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

这项拟议中的研究将探讨板块构造如何导致大陆的碎片“剥离”，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有数千公里。这一过程被称为构造逃逸，在过去的1亿年里对北美西部山区的形成起到了至关重要的作用。瓦尔迪恩和里根教授将通过揭示阿拉斯加西部阿赫克伦山脉的地质演化和隆起史来研究这一构造现象，因为该地区是沿北美西部向北移动的大陆碎片的最北端。这项研究将检验这一假设，即阿赫克伦山脉的岩浆活动和隆起与过去7000万年来构造逃逸量的时间波动有关。由于农村社区和阿拉斯加西部景观之间的偏远位置和内在联系，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。该项目的所有工作人员将参加伍德-提奇克州立公园的公共宣传演讲，强调基岩地质和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被唤起，通过将地壳物质转移到远离碰撞凹陷的地方来帮助造山空间限制(S)。然而，在增生造山带中，走滑变形是对板块相对倾斜运动的响应，并导致弧前碎屑的平移。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倾角和走滑断层的宽波长几何形状可以随着造山作用的持续而改变，因此作为逃逸的板块运动所占的比例可能随着时间的推移而变化很大。这个为期3年的项目旨在通过记录阿拉斯加西部阿赫克伦山脉德纳利断裂系统西南末端陆上段白垩纪-新生代的偏移和变形历史，来检验长期提出的科迪勒逃逸构造模型。这项研究将解决的关键问题包括：1)艾克伦山脉重新激活的缝合带断层和相关的伸展岩浆作用是否共同代表了在逃逸机制期间活动的分离的斜向会聚边缘？2)从科迪勒拉焦点集合体继承的构造是否在逃逸的降低尺度期间发生走滑和/或缩短？3)艾克伦山脉的抬升/折返记录了主要逃逸构造制度的转变？4)逃逸构造减少的时间是否与阿拉斯加南部古新世-始新世造山斜弯曲相一致？PiS Waldien和Regan将通过应用区域地质填图、构造分析、岩石学、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)确定阿赫克伦山脉岩浆作用和岩石折返的时间和原因，2)确定可用于恢复不同时间间隔的德纳利断层走滑位移的偏移标志，以及3)将断层恢复和折返/岩浆作用的时间与造山带规模的区域构造过程相结合。这项研究的结果将测试构造逃逸是稳定的还是沿着白垩纪-新生代德纳利断裂系统波动的，并确定与主要压痕、旋转和逃逸方案之间的转换相关的构造情景(S)。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智力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.