독도 화산암류의 암석학적 특성과 지구화학

Abstract

Petrological, geochemical, and geochronological studies of Dokdo volcanic rocks, East Sea, have been carried out to understand their petrogenesis. Dokdo volcanic activity is divided into three stages according to occurrences and eruption ages of rocks. The second-stage activity is accompanied by large volume of pyroclastics and lavas of intermediate composition, and occupies most of the East and West islets. K-Ar biotite and whole-rock ages indicate that Dokdo volcanic activity occurred during late Pliocene and became systematically younger toward later stages: namely, 2.7-2.4 Ma for the first-stage trachyte, 2.4-2.3 Ma for the second-stage trachyandesite and 2.2-2.1 Ma for the last-stage trachyte and dikes. Dokdo volcanic rocks are of intermediate to felsic compostions, and have OIB-like alkaline nature. The geochemical similarities between Dokdo and Ulleungdo volcanic rocks suggest that they were formed from the same mantle plume. However, considering the difference of eruption ages between Dokdo (2.7-2.1 Ma) and Ulleungdo (1.4-0.01 Ma) volcanic rocks, the former seems to have been formed by earlier hot spot activity.