Oxygen isotope fractionation factors between anhydrite and water from 100 to 550°C |
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| Authors: | Hitoshi Chiba Minoru Kusakabe Shin-Ichi Hirano Sadao Matsuo Shigeyuki Somiya |
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| Affiliation: | 1. Tokyo Institute of Technology, Department of Chemistry, O-okayama Meguroku, Tokyo 152Japan;2. Toyama University, Department of Earth Sciences, Gofuku, Toyama 930Japan;3. Nagoya University, Synthetic Crystal Research Laboratory, Chikusa, Nagoya 464Japan;4. Tokyo Institute of Technology, Research Laboratory of Engineering Materials, Midoriku, Yokohama 227Japan |
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| Abstract: | Oxygen isotope exchange between anhydrite and water was studied from 100 to 550°C, using the partial equilibrium method. The exchange rate was extremely low in NaCl solution. In the lower-temperature range, acid solutions were used to produce sufficient reaction to determine the oxygen isotope fractionation factors. The fractionation factors obtained in the present study are definitely different from those given by Lloyd [8]. They are similar to those for the HSO4?-water system studied by Mizutani and Rafter [19], and are consistently 2‰ higher than those of the barite-water system by Kusakabe and Robinson [5]. The temperature dependence of the oxygen isotope fractionation factors was calculated by the least squares method in which the weight was taken to be inversely proportional to the experimental error. The fractionation is given by:103lnαanhydrite-water=3.21×(103/T)2?4.72Available δ18O values of natural anhydrite were used to test the validity of this expression. It is shown that this newly revised geothermometer can be successfully applied to natural hydrothermal anhydrite. |
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