Collaborative Research: The great Alaskan escape room: Has Northern Cordilleran escape tectonics fluctuated with time and why?

合作研究：伟大的阿拉斯加逃生室：北科迪勒拉逃生构造是否随时间波动？为什么？

• 批准号: 2218920
• 负责人: Sean Regan
• 金额: $ 14.92万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-01 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2218920&HistoricalAwards=false
• 关键词: Collaborative; Research; great; Alaskan; escape

The proposed research will address how plate tectonics causes fragments of continents to “chip off” and move along the continental margin to a new location, often thousands of kilometers away from where they formed. This process has been termed tectonic escape and has played an essential role in shaping the mountainous terrain in western North America over the last ~100 million years. Professors Waldien and Regan will study this tectonic phenomenon by unraveling the geologic evolution and uplift history of the Ahklun Mountains in western Alaska because this region is the northernmost extent of continental fragments that have moved northward along western North America. The study will test the hypothesis that magmatism and uplift in the Ahklun Mountains is related to temporal fluctuations in the amount of tectonic escape over the last ~70 million years. Due to the remote location and inherent relationship between rural communities and the western Alaska landscape, the project will be used to train first-generation college student geologists from first-people communities in Alaska and South Dakota (locations of host institutions). All personnel working on the project will participate in public outreach presentations at Wood-Tikchick State Park emphasizing the relationship between the bedrock geology and the unique landscape of western Alaska.Escape tectonics is commonly evoked in collisional systems to aid in orogenic space limitations by translating crustal material away from collisional indenter(s). In accretionary orogens however, strike-slip deformation develops in response to oblique relative plate motion and results in the translation of forearc slivers. If persistent over prolonged time, the accumulated strike-slip displacement may manifest as forearc escape. Accretionary orogens present a challenge to classical models of escape tectonics because the obliquity of relative plate motion and the broad wavelength geometry of strike-slip faults can change over the duration of orogenesis, thus the proportion of plate motion taken up as escape may vary greatly through time. The 3-year project intends to test the long-proposed model of Cordilleran escape tectonics by documenting the Cretaceous-Cenozoic offset and deformation history along the southwestern terminal onshore segment of the Denali fault system in the Ahklun Mountains of western Alaska. Key questions addressed by the study will include: 1) Do reactivated suture zone faults in the Ahklun Mountains and associated extensional magmatism together represent a partitioned obliquely convergent margin that was active during an escape regime? 2) Do structures inherited from the assembly of the Cordillera focus strike-slip and/or shortening during the downscaling of escape? 3) Is the transition out of a primary escape tectonics regime recorded by the uplift/exhumation of the Ahklun mountains? and 4) Does the timing of reduced escape tectonics correspond with suggested Paleocene-Eocene oroclinal bending of southern Alaska? PIs Waldien and Regan will pursue answers to these questions by employing regional geologic mapping, structural analysis, petrography, thermochronology, geochronology, and geochemistry in a series of focus areas within the Ahklun Mountains to 1) determine the timing of and cause of magmatism and rock exhumation in the Ahklun Mountains, 2) identify offset markers that may be used to restore Denali fault strike-slip displacement at different time intervals, and 3) couple the fault restoration and timing of exhumation/magmatism to regional tectonic processes operating at the scale of the orogen. Results from this study will test whether tectonic escape was steadfast or fluctuated along the Cretaceous-Cenozoic Denali fault system and identify the tectonic scenario(s) associated with transitions among primarily indentation, rotation, and escape regimes.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.

拟议的研究将解决板块构造如何导致大陆碎片“脱落”并沿着大陆边缘移动到新位置，通常距离它们形成的地方数千公里，这一过程被称为构造逃逸，并发挥了重要作用。 Waldien 和 Regan 教授将通过揭示阿克伦的地质演化和隆起历史来研究这种构造现象。阿拉斯加西部的山脉，因为该地区是沿着北美西部向北移动的大陆碎片的最北端，这项研究将检验阿克伦山脉的岩浆活动和隆升与构造逃逸量的时间波动有关的假设。由于地理位置偏远以及农村社区与阿拉斯加西部景观之间的固有关系，该项目将用于培训来自阿拉斯加和南达科他州原住民社区的第一代大学生地质学家。所有参与该项目的人员都将参加在 Wood-Tikchick 州立公园举行的公共宣传演讲，强调基岩地质与阿拉斯加西部独特景观之间的关系。逃逸构造通常在碰撞系统中引发，通过平移地壳来帮助解决造山带空间限制。然而，在增生造山带中，走滑变形响应于倾斜的相对板块运动而发展，并导致材料的平移。如果弧前碎片持续较长时间，累积的走滑位移可能表现为弧前逃逸，这对逃逸构造的经典模型提出了挑战，因为相对板块运动的倾斜度和走滑断层的宽波长几何形状可以。随着造山作用的持续时间的变化，板块运动的比例可能会随着时间的推移而发生很大变化，这个为期三年的项目旨在测试长期以来提出的科迪勒拉逃逸模型。通过记录阿拉斯加西部阿克伦山脉德纳里断层系统西南终端陆上段的白垩纪-新生代偏移和变形历史，该研究解决的关键问题包括：1）阿克伦山脉缝合带断层是否重新活动。和相关的伸展岩浆作用一起代表了在逃逸状态期间活跃的分开的倾斜会聚边缘 2) 结构是否继承自岩浆的集合？逃逸规模缩小过程中科迪勒拉焦点走滑和/或缩短？ 3) 阿克伦山脉的隆升/折返记录了主要逃逸构造体系的转变吗？4) 逃逸构造缩小的时间是否与PIs Waldien 和 Regan 将通过区域地质测绘、结构分析、在阿克伦山脉一系列重点区域进行岩相学、热年代学、地质年代学和地球化学研究，以 1) 确定阿克伦山脉岩浆活动和岩石折返的时间和原因，2) 确定可用于恢复德纳利断层的偏移标记不同时间间隔的走滑位移，3）将断层恢复和折返/岩浆活动的时间与造山带规模的区域构造过程耦合起来。这项研究的结果将测试沿白垩纪-新生代德纳里断层系统的构造逃逸是稳定的还是波动的，并确定与主要压痕、旋转和逃逸状态之间的转变相关的构造情景。该奖项反映了 NSF 的法定使命，并具有通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。