Chlorite-Biotite Equilibrium Reactions in a Carbonate-Free System |
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| Authors: | MCNAMARA MALCOLM JAMES |
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| Institution: | Geological Survey of Sweden Stockholm 50, Sweden |
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| Abstract: | In a system open to both potassium and water, the conditionsfor two different chloritebiotite equilibrium reactions maybe depicted on an isobaric temperature–(K)/(H) diagram.At moderate values of the (K)/(H) ratio in the fluid phasepervading the system, muscovite is involved in the equilibriumreaction: chloritequartzKOH= biotitemuscoviteH2O. At high values of (K)/(H) K-feldspar is involved in the equilibriumreaction: chlorite quartzKOH = biotiteK-feldsparH2O. When the same system is closed to potassium, assemblages formingat lower values of (K/(H) resemble those developed on progressivemetamorphism, whereas higher (K)/ (H assemblages in the closedsystem resemble certain retrogressive mineral assemblages. Theassemblage muscovitebiotite is characteristic of higher temperaturesand lowyer values of µK/µS than the assemblageK-feldsparchlorite in carbonate-free rocks where both potassiumand water were perfectly mobile components and SiO2 was presentin excess. |
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