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

阿拉斯加的德纳利断层是一条长2000公里的活动断裂带，主要为水平运动(走滑)断裂带，与北美和太平洋构造板块之间的边界有关。断裂带是地壳中的裂隙，可以充当从极深(20英里)处输送水的管道。主要的问题是，这个断层深入地壳的深度有多深，断层的多股在深度上是如何连接的，以及沿其踪迹的断层类型的变化如何影响深层地下水的循环。为了了解这些未知因素，这项研究将检查沿德纳利断裂带喷发的泉水的同位素地球化学。这些结果将增进对德纳利断层的了解，特别是关于断层链的深度和相互关联性，对地震灾害以及地热和矿产资源的分布具有重要影响。这项研究促进了阿拉斯加和犹他州研究人员之间的新的跨学科合作，并促进了本科生的教育和培训，包括那些来自代表不足的群体的学生。这个为期一年的项目将检查沿德纳利断层系统和沿张开逆冲断层释放的泉水的氦同位素特征。该断裂系统自东向西从转换断裂向大陆走滑断裂过渡，并提供了一个检验大陆走滑断裂性质假说的系统，并将逆冲断层扩展为地幔流体的潜在通道。来自泉水的氦同位素(3He/4He)、碳、氧、氢稳定同位素和水化学数据将限制地幔流体对检验相互竞争的地球物理模型的贡献，这些模型涉及Denali断裂系统地壳规模的变化，深度展布断裂与Denali断裂主线的连接，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，沿着阿拉斯加德纳利断层系统的踪迹选择了10个泉水，其中包括6个富含二氧化碳的泉水，这些泉水沉积了钙华，以最大限度地捕获来自深部流动路径的信号。除了促进对流体-断层相互作用的结构和地球化学记录的理解外，这项研究还为未来沿德纳利断层系统、其他区域结构和负责阿拉斯加地热资源的构造-岩浆制度的其他泉水进行氦同位素分析提供了框架。该奖项反映了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。

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.