A direct determination of the oxygen isotope fractionation between quartz and magnetite at 600 and 800°C and 5 kbar |
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| Authors: | William F Downs Yen Touysinhthiphonexay Peter Deines |
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| Institution: | E.G. & G., Idaho, Inc., Idaho National Engineering Laboratory, Idaho Falls, ID 83401, U.S.A.;Department of Geosciences, The Pennsylvania State University, University Park, PA16802, U.S.A. |
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| Abstract: | The partitioning of oxygen isotopes between quartz and magnetite was measured at 600 and 800 C and 5 kbar, using an internally heated pressure vessel equipped with a Shaw-membrane. Through adjustment of the hydrogen fugacity the starting material, fayalite, was decomposed to form quartz and magnetite. The isotopic composition difference between the separated quartz and magnetite fraction was measured directly. As the mineral separates were not completely pure, a correction was applied to the measured fractionations. The independence of the measured isotopic composition differences of run length, the initial isotopic composition of the starting materials as well as the isotopic composition difference between them suggests that the fractionations, 1000 In αQ-M = 7.8 ± 0.4% at 600°C and 1000 In αQ-M = 6.1 ± 0.2% at 800°C, represent equilibrium values. |
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