Provenance studies and basin evolution: Insight from the Yukon–Koyukuk Basin, Alaska

Abstract

ABSTRACTThe Yukon–Koyukuk Basin is a wide, triangular depression in northern Alaska that initiated as the consequence of the collision between an intraoceanic arc and the Arctic Alaska margin. It is bordered by the metamorphic terranes of the Seaward Peninsula, the Brooks Range and the Ruby Terrane. The Yukon–Koyukuk Basin is divided into two sub‐basins separated by remnants of the volcanic arc. Two different models have been suggested for its formation. One model interprets the Yukon–Koyukuk Basin to have formed during collision in a forearc–backarc setting, while the other favours an extensional regime that was active after the cessation of collision. To test the two models, ten sedimentary samples from the two stratigraphically lowest units cropping out along the middle reaches of the Koyukuk River were analysed. Point counting and Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN®) are used to evaluate sedimentary provenance. This study also presents zircon U–Pb ages from three interbedded tuffaceous layers to better constrain the age of the units. The base of the succession indicates a volcanic source (enriched in clinopyroxene) deposited at ca 138.3 ± 0.8 Ma (2σ), while younger overlying strata are dominated by metamorphic input (enriched in garnet and epidote) reflecting the erosion of the surrounding metamorphic terranes at ca 112.6 ± 1.1 Ma (2σ). The application of a multi‐method provenance approach has been essential in constraining the formation and evolution of the northern Yukon–Koyukuk Basin. This is of significant importance for advancing the understanding of Alaskan geology and for providing insights into modern basins within analogous tectonic settings, such as the Banda Arc in Southeast Asia.