Collaborative Research: An Open Access Experiment to Seismically Image Galapagos Plume-Ridge Interaction

在地球上，火山的形成有三种基本方式。本研究将考察这两种风格在接近时的表现。加拉帕戈斯群岛是一个著名的热点火山活动的例子，它是由上升的热地幔羽流提供的，这个系统与加拉帕戈斯扩张中心（GSC）相互作用，在那里火山活动发生在两个构造板块分开的边界处，是海底扩张的反应。科学家们对加拉帕戈斯群岛的热点- gsc系统进行了几十年的研究，长期以来，他们一直对地球物理和地球化学观测结果与物理模型之间持续存在的差异感到困惑。这项研究将利用一种叫做地震层析成像的技术，成像质量和温度是如何运输的，以及岩浆是如何在加拉帕戈斯群岛系统下产生的。将部署一个横跨岛屿和邻近海底的仪器网络。这些地震仪将在15个月的时间里记录来自遥远地震的地震波和周围地面的位移。当地震波穿过研究区域下方时，它们会对地幔成分、温度、变形和岩浆存在的差异做出反应。对这些属性进行成像将使加拉帕戈斯群岛系统特有的许多未解之谜得以解决。这项研究还将探讨发生在地幔浅层的基本过程，即热而弱的部分，以及与形成地球构造板块的冷而硬的上覆部分的相互作用。本项目将培养3名海洋地球物理学研究生。此外，“申请航行”项目将允许其他机构的研究生和早期职业科学家以及社区大学教师参加研究巡航，以获得航海训练。最后，厄瓜多尔的科学家和研究生也将参加游轮活动，促进科学教育和国际研究合作。为了产生第一个地幔地震视图，地幔柱脊相互作用是如何真正起作用的，将在加拉帕戈斯系统周围收集一个开放访问的地震数据集。实验和随后的分析旨在解决三个主要的科学问题：(i)地幔柱物质在什么深度，以什么地理模式，以及通过什么机制向北流向加拉帕戈斯扩张中心并沿着山脊分散？（二）非均质性的规模和性质是否表明是小尺度的岩石圈次对流？（iii）熔融和挥发性释放的空间分布是什么，以及由于羽脊相互作用而导致的相关成分和流变性质的非均质性是什么？考虑到以往对地表表现的调查历史、加拉帕戈斯群岛下地幔层析成像的证据以及有利的震源方位分布，加拉帕戈斯群岛系统非常适合进行这样的研究。大量（53个）海底宽带地震仪将在横跨加拉帕戈斯群岛和西加拉帕戈斯传播中心之间地区的阵列中部署15个月。还将使用岛上7个宽频站的数据。这些数据将经过初步处理，包括环境噪声相互关联，并存档在IRIS-DMC中，供公众立即使用。各向同性速度层析模型将由体波、表面波和环境噪声组合的各向同性速度以及表面波的径向和方位各向异性产生。将分析接收函数以识别与岩石圈有关的不连续面，并使用熔融和横波分裂来绘制各向异性。羽脊相互作用的地球动力学模型将用于假设检验，通过比较模拟和观测到的地震波形，并使用地球动力学模型作为层析反演的先验信息。该项目还将大大促进对地幔柱过程、软流圈及其与海洋岩石圈相互作用的广泛理解；具体来说，该部署将作为太平洋阵列倡议中的一个单元阵列。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

On Earth there are three fundamental ways in which volcanoes form. This study will examine how two of these styles behave in proximity. The Galapagos archipelago is a well-known example of hotspot volcanism, fed by a rising plume of hot mantle, and this system is interacting with the Galapagos Spreading Center (GSC) where volcanism occurs in response to seafloor spreading at the boundary between two tectonic plates moving apart. Scientists have studied the Galapagos hotspot-GSC system for several decades and have long puzzled over persistent discrepancies between geophysical and geochemical observations and physical models for how the pair work together. This study will image how mass and temperature are transported, as well as how magma is generated beneath the Galapagos system, using a technique called seismic tomography. A network of instruments spanning a large area of the islands and adjacent seafloor will be deployed. These seismometers will record seismic waves traveling from distant earthquakes and ambient ground displacement over a period of 15 months. As the seismic waves pass beneath the study area, they respond to differences in mantle composition, temperature, deformation, and the presence of magma. Imaging these properties will allow many unanswered questions particular to the Galapagos system to be addressed. The study will also address the fundamental processes occurring in the shallow part of the mantle that is hot and weak and the interactions with the the cool, stiff overlying part that forms Earth's tectonic plates. This program will train three graduate students in marine geophysics. In addition, an Apply-to-Sail program will allow graduate students and early career scientists from other institutions and community college instructors to participate on the research cruises to gain sea-going training. Lastly, Ecuadorian scientists and graduate students will also participate on the cruises, bolstering science education and international research collaboration.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.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.