Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle
Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle
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DOI：
10.1029/2008gc001963
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发表时间：
2008-07
期刊：
影响因子：
3.7
通讯作者：
E. Syracuse;G. Abers;K. Fischer;Laura S Mackenzie;C. Rychert;M. Protti;V. González;W. Strauch
中科院分区：
文献类型：
--
作者：
E. Syracuse;G. Abers;K. Fischer;Laura S Mackenzie;C. Rychert;M. Protti;V. González;W. Strauch
中美洲俯冲带在沿弧线的短距离内，在地球化学性质、向下的板块粗糙度和倾角以及火山位置方面表现出很大的变化。哥斯达黎加和尼加拉瓜(图坎)下的层析成像实验的Vp、Vp/Vs和震源的联合反演结果使我们对其几何和结构有了深入的了解。在哥斯达黎加和尼加拉瓜，中等深度地震带都是厚度不超过10至20公里的单层。断层图像显示，在整个尼加拉瓜和哥斯达黎加，最慢的地幔P波速度出现在火山前锋下方和后面，表明最高温度区域可能延伸到80至120公里深处。尼加拉瓜火山正下方是一片被认为是由熔融引起的高Vp/V，而哥斯达黎加火山下面则是一个较弱、范围更广的异常，这可能表明尼加拉瓜地下有更大程度的融化。在下行板块内，异常低速度出现在瓦达蒂-贝尼奥夫带以下至少20-30公里处，尼加拉瓜下方140公里处，哥斯达黎加下方60公里处。它们表明尼加拉瓜下行板块的上地幔有10-20%是蛇纹状的，类似于海沟向海的折射，但继续延伸到弧下深度。这种异常水化的岩石圈可能会将更多的水引入尼加拉瓜地幔，引发更多的熔融量和流向弧区的流体流量。
The Central American subduction zone exhibits large variations in geochemistry, downgoing plate roughness and dip, and volcano locations over a short distance along the arc. Results from joint inversions for Vp, Vp/Vs, and hypocenters from the Tomography Under Costa Rica and Nicaragua (TUCAN) experiment give insight into its geometry and structure. In both Costa Rica and Nicaragua, the intermediate‐depth seismic zone is a single layer no more than 10 to 20 km thick. Tomographic images show that throughout Nicaragua and Costa Rica the slowest mantle P wave velocities appear below and behind the volcanic front, indicating likely zones of highest temperature extending 80 to 120 km depth. A sheet of high Vp/Vs, thought to be caused by melt, is imaged directly beneath the Nicaraguan volcanoes, whereas a weaker, broader anomaly is imaged beneath the Costa Rican volcanoes, potentially indicating a greater extent of melting beneath Nicaragua. Within the downgoing plate, anomalously low velocities occur at least 20–30 km below Wadati‐Benioff zone seismicity, to depths of 140 km beneath Nicaragua and to 60 km depth beneath Costa Rica. They indicate 10–20% serpentinized upper mantle of the downgoing plate beneath Nicaragua, similar to that inferred from refraction seaward of the trench, but continuing to subarc depths. This unusually hydrated lithosphere may introduce more water into the Nicaraguan mantle, initiating increased amount of melting and fluid flux to the arc.