Approach to chemical equilibrium in diagenetic chlorites (original) (raw)
Abstract
Electron microprobe analyses were made on diagenetic chlorites in sandstones and mudstones from two deep wells according to the petrographic character of the chlorite occurrence: as pseudomorphic phases, rims on quartz or glauconite or as distinct phases in the clay matrix. Chlorite compositions do not depend upon crystallization site (reacting phases) making it apparent that new chlorites can form in an approach to chemical equilibrium at or near the surface (40° C, 1 km depth). Comparison of this data with that for late diagenetic and early metamorphic chlorites indicates that the compositional range for different grains in the same thin section is similar for the samples throughout the 40°–270° C temperature span. Compositional range decreases upon further metamorphism.
Al content appears to be a more reliable indicator of temperature variations than other substitutions in the chlorite structure. The clay mineral assemblage which indicates sedimentary facies affects the trends in composition (Al increase or decrease) as a function of temperature. The octahedral site occupancy show a general increase in going from diagenesis to metamorphic conditions in pelitic rocks. The range of Fe-Mg ratios seems to depend more on the chemistry of each sample than the temperature of formation of the minerals.
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References
- Cathelineau M, Nieva D (1985) A chlorite solid solution geothermometer. The Los Azufres (Mexico) geothermal system. Contrib Mineral Petrol 91:235–244
Google Scholar - Goffé B (1984) Le facies a carpholite — chloritoide dans la couverture briançonnaise des alpes ligures. Mem Soc Geol It 28:461–479
Google Scholar - Hemley JJ, Montoya JW, Marnenko JW, Luce RW (1980) Equilibria in the system Al2O3-SiO2-H2O and some general implications for alteration mineralization processes. Econ Geol 75:210–228
Google Scholar - MacDowell SD, Elders WA (1980) Authigenic layer silicate minerals in bore hole Elmore 1, Salton Sea geothermal field, California. Contrib Mineral Petrol 74:293–310
Google Scholar - Nicot E (1981) Les phyllosilicates des terrains précambriens du Nord-Ouest du Montana (USA) dans la transition anchizone-épizone. Bull Mineral 104:615–624
Google Scholar - Paradis S (1981) Le métamorphisme hercynien dans le domaine centre armoricain occidental: essai de caractérisation par l'étude des phyllites des formations gréso-pélitiques. Thèse de 3e cycle, Université de la Bretagne Occidentale, p 167
- Paradis S, Velde B, Nicot E (1983) Chloritoid-pyrophyllite-rector-ite facies rocks from Britanny, France. Contrib Mineral Petrol 83:342–347
Google Scholar - Velde B (1985) Clay minerals: a physico-chemical explanation of their occurrence. Elsevier, Amsterdam, p 421
Google Scholar - Velde B, Suzuki T, Nicot E (1986) Pressure-temperature-composition of illite/smectite mixed-layer minerals: Niger delta mudstones and other samples. Clays Clay Miner 34:435–441
Google Scholar
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Authors and Affiliations
- Laboratoire de Géologie, ER224 CNRS, Ecole Normale Supérieure, 46 rue d'Ulm, F-75230, Paris, France
B. Velde & M. Medhioub
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- B. Velde
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Velde, B., Medhioub, M. Approach to chemical equilibrium in diagenetic chlorites.Contr. Mineral. and Petrol. 98, 122–127 (1988). https://doi.org/10.1007/BF00371916
- Received: 27 July 1987
- Accepted: 11 November 1987
- Issue Date: January 1988
- DOI: https://doi.org/10.1007/BF00371916