MESOZOIC-CENOZOIC SEDIMENTARY RECORD OF ARC ACCRETION TO THE CONTINENTAL MARGIN OF SOUTH-CENTRAL ALASKA

Accretion of the Wrangellia-Peninsular terrane to the Mesozoic continental margin of western North America defines one of the largest additions of arc-related crust to the northern Cordillera. Mesozoic-Cenozoic basinal deposits in south-central Alaska provide a >180 my sedimentary record of the migration and accretion of the Wrangellia-Peninsular terrane from an intraoceanic setting at low paleolatitudes during Triassic time to its present position along the continental margin of southern Alaska. Distinct stages of basin development define interaction between the arc complex and continental margin during migration. Intraoceanic arc - Middle Jurassic marine strata >400 m thick record sedimentation adjacent to a south-facing intraoceanic arc. Fine-grained lithologies and volcaniclastic petrofacies characterize these deposits. Oblique Collision - Upper Jurassic-Lower Cretaceous strata >3 km thick document oblique collision of the arc complex to the continental margin. Syndepositional thrusts, pluton exhumation, and synorogenic sedimentation in retroarc and forearc depocenters are diagnostic of this stage. Syncollisional strata are characterized by marine sediment gravity flow deposits that contain detritus eroded from deep structural levels of the accreted arc. Regional Suturing - Late Cretaceous suturing prompted regional folding, metamorphism, and uplift of older retroarc strata in a suture zone between the arc and former continental margin. Post-collisional continental arc – Renewed subduction produced a latest Cretaceous-Tertiary arc that intrudes older oceanic arcs, basinal strata, and former continental margin. Latest Cretaceous intrarc/retroarc basinal deposits >3 km thick record subaerial uplift of the suture zone. Marine forearc strata record erosion of coeval and accreted arcs. Transpressive shortening and strike-slip displacement - Paleomagnetic analysis of latest Cretaceous strata indicate >700 km of northward latitudinal displacement along strike-slip faults. Regional shortening prompted subsidence inboard of the suture zone and accumulation of >2 km of Tertiary nonmarine foreland basin strata. Outboard of the suture zone, >2.5 km of Tertiary nonmarine forearc basin deposits record subaerial uplift of the subduction complex and erosion of remnant and coeval arcs.