Geochronological cross section through northern Thailand

Abstract

Isotopic age determinations were carried out on seven different localities along a cross section through northern Thailand. First results of UPb investigations on zircons of rocks from the crystalline basement west of Tak indicates a maximum age of some 200 Ma for the last amphibolite facies overprint instead of Precambrian. Tertiary KAr ages of around 30 Ma on mica separates of these crystalline rocks must be interpreted as cooling ages requiring tectonic movements with strong uplift in Tertiary time. Additional information of the tectono-metamorphic evolution of northern Thailand is given by KAr ages on fine mineral fractions of slates which date the peak of a regional metamorphism and the time of deformation. The low grade metamorphic overprinting in the eastern parts of northern Thailand covers a range from 250 Ma to 60 Ma indicating a long lasting deformational history. The obtained data are consistent with the idea of a continuous transpressive regime since Permian/Triassic time resulting in thin-skinned tectonics in the eastern part and ramping, shearing and strong uplifting especially in Tertiary time in the western parts.