AW: [meteorite-list] There are no silly questions? Wait until youhaveread that :-)
star-bits at comcast.net
star-bits at comcast.net
Wed Oct 20 14:30:34 EDT 2004
Whoops that should have read non-irons swept clean in 100 million years not 100 thousand years.
--
Eric Olson
ELKK Meteorites
http://www.star-bits.com
> <If all ungrouped iron meteorites are derived from the cores of differentiated
> bodies, the question is:
> where is all the crust gone? Why don't we have many more (at least 92) different
> types of achondrites in our meteorite collections?>
>
> >From Mittlefehldt et al, chapter 4 p4-15 "Planetary Materials" Reviews in
> Mineralogy Vol 36
>
> "cosmic ray exposure ages of iron meteorites are typically in the range of 200
> to 1000 Ma, some 5 to 50 times longer than typical for stony meteorites. Tight
> clusters in exposure ages for groups IIIAB and IVA suggest discrete breakup
> events for their parent bodies 650 +/- 75 and 420 +/- 70 Ma ago, respectively
> (Voshage and Feldmann 1979). No other clusters have been observed. The highest
> 41K/40K exposure age measured for an iron meteorite is 2.3 Ga, or half the age
> of the solar system, for the ungrouped Deep Springs iron."
>
> The longest CRE exposure age I know of for a non-iron is Soko-Banja at 71.1
> Ma although there may be others I don't know of. This does exclude lunars
> which do have CRE ages of up to a billion years.
> So if the non-irons are swept clean in 100,000 years or less and the irons
> hang around for a up to a billion or more that would explain why we see more
> variety in iron parent bodies.
>
> --
> Eric Olson
> ELKK Meteorites
> http://www.star-bits.com
>
>
>
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