Vanadium isotope fractionation during differentiation of Kilauea Iki lava lake, Hawaii

Abstract

In order to understand the mechanism of vanadium (V) isotope fractionation during magmatic differentiation, we analyzed the V isotopic compositions of eruptive pumices, olivine-phyric basalts, and differentiated segregation veins from the Kilauea Iki lava lake, Hawaii. Most olivine-phyric samples contain whole rock δ51V ranging from −0.95‰ to −0.80‰ similar to the average value of the bulk silicate Earth (BSE; −0.91‰ ± 0.09‰), reflecting the composition of melt coexisting with olivine. One eruptive pumice is similar to most of the olivine-phyric samples with a δ51V value of −0.89‰, while the other eruptive pumice and the two highest-MgO olivine-phyric samples have δ51V shifting to slightly higher values of −0.81‰ to −0.63‰. For the segregation veins, the whole rock δ51V values vary from −0.81‰ to −0.53‰, suggesting an average mineral-melt fractionation factor (Δ51Vmineral-melt) of about −0.15‰ during fractional crystallization. The late differentiated veins exhibit the highest δ51V, δ56Fe, and δ49Ti values, showing isotope fractionation driven by the crystallization of Fe–Ti oxides. The estimated Δ51Vmineral-melt value for Kilauea Iki samples is much smaller than that reported for Hekla basalts from Iceland and Anatahan lavas from Mariana (−0.5‰ to −0.4‰; Prytulak et al., 2017), which may reflect differences in magma differentiation in terms of the timing of Fe–Ti oxide saturation, and the amount and mineralogy of the Fe–Ti oxides.