STRATIGRAPHIC FRAMEWORK, DETRITAL ZIRCON PROVENANCE, AND REGIONAL TECTONIC CONFIGURATION OF MESOZOIC SEDIMENTARY BASINS OF EAST-CENTRAL ALASKA

Jurassic-Cretaceous strata of the Nutzotin, Wrangell Mountains, and Wellesly basins exposed in east-central Alaska formed coeval with the accretion of the oceanic Wrangellia composite terrane (WCT) to the continental margin. This study presents new U-Pb and Hf isotope detrital zircon data from these basins in order to determine the provenance of sediment, as well as to assess the link between depositional and collisional processes along the northwestern Cordilleran margin.

U-Pb detrital zircon ages (n=2005) from upper Jurassic-lower Cretaceous strata in the Nutzotin basin have dominant populations of 314-297 and 172-127 Ma, (Mz=96%, Pz=4%, pC=<1%), and epsilon Hf values (n=100) that are juvenile to slightly evolved (+15.1 to -0.5). U-Pb detrital zircon ages (n=283) from upper Jurassic-upper Cretaceous strata of the Wrangell Mountains basin yield dominant populations of 310-297, 168-144, and 80-75 Ma (Mz=83%, Pz=14%, pC=3%). U-Pb detrital zircon ages (n=150) from upper Jurassic-lower Cretaceous strata of the Wellesly basin yield dominant populations of 1853-1030, 440-355, 204-199, 189-168, and 160-126 Ma (Mz=57%, Pz=30%, pC=13%), and epsilon Hf values (n=24) that are juvenile to highly evolved (+9.6 to -14.4). Our data show that detrital zircon ages from the Nutzotin and Wrangell Mountains basins overlap with magmatic sources associated with the WCT whereas ages from the Wellesly basin overlap with sources associated with the continental margin. Integrating our new data from the Nutzotin and Wrangell Mountains basins with published detrital zircon ages from age-equivalent basins delineate regional linkages of depositional and tectonic processes. This integration also documents a major reconfiguration in sediment transport pathways along the convergent margin between the Jurassic and Cretaceous. Finally, similar detrital zircon ages of the Wellesly basin and Kahiltna basin, exposed in the central Alaska Range, suggest that these basins were once linked prior to post-Cretaceous strike-slip displacement on the Denali Fault.

Overall, our data have major implications regarding the accretionary history of the WCT, which includes the timing of accretion, tectonic setting of sedimentary basins, subduction polarity, and post-accretion strike-slip displacement.