Geochemistry and geodynamic setting of Late Cretaceous-Miocene basalts in the southern Korean Peninsula

Newly obtained data highlight strong geological and geochemical differences between Late Cretaceous-Paleogene and Eocene-Middle Miocene volcanic rocks in the southern Korean Peninsula. The rocks are spatially separated and differ in the proportions of acid and basic varieties. The Late Cretaceous-Paleogene basalts are similar to suprasubduction rocks in having high Al^sub 2^O^sub 3^, LILE, and Th contents, and low TiO^sub 2^ and HFSE contents. The Miocene basalts have a composition intermediate between those of subduction and within-plate rocks. Compared to subduction rocks, they are lower in radiogenic Sr, K, LILE (Cs, Rb, Ba), and Th and higher in MgO, Ni, Ti, and HREE. A drastic change in U, Ba, Rb, Ce, Th, and ^sup 87^Sr/^sup 86^Sr in the basic volcanic rocks of the southern Korean Peninsula at the Late Cretaceous-Paleogene boundary suggests a decreasing sedimentary contribution to the magma. The latter testifies to a change in the direction of the motion of the oceanic and continental plates, increasing compressional forces and, finally, the cessation of subduction. The synthesis of the original authors and published data on Cenozoic volcanism of the southern Korean Peninsula and the eastern Sikhote Alin showed that the tectonic evolution of the eastern Eurasian margin occurred in four stages: Late Cretaceous-Paleogene, Eocene-Oligocene, Early, and Middle-Miocene.[PUBLICATION ABSTRACT]