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Kinetics of metamorphic reactions

Kinetics of metamorphic reactions - 1 Equilibrium vs...

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1 Equilibrium vs. non-equilibrium in metamorphic rocks Reaction Kinetics Reaction kinetics refers to the rates at which reactions take place. For metamorphic reactions, this type of study is very difficult. Most metamorphic reactions are very slow or sluggish, especially at low temperatures. This is evidenced by the preservation of relict minerals and textures in low grade rocks. It is therefore very important to identify the scale at which minerals have equilibrated in very low grade metamorphic rocks, because these scales may be much smaller than those of a thin section. In terms of the relative rates of metamorphic reactions, prograde reactions are faster than retrograde ones. This is evidenced by the common preservation of mineral assemblages that form under peak metamorphic conditions, as opposed to the rarity of assemblages that formed prior to peak conditions. Factors affecting reaction rates: (a) transport: if transport of ions and/or elements by fluids is facilitated, reaction rates are increased. (b) diffusion: Diffusion is the migartion of components (elements or ions) from higher concentrations to lower concentrations. Higher rates of diffusion of elements will lead to faster reaction rates. (c) temperature: generally, the higher the temperature, the faster the reaction.
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