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十亿年来该地区广泛的构造过程，包括与两个完整的超大陆组合和分裂旋回相关的俯冲和裂谷期。这些过程的记录保存在我们今天在地表看到的地质单元和地形中。然而，随着时间的推移，地壳和地幔岩石圈是如何对这些构造力作出反应的，以及保存在地表的地质单元是否以及如何与更深的结构有关，这些都是未知的。阿巴拉契亚地形的持久性一直是景观演化研究中的一个突出问题。侵蚀、地形、岩石类型和深层地幔流之间存在着持续的相互作用，它们控制着我们今天在地表看到的结构。然而，要理解这些因素所起的复杂作用，需要更好地约束地形变化的历史及其与地幔深部结构和动力学的关系。我们的项目，被称为中大西洋地球物理综合合作（MAGIC），旨在通过研究表面过程，地壳和岩石圈结构，以及穿越弗吉尼亚州，西弗吉尼亚州和俄亥俄州的深部地幔流来解决这些关于美国东部地球物理演化的基本问题。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。我们正在进行为期两年的部署，在从大西洋海岸到大陆内陆的密集线性样带上部署28个宽带地震仪。结合EarthScope USArray可移动阵列（TA）站，我们的实验几何将提供一个机会，利用剪切波分裂、接收函数分析和层析反演等技术，以前所未有的细节对从海岸到大陆内部的各向同性和各向异性地壳和地幔结构进行成像。密集的线性阵列使我们能够针对地壳和岩石圈的小尺度变化进行成像。我们的地球动力学建模工作侧重于定量测试地幔流动模式的几种不同假设，通过使用三维，时间相关的数值模型来对地幔各向异性和地表地形变化做出可测试的预测，这些预测将与项目地震学和地貌学组成部分的结果进行测试。该项目的地貌学部分使用定量的河流剖面数据和宇宙成因同位素来了解整个阿巴拉契亚地区的侵蚀速率和地形变化的历史。对隆升历史的深入了解以及岩性、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地幔流场和深部地壳和岩石圈结构的推断进行比较。这三种努力的洞察将结合起来，以获得从地壳和地幔岩石圈到软流圈和更深地幔的构造过程的垂直整合图像。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，并与我们研究区域内目前未参与EarthScope计划的学院和大学（包括许多主要的本科机构）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.