The thermoluminescence “ages” of a large and representative selection of limestone specimens from the Thai-Malayan geosyncline, ranging in stratigraphic age from Ordovician to Triassic, are related, not to stratigraphic age, but to tectonic and magmatic events in the Mesozoic Indosinian-Thai-Malayan orogeny.

It is deduced that the revolutionary phase of the orogeny extended from early Triassic to early Cretaceous; folding of the geosynclinal sediments and accompanying recrystallization of the limestones terminated in late Jurassic, but granitic activity extended to early Cretaceous. A post-orogenic phase of granitic intrusion, accompanied by secondary calcite veining of the limestones, occurred in early Tertiary and appears to be confined to a narrow zone along the western margins of the Main Range batholith.

The thermoluminescence “ages” indicate that the revolutionary phase of the orogeny extended over a period of approximately 150 million years, which is in agreement with the radiometric ages of Malayan orogenic granites.

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