Element partitioning: the role of melt structure and composition.

We segregated coexisting gabbroic and granitic melts by centrifuging them at high pressures and temperatures and measured the trace element compositions of the melts by laser ablation inductively coupled plasma mass spectrometry. Our results demonstrate that the effect of melt structure contributes about one order of magnitude to crystal/melt partition coefficients. Partitioning of alkali and alkaline earth elements strongly depends on field strength: Amphoteric and lone pair electron elements partition into the polymerized granitic melt; and rare earth, transition, and high field strength elements coordinated by nonbridging oxygens partition remarkably similar into the gabbroic melt. A regular solution model predicts these effects.