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

兰格尔火山场是过去260万年来地球上最大的火山岩喷发之一，但它与板块构造过程的关系仍然是个谜。阿拉斯加地下地震的位置表明，太平洋板块在俯冲过程中在阿拉斯加下方滑动。这些地震在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，用来测试地幔在板块结束时的行为，以及会聚如何在俯冲带引发地震的理论。这项研究的中心是一个由37个宽带地震台组成的临时网络，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。它正在提供数据，以告知是否在牧羊人之下发生俯冲，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，该团队通过部署地震阵列并将其结果与其他观测和模型结合起来，促进了我们对俯冲带的理解。正在进行的与岩石学家和地球动力学家的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。阿拉斯加大学费尔班克斯分校的外展项目提供了与该地区学校和科学教育中心的结构化链接，通过尖端研究接触到当地人口。它支持跨学科合作，为研究人员和学生之间持续的跨学科教育提供充足的机会。兰格尔火山场是北美总喷发记录的重要贡献者，这项研究也将为理解这一灾害提供关键框架。技术描述拟议的研究对提高我们对俯冲带动力学、岩石圈对浮壳俯冲的响应、板片扭曲的质量守恒以及弧火山活动的驱动因素的理解有很大帮助。临时部署37个宽带地震台的结果集中在除了环境噪声层析成像、速度和衰减成像、震动和地震活动研究以及由横波分裂测量各向异性之外，还根据接收器功能确定板材表面和楔形几何形状。它解决了以下问题：1)阿拉斯加-阿留申板块的东端在哪里，它的形状是什么？它是以撕裂结束，还是持续翘曲？2)雅库塔特地壳俯冲、伸展和兰格尔山脉火山活动之间有什么关系？常规俯冲是驱动兰格尔火山活动，还是在裂缝或边缘流动和高温？厚厚的雅库塔特地体地壳是否持续俯冲到兰格尔山脉之下？3)阿留申板块末端周围的流动是什么？与更大的板块规模的流动相比，它有多少是由俯冲驱动的？这些结果正被用来了解阿拉斯加地下俯冲物质的命运，以及它在驱动火山活动和构造中的作用。

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.