| Summary: | The southern Alaska continental margin is comprised of highly deformed, offscraped, and underplated deep-sea rocks that have been accreted from the Late Triassic to the present. These rocks constitute one of the largest subduction-related accretionary complexes in the world. The outboard part of the Mesozoic to Tertiary Chugach-Prince William composite terrane (CPW) is composed of deep-water turbidites (flysch) and associated volcanic rocks exposed for ~2,000 km in southern Alaska. In an effort to better understand the tectonic evolution of southern Alaska, this paper focuses on the Orca Group, the outboard Paleogene flysch of the CPW terrane. U-Pb zircon age data (n = 1400) from the Orca Group reveal an inboard to outboard (NW to SE) maximum depositional age progression from ~69 Ma to ~35 Ma. This time bracket is important because it spans the time when the CPW is proposed to have either 1) interacted with the fixed (relative to North America) Kula-Farallon trench-ridge-trench triple junction south of its present latitude and then migrated along the North American coast to its present position, or 2) interacted with the migrating Kula-Resurrection trench-ridge-trench triple junction at its present latitude. These maximum depositional ages also show that deposition was contemporaneous with the intrusion of the flysch by the near-trench plutons of both the 61 to 48 Ma Sanak Baranof belt and the ~37-39 Ma Eshamy suite. In addition, these ages suggest nearly continuous deposition (from 157 to 35 Ma) of the CPW from the inboard McHugh Complex through the outboard Orca Group. U-Pb detrital zircon age data in combination with fission track analysis divide the Orca Group into three unique fault-bounded belts. U-Pb detrital zircon ages from this study reinforce the along-strike correlation between the Kodiak Formation and the Valdez Group, the Ghost Rocks Formation and the inboard Orca Group, and the Sitkalidak Formation and the outboard Orca Group. U-Pb age spectra of the Orca Group and the Kootznahoo Formation in ...
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