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

该项目涉及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方沿海科迪勒拉地区沿着早白垩世岩浆弧切割的主要构造结构。 阿塔卡马断层系统等弧内结构在收敛边界处容纳板块运动方面发挥着关键作用，但围绕其发展仍存在重大不确定性。 这项研究的社会效益包括发展地球科学教师和科罗拉多州立大学和智利天主教大学的本科生/研究生之间的新合作。 来自科罗拉多州立大学和智利天主教大学的10名学生正在参加一个联合实地测绘计划，该计划包括研究基础，并为学生提供高影响力的学习体验。 为该项目提供的资金有助于扩大代表性不足的群体对科学、技术、工程和数学这一重要学科的参与，为来自科罗拉多州立大学的一名女博士生提供了支助。这笔资金还支持一名早期职业首席研究员的研究计划。 该研究为了解位于阿塔卡马断层系统沿着的经济铜-铁-金矿床提供了一个新的框架，其结果将通过针对阿塔卡马采矿社区的实地考察来介绍。该项目的主要科学目标是：a）确定穿越阿塔卡马断层系统的滑动的时间、幅度和速率，B）确定沿着阿塔卡马断层系统的岩浆活动和变形之间的空间和时间关系，以及c）确定沿着阿塔卡马断层系统的脆塑性转变附近的流变学和变形条件。 重建的主要地质结构，如阿塔卡马断层系统的滑动历史是必不可少的，了解斜收敛是如何划分俯冲带，断裂带流变学和岩浆活动和变形之间的关系的信息是必要的，以了解应变如何以及为什么在覆盖板本地化。 阿塔卡马断裂系是安第斯山脉中生代最重要的构造之一，对重要的金属矿床起着重要的控制作用。 尽管它的重要性，阿塔卡马断层系统的构造发展是知之甚少，由于该地区缺乏详细的地质测绘和地质年代学。 在他们的初步实地考察中，项目研究人员发现了不同的偏移标记和许多前，同步和后运动学火成岩单位，为解决滑动的幅度，时间和速率提供了巨大的潜力。 他们还发现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学和峰值强度。 除了建立关键的制约中生代构造演化的安第斯山脉中部边缘，这项研究将提供重要的洞察力斜收敛是如何容纳岩浆弧。 为了实现提议的目标，研究小组正在使用多学科研究方法，包括地质测绘、U-Pb地质年代学、40 Ar/39 Ar和（U-Th）/He热年代学、显微结构分析、电子背散射衍射、石英中的钛和氧同位素地质测温法以及傅里叶变换红外光谱法。 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，他们在野外测绘和结构数据分析方面发挥了重要作用。该奖项反映了NSF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.