ハワイの羽根の若い源である
Alexander V Sobolev1, Albrecht W Hofmann, Klaus Peter Jochum
1ISTerre, University Joseph Fourier, Grenoble 1 and CNRS, BP 53, 38041 Grenoble, France. alexander.sobolev@ujf-grenoble.fr
Nature
|August 12, 2011
まとめ
海洋島の火山活動には,海洋地殻のリサイクルが含まれる. ハワイの溶岩からの新しいストロンチウム同位体データは,海水の汚染を明らかにし,マントルの循環速度が以前に推定されたよりも速いことを示唆しています.
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
- マントル・ペトロロジー マントル・ペトロロジー
背景:
- 海洋島火山の発生は,海面の地殻が潜水とマントルの羽根を介して再利用することで説明される.
- この再利用の年代付けは,マントルの循環速度を理解するために重要です.
- 鉛とRe-Osのイソトープを用いた以前の年代測定法は,混合とレニウムの移動性のために制限があります.
研究 の 目的:
- マントルの羽ばたきで海洋の地殻が再利用される時間のスケールを調査する.
- ハワイの火山活動に寄与する海底地殻の年齢を決定する.
- マントルの循環速度の推定を精査する.
主な方法:
- マウナ・ロアオリヴィンフェノクリスタからの138の溶融インクルージョンのストロンチウム-87/ストロンチウム-86 ((87) Sr/ (86) Sr) の比率の分析.
- 海水と古代地殻のシグネチャーによる同位体組成の比較.
- 源汚染と年齢を推論するために,同位体データのモデリング.
主要な成果:
- マウナ・ロア・ラバでは,マントルの巨大な源の異質性が確認された.
- 枯渇した溶融インクルージョンの高放射性ストロンチウムは,2億~6億5千万年前の海水と一致する.
- これは,マウナ・ロアの源岩の沈殿前に海水汚染があったことを示している.
結論:
- 海水の汚染は,沈下した海洋地殻の"タイムスタンプ"を提供します.
- 2億~6億5千万年前の海洋地殻の存在は,より速いマントルの循環を暗示しています.
- マントルの平均循環速度は約2 (±1) cm/yrと推定されており,これはこれまで考えられていたよりも速い.
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