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

地球的陆壳被认为是在离散的地质时间间隔内形成的，在那里特殊的地质过程导致了地壳的形成和增长。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并组装成大陆和超大陆。位于蒙大拿州西南部怀俄明省西北边缘的岩石记录了北美大陆形成期间的这些过程。该项目将利用综合方法，应用岩石学、地球化学和地质年代学工具来确定地壳增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理解大陆组装期间地壳保存和增长之间的平衡。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课堂实地考察和实验室课程。将通过开发和改进新的地质年代学技术以及为学生提供最先进的分析设备培训来加强研究和教育的基础设施。该项目的新年龄数据将被整合到蒙大拿州目前的地质制图工作中，以更好地解释岩石单元和构造关系的总体年龄。外展工作将包括为在蒙大拿州西南部举办夏季实地课程的全国学校的学生和教职员工举办非正式的科学讲座。新太古代和古元古代的两个间歇期代表着北美和世界各大洲生长和聚集的主要时期。这些时期被推断为与陆壳增强生产的时期相对应。该项目将审查在这些时间间隔内为生产新的大陆地壳而运行的工艺，以及为重新加工和组装该地壳而运行的工艺。蒙大拿州西南部怀俄明省西北部边缘是这项研究的理想天然实验室，因为它由一套不同的变质沉积石榴石岩性组成，这些岩性适合于压力-温度-时间研究，以及包含年代较差的层间变质火成岩。这项拟议的工作将应用蒙大拿州变质沉积地体拉莱姆基底岩芯隆起中新太古代至古元古代岩石的变质相平衡和年代学的综合方法，以建立在这些时间间隔内的相对地壳生长与改造。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(U-Pb)地学和热年代学、锆石和独居石的Hf和Nd(Hf)和Nd(Nd)同位素分析以及石榴石的Lu-Hf/Sm-Nd(Lu-Hf/Sm-Nd)测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、岩浆和变质历史，并直接制约怀俄明省西北部的增长和改造历史。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.