晚古生代—三叠纪南盘江海的构造古地理问题

DISCUSSION ON TECTONIC PALAEOGEOGRAPHY OF NANPANJIANG SEA IN THE LATE PALAEOZOIC AND TRIASSIC

晚古生代—三叠纪 ,滇黔桂三省区和越南北部有南盘江海长期发育。地质构造上 ,北面为扬子地块 ,东南有云开地块和大明山微陆块 ,西南有越北地块。南盘江海内部有北部的田林海盆 ,中部的八布洋盆和南部的钦防海盆。中间有许多大小不一的海下台地 ,最大的是大明山台地 ,其次是靖西台地和西畴台地。早泥盆世晚期南盘江海的张开 ,可能是冈瓦纳板块反时针旋转、扬子地块北移 ,使其间滇桂—越北地块裂解的结果。进一步的海底扩张导致早石炭世时八布海盆出现洋壳 ,南盘江海成为南北超过 2 0个纬度的小洋盆。古地理再造表明 ,八布海盆的扩张脊可能连接西面哀牢山海的洋脊。晚二叠世云开地块北移 ,与大明山微陆块碰撞。早三叠世印支地块北移 ,和越北地块会聚。晚二叠世—中三叠世南盘江海南缘出现活动陆缘。晚三叠世印支—越北地块与扬子地块会聚 ,南盘江海闭合。南盘江海和哀牢山海及昌宁—孟连海的发生、发展和消亡基本同步 ,可能属古特提斯同一洋脊系统控制。

From Devonian to Triassic, the Nanpanjiang Sea developed in Yunnan, Guizhou and Guangxi in China and their adjacent areas in northern Vietnam. Geologically, there were the Yangtze Block on its north, the Yunkai Block and Damingshan Block on its southeast and the North Vietnam Block on its southwest. Within the Nanpanjiang Sea the Tianlin Basin located on its northern part, the Babu Basin with oceanic crust on its central part and the Qinfang Basin on its southern part. It also contained a lot of submarine platforms with different sizes, of which the largest was the Damingshan Platform, secondly were the Jingxi Platform and the Xichou Platform. The opening of the Nanpanjiang Sea at later Early Devonian might be the result that the counter-clockwise rotation of the Gandwanaland and the northward drift of the Yangtze Block caused the rifting of the Guangxi-Yunnan-North Vietnam Block among them at that time. Further sea-floor spreading led to the occurrence of oceanic crust in Babu Basin and the Nanpanjiang Sea exceeded beyond 20 latitudes from north to south in Early Carboniferous. The oceanic spreading ridge might link with that in Ailaoshan Sea to the west based on the palaeogeographic reconstruction. During Late Permian the Yunkai Block drifted northward and collided with the Damingshan Block. Then the Indosinian Block moved northward and amalgamated with North Vietnam Block in early Triassic. An active margin appeared in the southern border of the Nanpanjiang Sea from Late Permian to Middle Triassic. In Late Triassic the Indosinian-North Vietnam Block amalgamated with the Yangtze Block and the Nanpanjiang Sea closed. The opening, developing and closing of the Nanpanjiang Sea, Ailaoshan Sea and Changning-Menglian Sea were basically kept at the same pace. Those marine basins might be controlled by the same oceanic ridge system of the Paleo-Tethys.