火星,地球,そして月のスーパーコンドリティックSm/Nd比
Guillaume Caro1, Bernard Bourdon, Alex N Halliday
1Laboratoire Géochimie et Cosmochimie Institut de Physique du Globe de Paris-Université Denis Diderot, 4 place Jussieu, 75252 Paris Cedex 05, France. caro@crpg.cnrs-nancy.fr
Nature
|March 21, 2008
まとめ
ネオジム-142 (142Nd) の同位体分析により,火星は地球と同様に非コンドリート組成を有しており,初期の惑星の分化を示していることが明らかになった. 火星の隕石は,マントルの分化が太陽系から4000万年後に起こったことを示唆しています.
科学分野:
- 地質化学 地質化学
- 惑星科学は惑星科学である.
- イソトープ地球化学 イソトープ地球化学
背景:
- ネオジム-142 (142Nd) のイソトープの変動は,シリケート岩で,サマリウム-146 (146Sm) 崩壊による初期の惑星の分化を追跡しています.
- 年代的な解釈は,地球の大量のコンドリティックな組成を想定しており,これは真実ではないかもしれない.
- 陸上のサンプルのコンドリート値からの偏差は,初期のマントルの分離または非コンドリートの大量組成を示唆する.
研究 の 目的:
- 火星の隕石におけるネオジミウム142 (142Nd) の同位体組成を調べるために.
- 火星がコンドリート質または非コンドリート質の質量組成を持っているかどうかを判断する.
- 初期の火星のマントルの微分化のタイミングとメカニズムを制限するために.
主な方法:
- 16個の火星隕石の高精度142Nd同位体分析.
- 惑星アイソクロン技術を隕石データに適用する.
- 火星のイソトープデータをコンドリート基準値と地上の/月の組成と比較.
主要な成果:
- 火星は,その142Nd/144Nd比によって証明される,非コンドリート質の大量組成を示しています.
- シェルゴッタイト隕石は,太陽系形成から40年±1800万年後の火星マントルの分化イソクロンを定義しています.
- 火星のイソクロンはコンドリート基準点と一致せず,異なった同位体シグネチャーを示しています.
- 地球,月,火星は,小惑星帯の物質と比較して,Sm/Nd比で同様の濃縮を示しています.
結論:
- 太陽系内部の初期の惑星の微分化と蓄積過程は,化学的異質性をもたらした.
- 火星は歴史上比較的早い時期にマントルの分化を経験した.
- 火星と地球 (FOZO成分など) の間の観測された同位体相似性は,共有された蓄積環境またはその後の処理から生じる可能性があります.
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