Blueschists of the Kodiak Islands, Alaska: An extension of the Seldovia schist terrane

Abstract

The Kodiak Islands are composed of a series of northeast-trending belts of schists and deep-sea rock types that are interpreted as having been accreted to the continental margin during several discrete phases of subduction since early Mesozoic time. The Kodiak Islands schist terrane is the oldest of these accretionary belts and crops out discontinuously along the northwest side of the islands. Metamorphic rocks in this belt include quartz-mica schist, marble, metachert, greenschist, blueschist, and epidote amphibolite; the rocks yield Early Jurassic K-Ar mineral ages. These ages apparently provide a measure for the age of emplacement of the Kodiak Islands schists and are consistent with independently determined age estimates based on (1) biostratigraphy of the associated forearc basin deposits and (2) K-Ar ages from the associated plutonic arc on the Alaska Peninsula. Similarities in rock types, mineral ages, and tectonic setting indicate that the Kodiak Islands schist terrane is the southwestern extension of the Seldovia blueschists of the Kenai Peninsula.