Hello all,
I wonder if anyone is familiar with cordierite pseudomorphs after
andalusite and staurolite. I am working on metapelites from the Bossost
dome in the Axial zone of the Pyrenees. There, a moderately sized contact
metamorphic aureole is developed in previously foliated phyllites and
schist around a granitic intrusion. The intrusion seems to have happened at
shallow structural levels.
A typical feature of the schist is the occurrence of centimetre-sized
lenticular poikiloblastic andalusite porphyroblasts. These porphyroblasts
are symmetrical and oriented parallel mica mineral lineation. The
andalusite porphyroblasts overgrow the main foliation and have an internal
foliation showing a convex pattern, suggesting a component of pure shear.
Now, close to the contact with the granite, less than one hundred metres
away, cordierite crystals have exactly the same shape and size as the
andalusite further away from the contact. Furthermore, relics of andalusite
(and staurolite) are found within cordierite porphyroblasts. This indicates
to me that this is a case of pseudomorphism.
In these same rocks, different locality, there is a sample with large
cordierite porphyroblasts containing andalusite and staurolite inclusions
that seem to show consumption to form cordierite. In that sample there is a
lozenge shaped intergrowth of cordierite and staurolite, which I interpret
as incomplete replacement of staurolite by cordierite. Cordierite
pseudomorphism of staurolite.
I did not find anything in the literature regarding cordierite
pseudomorphism, and also have no comparison with my previous experience in
metapelitic rocks. I would welcome any suggestions or similar observations,
references regarding this matter.
Thanks a lot,
Jochen Mezger
P.S. If anyone is really interested, I can forward some thin section scans
or slides (still at the photo lab).
***************************************************************************
Dr. Jochen Mezger
Postdoctoral Fellow
Johannes Gutenberg-University Mainz Tel.: 49-(0)6131-3924767
Institut fuer Geowissenschaften Fax.: 49-(0)6131-3923863
Tectonophysics Group
Becherweg 21
55099 Mainz Email: [log in to unmask]
GERMANY http://www.uni-mainz.de/~mezger/
============================================================
"We're all recycled history machines,
cavemen in faded blue jeans." Jimmy Buffett
****************************************************************************
|