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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 RodrĄ^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®™guez
Dpto. Mineralog®™a y Petrolog®™a
Facultad de Ciencias, Univ. del Pa®™s Vasco
Apdo. Correos 644
E-48080 Bilbao, Spain

Tfn:  + 34 94 601 5456
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