Collaborative Research: Interrelations Between Foreland Deformation and Flat-slab Subduction: Integrated Analysis of the Sierras Pampeanas to Cordillera of the South-central Andes

南美洲西部的现代地形是两个构造板块汇聚和碰撞的结果，在这个过程中，纳斯卡板块被以浅角度推到南美板块下方，这个过程被称为俯冲。该项目将讨论平板俯冲在产生大陆形变方面的影响，该大陆形变导致南美洲西缘的安第斯山脉急剧隆起。PIs试图更好地了解导致阿根廷安第斯山脉生长的地质和地球动力学过程，其结果将对理解古代造山过程具有重要意义，例如，在Sevier和Laride造山期间形成美国西部落基山脉的构造过程。该项目涉及与阿根廷国家科学技术研究理事会的阿根廷地球科学家及其学生进行重大科学合作，他们将参与该项目的各个方面。该项目将通过让学生参与影响较大的研究项目和参与跨文化国际体验来促进对本科生的培训；它还将有助于扩大代表人数不足的群体在STEM中的参与。研究结果将纳入研究课程，并将通过在会议和出版物上的陈述广泛传播。该项目还有可能提高对研究区域地震风险的了解，该区域经历了多次破坏性的历史性地震。关于会聚板块边缘大陆变形的基本控制，仍然存在一级问题，包括薄皮上地壳到厚皮下地壳变形的原因和相互作用，先前存在的地壳弱点的影响，以及与俯冲动力学的关系。该项目将综合各种构造和岩石磁学技术，以便更好地了解纳萨板块平板俯冲造成的形变的时空变化及其与南美板块的相互作用。该项目将涉及断层、褶皱和断裂系统的测量和分析；测量磁化率的各向异性以表征变形组构；将利用古地磁分析来了解地壳块体如何因变形而旋转；将利用地球物理数据构建地质横断面。这项工作将集中在五个横跨正常到平板俯冲影响的横断面上，它们横跨阿根廷西北部厚皮Sierras Pampeas、薄皮Precordillera和混合模式主科迪莱拉带。该项目将：量化复杂山系(厚皮前陆、薄皮褶皱冲断带、混合模式带)的垂直轴旋转和应力/应变场的时空变化；为该地区的三维运动学演化提供新的模型；测试地球动力学模型，预测与从正常俯冲向平板俯冲过渡有关的构造样式、应力模式、旋转和板内缩短速率的不同沿向变化；评估地壳流变性、基底薄弱和盆地反转对构造趋势、应力折射和变形分区模式的影响；并统计比较从断层数据、磁组构分析、震源机制和可用的全球定位卫星数据估计的应力/应变方向。NSF国际科学与工程办公室正在提供资金支持与该项目相关的国际活动。

The modern-day topography of western South America results from the convergence and collision of two tectonic plates wherein the Nazca Plate is being shoved at a shallow angle beneath the South American plate in a process called subduction. This project will address the effects of flat-slab subduction in producing the continental deformation that has resulted in the dramatic uplift of the Andes along the western margin of South America. The PIs seek to provide better understanding of the geologic and geodynamic processes that have resulted in the growth of the Argentine Andes, and their results will have important implications for the understanding of ancient mountain building processes, such as the tectonic processes that formed the Rocky Mountains of the western United States during the Sevier and Laramide orogenies. The project involves a significant scientific collaboration with Argentinian geoscientists from the Argentina National Council of Scientific and Technical Research (CONICET) and their students, who will be involved in all facets of the project. The project will contribute to the training of undergraduate students through involvement of students in high-impact research projects and participation in cross-cultural international experiences; it will also contribute to the broadening of participation of underrepresented groups in STEM. Results of the research will be incorporated into research curricula and will be widely disseminated through presentations at meetings and publications. The project also has the potential to improve understanding of seismic risks in the study region that has experienced multiple devastating historic earthquakes. First-order questions persist regarding fundamental controls of continental deformation along convergent plate margins, including causes and interactions of thin-skin upper crustal to thick-skin lower crustal deformation, influences of pre-existing crustal weaknesses, and relations to subduction dynamics. This project will integrate a variety of structural and rock magnetic techniques in order to better understand the spatial and temporal changes in deformation that have resulted from flat slab subduction of the Naza plate and its interaction with the overriding South American plate. The project will involve the measurement and analysis of faults, folds, and fracture systems; measurements of the anisotropy of magnetic susceptibility to characterize deformation fabrics; will utilize paleomagnetic analysis to understand how crustal blocks have rotated due to deformation; and will use construction of geological cross-sections utilizing geophysical data. The work will focus on five transects that span the effects of normal to flat-slab subduction, and which cross the thick-skin Sierras Pampeanas, thin-skin Precordillera, and mixed mode Principal Cordillera belts of northwest Argentina. The project will: quantify both vertical-axis rotations and spatial-temporal changes in stress/strain fields across a complex mountain system (thick-skin foreland, thin-skin fold-thrust belt, mixed mode belt); provide a new model for the 3-dimensional kinematic evolution of the region; test geodynamic models that predict different along-strike variations in structural style, stress patterns, rotations, and intraplate shortening rates related to a transition from normal to flat-slab subduction; evaluate effects of crustal rheology, basement weaknesses, and basin inversion on patterns of structural trend, stress refraction, and deformation partitioning; and statistically compare stress/strain directions estimated from fault data, magnetic fabric analysis, earthquake focal mechanisms, and available global positioning satellite data.Funds to support the international activities associated with this project are being provided by the NSF Office of International Science and Engineering.