[meteorite-list] Lake Murray and Cosmic Reheating
bernd.pauli at paulinet.de
bernd.pauli at paulinet.de
Fri May 14 13:03:59 EDT 2004
Hello Roman, Mark and List,
> I was reading some info about the Lake Murry Iron in MetBase ver. 6.
> It mentions that this iron was cosmically reheated. What exactly does
> this mean? And how would one know especially since this iron has
> been on earth since the dinosaurs?
> ... this iron was cosmically reheated. What exactly does this mean?
- Lake Murray was separated from its parent body by a collision
- floating out there in the asteroid belt, it underwent another collision
- in this shock event it was severely reheated => cosmically reheated
> how would one know ...?
- The cohenite [(Fe,Ni,Co)3C] in Lake Murray is decomposed
to graphite and granular kamacite
- once numerous Neumann bands in the kamacite have almost
disappeared leaving distinct double rows of minute phosphide
particles, so-called "decorated Neumann lines"
- decomposed and spheroidized taenite lamellae (as in Juromenha)
- instead of "normal kamacite" a fine-grained structure of slightly
oriented gamma-grains (taenite) in a matrix of alpha-iron*
- presence of shock-melted troilite
* According to Buchwald, the alpha-iron in Cratheus (1931)
seems to have recrystallized to serrated 10-25 mü wide
irregular grains (p. 511).
Well, these are some of the features that have survived the ages
and the dinosaurs.
Reference:
Buchwald V.F. (1975) Handbook of Iron Meteorites, Volumes 1-3.
Some cosmically reheated irons:
Alatage - Cratheus (1931) - Juromenha - Lake Murray
Oscuro Mountains - Plymouth - Shrewsbury - Zerhamra
Best regards,
Bernd
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