The vanadium isotope composition of Mars: implications for planetary differentiation in the early solar system

Abstract

The V isotope composition of martian meteorites reveals that Bulk Silicate Mars (BSM) is characterised by δ51V = −1.026 ± 0.029 ‰ (2 s.e.) and is thus ∼0.06 ‰ heavier than chondrites and ∼0.17 ‰ lighter than Bulk Silicate Earth (BSE). Based on the invariant V isotope compositions of all chondrite groups, the heavier V isotope compositions of BSE and BSM relative to chondrites are unlikely to originate from mass independent isotope effects or evaporation/condensation processes in the early Solar System. These differences are best accounted for by mass dependent fractionation during core formation. Assuming that bulk Earth and Mars both have a chondritic V isotopic compostion, mass balance considerations reveal V isotope fractionation factors Δ51Vcore-mantle as substantial as −0.6 ‰ for both planets. This suggests that V isotope systematics in terrestrial and extraterrestrial rocks potentially constitutes a powerful new tracer of planetary differentiation processes accross the Solar System.