3-D Geometrical Reconstruction and Flexural Modeling of Colville Foreland Basin, Northern Alaska

Abstract

Brooks Range orogeny initiated in response to the collision of Arctic Alaska with an oceanic arc in Jurassic to early Cretaceous, and the Colville basin formed as a result of loading from the range topography. In this study Colville basin geometry is constrained and spatiotemporal variations of deflection is modeled in northern Alaska in order to estimate the elastic thickness (Te) of the lithosphere beneath the Colville foreland basin. Previous studies show that the effective elastic thickness of the Colville Basin in the northern Alaska region is 65 km which seems overestimated. That is because, the depth of frequent earthquakes dramatically reduces at 25 km under the Brooks Range and Colville foreland and wavelength of the Colville foreland is shorter than what one can expect for a plate with 65 km elastic thickness. To address these contrasting observations, a 3D flexural model technique is used to provide an accurate elastic thickness of northern Alaska lithosphere. The geometry of the Colville basin is characterized by using subsurface data and available structure maps, where the maximum depth reaches to 8 km towards the southwest of the basin. Flexural deflection of the northern Alaskan plate is modeled by various parameters (e.g., density, subsurface load), and results are compared to the observed data to optimize modeling results. The applied loads include basin and topographic loads along with crustal root loads with a ratio of 4.5 times to modern topography. Calculated elastic thickness is about 16 km and an average misfit between the model and observation is less than 3% and spans 83000 km2 of the basin. The results of this study indicate that the Colville basin geometry is mainly controlled by the loads of the Brooks Range and basin deposits and any other additional loads or density anomalies in the crust are not required for deflection of the Colville foreland basin.