Accurate Determination of Copper Partition Coefficients
In order to obtain accurate Cu partition coefficients between mineral and melt (D Cu), Xiong Xiaolin¡¯s research group in Guangzhou institute of Geochemistry, CAS, used piston cylinder high-pressure apparatus and a new experimental approach, i.e., Pt95Cu05 alloy capsule buffering Cu activity and double-capsule technique controlling oxygen fugacity (fO2), to determine DCu values between mantle minerals and silicate melts at upper mantle pressure-temperature-fO2 conditions. The results show that Cu is highly incompatible in olivine, orthopyroxene, clinopyroxene and garnet with D Cu values less than 0.2, and it is moderately incompatible in spinel with D Cu values of 0.2-0.8. The results also show that The D Cu values for olivine, orthopyroxene and spinel increase with increasing fO2. These accurate D Cu data serves as a foundation for quantitatively understanding the behavior of Cu during mantle melting. Model calculations indicate that (1) under oxidized, sulfide-absent conditions, Cu will be easily enriched in the derived melts during mantle partial melting and magmatic differentiation, and (2) mid-ocean ridge basalts and most primitive arc basalts must form by sulfide-present melting at relatively reduced conditions, but 10-30% arc basalts with high Cu contents (>70 ppm) may form at oxidized, sulfide-absent conditions. This work was recently published in Geochimica et Cosmochimica Acta (Liu, Xingcheng; Xiong, Xiaolin; Aud¨¦tat, Andreas; Li, Yuan; Song, Maoshuang; Li, Li; Sun, Weidong; Ding, Xing. Partitioning of copper between olivine, orthopyroxene, clinopyroxene, spinel, garnet and silicate melts at upper mantle conditions. 2014, 125: 1-22).