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根据对地磁场新老资料的分析,我们在南海盆地中辨识出一种对称的海底扩张模式。南海海底扩张的活动期是中渐新世——早中新世(3200万年—1700万年)。海底扩张的线性磁异常的方向近似于东西向,残存的扩张中心位置同北纬15°附近的海山链走向一致。只有盆地的东部才存在这种线性磁异常。在中国大陆边缘和礼乐滩地块边缘的大陆坡——深海盆地边界向陆一侧有一个磁场平静带。在磁场平静带上,重力自由空间异常的值极小,它可能是大洋地壳向大陆地壳的过渡带。中国大陆架和礼乐滩上的钻井资料证实了我们关于线性磁异常所表示的南海盆地的断裂和扩张时间的论断。巴拉望海槽最东端的俯冲带可能受尤鲁根断层的限制。在中渐新世以前,北巴拉望很可能连结在礼乐滩地块和中国大陆边缘上。南海西部三分之一地区的调查工作很少。根据有限的一点资料可以认为:这一部分地区的扩张结构和其余地区有很大的不同。
Based on the analysis of new and old data of geomagnetic field, we identify a symmetrical seafloor dilatancy pattern in the South China Sea Basin. The active phase of the South China Sea seabed expansion is the Miocene - Early Miocene (32 million to 17 million years). The direction of linear magnetic anomalies in seafloor expansion is similar to the east-west direction, and the remaining center of expansion is consistent with the seamount chain near 15 ° North Latitude. This linear magnetic anomaly exists only in the eastern part of the basin. On the continental margin at the edge of the Chinese mainland and at the edge of the ritach beach massif, there is a zone of calm at the continental side toward the continental margin. In the zone of calm magnetic field, the value of the gravity free space anomaly is very small, which may be the transitional zone from the oceanic crust to the continental crust. Drilling data from China’s continental shelf and Ritual Beach confirm our claim that the linear magnetic anomaly indicates the time of the South China Sea basin’s failure and expansion. The subduction zone at the easternmost part of the Palawan Trough may be limited by the Yurgen Fault. Before the Oligocene, North Palawan is likely to be linked to the plots of Rittal Beach and the margins of mainland China. Survey work in the western part of the South China Sea is rare. Based on a limited amount of information, it can be argued that the expansion structure in this part of the country is very different from the rest.