Discovery of sheeted dikes in the Cretaceous accretionary complex of the Idonnappu Zone, Hokkaido, Japan

Abstract

A tectonic slice consisting of sheeted dikes has been found in the Oku-Niikappu Dam Complex (ONDC), a mid-Cretaceous accretionary complex in the Idonnappu Zone, Hokkaido. The sheeted dikes are composed of gabbroic to diabasic rocks with relict clinopy-roxenes showing a character of island arc and transitional from arc to oceanic tholeiites. The dikes are considered to have originated from an intraoceanic remnant arc which was finally accreted, forming the ophiolitic assemblage of the ONDC. Pre-subduction exposure of the sheeted dikes in an pelagic environment, as suggested by the presence of gabbroic clasts in the oceanic debrite, allowed accretion of the sheeted dikes to the continental margin.