GEOSPATIAL ANALYSIS OF APATITE FISSION TRACK AND APATITE (U-TH)/HE IN RELATION TO ELEVATED TOPOGRAPHY ALONG ACTIVE FAULTS

Southern Alaska has been the focus of several targeted thermochronology studies over the last three decades. Despite the usefulness of these studies for highlighting cooling and exhumation in mountainous regions, the regional cooling patterns at the scale of southern Alaska remain unclear, with some local studies suggesting a relationship between young cooling ages and high topography along active fault lines. To address this issue, and to test this on a larger scale, we performed kriging on compiled bedrock apatite fission-track (AFT) and apatite (U-Th)/He (AHe) cooling ages from preexisting literature across southern Alaska south of the Tintina Fault. The kriging analysis of AFT data reveals discontinuous zones of young (< 10 Ma) cooling near the coast along the Fairweather Fault and to the west toward Prince William Sound. To the north, young AFT ages are spatially associated with restraining bends in the Denali fault system. In interior Alaska AFT ages are generally old (>~30 Ma) despite abundant crustal seismicity and the high geothermal gradient. Kriging of AHe dates reveals a continuous belt of young cooling along the Fairweather Fault, south of the Bagley Fault, and onto Montague Island. A zone of young AHe dates coincides with a high elevation region between the Contact Fault and Matanuska Valley. Along the Denali Fault to the north, AHe data are sparse, yet young (≤ 20 Ma) AFT dates suggest that AHe dates would also be young near the Denali Fault. Both the AFT and AHe datasets are sparse in low-relief regions between active fault systems, which is likely a sample bias related to the objectives of previous studies and may make interpolated age between the high relief regions questionable. Accordingly, locations of young AFT and AHe dates coincide with high relief regions spatially associated with Neogene-Quaternary faults. The study also highlights regions of moderate-high relief that could be promising target areas for future work focused on unraveling the history of topographic growth in southern Alaska.