Petrochemistry and tectonic setting of the Tertiary volcanic rocks from North Sikhote Alin

Abstract

Main volcanic rocks from North Sikhote Alin are the Late Eocene alkali and tholeiitic basalts, the Early Oligocene alkali and tholeiitic basalts, the Early Miocene calc-alkali andesites and latest Early Miocene shoshonites. Basalts of the Late Eocene and Early Oligocene are accompanied with calc-alkali andesites and dacites. The Late Eocene basalts have WPB character, whereas the Early Oligocene basalts and latest Early Miocene shoshonites have IAB character.
     In the initial εNd-εSr diagram, the Late Eocene basalts have more higher Sr and lower Nd isotopic ratios than those of the Early Oligocene basalts and latest Early Miocene shoshonites. Sr isotopic ratios of the Sikhote Alin volcanic rocks have changed under 0.7040 at about 30 Ma.
     From isotopic data, the Early Oligocene basalts and the latest Early Miocene shoshonites are inferred to have been derived from comparatively depleted mantle source and the Late Eocene basalts have been derived from more enriched source.
     The Late Eocene alkali basalt volcanism took place in an immature rift zone occurred along the Asian continental margin at the embryonal stage of opening of the Japan Sea. Before the final stage of the opening, the Early Oligocene basalt and latest Early Miocene shoshonite volcanisms took place in relation to subduction of the North American plate and Pacific plate, respectively.