The Mexican subduction system is an ideal region to study 3-D mantle deformation patterns in response to changes in slab geometry and the presence of tears. Shear-wave splitting measurements were made using and waves in southern Mexico, where the Cocos slab subducts beneath the North American and western Caribbean plates. For most of southern Mexico, the results are consistent with predominantly trench-normal fast polarization directions that can be interpreted as a consequence of sub-slab entrained flow and 2-D corner flow in the mantle wedge in the presence of A-type olivine fabric (or similar). This pattern of trench-perpendicular fast axes extends northward to the region southeast of the Trans-Mexican Volcanic Belt. Beneath its eastern end, fast axes rotate ∼20° clockwise and are likely controlled by the absolute motion of the North American plate. In southeastern Mexico, along the coast and above the mantle wedge tip, the fast axes are trench-normal and the delay times are the shortest. They were interpreted to result from a possibly serpentinized mantle wedge tip. In the same region above the mantle wedge core, the splitting parameters appear to result from different flow patterns in the mantle wedge and the sub-slab mantle.

中文翻译：

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墨西哥南部上地幔剪切波各向异性的远震测量


墨西哥俯冲系统是研究 3-D 地幔变形模式响应板片几何形状变化和撕裂存在的理想区域。剪切波分裂测量是利用墨西哥南部的波浪进行的，在那里科科斯板块俯冲到北美和西加勒比板块之下。对于墨西哥南部的大部分地区，结果与主要是海沟法线快速极化方向一致，这可以解释为在存在 A 型橄榄石组构的情况下地幔楔中的亚板夹带流和二维角流的结果（或类似）。这种垂直于海沟的快轴模式向北延伸至跨墨西哥火山带东南部地区。在其东端下方，快轴顺时针旋转约 20°，并且可能受到北美板块绝对运动的控制。在墨西哥东南部，沿海岸和地幔楔尖上方，快轴为海沟法向，延迟时间最短。它们被解释为可能是蛇纹石化的地幔楔尖的结果。在地幔楔核心上方的同一区域，分裂参数似乎是由地幔楔和亚板片地幔中不同的流动模式引起的。