地核条件下多元铁轻元素体系的熔化行为以及地核的热结构和轻元素分化研究

地核的主要成分包括铁和镍（约5-10%）以及一定量的轻元素，如Si，O，S，C和H。随着地核的逐渐冷却，当地核温度低于地核组分铁合金的熔化温度时，液态地核开始结晶并产生固态内地核。该过程伴随着轻元素的分化并在内外核边界产生了密度阶跃。地核中轻元素的存在和分化对地核的热力学状态和演化以及地核对流和地磁场的产生起到了至关重要的作用。因此研究铁轻元素合金在地核条件下的熔化行为、轻元素分化和物理性质等是了解地核状态和动力学的基础。本项目拟使用激光加热金刚石压腔和二级轻气炮高压技术研究地核候选组分Fe-Si-O和Fe-Si-C三元体系在地核压力下（135-360 GPa）的熔化行为和物理性质。研究结果可进一步确定地核的热力学状态、内外地核的轻元素分化，限定地核的轻元素种类和含量，并进一步认识地核的对流机制以及地核的热与化学演化过程。该项目可对地球科学和凝聚态物理之间的交叉融合产生积极推动作用。

Geophysical and cosmochemical constraints suggest that the Earth’s core is mainly composed of Fe-Ni alloy with a certain amount of light elements, such as Si, S, O, C, and H. Inner core formation happens as a result of the secular cooling of the liquid outer core when the core adiabat cools below the melting temperature of Fe-light element alloys. Light elements partition into liquid iron during the crystallization of iron alloys, causing a density jump across the inner-core boundary. The presence of light elements and its partitioning between solid and liquid core have an important effect on the core’s properties such as its thermal structure and evolution, and power the core convections and the Earth’s magnetism. Therefore, knowledge of melting behaviors, light-element partitioning and physical properties of iron alloys at the core’s conditions is fundamental to understanding the thermophysical state and geodynamic of the core. It has been a challenging task in experiments and theories due to ultra-high pressures in the core (~135-360 GPa) and thus the core remains unclear and controversial. Here, we will study the high-pressure melting behaviors, light-element partitioning and physical properties of ternary Fe-Si-O and Fe-Si-C systems as the most likely composition of the core at the relevant pressure-temperature conditions of the core. The expected results can be used to figure out the thermal state of the core and light element partitioning between outer and inner core, and further constrain the light elements and concentrations in the core. With the help of seismic observations and geophysical modeling, we can further understand the mechanism of the core’s convections and the generation and evolution of the inner core. This project will have a significant impact on the interdisciplinary field of condensed matter physics and geoscience.