Empirical calibration of the oxygen isotope fractionation between quartz and Fe–Mg-chlorite

Abstract

An empirical calibration has been made of the oxygen isotope fractionation between chlorite and quartz, using samples from localities in metamorphic terrains where the formation temperature has been constrained by independent methods (e.g., fluid inclusion homogenization temperatures, mineral assemblages and petrology of the host rocks to the veins, thermodynamic modeling, and Raman spectrometry). Textural equilibrium of chlorite and quartz was a pre-requisite and the chemical composition of chlorite was determined. The chlorite analyzed had a range in Fe/Mg varying between 0.35 and 0.7. Except for pure Mg-chlorite, Fe–Mg substitution within the range measured does not change the oxygen isotope fractionation between quartz and chlorite measurably. The results support a linear correlation for chlorite–quartz fractionation over the temperature range given by this study (240–550°C):1000lnα=-0.01323(±0.002)×T(°C)+10.97(±0.92)The presently established geothermometer can be applied to quartz–chlorite fractionations in low-grade metamorphic rocks and may be extrapolated to diagenetic systems.