Abstract
Tourmaline synthesised in an experiment with low boron excess was analysed in situ by secondary ion mass spectrometry. It revealed significant B isotope zonation with 11B/10B ratios increasing in the growth direction of the crystals. Trend, magnitude and absolute values strongly support results from high-B-excess isotope fractionation experiments. Furthermore, the closed system B-isotopic evolution of the experimental fluid was modelled by Rayleigh fractionation. The model results are in excellent agreement with the measured B-isotope composition of the run-product fluid. Consequently, low-element-excess experiments are proposed as an ideal approach to determine fluid-solid isotope fractionation factors for systems that are characterised by Rayleigh fractionation.
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Acknowledgments
We are grateful to R. L. Romer for fruitful discussions. Comments from two anonymous reviewers are appreciated. This study was financially supported by a European Union Marie-Curie Fellowship awarded to HRM (ID 025844: “Isotopes in subduction zones—the metamorphic perspective”), which is greatly acknowledged.
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Communicated by J. Hoefs.
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Marschall, H.R., Meyer, C., Wunder, B. et al. Experimental boron isotope fractionation between tourmaline and fluid: confirmation from in situ analyses by secondary ion mass spectrometry and from Rayleigh fractionation modelling. Contrib Mineral Petrol 158, 675–681 (2009). https://doi.org/10.1007/s00410-009-0403-8
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DOI: https://doi.org/10.1007/s00410-009-0403-8