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activity-composition model documentation

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page last updated: 28.11.2011

Input Files

This section looks at the information that is in the main thermocalc input files for phase diagram calculations. The input files are

The internally consistent dataset

The structure and contents of this file are discussed in the internally consistent dataset documentation.

The global preferences file – tc-prefs

This file determines the overall way thermocalc will run. Here you can set the The internally consistent dataset to be used, the type of calculation to be done (e.g. phase diagrams, avPT etc) the script file to be used whether the on-screen output is to be wrapped, window sizes etc.

The tc-prefs file is a simple text file with a set of scripts that control how thermocalc operates. Explanation of these scripts can be found in the script documentation.

A typical tc-prefs file (annotated) may look like:

setpagewidth 195              % for Mac; 80 on a PC
dontwrap yes                  % out put is not wrapped
dataset 55                    % dataset is tc-ds55
calcmode 1                    % mode 1 calcs ie phase diagram calculations
scriptfile ptpstute           % the script file ptpseudo is used
strictsyntax no               % strict syntax rules for a-x models not used
*                             % end of file

as with all thermocalc and drawpd datafiles, anything after a ‘%’ is not read by the software

The script file – eg tc-ptpseudo

The script file allows the user to define how the individual calculations will be undertaken, P-T windows, what is to be calculated, what goes into the output files and bulk rock compositions among other things. Below is the contents of a script file for a P-T pseudosection.

% This script file is set up for calculating a P-T pseudosection.
% The bulk rock composition in NCKFMASH is that used for Fig 8b in
% White, RW, Powell, R & Holland, TJB (2007) Progress relating to
% calculation of partial melting equilibria for metapelites. Journal of
% Metamorphic Geology, 25, 511-527.

% the above text explains what the file was used for and where the bulk rock
% composition comes from

axfile NCKFMASHp               % this tells thermocalc what ax file to use
infolevel 1                    % this controls the type of info that is produced
                               %–keep as 1

ignore                         % tells thermocalc which minerals in the ax filecan be
                               % automatically ignored (eg for granulites you could
                               % include chl, ctd & st here

printxyz yes                   % prints the composition variables in the tc-log file in
                               % format where they can be pasted in this file and used as
                               % starting guesses e.g. ‘readxyz x(bi) 0.7101’-see below

printbulkinfo yes              % outputs the modes and mineral comps into a matrix that
                               % can be used as a bulk rock composition

incax no                       % whether or not to print the a-x models used in
                               % the tc-log file

fluidpresent yes               % whether fluid may be present
fluidexcess no                 % whether fluid is in excess
setexcess                      % allows you to set any phases to excess. In
                               % pseudosections this just saves you from typing this
                               % phase in, it can still be consumed

calctatp ask                   % whether to set P’s and calc T’s or vice versa at each
                               % run, or always set P’s or T’s

setdefTwindow yes  200.001 1000.001      % default T window, allows you just to hit
                                         % return when prompted for T window

setdefPwindow yes  0.2 12      % default P window, allows you just to hit
                               % return when prompted for P window

project no                     % whether to do a compatibility projection

seta no                        % whether to set any activities
setiso no                      % whether to set any composition variables (eg xbi)

% calculated at P =   4.8; T =  732
readxyz x(bi)         0.7101            % this list sets starting guesses for
readxyz y(bi)         0.5659            % minerals that overwrites those in the
readxyz Q(bi)        0.06370            % ax file. the list can be printed in the
readxyz x(cd)         0.4700            % log file using the ‘printxyz’ script
readxyz h(cd)         0.5912
readxyz x(g)          0.8558
readxyz z(g)         0.01678
readxyz q(L)          0.1670
readxyz fsp(L)        0.3044
readxyz na(L)         0.5069
readxyz an(L)       0.006007
readxyz ol(L)       0.002631
readxyz x(L)          0.8205
readxyz h2o(L)        0.5042
readxyz na(ksp)       0.2799
readxyz ca(ksp)      0.01105
readxyz ca(pl)        0.2573
readxyz k(pl)        0.05377

pseudosection yes             % whether you are calculating a pseudosection.
                              % if yes thermocalc expects a bulk comp

%
% ---------------------------------
%            H2O    SiO2   Al2O3   CaO   MgO   FeO  K2O  Na2O  
setbulk yes  5.92   69.12  8.82    0.27  3.59  8.80 2.93 0.56      % the bulk comp
% -----------------------------
setmodeiso yes         % whether to set any modes for boundaries and contours
zeromodeiso yes         % whether to set zero modes for field boundaries

calcsdnle no                   % whether to calc uncertainties on each equilibria

smath no                % whether to format the output file for mathematica
drawpd yes              % whether to format the output file for drawpd

*           % end of file anything below this not read

There are lots of other scripts available to do various things. These are outlined in the scripts documentation, some preset script files are available on the datafiles page.

The activity-composition (ax) file – eg tc-NCKFMASHp

This file contains the a-x models for each solid solution phase as well as a list of pure endmember phases. Starting guesses can be set here or in the script file. Documentation on the activity-composition models and coding can be found on the activity composition models page.

