Sedimentary Record of Cenozoic Tectonics, Basin Development, and Climate Along the Eastern Margin of the Southern Alaska Convergent Plate Boundary

The northern Pacific plate boundary along the southern Alaska convergent margin is characterized by a west to east transition from normal (Aleutian trench) to flat slab subduction related to ongoing oblique collision of the Yakutat microplate. The deformation along the eastern part of the southern Alaska convergent margin is marked by the eastern Alaska Range inboard of the margin and the Chugach-St. Elias Mountains outboard of the margin. 

Inboard of the margin, the Denali fault outlines the trace of the eastern Alaska Range.

New stratigraphic, geochronologic, and provenance analysis from Eocene-Pliocene strike-slip basins along this fault system provides a record of both basin development and displacement amounts. Key findings include post-Eocene displacement of ~ 470 km on the eastern Denali fault, Miocene displacement of 230 km on the ~ Totschunda fault, and Late Miocene to Pliocene displacement of 80-90 km on the Kimball fault section. The strike-slip displacement history for this part of the fault has previously been interpreted as the product of Cretaceous to Eocene deformation. My results, in contrast, document that large components of the displacement along this 2,000-km-long fault system are post-Eocene.

Outboard of the convergent margin are the Chugach-St. Elias Mountains that are actively being eroded by extensive temperate glaciers that transport sediment directly into the Gulf of Alaska and the Aleutian trench. This natural source-to-sink system allows for investigation of sediment transport and provenance along a glaciated plate boundary. IODP Expedition 341 drilled five sites into the Gulf of Alaska to investigate the interplay between Neogene – Quaternary tectonics and climate from a provenance perspective. The IODP sites transect the continental shelf to distal submarine fan deposystems and encompass a 10 my record of sedimentation above the area of flat-slab subduction.

New results from U-Pb geochronologic data collected from 17 targeted sand beds and 12 lonestones indicate that the Coast Mountain batholith and the Chugach Metamorphic Complex have been important sources of sediment for depositional systems of the Gulf of Alaska. This sediment is likely reworked along the margin by being incorporated into thrust belts and accretionary prisms, and then are subsequently eroded by glacial processes.