Bildungsbedingungen von Al-Fe (III)-Epidoten |
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| Authors: | Paul-Karl Hörmann Michael Raith |
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| Institution: | 1. Mineralogisch-Petrographisches Institut und Museum der Universit?t, Kiel
2. Mineralogisch-Petrographisches Institut der Technischen Universit?t, Clausthal-Zellerfeld
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| Abstract: | Relations between the composition of Al-Fe(III)-epidotes and the Fe content and oxidation ratio of a series of metamorphic rocks from the Hohen Tauern area, Tyrol (Austria), were investigated. The Fe(III) content of the epidotes depends on the oxidation ratio Fe(III)×100/(Fe(III)+ Fe(II)) of the rocks. The Fe(III) content of the epidotes as well as the oxidation ratio decreases within the series from greenschist to almandin-amphibolite facies. The relation between epidote composition and oxidation ratio can be explained by the following redox reactions: 6 Fe(III) Al2 Ep+6 Mu+6 Qz+6 Hä+n Ab ? (1a) (12 An+n Ab) Plag+6 Bio+3 H2O+4 1/2O2. 6 Fe(III) Al2 Ep+6 Mu+6 Qz+n Ab ? (1b) (12 An+n Ab) Plag+2 Bio+4 Kf+7 H2O+1 1/2O2. These reactions are in good agreement with the observed mineral assemblages and may explain the increase of the An content of coexisting plagioclase with increasing metamorphic grade. |
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