火星のマグマの海洋の結晶化と地殻形成の証拠
Laura C Bouvier1, Maria M Costa1, James N Connelly1
1Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark.
Nature
|June 29, 2018
まとめ
最古の火星のジルコンは 4,476万年前のもので 火星は初期に原始の地殻を形成していたことを明らかにしています この初期の地殻形成は 惑星の急速な分化と太陽系形成直後のマグマの海洋結晶化を示しています
科学分野:
- 惑星科学
- 地化学
- 宇宙化学
背景:
- 地球上の惑星の原始的な地殻形成のタイミングは,惑星の進化を理解するために重要です.
- ジルコンのU-Pb年代測定とHf同位体分析は 初期の地殻の歴史を研究するのに理想的です
- 初期の火星の地殻形成は 隕石のジルコンを元に 約4,4億3000万年前に起きたと推測されています
研究 の 目的:
- NWA 7034 火星のレゴリトブレッチから 古代のジルコンを正確に年代測定する
- これらの古代ジルコンのHf同位体の組成と源貯蔵庫を決定する.
- 火星の原始地殻の形成と 初期の惑星の分化を制限するためです
主な方法:
- 高精度ウラン-鉛 (U-Pb) によるジルコンの同位体年代測定
- ルテシウム-ハフニウム (176Lu-176Hf) の同位体分析により,源貯蔵庫の特性を決定する.
- NWA 7034 火星レゴリトブレチアのジルコンの分析.
主要な成果:
- 7つのジルコンは,4,476.3 ± 0.9 と 4,429.7 ± 1.0 百万年前のU-Pbの年齢を示し,火星からの最も古い日付の材料を表しています.
- 分析されたすべてのジルコンは,放射性でない初期のHf同位体組成を示し,4,547万年前に形成された濃縮した地殻から派生したことを示している.
- データは原始的な地殻が 4,547万年前に存在し,1億年ほど後に再現されたことを示唆している.
結論:
- 火星は4,547万年前には 原始的な地殻を持ち アンドエシトのような資源から形成されました
- この地殻の急速な形成は,火星の蓄積,核の形成,そしてマグマの海洋結晶化は,太陽系の形成から200万年以内に完了したと示唆しています.
- これらの発見は,火星の初期に極めて急速な惑星の分化とマントルの転覆のモデルを裏付けている.
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