Influence of ferric iron on the stability of mineral assemblages

Ferric iron is present in all metamorphic rocks and has the ability to significantly affect their phase relations. However, the influence of ferric iron has commonly been ignored, or at least not been considered quantitatively, mainly because its abundance in rocks and minerals is not determined by...

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Bibliographic Details
Published in:Journal of metamorphic geology 2010-08, Vol.28 (6), p.599-613
Main Authors: DIENER, J. F. A., POWELL, R.
Format: Article
Language:English
Subjects:
corundum + quartz
ferric iron
Geochemistry
Iron
Metamorphic rocks
Mineralogy
Oxidation
oxygen activity
pseudosection
redox budget
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Summary:Ferric iron is present in all metamorphic rocks and has the ability to significantly affect their phase relations. However, the influence of ferric iron has commonly been ignored, or at least not been considered quantitatively, mainly because its abundance in rocks and minerals is not determined by routine analytical techniques. Mineral equilibria calculations that explicitly account for ferric iron can be used to examine its effect on the phase relations in rocks and, in principle, allow the estimation of the oxidation state of rocks. This is illustrated with calculated pseudosections in NCKFMASHTO for mafic and pelitic rock compositions. In addition, it is shown that ferric iron has the capacity to significantly increase the stability of the corundum + quartz assemblage, making it possible for this assemblage to exist at crustal P–T conditions in oxidized rocks of appropriate composition.
ISSN:0263-4929
1525-1314
DOI:10.1111/j.1525-1314.2010.00880.x