统计地质化学揭示了大约2.5 Gyr前世俗石质层进化中出现的破坏
C Brenhin Keller1, Blair Schoene
1Department of Geosciences, Princeton University, Guyot Hall, Washington Road, Princeton, New Jersey 08544, USA. cbkeller@princeton.edu
Nature
|May 25, 2012
概括
地球 地球 地球 地球 地球 地球
科学领域:
- 地质化学 地质化学
- 地力学是什么?地力学是什么?
- 地球历史 地球历史 地球历史
背景情况:
- 由于热量损失和放射性热量产量下降,地球已经冷却了45亿多年.
- 磁性地化学记录了不断变化的热流和古老地力学,但由于数据偏差而复杂化.
- 7万个样本的统计采样提供了一个全面的地化学进化记录.
研究的目的:
- 为了重建整个地球历史的世俗地化学演变.
- 研究地幔冷却对地球化学趋势的影响.
- 为了识别和解释大约25亿年前的地球化学不连续性.
主要方法:
- 统计采样技术应用于一个大型的地质化学数据库 (约. 7万个样本). 这些样本
- 在玄武岩中分析相容和不相容的元素,以追踪地幔融化分数.
- 对岩中的Na/K,Eu/Eu*和La/Yb比率进行研究,以确定地融化的指标.
主要成果:
- 玄武岩显示地幔融化分数逐渐减少,与世俗地幔冷却一致.
- 大约25亿年前的显著地化学不连续性表明地幔融化和深层地过程减少.
- 地厚度的增加和岩地质化学的变化与这种不连续性相吻合.
结论:
- 考古地幔融化很可能产生了厚厚的马菲亚底层,导致分层和色素-特朗德海米特-格拉诺迪奥里特岩.
- 地化学不连续性标志着地球地演变中的过渡.
- 地球深层地质化学的变化与大气中氧气的增加有关,这发生在阿基亚纪末期.
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