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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 Rodríguez
Dpto. Mineralogía y Petrología
Facultad de Ciencias, Univ. del País Vasco
Apdo. Correos 644
E-48080 Bilbao, Spain

Tfn:  + 34 94 601 5456
Fax:  + 34 94 601 3078
e-mail: [log in to unmask]
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