Thrust systems are a primary mechanism for accommodating the convergent component of oblique plate motion and are therefore key players in the structural development of transpressional orogens. In southern Alaska, the Denali fault system is a highly partitioned dextral-convergent fault system spatially coincident with Alaska Range topography and thus offers an opportunity to evaluate the evolution of range-bounding thrust systems in orogens resulting from oblique plate motion. Our analysis is focused on the late Miocene–Present McCallum Creek thrust system, which consists of the McCallum Creek reverse fault and a kinematically linked foreland thrust system south of the Denali fault in the eastern Alaska Range. Apatite fission-track cooling ages, tephrachronology, and balanced cross sections indicate that convergence partitioned to the McCallum Creek thrust system has accommodated ~4 km of rock exhumation and ~5.5 km of south-vergent shortening since hanging wall rocks passed through the apatite fission-track partial annealing zone at ca. 6 Ma. A blind foreland thrust system developed after ca. 3.8 Ma and was subsequently overtaken by out-of-sequence slip on the main McCallum Creek fault. Incised segments of modern streams, perched terraces, and tilted Quaternary deposits suggest that foreland structures are active in the Quaternary. Shortening on the McCallum Creek thrust system is oriented at a high angle to the Denali fault, making the McCallum Creek thrust system one of the only known structures south of the Denali fault in the Alaska Range to accommodate the collisional mode of active deformation in southern Alaska. The late Miocene reactivation of faults in the McCallum Creek area likely records evolution of the Denali fault system in response to modification of the southern Alaska convergent plate boundary.
Late Miocene to Quaternary evolution of the McCallum Creek thrust system, Alaska: Insights for range-boundary thrusts in transpressional orogens
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Trevor S. Waldien, Sarah M. Roeske, Jeffrey A. Benowitz, Wai K. Allen, Kenneth D. Ridgway, Paul B. O’Sullivan; Late Miocene to Quaternary evolution of the McCallum Creek thrust system, Alaska: Insights for range-boundary thrusts in transpressional orogens. Geosphere doi: https://doi.org/10.1130/GES01676.1
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