まとめ
モリブデナイトのレニウム・オスミウム年代測定は,ララミド・オロゲニーにおける基礎金属・ポルフィール鉱化の2つの異なる間隔を明らかにする. これらの広範囲にわたる同期的な出来事は,局所的なプロセスではなく,地域的な地殻-マントルの相互作用を示唆しています.
科学分野:
- 経済地質学 経済地質学
- 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:
- 北米南西部 (90~50万年前) のララミド・オロゲーニスは,40以上の基礎金属・ポルフィール鉱床と関連している.
- モリブデナイトは,レニウムに富んだ硫化物であり,これらの鉱石埋蔵地における一般的な鉱物です.
研究 の 目的:
- ララミド・ポルファイア銅鉱床に関連する鉱化事件の正確な年代を決定する.
- 鉱物化の時間的・空間的分布を調査する.
- 鉱石の形成を駆動する基礎的な地質学的プロセスを理解する.
主な方法:
- レーニウム・オスミウム (Re-Os) 同位体ジオクロノロジーは,様々な堆積物からのモリブデナイトサンプルに適用されました.
- 地質的地図作成と地下層の年齢分析は,鉱物化のタイミングを文脈化するために使用されました.
主要な成果:
- 個々の堆積物の鉱化は,マグマの持続時間や強度に関係なく,マグマの活動に遅れて一貫して発生しました.
- レーニウム・オスミウム年代測定は,74~70万年前と60~55万年前という2つの主要な鉱化間隔を特定した.
- 古い堆積物は主にアリゾナ州北西部のプレカンブリア時代地下層にあり,若い堆積物はアリゾナ州南部とメキシコ北部のプレカンブリア時代地下層にある.
結論:
- 異なる地質的環境における同期的で広範な鉱化は,地域規模の地殻-マントルの相互作用を示唆している.
- この発見は,これらの鉱石堆積物が局所的なマグマ的プロセスによって形成されたという考えに異議を唱える.
- 2つの異なる年齢クラスターは,ララミドオロゲニーにおけるパルスメタルジェニックイベントを示唆しています.
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