Ages and Evolutions of the Volcanic Rocks from Ulleung-do and Dok-do

We report new K-Ar ages of volcanic rocks from Ulleung-do and Dok-do islands located at the middle of the Korea Sea; Ma for the Dok-do and Ma for the Ulleung-do. Such ages reveal that igneous activities of both Dok-do and Ulleung-do extend longer than previously reported. It is likely that igneous activity of Ulleung-do started as early as Ma which is much older than age known currently, and latest eruption and intrusion of trachyte of Dok-do lasted until Ma, which overlaps previously reported igneous activity of Ulleung-do. However, it seems that the main volcano-building stage of Ulleung-do started after 2.7 Ma and igneous activities of Dok-do were finished mostly before then, which suggests that Dok-do was farmed before Ulleung-do in the respect of main stages of volcano-building. Such explanation agrees well with the hypothesis that southeastern seamounts, Dok-do and Ulleung-do were sequentially generated by relatively fixed hotspot.