Mesozoic and Cenozoic regional tectonics and metallogenesis in Mainland SE Asia

Author : Mitchell, A.H.G.
Publication : Bulletin of the Geological Society of Malaysia
Page : 221-239
Volume Number : 20
Year : 1987

Bulletin of the Geological Society of Malaysia, Volume 20, August 1986, pp. 221 - 239


Mesozoic and Cenozoic regional tectonics and metallogenesis in Mainland SE Asia


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Abstract: The major Mesozoic tectonic event in mainland SE Asia was the late Triassic Indosinian orogeny. Deformation and uplift in the Main Range Malaysia and northern Thailand, emplacement of syn- to late-tectonic two-mica granites of the Central Tin Belt, and the recently reported imbricate thrusting in Bangka Island, can best be explained by early Triassic collision of the Shan-Thai block foreland with the Indochina block to the east. Syncollision east-verging back-thrusts can explain the narrow gap between the Shan-Thai block and magmatic arc. The Mogok Belt of Central Burma was metamorphosed and elevated above a major collision-related west-verging foreland thrust. Regional stress related to foreland thrusting initiated eastward subduction of oceanic lithosphere at a Jurassic spreading centre in a small ocean basin west of the Shan-Thai block. Subduction of the spreading system and ophiolite detachment were followed by eastward subduction of the remnant ocean basin.

A continental fragment, exposed in the Indoburman Ranges, collided with Burma in the latest Jurassic, and-was underthrust beneath the ophiolite. East-verging thrusts of the Shan Scarps and Thai-Burma border were related to the collision, and caused partial melting and emplacement of anatectic granites of the Western Tin Belt. Generation of mineralized granites in both the Central and Western Tin Belts may have been related to expulsion of fluids from a common source tectonically buried in the late Triassic and Cretaceous. The Cretaceous heating event well-documented in the Main Range granites was possibly related to their position above converging Benioff zones at a depth of a few hundred kilometres.

Cenozoic relaxation of compressive stress probably permitted isostatic rise of the Shan Plateau. Dextral movement on the Sagaing transform fault was accompanied to the east, in northern Thailand, by crustal thinning, emplacement of basaltic magma at depth, and uplift of the Khorat Plateau. Hydrothermal activity related to the sub-surface intrusions and crustal extension caused widespread antimony and fluorite mineralization. Similarities in the regional tectonic setting of northern Thailand to that of the Great Basin in western USA suggest the possibility that epithermal gold-silver mineralization could occur at depth.

Subduction of Indian Ocean floor beneath the Indoburman Ranges collision belt began in the Aptian, with magmatism in the Burma volcanic arc and probably its continuation through Sumatra. Olistostromes of probable Campanian age in the Indoburman Ranges are interpreted as debris flows formed by diapiric rise and extrusion of mud-matrix melanges. Bodies of jadeite and schist were possibly elevated in serpentinite melange diapirs.