Ferric iron partitioning between melts and bridgmanite/Ca-perovskite from equilibration experiments at 30-80 GPa: redox evolution processes

The partitioning of ferric iron during magma ocean crystallization and solidification of the lower mantle exerts key control on the early redox evolution of Earth-sized planets, as it determines the character of the earliest atmosphere and the potential formation of deep oxidized domains which may later drive geochemical of the entire planet and surface. We propose to use synchrotron Mössbauer spectroscopy to determine partitioning of Fe3+ between silicate melt coexisting bridgmanite [nominally (Mg,Fe,Al)(Si,Al)O3] and Ca-perovskite [(Ca,Mg,Fe)SiO3], precipitated in diamond anvil experiments at 30-80 GPa and 3500-4500 K. The high accuracy of SMS and the high spatial resolution afforded at ID14 are uniquely capable of the required analyses. Results will be used to calibrate a thermodynamic model for Fe3+ stability in lower mantle molten and solid silicates and applied to better understand the redox evolution of solidifying terrestrial planets

岩浆洋结晶过程中三价铁的分异与下地幔的固化过程，对地球大小行星的早期氧化还原演化起到关键调控作用：该过程决定了原始大气的特征，以及深部氧化域的潜在形成；而深部氧化域后续可能驱动整个行星及地表的地球化学过程。本研究拟采用同步辐射穆斯堡尔光谱（synchrotron Mössbauer spectroscopy），测定在30~80 GPa、3500~4500 K的金刚石压腔实验中析出的布里奇曼石（bridgmanite，标称化学式为(Mg,Fe,Al)(Si,Al)O3）与钙钛矿（Ca-perovskite，[(Ca,Mg,Fe)SiO3]）共存体系中，三价铁在硅酸盐熔体与两种矿物间的分配行为。同步辐射穆斯堡尔光谱的高精度特性，加之ID14线站所具备的高空间分辨率，恰好能够满足本次分析的独特要求。本研究所得结果将用于校准下地幔熔融态及固态硅酸盐中三价铁稳定性的热力学模型，进而助力我们更深入地理解固化过程中类地行星的氧化还原演化。