利用区域磁异常研究东海陆架区基底构造

The Study on the Basement Structure with the Regional Magnetic Anomalies in the East China Sea

根据海磁异常求取了东海陆架区区域磁力异常,由此反演了磁性界面和视磁化强度分布。结合其他地质、地球物理资料,对该区基底构造特征作出分析。指出本区基底的南北两部分分别属于两种不同性质的块体;其分界是北到舟山—国头断裂,南到鱼山—久米断裂之间的复杂带;而沿西湖凹陷与基隆凹陷一线,在盆地发育前可能发生过较大规模的隆起剥蚀。这些基底构造特征,受到后期北北东向断裂的改造。

On the basis of the magnetic data in the East China Sea, the authors quantitatively inverse the depth of the magnetic boundary by the spectral analysis of moments, and using seismic information, calculate the apparent magnetization in space-domain and the thickness contour map of the basement of weaker magnetism. Combining with other geophysical and geological data there, the authors come to some conclusions as follows: (1) The basement of the East China Sea may be subdivided into two pa-rts by the zone from Zhoushan-Guotou fault to Yishan-Jiumi fault. In the southern part, values of apparent magnetization are larger, the outline of magnetic boundary is similar to that of the seismic basement, and the age of basement rock is 1680Ma. According to Lingfeng borehole, in the northe-rn part, values of apparent magnetization are very low even near zero, the thickness of the basement with weaker magnetism is much thicker except in the Xihu depression, and there are different structural styles in magnetic boundary and seismic basement. (2) Along the Xihu and Jilong depression, depths of both surfaces of mag-netic and seismic basements are the same, and there exist some isolated magnetic anomalies, which may be caused by the basic rocks such as basalt and the like. Thus, there had been a rifting process which caused the deve-lopment of the depression in this area. (3) The characteristics of the basement in the East China Sea was effec-ted by the fault system in the NNE direction, which was formed in Indo-Sinian and/or Yanshanian.