Abstract
Subduction zone or arc magmas are known to display a characteristic depletion of High Field Strength Elements (HFSE) relative to other similarly incompatible elements, which can be attributed to the presence of the accessory mineral rutile (TiO2) in the residual slab. Here we show that the partitioning behavior of vanadium between rutile and silicate melt varies from incompatible (∼0.1) to compatible (∼18) as a function of oxygen fugacity. We also confirm that the HFSE are compatible in rutile, with D(Ta)> D(Nb)>> (D(Hf)>/∼ D(Zr), but that the level of compatibility is strongly dependent on melt composition, with partition coefficients increasing about one order of magnitude with increasing melt polymerization (or decreasing basicity). Our partitioning results also indicate that residual rutile may fractionate U from Th due to the contrasting (over 2 orders of magnitude) partitioning between these two elements. We confirm that, in addition to the HFSE, Cr, Cu, Zn and W are compatible in rutile at all oxygen fugacity conditions.
Highlights
Despite their similar compatibility during mantle melting, the High Field Strength Elements (HFSE: Nb, Ta, Zr and Hf) display a characteristic depletion relative to the Rare Earth (REE) and Large Ion Lithophile (LILE) elements in subduction-related or arc magmas
Experimental studies have demonstrated that HFSEs are compatible in rutile, but their partitioning behavior appears to be strongly dependent on melt composition (Horgn and Hess 2000, Klemme et al 2005)
In this paper we report the results of an experimental study aimed at determining the effect of oxygen fugacity on the partitioning of trace elements between rutile and silicate melt
Summary
Despite their similar compatibility during mantle melting, the High Field Strength Elements (HFSE: Nb, Ta, Zr and Hf) display a characteristic depletion relative to the Rare Earth (REE) and Large Ion Lithophile (LILE) elements in subduction-related or arc magmas (see Tatsumi and Eggins 1995). This geochemical signature has long been used as a distinctive feature of arc magmas, yet its reason. At appropriate redox conditions, vanadium should behave to the HFSEs. Interestingly, the transition between the various vanadium valence states occurs over the range of oxygen fugacities inferred for the genesis of terrestrial magmas. High temperature and pressure partitioning experiments were carried out over a range of oxygen fugacities (from 10-12 to 10+4.3 bars at 1300°C) sufficiently large to cover the transition from V3+ to V4+ to V5+ and, most importantly, the redox conditions inferred for terrestrial magmas
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