Collaborative Research: Mantle Dynamics, Lithospheric Structure, and Topographic Evolution of the Southeastern US Continental Margin

美国东部的地表地质异常复杂。这种复杂性反映了过去10亿年来在该区域运行的广泛的构造过程，包括与两个完整的超大陆组装和解体周期有关的俯冲和裂谷事件。这些过程的记录保存在我们今天在地表看到的地质单位和地形中。然而，随着时间的推移，地壳和地幔岩石圈如何对这些构造力做出反应，以及保存在地表的地质单元是否以及如何与更深层次的结构有关，目前尚不清楚。阿巴拉契亚地貌随时间的持续性一直是景观演化研究中的一大突出问题。侵蚀、地形、岩石类型和深部地幔流动之间存在着持续的相互作用，控制着我们今天在地表看到的结构。然而，要了解这些因素发挥的复杂作用，就需要更好地约束地形变化的历史及其与地幔深层结构和动力学的关系。我们的项目名为中大西洋地球物理综合合作(MAGIC)，旨在通过研究横跨弗吉尼亚州、西弗吉尼亚州和俄亥俄州的地表过程、地壳和岩石圈结构以及深部地幔流动来解决美国东部地球物理演化的这些基本问题。MAGIC涉及地震学家、地球动力学家和地貌学家之间的合作努力。我们正在进行一项为期两年的部署，在从大西洋海岸到大陆内陆的密集线性断面上部署28台宽带地震仪。与EarthScope USArray可移动阵列(TA)站相结合，我们的实验几何结构将提供一个机会，使用剪切波分裂、接收器函数分析和层析反演等技术，以前所未有的详细程度成像从海岸到大陆内陆的各向同性和各向异性地壳和地幔结构。密集的线性阵列使我们能够针对小范围的地壳和岩石圈变化进行成像。我们的地球动力学模拟工作重点是通过使用三维、随时间变化的数值模型对地幔流动模式的几种不同假设进行定量测试，以对地幔各向异性和地表地形变化做出可检验的预测，并将与该项目的地震学和地貌学部分的结果进行验证。该项目的地貌部分使用定量的河流剖面数据和宇宙成因的同位素，以了解整个阿巴拉契亚地区侵蚀速率和地形变化的历史。对隆升历史的洞察以及岩性、地形和侵蚀(及其空间变化)之间的平衡方法，将与从该项目的地球动力学和地震学组成部分获得的对地幔流场以及地壳和岩石圈深部结构的推断进行比较。所有这三项工作的洞察力将结合在一起，以获得从地表、地壳和地幔岩石圈到软流圈和更深的地幔的垂直综合构造过程图景。该项目的教育和推广部分侧重于本科生参与科学研究，为研究生提供指导和建议本科生的机会，以及与我们研究区域内目前没有参与地球范围倡议的学院和大学(包括许多本科生机构)建立联系。

The surface geology of the eastern United States is extraordinary in its complexity. This complexity reflects a wide range of tectonic processes that have operated in the region over the past billion years, including episodes of subduction and rifting associated with two complete cycles of supercontinent assembly and breakup. A record of these processes is preserved in the geological units and topography we see at the surface today. It is unknown, however, how the crust and mantle lithosphere have responded to these tectonic forces over time, and whether and how the geological units preserved at the surface relate to deeper structures. The persistence of Appalachian topography through time remains a major outstanding problem in the study of landscape evolution. There is an ongoing interplay among erosion, topography, rock type, and mantle flow at depth that controls the structures we see at the surface today. However, understanding the complex role played by each of these factors requires better constraints on the history of topographic change and its relationship to the deep structure and dynamics of the mantle. Our project, known as the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC), aims to address these fundamental questions about the geophysical evolution of the eastern United States by studying surface processes, crustal and lithospheric structure, and deep mantle flow across Virginia, West Virginia, and Ohio.MAGIC involves a collaborative effort among seismologists, geodynamicists, and geomorphologists. We are undertaking a two-year deployment of 28 broadband seismometers in a dense linear transect from the Atlantic coast to the continental interior. In combination with EarthScope USArray Transportable Array (TA) stations our experiment geometry will provide an opportunity to image isotropic and anisotropic crust and mantle structure from the coast to the continental interior in unprecedented detail, using techniques such as shear wave splitting, receiver function analysis, and tomographic inversions. The dense linear array allows us to target small-scale crustal and lithospheric variations for imaging. Our geodynamical modeling effort focuses on quantitatively testing several different hypotheses for the pattern of mantle flow by using 3-D, time-dependent, numerical models to make testable predictions about mantle anisotropy and surface topographic change, which will be tested against results from the seismology and geomorphology components of the project. The geomorphology component of the project uses quantitative stream profile data and cosmogenic isotopes to understand the history of erosion rates and topographic change throughout the Appalachian region. Insights into uplift history and the approach to equilibrium among lithology, topography, and erosion (and their spatial variation) will be compared to inferences on the mantle flow field and deep crustal and lithospheric structure gained from the geodynamics and seismology components of the project. Insight from all three efforts will be combined to obtain a vertically integrated picture of tectonic processes from the surface through the crust and mantle lithosphere to the asthenosphere and deeper mantle. The education and outreach component of this project focuses on the involvement of undergraduates in scientific research, opportunities for graduate students to mentor and advise undergraduate students, and forging ties with colleges and universities (including many primarily undergraduate institutions) in our study region that are not currently involved with the EarthScope initiative.