Whether arc mantle is more oxidized than oceanic mantle is persistently debated. The behavior of multivalent vanadium (V) is oxygen fugacity (fO 2 ) sensitive, and the ratios of V to a homovalent element (e.g., Sc, Ti, or Yb) in basalts were commonly used as fO 2 proxies. Similar ratios, such as V/Sc, between arc basalts and mid-ocean ridge basalts were previously taken as evidence for similar fO 2 s in their mantle sources. However, this claim may be problematic because elemental ratios are primarily controlled by partition coefficients (D values), which are further affected by various factors. Here we determined D values of V and other transition elements between mantle minerals and basaltic melts at typical arc T-P-H 2 O conditions and variable fO 2 s. Combining experimental results with published data, the effects of fO 2 , T, P, and phase compositions on D V , D Sc , and D Ti for olivine, orthopyroxene (opx), clinopyroxene (cpx), and spinel were evaluated using multiple linear regressions. The results show that D V values for these four minerals all increase with decreasing fO 2 and temperature, leading to higher D V /D Sc and D V /D Ti ratios at low temperatures than those at high temperatures given a certain fO 2 . Thus, similar V/Sc and V/Ti ratios between arc basalts and mid-ocean ridge basalts reflect a relatively oxidized arc mantle due to its lower melting temperatures. In light of the highly incompatible behavior of Ti during mantle melting, V-Ti systematics are regarded to be more superior than V-Sc systematics in the fO 2 estimation. Partial melting modelling results using V-Ti systematics reveal that arc mantle is, on average,~0.9 log units higher in fO 2 than oceanic mantle.Plain Language Summary The oxidation state of the Earth`s mantle, often expressed as oxygen fugacity (fO 2 ), could control the behavior of multivalent elements and thus exert a significant influence on the formation of magmatic ore deposits and the secular evolution of Earth`s atmosphere. Whether arc mantle is more oxidized than oceanic mantle remains a controversial topic. As a multivalent element, partitioning behavior of vanadium is fO 2 sensitive and is capable of tracking mantle redox state. However, except fO 2 , other factors (temperature, pressure, and phase composition) that may affect vanadium partitioning behavior have not been clearly evaluated. Here we conducted high temperature and pressure experiments to determine partition coefficients of vanadium during mantle melting under various fO 2 conditions. Combining our and published data, we evaluated the effects of fO 2 , T, P, and compositions of mineral and melt on the vanadium partitioning using multiple linear regressions. The results indicate that, in addition to fO 2 , temperature exerts a significant control on the vanadium partitioning. Additionally, we estimated fO 2 of the arc mantle via numerical modelling using appropriate partition coefficients for vanadium. Our results clarify and reconcile the discrepancies between previous studies and reveal that a...
