Stratigraphic framework and detrital history of upper Triassic-Cretaceous strata in the northwestern Talkeetna Mountains, southern Alaska: A preserved record of arc accretion along a continental margin

Mesozoic strata of the northwestern Talkeetna Mountains of south-central Alaska are located in a regional suture zone between the allochthonous Wrangellia composite terrane (composite island arc) and the former Mesozoic continental margin of North America (i.e., the Yukon-Tanana composite terrane). The record of island arc accretion to the continental margin is recorded by a distinct three-part stratigraphy that is interpreted to represent pre-, syn-, and post-collisional stages of accretion during Late Triassic-Cretaceous time. Pre-collisional stratigraphy is represented by interbedded lavas, fossiliferous limestone, and volcaniclastic strata of the Upper Triassic-Lower Jurassic Honolulu Pass formation. Syn-collisional strata are represented by Upper Jurassic-Lower Cretaceous clastic marine strata of the Kahiltna assemblage. A transition from syn- to post-collision is represented by Cretaceous nonmarine strata of the Caribou Pass formation. A similar three-part Mesozoic stratigraphy appears to exist in other parts of south-central and southwestern Alaska along the suture zone based on previous regional mapping studies. The top of the Honolulu Pass formation and base of the Kahiltna assemblage is defined by a condensed stratigraphic interval and depositional hiatus that is interpreted to represent a ∼45 m.y. period of limited to no sedimentation during Middle and part of Late Jurassic time. U-Pb detrital zircon ages from syncollisional strata of the Kahiltna assemblage reveal three stages of uplift and erosion associated with Upper Jurassic-Cretaceous island arc accretion. The initial stage occurred during Late Jurassic time (latest Oxfordian) and is recorded by the occurrence of detrital zircon ages that overlap with source areas in the Wrangellia composite terrane. The second stage occurred during Early Cretaceous (Barremian-Aptian) time and suggests detrital input from the continental margin and Wrangellia composite terrane. The final stage occurred during latest Cretaceous (Albian) time and is recorded by the occurrence of detrital detrital zircon ages that overlap primarily with source areas from the continental margin. A similar uplift and erosional history appears to be recorded from U-Pb detrital zircon populations of age-equivalent strata in southeastern Alaska