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

该项目研究了阿塔卡马断层系统的位移历史和力学行为。阿塔卡马断层系统是智利北部科迪勒拉海岸沿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，在协调板块在会聚边界的运动方面发挥了关键作用，但围绕它们的发展仍存在重大不确定性。这项研究的社会效益包括在地球科学教师与科罗拉多州立大学和智利加托利卡州立大学的本科生/研究生之间开展新的合作。来自科罗拉多州立大学和智利哥伦比亚大学的10名学生参加了一个联合领域测绘项目，该项目包括研究的基础，并为学生提供高影响力的学习体验。为该项目提供资金，通过支持科罗拉多州立大学的一名女博士生，有助于扩大代表人数不足的群体对一门重要的科学、技术、工程和数学(STEM)学科的参与。这笔资金还支持一名职业生涯早期首席研究员的研究计划。这项研究为理解位于阿塔卡马断裂系统的经济铜铁金矿床提供了一个新的框架，其结果将通过以阿塔卡马矿业社区为目标的实地考察而呈现。该项目的主要科学目标是：a)确定跨越阿塔卡马断裂系统的时间、强度和滑动速率；b)确定岩浆作用与沿阿塔卡马断裂系统的变形之间的时空关系；以及c)确定沿阿塔卡马断裂系统的脆塑性转变附近的流变和变形条件。重建主要地质构造的滑动历史，如阿塔卡马断裂系统，对于理解俯冲带上方斜向会聚是如何划分的至关重要，而需要有关断裂带流变性和岩浆作用与变形之间关系的信息来理解应变如何以及为什么在覆盖板块中定位。阿塔卡马断裂系是安第斯中生代最重要的构造之一，对经济金属矿床具有重要的控制作用。尽管意义重大，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展知之甚少。在他们的初步野外工作中，项目研究人员发现了明显的偏移标志和许多运动前、同步性和运动学后的火成岩单元，这些单元为解决滑动的幅度、时间和速度提供了巨大的潜力。他们还确定了广泛的脆塑性变形的证据，使他们能够评估断层系统的流变性和峰值强度。除了建立对安第斯中央边缘中生代构造演化的关键限制外，这项研究还将提供重要的洞察，了解岩浆弧内如何适应斜向会聚。为了实现提议的目标，研究小组采用了多学科研究方法，其中包括地质填图、铀-铅地质年代学、40Ar/39Ar和(U-Th)/He热年代学、微观结构分析、电子背散射衍射、石英钛和氧同位素地质测温法和傅立叶变换红外光谱。这项研究是与智利加多利卡大学的智利地质学家合作进行的，他们在野外测绘和结构数据分析方面发挥着重要作用。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 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.