Fe3+ partitioning between clinopyroxene and silicate melt at 1–2.5 GPa: Implications for Fe3+ content of MORB and OIB source mantle

Pyroxene is the chief reservoir of Fe 3+ in upper mantle peridotite, but experiments exploring pyroxene/melt partitioning ( D Fe3+ pyx/liq ) have been restricted to 100 kPa and pyroxene with low alumina. Here we present between clinopyroxenes (cpx) mafic melt at elevated pressures (1–2.5 GPa). Experiments were conducted f O2 buffered modulated by Ru + RuO 2 Fe-Pt alloy capsules, respectively, ΔQFM −2.7 +5.1. /Fe T both cpx determined K -edge X-ray absorption near edge structure spectroscopy. The experimentally synthesized compositions (Al O 3 = 2.36–6.01 wt.%, CaO 19.33–22.21 wt.%) approximate those expected basalt source regions. We find that moderately incompatible cpx/liq correlates Al content, increasing from 0.05 ± 0.09 0.81 0.04. also increases . Comparison natural peridotites indicates influences temperature composition on for spinel garnet peridotites. combined effects decreased concentration mode progressive partial melting peridotite diminishes bulk partition coefficients , leading greater contents high degree melts, this accounts an inverse relationship Na observed mid-ocean ridge basalts (MORB). numerical pMELTS model Jennings Holland (2015) show these models overpredict mantle, so they do not accurately determine To estimate ratio MORB, modeled liquid during isentropic batch three potential temperatures (1320 °C, 1400 1440 °C) peridotitic sources ratios 0.02–0.06. A 0.038 0.007 matches most span MORB. This similar typical continental lithospheric sampled xenoliths, lower than surmised several recent experimental thermodynamic studies. Considering extending calculations higher (2.5–4 GPa) reveals perid/liq significantly decreases relative because become less aluminous pressure. results pressure melts ratios. Therefore, some oceanic island (OIB), such as Hawaii Iceland, reflect part differences conditions may require regions more oxidized produce