Bulletin of the Geological Society of Malaysia, Volume 60, December 2014, pp. 1 – 18
Department of Geology, University of Malaya, 50603, Kuala Lumpur
Abstract: The prominent N–S Palaeo-Tethys Bentong-Raub suture divides Peninsular Malaysia into a Sibumasu block on the west and an Indochina block on the east, known locally as East Malaya. The suture zone is characterized by an imbricated complex resembling an accretionary prism, of carbonaceous pelitic schist, serpentinite, amphibole schist, mélange-olistostrome and chert, as well as undated post-suture redbeds. Oceanic cherts record a Palaeo-Tethys history from Late Devonian to at least Late Permian. Extrapolation southwards is towards the Indonesian islands of Bangka and Billiton, and northwards along the Gulf of Thailand to the Sa Kaeo suture that has been strongly offset left-laterally by the Chao Phraya and Mae Ping faults to the Nan Uttaradit Suture, associated with less prominent island arcs of the Sukhothai zone, that correlates with the western part of East Malaya. Sa Kaeo and Nan-Uttaradit are now interpreted as closed back-arc basins. The suture zone accretionary prism and associated island arc rocks are known in northern Thailand as the Inthanon zone associated with the Chiang Mai suture, equivalent to the Bentong-Raub suture zone of Peninsular Malaysia, but problems of polarity remain.
Sibumasu is characterized by Carboniferous–Permian glacial pebbly mudstones, whereas the East Malaya and Indochina Block are characterized by fusulinid limestones and Cathaysian equatorial Gigantopteris flora. Sumatra has a Cathaysian affinity terrain west of the Sibumasu Block, formerly referred to as the “Jambi Nappe”. Characteristic Lower Palaeozoic fossils allow the Sibumasu localities of Langkawi, Tarutau and Phuket to have been positioned near the Canning Basin of Australia before its Lower Permian rifting from Gondwanaland. The Indochina and South China terranes had rifted from Gondwanaland in the Early Devonian and were spared the Upper Palaeozoic glaciation and instead developed equatorial Gigantopteris flora.
Sibumasu collided with East Malaya and Indochina in the Late Triassic (the Indosinian Orogeny), causing crustal thickening resulting in important tin-bearing S-type granites, characterised by the Main Range of the Peninsula, the ‘tin islands’ of Indonesia and parts of central Thailand. Late Cretaceous granites, commonly associated with high grade metamorphic core complexes, have not yet been successfully integrated into the regional tectonic analyses.
Eocene collision of India, with maximum impact at the Assam–Yunnan syntaxis, caused escape tectonics, resulting in oroclinal clockwise rotation of northern Sundaland brought about by a large number of right-lateral wrench faults and regional oroclines. The faults are associated with transtensional Tertiary basins and tanspressional transverse ranges of Jurassic–Cretaceous formations. Oroclinal bending of southern Sundaland resulted in anticlockwise rotations, forming a great arcuate structure known as the Anambas Zone. The right-lateral faulting of Sumatra is attributed to ongoing oblique subduction at the active trench.
Keywords: tectonics, Southeast Asia, Bentong-Raub suture, Sibumasu block, Indochina block