南海西北海盆的构造特征及南海新生代的海底扩张

分析了南海西北海盆及其邻区的地形地貌、重磁场异常和地壳结构特征，并对穿过西北海盆和中央海盆的地震剖面进行精细解释。结果发现，西北海盆的地球物理场异常、地质构造和地壳厚度均呈ＮＥ走向展布，而中央海盆则表现为ＥＷ向特征；西北海盆中的新生代沉积比中央海盆多一套地层（Ｔ４－Ｔｇ），说明西北海盆的年龄比中央海盆老。联系到南海西南海盆和西北海盆在区域构造、地球物理场异常和地形地貌特征等方面的相似，以及西南海盆和中央海盆由磁异常条带对比得出的年龄差异，我们认为，西北海盆和西南海盆是在第一次海底扩张时（４２－３５ＭａＢ．Ｐ．）形成的，中央海盆是在第二次海底扩张时形成的。

TECTONIC CHARACTERISTICS OF NORTHWEST SUBBASIN AND SEAFLOOR SPREADING HISTORY OF SOUTH CHINA SEA IN CENOZOIC

By analyzing the topography, landform, gravity anomalies, geomagneticanomalies and crustal structure, and interpreting the seismic profile across theNorthwest Subbasin and the Central Basin, it is found that the trends of geophysicalanomalies, geological structure and crustal isopach are to the northeast in theNorthwest Subbasin. and to the east in the Central Basin. The Northwest Subbasin hasone more set of strata (T4-Tg) than the Central Basin, which means that the age ofthe Northwest Subbasin is older than the Central Basin. According to the similaritiesin the regional structure, geophysical anomalies, topography and landform, and the agedifference between the Southwest Subbasin and the Central Basin acquired byinterpreting magnetic anomaly lineations, it is believed that the Northwest Subbasinand the Southwest Subbasin formed during the firet seafloor spreading between the lateEocene and the early Oligocene (42-35 million yrs. B. P.), and the Central Basinformed during the second seafloor spreading between the late Oligocene and the earlyMiocene (32-17 million yrs. B. P.).