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

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 delta V-51 ranging from -0.95 parts per thousand to -0.80 parts per thousand similar to the average value of the bulk silicate Earth (BSE; -0.91 parts per thousand +/- 0.09 parts per thousand), reflecting the composition of melt coexisting with olivine. One eruptive pumice is similar to most of the olivine-phyric samples with a delta V-51 value of -0.89 parts per thousand, while the other eruptive pumice and the two highest-MgO olivine-phyric samples have delta V-51 shifting to slightly higher values of -0.81 parts per thousand to -0.63 parts per thousand. For the segregation veins, the whole rock delta V-51 values vary from -0.81 parts per thousand to -0.53 parts per thousand, suggesting an average mineral-melt fractionation factor (Delta V-51(mineral-melt)) of about -0.15 parts per thousand during fractional crystallization. The late differentiated veins exhibit the highest delta V-51, delta Fe-56, and delta Ti-49 values, showing isotope fractionation driven by the crystallization of Fe-Ti oxides. The estimated Delta V-51(mineral-melt) value for Kilauea Iki samples is much smaller than that reported for Hekla basalts from Iceland and Anatahan lavas from Mariana (-0.5 parts per thousand to -0.4 parts per thousand; 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. (C) 2020 Elsevier Ltd. All rights reserved.