JpGU-AGU Joint Meeting 2020

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[E] 口頭発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT31] 惑星中心核:構造,形成と進化

コンビーナ:寺崎 英紀(岡山大学理学部)、大谷 栄治(東北大学大学院理学研究科地学専攻)、Gerd Steinle-Neumann(Bayerisches Geoinstitut, Universitaet Bayreuth)、William F McDonough(Department of Earth Science and Research Center for Neutrino Science, Tohoku University, Sendai, Miyagi 980-8578, Japan)

[SIT31-05] Sound velocity of B2-FeNiSi alloy at high pressure determined with inelastic X-ray scattering: Implications for the composition of the Earth's inner core

Serena Dominijanni1、*大谷 栄治2生田 大穣2坂巻 竜也2福井 宏之3McCammon Catherine1Dubrovinsky Leonid1内山 裕士4Baron Alfred5 (1.バイロイト大学バイエルン地球科学研究所、2.東北大学大学院理学研究科地学専攻、3.兵庫県立大学、4.高輝度光科学研究センター、5.理化学研究所)

キーワード:音速、内核、B2型FeNiSi合金、高圧、X線非弾性散乱

Geochemical and geophysical studies provide evidence that Earth’s core contains iron with 5-7 wt.% of nickel [1] and a small amount of light elements (such as silicon, sulfur, oxygen, hydrogen, and carbon) that can justify the observed density deficit with respect to pure iron [e.g., 2]. The cosmochemical abundance of Si and its involvement in chemical reactions at the core mantle boundary (CMB) indicate that it can be considered as one of the major alloying elements in the Earth’s core [1].

We measured the sound velocity of Fe78Ni7Si15 alloy with a B2 structure at room temperature up to 90 GPa employing inelastic X-ray scattering to constrain the constitution of the inner core. The density of the alloy was also determined by X-ray diffraction under the same conditions. The relation of the P-wave velocity (vP) and density (ρ) of B2-Fe78Ni7Si15 alloy follows Birch’s law. We discuss the possibility that the inner core is composed of the B2-Fe78Ni7Si15 alloy or the mixture of hcp and B2 alloys based on Birch’s law determined here for B2-Fe78Ni7Si15 alloy and that for hcp-Fe and FeSi alloys reported previously [3, 4]

References:
[1] McCDonough W.F. and Sun S., (1995), Chem. Geol. 120, 223-253;
[2] Dubrovinsky L., et al., (2000), Phy. Rev. Lett., 84, 1720-1723
[3] Sakamaki et al. (2016), Science Advances, 2, e1500802.
[4] Sakairi et al. (2018), Am Min., 102, 85-90.