桥石颗粒大小的变化解释了中层粘度的跳跃
Hongzhan Fei1,2, Maxim D Ballmer3, Ulrich Faul4
1Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany. feihongzhan@zju.edu.cn.
Nature
|July 5, 2023
概括
中层地幔的粘度跳跃对于地球的地幔动态至关重要,其原因在于地幔下层的更大,更粘的布里格曼岩. 这些古老的岩石因其高粘度而保存,影响地幔对流和地化学.
科学领域:
- 地质学
- 矿物物理
- 星球科学
背景情况:
- 一个显著的粘度增加,中层地幔粘度跳跃,存在于地球下层地幔800-1,200公里深处.
- 这种跳跃影响了板块沉降,羽毛升起和化学混合,但它的起源无法通过已知的矿物相变来解释.
- 现有的模型很难将地质观测与这种深度的相位过渡相结合.
研究的目的:
- 为了调查中层层粘度跳跃的起源.
- 确定下层地幔的矿物学差异是否可以解释观察到的粘度对比.
- 解释深层地幔物质的长期保存.
主要方法:
- 分析石和石之间的颗粒大小和粘度对比.
- 模拟这些对比对地幔动态的影响.
- 将发现与地化学异常和地震观测联系起来.
主要成果:
- 深层地幔中的布里格曼石丰富岩石的颗粒大小比上层火石岩石大十倍,粘度至少比上层火石岩石高十倍.
- 这种矿物质和质地差异足以解释中层粘度的跳跃.
- 布里格曼丰富岩石的早期快速谷物生长导致它们在地幔对流作用下得到保护.
结论:
- 中层地幔的粘度跳跃是由于深层地幔中存在古老,大粒度,高粘度的桥岩.
- 这些岩石的保存解释了各种地化学特征 (例如,同位素比例) 和地质现象 (例如,板块停滞,羽毛偏移).
- 这为下层地幔结构,动力学和化学进化提供了统一的解释.
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