[meteorite-list] Norton County

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:30 2004
Message-ID: <3B4B6501.5BC1BFDB_at_lehrer1.rz.uni-karlsruhe.de>

OKADA A. et al. (1988) Igneous history of the aubrite parent
asteroid: Evidence from the Norton County enstatite achondrite
(Meteoritics 23, 1988, 59-74):



Abstract (p.59):

We studied numerous specimens ot the Norton County enstatite
achondrite (aubrite) by optical microscopy, electron microprobe,
and neutron-activation analysis. Our main conclusions are the
following:

1. Norton County is a fragmental impact breccia, consisting of a
clastic matrix made mostly of crushed enstatite, into which are
embedded a variety of mineral and lithic clasts of both igneous
and impact melt origin.

2. The Norton County precursor materials were igneous rocks, mostly
plutonic orthopyroxenites, not grains formed by condensation from the
solar nebula.

3. The Mg-silicate-rich aubrite parent body experienced extensive
melting and igneous differentiation, causing formation of diverse
lithologies, some of which have not been described previously.
These lithologies include dunites (represented by forsterite
crystals), plutonic orthopyroxenites (represented by most enstatite
crystals in the matrix), plutonic pyroxenites (the pyroxenitic clasts),
and plagioclase-silica rocks (like the feldspathic clasts). Presence
of impact melt breccias (the microporphyritic clasts and the diopside-
plagioclase-silica clast) of still different compositions further attest
to the lithologic diversity of the aubrite parent body.
Received on Tue 10 Jul 2001 04:26:41 PM PDT