[meteorite-list] Lake Murray and Cosmic Reheating

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Fri May 14 13:04:01 2004
Message-ID: <DIIE.0000001B0000218E_at_paulinet.de>

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 m? 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
Received on Fri 14 May 2004 01:03:59 PM PDT