ブリッジマニットの粒子の大きさの変動は,マントルの真ん中の粘度ジャンプを説明します
Hongzhan Fei1,2, Maxim D Ballmer3, Ulrich Faul4
1Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany. feihongzhan@zju.edu.cn.
Nature
|July 5, 2023
まとめ
地球のマントルのダイナミクスにとって極めて重要な中層マントルの粘度ジャンプは,下層マントルのより大きく,より粘性のあるブリッジマニットに富んだ岩石によって説明されます. これらの古代の岩は高粘度で保存され,マントルのコンベクションと地化学に影響を与えます.
科学分野:
- 地理学
- 鉱物物理学
- 惑星科学
背景:
- 重要な粘度上昇,中層マントルの粘度ジャンプは,地球の下層マントルの800〜1200kmの深さにあります.
- このジャンプはスラブ沈殿,羽根上昇,化学混合に影響しますが,その起源は既知の鉱物相移行によって説明されていません.
- 現存するモデルは地質学的観測と この深さでの相変化の欠如を 調和させるのに苦労しています
研究 の 目的:
- 中間マントルの粘度ジャンプの起源を調査する
- 下層マントルの鉱物学的差異が観測された粘度コントラストを説明できるかどうかを判断する.
- 深い下層マントルの材料の長期保存を説明するために
主な方法:
- ブリッジマニットで濃縮された岩石と,その上にある火石岩石の粒子の大きさと粘度が対照的に分析される.
- マントルのダイナミクスに対するこれらのコントラストの影響をモデル化します.
- 地化学の異常と地震の観測を 関連付けている
主要な成果:
- 深い下層マントルのブリッジマニットに富んだ岩は,上層の火石岩よりも10倍以上の粒度と粘度を持っています.
- この鉱物学的および質感的な違いは,マントルの真ん中の粘度ジャンプを説明するのに十分です.
- ブリッジマニットに富んだ岩石の急速な初期粒子の成長は,マントルのコンベクションに対する保存につながった.
結論:
- 中部マントルの粘度ジャンプは,深い下部マントルの古い,大きな粒度,高粘度ブリッジマニットに富んだ岩の存在によって引き起こされます.
- これらの岩の保存は,様々な地化学的サイン (例えば,同位体比) と地物理的現象 (例えば,スラブ停滞,羽根の傾斜) を説明する.
- これは下層マントルの構造,動力学,化学的進化について統一された説明を提供する.
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