Dear Simon:
You must be careful about the real meaning of
pseudo-sections, as sometimes, minor components can strongly
affect equilibria…
Besides that, I think you may be right.
Overprinting like that is surely a common phenomenon.
Is there any sample in which you can see
staurolite relicts ? Otherwise, I think that it will be
difficult to confirm your hypothesis.
The fact that pseudomorphs are sometimes
present and sometimes absent could reflect different speeds
of crystallisation.
Cheers
Nuno
De:
Metamorphic Studies Group
[mailto:[log in to unmask]] Em nome de
Simon
Enviada: 13 de setembro de 2015 18:38
Para: [log in to unmask]
Assunto: Chloritoid Pseudomorphs
Dear
all,
In the study area for my masterthesis (southern Saualpe,
Eastern Alps) large prismatic chloritoid pseudomorphs
occur in a (lower) amphibolite grade
g-st-ctd-chl-paragonite micaschist. Inside the
pseudomorphs fine grained sericite as well as paragonite
are common (please see the attached figure).
I suspect that they are replacement products after
coarse-grained staurolites which seem to have grown during
prograde permian HT/LP metamorphism (~600°C & 6kbar)
as shown by pseudosection modelling. After that, the rocks
were overprinted by the eoalpine HP/LT metamorphism where
I think the replacement occured, as the prograde path lies
largely within the ctd-stabilityfield and outside the
st-field.
The pseudomorphs occur only in a restricted locality,
although rocks with virtually the same composition occur
nearby, showing the same paragensis but lacking the
pseudomorphs. In this case staurolite of eoalpine
generation is in equilibrium with chloritoid (as it is
also in the samples with the pseudomorphs), but, the
striking pseudomorphs are lacking.
I'd like to investigate the replacement further, can you
please give me a hint how to proceed? Or is there maybe a
paper where such microstructures have been described?
I am thankful for every thought!
Thank you very much!
Cheers
Simon
ctd-pseudomorph.jpg