Redox-dependent Ti stable isotope fractionation on the Moon: implications for current lunar magma ocean models

Abstract In terrestrial magmas titanium is predominantly tetravalent (Ti 4+ ), in contrast, lunar are more reduced (IW-1) and hence approximately 10% of their bulk Ti content trivalent 3+ ). Changes oxidation state coordination number both important parameters that can serve to drive stable isotope fractionation. As such, mineral–mineral mineral-melt fractionation factors determined for samples may not be appropriate formed under reducing conditions. To address this issue, several experiments were carried out gas mixing furnaces over a range f O 2 (air IW-1) determine minerals, such as ilmenite, clinopyroxene rutile highly abundant on the Moon. Results show extent significantly increases with decreasing . For example, isotopic difference between ilmenite residual melt (Δ 49 ilmenite-melt ) resolvably lower by ~ 0.44 ‰ from terrestrial-like FMQ-0.5 lunar-like IW-1 at an intermediate precision ± 0.003 (95% c.i. OL–Ti). This confirms conditions indeed applicable settings. Our new silicate mostly consistent those previously ab initio modelling based density-functional theory. Using our experimental data conjunction published high-precision HFSE basalts, we modelled solidification Lunar Magma Ocean (LMO). The model LMO included isotopes only Ti-oxides, but also typical minerals pyroxene or olivine. resulting δ urKREEP ilmenite-bearing cumulates within error previous estimates, indicate must have contained around 15% ilmenite.