<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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