Collaborative Research: Fate and Consequences of Yakutat Terrane Subduction Beneath Eastern Alaska and the Wrangell Volcanic Field

合作研究：阿拉斯加东部和兰格尔火山场下雅库塔特地体俯冲的命运和后果

• 批准号: 1460318
• 负责人: Douglas Christensen
• 金额: $ 39.83万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-05-01 至 2019-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1460318&HistoricalAwards=false
• 关键词: Collaborative; Research; Fate; Consequences; Yakutat

Non-Technical SummaryThe Wrangell Volcanic Field is one of the largest outpourings of volcanic rocks on the planet in the past 2.6 million years, but its relationship to processes of plate tectonics remains enigmatic. Locations of earthquakes underneath Alaska indicate that the Pacific plate is sliding beneath Alaska in a process of subduction. These earthquakes stop abruptly west of the Wrangell mountains, but somehow the plates continue to converge for several hundred kilometers eastward through the Wrangell region. Because of the close connections between subduction and mountain building, the south Alaska region provides an exceptional testing ground to test theories of how the mantle behaves when slabs end, and how convergence makes earthquakes in subduction zones. The centerpiece of this study is a temporary network of 37 broadband seismic stations deployed across southern Alaska to complement the EarthScope Transportable Array network along critical transects. It is providing data to tell whether or not subduction occurs under the Wrangells, and how the Alaska-Aleutian subduction zone ends. The research is being performed by a team with a well-established collaborative track record in advancing our understanding of subduction zones by deploying seismic arrays and integrating their results with other observations and models. Ongoing collaborations with petrologists and geodynamicists are helping spread the results to a broader geoscience audience. The project supports the training and professional development of two graduate students and provides excellent field-based opportunities to engage undergraduates in research. Outreach programs at the University of Alaska Fairbanks provide structured links to schools and science education centers in the region, reaching native populations with cutting-edge research. It supports an interdisciplinary collaboration with ample opportunity for the continued cross-disciplinary education among researchers and students. The Wrangell Volcanic Field represents a significant contributor to the total eruptive record in North America, and this study will provide critical framework for understanding this hazard as well.Technical DescriptionThe proposed research is aiding significantly in improving our understanding of the dynamics of subduction zones, the response of lithosphere to subduction of buoyant crust, mass conservation in slab contortions, and the drivers of arc volcanism. Results from the temporary deployment of 37 broadband seismic stations focus on determining slab surface and wedge geometry from receiver functions in addition to ambient noise tomography, velocity and attenuation imaging, tremor and seismicity studies, and measuring anisotropy from shear wave splitting. It addresses the following questions: 1) Where is the eastern end of the Alaska-Aleutian slab, and what is its configuration? Does it end as a tear, or is it continuously warped? 2) What is the relationship between Yakutat crust subduction, transtension, and volcanism in the Wrangell mountains? Does regular subduction drive Wrangell volcanism, or flow and high temperatures at a tear or edge? Does thick Yakutat terrane crust subduct continuously beneath the Wrangell mountains? 3) What is the flow around the end of the Aleutian slab and how much is it driven by subduction versus larger plate-scale flow? Results are being used to understand the fate of subducted material beneath Alaska and its role in driving volcanism
 and tectonics.

在过去的260万年里，弗兰格尔火山场是地球上最大的火山岩喷发场之一，但它与板块构造过程的关系仍然是个谜。阿拉斯加下面的地震位置表明太平洋板块在俯冲过程中在阿拉斯加下面滑动。这些地震在弗兰格尔山脉以西突然停止，但不知何故，板块继续向东汇聚数百公里，穿过弗兰格尔地区。由于俯冲和造山之间的密切联系，南阿拉斯加地区提供了一个特殊的试验场，可以测试板块结束时地幔的行为，以及汇聚如何在俯冲带产生地震。这项研究的核心是一个由37个宽带地震站组成的临时网络，部署在阿拉斯加南部，以补充沿关键横断面的EarthScope可移动阵列网络。它提供了数据来判断是否在弗兰格尔板块下发生俯冲，以及阿拉斯加-阿留申俯冲带如何结束。这项研究是由一个有着良好合作记录的团队进行的，他们通过部署地震阵列并将其结果与其他观测和模型相结合，提高了我们对俯冲带的理解。与岩石学家和地球动力学家的持续合作正在帮助将结果传播给更广泛的地球科学受众。该项目支持两名研究生的培训和专业发展，并为本科生参与研究提供了极好的实地机会。阿拉斯加费尔班克斯大学（University of Alaska Fairbanks）的外展项目为该地区的学校和科学教育中心提供了结构化的联系，向当地居民提供前沿研究。它支持跨学科合作，为研究人员和学生之间的持续跨学科教育提供充足的机会。弗兰格尔火山场代表了北美总喷发记录的重要贡献者，这项研究也将为理解这种危险提供关键框架。提出的研究有助于提高我们对俯冲带动力学的理解，岩石圈对浮力地壳俯冲的响应，板块扭曲中的质量守恒，以及弧火山作用的驱动因素。临时部署的37个宽带地震台站的结果侧重于从接收函数确定板表面和楔形几何形状，以及环境噪声层析成像、速度和衰减成像、地震和地震活动性研究，以及从横波分裂测量各向异性。它解决了以下问题：1)阿拉斯加-阿留申板块的东端在哪里？它的构造是什么？它是以撕裂结束，还是持续扭曲？2)弗兰格尔山脉的雅库塔地壳俯冲、张拉与火山活动有何关系？是否有规律的俯冲作用驱动弗兰格尔火山活动，或裂缝或边缘的流动和高温？厚的雅库特地壳是否在Wrangell山脉下连续俯冲？3)阿留申板块末端的流动是什么？它在多大程度上是由俯冲作用驱动的，而不是更大的板块规模的流动？研究结果被用来了解阿拉斯加地下俯冲物质的命运及其在推动火山活动中的作用。和构造。