ハデアンのマグマの酸化状態と,初期の地球の大気への影響
Dustin Trail1, E Bruce Watson, Nicholas D Tailby
1Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180, USA. traild@rpi.edu
Nature
|December 2, 2011
まとめ
初期の地球の大気組成は,火山からの放出ガスの影響を受けていた. 研究によると,ハデアンのマグマは,今日の酸素レベルに類似しており,減少しない初期の大気を示唆しています.
科学分野:
- 地質化学 地質化学
- 惑星科学 惑星科学
- 初期の地球の歴史 初期の地球の歴史
背景:
- マグマの放出ガスは,地球の初期の大気 (4000万年以上前) を著しく形作りました.
- 大気組成は,火山噴出の酸素流動性 (酸素圧) に依存する.
- マグマの酸化状態の直接的な証拠は,限られた岩石記録のため希少である.
研究 の 目的:
- ハーデア紀のマグマの溶融の酸化状態を決定するために.
- 地球の初期の大気の組成を制限するために.
- 初期の地上のマグマの酸化還元条件を調査する.
主な方法:
- ジルコンの結晶にセリウムの組み込みを用いたリドックス感受性校正を開発した.
- 約4億400万年前に遡る古代の岩性デトリタルジルコンを分析した.
- ハーデア紀のジルコンの酸素流動性を,現代およびアーカイア紀のマントル由来の溶岩と比較した.
主要な成果:
- ハデアンのマグマの溶融は,現在の条件に似た,ファヤライト-マグネチート-クォーツのバッファと一致する酸素の逃逸性を示した.
- 選択されたハデア紀のジルコンは,4,350万年前という早い時期に,現代のマントル由来の溶岩に匹敵する酸素の流動性を示しています.
- 初期の地上のマグマの酸化状態は,今日のものとは著しく異なるものではありませんでした.
結論:
- 太陽系の形成から約2億年後の地球の内部からの排気は,大気減少につながらなかった.
- ファヤライト・マグネチート・クォーツ・バッファは,ハデアン・マグマの酸化還元条件を左右した可能性が高い.
- 初期の地球の大気は,おそらく酸化組成があり,その進化に影響を与えた.
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