Formation of interior basins associated with curved faults in Alaska

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The positions of certain nonmarine sedimentary basins in central and southern Alaska are spatially related to the geometry of adjacent curved faults. These interior basins occur along the northern, convex side of these fault systems which change trend from northwest in Canada and eastern Alaska to east‐west in central Alaska and to northeast in western Alaska. The basins probably initiated in early to middle Tertiary time and deposition within all basins continued through the Quaternary, broadly synchronous with Tertiary strike‐slip displacements along the Tintina, Denali, and Border Ranges fault systems. We examine the spatial and temporal relationship between basins and faults by using a mechanical model of curved strike‐slip faults based on boundary elements. We relate slip along the curved faults to Tertiary Pacific‐North American plate motions by using principal stress directions inferred from the plate motion directions. Locations of the predicted mean stress reductions around the fault bends caused by fault slip correlate well with positions of the interior basins. Our results suggest that basin subsidence and location were controlled primarily by the geometry of adjacent curved fault systems and the state of stress in Alaska during the Tertiary. Mechanical interaction between curved Alaskan fault systems increases the tendency for basin subsidence. Stresses inferred from early Tertiary plate motion vectors are not oriented correctly to drive right lateral slip along Kaltag, Farewell, and parallel faults in western Alaska. Furthermore, these stress states would have produced left lateral displacements, for which there is no evidence, along these western faults in their present orientations. We find that a combination of slightly rotated fault geometry and low friction along the faults appears to facilitate right lateral slip along the faults in western Alaska. Our results show that deformation well inside the continent can be explained in terms of the Pacific‐North American plate motions. Thus Tertiary plate motions have resulted in a broad zone of fault slip, uplift, and subsidence in the nonrigid North American plate, producing several large basins.