Permalink : http://hdl.handle.net/2115/36785

Basalts and dolerites from the late Jurassic to early Cretaceous Sorachi Group and the Cretaceous melange complex in the central axial zone of Hokkaido are classified into the following three types: high K2O type alkaline basalts, characterized by high abundance in K2O, TiO2, P2O5 and normative nepheline, low K2O type alkaline basalts with high Na2O/K2O ratio and normative nepheline, and MORB type tholeiites, poor in K2O, TiO2, P2O5. The basaltic pillow lavas, dolerite dykes and sheets, observed as autochthonous members of the Upper Sorachi Group, correspond to the low K2O type alkaline basalts. The basaltic pillow lavas in the Lower Sorachi Group are of the MORB type tholeiites. Exotic blocks of basalt and dolerite in the Cretaceous accretionary melange complexes involve both the high K2O type alkaline basalts and the MORB type tholeiites.