深層の水性マントルの貯水池は,33億年前に地殻が再利用された証拠を提供します
Alexander V Sobolev1,2, Evgeny V Asafov3, Andrey A Gurenko4
1Université Grenoble Alpes, Université Savoie Mont Blanc, Institute Science de la Terre (ISTerre), CNRS, IRD, IFSTTAR, Grenoble, France. alexander.sobolev@univ-grenoble-alpes.fr.
Nature
|July 17, 2019
まとめ
地球の奥深くにある水
科学分野:
- 地化学と地物理学
- マントルダイナミクス
- 地球 の 初期 の 進化
背景:
- 水はマントルの性質に大きく影響し,融解とコンベクションに影響する.
- 水を追跡すると 表面物質が深層のマントルに 循環する事が分かり 地球の地力学を理解するのに 極めて重要です
- 高度なマントルの融解から生じるコマチートは,マントルの深層の構成と水分量の重要な指標です.
研究 の 目的:
- 初期の地球マントルの水の存在と起源を調査する
- パレオアルカイア時代まで 深い水分貯蔵庫が存在していたか 調べるため
- 海水によるリトスフィアの 循環を深層のマントルに辿るため
主な方法:
- 古代コマチート内の溶融インクルージョンにおけるデュテリウムと水素 (D/H) の比率の分析.
- 水,塩素,鉛を含むコマチートの溶融含有物の地化学分析
- 表面貯水池,典型的なマントル,そして変化した海洋地殻との同位体組成の比較.
主要な成果:
- 古代のコマタイト (3.3億年) は,マントルの水源を示す水素同位体シグネチャーを示しています.
- これらの発見は,少なくともパレオアルカイア時代以来,深い水性マントルの貯水池の存在を確認しています.
- 同位体成分からすると 海水によって変化した石層は 沈殿時に脱水し 深いマントルに再利用されたと推測されます
結論:
- 地球の内部には少なくとも36億年前から 深い水性マントルの貯水池が存在しています
- 海水の変化と深層マントルの土層沈殿は 33億年前に起こった.
- この初期の再利用は 深いマントルの組成と水分量に影響を与えました
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