Mg-Fe Fractionation in Metamorphic Environments

  • H. P. Eugster
  • E. S. Ilton
Chapter
Part of the Advances in Physical Geochemistry book series (PHYSICAL GEOCHE, volume 3)

Abstract

Metamorphic reactions generally proceed in and depend on the presence of an aqueous fluid, whether as a separate phase or as an aqueous grain boundary phase. Walther and Orville (1982) believe that

Regionally metamorphosed rocks will have a discrete fluid phase only when devolatilization reactions are actually taking place. At other times only an absorbed surface monolayer of volatiles on the minerals will be present. (p. 252)

Whichever is the case, this fluid is the principal transport medium for chemical exchanges between reactants and product minerals. The composition of this fluid must be known in order to define concentration gradients and calculate mass balance conditions. In earlier contributions (Gunter and Eugster, 1980; Eugster, 1981, 1982; Eugster and Gunter, 1981) we have used mineral assemblages and their experimentally determined solubilities to estimate fluid compositions. This approach rests on the assumption that for most metamorphic reactions mineral assemblages buffer the composition of the surrounding fluid. Effects of solid solution on solid-fluid fractionation were also evaluated briefly.

Keywords

Fluid Inclusion Mineral Assemblage Compositional Range Chloride Complex Exchange Equilibrium 
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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Copyright information

© Springer-Verlag New York Inc. 1983

Authors and Affiliations

  • H. P. Eugster
  • E. S. Ilton

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