EVOLVING CRETACEOUS–CENOZOIC DETRITAL ZIRCON U-Pb PROVENANCE SIGNATURES AS A RECORD OF CORDILLERAN ASSEMBLY IN THE KANDIK RIVER REGION, EAST-CENTRAL ALASKA

The Kandik River region of east-central Alaska lies near the intersection of Arctic, North American, and Intermontane Terranes. New detrital zircon U-Pb (DZ) data from Cretaceous–Cenozoic strata illuminate evolving provenance patterns and paleogeography during Cordilleran terrane assembly. Following a protracted period of Triassic–Jurassic shale deposition along a passive margin, coarser clastic deposition of the Early Cretaceous Kandik Group commenced with the Valanginian Keenan Quartzite, which is dominated by 0.9–2.0 Ga and ~2.7 Ga Laurentian DZ grains (80% of age distribution). Coeval quartz arenites with similar DZ age spectra are common regionally, including sandstones in Arctic Alaska and Yukon associated with opening of the Canada Basin. The overlying Neocomian Biederman Argillite contains fine-grained turbidites with framework grains and Precambrian DZ age distributions that are similar to the Keenan Quartzite and suggest sourcing from the same continental provenance areas. In contrast, the Aptian–Albian Kathul Greywacke contains volcaniclastic turbidites that mark a major change in provenance with an influx of 160–240 Ma DZ grains (50% of age distribution). These grains were likely derived from an oceanic arc associated with the adjacent Angayucham-Tozitna terrane that collided with the continental margin during the Late Jurassic–Early Cretaceous Brookian Orogeny. North of the Brooks Range, the dearth of 160–240 Ma DZ grains in coeval strata of the Colville Basin suggest that a drainage divide routed Angayucham detritus mostly southward, into the Koyukuk and Kandik basins. Previous work indicates that the Kandik Group was subsequently shortened by the Charley River fold-thrust belt in the Late Cretaceous and dismembered by the Tintina strike-slip fault in the Paleogene. The Kandik Group DZ age spectra and upsection change from dominant Precambrian Laurentian to Mesozoic Angayucham grains correlates well with coeval Manley Basin units on the opposite side of the Tintina fault, supporting a hypothesized depositional connection between these two regions before strike-slip offset. Finally, Maastrichtian–Eocene nonmarine strata that unconformably overlie the Kandik Group and older rocks are dominated by 90–100 Ma DZ grains (50% of age distribution), likely derived from plutonic and volcanic rocks in the nearby Yukon-Tanana Upland to the south.