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Arc-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua

机译：哥斯达黎加和尼加拉瓜下面的地幔楔中弧平行流动

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Resolving flow geometry in the mantle wedge is central to understanding the thermal and chemical structure of subduction zones, subducting plate dehydration, and melting that leads to arc vol-canism, which can threaten large populations and alter climate through gas and particle emission. Here we show that isotope geochemistry and seismic velocity anisotropy provide strong evidence for trench-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua. This finding contradicts classical models, which predict trench-normal flow owing to the overlying wedge mantle being dragged downwards by the subducting plate. The isotopic signature of central Costa Rican volcanic rocks is not consistent with its derivation from the mantle wedge or eroded fore-arc complexes but instead from seamounts of the Galapagos hotspot track on the subducting Cocos plate. This isotopic signature decreases continuously from central Costa Rica to northwestern Nicaragua. As the age of the isotopic signature beneath Costa Rica can be constrained and its transport distance is known, minimum northwestward flow rates can be estimated (63-190 mm yr~(-1)) and are comparable to the magnitude of subducting Cocos plate motion (～85mmyr~(-1)). Trench-parallel flow needs to be taken into account in models evaluating thermal and chemical structure and melt generation in subduction zones.
机译：解决地幔楔中的流体几何形状对于理解俯冲带的热和化学结构，俯冲板片脱水以及导致弧形火山作用的融化至关重要，弧形火山作用会威胁大量人口并通过气体和颗粒物排放改变气候。在这里，我们表明同位素地球化学和地震速度各向异性为哥斯达黎加和尼加拉瓜下面的地幔楔中的沟渠平行流动提供了有力的证据。这一发现与经典模型相矛盾，经典模型预测了由于上覆的楔形地幔被俯冲板向下拖拉而导致的沟渠垂直流动。哥斯达黎加中部火山岩的同位素特征与其衍生自地幔楔或侵蚀的前弧复合体不一致，而是源自俯冲的科科斯板块上加拉帕戈斯热点轨迹的海山。从哥斯达黎加中部到尼加拉瓜西北部，这种同位素特征不断减少。由于哥斯达黎加下方的同位素特征年龄可以被限制并且其传输距离是已知的，因此可以估计最低的西北向流速（63-190 mm yr〜（-1）），并且与俯冲科科斯板块运动的幅度相当（〜85mmyr〜（-1））。在评估俯冲带的热化学结构和熔体生成的模型中，必须考虑平行于海沟的流动。

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