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

西北太平洋地区有许多边缘盆地，其中对日本海和南海的研究远远好于该地区的其他边缘盆地。人们经常提到日本海和南海中国海不仅从一般地形形态上看具有很好的相似性，而且从地震和磁学资料上看也是如此。这两个边缘盆地都有洋壳和陆壳，具有一些清晰可定义的磁性线条。两个大洋的磁势趋势的不稳定变化的相似特征，推断出隐藏在厚厚的沉积物覆盖下的断层的数量，仅通过水深观测很难察觉到。这些边缘海被认为处于大洋和大陆板块交界处的拉张裂谷阶段。1993年初夏，石艳二号海洋物理研究所在南中国海北缘进行了一系列海洋地球物理观测。这次科学巡航的目标是…更多的是收集数据，以研究边缘海，即日本海和南中国海，大陆和深海盆地过渡边界的地震结构和磁性特征的转换。这些数据包括单通道地震反射、气枪-OBS折射剖面、总和三分量磁数据以及重力数据。质子、进动和磁通门磁力计数据以及利用水平和垂直陀螺仪测量装置的倾角由微型计算机采集，并沿400公里长的轨道线每隔2秒记录在MO磁盘上。为了从现场数据中消除船舶磁化的影响，在巡航过程中航行的船舶运行了完整的圆形转弯次数。这组新的三个矢量地磁异常表明，不对称和不连续的海底地形以及声学基底的粗糙度反映了空间和临时扩展速率和方向的变化。较少

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