Sievwright, RHWilkinson, JJO'Neill, HSCBerry, AJ2020-05-262020-05-2607/07/20172017-07-10Sievwright, R.H., Wilkinson, J.J., O’Neill, H.S.C. et al. Thermodynamic controls on element partitioning between titanomagnetite and andesitic–dacitic silicate melts. Contrib Mineral Petrol 172, 62 (2017). https://doi.org/10.1007/s00410-017-1385-60010-799910.1007/s00410-017-1385-6http://hdl.handle.net/10141/622768Titanomagnetite–melt partitioning of Mg, Mn, Al, Ti, Sc, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Hf and Ta was investigated experimentally as a function of oxygen fugacity (fO2) and temperature (T) in an andesitic–dacitic bulk-chemical compositional range. In these bulk systems, at constant T, there are strong increases in the titanomagnetite–melt partitioning of the divalent cations (Mg2+, Mn2+, Co2+, Ni2+, Zn2+) and Cu2+/Cu+ with increasing fO2 between 0.2 and 3.7 log units above the fayalite–magnetite–quartz buffer. This is attributed to a coupling between magnetite crystallisation and melt composition. Although melt structure has been invoked to explain the patterns of mineral–melt partitioning of divalent cations, a more rigorous justification of magnetite–melt partitioning can be derived from thermodynamic principles, which accounts for much of the supposed influence ascribed to melt structure. The presence of magnetite-rich spinel in equilibrium with melt over a range of fO2 implies a reciprocal relationship between a(Fe2+O) and a(Fe3+O1.5) in the melt. We show that this relationship accounts for the observed dependence of titanomagnetite–melt partitioning of divalent cations with fO2 in magnetite-rich spinel. As a result of this, titanomagnetite–melt partitioning of divalent cations is indirectly sensitive to changes in fO2 in silicic, but less so in mafic bulk systems.enopenAccesshttp://creativecommons.org/licenses/by/4.0/Journal Article1432-0967Contributions to Mineralogy and Petrology172862MagnetiteTrace-element partitioningAndesiteDaciteOxygen fugacityPetrogenetic indicator