is
concerned. But Dave’s question is in so far justified as there are several
exceptional L-chondrites that show particular differences in their
lithology compared to other L-chondrites. If my information on this
subject isn’t out of date, the group of L-chondrites around Mt. Tazerzait,
Baszkówka and Tjerebon are believed to originate from a different parent
body as the other L-chondrites.
If my memory doesn’t cheat me in this matter these chondrites show a
lesser degree of compaction and a high amount of interstitial pores with
growth of euhedral to anhedral crystals in these vugs. A group around A.
Pilski even argued that these crystals provide evidence for hydrothermal
activity in the particular mother body of these L-chondrites.
Perhaps someone wants to look up the cosmic ray exposure data on the Mt.
Tazerzait "grouplet" to see if a different shock event played a role in
the production & delivery of these meteorites ...
I am clearly not an expert in this field so please beat me if I’am wrong
here.
Cheers
Svend
www.meteorite-recon.com
---------------
Jeff Grossman wrote:
I'm not sure why you thought there was a definition that requires L5
and L6 chondrites to come from different parent asteroids... there
isn't. Questions like this are open to investigation. Isotopic data
show that the different petrologic types of L chondrites all
experienced a major shock event around 500 million years ago, which
means that at least many of them came from a single parent
body. Similarly, different petrologic types of H chondrites show
evidence for a break-up event around 7.5 million years ago. There is
still debate over the importance of "onion shell" vs. "rubble pile"
models of the asteroids, but not so much over whether the different
petrologic types come (or came) from a single asteroid.
jeff
At 11:40 PM 9/8/2009, Dave Gheesling wrote:
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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Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
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