Magnetotelluric image of the fluid cycle in the Costa Rican subduction zone
Magnetotelluric image of the fluid cycle in the Costa Rican subduction zone
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DOI：
10.1038/ngeo1041
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发表时间：
2011-02
影响因子：
18.3
通讯作者：
T. Worzewski;M. Jegen;H. Kopp;H. Brasse;Waldo Taylor Castillo
中科院分区：
文献类型：
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作者：
T. Worzewski;M. Jegen;H. Kopp;H. Brasse;Waldo Taylor Castillo
进入俯冲带的流体在俯冲过程中起着关键作用。它们引起俯冲带的动力学和热结构的变化，并在变质作用期间从俯冲板块释放出来时引发地震。流体由海洋地壳输送到俯冲带，当海洋板块在板块边界向下弯曲时，流体也进入海洋板块。然而，进入俯冲带的流体数量与通过火山喷发或转移到深部地幔的流体数量并不匹配，这意味着地壳中可能存在流体储存。在这里，我们使用大地电磁数据绘制了哥斯达黎加俯冲带120公里深度的整个水化和脱水循环。沿着即将到来的板块弯曲，我们探测到一个电导率异常，我们将其解释为海水穿过伸展断层和裂缝进入上地幔。沿着俯冲板块界面，我们记录了沉积物、地壳和地幔的脱水。我们在火山弧向海30公里处的~ 20-30公里深度处发现了流体聚集。与其他俯冲带，，，，，，，，，的对比表明，这种流体聚集是全球性的现象。虽然我们无法测试这些流体储层是否随时间增长，但我们认为它们可以解释俯冲带丢失的一些流体流出。
Fluids entering the subduction zone play a key role in the subduction process. They cause changes in the dynamics and thermal structure of the subduction zone, and trigger earthquakes when released from the subducting plate during metamorphism,. Fluids are delivered to the subduction zone by the oceanic crust and also enter the oceanic plate as it bends downwards at the plate boundary. However, the amount of fluids entering subduction zones is not matched by that leaving through volcanic emissions or transfer to the deep mantle, implying possible storage of fluids in the crust. Here we use magnetotelluric data to map the entire hydration and dehydration cycle of the Costa Rican subduction zone to 120 km depth. Along the incoming plate bend, we detect a conductivity anomaly that we interpret as sea water penetrating down extensional faults and cracks into the upper mantle. Along the subducting plate interface we document the dehydration of sediments, the crust and mantle. We identify an accumulation of fluids at ∼20–30 km depth at a distance of 30 km seaward from the volcanic arc. Comparison with other subduction zones,,,,,,,,,indicates that such fluid accumulation is a global phenomenon. Although we are unable to test whether these fluid reservoirs grow with time, we suggest that they can account for some of the missing outflow of fluid at subduction zones.