難解なハデア紀の濃縮貯水池は,イサウア紀の岩石の142Nd赤字によって明らかになりました
Hanika Rizo1, Maud Boyet, Janne Blichert-Toft
1Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, CNRS UMR 6524, IRD R 163, BP 10448, 63000 Clermont-Ferrand, France. h.rizo@opgc.univ-bpclermont.fr
Nature
|November 7, 2012
まとめ
初期の地球のマントルの差異化は,グリーンランドの南西部の34億年前の岩石のネオジミウム-142 (142Nd) の欠乏によって証明されています. この発見は,これまで検出されていなかった,ハデオン時代に形成された補完的な濃縮成分を明らかにしています.
科学分野:
- 地質化学 地質化学
- 初期の地球における微分化.
- 同位体クロノメトリー (Isotopic Chronometry) とは
背景:
- 絶滅したサマリウム-146 (146Sm) ・ネオジミウム-142 (142Nd) システムは,初期のシリケート地球分化のための証拠を提供します.
- 37億年前のイシュア岩のネオジミウム142 (142Nd) の過剰発見は,ハデア紀のエオンが枯渇したマントルの由来を示唆している.
- 質量バランスは,早期の差別化は,補完的な豊かな構成要素も生み出さなければならないと規定しており,これは難解なままです.
研究 の 目的:
- イサ岩の岩石で見つかった枯渇した貯水池を補完する,ハデアン期に富んだマントルの構成要素のサインを特定するために.
- 地球のマントルの初期の形成された異質性の存在と性質を調査する.
主な方法:
- グリーンランド南西部の34億年前のマフィック堤防のネオジミウム同位体比 ((142Nd/144Nd)) の分析.
- 測定された142Nd値を地上標準と比較して,欠陥を検出する.
主要な成果:
- 7つのマフィックの堤防のうち7つの堤防は,陸上の基準に比べて142Ndの赤字を示した.
- 3つのサンプルは,解決可能な重大な赤字を示し, -10.6百万分の1に低下しました.
- これらの赤字は,ハデアン系に富んだマントルの構成要素の存在を示している.
結論:
- 特定された142Nd赤字は,ハデアンの濃縮成分の存在を確認しています.
- この濃縮された成分は,微分されたマグマの海洋貯蔵庫,またはマフィックの原地殻を表す可能性があります.
- この結果は,南西グリーンランドのマントルは,少なくとも34億年前まで,初期に形成された異質性を保持していたことを示唆している.
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