TWO PALAEO-OCEANS AND SEDIMENTARY BASINS DURING MESOZOIC ERA IN CHINA

The Tethys Ocean is composed of the Bangong Lake-Nujiang Small Ocean and Yarlung-Zangbo Main Ocean,as well as the Lhasa small blocks in the West China.The evolution of Tethys can be divided into 5 stages.1)Rifting stage(P);2)Spreading stage(T-J_2-3).3)Closing stage of Bangong Lake-Nujiang Ocean(J_2-3-K₁).The Lhasa blocks drifted to the north.The Bangong Lake-Nujiang Ocean closed from east to west.At the same time, the Lhasa blocks cottaged to the Asian Massif.4)Subduction stage(K₁-E₂).The Yarlung-Zangbo Main Ocean Basin subducted to the north.The Gangdese continental margin volcanic island and the Xigaze fore-arc flysch were formed.It was changed from passive margin sedimentation(K_2-3) to relict platform shallow sea deposition(E₁-E₂²) in the Himalayan area.5) Collision stage(E₂³-Q).The Indian Massif and the Asian Continent collided,influencing the West China.Intracontinental foreland basin as well as pull-apart basin were formed.There did exist a Mesozoic Tethys Ocean in the South China Sea.The fauna had the same characteristics as the Pacific fauna.It is illustrated that,the Tethys Ocean was connected with the Pacific Ocean.The NE South China Sea was connected with the West Pacific Ocean.Tectonic evolution of the continental margin of SE China in the Mesozoic is stated as follow.1)The subduction stage of the Palaeo-Tethys(T₂-J₂).The oceanic crust subducted into the Asian Continent and paralleled displacement along transfer fault in N-S direction.The eastern margin of Asian Continent was accreted.It is pointed out that,the oceanic basin was part of the Palaeo-Tethys extending directly.2)Great changes have taken place since the Late Jurassic in the East part of China.The Pacific Ocean was formed by the expansion of three conjunction points in 185 Ma.The Kula Plate(J₃-K₁) moved to the north and subducted to tie NE Asia.Micro-massifs were collaged.Clino-subduction along the S-N transfer fault and micro-massifs took place in the South China and Taiwan.The subuducted accreting orogenic belt in Sikhote-Alin-SW Japan-Ryukyu Islands-Middle Taiwan and the volcano-magmatic belts in South China were formed.Rifting basins and pull-apart basins were formed.