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南部落基山脉和里约热内卢格兰德裂谷形成过程中结构的变形历史。通过详细的实地考察和实验室分析，研究人员将评估断层带运动的时间和方向，以及流体在削弱这些断层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报告传播研究成果。Sangre de Cristo山脉的研究区域与每年接待超过50万游客的大沙丘国家公园接壤，调查人员将与公园地质学家交流研究结果，以帮助提供额外的地质背景，以进行教育推广。该项目还将支持科罗拉多州立大学地球科学系为期三年的跨学科研究研讨会，该研讨会以学生为主导，研究桑格德克里斯托山脉。本次研讨会将涉及至少15名学生（研究生和本科生）和7名教师来自整个部门，让学生接触到一个高度跨学科的研究方法。项目区位于Sangre de Cristo山脉，暴露了落基山脉地区最深的Laramide和里约热内卢大裂谷构造水平，为研究脆性-塑性过渡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该地区的断层，使拉拉米造山运动期间在相对较低的应力下发生收缩变形，并在里约热内卢大裂谷发育期间在不适合破坏的构造上发生伸展恢复。拉腊米造山带的广泛缩短可能是由于流体相关的弱化作用，逆冲断层的伸展重新激活可能是造山带坍塌的一个基本组成部分。研究人员将使用多学科研究方法来验证他们的假设，包括地质测绘、微观结构分析、电子背散射衍射、傅立叶变换红外光谱、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。该项目生成的数据将为地壳最强部分附近与板内缩短相关的应力、温度、变形机制和流体参与提供关键约束。该研究还将揭示Laramide收缩与里约热内卢大裂谷伸展之间的关系，以及剪切带几何和流变学对伸展再激活的作用，为理解其他造山带逆冲构造的伸展再激活提供框架。该奖项反映了美国国家科学基金会的法定使命，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。

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.