Thermal and melt structure of the Juan de Fuca plate from ridge to trench to arc, inferred from seismic attenuation across the Amphibious Array

根据两栖阵列的地震衰减推断，胡安德富卡板块从山脊到海沟再到弧线的热结构和熔体结构

• 批准号: 1536566
• 负责人: Geoffrey Abers
• 金额: $ 8.05万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536566&HistoricalAwards=false
• 关键词: Thermal; melt; structure; Juan; de

The primary goal of this study is to better understand the mantle beneath tectonic plates that floor the ocean basins. The Cascadia Initiative deployed an Amphibious Array of seismic stations across the complete Juan de Fuca plate and adjacent Cascadia margin, in the Pacific Northwest. This is the first time a seismic array has covered a complete plate from spreading center to trench to volcanic arc. The cooling, rigid structure that characterizes an oceanic plate from its formation, through aging, and its eventual subduction at the continental margin is well understood. In contrast, the nature of the ductile, partially molten mantle underneath is less certain. Does melt occur in the mantle only beneath the magma-producing upwelling zone beneath the oceanic spreading center, or are small amounts of magma beneath the aging plate? As the plate approaches a trench and bends downward to subduct, does fracturing let seawater filter down into the plate, to be absorbed in minerals and carried into the mantle? If so, how and where do these volatiles later emerge to affect the fluidity of the slowly circulating mantle? The seismic analysis carried out in this study aims to answer these questions. A graduate student will carry out most of the analysis, expanding skills in a final PhD training year beyond what has already been gained in earlier thesis research.Although the thermal structure of oceanic lithosphere is well understood, basic questions regarding asthenosphere still exist. Both partial melt and bound water are proposed to explain low asthenosphere seismic velocities and viscosities but their distribution is not well constrained. It is not known if the base of the asthenosphere is defined by a constant pressure / homologous temperature, or if the asthenosphere is entrained at a subduction zone and carried to depth. Additional questions about temperature, water distribution and melt exist once plates subduct. This study focuses on seismic attenuation across the Cascadia Amphibious Array measured from body waves, since these physical properties can be better elucidated than from seismic velocity studies alone. Because the Amphibious Array provides such comprehensive broadband seismic data, the expected variations in body-wave attenuation can be seen here better than any other oceanic region. Comparisons with geodynamic models and with surface-wave derived images will allow calibration of laboratory-based theories of anelasticity.

这项研究的主要目的是更好地了解海盆底层下方的地幔。 Cascadia倡议在太平洋西北部的完整胡安·德福卡板和邻近的卡斯卡迪亚边缘部署了一系列的地震站。这是地震阵列第一次覆盖了从扩展中心到沟渠再到火山弧的完整板。 众所周知，从其形成到衰老的海洋板的冷却，刚性结构也充分了解了大陆边缘的最终俯冲。相比之下，下面的延性，部分熔融地幔的性质不确定。熔体在海洋传播中心下方的岩浆产生的上升区域下方的地幔发生，还是在老化板下方少量的岩浆？当盘子接近沟渠并向下弯曲到俯冲时，破裂是否让海水向下过滤到板上，以矿物质吸收并携带到地幔中？如果是这样，这些挥发物后来出现如何以及在哪里影响慢慢循环地幔的流动性？本研究中进行的地震分析旨在回答这些问题。研究生将进行大多数分析，在最后的博士学位培训年内扩大技能，超出了早期论文研究中已经获得的。提出了部分熔体和结合的水来解释低下动量磷酸地震速度和粘度，但它们的分布不太受限。不知道运动圈的底部是否由恒定压力 /同源温度定义，还是在俯冲带夹带并携带到深度上的软圈。一旦板块俯冲，就存在有关温度，水分分布和熔体的其他问题。这项研究的重点是从体波测得的Cascadia两栖阵列上的地震衰减，因为这些物理特性可以比单独的地震速度研究更好地阐明。由于两栖阵列提供了如此全面的宽带地震数据，因此在这里可以比任何其他海洋地区更好地看到人体波衰减的预期变化。与地球动力学模型和表面波衍生的图像的比较将允许校准基于实验室的抗弹性理论。