Origin of azimuthal seismic anisotropy in oceanic plates and mantle
Origin of azimuthal seismic anisotropy in oceanic plates and mantle
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DOI：
10.1016/j.epsl.2014.06.014
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发表时间：
2014-09-01
影响因子：
5.3
通讯作者：
Lebedev, Sergei
中科院分区：
文献类型：
--
作者：
Becker, Thorsten W.;Conrad, Clinton P.;Lebedev, Sergei
地震各向异性在地幔中普遍存在，但在其热力学边界层中最强。海洋岩石圈和软流圈的方位各向异性可以通过表面波成像，并且应该特别直接地与已被充分理解的板块运动学和大规模地幔流动联系起来。然而，对于各向异性古扩张模型和地幔流动模型的适用深度和范围，以往的研究得出了不同的结论，并且不存在简单的、全球有效的关系。本文表明，从地幔流计算中推断出的晶格优先取向（LPO）为海洋岩石圈下软流圈各向异性提供了一个可信的全球背景模型。对于绝对板块运动（APM）模型，情况并非如此。在200千米厚的层中，流动模型LPO与层析成像观测结果相匹配，位于类似于1200摄氏度的半空间冷却模型等温线下方，这表明控制方位各向异性发展的过程对温度有很强的依赖性。我们推断，剪切的深度范围，从而一个相对强大的海洋岩石圈的厚度，可以用这种方法来绘制。背景模式的这些发现，以及海洋-盆地与半空间冷却模式的特定偏差，在最近考虑的三个独立层析模式中都发现了。进一步探索与背景模式的偏差可能对海洋板块形成和动力学的一般研究以及区域尺度的构造分析有用。(C) 2014 Elsevier B.V.版权所有
Seismic anisotropy is ubiquitous in the Earth's mantle but strongest in its thermo-mechanical boundary layers. Azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well-understood plate kinematics and large-scale mantle flow. However, previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo-spreading and mantle flow models of anisotropy, and no simple, globally valid, relationships exist. Here, we show that lattice preferred orientation (LPO) inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere. The same is not true for absolute plate motion (APM) models. A similar to 200 km thick layer where the flow model LPO matches observations from tomography lies just below the similar to 1200 degrees C isotherm of a half-space cooling model, indicating strong temperature-dependence of the processes that control the development of azimuthal anisotropy. We infer that the depth extent of shear, and hence the thickness of a relatively strong oceanic lithosphere, can be mapped this way. These findings for the background model, and ocean-basin specific deviations from the half-space cooling pattern, are found in all of the three recent and independent tomographic models considered. Further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional-scale tectonic analyses. (C) 2014 Elsevier B.V. All rights reserved.