Shear Wave Splitting Beneath Eastern North American Continent: Evidence for a Multilayered and Laterally Variable Anisotropic Structure
Shear Wave Splitting Beneath Eastern North American Continent: Evidence for a Multilayered and Laterally Variable Anisotropic Structure
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北美大陆东部下方的剪切波分裂：多层横向可变各向异性结构的证据
DOI：
10.1029/2018gc007646
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发表时间：
2018
期刊：
影响因子：
3.7
通讯作者：
V. Levin
中科院分区：
文献类型：
--
作者：
Xiaoran Chen;Yiran Li;V. Levin
北美东部记录了一个超过3 Ga的构造历史。这些记录的大部分都保存在岩石圈内，可以通过对其内部结构的详细研究来解开。过去的构造活动可能以各向异性形成岩石组构的形式留下了印记，这些岩石组构目前保存在大陆的岩石圈中。我们使用从魁北克的詹姆斯湾延伸到缅因州的芬迪盆地的约1，300 km长的阵列收集的岩心折射波的观测值进行横波分裂测量，仪器之间的横向间距为10-100 km。近距离的仪器有助于我们将各向异性特性与地质边界联系起来。结果表明，快极化主要集中在N60°E ~ N90°E之间，平均值为N80°E，并随后方位角发生系统性变化。此外，我们观察到延迟时间从阵列西北端的0.56 ±0.25 s横向增加到东南端的0.90 ± 0.41 s。延迟时间的横向变化的位置不匹配的地质边界上的表面，但似乎匹配的地球物理边界在160公里的深度。我们解释这个边界在分裂值的边缘，岩石圈的深层。我们的观察表明，我们的研究区域之下的各向异性结构是复杂的，可能是多层和横向变化。
Eastern North America records a tectonic history of over 3 Ga in duration. Much of this record is preserved within the lithosphere and may be unraveled by detailed studies of its interior structure. Past episodes of tectonic activity likely left their imprints in the form of anisotropy‐forming rock fabric presently preserved in the lithosphere of the continent. We perform shear wave splitting measurements using observations of core‐refracted waves collected from a ~1,300‐km‐long array extending from James Bay in Quebec to the Fundy basin in Maine, with lateral spacing of 10–100 km between instruments. Close spacing of instruments helps us associate anisotropic properties with geological boundaries. We find that the fast polarizations concentrate between N60°E and N90°E with an average of N80°E and change systematically with backazimuth. In addition, we observe a lateral increase in delay time from 0.56 ±0.25 s at the NW end of the array to 0.90 ± 0.41 s at the SE end. The location of lateral change in delay time does not match geological boundaries on the surface but seems to match the geophysical boundary at depth of 160 km. We interpret this boundary in splitting values to be the edge of cratonic lithosphere at depth. Our observations suggest that the anisotropic structure beneath our study area is complex and possibly both multilayered and laterally variable.