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Octahedral occupancy and the chemical composition of diagenetic (low-temperature) chlorites

  • S. Hillier (a1) and B. Velde (a1)


The chemical composition of about 500 diagenetic chlorites, determined by electron microprobe, has been studied in six different sedimentary sequences spanning conditions from early diagenesis to low-grade metamorphism, in the temperature range 40–330°C. The range of Fe/(Fe + Mg) is almost complete and is positively correlated with Al. Five sequences show the same compositional variation. In each, the most siliceous chlorites have the lowest R2+, substantially more octahedral than tetrahedral Al, and the lowest octahedral totals. Conversely, the least siliceous have the highest R2+, nearly equal octahedral and tetrahedral Al, and octahedral totals close to that for an ideal trioctahedral mineral. A dioctahedral substitution Si[]R2−2 (where [] represents a vacant octahedral site) which decreases with temperature, describes this variation. Low octahedral totals are, however, induced by the method of calculation and need not indicate vacancies; for published wet chemical analyses of metamorphic chlorites they may simply indicate oxidation of Fe. Intergrown dioctahedral phyllosilicates may partly account for apparent vacancies in diagenetic chlorites. Nevertheless, the correlation of composition with temperature and similarities to the temperature-related evolution of synthetic chlorites, suggest that diagenetic chlorites are compositionally distinct from, but metastable with respect to, fully trioctahedral metamorphic chlorites. Temperature-related trends are modified by bulk composition, complicating their potential use for low-temperature geothermometry.



