Nb/Ta体系から惑星の核と地球・月系の進化
Carsten Münker1, Jörg A Pfänder, Stefan Weyer
1Institut für Mineralogie, Corrensstrasse 24, Universität Münster, 48149 Münster, Germany. muenker@nwz.uni-muenster.de
まとめ
ナイオビウム (Nb) は高圧下では適度なシデロフィールであることが明らかになり,以前の仮定に異議を唱えました. この発見は,惑星の分化と月の形成の歴史について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
- 惑星科学は惑星科学である.
- 宇宙化学 (コスモケミストリー)
背景:
- ニオビウム (Nb) とタンタール (Ta) は,伝統的にリトファイルの元素と考えられ,それは彼らがシリケート相と好意的に関連することを意味します.
- 以前の仮定では,惑星の微分化過程で,NbとTaの有意な分化がないことが示唆されていた.
- Nb/Taのコンドリート比は,惑星の組成を理解するための重要な基準点です.
研究 の 目的:
- 高圧差分化過程におけるNbとTaの振る舞いを調査する.
- 高精度の同位体測定に基づいて,Nbのシデロフィルの性質を再評価する.
- 月と地球の組成と形成を制限するために.
主な方法:
- ニオビウム/タンタール (Nb/Ta) の比率の高精度測定.
- 比較プロキシとして,ジルコニウム/ハフニウム (Zr/Hf) の比率の高精度測定.
- 大量シリケート地球,月,火星,小惑星におけるNb/Ta値の分析.
主要な成果:
- 高精度測定により,ニオビウム (Nb) は高圧下では,以前の考えに反して,適度なシデロフィール (鉄好き) であることを明らかにしました.
- 大量のシリケートである地球 (14.0 ± 0.3) と月 (17.0 ± 0.8) のNb/Ta比は,コンドリート比 (19.9 ± 0.6) よりも著しく低い.
- 火星と小惑星は,Nb / Ta比率がコンドリート値に近いことを示しており,異なる微分の歴史を示唆しています.
結論:
- 観測されたNb/Ta比は,Nbが高圧下での惑星の微分化中に金属の核に分割されることを示している.
- 月面のNb/Ta比は,月を形成したインパクター物質の質量分数を65%未満に制限しています.
- 月形成の衝突イベントは,約4533億年前に起こった地球の最終的なコア-マントルの均衡と一時的に関連しています.
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