동해 울릉분지 독도 해산들의 고지자기 연구

Abstract

Paleomagnetism and loading history of Dokdo seamounts are studied from analysis of magnetic data. Our study area is the northeastern part of the Ulleung Basin where an island (i.e. Dokdo), which is consisted of very small subaerial islets and a large submerged volcanic edifice, and two seamounts (i.e. Simheungtaek and Isabu Tablemounts) are located. They have submerged guyot summits which are flat and gently slope but their flanks are steep. Magnetic anomalies occur most complicated over the Dokdo, SWW-NEE linear pattern over the Simheungtaek Tablemount and small amplitude over the Isabu Tablemount. VGPs (Virtual Geomagnetic Poles) of the Dokdo seamounts were determined by the least square and the seminorm magnetization methods with 1500 m upward continued magnetic anomalies. Because of magnetic anomalies of combined dipoles for the Dokdo, it is considered that the VGPs of the Dokdo with all magnetic anomalies have some errors that the VGPs are the low latitude and the large difference between both VGPs occurs. The VGP of the Isabu Tablemount shows the low latitude due to overprints of reversals in Tertiary, the effect of nondipole geomagnetic field and the distortion of magnetization owing to intrusion after the formation of the seamount. The VGPs of the Simheungtaek Tablemount and the Dokdo with normal dipole anomaly are located near to the magnetic pole at the present time. VGP dispersion shows they are acceptable. The successive formation of the Dokdo seamounts based on the previous results of age dating and flexure model, the VGPs of this study, and the geomagnetic polarity time scale suggest that the Isabu Tablemount and the Simheungtaek Tablemount formed at 10 1 Ma and 7 1 Ma in normal polarity intervals, respectively. Also, they indicate that the first large eruption of the Dokdo was in normal polarity interval and the second large eruption in reversed polarity interval after the formation of the Simheungtaek Tablemount. The formation times for the Dokdo sea