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。这项研究将研究这两种风格的邻近行为如何。加拉帕戈斯群岛是热点火山活动的一个著名例子，由上升的热地幔羽流供给，该系统与加拉帕戈斯扩张中心（GSC）相互作用，在加拉帕戈斯扩张中心，火山活动的发生是对两个分开的构造板块之间边界处的海底扩张的反应。 科学家们对加拉帕戈斯热点-GSC系统进行了数十年的研究，长期以来一直对地球物理和地球化学观测结果以及两者如何协同工作的物理模型之间持续存在的差异感到困惑。 这项研究将利用地震层析成像技术对质量和温度如何传输以及加拉帕戈斯系统下方岩浆如何产生进行成像。 将部署覆盖大片岛屿和邻近海底的仪器网络。 这些地震仪将记录 15 个月内从远处地震传播的地震波和周围地面位移。 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。对这些特性进行成像将能够解决加拉帕戈斯系统特有的许多未解答的问题。这项研究还将解决地幔浅部发生的基本过程，该浅部又热又弱，以及与形成地球板块的凉爽、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学研究生。此外，“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以及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，以促进科学教育和国际研究合作。 为了制作第一个地幔地震视图，了解地幔柱-山脊相互作用如何真正发挥作用，将在加拉帕戈斯系统周围收集开放获取的地震数据集。该实验和随后的分析旨在解决三个主要科学问题：（i）地幔柱物质在什么深度、以什么地理格局、通过什么机制向北流到加拉帕戈斯群岛扩散中心并沿着洋脊分散？ (ii) 不均匀性的规模和性质是否表明存在小规模的亚岩石圈对流？ (iii) 熔化和挥发物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学的相关异质性是什么？考虑到之前对地表现象的研究历史、加拉帕戈斯群岛下方地幔层析成像的证据以及有利的震源方位角分布，加拉帕戈斯系统非常适合此类研究。大量（53 个）海底宽带地震仪将部署在横跨加拉帕戈斯群岛和西加拉帕戈斯传播中心之间的阵列中，为期 15 个月。岛上 7 个宽带站的数据也将被使用。数据将经过初步处理，包括环境噪声互相关，并存档在 IRIS-DMC 中以供公众立即使用。各向同性速度的层析成像模型将由体波产生，各向同性速度由表面波和环境噪声的组合产生，以及由表面波产生径向和方位各向异性。将分析接收器函数以识别与岩石圈相关的不连续性，并使用熔融和剪切波分裂来绘制各向异性图。羽状脊相互作用的地球动力学模型将用于通过比较建模和观测的地震波形以及使用地球动力学模型作为层析成像反演的先验信息来进行假设检验。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计划内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价值和更广泛的影响审查标准进行评估，被认为值得支持。