PETROGRAPHIC AND DETRITAL ZIRCON DATA FROM THE KAHILTNA BASIN SUGGEST EARLY CRETACEOUS JUXTAPOSITION OF THE CONTINENTAL MARGIN AND THE PENINSULAR TERRANE IN THE WESTERN ALASKA RANGE
Sandstone petrofacies indicate different sources for the opposite sides of the Kahiltna basin. Clasts in the NW section, including black radiolarian argillite cut by quartz veins, resemble rocks in the adjacent Farewell terrane; sparse Lv reflect sparse volcanic rocks near the NW basin margin. NW section DZ age peaks resemble those of the Farewell and Yukon Tanana terranes, and support continental margin sources for the NW section. Abundant Lv and cpx in SE petrofacies support sources in volcanic arc rocks of the Peninsular terrane SE of the basin. Sparse Precambrian DZ ages in the Old Man petrofacies near the basin center suggest limited sediment input in the Late Cretaceous from multiple sources.
Sandstone compositions and ages suggest deposition dominated by local basin margin sources and initial deposition in the Early Cretaceous for the NW section, and local margin sources and initial deposition in the Late Jurassic for the SE section. Our data support Early Cretaceous uplift and erosion of the NW flank of the Kahiltna basin in the western Alaska Range, and juxtaposition of the Peninsular terrane and continental margin at this time.