Abstract
Four formational-geochemical types of Cenozoic basaltoids were distinguished in the Japan Sea: (1) continental tholeiites, (2) volcanic rocks of island-arc type, (3) marginal sea tholeiites and products of their differentiation, (4) alkali volcanic rocks of continental rift type. The rocks have a geochemical affinity both to oceanic tholeiites and to basalts of the calc-alkali series of island-arc type. The study of Cenozoic basaltoids has enabled us to suggest a theory of the origin of the Japan Sea and its structures.
