MARGINS: Collaborative Research: A 21st Century Reconnaissance of Aleutian Arc Inception

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The Alaska/Aleutian Arc is the most geologically active region in North America with abundant large earthquakes and eruptions from more than 50 active volcanoes. Determining precisely how and when the Aleutian Arc began to form is one of the key elements for understanding the origin of the Bering Sea-Alaska-North Pacific region as well as how several circum-Pacific volcanic zones are related to one another. Our understanding of how volcanism initiated in the Aleutian Arc is clouded due in large part to the scarcity of data that bear on the ages of the earliest volcanic rocks in the Aleutian Islands. The proposed reconnaissance investigation of Aleutian Arc inception involves sampling and determining the ages of the oldest records of volcanism. The aim is to define when Aleutian arc volcanism started and highlight potential linkages with the initiation of volcanism elsewhere in the Pacific and the rapid change in the relative motions of oceanic plates that occurred 52 million years ago. In addition, the proposed research will generate basic information regarding how and why the Aleutian arc poses significant volcanic and earthquake hazards to the population in Alaska and around the Pacific Rim.The proposed research will employ state-of-the-art 40Ar/39Ar and U-Pb geochronology, along with geochemical, and isotopic analysis of the dated rocks. The focus is on subaerial outcrops on Amatignak, Ulak, and Kiska islands, which hold the greatest potential for exploration into the early history of the Aleutians. New geochronologic and geochemical data will precisely constrain when the Aleutian arc inception began, what the compositions of the eruptive products were, and how they evolved through the earliest history of the arc. This information will also be used to evaluate the existing tectonic models of Aleutian arc inception and Pacific Plate motion during the middle Eocene. This project will forge a new collaboration between scientists at UW-Madison, Cornell University, and the University of Alaska-Fairbanks/USGS that may benefit the GeoPRISMS program for its duration. Our findings will be used immediately to determine where future efforts to examine the Aleutian Arc and its fore-arc structures via submersible ROVs, dredging, and geophysical imaging should concentrate to best address questions of subduction zone initiation.