Mapping the Lithosphere and Asthenosphere Beneath Alaska With Sp Converted Waves
Mapping the Lithosphere and Asthenosphere Beneath Alaska With Sp Converted Waves
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用Sp转换波绘制阿拉斯加岩石圈和软流圈
DOI：
10.1029/2022gc010517
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发表时间：
2022-10
期刊：
影响因子：
3.7
通讯作者：
I. Gama;K. Fischer;J. Hua
中科院分区：
文献类型：
--
作者：
I. Gama;K. Fischer;J. Hua
我们使用NSF EarthScope便携式阵列和其他便携式阵列和永久网络的数百个台站记录的S到p转换体波的公共转换点（CCP）叠加获得了阿拉斯加州地壳和地幔地震速度梯度的3D图像。莫霍面深度描绘了雅库塔特山脉俯冲带的厚地壳和布鲁克斯山脉下的地壳根。在阿拉斯加俯冲带的俯冲岩石圈附近，北美岩石圈特别薄，这与俯冲带流动和地幔楔上的熔体使上板块变薄一致。岩石圈仍然相对较薄，远到西北和北部，包括苏厄德半岛和布鲁克斯山脉以南的地区，岩石圈的伸展和下沉可能发挥了作用。岩石圈在布鲁克斯山脉和北方北极阿拉斯加山脉下面急剧增厚，那里似乎既冷又粘。CCP叠加还显示，在130-230公里深处存在明显的正速度梯度，这代表了软流圈内一层的底部，软流圈的低速最好用部分熔融的存在来解释。虽然这种梯度存在于俯冲岩石圈附近，在那里部分熔融是由板片衍生的流体实现的，但在苏厄德半岛和兰格尔火山场东北部最强，这表明在距离板片数百公里的软流圈中存在部分熔融，可能是由于上涌软流圈中的减压熔融。
We obtained a 3D image of crust and mantle seismic velocity gradients beneath the state of Alaska using common‐conversion point (CCP) stacking of S‐to‐p converted body waves recorded by hundreds of stations from the NSF EarthScope Transportable Array and other portable arrays and permanent networks. Moho depths delineate the thick crust of the underthrust Yakutat terrane and the crustal root beneath the Brooks Range. The North American lithosphere is particularly thin close to the subducting lithosphere in the Alaska subduction zone, consistent with thinning of the upper plate by subduction zone flow and melt rising from the mantle wedge. The lithosphere remains relatively thin far to the northwest and north, including the Seward Peninsula and regions to the south of the Brooks Range where lithospheric extension and foundering may have played a role. The lithosphere dramatically thickens beneath the Brooks Range and northern Arctic Alaska terrane where it appears to be both cold and highly viscous. The CCP stack also revealed a pronounced positive velocity gradient at depths of 130–230 km that represents the base of a layer within the asthenosphere whose low velocities are best explained by the presence of partial melt. Although this gradient is present close to the subducting lithosphere, where partial melting is enabled by slab‐derived fluids, it is strongest beneath the Seward Peninsula and northeast of the Wrangell volcanic field, suggesting the presence of partial melt in the asthenosphere hundreds of kilometers away from the slab, likely due to decompression melting in upwelling asthenosphere.