Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT18] Planetary cores: Structure, formation, and evolution

Mon. May 21, 2018 1:45 PM - 3:15 PM A11 (Tokyo Bay Makuhari Hall)

convener:Hidenori Terasaki(Graduate School of Science, Osaka University), Eiji Ohtani(Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University), William F McDonough (共同), George Helffrich(Earth-Life Science Institute, Tokyo Institute of Technology), Chairperson:Terasaki Hidenori, McDonough William(University of Maryland / Tohoku University)

3:00 PM - 3:15 PM

[SIT18-06] Effect of pressure and sulfur content on sound velocity in liquid Fe-S to 20 GPa

*Keisuke Nishida1, Yuki Shibazaki2, Hidenori Terasaki3, Yuji Higo4, Daisuke Wakabayashi5, Nobumasa Funamori5, Akio Suzuki6 (1.Department of Earth and Planetary Science, The University of Tokyo, 2.Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 3.Graduate School of Science, Osaka University, 4.Japan Synchrotron Radiation Research Institute, 5.Institute of Materials Structure Science, High Energy Accelerator Research Organization, 6.Department of Earth Science, Graduate School of Science, Tohoku University)

Keywords:Mars, Moon, core, sound velocity, Fe-S, liquid

In order to understand the structure and composition of the molten core of the terrestrial planets such as Mars, it is important to know the physical properties of liquid Fe alloys at high pressure and high temperature. Sound velocity is a key physical property because it can be directory compared with seismic observations. However, longitudinal sound velocity (VP) measurements of liquid Fe alloy by ultrasonic methods combined with multi anvil apparatus have been limited to below 8 GPa (e.g. Nishida et al. 2016). We therefore have been developing and improving the techniques. Here we report the latest results of sound velocity measurements of liquid Fe, Fe80S20, and Fe57S43 up to 20 GPa corresponding to the Martian core mantle boundary (CMB).

High-pressure and high-temperature experiments were conducted at BL04B1 beamline of SPring-8 and AR-NE7A beamline of KEK PF. Sound velocity was measured using ultrasonic pulse-echo method. The starting materials were pellets consisting of Fe, and mixture of Fe and FeS powders. Chemical analyses of the run products were conducted using FE-EPMA to evaluate contamination from surrounding materials.

The VP of liquid Fe57S43 were lower than that of liquid Fe80S20 in all of the conditions of up to 20 GPa. However, the pressure dependence of VP of liquid Fe is different from that of both liquid Fe80S20 and Fe57S43. The VP of liquid Fe80S20 is ~10% slower than that of liquid Fe at 5 GPa (the lunar core condition) while they are almost equal to each other at 20 GPa (the Martian CMB). The effect of sulfur on VP depends largely on pressure. The VP in liquid Fe-S monotonically decreases with increasing sulfur content at the lunar core condition while the VP may have local maximum at intermediate composition under the Martian core condition (20-40 GPa).