Upper mantle seismic anisotropy as a constraint for mantle flow and continental dynamics of the North American plate
Upper mantle seismic anisotropy as a constraint for mantle flow and continental dynamics of the North American plate
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上地幔地震各向异性作为北美板块地幔流和大陆动力学的约束
DOI：
10.1016/j.epsl.2019.03.019
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发表时间：
2018
影响因子：
5.3
通讯作者：
T. Becker
中科院分区：
文献类型：
--
作者：
Wanying Wang;T. Becker
固有各向异性橄榄石晶体在对流作用下的排列通常被认为是由剪切波分裂（SWS）推断出的大部分地震各向异性的原因。这提供了一种限制大陆动力学和深部地幔之间相互作用的方法，特别是对于仪器密集的地区，如USArray之后的北美。在那里，SWS的“快速定向”与绝对板块运动（APM）的比较表明各向异性主要由板块运动控制。然而，大的区域不匹配和APM模型有限的真实性促使我们进一步探索基于SWS的各向异性。如果根据地幔环流中的橄榄石排列来估计SWS，那么板块驱动的流动本身就会产生与SWS有很大不匹配的各向异性。大规模地幔密度异常和横向粘度变化的加入显著改善了模型。尽管强大的大陆克拉通是必不可少的，但改变它的几何形状并不能改善板块尺度的不匹配。此外，基于高分辨率层析成像的模型降低了拟合，表明流动模型假设存在问题和/或缺少对各向异性的贡献。因此，我们计算“岩石圈补”，以获得软流圈和冻结岩石圈各向异性的最佳拟合联合表示。补体与独立成像的地壳和上地幔各向异性具有相干结构和区域相关性。因此，密集的SWS测量提供了与构造相关的深度各向异性信息，但关于大陆各向异性及其起源仍有许多有待了解。
The alignment of intrinsically anisotropic olivine crystals under convection is typically invoked as the cause of the bulk of seismic anisotropy inferred from shear-wave splitting (SWS). This provides a means of constraining the interplay between continental dynamics and the deep mantle, in particular for densely instrumented regions such as North America after USArray. There, a comparison of “fast orientations” from SWS with absolute plate motions (APM) suggests that anisotropy is mainly controlled by plate motions. However, large regional misfits and the limited realism of the APM model motivate us to further explore SWS based anisotropy. If SWS is estimated from olivine alignment in mantle circulation instead, plate-driven flow alone produces anisotropy that has large misfits with SWS. The addition of large-scale mantle density anomalies and lateral viscosity variations significantly improves models. Although a strong continental craton is essential, varying its geometry does, however, not improve the plate-scale misfit. Moreover, models based on higher resolution tomography degrade the fit, indicating issues with the flow model assumptions and/or a missing contributions to anisotropy. We thus compute a “lithospheric complement” to achieve a best-fit, joint representation of asthenospheric and frozen-in lithospheric anisotropy. The complement shows coherent structure and regional correlation with independently imaged crustal and upper mantle anisotropy. Dense SWS measurements therefore provide information on depth-dependent anisotropy with implications for tectonics, but much remains to be understood about continental anisotropy and its origin.
影响因子：
5.8
作者：
M. Bodmer;D. Toomey;E. Hooft;John Náb;lek;J. Braunmiller
通讯作者：
M. Bodmer;D. Toomey;E. Hooft;John Náb;lek;J. Braunmiller
影响因子：
5.3
作者：
Quan Zhou;Jiashun Hu;Lijun Liu;T. Chaparro;D. Stegman;M. Faccenda
通讯作者：
Quan Zhou;Jiashun Hu;Lijun Liu;T. Chaparro;D. Stegman;M. Faccenda