Seismic Anisotropy and Mantle Flow Driven by the Cocos Slab Under Southern Mexico
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- 作者：Leslie A. Bernal-López ; Berenice R. Garibaldi…
- 关键词：Shear wave splitting ; upper mantle anisotropy ; mantle flow ; Mexico ; Middle America Trench ; flat slab subduction
- 刊名：Pure and Applied Geophysics
- 出版年：2016
- 出版时间：October 2016
- 年：2016
- 卷：173
- 期：10-11
- 页码：3373-3393
- 全文大小：1,385 KB
- 刊物类别：Earth and Environmental Science
- 刊物主题：Earth sciences
Geophysics and Geodesy - 出版者：Birkh盲user Basel
- ISSN：1420-9136
- 卷排序：173
文摘
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.