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

三价铁在岩浆洋结晶及下地幔固化过程中的分配作用，对地球大小行星的早期氧化还原演化起到关键控制作用：其决定了原始大气的特征，以及深部氧化域的潜在形成，而这些氧化域后续可驱动整个行星及其地表的地球化学过程。本研究拟采用同步穆斯堡尔谱学（Synchrotron Mössbauer spectroscopy，SMS），测定共生于布里奇曼石（bridgmanite）[标称成分为(Mg,Fe,Al)(Si,Al)O3]与钙钛矿（Ca-perovskite）[(Ca,Mg,Fe)SiO3]的硅酸盐熔体之间三价铁的分配行为；实验样品通过金刚石压砧（diamond anvil）实验在30-80吉帕斯卡（GPa）与3500-4500开尔文（K）条件下合成析出。同步穆斯堡尔谱学的高精度特性，以及ID14光束线所提供的高空间分辨率，可唯一满足本次分析的需求。本研究所得结果将用于校准下地幔熔融态与固态硅酸盐中三价铁稳定性的热力学模型，并借此更深入理解正在固化的类地行星的氧化还原演化过程。