Neotectonic framework of the north-central Alaska Range foothills

Abstract

The northern foothills of the Alaska Range form a northward-convex salient at the apex of this orogen and the Denali fault. Despite the proximity of the northern foothills to the Denali fault and several historic large-magnitude earthquakes, the tectonic framework of this region has not been well-studied. A distinct pattern of east-trending folds and faults exists in both the bedrock and the geomorphic features. To assess the active structures of the region, I interpreted previous geologic mapping, developed cross-sections across the foothills belt, analyzed topographic and stream profiles, mapped the sequence of Quaternary fluvial terraces, and performed GPS transects across several terrace treads. A northward topographic slope across the northern foothills corresponding with the pattern of faulting and folding suggests the presence of an orogenic wedge overlying a south-dipping basal detachment. Mapping and GPS transects show evidence for progressive deformation of the terraces. Geomorphic analyses suggest deformation and differential uplift over the entire foothills belt. These results indicate that the northern foothills are an active fold-and-thrust belt and are prograding northward into the Tanana Basin. Tectonic activity of these structures suggests that this region represents a potential seismic hazard for nearby military facilities and important transportation corridors.