隕石のリン酸塩は,4億5,5億7千万年前の4億5,5億7千万年前から,176Luの衰退率を常に示しています
1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada. yamelin@nrcan.gc.ca
まとめ
精密なルテチウム-176 (176Lu) 崩壊定数値は,隕石のリン酸鉱物を用いて決定した. これは不一致を解決し,地球進化の研究のためのジオクロノロジーを洗練します.
科学分野:
- 地質化学 地質化学
- 宇宙化学 (コスモケミストリー)
- ラジオメトリック・デッティング
背景:
- 精確なジオクロノロジーは,地球の進化を理解するために不可欠です.
- ルテシウム-176 (176Lu) からハフニウム-176 (176Hf) までの放射性崩壊システムは,このために不可欠です.
- 以前の176Lu崩壊定数の決定は,地上のデータと隕石のデータとの不一致を示した.
研究 の 目的:
- 176Luの衰退定数を正確に決定するには,
- 陸上の鉱物と隕石から得られた矛盾する値を調和させるため.
- Lu-Hfジオクロノロジーの精度を向上させるため.
主な方法:
- フォスファート鉱物からの高放射性Lu-Hfデータの分析.
- リチャードトン (普通のコンドライト) とアカプルコ (原始的なアコンドライト) の隕石からのリン酸鉱物を利用する.
- 精度がよく計測されたウラン-鉛 (U-Pb) 同位体系と比較.
主要な成果:
- 隕石から得られた新しい崩壊常数値は1.864 x 10^-11 +/- 0.016 x 10^-11年^-1 (リチャードトン) と1.832 x 10^-11 +/- 0.029 x 10^-11年^-1 (アカプルコ) である.
- これらの値は,地上の鉱物から以前に決定された値と統計的に同一です.
- 隕石データと地上の鉱物データとの間の内部一貫性が達成されました.
結論:
- 176Luの崩壊定数は,地球外 (隕石) と地球上のサンプルの間で一致しています.
- これにより,以前の不一致が解消され,両者に対してLu-Hf年代測定法の使用が正当化されました.
- ジオクロノロジーの精度向上により,地球と惑星の進化のモデルが改善されます.
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