Greetings,
I have been using Perple_X for my thermodynamic modeling, and have
been frustrated by differences in the predictions in different sort
of calculations. the two types in question are designated in the
"in" file as "calculation type 5" (what I think of as the "normal"
calculations--this is the one for which I enter a bulk rock
composition give it a P/T range of interest and obtain
"pseduosections") and "calculation type 7" (which I call "path"
calculations--this is the one for which I enter the same bulk rock
composition, give it a relationship between temperature and pressure
and tell it the range of pressure (or T) of interest, and which
mineral(s) should fractionate over time). It seems to me that, in
theory, the first "step" in the "path" for calculation type 7 should
predict minerals of the exact same composition at a given P/T as was
predicted in calculation type 5 for that P/T.
I have been using calculation type 5 first, using the resultant
graphs and the "werami" program to determine the P/T at whcih garnets
are predicted to have the same composition as those measured in my
garnet cores, and then trying to use type calculation type 7 to
calculate P/T paths over which garnet composition changes with
fractionation such that they achieve the same composition as those
measured in my garnet rims. However, this is complicated because
often (always?) the predicted composition of garnet at the first step
of the path doesn't match what was predicted by the type 5
calculations for that P/T. (The amount by which it doesn't match
seems to vary) Has anyone else faced this complication? If so, have
you found a way to get that path calculations to start with the same
composition of garnet (or whatever mineral you told it to
fractionate)? Am I doing something wrong? Am I being unreasonable
to want them to be the same? How different can they be and still
have results that are "useable"?
thanks,
--Reia
Reia M. Chmielowski
PhD Candidate
Department of Earth Sciences/CODES
University of Tasmania, Australia
(03) 6239 6666
0408 238 590
http://utas.academia.edu/ReiaChmielowski
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