3-D GEOMETRICAL RECONSTRUCTION AND FLEXURAL MODELING OF COLVILLE FORELAND BASIN, NORTHERN ALASKA

Brooks Range orogeny initiated in response to 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 we constrain geometry and model spatial and temporal variations of deflection in northern Alaska to estimate effective 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 Brooks Range and Colville foreland and the 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, We adapt 3D flexural model technique to provide accurate elastic thickness for the Colville foreland basin. The geometry of Colville basin is characterized by using subsurface data and available structure maps, where the maximum depth reaches to 8 km towards 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 observation to optimize modeling results. We applied basin and topographic loads along with crustal root loads with a ratio of 4.5 times to modern topography. Calculated effective elastic thickness is about 16 km and an average miss fit between model and observation is less than 3%. The best-fit model spans 83000 sq.km of the basin. The results of this study indicate that the Colville basin geometry mainly controlled by a load of Brooks Range and basin deposits and any other additional load sources or density anomaly in the crust is not required for deflection of Colville foreland basin.