THE CRUSTAL STRUCTURE IN THE EASTERN PART OF THE NORTHERH MARGIN OF THE SOUTH CHINA SEA
YAO BO-CHU; ZENG WEI-JUN; CHEN YI-ZHONG ZHANG XI-LING(Guangzhou marine Geological Survey, Ministry of Geology and Mineral Resources,Guangzhou 510760)D.E.HAYES J. DIEBOLD P.BUHL S.SPANGLER(Lamont-Doherty Geological Obser vatory of Colnmbia University,N.Y.
North continental margin of South China Sea was passive in Cenozoic which developed 60 Ma B.P.The margin is a ideal one in the world for study of tectonic evolution of passive continental margin.The crustal structure is studied by using the data of two-ship seismic extended spread profiles acquired in project"USA-China Joint Investigation on Marine Geology of South Chine Sea". The crustal structure is featured by four-terrace thinned crust from continental shelf to deep sea plain. Crust thicknesses of the four terraces are 26-28 km,23-24km,13-15km and 5-7 km (oceanic crust)in South Chins Sea basin. This shows that it was episodic extensional in early Cenozoic. High-velocity layer with seismic velocity of 7.1-7.4 km/s is found on the bottom of the crust. The layer was brought about by the process that melted materals from upper mantle cooled on the bottom of the crust after extension of the crust.