Collaborative Research: How have orogenies, rifting, and recent mantle dynamics shaped the lithosphere beneath the New England Appalachians?

大陆是地球板块构造系统的重要组成部分。板块构造在我们太阳系的所有行星体中似乎是独一无二的，它在使我们的星球适合生命居住方面起着至关重要的作用。大陆是由基本的板块构造过程形成和改造的，包括火山作用、造山、与其他大陆块体的碰撞以及超级大陆的裂谷或分裂。了解大陆岩石圈（即大陆下面的地壳和上地幔）随时间的演变仍然是地球科学中最重要的挑战之一。该项目将利用多学科方法，包括地壳和上地幔地震成像、地质结构分析和古断层运动测年，通过地质时间研究新英格兰阿巴拉契亚山脉下形成大陆岩石圈的过程。研究人员将利用部署在两个线性阵列（一个横跨纽约和马萨诸塞州，另一个横跨佛蒙特州、新罕布什尔州和缅因州）的地震仪测量的来自遥远地震的地震波进行详细成像。他们将把地震成像工作与地表暴露的地质结构研究结合起来，为板块构造史提供必要的背景资料。从这两种方法中获得的信息的整合将阐明在地质历史上形成新英格兰地下岩石圈的过程，为了解大陆岩石圈作为地球板块构造系统的一部分是如何演变的打开一扇窗。该项目旨在了解裂谷、俯冲和地层增生是如何塑造新英格兰地区岩石圈结构的：岩石圈是保留了俯冲和增生的记录，还是岩石圈结构随着时间的推移而愈合？随后的吸积事件是如何覆盖早期碰撞的结构的？中生代裂陷作用如何影响古生代增生构造？最近或正在进行的地幔过程是否改变了岩石圈结构？研究人员将分析来自NEST（新英格兰地震样带）实验的数据，该实验部署了约25个宽带地震仪，用于解析地壳目标的长度尺度，这些目标适合与地质结构直接联系。他们将应用一套成像技术（接收函数分析、体波传播时间分析、波场偏移成像和SKS分裂测量），提供新英格兰地壳和上地幔各向同性和各向异性结构的综合视图，包括所谓的北阿巴拉契亚异常（NAA）下的区域。U-Pb年代学工作将侧重于识别和分析谢尔本瀑布和布朗森山弧的弧深裂和火山岩的锆石颗粒中的异晶（继承）岩心，以了解塔尼克（及以后）造山过程的历史和时间。研究人员还将进行实地工作和结构分析，以调查新英格兰西部和纽约的基底地块和塔科尼克山脉的锋面逆冲的范围和相对时间，以及新英格兰中部的康涅狄格谷边界断层系统。他们将通过收集来自这些地区的40Ar/39Ar地质年代学样品并确定其年代，从而限制变形的时间，以确定整个地区旧断层的重新激活（以及新断层的位移）的广泛程度。该项目强调本科生参与跨学科研究和实地工作，特别是来自历史上在地球科学领域代表性不足的群体的参与者，这是由文理学院和研究机构的教师合作实现的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Continents represent a key component of the Earth’s plate tectonic system. Plate tectonics appears to be unique among all planetary bodies in our solar system and plays a crucial role in making our planet hospitable to life. Continents are formed and modified by fundamental plate tectonic processes, including volcanism, mountain-building, collisions with other continental masses, and rifting or breakup of supercontinents. Understanding the evolution of continental lithosphere (that is, the crust and uppermost mantle beneath continents) through time remains one of the most important challenges in Earth science. This project will study the processes that have shaped the continental lithosphere beneath the New England Appalachians through geologic time using a multi-disciplinary approach that includes seismic imaging of the crust and upper mantle, the analysis of geological structures, and dating the motion on ancient faults. The investigators will carry out detailed imaging using seismic waves from distant earthquakes measured at seismometers deployed in two linear arrays (one across New York and Massachusetts, the other across Vermont, New Hampshire, and Maine). They will pair their seismic imaging work with studies of geologic structures exposed at the surface that will provide essential context on its plate tectonic history. The integration of information obtained from both approaches will illuminate the processes that have shaped the lithosphere beneath New England through the geologic past, opening a window into how continental lithosphere evolves as a part of the Earth’s plate tectonic system.This project aims to understand how rifting, subduction, and terrane accretion have shaped lithospheric structure beneath New England: Does the lithosphere preserve a record of subduction and accretion or does lithospheric structure heal over time? How do subsequent accretion events overprint the structure of earlier collisions? How did Mesozoic rifting affect the structure of Paleozoic accretions? Are recent to ongoing mantle processes modifying the lithospheric structure? The investigators will analyze data from the NEST (New England Seismic Transects) experiment, a deployment of ~25 broadband seismometers that is configured to resolve crustal targets on length scales that are appropriate for direct linkage with geological structures. They will apply a suite of imaging techniques (receiver function analysis, body wave travel time analysis, wavefield migration imaging, and SKS splitting measurements) that will provide a comprehensive view of both the isotropic and anisotropic structure of the New England crust and upper mantle, including the region underlain by the so-called Northern Appalachian Anomaly (NAA). The U-Pb geochronology work will focus on the identification and analysis of xenocrystic (inherited) cores in zircon grains from arc plutonic and volcanic rocks from the Shelburne Falls and Bronson Hill arcs, in order to understand the history and timing of Taconic (and later) orogenic processes. The investigators will also conduct field work and structural analyses to investigate the extent and relative timing on frontal thrusts of basement massifs and the Taconic Mountains in western New England and New York, and the Connecticut Valley border fault system in central New England. They will constrain the timing of deformation by collecting and dating samples via 40Ar/39Ar geochronology from these regions, in order to determine how widespread reactivation of old faults (and displacement on new faults) has been throughout the region. The project emphasizes undergraduate involvement in cross-disciplinary research and field work, particularly by participants from groups that have been historically underrepresented in Earth science, enabled by collaboration among faculty at a liberal arts college and research institutions.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.