[meteorite-list] Chondritic parent bodies

[Alan Rubin]

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" <info at niger-meteorite-recon.de>
To: <Meteorite-list at meteoritecentral.com>
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 subject isn’t out of date, the group of L-chondrites around Mt.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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