Basement of the South China Sea Area:Tracing the Tethyan Realm

The basement of the South China Sea（SCS）and adjacent areas can be divided into six divisions（regions）-Paleozoic Erathem graben-faulted basement division in Beibu Gulf,Paleozoic Erathem strike-slip pull-apart in Yinggehai waters,Paleozoic Erathem faulted-depression in eastern Hainan,Paleozoic Erathem rifted in northern Xisha（Paracel）,Paleozoic Erathem strike-slip extending in southern Xisha,and Paleozoic-Mesozoic Erathem extending in Nansha Islands（Spratly）waters.The Pre-Cenozoic basement in the SCS and Yunkai continental area are coeval within the Tethyan tectonic domain in the Pre-Cenozoic Period.They are formed on the background of the Paleo-Tethyan tectonic domain,and are important components of the Eastern Tethyan multi-island-ocean system.Three branches of the Eastern Paleo-Tethys tectonic domain,North Yunkai,North Hainan,and South Hainan sea basins,have evolved into the North Yunkai,North Hainan,and South Hainan suture zones, respectively.This shows a distinctive feature of localization for the Pre-Cenozoic basement.The Qiongnan（i.e.South Hainan）Suture Zone on the northern margin of the South China Sea can be considered the vestige of the principal ocean basin of Paleo-Tethys,and connected with the suture zone of the Longmucuo-Shuanghu belt-Bitu belt-Changning-Menglian-Bentong-Raub belt,the south extension of Bitu-Changning-Menglian-Ching Mai belt-Chanthaburi-Raub-Bentong belt on the west of South China Sea,and with the Lianhua-Taidong suture zone（a fault along the east side of Longitudinal Valley in Taiwan）-Hida LP/HT（low pressure-high temperature）metamorphic belt-Hida -marginal HP/LT metamorphic belt in southwestern Honshu of Japan,on the east of the South China Sea.The Qiongbei（North Hainan）suture zone may eastwards extended along the Wangwu-Wenjiao fault zone,and connects with the Lufeng-Dapu-Zhenghe-Shangyu（Lianhuashan）deep fault zone through the Pearl River Mouth Basin.The Meso-Tethys developed on the south of the South China Sea.The Nansha Trough may be considered the vestige of the northern shelf of the Meso-Tethys. The oceanic crust of the Meso-Tethys has southwards subducted along the subduction-collision-thrust southern margin of the Nansha Trough with a subduction-pole opposite to those of the Yarlung Zangbo-Mytkyina-Bago zone on the west of the South China Sea,and the Meso-Tethyan（e.g.Northern Chichibu Ocean of the Meso-Tethys）suture zone＂Butsozo tectonic line＂in the outer belt of the Jurassic-Early Cretaceous terrene group in southwest Japan,on the east of the South China Sea.