An Open Access Experiment to Seismically Image Galapagos Plume-Ridge Interaction
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To produce the first mantle seismic view of how mantle plume-ridge interaction really works, an open-access seismic dataset will be collected around the Galapagos system. The experiment and subsequent analyses are designed to address three main scientific questions: (i) At what depths, in what geographic pattern, and by what mechanism does mantle plume material flow northward to the Galapagos Spreading Center and disperse along the ridge? (ii) Do the scale and nature of heterogeneity indicate small-scale, sub-lithospheric convection? and (iii) What is the spatial distribution of melting and volatile release, as well as the associated heterogeneity in composition and rheology due to plume-ridge interaction? The Galapagos system is exceptionally well-suited for such a study given the history of previous investigations of the surface manifestations, the evidence from mantle tomography below the Galapagos Archipelago, and the favorable azimuthal distribution of seismic sources. A large number (53) ocean-bottom, broadband seismometers will be deployed for 15 months in an array spanning the area between the Galapagos Islands and the Western Galapagos Spreading Center. Data from 7 broadband stations on the islands also will be used. The data will undergo initial processing, including ambient noise cross-correlation, and be archived in the IRIS-DMC for immediate public use. Tomography models of isotropic velocity will be produced from body waves, isotropic velocity from the combination of surface waves and ambient noise, as well as radial and azimuthal anisotropy from surface waves. Receiver functions will be analyzed to identify discontinuities related to the lithosphere and melting and shear wave splitting will be used to map anisotropy. Geodynamic models of plume-ridge interaction will be used for hypothesis testing by comparing modeled and observed seismic waveforms, and by using the geodynamic models as a priori information for the tomographic inversions. The project will also substantially advance a broad understanding of mantle plume processes, the asthenosphere, and their interactions with oceanic lithosphere; specifically, the deployment will function as a unit array within the Pacific Array Initiative.
为了首次获取地幔柱（mantle plume）-洋脊相互作用真实运作机制的地幔地震成像视角，研究团队将在加拉帕戈斯（Galapagos）系统周边采集开放获取的地震数据集。本实验及后续分析旨在解答三大核心科学问题：（1）地幔柱物质以何种深度分布、地理格局与运移机制，向北流入加拉帕戈斯扩张中心（Galapagos Spreading Center）并沿洋脊扩散？（2）物质不均一性的尺度与特征是否指示了岩石圈下方的小尺度对流？（3）由地幔柱-洋脊相互作用引发的熔融与挥发分释放的空间分布，以及由此产生的成分与流变学不均一性究竟如何？ 加拉帕戈斯海域具备开展此类研究的绝佳条件：过往针对其地表表现的研究积累、加拉帕戈斯群岛下方地幔层析成像（mantle tomography）的相关证据，以及地震源的有利方位分布，均为本次研究提供了坚实支撑。 研究团队将在横跨加拉帕戈斯群岛与西加拉帕戈斯扩张中心（Western Galapagos Spreading Center）的区域内，部署共计53台海底宽频带地震仪，部署时长为15个月；同时还将利用群岛上7个宽频台站的观测数据。 数据集将进行包括环境噪声互相关在内的初始处理，并归档至IRIS-DMC，以供公众即时获取使用。研究将基于体波构建各向同性速度层析成像模型，基于面波与环境噪声的联合数据重建各向同性速度模型，同时基于面波提取径向与方位各向异性参数。将通过接收函数分析识别与岩石圈及熔融作用相关的界面，并利用横波分裂技术绘制各向异性分布图。 本研究将借助地幔柱-洋脊相互作用的地球动力学模型开展假设检验：一方面对比模拟与观测得到的地震波形，另一方面将地球动力学模型作为层析成像反演的先验信息。本项目还将大幅推动学界对地幔柱活动、软流圈（asthenosphere）及其与大洋岩石圈相互作用的全面认知；具体而言，本次地震台阵部署将作为太平洋阵列倡议（Pacific Array Initiative）的组成单元发挥作用。
