Phanerozoic geology of mainland Southeast Asia

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Chaodumrong, Pol
Holding Date 08 September 2008

Mainland Southeast Asia, is generally believed to consist of three principal Gondwana-derived terranes, which are from east to west Indochina, Shan-Thai and West Burma. The Nan-Uttaradit Suture represents the Paleo-Tethys with closure in the Late Triassic and the Shan Boundary representing the Meso-Tethys with closure in the Cretaceous. There are, however, many opinions on tectonic boundaries and kinematic histories. The discovery of Devonian to Triassic oceanic chert, and Carboniferous to Permian Tethyan sea-mount carbonates with Cathaysian affinities in northern Thailand which were formerly regarded as part of Shan-Thai, led to the nomination of new Paleo-Tethyan suture; the Chiang Mai Suture and Mae Yuam Fault. The Devonian chert overlies conformably Lower Paleozoic clastics that resemble those of Shan-Thai. Of the three sutures proposed, only the Nan-Uttaradit contains ophiolite and blueschist, as well a magmatic arc, Permian to Triassic oceanic chert and Triassic forearc sediments. This Paleo-Tethys suture extended southward to the Sra Kaeo Suture in eastern Thailand and the Bentong-Raub Suture in Malaysia.
The Shan-Thai rifted from the NW Australian part of the Gondwana in the Early Permian, and displays sequences of the Upper Cambrian siliciclastic to Ordovician platform carbonates and Silurian-Devonian fine-grained sediments with brachiopods, graptolites and tentaculites, and Permian glacial marine clastics and carbonates that outcrop widely from NW Malaysia northward to eastern Myanmar and western Yunnan. The Indochina drifted away from the Gondwana in the Devonian. Lower Paleozoic sequences are predominantly siliciclastics. Their Carboniferous to Permian platform carbonates and clastics exhibited Cathaysian. Deep to shallow marine Triassic clastics and shallow marine Jurassic sequences are restricted to long, narrow belts in both terranes. Continental Jurassic and Cretaceous red beds and evaporites occurred widely on the Indochina terrane. They exhibit mainly southwestward and westward paleocurrent directions. The effect of the India-Eurasia collision in the Cenozoic created not only clockwise rotation but also the wide development of extensional, intermontane basins, which contain petroleum and coal deposits.
Granitoid and volcanic rocks occurred in several NS trending belts which young to the west. Although inadequate age data, present morphology of the volcanic craters suggests that the Neogene rift basalts, exposed in the southern Khorat Plateau through to Laos and Vietnam belong to hot spots.
Regional stratigraphic gaps probably caused by regional orogeny, occur widely: the Shan-Thai in Middle to Late Carboniferous, Early to Middle Triassic, Early Jurassic, and Cretaceous to Paleogene; the Indochina in Middle Carboniferous, Late Permian to Middle Triassic, and Middle Cretaceous. While Plio-Pleistocene gap occurred in the whole region. These were probably related to Variscan, Indosinian and Himalayan orogenies.