在地球下层地幔中,通过固态对流来形成异型结构的发展
Allen K McNamara1, Peter E van Keken, Shun-Ichiro Karato
1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1063, USA. mcnamar@umich.edu
Nature
|March 22, 2002
概括
沉积的构造板与核心-地幔边界碰撞,导致地球下层地幔的强烈地震异性. 这种变形使矿物质对齐,形成可观测的异型斑块,特别是在环太平洋地区.
科学领域:
- 地质物理学 地质物理学
- 矿物物理 矿物物理
- 地震学 地震学
背景情况:
- 地震观测显示,在地球下层地幔的底部存在高度异质的斑块,与大致同质的大质量地幔形成鲜明对比.
- 假设这些异性otropic区域起源于过去的沉积或地幔羽毛上升,但异性otropy的原因仍然不清楚.
- 提出的机制包括异质材料的形状偏好方向 (SPO) 或同质材料的格子偏好方向 (LPO),这意味着不同的地力学过程.
研究的目的:
- 为了研究下层地幔中不同异构性机制的地球动力学影响.
- 为了确定浮沉板块的大张力变形是否可以解释观测到的地震异构性.
- 模拟矿物质结构的发展及其对地震异性质的贡献.
主要方法:
- 数字建模结合矿物质物理弹性.
- 通过固态变形来建模晶格偏好方向 (LPO) 的发展.
- 模拟了沉浮板块与核心-地幔边界的碰撞.
主要成果:
- 这项研究表明,深层下层地幔的板块变形可以产生强烈的地震异质性.
- 基于化学均的地幔材料开发的模型显示,在高应力下由大应力变形产生的异构性.
- 这种机制有效地解释了环太平洋地区观察到的异构性.
结论:
- 化学同质的地幔材料的固态变形,特别是与核心-地幔边界相碰撞的沉积板块,是下层地幔地震异性质的可行原因.
- 由于在高应力下的大张力变形而导致的格子偏向 (LPO) 是这些区域产生强异质性的主要机制.
- 这些发现使地震学观测与地球地幔底部发生的地力学过程相协调.
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