内核条件下でのhcp-Feの弾性特性に強いプレメルト効果があります

Benjamí Martorell¹, Lidunka Vocadlo, John Brodholt

¹Department of Earth Sciences, University College London, London WC1E 6BT, UK.

Science (New York, N.Y.)

|October 12, 2013

まとめ

地球の核のシェア波速度 (VS) は驚くほど低い. 新しいシミュレーションでは,鉄が溶解点の近くで著しく弱くなり,内核のこれらの地震観測を説明することを明らかにしています.

科学分野:

地質物理学地質物理学とは地質物理学です.
ミネラル物理学ミネラル物理学
コンピューティング・マテリアル・サイエンス・サイエンス

背景:

地震学的な観測は,地球の核におけるシェア波速度 (VS) が,鉱物物理モデルによって予測されるよりも低いことを示している.
この不一致に対する既存の説明は,理論的データと観測データを調和させるのに不十分である.

研究の目的:

鉄の弾性特性を内核条件下において,高度な計算方法を用いて調査する.
鉄の溶解点付近の振る舞いが,観測された低いVSを説明できるかどうかを判断する.

主な方法:

六角形の密集鉄 (hcp-Fe) の弾性特性を計算するために,アビニシオ分子動力学シミュレーションを使用しました.
シミュレーションは高圧 (360 GPa) で,融解温度 (Tm) に相対的な温度範囲で実施されました.

主要な成果:

0.96 * Tm以上の温度でhcp-Feの強い非線形切断弱化を特定しました.
この溶解前の切断弱化に関連したVSの有意な減少が観察されました.
内核内の予測される温度範囲 (T/Tm ≈0.99 から 1) は,この重要な弱体化体制に該当します.

結論:

溶解点近くの鉄の非線形切断弱化は,地球の内核で観測された異常な低いVSの説得力のある説明を提供します.
この発見は,鉱物学的モデルと地球の深い内部における地震学的データとの不一致を調和させるものである.

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