現代の弧における古代のマントル: izu-bonin-mariana forearcにおけるオスミウム同位体,peridotitesにおけるオスミウム同位体
Parkinson1, Hawkesworth, Cohen
1Department of Earth Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA, UK.
まとめ
イズー・ボニン・マリアナ前弓のマントル・ペリドータイトにおけるオスミウム同位体は,古代の枯渇現象を明らかにしている. これらの発見は,サブドクションゾーンが,マントルの初期の融解の証拠を保存している可能性を示唆し,コンベクトの上層マントルの私たちの理解に影響を与えます.
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
- 同位体地質学とは,同位体地質学である.
背景:
- マントルのペリドータイトは,地球のマントルの構成と進化についての洞察を提供します.
- オスミウム (Os) のイソトープは,オスの高度な siderophile 自然と長寿命のイソトープのために,マントルのプロセスの敏感なトレーサーです.
研究 の 目的:
- イズー・ボニン・マリアナ・フォアークのマントル・ペリドータイトにおけるオスミウムの同位体組成を調べる.
- これらの同位体シグネチャーの含意を古代マントルの融解現象と潜水地帯のプロセスを理解するために決定する.
主な方法:
- マントルのペリドチートサンプルにおけるオスミウム同位体比 (187Os/188Os) の分析.
- オスミウムイソトープデータに基づくプロテロゾイックモデル年齢の計算.
- ペリドータイトの組成を海洋中部のベースタルト (MORB) の源と比較する.
主要な成果:
- ペリドータイトは放射性でない187Os/188Osの比率を示しており,0.1193から0.1273.3の範囲です.
- これらの比率は,プロテロゾーイクモデルで8億2000万年~1億2300万年前の年齢を示しています.
- これらのペリドータイトによって示された枯渇したマントルの源は,MORB源よりも互換性のない元素で著しく枯渇しています.
結論:
- フォアアーク・ペリドータイトのオスミウム同位体は,コンベクトした上層マントルの古代の融解を記録し,最近の潜水開始より前のものである.
- サブドクションゾーンは,古代の,枯渇したマントルの材料の貯蔵庫として機能します.
- 流動的な上層マントルの部分には,以前に推測されたよりも放射性オスミウム同位体成分が少ない可能性があります.
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