Geochemical investigation has been carried out for the volcanic rocks from Ulreung island, Korea. The volcanic rock suite is characterized by highly alkalic nature, and some of them contain more than 6wt.% K_2O and Na_2O. The igneous activity may not be related to Pacific plate subduction, or the Japan Sea spreading. It will be hardly possible to explain how to concentrate the abundant incompatible elements in the mantle source in a limited short period beneath Ulreung island. Most of the chemical features of the volcanic rocks are consistent with simple fractional crystallization. It should be pointed out, however, that significant compositional gap was recognized only in K_2O content, but not in the other LILEs. The difference between K_2O and the other LILEs will be hardly explained if fractional crystallization differentiation plays a major role. The volcanic rocks from the island are either highly enriched in K_2O or not so enriched in K_2O. No intermediately K_2O-enriched sample was found. This is contrasted with gradual increase in Na_2O content. This chemical features will require complicated mechanisms.論文Articl
