Bulletin of the Geological Society of Malaysia, Volume 9, Nov. 1977, pp. 123 – 140
c/o UNDP, P.O.Box 650, Rangoon, BURMA
Abstract: Most tin-bearing granitic rocks in Southeast Asia occur in one of three main belts: an eastern belt largely of Late Carboniferous to Early Triassic age, a central belt with abundant Late Triassic granites, and a western belt with widespread Cretaceous to Early Eocene plutons. From the Palaeozoic to Early Triassic four main stratigraphic-structural zones are recognised: the Shan States-Northwest Thailand-Peninsular Burma and Thailand-Western Malaya (Zone 1); the Eastern Foothills of Malaya (Zone 2); medial Malaya and central Thailand (Zone 3) and eastern Malaya and east central Thailand (Zone 4). Lithology and deformation of these Zones indicates that the eastern belt of tin-bearing granites was emplaced in continental crust of Zone 4 above an eastward-dipping Benioff zone; subduction took place beneath an outer arc (Zone 2) to the west of a volcanic arc (Zone 3 and 4). Middle to Late Triassic closure of the ocean basin between Zone 1 and Zones 2 and 3 was accompanied by continental collision resulting in ‘the Indosinian orogeny‘ with emplacement of the central belt syn-collision late-orogenic granites in Zones 1 and 2. The western belt of granites was emplaced in Zone 1 above an eastward-dipping Benioff zone approaching the surface beneath or west of the IndoBurman Ranges, prior to Late Cenozoic northward movement of western Burma with respect to the Shan States. The abundance of tin in Southeast Asia is probably directly related to the fortuitous emplacement within continental crust of the three adjacent belts of subduction and collision-related magmatic rocks; there is little evidence of either a pre-Carboniferous concentration of metal in the crust, or of remobilisation of metal in the older mineraIised granites by the younger granites.