隕石NWA 753333からの最も古い火星地殻の起源と年齢
M Humayun1, A Nemchin, B Zanda
1Department of Earth, Ocean and Atmospheric Science, and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA.
Nature
|November 22, 2013
まとめ
隕石ノースウェスト・アフリカ (NWA) 7533は,火星のレゴリット・ブレッチアとして識別され,初期の火星地殻形成と組成の洞察を提供している. この発見は,地球にとって重要な証拠を提供する.
科学分野:
- 惑星科学 惑星科学
- 地質化学 地質化学
- 宇宙化学 (コスモケミストリー)
背景:
- 火星の南部の高地,古代のクレーターで覆われた地形は,初期の惑星の分化を理解するための鍵です.
- 以前は火星のレゴリット・ブレキアが発見されていなかったため,初期の火星の材料の直接分析は限られていた.
研究 の 目的:
- 火星のレゴリットブレッチャを特定し,特徴づけるために.
- 隕石分析を用いて初期の火星地殻の分化と組成を調査する.
- 火星の地殻の厚さを推定するために.
主な方法:
- 隕石ノースウェスト・アフリカ (NWA) 7533 (NWA 7034とのペアリング) の分析.
- 岩石構造の岩石や衝撃で溶けた岩石を含むブレッチア成分の石油学および地化学分析.
- ジルコンの年代測定は,年齢と障害の発生を決定する.
- シデロフィールと相容れない元素の豊富さの測定.
主要な成果:
- NWA 7533は,ポリミクト・ブレチア,おそらく火星のレゴリット・ブレチアで,隕石のシドロフィールが豊富に存在する.
- 隕石内のジルコンは,4,428 ± 25百万年の年齢を出し,1,712 ± 85百万年の後の乱れを示しています.
- 地化学的なデータは,火星の歴史の最初の1億年以内に早期の地殻の分化を示唆しています.
- 火星の地殻の平均厚さは50kmと推定されている.
結論:
- NWA 7533は,火星のレゴリットブレッチアの最初の直接的な証拠を提供し,早期の地殻の分化を確認しました.
- 火星の地殻とその揮発性物質は,地球の歴史の非常に早い時期に,地球と月と同時期に形成されました.
- 隕石からの地化学データは,火星の地殻の厚さの地物理学的な推定を裏付けている.
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