Significance of greentones for the formation of accretionaly complex of Japanese Islands during Jurassic to Paleogene

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The results obtained from this research project are summarized as follows.Petrological features and mode of occurrences of greenstones especially exposed in the Sorachi-Yezo belt were reexamined. Geochemical characteristics in respect to minor elemetns, rare earth elements, isotopic compositions of the greenstone, which are previously regarded to have N-MORB signatures, show that they are rather resemble to those of oceanic plateau basalts. In particular, Nb contents are slightly higher than N-MORB whereas HFS elements such as Y and Zr are depleted than N-MORB.Furthermore, intrusive relations of the greenstones against chert were found from several localities, indicating that the igneous activity initiated after the deposition of pelagic sediments. Therefore, these intrusive rocks may correspond to the initial stage of magmatism such as hot-spot type or oceanic plateau type magmatism, Geochemical and age data for the greenstones in the Mikabu belt in Southwest Japan have been carried out also.In situ greenstones with MORB features which were prpbably generated by the subduction of ocean ridge, are extensively described in the shimanto belt and Hidaka belt from Okinawa Island to Hokkaido along thorough Japanese Island. Age determination, mode of occurrence, petrographical and petrological features were studied for them. Systematic younging toward north of radiolarilan fossil ages in the sediments associating with the insitu greenstones bcomes to clear. Besides, interaction between basaltic rocks and intruded sediments was clarified in respect to chemical exchange between them. Some LIL elements such as K and Rb are significantly removed from the sediments whereas Si is added into the sediments near the boundary. Thus, such chmical characteristics of the silicifie sediments can be used as an indicator showing basaltic intrusions into unsolidifed sediments.