Cenozoic tectono‐thermal history of the Tordrillo Mountains, Alaska: Paleocene‐Eocene ridge subduction, decreasing relief, and late Neogene faulting

Abstract

Topographic development inboard of the continental margin is a predicted response to ridge subduction. New thermochronology results from the western Alaska Range document ridge subduction related orogenesis. K‐feldspar thermochronology (KFAT) of bedrock samples from the Tordrillo Mountains in the western Alaska Range complement existing U‐Pb, 40Ar/39Ar and AFT (apatite fission track) data to provide constraints on Paleocene pluton emplacement, and cooling as well as Late Eocene to Miocene vertical movements and exhumation along fault‐bounded blocks. Based on the KFAT analysis we infer rapid exhumation‐related cooling during the Eocene in the Tordrillo Mountains. Our KFAT cooling ages are coeval with deposition of clastic sediments in the Cook Inlet, Matanuska Valley and Tanana basins, which reflect high‐energy depositional environments. The Tordrillo Mountains KFAT cooling ages are also the same as cooling ages in the Iliamna Lake region, the Kichatna Mountains of the western Alaska Range, and Mt. Logan in the Wrangell‐St. Elias Mountains, thus rapid cooling at this time encompasses a broad region inboard of, and parallel to, the continental margin extending for several hundred kilometers. We infer these cooling events and deposition of clastic rocks are related to thermal effects that track the eastward passage of a slab window in Paleocene‐Eocene time related to the subduction of the proposed Resurrection‐Kula spreading ridge. In addition, we conclude that the reconstructed KFATmax negative age‐elevation relationship is likely related to a long period of decreasing relief in the Tordrillo Mountains.