水に富んだ玄武岩は,海中の寒い場所にある
Marco Ligi1, Enrico Bonatti, Anna Cipriani
1Istituto Scienze Marine, Geologia Marina, CNR, Via Gobetti 101, 40129 Bologna, Italy.
Nature
|March 4, 2005
まとめ
寒い地域の海洋ベースルトには,驚くほど高い含水量があり,以前の仮定に異議を唱えます. この発見は,水に富んだ玄武岩がホットスポット近くだけでなく,ホットスポットにも形成されることを示唆しています.
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
- 海洋学 海洋学とは
背景:
- サブオセアンの上層マントルの水は,マントルの粘度,融解,そして中海の山脊で地殻の生成に影響を与えます.
- 海洋の玄武岩は,通常",湿った"マントルの羽根と関連しているホットスポットからのものを除けば,0.2 wt%未満の水を含んでいます.
研究 の 目的:
- 中洋山頂システムの寒い地域からの玄武岩の異常な高い水分含有量の発生と起源を調査する.
- 熱的に最小のマントル地域における水豊富な玄武岩の影響を理解する.
主な方法:
- 赤道大西洋中部海系からのベースアルティックガラスの分析.
- 地化学分析,含水量,主要元素 (ナトリウム),稀土元素の比率を含む.
- マントルの融解プロセスの数値モデリング.
主要な成果:
- 寒い海中山脈地帯の玄武岩のガラスに異常な水分量が検出されました.
- これらの玄武岩はナトリウムが豊富で,高光対重稀土元素の比率が高く,融解中にガーネットの存在を示しています.
- 数値モデリングは,60km以上の深さで"湿った"マントルの低度な融解から派生することをサポートしています.
結論:
- 海洋の玄武岩は,ホットスポットの近くだけに限らず",寒いスポット"でも水分が豊富である可能性があります.
- かなりの深さでの低度"湿った"融解が,これらの水分豊富な玄武岩を生成するための重要なプロセスであることを示唆しています.
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