Sound velocities and melting of Fe-Ni-Si system at high pressures under shock loading

Monday, 15 December 2014: 11:05 AM
Youjun Zhang1, Toshimori Sekine1, Hongliang He2, Yin Yu2, Fusheng Liu3 and Mingjian Zhang3, (1)Hiroshima University, Higashi-Hiroshima, Japan, (2)China Academy of Engineering Physics, Institute of Fluid Physics, Miangyang, China, (3)Southwest Jiaotong University, College of Physical Science and Technology, Chengdu, China
The Earth’s liquid outer core is dominantly composed of iron and nickel (~5−10%), with a density lower by ~8% than that of the liquid iron at the core conditions [e.g., 1], requiring the presence of light element(s) [e.g., 2]. Silicon, geochemically abundant, has long been considered as a major potential light element in the Earth’s outer core because of its high solubility in iron, iron-silicate interactions at core-mantle boundary, the Si isotope data, and core formation modeling [3]. To examine effects of Si on physical properties of Fe-Ni system, we directly measured densities, sound velocities, and melting of Fe-9Ni-10Si (in weight percent) system up to ~280 GPa by shock experiments using a two-stage light-gas gun. The sound velocities were determined by the optical analyzer technique [4]. The results, compared with the seismic observations, show that silicon-rich liquid Fe-Ni system can satisfy the observed density deficit and seismological data simultaneously at the physical conditions of the outer core. Analyses of the melting temperatures of Fe-9Ni-10Si system imply the Fe-Ni-Si core will be at lower temperatures by ~600−1000 K than the pure iron core at ~330 GPa of the inner-core boundary.

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