Partitioning of V and 19 other trace elements between rutile and silicate melt as a function of oxygen fugacity and melt composition: Implications for subduction zones

Abstract

Vanadium is a multivalent element that can speciate as V2+, V3+, V4+, and V5+ over a range of geologically relevant oxygen fugacities (fO2). The abundance of V in planetary materials can be exploited as a proxy for fO2 when its partitioning behavior is known. The mineral rutile (TiO2) is an important carrier of the high field strength elements Nb and Ta in the solid Earth, but it can also incorporate substantial quantities of vanadium (up to ~2000 ppm; e.g., Zack et al. 2002). However, little work has been done to systematically investigate how the partitioning of V in rutile-bearing systems changes as a function of both fO2 and composition. We measured the partitioning of V and 19 other trace elements (Sc, Cr, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu, Hf, and Ta) between rutile and three silicate melt compositions equilibrated at 1 atm pressure, 1300 °C and fO2 values from two log units below the quartz-fayalite-magnetite oxygen buffer (QFM-2) to air (QFM+6.5). Rutile/melt partition coefficients (DVrt/melt) change dynamically over an eight-log unit range of fO2 and are greatest at fO2 = QFM-2 in all compositions. Vanadium solubility in rutile declines continuously as fO2 increases from QFM-2 and approaches unity in air. Trace-element partitioning between rutile and melt is also correlated with melt composition, with the greatest values of Drt/melt measured in the most polymerized melt systems containing the least TiO2. We do not find any circumstances where V becomes incompatible in rutile. Our results indicate that rutile is a considerable sink for V at terrestrial fO2 values and will contribute to the retention of V in refractory slab residues in subduction zones. In agreement with previous work, we find that DTart/melt>DNbrt/melt under all conditions investigated, suggesting that rutile fractionation does not lead to low Nb/Ta ratios in Earth's continental crust.

Trace element partitioning between pyrochlore, microlite, fersmite and silicate melts

“…4 ). D Ta is very similar to D Nb , but overall we find that D Ta are systematically higher than D Nb , which is in good agreement with previous data for perovskite, rutile and other Ti–rich oxide minerals [ 2 , 3 , 5 , 7 , 8 , 10 , 13 , 48 – 50 ]. Our data shows that D HFSE for Ta-pyrochlore (HW1-3) are mostly above 1, only D Mo in the HW runs are systematically below 1.…”

“…To understand the behavior of trace elements in igneous rocks, trace element partition coefficients between minerals and melts are needed. Over the last decades, numerous experimental studies focused on the trace element partitioning between major rock forming minerals and melts [1], but few experimental partition coefficients are available for accessory phases such as rutile, ilmenite, spinel or apatite in basaltic compositions [2][3][4][5][6][7][8][9][10][11][12] and even less data are available for accessory mineral phases such as perovskite or pyrochlore in alkaline rock compositions [13]. As the aforementioned accessory mineral phases commonly occur in alkaline igneous rocks, they may exert a strong control on the trace element evolution of alkaline magmas.…”

Genesis of Intermediate and Silicic Arc Magmas Constrained by Nb/Ta Fractionation

“…Although there is an increase in D Nb /D Ta with decreasing temperature and melt H 2 O concentration, D Ta is always larger than D Nb for each experiment (Figure 3a). Our data show a good agreement with previous studies on rutile‐liquid partitioning (Figure 3b), and this conclusion holds across a temperature range of 650–1900°C, a pressure range of 1 atm–10 GPa, and a liquid compositional range of aqueous fluid, supercritical fluid, and dry melt to hydrous melt (Bromiley & Redfern, 2008; Chen et al., 2018; Green & Adam, 2003; Green & Pearson, 1987; Holycross & Cottrell, 2020; Horng & Hess, 2000; Jenner et al., 1993; Kessel et al., 2005; Klemme et al., 2002, 2005; Rustioni et al., 2019; Schmidt et al., 2004; X. L. Xiong, 2006; Xiong et al., 2005, 2011). The stronger compatibility of Ta relative to Nb in rutile should be ascribed to the crystal chemistry and the slight difference in properties between Nb 5+ and Ta 5+ .…”

Evidence for oxygen-conserving diamond formation in redox-buffered subducted oceanic crust sampled as eclogite

“…For further insights into ƒO 2 effects on D(V), we consider both experimental and natural mineral pairs. The combination of parameterisations of experimental clinopyroxenemelt and rutile-melt D(V) 12,26 as a function of ƒO 2 (both obtained at 1300 °C) reveals a marked increase in clinopyroxene/ rutile D(V) with decreasing ƒO 2 , relative to the Fayalite-Magnetite-Quartz buffer expressed as ΔlogfO 2 (FMQ), from 0.20 at FMQ-1 to 1.9 at FMQ-5. This roughly corresponds to the ƒO 2 range in eclogite xenoliths in this study (Fig.…”

“…Rutile solubility in garnet from eclogite xenoliths shows a strong positive temperature dependence, such that garnet in high-temperature eclogites has higher TiO 2 contents 25 , and rutile is known to be an important V host 26 . Median TiO 2 contents in DI garnet (0.56 wt.%) are higher than those in xenolith garnet (0.18 wt.%) (Fig.…”