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

阿勒格尼亚-海西-瓦里斯坎联合造山运动(约3亿年前)标志着地球的顶峰--S，这是超级大陆(盘古大陆)形成和扩散的最新例证。南部阿巴拉契亚山脉记录了盘古大陆形成的关键地带，因为它们标志着三个现代大陆(北美、南美洲和非洲)的前驱物质的碰撞。盘古大陆随后的破裂形成了这三个大陆，并随着大西洋的扩张而继续下去。佛罗里达大学和密西西比州立大学的教职员工和学生组成的研究小组正在对一套花岗岩火成体的空间分布、年龄和地球化学成分进行详细的地球化学调查，这些火成体侵入了早在10亿年前形成于山带根部的结晶岩石，现在位于佐治亚州、佛罗里达州、阿拉巴马州和南卡罗来纳州。这些花岗岩是已知的两个古代大洋(伊阿普图斯和瑞克)被破坏的唯一岩浆表现。了解花岗岩体的年龄和成因对于了解大陆的总体增长，特别是了解大陆地壳在盘古超大陆旋回期间是如何交换的至关重要。特别是，他们的重点是确定边界和活动的构造和岩浆过程，这些过程以最终形成盘古大陆的大陆汇聚为特征。根据地球物理数据，已经初步确定了会聚边界，该区域被称为Suwannee缝合线；拟议的缝合线与佛罗里达州和佐治亚州的边界次平行。盘古大陆破裂后，形成了现代大西洋、非洲大陆、南美洲大陆和北美大陆，形成了新的边界。这一断裂的位置尚不清楚，但受到该项目的进一步限制。参与该项目的教师和学生(研究生和本科生)正在采样来自下大陆地壳熔融的花岗岩，这是对阿勒格尼亚构造作用和岩浆活动之间的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。这些数据将为盘古碰撞带的岩石圈结构和演化提供独特的约束条件。所选择的区域包含许多阿勒冈尼亚期的岩浆岩，这些岩浆岩侵入了一系列通常被认为是古代北美的一部分的前阿勒冈尼亚期地体，以及一些被认为基本上是冈德瓦南或冈德瓦南周(例如，非洲或南美洲)的地体。花岗岩体内的铀铅锆石年代学和同位素组成被用来对拟议的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中的并置。岩石圈结构的这一“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重要补充，这些研究是北美地球望远镜计划任务的组成部分；2)提供重要的洞察，揭示主要是岩浆作用的海洋闭合的全球构造之谜；以及3)有助于我们了解墨西哥湾东部石油省的基底结构。该项目支持佛罗里达大学和密西西比州立大学的研究人员之间重要的地区性科学合作。它正在为STEM学科的研究生和本科生的培训做出贡献。由于这两所大学的学生人口结构，它有可能有助于扩大未被充分代表的群体对地球科学的参与。正在进行的这项研究的结果正在通过指南、专业会议座谈会和参考的科学出版物进行交流。这个项目得到了NSF构造和地球范围计划的支持

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