トングステン-182の異質性 現代の海洋島の玄武岩
Andrea Mundl1, Mathieu Touboul2, Matthew G Jackson3
1Department of Geology, University of Maryland, College Park, MD 20742, USA. amundl@umd.edu.
まとめ
海の島岩 (OIB) についての新しい研究は,金属と高貴なガスを含む古代の地球領域を明らかにしています. これらの発見は,特定の深層マントルの構造,メガ-超低速度ゾーンが,ユニークなOIB同位体シグネチャの源であることを示唆しています.
科学分野:
- 地化学
- 同位体地質学
- 惑星科学
背景:
- 海洋島ベースルト (OIB) は,地球のマントルの構成と進化の洞察を提供します.
- 以前の研究では,OIBの同位体組成の変動が観察され,異質なマントルの源に示唆されました.
- 地球と太陽系の初期の歴史は 特定のマントルの領域に 独特の化学的痕跡を残しました
研究 の 目的:
- ハワイ,サモア,アイスランドからのOIBの異常なボルンガム (W) 同位体の比率の起源を調査する.
- トングステンの同位体データをOIBのヘリウム (He) 同位体比 (3He/4He) と相関させる.
- 化学的に独特な地幔の貯水池を 収容する地球深層構造を特定する
主な方法:
- 現代のOIBサンプルから得られた新しいボルンガム同位体 (182W/184W) の分析.
- 同じOIBサンプルにおける既存の3He/4HeデータとW同位体のデータを比較する.
- 潜在的マントル源地域の特徴を推論するための地化学モデリング.
主要な成果:
- ハワイ,サモア,アイスランドからのOIBのトングステン同位体比は,環境上のマントルより18ppmまで低い割合で,著しい変動を示している.
- 182W/184Wの比率と3He/4Heの比率の間に負の相関が観察された.
- これらの同位体変動は,太陽系の歴史の最初の6000万年以内に形成されたマントルの領域の関与を示唆しています.
結論:
- OIBシステムは,地球の初期の形成以来,孤立した古い地上の領域をサンプリングしています.
- これらの古代領域は金属の存在によって特徴づけられ,高貴なガスの貯蔵庫として機能します.
- ハワイ,サモア,アイスランドの下の超低速帯 (ULVZ) は,これらの古代貯水池の最も可能性の高い候補として提案されており,観測された同位体異常を説明しています.
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