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首页> 外文期刊>Pure and Applied Geophysics >Toroidal, Counter-Toroidal, and Upwelling Flow in the Mantle Wedge of the Rivera and Cocos Plates: Implications for IOB Geochemistry in the Trans-Mexican Volcanic Belt
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Toroidal, Counter-Toroidal, and Upwelling Flow in the Mantle Wedge of the Rivera and Cocos Plates: Implications for IOB Geochemistry in the Trans-Mexican Volcanic Belt

机译：里维拉和科科斯板块地幔楔中的环向，反环向和上升流：跨墨西哥火山带的IOB地球化学意义

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We carried out analog laboratory modeling at a scale 1:4,000,000 and computer rendering of the flow patterns in a simulated western Middle American subduction zone. The scaled model consists of a transparent tank filled with corn syrup and housing two conveyor belts made of polyethylene strips. One of the strips dips 60A degrees and moves at a velocity of 30 mm/min simulating the Rivera plate. The other one dips 45A degrees, moves at 90 mm/min simulating the subduction of the Cocos plate. Our scaled subduction zone also includes a gap between the simulated slabs analogous to a tear recently observed in shear wave tomography studies. An acrylic plate 3 mm thick floats on the syrup in grazing contact with the polyethylene strips and simulates the overriding North America plate. Our experiments reveal a deep toroidal flow of asthenospheric mantle through the Cocos-Rivera separation. The flow is driven by a pressure gradient associated with the down-dip differential-motion of the slabs. Similarly, low pressure generated by the fast-moving Cocos plate creates a shallow counter-toroidal flow in the uppermost 100 km of the mantle wedge. The flow draws mantle beneath the western Trans-Mexican Volcanic Belt to the Jalisco block, then plunges into the deep mantle by the descending poloidal cell of the Cocos slab. Moreover, our model suggests a hydraulic jump causes an similar to 250 km asthenosphere upwelling around the area where intra-arc extensional systems converge in western Mexico. The upwelling eventually merges with the shallow counter-toroidal flow describing a motion in 3D space similar to an Archimedes' screw. Our results indicate the differential motion between subducting slabs drives mixing in the mantle wedge of the Rivera plate and allows the slab to steepen and retreat. Model results are in good agreement with seismic anisotropy studies and the geochemistry of lavas erupted in the Jalisco block. The model can explain the eruption of OIB lavas in the vicinity of the City of Guadalajara in western Mexico, and the south shoulder in the central part of the Tepic-Zacoalco fault system.
机译：我们以1：4,000,000的比例进行了模拟实验室建模，并在模拟的中西部俯冲带中对流动模式进行了计算机渲染。比例模型由一个装有玉米糖浆的透明罐组成，并装有两条由聚乙烯条制成的输送带。其中一条下降60A度，并以30 mm / min的速度移动，模拟了Rivera板。另一个倾斜45A度，以90 mm / min的速度运动，模拟Cocos板的俯冲。我们的缩小俯冲带还包括模拟平板之间的缝隙，类似于最近在剪切波层析成像研究中观察到的裂缝。 3毫米厚的丙烯酸板漂浮在糖浆上，与聚乙烯条掠过接触，并模拟了最重要的北美板。我们的实验通过Cocos-Rivera分离揭示了软流圈地幔的深环形流动。流量由与平板的下倾差动相关的压力梯度驱动。同样，快速移动的Cocos板产生的低压在地幔楔的最上方100 km处产生浅的反环形流动。流动将地幔从西部的墨西哥西部火山带之下吸引到哈利斯科州地块，然后被科科斯板块的下降的倍性细胞浸入深部的地幔中。此外，我们的模型表明，在墨西哥西部弧内伸展系统汇聚的区域附近，水力跃迁引起了类似250 km的软流圈上升。上升流最终与浅环形反流合并，描述了类似于阿基米德螺杆的3D空间中的运动。我们的结果表明，俯冲板之间的差异运动驱动了Rivera板的地幔楔中的混合，并使板变陡和后退。模型结果与地震各向异性研究以及哈利斯科州区块喷发的熔岩的地球化学非常吻合。该模型可以解释墨西哥西部瓜达拉哈拉市附近以及Tepic-Zacoalco断层系统中央的南肩O​​IB熔岩的喷发。

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