深海钻探与南海

OCEAN DRILLING PKOGRAM AND THE SOUTH CHINA SEA

本文从南海北部陆缘、南部陆缘和南海中央海盆的地质构造与地球物理主要特征及尚未解决的重要地质问题来阐述在南海进行深海钻探的意义。南海北部陆缘是离散型大陆边缘。在陆壳与洋壳之间的磁静区是两者的过渡区。对它的研究直接关系到南海的形成演化与沉积盆地的成因。深海钻探需解决的主要问题是了解磁静区基底下的物质是减薄的过渡壳还是古洋壳。南海南部陆缘与北部陆缘不同，是聚敛型大陆边缘，它的构造与地球物理场特征与北部陆缘也不相同。钻探的目的主要是了解南沙岛礁区早第三纪与前第三纪地层特征，研究它的来源及新生代地层的含油气性。南海中央海盆的磁异常１１－７的走向近Ｅ－Ｗ向，异常６－５ｅ的走向为ＮＥ向。南海西南海盆的磁异常走向为ＮＥ向，因此应在上述磁异常走向不同及年龄不同海区及西南海盆进行深海钻探，确定异常的年龄及洋壳的物质组成。

The paper discusses the significance of proposed ocean drilling sites in the South Chi-na Sea(SCS)on the bases of geological and geophysical characteristics of the northern andthe southern continental margins and the central basin of the SCS , as well as unresolvedtectonic problems for the area. The northern continental margin of the SCS is a divergent one. In between the conti-nental and oceanic crusts there is a magnetic quiet zone , with southward thinning uppercrust and lower crust. The proposed drilling sites are to investigate the materials underly-ing the magnetic quiet zone and the nature of this zone. The southern continental margin of the SCS is a convergent one,in contrast with thenorthern margin in structural and geophysical styles. Drillings in the southern margin havebeen concentrated in the shelf areas to the south. It is necessary to drill the Nansha area(the Dangerous Grounds)in order to understand the tectonic evolution of the entire south-ern margin. Major objectives of the proposed drilling sites are to study Tertiary and pre-Tertiary stratigraphy and material source of the area. In cooperation with the scientists from the Tokyo University ,we surveyed the north-ern portion of the central basin of the SCS with a three-axial magnetometer, Results showmagnetic anomalies 11 to 7 with nearly E-W orientation,and anomalies 6 to 5e with a NEorientation. In the SW subbasin of the SCS, magnetic anomalies strike in a NE direction.Drilling sites in these areas are proposed to determine the ages of these magnetic anomaliesand the materials of the oceanic crust of the SCS.