南海西部围区中特提斯东延通道问题

ROUTE FOR THE EASTERN EXTENSION OF MESO-TETHYS IN THE WESTERN ENVIRONS OF THE SOUTH CHINA SEA

通过对南海西部围区中生代岩相古地理资料的收集整理和分析,编制了该区T2,T13,T23,T33,J1-J2,J3-K1共6个时段的岩相古地理简图,根据其中生代海相地层的时空分布和岩相特征,讨论了尚存争议的中特提斯进入南海的通道问题.实际资料表明,黑水河盆地在三叠纪受印支运动影响完成了从海到陆的过程,之后不再出现海相沉积,中特提斯不可能从红河裂谷带进入南海.在新加坡所见的晚三叠世至早侏罗世浅海至陆相沉积代表古特提斯的残余海,到中侏罗世完全消失.早侏罗世时期在印支半岛南部出现的近南北走向的海湾可能经过泰国湾与当时的滇缅海相通;但是这个海湾浅而短暂,滇缅海能否从这里进入南海值得怀疑,更不可能是中特提斯的通道.在南海西部围区,迄今已证实的中生代洋壳碎片(蛇绿岩套)和深海沉积仅见于南部Woyla-Maratus-Lupar一线及其附近.这套延伸2 000余km,从洋壳、深海到浅海岩相齐全的岩石所代表的晚侏罗世至早白垩纪世大洋应是中特提斯洋的一部分.中特提斯东延而最可能是走南路,即从班公-怒江带南下之后,经Woyla线穿过苏门答腊岛,绕加里曼丹岛南缘到Maratus线,向北再经沙巴到Lupar线,在沙捞越北部或纳土纳岛附近进入南海.

Lithofacies and paleogeography maps of 6 Mesozoic time slices (T2 ,T_3~1 ,T_3~2 ,T_3~3 ,J1-J2 ,J3-K1 ) are compiled for the western environs of the South China Sea (23°N to 3°S,98°E to 110°E) based on col-lected data. The controversial problem that on which route Meso-Tethys entered the area where the present-day South China Sea occupies is explored based on this compilation. The Song Da basin in northern Indochina Peninsular completed its evolution from sea to land by the end of Late Triassic, and has kept emergent ever since. Thus Meso-Tethys could not enter the South China Sea through the Song Da basin. The Late Trissic to Early Jurassic shallow marine to continental elastics once found in Singapore represents a piece of residual sea of Paleo-Tethys which disappeared in Middle Jurassic. In Early Jurassic a S-N elongated wide gulf appeared in the southern Indochina peninsular and might be connected westward to the Yunnan-Burma Sea. But this gulf was shallow and ephemeral and could not be the route for Meso-Tethys. In the entire region, Mesozoic abyssal sediments and ophiolites are seen only along the Woyla-Maratus-Lupar line in the south. A complete set of Late Jurassic to Early Cretaceous oceanic crust, abyssal to shallow marine rocks extending over 2 000 km along this line should be the remains of Meso-Tethys. Thus our compilation supports the proposition that Meso-Tethys extended from the Bangong-Nujiang line southward, through Sumatera along the Woyla line, then circled the SW Borneo micro-continent along the Maratus line, then reached the Lupar line, and finally entered the area of the South China sea at some places near the Natuna Islands or NW Sarawak.