Abstract

Late Jurassic to Miocene strata exposed on the western Alaska Peninsula record major changes in plate kinematics and sedimentary basin development along the northern Pacific region. These changes include Late Jurassic to Late Cretaceous accretion of the oceanic Wrangellia composite terrane, subsequent establishment of a Late Cretaceous continental volcanic arc, and middle Eocene Pacific plate reorganization and subduction initiation marked by the Alaska Peninsula–Aleutian volcanic arc. Stratigraphic descriptions and detrital zircon geochronology allow reconstruction of sediment dispersal and basinal response to these plate-scale events. Upper Jurassic strata, for example, contain a dominant population of Late Triassic–Late Jurassic detrital zircons that reflect sediment input from the adjacent oceanic Talkeetna arc located to the north into a marine forearc basin situated on the outboard side of the Wrangellia composite terrane. The dominant population of 180–140 Ma detrital zircons in the Jurassic strata is related to a large-magmatic-flux event that extended throughout the northwestern Cordillera. By Late Cretaceous time, after final suturing of the Wrangellia composite terrane, detrital zircon ages indicate the presence of a new coeval continental volcanic arc system to the north with minor sediment input from older inboard terranes. With final subduction of the Resurrection plate during early Eocene time, the southern margin of the northwestern Cordillera was again reconfigured. Along the western Alaska Peninsula, the Aleutian and Meshik volcanic arcs initiated in response to a shift toward more orthogonal subduction. These arcs are part of a mainly oceanic arc system that initiated in middle-late Eocene time and extend over 3000 km on the northern rim of the Pacific Basin. The basinal response to this event was a shift from nonmarine to marine depositional systems and to a southerly provenance. Middle Eocene through Miocene strata have detrital zircon ages that indicate recycling of the older Mesozoic forearc strata into a developing backarc basin. Dynamic subsidence associated with the change in subduction parameters and flexural subsidence associated with loading from the volcanic arc and backarc basin strata produced the southward-thickening asymmetric sedimentary package observed today. Results from this study provide insight into both the development and the reconfiguration of sedimentary basins associated with changing plate parameters along a convergent margin.

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