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Seismic Anisotropy and Mantle Flow Driven by the Cocos Slab Under Southern Mexico

机译：墨西哥南部Cocos平板驱动的地震各向异性和地幔流动

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Shear wave splitting measurements were made using SKS and SKKS waves recorded by the Meso-American Subduction Experiment, which was deployed in southern Mexico starting at the coast of the Pacific Ocean and running north toward the Gulf of Mexico. In this segment of the Middle America Trench the oceanic Cocos plate subducts under the continental North American plate. The active volcanic arc is located at the southern end of the Trans-Mexican Volcanic Belt. Unlike most subduction zones, however, the volcanic arc is not subparallel to the trench. In the fore-arc, between the trench and the Trans-Mexican Volcanic Belt, the Cocos slab subducts subhorizontally. Beneath the volcanic belt, however, the slab dives steeply into the mantle. A marked difference in the orientation of the fast polarization directions is observed between the fore-arc and the back-arc. In the fore-arc the fast axes determined using SKS phases are oriented NE-SW, in the same direction as the relative motion between the Cocos and North American plates, and are approximately perpendicular to the trench. Physical conditions in the subslab mantle are consistent with the existence of A-type olivine and consequently entrained mantle flow is inferred. Strong coupling between the slab and the surrounding mantle is observed. In the back-arc SKS fast polarization directions are oriented N-S and are perpendicular to the strike of the slab. Given the high temperatures in the mantle wedge tip, the development of A-type, or similar, olivine fabric throughout the mantle wedge is expected. The orientation of the fast axes is consistent with corner flow in the mantle wedge.
机译：剪切波分裂测量是使用中美俯冲实验记录的SKS和SKKS波进行的，该实验部署在墨西哥南部，从太平洋海岸开始，向北延伸到墨西哥湾。在中美洲海沟的这一部分中，洋可可板块俯冲在北美大陆板块之下。活火山弧位于跨墨西哥火山带的南端。但是，与大多数俯冲带不同，火山弧并不平行于海沟。在前弧中，海沟和跨墨西哥火山带之间，科科斯板块在水平方向俯冲。然而，在火山带之下，板块陡峭地潜入地幔中。在前弧和后弧之间观察到快速极化方向的取向存在明显差异。在前弧中，使用SKS相确定的快速轴的方向为NE-SW，其方向与Cocos和北美板块之间的相对运动相同，并且大致垂直于沟槽。平板下地幔的物理条件与A型橄榄石的存在相一致，因此推断出夹带的地幔流动。观察到板与周围地幔之间的强耦合。在后弧SKS中，快速极化方向为N-S，垂直于平板的走向。考虑到地幔楔尖端的高温，预计整个地幔楔会出现A型或类似的橄榄石织物。快速轴的方向与地幔楔中的角流一致。

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