A Late Paleozoic Volcanic Arc in the Eastern Alaska Range, Alaska

Upper Paleozoic strata in the eastern Alaska Range consist of a submarine volcanogenic complex over 2,800 m thick (Delta River sequence) overlain by at least 1,300 m of terrigenous sediments, limestones, and black shales (Mankomen Formation). The volcanic complex is calc-alkaline in character, and more than half are andesitic to dacitic in composition. Terrigenous sediments in the Delta River sequence and in most of the Mankomen Formation were derived from volcanic sources. However, in the middle part of the Mankomen Formation near Gulkana Glacier, terrigenous sediments appear to have been derived largely from a chert-quartzose metamorphic source. The calc-alkaline character of the upper Paleozoic volcanic rocks suggests the existence of a late Paleozoic volcanic arc-subduction zone in the eastern Alaska Range. Large amounts of siliceous volcanic material in the Delta River sequence and clasts of quartzose metamorphics in the Mankomen Formation further suggest that the late Paleozoic arc developed on continental crust. If this tentative conclusion is correct, then the late Paleozoic volcanic arc may be a northerly continuation of the late Paleozoic continental arcs thought to exist in southeastern Alaska and westernmost Canada.