The oxygen isotope fractionation behaviour of kyanite in experiment and nature

The oxygen isotope fractionation between kyanite and calcium carbonate has been investigated experimentally at four temperatures in the range between 625 and 775 °C at 13 kbar. Because of low exchange rates, the isotopic reaction was enhanced by polymorphic transformation of andalusite to kyanite. W...

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Bibliographic Details
Published in:Contributions to mineralogy and petrology 1998-12, Vol.133 (4), p.346-355
Main Authors: Tennie, Andreas, Hoffbauer, Radegund, Hoernes, Stephan
Format: Article
Language:English
Subjects:
Calcium carbonate
Fractionation
Geology
Isotope fractionation
Isotopes
Mineralogy
Minerals
Oxygen
Oxygen isotopes
Petrology
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Summary:The oxygen isotope fractionation between kyanite and calcium carbonate has been investigated experimentally at four temperatures in the range between 625 and 775 °C at 13 kbar. Because of low exchange rates, the isotopic reaction was enhanced by polymorphic transformation of andalusite to kyanite. With this experimental modification a close approach to equilibrium was reached in all runs. The temperature dependence of the equilibrium fractionation is described by the equation 1000 ln ky-cc=-2.62×106/T2. Application of the experimental results to natural quartz-kyanite-garnet assemblages indicates the preservation of the oxygen isotope composition of kyanite acquired during its formation, reflecting its extremely low oxygen diffusivity. This refractory behaviour restricts the use of kyanite for thermometry but opens the possibility to use its O-isotope composition as an indicator for recognition of polymetamorphic rock histories and reconstruction of the prograde evolution of a metamorphic sequence.
ISSN:0010-7999
1432-0967
DOI:10.1007/s004100050457