AW: [meteorite-list] There are no silly questions? Wait until youhaveread that :-)

From: star-bits_at_comcast.net <star-bits_at_meteoritecentral.com>
Date: Wed Oct 20 14:06:04 2004
Message-ID: <102020041806.3893.4176A906000DAF4C00000F3522007614389C9B070DD39D0E9B9C_at_comcast.net>

<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

Received on Wed 20 Oct 2004 02:06:00 PM PDT