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.

拟议中的研究将解决板块构造如何导致大陆碎片“剥落”并沿大陆边缘沿着移动到一个新的位置，通常距离它们形成的地方数千公里。这个过程被称为构造逃逸，在过去的1亿年里，它在塑造北美西部山区地形方面发挥了重要作用。教授Waldien和里根将通过解开阿拉斯加西部的阿克伦山脉的地质演化和隆起历史来研究这种构造现象，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。该研究将检验这样的假设：阿克伦山脉的岩浆活动和隆升与过去7000万年来构造逃逸量的时间波动有关。由于偏远的位置和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（主办机构所在地）第一民族社区的第一代大学生地质学家。参与该项目的所有人员将参加在伍德-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起，通过将地壳物质从碰撞压头中平移出来，来帮助造山空间限制。然而，在增生造山带中，走滑变形的发展是对斜向相对板块运动的响应，并导致弧前岩条平移。如果持续时间较长，累积的走滑位移可能表现为弧前逃逸。增生造山带对逃逸构造的经典模型提出了挑战，因为相对板块运动的相似性和走滑断层的宽波长几何形状可以在造山作用期间发生变化，因此，作为逃逸的板块运动的比例可能随时间而变化很大。这个为期3年的项目旨在通过记录阿拉斯加西部Ahklun山脉Denali断层系统西南终端陆上段沿着的地壳-新生代偏移和变形历史，测试长期提出的科迪勒拉逃逸构造模型。该研究解决的关键问题包括：1）在阿克伦山脉重新激活的缝合带断层和相关的伸展岩浆活动一起代表一个分区的斜向收敛的边缘，是活跃在逃逸制度？2)继承的结构从组装的科迪勒拉集中走滑和/或缩短在缩小规模的逃逸？3)阿克伦山脉的隆升/折返是否记录了主要逃逸构造体制的转变？以及4）减少逃逸构造的时间是否与阿拉斯加南部古新世-始新世的斜造山弯曲相对应？PI Waldien和Regan将通过在阿克伦山脉内的一系列重点地区采用区域地质测绘、结构分析、岩相学、热年代学、地质年代学和地球化学来寻求这些问题的答案，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）识别可用于恢复不同时间间隔的德纳里断层走滑位移的偏移标志，（3）将断裂恢复和折返/岩浆作用的时间与造山带尺度上的区域构造过程耦合起来。这项研究的结果将测试构造逃逸是否是稳定的或波动沿着新生代德纳里断层系统，并确定与主要的压痕，旋转和逃逸regimes.This奖项之间的过渡的构造情景（S）之间的转换反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。