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

合作研究：加拉帕戈斯羽流-山脊相互作用地震成像的开放获取实验

• 批准号: 1927087
• 负责人: Garrett Apuzen-Ito
• 金额: $ 32.78万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-15 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1927087&HistoricalAwards=false
• 关键词: Collaborative; Research; Open; Access; Experiment

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.

在地球上，火山的形成有三种基本方式。这项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，该火山活动是由上升的地幔热柱提供的，该系统与加拉帕戈斯扩散中心(GSC)相互作用，在那里火山活动是对两个构造板块之间分离的边界上的海底扩张的响应。科学家们研究加拉帕戈斯热点-GSC系统已经有几十年了，长期以来一直困扰着地球物理和地球化学观测之间的持续差异，以及这两个系统如何协同工作的物理模型。这项研究将使用一种名为地震层析成像的技术来成像质量和温度是如何输送的，以及岩浆是如何在加拉帕戈斯系统下产生的。将部署一个覆盖大片岛屿和邻近海底的仪器网络。这些地震仪将记录来自远距离地震的地震波和15个月内周围地面的位移。当地震波在研究区域下方传播时，它们对地幔成分、温度、变形和岩浆存在的不同做出反应。想象这些特性将使加拉帕戈斯系统特有的许多悬而未决的问题得到解决。这项研究还将探讨地幔浅部发生的热而弱的基本过程，以及与形成地球构造板块的凉爽、坚硬的上覆部分的相互作用。该项目将培养三名海洋地球物理研究生。此外，一项申请航行计划将允许来自其他机构的研究生和早期职业科学家和社区大学教师参加研究巡航，以获得航海培训。最后，厄瓜多尔科学家和研究生也将参加巡航，支持科学教育和国际研究合作。为了制作第一个地幔地震图，说明地幔羽流-海脊相互作用是如何工作的，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：(1)地幔物质在多深、什么地理模式和什么机制下向北流向加拉帕戈斯扩张中心并沿着山脊扩散？(2)非均质性的规模和性质是否表明岩石圈以下的小尺度对流？以及(Iii)熔融和挥发分释放的空间分布是什么，以及由于羽流-脊相互作用而导致的成分和流变性的相关非均质性？加拉帕戈斯系统特别适合于这样的研究，考虑到以前对地表现象的研究历史，加拉帕戈斯群岛下方的地幔层析成像证据，以及震源的有利方位分布。将在加拉帕戈斯群岛和西加拉帕戈斯传播中心之间的地区部署大量(53台)海底宽带地震仪，部署时间为15个月。来自岛屿上7个宽带站的数据也将被使用。这些数据将经过初步处理，包括环境噪声互相关，并将在IRIS-DMC中存档，以便立即供公众使用。各向同性速度的层析成像模型将由体波、面波和环境噪声的组合产生的各向同性速度以及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性，并将使用熔融和横波分裂来绘制各向异性图。羽流-山脊相互作用的地球动力学模型将用于假设检验，方法是将模拟的地震波形与观测的地震波形进行比较，并将地球动力学模型用作层析反演的先验信息。该项目还将大大促进对地幔热柱过程、软流圈及其与海洋岩石圈相互作用的广泛了解；具体地说，该部署将作为太平洋阵列倡议中的一个单元阵列发挥作用。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。