RUI: Modes of Dome Formation in the Southern Appalachians

塔卢拉福尔斯和托克斯韦圆顶是地图规模的结构特征，中断了南阿巴拉契亚蓝岭山脉的区域趋势。从地图上看，这两个穹丘与北美西部的穹丘地质结构有着惊人的相似之处，而北美西部的穹丘地质结构长期以来被认为是大陆地壳伸展和变薄的结果。然而，塔卢拉福尔斯和托克斯韦穹丘，以及沿着其他一些南阿巴拉契亚穹丘被认为是在板块会聚期间形成了主要的地壳缩短和增厚。事实上，在南阿巴拉契亚山脉中，没有任何一个地方有明显的局部地壳伸展的证据，尽管它存在于世界范围内的每一个主要山脉和板块构造边界，包括会聚（喜马拉雅山，阿尔卑斯山），转换（安纳托利亚，委内瑞拉）和发散边缘（洋中脊）。因此，在南阿巴拉契亚山脉，一个板块边缘，经历了几个阶段的碰撞和随后的裂谷，是值得注意的，因为它显示了一套独特的动态过程，或这些结构尚未被记录。该项目旨在区分记录在塔卢拉福尔斯和托克斯韦圆顶中的造山过程的竞争模型，并确定其起源。这项研究将实现NSF在社会福利方面寻求实现的许多成果，包括：妇女充分参与科学，改善科学技术，工程和数学（STEM）教育，提高公众科学素养和参与科学，以及准备和参与多元化的STEM劳动力。 该项目将最大限度地提高学生参与项目的各个方面，从实地考察和实验室分析，到数据分析和结果展示。 这些学生将接受尖端科学技术的培训，从而为地球科学的职业生涯做好更好的准备。在现场，本科生和主要研究人员将与阿巴拉契亚州立大学入门课程的学生进行现场交流，就目前正在进行的地质研究的方式和类型进行对话。研究结果将通过同行审查的出版物和在专业会议上的介绍加以传播。 在南阿巴拉契亚山脉，中地壳隆起和折返的机制和时间是未知的，这里的结晶复合体被认为是收缩特征的例子。这种解释与低角度正断层（现在被广泛接受为主要地壳伸展的位置）被识别之前的科迪勒纳变质核杂岩的解释有着惊人的相似性。中地壳岩石的伸展折返与现存的阿巴拉契亚造山模型有很大的不同，阿巴拉契亚造山模型遵循一个框架，其中所有主要结构都表现出逆冲或走滑位移。这项研究将集中在两个假定的收缩圆顶，塔卢拉福尔斯和托克斯韦圆顶，这两个圆顶横跨格鲁吉亚，北卡罗来纳州和南卡罗来纳州边界。本项目的目标是调查必要的标准，以确定时间和区分收缩和伸展相关的圆顶形成和掘出模型。为了完成这一任务，主要研究人员将确定：1）塔卢拉福尔斯和托克斯韦穹丘及其覆盖层之间边界的性质; 2）折返的时间与穹丘和构造侵位的关系; 3）这些穹丘内变质等级的变化如何分布。 该项目将包括实地和实验室结构观测以及地质和热计时测量。剪切带组构将在现场和薄片分析，以确定圆顶折返的运动学和变质条件，并与特定的构造事件使用独居石铀钍铅（U-Th-Pb）定年。剥露时间的确定将基于跨边界的相对冷却年龄，使用氩-氩（40 Ar/39 Ar）测年法测定白色云母和角闪石的年龄，以及锆石的裂变径迹测年法。

The Tallulah Falls and Toxaway domes are map scale structural features that interrupt the regional trend of the Southern Appalachian Blue Ridge mountains. In map pattern these two domes bare striking resemblance to domal geologic structures in western North America that have long been understood as the result of extension and thinning of the continental crust. However, the Tallulah Falls and Toxaway domes, along with a number of other Southern Appalachian domes are considered to have been thought to have formed major crustal shortening and thickening during plate convergence. Indeed, nowhere in the Southern Appalachians has evidence for major localized crustal extension been recognized despite its presence in every major mountain range and type of plate tectonic boundary world wide, including convergent (Himalayas, Alps), transform (Anatolia, Venezuela), and divergent margins (mid-ocean ridges). Consequently, the absence of major extension within the Southern Appalachians, a plate margin that has experienced several phases of collision and subsequent rifting, is notable either because it displays a unique set of dynamic processes, or these structures have yet to be documented. This project is aimed at distinguishing between competing models of mountain building processes as recorded in the Tallulah Falls and Toxaway domes, and to determine their origin. This research will accomplish many of the outcomes NSF seeks to achieve in terms of benefits to society, including: full involvement of women in science, improved science technology, engineering, and mathematics (STEM) education, increased public scientific literacy and engagement with science, and preparing and engaging a diverse STEM workforce. This project will maximize student involvement in all aspects of the project from field-work and laboratory analyses, to data analysis and presentation of results. These students will be trained in cutting edge scientific techniques, and consequently will be better prepared for careers in earth science. While in the field, undergraduates and the principal investigators will communicate live with students enrolled in introductory courses at Appalachian State University, allowing a dialogue both about how and what kind of geologic research is currently being conducted. Results of the study will be disseminated through peer-reviewed publications and presentations at professional meetings. The mechanism and timing of mid-crustal doming and exhumation is unknown in the Southern Appalachians, and here crystalline complexes are considered exclusively as examples of contractional features. This interpretation bares striking similarity to that of Cordilleran metamorphic core complexes prior to the recognition of low-angle normal faults, now widely accepted as the locations of major crustal extension. Extensional exhumation of mid-crustal rocks would represent a significant departure from extant models of Appalachian mountain building, which adhere to a framework wherein all major structures exhibit thrust, or strike-slip displacement. The study will focus on two supposed contractional domes, the Tallulah Falls and Toxaway Domes, which straddle the Georgia, North Carolina, and South Carolina borders. The objectives of this project are to investigate the criteria necessary to determine timing and distinguish between contraction and extension related dome formation and exhumational models. In order to accomplish the principal investigators will determine: 1) the nature of the boundaries between the Tallulah Falls and Toxaway Domes and their cover; 2) how the timing of exhumation relates to doming and structural emplacement; and 3) how metamorphic grade variation is distributed within these domes. This project will incorporate field and laboratory structural observations, and geo- and thermochronometric measurements. Shear zone fabrics will be analyzed in the field and in thin section in order to determine the kinematics and metamorphic conditions of dome exhumation, and correlated with specific tectonic events using monazite Uranium-Thorium-lead (U-Th-Pb) dating. Timing of exhumation will be based on relative cooling ages across the boundary using Argon-Argon (40Ar/39Ar) dating in white mica and amphibole, and fission track dating in zircon.