Vanadium isotope composition of the Bulk Silicate Earth: constraints from peridotites and komatiites

Abstract In order to apply the vanadium (V) stable isotope system for studies of planetary accretion and evolution in the solar system and redox variations in terrestrial magmatic processes, the V isotope composition of the Bulk Silicate Earth (BSE) needs to be precisely constrained. Previous studies have shown that fertile peridotites have systematically higher 51 V/ 50 V ratios than MORB. This, however, is in conflict with the theoretical prediction that mantle melting residues should be enriched in 50 V rather than 51 V. To address these issues, a more precise estimate of the V isotope composition of the BSE is required. This study presents δ 51 V data for eleven peridotite xenoliths from two late Cenozoic eruption centers at Tariat in central Mongolia, ten komatiites from five localities ranging in age between 3.48 and 2.41 Ga, and four 1.98 Ga picrites from the Onega Plateau in Fennoscandia. The mean δ 51 V for fertile spinel lherzolites is -0.91 ± 0.06‰ (2SD, n = 8). They show no resolvable difference in V isotope compositions compared to three moderately to highly refractory peridotite xenoliths analyzed, with a mean δ 51 V of -0.93 ± 0.01‰ (2SD, n=3). The mean δ 51 V for the komatiites is -0.91 ± 0.05‰ (2SD, n = 10), which is identical to that for the fertile peridotites. Based on the V isotope compositions of the peridotites and komatiites analyzed in this study, the mean δ 51 V of the BSE is estimated to be -0.91 ± 0.09‰ (2SD, n = 18). In contrast, the mean δ 51 V for the Onega Plateau picrites and related cumulates is -0.80 ± 0.05‰ (2SD, n = 4), which is identical to a recent δ 51 V estimate for MORB. The mean δ 51 V for picrites and MORB are somewhat higher than the new BSE estimate, indicating that low-degree ( 51 V than their mantle sources. The new estimate of δ 51 V for the BSE overlaps with current estimates for δ 51 V in the silicate Moon and Mars, which may imply that these bodies have a common V isotope composition.