Rifting characteristics of eastern subbasin of South China Sea and its spreading pattern

With processing and interpretation of 25 000 km full-coverage multibeam swath data from the eastern South China Sea,it is found that NE-trending and NW-trending linear morphological features such as scarps,horsts and grabens,govern the central part (14°-17° N) of eastern subbasin.Compared with reflection seismic profiles,these NE-trending linear morpho-structures are considered to be the representation of basement structures on seabed and can be divided into three linear structural zones.The trend of the central zone is NE45°-50° occurring around extinct spreading center,the trend of the second zone is NE70°-78° on both sides of the central one and the trend of the third zone is about NE60° just on the north of the second one.These three NE-trending linear zones are formed in late-stage NW-SE-trending seafloor spreading of the eastern subbasin along NW-trending linear faults,and respectively correspond to three spreading episodes:17.0-19.0 Ma (5d-5e),19.0-21.0 Ma (5e-6a) and 21.0~24.2 Ma (6a-6c) based on the contrast of morpho-structures to magnetic lineation anomalies.