摘要
根据海底地形地貌特征和区域构造走向,可将南海海盆分为三个次海盆:西北次海盆、西南次海盆和中央次海盆。通过地磁异常资料之分析对比,在中央次海盆中鉴别出5d-11号磁异常条带,推测其海底扩张年代为晚渐新世-早中新世(32-17 MaBP);在西南次海盆中鉴别出18-13号磁异常条带,推测其海底扩张年代为晚始新世-早渐新世(42-35 MaBP)。通过对穿过中央次海盆与西南次海盆的地震反射剖面之分析,发现西南次海盆比中央次海盆多一套新生代沉积(T_6-T_g),证明西南次海盆的形成年代早于中央次海盆。用大洋基底的深度资料计算洋壳的年龄,发现西南次海盆洋壳的年龄也老于中央次海盆。由此可见,后两类资料证明了由磁异常条带所推测洋壳年龄的正确性。因此,我们认为,南海海盆存在三条扩张脊,至少经历过两次海底扩张。多扩张中心和多次海底扩张是南海海盆构造演化史的重要特征。
Based on the geomorphology and the regional tectonic trends, the South China Sea Basin is subdivided into three subbasins: i.e.NW Subbasin, SW Subbasin and Central Sub- basin. Analysing the magnetic anomalies in the Central Subbasin, 5d 11 magnetic anomaliy lineations are recognized there and might be infer that its sea floor spreading age was late Oligocene to early Miocene (32 - 17 MaB.P. ). Correspondingly, In the SW Subbasin, 13 - 18 magnetic anomaly lineations are recognized and infered that its spreading age of sea floor was late Eocene to early Oligocene (42 - 35 Ma B. P.) . Whereas interpretes the seismic profile crossing the Central Subbasin and SW Subbasin, the author finds out that there has one more layer (T_6-T_g) in the SW Subbasin than the Cen- tral Subbasin, it shows that the former is older than the later. After calculating the the depth data of the basement of the oceanic crust, the author finds that the the SW Subbasin is older than the Central Subbasin.Therefore, all the sedimentary sequences and the depth of the o- ceanic crust basement data prove the ages of the sea floor infered from magnetic anomaly lin- eations are correct. So we believe that there exist three spreading ridges and two-times of seafloor spreadings at least in the South China Sea Basin.The multi-spreading ridges and multi- times of sea floor spreding are the important characteristics in the tectonic evolution of the South China Sea Basin.
引文
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