Geoscience

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; Audétat, 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).