Isotopic fractionation of neon during magma degassing

Determining the neon isotope composition of the Earth’s mantle is key to unravelling how light noble gases became part of the primordial Earth. However, accurately measuring neon abundance and isotopic composition in primary mantle melts is challenging due to the low concentration of neon, coupled with potential isotopic fractionation during transport and degassing. Interestingly, natural samples that exhibit solar-like neon isotopic compositions, ranging between the values calculated for the Sun (20Ne/22Ne = 13.36 ± 0.09; Heber et al., 2012) and those resulting from solar wind implantation and sputtering (20Ne/22Ne = 12.73; Moreira and Charnoz, 2016), support the idea that the Earth’s mantle might have trapped a primordial nebula in its early formation stages. Analyses of three synthetic vesiculated glasses, produced at ∼1.7 kbar and 1200 °C using a starting material with an air-like isotopic composition (20Ne/22Ne = 9.81 and 21Ne/22Ne = 0.0287) fluxed with CO2, reveal significant isotopic fractionation of Ne within trapped vesicles. Measured values reach 20Ne/22Ne = 10.50 ± 0.14. The isotopic variations among individual vesicles align with expectations for kinetic fractionation, suggesting that degassing processes affect Ne isotope composition of basaltic melts.