A typical (but contracted) ax file is shown below. The top section is just explanation and the sources for the models used, followed by the models, then the pure phases

% THERMOCALC datafile in NCKFMASH for calculations in pelitic and semipelitic
% rock compositions at subsolidus and suprasolidus conditions.

% File contains coding for:

% liq, bi, g, opx, ged, anth, cd, sp, osm, ksp, pl, st, ctd, chl, mu, pa.

% ------------------------------------------------------------------------------------
%
% When using this datafile, please cite the following references as required:
%
% Amphiboles (ged & anth):
% Diener, JFA, Powell, R, White, RW & Holland, TJB (2007) A new thermo-
% dynamic model for clino- and orthoamphiboles in Na2O-CaO-FeO-MgO-Al2O3-
% SiO2-H2O-O. Journal of Metamorphic Geology, 25, 631-656.
%
% Biotite:
% White, RW, Powell, R & Holland, TJB (2007) Progress relating to calculation
% of partial melting equilibria for metapelites. Journal of Metamorphic Geology,
% 25, 511-527.
%
% cordierite, spinel, staurolite & chloritoid:
% Holland, T.J.B., & Powell, R., 1998. An internally consistent thermodynamic dataset for
% phases of petrological interest. Journal of Metamorphic Geology, 16, 309-343.
%
% Chlorite:
% Holland, TJB, Baker, JM & Powell, R (1998) Mixing properties and activity-
% composition relationships of chlorites in the system MgO-FeO-Al2O3-SiO2-H2O.
% European Journal of Mineralogy, 10, 395-406.
%
% Garnet:
% White, RW, Powell, R & Holland, TJB (2007) Progress relating to calculation
% of partial melting equilibria for metapelites. Journal of Metamorphic Geology,
% 25, 511-527.
%
% Muscovite & Paragonite:
% Coggon, R. & Holland, T.J.B., 2002. Mixing properties of phengitic micas and revised
% garnet-phengite thermobarometers. Journal of Metamorphic Geology, 20, 683-696.
%
% Orthopyroxene:
% Powell, R., and Holland, T.J.B., 1999. Relating formulations of the thermodynamics of
% mineral solid solutions: activity modelling of pyroxenes, amphiboles and micas.
% American Mineralogist, 84, 1-14.
%
% Melt:
% White, RW, Powell, R & Holland, TJB (2007) Progress relating to calculation
% of partial melting equilibria for metapelites. Journal of Metamorphic Geology,
% 25, 511-527.
%
% Plagioclase and K-feldspar:
% Holland, TJB & Powell, R (2003) Activity-composition relations for phases in
% petrological calculations: an asymmetric multicomponent formulation. Contributions
% to Mineralogy and Petrology, 145, 492-501.
%
% Osumilite:
% Holland, T.J.B., Babu, E.V.S.S.K, & Waters, D.J., 1996. Phase relations of Osumilite and
% dehydration melting in pelitic rocks: a simple thermodynamic model for the
% KFMASH system. Contributions to Mineralogy and Petrology, 124, 383-394.
%
% =====================================================================
% Cordierite: FMASH
% Holland, T.J.B., & Powell, R., 1998. An internally consistent thermodynamic dataset for
% phases of petrological interest. Journal of Metamorphic Geology, 16, 309-343.
%
% x(cd) = Fe/(Fe + Mg)
% h(cd) = H2O on Hydroxyl site

cd 3
   x(cd)         0.2307
   h(cd)         0.5766   

% --------------------------------------------------
  p(crd)    1 1      1  2 -1  x -1  h
  p(fcrd)   1 1      0  1  1  x
  p(hcrd)   1 1      0  1  1  h
% --------------------------------------------------

ideal
% --------------------------------------------------
4  x(Mg)    1 1      1  1 -1  x
   x(Fe)    1 1      0  1  1  x
   h        1 1      0  1  1  h
   noth     1 1      1  1 -1  h
% --------------------------------------------------
      crd     1    2      x(Mg)  2    noth  1
      fcrd    1    2      x(Fe)  2    noth  1
      hcrd    1    2      x(Mg)  2       h  1
% =====================================================================
% Staurolite: FMASH
% Holland, T.J.B., & Powell, R., 1998. An internally consistent thermodynamic dataset for
% phases of petrological interest. Journal of Metamorphic Geology, 16, 309-343.
%
% x(st) = Fe/(Fe + Mg)
     
st 2 
     x(st) 0.89
% --------------------------------------------------    
  p(mst)   1 1      1  1 -1  x
  p(fst)   1 1      0  1  1  x
% -------------------------------------------------- 
  sf    
  w(st) -8 0 0
% --------------------------------------------------
  2  x(Mg)   1 1      1  1 -1  x
     x(Fe)   1 1      0  1  1  x
% --------------------------------------------------
  mst     1  1      x(Mg)  4
             
  fst     1  1      x(Fe)  4
           
% =====================================================================
next model
next model etc
%__________________________________________________________________
ky sill and q H2O                   %pure phases
*                                   % end of file