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

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.