Time-space distribution and petrologic diversity of Japanese ophiolites

Abstract

The Japanese ophiolites occur as nappes and melanges. Nappe-type ophiolites formed and were emplaced within 20-30 Ma in the Ordovician, Permian, and Jurassic-Cretaceous periods, corresponding to the circum-Pacific ophiolite pulses. The Paleozoic ophiolite nappes are distributed in Honshu, while the Mesozoic ones are in Hokkaido. In southwestern Honshu, the Jurassic accretional complex is overthrust by the Permian Yakuno ophiolite which in turn is overridden by the Ordovician Oeyama ophiolite. Most of Japanese nappe-type ophiolites may be fragments of ancient oceanic crust-mantle forming island arc-marginal basin systems, and the melange-type ophiolites may represent underlying subduction zone, in which subducting MORB crust-mantle, seamounts and oceanic arc volcanoes were crushed and mixed-up. -from Author