Hi Martin,
for the moment there is no good MnNCKFMASHTO a-x
file available, although, as far as I know, some
people around Roger Powell are working on it.
Then, if one wants to deal with this system, one
has to do some choices. If Mn is an important
component, then it certainly is important in
garnet and you then have to choose the garnet
model with Mn and without Fe3. Such approach has
been adopted e.g. by Hasalova et al. (including
RP) (2008) and this point is discussed there on
p. 63.
As far as biotite is concerned, given its
systematically low contents of Mn, it is
certainly much more important to keep the
Ti-bearing model.
If one is interested in low T conditions (and the
beginning of garnet growth), other Mn-bearing
phases have to be included and chlorite comes to
mind as the most important candidate (there is no
model for Mn-bearing ilmenite). This is what we
have done in Le Bayon et al. (2006) - the model
is described there (and I can send you the file).
Mn can be also included by ideal mixing (although
it probably is not ideal ;)) into cd, st and ctd.
this is what we are currently using - it sort of works...
Good luck,
Pavel
Hasalová, P., Stípská, P., Powell, R., Schulmann,
K., Janousek, V. & Lexa, O., 2008. Transforming
mylonitic metagranite by open-system interactions
during melt flow. Journal of Metamorphic Geology,
26(1), 55-80.
Le Bayon, B., Pitra, P., Ballčvre, M. & Bohn, M.,
2006. Reconstructing P-T paths during continental
collision using multi-stage garnet (Gran Paradiso
nappe, Western Alps). Journal of Metamorphic
Geology, 24(6), 477-496.
----
>Unfortunately that will not work.
>The MnNCKFMASHTO file contains the a-X
>relationships for garnet and biotite, amongst
>others, which includes 'O' in their formulation.
>I cannot simply delete the oxides. Moreover, I
>cannot use the MnNCKMASH datafile for biotite
>because Ti is then missing!
>
>
>Dr Martin J. Rigby
>Department of Geology
>University of Pretoria
>Pretoria 0002
>Republic of South Africa
--
Pavel PITRA
Geosciences Rennes email: [log in to unmask]
Université Rennes 1 tel: (++33) 2.23.23.65.06
Campus de Beaulieu - Bat. 15 fax: (++33) 2.23.23.60.97
F - 35 042 RENNES CEDEX
FRANCE http://www.geosciences.univ-rennes1.fr/
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