Arc-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua
Arc-parallel flow in the mantle wedge beneath Costa Rica and Nicaragua
复制标题
DOI：
10.1038/nature06550
复制
发表时间：
2008-02-28
期刊：
影响因子：
64.8
通讯作者：
Strauch, Wilfried
中科院分区：
文献类型：
--
作者：
Hoernle, Kaj;Abt, David L.;Strauch, Wilfried
解决地幔楔中的流动几何形状对于了解俯冲带的热和化学结构、俯冲板块脱水以及导致弧火山作用的熔融至关重要，弧火山作用可能威胁大量人口并通过气体和颗粒排放改变气候。在这里，我们表明，同位素地球化学和地震速度各向异性提供了强有力的证据，在哥斯达黎加和尼加拉瓜地幔楔沟平行流。这一发现与经典模型相矛盾，经典模型预测海沟正常流动是由于上覆的楔形地幔被俯冲板块向下拖曳。哥斯达黎加中部火山岩的同位素特征与其来自地幔楔（1-3）或侵蚀弧前复合体（4）的情况不一致，而是来自俯冲科科斯板块上加拉帕戈斯热点轨迹的海山。这种同位素特征从哥斯达黎加中部到尼加拉瓜西北部不断减少。由于哥斯达黎加下方同位素特征的年龄可以被限制，并且其迁移距离已知，因此可以估计西北方向的最小流速（63 - 190 mm yr（-1）），并且与俯冲科科斯板块运动的幅度（类似于85 mm yr（-1））相当。在评估俯冲带的热结构和化学结构以及熔体生成的模型中，需要考虑到沟槽平行流动。
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 volcanism, 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(1-3) or eroded fore- arc complexes(4) 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 (similar to 85 mm yr(-1)). Trench- parallel flow needs to be taken into account in models evaluating thermal and chemical structure and melt generation in subduction zones.