Hf-Nd同位体の証拠は,初期の地上のマントルの一時的なダイナミック・レジムの証拠である
Albarede1, Blichert-Toft, Vervoort
1Ecole Normale Superieure de Lyon, France. albarede@ens-lyon.fr
Nature
|April 13, 2000
まとめ
初期の地球 初期の地球
科学分野:
- 地質化学 地質化学
- 惑星科学 惑星科学
- イソトープ地球化学 イソトープ地球化学
背景:
- 初期の地球のマントルの組成は,限られた古代の岩石サンプルのために,ほとんど理解されていません.
- 惑星の蓄積とマグマの海洋段階からの初期化学分割は,後の地動力学的プロセスによって覆われると予想されます.
- 原始的な,熱を失う地球から現代的な,地動力学的に活発な惑星への移行は,よく定義されていません.
研究 の 目的:
- アーカイアンマントルの地化学的シグネチャーを調査するために.
- 初期の地球の分化プロセスが後のマントルの組成に影響を与えた程度を決定する.
- 約38億年前の地球の熱状態と地動力学的状態を理解するために.
主な方法:
- アーカイア期 (グリーンランド・イスワ) の地殻上の岩石から得られたハフニウム・ネオジミウム (Hf-Nd) の同位体データとの比較.
- 月面の岩石と火星の隕石 (SNC) から得たHf-Nd同位体データの分析.
- マントルの継承と熱史を推論するための同位体シグネチャーの相関.
主要な成果:
- 古代マントルの地化学 (約3.8Gyr前) は,初期の地球分化からの重要な継承を示しています.
- 証拠によると,初期の地球はまだかなりの原始的な熱を失っていた.
- 初期のマントルの層構造の残骸は,現代の深層地球にも残っているかもしれない.
結論:
- 初期の地球マントルの地化学的記憶は完全に失われていないが,同位体信号は重要な洞察を提供している.
- アルカイア時代のマントルの構成は,原始的な分化と進行中の地動力学的プロセスを反映しています.
- 初期の地球の熱と組成の進化を理解することは,今日のマントルの異質性を説明する鍵です.
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