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

拟议中的研究将探讨板块构造是如何导致大陆碎片“脱落”，并沿着大陆边缘移动到一个新的位置，通常距离它们形成的地方数千公里。这一过程被称为构造逃逸，在过去约1亿年里，它在形成北美西部山区地形方面发挥了重要作用。Waldien教授和Regan教授将通过解开阿拉斯加西部阿克伦山脉的地质演化和隆起历史来研究这种构造现象，因为该地区是沿北美西部向北移动的大陆碎片的最北端。该研究将验证阿克伦山脉的岩浆活动和隆起与过去~ 7000万年构造逃逸量的时间波动有关的假设。由于偏远的地理位置和农村社区与阿拉斯加西部景观之间的内在关系，该项目将用于培训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。该项目的所有工作人员都将参加在Wood-Tikchick州立公园举行的公众宣传活动，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移开来辅助造山带空间的限制。然而，在增生造山带中，走滑变形是对斜向相对板块运动的响应，并导致弧前断层的平移。如果长期持续，累积的走滑位移可能表现为弧前逸出。增生造山带对经典的逃逸构造模型提出了挑战，因为相对板块运动的倾角和走滑断层的宽波长几何形状可以在造山带的持续时间内发生变化，因此作为逃逸的板块运动的比例可能随着时间的推移而发生很大变化。该项目为期3年，旨在通过记录阿拉斯加西部Ahklun山脉Denali断裂系统西南终端陆上段的白垩纪-新生代偏移和变形历史，验证长期提出的Cordilleran逃避构造模型。研究将解决的关键问题包括：1)阿克伦山脉重新激活的缝合带断裂和相关的伸展岩浆活动是否共同代表了一个在逃逸期活跃的分裂的斜辐合边缘？2)从科迪勒拉组合继承下来的构造是否集中走滑和/或在降尺度逃逸过程中缩短？3)阿赫伦山隆升/掘出所记录的原始逃逸构造体制是否发生了转变？4)减少逃逸构造的时间是否与阿拉斯加南部古新世-始新世的造山斜弯曲相一致？PIs Waldien和Regan将利用区域地质制图、构造分析、岩石学、热年代学、地质年代学和地球化学在阿克伦山脉的一系列重点区域寻找这些问题的答案：1)确定阿克伦山脉岩浆活动和岩石挖掘的时间和原因；2)确定可用于恢复迪纳里断层不同时间间隔走滑位移的偏移标志；3)将断层恢复和挖掘/岩浆活动的时间与造山带尺度上的区域构造作用耦合起来。本研究的结果将测试沿白垩纪-新生代迪纳里断裂系统的构造逃逸是稳定的还是波动的，并确定与主要压痕、旋转和逃逸机制之间过渡相关的构造情景。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。

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.