Dear Eric, A good question which I don't have an answer to. In terms of orbital evolution and probabilities to be catched up the larger solar system bodies, I do not se a reason, why iron meteoroids shall survive longer than stony meteoroids. May be, the differences in CRE ages are a result of cosmic-ray shielding effects. Does someone else has a good idea to explain these differences?
Cheers, J�rn / MetBase > -----Urspr�ngliche Nachricht----- > Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Gesendet: Mittwoch, 20. Oktober 2004 20:06 > An: J�rn Koblitz; almitt; Bernhard Rems > Cc: [EMAIL PROTECTED] > Betreff: Re: AW: [meteorite-list] There are no silly questions? Wait > until youhaveread that :-) > > > <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 > > > > ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://six.pairlist.net/mailman/listinfo/meteorite-list
