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

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 V-51/V-50 ratios than MORB. This, however, is in conflict with the theoretical prediction that mantle melting residues should be enriched in V-50 rather than V-51. To address these issues, a more precise estimate of the V isotope composition of the BSE is required. This study presents delta V-51 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 delta V-51 for fertile spinel lherzolites is -0.91 +/- 0.06 parts per thousand (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 5 51 V of -0.93 +/- 0.01 parts per thousand (2SD, n = 3). The mean delta V-51 for the komatiites is -0.91 +/- 0.05 parts per thousand (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 delta V-51 of the BSE is estimated to be -0.91 +/- 0.09 parts per thousand (2SD, n = 18). In contrast, the mean delta V-51 for the Onega Plateau picrites and related cumulates is -0.80 +/- 0.05 parts per thousand (2SD, n = 4), which is identical to a recent delta V-51 estimate for MORB. The mean 5 51 V for picrites and MORB are somewhat higher than the new BSE estimate, indicating that low-degree (< 10%) partial melts have higher delta V-51 than their mantle sources. The new estimate of delta V-51 for the BSE overlaps with current estimates for delta V-51 in the silicate Moon and Mars, which may imply that these bodies have a common V isotope composition. (C) 2019 Elsevier Ltd. All rights reserved.