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Ahn, H. J. & Peacor, D.R. (1985) Transmission electron microscopic study of chlorite in Gulf Coast argillaceous sediments. Clays Clay Miner., 33, 228–236.
Bailey, S.W. & Brown, B.E. (1962) Chlorite polytypism: I. Regular and semi-random one layer structures. Am. Miner., 47, 819–850.
Barker, C.E. & Pawlewicz, M.J. (1986) The correlation of vitrinite reflectance with maximum temperature in humic organic matter. Pp. 7993 in: Lecture Notes in Earth Sciences 5. Palaeogeothermics(Bunterbath, G. & Stenga, L., editors). Springer-Verlag, Berlin.
Beaufort, D. (1986) Defenition des equilibres chlorite-mica blanc dans la metamorphisme et la metasomatimse: etude des metasediments encaisant Vamas sulfure de Rouez. These, Univ. Poitiers, France.
Bettison, L. A. & Schiffmann, P. (1988) Compositional and structural variations of phyllosilicates from the Point Sal ophiolite, California. Am. Miner., 73, 62–76.
BoleS, J.R. & Franks, S.G. (1979) Clay diagenesis in Wilcox sandstones of southwest Texas: implications of smectite diagenesis on sandstone cementation. J. Sed. Pet., 49, 55–70.
Cathelineau, M. & Nieva, D. (1985) A chlorite solid solution geothermometer: The Los Azufres (Mexico) geothermal system. Contrib. Mineral. Pet., 91, 235–244.
Cathelineau, M. (1988) Cation site occupancy in chlorites and illites as a function of temperature. Clay Miner., 23, 471485.
Curtis, C.D., Ireland, B.J., Whiteman, J.A., Mulvaney, R. & Whittle, C.K. (1984) Authigenic chlorites: problems with chemical analysis and structural formula calculation Clay Miner., 19, 471–481.
Curtis, C.D., Hughes, C.R., Whiteman, J.A. & Whittle, C.K. (1985) Compositional variation within some sedimentary chlorites and some comments on their origin. Mineral. Mag., 49, 375–386.
Eslinger, E.V. & Savin, S.M. (1973) Oxygen isotope geothermometry of the burial metamorphic rocks of the Precambrian Belt Supergroup, Glacier National Park, Montana. Geol. Soc. Am. Bull., 84, 2549–2560.
Fransolet, A.M. & Schreyer, W. (1984) Sudoite, di/trioctahedral chlorite: a stable low-temperature phase in the system MgO-Al2OrSiO2-H2O. Contrib. Mineral. Pet., 86, 409–417.
Foster, M.D. (1962) Interpretation of the composition and a classification of the chlorites. Geol. Surv. Prof. Pap., 414A.
Frey, M. (1987). The reaction-isograd kaolinite + quartz = pyrophyllite + H20, Helvetic Alps Switzerland. Schweiz. Miner. Petrogr. Mitt., 67, 1–11.
Hayes, J.B. (1970) Polytypism of chlorite in sedimentary rocks. Clays Clay Miner., 18, 285–306.
Hey, M.H. (1954). A new review of the chlorites. Mineral. Mag., 30, 277–292.
Hillier, S.J. (1989) Clay mineral diagenesis and organic maturity indicators in Devonian lacustrine mudrocksfrom the Orcadian Basin, northern Scotland. PhD thesis, Univ. Southampton, UK.
Inoue, A., Utada, M., Nagata, H. & Watanabe, T. (1984). Conversion of trioctahedral smectite to interstratified chlorite/smectite in Pliocene acidic pyroclastic sediments of the Ohyu district, Akita Prefecture, Japan. Clay Sci., 6, 103116.
Jahren, J.S. & Aagaard, P. (1989) Compositional variation in diagenetic chlorites and illites, and relationships with formation-water chemistry. Clay Miner., 24, 157–170.
Laird, J. (1988) Chlorites: metamorphic petrology. Pp. 405-447 in: Hydrous Phyllosilicates (Exclusive of Micas) (Bailey, S.W., editor). Reviews in Mineralogy, 19, Mineralogical Society of America, Washington, DC.
Lee, J.H., Ahn, J.H. & Peacor, D.R. (1985) Textures in layered silicates progressive changes through diagenesis and low temperature metamorphism. J. Sed. Pet., 55, 532–540.
Maxwell, D.T. & Hower, J. (1967) High-grade diagenesis and low-grade metamorphism of illite in the Precambrian Belt series. Am. Miner., 52, 843–857.
Medhioub, M. (1987) Chlorites de neogenese et approche a Vequilibre chimique. Thèse de Doctoral, Univ. Paris 6, France.
Newman, A.C.D. & Brown, G. (1987) The chemical constitution of clays. Pp. 1128 in: Chemistry of Clays and Clay Minerals (Newman, A.C.D., editor). Mineralogical Society, London.
Paradis, S. (1981) Le metamorphisme Hercynien dans le domaine centre Armoricain occidental: Essai de characterisation par Vetude des phyllite des formations greso-pelitiques. Thèse de Doctorat, Univ. Bretagne Occidental, France.
Paradis, S., Velde, B. & Nicot, E. (1983) Chloritoid-Pyrophyllite-Rectorite facies rocks from Brittany, France. Contrib. Mineral. Pet., 83, 342–347.
Shau, Y-H. Peacor, D.R. & Essene, E.J. (1990) Corrensite and mixed-layer chlorite/corrensite in metabasalt from northern Taiwan: TEM/AEM, EMPA, XRD, and optical studies. Contrib. Mineral. Pet,, 105, 123–142.
Shirozu, H. (1960) Ionic substitutions in Fe-Mg chlorites. Mem. Faculty Sci. Kyushu Univ. D, Geol., 9, 183–186.
Velde, B. (1973) Phase equilibria in the system MgO-Al2O3-SiO2-H2O: chlorites and associated minerals. Mineral. Mag., 39, 297–312.
Velde, B. & Rumble, D. (1977) Alumina content of chlorite in muscovite bearing assemblages. Carnegie Inst. Wash. Yearbook, 76, 621–623.
Velde, B. (1984) Electron microprobe analysis of clay minerals. Clay Miner., 19, 243–247.
Velde, B. (1985) Clay Minerals: a Physico Chemical Explanation of their Occurrence.Developments in Sedimentology No. 40, Elsevier, Amsterdam
Velde, B., Suzuki, T. & Nicot, E. (1986) Pressure, temperature composition of illite/smectite mixed-layer minerals: Niger Delta mudstones and other examples. Clays Clay Miner., 34, 431–435.
Velde, B. & Medhioub, M. (1988) Approach to chemical equilibrium in diagenetic chlorites. Contrib. Mineral. Pet. 98, 122127.
Wiewiora, A. & Weiss, Z. (1990) Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: II. The chlorite group. Clay Miner., 25, 83–92.
Yau, Y., Peacor, D.R., Beane, R.E., Essene, E.J. & McDowell, S.D. (1988) Microstructures, formation mechanisms, and depth zoning of phyllosilicates in geothermally altered shales, Salton Sea, Californa. Clays Clay Miner., 36, 1–10.

Octahedral occupancy and the chemical composition of diagenetic (low-temperature) chlorites

  • S. Hillier (a1) and B. Velde (a1)


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