Vanadium Isotopic Compositions of the High-3He/4He Baffin Island Lavas

Abstract

The isotopic composition of vanadium (V) in hotspot lavas provides new insight into the source of deep mantle heterogeneities. We measured V isotopic compositions in Paleogene Baffin Island lavas, which erupted above the Iceland plume head, to constrain the mantle plume source. These lavas have V isotopic compositions that are lighter (−0.96 ± 0.02‰, 2 s.e., n = 25) than most other mantle-derived lavas (δ⁵¹V = −0.89 ± 0.02, 2 s.e., n = 69). This difference is statistically significant with a 99.8% confidence interval. The measured ⁵¹V/⁵⁰V ratio in Baffin Island is difficult to reconcile with the assimilation of continental crust, fractional crystallization, crystal accumulation, isotopic fractionation during mantle melting, or the recycling of sediments. Possibly, the Baffin Island lavas sample an ancient (>3 Ga) melt-depleted mantle reservoir. However, this cannot explain the similarly low ⁵¹V/⁵⁰V measured in younger lavas related to the Iceland plume. Instead, the V isotopic composition of Baffin Island lavas may be consistent with the incorporation of core-affected material into the Iceland plume. The advection of bulk core into the lowermost mantle is improbable, so we hypothesize that, if the V isotopic difference is due to core-mantle interactions, V partitioned into core-exsolved oxides that imparted a core-like V isotopic composition on the Baffin Island mantle source.