Collaborative Research: Brittle-plastic deformation, fluid-rock interaction, and extensional reactivation along Laramide thrust faults in the Sangre de Cristo Mountains, Colorado

这个合作项目调查了科罗拉多州南部落基山脉和里奥格兰德裂谷形成过程中涉及的构造的变形历史。通过详细的野外工作和实验室分析，研究人员将评估沿断裂带运动的时间和方向，以及流体在削弱这些带和促进构造活动方面的作用。这些结果将帮助地球科学家更好地了解岩石强度如何影响基本的造山过程。该项目将直接支持三名科罗拉多州立大学研究生和三名华盛顿与李大学本科生的论文工作，他们将通过出版物和会议演示来传播研究成果。Sangre de Cristo山脉的研究区域毗邻大沙丘国家公园，该公园每年接待超过50万游客，调查人员将与公园地质学家交流研究结果，以帮助为教育宣传提供额外的地质背景。该项目还将支持科罗拉多州立大学地球科学系内由学生领导的关于Sangre de Cristo山脉的跨学科研究研讨会，为期三年。这次研讨会将有至少15名学生(研究生和本科生)和7名来自整个系的教职员工参加，让学生接触到高度跨学科的研究方法。Sangre de Cristo山脉项目区暴露了落基山脉地区一些最深的拉拉米德和里奥格兰德裂谷构造水平，为研究脆性-塑性转变附近的变形提供了难得的机会。研究人员假设，流体-岩石相互作用削弱了这一地区的断层，使拉拉米德造山期间以相对较低的应力发生收缩变形，并在里奥格兰德裂谷发育期间发生伸展重新激活，而不是以最佳的破裂方向定位。拉拉米德造山带的广泛缩短可能是由流体相关的减弱所促进的，而逆冲断层的伸展重新激活可能是造山坍塌的基本组成部分。研究人员将使用包括地质填图、微结构分析、电子背向散射衍射、傅里叶变换红外光谱、稳定同位素分析、流体包裹体分析、地球化学和地质/热年代学在内的多学科研究方法来验证他们的假设。该项目产生的数据将提供与地壳最强部分附近的板内缩短相关的应力、温度、变形机制和流体参与的关键约束条件。这项研究还将阐明拉莱姆收缩和里奥格兰德裂谷伸展之间的关系，以及剪切带几何学和流变学在伸展重新激活中的作用，为理解其他造山带中推覆的伸展重新激活提供一个框架。这一奖项反映了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。

This collaborative project investigates the deformation history of structures involved in formation of the Rocky Mountains and Rio Grande rift in southern Colorado. Through detailed fieldwork and laboratory analyses, the investigators will evaluate the timing and directions of motion along fault zones and the role of fluids in weakening these zones and facilitating tectonic activity. These results will help geoscientists better understand how rock strength affects fundamental mountain-building processes. This project will directly support thesis work for three Colorado State University graduate students and three Washington and Lee University undergraduate students, who will disseminate research results via publications and conference presentations. The study area in the Sangre de Cristo Mountains borders Great Sand Dunes National Park, which receives over half a million visitors each year, and the investigators will communicate research results with the park geologist to help provide additional geological context for educational outreach. This project will also support three years of an interdisciplinary student-led research seminar on the Sangre de Cristo Mountains within the Colorado State University Department of Geosciences. This seminar will involve at least 15 students (graduate and undergraduate) and 7 faculty members from across the Department, exposing students to a highly interdisciplinary approach to research. The project area in the Sangre de Cristo Mountains exposes some of the deepest Laramide and Rio Grande rift structural levels in the Rocky Mountain region, offering a rare opportunity to investigate deformation near the brittle-plastic transition. The investigators hypothesize that fluid-rock interactions weakened faults in this region, allowing contractional deformation to take place at relatively low stresses during the Laramide orogeny and extensional reactivation to occur on structures not optimally oriented for failure during development of the Rio Grande rift. Widespread shortening across the Laramide orogen may have been facilitated by fluid-related weakening, and extensional reactivation of thrust faults may represent a fundamental component of orogenic collapse. The investigators will test their hypotheses using a multidisciplinary research approach that includes geologic mapping, microstructural analysis, electron backscatter diffraction, Fourier transform infrared spectroscopy, stable isotope analysis, fluid inclusion analysis, geochemistry, and geo/thermochronology. Data generated in this project will provide key constraints on the stresses, temperatures, deformation mechanisms, and fluid involvement associated with intraplate shortening near the strongest part of the crust. This research will also shed light on the relations between Laramide contraction and Rio Grande rift extension and the role of shear zone geometry and rheology on extensional reactivation, providing a framework for understanding extensional reactivation of thrusts in other orogens.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.