Collaborative Research: Investigating Lithospheric Evolution Beneath the Southern and Northeastern United States

纵观地球-S的历史，组成岩石圈的构造板块汇聚成超级大陆，然后在数亿年的时间尺度上撕裂。靠近墨西哥湾沿岸的美国南部和与大西洋接壤的美国东部经历了两个超级大陆形成和解体的周期。这些碰撞和裂谷事件改变了北美板块的地壳和地幔岩石圈，在一些地区增厚了这些层，在另一些地区减薄了这些层，并通过排列矿物颗粒和熔化少量岩石产生了独特的结构。在这个项目中，我们将利用地震波构建地壳和地幔岩石圈的三维模型，并对这些模型进行解释，以更好地了解大陆碰撞和裂谷如何影响大陆岩石圈。这项工作的目标是提高美国南部和东部地壳和地幔结构的分辨率，以便更好地了解通过最后一次威尔逊旋回的岩石圈演化和改造。北美大陆的南缘和东缘经历了两个完整的威尔逊造山和裂谷旋回，在这些地区的地壳和地幔岩石圈中留下了不同的变形和岩浆活动特征。然而，地壳和地幔结构的许多方面在与区分造山作用、裂谷作用和其他过程(如热点相互作用)相关的尺度上仍然知之甚少。利用美国国家科学基金会地球天文台阵/可移动台阵(TA)的数据，我们建议对地壳和地幔的地震结构进行新的细节成像。我们将重点关注两个地区：一个横跨克拉通南部边缘、整个瓦奇塔造山带和墨西哥湾沿海平原，另一个包括克拉通东部边缘、阿巴拉契亚山脉中部和北部以及大西洋海岸。我们将使用TA台站的地震数据，辅以其他临时和永久宽带台站，使用Sp和Ps接收函数来成像地壳和地幔不连续，建立基于瑞利波、Love波和横波分裂分析的三维各向异性模型，并通过联合分析和反演将这些数据和方法整合在一起。地震模型将被用来约束由于造山和裂谷作用的最后一幕而导致的地壳和地幔岩石圈的变形方式和几何形状。这一解释将以浅层地壳形变的地质和活动源指标以及整个区域岩浆作用的类型和年龄为指导，同时铭记，地壳和地幔结构的某些方面可能反映上一次造山和大陆裂谷循环之前或之后的事件。造山作用和裂谷作用对岩石圈影响的差异将在研究区域之间和区域内进行比较。拟议的项目将支持休斯顿大学和布朗大学研究生的教育和职业发展。它还将为本科生和研究生课程中的本科高级论文、实验室练习和小组研究项目以及与当地公立学校的科学推广活动做出贡献。来自不同背景的学生将被招募参与这项研究。

Throughout Earth?s history, the tectonic plates that make up the lithosphere have converged to form super-continents and then pulled apart over time-scales of hundreds of millions of years. The southern U.S. near the Gulf Coast and the eastern U.S. bordering the Atlantic experienced two cycles of super-continent formation and break-up. These episodes of collision and rifting altered the crust and mantle lithosphere of the North American plate, thickening these layers in some regions, thinning them in others, and producing distinctive structures by aligning mineral grains and melting small amounts of rock. In this project we will use earthquake waves to construct three-dimensional models of the crust and mantle lithosphere, and we will interpret these models to better understand how continental collision and rifting affect continental lithosphere.The goal of this work is to improve resolution of crust and mantle structure in the southern and eastern U.S. in order to better understand lithospheric evolution and modification through the last Wilson cycle. The southern and eastern margins of the North America continent experienced two complete Wilson cycles of orogeny and rifting, leaving varied signatures of deformation and magmatism in the crust and mantle lithosphere of these regions. However, many aspects of crust and mantle structure remain poorly known at the scales relevant to distinguishing the effects of orogeny, rifting, and other processes such as hotspot interaction. Using data from the NSF EarthScope USArray/Transportable Array (TA), now completed in the contiguous U.S., we propose to image crust and mantle seismic structure in new detail. We will focus on two regions: one spanning the southern craton edge, the entire Ouachita orogeny and the Gulf of Mexico coastal plain, and the other containing the eastern craton edge, the central and northern Appalachians, and the Atlantic coast. We will use seismic data from TA stations, supplemented by other temporary and permanent broadband stations, to image crustal and mantle discontinuities using Sp and Ps receiver functions, construct 3-D anisotropic models based on Rayleigh wave, Love wave and shear-wave-splitting analyses, and we will integrate these data and methods through joint analyses and inversions. The seismic models will be used constrain the style and geometry of deformation in the crust and mantle lithosphere due to the last episodes of orogeny and rifting. This interpretation will be guided by geological and active source indicators of deformation in the shallow crust and by the type and age of magmatism across the region, bearing in mind that some facets of crust and mantle structure may reflect events that predated or followed the last cycle of orogeny and continental rifting. Variations in the impact of orogeny and rifting on the lithosphere will be compared between and within the study regions. The proposed project will support the education and career development of graduate students at the University of Houston and at Brown. It will also contribute to undergraduate senior theses, lab exercises and group research projects in undergraduate and graduate courses, and to science outreach activities with local public schools. Students from diverse backgrounds will be recruited to participate in this research.