Accretion in the wake of terrane collision: The Neogene accretionary wedgeoff Kenai Peninsula, Alaska

Subduction accretion and repeated terrane collision shaped the Alaskan conv ergent margin. The Yakutat Terrane is currently colliding with the continen tal margin below the central Gulf of Alaska. During the Neogene the terrane 's western part was subducted after which a sediment wedge accreted along t he northeast Aleutian Trench. This wedge incorporates sediment eroded from the continental margin and marine sediments carried into the subduction zon e on the Pacific plate. Prestack depth migration was performed on six seism ic reflection lines to resolve the structure within this accretionary wedge and its backstop. The lateral extent of the structures is constrained by h igh-resolution swath bathymetry and seismic lines collected along strike. A ccretionary structure consists of variably sized thrust slices that were de formed against a backstop during frontal accretion and underplating. Toward the northeast the lower slope steepens, the wedge narrows, and the accrete d volume decreases notwithstanding a doubling of sediment thickness in the trench. In the northeasternmost transect, near the area where the terrane's trailing edge subducts, no frontal accretion is observed and the slope is eroded. The structures imaged along the seismic lines discussed here most l ikely result from progressive evolution from erosion to accretion, as the t railing edge of the Yakutat Terrane is subducting.