Oxygen isotope fractionation between zircon and water; experimental determination and comparison with quartz-zircon calibrations

Oxygen isotope fractionation between synthesised zircon and water has been experimentally quantified at 700, 800, 900, and 1000 degrees C. The results are interpolated by: Delta (sub zrn-H2O) = -3.70+2.74+ or -0.19 x (super 2) , where x = 10 (super 3) /T (K). Combined with the fractionation between quartz and water (Bottinga & Javoy, 1973) this yields: Delta (sub qtz-zrn) = 1.36 x (super 2) . Theoretical evaluations of the reduced partition function ratios for zircon and two (alpha - and beta -) modifications of quartz are expressed in terms of the following polynomials: 1000 lnf (sub zrn) = 8.3306 x (super 2) + 1.9402 x - 0.6896 (400<T<1100 degrees C). 1000 lnf (sub alpha -qtz) = 7.8963 x (super 2) + 7.4091 x - 3.6015 (200 degrees C<T<alpha -quartz stability field). 1000 lnf (sub beta -qtz) = 9.3362 x (super 2) + 2.4514 x - 0.7844 (beta -quartz stability field up to 1100 degrees C). These expressions are in excellent agreement both with the experimentally derived factors of oxygen isotope fractionation for beta -quartz and zircon, and incremental calibrations for alpha -quartz and zircon (Hoffbauer et al., 1994). The effect of alpha -beta -quartz transition on oxygen isotope fractionation implies, that those calculations, anchored to the theoretically evaluated reduced partition function ratios of quartz (e.g., Zheng, 1993), can predict fractionations only within the P-T stability field of the respective modification of quartz (i.e. alpha -quartz).