Imaging the Eastern Trans-Mexican Volcanic Belt With Ambient Seismic Noise: Evidence for a Slab Tear
Imaging the Eastern Trans-Mexican Volcanic Belt With Ambient Seismic Noise: Evidence for a Slab Tear
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DOI：
10.1029/2018jb015783
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发表时间：
2018-09-01
影响因子：
3.9
通讯作者：
Perez-Campos, Xyoli
中科院分区：
文献类型：
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作者：
Castellanos, Jorge C.;Clayton, Robert W.;Perez-Campos, Xyoli
跨墨西哥火山带 (TMVB) 的东段是一个神秘的狭窄区域，位于墨西哥中部科科斯板块倾角急剧转变处的正上方。目前的板块模型表明，从平坦俯冲到陡峭俯冲的过渡是连续穿过该区域的，但 TMVB 的突然结束表明俯冲类型的差异更有可能被板片撕裂所适应。基于该区域的高分辨率剪切波速度和径向各向异性模型，我们认为南科科斯内的板块撕裂可以解释 TMVB 的突然结束。我们还量化了每个地震台下方的方位各向异性，并提出了明确的流动模式，显示地幔物质如何通过俯冲科科斯板块的撕裂从板块下方转移到地幔楔。我们认为板片边缘周围形成的环形地幔流是墨西哥中部火山间隙存在的原因。此外，我们提出，由热的、密度较小的地幔物质通过撕裂流流入韦拉克鲁斯地区而引起的温度升高可能对俯冲板片的热机械状态产生重大影响，并解释了为什么中深度地震活动在韦拉克鲁斯盆地的南部边界突然结束。墨西哥西部和南部的地幔物质通过板块撕裂运动形成的复合地幔流可能使科科斯板块分段回滚。跨墨西哥火山带（TMVB）是墨西哥俯冲系统的一个突出而神秘的特征。里维拉和科科斯板块俯冲参数沿走向的巨大变化解释了其火山样式的多样性和与海沟的倾斜方向。然而，TMVB 在其东端与奥里萨巴火山的突然终止令人费解，因为当前的板块模型表明，科科斯板块几何形状到正常俯冲的过渡在该区域是平滑的。有证据表明，板块中可能正在形成撕裂，但尚不清楚这一特征如何支持连接火山高峰与火山前缘以南韦拉克鲁斯盆地的异常大的地形梯度。为了进一步了解这部分俯冲板片的转变解剖结构及其与表面地形的关系，我们提出了墨西哥中部地壳和上地幔速度结构的详细且统一的模型。
The eastern sector of the Trans-Mexican Volcanic Belt (TMVB) is an enigmatic narrow zone that lies just above where the Cocos plate displays a sharp transition in dipping angle in central Mexico. Current plate models indicate that the transition from flat to steeper subduction is continuous through this region, but the abrupt end of the TMVB suggests that the difference in subduction styles is more likely to be accommodated by a slab tear. Based on a high-resolution shear wave velocity and radial anisotropy model of the region, we argue that a slab tear within South Cocos can explain the abrupt end of the TMVB. We also quantify the azimuthal anisotropy beneath each seismic station and present a well-defined flow pattern that shows how mantle material is being displaced from beneath the slab to the mantle wedge through the tear in the subducted Cocos plate. We suggest that the toroidal mantle flow formed around the slab edges is responsible for the existence of the volcanic gap in central Mexico. Moreover, we propose that the temperature increase caused by the influx of hot, less dense mantle material flowing through the tear to the Veracruz area may have significant implications for the thermomechanical state of the subducted slab and explain why the intermediate-depth seismicity ends suddenly at the southern boundary of the Veracruz basin. The composite mantle flow formed by the movement of mantle material through the slab tears in western and southern Mexico may be allowing the Cocos plate to roll back in segments.The Trans-Mexican Volcanic Belt (TMVB) is a prominent and enigmatic feature of the subduction system in Mexico. Its volcanic style diversity and oblique orientation to the trench are explained by the large along-strike variations in the subduction parameters of the Rivera and Cocos plates. However, the abrupt termination of the TMVB on its eastern end with the Pico de Orizaba volcano is puzzling as the current slab model suggests that the transition of the Cocos flat-slab geometry to normal subduction is smooth through this region. There is evidence that suggests that a tear in the slab might be developing, but it is unclear how this feature can support the unusually large topographic gradient that connects the volcanic high peaks with the Veracruz basin just south of the volcanic front. To provide further insight into the transition anatomy of this portion of the subducted slab and its relation with surface topography, we present a detailed and unified model of the velocity structure of the crust and uppermost mantle of central Mexico.