边缘海构造旋回:南海演化的新模式

Tectonic cycle of marginal oceanic basin:A new evolution model of the South China Sea

南海边缘海构造旋回包括古南海形成与萎缩及新南海形成与萎缩两个构造旋回,形成中央洋壳、大陆坡和大陆架。古南海扩张前南海具有统一拼合基底"古南海陆块",古南海白垩纪末—始新世为扩张期,渐新世—第四纪为萎缩期,现今洋壳已基本消减殆尽。新南海古—始新世为陆内裂谷期,渐新世晚期—中中新世为洋壳扩张期,中中新世至今为萎缩期,表现为南北向扩张停滞,菲律宾岛弧向西仰冲,但处于萎缩期早期。上述两个旋回叠加控制了南海区域构造格局的形成。边缘海构造旋回控制了南海各大陆边缘及地块性质。北部大陆边缘为被动大陆边缘;南沙地块具有漂移性质;南部大陆边缘为多期叠加型活动大陆边缘,西部具有转换特征,东部为挤压岛架型大陆边缘。

The South China Sea is tectono-geographically composed of the central ocean crust, continental slopes, and continental shelves. The tectonic evolution of the marginal oceanic basin in the South China Sea includes two cycles.. Paleo- and New South China Sea tectonic periods, both of which had undergone formation and shrink stages. Prior to the Paleo-South China Sea, there used to be a united basement in the present basin area before the Cenozoic. The Paleo-South China Sea had undergone rifting, drifting and subduction stages. The two former stages are characterized by extension in the periods from the Late Cretaceous to the Eocene. The subsequent shrinking period was from the Oligocene to the Quaternary, and the related oceanic crust had been subducted and disappeared. The new South China Sea had undergone two construction stages including intracontinental rifting during the Paleocene to the Eocene and marginal continental drifting during the late Oligocene to the middle Miocene, which were followed by the shrinking episode since the middle Miocene. The shrinking stage was characterized by ceasing of the north-south expansion in the area probably owing to the Philippine island arc westward obduction from the middle Miocene to the present. The two tectonic cycles of marginal oceanic basin controlled the regional tectonic patterns, natures of the component blocks, and attributes of the basin margins. As the results of the two tectonic cycles, the northern margin is a passive continental margin; its southern Nansha block is a drifted block from south; the southern edge is a kind of polyphase active continental margin; its western margin is bounded by strike-slip fault system; and the eastern part is enclosed by the Philippine Island Arc showing compressional features.