Collaborative Research: Growth, preservation, and modification of Neoarchean to Paleoproterozoic crust, an example from the Wyoming province, Montana

地球的大陆地壳被认为是在地质时间的离散间隔中形成的，其中特定的地质过程导致了地壳的形成和生长。前寒武纪的这些时间间隔也反映了向现代板块构造过程的过渡，导致较小的地壳碎片碰撞和组装成大陆和超级大陆。蒙大拿州西南部怀俄明州西北边缘的岩石提供了北美大陆形成期间这些过程的记录。该项目将采用综合方法，应用岩石学、地球化学和地质年代学工具，确定地壳生长与随后的构造过程修改的相对贡献。这项工作的主要成果将是更好地了解大陆组装期间地壳保存和生长之间的平衡。该项目将通过支持研究生和本科生的研究来促进教学和培训，这项研究的结果将纳入本科生的实地考察和实验室课程。将通过发展和改进新的地质年代学技术，并通过为学生提供最先进的分析设备方面的培训，加强研究和教育的基础设施。来自该项目的新年龄数据将被整合到目前蒙大拿州的地质测绘工作中，以更好地解释岩石单元和结构关系的整体年龄。外展工作将包括为全国学校的学生和教师提供非正式的科学讲座，这些学校在蒙大拿州西南部进行夏季实地课程。新太古代和古元古代的两个间隔代表了北美以及世界各地大陆的生长和组装的主要时期。据推断，这些时期对应于大陆地壳产量增加的时期。本项目将研究在这些时间间隔期间产生新大陆地壳的过程以及重新加工和组装该地壳的过程。蒙大拿州西南部的怀俄明州省的西北边缘是一个理想的天然实验室，因为它是由一套不同的变沉积石榴石轴承岩性，适合压力-温度-时间的研究，以及包含层间变火成岩，日期不佳。拟议的工作将适用于一个综合的方法，变质相平衡和地质年代学的新太古代古元古代岩石在Laramide基底核心隆起的蒙大拿州变质沉积岩地体，以建立相对地壳生长与修改在这些时间间隔。所收集的数据将通过变质相平衡、锆石、独居石和钛铁矿的铀铅地质年代学和热年代学、锆石和独居石的铪和钕同位素分析以及石榴石的镥-铪/钐-钕定年来确定岩浆作用和变质作用的条件、时间、持续时间和空间范围。这种工具的集成将提供时间分辨率的岩浆和变质的历史，并直接约束的增长和修改历史的西北部怀俄明州provincial.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

Earth's continental crust is thought to have formed over discrete intervals of geologic time, where particular geologic processes resulted in enhanced crust formation and growth. These time intervals in the Precambrian also reflect a transition to modern plate tectonic processes, resulting in collision and assembly of smaller crustal fragments into continents and supercontinents. Rocks at the northwest margin of the Wyoming province in southwestern Montana provide a record of these processes during formation of the North American continent. This project will utilize an integrated approach by applying petrologic, geochemical, and geochronologic tools to establish relative contributions of crustal growth versus subsequent modification by tectonic processes. The major outcomes of this work will be a better understanding of the balance between crustal preservation and growth during continental assembly. This project will promote teaching and training by supporting graduate and undergraduate research, and results of this study will be incorporated into undergraduate class field trips and laboratory curricula. Infrastructure for research and education will be enhanced through the development and refinement of new geochronological techniques, and by providing training for students in state-of-the-art analytical equipment. New age data from this project will be integrated into current Montana state geologic mapping efforts to better interpret the overall ages of rock units and structural relationships. Outreach efforts will include presenting informal science talks for students and faculty from schools nationwide that conduct summer field courses in southwest Montana.Two intervals in the Neoarchean and Paleoproterozoic represent major periods in the growth and assembly of North America as well as continents worldwide. These periods have been inferred to correspond to times of enhanced production of continental crust. This project will examine the processes that have operated during these time intervals to produce new continental crust as well as the processes operating to rework and assemble this crust. The northwest margin of the Wyoming province in southwestern Montana is an ideal natural laboratory for this study because it is comprised of a diverse suite of metasedimentary garnet-bearing lithologies that are amenable to Pressure-temperature-time studies, as well as containing interlayered meta-igneous rocks that are poorly dated. The proposed work will apply an integrated approach of metamorphic phase equilibria and geochronology of Neoarchean to Paleoproterozoic rocks in the Laramide basement-cored uplifts of the Montana Metasedimentary Terrane to establish relative crustal growth versus modification during these time intervals. Data collected will determine the conditions, timing, duration, and spatial extent of magmatism and metamorphism through metamorphic phase equilibria, Uranium-Lead (U-Pb) geo- and thermochronology of zircon, monazite, and titanite, Hafnium (Hf) and Neodymium (Nd) isotopic analysis of zircon and monazite, and Lutetium-Hafnium/Samarium-Neodymium (Lu-Hf/Sm-Nd) dating of garnet. This integration of tools will provide temporal resolution magmatic and metamorphic histories and directly constrain the growth and modification history of the northwestern Wyoming province.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.