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关键组成部分。板块构造似乎在我们太阳系的所有行星体中是独一无二的，在使我们的星球适合生命方面发挥着至关重要的作用。大陆是由基本的板块构造作用形成和改变的，包括火山作用、造山、与其他大陆块的碰撞以及超级大陆的裂解或分裂。了解大陆岩石圈(即大陆之下的地壳和最上层地幔)随时间的演化仍然是地球科学中最重要的挑战之一。该项目将使用多学科方法研究新英格兰阿巴拉契亚山脉下大陆岩石圈在地质时期的形成过程，其中包括地壳和上地幔的地震成像、地质结构分析和古断层上的运动年代测定。调查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、新罕布夏州和缅因州)的地震仪上测量的远距离地震的地震波进行详细的成像。他们将把他们的地震成像工作与对地表暴露的地质结构的研究结合起来，这将提供关于其板块构造历史的基本背景。这两种方法获得的信息的整合将阐明在地质历史中塑造新英格兰之下岩石圈的过程，打开一扇窗，了解大陆岩石圈是如何作为地球板块构造系统的一部分演化的。该项目旨在了解裂谷作用、俯冲作用和地体吸积作用如何塑造新英格兰之下的岩石圈结构：岩石圈是否保留了俯冲和吸积的记录，或者岩石圈结构是否随着时间的推移而愈合？后续的吸积事件是如何叠加早期碰撞的结构的？中生代裂谷作用如何影响古生代增生构造？最近正在进行的地幔作用是否改变了岩石圈的结构？研究人员将分析来自Nest(新英格兰地震横断面)实验的数据，该实验部署了~25个宽带地震仪，配置成在适合与地质结构直接联系的长度尺度上解析地壳目标。他们将应用一套成像技术(接收函数分析、体波旅行时分析、波场偏移成像和SKS分裂测量)，提供新英格兰地壳和上地幔的各向同性和各向异性结构的全面视图，包括被所谓的北阿巴拉契亚异常(NAA)覆盖的区域。U-Pb年代学工作将侧重于从谢尔本瀑布和布朗森山弧的弧状深成岩和火山岩中鉴定和分析锆石颗粒中的捕虏晶(继承)核，以了解塔肯(和后来的)造山作用的历史和时间。调查人员还将进行实地工作和构造分析，以调查新英格兰西部和纽约的基底地块和塔科尼克山脉以及新英格兰中部的康涅狄格河谷边界断层系统的正面冲断的范围和相对时间。他们将通过40Ar/39Ar年代学从这些地区收集样品并测定其年代，从而限制变形的时间，以确定老断层(以及新断层上的位移)在整个地区重新活动的广泛程度。该项目强调本科生参与跨学科研究和实地工作，特别是来自地球科学历史上代表性不足的群体的参与者，这是由一所文理学院的教师和研究机构之间的合作促成的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.