GEOLOGIC HISTORY OF THE YAKUTAT TERRANE BASED ON DETRITAL ZIRCON FISSION-TRACK ANALYSIS, SOUTHERN ALASKA

Northward transport of the Yakutat terrane along the Transition and Queen Charlotte-Fairweather transform faults led to Neogene collision of the Yakutat terrane with the southern continental Alaska margin. The sequential northwestward transport of the Yakutat terrane resulted in an overlying stratigraphy that records the erosional exhumation of thermotectonic terranes along its transport path. Strata of the Yakutat terrane include the Lower Oligocene to Lower Eocene Kulthieth Formation, the Upper Eocene to Lower Miocene Poul Creek Formation, and the Miocene-Pleistocene Yakataga Formation. Detrital zircon fission-track ages from stratigraphically coordinated samples collected in the Northern Robinson Mountains yield provenance information of the units that shed light on their transport history. For all dated samples, 50 grains were counted, morphology/color noted, and FT grain ages were deconvolved into component populations. The Kulthieth Formation has three primary cooling age populations at ~70-100 Ma, 38-58 Ma and 28-31 Ma. The Poul Creek Formation has three primary cooling age populations at ~61-67 Ma, 39-42 Ma and 24-33 Ma. The Yakataga Formation has three primary cooling age populations at ~68-77 Ma, 30-35 Ma and 15-21 Ma. The Kulthieth Formation young peak age is may be younger than deposition and so has partial resetting is a possibility. The Poul Creek and Yakataga Formations have a young population of euhedral grains that may represent a Mid-Tertiary Volcanic source and may be tied to thermotectonic sources in western British Columbia and southeastern Alaska.