オリヴィンにおけるヘリウム溶解性と,海洋島の玄武岩における高い3He/4Heへの影響
Stephen W Parman1, Mark D Kurz, Stanley R Hart
1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Building 54, Cambridge, Massachusetts 02139, USA. stephen.parman@durham.ac.uk
Nature
|October 21, 2005
まとめ
海洋島の玄武岩のヘリウム-3/ヘリウム-4の比率が高く,ガスのないマントルが存在することを示唆しています. 新しい実験では,マントルの融解中にヘリウムがウランとソリウムよりも互換性が高く,これらの比率は枯渇した残留物で保たれていることが示されています.
科学分野:
- 地質化学 地質化学
- イソトープ地球化学 イソトープ地球化学
- ペトロロジー・ペトロロジーとは
背景:
- 海洋島ベサルト (OIB) の高い3He/4He比は,ガスのないマントルの貯水池の重要な証拠です.
- マントルの融解モデルは,ヘリウムの化学的振る舞いに依拠しているが,分断の推定は矛盾している.
研究 の 目的:
- オリヴィンでヘリウム溶解性を実験的に決定する.
- マントルの融解中のヘリウムの分割行動を明らかにするために.
主な方法:
- 大気圧での天然および合成オリビンのヘリウム溶解性の実験測定.
- ヘリウム大気で均衡を保ち,次に粉砕と融解の分析を行います.
主要な成果:
- 0.0025 ± 0.0005から 0.0060 ± 0.0007.7までのヘリウムに対するオリヴィン溶融分離係数を決定した.
- ヘリウムは,マントルの融解中にウランとソリウムよりも互換性があるように見える.
結論:
- 実験データによると,溶解中のヘリウムとの互換性が示唆され,枯渇した残留物の中で3He/4Heの高い比率を潜在的に保ちます.
- これにより,OIBと海中のベースタルトヘリウム濃度の不一致が解消され,高い3He/4He OIBの枯渇した源を支えている.
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