メタモルフィズムとプレート構造の進化
Robert M Holder1,2, Daniel R Viete3, Michael Brown4
1Morton K. Blaustein Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA. roholder@umich.edu.
Nature
|August 9, 2019
まとめ
プレート構造はネオアルカイア期以来,地球の冷却マントルとともに徐々に進化した. 変形岩の分析は,現代的な地質学的プロセスへのゆっくりとした移行を示唆する,バイモダルの熱グラデントの漸進的な出現を明らかにします.
科学分野:
- 地球科学
- 地質学
- 構造学
背景:
- 地球のマントルのコンベクションが プレート構造と惑星の熱損失を 引き起こします
- プレート構造のタイミングと進化は 地球科学における 根本的な課題です
- 変形岩は圧気温 (P-T) 条件を記録し,構造環境を反映しています.
研究 の 目的:
- 地球の構造の進化を調査する
- プレート構造が地質学的にいつ,どのように出現し,発展したかを決定する.
- 構造変化のプロキシとして P-Tデータを使用する.
主な方法:
- 時間の経過による変形性P-T分布の統計的評価
- 岩石の表面的な熱グラデント (変形性T/P) の分析
- 古代の岩の記録と現代のバイモダルの変形パターンの比較
主要な成果:
- 地球の現代のプレート構造は,ネオアルカイア時代 (2.5億年前) から徐々に発達した.
- メタモルフのP-T分布は,ネオアルカイアから現在まで,漸進的な拡大と双方向性の増加を示している.
- 平均的な変形性T/Pは,古プロテロゾイク時代から減少した.
結論:
- プレート構造は急激に変化するのではなく,マントルの冷却とともに徐々に進化した.
- バイモダル変異の出現は,近代的な地質学過程の遅い発展を意味しています.
- これは,突発的な構造変化や,近代的なプレート構造の初期の始まりに関する以前の仮説と対照的である.
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