No Measurable Calcium Isotopic Fractionation During Crystallization of Kilauea Iki Lava Lake

In order to investigate possible Ca isotopic fractionation during basaltic magma differentiation, we measured Ca isotopic compositions of lavas recovered from Kilauea Iki lava lake at Hawaii. This set of lavas record the whole crystal fractionation history of basaltic magma, ranging from olivine accumulation/fractionation to multiple phase crystallization, including plagioclase and clinopyroxene. Our results show no detectable Ca isotopic variation in all measured Kilauea lavas at a precision of ±0.07‰ for 44Ca/40Ca (δ44/40Ca = 0.80 ± 0.08, 2 SD, n = 19). Using such observation and published intermineral Ca isotopic fractionation factors, a Monte Carlo approach is used to estimate the mineral‐melt 44Ca/40Ca fractionation factors. We found that Ca isotopic fractionation between clinopyroxene and basaltic melt is small, with Δ44/40Cacpx‐melt = 0.04 ± 0.03 at 1200 °C. To the best of our knowledge, this is the first estimated mineral‐melt Ca isotopic fractionation factor reported. We use this estimated Δ44/40Cacpx‐melt and intermineral Ca isotopic fractionation factors to investigate Ca isotopic effects during mantle partial melting under 1–2 GPa. Our simulations show that the largest 44Ca/40Ca effect, up to +0.3‰, is achieved in large degree melting residues during fractional and dynamic melting. In contrast, partial melts show negligible 44Ca/40Ca isotopic effect,