Ambient noise tomography reveals upper crustal structure of Icelandic rifts
Ambient noise tomography reveals upper crustal structure of Icelandic rifts
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DOI：
10.1016/j.epsl.2017.02.039
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发表时间：
2017-05
影响因子：
5.3
通讯作者：
R. Green;K. Priestley;R. White
中科院分区：
文献类型：
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作者：
R. Green;K. Priestley;R. White
海洋扩张中心的结构和新形成的地壳内的地下熔体分布在很大程度上是从海洋地震实验中了解的。然而，在冰岛，空中裂谷高程既可以进行精确的地表测绘，也可以安装大型宽带地震阵列。我们提出了一项研究，使用环境噪声瑞利波层析成像的火山蔓延中心在冰岛。我们的高分辨率模型图像连续带的低地震速度，平行于所有三个部分的分支裂谷在冰岛。10 km以上的区域包含强烈的速度变化，较老的非火山活动区域的剪切波速度比活动裂谷快0.5 km s− 1。慢速度与地质表面测绘密切相关，异常的轮廓与新火山区的边缘平行。低速带延伸到新火山区的整个50公里宽，与快速扩张脊处的狭窄（8公里宽）岩浆区形成鲜明对比，在快速扩张脊处，熔体供应速率同样很高。在地震慢裂谷带内，异常的最低速度核心出现在Vatnajökull冰盖下的地幔柱中心上方，以及卡特拉火山中心下的东部火山带。这表明在这些特定的火山中心的熔体积累的本地化，表现出变化的熔体供应到浅地壳沿着裂谷轴。随深度的剪切速度反演表明，最强的速度对比被发现在上8公里，并显示在通过中地壳（10-20公里）在裂谷的剪切速度略有下降。我们的模型还显示，在西部火山带的缓慢裂谷异常强度较低，支持的概念，这里的裂谷活动正在减少的山脊跳跃到东部火山带。
The structure of oceanic spreading centres and subsurface melt distribution within newly formed crust is largely understood from marine seismic experiments. In Iceland, however, sub-aerial rift elevation allows both accurate surface mapping and the installation of large broadband seismic arrays. We present a study using ambient noise Rayleigh wave tomography to image the volcanic spreading centres across Iceland. Our high resolution model images a continuous band of low seismic velocities, parallelling all three segments of the branched rift in Iceland. The upper 10 km contains strong velocity variations, with shear wave velocities 0.5 km s−1faster in the older non-volcanically active regions compared to the active rifts. Slow velocities correlate very closely with geological surface mapping, with contours of the anomalies parallelling the edges of the neo-volcanic zones. The low-velocity band extends to the full 50 km width of the neo-volcanic zones, demonstrating a significant contrast with the narrow (8 km wide) magmatic zone seen at fast spreading ridges, where the rate of melt supply is similarly high. Within the seismically slow rift band, the lowest velocity cores of the anomalies occur above the centre of the mantle plume under the Vatnajökull icecap, and in the Eastern Volcanic Zone under the central volcano Katla. This suggests localisation of melt accumulation at these specific volcanic centres, demonstrating variability in melt supply into the shallow crust along the rift axis. Shear velocity inversions with depth show that the strongest velocity contrasts are found in the upper 8 km, and show a slight depression in the shear velocity through the mid crust (10–20 km) in the rifts. Our model also shows less intensity to the slow rift anomaly in the Western Volcanic Zone, supporting the notion that rift activity here is decreasing as the ridge jumps to the Eastern Volcanic Zone.