The southern Kahiltna terrane: Implications for the tectonic evolution of southwestern Alaska

Regionally extensive and highly deformed Jurassic to Cretaceous basinal turbidite deposits occur along most of the inboard boundary of the Talkeetna superterrane in southern Alaska and western Canada. The southern Kahiltna terrane of southwestern Alaska consists largely of such basinal deposits. Regional and detailed studies in and adjacent to this terrane suggest several new conclusions regarding the origin of the basin and its role in the tectonic evolution of southwestern Alaska. Stratigraphic, sedimentologic, compositional, and structural evidence suggests that the Upper Jurassic to Lower Cretaceous strata of the southern Kahiltna terrane were derived from and deposited on rocks of the adjacent Talkeetna superterrane. Deposition of these clastic rocks apparently postdated arc magmatism in the Talkeetna superterrane, suggesting deposition in a basin developed on the suture between the Talkeetna superterrane and North America. If true, this observation implies that collision of the Talkeetna superterrane with North America began prior to latest Jurassic time, probably at a more southerly location. The superterrane has since been translated northward, probably by coast-parallel strike-slip displacement, to its present location, where it was structurally juxtaposed with middle to Upper Creteceous rocks of the Kuskokwim group. A magmatic overprint indicates that the Talkeetna superterrane was in approximately its present location by latest Cretaceous to Paleocene time.