Segmentation and Radial Anisotropy of the Deep Crustal Magmatic System Beneath the Cascades Arc
Segmentation and Radial Anisotropy of the Deep Crustal Magmatic System Beneath the Cascades Arc
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DOI：
10.1029/2022gc010738
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发表时间：
2023-03
期刊：
影响因子：
3.7
通讯作者：
Chengxin Jiang;B. Schmandt;G. Abers;E. Kiser;M. Miller
中科院分区：
文献类型：
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作者：
Chengxin Jiang;B. Schmandt;G. Abers;E. Kiser;M. Miller
火山弧由许多不同的喷口组成，这些喷口最终由俯冲带地幔楔中的共同熔融过程提供燃料。地壳尺度岩浆系统的地震成像可以提供对熔体如何在地壳深部组织并最终在其上升和演变时集中在不同喷口下方的洞察。在这里，我们调查了跨四个主要成层火山的卡斯卡德弧的一部分下的地壳尺度结构：胡德山St. Helens（MSH），Mt.亚当斯（MA）和Mt.雷尼尔，基于234个地震仪的环境噪声数据。瑞利波和洛夫波频散的同时反演约束各向同性剪切速度（Vs），并确定径向各向异性结构。各向同性Vs显示了两个亚平行的低Vs区（3.45-3.55 km/s），深度为15-30 km，其中一个连接Mt。雷尼尔到马，另一个连接MSH到山。Hood，被解释为含有高达2.5%-6%熔体的深部地壳岩浆库，假设熔体几何形状接近平衡。负的径向各向异性，从垂直裂缝像堤防，是普遍存在的卡斯卡迪亚的这一部分，但正的径向各向异性中断，从近水平的功能，如窗台，垂直延伸到MA和山。雷尼尔在10-30公里深度和较弱的和西倾斜的正各向异性下MSH。正各向异性区域与各向同性低Vs异常相邻，而不是位于同一位置。上升熔体停滞，大部分结晶在岩床中，可能与围岩的成分不同，这可能解释了接近平均值的Vs和活跃的深部地壳岩浆储层附近的正径向各向异性。
Volcanic arcs consist of many distinct vents that are ultimately fueled by the common melting processes in the subduction zone mantle wedge. Seismic imaging of crustal‐scale magmatic systems can provide insight into how melt is organized in the deep crust and eventually focused beneath distinct vents as it ascends and evolves. Here, we investigate the crustal‐scale structure beneath a section of the Cascades arc spanning four major stratovolcanoes: Mt. Hood, Mt. St. Helens (MSH), Mt. Adams (MA), and Mt. Rainier, based on ambient noise data from 234 seismographs. Simultaneous inversion of Rayleigh and Love wave dispersion constrains the isotropic shear velocity (Vs) and identifies radially anisotropic structures. Isotropic Vs shows two sub‐parallel low‐Vs zones (∼3.45–3.55 km/s) at ∼15–30 km depth with one connecting Mt. Rainier to MA, and another connecting MSH to Mt. Hood, which are interpreted as deep crustal magma reservoirs containing up to ∼2.5%–6% melt, assuming near‐equilibrium melt geometry. Negative radial anisotropy, from vertical fractures like dikes, is prevalent in this part of the Cascadia, but is interrupted by positive radial anisotropy, from subhorizontal features like sills, extending vertically beneath MA and Mt. Rainier at ∼10–30 km depth and weaker and west‐dipping positive anisotropy beneath MSH. The positive anisotropy regions are adjacent to rather than co‐located with the isotropic low‐Vs anomalies. Ascending melt that stalled and mostly crystallized in sills with possible compositional differences from the country rock may explain the near‐average Vs and positive radial anisotropy adjacent to the active deep crustal magma reservoirs.