The effect of Rayleigh degassing of magma on sulphur isotope composition: a quantitative evaluation |
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| Authors: | Y-F Zheng |
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| Institution: | Geochemisches Institut, Universität Göttingen, Goldschmidtstr. 1, 3400 Göttingen, West Germany |
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| Abstract: | The effect of Rayleigh distillation by outgassing of SO2 and H2O on the isotopic composition of sulphur remaining in silicate melts is quantitatively modelled. A threshold mole fraction of sulphur in the sulphide component of the melts is reckoned as being critically important in shifting the δ34S value of degassed melts with respect to the original magmas. During the outgassing, melts above the threshold are depleted in 34S, whereas melts below the threshold are enriched in 34S. In particular, the outgassing of SO2 above the sulphide threshold can produce large negative δ34S values in the degassed melts, whereas the outgassing of H2S below the threshold will strongly drive the δ34S value of the melts in the positive direction. The correlation between δ34S value and sulphur content of total sulphur in the solidified rocks is indicative of the Rayleigh-type degassing. |
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