[SMP34-P11] Tectonic reconstructions and origin of Cretaceous greenrocks, Tokoro Belt, NE-most of Japan
Keywords:Tokoro Belt, Accretionary complex, Mid-ocean ridge basalt, Oceanic island basalt
As mentioned above, geochemical compositions of the western Nikoro Group designate the typical composition of tholeiitic OIB. The greenstones in eastern Nikoro Group are further divided each into their localities on the basis of geochemical variation of them; moreover, the new data in this study show more detailed divisions. The eastern Nikoro Group particularly resulted from the underplating process both of MORB and OIA (oceanic island alkaline basalt) at the deeper part of subduction zone. This study proposes a new model about the origin of Tokoro Belt on the basis of the geochemistry of greenstones with geological data as follows; 1) tectonic structures of the greenstones and chert, 2) microfossil ages of chert and limestone associated with greenstones, 3) variation of metamorphic grades, 4) the exposing volume of MORB, and 5) mode of occurences of chert and limestone.