The stable vanadium isotope composition of the mantle and mafic lavas J. Prytulak a,b,n , S.G. Nielsen b,c , D.A. Ionov d , A.N. Halliday b , J. Harvey e , K.A. Kelley f , Y.L. Niu g , D.W. Peate h , K. Shimizu i , K.W.W. Sims j a Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK b Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK c Department of Geology & Geophysics, Woods Hole Oceanographic Institute, 266 Woods Hole, MA 02543-1050, USA d Universite´ de Saint Etienne & UMR6524-CNRS, F-42023, France e School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK f Graduate School of Oceanography, University of Rhode Island, RI 02882-1197, USA g Department of Earth Science, University of Durham, Durham DH1 3LE, UK h Department of Geosciences, University of Iowa, IA 52242, USA i Institute for Research on Earth Evolution, Japan Agency of Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka 237-001, Japan j Department of Geology and Geophysics, University of Wyoming, USA article info Article history: Received 10 August 2012 Received in revised form 4 January 2013 Accepted 11 January 2013 Editor: B. Marty Keywords: vanadium isotopes bulk silicate Earth high temperature stable isotope fractionation abstract Vanadium exists in multiple valence states under terrestrial conditions (2 þ ,3 þ ,4 þ ,5 þ ) and its isotopic composition in magmas potentially reflects the oxidation state of their mantle source. We present the first stable vanadium isotope measurements of 64 samples of well-characterized mantle-derived mafic and ultramafic rocks from diverse localities. The d 51 V ranges from 0.27% to 1.29%, reported relative to an Alfa Aesar (AA) vanadium solution standard defined as 0%. This dataset is used to assess the effects of alteration, examine co-variation with other geochemical characteristics and define a value for the bulk silicate Earth (BSE). Variably serpentinised peridotites show no resolvable alteration-induced d 51 V fractionation. Likewise, altered mafic oceanic crustal rocks have identical d 51 V to fresh hand-picked MORB glass. Intense seafloor weathering can result in slightly ( 0.2–0.3%) heavier isotope compositions, possibly related to late-stage addition of vanadium. The robustness of d 51 V to common alteration processes bodes well for its potential application to ancient mafic material. The average d 51 V of mafic lavas, including MORB, Icelandic tholeiites and lavas from the Shatsky Rise large igneous province is 0.88 70.27% 2sd. Peridotites show a large range in primary d 51 V( 0.62% to 1.17%), which co- varies positively with vanadium concentrations and indices of fertility such as Al 2 O 3 . Although these data suggest preferential extraction of heavier isotopes during partial melting, the isotope composition of basalts (d 51 V¼ 0.88 70.27% 2sd) and MORB glass in particular (d 51 V¼0.95 70.13% 2sd) is lighter than fertile peridotites and thus difficult to reconcile with a melt extraction scenario. Determination of fractionation factors between melt and mineral phases such as pyroxenes and garnet are necessary to fully understand the correlation. We arrive at an estimate of d 51 V BSE ¼ 0.7 70.2% (2sd) for the bulk silicate Earth by averaging fertile, unmetasomatised peridotites. This provides a benchmark for both high and low temperature applications addressing planet formation, cosmochemical comparisons of the Earth and extraterrestrial material, and an inorganic baseline for future biogeochemical investigations. Whilst d 51 V could relate to oxidation state and thus oxygen fugacity, further work is required to resolve the isotopic effects of oxidation state, partial melting, and mineral fractionation factors. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Radiogenic isotopic compositions measured in mantle rocks and mantle-derived magmas provide compelling evidence for the existence of mantle heterogeneity as well as constraints on its creation and preservation (e.g., Hofmann, 2003; Zindler and Hart, 1986). However, long-lived radiogenic isotope signatures are not without ambiguity. The variability in isotopic compositions of Sr, Nd, Pb, and Hf, for example, reflects the time-integrated fractio- nation of parent from daughter element. The magnitude of this elemental fractionation, the initial source composition and the age of the fractionated material all contribute to uncertainty in interpreting the final isotope composition. Thus, deducing the Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/epsl Earth and Planetary Science Letters 0012-821X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2013.01.010 n Corresponding author at: Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK. Tel.: þ44 207 954 6474. E-mail address: j.prytulak@imperial.ac.uk (J. Prytulak). Earth and Planetary Science Letters 365 (2013) 177–189