[meteorite-list] Chondritic parent bodies

From: Dave Gheesling <dave_at_meteoritecentral.com>
Date: Wed, 9 Sep 2009 11:04:43 -0400
Message-ID: <94BAAD0814484D8087C550448E6216DC_at_meteorroom>

Hi, Jeff,

Thanks for your response. I always look forward to learning something from
your posts to the list, and below I'm reminded of the dating of the L and H
shock events. Do you recall such a date for amphoterites by chance?

I followed up my question with a rather clear and somewhat self-depricating
note...last night and well before your response this morning. Assuming you
may have missed it, I explained that I'd picked this notion up on the list
but couldn't recall when or from whom, etc. I either misread a post or the
post was just simply wrong. And it was late last night, so my question
wasn't crafted very well either...obviously.

Svend beat me to the punch, but there are obviously exceptions and even some
questions to the existing definition. Even your mention below that "at
least many of them came from a single parent body" prompts some interesting
questions in my mind. Without the context and foundation of having spent a
few decades as a professional meteoriticist, as I referenced before in the
thought re: MAPS, it is not always easy for an general enthusiast like me to
understand where the gray areas are. And as people like you thankfully
continue to rapidly raise the bar of knowledge, I've learned to accept that
a lot of iron clad definitions aren't so iron clad.

All best,

Dave

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Jeff
Grossman
Sent: Wednesday, September 09, 2009 9:00 AM
To: meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] Chondritic parent bodies

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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Received on Wed 09 Sep 2009 11:04:43 AM PDT