Radiolarian age of greenrock-chert-limestone sequence and its accretionary process of the Nikoro Group in the Tokoro Belt, eastern Hokkaido, Japan

Abstract

Radiolarian ages and mode of occurrence of chert and red shale of Mesozoic greenrock complex (the Nikoro Group) of the Tokoro belt, eastern Hokkaido have been investigated. The Nikoro Group is an accretionary complex formed by subduction of the Kula plate along the southern margin of the Okhotsk microcontinental block in the Late Cretaceous. The Nikoro Group is composed mainly of greenrocks, including pillow lava, dyke, hyaloclastite, volcanic sedimentary rocks, red shale, chert and limestone. On the basis of the geologic structure, lithologic characteristics and metamorphic condition, the Nikoro Group can be subdivided into four units, I, II, III, and IV. The rocks range in age from Middle Jurassic to late Cretaceous. -from English summary