The oxygen isotope fractionation behaviour of kyanite in experiment and nature |
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| Authors: | Andreas Tennie Radegund Hoffbauer Stephan Hoernes |
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| Institution: | Mineralogisch-Petrologisches Institut der Universit?t Bonn, Poppelsdorfer Schloss, D-53115 Bonn, Germany; E-mail: r.hoffbauer@uni-bonn.de, DE
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| Abstract: | 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/T
2. 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.
Received: 8 June 1998 / Accepted: 24 August 1998 |
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