Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 95 – 102
School of Geotechnology, Suranaree University of Technology, Nakhon Ratchasima, Thailand
Abstract: Plate tectonic reconstructions of Southeast Asia is quite complicated as the areas are composed of several terranes accreted by complex processes of subduction, collision and transform faulting. Four main Triassic sedimentary facies can be distinguished, viz. the continental facies, the continental platform facies, the marine intra-arc facies, and the deep marine and oceanic facies. The continental facies characterized by alluvial fan, fluvial and lacustrine sequence (Huai Hin Lat and Kuchinarai Formations) represents the sediments of retroarc foreland basins covering the areas of northeastern Thailand (amalgamated Indosinia and Sukhothai terranes). The continental platform facies consists of shallow marine shelf clastics and carbonates distributed in the "Shan-Mergui" (Lower Mae Moei and Si Sawat Groups) and the Chiang Mai (Phrao Limestone, Klaeng Limestone) terranes. The marine intra-arc facies (Lampang and Phrae Groups, Nam Pat and Pong Nam Ron Formations) is distributed extensively within a volcanoplutonic setting on the western part of amalgamated Sukhothai-Indosinia terranes. It consists of shallow water siliciclastics and carbonates, the deeper water turbidites and its associated rhyolitic and andesitic volcanics. The deep marine and oceanic facies consist of radiolarian chert, pelagic limestone, turbidite and basalts distributed in two zones representing two distinct Triassic sutures in these areas. One is the Chiangrai-Chanthburi belt which extends southward into the Bentong-Raub suture of Malaysia. The other is Mae Sariang-Kanchanaburi belt and it extends southward to western Malaysia and central Sumatra. The distribution of the Permian and Triassic sequences and its tectonic setting indicate that Thailand and adjacent territories is a complex orogenic collage. The famous and well-known Nan-Uttaradit-Sra Kaeo ophiolite belt previously considered as representing a Late Triassic suture is a Late Permian one. The major terrane accretions are in the Late Triassic by the processes of subduction to the east in the Late Carnian and the Middle to Late Norian respectively.