Collaborative Research: Causes and Mechanisms of Focused Exhumation Along the Denali Fault, Eastern Alaska Range

合作研究：阿拉斯加东部德纳利断层沿线集中折返的原因和机制

• 批准号: 0952800
• 负责人: Paul Fitzgerald
• 金额: $ 13.99万
• 依托单位: Syracuse University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-02-01 至 2013-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0952800&HistoricalAwards=false
• 关键词: Collaborative; Research; Causes; Mechanisms; Focused

The 1,200 km long Alaskan Denali Fault system is a major intra-continental right-lateral strike-slip fault system. Since the 2002 Denali earthquake (magnitude 7.9), which initiated along a previously undescribed thrust fault in the eastern Alaska Range, scientists have increasingly focused on how much slip and convergence occurs along this fault system, and where deformation is being accommodated. Mountainous terrain and basins have formed along the Denali fault and the locations and age of formation of these features can be used to constrain the distribution of crustal deformation through time. The eastern Alaska Range, the topographic signature of the eastern Denali Fault, rises dramatically from the tundra (about 200 meters) to sharp glaciated peaks (about 4,000 meters), forming a narrow but high-relief region immediately north of the fault. As the fault continues west, the topography drops significantly, then rises again to form the central Alaska Range, home to Mt. McKinley and Denali National Park. Uplift of the Alaska Range is related to plate tectonic processes associated with subduction and accretion along Alaska's southern margin, but why the uplift is focused along the fault in the eastern Alaska Range is not clear. This research project seeks to understand the thermal history of rocks in the eastern Alaska Range and hence place constraints on regional patterns of exhumation and uplift through time. This will allow evaluation of the relative importance of near-field boundary conditions versus far-field driving forces. The research team is conducting a high-resolution multi-technique thermochronological approach combined with macro-and microstructural work along the eastern Denali Fault. This approach will document variations in exhumation rates during the last 30 million years to understand exhumation patterns in the mountains. Structural studies are focused on the regions with the most extreme exhumation, both in terms of rate and total amount, to understand what controls these patterns. Linking the structural history to exhumation rates will permit the temporal and spatial influence of geodynamic drivers such as changes in Pacific versus North America plate motion, dip of the subducting slab, and the collision of buoyant Yakutat block at the eastern edge of the subduction zone to be evaluated. This study has relevance to fundamental problems of major strike-slip fault systems, including what causes localized exhumation and how strike-slip deformation is transferred into the lower crust. Results will contribute to earthquake hazard prediction in this region by constraining locations of high neotectonic deformation, variations in Denali fault geometry and identification of reverse faults. A better understanding of contributing factors for seismic behavior along the Denali Fault will benefit seismic hazard maps. The Trans-Alaska oil pipeline and future 26 billion dollar Alaska gas pipeline cross the eastern Alaska Range and Denali fault. The pipeline is designed to withstand strike-slip motion, but if the there is a significant dip-slip component the effects could be disastrous.

阿拉斯加德纳利断裂系统全长1200公里，是一个主要的陆内右行走滑断裂系统。自2002年德纳利地震(里氏7.9级)以来，科学家们越来越关注沿着这个断层系统发生了多少滑动和会聚，以及在哪里容纳了变形。德纳利地震发生在阿拉斯加东部一条此前未被描述的逆冲断层上。沿德纳利断裂形成了多山的地形和盆地，这些地貌的形成位置和形成时代可以用来限制地壳形变在时间上的分布。东阿拉斯加山脉是东部德纳利断层的地形标志，从苔原(约200米)到尖锐的冰川峰(约4000米)戏剧性地上升，在断层的正北方形成了一个狭窄但高度起伏的地区。随着断层继续向西，地形显著下降，然后再次上升，形成阿拉斯加中部山脉，这里是Mt.麦金利和德纳利国家公园。阿拉斯加山脉的隆升与阿拉斯加南缘与俯冲和吸积有关的板块构造过程有关，但为什么隆起集中在阿拉斯加山脉东部的断层上尚不清楚。该研究项目试图了解东阿拉斯加山脉岩石的热历史，从而限制随时间推移的区域折返和抬升模式。这将允许评估近场边界条件与远场驱动力的相对重要性。研究小组正在进行高分辨率、多技术的热年代学方法，并结合沿德纳利断层东部的宏观和微观结构工作。这种方法将记录过去3000万年来掘尸速度的变化，以了解山区的掘尸模式。构造研究的重点是最极端的挖掘区域，无论是在速度上还是总量上，以了解是什么控制了这些模式。将构造历史与折返速率联系起来，将允许评估地球动力学驱动因素的时间和空间影响，如太平洋与北美板块运动的变化，俯冲板块的倾角，以及浮力雅库塔特地块在俯冲带东缘的碰撞。这项研究与主要走滑断裂系统的基本问题有关，包括是什么导致了局部折返以及走滑变形如何转移到下地壳。这些结果将通过约束新构造高变形的位置、德纳利断裂几何形状的变化和反转断裂的识别，为该地区的地震危险性预测提供帮助。更好地了解德纳利断层沿线地震行为的影响因素将有助于绘制地震危险性图。横贯阿拉斯加的石油管道和未来价值260亿美元的阿拉斯加天然气管道横跨阿拉斯加东部山脉和德纳利断层。这条管道的设计可以承受走滑运动，但如果存在显著的倾滑分量，其影响可能是灾难性的。