EAR-PF Continuous vs. mixed-mode deformation during construction of the southern central Andes: Investigating the spatiotemporal scales of Cordilleran tectonic regimes

Chelsea Mackaman-Lofland博士被授予NSF EAR博士后奖学金，在康涅狄格大学（UConn）的Julie Fosdick教授和Michael Hren教授的指导下进行研究，专业发展和教育活动。本项目研究了南美洲安第斯山脉中南部（~30°S）构造过程中地壳变形的时空尺度。项目成果将提高对推动与俯冲有关的造山运动的力量和地球动力学机制的科学认识。安第斯山脉是大陆板块下海洋地壳俯冲过程中造山的重要例证，也是包括海洋/大气环流模式、生物多样性、自然灾害和资源分布在内的地球系统的组成部分。在~30°S，安第斯山脉构造的对比模式引起了地壳的连续缩短与上覆板块的幕式缩短、伸展和可能的中性条件。该项目整合了构造测图、盆地分析、地质/热年代学、基岩古高程测量和~30°S腹地盆地填充物，以(1)解决相互矛盾的缩短、伸展和/或中性变形模式解释；(2)量化时间、震级和变形速率、地壳演化、地表隆起和安第斯科迪勒拉的形成。研究和专业发展将包括对阿根廷本科生进行地质实地培训，并在东道国培训本科生论文项目。康涅狄格大学的本科生将通过新资助的GEOPAths实习和职业指导计划招募，该计划强调招募和保留代表性不足的学生群体。项目成果将纳入阿根廷和智利学生的实地考察活动，以及康涅狄格大学“山脉、河流和碳”和“古地理、构造学和全球气候”教育推广项目的活动。长期以来，与俯冲有关的造山活动被认为是由于板块汇聚的边缘尺度变化导致上覆板块的不断缩短和增厚。然而，越来越多的构造、地层和岩浆证据表明，在科迪勒拉造山带的构造过程中，可能存在幕式变形，可能存在区域缩短、伸展和/或中性状态。在安第斯山脉中部向南部（~25 ~ 35°S）过渡的过程中，上板块变形明显由连续缩短向混合变形转变。描述这种转变的性质对于理解收敛边缘过程的时间、速度和空间连续性是至关重要的，但是现有的重建引起了冲突的构造条件，在~30°S的单个造山带上最明显。本研究旨在解决相互冲突的变形模式解释，并提供地理和时间参数，以询问控制科迪勒拉变形的潜在区域或板块尺度机制。结合锆石Lu-Hf （lutetium -铪）和U-Pb（铀-铅）地质年代学、低温热年代学和稳定同位素古高程分析，将建立变形、掘出、地壳增厚和地表隆起之间的定量关系。重建前体变形和沉积史将为研究继承的构造制度和盆地结构对现代安第斯山脉新近纪发育的影响提供一个框架。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。

Dr. Chelsea Mackaman-Lofland has been awarded an NSF EAR Postdoctoral Fellowship to conduct research, professional development, and educational activities at the University of Connecticut (UConn) under the mentorship of Professors Julie Fosdick and Michael Hren. This project investigates the spatial and temporal scales of crustal deformation during construction of the southern central Andes (~30°S) in South America. Project results will improve scientific understanding of the forces and geodynamic mechanisms driving subduction-related mountain building. The Andes define key examples of mountain building during the subduction of oceanic crust beneath a continental plate, and are integral to Earth systems including ocean/atmospheric circulation patterns, biological diversity, and natural hazard and resource distribution. At ~30°S, contrasting models of Andean mountain building invoke continuous crustal shortening vs. episodic shortening, extensional, and possibly neutral conditions in the overriding plate. This project integrates structural mapping, basin analysis, geo/thermochronology, and paleoaltimetry of bedrock and hinterland basin fill at ~30°S to (1) resolve conflicting shortening, extensional, and/or neutral deformation mode interpretations and (2) quantify the timing, magnitude, and rates of deformation, crustal evolution, surface uplift, and establishment of the Andean Cordillera. Research and professional development will involve geological field training for Argentine undergraduate students and training for an undergraduate thesis project at the host institution. The UConn undergraduate will be recruited through the newly funded GEOPAths internship and career-mentoring program, which emphasizes the recruitment and retention of underrepresented student groups. Project results will be incorporated into a field trip for Argentine and Chilean students and activities for the “Mountains, Rivers, and Carbon” and “Paleogeography, Tectonics, and Global Climate” educational outreach programs at UConn. Subduction-related mountain building has long been attributed to continuous shortening and thickening of the overriding plate following margin-scale changes in plate convergence. However, an increasing body of structural, stratigraphic, and magmatic evidence points to episodic deformation, with potentially regional shortening, extension, and/or neutral regimes during the construction of Cordilleran orogens. Along the transition from central to southern Andes (~25−35°S), upper-plate deformation involved an apparent shift from continuous shortening to mixed-mode deformation. Characterizing the nature of this transition is fundamental to understanding the timing, tempo, and spatial continuity of convergent margin processes, but existing reconstructions invoke conflicting tectonic conditions most apparent along a single orogenic transect at ~30°S. This research seeks to resolve conflicting deformation mode interpretations and provide geographic and timing parameters with which to interrogate potential regional or plate-scale mechanisms controlling Cordilleran deformation. Combined zircon Lu-Hf (Lutetium-Hafnium) and U-Pb (Uranium-Lead) geochronology, low-temperature thermochronology, and stable isotope paleoaltimetry analyses will establish quantitative relationships between deformation, exhumation, crustal thickening, and surface uplift. Reconstruction of precursor deformation and sedimentation history will provide a framework with which to investigate the influence of inherited tectonic regimes and basin architectures on Neogene growth of the modern Andes.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.