Along-strike Variation in Alaska Forearc Deformation: From Shortening to Extention

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Presenter

Dr. Suoya Fan
Research Assistant Professor
Department of Geology and Environmental Science
The University of Pittsburgh

Description

The Alaska subduction zone exhibits an along-strike transition from weak plate-interface coupling in the west to strong coupling in the east. Subaerial forearc exposures in the Kodiak Islands (strong coupling segment) and the Chirikof Island (transition segment) provide a window to study how upper-plate structures and plate-interface processes interact to accommodate long-term forearc deformation. In the Kodiak segment, zircon and apatite (U-Th)/He thermochronologic data, combined with stratigraphic, geomorphic, and detrital zircon analyses, reveal an early-middle Miocene change in exhumation pattern, suggesting a change in the dominant deformation mechanisms. In contrast, on the Chirikof Island, field surveys document a Quaternary-active, approximately 60° arcward-dipping normal fault (the Chirikof Fault) with vertical separations of 4–9.5 m across geomorphic surfaces. These findings highlight an along-strike change in the Alaska forearc, from long-lived shortening controlled by splay faulting in the Kodiak segment to active extension in the Chirikof segment.