Structural evolution of the Atacama fault system, northern Chile: Insights into rheology and strain in a magmatic arc during oblique convergence

该项目研究了Atacama断层系统的位移历史和力学行为，Atacama断层系统是沿智利北部海岸Cordillera早白垩世岩浆弧切割的主要构造结构。弧内构造，如阿塔卡马断裂系统，在收敛边界的板块运动中起着关键作用，但其发展仍存在很大的不确定性。该研究的社会效益包括在科罗拉多州立大学和智利天主教大学的地球科学教师和本科生/研究生之间开展新的合作。来自科罗拉多州立大学和智利天主教大学的10名学生参加了一项联合实地测绘计划，该计划为研究奠定了基础，并为学生提供了高影响力的学习经验。该项目的资助有助于扩大代表性不足的群体参与重要的科学、技术、工程和数学（STEM）学科，为科罗拉多州立大学的一名女博士生提供支持。这笔资金还支持一位早期职业首席研究员的研究项目。该研究为了解阿塔卡马断层系统沿线的经济铜铁金矿提供了一个新的框架，并将通过针对阿塔卡马矿业社区的实地考察来展示结果。该项目的主要科学目标是：a)确定阿塔卡马断层系统的滑动时间、幅度和速率；b)确定阿塔卡马断层系统的岩浆活动与变形之间的时空关系；c)确定阿塔卡马断层系统脆塑性过渡附近的流变学和变形条件。重建主要地质构造的滑动历史，如阿塔卡马断层系统，对于理解斜辐合如何在俯冲带上方划分是必不可少的，并且需要断层流变学和岩浆活动与变形之间的关系的信息，以了解应变如何以及为什么局限于上覆板块。阿塔卡马断裂系是安第斯山脉中生代最重要的构造之一，对经济金属矿床起着重要的控制作用。尽管具有重要意义，但由于该地区缺乏详细的地质测绘和地质年代学，人们对阿塔卡马断裂系统的构造发育知之甚少。在初步的现场工作中，项目研究人员发现了明显的偏移标记和许多运动前、同步和运动后的火成岩单元，它们为解决滑动的大小、时间和速率提供了巨大的潜力。他们还发现了广泛存在脆性-塑性变形的证据，使他们能够评估断层系统的流变学和峰值强度。除了建立安第斯山脉中部边缘中生代构造演化的关键约束条件外，该研究还将为岩浆弧内斜向辐合如何调节提供重要的见解。为了实现提议的目标，研究团队正在使用多学科研究方法，包括地质测绘、U-Pb地质年代学、40Ar/39Ar和(U-Th)/He热年代学、微观结构分析、电子背散射衍射、ti -in-石英和氧同位素地热测量以及傅里叶变换红外光谱。这项研究是与智利天主教大学的智利地质学家合作进行的，他们在实地测绘和结构数据分析方面发挥着重要作用。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 project addresses the displacement history and mechanical behavior of the Atacama fault system -- a major tectonic structure that cuts along the Early Cretaceous magmatic arc in the Coastal Cordillera of northern Chile. Intra-arc structures such as the Atacama fault system play a critical role in accommodating plate motion at convergent boundaries, yet significant uncertainty remains surrounding their development. Societal benefits of the research include the development of a new collaboration between geoscience faculty and undergraduate/graduate students from Colorado State University and Pontificia Universidad Catolica de Chile. Ten students from Colorado State University and Pontificia Universidad Catolica de Chile are participating in a joint field-mapping program that comprises a foundation for the research and provides a high-impact learning experience for the students. Funding for this project contributes to broadening of participation of underrepresented groups in an important Science, Technology, Engineering and Mathematics (STEM) discipline by providing support a female doctoral student from Colorado State University. The funding also supports the research program of an early-career principal investigator. The research provides a new framework for understanding economic copper-iron-gold deposits located along the Atacama fault system, and the results will be presented by a field trip that targets the Atacama mining community.The main scientific goals of this project are to: a) determine the timing, magnitude, and rate of slip across the Atacama fault system, b) determine the spatial and temporal relationship between magmatism and deformation along the Atacama fault system, and c) determine the rheology and deformation conditions near the brittle-plastic transition along the Atacama fault system. Reconstructing the slip histories of major geologic structures such as the Atacama fault system is essential for understanding how oblique convergence is partitioned above subduction zones, and information on fault zone rheology and the relationship between magmatism and deformation is needed to understand how and why strain localizes in the overriding plate. The Atacama fault system is one of the most important Andean Mesozoic structures, and it played a major role in controlling economic metal deposits. Despite its significance, the tectonic development of the Atacama fault system is poorly understood due to the lack of detailed geologic mapping and geochronology in the region. During their preliminary fieldwork the project researchers discovered distinct offset markers and numerous pre-, syn-, and post-kinematic igneous units that offer great potential for addressing the magnitude, timing, and rate of slip. They also identified evidence for widespread brittle-plastic deformation, allowing them to evaluate the rheology and peak strength of the fault system. In addition to establishing critical constraints on the Mesozoic tectonic evolution of the central Andean margin, this research will provide important insight into how oblique convergence is accommodated within magmatic arcs. To address the proposal objectives, the research team is using a multidisciplinary research approach that includes geologic mapping, U-Pb geochronology, 40Ar/39Ar and (U-Th)/He thermochronology, microstructural analysis, electron backscatter diffraction, Ti-in-quartz and oxygen isotope geothermometry, and Fourier transform infrared spectroscopy. This research is being carried out in collaboration with Chilean geologists from Pontificia Universidad Catolica de Chile, who are playing a major role in field mapping and structural data analysis.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.