Tectonic assembly of east-central Alaska: Evidence from Cretaceous–Tertiary sandstones of the Kandik River terrane

Abstract

East-central Alaska is a tectonically significant region between parautochthonous North America and the Arctic Alaska terrane to the north. The tectonic evolution of the area is recorded in Late Jurassic to early Tertiary sedimentary rocks of the Kandik River terrane. Fine-grained clastic rocks deposited in the area from Late Jurassic to Valanginian time represent a continuation of the passive margin sequence that persisted since the late Precambrian on the nearby North American margin. A pulse of quartz arenites (sandstones in the uppermost Glenn Shale and the Keenan Quartzite) reflects Valanginian rift-shoulder uplift, marking initiation of crustal upwarping and thinning that would later lead to the opening of the Canada basin. Fine-grained turbidites interpreted as distal submarine fan deposits (Biederman Argillite), Valanginian to possibly as young as Aptian, were next deposited along the passive margin. These quartz wackes contain framework grains with the same continental source as the quartz arenites, but geochemical evidence points to arc detritus in the fine-grained (pelagic) intervals. Compressional tectonics began in the Aptian, and are recorded by arc-derived volcaniclastic turbidites (Kathul Graywacke) that were quickly overthrust, buried to depths of 5–8 km, then uplifted and eroded in the Late Cretaceous. These events record the accretion of a previously unreported island arc to the Porcupine and Kandik River terranes, followed by accretion of this complex to North America. A second orogenic event followed in the latest Cretaceous to early Tertiary, when extension, possibly associated with emplacement of Yukon-Tanana terrane along the Tintina fault to the south, produced a half graben (Nation River basin) and a pull-apart basin that were filled with litharenites derived from local sources (unit TKs). These deposits were broadly uplifted and warped in the middle Tertiary, probably by regional Laramide-age events. These results are significant in that they provide evidence for a previously unreported Aptian–Albian volcanic arc in east-central Alaska. In addition, comparison of sedimentation events in east-central Alaska with those recorded in the North Slope sequence of northern Alaska provides constraints on tectonic models for the evolution of northern Alaska.