The pressure dependence of the zirconium-in-rutile thermometer |
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| Authors: | H S TOMKINS R POWELL & D J Ellis |
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| Institution: | Department of Earth and Marine Sciences, Australian National University, Canberra, ACT 0200, Australia;
School of Earth Sciences, University of Melbourne, Melbourne, Vic. 3010, Australia |
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| Abstract: | The solubility of ZrO2 in rutile is strongly temperature-dependent and has been identified as a potentially powerful thermometer when the rutile coexists with an appropriate buffer assemblage, e.g. zircon + quartz. In combination with experimental data at 10 kbar, previous consideration of data on natural rutile has not identified a pressure dependence for the thermometer. However, the expected volume change as a result of substitution of the larger Zr4+ cation for Ti4+ suggests that the Zr content of rutile should decrease with increasing pressure. To investigate the pressure dependence of the thermometer, piston cylinder (at 10, 20 & 30 kbar) and 1 atm furnace experiments were performed in the system ZrO2-TiO2-SiO2. The solubility of ZrO2 in rutile, in the presence of zircon and quartz was reversed at each pressure value. From these experiments, the thermodynamics of the end-member reaction ZrSiO4 = SiO2 + ZrO2 (in rutile) have been determined. There is a secondary pressure effect accompanying the primary temperature dependence of the Zr content of rutile. New thermometer equations are, in the α -quartz field:  in the β -quartz field  and in the coesite field  in which φ is ppm Zr, P is in kbar and R is the gas constant, 0.0083144 kJ K?1. Thermometric results using these equations are shown for a range of geological settings. |
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| Keywords: | pressure dependence rutile thermometer zirconium |
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