EXPERIMENTALLY DETERMINED PARTITIONING OF HIGH-FIELD STRENGTH-ELEMENTS AND SELECTED TRANSITION-ELEMENTS BETWEEN SPINEL AND BASALTIC MELT

Partition coefficients for the elements Ta, Nh, Hf, Zr, Sc, V, Ga, Zn and Co have been determined by laser ablation ICP-MS and/or electron microprobe between spinel and melt using an alkali olivine basalt at 1 atm. The D-sp/lq for high field strength elements (HFSE) are uniform (D-Nb(sp/lq)=0.08, D-Ta(sp/lq)=0.06, D-Hf(sp/lq)=0.05, D-Zr(sp/lq)=0.06), negating the possibility of intra-HFSE fractionation during partial melting or fractional crystallization processes. Results for D-V(sp/lq) continue an approximately linear trend of decreasing D-V(sp/lq) with increasing f(O2) from D-V(sp/lq)=68 at IW from previous studies to values of D-V(sp/lq)=0.09 at f(O2)=air. D-Sc(sp/lq) is also f(O2) dependent (0.24-0.56 with increasing f(O2)), whereas D-Ga(sp/lq) is constant at 3.2. A compositional dependence of partitioning behaviour was found for the Ti-poor solid-solution series between chromite- and magnetite-rich spinels in the log f(O2) range from air to FMQ -1 for Co, Zn and Sc. Zn and Co showed deviation from Henry's law behaviour. An approximate value for D-Zn(sp/lq) of 4.5 agrees well with the observed partitioning in natural peridotites, but is much larger at lower temperatures. Cobalt partitioning shows a strong negative correlation with temperature and is complicated by f(O2) effects.