High Pressure Synchrotron Radiology and Microtomography Studies of Mechanisms and Kinetics of Liquid Iron -Silicate Segregation: Implications for Formation of the Earth's Core

所有的核心形成模型都依赖于对液态铁-硅酸盐分离机理的认识。研究人员建议在GSECARS和高级光子源的大容量压机中通过原位同步加速器X射线照相术研究铁硅酸盐分离过程。他们的中试实验表明，在分离过程中，可以通过原位射线照相术观察到来自硅酸盐和Fe（具有受控量的轻元素）的机械混合物的富Fe熔体的液滴。计算机显微断层扫描已被应用到回收的样品，以产生三维重建的熔体液滴的大小和空间分布的压力，温度，组成和时间的函数。在拟议的研究中，研究人员将检查包含选定的轻元素，如C，S，H，O和Si的系统，在高达15 GPa和2000 K的压力下具有各种金属/硅酸盐体积比。他们将通过选择纯成分从简单的组成开始，但随着了解的增加，将研究更现实的组成，如铁陨石和碳质陨石。目前，白色光束用于射线照相实验，但单色辐射将用于未来的实验，以提高图像分辨率和对比度。此外，该团队还计划开发一种用于原位显微层析成像的X射线透明Drickamer型高压池，这将大大提高分辨率到微米级。将在实验的各个阶段通过显微断层扫描检查样品，以重建富Fe液滴的大小和空间分布随光元素、压力、温度和时间的变化。将对采集的样品进行切片，并通过扫描和透射电子显微镜进行检查，以将金属-硅酸盐相互作用解析至亚微米水平。将使用电子探针和X射线荧光探针进行成分分析和元素分配研究。这些实验将提供关于铁硅酸盐分离的第一手实验室观察，并提高我们对可能的核形成机制和核幔边界动力学的理解。结果将被用来限制现有的模型，关于物理和化学过程的核心形成。

Wang 0001088 All core formation models depend on knowledge of mechanisms of the liquid iron-silicate separation. The investigators propose to study the iron-silicate separation process by in-situ synchrotron X-ray radiography in the large-volume press at GSECARS and the Advanced Photon Source. Their pilot experiments have demonstrated that droplets of Fe-rich melt from a mechanical mixture of silicates and Fe (with controlled amounts of light elements) can be observed by in situ radiography during the separation process. Computed microtomography has been applied to the recovered samples to generate three-dimensional reconstructions of the size and spatial distribution of the melt droplets as a function of pressure, temperature, composition, and time. In the proposed study, the investigators will examine systems containing selected light elements, such as C, S, H, O, and Si, with various metal/silicate volume ratios at pressures up to 15 GPa and 2000K. They will start with simple compositions by selecting pure constituents but as understanding increases will work on more realistic compositions such as iron meteorite and carbonaceous meteorite. Currently a white beam is used for the radiography experiments but monochromatic radiation will be used in future experiments to enhance image resolution and contrast. In addition, the team plans to develop an X-ray transparent Drickamer-type high-pressure cell for in-situ microtomography, which will greatly enhance resolution power to the micron level. Samples will be examined at various stages of the experiment by microtomography to reconstruct the evolution of the size and spatial distribution of the Fe-rich droplets as a function of light element, pressure, temperature, and time. Recovered samples will be sectioned and examined by scanning and transmission electron microscopy to resolve metal-silicate interaction to sub-micron level. Composition analyses will be performed and element partitioning will be studied using electron microprobe and X-ray fluorescence microprobe. These experiments will provide first-hand laboratory observations on iron-silicate separation and improve our understanding of possible core formation mechanisms and dynamics of the core-mantle boundary. The results will be used to constrain existing models regarding physical and chemical processes of the formation of the core.