Element partitioning between transition-zone minerals and ultramafic melt under hydrous conditions

Element partitioning between wadsleyite, garnet, and hydrous ultramafic melt has been determined at 16 GPa and 1600°C using a Kawai-type multi-anvil high-pressure apparatus. Element partitioning between olivine and hydrous ultramafic melt was also studied at 5 GPa and 1500°C in order to compare element partitioning behavior between wadsleyite and olivine. Major and trace elements analyses of the quenched melt and coexisting wadsleyite, garnet, and olivine were made with an EPMA and LA-ICP-MS, respectively. The experimental results demonstrate that LIL (Rb, Sr, Ba) and HFS (Ti, Zr, Nb, Hf, Ta, Th, U) elements are preferably incorporated into wadsleyite relative to olivine, suggesting that the concentration of these elements in the hydrous transition zone could be greater than that in upper mantle. Our results contribute to understand magmatism and chemical differentiation in the Earth's interior.