Origin and causes of complex magnetic anomalies of Dokdo and neighboring guyots

Abstract

To identify the causes of complex magnetic anomalies on the three guyots located in the northeastern part of the Ulleung Basin, East Sea, a linear least-squares inversion method was implemented. Modeling under the assumption that the guyots are uniformly magnetized did not yield reliable results. However, an inhomogeneously-magnetized model shows relatively high goodness-of-fit parameters and low residual magnetic anomalies, indicating that these guyots are considerably nonuniformly magnetized. Our modeling results show that all three guyots show similar magnetic patterns. Magnetic anomalies north of guyots have different magnetic polarities at similar depths in the south, indicating that these magnetic anomalies were formed at different times. These results suggest that relatively short wavelengths and complicated magnetic anomalies in the study area are the compound result of different magnetic polarities. Paleomagnetic analysis on trachyandesite lavas and pyroclastic breccia indicates a thermo-chemical remagnetization activity after Reunion Subchron (2.138–2.122 Ma). This result also suggests that remagnetization contributes to the creation of complex magnetic anomalies to some extent as well. In addition, the upward continuation results up to 1500 m using a FFT routine show high positive magnetic anomalies with a linearly segmented shape at the base of guyots. These linear and positive magnetic anomalies are interpreted as volcanic eruptions along fissures because mafic lava should have much higher magnetic anomalies compared to continental crust, where guyots are located. Therefore, we interpret that the complex magnetic anomalies distributed in the study area are due to polarity reversals occurring at least twice, and were formed during the formation of the current guyots as volcanic eruptions derived from fissures.