EAGER: Collaborative Research: Mantle fluid contribution to springs along the Denali Fault System: Constraints on the crustal scale nature of the main strand and splays

阿拉斯加的德纳里断裂带是一条长2000公里的活动断层，主要是水平运动（走滑）断裂带，与北美和太平洋构造板块的边界有关。断裂带是地壳上的断裂，可以作为管道从深处（20英里）输送水。目前存在的主要问题是，这条断层深入地壳的深度有多深，断层的多股是如何在深处连接起来的，以及沿其轨迹的断层样式的变化是如何影响深层地下水的循环的。为了了解这些未知因素，这项研究将检查沿德纳里断裂带流出的泉水的同位素地球化学。研究结果将增进对德纳里断裂带的了解，特别是对断裂带的深度和相互联系的了解，对地震危险以及地热和矿产资源的分布具有重要意义。这项研究促进了阿拉斯加和犹他州研究人员之间新的跨学科合作，并促进了对本科生的教育和培训，包括那些来自代表性不足群体的学生。这个为期一年的项目将研究沿迪纳里断裂系统和沿展向逆冲断层流出的弹簧的氦同位素特征。该断裂系统由一条转换断层向东向西过渡为一条大陆走滑断层，为验证大陆走滑断层和展向逆冲断层作为幔源流体潜在通道的性质假设提供了一个系统。氦同位素（3He/4He）、碳、氧和氢稳定同位素以及泉水的水化学数据将约束地幔衍生流体的贡献，以测试Denali断裂系统地壳尺度变化的相互竞争的地球物理模型，以及与Denali断裂主链连接的深展断层，以及下伏俯冲板块几何形状对流体同位素组成的可能影响。在这项探索性研究中，沿着阿拉斯加德纳里断层系统的轨迹选择了10个泉，其中包括6个富含二氧化碳的泉，这些泉可以沉积钙华，以最大限度地从深层流动路径捕获信号。除了推进对流体-断层相互作用的构造和地球化学记录的理解之外，这项研究还为未来沿迪纳里断裂系统、其他区域构造和阿拉斯加地热资源的构造-岩浆体系的其他弹簧的氦同位素分析提供了一个框架。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。

The Denali Fault in Alaska is a 2000-km-long, active, predominately horizontal motion (strike-slip) fault zone associated with the boundary between the North American and the Pacific tectonic plates. Fault zones are breaks in the Earth’s crust that can act as conduits for transport of water from great depths (20 miles). Major questions exist about how deeply this fault penetrates into the crust, how the multiple strands of the fault are connected at depth, and how the changes in the style of faulting along its trace impact the circulation of deep groundwater. To inform these unknowns, this study will examine the isotope geochemistry of springs that discharge along the Denali fault zone. Results will improve the understanding of the Denali Fault, particularly with respect to the depth and interconnectedness of fault strands, with important implications for earthquake hazards and the distribution of geothermal and mineral resources. This study fosters a new interdisciplinary collaboration between investigators in Alaska and Utah, and advances education and training for undergraduate students, including those from underrepresented groups.This one-year project will examine the helium isotope signature of springs discharging along the Denali Fault system and along splay thrust faults. The fault system transitions east-to-west from a transform fault to a continental strike-slip fault, and provides a system to test hypotheses on the nature of continental strike-slip faults and splay thrust faults as potential conduits for mantle-derived fluids. Helium isotope (3He/4He), carbon, oxygen, and hydrogen stable isotope, and water chemistry data from springs will constrain the contribution of mantle-derived fluids to test competing geophysics models on variations in the crustal scale of the Denali Fault system, the depth splay faults connect with the master strand of the Denali Fault, and possible influences of the underlying subducting slab geometry on fluid isotopic composition. For this exploratory study, ten springs were selected along the trace of the Denali Fault system in Alaska, including six CO2-rich springs that deposit travertine to maximize capturing signals from deep flow paths. In addition to advancing understanding of the structural and geochemical record of fluid-fault interaction, this study provides a framework for future helium isotopic analysis of additional springs along the Denali Fault system, other regional structures, and the tectonic-magmatic regime responsible for geothermal resources across Alaska.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.