青藏高原羌塘地区晚三叠世构造-古地理研究

Late Triassic tectono-palaeogeography of the Qiangtang area on the Qinghai-Xizang Plateau

羌塘地区晚三叠世构造-古地理面貌总体呈多岛海格局,自北向南可分出3个次级构造-古地理单元:北羌塘弧后前陆盆地、龙木错-双湖残留盆地、南羌塘边缘海。北羌塘前陆盆地又分出5个古地理单元:以复理石沉积为特征的藏夏河-明境湖半深海;以细碎屑岩沉积为特征的唐古拉浅海陆棚;以碳酸盐沉积为特征的菊花山台地;以含煤碎屑岩系沉积为特征的土门格拉-双湖滨岸-三角洲和以酸性火山岩-火山碎屑岩喷发为特征的那底岗日-各拉丹东火山岛弧。盆地基底显示为南浅北深的箕状格局;盆地充填物为南薄北厚的楔形沉积体;盆地具有双物源、沉降中心和沉积中心不一致等特征,表明北羌塘盆地具有前陆盆地构造-沉积特征。南羌塘边缘海自北向南可分出3个古地理单元:以基性火山岩、碳酸盐岩和砂泥质碎屑岩为特征的肖茶卡浅海;以碳酸盐岩为特征的日干配错台地;以泥页岩夹粉砂岩、泥质灰岩为特征的南羌塘南缘半深海。南羌塘盆地基底显示为南、北低,中部高的丘状格局,盆地充填物为南薄北厚的楔形沉积体;盆地物源来自北部的中央隆起和那底岗日岛弧、盆地沉降中心在北部,而沉积中心在南部等特征,表明南羌塘盆地具有边缘海构造-沉积特征。羌塘地区晚三叠世构造-古地理研究对恢复南、北羌塘原型盆地的构造属性具有重要意义。

Tectonically,the Qiangtang area on the Qinghai-Xizang Plateau is sandwiched between the Rola Kangri-Ulan Ul suture zone and Bangong Lake-Nujiang suture zone,and separated by the Lungmu Lake-Shuanghu suture zone into the North and South Qiangtang blocks.The Late Triassic tectono-palaeogeographic features of this area display the overall archipelagic sea framework and may be divided,from north to south,into three secondary tectono-palaeogeographic units： North Qiangtang back-arc foreland basin,Lungmu Lake-Shuanghu residual basin and South Qiangtang marginal sea.The North Qiangtang foreland basin may further be subdivided into five palaeogeographic units： Zangxia River-Mingjing Lake bathyal sea characterized by the flysch deposits,Tanggula shallow-sea shelf with the fine-clastic rocks,Juhuashan carbonate Platform dominated by the carbonate deposits,Tumengela-Shuanghu littoral-delta with the coal-bearing clastic rock series,and Nadigangri-Geladaindong volcanic island arc with acidic volcanic rocks and volcaniclastic rocks.The South Qiangtang marginal sea may be separated,from north to south,into three palaeogeographic units： Xiaochaka shallow sea characterized by basic volcanic rocks,carbonate rocks and sandy and muddy clastic rocks,Rigain Punco platform dominated by carbonate rocks,and southern marginal bathyal sea of the South Qiangtang basin with mudstone intercalated with siltstone and muddy limestone.The North Qiangtang basin has the tectonic and sedimentary features of foreland basins,while the South Qiangtang basin has the tectonic and sedimentary features of marginal seas.The results of research in this paper have important implications for the reconstruction of the tectonic attributes of the North and South Qiangtang basins.