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American Journal of Science


Theoretical models of intergranular diffusion demonstrate that grain size and grain boundary width are the most important textural parameters influencing diffusion in metamorphic rocks. Taking diffusion in an aqueous solution as a limiting case for diffusion in the intergranular region of metamorphic rocks, it appears that the diffusivities of many species will be similar and relatively insensitive to variations in temperature and pressure over a wide range of metamorphic conditions. Observed variations in the mobility of chemical components during metamorphism may be related principally to variations in the ratio of the component density in the intergranular region to the component density in the minerals. Experimental studies of the growth of forsterite reaction zones around periclase crystals at 650° and 700°C and I kb water pressure provide an upper limit to the effective diffusivity of silica through polycrystalline forsterite: DSiO2 ~ I0- 9/a cm 2/s where a is the grain size in microns. This maximum diffusivity can be used to obtain minimum times for the growth of reaction zones in metamorphic rocks.



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Archived as published. Open access article in Studies in Metamorphism and Metasomatism: a special volume of the American Journal of Science.

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