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

Abstract

Abstract: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.