Characteristics of crustal magnetic structures in the Tsushima (Ulleung) and Japan Basins from vector magnetic anomalies

Hiroyuki Kato,Masao Nakanishi,Chan Hong Park,Nobuhiro Isezaki,Chang Hwan Kim

doi:10.1186/bf03352751

Hiroyuki Kato, Masao Nakanishi + Show 3 more

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https://doi.org/10.1186/bf03352751

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Abstract

Abstract Magnetic surveys by a Deep-tow Three-Component Magnetometer (DTCM) were conducted in the northeastern part of the Japan Basin and the central part of the Tsushima (Ulleung) Basin. Magnetic lineations are recognized clearly in the former area, whereas they were not recognized by previous studies in the latter area. The high-quality vector magnetic anomaly data obtained by DTCM enables the precise determination of the strikes of magnetic lineations and the positions of magnetic boundaries. Magnetic anomalies measured by DTCM show the characteristics of linear magnetic anomalies in both basins. The strikes of magnetic lineations are N47°E in the Japan Basin and N82°E in the Tsushima Basin. The estimated magnetization intensities of magnetic source models constructed from the amplitudes of analytic signal calculated from vector anomalies and the crustal structures determined by seismic studies are similar to those of typical extrusive basalt in both basins. The observed anomalies in the Japan Basin contain a short wavelength anomaly which cannot be explained by the model. Their ages may be chrons C5Cr (16.726–17.277 Ma), C5Dn (17.277–17.615 Ma), C5Dr (17.615–18.281 Ma), and sub-chron C5Dr.1n which was identified by a paleomagnetic study. The estimated half-spreading rate is 2.0 cm/yr, which is slower than that estimated by previous study. The observed anomalies in the Tsushima Basin show that there is a partial magnetization high. This may indicate that not all of the sources of magnetic lineations in the Tsushima Basin changed to low magnetization by the effect of thick sediment cover and the intrusions of a large amount of dikes after the formation.

Highlights

The Japan Sea (East Sea) is one of the back-arc basins in the northwestern Pacific and comprises three main basins, the Japan, Yamato, and Tsushima (Ulleung) Basins (Fig. 1)
The studies based on magnetic methods support the conclusion that the crust of the eastern part of the Japan Basin was formed by seafloor spreading, the strikes of magnetic lineations determined by proton precession magnetometer (PPM) and STCM are different
We have shown that the vector geomagnetic field data acquired by Deep-tow Three-Component Magnetometer (DTCM) is more effective than a single component field and three-component field measured by STCM to examine the characteristics of magnetic anomaly and crustal magnetic structure

Summary

Introduction

The Japan Sea (East Sea) is one of the back-arc basins in the northwestern Pacific and comprises three main basins, the Japan, Yamato, and Tsushima (Ulleung) Basins (Fig. 1). The unfiltered anomalies obtained by STCM and DTCM in the Tsushima Basin show the azimuths N32◦E and N86◦E which minimize the RMSs of H 2 The unfiltered anomalies obtained by STCM and DTCM in the Japan Basin show the same azimuth N47◦E which minimizes the RMSs of H 2 The distance where the amplitudes of the four large peaks (L1 to L4) decrease by a half is 3.7 ± 0.5 km This result shows that the depth of the magnetic sources is 6.2 ± 0.5 km below the sea-surface (taking the depth of DTCM (2.5 km) into account), which is almost identical with that of Layer 2A (5.5–6.0 km) and Layer 2B (6.0–7.0 km) determined by Hirata et al (1992).

Tsushima Basin

Conclusion