Experimental calibration of oxygen isotope fractionation between quartz and zircon |
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| Authors: | Dustin Trail Ilya N Bindeman E Bruce Watson Axel K Schmitt |
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| Institution: | aDepartment of Earth & Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA;bDepartment of Geological Sciences, University of Oregon, Eugene, OR 97403, USA;cDepartment of Earth and Space Sciences & Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, USA |
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| Abstract: | We report the results of an experimental calibration of oxygen isotope fractionation between quartz and zircon. Data were collected from 700 to 1000 °C, 10–20 kbar, and in some experiments the oxygen fugacity was buffered at the fayalite–magnetite–quartz equilibrium. Oxygen isotope fractionation shows no clear dependence on oxygen fugacity or pressure. Unexpectedly, some high-temperature data (900–1000 °C) show evidence for disequilibrium oxygen isotope partitioning. This is based in part on ion microprobe data from these samples that indicate some high-temperature quartz grains may be isotopically zoned. Excluding data that probably represent non-equilibrium conditions, our preferred calibration for oxygen isotope fractionation between quartz and zircon can be described by: This relationship can be used to calculate fractionation factors between zircon and other minerals. In addition, results have been used to calculate WR/melt–zircon fractionations during magma differentiation. Modeling demonstrates that silicic magmas show relatively small changes in δ18O values during differentiation, though late-stage mafic residuals capable of zircon saturation contain elevated δ18O values. However, residuals also have larger predicted melt–zircon fractionations meaning zircons will not record enriched δ18O values generally attributed to a granitic protolith. These results agree with data from natural samples if the zircon fractionation factor presented here or from natural studies is applied. |
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