Carbon isotopic thermometry calibrated by dolomite-calcite solvus temperatures |
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| Authors: | Hideki Wada Kazuhiro Suzuki |
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| Institution: | Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422, Japan;Depanment of Earth Sciences, Faculty of Science, Nagoya University, Chikusa, Nagoya 464, Japan |
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| Abstract: | The temperature dependence of carbon isotopic fractionations between calcite and graphite, and between dolomite and graphite are calibrated by the calcite-dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the Kasuga area, central Japan. The carbon isotopic fractionations (Δ13CCc-Gr and Δ13CDoGr) systematically decrease with increasing metamorphic temperature. The concordant relationships between the fractionations and solvus temperatures are approximately linear with T?2 over the temperature range. 400° to 680°C: Δ13CCcGr (%.) = 5.6 × 106 × T?2 (K) ? 2.4 Δ13CDoGr (%.) = 5.9 × 106 × T?2 (K) ? 1.9 These systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases. The equation for the calcite-graphite system has a slope steeper than Bottinga's (1969) results. It is, however, in good agreement with that of Valley and O'Neil (1981) in the temperature range from 600° to 800°C.Because of the relatively high sensitivity to temperature, these isotopic geothermometers are useful for determining the temperatures in moderate- to high-grade metamorphosed carbonate rocks. |
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