大氧化事件的高潮时空中氧化动员
Ann M Bauer1, Weiqiang Li1,2,3, Kyle S Rybacki4,5
1Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706.
概括
地球的早期
科学领域:
- 地质化学
- 同位素地质时间学
- 地球的早期历史
背景情况:
- 氧化回收敏感元素是理解地球表面氧化回收状态演变的关键.
- 古新生代的大氧化事件标志着大气氧气的显著增加.
- 前坎布里亚岩石的多阶段地质热历史使地化学解释变得复杂.
研究的目的:
- 为了限制约2.06亿年前库埃茨雅尔维火山形成的 (U) 氧化年龄和程度.
- 使用U-Th-Pb同位素研究表面氧化与地球深层过程之间的联系.
- 区分早期的U氧化与后来的变态U和Pb变化.
主要方法:
- 在Kuetsjärvi火山形成中应用的U-Th-Pb同位素地质年代学.
- 分析Pb同位素以对比U和 (Th) 的相对流动性.
- 使用多个地质时间系统 (207Pb-206Pb,238U-206Pb,235U-207Pb,232Th-208Pb).
主要成果:
- 完全或几乎完全的氧化和U的去除发生在约2.06亿年前的喷发后不久.
- 这种U损失表明大气中的氧含量很高,导致氧化气候和全球U脉冲到海洋.
- 在大约2 Ga的地幔储库中观察到的变化,包括232Th/238U的减少和HIMU源的开始,与此U脉冲有关.
结论:
- 大约在2.06亿年前的氧化损失可以从地质年代学上区分出后来的U和Pb变化事件.
- 这项研究强调了多阶段地质历史的岩石中氧化还原敏感元素的复杂行为.
- 单独的元素丰度不足以反映这些复杂的岩石记录中的氧化还原条件.
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