サモア・ラバに沈んだ大陸の地殻が戻ってきたこと
Matthew G Jackson1, Stanley R Hart, Anthony A P Koppers
1Massachusetts Institute of Technology, Woods Hole Oceanographic Institution Joint Program, Woods Hole, Massachusetts 02543-1525, USA. mjackson@whoi.edu
Nature
|August 10, 2007
まとめ
サモア・ラバの独特のストロンチウム (Sr) とネオジミウム (Nd) の同位体によって特定されたリサイクルされた大陸の地殻は,マントルの羽根を経由して地球表面に戻った沈殿した堆積物の証拠を提供します.
科学分野:
- 地質化学 地質化学
- イソトープ地球化学 イソトープ地球化学
- マントルの地力学 マントルの地力学
背景:
- サブドクションゾーンは,地球マントルに相当な土着の堆積物をリサイクルします.
- マントル羽根内の沈殿した堆積物の最終的な運命と同位体シグネチャーは,まだ十分に理解されていません.
- ホットスポットラバのリサイクルされた堆積物成分は希少であり,その識別はマントルの組成研究にとって不可欠である.
研究 の 目的:
- サモア・ラバのイソトープと微量元素の組成を調べるために.
- サモアのマントルの羽根の中で,潜在的にリサイクルされた堆積物成分を特定するために.
- EM2 (濃縮マントル2) マントルの端末の地化学的特性を再定義する.
主な方法:
- 西サモア州サヴァイイの海底溶岩の87Sr/86Srと143Nd/144Nd同位体比の分析. 西サモア州サヴァイイの海底溶岩の87Sr/86Srと143Nd/144Nd同位体比の分析.
- Ce/PbとNb/Uの比率を含む微量元素データの検討.
- 地化学的シグネチャを,上部大陸の地殻の既知の構成と比較した.
主要な成果:
- サモア・ラバは,非常に濃厚な87Sr/86Srと143Nd/144Nd同位体シグネチャーを表しており,これは海洋島の玄武岩で報告されている中で最も極端です.
- 微量元素のデータは,低いCe/PbとNb/U比率を含む上部大陸地殻との親和性を明らかにしています.
- これらの地化学的シグネチャーは,サモアのマントルにリサイクルされた上部大陸地殻の成分が存在することを強く示している.
結論:
- サモア・ラバからの地化学的データは,サモア・マントルの羽根の中でリサイクルされた上部大陸殻の有力な証拠を提供します.
- これらの発見は,EM2マントルの端末構成の理解を大幅に洗練します.
- この研究は,地球深層の沈殿した物質の運命を追跡する上で,同位体および微量元素分析の重要性を強調しています.
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