Geodynamic Framework for the Tectonic Trigger of Late Neogene Deformation in Southern Alaska

阿拉斯加南部晚第三纪构造的各个方面，如沿弱挤压边界的隆升或板块边界应力向大陆内陆的转移，已在其他活动边缘单独进行了研究。阿拉斯加南部这些过程的叠加为利用三维地球动力学模型量化构造驱动力和板块结构的相对重要性和相互作用提供了独特的机会。这个项目有两个组成部分。第一部分集中于确定先前存在的构造特征(板片形状、板块边界耦合、狭窄的岩石圈规模薄弱带和区域强度对比)如何相互作用来转移和定位大陆内部的变形。该项目第一部分的结果提供了一个提问的背景：是什么触发了500万至600万年前阿拉斯加山脉的隆起？该项目的第二部分测试了构造触发的两个假说：太平洋板块运动的变化或雅库塔特地体的碰撞，雅库塔特地体是一个小型海洋高原，目前正在阿留申海沟吸积和俯冲。将三维时间相关模型的预测与阿拉斯加山脉隆升的时间和位置以及形变的区域分布的观测约束进行了比较。这项工作将提供第一个三维地球动力学模型，用来检验阿拉斯加南部最近构造演化的地质假设，并对阿拉斯加山脉周围观测限制较少的地区的变形开始做出可检验的预测。板块构造理论认为，板块内部是刚性的，板块之间的相对运动是在一个狭窄的板块边界区域内通过变形发生的。然而，在挤压或伸展的大陆边缘，变形区域可以是宽的，也可以是窄的，但远离板块边界。这项研究利用在阿拉斯加南部观测到的形变来了解大陆上的哪些构造决定了形变的特征，从而将扩大对世界其他汇聚边缘的形变的理解。结果的三维可视化正在被整合到本科课程中，以教授学生如何观察和解释复杂的三维结构，并在公共宣传活动中。德纳利国家公园的计划展示将纳入这个项目的模拟电影。

Various aspects of Late Neogene tectonics in southern Alaska, such as uplift along a weak transpressional boundary or transfer of plate boundary stresses to the continental interior, have been studied individually at other active margins. The superposition of these processes in southern Alaska provides a unique opportunity to quantify the relative importance and interaction of tectonic driving forces and plate structure using 3-D geodynamic models. This project has two components. The first part focuses on determining how pre-existing structural features (the slab shape, plate boundary coupling, narrow lithospheric-scale weak zones, and regional strength contrasts) interact to transfer and localize deformation in the continental interior. The results from the first part of the project provide the context in which to ask: What triggered the uplift of the Alaska Range 5 to 6 million years ago? This second part of the project tests two hypotheses for the tectonic trigger: a change in Pacific Plate motion or collision of the Yakutat Terrane, a small oceanic plateau that is currently accreting to and subducting in the Aleutian Trench. Predictions from 3-D time-dependent models are compared with the observational constraints on the timing and location of uplift of the Alaska Range and the regional distribution of deformation. This work will provide the first three-dimensional geodynamic model with which to test geologic hypotheses for the recent tectonic evolution of southern Alaska, and makes testable predictions for the onset of deformation in regions surrounding the Alaska Range where there are fewer observational constraints. The theory of plate tectonics assumes that interiors of plates are rigid and relative motion between plates occurs through deformation in a narrow plate boundary region. However, on continental margins that are under compression or extension, the regions of deformation can be broad or narrow, but far from the plate boundary. This study uses the observed deformation in southern Alaska to learn which structures in the continent determine the character of the deformation and will, consequently, broaden understanding of deformation in other convergent margins around the world. Three-dimensional visualization of the results are being integrated into undergraduate courses to teach students how to view and interpret complex three-dimensional structures and in public outreach activities. Planned displays at Denali National Park will incorporate simulation movies from this project.