Dear Renato,
You asked about calibrated petrogenetic grids relating to the equilibrium Qtz+Grt+melt=Opx+Crd+Bt
Your reaction is univariant (appearing as a line) in the KFASH endmember system, part of which is shown in Grant's 1985 Fig 3.11. For Fe-Mg mineral compositions (KFMASH system) the reaction is divariant (ie it is continuous) and occurs over a range of P & T. The phase compositions in your reaction vary across the PT field.
The osumilite KFMASH grid of Holland et al 1996 Contr. Min. & Pet. (Fig 1a) shows two univariant reactions which form boundaries to the PT field you are interested in. The reactions are (osm ksp) and (osm sill). The divariant field between them can be contoured with isopleths for each phase composition using THERMOCALC.
best wishes,
Neil Hudson
>>> Renato de Moraes <[log in to unmask]> 07/18/00 09:30pm >>>
Dear all,
I am working with some sapphirine bearing rocks from central Brazil. In
one sample Spr+Qtz are rare and occuring in contact only as inclusions
inside Grt. Some Grt grains are substituted by Crd+Spl+Sil and in
subsequent step Grt has its borders substituted by Opx+Crd+/-Bt. I
interpret that these assemblages were formed by the breakdown of Qtz+Spr
at an ITD P-T path followed by some cooling (?) until the remained Grt be
consumed by the reaction:
Qtz+Grt+melt=Opx+Crd+Bt
The topology of this reaction appears in the Fig 3.11 of Grant (1985). Is
there any petrogenetic grid with this reaction plotted in a quantified P-T
space? Can anybody help me?
Best regards
Renato
Grant, J.A. 1985. Phase equilibria in partial melting of pelitic rocks. In:
Ashworth, J.R. (ed). Migmatites, 86 - 144. Glasgow: Blackie.
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