Evolution of Oceanic Crust of the Marginal Seas in the South China Sea

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There are number of marginal basins in the Northwestern Pacific region of which the Japan and South Chine Seas are studied far better than other marginal basins of the region. It is frequently referred that Japan Sea and South China Sea have good similarities from the viewpoint of not only general topographic shape but also seismic and magnetic data. Both marginal basins have oceanic and continental crust with some clearly definable magnetic lineations. The similar characteristics of the erratic change in the trend of the magnetic trend in both seas infers number of faults hidden under the thick sediment cover hardly noticeable only by bathymetric observations. These marginal seas are thought to be in the tension-induced rifting stage along the boundary between oceanic and continental plates.A series of marine geophysical observations by the R/V Shi Yan II in the northern margin of the South China Sea were carried out in early summer of 1993. The objective of this scientific cruise is … More to collect data to study comparative geosciences on the marginal seas, i.e., Japan and South China Seas, in terms of the transition in the seismic structure and magnetic characteristics in the transient boundary between continental and abyssal basin. The data include single channel seismic reflection, airgun - OBS refraction profiles, total and three component magnetic data, and gravity data.The proton, precession and fluxgate magnetometer data, tilt of the measuring devices by use of horizontal and vertical gyroscope are collected by a microcomputer and recorded on a MO disk every two seconds along 400 km-long track lines. Number of complete circular turns of the vessels heading were run during the cruise in order to eliminate the effect of the ship's magnetization from the field data. The three component anomalies can then be calculated by referring to the IGRF90.The set of new three vector geomagnetic anomalies obtained by this study, and the total magnetic profiles compiled so far show that asymmetric and discontinuous seafloor geography and roughness of the acoustic basement reflect the variability of the spatial and temporary spreading rate and direction. Less