Bulletin of the Geological Society of Malaysia, Volume 9, Nov. 1977, pp. 187 – 207
Department of Geology, University of Malaya, Kuala Lumpur, Malaysia
Abstract: Peninsular Malaysia can be subdivided into four major tectonic regions-the Western Stable Shelf, the Main Range Belt, the Central Graben, and the Eastern Belt. Large granitic batholiths of predominantly Permian to Triassic age characterise the Main Range and Eastern belts.
The granites of the Main Range Belt are commonly coarsely porphyritic and their alkali feldspar is invariably perthitic maximum microcline as determined by X-ray diffraction and 2V. Their country rocks are phyllitic and isoclinally folded and contact metamorphic aureoles are generally absent. Rb:Sr and K:Ar dates are strongly discordant. These features together imply that the Main Range Belt has been uplifted since the Triassic by several kilometers. Uplift is suggested along the major ophiolitic mélange zone of Bentong-Raub. The nature and position of the western limit of the Main Range Belt is as yet undefined, but it probably lies close to the west coast of Penang Island.
The granites of the Eastern Belt are characterised by an equigranular to weakly porphyritic texture and their alkali feldspar is in the range orthoclase to intermediate microcline. Their country rocks are gently deformed sedimentary, volcanic and pyroclastic formations, and several well developed contact aureoles have been mapped. The Rb:Sr and K:Ar dates are consistently concordant. These features together imply that the granitoid rocks were emplaced epizonally and the Eastern Belt has been stable since the Triassic.
The granites of Langkawi are of the Western Stable Shelf. They contain intermediate microcline and have a pronounced contact metamorphic aureole.
Granites are few in the Central Graben, and confined to a complex belt passing through Gunung Benom and Gunung Stong, in which high-grade metamorphic rocks have been uplifted. Unlike the Main Range, the Benom granite has high-level characteristics. Highly sodic fine grained granitoid rocks also characterise parts of this region.
Late Cretaceous granites occur locally and have high-level characteristics. They are apparently devoid of tin mineralization. The style of mineralization is dramatically different in the Main Range and Eastern belts, and this can be ascribed to their different sialic basements and tectonic histories. Rock geochemistry and strontium isotope ratios indicate that a well established continental sialic basement underlies the Main Range and Western Stable Shelf belts, unlike the other two tectonic regions.
Extrapolation of the tectonic belts into Indonesia, Thailand and Burma must await detailed mineralogical studies of the granitoid rocks of those countries.