Models for diffusion-controlled, steady-state processes

MODELS FOR DIFFUSION-CONTROLLED, STEADY-STATE PROCESSES 

Fisher (1975) developed a simpler approach, which solves eqs. (1.1) and (1.4) at zone boundaries only. This procedure, as modified below, will predict the same bulk composition and relative volvime for each zone in a structure as the more exact approach, but it will ignore any variation in modal composition within zones. If these variations are important, one of the more exact approaches should be used, but in many metamorphic structvires, the reaction zones are nearly uniform in composition, and the simpler approach will be sufficiently accurate. I will use it here. 

Consider a hypothetical three-conponent system containing minerals A, B and C, with the molar coitqpositions 

In order for the assemblage ABC to remain at the invariant, these fluxes must be balanced by reactions among A, B and C. 

The net reaction must be a linear combination of the individual precipitation/solution reactions for A, B and C, each of the form A = n i + + n3 3 The rates of these three reactions 

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