日本地球惑星科学連合2019年大会

講演情報

[E] 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-IT21] 核-マントルの相互作用と共進化

2019年5月27日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:河合 研志(東京大学大学院理学系研究科地球惑星科学専攻)、飯塚 毅(東京大学)、太田 健二(東京工業大学大学院理工学研究科地球惑星科学専攻)、土屋 卓久(愛媛大学地球深部ダイナミクス研究センター)

[SIT21-P25] Stable carbon isotope fractionation in Fe-C system from first principles

*出倉 春彦1土屋 卓久1 (1.愛媛大学地球深部ダイナミクス研究センター)

キーワード:Isotope fractionation、First-principles calculation

Carbon is the fourth most abundant element in the solar system and likely one of the constituent light elements in the Earth’s core. Determination of its equilibrium isotope fractionation factor (α) under high pressure (P) and temperature (T) is a key for understanding chemical evolution such as the whole Earth carbon distributions and the amount in the Earth’s core (e.g., Kumar et al., 2011). Because experimental measurement of the isotope fractionation remains technically challenging at the deep mantle condition, attempts to evaluate the α among mantle minerals by first-principles calculations have been made in recent years (e.g., Huang et al., 2014). Recently, our group initiated the theoretical determination of the α in the Fe-C system in the Earth’s deep interior with a full ab initio approach based on the density-functional theory. We performed ab initio lattice dynamics calculations for diamond and iron-carbide (hexagonal Fe7C3) having the two stable carbon isotopes (12C and 13C). The α between the two phases were then determined by using the Gibbs free energies calculated at P ~300 GPa and T ~2000-6000 K. The obtained 103lnαdia-Fe7C3 is found to vary with T from ~+8‰ (2000 K) to ~+5‰ (6000 K). This result indicates that the Fe7C3 is enriched in the heavier isotope (13C) compared with diamond. This trend is qualitatively consistent with low-pressure experimental observations (Kumar et al., 2011).