JpGU-AGU Joint Meeting 2017

講演情報

[EE] ポスター発表

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-IT22] [EE] 核-マントルの相互作用と共進化

2017年5月21日(日) 13:45 〜 15:15 ポスター会場 (国際展示場 7ホール)

コンビーナ:土屋 卓久(愛媛大学地球深部ダイナミクス研究センター)、寺崎 英紀(大阪大学大学院理学研究科)、Satish-Kumar Madhusoodhan(Department of Geology, Faculty of Science, Niigata University)、入舩 徹男(愛媛大学地球深部ダイナミクス研究センター)、Hernlund John(Earth-Life Science Institute, Tokyo Institute of Technology)、大谷 栄治(東北大学大学院理学研究科地学専攻)

[SIT22-P16] Determination of the noble gas partition coefficients between metal-silicate melts using laser microprobe analysis

*貴志 智1ジャクソン コリン2野村 龍一3角野 浩史1三部 賢治4舘野 繁彦5鍵 裕之6 (1.東京大学大学院総合文化研究科広域科学専攻、2.カーネギー地球物理学研究所、3.愛媛大学地球深部ダイナミクス研究センター、4.東京大学地震研究所、5.岡山大学惑星物質研究所、6.東京大学大学院理学系研究科地殻化学実験施設)

キーワード:core, mantle, noble gas, partition coefficient, high P-T experiment

Analyses of ocean island basalts (OIBs) reveal a geochemical reservoir characterized by unradiogenic, “primordial” noble gas signatures (e.g., high 3He/4He and low 40Ar/36Ar ratios), likely residing in the deep mantle. There has been much debate about the area holding the “primordial” noble gases deep in the Earth (Porcelli & Ballentine, 2002), including that the “primordial” noble gasses have been retained in the deepest region of the mantle since 4.4 Ga (Mukhopadhyay, 2012) or in the core since the core-mantle separation (Trieloff & Kunz, 2005). However, the validity of latter strongly depends on the quantity of noble gases the core incorporates during accretion and can hold in the present day.
In this study, in order to investigate noble gas partitioning behavior between the core and mantle, noble gases were dissolved into metal-silicate melts under high temperature and pressure conditions, and then the samples were quenched. Two series of sample synthesis were performed at different pressure-temperature ranges and experimental approaches. At the Geophysical Laboratory, Carnegie Institute of Washington, Ar partitioning experiments were conducted using a piston cylinder apparatus. Temperatures were 1700 °C, and pressures were 1 GPa. Experimental samples were contained by a double capsule: Pt outer capsule and graphite inner capsule. A Fe metal-silicate mixture was packed into the graphite capsule. Argon was added to the Pt outer capsule as a liquid, and the Pt capsule was welded shut while held in a bath of liquid N2. At the Geodynamics Research Center, Ehime University, noble-gas doped hydrous silicate glass and iron were melted and equilibrated under high pressure and temperature (~ 30 GPa, 1700 °C) using a laser-heated diamond anvil cell. After that, the noble gas concentrations contained in the each phase were analyzed using an ultraviolet laser ablation apparatus and a noble gas mass spectrometer at the University of Tokyo.
Preliminary results for argon showed that the partition coefficient D, where D = (noble gas in metal phase)/(noble gas in silicate phase), is in the order of 10-4, which is three orders of magnitude lower than the previous work (Matsuda et al., 1993). However, the apparent noble gas concentrations in the metal phase seem significantly controlled by contaminant phases, such as metal inclusions and micro- or nano-noble gas bubbles. Further experiments are necessary to distinguish noble gases dissolved in metal and retained in the contaminants to better constrain noble gas behaviors between silicate and metal.

References: Matsuda et al., Science 259, 788-791, 1993; Mukhopadhyay, Nature 486, 101-104, 2012; Porcelli & Ballentine, Rev. Mineral. Geochem. 47, 411-480, 2002; Trieloff & Kunz, Phys. Earth Planet. Inter. 148, 13-38, 2005.