Collaborative Research: Quantifying Plume-Lithosphere Interactions with GNSS Geodesy, Seismology, and Geodynamic Modeling

合作研究：利用 GNSS 大地测量学、地震学和地球动力学建模量化羽流-岩石圈相互作用

• 批准号: 1551767
• 负责人: Andrew Nyblade
• 金额: $ 20.39万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1551767&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantifying; Plume; Lithosphere

Part 1: Continental rifting is a physical process that shapes the Earth's surface and causes a range of geohazards for local populations. The East African Rift System (EARS) is the Earth's archetype continental rift system in its early stages of development and one of the focus sites of the NSF GeoPRISMS program. Understanding the physics of deeper mantle interactions with continental rifting at the shallow parts of the Earth remains an outstanding challenge in the geosciences. In this project the physics of mantle-lithosphere interactions will be addressed, with a focus on testing long-standing mantle plume hypotheses using computational modeling and new seismic and Global Navigational Satellite System / Global Positioning System (GNSS/GPS) precision positioning data to constrain movements in the mantle and at the surface. Part 2: It has long been recognized that the mantle beneath the East African Rift System (EARS) is thermally perturbed. A host of geophysical and geochemical data are used to argue for a plume origin of the thermal perturbations. Whether the EARS is underlain by a single, superplume or multiple plumes is hotly debated. Fundamental to understanding the physical processes influencing the East African GeoPRISMS focus site (Eastern Branch), and more broadly of large-scale mantle dynamics, is testing the superplume model. New seismic and GNSS data are needed from the GeoPRISMS focus-site along with thermomechanical modeling of lithosphere-plume interactions to fully evaluate the superplume and multiple plume models and advance our understanding of continental rifting processes. The proposed work will allow two GeoPRISMS questions to be addressed: (1) How does the presence or absence of an upper-mantle plume influence extension? (2) How is strain accommodated and partitioned throughout the lithosphere, and what are the controls on strain localization and migration? Seismic data from 9 new stations in northeastern Uganda will be installed to collect data for generating mantle flow indicators (seismic shear wave splitting, SKS) and improved sub-surface images (seismic tomography) of the Eastern Branch. If a consistent northerly fast polarization direction in the SKS measurements is discovered for most or all of the seismic stations the superplume model would be corroborated. If a more complex pattern of fast polarization directions is observed, then alternative interpretations will be examined, including the multiple plume hypothesis. The tomography models will constrain initial conditions of the proposed geodynamic modeling. A transect of new GNSS stations across the Eastern Branch spanning Kenya (7) and Uganda (3 co-located) will also be installed. If the GNSS data have along-rift motions that align with SKS observations, then the superplume model with strong plume-lithosphere interactions is favored. If SKS observations are consistent with the superplume model, but GNSS are not, then surface-mantle decoupling is indicated. These and alternative outcomes of the GNSS-SKS comparisons will be explored with 3D computational modeling of the lithosphere-mantle system that is constrained by the new seismic tomography. To characterize lithospheric coupling mechanics to upper mantle flow a suite of material models will be developed to determine coupling properties at the lithosphere-asthenosphere boundary (LAB). Modeled flow will be scored with new GNSS and SKS-splitting observations at the surface and LAB, respectively. In addition to the above scientific objectives this project will (1) enhance diversity by providing graduate research opportunities in seismology for underrepresented minority students supported through AfricaArray; (2) provide training to African scientists through GNSS short courses and the AfricaArray education program, (3) geodynamic modeling extensions will become publically available as part of the ASPECT software package, (4) the GNSS stations will become part of the permanent AfricaArray network and provide open data to the community long after the project is over, and (5) seismic data will become publically available. This project has been supported in part by the Office of International Science and Engineering at NSF.

第一部分：大陆裂谷作用是一个塑造地球表面的物理过程，并对当地居民造成一系列地质灾害。东非裂谷系统（EARS）是地球早期发展阶段的原型大陆裂谷系统，也是NSF GeoPRISMS计划的重点地点之一。了解地球浅层地幔与大陆裂谷作用的物理相互作用仍然是地球科学中的一个突出挑战。在这个项目中，将讨论地幔-岩石圈相互作用的物理学，重点是利用计算建模和新的地震和全球导航卫星系统/全球定位系统（GNSS/GPS）精确定位数据来测试长期存在的地幔柱假说，以限制地幔和地表的运动。第二部分：人们早就认识到东非裂谷系（EARS）下的地幔是热扰动的。大量的地球物理和地球化学数据被用来论证热扰动的羽状起源。EARS是否由单一的超级羽流或多个羽流支撑，这是一个激烈的争论。要了解影响东非GeoPRISMS重点站点（东部分支）的物理过程，以及更广泛的大规模地幔动力学，测试超级地幔柱模型至关重要。新的地震和全球导航卫星系统的数据需要从GeoPRISMS焦点网站沿着与岩石圈-羽相互作用的热机械建模，以充分评估超级羽和多羽模型，并推进我们的大陆裂谷过程的理解。拟议的工作将允许两个地球PRISMS问题得到解决：（1）如何存在或不存在的上地幔柱的影响延伸？(2)应变在整个岩石圈中是如何调节和分配的，应变局部化和迁移的控制因素是什么？ 将在乌干达东北部安装9个新台站的地震数据，以收集数据，生成地幔流指标（地震剪切波分裂，SKS）和改进东分支的地下图像（地震层析成像）。如果在SKS测量中发现大多数或所有地震台站的一致的偏北快速偏振方向，则超级羽流模型将得到证实。如果观察到更复杂的快速偏振方向模式，则将检查其他解释，包括多羽流假设。层析成像模型将约束所提出的地球动力学建模的初始条件。 还将在横跨肯尼亚（7个）和乌干达（3个共设）的东部分支安装一个新的全球导航卫星系统台站。如果GNSS数据具有与SKS观测一致的沿裂谷运动，那么具有强地幔柱-岩石圈相互作用的超级地幔柱模型是有利的。如果SKS观测结果与超级羽流模型一致，但GNSS不一致，则表明地表-地幔解耦。这些和其他结果的GNSS-SKS比较将探讨与三维计算建模的岩石圈地幔系统，是由新的地震层析成像的约束。为了描述岩石圈与上地幔流动的耦合机制，将建立一套物质模型来确定岩石圈-软流圈边界（LAB）的耦合性质。模拟流将分别在地面和实验室用新的GNSS和SKS分裂观测进行评分。除上述科学目标外，该项目还将（1）通过非洲阵列的支助，为代表性不足的少数民族学生提供地震学研究生研究机会，从而增强多样性;（2）通过全球导航卫星系统短期课程和AfricaArray教育方案向非洲科学家提供培训，（3）地球动力学建模扩展将作为ASPECT软件包的一部分提供，（4）全球导航卫星系统台站将成为永久性非洲阵列网络的一部分，并在项目结束后很长一段时间内向社区提供开放数据，以及（5）地震数据将可通过电子方式获得。该项目得到了NSF国际科学与工程办公室的部分支持。