华南东部中生代构造特征及沉积盆地

THE MESOZOIC TECTONIC CHARACTERISTICS AND SEDIMENTARY BASINS IN THE EASTERN MARGIN OF SOUTH CHINA

通过华南陆区与海域中生代岩相古地理与沉积分布特征之研究,认识到本区中生代构造发育历史经历了三叠纪到早侏罗世由于华北地块沿秦岭-大别造山带向西南方向挤压,和印支地块沿哀牢山-红河-莺歌海碰撞逢合带向东北方向挤压而使华南地块发生陆内挤压变形,以及东南部被动大陆边缘构造发育历史,和晚侏罗世到早白垩世伊佐奈歧(Izangi)板块(古南海板块)向华南俯冲而形成活动大陆边缘的构造发育历史,特别是在早白垩世期间,南沙地块和华南地块沿今日的洋-陆边界处发生过构造碰撞,使包括下白垩统地层在内的早先沉积发生了挤压构造变形,并向西北方向逆冲。在此构造框架下,南海北部陆缘(包括华南陆地)沉积了晚三叠世到早侏罗世海湾相深水至浅水海湾相沉积,其东南陆缘上沉积了被动大陆边缘沉积;在晚侏罗世至早白垩世期间,在火山岛弧背后(今日华南陆上及内陆架区)发育了一系列小型弧后张裂断陷盆地,盆地内接收了陆相沉积;在火山弧前的前弧盆地内沉积了深水到浅水海相沉积。由于早白垩世期间南沙地块和华南地块发生碰撞挤压,使此前之沉积发生了褶皱变形,并向西北方向逆冲,我们从穿过潮汕坳陷(中生代燕山运动时期的前弧盆地)LF35-1-1井的地震剖面上可见此特征。由此可见,华南大陆边缘在燕山运动时期(晚侏罗世到早白垩世)不是简单的安第斯型大陆边缘,而是阿尔卑斯碰撞型大陆边缘。

Through the researches on the distribution of Mesozoic sediments and it＇s characteristics in the South China and offshore,we realize that there occur two tectonic stages.In the first stage from Triassic to early Jurassic,the Yindosinian block collided with the South China block and pushed the later moving northeastward.At the same time,the Sino-Korean block collided with the South China block and pushed the later moving southwestward.In the second stage from the later Jurassic to early Cretaceous,the Izangi block（the ancient South China Sea block in South China Sea area） subducted under the South China block and in the early Cretaceous the Nansha block collided with the South China block along the present ocean-continent boundary,and pushed the later moving northwestward.Therefore,the sediments before Cretaceous were deformed and denuded.Under such a tectonic framework there deposited deep to shallow marine sediments of the late Triassic to early Jurassic,with passive margin sediments at the eastern margin.In the second stage,there were continental sediments deposited in back arc rifting basins,with deep to shallow marine sediments in the fore arc basins.It is observed from the seismic profile across the well LF35-1 in the Chaoshan depression（the fore arc basin in the second stage） that the early Cretaceous sediments had obducted northwestward.Therefore,the southeastern margin of the South China block had been an Alpine collision-type margin during the Yanshan movement.