18億8千万年前の鉄の堆積は,地殻の急速な成長の結果である
Birger Rasmussen1, Ian R Fletcher, Andrey Bekker
1Department of Applied Geology, Curtin University, Kent Street, Bentley, Western Australia 6102, Australia.
Nature
|April 28, 2012
まとめ
約188億年前の鉄の形成の再出現は,マントルの活動と火山活動の増加と関連していた. これにより鉄が放出され,大気中の酸素濃度が上昇したにも関わらず,一時的に鉄質の海洋状態が生まれました.
科学分野:
- 地質化学 地質化学
- 堆積物学 堆積物学 堆積物学 堆積物学 堆積物学
- パレオセアノグラフィー
背景:
- 鉄の形成 (化学的堆積岩) は,無酸素で鉄が豊富な海水を必要とします.
- その堆積は,大気中の酸素が上昇した後,約232億年前に停止した.
- 5億年後の再出現は科学的なパズルを提示する.
研究 の 目的:
- 紀元前新生代後半の鉄形成堆積の原因を調査する.
- オーストラリアの鉄の形成が北米の鉄の形成と同時代であったかどうかを判断するために.
- 鉄形成の堆積を地球規模の地質現象と結びつけるために.
主な方法:
- 西オーストラリアのフレレ・フォーメーション内のタフ層のジルコン年代測定.
- 岩層の地化学分析. 岩層の地化学分析. 岩層の地化学分析.
- 世界的な地質学とマントルの活動データとの相関.
主要な成果:
- デッティングが確認されたオーストラリアの鉄の形成は18億8千万年前のもので,北米の形成と同時代である.
- この同時代の堆積は,世界の海洋化学が鉄の形成に影響を与えたことを示唆しています.
- このイベントは,マントルの活動,地殻形成,および火山由来の大規模な硫化物形成のピークと一致しました.
結論:
- 強化された海底火山活動と水熱活動により,鉄が放出され,海洋の酸化物質が圧倒されました.
- これにより,一時的に鉄酸化状態が戻り,大気と海洋の酸化還元状態が分離した.
- 鉄の形成の後の減少は,マントルの活動と水熱鉄流の減少を反映している可能性が高い.
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