Bulletin of the Geological Society of Malaysia, Volume 6, Jul, 1973, pp. 61 – 86
Department of Geology, University of Malaya, Kuala Lumpur, Malaysia
“You behold a range of exhausted volcanoes.”
-Benjamin Disraeli, 3 April, 1872
Abstract: The palaeo-tectonic evolution of the Sundaland region is interpreted in terms of the plate tectonic model, with special reference to igneous events.
In Lower Palaeozoic time, the Malay Peninsula lay along the subducting contact between an easterly oceanic and a westerly Precambrian continental plate, with the trench occupying the eastern foothills of the Main Range. A volcanic arc extended along the western margin of the Main Range. Miogeoclinal shelf sedimentation occupied the backarc region between the volcanic arc and the Precambrian landmass, while eugeosynclinal sedimentation occupied the trench region east of the Main Range. The Malayan plate became detached from its Precambrian foreland in the mid Palaeozoic and drifted eastwards ahead of the ocean spreading of a new marginal basin.
From Late Carboniferous onwards, Sundaland played the role of a small continental plate, with active eastwards oceanic subduction underneath it from a trench located along the axis of Sumatra, and westwards subduction from a trench located in the South China Sea. Volcanic and plutonic arcs of Late Carboniferous, Permian and Triassic in the Malay Peninsula, Sumatra and West Borneo can be related to these opposite-facing arc-trench systems. Igneous arcs in the Malay Peninsula are commonly broad, often with no clear time separation-attributed to the median position of the Peninsula between the two subduction systems, and the shallow dips of the Benioff Zones.
The trenches moved progressively away from the Malay Peninsula as Sundaland grew by sedimentary accretion on its eastern and western sides. By Late Cretaceous, the western Sumatran and the eastern South China Sea arc-trench systems formed one convoluted arc wrapped around the southern end of Sundaland. The arc-trench system has straightened in the Late Cenozoic, and now occupies the southern coast of Java and western coast of Sumatra.
Shallow dips of the Benioff Zones and interaction between their eastern and western subduction components caused uplift of the East Coast and Main Range zones of the Malay Peninsula, resulting in a restriction of the Mesozoic sedimentary trough to the central axis of the Peninsula, and eventually its transformation from shallow marine to a continental environment. The deeper parts of this trough were metamorphosed in amphibolites facies and later uplifted as gneiss domes.
The sequence of granite emplacement in the Peninsula evolved progressively from dioritic in the Late Carboniferous to highly differentiated granite in the Late Cretaceous, in keeping with the progressive transformation of the Peninsula from mainly oceanic in the Palaeozoic to predominantly sialic and continental in the Late Mesozoic.
Uplift and cratonization of the Peninsula and the surrounding Sundaland region caused important deep-seated wrench and block faulting in the Late Mesozoic and Cenozoic, which has controlled the patterns of sedimentation, the Late Cretaceous high-level granite emplacement, and the highly alkaline Cenozoic basalt flows.