From¡¡Shohei¡¡Banno
You may find the report of sector zoned zoisite by Enamai
in1970's in Mineralogical Abstracts if you have access to this.
Sector zoning shows non-equilibrium crystallization.
Shohei BANNO
1-23-16-104
Takano Higashi-Hiraki, Sakyo-ku, Kyoto ,606-8107 Japan
T &F :81-(0)75-722-7175
-----Original Message-----
From: No title defined [mailto:[log in to unmask]] On
Behalf Of Javier Rodr„^uez Aller
Sent: Friday, December 14, 2001 12:17 AM
To: [log in to unmask]
Subject: sector-zoned zoisite in eclogite
Dear all,
I've read about chemical aspects of sector zoning in zoisite (variations
in
Fe3/Fe3+Al ratios: Deer, Howie & Zussman, 1986)... Going further, does
anybody have any opinion about the origin(s) of this rare feature?
I've found sector-zoned zoisite porphyroclasts in poorly deformed
eclogite.
Zoisite coexists with omphacite porphyroclasts and garnet, which is
arranged in honeycomb patterns (surrounding omphacite and zoisite
clasts/domains).
It seems therefore that eclogitization took place in this rock at nearly
static conditions, with low-range chemical diffusion... Is then zoisite
reflecting some chemical inhomogeneity in a pristine (now diappeared)
phase? ... I'm thinking about possible An-rich, (zoned?) igneous
plagioclase.
PS:... Trace amounts of trivalent cations in the former phase can also
account for tiny rutile inclusions, arranged in preferred orientations
within zoisite clasts.
Thanks,
-------------------ooo---------------------
Javier Rodr¨ªguez
Dpto. Mineralog¨ªa y Petrolog¨ªa
Facultad de Ciencias, Univ. del Pa¨ªs Vasco
Apdo. Correos 644
E-48080 Bilbao, Spain
Tfn: + 34 94 601 5456
Fax: + 34 94 601 3078
e-mail: [log in to unmask]
===========================================
|