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

Cornell University, Ithaca NY

Investigators

Abstract

Non-Technical Summary The 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 Description The 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.