地殻の浅い断層の年代測定は,地殻の浅い断層の年代測定である
B A van der Pluijm1, C M Hall, P J Vrolijk
1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA. vdpluijm@umich.edu
Nature
|July 13, 2001
まとめ
浅い断層の放射線年代測定は,鉱物の年齢が混合されているため,困難です. この研究は,X線モデリングを用いた新しい方法を導入し,地表近くの断層活動の時期を確実に決定し,北米西部の重要なストレス体制の変化を明らかにします.
科学分野:
- 地質学 地質学 地質学
- ジオクロノロジー (Geochronology) について
- テクトニクス (地質学) とは
背景:
- 浅い地殻の断層の放射線年代測定は,鉱物の再結晶を防ぐ低温のために困難です.
- 浅い断層地帯は,デトリタルとオウチジェニックのフィロシリケートの混合群を保ち,年齢の決定を複雑にします.
- 放射線照射中のアルゴン-39 (39Ar) 損失は,粘土鉱物の年代測定時に誤って古い年齢につながる可能性があります.
研究 の 目的:
- 地表近くの断層活動の年代測定のための信頼できる方法を開発し,提示する.
- X線モデリングとサンプルエンカプスレーションを使用して,断層掘削の粘土集団を特徴付ける.
- カナダのロッキー山脈のルイス突起断層の年齢を判定し,構造の歴史を推論する.
主な方法:
- X線モデリングを用いて,断層掘削における粘土鉱物集団を特徴づける.
- デッティングの精度を向上させるためにサンプルエンカプスレーション技術を使用する.
- ルイス推力断層からの断層掘削サンプルに放射線年代測定を適用する.
主要な成果:
- カナダ南部のロッキー山脈にあるルイス推力断層は,約5200万年前のものである.
- この年齢は,北米西部のストレス状態が,エオセーン時代に収縮から拡張へと急激に変化したことを示している.
- 岩の持ち上げ/発掘年齢と堆積源は,およそ1.72億年前のものと推定された.
結論:
- 提出された方法は,近地断層活動の時期を確実に決定します.
- ルイス推力断層のエオセンの時代は,北米西部の地形構造の進化に関する重要な洞察を提供します.
- この研究は,脆い断層地帯における正確な地質年代測定の研究のための鉱物集団の特徴づけの重要性を強調しています.
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