Empirical and Experimental Constraints on Fe-Ti Oxide-Melt Titanium Isotope Fractionation Factors

Molybdenum and titanium isotopic signatures of arc-derived cumulates

“…The reason for the difference in the Ti isotopic composition between these magmatic series is debated, but likely primarily linked to the Fe and Ti contents of parental melts and the oxide mode (i.e. mainly ilmenite and/ or magnetite) that fractionates (Aarons et al, 2020(Aarons et al, , 2021Hoare et al, 2020Hoare et al, , 2022. Data from mineral separates of natural rocks (i.e.…”

“…Data from mineral separates of natural rocks (i.e. clino-and orthopyroxene, Fe-Ti oxides, olivine, plagioclase, biotite and quartz; Mandl, 2019;Nie et al, 2021;Greber et al, 2021;Rzehak et al, 2021;Anguelova et al, 2022) and in situ derived data obtained by micromilling (Hoare et al, 2022) show that Fe -Ti oxides are isotopically light. Neso-and tectosilicates like olivine, quartz, and plagioclase are isotopically heavy, and amphibole and biotite exhibit intermediate δ 49 Ti signatures (Mandl, 2019;Greber et al, 2021;Nie et al, 2021;Rzehak et al, 2021).…”

The effect of alkalinity on Ni–O bond length in silicate glasses: Implications for Ni isotope geochemistry

“…Our results suggest that the magnitude and potentially sign of mineral-melt Ni isotope fractionation factors, for instance between olivine and melt (Δ 60/58 Niolivine-melt), will also subtly depend on melt alkalinity. As such, these results provide an important clue that the magnitude of mineral-melt isotopic fractionation factors might not only be dependent on the composition of the mineral phase, such as next-nearest neighbour in a solid solution (e.g., Feng et al, 2014;Rabin et al, 2021;Hoare et al, 2022), but also on the composition of the silicate melt and specifically melt alkalinity. This warrants caution in extrapolating mineral-melt fractionation factors determined in simple chemical systems, for instance through experiments with a simplified silicate melt composition, to natural compositions, or fractionation factors across a large difference in melt alkalinity.…”

“…To allow quantitative modelling of such processes, accurate mineral-melt fractionation factors are required. Whereas it is increasingly recognized that mineral composition, for instance the next-nearest neighbouring element in a solid-solution series, can have a notable effect on the magnitude of isotopic fractionation factors (Feng et al, 2014;Rabin et al, 2021;Hoare et al, 2022), the potential role of silicate melt composition is often overlooked. Our new data show that there is minor but systematic variation in Ni coordination and Ni-O bond length in silicate melts as a function of their alkalinity, which might introduce differences in the β factors for Ni in these melts.…”

“…Beta factors for silicate glasses and melts can be measured using nuclear resonant inelastic X-ray scattering (NRIXS) for a few elements such as Fe and Sn (e.g., Dauphas et al, 2014;Prissel et al, 2018;Roskosz et al, 2020;Roskosz et al, 2022). For most other elements, mineral-melt isotopic fractionation factors have to be derived through the measurement of experimental or natural phenocryst-melt pairs (e.g., Prissel et al, 2018;Rzehak et al, 2021;Hoare et al, 2022, Liu et al, 2022, or through the inversion of natural magmatic differentiation suites (e.g., Teng et al, 2007;Zhang et al, 2018). Given this complexity, it is challenging to explicitly consider the potentially significant influence of the silicate melt composition on the magnitude of mineral-melt isotopic fractionation factors.…”