Provenance, U-Pb detrital zircon geochronology, Hf isotopic analyses, and Cr-spinel geochemistry of the northeast Yukon-Koyukuk Basin : Implications for interior basin development and sedimentation in Alaska

• Published in: GSA Bulletin
• Main Authors: O’Brien, Timothy M., Miller, Elizabeth L., Pease, Victoria, Hayden, Leslie A., Fisher, Christopher M., Hourigan, Jeremy K., Vervoort, Jeff D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper 2018
• Subjects: Earth and Related Environmental Sciences; Geovetenskap och miljövetenskap; Arctic; Yukon; Brooks Range; Alaska
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-155028; https://doi.org/10.1130/B31825.1

The Yukon-Koyukuk Basin is a large depression that covers ∼118,000 km2 in western interior Alaska and is divided into two subbasins by a volcanic arc assemblage. Interpretations of the depositional setting of the northern Kobuk Koyukuk subbasin vary from a syncollisional forearc basin to a postorogenic successor basin formed by lithospheric extension. New results from sandstones and conglomerates collected from the Kobuk Koyukuk subbasin provide evidence for the timing of basin development, insight into the provenance of coarse siliciclastic sediments, and understanding of the nature of Cretaceous paleogeography and paleodrainage of Arctic Alaska. Early sedimentary rocks of the Kobuk Koyukuk subbasin contain abundant mafic to ultramafic volcanic and plutonic lithic fragments and mafic heavy minerals (e.g., spinel, clinopyroxene, and amphibole). They also contain abundant Middle Triassic to early Late Jurassic zircons (240−160 Ma; peak maximum ca. 200 Ma) that yield highly juvenile Hf isotopic compositions. Geochemistry of chromium spinels (Cr# = 0.17−0.86) suggests crystallization in an immature arc setting that likely developed over mid-ocean-ridge basalt−type crust. These early sediments originated from the mafic and ultramafic rocks of the Angayucham terrane, which was once much more extensive. These results suggest that the Angayucham terrane consists of an obducted Middle Triassic to early Late Jurassic oceanic arc complex that was coeval with oceanic- to continental-margin mafic arc magmatism in the Canadian Cordillera. Our generalized stratigraphy, along with U-Pb ages and Lu-Hf isotope analyses of zircons from sedimentary rocks of the Kobuk Koyukuk subbasin, reflects the tectonic and/or erosional unroofing of the adjacent southern Brooks Range and Ruby terrane. U-Pb ages of detrital zircons collected from the stratigraphically lowest mafic- to ultramafic-rich strata yield maximum depositional ages (107 Ma) that reflect initial erosion of the structurally highest Angayucham terrane and initiation of basin ...