表面に上昇する脱ガスマグマのレドックス進化
Alain Burgisser1, Bruno Scaillet
1ISTO, UMR 6113 Université d'Orléans-CNRS, 1a rue de la Férollerie, 45071 Orléans cedex 2, France. burgisse@cnrs-orleans.fr
Nature
|January 12, 2007
まとめ
マグマの上昇は,火山ガスの酸化還元状態を大幅に変化させ,その源との関連に関する仮定に挑戦します. ガス組成と量は,噴火中の酸素流動性 (f(O2) の変化を決定的に影響する.
科学分野:
- 地質化学 地質化学
- 火山学 火山学とは
- 地球科学 地球科学 地球科学
背景:
- 火山ガスは地球の大気とマグマの動態に影響を与えます.
- 火山ガスのレドックス状態は,マグマ源の条件を反映していると考えられています.
- 火山ガスによる酸素の気流性 (f(O2) の観測された変動は,未だに説明されていない.
研究 の 目的:
- マグマの上昇が火山ガスの酸化還元状態にどのように影響するかを調査する.
- 酸素の気流性 (f) (O2) の進化に対するガス組成と量の影響を決定する.
- ガス排出量のプロキシとして噴火したマグマの酸化還元状態の信頼性を評価する.
主な方法:
- マグマ管流の結合化学物理モデルを利用した.
- 上昇するマグマとそのガス相のシミュレートされたリドックス状態の進化.
- 異なるガス組成 (硫黄を含む) と貯蔵量による影響を分析した.
主要な成果:
- 硫黄のない上昇するマグマは,酸素の逃逸率 (f(O2) を最大 2 ログ単位で体系的に増加させる.
- 硫黄含有マグマは,初期貯蔵条件に依存する酸化還元状態の変化を示す.
- モデル化されたH2S/SO2比は,収束した火山地帯からの観測結果と一致しています.
結論:
- 表面のガスのリドックス状態は,マグマ源の酸素逃逸率 (f(O2) を正確に表さない場合があります.
- マグマ貯水池と火山管の出口の間には,重要な酸化還元状態の変化 (最大1.5ログ単位) が起こります.
- 地質学的過程における岩石の揮発性物質の役割に関するモデルの再評価は正当である.
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