Contributions to Mineralogy and Petrology

, Volume 147, Issue 5, pp 511–527 | Cite as

The influence of melt structure on trace element partitioning near the peridotite solidus

  • Glenn A. Gaetani
Original Paper


This experimental study examines the mineral/melt partitioning of Na, Ti, La, Sm, Ho, and Lu among high-Ca clinopyroxene, plagioclase, and silicate melts analogous to varying degrees of peridotite partial melting. Experiments performed at a pressure of 1.5 GPa and temperatures of 1,285 to 1,345 °C produced silicate melts saturated with high-Ca clinopyroxene, plagioclase and/or spinel, and, in one case, orthopyroxene and garnet. Partition coefficients measured in experiments in which clinopyroxene coexists with basaltic melt containing ~18 to 19 wt% Al2O3 and up to ~3 wt% Na2O are consistent with those determined experimentally in a majority of the previous studies, with values of ~0.05 for the light rare earths and of ~0.70 for the heavy rare earths. The magnitudes of clinopyroxene/melt partition coefficients for the rare earth elements correlate with pyroxene composition in these experiments, and relative compatibilities are consistent with the effects of lattice strain energy. Clinopyroxene/melt partition coefficients measured in experiments in which the melt contains ~20 wt% Al2O3 and ~4 to 8 wt% Na2O are unusually large (e.g., values for Lu of up to 1.33±0.05) and are not consistent with the dependence on pyroxene composition found in previous studies. The magnitudes of the partition coefficients measured in these experiments correlate with the degree of polymerization of the melt, rather than with crystal composition, indicating a significant melt structural influence on trace element partitioning. The ratio of non-bridging oxygens to tetrahedrally coordinated cations (NBO/T) in the melt provides a measure of this effect; melt structure has a significant influence on trace element compatibility only for values of NBO/T less than ~0.49. This result suggests that when ascending peridotite intersects the solidus at relatively low pressures (~1.5 GPa or less), the compatibility of trace elements in the residual solid varies significantly during the initial stages of partial melting in response to the changing liquid composition. It is unlikely that this effect is important at higher pressures due to the increased compatibility of SiO2, Na2O, and Al2O3 in the residual peridotite, and correspondingly larger values of NBO/T for small degree partial melts.


Partition Coefficient Partial Melting Na2O High Field Strength Element Spinel Lherzolite 
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P.D. Asimow and P.C. Hess provided thoughtful and constructive reviews that led to improvements in the final version of this paper. I am grateful to E.B. Watson for providing advice, encouragement, and support over the course of this study. Discussions with B.O. Mysen and T.W. Sisson were helpful in formulating some of the ideas presented here. This work was supported by the National Science Foundation under grants no. EAR-9804794 (to E.B. Watson) and OCE-0118198. WHOI contribution 11153.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Department of Earth and Environmental SciencesRensselaer Polytechnic Institute TroyUSA
  2. 2.Department of Geology and GeophysicsWoods Hole Oceanographic InstitutionWoods HoleUSA

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