Zn/Feの体系論を用いた弧マントルのリドックス状態
Cin-Ty A Lee1, Peter Luffi, Véronique Le Roux
1Department of Earth Sciences, Rice University, Houston, Texas 77005, USA.
Nature
|December 3, 2010
まとめ
原始的な弓状マグマにおける亜鉛と鉄の比率 (Zn/Fe(T)) は,マントルの酸化が潜水からのみではないことを示唆している. マントルのの変化ではなく,浅層の微分化が,アーク・ラバにおけるより高い酸化状態を引き起こす可能性が高い.
科学分野:
- 地質化学 地質化学
- ペトロロジー・ペトロロジーとは
- マントルの地力学 マントルの地力学
背景:
- アーク・ラバは通常,海中の玄武岩よりも酸化が強い.
- サブドクションは,酸化した成分をマントルに導入し,酸化した亜弧マントルのにつながると考えられている.
- 亜弧マントルの鉄酸化状態を直接決定することは困難であり,その内在の酸化状態に関する議論を煽っています.
研究 の 目的:
- 弧形マグマのマントル源のリドックス状態を調査する.
- サブダクションがマントル・ケイジの酸化状態を大幅に変化させるかどうかを判断する.
- アークラバの鉄酸化を制御するプロセスを理解するために.
主な方法:
- 酸化還元反応に敏感な Zn/Fe (T) の比率を用いて,主弧ベースアルトとそのマントルの源における鉄のバレンスの状態をプロキシとして計算する.
- マントルの融解とマグマの微分化におけるFe(2+),Fe(3+),Znの振る舞いを分析した.
- 弧形マグマのZn/Fe (T) と,海中の玄武岩を比較したところ.
主要な成果:
- 原始的な弧マグマは,中海のの玄武岩に似たZn/Fe(T) の比率を示しており,これは原始マントルの溶解物におけるFeの酸化状態が類似していることを示している.
- 初期のオリヴィン分断では,Zn/Fe (T) の比率が一定であり,マグマのFe (T) /Fe (T) が低いことを意味します.
- 鉄の酸化状態 (Fe(3+) /Fe(T)) は増加し,磁石は漸進的な分数結晶化後にのみ安定する.
結論:
- 酸化した地殻物質の潜水は,マントルののリドックス状態を大きく変えないかもしれない.
- 弧状のラバで観測されるより高い酸化状態は,浅いレベルのマグマ的微分化プロセスの結果である可能性が高い.
- これらの浅いレベルの差別化プロセスを完全に理解するためには,さらなる研究が必要です.
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