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Hydrothermal. Alteration of a Variscian Granite, Magmatic Autometasomatism and Fault Related Vein Metasomatism

  • Tj. Peters
Part of the NATO ASI Series book series (ASIC, volume 218)

Abstract

Two types of hydrothermal alteration can be recognized in a biotite granite of Variscan age in Northern Switzerland. The first is related to the intrusion of the granite and lead to the replacement of K-spar and biotite by muscovite, of plagioclase by sericite and calcite and to a chloritization of biotite. This process affected the granite as a whole. Mass transfer calculations using analysed mineral compositions indicated locally mass balanced reactions without transport beyond neighbouring grains. Using the H2O and CO2 (from C?) already present in the granitic melt, this alteration process is an autometasomatism during cooling leading to sericitization/chloritization taking place at 350°C by a fluid with 6.5 weight aeq. NaCl. The second process, the main hydrothermal alteration is connected with young Palaeozoic faulting and locally anomalous heat flow. This process has lead to a vein parallel zonation shown by clay minerals. During this stage of alteration process the granite was depleted in the major elements Si and Na and in the trace elements Sr, Ba and U. This depletion lead to an increased porosity. Fluids evolved from 7 weight% NaCl aeq. at T 350°C down to 0,1 weight% NaCl at T 90°C. The composition of this fluid was calculated, assuming equilibrium with the fissure minerals quartz, albite, K-spar and illite. Because of the low water/rock ratio indicated by stable isotope data, a model of repeated water recycling between the fissure and the rock is proposed.

Keywords

Country Rock Hydrothermal Alteration Fluid Composition Biotite Granite White Mica 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Aagard, P. and Helgeson, H.C. (1983): Activity/Composition Relations among Silicates and Aqueous Solutions: II. Chemical and Thermodynamic Consequences of Ideal Mixing of Atoms on Homological Sites in Montmorillonites, Illites and Mixed-Layer Clays. Clays and Clay Miner. 31/3, 207–217.CrossRefGoogle Scholar
  2. Chayes, F. (1955): Potash Felspar as a By-Product of the Biotite-Chlorite Transformation. J. Geol. 63, 75–82.CrossRefGoogle Scholar
  3. Eggler, D.H., Mysen, B.O. and Seitz, M.G. (1974): Solubility of CO2 in Silicate Liquids and Crystals. Yb. Carnegie Instn. Washington 73, 226–228.Google Scholar
  4. Ferry, J.M. (1978): Fluid Interaction between Granite and Sediment during Metamorphism, South Central Maine. Amer. J. Sci. 278, 1025–1056.CrossRefGoogle Scholar
  5. Ferry, J.M. (1979): Reaction Mechanisms, Physical Conditions, and Mass Transfer During Hydrothermal Alteration of Mica and Feldspar in Granitic Rocks From South Central Maine, USA. Contr. Mineral. Petrol. 68, 125–139.CrossRefGoogle Scholar
  6. Hammerschmidt, K. and Friedrichsen, H. (1985): Sauerstoff-und Wasserstoffisotopenuntersuchungen an primaren und sekundaren Mineralien. In: Sondierbohrung Bottstein-Geologie, TJ. Peters et al. eds. NAGRA Techn. Bericht 85–02.Google Scholar
  7. Hewitt, D.A. and Wones, D.R. (1975): Physical Properties of some Synthetic Fe-Mg-Al Trioctahedral Biotites. Amer. Mineralogist 60, 854–862.Google Scholar
  8. Hofmann, B. (1985): Die Erzmineralien. In: Sondierbohrung Bottstein-Geologie, TJ. Peters et al. eds. NAGRA Techn. Bericht 85–02.Google Scholar
  9. Hunziker, J.C., Steiner, H. and Hurford, A. (1985): Absolute Altersbestimmungen mit der K-Ar, Rb-Sr und Apatit-Spaltspur Methode. In: Sondierbohrung Bottstein-Geologie, TJ. Peters et al. eds. NAGRA Techn. Bericht 85–02.Google Scholar
  10. Perkins, E.H. (1980): A Reinvestigation of the Theoretical Basis for the Calculation of Isothermal-Isobaric Mass Transfer in Geochemical Systems involving an Aqueous Phase. M.Sc. Thesis, Univ. British Columbia, 149 p.Google Scholar
  11. Peters, TJ. and Hofmann, B. (1984): Hydrothermal Clay Formation in a Biotite Granite in Northern Switzerland. Clay Miner. 19, 579–590.CrossRefGoogle Scholar
  12. Robie, R.A., Bethke, P.M. and Beardsley, K.M. (1967): Selected X-Ray Crystallographic Data, Molar Volumes, and Densities of Minerals and related Substances. Bull. U.S. Geol. Survey 1248.Google Scholar
  13. Stalder, H.A. (1985): Flussigkeitseinschlusse. In: Sondierbohrung Bottstein-Geologie, TJ. Peters et al. eds. NAGRA Techn. Bericht 85–02.Google Scholar
  14. Veblen, D.R. and Ferry, J.M. (1983): A TEM Study of the Biotite-Chlorite Reaction and Comparison with Petrologic Observations. Amer. Mineralogist 68, 1160–1168.Google Scholar

Copyright information

© D. Reidel Publishing Company 1987

Authors and Affiliations

  • Tj. Peters
    • 1
  1. 1.Min.-petr. InstituteUniversity of BerneBernSwitzerland

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