A model for metamorphic differentiation relying on the contrasting equilibria between the intergranular solution and both mineral recrystallization reactions and surface exchange reactions has been developed. Deformation at constant temperature and pressure will tend to increase the surface area of the minerals present, which in turn will increase the relative influence of surface reactions on the chemistry of the intergranular solution. In the examples described, cation exchange on muscovite surfaces shifts the alkali/H+ activity ratio of the solution into a feldspar stability field. This results in the crystallization of feldspar.

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