[meteorite-list] Chondritic parent bodies
From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Wed, 09 Sep 2009 08:59:32 -0400 Message-ID: <OFB69C8052.E531D843-ON8525762C.004761EE_at_usgs.gov> 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 > >______________________________________________ >http://www.meteoritecentral.com >Meteorite-list mailing list >Meteorite-list at meteoritecentral.com >http://six.pairlist.net/mailman/listinfo/meteorite-list Dr. Jeffrey N. Grossman phone: (703) 648-6184 US Geological Survey fax: (703) 648-6383 954 National Center Reston, VA 20192, USA Received on Wed 09 Sep 2009 08:59:32 AM PDT |
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