[meteorite-list] More on CAIs

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:54:04 2004
Message-ID: <3C695577.317CAC5A_at_lehrer1.rz.uni-karlsruhe.de>

"S.Singletary" wrote:

> They are indeed complicated little beasties.

CAIs are characteristically enriched in refractory elements and cannot
only be found in carbonaceous chondrites but also in primitive ordinary,
enstatite, and K chondrites. Their isotopic anomalies originated in
nucleosynthesis processes in stars, novae, and supernovae.

Petrological classification of CAIs: Type A, type B, and type C

=> petrological diversity reflects difference
   in formation temperature (melted or not)

Chemical classification of CAIs: Groups I–V

=> chemical diversity reflects the condensation
   and/or evaporation history.

The two classifications are independent which suggests the high
temperature event responsible for texture might differ from that
which caused evaporation/condensation.

Two types of rims of CAIs:

- fine-grained rims: a mixture of several mineral species
- Wark–Lovering rims: series of mineral layers, suggesting
  different formation process(es).

Wark–Lovering rims have average thickness of 50 µm, where
spinel with perovskite inclusions, melilite or its alteration pro-
ducts (anorthite, nepheline, sodalite, grossular and phyllo-
silicates), and diopsidic pyroxene successively cover the
inclusions.

Reference:

NAGAHARA H. (2001) Flash heating of CAI-rich inclusions
(MAPS 36-8, 2001, p. 1011, From the Editors).


Cheers,

Bernd
Received on Tue 12 Feb 2002 12:48:39 PM PST