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

University Of Chicago, Chicago IL

Investigators

Abstract

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.