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: 2015604
• 负责人: Matthew McKay
• 金额: $ 12.3万
• 依托单位: Missouri 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 2024-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2015604&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.

造山运动通常是由构造板块之间的碰撞造成的。在造山过程中，曾经深埋的岩石经常被挖掘出来并被运送到地球表面。该项目将调查爱达荷州中部的一个地区，该地区经历了海洋岛屿系统和北美大陆之间的古代碰撞，这导致了深埋40公里的岩石的挖掘。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出来，随后沉入下面的地幔，导致上覆岩石向地表隆起，或者是否沿着陡峭断层的运动导致了它们的折返。为了评估这些假设，将收集和评估岩石样本，以提供有关这些深层岩石何时以及以何种速度向地表平移的信息。该项目的结果将提高我们对板块碰撞和造山活动期间活跃的构造过程的理解，这些过程可能影响地质资源的分布和质量。该项目将通过为华盛顿州立大学和密苏里州州立大学的本科生和研究生提供实地学习和研究机会，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学生开发适合年级的演示文稿，向他们介绍当地的地质学，并允许讨论STEM职业生涯。量化碰撞构造过程中挖掘出深层变质岩的过程的贡献是理解山脉带如何演变的基础。在爱达荷州中部的北美科迪勒拉造山带中，Salmon River缝合带是一个约30千米宽的区域，经历了侏罗纪-早白垩世收缩变形，与火山岛弧与北美大陆西缘的碰撞有关。缝合带中的岩石记录了高达40公里深处的结构埋藏和随后的折返，因此是研究加积事件期间驱动高强度折返的过程的理想选择。该项目将检验两个主要假设：1）Salmon河缝合带的岩石是在岩石圈拆沉之后通过铰接去顶而被挖出的，这预测了缝合带宽度上与挖出相关的冷却以及向东增加的折返速率和幅度;或2）鲑鱼河缝合带的岩石通过前向断裂逆冲扩展被挖出，它预测了一个系统的向西迁移的时间高峰埋葬，最初的折返，和运动的逆冲断层。为了验证这些假设，本项目将整合结构分析和地质年代学领域的关系，时间和压力-温度条件的高峰变质作用，和多部分温度-时间路径作为一个代理的挖掘相关的冷却。这个项目的结果将影响我们的地球动力学过程中的增生事件的理解。此外，项目成果将解决岩石圈移动的存在，规模和影响，以及与增生相关的埋藏和上覆中地壳的相关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知识价值和更广泛的影响审查标准进行评估，被认为值得支持。