Collaborative Research: Geochemical Imaging of Post-Pangean Lithospheric Structure in the Southern Appalachians

阿勒卡尼亚-海西尼亚-瓦里斯坎联合造山运动（大约3亿年前）标志着地球的顶峰。这是超大陆（泛大陆）形成和扩散的最新例证。南阿巴拉契亚山脉记录了盘古大陆形成的一个关键地带，因为它们标志着三个现代大陆（北美、南美和非洲）前身的碰撞。盘古大陆随后的断裂产生了这三个大陆，并随着大西洋的扩张而继续。来自佛罗里达大学和密西西比州立大学的教师和学生组成的研究小组正在对一组花岗岩火成岩的空间分布、年龄和地球化学组成进行详细的地球化学调查，这些火成岩侵入了10亿年前形成于山带根部的结晶岩石，现在分布在乔治亚州、佛罗里达州、阿拉巴马州和南卡罗来纳州。这些花岗岩体是两个古代海洋（Iapetus和Rheic）毁灭的唯一已知的岩浆表现。了解花岗岩体的年龄和起源对于理解大陆的生长，特别是在泛古陆超大陆旋回期间大陆地壳是如何交换的至关重要。特别是，他们的重点是确定边界和有效的构造和岩浆过程，这些过程具有最终形成盘古大陆的大陆汇合的特征。在地球物理资料的基础上，初步确定了会聚边界发生在苏万尼缝合带上；拟议的缝合线与佛罗里达州和佐治亚州的边界几乎平行。在盘古大陆断裂之后，一个新的边界被建立起来，盘古大陆产生了现在的大西洋和非洲、南美和北美大陆。断裂的位置尚不清楚，但该项目进一步限制了断裂的位置。参与该项目的教师和学生（研究生和本科生）正在对来自下大陆地壳熔融的花岗岩进行采样，作为阿勒卡尼构造运动和岩浆活动之间时空关系的综合地质年代学、热年代学和地球化学研究的一部分。这些数据将为研究盘古碰撞带岩石圈结构和演化提供独特的约束条件。所选择的地区包含大量的阿勒卡尼亚岩浆岩，这些岩浆岩侵入了一系列通常被认为是古北美洲一部分的前阿勒卡尼亚地体，以及一些被认为基本上是冈瓦纳或近冈瓦纳的地体（例如，非洲或南美洲）。利用岩体的铀铅锆石年代学和同位素组成对苏万尼缝合线两侧进行地球化学成像，以更好地了解不同大陆碎片在4-D上的并置。这种岩石圈结构的“地球化学成像”是：1)为该地区正在进行的地球物理研究提供了重要的补充，这是地球范围计划在北美的使命不可或缺的一部分；2)为大规模岩浆海洋封闭的全球构造之谜提供了重要的见解；3)有助于我们对墨西哥湾东部石油省基底结构的理解。该项目支持佛罗里达大学和密西西比州立大学研究人员之间的重要区域科学合作。它有助于培养STEM学科的研究生和本科生。由于两所大学的学生人口统计数据，它有可能有助于扩大代表性不足的群体参与地球科学。这项研究正在进行的结果正在指南、专业会议专题讨论会和科学出版物中进行交流。该项目由美国国家科学基金会大地构造和地球观测项目资助

The combined Alleghanian-Hercynian-Variscan orogeny (approximately 300 million years ago) marks the culmination of Earth?s most recent example of the formation and dispersal of a supercontinent (Pangea). The southern Appalachian Mountains record a critical zone in the formation of Pangea because they mark the collision of the precursors of three modern continents (North America, South America, and Africa). Pangea's subsequent rupture produced these three continents and continues with the expansion of the Atlantic Ocean. The research team of faculty and students from the University of Florida and Mississippi State University are conducting detailed geochemical investigations into the spatial distribution, ages, and geochemical compositions of a suite of granitic igneous bodies that intruded crystalline rocks that formed up to one billion years earlier in the roots of the mountain belt and are now in Georgia, Florida, Alabama, and South Carolina. These granitic bodies are the only known magmatic manifestation of the destruction of two ancient oceans (Iapetus and Rheic). Understanding the age and origin of the granitic bodies is critical to understanding the growth of continents in general and, particularly, how continental crust was exchanged during the Pangean supercontinent cycle. In particular, they are focusing on identifying the boundary and the operative tectonic and magmatic processes that characterized convergence of the continents that ultimately formed Pangea. The convergent boundary has tentatively been identified on the basis of geophysical data to occur in a zone known as the Suwannee suture; the proposed suture lies sub-parallel to the Florida-Georgia border. A new boundary was established after the rupture of Pangea, which produced the modern Atlantic Ocean and the African, South American, and North American continents. The location of this rupture is not known, but is being further constrained by this project.Faculty and students (graduate and undergraduate) involved in this project are sampling the granitic rocks derived from melting of the lower continental crust as part of an integrated geochronologic, thermochronologic, and geochemical study of the spatial and temporal relationships between Alleghanian tectonism and magmatism. These data will provide unique constraints on lithospheric structure and evolution in the Pangean collision zone. The region chosen contains numerous Alleghanian magmatic rocks that intrude a range of pre-Alleghanian terranes typically considered part of ancient North America, as well as some considered to be fundamentally Gondwanan or peri-Gondwanan (e.g., African or South American). The uranium-lead zircon geochronology and isotopic composition of the granitic bodies are being used to geochemically image both sides of the proposed Suwannee suture to better understand the juxtaposition of the different continental fragments in 4-D. This "geochemical imaging" of lithospheric structure is: 1) providing a critical complement to on-going geophysical studies in this region that are integral to the mission of the EarthScope Program in North America, 2) providing important insight into the global tectonic enigma of largely amagmatic ocean closures, and 3) contributing to our understanding of the basement architecture of the eastern Gulf of Mexico petroleum province. The project supports an important regional scientific collaboration between researchers at the University of Florida and Mississippi State University. It is contributing to the training of graduate and undergraduate students in a STEM discipline. Because of the demographics of the student populations at both universities, it has the potential to contribute to the broadening of participation of underrepresented groups in the geosciences. The ongoing results of this research are being communicated in guidebooks, professional meeting symposia, and refereed scientific publications.This project is being supported by the NSF Tectonics and EarthScope Programs