Collaborative research: Evaluating the drivers of exhumation during accretionary orogenesis: A field-based investigation in the Salmon River Suture Zone, Idaho

合作研究：评估增生造山作用期间折返的驱动因素：爱达荷州萨蒙河缝合带的实地调查

• 批准号: 2015601
• 负责人: Sean Long
• 金额: $ 19.78万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-05-15 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2015601&HistoricalAwards=false
• 关键词: Collaborative; research; Evaluating; drivers; exhumation

Mountain building events typically result from collisions between tectonic plates. During mountain building, rocks that were once deeply buried often become exhumed and transported to the Earth’s surface. This project will investigate a region of central Idaho that experienced an ancient collision between an ocean island system and the North American continent, which resulted in exhumation of rocks that were buried as deeply as 40 kilometers. This study will test whether a portion of the lower crust detached from the overlying tectonic plate and subsequently sank into the mantle below, causing the overlying rocks to be uplifted towards the surface, or alternatively whether movement along steep faults resulted in their exhumation. To evaluate these hypotheses, rock samples will be collected and evaluated to give information on when, and at what rates, these deep rocks were translated towards the surface. The results of this project will improve our understanding of the tectonic processes that are active during plate collisions and mountain building events, which can impact the distribution and quality of geologic resources. This project will improve STEM education by generating field-based learning and research opportunities for undergraduates and graduate students at Washington State and Missouri State universities. The results of this project will introduce STEM research to undergraduates each year through geology lectures. Grade-appropriate presentations will be developed for K-12 students to introduce them to their local geology and allow for the discussion of STEM careers.Quantifying the contributions of processes that exhume deep-seated metamorphic rocks during collisional tectonics is fundamental for understanding how mountain belts evolve. In the North American Cordilleran orogen in central Idaho, the Salmon River suture zone is a ~30 kilometer-wide region that experienced Jurassic-Early Cretaceous contractional deformation associated with collision of a volcanic island arc terrane with the western edge of the North American continent. Rocks in the suture zone record structural burial to and subsequent exhumation from depths as great as 40 kilometers, and therefore are ideal for investigating the processes that drive high-magnitude exhumation during accretionary events. This project will test two primary hypotheses: 1) Rocks in the Salmon River suture zone were exhumed via hinged unroofing following lithospheric delamination, which predicts contemporaneous exhumation-related cooling across the width of the suture zone and eastward-increasing exhumation rates and magnitudes; or 2) Rocks in the Salmon River suture zone were exhumed via forward-breaking thrust propagation, which predicts a systematic westward younging of the timing of peak burial, initial exhumation, and motion on thrust faults. To test these hypotheses, this project will integrate structural analysis and geochronology of field relationships, the timing and pressure-temperature conditions of peak metamorphism, and multi-part temperature-time paths as a proxy for exhumation-related cooling. The results of this project will have implications for our understanding of the geodynamic processes that operate during accretionary events. In addition, project results will address the existence, scale, and effects of lithospheric removal, and the temporal and spatial relationships between accretion-related burial and associated shortening and exhumation in the overlying middle and upper crust.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.

造山事件通常是构造板块之间碰撞的结果。在造山过程中，曾经埋得很深的岩石往往会被挖出并运往地球表面。该项目将调查爱达荷州中部的一个地区，该地区经历了一个海洋岛系与北美大陆之间的古代碰撞，导致挖掘出深达40公里的岩石。这项研究将测试下地壳的一部分是否从上覆构造板块分离并随后沉入下面的地幔，导致上覆岩石向地表隆起，或者是否沿着陡峭的断层运动导致它们的折返。为了评估这些假说，将收集和评估岩石样本，以提供关于这些深部岩石何时以及以什么速度向地表转化的信息。该项目的成果将提高我们对板块碰撞和造山事件期间活跃的构造过程的理解，这些过程可能会影响地质资源的分布和质量。该项目将通过为华盛顿州和密苏里州大学的本科生和研究生提供实地学习和研究机会来改善STEM教育。该项目的成果将每年通过地质学讲座向本科生介绍STEM研究。将为K-12年级的学生制作适合年级的演示文稿，向他们介绍当地的地质情况，并允许讨论STEM的职业生涯。量化碰撞构造期间剥离深层变质岩的过程的贡献，是理解山脉带如何演化的基础。在爱达荷州中部的北美科迪勒拉造山带，萨蒙河缝合带是一个约30公里宽的区域，经历了侏罗纪-早白垩世的收缩变形，伴随着火山岛弧地体与北美大陆西缘的碰撞。缝合带中的岩石记录了深达40公里的构造埋葬和随后的挖掘，因此是研究在吸积事件期间驱动高强度挖掘的过程的理想选择。该项目将检验两个主要假设：1)Salmon River缝合带中的岩石是在岩石圈拆沉后通过铰链剥离而被折返的，这预示着整个缝合带宽度上与折返相关的同期降温，以及向东递增的折返速率和震级；或2)Salmon River缝合带中的岩石是通过向前断裂的逆冲传播折返的，这预示着顶峰埋葬、初始折返和逆冲断层上的运动的时间系统地向西年轻。为了验证这些假说，该项目将整合野外关系的构造分析和地质年代学，峰期变质作用的时间和压力-温度条件，以及多部分温度-时间路径作为与折返相关的冷却的替代。这一项目的结果将对我们理解在吸积事件中运行的地球动力学过程具有重要意义。此外，项目成果将涉及岩石圈移除的存在、规模和影响，以及与沉积相关的埋葬和相关的中上地壳缩短和折返之间的时间和空间关系。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。