The Earth’s mantle is chemically heterogeneous in space and time, which is often reflected by variable isotopic compositions of mantle derived basalts. Basalts from the first 40 days of the 2021 Fagradalsfjall eruption, Reykjanes Peninsula, Iceland, display systematic temporal variations in the ratios of incompatible elements alongside resolvable variations in Sr, Nd and Pb radiogenic isotopes. These variations reflect progressive influx of magma derived from melting of a deeper, more enriched and potentially lithologically distinct source. We use this eruptive time series to conduct the first combined V-Fe-Zn isotope study, exploring the sensitivity of the combined isotopic approach, with particular focus on fingerprinting source lithological

heterogeneity. We find no analytically resolvable change in V (δ⁵¹V_AA between −0.95 ± 0.09 % 2 s.d. and −0.86 ± 0.07 % 2 s.d.), Fe (δ⁵⁶Fe_IRMM-524 between +0.047 ± 0.042 % 2 s.d. and +0.094 ± 0.049 % 2 s.d.) and Zn (δ⁶⁶Zn_AA-ETH between −0.042 ± 0.003 % 2 s.d. and +0.013 ± 0.027 % 2 s.d.) isotopic compositions. The lack of variability in V-Fe-Zn isotopes, despite the evolving trace element and radiogenic isotope ratios, suggests there is no significant contribution of melts from a lithologically distinct (pyroxenite) mantle component under the Reykjanes Peninsula.