シリケート土の初期の (>4.53 Ga) グローバル分化に関する142番目の証拠です
1Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, USA. boyet@dtm.ciw.edu
まとめ
新しい隕石のデータは,地球のマントルが特定の元素で枯渇していることを明らかにし,早期の地球差異化を示唆しています. この発見は,惑星形成のモデルと地球,月,火星の初期の分化タイムラインに影響を与えます.
科学分野:
- 地質化学 地質化学
- 惑星科学は惑星科学である.
- 同位体地質学とは,同位体地質学である.
背景:
- コンドリート隕石は,初期の太陽系の組成に関する洞察を提供します.
- サマリウム-ネオジミウム (Sm-Nd) 同位体系は,マントルの進化の年代測定と追跡の重要なツールである.
- 地球の初期の分化に関する以前のモデルは依然として議論の余地がある.
研究 の 目的:
- コンドリート隕石からの高精度のSm-Nd同位体データを用いて,地球のマントルの初期の微分化を調査する.
- 隕石の同位体組成を地上の岩石と比較してマントルの特徴を推測する.
- 地球の構成構造と初期の惑星の微分化のモデルを精錬する.
主な方法:
- 高精度のサマリウム-ネオジミウム (Sm-Nd) の同位体データを取得する.
- コンドリート隕石の分析と,地上の岩組成との比較.
- 地球のマントルの組成と分化プロセスのモデリング.
主要な成果:
- コンドリート隕石は142Nd/144Ndの比率を示しており,ほとんどの地上の岩石よりも約100万分の20程度低い.
- この同位体差は,地球のマントルの70~95%が不適合な元素の枯渇した源に似ていることを示唆している.
- 地球の形成から3千万年以内 (4530億年前) に,地球規模の差異化イベントが起った可能性が高い.
結論:
- 地球のマントルはほとんど枯渇しており,マントルの底部に補完的な濃縮された貯水池が隔離されている可能性が高い.
- 初期の地球は,急速かつ広範な分化を経験し,現在の構成構造に影響を与えました.
- 地球,月,火星の初期の微分化のタイミングは,これらの発見に基づいて修正する必要があります.
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