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Published July 2003 | public
Journal Article

Mineral/melt partitioning of trace elements during hydrous peridotite partial melting


This experimental study examines the mineral/melt partitioning of incompatible trace elements among high-Ca clinopyroxene, garnet, and hydrous silicate melt at upper mantle pressure and temperature conditions. Experiments were performed at pressures of 1.2 and 1.6 GPa and temperatures of 1,185 to 1,370 °C. Experimentally produced silicate melts contain up to 6.3 wt% dissolved H_2O, and are saturated with an upper mantle peridotite mineral assemblage of olivine + orthopyroxene + clinopyroxene + spinel or garnet. Clinopyroxene/melt and garnet/melt partition coefficients were measured for Li, B, K, Sr, Y, Zr, Nb, and select rare earth elements by secondary ion mass spectrometry. A comparison of our experimental results for trivalent cations (REEs and Y) with the results from calculations carried out using the Wood-Blundy partitioning model indicates that H_2O dissolved in the silicate melt has a discernible effect on trace element partitioning. Experiments carried out at 1.2 GPa, 1,315 °C and 1.6 GPa, 1,370 °C produced clinopyroxene containing 15.0 and 13.9 wt% CaO, respectively, coexisting with silicate melts containing ~1–2 wt% H_2O. Partition coefficients measured in these experiments are consistent with the Wood-Blundy model. However, partition coefficients determined in an experiment carried out at 1.2 GPa and 1,185 °C, which produced clinopyroxene containing 19.3 wt% CaO coexisting with a high-H_2O (6.26±0.10 wt%) silicate melt, are significantly smaller than predicted by the Wood-Blundy model. Accounting for the depolymerized structure of the H_2O-rich melt eliminates the mismatch between experimental result and model prediction. Therefore, the increased Ca^(2+) content of clinopyroxene at low-temperature, hydrous conditions does not enhance compatibility to the extent indicated by results from anhydrous experiments, and models used to predict mineral/melt partition coefficients during hydrous peridotite partial melting in the sub-arc mantle must take into account the effects of H_2O on the structure of silicate melts.

Additional Information

© 2003 Springer Verlag. Received: 17 January 2002 Accepted: 6 January 2003 Published online: 13 May 2003. Editorial responsibility: J. Hoefs. The authors are grateful to J. M. Brenan and C. E. Lesher for thoughtful and constructive reviews. We would like to thank S. Newman for performing the FTIR analyses. E. H. Hauri for carrying out the SIMS analysis of B394, and R. A. Sohn for helping with the statistics. The first author is grateful to G. Hirth and P. Kelemen for helpful discussions. This work was supported by the MARGINS Program of the National Science Foundation under grant no. EAR-0112013, and funded by Lawrence Livermore National Laboratory under the Laboratory Directed Research and Development (LDRD) program and was performed under the auspices of the US Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48.

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